Fabric Dust Collector Systems

Transport and Dust Collecting Manual Version 1.08

Fabric Dust Collector Systems Werner Flückiger Leticia Nacif Flückiger B1 (MPT 03/14902/E)

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Table of Content 1.

INTRODUCTION

4

2.

TECHNOLOGY OF PULSE-JET DUST COLLECTORS … How the pulse-jet dust collectors work … Design configurations … Mechanical elements … Bag Cleaning Systems … Comparison between reverse air type and pulse-jet dust collector … Bag fixation … Filter cloth

4 4 5 5 6 6 7 8

3.

HOLCIM-CTS DUST COLLECTOR DESIGN GUIDELINES

12

3.1

General theoretical design guidelines … Filtration velocity … Air-to-cloth ratio (A/C ratio) … Can velocity

12 12 13 13

3.2

Dust collecting system design guidelines … Amount of dust sources to vent … Venting air volume … Venting hood design … Ductwork design

13 13 13 14 14

3.3

Dust collector construction design guidelines … Gas flow / dust distribution … Clean gas plenum / housing … Dust hopper … Filter bag dimension … Distance between the bags … Number of bags per row … Venturis … Bag cages … Filter cloth … Airlocks … Fan

15 15 17 17 19 19 19 19 20 20 21 21

3.4

Dust collector cleaning control … General … Pulse sequence … Pulse cycle … Diaphragm and solenoid valves … Purge valve

21 21 21 22 23 23

3.5

Problem solving guide / trouble shooting

24

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1.

INTRODUCTION The modern cement plant continually faces the challenge of keeping the process running and producing a high quality product in a timely manner whilst remaining in compliance with the national and local environmental regulations. The trouble-free operation of air pollution control systems therefore has a key role to play, since there are plenty of dust collectors in each cement plant. The cement manufacturing is characterized by the extraction, transport, storage and processing of very large quantities of solid material, often in a dry and powdered state. There is an obvious potential for the generation of dust emission from the quarry to the shipping station. For environmental protection reasons, work safety, equipment wear rate and waste of money, it is urgently necessary to collect the dust and bring it back to the main material flow. This manual is focused on nuisance dust collecting of auxiliary equipment that allows to correctly design a pulse-jet dust collecting system and to make the right choice between different filter types/makes on the market. We want to help keep our group plants running and producing.

2.

TECHNOLOGY OF PULSE-JET DUST COLLECTORS …

How the pulse-jet dust collectors work The dust-tight casing has three sections (see figure 1); a clean-air plenum at the top, a filtration housing containing a number of cylindrical or envelope type filter bags in the middle, and a dust storage hopper at the bottom. The filter elements are supported by a tube sheet that separates the filtration housing from the plenum. Dust-laden air enters the collector through a diffuser, which absorbs the impact of the high velocity dust particles, distributes the air, and reduces its velocity. The slow air speed causes the heavier particles to drop into the hopper. The air steam then flows through the filter units, depositing the fine dust on the outside of the cloths. The cleaned air continues upward into the plenum and exhausts into the atmosphere. The filter elements are cleaned by a momentary, high-pressure back-pulse of compressed air from the clean side of the filter element. Blowpipes, arranged over each row of filter elements, deliver the pulses. The bursts of air are optimized by venturis located at the top of the filter elements to effectively dislodge dust along the length of the elements. A pulse control timer times the cleaning cycles. A differential pressure (between the clean and dirty sides) gauge helps to determine cleaning frequency.

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Design configurations Dust collector supplier offers 5 basic designs to choose from: • Bin vent collectors for mounting on silos or bins • Small, self-contained insertables for existing enclosures • Pre-assembled modular units for up to approximately 450 m2 • Large application sectional units for larger than 450 m2 • Cylindrical units for high pressure / high vacuum applications

…

Mechanical elements 7

8

9

4

11 12 5

10

19

3 14

6 1 Raw gas inlet

Clean gas outlet 15

2 17

16 18 13

1

Dust loaden air

11

Diaphragm pulse valve

2

Diffuser

12

Pulse control timer

3

Bag cage

13

Rotary valve

4

Clean air outlet (Plenum)

14

Differential pressure gauge

5

Tube sheet

15

Closing valve

6

Filter bag

16

Compressed air bin

7

Venturi

17

Regulation damper valve

8

Locking ring (or snap band fixation)

18

Fan

9

Blowpipe

19

10

Header (compressed air tank)

Purge unit with hand reducer and filter set

Fig. 1: Mechanical elements of a pulse-jet dust collector. Holcim Group Support Ltd CMS - Mechanical Process Technology

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Bag Cleaning Systems Summary of the various cleaning principles used for bag filters

(a)

(b)

(c)

(d)

(e)

Vibrator

a, b: manual or mechanical, by rapping or shaking c: mechanical, by vibrating d:

pneumatic, by reverse air flow (often combined with shaking or vibrating)

e:

pneumatic, by compressed air (pulse-jet)

Since most of the mechanically cleaned filters have been replaced by compressed air ones, mainly in the cement industry, the mechanical cleaning devices will not be described further here. …

Comparison between reverse air type and pulse-jet dust collector Pulse-jet type with low pressure cleaning

Pulse-jet type with high pressure cleaning

large due to low filtration velocity 2 extra chambers for offline cleaning 10 - 20 mbar

small due to longer bags no separate chamber necessary

medium due to shorter bags no separate chamber necessary

8 -12 mbar

8 -12 mbar

Ø300 x 10 m

Ø130-150 x 7-8 m

Ø120-150 x 4,5-6 m

3 - 5 years due to smooth cleaning

3 - 5 years due to smooth cleaning

Tank pressure Cleaning air flow Cleaning air quality

(30 - 40 mbar) 2.0 - 3.5 Nm3/m2h uses clean gas

Cleaning time (opening time of valve)

10 - 30 sec

0.6 - 2 bar 0.05 -0.3 Nm3/m2h refrigeration dried or heated by roots blower 600 ms

3 years due to harder cleaning by pressure pulses 3 - 6 bar 0.02 - 0.10 Nm3/m2h absorption dried

Reverse air type Foot print of filter Number of chambers Pressure drop across bag filter Bag dimensions (available) Bag life expectances

150 ms

All three bag filter types are successfully in operation. The choice has to be made by price comparison.

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Bag fixation Filter bag fixation with snap-band

Snap-band

Filter bag

Fig. 2: Bag fixation by snap-band Filter bag fixation with roll band / twist lock

Roll band

Fig. 3: Bag fixation by roll band Filter bag fixation screwed

Fig. 4: Mechanical fixation of bag cages

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Filter cloth Filter media are available either in form of woven fabric or felt fabrics. The structure of these two filter media is shown as follows:

Fig. 5: Woven fabric and needle felt filter cloth The characteristics of woven fabric are its system of warp and weft threads crossing one to another. Needle felts are "three-dimensional" filter media. Most used filter media in the cement industry are needle felts due to a lower pressure drop and higher dust collection efficiencies compared to the woven fabric. Selection criteria The filter medium is the all-important central feature of any dust collector operating on the filtration principle. With the correct or incorrect choice of the filter material, the whole dust collection operation will stand or fall in actual practice. Important selection criteria are: • filter type, particularly cleaning principle • moisture level • gas temperature (average and peaks) • composition and chemical properties of the gas • raw gas dust load, particle size • particulate abrasiveness • allowed dust load in the clean gas • physical and chemical properties of the dust Furthermore, the filter medium must satisfy the following conditions: • high air permeability (low pressure losses) • good mechanical strength • good thermal stability at operational temperature • good dimensional stability at operational temperature

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Legend: 1 exellent 2 very good 3 good 4 fair 5 poor

Properties of Various Filter Media

Natural

Fabric, Trademark

Chemical Classification

DIN 60 001

Tensile strength N/mm2

Cotton

max. Operating Temperature [°C] long time short time

Acide Resist.

Alkali Resist.

Abrasion Resist.

Moist Heat Resist.

Price Rating

Density 2 [g/m ]

Cellulose

(CO)

410-670

70-90

120

5

3

2

3-4

$

150-400

Wool

Keratin (protein)

(WO)

120-230

90

120

3-4

4

3-4

3-4

$$

400-600

Acrilan, AC/AC

Polyacrylnitrile

(PAN)

200-530

100-110

100-120

3

3-4

3-4

1

$$

500-600

(PAN)

200-530

110-120

120-140

2-3

3-4

3-4

1

$$

500-600

(PP)

260-640

90-100

100-120

1-2

1-2

1-2

1-2

$

550

(PES)

560-820

130-150

150-160

3-4

3-4

2

5

$

400-600

Fibers

- copolymer Dralon,

Orlon,

Zefran, Polyacrylnitrile

Dolanit

- homopolymer

Synthetic

Polypropylene, Meraklon

Polypropylene

Organic

Trevira, Dacron, Terylene, Polyester

Fibers

Tergal, Vestan, Kodel

(dry)

Nylon, Perlon

Polyamide (alipahtic)

Nomex, Conex, Trol

Polyamide

(aromatic)

(Aramide) Teflon Ryton,

Polytetra-Fluorethylene PPS,

Rastex, Polyphenylene-

Procon

Sulfid (PPS)

P 84

Polyimid (PI)

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PA

370-850

90-110

100-120

4

2

1-2

3-4

$

300

570-690

180-210

200-240

good in

Excellent at

1-2

3-4

$$$$

500-600

weak acids

low temp. 1

$$$$$$$

750-940

(AR) (PTFE)

380

260

280

1-2

1-2

3-4

1000-1200

180 max.

200 max.

1

1

2-3

$$$$$$

500-800

5%O2

15% O2

240-260

280

1-2

1-2

4-5

$$$$$$

550

850-900

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Fabric, Trademark

Chemical Classification

Glass, Fiberglass

Glass

Synthetic

Stone Wool

Mineral

120-260

Anorganic

Various Steels

Metals

500-750

Ceramic

Silicium Oxyde

Fibers

Holcim Group Support Ltd CMS - Mechanical Process Technology

DIN 60 001

Tensile strength N/mm2 1500-2500

max. Operating Temperature [°C]

Acid Resist.

Alkali Resist.

Abrasion Resist.

Moist Heat Resist.

Price Rating

Density 2 [g/m ]

3-4

3-4

4

3

$$$

300-400

300-350

3-4

3-4

up to 600

1

1

1

870

1

4

4

$$$$$$$$

> 30

230-270

350

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Special Treatment of the Bag Surface •

Special treatment of the fabrics and needle felts can significantly improve the properties of the bags.

NonFiberglass Singe

Finish Purpose

Recommended for improved cake release

Available For

Polyester, Polypropylene, Acrylic, Nomex, Ryton, P 84 (felts)

Glaze

Provides short-term improvements for cake

Polyester, Polypropylene (felts)

release (may impede airflow) Silicone

Aids initial cake development and provides

Polyester (felt and woven)

limited water repellence Flame Retardant

Retards combustibility (not flame- proof)

Polyester, Polypropylene (felt and woven)

Acrylic Coatings

Improves filtration, efficiency and cake

Polyester and Acrylic felts

(Latex base)

release (may impede flow in certain applications)

PTFE Surface

For capture of fine particulate, improved

Nomex, Polyester, Acrylic, Polypropylene

Treatments and

filtration efficiency, cake release

(felt) (Laminates available in Polypropylene,

Laminates

Ryton and Polyester only)

PTFE Penetrating

Improved water and oil repellence; limited

Finishes

cake release

Acid Resistant

Improved acid resistance and water

Nomex (felt)

Nomex (felt)

retardance

Fiberglass Silicone, Graphite

Finish Purpose Protects glass yarns from abrasion, adds lubricity

Teflon Acid Resistant

Applications For non-acidic conditions, primarily for cement and metal foundry applications

Shields glass yarn from acid attach

Coal-fired boilers, carbon black, incinerators, cement, industrial and small municipal boiler applications

Teflon B

Blue Max- CRF/70

Provides enhanced abrasion resistance and

Industrial and utility base load boilers under mild

limited chemical resistance

pH conditions

Provides improved acid resistance and release

Coal-fired boilers (high and low sulfur) for peak

properties, superior abrasion resistance, resistant

load utilities, fluidized bed boilers, carbon black,

to alkaline attack, improved fiber encapsulation

incinerators

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Membrane filter bag surface •

Special finishing or the application of membranes on the bag surface becomes more and more important. The purpose of this treatment is to improve the bags' resistance against chemical attack as well as optimum filtration efficiency and cake release, especially for fine dust particles.

Fig. 6: Filter bag without membrane Fig. 7: Filter bag with membrane

3.

HOLCIM-CTS DUST COLLECTOR DESIGN GUIDELINES The choice between different bag filter types/makes for the dust collection of a gas flow is always based on the same technical questions that must be answered before deciding about the investment. According to our experience, gained in many applications, all nuisance dustcollecting systems should fulfill the requirements as follows:

3.1

General theoretical design guidelines …

Filtration velocity The maximum allowed filtration velocity depends on the flow resistance of the bag pulse filter cake and the cleaning ability of the filter bag and of course on the cleaning method. The pressure difference (Δp) across the filter bags increases: • the higher the filtration velocity • the thicker the filter cake (residual dust layer after cleaning) and the quicker it builds up (dust load time/cleaning interval) • the higher the Blaine value of the dust (the finer the dust) • the more compressible or sticky the dust (important for AFR usage) • the older the bags (due to penetration of fine dust particles into the fabric)

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For sufficient cleaning of the filter bags it is necessary to reverse the gas flow through the bags. This can be done either by having a high pressure inside (high cleaning pressure) or by having a huge amount of gas flowing in opposite direction (low cleaning pressure or reverse air). When the pressure drop across filter bags is too high, then the cleaning becomes insufficient and the filter clogs up rapidly. …

Air-to-cloth ratio (A/C ratio) The air-to-cloth ratio (A/C ratio) is simply a mathematical expression used to measure the amount of filtering cloth area available to filter a given volume of air at a given flow rate. There are standard air-to-cloth ratios based on cleaning mechanism styles, and this ratio is used to determine the operating limits of the bag house. The guide ratios for collectors with pulse-jet cleaning are as a function of the bulk material to handle for auxiliary equipment venting as follows: ƒ1.2 m3/m2 x min for slag, coal and clinker dust 3 2 ƒ1.5 m /m x min for limestone and cement dust

…

Can velocity The can velocity is the theoretically calculated raw gas velocity between the filter bags at the bag bottom area. This is valid independently of raw gas inlet design. The maximum allowed velocity depends on the gas flow direction between the bags and the terminal velocity of particle collectives/agglomerates that have to fall into the hopper by gravity. From experience, we know that the vertical upward vector of the gas flow velocity should be between 1.0 and 1.3 m/s for auxiliary dust collecting systems. The formula presented below can be used to calculate the can velocity: Can velocity [m/s] = Total Venting Air Volume [m3/s] ÷ {Total Tubesheet Area [m2] – (Hole Area [m2] * Number of Holes)}

3.2

Dust collecting system design guidelines …

Amount of dust sources to vent No more than six (6) to eight (8) dust sources to vent should be connected to one dust collector.

…

Venting air volume The true required venting air volume that the ventilation system has to handle must be determined first. Therefore, it has to be determined how much vent air is required at each dust point. The recommended standard volumetric requirements for the venting of typical applications in ambient air are shown in Appendix 1. The air flow for the remaining venting pipes before the filter should be the sum of the presented values as shown in mentioned appendix.

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Venting hood design The hooding design at pickup points should provide ventilation of the dust point without capturing product from the main material flow. If it will be done in this way, only airborne particles will be introduced into the dust collection system. Improperly designed hoods tend to increase the grain loading beyond of what the collector was originally designed to handle. The recommended standard design practices for hood design are shown in Appendix 2.

…

Ductwork design Once the volume on each individual vent point is known, the ductwork has to be designed correctly. The proper gas velocity will depend on the dust being conveyed, but a general rule for good ductwork design is to size the duct cross-sectional area for a velocity of 15 to 18 m per second. For explosive dust, the pipes should be sized to an air velocity between 18 and 24 m/s. Ducts with lower velocity will encourage material to fall out. Ducts that have higher velocities encourage abrasion. The guide values for gas velocity in ductwork are: - 16 m/s for abrasive dust (clinker, slag) - 18 m/s for non-abrasive dust (limestone, cement, raw meal) Frequently encountered ductwork problems are poorly designed branch entries, elbows and size variations that hamper airflow and/or cause accelerated wear. Correct and incorrect ductworks are shown for your reference in Appendix 2. Dust collecting systems with an excessive number of connected vent points cannot be controlled / calibrated in a way that pollution control is effective. That is why we recommend limiting the number of vent points connected to one filter to at maximum of 8 points. The minimum duct diameter shall be 133 mm (5") outside, and the minimum duct and hood wall thickness 3 mm (1/8"). Up- and downward sloping for dust-laden air shall have - to avoid dust accumulation - a minimum slope of 60° for limestone, slag and cement and 45° for clinker, 70° for coal measured from the horizontal.

min. 60°

Limestone, Slag, Cement

Fig. 8: Duct-slope for limestone, slag, cement dedusting

min. 70°

min. 45° Clinker

Fig. 9: Duct-slope for clinker dedusting

Coal

Fig. 10: Duct-slope for coal dedusting

Ductwork in horizontal should be avoided! Holcim Group Support Ltd CMS - Mechanical Process Technology

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For a fan discharge duct, the velocity shall be between 15 and 20 m/s. Silencer to be provided, if required. Orifice plates with wear protection shall be used for balancing systems, which handle abrasive dust (e.g. clinker, slag). All other systems shall have butterfly dampers of a minimum 6 mm thick plate construction.

Fig. 11: Typical orifice plate design 3.3

Dust collector construction design guidelines …

Gas flow / dust distribution A good gas flow distribution does not necessarily mean having also a good dust distribution. But a good gas flow distribution indicates a more even dust distribution. Gas flow jets loaded with dust do not lead to wear of bags or other internals very much. Uneven dust distribution results in short cleaning cycles with high cleaning air consumption and shorter bag life expectance. During the filter design the suppliers should take care about gas and dust distribution. The general rule is to ask the suppliers for a dust drop -out box at the gas entrance if the raw gas dust content is above 300 g/m3. As follows some examples of good gas distribution design at the dust collector entrance: Typical design

Fig. 12: Typical raw gas inlet design Holcim Group Support Ltd CMS - Mechanical Process Technology

Recommended design

Fig. 13: Recommended raw gas inlet design B1/15

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Preferred deflector plate design 6"

3" Overlap Type

Inlet

3" m

in.

6"

1" Parting Line Wall and Hopper Inlet Slide of Colector

3"

6" x 1/4" Flat Bar

Fig. 14: Deflector plate design

Raw gas top inlet configurations

Fig. 15: Not recommended raw gas inlet design

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Fig. 16: Recommended raw gas inlet design

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Drop-out box design configurations All dust collectors installed at the clinker transport in the section from clinker cooler to silos must be equipped with a cyclone or drop-out box, in order to prevent damage filter bags due to hot clinker particles.

Fig. 17: Drop out box design configurations …

Clean gas plenum / housing Using a clean gas plenum instead of a liftable compartment cover has the advantage of better gas tightness because it has one door per compartment only. The plenum height has to be very high when undivided cages with long length bags are installed. Outdoor filters larger than approximately 1.5 / 1.5 m should be equipped with weather protection or walk-in-plenum for maintenance access i.e. sufficient height. For small filters (< 1.5 / 1.5m) located outdoors and all filters located inside buildings, top access (without walk-in-plenum) are also acceptable. Bin vent type filters shall be provided with suitably reinforced bag/man catcher screen for safety reasons. Casing insulation shall be provided for outdoor filters, which are exposed to operation below the dew point. The insulation wall thickness shall be minimum 50 mm.

…

Dust hopper For dust, which tends to agglomerate or leads to clogging, the corners of the hoppers should be rounded. Anyway the valley (corner) angles of the hoppers should not be lower then 550 in all applications, respectively 700 for coal, separator and bypass dust. In the Appendix 3 there is a chart to find the hopper valley angle considering the different angles of the hopper.

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A very serious problem in most group plants is the agglomeration of dust in the pyramid hoppers due to a much too small discharge opening and a too low inclination of the hopper walls. In such cases, which are problems of the supplier filter design, many dust collectors have already been modified by replacing the rotary feeder with a screw conveyor as shown below. Fig. 18: Typical blocked dust hopper outlet

∼ 700

440

∼ 700

50

250

350

650 1250

250

Fig. 19: Modification of dust hopper by installing vertical side walls

∼ 750

~ 450

∼ 750

50

250

1250

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Fig. 20: Modification of dust hopper by installing conically side walls, (for extremely sticky material)

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Filter bag dimension The filter bag dimension depends on the cleaning system efficiency and the geometrical allocation of the filter bags. The diameter of the bags is usually between 120 and 160 mm. For standardization reasons most filters should be matched in such a way that only one size and type of bags is used. The maximum allowed bag length depends on the cleaning system efficiency and the geometrical allocation of the bags.

The following bag lengths are recommended not to be exceeded:

reverse air low pressure pulse-jet high pressure pulse-jet

new installation 11.0 m 6.0 m 4.5 m

conversion 11.0 m 8.0 m 6.0 m

The longer the bags, the more likely not perfectly vertical mounted, which provokes bags touching each other at bottom area. This causes a high wear rate due to friction between the bags. Furthermore, long bags are more difficult to clean and to remove if filled up with dust or having a hole in the fabric. …

Distance between the bags The minimum distance between the bags should be 50 mm. The distance between bags and inside walls/internal stiffeners has to be 75 mm at the minimum.

…

Number of bags per row The maximum number of bags per row should not be more than 16 bags.

…

Venturis A venturi is an integral component of most pulse-jet collectors. It directs the blast of compressed air into the center of the filter bag to prevent abrasion caused by misaligned blowpipes and turbulent airflows. A good nozzle venturi configuration guarantees an efficient jet gentle dust release while conserving compressed air consumption through secondary air in draft into the venturi. If venturis become damaged or worn, compressed air does not gain the velocity required to effectively clean the filter bags.

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Bag cages The bag cages have to be provided with longitudinal wires: • 8 to 12 for filter bag diameter < 160 mm • 16 to 20 for filter bag diameter > 200 mm The bag cages shall be preferably of single piece design and shall be corrosion-resistant (galvanized, stainless steel or epoxy coated) depending on their application. Cartridge pleated filter and star bags shall not be used (except for electrical room pressurization or special application). Envelope type dust collector should only be applied for low venting air volume of < 5'000 m3/h.

…

Filter cloth The filter cloth specification and design data to be provided by the supplier have carefully been checked by the consumer. • For general application (dry gas) up to 1200 C (long time operation), needle felt fabric made from high quality Polyester fibers are used. • For an application in drying/grinding (humid gas) up to 1200 C (long time operation), Polyacrylnitrile or similar fiber cloth is recommended. • Application for temperatures above 1200 C, Polyamide (Nomex), Polyphenylene, Glass-fiber, Teflon/graphite coated or similar. One of the greatest enemies of the textile filter media is hydrolysis. This means the breakdown of the molecular chain of the polymerization caused by moisture. Hydrolysis is intensified by heat, acids and alkalis. Polyester, for example, should not be used when moisture and elevated temperatures occur in combination. Also aromatic polyamides (Nomex) are subject to hydrolytic influences at temperatures above 70°C, especially if acids or alkaline agents additionally act as a catalyzer. Fortunately, in recent years chemical modification processes have emerged, which have enabled these polyamides and also polyester to be substantially improved in this respect.

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Airlocks • •

• …

Fan • • • •

3.4

Rotary type for raw material, raw meal and cement dust. Double pendulum type shall be provided for all clinker dust and abrasive bulk material applications. Motor operated units requiring power-to-open and power-toclose are preferred. Gravity operated airlocks are also accepted. The minimum size for airlocks shall be 250x250 mm.

All fans should be selected with a 15% safety margin. As a consequence, air quantity for fans is at least 15% higher than required. The fans with manually operated damper at inlet duct are preferred. The fan speed should preferably not exceed 1'800 rpm. In the absence of ducting layout and pressure drop calculations, the static pressure for the dust collector fans should be specified as follows: - For impact crusher and bag packing machine venting systems, the minimum fan static pressure should be 30 mbar. - For bin / silo vent units and electrical rooms pressurizing systems, the minimum fan static pressure should be 23 mbar. - For all other dust collectors, the minimum fan static pressure should be 28 mbar.

Dust collector cleaning control …

General In pulse-jet collectors, the cleaning function not only removes the collected dust, it rearranges the remaining dust cake structure on the bag, resulting in a change of differential pressure. In a unit with high upward gas velocities (can velocity), mechanical separation of the fine sub micron dust can occur, creating a dust cake structure that is very dense. A dense dust cake creates a resistance to airflow, and higher differential pressures. Essential for a smooth trouble free operation of each dust collector is the availability of sufficient dry compressed air volume in adequate quality. The usually required air pressure to clean conventional filter bags is 6 bar and for bags with membrane layers 5 bar.

…

Pulse sequence The pulsing sequence can play an important part in lessening the re-entrainment of material. Pulsing one row right next to another row (sequential order) can cause the fine, sub-micron material to migrate to the cleaned row. Staggering the order of rows to be pulsed can improve the dust cake for optimum filtration as shown in next picture.

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Typical cleaning sequence

Recommended cleaning sequence

7

7

Fig. 21: Typical bag cleaning sequence

Fig. 22: Recommended bag cleaning sequence

Example How a cleaning sequence on a dust collector with 17 respectively 12 bag rows and 10 timer positions can look like it is presented in the following tables. Timer Position Valve Numb.

Timer Position Valve Numb.

…

1

2

3

4

5

6

7

8

9 10

1 4 7 10 2 5 8 3 6 9 11 14 17 12 15 13 16

1

2

1 4 11

3

4

5

6

7

8

9 10

7 10 2 5 12

8

3

6

9

Pulse cycle The cleaning cycle for pulse-jet collectors should be designed, so that the pulse duration produces a short, crisp pulse in order to create an effective shock wave in the bag. This duration is generally set to fire for 0.10 to 0.15 second. The frequency of pulse-jet cleaning is also vital to proper dust cake retention. This frequency can vary from 7 to 30 seconds or more and is adjusted by means of a potentiometer on the timer panel. The frequency should be adjusted, so that the differential pressure across the collector ranges from 75 - 150 mm WG. To ensure proper cleaning frequency, an automatic "cleaning-on-demand" system utilizing a pressure switch gauge can be installed as shown in the following picture. Good practice is to put the low set point at about 10 mbar and the set point high at 12.5 mbar.

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Set point high (app. 12.5 mbar)

Set point low (app. 10 mbar)

Fig. 23: Pressure switch gauge for bag cleaning control

This type of system will automatically step through a cleaning cycle that starts when the high differential pressure set point is reached and stops when it cleans down to the low differential pressure set point it will also save on compressed air usage. On pulse-jet collectors, the pulse frequency can of course be increased, but the next pulse should not be programmed to fire until the compressed air pressure is regained so the same force of pulse is obtained for each row cleaned. The regain of air pressure is dependent on the capability of the compressed air system tied to the bag house and the size of the compressed air piping run to the header tank. …

Diaphragm and solenoid valves Diaphragm and solenoid valves work together for an efficient operation of the bag house cleaning system. If either is malfunctioning, the entire system can be affected. Good practice is to use CR (Chlorbutadien-Elastomer) diaphragm for operating temperatures up to 800 C, Buna N (Styrol-Butadien-Elastomer) up to 900 C and Viton for temperatures < 1800 C. There are integral solenoid valves, which are mounted directly on the diaphragm valve or remote solenoids mounted in a separate enclosure for special applications.

…

Purge valve Purge valves are designed to eliminate moisture build-up in the compressed air header before entering the unit, in order to avoid corrosion and dust caking on the top of bags. This manually operated valve is usually located in the pipeline to the air header. Today there are automatic purge valves located at the bottom of the air header assembly and connected to a pulse valve. When the pulse valve fires, the valve opens a discharge port on the air header assembly, removing excessive moisture.

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3.5

Problem solving guide / trouble shooting

Jet-Pulse Dust Collector Is there Power in and out of timer ?

Problem

Problem

Lake of air at process

Emissions from stack

Is System turned on ?

Yes

No

Does baghouse have high differential pressure ?

Are emissions visible at the stack ?

Yes

Yes

Visually check for bag leaks; repair leaks and check pressure

No

Yes

Next page

No

Are belts tensioned properly ?

Yes

Next page

Holcim Group Support Ltd CMS - Mechanical Process Technology

Do solenoids and diaphragm operate properly ?

No

No

Repair solenoid or diaphragm and check differential pressure

Retension and check differential pressure

Is cleanig interval at the lowest setting that will allow air manifold pressure to rebuild ?

Yes

Next page

Turn on power and / or repair timer

Are isolation dampers sealing properly ?

No

Adjust and/or repair and check differential power

Is reverse air fan running ?

No

Turn on and check differential pressure

No

Change motor leads and check differential pressure

No

Change setting and check differential pressure

Yes No

Change setting and check differential pressure

Is reverse air fan rotation correct ?

Yes

Yes No

No

Yes

Yes Is pulse duration at recommanded setting ? (0,1 - 0,15 sec)

Is there Power in and out of timer ?

Yes Check for leaking solenoids and pulse valves;check compressed air sources and check differnetial press.

Yes Check cleaning mechanism

Fan Ductwork Is fan pulling design load amps ?

Turn on Power and /or repair timer

Yes Is manifold pressure at manufacturer's recommanded setting ?

No

Start System and check differnetial pressure

No

Reverse air Dust Collector

No

Change setting and check differential pressure

Is cleaning cycle for reverse air dwell set at manufacturer's specifications ?

Yes

Next page

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From previous

From previous Yes

Yes No Is fan vibrating ?

Yes Check for damage or material buildup on fan wheel and repair and clean

From previous

Is fan rotation correct ?

Yes No

Change motor leads and check differential pressure

Is the differential pressure reduced by stopping fan while pulsing ?

Open damper and check differential pressure

Does air/cloth ratio exceed 6:1 if pulse-jet, or 4:1 if plenum pulse or reverse air ?

Yes Is fan damper open ?

No

No

Is cleaning interval set at its shortest interval ?

No

Change setting and check differential pressure

Yes No

Damper fan volume down / evaluate pleated media conversion

Pull a bag and run a permeability test to check for blinding

Yes No

Check for obstructions in ductwork and remove

Yes Is ductwork or system leaking ?

Yes

Yes

Yes Is air volume at fan rated capacity ?

From previous

Are bags experiencing high grain loading ?

No

Add mechanical device to reduce load and check differential pressure

Yes No

Check differential pressure gauge for proper operation

Is material stored or accumulated in hopper ?

No

Is bag blinding ?

Yes No

Remove material continously and check differential pressure

Analyze for cause of blinding and correct; replace bags and check differential pressure

Yes Repair leaks and check differential pressure

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Check inlet duct entry design and modify to reduce load; check differential pressure

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APPENDIX 1

Recommended Venting Air Volume

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Dedusting Air Quantities

MACHINE UNIT BELT CONVEYORS

A B

C

SIZE (mm)

m3/h

DETAILS / REMARKS

650 850 1000 1200 1400 1600

4250 5250 6500 7750 8750 10'000

A 2000 1500 2500 2000 3000 2500 3500 3000 4000 3500 4500 4000

B 1250 1750 1750 2250 2250 2750 2750 3250 3250 3750 3750 4250 B

6500 7500 8750 9750 10'000 1

A 3500 4000 4500 5000 5500

2000 2500 3000 3500 4000

1000 1000 1250 1500 1500

A

B

C

APRON CONVEYORS

800 1000 1200 1400 1600

A B

C

PIVOTING PAN APRON CONV.

A C

B

800 1000 1200 1400

2500 3000 3500 4000

400 500 630 800 1000 1250 1600

CHAIN m 3/h A B 1000 1250 1000 1500 1250 2000 1250 2500 1500 3000 1500 3500 1500 4000

BUCKET ELEVATORS

A

B

TROUGH CHAIN AND SCREW CONVEYORS

200 250 315 400 500 630 800 1000

500 500 500 750 750 1000 1000 1250

C 1000 1000 1250 1500 1500 1750 C

9000 9000 10'000 10'000 11'000 11'000 12'000 12'000

m3/h

m3/h

BELT m 3/h A B 2000 1000 2250 1000 2500 1250 3000 1250 3500 1500 4500 1500 6000 1500

m3/h

PER 10m LENGHT

150% OF THE AIR BLOWER 120

AIR SLIDES CALSSIFING-SCREEN

50

VIBRATORY-SCREEN

450

PER m2 (CLOSED)

SWING-SCREEN

600

PER m2 (CLOSED)

Holcim Group Support Ltd CMS - Mechanical Process Technology

m3/h

PER t/h (OPEN)

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Example Packing Plant 1

According Machine Unit

m3/h

2

Bucket Elevator Food

1250 m3/h

3

Bucket Elevator Head

2500 m3/h

4

Swing Screen

1500 m3/h

5

Storage Bin

500 m3/h

6

Rotary Packer Feed

300 m3/h

7

Rotary Packer 8-Spouts

8000 m3/h

8

Takeway Belt Conveyor

2000 m3/h

9

Bag Cleaning Unit

2500 m3/h

3

4

5

6

9 8

2 1

7 Holcim Group Support Ltd CMS - Mechanical Process Technology

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Dedusting Air Quantities Guiding rates for plant engineering Machine unit Vibrating feeder

Air lift Fuller pump Pressure vessel Fluidstat (Bühler) Bin

Size (mm) 600 800 1'000 1'200

Big Small

Clinker storage Roller crusher Jaw crusher

Hammer crusher Impact crusher

Gyratory crusher (cone crusher)

to 50 t/h 50 - 100 t/h to 100 t/h 100 - 400 t/h 400 - 700 t/h to 100 t/h to 100 t/h to 300 t/h > 300 t/h to 100 t/h 100 - 400 t/h 400 - 700 t/h

Packing machine

Loading mobile

Loading head

Tanker vehicles

Holcim Group Support Ltd CMS - Mechanical Process Technology

m3/h

Remarks

900 1'500 2'400 3'600 60 50 40 30 1'000 500 12 - 20’000 40 - 60’000 36 60 60 45 30 120 90 60 40 60 45 30 8'000 6'000 300 2'500 1'500 2'000 2'500 5'000 5'000 1'500 4'000 900 1'500 12'000 540 - 660 660

Per t Per t 1.5-times of the expanded Per t compressed air volume Per t Mechanical feeding Mechanical feeding Cylindrical Silo Circular Silo (clinker dome) Per t Per t Per t Per t Per t Per t Per t Per t Per t Per t Per t Per t 8-spouts rotary packer 6-spouts rotary packer Feed Per spout in-line packer collecting funnel Niagara-swing screen 1 x 2.5 m Takeaway belt conveyor Bag cleaning unit Air slide 400 mm Screw 1630/1800 Hopper mobile Double articulated (air slide or screw) Cement 300 m3/h Cement 600 m3/h Clinker 300 m3/h Road 60 t/h at 2.5 bar Rail 60 t/h at 2.5 bar

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APPENDIX 2

Ductwork and Venting Hood Design

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Venting Hood Design v2

Vertical

Longitudinal

Transversal

E

H ØG

ØC

ØG

B

L

D

L

ØC

B

B

L

v1

Air Quantity 3

m /h 250 500 750 1000 1250 1500 1750 2000 2500 3000 3500 4000 4500 5000 6000

v1

v2

L

B

H

ØC

ØG

L

B

E

D

m /min

ms-1

ms-1

mm

mm

mm

mm

mm

mm

mm

mm

mm

4.2 8.3 12.5 16.6 20.8 25.0 29.2 33.3 41.6 50.0 58.3 66.6 75.0 83.3 100.0

1.40 1.40 1.40 1.40 1.40 1.44 1.43 1.39 1.41 1.40 1.44 1.40 1.42 1.42 1.42

18.0 17.5 17.0 17.2 17.7 17.9 17.9 17.9 18.0 17.9 17.8 18.0 17.9 17.9 17.9

260 370 450 520 580 630 680 740 820 900 960 1040 1100 1150 1260

190 270 330 380 425 460 500 540 600 660 700 760 800 850 930

165 235 280 325 365 400 430 470 520 570 610 660 700 740 800

70.0 100.5 125.0 143.5 158.0 172.0 186.0 198.0 222.0 244.0 262.0 280.0 298.0 314.0 344.0

97 143 178 207 233 253 276 299 334 368 391 426 449 475 524

260 370 450 520 580 630 680 740 820 900 960 1040 1100 1150 1260

190 270 330 380 425 460 500 540 600 660 700 760 800 850 930

157.0 227.0 278.0 323.5 365.0 396.0 430.0 471.0 522.0 574.0 609.0 666.0 701.0 739.0 810.0

122.0 177.5 218.0 253.5 287.5 311.0 340.0 371.0 412.0 454.0 479.0 526.0 557.0 589.0 645.0

3

* * * *

*Commercial Pipes and Bends Sheet Thickness for Suction Hoods and Ducts: 3-4mm Intake Velocity at Hoods according to Above Table: V1 = ~ 1.4m/s Air Velocity in Dedusting Duct : V2 = > 18m/s Holcim Group Support Ltd CMS - Mechanical Process Technology

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Duct Elbow, Joint and Branch Design

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Hooding Design at Pickup Points Hooding for Airslide

Recommended

Typical

High velocity

Hooding for belt conveyor

Min. 2*belt width

Min. cover hood height: 400 mm

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Hooding for steel conveyor

2 x conveyor width 1/3 belt width

600 mm min. Rubber skirt

Additional venting may be required for dusty material

Dust curtain

50 mm clearance for load on belt

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Hooding for Bucket elevator head

Alternativ

Typical Vent point

Relocated vent point

Impact flow meter dedusting

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Gas velocity in ductwork For Abrasive Dust

For Non-Abrasive Dust

Tube

Tube

Tube

Gas

Tube

Tube

Tube

Gas

diameter

diameter

diameter

speed

Inch

mm

m

m/s

diameter

diameter

diameter

speed

mm

m

m/s

16.00

m /h 591

inch 4.5

114.30

0.114

18.00

m3/h 665

4.5

114.30

0.114

6

152.40

0.152

16.00

1051

6

152.40

0.152

18.00

1182

7 8

177.80

0.178

16.00

1430

7

177.80

0.178

18.00

1609

203.20

0.203

16.00

1868

8

203.20

0.203

18.00

2101

Airflow 3

Airflow

9

228.60

0.229

16.00

2364

9

228.60

0.229

18.00

2660

10

254.00

0.254

16.00

2919

10

254.00

0.254

18.00

3283

11

279.40

0.279

16.00

3531

11

279.40

0.279

18.00

3973

12

304.80

0.305

16.00

4203

12

304.80

0.305

18.00

4728

13

330.20

0.330

16.00

4932

13

330.20

0.330

18.00

5549

14

355.60

0.356

16.00

5720

14

355.60

0.356

18.00

6435

15

381.00

0.381

16.00

6567

15

381.00

0.381

18.00

7388

16

406.40

0.406

16.00

7471

16

406.40

0.406

18.00

8405

17

431.80

0.432

16.00

8435

17

431.80

0.432

18.00

9489

18

457.20

0.457

16.00

9456

18

457.20

0.457

18.00

10638

19

482.60

0.483

16.00

10536

19

482.60

0.483

18.00

11853

20

508.00

0.508

16.00

11674

20

508.00

0.508

18.00

13133

21

533.40

0.533

16.00

12871

21

533.40

0.533

18.00

14480

22

558.80

0.559

16.00

14126

22

558.80

0.559

18.00

15891

23

584.20

0.584

16.00

15439

23

584.20

0.584

18.00

17369

24

609.60

0.610

16.00

16811

24

609.60

0.610

18.00

18912

25

635.00

0.635

16.00

18241

25

635.00

0.635

18.00

20521

26

660.40

0.660

16.00

19729

26

660.40

0.660

18.00

22196

27

685.80

0.686

16.00

21276

27

685.80

0.686

18.00

23936

28

711.20

0.711

16.00

22881

28

711.20

0.711

18.00

25742

29

736.60

0.737

16.00

24545

29

736.60

0.737

18.00

27613

30

762.00

0.762

16.00

26267

30

762.00

0.762

18.00

29550

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APPENDIX 3 Hopper Valley Angle

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APPENDIX 4 Dust Suppression for Feed Hoppers

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Attached bag filter to hopper enclosure

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