liquefaction cycles 00

Slide No: 1Yemen LNG Technical TrainingLiquefaction Cycles

REFRIGERANT AND CRYOGENIC

LIQUEFACTION CYCLES

LIQUEFACTION CYCLES


Main Heat

Exchanger

LIQUEFACTION CYCLES


DISCUSSION OUTLINE

- THE INTENT OF LIQUEFACTION

- FEED PREPARATION PROCESSES

- TYPICAL LIQUEFACTIONS

- MECHANISM OF APCI LIQUEFACTIONS

- THE LICENSED LIQUEFACTION PROCESSES

LIQUEFACTION CYCLES


I. THE INTENT OF LIQUEFACTION

- To liquefy natural gas

- To decrease the volume

- To make transportation easier

600 m3 GAS

1 m3 LIQUID

LIQUEFACTION CYCLES


LNG LIQUEFACTION

- Works at cryogenic temperature (very low temperature)

- Built with special metal

- The most costly operation in LNG processing

(2002)

LNG Cost Chain

LIQUEFACTION CYCLES


II. FEED PREPARATION PROCESSES PRIOR TO LIQUEFACTION

� ACID GAS REMOVAL

� DEHYDRATION

� PRECOOLING (REFRIGERATION)

� FRACTIONATION

LIQUEFACTION CYCLES


III. TYPICAL LIQUEFACTION CYCLE

1. CASCADE CYCLE

Uses three different gases as refrigerant in three different refrigeration loops

2. EXPANDER CYCLE

Uses a centrifugal or axial flow turbine through which high pressure gas is expanded to decrease temperature and give out energy that is typically used to drive compressor or electric generator

3. MIX COMPONENT REFRIGERANT CYCLE

Uses mixed gases together as refrigerant in one refrigeration loop (stream)

LIQUEFACTION CYCLES


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C REFRIG 1 CYCLE C REFRIG 2

CYCLEC

REFRIG 4

CYCLEC

REFRIG 3

CYCLE

LNGFEEDGAS

EVAPORATOR

CONDENSOR

EVAPORATOR

EVAPORATOR EVAPORATOR

CONDENSOR

CONDENSOR CONDENSOR

EVAPORATOR

CASCADE LIQUEFACTION CYCLE

LIQUEFACTION CYCLES


CASCADE LIQUEFACTION CYCLE

� The process gas flows through a series of evaporators for each refrigeration cycle

� Each refrigerant cycle uses a single component of refrigerant

� Each refrigeration cycle has one dedicated complete set of equipment

ADVANTAGES & DISADVANTAGES

(+) Very low temperature

(-) Very complex, large volume of equipment required

(-) High initial cost

LIQUEFACTION CYCLES


- Propane refrigerant cools the feed gas and the ethylene refrigerant

- The cooled ethylene is expanded to cool feed gas (2nd cooling)

- The LNG vapor from flash drum is used to cool feed gas from the ethylene evaporator

PHILLIPS CASCADE LIQUEFACTION CYCLE

LNGLNG

CMETHANE

CYCLECPROPANE

CYCLE

Nat. Gas

(CH4)

CETHYLENE

CYCLE

-36°F -100°C

-156°C

EVAPORATOR

EVAPORATOR EVAPORATOR

CONDENSOR CONDENSOR

COMPRESSOR COMPRESSOR COMPRESSOR

CONDENSOR

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LIQUEFACTION CYCLES


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MAIN HEAT EXCHANGER (PLATE-FIN COLD BOX)

LIQUEFACTION CYCLES


Advantage & disavantage

� Very simple cycle

� Lower inherent efficiency for simple cycles (single-expander)

EXPANDER LIQUEFACTION CYCLE

MAIN RECUPERATIVEHEAT EXCHANGER

AFTER-

COOLER

TURBO-

COMPRESSOR

AFTER-

COOLER

EXPANDER

TURBO

SHAFT

COMPRESSOR

FEED GAS PRODUCT LNG

1

2

3

4

5

6

7

98

W2W1

Q1

Q2

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LIQUEFACTION CYCLES


EXPANDER LIQUEFACTION CYCLE

� The refrigerant, typically N2 or natural gas, is compressed in the main compressor with stream (1) as its discharge

� Heat is released from the cycle to the environment as the heat of compression in the after-cooler (2) prior to a second stage of compression in the turbo-compressor

� Stream (3) has the highest pressure developed in the cycle. Stream (3) then flows through a second after-cooler to transfer additional heat to the environment

� Next, stream (4) enters the recuperative heat exchanger where the refrigerant is cooled to well below ambient temperature. After leaving heat exchanger (5), the cooled refrigerant undergoes an isentropic expansion in the turbo-expander, which causes a large temperature drop in the refrigerant and produces shaft work

LIQUEFACTION CYCLES


� The lower pressure cold refrigerant in stream (6) is used for cooling and liquefying natural gas in the recuperative heat exchanger toproduce LNG

� The warm, low-pressure refrigerant in stream (7) is then recompressed in the primary compressor to complete the refrigeration cycle

� The feed gas enters the main heat exchanger and is cooled to a liquefying temperature (about -155°C)

EXPANDER LIQUEFACTION CYCLE (continued)

LIQUEFACTION CYCLES


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Fuel Gas

LNG

Nat. Gas

MCR

(N2, C1, C2, C3, C4)

CYCLEC

CONDENSER CONDENSER

MAIN HEAT EXCHANGER

CompressorExpansion valve

MIXED COMPONENT REFRIGERATION (PRICO)

C/W C/W

LIQUEFACTION CYCLES


Fuel Gas

LNG

Natural Gas

C

MCR

(N2, C1, C2, C3)

CYCLE

CPROPANE

CYCLE

MAIN HEAT EXCHANGER

EVAPORATOR

EVAPORATOR

CONDENSER

- High efficiency

- Less equipment

- Refrigerant from feed gas

MIXED COMPONENT REFRIGERATION CYCLE( APCI Process )

C/W

C/W

C/W

LIQUEFACTION CYCLES


MAIN HEAT EXCHANGER (APCI)

LNG to Storage

-45°C

Feed Gas – 34°C

L/P MCR Vapor to Compressor

Multi ComponentRefrigerant (MCR)

- 36°C

MCR Liquid

MCR Vapor

COLD BUNDLE

WARM BUNDLE

JT-Valve

JT-Valve

From Scrub Column

-155°C

-110°C

-150°C

- 36°C

LIQUEFACTION CYCLES

LIQUEFACTION CYCLES


THE LICENSED LIQUEFACTION PROCESSES

� APCI (AIR PRODUCTS CHEMICAL INDUSTRY)

� PHILLIPS OPTIMIZED CASCADE

� MIXED FLUID CASCADE – LINDE

� LIQUEFIN - AXENS

LIQUEFACTION CYCLES


APCI PROCESS

12

678

54

3

Warm bundle

Cold bundle

C

A

MCHE

B

A

LNG product

LNG product

JT-2

JT-1

LIQUEFACTION CYCLES


� After sweetening in the acid gas removal units, the feed gas is cooled down by cooling water and propane vaporisation in the evaporator HP C3 (1)

� This chilling reduces the amount of water to be removed in the drying unit (2)

� The feed gas then flows to the mercury removal unit (3)

� The clean feed gas is now further cooled against vaporising propane in the evaporators MP C3 and LP C3 (4), where heavier hydrocarbons will condense

� Then, both condensed HC and gas enter the scrub column (5) for further separation

� Gas from the top of scrub column is routed to the warm bundle of the Main Cryogenic Heat Exchanger (MCHE) (6) where it partially condenses. The mixed flow is then separated into liquid and vapour in the reflux drum (7) of the scrubber column

FEED GAS CIRCUIT OF APCI PROCESS

LIQUEFACTION CYCLES


� Gas from the top of scrub column is routed to the warm bundle of the Main Cryogenic Heat Exchanger (MCHE) (6) where it partially condenses. The mixed flow is then separated into liquid and vapour in the reflux drum (7) of the scrubber column

� The vapour phase of the scrubber column’s reflux drum enters the tube side of the MCHE. It condenses at a temperature in the range of –110 to –120°C in the warm bundle, and it is sub-cooled in the cold bundle of the MCHE down to typically –145 to – 155°C. Gas liquefied at such conditions is called LNG

� The hydrocarbon liquid from the bottom of the scrubber column is routed into the fractionation unit where it is separated into ethane, propane, butane and condensate products (8)

FEED GAS CIRCUIT OF APCI PROCESS (continued)

LIQUEFACTION CYCLES


MR CIRCUIT OF APCI PROCESS

� The mixed refrigerant (MR) (all in vapour form) is compressed in a two-stage compressor (A) with a water-cooled intercooler to raise its pressure

� When it comes out of the second compressor (B), the refrigerant goes through a second cooler, also water-cooled

� From the second cooler, the MR is then further cooled respectively in the HP, MP and LP propane (C3) evaporators. The mixture then moves to the high pressure (HP) MR separator (C). In this separator, liquid refrigerant goes to the bottom and vapour goes to the top

� The MR liquid leaving the bottom of the separator, and the MR vapor leaving through the top of the separator, enter the warm bundle MCHE. Here, they are cooled down by a returning stream of the same mixture

� The MR liquid leaves the warm bundle, and is cooled further by going through an expansion valve (JT-1)

LIQUEFACTION CYCLES


MR CIRCUIT OF APCI PROCESS (continued)

� The expanded MR liquid now enters the warm bundle separator, then it is sprayed down to cool the MR liquid, the MR vapor and the feed-gas coils in the warm bundle

� The MR vapor from HP MR separator (C) goes to the warm bundle, then is further cooled in the cold bundle of MCHE. The liquefied part of the refrigerant goes through an expansion valve (JT-2). Here it is cooled further by expansion and then enters the cold bundle separator. From the separator the cooled MR is sprayed down to cool MR vapor and feed gas coils in the cold bundle

� The MR vapor from the cold bundle (shell) then joins with MR vapor of the warm bundle (shell) to cool MR liquid, MR vapor and feed-gas coils and then goes to compressor suction

LIQUEFACTION CYCLES


PHILLIPS OPTIMIZED CASCADE PROCESS

Scrubber

Column

LIQUEFACTION CYCLES


� This liquefaction process is based on the use of three pure-component refrigeration cycles

� Each refrigerant works at the appropriate level of temperature and the cooling is successively achieved from the warm to the cold end by propane, ethylene and methane cycles

� The natural gas is successively cooled step-by-step by the propane, ethylene and finally methane cycle

� The scrub column inlet is located at the outlet of the lowest propane chiller and the reflux of it is ensured by high pressure ethylene level

� For energy saving reasons, each cycle consists of three to four vaporisation steps, the intermediate pressure vapour being fed to the inter-stage of the compressors

PHILLIPS OPTIMIZED CASCADE PROCESS

LIQUEFACTION CYCLES


MIXED FLUID CASCADE PROCESS

Reflux

SC

To Fractionation

LIQUEFACTION CYCLES


MIXED FLUID CASCADE PROCESS

� The Mixed Fluid Cascade is a further development of the classical cascade where the pure components are replaced by Mixed Component Refrigerant

� The natural gas from the purification and drying units enters the pre-cooling heat exchangers (E1A & E1B) where it is cooled down to typically –50°C

� At an intermediate temperature in the pre-cooling heat exchanger, the natural gas is withdrawn and enters the scrub column (SC)

� The gas from the top of scrub column, which is free from the heavy hydrocarbons and aromatics, enters the pre-cooling heat exchanger (E2) for further cooling to the cold end of the pre-cooling cycle

� The natural gas is liquefied from about – 80°C and finally sub-cooled in the sub-cooling heat exchanger (E3) to –155°C

LIQUEFACTION CYCLES


LIQUEFIN PROCESS

Feed Gas

MR-1MR-2

MR-2

MR-1

LIQUEFACTION CYCLES


� Liquefin process is basically a Dual Mixed Refrigerant (DMR) process in cascade

� The natural gas, after pre-treatment, is fed with the MR2 to the heat exchangers

� The cold duty in the top exchanger is performed by vaporization of the pre-cooling cycle (MR 1) through three expansion valves

� MR1 is compressed in the MR1 compressor and fully condensed against cooling water before being fed back to the heat exchangers

� In the course of pre-cooling, the natural gas is withdrawn and fed to the the scrub column

� The overhead gas from the scrub columns re-enters the pre-cooling heat exchanger to be further cooled and partly condensed. The condensed liquid is separated from the vapour phase and is used as reflux in the scrub column

LIQUEFIN PROCESS

LIQUEFACTION CYCLES


� The vapour is then routed to the second cryogenic heat exchanger for liquefaction

� The cryogenic MR 2 cycle leaves the pre-cooling heat exchanger fully liquefied. It leaves the cold exchanger at the same temperature as the LNG, is expanded in a valve and vaporises to provide the duty for its own sub-cooling and the LNG liquefaction and sub-cooling.

� After it vaporises, the MR2 is compressed in the MR2 compressor.The MR2 is too light a mixture to be condensed against cooling water and it enters the pre-cooling heat exchanger at ambient temperature but in the vapour phase. It is condensed in the pre-cooling heat exchanger

LIQUEFIN PROCESS (continued)

liquefaction cycles 00

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