Gas Processing Journal

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1 Gas Processng Journal Vol. 5, No. 1, Savng Energy by Exergetc Analyss of MTP Process Refrgeraton System Fard Sadeghan Jahrom 1, Masoud Behesht 2,3* 1 Department of Chemcal engneerng, Unversty of Isfahan, Isfahan, Iran 2 Department of Chemcal Engneerng, Unversty of Isfahan, Isfahan, Iran 3. Process Engneerng Insttute, Unversty of Isfahan, Isfahan,Iran Artcle Hstory Receved: Revsed: Accepted: Abstract The exergetc analyss s a tool that has been used successfully n many studes amng a more ratonal energy consumpton to reduce the cost of processes. Wth ths analyss, t s possble to perform an evaluaton of the overall process, locatng and quantfyng the degradaton of exergy. Ths paper apples exergy approach for analyzng the heat exchanger network desgn and refrgeraton of MTP process. For ths purpose, the behavor of some ndustral processes and refrgeraton cycle wth propylene refrgerant has been nvestgated by exergy method. The equatons of exergy destructon and exergetc cency for man components such as compressors, heat exchangers and expanson valves were studed. A specfed secton of propylene recovery unt wth ts refrgeraton cycle has been smulated to perform the exergy analyss. Addng a new valve wth optmum pressure drop accordng to process constrants and an expander results n hgh performance of mult-stream heat exchanger, savng cold utlty consumpton, usng excess heat of the process secton, and low requred compresson power (n the refrgeraton secton) whch are the most mportant characterstcs of the proposed confguraton. Results show that the annual proft reaches 4.3 %. Keywords MTP process, Refrgeraton system, Energy savng, Exergy analyss. 1. Introducton In process plants such as petrochemcal plants and refneres, whch are the major energy consumers, heat recovery of heat exchanger network s an mportant ssue (Sun, Luo, and Zhao,2015) because heat exchanger networks play an mportant role n heat ntegraton. Normally, a sub-ambent temperature process, such as propylene plant cold-end, comprses of three major parts ncludng the process, the heat exchanger network and the refrgeraton system. Depletng energy resources, ncreasng envronmental concerns, and energy prces are the major mpetuses to mprove heat ntegraton n exstng process plants (Sreepath and Rangaah,2014). In order to analyze systems that nvolve heat and power, the consderaton of heat loads and thermal gradents n a process s not suffcent. So, exergy analyss s ntroduced. The exergy analyss s a tool that allows dentfyng and quantfyng ncent equpment n a system nvolvng heat and power, not only n terms of heat loads (quantty of energy), but also n terms of temperature and pressure gradents (energy qualty) wth respect to the ambent condtons. Propylene producton from methanol s economcally mportant but s hghly senstve to energy because t requres refrgeraton at low temperatures. So, contnung development of the methods to reduce net power to provde ths refrgeraton s mportant n the petrochemcal ndustry. * Correspondng Author. Authors Emal Address: 1 Fard Sadeghan Jahrom (s.fard1367@gmal.com), 2 Masoud Behesht (m.behesht@eng.u.ac.r) ISSN (Onlne): , ISSN (Prnt): Unversty of Isfahan. All rghts reserved

2 90 Gas Processng Journal, Vol. 5, No. 1, 2017 Exergetc analyss of the refrgeraton system n ethylene and propylene producton process was nvestgated by Fabrega, Ross, and Angelo (2010). Results have shown that exergy of refrgeraton system of the process can be reduced by about 13%. Exergy analyss of multstage cascade low temperature refrgeraton systems n olefn plants was done by Maf, Naeynan, and Amdpour (2009). They developed an expresson for mnmum work requrement for the refrgeraton systems of olefn plants. They have shown that exergetc cency of chosen olefn refrgeraton plants s 30.8%, so they have demonstrated a suggeston for ncreasng the cency of refrgeraton plant. Lquefed natural gas (LNG) plant s nvestgated for reducng energy consumpton by Mortazav et al. (2012). For ths purpose, genetc algorthm (GA) from Matlab optmzaton tool box s used to optmze propane pre-cooled mxed refrgerant (C3-MR) LNG plant. Results of MCR cycle optmzaton show that power savng s as hgh as 13.28%. Propane cycle optmzaton causes power savng by about 17.16%. Ghorban et al. (2013) have nvestgated mnmzng the work consumed n refrgeraton cycle of ethylene producton. The objectve was to provde mprovements through mxed workng fluds nstead of pure workng flud n cryogenc secton of low temperature processes wth a vew to decrease the power consumpton for provdng the same refrgeraton duty. Results show that power consumpton n the new refrgeraton cycle confguraton can be decreased by about 22.3 %. Maf et al. (2014) have researched mxed refrgerant cycles of olefn plant cryogenc secton. The objectve of ths paper was to present a methodology for fndng the optmal MRC confguraton for provdng refrgeraton n a certan low temperature process. By consderng the ECC and GCC charts of these cycles, t s concluded that usng mult-stream heat exchangers n the cycle confguraton wll lead to better matchng between hot and cold composte curves. Energy and exergy analyss of the process has been developed for hydrocarbon recovery process by Mehrpooya et al. (2015). They have presented a new method for refrgeraton of NGL recovery that needs only two mult heat exchangers. Results show that compressor work for refrgeraton secton can be reduced by %. Ghorban, Hamed, and Amdpour (2016) have probed ntrogen rejecton unt wth LNG and NGL co-producton processes. In ths paper, mxed flud cascade natural gas lquefacton process of NGL LNG and NGL co-producton s assessed through the exergy and exergoeconomc analyss methods. After replacng one of the vapor compresson cycles wth a water-ammona absorpton refrgeraton cycle, ther exergy destructon cost was much hgher than other devces due to the hgh value of fuel cost n compressor; the fourth compressor had the hghest exergy destructon cost ( $/hr) and one of the shell and tube exchanger n the absorpton refrgeraton cycle had the lowest exergy destructon cost (2.033 $/hr). In ths study, the MTP process of Lurg technology, energy consumpton and utlty consumpton of ths process are nvestgated. At the begnnng, the operaton of cascade refrgeraton system of a typcal propylene plant for coolng of deethanzer feed s descrbed. Equatons have been studed for each component of the refrgeraton system. Then, exergy analyss s appled to calculate exergetc cency and exergy destructon for each component. Ths paper suggests some methods for decreasng of refrgeraton compressors work. In ths work, exergy analyss has been used for mprovng exergetc cency of the refrgeraton system, decreasng cold utlty consumpton and nvestment. 2. Materals and Methods 2.1. MTP refrgeraton cycle In ths secton, the cascade refrgeraton system of MTP deethanzer feed s analyzed that conssts of propylene refrgeraton system, mult-heat exchanger, drums and Joule Thomson expanson valve. GPJ

3 Savng Energy by Exergetc Analyss of MTP Process Refrgeraton System 91 Feed to 01-T E C -35 C Feed to 01-T C Feed to 01-E-1115 To Flare 20 C -43 C 586 C3 refrgerant gas 01-D D C3 refrgerant gas -43 C -40 C From 01-T C Reflux Stream 17 bar V-3 V-1 Separator 01-E-7311 V-2 01-E-7312 Compressor 01-D D-7312 Heatng & coolng Expanson-Valve 01-C C D-7311 Fgure.1. Flow dagram of propylene refrgeraton cycle and coolng of deethanzer feed secton Fgure.1 shows the flow dagram of propylene refrgeraton cycle and coolng of deethanzer feed secton n propylene producton plant whch s desgned for capacty of and comprses of fve process unts, ncludng Reacton, Regeneraton, Gas Separaton, Compresson, and Dryng and Purfcaton. In the reacton secton, methanol s entered nto the process through the nlet gas stream at 25 C and ambent pressure. In ths secton, after pre-heatng to 275 C at 16 bar, methanol s converted to dmethyl ether va DME Reactor (01-R-1111). Hgh converson and extraordnary selectvty cause dmethyl ether to be produced wthout any purfcaton whch then entered to adabatc MTP Reactor (01-R- 1511) drectly, where dmethyl ether s converted to propylene and by-products (such as propane, butane, pentene, pentane, hexane, hexane and heavy hydrocarbons) at hgh temperatures of about 480 C and ambent pressure. Propylene together wth other byproducts s sent to the next secton for separaton and purfcaton. Propylene refrgerant system supples propylene at two temperature levels: -43 C and -15 C. A fracton of produced propylene n the MTP process that was sent to Buffer 01-D s used as propylene refrgeraton unt va the propylene product pump. The propylene leaves the Propylene Buffer Tank n lqud state. It s cooled wth coolng water n the Propylene sub-cooler 01-E A part of cooled propylene s sent to propylene separator 01-D-7312 as lqud state. The other part of refrgerant propylene, after depressurzng va expanson valve to 8.9 bar and evaporated n the users at 15 C, s sent as vapor to the propylene separator 01-D The vapor phase from Separator 01-D-7312 s recycled to the sucton sde of the propylene Compressor 01-C The lqud phase from 01-D-7312 s depressurzed va expanson valve to 1.2 bar and t s drected to the users (01-E-5313) at - 43 C n the deethanzer column secton and then entered to the propylene separator 01-D as vapor phase. The propylene separator outlet vapor (01-D-7313) s fed to the 1st stage of propylene compressor 01-C The

4 92 Gas Processng Journal, Vol. 5, No. 1, 2017 vapor s compressed n two stages, and then t s condensed n the propylene condenser 01-E Fnally t s sent back to the propylene buffer 01-D Deethanzer column (01-T- 5311) s used to separate ethane from propane and propylene at -40 C and 19 bar. The output stream from bottom of debutanzer column s entered to the dehexanzer column at 172 C and 23 bar (01-T-5411) to separate C6 - from C7 + hydrocarbons for gasolne producton. The vaporous C2 top product s lquefed by propylene refrgeraton and then t s splt nto two streams. One of two streams s returned to the deethanzer column as reflux stream and the other stream s entered to LNG exchanger (01-E-5313). Ths stream s used for coolng the deethanzer feed, so, t reduces refrgerant consumpton. Part of heated output stream from LNG exchanger s sent to the MTP Reactor as recycled stream and the remanng output stream s sent to the flare Smulaton and selecton of the equaton of state for the system The smulaton of the entre plant s done by usng HYSYS smulator. Equatons of state are one of the key parameters n smulators.there are papers and books that deal wth the dfferences between present equatons of state. The flud package chosen n the smulator for the determnaton of thermodynamc propertes s PRSV equaton of state (Campbell, Llly, and Maddox 1992). After smulatng the process va HYSYS; t s lnked to MATLAB to evaluate the cency and the lost work by changng the Refrgeraton cycle. Fgure.2 shows the steps nvolved n the nformaton transfer n the senstve analyss. Hysys Smulaton Matlab Matlab Senstve Analysys Fgure.2. MTP plant analyss approach 2.3. Exergy analyss Exergy analyss combnes the frst and second laws of thermodynamcs, and s a powerful tool for analyzng both the quantty and qualty of energy utlzaton. Exergy s defned as the maxmum work possble to obtan from a system durng a process that brngs ths system nto equlbrum wth envronmental as reference state (Kotas,1985). Accordng to physcal exergy s equal to the maxmum amount of work obtanable when the stream of substance s brought from ts ntal state to the envronmental state whch s defned by equaton (1. e e h h T s s (1) ph1 ph where h and s are the enthalpy and entropy, respectvely, T0 s the reference envronmental temperature, ho and so are the correspondng propertes at the dead state. Based on exergy balance between nput and output streams, exergetc cency and exergy loss for equpments n varous refrgeraton systems and coolng of deethanzer feed secton are descrbed below Exergy balance for process equpment Compressors A gas compressor s a mechancal devce that ncreases the pressure of the flud and t s able to transport the flud through a ppe. If the compressor work s reversble, there wll be no exergy destructon. It means that rreversblty can be totally elmnated, whch GPJ

5 Savng Energy by Exergetc Analyss of MTP Process Refrgeraton System 93 results n mnmzng consumpton work of compressor. In the absence of heat transfer, the exergy balance for one multstage compressor s obtaned wth the followng Equaton 2:.. x x + o c c 0 I E E w m. e m. e w (2) In Equaton (2), ncreasng of exergy s equal to e0 e and w c s the actual power nput.. m s the molar flow and e s the exergy of streams. So exergetc cency of a compressor s defned as Equatons (3) or (4):.. m. e m. e 0 w c (3) I 1 (4) w c Valve Expanson valve s usually used n gas lquefacton plants and thermal plants such as refrgerators and heat pumps. Expanson processes occur mostly at below ambent temperature. The prmacy purpose of such expanson processes s the producton of coolng ect (Kotas, 1985). It s known that expanson valves are essentally senthalpc devces wth no work nteracton, so the rreversblty of the throttlng process can be obtaned from the exergy balance by neglectng heat transfer wth the surroundngs s obtaned from Equaton (5: e e e e T e T P T P I (5) P e and are defned as Equatons (5 and(6, respectvely: e T0 T T T 0 dh T T (6) P P e h h0 T0 s s0 (7) So exergy cency of expanson valve can be obtaned from Equaton (5: e e T 0 P e e T P 0 (8) If the valve s not an expanson valve and t s just a control valve, exergy cency for ths type of valve s obtaned by Equaton (9: Exo (9) E x Heat Exchangers There are four categores of heat exchangers n the process and refrgeraton system. The most complcated heat exchangers are LNG or mult-stream heat exchanger. At last, for mult-heat exchanger, the rreversblty and exergy cency based on the above explanatons and neglectng heat transfer wth the surroundng are EquatonsError! Reference source not found. and(11. I E E [(m e ) (m e ) (m e )] [(m e ) (m e ) (m e )] X n X out e e c c h h n e e c c h h (10) [( m e ) ( m e ) ] [( m e ) ( m e ) ] e e out e e n c c c out c c n [( m e ) ( m e ) ] [( m e ) ( m e ) ] e e n e e out h h h n h h out (11) Subscrpts n, out, c, h and e stand for nlet, outlet, cooler, heater and process stream, respectvely. 3. Results and dscussons 3.1. Exergy analyss and mnmzng compressor power The exergy analyss of low temperature refrgeraton system and coolng of deethanzer feed secton of MTP plant was studed n the present study to evaluate the amount of exergy destructon and exergetc cency for each equpment Compressors The exergy destructon and exergy cency of the compressor accordng to Equaton (3) or (4) are shown n Table 1. Table 1.Exergy destructon and exergy cency of compressor C C Power(kW) Lost(kW) η out

6 94 Gas Processng Journal, Vol. 5, No. 1, Heat exchangers The exergy destructon and exergetc cency of the mult-heat exchangers accordng to Equatons Error! Reference source not found. and (11 are shown n Table 2. The results show that compressors have hgh amount of exergy destructon, so ther performance shall be mproved. In the followng, some practcal ways are suggested to mprove the exegetc cency of the refrgeraton compressors through pressure drop of process stream and employng a turboexpander. The amount of exergy loss of each seres devces s llustrated n Fgure.3. Table 2. Exergy destructon and exergy cency of mult-heat exchanger E-5313 Duty (kw) 3076 Lost (kw) η Fgure.3. Dagram of exergy loss percentage of each seres devces Senstvty analyss Senstvty analyss and changng of operatng parameters are cent methods n order to determne the behavor and mprove exergy loss of equpment. Feed to 01-T E C -35 C Feed to 01-T C Feed to 01-E-1115 To Flare 20 C -43 C 586 V-4 C3 refrgerant gas 01-D D-5311 C3 refrgerant gas -43 C -40 C From 01-T Reflux Stream C Separator 17 bar 582 Compressor 01-EX-5311 V-1 01-E-7311 Heatng & coolng V-2 01-E-7312 Expanson-Valve 01-D D-7312 Turbo-Expander 01-C D C Fgure.4. Flow dagram of new desgn of propylene refrgeraton cycle and coolng of deethanzer GPJ

7 Exergy Loss Exergy Loss Savng Energy by Exergetc Analyss of MTP Process Refrgeraton System 95 The reducton of power consumpton of compressors n the refrgeraton cycle can be acheved by reducng the necessary coolng va refrgerant. One of the avalable solutons s to use the energy of low temperature process streams. As can be seen n Fgure.1, hot process stream s cooled from 28 C to -35 C durng four stages. Coolng stages consst of top product of deethanzer n three levels of temperature and one propane refrgerant stream n mult heat exchanger (01-E-5313). Frst, the C2 - recycled stream comng from 01-D A/B s heated up to 20 C and s drected to 01-E In the second stage, the C2 - purge comng from 01-D-5311 s heated to 20 C and s sent to the flare lne. Thrd, heat of feed deethanzer s used to evaporate the C2 - recycle sent from 01-D-5311 to 01-D-5312 A/B and fnally, t s cooled by propylene refrgerant. One of the parameters that affect the reducton of the requred propane refrgerant s the changng of the nlet process streams pressure drop whch has no ect on the performance of other equpments. Fgure.4 shows the novel desgn of coolng deethanzer column feed. It s clear that pressure drop of a stream decreases the stream temperature. So,by addng a new Joule-Thomson valve on the 540 stream lne, the stream s partally vaporzed and ts temperature would be decreased. Then, by addng an expander on 582 process stream for pressure drop, the 583 stream temperature and pressure are decreased to C and 17 bar. Fgure.5 llustrates the varatons of exergy loss as a functon of pressure drop for LNG exchanger and Joule-Thomson valve, whle fgure Fgure.6 shows varatons of exergy loss and compressor work as a functon of pressure drop compressor work of refrgeraton cycle when the pressure drop of new valve on 540 stream lne changes from 0 kpa (ndustral desgn) to 1900 kpa (new desgn). 740 a 20 b Pressure Drop (kpa) Pressure Drop (kpa) Fgure.5. Varaton of exergy loss a) LNG exchanger (01-E-5313), b) Joule-Thomson valve (V-4) versus valve (V-4) pressure drop

8 Exergy Loss Exergy Loss Compressor Work (kw) Compressor Work (kw) 96 Gas Processng Journal, Vol. 5, No. 1, a 01-C C b 01-C C Pressure Drop (kpa) Pressure Drop (kpa) 5404 Fgure.6. Varatons of a) exergy loss, b) compressor work of refrgeraton cycle versus valve (V-4) pressure drop As can be seen from Fgure.5, when the valve pressure drop s ncreased, the exergy loss of LNG exchanger and new valve (V-4) ncreases gradually to 1200 kpa, then exergy ncreases dramatcally, whle Fgure.5 shows compressors work and ts exergy loss have dfferent behavor and they decrease n lower slope to 1200 kpa, then varaton of compressor work and exergy loss are approxmately constant. In ths case, we should set valve operatng pressure drop to 1200kPa. Accordng to Fgure.4, a turbo-expander s used nstead of valve on 582 stream lne (V-3), whch can decrease the compressor work of refrgeraton cycle. So, the work produced by the turbo-expander should be consdered. Turbo-expander outgong stream temperature s much lower than that of the expanson valve. Further decrease of turbo-expander outgong stream temperature reduces the amount of requred propylene refrgerant, so that the compressor work of refrgeraton cycle would be decreased. Specfcatons of the cold process, feed and C 3 refrgeraton streams are summarzed n Table 3. Accordng to Table 3 and pervous dscusson, the amount of requred propylene refrgerant for turboexpander s lower than expanson valve. By applyng optmum pressure drop of new valve and usng a turbo-expander accordng to operatonal condtons (e.g. outgong stream pressure of turbo-expander cannot be lower than 17.0 bar), optmzed refrgeraton cycle s calculated and lsted n Table 4 and Table 5. Parameters of turbo-expander Exergy loss (kw) Turbo-Expander Work (kw) Captal Cost The total annual proft 01-EX Captal cost of addng a new turbo-expander s obtaned by usng equaton Error! Reference source not found.: (12) Nelson cost ndex s equal to Equaton (12) shows captal cost of turbo-expander for one year. In above equaton, CRF s captal recovery factor whch s calculated usng equaton (13): ( 1 ) CRF ( 1 ) 1 (13) s plant economc lfe that s consdered 25 years and s average annual rate of the cost of money that s equal to 10%. Captal Cost =PEC CRF (12) Table 3. Specfcatons of process streams and refrgeraton cycle shown n Fgure.4 GPJ

9 Savng Energy by Exergetc Analyss of MTP Process Refrgeraton System 97 Feed Stream V-4 streams Wth valve Wth turboexpander C3 refrgeraton streams Input temperature ( C) : Output temperature ( C) : Input pressure (bar) : Output pressure (bar) : Input vapor fracton (%) : Output vapor fracton (%) : Flow rate (kmoleh -1 ) Wth valve: Wth turboexpander: Table 4. The ect of pressure drop of new valve and turbo-expander on refrgeraton cycle compressors work 01-C C Industral desgn New desgn Reducton rate (%) Industral desgn New desgn Reducton rate (%) Exergy loss (kw) Compressor Work (kw) The total annual proft Table 5. Parameters of turbo-expander Exergy loss (kw) Turbo-Expander Work (kw) Captal Cost The total annual proft 01-EX Captal cost of addng a new turbo-expander s obtaned by usng equaton Error! Reference source not found.: (12) Nelson cost ndex s equal to Equaton (12) shows captal cost of turbo-expander for one year. Captal Cost =PEC CRF (12) In above equaton, CRF s captal recovery factor whch s calculated usng equaton (13): ( 1 ) CRF ( 1 ) 1 (13) s plant economc lfe that s consdered 25 years and s average annual rate of the cost of money that s equal to 10%. Fgure.7 shows the rate of compressors work before and after of refrgeraton cycle, by consderng the smulated process and actual operatonal condtons. Accordng to Table 4 and Table 5. Parameters of turbo-expander

10 98 Gas Processng Journal, Vol. 5, No. 1, 2017 Exergy loss (kw) Turbo-Expander Work (kw) Captal Cost The total annual proft 01-EX Captal cost of addng a new turbo-expander s obtaned by usng equaton Error! Reference source not found.: (12) Nelson cost ndex s equal to Equaton (12) shows captal cost of turbo-expander for one year. Captal Cost =PEC CRF (12) In above equaton, CRF s captal recovery factor whch s calculated usng equaton (13): ( 1 ) CRF ( 1 ) 1 (13) s plant economc lfe that s consdered 25 years and s average annual rate of the cost of money that s equal to 10%., the exergy loss of refrgeraton cycle compressors has been decreased n comparson wth the prmtve desgn. Compressor exergy loss represents the amount of addtonal work that compressors must consume for compresson of stream to the desred pressure. So, decreasng the compressor exergy loss wll result n lower compressor power consumpton. As can be seen n Table 4, by ncreasng the process ntegraton wth refrgeraton cycle, the exergy loss and power consumpton of compressors refrgeraton cycle has sgnfcantly decreased. The amount of power consumpton for compressor 01-C and 01-C are decreased by about 155 kw and 130 kw, respectvely. Snce the producton work n turbo-expander s low (Table 5. Parameters of turboexpander Exergy loss (kw) Turbo-Expander Work (kw) Captal Cost The total annual proft 01-EX Captal cost of addng a new turbo-expander s obtaned by usng equaton Error! Reference source not found.: (12) Nelson cost ndex s equal to Equaton (12) shows captal cost of turbo-expander for one year. Captal Cost =PEC CRF (12) In above equaton, CRF s captal recovery factor whch s calculated usng equaton (13): ( 1 ) CRF ( 1 ) 1 (13) s plant economc lfe that s consdered 25 years and s average annual rate of the cost of money that s equal to 10%. ), t can also be used for drvng pumps motor. GPJ

11 Savng Energy by Exergetc Analyss of MTP Process Refrgeraton System 99 Fgure.7. Rate of compressors work before and after of refrgeraton cycle 4. Conclusons Ths paper presents an exergetc analyss of the propylene producton and ts refrgeraton cycle. The exergy method used here s found to be a powerful tool n optmzng the performance of such complex process unts. The equatons of exergy cency and exergy destructon for each component of refrgeraton system are nvestgated. In ths paper, a basc practcal way ncludng exergy analyss s used. For mprovng exergetc cency and decreasng exergy loss of the refrgeraton system and due to operaton constrants, new operatonal condtons for coolng of deethanzer feed and propylene cycle equpments are proposed. It s found that the refrgeraton cycle wth excess expanson valve and a turbo-expander surpasses the refrgeraton cycle wthout turbo-expander n terms of the net power consumpton and the total rreversblty. After ntegraton and optmzaton, the net power of refrgeraton cycle s that s reduced by about 4.3 % relatve to Lurg desgn. The results show that the total annual proft s decreased about $ for each year. By addng an expanson valve and a turbo-expander t was possble to produce power for rotatng motor of pumps and also use excess heat n the process for preheatng the deethanzer feed. References Campbell, J., Llly, L., & Maddox, R. (1992). Gas Condtonng and Processng: The equpment modules. Gas Condtonng and Processng Vol. 2. Fábrega, F. M., Ross, J. S., & d Angelo, J. V. H. (2010). Exergetc analyss of the refrgeraton system n ethylene and propylene producton process. Energy, 35(3), Ghorban, B., Hamed, M.-H., & Amdpour, M. (2016). Exergoeconomc Evaluaton of an Integrated Ntrogen Rejecton Unt wth LNG and NGL Co-Producton Processes Based on the MFC and Absorbton Refrgeraton Systems. Gas Processng Journal, 2(2). Ghorban, B., Maf, M., M, M., Nayenan, M., & Saleh, G. R. (2013). Mathematcal Method and Thermodynamc Approaches to Desgn Mult-

12 100 Gas Processng Journal, Vol. 5, No. 1, 2017 Component Refrgeraton Used n Cryogenc Process Part I: Optmal Operatng Condtons. Gas Processng Journal, 1(2), Kotas, T. J. (1985). Preface. In The Exergy Method of Thermal Plant Analyss (pp. v v). Elsever. Maf, M., Ghorban, B., Saleh, G., Amdpour, M., & Mousav Nayenan, M. (2014). The Mathematcal Method and Thermodynamc Approaches to Desgn Mult-Component Refrgeraton used n Cryogenc Process Part II: Optmal Arrangement. Gas Processng Journal, 1(2). Maf, M., Naeynan, S. M. M., & Amdpour, M. (2009). Exergy analyss of multstage cascade low temperature refrgeraton systems used n olefn plants. Internatonal Journal of Refrgeraton, 32(2), Mehrpooya, M., Vatan, A., Sadeghan, F., & Ahmad, M. H. (2015). A novel process confguraton for hydrocarbon recovery process wth auto e refrgeraton Nomenclature I Ex T P S H X m 0 Q W Ė Irreversblty (kw) Exergy (kj/kgmole) Temperature ( C) Pressure (bar) Entropy (kj/kgmole C) Enthalpy (kj/kgmole) Component mole fracton Flow rate (kgmole/hr) Heat duty (kw) Work transfer rate (kw) Rate of exergy Greek letters η Exergy cency system. Journal of Natural Gas Scence and Engneerng, 1 9. Methods, P. (n.d.). A Property Methods and Calculatons, Mortazav, A., Somers, C., Hwang, Y., Radermacher, R., Rodgers, P., & Al- Hashm, S. (2012). Performance enhancement of propane pre-cooled mxed refrgerant LNG plant. Appled Energy, 93(6 7), Sreepath, B. K., & Rangaah, G. P. (2014). Revew of heat exchanger network retrofttng methodologes and ther applcatons. Industral and Engneerng Chemstry Research, 53(28), Sun, L., Luo, X., & Zhao, Y. (2015). Synthess of multpass heat exchanger network wth the optmal number of shells and tubes based on pnch technology. Chemcal Engneerng Research and Desgn, 93(June), Superscrpts P Pressure component T Thermal component Standard condton Ph Physcal Abbrevatons MTP J-T E C V D Methanol to propylene Joule- Thomson valve heat exchanger Compressor Expanson valve Flash drum Subscrpts Inlet o Outlet sh Shaft a Ar c Cold h Hot GPJ