93-1315 Deoiling Manual
March 31, 2017 | Author: Manash Mudoi | Category: N/A
Short Description
Download 93-1315 Deoiling Manual...
Description
Report EP 93 - 1315 November 1993 Confidential
DEOlLlNG MANUAL Revision 1.1
Author:
A. C. Lawrence, EPDi421
Reviewed by: K. M. Perrin, EPDi421 Approved by: G. 0. Hajek, EPD/42
This dociinient I S confidential Neither the whole nor any part of this document m a y he ilisclosed to any third party without the !mor written consent of Shell Internationale Petroleum Maatschappij B.V., The Hague. the Netherlands. The copyright of this docuiiieiit is vested in Shell lriteriiationale Petroleum blaatschappi] B V.. The Hague. the Netherlands All rlyhts reserved. Neither the whole nor any pan of this docuinent m a y he reproduced, stored in airy retrieval systciii ot traiisniitled In aiiy form or hy any means (electronic, mechanical. reprographic. recording or otherwise) withoot the prior writlnri consent of the copyright owner
SHELL INTERNATIONALE PETROLEUM MAATSCHAPPIJ B.V., THE HAGUE Exploration and Production
Revision history
REVISION HISTORY
Revision
_____
Issue date
By
Revision details
Draft
14 May 1993 Allan Lawrence EPD/42I
First draft of revised manual. Developed from existing SIPM DehydratiodDeoiling Manual EP 89-1 50. Update based on literature searches of SlPM EP report database, in-house files, OWTC test work and a questionnaire circulated to operating companies. Diagrams not included.
Revision 1 .O
16 Aug 1993 Allan Lawrence EPD/42 1
Updated based on comments received on the Draft. Significant changes included the inclusion of all diagrams, a section introducing sludge treatment, clarification of iso-kinetic and isoenergetic sampling, inclusion of tables summarising the performance of equipment in tests, trials and operating installations and an appendix summarising the equations used to predict hydrocyclone performance.
Revision 1.1
S Nov 1993
Updated with remaining comments received from Revision 1.O issue. Equations in Appendix A and B corrected. Sizing of sampling quill added to Appendix B. Section 7 updated. Results from Galai trial included.
Allan Lawrence EPD/42 1
Corrections
CORRECTIONS - ADDITIONS - SUGGESTIONS This Deoiling Manual will only remain accurate and relevant if feedback is received from operating companies and all other users. Users are invited to forward any relevant information such as corrections to information given i n this manual, additional information on equipment installations, performance trials or new developments and any suggestions for improvements to this manual such as changes in structure or emphasis, new sections or topics for inclusion etc. This page can be photocopied and completed, including attachments as required, and forwarded to the address given below.
From:
Date:
Company:
Indicator:
Location:
TeVFax:
Forward to: SIPM, Posthus 162, 2501 AN Dcn Haag, The Netherlands - Attention EPD/42
I’trp, ii
SIPM Deoiliiig M ~ i i i i i dEP , 93-1335. Rev 1.1, Nov 1993, File iiamr = 0TITLE.DOC
Table of contents
1
.
................................................................................................................
INTRODUCTION 1.1.
GENERAL ...........................................................................................................................
1-1
1.2.
PURPOSE OF MANUAL .....................................................................................................
1-1
1.3. 1.4. 1.5. 1.6. 1.7. 1.8.
2
3
.
.
................................................................................................................... ORDER OF DOCUMENT PRECEDENCE............................................................................ STRUCTURE OF DEOlLlNG MANUAL............................................................................... INFORMATION BASE......................................................................................................... EQUIPMENT BRANDS AND SUPPLIERS........................................................................... ABBREVIATIONS ............................................................................................................... DISTRIBUTION
CHARACTERISATION OF WASTE WATER
...........................................................................................................................
2.1.
GENERAL
2.2.
SOURCES OF WASTE WATER ..........................................................................................
2.3.
CONTAMINANTS OF WASTE WATER ...............................................................................
2.4.
DROPLET SIZE DISTRIBUTIONS
2.2.1. 2.2.2. 2.2.3. 2.2.4. 2.2.5.
2.3.1 . 2.3.2. 2.3.3. 2.3.4. 2.3.5. 2.3.6. 2.3.7. 2.3.8. 2.3.9. 2.3.10.
1-1 1-1 1-2 1-3 1-3 1-3
.....................................................................
Produced water ...................................................................................................... Ballast water .......................................................................................................... Process water ........................................................................................................ Drainage water ...................................................................................................... Other waters ..........................................................................................................
Hydrocarbons derived from production streams ..................................................... Treatment chemicals.............................................................................................. Suspended solids ................................................................................................... Heavy metals ......................................................................................................... Salinity .................................................................................................................. pH ......................................................................................................................... Hardness ............................................................................................................... Thermal contamination .......................................................................................... Dissolved oxygen ................................................................................................... Organic carbon ......................................................................................................
.......................................................................................
......................................................................................................................
EMULSIONS
SlPM Dcoiliiig
1-1
2-1 2-1 2-1
2-1 2-1 2-2 2-2 2-3
2-3
2-3 2-5 2-5 2-6 2-6 2-7 2-7 2-7 2-7 2-8
2-8
3-1
3.1.
DEFINITIONS......................................................................................................................
........................ ......................
3-1 3-1
3.2.
FORMATION OF EMULSIONS ...........................................................................................
3-2
3.3.
STABlLlSATlON OF EMULSIONS......................................................................................
Miiniiiil.
EP 9.7-131.7, Kuil 1.1, Niiv 199.7, I;ilr
3.1 .1. 3.1 .2. 3.1 .3. 3.1.4.
3.2.1. 3.2.2. 3.3.1, 3.3.2.
General................................................................................... Distribution of phases ............................................................... Stability ............................................................................................. Size distributions................................................................
Formation locations ............................................................................................... Mixing energy and droplet size distributions............................................................
Immiscible liquids .................................................................................................. Surface tension ......................................................................................................
itioiic
= Ollll~I~.DOC
3-1
3-2 3-2
3-2 3-2 3-2
P q e iii
Table of contents Interfacial tension ................................................................................................... Contact angles and wetting of solids....................................................................... Emulsion stabilisers ...............................................................................................
3-3 3-3 3-4
TREATMENT OF EMULSIONS ...........................................................................................
3-6
3.3.3. 3.3.4. 3.3.5.
3.4.
3.4.1. 3.4.2. 3.4.3.
General .................................................................................................................. Emulsion breaking chemicals ................................................................................. Other methods of emulsion treatment .....................................................................
4 . WATER DISPOSAL
3-6 3-6 3-8
..........................................................................................................
4-1
4.1.
GENERAL ........................................................................................................................... 4-1
4.2.
SURFACE DISPOSAL
4.3.
WATER INJECTION ............................................................................................................
4.4.
DISPOSAL INJECTION ....................................................................................................... 4-5
4.5.
SECONDARY (REJECT) STREAM DISPOSAL ...................................................................
4.2.1. 4.2.2.
4.3.1. 4.3.2. 4.3.3. 4.3.4.
4.4.1. 4.4.2.
4.5.1 . 4.5.2. 4.5.3.
.........................................................................................................
Regulatory discharge limitations ............................................................................. Setting of environmental discharge standards.........................................................
General .................................................................................................................. Water compatibility ................................................................................................ Permeability impairment......................................................................................... Secondary waste water streams .............................................................................
4-1
4-1 4-3
4-3
4-3 4-3 4-4 4-5
General .................................................................................................................. 4.5 Water quality constraints ........................................................................................ 4-5 General .................................................................................................................. Disposal options ..................................................................................................... Sludges ..................................................................................................................
4-6
4-6 4-6 4.7
5 . WASTE WATER SAMPLING ............................................................................................ 5.1.
GENERAL ........................................................................................................................... 5-1
................................................................................................................
SAMPLE POINTS 5.2.1. Location of sampling points ....................................................................................
5-1
5.3.
SAMPLE CONTAINERS......................................................................................................
5-3
5.4.
SELECTION OF SAMPLING METHOD ...............................................................................
5-4
5.5.
ROUTINE SAMPLING .........................................................................................................
5-5
5.6.
SAMPLING TO MEASURE DROPLET SIZE DISTRIBUTIONS
5.7.
SAMPLE PRESERVATION AND STORAGE
5.2.
5.2.2. 5.2.3.
P ( q y iv
5-1
5.3.1. 5.3.2.
5.5.1. 5.5.2. 5.5.3.
5.6.1. 5.6.2. 5.6.3.
5.7.1. 5.7.2. 5.7.3.
5-1
Orientation of sampling points ................................................................................ 5-2 Design of sampling quills........................................................................................ 5-2 Materials ................................................................................................................ 5-3 Cleaning of sample containers................................................................................ 5-4
Introduction............................................................................................................ 5-5 lsokinetic conditions ............................................................................................... 5-5 Procedure for routine sampling............................................................................... 5-6
............................................
5-6
.......................................................................
5-8
Introduction............................................................................................................ 5-6 Sampling procedure to determine droplet size distribution....................................... 5-7 Effect of process pressure on sampling and droplet size distributions ..................... 5-7
Introduction............................................................................................................ 5-8 Chemical Preservation ........................................................................................... 5-9 Sample storage ...................................................................................................... 5-9
SlPM Droilinfi Miiituril. EP 93.1315. Rev 1.1. Nriv 1993. File niime = 0TITLE.DOC
Table of contents 6
.
WASTE WATER ANALYSIS
.............................................................................................
6.2.
........................................................................................................................... HYDROCARBONS.INFRARED ABSORPTION ANALYSIS ...............................................
6.3.
HYDROCARBONS.OTHER METHODS
6.4.
ON-LINE OIL-IN-WATER ANALYSERS
6.5.
MEASUREMENTOF PARTICLE AND DROPLET SIZES
6.1.
GENERAL 6.2.1 . 6.2.2. 6.2.3. 6.2.4. 6.2.5.
6.3.1 . 6.3.2. 6.3.3. 6.3.4. 6.3.5.
6.4.1 . 6.5.1 . 6.5.2. 6.5.3. 6.5.4. 6.5.5.
Introduction............................................................................................................ Sample preparation................................................................................................ Hydrocarbon extraction .......................................................................................... Removal of polar.compounds................................................................................. Infrared analysis ....................................................................................................
.............................................................................
Dispersed and dissolved hydrocarbons .................................................................. Gravimetric analysis .............................................................................................. Visible spectrum colourimetry ................................................................................ Gas chromatography ............................................................................................. Others ...................................................................................................................
Introduction...................................................................................................................... Sources and magnitude of water streams (1) .................................................................... Identify contaminants in the waste water stream (2) .......................................................... Identify treated water quality requirements (3) ................................................................... Select a suitable process location for the water treatment system (4) ................................ Identify upstream methods of improving ease of water treatment (5)................................. Select the number of treatment stages (6) ........................................................................ Select the suitable deoiling equipment (7) ......................................................................... Treatment or disposal of secondary streams (8) ............................................................... System optimisation and integration (9) ............................................................................
..................................
Introduction...................................................................................................................... Maximising droplet size .................................................................................................... Minimising the hydrocarbon content in the feed stream ..................................................... Production separators ...................................................................................................... Stable feed streams .......................................................................................................... Recycle streams ............................................................................................................... Mixing of water streams .................................................................................................... Treatment chemicals ........................................................................................................
............................................................. WATER CHARACTERISATIONCONSULTANCY SERVICES ............................................. PILOT PLANT TRIALS........................................................................................................ EXAMPLES OF WATER TREATMENT SCHEMES
....................................................................................
8. DISPERSED HYDROCARBONS 8.1.
INTRODUCTION .............................................................................................................. 8.1 .1. 8.1.2.
6-7
...............................................
SYSTEM OPTlMlSATlON AND INTEGRATION CONSIDERATIONS
7.6.
6-5 6-5 6-6 6-6 6-6
6-8
7.3.
7.5.
6-5
....................................................
7.2.
7.4.
6-1 6-2 6-2 6-3 6-3
General.................................................................................................................. 6-8 6-8 Sampling ............................................................................................................... Potential problems in measuring droplet size distributions...................................... 6-8 Droplet size distribution analysers .......................................................................... 6-8 Particle size analyser trials ................................................................................... 6-10
................................................................................................................. EQUIPMENT SELECTION AND SYSTEM DESIGN.............................................................
7.3.1. 7.3.2. 7.3.3. 7.3.4. 7.3.5. 7.3.6. 7.3.7. 7.3.8.
6-1
6-7
INTRODUCTION
7.2.1. 7.2.2. 7.2.3. 7.2.4. 7.2.5. 7.2.6. 7.2.7. 7.2.8. 7.2.9. 7.2.10.
~1
..............................................................................
General..................................................................................................................
7. EQUIPMENT SELECTION AND SYSTEM INTEGRATION 7.1.
6-1
7-1 7-1 7-1
7-1 7-1 7-2 7-2 7-3 7-3 7-3 7-4 7-5 7-5
7-7
7-7 7-7 7-7 7-8 7-8 7-8 7-8 7-8
7-9 7-9 7-9
8-1-1
8-1-1 Scope of chapter ................................................................................................. 8-1-1 Equipment for dispersed hydrocarbons .Summary tables ................................... 8-1-1
Table of contents 8.2.
DEFINITIONS..................................................................................................................
8-2-1
8.3.
COALESCERS
................................................................................................................
8-3-1
8.4.
FLOCCULATION.............................................................................................................
8-4-1
8.5.
SKIMMING TANKS AND VESSELS ................................................................................
8-5-1
8.6.
DISCHARGE CAISSONS.................................................................................................
8-6-1
8.7.
API SEPARATOR
8.8.
PLATE INTERCEPTORS .................................................................................................
8.9.
STATIC HYDROCYCLONE..............................................................................................
8.2.1.
8.3.1. 8.3.2. 8.3.3. 8.3.4. 8.3.5. 8.4.1. 8.4.2. 8.4.3.
8.5.1. 8.5.2. 8.5.3. 8.5.4. 8.5.5. 8.6.1. 8.6.2. 8.6.3. 8.6.4.
8.7.1. 8.7.2. 8.7.3. 8.7.4.
8.8.1. 8.8.2. 8.8.3. 8.8.4. 8.8.5.
8.9.1. 8.9.2. 8.9.3. 8.9.4. 8.9.5. 8.9.6.
..
Deoiling efficiencies............................................................................................
General .............................................................................................................. Definitions .......................................................................................................... Performance variables........................................................................................ Installation/Configuration.................................................................................... Coalescer designs .............................................................................................. General .............................................................................................................. Floc separation .................................................................................................. Operation considerations.................................................................................... Introduction ........................................................................................................ performance variables........................................................................................ Installation/Configuration.................................................................................... Design guidelines ............................................................................................... Control configuration ..........................................................................................
Introduction ........................................................................................................ Design guidelines ............................................................................................... Caisson internals................................................................................................ Operational considerations.................................................................................
............................................................................................................
Introduction........................................................................................................ Performance variables........................................................................................ Installation/Configuration.................................................................................... Design guidelines ...............................................................................................
Introduction........................................................................................................ Performance variables........................................................................................ Installation/Configuration.................................................................................... Design guidelines ............................................................................................... Operational considerations.................................................................................
Introduction........................................................................................................ Definitions.......................................................................................................... Performance variables........................................................................................ InstallationlConfiguration.................................................................................... Control configuration.......................................................................................... Operational considerations ................................................................................
8-2-1 8-3-1 8-3-1 8-3-1 8-3-2 8-3-2 8-4-1 8-4-1 8-4-2 8-5-1 8-5-1 8-5-1 8-5-1 8-5-2
8-6-1 8-6-1 8-6-1 8-6-2
8-7-1
8-7-1 8-7-1 8-7-2 8-7-2
8-8-1
8-8-1 8-8-1 8-8-3 8-8-4 8-8-5
8-9-1
8-9-1 8-9-1 8-9-1 8-9-8 8-9-9 8-9-11
8.10. ROTARY HYDROCYCLONE .......................................................................................... 8-10-1 8.10.1 . 8.10.2. 8.10.3. 8.10.4. 8.10.5. 8.10.6. 8.10.7.
Introduction ....................................................................................................... Definitions......................................................................................................... Performance variables....................................................................................... Installation/Configuration................................................................................... Design guidelines .............................................................................................. Control configuration......................................................................................... Operational considerations ................................................................................
8-10-1 8-10-1 8-10-1 8-10-5 8-10-6 8-10-7 8-10-7
8.11. CENTRIFUGES .............................................................................................................. 8-11-1 8.11.1. 8.1 1.2. 8.1 1.3. 8.1 1.4. 8.1 1.5.
Introduction....................................................................................................... Performance variables....................................................................................... Installation/Configuration................................................................................... Control configuration......................................................................................... Operational considerations ................................................................................
8.12. INDUCED GAS FLOTATION..........................................................................................
8-11-1 8-11-1 8-11-2 8-11-4 8-1 1-4
8-12-1
8.12.1 . Introduction....................................................................................................... 8-12-1
Ptrxc
vi
.
SlPM Droiling Mimlvtl. EP 93.1315. Rev I.!,Nov 1993 Filr name = 0TlTLE.DOC
Table of contents Performance variables ...................................................... :............................... Installation/Configuration.................................................................................. Design guidelines .............................................................................................. Control configurations ....................................................................................... Operational considerations................................................................................
8.12.2. 8.1 2.3. 8.1 2.4. 8.12.5. 8.12.6.
......................................................................................
8.13. DISSOLVED GAS FLOTATION
Introduction....................................................................................................... Performance variables ...................................................................................... Installation/Configuration .................................................................................. Design guidelines .............................................................................................. Operational considerations................................................................................
8.13.1. 8.13.2. 8.13.3. 8.13.4. 8.13.5.
....................................................................................
8.14. DEEP BED MEDIA FILTRATION
Introduction....................................................................................................... Performance variables ...................................................................................... Installation/Configuration .................................................................................. Design guidelines .............................................................................................. Control configuration......................................................................................... Operational considerations................................................................................ Crushed nut shell deep bed media filters ...........................................................
8.14.1. 8.14.2. 8.14.3. 8.14.4. 8.14.5. 8.14.6. 8.14.7.
8.15. CARTRIDGE FILTERS...................................................................................................
Introduction....................................................................................................... Performance variables ...................................................................................... Installation/Configuration.................................................................................. Design guidelines..............................................................................................
8.15.1. 8.15.2. 8.15.3. 8.1 5.4.
8.16. PRE-COAT FILTRATION ............................................................................................... 8.16.1 . 8.16.2. 8.16.3. 8.1 6.4. 8.16.5.
Introduction....................................................................................................... Performance variables ...................................................................................... Installation/Configuration .................................................................................. Design guidelines.............................................................................................. Operational considerations................................................................................
................................................................................................................
8.17. MEMBRANES
Introduction....................................................................................................... Performance variables ...................................................................................... Installation/Configuration .................................................................................. Membrane trials ................................................................................................
8.1 7.1 . 8.1 7.2. 8.1 7.3. 8.1 7.4.
9. DISSOLVED HYDROCARBONS
....................................................................................
8-12-3 8-12-6 8-12-7 8-12-7 8-12-8
8-13-1
8-13-1 8-13-2 8-13-4 8-13-5 8-13-5
&-14-1
8-14-1 8-14-2 8-14-5 8-14-6 8-14-6 8-14-6 8-14-7
8-15-1
8-15-1 8-15-1 8-15-1 8-15-2
8-16-1
8-16-1 8-16-1 8-16-2 8-16-2 8-16-2
8-17-1
8-17-1 8-17-2 8-17-3 8-17-3
9-1-1
9.1.
INTRODUCTION
..............................................................................................................
9-1-1
9.2.
LEVELS OF DISSOLVED HYDROCARBONS IN WATER ................................................
9-2-1
9.3.
GAS STRIPPING..............................................................................................................
Introduction......................................................................................................... Performance variables ........................................................................................ Installation/Configuration .................................................................................... Design guidelines................................................................................................
9-3-1
9-3-1 9-3-2 9-3-3 9-3-4
9.4.
STEAM STRIPPING .........................................................................................................
9-4-1
9.5.
BIOLOGICAL TREATMENT.............................................................................................
9.3.1. 9.3.2. 9.3.3. 9.3.4.
9.4.1 . 9.4.2. 9.4.3. 9.4.4.
Introduction......................................................................................................... Performance variables ........................................................................................ Installation/Configuration .................................................................................... Design guidelines................................................................................................
Introduction......................................................................................................... Aerobic processes............................................................................................... Anaerobic processes........................................................................................... Performance variables ........................................................................................ Installation/Configuration ....................................................................................
9.5.1. 9.5.2. 9.5.3. 9.5.4. 9.5.5.
.
.
.
SlPM Dtwilittg Mntlurtl El' 93.1315 Rev 1.1. Nov IY93 File
ititiw
= 0TITLE.DOC
9-4-1 9-4-1 9-4-2 9-4-2
9-5-1
9-5-1 9-5-1 9-5-3 9-5-4 9-5-4
P u p vi;
Table of contents
.
....................................................................................................
9.6.
ACTIVATED CARBON 9.6.1. Introduction........................................................................................................ 9.6.2. Performance variables........................................................................................ 9.6.3. Installation/Configuration....................................................................................
9.7.
SOLVENT EXTRACTION 9.7.1. Introduction ........................................................................................................ 9.7.2. Co-current extraction..........................................................................................
.................................................................................................
~~
~~~
10 NEW TECHNOLOGY
......................................................................................................
9-6-1 9-6-1 9-6-1 9-6-2 9-7-1 9-7-1 9-7-1
10-1
10.1. GENERAL .......................................................................................................................... 0-1
..................................................................................................... ADSORPTION ON MODIFIED ZEOLITES ......................................................................... MEMBRANE LIKE MATERIAL ..........................................................................................
10.2. OZONEILILTRAVIOLET
10-1
10.3.
10-1
10.4.
10.5. PERVAPORATION.............................................................................................................
0-1
........................................................
10-2
10.6. MEMBRANES FOR DISSOLVED HYDROCARBONS
Appendix A A.l.
A.2.
.Emulsification and coalescence .................................................................... Introduction....................................................................................................................... A.l .1 A.1.2 A.1.3
Mixing intensity ..................................................................................................... Prediction of droplet size ....................................................................................... Mixing energy in piping ..........................................................................................
Optimum Mixing Intensity For Coalescence
.
Appendix B Sampling t o determine droplet size B.l. 8.2. 8.3. 8.4. 8.5.
....................................................................
...............................................................
....................................................................................................................... Calculation of the mixing intensity in the process line ................................................... Pressure drop in the sampling system ............................................................................ Sizing the sample quill for isokinetic conditions ............................................................ Contrast with iso-kinetic sampling .................................................................................. Introduction
.
Appendix C Published infrared analysis procedures
.......................................................
............................................................................................. Key characteristics of identified IR analysis procedures ...................................................
A-I A-1
A-1 A-1 A-2
A-3
8-1 B-1 B-1 8-2 8-5 B-6
C-1
C.l List of IR analysis procedures
C-1
C.2
C-2
Appendix
D .Oil-in-water
monitor trials
............................................................................... ................................................................................
D.l Oil-In-Water Monitor Testing .Phase I D.l .1. General ................................................................................................................. D.1.2. Monitors tested...................................................................................................... D.1.3. Variables investigated ........................................................................................... D.1.4. Summary of results ............................................................................................... I ’ u ~ : cv i i i
10-1
.
D.1 D-1
D-1 D-1 D-1 D-2
SIPM Deoilinl: Monriol. EP 9.7-1.loo' 100 No more than 4% >loo' 42
29
3. USA figure is new
* 4% of samples taken
The discharge limits for territorial seas and offshore continental shelf installations in the USA were lowered in January 1993. The new limits are an average of 29 mg/l per month with a maximum of 42 mg/l per day. Both new and existing installations will be required to satisfy the more stringent regulations. In general the regulations covering water discharges are most stringent for inland locations, with the regulations often controlling a wide variety of substances including both dispersed and dissolved hydrocarbons, heavy metals, biological oxygen demand etc. In contrast, regulations covering offshore effluent discharges are less coherent. Limits have typically been set on the basis of expected performance levels of available deoiling equipment and not on environmental impact considerations.
It should be noted that regulations from different countries or within the same country often have considerable variation in areas such as defining which components are considered hydrocarbons, whether dissolved and polar hydrocarbons are included and which hydrocarbon analysis method should be used. A good example is the gravimetric analysis method required by some regulations tends to measure a lower hydrocarbon content than the infrared analysis method required by other regulations. Some regulations allow gas sparging of the sample which strips volatile hydrocarbons from the sample. Due to these variations, a limit set or measured under one set of regulations is not always directly comparable to a limit under a different set of regulations.
Table 4.3 gives a qualitative guide to the surface appearance of water containing small quantities of hydrocarbons. Although each hydrocarbon and water combination will be different, for this particular oil/water combination it is apparent that it is difficult to visually detect low levels of hydrocarbons.
Oil concentration (mgll)
Effect on surface of water sample
0 to 30 30 to 60 60 to 100 > 120
Not visible Silvery sheen Traces of colour Bright colour Dull colour Dark colour
> 400 > 800
Source:
P U ~4-2 C
I
SlPM Dehydration/Deoilingmanual EP 89-0150.
SlPM Deoilinx M~rrtu~il, EP 93-1315, Rev 1.1, Nov 1993, File nume = 4CHAP.DOC
4. Water disposal 4.2.2.
Setting of environmental discharge standards In addition to regulatory limitations, the treatment of waste water streams should be governed by local environmental considerations. An Environmental Quality Objectives (EQO) approach can be followed to establish suitable effluent quality targets. The EQO method consists of the following steps; Evaluation of the local environmental characteristics. Identification of all potential contaminating components of all effluent streams. Identification of environmental characteristics sensitive to effluent discharge levels. Consideration of the potential end use of waters in the receiving environment e.g. drinking water supply, agricultural use. 0
Determining the distribution, fate and impact of all substances contained in the effluent steam. Impact should consider factors including toxicity, persistency, accumulation and biodegradability.
Taking all these factors into consideration allows the setting of realistic and environmentally responsible standards governing the level of contaminants in waste water discharges to ensure minimal environmental impact. In some instances, the EQO approach may lead to the adoption of standards that are more stringent than that required by local regulations. However, in other cases the EQO approach may be used as a logical and defensible basis to support the setting of realistic discharge levels for a particular environment. SlPM EP0/6 should be contacted for more information on the EQO approach.
4.3.
WATER INJECTION
4.3.1.
General For the purposes of this manual, the term water injection is used to mean the injection of waste water into the production reservoir for the purpose of assisting hydrocarbon recovery. However, in some cases, only the production water component of the waste waters is considered suitable for water injection, with the remaining waste waters disposed using alternative methods. The term disposal injection is used to define the injection of waste water into non-producing formations for the purposes of disposal only. This is discussed separately in section 4.4 The injection of water into a production reservoir to assist the recovery of oil reserves is a relatively well established procedure. Both surface waters (sea, river and lake water) and subsurface waters (aquifer and produced water) have been satisfactorily injected in a variety of locations. The following discussions briefly introduce the water treatment considerations that need to be addressed to ensure the satisfactory injection of water as a means of both hydrocarbon recovery and waste water disposal. The discussions are orientated to the injection of produced waters which are normally the largest waste water stream, however the general principles apply to most water sources. This information has been summarised from the SlPM Water Injection Manual (currently EP-63600, revised edition expected by 1st quarter of 1994). For more detailed information on water injection the SlPM Water Injection Manual (currently being updated) takes precedence over this manual.
4.3.2.
Water compatibility Water injection of produced water is only possible if the water is determined to be compatible with the production reservoir. The investigation of water compatibility should address the following considerations: 0
0
Compatibility with the formation. Chemical incompatibility may result in the expansion of clay minerals or oxidation reactions due to the presence of oxygen (most injection water is maintained oxygen free). Physical incompatibility may result in the migration of fine solid particles through the formation (either carried by the injection water or dislodged from the formation) with the potential for blocking pores and consequent reduction in formation permeability. Compatibility with formation fluids. Incompatibility with formation fluids can result in changes in the chemical equilibrium of the formation fluids, potentially leading to scale formation in the
SlPM Droiling Mrriiivcl. EP 93-1315, Rrv I . I .
Noit
1993, Filr
twiie
= .IC//AP.DOC
Puge 4-3
4. Water disposal reservoir, tubing or in surface production facilities.
Compatibility with other injection waters. In some cases, waste water will form only part of the total volume of required injection water. In this instance the compatibility of the waste water with the other injection waters (e.g. sea water) must be established, as well as the compatibility of the combined waters with the formation itself and the formation fluids.
4.3.3.
Permeability impairment Treatment of water before injection is required to avoid potential impairment of the permeability of the formation. Table 4.4 lists potential means of permeability impairment and references the sections of the current SlPM Water Injection Manual (EP-63600) where additional information can be found. Of these potential means of permeability impairment, the removal of suspended solids and dispersed hydrocarbons from the produced water are of most importance to the selection of water treatment equipment. Table 4.4 Potential sources of permeability impairment Impairment source Suspended solids
.
Coalescing oil droplets Formationof insoluble scales
Bacteriologicalsolids Corrosion products
Source water survey Evaluation of filtration specification
. 0
Source water analysis
.
Swelling of reservoir clays Movement of reservoir fines
Method of prevention
Pre-engineering evaluation method
. . .
Analysis of source water and formation water Computer aided scale prediction Dynamic tests of chemical inhibitors Core sample flooding tests Petro-graphicalanalysis Core sample flooding tests Petro-graphicalanalysis Source water analysis Source water analysis
. . . I
I
[ I ] Ref: SlPM Water Injection Mal
4.3.3.1.
31,
EP-63600, August 1985
Fine filtration Fine filtration
Ref
L 3.2.1 3.2.1
Fine filtration Emulsification
3.2.3 3.3.3
Prevent commingling of incompatible fluids or use chemical inhibitors Sulphate removal membranes
3.2.2 4.4
Modify water injection program Chemical injection
4.3
Modify water injection program Chemical injection
4.3
Inject chemical biocides
3.2.5 7.2
Materials and coatings selection Chemical inhibitor injection Cathodic protection
6.0
Solids removal Solids present in injected water have the potential to be trapped in the formation around the well bore, resulting in a flow restriction and a deterioration in injectivity. Such blockage will adversely affect the ability of the injection well to accept the requisite waste water volumes. Individual reservoirs differ in tolerance for both the quantity and the size distribution of the solids in the injection water. Factors that will affect the ability of the reservoir to tolerate solids include; The permeability and pore structure of the basic reservoir material. The degree of fracturing present in the reservoir. The physical properties of the hydrocarbons present in the reservoir. Core flooding tests can give some indication to the tolerance of the reservoir to the presence of solids. However field experience often contradicts the results of core flooding tests, either by injectivity impairment of “tolerant” reservoirs or in the unexpected tolerance of supposedly “tight” reservoirs. Typical quality requirements for water injection of sea water in the North Sea are 98% removal of solid particles larger than 2 pm with a particle number count of less than 25 parlicl,es per 0.05 ml of water. This corresponds to the typical water quality that can be achieved with conventional filtration equipment. A well-head guard filter can be used to achieve a further reduction in solids by the removal of up to 100% of particles larger than 0.6 pm.
Pujic 4-4
SIPM Deoiling Mitiiurrl. EP 93-1315, Rev 1.1, Nov 1993, File nitme = 4CHAP.DOC
4. Water disposal However, the setting of excessively strict water injection specifications is very expensive in terms of additional process equipment, particularly for offshore installations. Specifications should not be set as simply the best achievable quality, but should be justified by consideration of all relevant information. Issues such as down hole contamination of the water with corrosion/erosion products, the thermal fracturing of reservoirs and the costhenefit analysis of different treatment options should be considered.
4.3.3.2.
Hydrocarbon removal The presence of dispersed hydrocarbons in the injected water can also lead to permeability impairment. Dispersion of the hydrocarbon into the reservoir may result in the formation of a stable emulsion or sludge, often stabilised by the presence of solids. This emulsion may exhibit a very high viscosity and non-Newtonian rheological behaviour, resulting in plugging of the reservoir. In addition, dispersed oil may alter the wetting properties of the formation and may form an oil bank in the proximity of the well bore, also reducing permeability. For many water injection schemes the dispersed hydrocarbons are removed along with the suspended solids by filtration. In this case the hydrocarbon droplet size in the feed stream and the level of dissolved hydrocarbons present will determine the level of hydrocarbons remaining in the filtered water. Typical design levels are less than 5 mg/l of dispersed hydrocarbons.
4.3.4.
Secondary waste water streams While water injection can be an efficient method for disposal of waste water, particularly produced water, consideration must also be given to the disposal of secondary waste water streams from the production facilities such as process water, drains water and ballast water. In some cases, it may be possible to mix secondary waste waters with the water for water injection. However the suitability of this must be carefully evaluated as it may potentially introduce more problems than it solves, due to the following considerations; 0
The possibility of scale formation from mixing incompatible waters
0
The introduction of bacteria and/or oxygen into the injection water.
0
0
The optimum rate of water injection for production purposes may not correspond with the rate required for disposal of secondary waste waters. During initial years of production there may be no requirement for any water injection. Flow rates of secondary water may be seasonally variable.
In most instances, waters for injection and secondary sources of water are riot mixed. In these circumstances, even though the bulk of the waste water may be disposed of through water injection, waste water treatment facilities must still be provided for the disposal of secondary waste water streams.
4.4.
DISPOSAL INJECTION
4.4.1.
General Disposal injection differs from water injection in that the water stream is injected only for the purpose of disposal, not as a means of assisting production rates. Disposal injection injects waste water into subsurface formations other than the production reservoir, such as aquifers or exhausted production reservoirs.
As with water injection, the information provided in this Deoiling Manual is a summary only, concentrating on the aspects of disposal injection relevant to the selection and design of deoiling equipment. For more detailed information the user is referred to the SlPM Water Injection Manual (currently EP-63600, revised edition expected by 1st quarter of 1994).
4.4.2.
Water quality constraints
4.4.2.1. Disposal reservoir constraints The drilling and completion of any well is expensive and the water for disposal should be treated to a quality sufficient to ensure that the capacity of the disposal formation is not restricted by avoidable damage. Therefore, until proven otherwise, the constraints imposed by the reservoir on disposal water are broadly similar to those outlined for water injection in section 4.3. SlPM Deorltng
Mntrriiil.
EP 97-1315, Rev 1 I , Niiv 1993. File
iiitine
= 4ClIAP DOC
PuRe 4-5
4. Water disposal However, there is typically more latitude allowed in the treatment of disposal water than allowed for injection water and there are numerous cases of the disposal injection of waste water with minimal treatment. A more relaxed water quality specification for disposal water is often acceptable on the basis of: The disposal formation may be specifically chosen on the basis of a high tolerance for poor quality disposal water. Stimulation of the disposal formation may be possible. In many cases, water for disposal injection may only need to be treated to level similar to typical offshore surface disposal specifications, i.e. below 40 mg/l dispersed hydrocarbons. This can be used as a starting point for design. However, considering the potential impact on equipment design, these limits should be confirmed through normal reservoir plugging evaluations as discussed in the SlPM Water Injection Manual.
4.4.2.2.
Environmental constraints Disposal injection of waste water should avoid subsurface structures that may be used or linked to sources of water for industrial, agricultural or domestic purposes.
4.4.2.3.
Regulatory constraints Countries which utilise aquifers as a source of water for industrial, agricultural or domestic purposes will often have regulations governing the disposal of waste waters in subsurface structures.
4.5.
SECONDARY (REJECT) STREAM DISPOSAL
4.5.1.
General The main focus of most deoiling system designs is generally the quality of effluent water stream. However, the contaminants removed from a waste water stream are simply moved from the waste water stream to some secondary waste stream. The design of a water treatment facility must consider the potential disposal requirements of secondary waste streams that may be generated. Secondary waste streams may include concentrated hydrocarbon streams, sludge and waste gas streams. In particular, the techniques used for the removal of dissolved hydrocarbons often result in the generation of large secondary streams that must be treated, regenerated or disposed.
4.5.2.
Disposal options
4.5.2.1.
Export with hydrocarbons Secondary waste streams may often be spiked into the product hydrocarbon stream and exported. This is often possible as the secondary waste stream may be relatively concentrated and small in volume compared to the overall product stream. This is a common method of "disposing" the hydrocarbons recovered from deoiling processes. However, it should be recognised that this method of disposal is simply transferring potential contaminants to downstream processing activities where the same contaminants may need to be removed a second time. In some cases it may be more economic to treat the waste upstream rather than transfer the problem downstream.
4.5.2.2.
Recycling to process Many process schemes recycle secondary waste streams to the start of the process. This is satisfactory provided at some point in the process there is a satisfactory purge of the contaminant from the process systern. Care must be taken to avoid the potential accumulation of contaminants in the process through recycling. For example, the recycling of sludge, such as from oil/water interfaces, should be avoided. Such sludges are relatively stable and are unlikely to break down without additional treatment. As a result they will tend to accumulate in the process. Solids may also accumulate in the process and may eventually reach a stage where they are responsible for the stabilisation of sludges or emulsions.
PUKE4-6
SlPM Deoilinx Mmiud, EP 93-1315. Rrv 1.1. Nov 1993, File name = ICHAPDOC
4. Water disposal 4.5.2.3.
Disposal to atmosphere Some deoiling processes will result in the generation of a waste gas stream, for example stripping of hydrocarbons from water using a gas. The resulting gas stream containing the stripped hydrocarbons is typically discharged to the flare system or fuel gas system, and may be subject to regulations governing discharges to atmosphere.
4.5.2.4.
Disposal for separate treatment In some circumstances, secondary waste streams will be removed from the process for separate treatment. The two best examples are emulsion sludges and solid sludges. Solid sludges are discussed in more detail in section 4.5.3. Emulsion sludges are stable oil/water emulsions, oflen accumulating at the oiVwater interface. Such emulsions are oflen stabilised by the presence of emulsifying agents such as surfactants, waxes or fine solids. These emulsions are often withdrawn for separate treatment in dedicated sludge treatment plants. The handling and treatment of emulsion sludges is addressed in more detail in the current SlPM Dehydration/Deoiling manual (EP 89-0150, section 5.7, due to be updated by mid 1994). Some of the processes discussed for solid sludges in the following section can also be applied to emulsion sludges.
4.5.3.
Sludges
4.5.3.1.
General Sludges are secondary waste streams containing accumulated solids, organic material and biomass. Sludge is typically produced by biological waste treatment, but also includes accumulated solid wastes from other types of deoiling equipment and hydrocarbon and water emulsion sludges. The handling and treatment of emulsion sludges is addressed in more detail in the current SlPM Dehydration/Deoiling manual (EP 89-0150, section 5.7, due to be updated). However a number of the sludge treatment processes presented in the following discussions may also be applied to emulsion sludges. The potential significance of sludge streams should not be underestimated. They may contain concentrated levels of environmentally significant components such as hydrocarbons, heavy metals and radionuclides and may be subject to special environmental regulations. Adequate provision must be made for the removal, handling, storage and treatment of solid and sludge waste products at the design stage. Table 4.5 summarises the various treatment stages that can be applied to sludges. Depending on the application, a sludge treatment process may utilise all or only some of these stages. Each unit operation is briefly addressed in the following discussions. The "Sand Wash Design Manual'' EP 93-1270, due to be issued in the 4th quarter of 1993, contains additional information on the handling and treatment of accumulated solids.
4.5.3.2.
Stabilisation Stabilisation is the treatment stage designed to convert the sludge to a safe and stable state. This involves the breakdown of degradable organic material to discourage microbial growth (putrescibility control) and to reduce the levels of micro-organisms to minimise any threat of pathogens. A number of biological and chemical processes can be used to stabilise the sludge. Stabilisation can also be used as a means of reducing the volume and weight of sludge.
4.5.3.3.
Conditioning Conditioning is designed to improve the dewatering characteristics of the sludge. Chemical conditioning includes the use of coagulation and flocculation chemicals to form larger, more readily separated agglomerations of solids. Elutriation is a washing stage that can be used before chemical conditioning to improve the effectiveness of the chemical treatment. Heat treatment can break down the structure of the sludge, resulting in a more easily dewatered sludge.
4.5.3.4.
Concentration Concentration of the sludge often precedes dewatering to reduce the volume of sludge to be dewatered.
SlPM Deoilinl: M(r111ra1. EP 93-1315. Rev 1.1. Nov 1993, File minw = 4CIIAP.DOC
PuKe 4- 7
4. Water disposal Concentration can be achieved by gravity thickening, dissolved air flotation or centrifuging, with gravity thickening being the most common method, The concentrated sludge underflow from a gravity thickener would typically contain in the order of 8 to 15% solids by volume.
4.5.3.5.Dewatering Sludge dewatering removes sufficient water from the sludge to form a damp solid or sludge cake. A range of processes are available, including centrifuging, filtration, drying beds and drying lagoons. Centrifuges can typically achieve a dewatered sludge of 25 to 40% volume solids, while filtration can typically achieve 40 to 60% volume solids. A vibrating membrane has also been developed for dewatering sludges.
4.5.3.6.Drying Drying of a sludge typically takes the form of heat treatment to produce a relatively dry sludge with a water content of only 8 to 10%. Incineration is a more extreme form of drying where the combustible elements of the sludge are converted to combustion products. Incineration will still leave some sludge residue in the form of ash which will still require a suitable form of disposal.
4.5.3.7.Residual disposal Any sludge handling system must include a method for the disposal of final residues. The most common methods of disposal are sanitary land fill, application on agricultural land and deep well injection. Land farming of sludges can be particularly effective in tropical regions. Residual disposal will usually require suitable facilities for the handling, storage and transportation of the residue. Table 4.5 Sludge treatment unit operations Unit operation
Methods
Stabilisation
Conditioning Concentration Dewatering
Residual disposal
I
Aerobic or anaerobic digestion Chemical stabilisation Composting Heat treatment Irradiation Lagooning Chemical addition Elutriation Heat treatment Centrifuging Dissolved air flotation Gravity settling Centrifuging Drying beds Lagoons Filtration Chemical fixation Land application/farming Land fill Well injection
Reference: Standard handbook of Environmental Engineering
Pup? 4-8
Function Putrescibility control Pathogen destruction Odour control Volume and weight reduction Gashy product production Improve dewatering Improve solids capture Improve processing rate Thickening Water removal Blending of sludges Water removal Volume and weight reduction End product utilisation Disposalto waste End product utilisation ;orbitt, R.A., ISBN 0-07-013158-9,
SIPM Droilinh. Mwuol. EP 93-1315, Rrv 1.1, Niiv 1993, File ncirnr = 4CHAP.DOC
5. Waste water sampling . ..
...... ... .......... .......... ... .... ...
......... .. ...
.....
5.1.
GENERAL A waste water stream is a complex mixture of constituents, both dissolved in the water and present in the dispersed hydrocarbon phase. In addition to the liquid phases, gas and solid phases may also be present. In E & P operations, most routine samples of effluent water are taken for the determination of hydrocarbon content. For this analysis, the most important consideration is obtaining a representative sample of the dispersed hydrocarbons. A representative sample is required to ensure; Accurate measurement of the overall hydrocarbon content. An inaccurate measurement indicating a high hydrocarbon concentration may have implications in meeting regulatory effluent quality standards. Effective process design and operation. The accurate measurement of hydrocarbon concentration and droplet size distribution of the dispersed phase is critical for the correct selection, design and operation of deoiling equipment. Because of the potential complexity of a waste water effluent stream, and the regulatory significance of the results of waste water analysis, it is important that there is a clear understanding of the factors associated with sampling that may influence the results of subsequent analysis procedures. The importance of following good sampling practices cannot be understated. Laboratory analyses, operational decisions, process and equipment design and environmental protection are all activities of which sampling forms the first step. Poor sampling degrades the value of these subsequent activities. At the very least, poor sampling wastes time and effort as repeat samples are required to confirm uncertain results. The procedures discussed in this section are designed for the sampling of waste water streams. For the sampling of well stream fluids (oil, gas, condensate etc.) the user is referred to "Guidelines for manual sampling and analysis of hydrocarbon fluids", SIPM EP 92-0980. A number of references are made to ASTM standard methods (American Society for Testing and Materials). These standards are readily available through most technical library services or can be requested from SIPM.
5.2.
SAMPLE POINTS
5.2.1.
Location of sampling points The following guidelines should be followed to ensure the correct location of a sample point.
d
Sample points should preferably be located in a region of turbulent flow. The transition to turbulent flow starts when the Reynolds number is greater than 3000.
d
Sample points.should be at least 3 pipe diameters downstream and 1 pipe diameter upstream of any flow disturbance such as a bend, pump, manifold etc. (ASTM D 4177-82, Ref.l.07.1 .c).
d
Sample points should preferably be located in vertical sections of piping where the fluid flow is upwards. The fluids in vertical piping are not subject to phase separation and stratification due to gravity.
d
Sample points should be located both immediately upstream and downstream of the deoiling equipment with no potential shear sources (e.g. control valves) between the deoiling equipment and the sample point.
d
Sample points should provide an effective and safe means for the collection and disposal of the fluid flow required to flush the sample point.
%
Sample points should not be located on or immediately after bends or other flow disturbances. Forces exerted on the fluid by flow disturbances (particularly bends) will result in a separation of phases of different densities.
SIPM Droiliitx Monitril, EP 93-1315, Rcv 1.1. Nov 1993. File ii(iiiir = SCIIAP.DOC
Pup2 5- 1
5. Waste water sampling %
Samples should not be taken from the surface of either a water stream or a body of water (e.g. sampling from the liquid surface in a vessel or tank). The surface layer will not be representative of the bulk of the fluid.
Effective operation and trouble-shooting of deoiling operations can only be performed with the provision of adequate sampling points both upstream and downstream of all stages of deoiling equipment. Designs for new facilities should always be reviewed for the provision of sufficient and suitably sited sampling points. In some cases, legislation may specify a particular sampling location for the monitoring of effluent water streams before discharge into the environment. Such a sample point may be required in addition to the sampling points required for the normal monitoring and control of deoiling equipment.
5.2.2.
Orientation of sampling points The following guidelines should be followed to ensure the correct orientation of a sample point.
5.2.3.
4
Sample points should always use a sample quill to ensure a representative sample.
4
The sample quill should preferably extend to the centre of the pipe or at least a distance of D/3 away from the piping wall (Ref.l.07.1 .n).
%
If sampling from horizontal piping cannot be avoided, samples should not be taken from the top or bottom of piping. The sample quill should be installed either to allow sampling from the centre of the pipe or at a point along the line of the "nine o'clock'' or "three o'clock'' positions.
Design of sampling quills To date, most water samples taken in the field are from sample points mounted directly on the pipe wall. However this is a poor sample location as the velocity and turbulence of the fluid at the pipe wall is relatively low and surface and wall effects may bias the sample. In addition, sampling from the wall requires the flow profile to divert through 90" to enter the sample piping. Due to these changes in the flow profile, the concentration and size distribution of any dispersed solid, liquid or gas phase in the sample is unlikely to be representative of the bulk fluid. To ensure a more representative sample, sample points should be fitted with a quill extension. Figure 5.1 illustrates two suitable sampling quills designed to allow the sample to enter the quill with minimum disturbance. These designs are taken from the reference "On-line process stream analysis - Sample take-off and transportation, March 1992", DEP 32.31.50.1 O-Gen.
I
Figure 5.1 Sample quills from DEP 32.31.50.10-Gen
The first design has the end of the sampling quill bevelled at 45".This is a cheap and relatively simple design. The second design uses a curved end to smooth the flow path into the sample quill. Both designs have the advantage of being straight which allows the quill to be inserted in a slim fitting similar to a thermowell and allows the probe to be easily withdrawn as required for maintenance. The sample point design illustrated in Figure 5.2 has a long radius bend designed to minimise any
P(J#C
5-2
SlPM Droilinl: Miuiitctl. EP 93-1315. Rrv 1.1. Nov 1993, File nume = 5CHAP.DOC
5. Waste water samtdinn disturbance to the flow pattern at the tip of the quill. A larger fitting is required to allow the curved quill to be inserted. The quill is offset to ensure the tip of the quill is as far away as possible from any flow disturbances around the fitting.
HIJOZb16P
Figure 5.2 Sample point design utilising a curved quill
The following guidelines should be applied to all sample quills. The wall thickness of the quill should be as thin as possible and the tip of the quill should be bevelled to a sharp edge. With a blunt edged quill a damming effect can occur upstream of the tip, deflecting droplets away from the quill. As previously mentioned, the quill should preferably extend to the centre of the pipe or at least a distance of D/3 away from the piping wall. However the length of the quill may be restricted by the need to withstand the mechanical forces exerted by the flow in the pipe. A procedure for determining the maximum length of a sample quill is given in “Standard Practice for Automatic Sampling of Petroleum and Petroleum Products”, ASTM D 4177-82 (Ref.l.07.1 .c). Care must be taken to ensure that the quill is installed with the opening facing in the upstream direction. The sample quill should be fabricated with an integral labelled tab to ensure correct orientation. The internal diameter of the sample quill must be sized to allow an isokinetic fluid velocity through the quill while ensuring the volumetric flow rate is within the capacity of the sampling equipment. Section 5.5.2 discusses isokinetic sampling in more detail.
5.3.
SAMPLE CONTAINERS
5.3.1.
Materials
5.3.1.1, Glass Glass sample containers are suitable for most water analyses. Glass sample bottles are preferred for non-routine samples, especially for the determination of heavy metals or when the sample will not be analysed immediately. The use of dark glass bottles will reduce photo-degradationof the sample. However, glass sample containers should not be used for samples from which small quantities of hardness, silica, sodium or potassium are to be determined.
5.3.1.2.
Plastics High density linear polyethylene, polypropylene and Teflon containers are suitable for most water analysis duties. However users should be aware that these containers are slightly permeable to light volatile hydrocarbons and gases such as carbon dioxide. Mercury will also be lost from the sample through the walls of the sample container. Plastic containers are acceptable for routine determination of hydrocarbon content of water samples, as errors introduced by sampling considerations will far outweigh potential errors from sample container materials. However glass sample containers should preferably be used for non-routine analyses, heavy metal analyses, or when samples will not be analysed immediately.
SlPM Duriiling Mciriitcrl. EP 93-1315. Rev 1 . 1 .
Niiv
199.3. File
i i i i i ~ i e=
SC//Af’.DOC
Puxe 5-3
5. Waste water sampling 5.3.1.3. Sample container closures In addition to the sample containers themselves, some consideration should also be given to the sample container lids and stoppers. These should also be made from glass or suitable inert plastics which will not absorb hydrocarbons from the sample. Aluminium foil lined closures should not be used when analysing for aluminium in samples that are strongly alkaline or acidic. Absorbent materials such as cork should not be used for lids or stoppers. Greases should not be used to assist the sealing of ground glass fittings.
5.3.2.
Cleaning of sample containers All sample containers, new or used should be thoroughly cleaned before use. Sample bottles and lids should be scrupulously clean of all hydrocarbon residues. No traces of cleaning detergents should be left in the bottles as these may influence the coalescing and settling of the dispersed phase. The following typical glassware cleaning procedure has been extracted from ASTM D 3325-90, “Standard practice for preservation of water-borne oil samples” (Ref.l.07.2.a).
The cleaning steps consist of an initial wash with a warm aqueous detergent mixture followed by six hot tap water rinses, two rinses with reagent water, a rinse with reagent grade acetone and a final rinse with solvent such as pentane, hexane, cyclohexane, dichloromethane, or chloroform followed by drying in a clean oven at 105°C or hotter for 30 minutes. If the glassware requires cleaning under field conditions, it should be washed with warm aqueous detergent followed by extensive water rinsing. A solvent rinse with acetone should be made, if possible, followed by a lengthy air drying to remove residual solvent More stringent cleaning procedures for both plastic and glass sample containers can be found in ASTM D 3694-92, “Standard Practice for Preparation of Sample Containers and for Preservation of Organic Constituents” (Ref.l.07.2.b). Sample containers for determination of trace substances such as heavy metals will require an even more thorough cleaning procedure. A typical procedure taken from the Thornton Research Centre (Ref.1.02.2.d) is as follows;
Sample containers are cleaned by standing overnight at room temperature containing 1:l hydrochloric acid. The containers are then rinsed clean with de-ionised water and allowed to stand overnight at room temperature containing 20% v/v nitric acid. The containers are finally thoroughly rinsed clean with de-ionised water, then stored in a particle and fume free environment prior to dispatch. Acids used should be analytical reagent grade.
5.4.
SELECTION OF SAMPLING METHOD The selection of the correct method for sampling water containing a dispersed liquid phase can be simply summarised by the following decision tree; Sampling to measure droplet size distribution? I
I
I
I I
I
Routine Sampling
Droplet Size Distribution Sampling
at the point the sample enters the sample quill. This ensures a representative sample enters the sample system.
the sampling. lsokinetic conditions to be followed where the sample enters the sample quill with neutral behaviour in the remainder of the sample system.
I Droplet size distribution must not be altered by Simply ensure isokinetic conditions are followed Reference section 5.5
Puge 5-4
Reference section 5.6
SlPM Deoilinl: Mnnucrl, EP 93-1315, Rev 1.1. Nov 1993, File nume = 5CHAP.DOC
5. Waste water sampling Routine sampling does not consider the droplet size distribution of the dispersed phase, thus provided isokinetic conditions exist in the sample quill, the conditions in the remainder of the sampling system will not influence the subsequent analysis. Droplet size distribution sampling requires a more careful design of the sampling system to ensure that the droplet size distribution is not altered by the sampling. These requirements are covered in more detail in section 5.6.
It should be noted that for both routine sampling and sampling for the measurement of droplet size distribution, to ensure a representative sample enters the sample system; A sample quill should be used. lsokinetic conditions should be maintained in the sample quill itself.
0
5.5.
ROUTINE SAMPLING
5.5.1.
Introduction The concentration of contaminants in effluent waters is often very low. The concentration of mineral hydrocarbons in effluent waters is generally lower than 40 parts hydrocarbon per million parts water (typical offshore effluent specification) while the concentration of other contaminants such as heavy metals is typically a thousand times lower, in the order of parts per billion. Due to these low concentrations, careful sampling practices are required to ensure samples of effluent water are representative and not contaminated.
5.5.2.
lsokinetic conditions lsokinetic sampling is simply achieved by ensuring that the velocity of the sample in the sampling quill is equal to the velocity of the fluid in the process line being sampled. This is critical when sampling streams containing a dispersed phase such as hydrocarbon droplets or suspended solids.
L O
L
* =
0
-
0
0
- 0
-/------
Vsarnple
Visokinetic
Vsarnple = Visokinetic
Vsarnple
> Visokinetic
Figure 5.3 Effect of sampling under isokinetic and non isokinetic conditions
Figure 5.3 illustrates the influence of the sampling velocity at the tip of the sampling quill. When not sampling at the correct isokinetic velocity the disturbance in the flow profile can result in a bias in the sampled size distribution due to the different inertial properties of the various sized elements of the dispersed phase. lsokinetic sampling is only effective when a sampling quill is used. Sampling from a simple side mounted sample point will introduce large changes in the flow profile which will tend to bias the sample whether or not isokinetic conditions are followed. For consistency isokinetic conditions should be used when sampling from a side mounted sample point, however to ensure a representative sample a sample quill should be fitted.
To determine the isokinetic sampling rate, the velocity of the fluid in the main process line should be calculated. Then, knowing the internal diameter of the sample quill, the appropriate volumetric sampling flow rate can be calculated which will result in the same fluid velocity in the sample quill as in the process line. The sampling flow rate for a non-hazardous water stream would usually be simply measured by timing the filling of a known volume (bucket and stop-watch technique). Table 5.1 gives an indication of the typical sampling rates required to achieve isokinetic sampling through different sized sample quills, based on an typical flow velocity of 2.5 m/s in the process line being sampled. Figures 5.5 and 5.6 at the end of this chapter can be used to quickly determine the SlPM Deoilir~gMiiniral. EP 93-1 715, Rev I 1. Nov 1993. File m r i i i c = SCIIAP DOC
Puxc 5-5
5. Waste water sampling correct sampling rates for other flow velocities. Table 5.1 Typical sampling rates for isokinetic sampling Sampling quill
I
(mm)
Required sampling . flow rate (m3/h)
12.5 15.8 20.9 26.6
1.11 1.76 3.10 5.02
&diameter
I
I
Time to fill a 10 litre bucket (seconds)
32 20 12 7 I
Basis: Assumes 2.5 m/sec fluid velocity in process line. Inside diameters correspondto schedule 40 pipe with 3/8",1/2", 3 4 " and 1' nominaloutside diameters .
5.5.3.
Procedure for routine sampling The following procedures can be followed for most routine sampling of low pressure waste water streams. Section 5.6 discusses techniques for sampling from higher pressure lines and sampling to measure droplet size distributions. Care must be taken to ensure that the inside of the sample container or container closure is not contaminated once in the field. Contamination could result from thin hydrocarbon films deposited from the production environment or from hands or gloves. The sample point should be opened and allowed to run to flush the sampling line. The sampling system should be designed for the safe containment and disposal of this flushing flow. Once the sample point has been flushed the flow rate from the sample line should be adjusted to give the required isokinetic sampling flow rate. Once the flow has stabilised the sample may be taken. The sample should be taken without rinsing the sample container. Rinsing will result in a higher hydrocarbon content by leaving a film of hydrocarbons on the internal surfaces of the container. When filling, the sample bottle should not be allowed to overflow as this will result in the concentration of dispersed solids or hydrocarbons which remain in the sample container as the water overflows. Samples should be clearly labelled and any abnormal conditions such as process upsets, operational problems or difficulties in obtaining samples should be noted. If a sample is to be retaken the initial sample should be discarded and a new sample taken using a fresh sample bottle. Repeat samples should be taken to confirm unusual results. Unusual results which are not confirmed are often simply disregarded as "spurious" results which may conceal an actual operating problem. Samples containing dispersed hydrocarbons should not be subdivided as phase separation and coalescence of the hydrocarbons may result in an uneven division. When determining the hydrocarbon concentration the entire sample should be analysed and the size of the sample collected should take this into consideration.
5.6.
SAMPLING TO MEASURE DROPLET SIZE DISTRIBUTIONS
5.6.1.
Introduction Sampling to measure droplet size distribution is more complicated than routine sampling as the size distribution of the dispersed droplets must not be altered by the sampling procedure. Two steps must generally be followed. The sampling conditions at the point that the sample enters the sample quill must be isokinetic to ensure that the dispersed material is representatively sampled.
POKC5-6
SIPM Deoilinp Momctrl. EP 93-1315. Rrv 1.1, Nirv 1993, File ncrmr = 5CHAP.DOC
5. Waste water sampling The conditions after the sample quill must be neutral. This maintains the droplet size distribution without encouraging either further droplet shearing or coalescence.
5.6.2.
Sampling procedure to determine droplet size distribution The first step in sampling to determine the droplet size distribution is maintaining isokinetic conditions in the sampling quill. As previously discussed in section 5.4.2, isokinetic sampling simply requires that the velocity of the sample through the sampling quill is the same as the velocity in the line being sampled. lsokinetic sampling should be used as the first stage of all sampling to ensure a representative sample enters the sampling system. Once a representative sample has entered the sample system, the objective is then to ensure the droplet size distribution is not altered. Thus after the isokinetic sample quill the sampling system should be designed to avoid both shearing and coalescing forces i.e. maintaining neutral conditions. Neutral sampling is not quite the same as isoenergetic sampling. lsoenergetic sampling is strictly defined as ensuring that the mixing energy exerted on the sample by the sampling system is approximately equal to the mixing energy that would be exerted on the fluid in the process line being sampled. In practice, what is actually required is that the sampling system does not alter the droplet size distribution of the sample once it has left the process line. Thus if a sample is taken from a coalescing zone, further coalescence in the sample system is not desired, just as further shear is not required when sampling from a high shear area. The user is required to exercise some judgement in designing a sampling system such neutral conditions are maintained and droplet size distribution is not altered, avoiding both droplet shear or coalescence. Appendix B contains an example illustrating a calculation procedure that may be used to estimate the correct sampling rate for any sampling configuration.
5.6.3.
Effect of process pressure on sampling and droplet size distributions
5.6.3.1.
Discharging to atmospheric pressure The majority of water samples are taken through a sample line and an isolation valve with the sample discharged to atmospheric pressure. Due to the inherent pressure drop through the sampling system this method of sampling is unlikely to be neutral and it is probable that the droplet size distribution of the dispersed phase will be altered by the sampling. Thus unless the pressure drop is low and special precautions are taken to prevent droplet shearing, droplet size distributions should not be measured when discharging a sample to atmospheric pressure.
5.6.3.2.
Pressurised sampling Where the droplet size distribution is to be measured, sampling should be conducted using a pressurised sampling method. Figure 5.4 illustrates one such sampling technique using a flow-through sample bottle. The sample quill should be sized to achieve isokinetic conditions at the point where the sample enters the sample system, however the remainder of the sample piping should be sized to achieve neutral conditions. Isolation valves should be full bore valves to minimise shear and the flow rate through the sample bottle should be regulated by using the downstream needle valve.
H Full bore isolationvalves
w Needle valve
3 1 Ouick releasecoupling
Figure 5.4 Flow-through sample bottle
~~
SlPM Droilinx Moiiicol. EP 93-1315, Rrv I I . Nov 1993, Fik
iiiiiiie
= SCIIAP DOC
PuRe 5-7
5. Waste water sampling The sample stream should be allowed to flow through the sample bottle until at least twice the volume of the sample bottle has been passed. Care should be taken to ensure that upstream valves are fully open to minimise pressure drop. Once the sample bottle has been flushed through, the downstream isolation valve should be closed, followed by the upstream isolation valve. The sample bottle can then be disconnected from the sample line and with the sample bottle orientated vertically the sample can be carefully depressurised using the upper valve. The depressurised sample can then be drained from the bottle and the size distribution of the sample measured. This sampling procedure ensures that the sample is not sheared across a valve during depressurisation. The orientation of the sample bottle should consider the relative density of the fluids. For example, if the dispersed phase is heavier than water (e.g. solids or some heavy oils), when the sample fluid velocity slows as it enters the sample bottle these dense particles or droplets may be able to settle against the upwards flow and accumulate in the sample bottle. In this case the sample bottle may need to be orientated downwards. Where visual inspection of the sample during sampling is required, a transparent sample container with a working pressure and temperature of 50 barg and 60°C respectively can be ordered from KSEPL (reference 1.07.1 .f). An alternative system which does not require flushing is a sample bottle fitted with a floating piston. Prior to sampling the piston is forced against one end of the sampler by charging with a liquid or inert gas. The sample bottle is then fitted to the sample point and the sample admitted to the sample bottle by withdrawing the charging liquid or gas at the desired rate. This sampling device is discussed in more detail in Appendix 2 of “Guidelines for manual sampling and analysis of hydrocarbon fluids”, EP 92-0980, (Ref 1.07.1 .m).
5.6.3.3.
Depressurisation Both the atmospheric and pressurised sampling methods discussed above eventually depressure the sample. This depressurisation is required by some analytical equipment for the measure of the droplet size distribution. However, depressurisation may lead to the generation of gas bubbles which may have a number of detrimental effects such as; Interference with the method used to measure the droplet size distribution e.g. by obscuration or optical interference. Gas bubbles may be registered as dispersed droplets. Gas bubbles generated within a dispersed droplet may shear the droplet as they evolve, altering the droplet size distribution.
If gas evolution may be a problem, droplet size distributions should be measured at process conditions without depressurisation using either the KSLA microphotograph technique or the GalaiNortoil particle/droplet size analyser (see chapter 6).
5.7.
SAMPLE PRESERVATION AND STORAGE
5.7.1.
Introduction After sampling, a sample will tend to ”age” through the action of chemical and biological reactions. This ageing will tend to alter the composition and character of the sample and thus should be prevented or minimised. Samples should preferably be analysed or utilised immediately to minimise the effect of ageing. However when this is not possible, appropriate storage and preservation techniques should be used to extend the representative life of the sample. Brief summaries on sample preservation and storage are given in the following discussions. Additional information can be obtained from the following references, 0
0
0
Puae
5-8
“Standard Practice for the Preservation of Waterborne Oil Samples”, ASTM (Ref.l.07.2.a).
D
3325-90
“Standard Practice for Preparation of Sample Containers and for Preservation of Organic Constituents”, ASTM D 3694-92 (Ref.1.07.2.b). “Standard Practice for Estimation of Holding Time for Water Samples Containing Organic SIPM Denilinp Mii/iwi/,EP 9.1-1315, Rev I . I , NOV1993. File nomr = 5CliAP.DOC
5. Waste water sampling Constituents”, ASTM D 451 5-85 (Ref.l.07.2.c).
5.7.2.
Chemical Preservation The life of a sample can be extended by the addition of preservative chemicals to the sample. These chemicals inhibit the chemical and biological changes that may alter the composition of the sample over time. The most common preservation technique used is the acidification of samples which are to be analysed for hydrocarbon content. Acidification (typically using hydrochloric acid) to a pH 30001 &=
Where:
q f
p D
32xfxq3
n3 xD7
or
E=-
fXV3
2xD
Eq. A.6
= flow rate (m3/s) = friction factor read from a Moody diagram
= dynamic viscosity (kg/(m.s)) = piping inside diameter (m)
The friction factor f is the Moody-Weissbach friction factor and should not be confused with the Fanning friction factor. The friction factor may be read from a Moody diagram such as in the Shell Production Poxe A-2
SIPM Deoiling Mor~iiol.EP 9.7-131.5, Hev I./. N(IV19Y3. Filv iwnir = YYAAI~INZ DOC
Appendix A - Emulsification and coalescence Handbook, Volume 8, Pipelines, page 28, Figure 1.1-10. Alternatively, page 26 of the same reference presents an equation which can be solved to determine f. An example of the calculation of mixing intensity is included in Appendix B where it used to determine the isoenergetic sampling velocity.
A.2.
Optimum Mixina lntensitv For Coalescence Using a dynamic coalescer, KSEPL have run laboratory trials to determine the optimum mixing energies that should be exerted upon a system to promote coalescence. The following results were obtained. Dehydration
Best coalescence in range of 2200 - 11,000 c m W with an optimum at 5500 cmVs3
Deoiling
Best coalescence in range of 11,000 - 110,000 cm2/s3
These optimum mixing energy figures are difficult to apply to conventional deoiling equipment where it can be difficult to identify the location and length of time that a fluid is exposed to mixing energy in the form of pressure drop. However, pipelines provide a readily identifiable source of mixing intensity. The mixing intensities given above can be used to evaluate the possibility of using a pipeline to promote coalescence. The full results of these coalescence tests can be found in reference 1.08.1.d. and this reference also includes discussions on the application of these mixing intensities to pipeline systems in Oman and Nigeria.
100000
-
10000
5
I
v
al
Q
c
1000
al
a
_.
9
5
-0
.!i 2
100
10
1 0.001
0.01
0.1
...x..
10
1
. 1 mN/m
100
1000
10000
100000
Mixing intensity (m*/s') -D--
5mN/m
-30mN/m
Figure A.l Relationship between maximum droplet size and mixing energy for a selection of hydrocarbon surface tensions
SlPM nroiliiiji
Miiiiiiiil,
EP 93-13lS. Rrv I . 1. No11 199.1. File iiioiir = 99AAlllNZDOC
Puge A-3
Appendix A - Emulsification and coalescence
Appendix B - Sampling to determine droplet size
B.l.
Introduction When sampling to measure a droplet size distribution, isokinetic sampling is required in the sample quill, however neutral conditions should exist in the majority of the sampling system. This method of sampling ensures that the droplet size distribution is not altered by the sampling procedure. In many cases, samples of dispersed hydrocarbons in water will be taken from relatively stable locations such as process piping where there is likely to be fairly neutral shear/coalescence behaviour. Thus the example calculation in this appendix actually demonstrates isoenergetic sampling, where the mixing intensity in the sampling system is kept equal to the mixing intensity of the process piping. In practice, the user should exercise their judgement in setting an acceptable mixing energy to maintain neutral behaviour in the sampling system. If the conditions at the point where the sample is taken are not neutral, the mixing energy in the sample system should be set to try and maintain neutral conditions. Some guidance on acceptable mixing energies can be found at the end of Appendix A. The following worked example is used to demonstrate the calculation of mixing intensities, the determination of the isoenergetic sampling rate and selection of the sampling quill size to achieve isokinetic sampling at the point where the sample enters the sampling system.
8.2.
Calculation of the mixina intensity in the process lint: A sample is to be taken of an effluent water stream containing a relatively small quantity of dispersed hydrocarbons. The stream to be sampled has the following properties
= 790 m3/h = 0.2194 m3/s = 1025 kg/m3 = 0.3048 m internal diameter = 0.0006 Pa.s
q
p D p
From this information the mixing intensity being exerted on the fluid in the process line can be calculated using the equations presented in Appendix A. First the Reynolds number can be calculated from equation A.4.
-
4 x 1025 x 0.2194
R x 0.0006 x 0.3048
= 1,565,685 = 1,600,000
As Re > 3000, the flow is turbulent. From a Moody diagram, assuming that for clean steel the roughness is 0.02 mm, the friction factor f is 0.0124. The mixing intensity E can now be determined from equation A.6. E
=
E
=
32xfxq
n3 xD’ 32 x 0.0124 x 0.2194
n3 x 0.3048’
Appendix B - Sampling to determine droplet size E
= 0.5530 m2/s3
E = 5530 cm2/s3
8.3.
Pressure drorJ in the samplina svstem The sample is to be analysed to determine the size distribution of the dispersed phase and thus neutral sampling is to be used. The sample is to be taken in a pressurised sample bottle configuration as illustrated in Figure B.1. The sampling lines are nominal % inch outside diameter with an internal diameter of 15.8 mm. The overall length of piping in the system is 1.3m.
0
0 0
0
H Full bore isolationvalves
w Needle valve
-I) Quick release coupling
Total piping length 2 x full bore valves 1 x quick fit union, assume the same as a full bore valve 1 x straight through tee piece 2 x long radius bends Entrance loss into quill Exit into sample container
K K K K K K
-
= = = =
= =
1300 mm 1.3 m 3 x f (for each valve) 3xf 20 x f 12 x f (for each bend) 0.78 1.o
Losses after the last isolation valve will not affect the sample. The pressure loss within the sample container itself is assumed to be negligible. 2. Assume a samplina velocitv.
As the calculation is iterative a initial sampling velocity must be chosen. Try 1.O m/s as the initial guess. 3. Determine the samplina flow reaime in the samde line. The Reynolds number can be calculated from equation A.3. Re =
Re =
pcxvxD iJ
1025 x 1 .O x 0.0158 0.0006
R e = 26.992 Re= 27,000 As Re z 3000, the flow in the sampling lines is turbulent.
Puge 8 - 2
SlPM Droiliirg Mnnictrl, EP 93-1315. Rev 1.1, Niiv 1993, File ntrme = 99BBISO.DOC
Appendix B - Sampling to determine droplet size 4. Determine the friction factor, From a Moody diagram, the friction factor f for a Reynolds number of 27,000, an internal diameter of 15.8 mm and a roughness of 0.02mm is 0.027.
5. Determine the total flow resistances across the samplina svstem. Knowing the friction factor, the total piping and fitting resistance KT can be determined. For piping, K = (f x L) / D, therefore; KT =
(fxDL)
KT=
fX(
+ (2 ~
( x 3f)) + (1x ( 3 f))~+(20 x f) + (2 ~ ( 1 x21)) +0.78 + 1.0
1.3 15.8 x
+ (2 x 3) + 3 + 20 + (2 x 12)
KT = 0.027~(135.2785)+1.78 KT = 5.4325 6. Determine the pressure drop across the samplina svstem.
The following expression for pressure drop is taken from the Crane reference, equation 3-14. AP = 5 ~ 1 x 0K T~x p x ? AP = 5 ~ 1 0 ~- 5~ . 4 3 2 5 ~ 1 0 2 5 ~ 1 . 0 ~ AP = 0.0278 bar AP= 2784Pa 7. Determine the time sDent in the samplina svstem. Assume that the pressure drop is spread relatively evenly through the sampling system. This assumption is reasonable as there are no large point sources of pressure drop in the sampling system and the pressure drop through the piping dominates. Thus, the duration of the pressure drop is the time taken to traverse the sample piping.
V
1.3
t
= -
t
= 1.3seconds
1.0
8. Calculate the mixina intensity
2784
E
=
E
= 2.0893 mVs3
E
=
1025 x 1.3
20.893 cm2/s3
9. Assume a new samdina velocitv.
Now this mixing energy is significantly higher than the mixing energy of 5530 cm2/s3in the main process
Appendix B - Sampling to determine droplet size line. We can get a closer result by assuming a lower velocity and recalculating. Assume new velocity of 0.65 m/s.
IO. Check the samplina flow reaime in the sample line. Re =
Re =
pcxvxD
m 1025 x 0.65 x 0.0158 0.0006
Re = 17,545 As Re > 3000, the flow in the sampling lines is still turbulent.
From a Moody diagram, the friction factor f for a Reynolds number of 17,545 an internal diameter of 15.8 mm and a roughness of 0.02mm is 0.0292. 12. Determine the total flow resistances across the samdina svstem. Recalculate the total piping and fitting resistance KT.
KT = 0.0292 x (135.2785) + 1.78 KT = 5.7301 13. Determine the pressure droD across the samplina svstem. AP = 5x1OW6xKTX AP =
2
~ X V
5 ~ 1 ~ 05 . 7~ 3 0 1 ~ 1 0 2 5 ~ 0 . 6 5 ~
AP = 0.0124 bar AP = 1241 Pa 14. Determine the time spent in the samdina svstem. The duration of the pressure drop is the time taken to traverse the sample piping.
1.3
t
= -
t
= 2.0seconds
0.65
15. Calculate the rnixina intansity
PURC8-4
1241
E
=
E
= 0.6054 m2/s3
E
= 6.054 cm2/s3
1025 x 2.0
SIPM Deoiliiig Mmiiwl, El' 93-1315, Rev 1.1. Nov 1993. File noinr = 99BBISO.DOC
Appendix B - Sampling to determine droplet size 16. Conclusions
The mixing intensity with a sampling velocity of 0.65 mls is very similar to the original mixing intensity in the pipeline. Thus 0.65 m/s is a suitable sampling velocity to achieve isoenergetic sampling.
B.4.
Sizina the sample quill for isokinetic conditions The previous calculation has shown that the sampling velocity through the majority of the sampling system should be 0.65 m/s to avoid any changes to the droplet size distribution. However, as discussed in section 5.5, the fluid velocity in the sample quill itself should be isokinetic to ensure a representative sample enters the sampling system. The sampling velocity and size of the sample piping determine the overall volumetric sampling flow rate. We need to specify the size of the sampling quill such that isokinetic conditions are achieved at this flow rate. 1. Determine the overall volumetric samplina flow rate
The overall volumetric sampling flow rate C is calculated by multiplying the sampling velocity and the cross sectional area of the sampling piping. q, =
vx-
xxD2 4
4, = 0 . 6 5 ~
-3
4
)2
q, = 1 . 2 7 4 4 ~ 1 0 -m3/s ~ 2. Determine velocitv in the main Drocess line
The fluid velocity in the process line being sampled is calculated from the volumetric flow rate and the internal diameter. vp =
vp =
4xa nxD2
4 x 0.21 94
n x 0. 30482
vp = 3.0 m3/s
3. Calculate the size of sample quill to achieve isokinetic samDling We now have the overall volumetric sampling flow rate and we know that to achieve isokinetic conditions the velocity in the sampling quill must be 3.0 m/s. From this information we can calculate the required internal diameter of the sample quill.
D, =
/
4 x 1.2744 x 10-4 ~ ~ 3 . 0
D, = 7.3544 x 10-3 m
D, = 7.35 mm
SIPM Deoiling M u ~ i r dEP , 93-1315. Hrv 1.1. N i w 1993. File 1 1 1 1 1 ~ 1=~ 99N11ISO.DOC
Puxe B-5
Appendix B - Sampling to determine droplet size 4. Conclusions
The sample quill should have an internal diameter in the order of 7.4 mm. With the velocity in the main sampling lines of 0.65 m/s, isokinetic conditions will be achieved in the sample quill and isoenergetic conditions will be achieved in the remainder of the sampling system. The sample quill should be kept as short as possible to avoid adding mixing energy to the sample.
8.5.
Contrast with iso-kinetic samDlinq The mixing intensity calculated above can be contrasted with the pressure drop and mixing intensity that would be experienced if the entire sample system was operated at the isokinetic sampling velocity. 1. Determine the iso-kinetic samDlina velocitv. We know from the previous calculation that the isokinetic sampling velocity is 3.0 m/s. 3. Check the samplina flow reaime.
The Reynolds number in the sample line can be calculated from equation A.3.
Re =
1025 x 3.0 x 0.01 58 0.0006
R e = 80,975 As Re > 3000, the flow in the sampling lines is turbulent. 3. Determine the friction factor. From a Moody diagram, the friction factor f for a Reynolds number of 80,975 in an internal diameter of 15.8 mm and a roughness of 0.02 mm is 0.0235. 4. Determine the total flow resistances across the samplina system. Recalculate the total piping and fitting resistance KT.
K, = 0.0235 x (135.2785) + 1.78 K, = 4.9590 5. Determine the Dressure drop across the samDlina svstem.
A P = 5 ~ 1 0 ~- 4~ . 9 5 9 0 ~ 1 0 2 5 ~ 3 . 0 ~ AP = 0.2287 bar
A P = 22874Pa 6. Determine the time spent in the samplina svstem.
The duration of the pressure drop is the time taken to traverse the sample piping t
= -
L V
E U ~ E-6 C
Appendix B - Sampling to determine droplet size t = -
t
1.3 3.0
= 0.433seconds
7. Calculate the mixina intensity
22874
E
=
E
= 51.5383 m2/s3
1025 x 0.433
E = 515.383 cm2/s3 8. Conclusions
It can be seen that the mixing intensity from iso-kinetic sampling is in the order of two magnitudes higher than the isoenergetic sampling (which in this case i s assumed to be neutral). This highlights the importance of not using iso-kinetic conditions throughout the whole sampling system and trying to maintain neutral sampling when the size distribution of the dispersed phase is to be determined.
Appendix B - Sampling to determine droplet size
P U ~8-8 C
SlPM Deoilirtx
Mtriirctil. EP
YJ-lJ1.5. Rrv 1. I . Nos 1YY.1, Fllr
iltitiir
= 99BBISO.DOC
Appendix C - Published infrared analysis procedures
c.1
List of IR analvsis procedures
Test reference
Brief Designation
[l]
API Method 733 58
[2]
DEV H 17/181971
[3]
CONCAWE
[4] [5]
-
I
~UNICHIM
Date
Determinationof volatile and non-volatileoil material. Infrared spectrometric method
I I I
I
1971
Bestimmungvon Kohlenwasserstoffenmittels der lnfrarotintensitrits-Spektroskopie. (Determination of hydrocarbons by infrared intensity spectroscopy).
1972
Mineral oil in water by infrared spectrophotometry.
1U.S.A.
1978
Petroleum hydrocarbons, total recoverable. (Spectrophotometric,infrared.)
lMCO1978
1978
AFNOR
[9]
German
IItalian
I lDutch
Dtltermination des hydrocarbures par spectrophotometrie Belgium infra-rouge. Bepaling van de koolwaterstoffendoor infrarood spectrofotometrie.
NBN
IEnglish
Netherlands English
1975 IDeterminazionedegli oli mineral per spettrofotometria I.R. Italy
T91-502(1 977)
Language
I 1 Germany
I
I
EPA 1978
[6]
Country
Title
French and
U.S.A.
English
Method for the determination pf oil content.
UK
English
1979
Effluents aqueux des raffineriesde petrol. Dosage des hydrocarburestotaux.
France
French
Paris Commission Commission de Pans
1979
Method of analysis for discharges from oil and gas production platforms. Methode d‘analyse pour les dtlversements des plateformes de production de gaz et d‘huile.
[lo]
Swedish Standard
1979
Determinationof oil and grease in water. Infrared spectrophotometricmethod
Sweden
[ll]
RlZA
1980
Bepalingvan de olie-index met behulp van infraroodspektrometrie.(determination of the oil-index by infrared spectrometry)
Netherlands Dutch
[12]
ASTM D 3921-80
1980
Standard test method for oil and grease and petroleum hydrocarbonsin water.
U.S.A
English
[13]
APHA 1980 Parts 502B,502E
1980
Partition-infraredmethod (tentative) Hydrocarbons.
U.S.A
English
[14]
NEN
1989
Water Bepaling van het gehalte aan minerale olie met behulp van infrarood-spectrofotometrie (Water Determinationof mineral oil content by infrared spectrophotometry)
Netherlands Dutch
1981
Bestimmungvon Kohlenwasserstoffen. (Determinationof hydrocarbons.)
Germany
[7]
[8]
418.1
T90-203/79
SS028145 (1979)
NEN 6675
1989
[I51
DIN DIN 38409 H18
-
____
English and French
Swedish
-
German
Source: Determinationof hydrocarbons in aqueous effluents by infrared analysis, Concawe Report No. 1/84, March 1984. NEN method upgraded from
tiQ!.M 1.
2.
NEN 6673 (1981) to NEN 6675 (1989).
The informationcontained in this table has been reported as stated in the texts of the individual methods. No attempt has been made to amend it, even if it appears inconsistantin some cases. st: overall (total) standarddeviation so: single operator standard deviation
Appendix C - Published infrared analysis procedures c.2
Kev characteristics of identified IR analvsis procedures
(Page 1 of 3) Test reference METHOD Matter revealed
[l] 121 API Method DEV H 17/18 733 58 1971 hydrocarbons, hydrocarbons hydrocarbon derivatives, all substances with CH, CH2, CH3 groups.
[3] CONCAWE
-
141
151 NBN T91-502 (1977) hydrocarbons
UNICHEM 1975
hydrocarbons, or mineral oils hydrocarbon derivativesof any kind
Minimum 1 determinability (ppm) 3 Sample volume (I)
0.1
0.1
0.5
0.2
1
3
variable
1
pH adjusted to
5
___-
5
5
5
Extractionsolvent
CCI4
cc14
cc14
cc14
cc14
Boiling point (“C)
77
77
77
77
77
Volume (ml)
loo+ 100
25
50
50
50
In
original container
original container
original container
original container
original container
By means of
shaking machine 100 mechanical strirrer strokeshin, amplitude 3.8cm 15 min 30 sec
shaking machine 100 strokeshin, amplitude 3.8cm 15 min
magnetic stirrer (4 cm hand or shaking machine 100 strokes long) per minute 15 rnin 15 min
Florisil added
Florisil added
Extractionperformed:
For Chrornatogpaphic adsorbent Column diameter (cm) Height of filling (cm)
Florisil added
Quantity (9)
1
5
5
Matter removed
non-hydrocarbons
most of the nonhydrocarbons
Florisil 1
5 to 6
Wavelength (pn)
3.42 3.50
3.30 3.38 3.42
3.38 3.42
non-hydrocarbonpolar components aceous polar organic compounds 3.38 3.42 3.30 3.38 3.42
Groups detected
CH2 CH2
CH
CH3 CH2
CH3 CH2
CH
Calibration
known oil or reference typical specific oil (37.5% iso-octane, absorptivities for CH, 37.5% cetane, 25% CH, CH, bands benzene) to the nearest ppm < 10 to 0.1 ppm > 10 to 1 ppm about *lo% for not suitable for highly known oil, &O% for aromatic products reference oil, such as tar oil and benzene, xylene, aromatic extract cumene essentially undetected about *lo%
know oil or typical absortivities (one normal, one for gasoline)
known oil or typical absorptivities (one normal, one for gasoline)
typical absorptivities for CH, CH2, CH:,
Results reported Accuracy
Precision
CH3 CH2
less suitable for highly aromatic hydrocarbons
in the case of gasolines less accurate values are to be expected repeatabilitybetter than 10%
CH3 CH2
at 2pprn level st = 0.24 so = 0.06
reproducibility20%
Source: Determination of hydrocarbons in aqueous effluents by infrared analysis, Concawe Report No. 1/84, March 1984. NEN method upgraded from
I’ll@
c-2
SII’M D t w i / ; f Moriifol, !~ EP 93-1315, Rev I . I. Nov 1993. Filr
iiifiiie
= 99CCIRED.DOC
Appendix C - Published infrared analysis procedures
Test reference METHOD
Table C.2 Published infrared procedures for determination of hydrocarbons in water (Page 2 of 3) [SI [7] [E] [9] IMCO 1978 AFNOR Paris Commission EPA 1978 418.1 T90-203179 1979 oils, including most petroleum oil, inclusive of most total hydrocarbons hydrocarbons light oil fractions light fractions inclusive of light fuels
[lo]
Minimum C1 determinability(ppm) 1 Sample volume (I)
0.1
_-__
0.1
Swedish Standard SS028145 (1979) most components in mineral oil, some organic solvents, petroleum based part ot greases, petroleum based waxes 0.1
1
0.9
1
1.2
pH adjusted to
c2
View more...
Comments
