macam refrigerant

7/23/2019 Macam Refrigerant

1/18

As the industry matured, the market has demanded trainswith larger and larger capacity (Figure 1). This trend hasbeen facilitated by developing larger gas turbines to drivelarger refrigerant compressors and by improving the designof process cycles and !"#s. The largest of these base

load trains are in $atar. #ach of these si% trains utili&es theAir 'roducts A'* +- 'rocess that combines a C3MR(Propane-Precooled Mixed Refrigerant) liue/er and0 recycle e%pansion process sub cooler to make over .23T'A of +-. All are running reliably with the /rst two inoperation for over two years.

INTRODUCTION


2/18

Refrigerant Syte! for "N# Plant

4ingle 3i%ed 5efrigerant (435) 6ouble 3i%ed 5efrigerant (635)

itrogen 5ecycle (0)

0 5ecycle with "idro7ourocarbon ("F) 'recooling

Fa8ar Amin !ahyullah0


3/18

3ain ryogenic "eat #%changer (3"#) is one of key euipmentin natural gas liuefaction (+-) plant. 3"# used in

liuefaction of natural gas having some special characteristic : ;ntensive ?>> k! < ton +-) omple% heat transfer "eat transfer from one (or several)

very high pressure natural gas stream to one or several lowpressure refrigerant streams

Thermal stress deg) and outlet temperature (1B0 deg)

Cperate at very low temperature (1B0 deg) "igh heat transfer eDciency @ery low temperature approach

(0= deg) to ma%imi&e heat transfer per unit area ;nvolve phase change and risk of phase separation and

proper distribution "igh risk of leakage and safety related issue "igh risk of blockage


4/18

Two type of compact 3"# widely used in +- plant. There are'lateFin "eat #%changerand oil (4piral) !ound "eat#%changer. elow images are typical !"# and 'F"#

!"# is coils


5/18

'F"# is corrugated or serrated plate stacking on each and

others to creates cross and


6/18

Although both type of "# have been widely used, !"# and'F"# have their own special features and advantages. eloware simple comparison between both !"# and 'F"#.


7/18

The most common liuefaction process currently used for landbased +- plants is the C3MR (Propane-Precooled Mixed

Refrigerant) process. 'recooling of the natural gas feed isperformed with propane refrigerant, and liuefaction and subcooling are completed with a mi%ed refrigerant composed ofnitrogen, methane, ethane or ethylene, and propane.

C3MR

3ost of the worldGs +- is liue/ed using the A'=35 process,using a C&$% (Coil Wound Heat Exchanger)(Figure =).


8/18

'dantageThe =35 process achieves High efciencydue to the ability

to match the 35 boiling curve to the feed condensation curve,

High reliability, Ease o operation

There are some conditions that make it less attractive. Themost obvious is the use of propane refrigerant in theprecooling loop, and the conseuent large inventory o

propane that is required, especially when kettletypee%changers are used. A second issue is the relatively largeplot spacethat is reuired for the propane evaporators.

Deciency


9/18

The 4ingle 35 cycle uses only one 35 loop for precooling,liuefaction, and sub cooling (Figure H).

SMR(Single MixedRefrigerant)

This provides the bene/t of reduced equipment count, butcomes at the cost of lower eDciency than =35 and 635(6ual


10/18

The 435 process reuires a taller and larger liuefaction !"#

for a given +- production than the 635 cycle, as it must

handle all of the liuefaction duty including precooling. ;naddition, at capacities approaching 2 M!"# t$o CWHEs

$ould li%ely be required.A basic 435 process has a lo$er efciency than a =35 or

635 cycle. ;n addition to the con/guration shown in Figure H,

Air 'roducts has developed several variations of the A'435

process to enable increased eDciency, through the use of

additional levels of compression and e%changer comple%ity.


11/18

;n the 6ual 35 cycle, the precooling propane refrigerant isreplaced with a high boiling point !arm 3i%ed 5efrigerant

(!35) containing methane, ethane, propane and butane.

DMR(Dual/Double MixedRefrigerant)


12/18

This signi/cantly reduces the propane inventory in the vessel.Furthermore, the optimi&ed !35 composition will freuentlycontain little or no propane, and the performance penalty to

eliminate propane is typically minimal. 'recooling is performedin a !"#, which provides the proven mechanical performanceof wound coil heat e%changers, countercurrent 7ow for betterheat transfer performance and also may reduce the plot spacereuired. The 635 process achieves an eDciency comparable to=35. ;t has also been used successfully in landbased +-.Figure ? shows an A'635 process which uses two stages of!35 compression. The discharge from the /rst stage is partiallycondensed and the liuid portion is pumped around the secondstage compression. The !35 is totally condensed after thesecond stage compression, cooled in the !"# 're cooler, and7ashed to a single pressure level to provide precoolingrefrigeration. Cther compression and 're cooler con/gurationsare possible, with various advantages and disadvantages. Theprocess can therefore be con/gured and optimi&ed to meet thepro8ect reuirements.


13/18

All of the foregoing process cycles use 7ammable refrigerants.ecause the feed gas and product themselves are 7ammable,and +'- recovery may result in signi/cant +'- storage, it is not

possible to entirely eliminate risks due to hydrocarbon storageon an F+-. "owever, minimi&ation of 7ammable inventorydrives interest in refrigeration cycles which contain no7ammable components.

N* Recycle

The nitrogen recycle expander plant is a well-known technology, used

extensively in the air separation industry for producing liquid N2 and O2.


14/18

The process uses the reverse Brayton cycle to create refrigeration y co!pressing

nitrogen, re!oving the heat of co!pression, expanding the nitrogen through a

turo-expander to create a cold strea!, and war!ing the strea! against the heat

load. The cycle has een used in hundreds of "ir #eparation $nits as well as

do%ens of &N' peakshaver plants.

(n the last decade, the ")-*+ &N' )rocess increased aseload plant capacity y!ore than , y adding a nitrogen refrigeration loop to the successful /01

technology 34igure 56. The ")-* process utili%es propane for precooling, a

!ixed refrigerant for liquefaction, and a nitrogen refrigeration loop for

sucooling. The nitrogen loop provides refrigeration that the /01 portion of

the liquefaction area would otherwise e required to provide and enales single

train production greater than 7 1T)".

"owever, the A' nitrogen loop as it stands would not be theoptimum design to perform all three functions of precooling,liuefaction and subcooling. Air 'roducts has developed severalvariations which are tailored to this purpose. These optimi&e the

number of e%panders, pressure and temperature levels alongwith process eDciency.


15/18

Figure shows an Air 'roducts A'I +- process with a singlepressure level and two e%pander temperatures. The nitrogen iscompressed and enters an economi&er in which it is cooled.3ost of the nitrogen is withdrawn at an intermediate point,e%panded through a turboe%pander to reduce the temperature,

and enters the liuefaction e%changer to provide the ma8ority ofthe refrigeration duty to liuefy the natural gas. The remainingnitrogen is further cooled in the economi&er before beinge%panded to provide refrigeration to the subcooling portion ofthe main e%changer.


16/18

For F+-, the 0 recycle process has the obvious advantage of

using a non7ammable refrigerant. "owever, the eDciency ofthe cycle is signi/cantly lower than those which use aprecooled 35 cycle. The 0 refrigerant is entirely vapor andthe heat transfer therefore entirely sensible.ecause sensible heat produces less refrigeration per unitmass, the refrigerant 7ow rates are signi/cantly higher for the

0 recycle process. This results in larger heat e%changer andpipe si&es, often reuires parallel rotating machinery, and limitssingle train 0 recycle systems to between 1 and 0 3T'A.

4ome of the nitrogen refrigerant is used to providerefrigeration in the economi&er before all the refrigerant isreturned to the compressor suction. The compression work isperformed in several machines, with the /rst stage(s) drivenby an e%ternal driver and the last stage driven by the turboe%panders (companders). ote that the +- is liue/ed in a!"#. The !"# has a proven history of withstanding thehigh thermal stresses which can occur in liuefaction service.


17/18

N* Recycle + $,C

The reverse rayton cycle is not the best option to create thewarm refrigerant reuired for precooling, and therefore, using0 to provide precooling lowers the process eDciency. A way to

improve the overall cycle performance is to use a secondrefrigerant loop for precooling. This approach can increase theeDciency of the process nearly to that of an 435 cycle. !hilepropanewould be a good choice based on eDciency alone, thisobviously introduces a 7ammable refrigerant, which eliminates

much of the advantage of the 0 recycle process. ;nstead, theprecooling can be performed by using a hydro7uorocarbon("F) refrigerant.J=K The "F system is similar to a propanesystem, with the substitution of "F?1>A or another suitablerefrigerant and a compressor designed for the heaviermolecular weight of the "F.


18/18

Figure 2 shows an A'" process similar to the A' processof Figure , where an "F precooling system has replaced theprecooling bundle. "F refrigerant systems are widely usedin marine applications, as well as countless industrial and

household functions.

macam refrigerant

Documents