NGL trains description.pdf

SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 1 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

CONTENT This instruction outlines the process descriptions of NGL trains. There are three (3) NGL trains, which are identical. The description is mentioned based on train number 1. All instrument tag numbers on this section is prefixed “41-“ for Train 1 and “42-“ and “43-“ for Train 2 and 3 unless otherwise noted. The text includes:

1.

INTRODUCTION

2.

DESIGN BASIS

3.

PROCESS DESCRIPTION AND CONTROL

4.

OVERALL PLANT CONTROL

5.

PROCESS CONTROL

6.

COMPLEX CONTROL

7.

REGENERATION /ABSORPTION LOGIC SEQUENCE DESCRIPTION

8.

PROCESS THEORY

9.

PROCESS VARIABLE

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1

INTRODUCTION

The NGL Recovery Trains recover ethane and heavier hydrocarbons. The ethane recovery is limited only by the minimum gross heating value specification on the residue gas of 930 BTU/SCF. The carbon dioxide content of the ethane plus NGL is specified as less than 1500 ppmv. The NGL recovery unit consists of three identical trains; each designed to handle 33.3% of the peak total inlet gas flow rate. The capacity of each train is 1333 MMSCFD. Although the Haradh and Hawiyah inlet gas streams to each NGL recovery unit have been dew-point controlled, it contains impurities such as nitrogen, carbon dioxide, mercury and water, which adversely affect cryogenic processing to recover ethane and heavier hydrocarbons (ethane plus). The Haradh and Hawiyah inlet gas streams to each NGL recovery unit will be mixed inside the train and then pre-cooled before passing through the molecular sieve beds for dehydration and the activated carbon beds for mercury removal. The water is removed using a molecular sieve dehydration system, since cryogenic temperatures are required to recover ethane product and water freezing and hydrate formation shall be prevented. Since brazed aluminum heat exchangers (BAHE) are used in the cryogenic process; mercury that could attack the aluminum material removed in the activated carbon beds. The ethane and heavier hydrocarbons are extracted from the methane component of the inlet gas by fractionation in a demethanizer column. This is accomplished by liquefying the gas streams using heat exchangers, turbo expanders, or Joule-Thompson (JT) valves before it enters the demethanizer column.

The demethanizer column operates at a controlled

pressure with heat being added to the bottom by means of reboilers and overhead temperature being controlled by the cold feed stream. The overhead residue gas stream is essentially ethane free and passes to the sales gas compression unit (B68) after

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SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 3 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

recompression by brake compressors. The nitrogen is not removed from the inlet gas and simply passes through the plant with the residue gas unaffected by the process. The NGL products coming off the bottom of the demethanizer are primarily ethane, heavier hydrocarbon liquids. Major part of carbon dioxide (CO2) in Haradh gas is removed in B65, and remaining CO2 in Haradh gas and CO2 containing in Hawiyah gas pass through the process with the ethane plus product and is send to NGL surge spheres (B67) as part of the ethane plus liquid. A simplified block diagram of the NGL trains is shown on the next page and Attachment 10.

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The following is a brief description of the main facilities included in each NGL Train: •

Precondition System Two Feed Gas enters this system, one from HUG-1 and the other from HDUG-1. The Dry Hawiyah Feed Gas is coming from HUG-1 after filtration in B64. The Hawiyah gas inlet does not have to be treated as the Carbon dioxide (CO2) was removed at the existing Hawiyah Gas Plant. The Hawiyah gas goes through two heat exchangers which will lower its temperature from 139 °F to 80 °F. The Haradh Gas is wet gas because it is coming from DGA gas treating facility (B65) after removing CO2. The wet Haradh gas enters a heat exchanger and a separator where the temperature is reduced to 80 °F and the condensed liquid separated. Both Gas will then join in a Static Mixer and fed to the Dehydration System.

•

Molecular Sieve Gas Dehydration The Feed Gas Dehydration Beds contain the molecular sieve used to dehydrate the feed gas. There are 6 beds per train, 5 beds are on absorption and one is on regeneration/stand-by at any time.

•

Mercury Removal The Mercury Removal Beds use activated carbon to remove the mercury from the feed gas. The carbon beds are disposable, and when fully loaded with mercury, must be replaced with fresh material. The dehydrated mercury free gas flows to the dust filters where it is filtered to remove any entrained fine dust and particles.

•

Regeneration Gas System

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SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 6 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

Sales gas heated to 550 °F is used to regenerate the beds. The regeneration gas is heated in two Heaters. The first heater utilizes medium pressure hot water to heat the regeneration gas to 400 °F. The second heater utilizes electricity to further heat the regeneration gas to 550 °F. •

Cryogenic System The gas is cooled through the Brazed Aluminum Heater Exchanger to approximately -55 °F, and separated liquids are routed to the Demethanizer. Gas from the expander feed separator is split into two streams. One stream (28 %vol) is fed to the Demethanizer Overhead Exchanger where it is cooled and passes through an expansion valve where the pressure is dropped to 259 psig. This stream is then fed to the top separator section of the Demethanizer. The remaining gas (72 %vol) from the expander separator is fed to the turbo expanders. The gas exits the turbo expanders at approximately 260 psig and -124 °F and is fed to the top tray of the Demethanizer. Power recovered from the expanders is utilized in the brake compressor portion to increase the pressure of the residue gas. There are two 50% capacity Turbo-Expanders in each NGL train. The Demethanizer distills the liquefied NGLs to produce an ethane rich NGL product that meets the required specifications. It is required to have a CO2 content of less than 1500 ppmv, and no more than 2.5% methane in ethane. (The NGL liquid produced as bottoms product is pumped to the surge spheres).

•

Demethanizer The Demethanizer overhead gas stream (Residue Gas) flows through a series of Brazed

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Aluminum Heat Exchanger and is routed to the suction of the Brake Compressors where those are compressed and sent to the Sales Gas Compression trains (Plant B68). There are three reboilers on the Demethanizer, two side reboilers and a bottom reboiler with auxiliary reboiler. •

Propane Refrigeration Propane Refrigeration is used to assist in cooling the feed gas stream. Each NGL train has a dedicated system and consists of two-motor driven, two-stage centrifugal compressors.

2

DESIGN BASIS The NGL recovery unit consists of three identical trains that include the following main facilities. The description is mentioned based on train number 1. All instrument tag numbers on this section is prefixed “41-“ for Train 1 and “42-“ and “43-“ for Train 2 and 3 unless otherwise noted.

2.1

SYSTEM CAPACITY The NGL recovery unit consists of three identical trains; each designed to handle 33.3% of the peak total inlet gas flow rate. The capacity of each train is 1,323 MMSCFD. Turndown capability is a minimum of 50% of design capacity. The HNRP will recover from the inlet gases approximately 310,000 BPD of C2+ NGL (180,000 – 185,000 BPD), whose ethane content is 60 mol%. Each NGL train consists of the follows: •

six 20% capacity molecular sieve beds per train – 5 beds are on adsorption and one is on regeneration at any point in time.

•

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five 20% capacity activated carbon beds for mercury removable system

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2.2

•

two 50% capacity turbo expander / brake compressors (50% x 2, no spare)

•

one demethanizer column with reboilers

•

two 50% capacity two-stage refrigerant compressors (no spare)

•

Pre-coolers and Brazed aluminum heat exchangers, etc.

FEED AND PRODUCT DATA The ethane recovery is limited only by the minimum gross heating value specification on the residue gas of 930 BTU/SCF. The CO2 content of the C2+ NGL is specified as less than 1500 ppmv. The design parameters of the NGL unit are as follows: •

Capacity of each train: 1,323 MMSCFD

•

Turndown capability: to a minimum of 50% of design capacity

1) Feed Gas Pre-cooling •

Dry inlet gas temperature of Hawiyah gas stream: 140 ºF

•

Wet inlet gas temperature of Haradh gas downstream of gas treating: 146 ºF (water saturated)

•

Pre-cooling temperature for dehydration: 80 ºF

2) Molecular Sieve Gas Dehydration •

Design water content of the wet gas for molecular sieve: 20 lb/MMSCF at 1,323 MMSCFD and saturated at 680 MMSCFD (Haradh gas only case)

•

Water content of the dehydrated gas: less than 0.1 ppmv.

•

Designed bed life is 3 years

•

Regeneration gas temperature: 550 ºF (heating) and 90 ºF (cooling)

•

Regeneration gas flow rate: Maximum 60 MMSCFD

3) Mercury Removal

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Design mercury content of the inlet gas: 70 micrograms/ Nm3

•

Mercury content of the dehydrated gas: less than 0.01 microgram/Nm3 of Revised:

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gas. •

Designed bed life is 3 years

4) C2+ NGL recovery •

Heat content of residue gas 930 BTU/SCF (minimum gross heating value)

•

NGL liquid produced as a bottoms product when processed at Saudi Aramco’s NGL Fractionation plants to meet the following ethane specifications: - CO2 content of less than 1500 ppmv - No more than 2.5% mole methane in ethane.

5) Propane Refrigeration •

Refrigeration design levels: (1) 1st suction: -14 ºF at 13 psig (2) side stream: economizer 52 ºF at 83 psig, chillers 55 ºF at 83 psig and 75 ºF at 118 psig (3) condenser 140 ºF at 302 psig

•

The heat gain in the propane refrigeration system is 2% of the chiller duties in summer operation and 1% of the chiller duties in winter operation.

3

PROCESS DESCRIPTION AND CONTROL The following description is based on train 1 (Unit 41), but is also applicable to train 2 & 3 (Unit 42 & 43).

3.1

FEED GAS PRE-COOLING The pre-cooling area equipment is used to lower the temperature of the feed gas stream to 80 °F, which is based on hydrate formation temperature of approximately 62 °F plus 18 °F margin, before it passes into the Molecular Sieve Dehydrators. The feed gas streams are Hawiyah gas and Haradh gas. Haradh gas is coming from gas tearing trains (B65) and water saturated, although Hawiyah gas is dry.

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SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 10 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

The Feed Gas/Residue Gas Exchanger (B66-E-0101 A/B) is the first set of shell-and-tube type heat exchangers on Hawiyah feed gas lines in the NGL recovery process. It is used to cool the Hawiyah inlet gas to 90 °F. Due to the presence of mercury in the gas, this exchanger is a shell-and-tube type heat exchanger of steel material. After the Feed Gas/Residue Gas Exchanger, the Hawiyah gas is fed to the Hawiyah Gas Chiller (B66-E-0102). It is a steel tube bundle inside a propane-bath kettle-type heat exchanger and is used to cool the gas to 80 °F. The propane refrigerant for this chiller is fed from the propane sub-cooler (B66-E-0117 A/B). The outlet gas from this chiller is fed to the static mixer where it is mixed with the chilled Haradh gas. The Haradh Gas Chiller (B66-E-0108) is a steel tube bundle inside a propane-bath kettle-type heat exchanger and is used to cool the wet Haradh gas from 146 °F to 80°F and condense the majority of the water vapor. The propane refrigerant for this chiller is fed from the propane sub-cooler (B66-E-0117 A/B). Gas from the Haradh Gas Chiller is fed to Haradh Gas Chiller Separator (B66-D-0101) to remove the water/entrained DGA condensed in the Haradh Gas Chiller. The condensed is recycled back to the gas treating trains (B65) where the water/entrained DGA is reused by adding it to the Diglycolamine (DGA) solution to minimize DGA loss. The chilled Hawiyah gas and the chilled Haradh gas are commingled and mixed in the static mixer (B66-SM-001). The purpose of this mixer is to ensure the mixture is homogeneous and is without stratification, which could cause unequal loadings of water in the molecular sieve dehydration beds. If temperature of Hawiyah gas is lower than that of Haradh gas, Condensation of water may take place and, thereby, performance of molecular sieves dehydrator worsens. Therefore, the differential temperature between Hawiyah and Haradh gas at mixer inlet is monitored and the alarm signal is initiated when warmer Haradh gas (i.e. lower Hawiyah gas) is

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detected.

3.2

MOLECULAR SIEVE GAS DEHYDRATION The Feed Gas Dehydration Beds (B66-D-0102A/B/C/D/E/F) contain the molecular sieve used to dehydrate the feed gas to 0.1 ppmv (0.1 ppmV water content corresponds to less than -174degF at 263psig which is the operating condition of demethanizer reflux line). This low water content is required to prevent hydrate formation in the cryogenic section of the plant. There are 6 beds per train – 5 beds are on adsorption and one is on regeneration or stand-by at any point in time. Each bed is sized to process 20% of the inlet gas flow. Adsorption is done with the gas flowing vertically down through the bed. Regeneration gas is lean sales gas and taken from the discharge of each sales gas compressors (B68) and flowing vertically up through bed. Once a bed has adsorbed as much water as the molecular sieve can handle, it is placed on regeneration. Sales gas heated to 550 °F is used to regenerate the beds. Following regeneration, the bed is cooled down to 90 °F, which is the normal operating temperature plus 10 °F, using cooled lean sales gas. Sequencing of the dehydration bed switching valves is to be controlled by timer sequencers programmed into the DCS control system. The water content of the dehydrator outlet gas will be monitored with an on-line moisture analyzer. The time span the beds are on adsorption shall be adjusted to ensure that the beds are on adsorption as long as possible while ensuring that water break-through does not occur. The outlet gas from the Feed Gas Dehydration Beds is fed to the Mercury Removal Beds. During the regeneration heating cycle, the sales gas is heated in two regeneration gas heaters. The first of the heaters, the Regen Gas Hot Water Heater (B66-E-0103A/B), utilizes medium pressure hot water to heat the regeneration gas to 400 °F. The second heater, the

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Regen Gas Electric Heater (B66-E-0105 A/B), utilizes electricity to further heat the regeneration gas to 550 °F. The regeneration gas can be automatically heated in two steps by activating or deactivating the electric heater and by controlling the hot-water flow rate. During the regeneration cooling cycle, the Regen Gas Cooling Cycle Chiller (B66-E-0104) cools the sales gas to 90 °F using propane refrigerant. Two coolers in series cool the regeneration gas from the gas dehydration beds. The first cooler is the Regen Gas Air Cooler (B66-E-0106), a fin-fan cooler that cools the gas to approximately 145 °F. The second cooler, the Regen Gas/Propane Chiller (B66-E-0107), cools the gas to 80 °F using propane refrigerant. This is to condense as much water vapor as practicable. Hydrate formation temperature is approximately 51 °F. The gas is then routed to the Regen Gas Separator. The Regen Gas Separator (HP) (B66-D-0105) separates any water that condenses out of the regeneration gas stream as it is cooled. The gas from B66-D-0105 is then routed to sales gas pipeline via the regeneration gas blowers KO drums and Blowers (B64). The water from B66-D-0105 is flashed to the Regen Gas LP Knock Out Drum (B66-D-0106) to depressurize it to 5 psig. Condensed water is routed to the Oily Water Sewer (OWS) and the flashed gas is routed to LP flare.

3.3

MERCURY REMOVAL The gas from the Dehydration Beds passes through the Activated Carbon Beds (B66-D-0107A/B/C/D/E). Flow direction is vertically down through the beds. The beds contain an activated carbon that removes the mercury from the feed gas. The activated carbon is disposable, and when fully loaded with mercury, the bed must be replaced with fresh material. There are five beds for each NGL train. Each is sized for 20% of the inlet-gas flow.

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SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 13 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

The Carbon Bed Outlet Dust Filters/Basket Strainers (B66-D-0103A/B/C/D/E and B66-D-0104 A/B/C/D/E) are used to remove the fine dust and particles to prevent foiling or plugging of the downstream brazed aluminum heat exchangers. Each dust filter/basket strainer is dedicated to one of the activated-carbon beds.

3.4

C2+ NGL RECOVERY The NGL Recovery Area equipment is used to lower the temperature of the gas stream to liquefy and distill the NGLs. The Feed Gas Exchanger (B66-E-0110 A/B) receives gas from the molecular-sieve dehydration unit. The gas is fully dehydrated and is free of mercury. The exchanger is a brazed aluminum heat exchanger (BAHE) and has three sections (passes) – the feed gas section (Pass A), a residue gas section (Pass B), and the Demethanizer reboiler section (Pass C). It is used to cool the feed gas to approximately 30 ºF. Two 50% units (A &B) have been provided to allow one unit to be taken out of service for maintenance (back puffing) without shutting down the entire train. Following this exchanger, the gas is split into two streams, approximately 42% being fed to the Second Stage Feed Gas Chiller (B66-E-0114), and the remaining 58% being fed to the Warm Gas Exchanger (B66-E-0111). The Second Stage Feed Gas Chiller (B66-E-0114) is a BAHE (core) inside a propane-bath kettle-type heat exchanger and is used to cool the gas to approximately -9 ºF. The propane refrigerant for this chiller is fed from the Refrigerant Economizer (B66-D-0115). The Warm Gas Exchanger (B66-E-0111) receives gas from the Feed Gas Exchanger. The exchanger is a brazed aluminum heat exchanger (BAHE) and has three sections (passes) – the feed gas section (Pass A), a residue gas section (Pass B), and the Demethanizer bottom side reboiler section (Pass C). It is used to cool the inlet gas to approximately -9 ºF.

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The feed gas fluid stream from the Warm Gas Exchanger is commingled with the feed gas fluid stream from the Second Stage Feed Gas Chiller and is routed to the Chiller Separator. The Chiller Separator (B66-D-0110) receives a two-phase fluid stream from the Second Stage Feed Gas Chiller and from the Warm Gas Exchanger. The separator is designed with a single inlet, a single liquid outlet and two vapor outlet connections, one vapor outlet at each end of the vessel. Each of these vapor outlet connections is provided with a mist eliminator pad. Liquids separated are routed to the Demethanizer as a side feed. The remaining gases are fed to the Cold Gas Exchanger. The Cold Gas Exchanger (B66-E-0112) receives feed gas from the Chiller Separator. The exchanger is a brazed aluminum heat exchanger (BAHE) and has three sections (passes) – the feed gas section (Pass A), a residue gas section (Pass B), and the Demethanizer top side reboiler section (Pass C). It is used to cool the inlet gas to approximately -56 ºF. The Expander Feed Separator (B66-D-0111) receives a two-phase stream from the Cold Gas Exchanger. The separator is designed with a single inlet, a single liquid outlet and two vapor outlet connections, one vapor outlet at each end of the vessel. Each of these vapor outlet connections is provided with a mist eliminator pad. Liquids separated are routed to the Demethanizer as a side feed. Following this separator, the gas is split into two streams, approximately 28% being fed to the Demethanizer Overhead Exchanger (B66-E-0113), and the remaining 72% being fed to the Turbo-Expanders. The Demethanizer Overhead Exchanger (B66-E-0113) receives feed gas from the Expander Feed Separator. The exchanger is a brazed aluminum heat exchanger (BAHE) and has two sections (passes) – the feed gas section (Pass A), and a residue gas section (Pass B). It is used to cool the feed gas to approximately -159 ºF. The liquid stream exiting the exchanger is passed through a Joule-Thompson (J-T)

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expansion valve where the pressure is dropped to 264 psig and the temperature is decreased to -174 ºF. The fluid is then fed to the top packed section of the Demethanizer. The Turbo-Expander/Brake Compressor Units (B66-K-0110A/B) receive gas from the Expander Feed Separator. The two-phase fluid stream exits each of the expanders at approximately 276 psig and -123 ºF, and are fed individually to the top tray of the Demethanizer. Power recovered in the expander portion of the Turbo-Expander is utilized in the compressor portion to increase the pressure of the residue gas. There are two 50% capacity Turbo-Expanders in each NGL train; there are no spare or stand-by units. The Turbo-Expander/Brake Compressor units are connected in parallel. The Demethanizer (B66-C-0110) is used to distill the recovered liquid NGLs and produce an ethane rich NGL product, which meets the methane and carbon dioxide content specifications. The Demethanizer receives a two- phase (gas and liquid) feed from the Demethanizer Overhead Exchanger and from the two Turbo-Expanders. It also receives flashed liquid NGLs from the Expander Feed Separator and from the Chiller Separator. The demethanizer smaller diameter section has 34 Flexitrays (Valve trays) with four chimney trays and larger diameter section has random packing with two chimney trays. There are three reboilers on the Demethanizer. The bottom reboiler is heated by the Feed Gas Exchanger, the bottom side reboiler is heated by the Warm Gas Exchanger, and the top side reboiler is heated by the Cold Gas Exchanger. The NGL liquid produced as a bottoms product shall meet the ethane product specification when further processed at Saudi Aramco’s NGL Fractionation plants. A Demethanizer Auxiliary Reboiler (B66-E-0118) is provided for one JT / one Turbo-Expander operation mode so that the produced NGL liquids meet the required specifications.

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Propane Refrigeration is used to supply the cold source for heat removal. The Propane Refrigeration system in each NGL train has two 50% (Unit A & Unit B) capacity compressors, suction drums, condensers and accumulators. The sub-cooler and economizer are common to both Unit A and Unit B. The Propane Refrigerant Compressors (B66-K-0111A/B) are centrifugal compressors and have two stages. The low pressure stage takes propane vapors from the Second Stage Feed Gas Chiller (B66-E-0114) and the high pressure stage takes propane vapors from the Refrigerant Economizer (B66-D-0115), Hawiyah Gas Chiller (B66-E-0102), Regen Gas Cooling Cycle Chiller (B66-E-0104), Regen Gas/Propane Chiller (B66-E-0107), and Haradh Gas Chiller (B66-E-0108). The discharge from the compressors is routed to the Refrigerant Condensers (B66-E-0115 A/B). The Refrigerant Compressors are equipped with anti-surge flow-control loops on the first and second stages. Each recycle-gas stream is temperature controlled by quenching (i.e., mixing) with liquid refrigerant. The Refrigerant First Stage Compressor Suction Drums (B66-D-0112A/B) and the Refrigerant Second Stage Compressor Suction Drums (B66-D-0113A/B) are intended to prevent any liquid propane from entering the suction of the compressors. Each of the drums is equipped with a mist eliminator pad and heating coil in the bottom of the drum used to vaporize any liquid propane which accumulates in the drum. The coils are heated using hot refrigerant compressor discharge gas. Each compressor discharges into a Refrigerant Condenser (B66-E-0115A/B). This is a battery of air cooled heat exchangers. Condensed propane refrigerant from the condenser is combined and fed to the Refrigerant / Water Sub-cooler (B66-E-0117 A/B).

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SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 17 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

A Refrigerant Accumulator (B66-D-0114A/B) is installed between the Refrigerant Condenser and the common sub-cooler. System liquid fluctuations will be accommodated in the accumulator. In order to ensure there is always sufficient pressure in the accumulator to allow flow through the chillers, a hot gas by-pass is installed around the Refrigerant Condenser. This maintains pressure in the Refrigerant Accumulator when ambient temperatures decrease. A Refrigerant / Water Sub-cooler (B66-E-0117 A/B) is installed downstream of the Refrigerant Accumulators. The Refrigerant / Water Sub-cooler uses chilled cooling water that has been further cooled by the export NGL in the Product Surge area (B67). The compressors are equipped with a common Refrigerant Economizer (B66-D-0115) to reduce the overall load on the compressors. Propane refrigerant transferred from the storage facility in Plant B67 to Plant B66 is filtered through a Refrigerant Filter (B66-D-0116) before being distributed into the refrigerant circuit. During a unit shutdown, propane refrigerant is transferred from Plant B66 to B67 via the Refrigerant Return Pump (B66-G-0114) from economizer and accumulators. During Haradh gas only operation, refrigerant compressors' side stream duty is almost same as that of normal operation, however, 1st suction stream duty is reduced to less than 45% of normal and possible minimum flow recycle is required for 1st stage only. To prevent minimum flow recycle and save energy consumption, side stream flow is bypassed to 1st suction via letdown valve.

4

OVERALL PLANT CONTROL On the main gas line, there are five control valves for overall plant control as below: 1. Hawiyah Feed Gas Line, 41/42/43-FV-001 2. Haradh Feed Gas Line, 31/32-FV-003 3. 41/42/43-HV-311/330 (Expander inlet guide vane) and FV-238 (DeC1 reflux)

_ _ _ __ RA| D __| N I ||___ Issued: APR 2006

006 CT-2 03-O

Revised:

SEP 2006 Job No: 0-3850 Doc No: S-660-1283-001

SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 18 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

4. 41/42/43-PV-537 (DeC1 overhead) 5. 61/62/63/64-FV-001, Sales Gas Compressor Inlet The detail of control is mentioned the following section and B74-J-BE530023 (S-741-1371-101), Specification for Complex Control Strategies, para 6.

4.1

PURPOSE The priority of purpose is the follows. a.

To maintain inlet pressure to turbo expander (K-0110A/B, K-0210A/B, K-0310A/B).

b.

To maintain constant pressure in both inlet pipelines (to match the plant processing rate to the supply from both pipelines).

c.

To provide flexibility of evenly splitting both Hawiyah and Haradh gas flows between all three NGL recovery trains.

d.

To limit gas flow through each NGL train to the train design capacity and to allow any single train capacity testing during multi-train operation, also to limit Hawiyah gas flow through a single line train.

e.

To automatically perform all the above independently of number DGA, NGL and sales compression trains in operation.

f.

To ensure priority of operation with Haradh gas, over Hawiyah gas, in case of reduced plant capacity.

g.

To perform all the above with minimum pressure drop to the gas flow.

Demethanizer overhead pressure is controlled by 4x-PV-537 during normal operation. During JT operation, Demethanizer overhead pressure is depend on sales gas compressor master pressure control and pipeline pressure.

_ _ _ __ RA| D __| N I ||___ Issued: APR 2006

006 CT-2 03-O

Revised:

SEP 2006 Job No: 0-3850 Doc No: S-660-1283-001

SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 19 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

4.2

STRADDLE CONTROL (PLANT BYPASS): (GTCC PORTION.) This control loop operates the plant bypass on the Haradh & Hawiyah sales gas lines. In the event of a plant trip or emergency, gas feed is bypassed around the Hawiyah NGL plant. This loop is controlled by continually monitoring the Pressure in the HUG-1 and HDUG-1 pipelines In and Out of the plant. If the Hawiyah gas supply header pressure exceeds its preset value, Hawiyah Gas supply header high pressure protection controller 21-PIC-005 opens pipeline bypass valves, 21-PV-005A/B to reduce the header pressure. Differential Pressure 21-PDI-007 will provide permissive-to-open bypass valves, 21-PV-005A/B via DCS logic. If the pressure difference between supply header pressure and return pressure becomes less than preset value, this DCS logic will close the pipeline bypass valves to avoid reverse flow. A 48 inches check valve is also available to mechanically ensure that no back flow will occur. If the Haradh gas supply header pressure exceeds its preset value, Haradh Gas supply header high pressure protection controller 22-PIC-105 opens pipeline bypass valves, 22-PV-105A/B to reduce the header pressure. Differential Pressure 22-PDI-008 will provide permissive-to-open bypass valves, 22-PV-105A/B via DCS logic. If the pressure difference between supply header pressure and return pressure becomes less than preset value, this DCS logic will close the pipeline bypass valves to avoid reverse flow. A 48 inches check valve is also available to mechanically ensure that no back flow will occur.

4.3

HAWIYAH GAS AND HARADH GAS FLOWRATE CONTROL Nitrogen component of Hawiyah feed gas is higher than that of Haradh feed gas. If Hawiyah gas is only feed to DeC1, Nitrogen content of sales gas is increased and possible off-spec sales gas occurs. In view of keep the heating value of sales gas as minimum 930 MMBTU/SCF, Hawiyah gas is to be reduced first in case of reduced plant capacity.

_ _ _ __ RA| D __| N I ||___ Issued: APR 2006

006 CT-2 03-O

Revised:

SEP 2006 Job No: 0-3850 Doc No: S-660-1283-001

SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 20 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

For C2 recovery rate, the difference between the Hawiyah gas maximum case and Haradh gas maximum case is +/- 0.3% and negligible. Therefore, ratio control for Haradh gas and Hawiyah gas flow rate is not required and Haradh feed gas flow to each NGL train is controlled by balance of NGL train Maximum total

flow

controller

(41/42/43-FIC-237)

and

Hawiyah

gas

flow

controller

(41/42/43-FIC-001). Haradh gas and Total NGL feed gas flow ratio of each NGL train is calculated (41/42/43-FY-009) and indicated in DCS (41/42/43-FI-009) as a reference for operator.

4.3.1

Maximum Flow Limit Control on Total Hawiyah and Total Haradh Feed Lines The maximum total feed gas flow from Hawiyah can be set through 40-HIC-004. When measured total gas feed flow from Hawiyah gas pipeline exceeds this limit, 40-HIC-004 will override signal from 21-PIC-006 via low signal selector, 40-PY-036 and thus limit the setpoint of 40-FIC-002. The maximum total feed gas from Hawiyah and Haradh to NGL train is limited by 41/42/43-FIC-237. 41/42/43-FIC-237 setpoint is about 1,400 MMSCFD in consideration of the Demethanizer, B66-C-0*10 capacity. When this value is exceeded, 41/42/43-FIC-237 will manipulate the expander Inlet guide vane to close via low signal selector, 41/42/43-PY-499A and override signals from 41/42/43-PIC-499A. The maximum total Haradh feed gas to DGA units is around 1,700 MMSCFD in consideration of the DGA unit capacity of 816 MMSCFD per DGA unit. This maximum limit can be set through 22-HIC-004. When this limit is exceeded, 22-HIC-004 will override signal from 22-PIC-004 via low signal selector, 22-PY-004 and thus limit the setpoint of 22-FIC-003. When one or two NGL trains are shutdown, the total Haradh gas max total flow limit will be

_ _ _ __ RA| D __| N I ||___ Issued: APR 2006

006 CT-2 03-O

Revised:

SEP 2006 Job No: 0-3850 Doc No: S-660-1283-001

SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 21 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

calculated by 40-FY-004. When 41/42/43-FIC-004 process value read lower than a preset value, 40-FY-004 will consider that train to be blocked/shutdown and reduce 22-FIC-003 setpoint via low signal selector 22-PY-004 and override signal from 22-PIC-004 and 22-HIC-004. No. of Running Trains

Max. Total Haradh Gas Feed Flow Rate

0 or 1

900 MMSCFD

2 or 3

1700 MMSCFD

The set point of maximum feed gas rate of total feed gas (Hawiyah and Haradh) and Haradh gas is calculated from the number of operating trains as below: NGL train #

Hawiyah + Haradh Gas output

Haradh Gas (10-FY-004)

1

1,400 MMSCFD

900 MMSCFD

2

2,800 MMSCFD

1,700 MMSCFD

3

4,380 MMSCFD

1,700 MMSCFD

Logic for 40-FY-004 output is as follows: Three NGL Trains in operation If 41-FIC-004.PV >= X and 42-FIC-004.PV >= X and 43-FIC-004.PV >= X Then 40-FY-004.MV= 1700 Two NGL Trains in operation If 41-FIC-004.PV < X and 42-FIC-004.PV >= X and 43-FIC-004.PV >= X or If 41-FIC-004.PV >= X and 42FIC004.PV< X and 43-FIC-004.PV>=X or If 41-FIC-004.PV >= X and 42-FIC-004.PV >= X and 43-FIC-004.PV < X

_ _ _ __ RA| D __| N I ||___ Issued: APR 2006

006 CT-2 03-O

Revised:

SEP 2006 Job No: 0-3850 Doc No: S-660-1283-001

SAUDI ARABIAN OIL COMPANY (SAUDI ARAMCO) HAWIYAH NGL RECOVERY PLANT INSTRUCTION PLANT: NGL RECOVERY TRAINS (B66) PAGE 22 OF 80 SECTION: PROCESS DESCRIPTION INSTRUCTION NO: B66.02 ______________________________________________________________________________________________

Then 40-FY-004.MV= 1700 (MMSCFD) One NGL Train in operation If 41-FIC-004.PV < X and 42-FIC-004.PV= X or If 41-FIC-004.PV < X and 42-FIC-004.PV>= X and 43-FIC-004.PV= X and 42-FIC-004.PV< and 43-FIC-004.PV