INVESTIGATION OF THE PERFORMANCE CHARACTERISTICS OF AN AMMONIA-WATER ABSORPTION CHILLER IN A TRIGENERATION SYSTEM ARRANGEMENT

Transcription

1 INVESIGAION OF HE PERFORMANCE CHARACERISICS OF AN AMMONIA-WAER ABSORPION CHILLER IN A RIGENERAION SYSEM ARRANGEMEN INyman Suamir a *, Savvas A assu a, Abas Hadawey a, Issa Chaer b, Dug Marritt c a Schl f Engineering and Design, Brunel University, Uxbridge, Middlesex, UB8 3PH, UK * el: ; Fax: address: INymanSuamir@brunelacuk b Faculty f Engineering, Science and the Built Envirnment, Lndn Suth Bank University, UK c Dug Marritt Assciates, UK ABSRAC rigeneratin systems have been used in a number f applicatins including cmmercial buildings and industrial facilities Mst f these have been fr space cling applicatins with a smaller number fr refrigeratin applicatins in the fd prcessing industry which requires temperatures belw C his paper is cncerned with the investigatin and develpment f mdular trigeneratin systems fr fd industry applicatins based n the integratin f micrturbines and ammnia water absrptin refrigeratin systems Specifically, the paper presents results f experimental investigatins n the perfrmance f a 12 kw capacity ammnia-water absrptin refrigeratin system driven by thermal energy recvered frm the exhaust gases f a micrturbine in a trigeneratin arrangement he heat transfer between the micrturbine exhaust heat exchanger and the generatr f the absrptin refrigeratin system is perfrmed by a heat transfer fluid in a clsed heat transfer lp ests were perfrmed at different brine temperatures and heat transfer fluid temperatures he perfrmance f the unit was evaluated and fund t cmpare favurably with the perfrmance f a directly gas fired absrptin chiller In additin, the verall efficiency f the trigeneratin system was als evaluated Keywrds: ammnia-water absrptin chiller, trigeneratin, perfrmance characteristic, heat transfer fluid INRODUCION Absrptin cling is a technlgy that uses heat instead f electricity t prduce cling he heat t the generatr f the absrptin chiller can be prvided directly by a gas fired system r indirectly using a heat transfer fluid Rssa et al 27, reprted n the use f a thermal fluid system t drive the generatr f an ammnia-water absrptin chiller he authrs shwed that the system culd start prducing refrigeratin at a thermal fluid temperature f 12 C, and achieved a COP f arund 26 Flrides et al 22, reprted n an ammnia-water system with air cled absrber and cndenser that required a generatr temperature in the range f 125 t 17 C he cmbinatin f absrptin refrigeratin with a CHP plant enables the use f the generated heat t prduce cling and refrigeratin Bassls et al 22, illustrated examples f typical ammnia-water plant in the fd industry Jalalzadeh-Azar et al 22, reprted n successful integratin f cgeneratin plant with absrptin clers fr industrial and cmmercial applicatins hese systems have nt been applied widely t the fd industry, hwever, due t the unavailability f small size lw temperature and lw cst absrptin refrigeratin systems ff-the-shelf he energy and carbn savings frm CHP installatins can be as high as 3% cmpared t separate heat and pwer generatin but this depends n many factrs such as the size f the scheme and the nature f the heat lad (DI, 27 Fr maximum savings there needs t be simultaneus demand f heat and electricity and a fairly cnstant heat demand thrughut the year In many applicatins where the demand fr heat des nt remain cnstant thrughut the year, the utilisatin efficiency f a CHP plant can be increased if the excess heat is used t drive thermally driven (srptin refrigeratin systems he integratin f CHP with srptin refrigeratin technlgies is knwn as Cmbined Heating Refrigeratin and Pwer (CHRP r trigeneratin

2 assu et al 27 and Sugiartha et al 28 shwed that trigeneratin technlgy based n a micr gas turbine integrated with an absrptin refrigeratin system can prvide prmising ecnmic and envirnmental benefits when used in supermarket applicatins he authrs indicated that payback perids f between 3 and 5 can be achieved fr gas t electricity price ratis less than 3 Artecni et al 29 reprted that trigeneratin systems in supermarket applicatins can prduce primary energy savings f 56% with payback perid f less than 5 years his paper presents results f experimental investigatins n the perfrmance f a 12 kw capacity ammnia-water absrptin refrigeratin system driven by thermal energy recvered frm the exhaust gases f a micrturbine in a trigeneratin arrangement he heat transfer between the micrturbine exhaust heat exchanger and the generatr f the absrptin unit system is perfrmed by a heat transfer fluid in a clsed heat transfer lp arrangement ES FACILIY he trigeneratin test facility incrprates three main mdules; CHP mdule, absrptin refrigeratin system mdule, and a refrigeratin lad mdule hese mdules which are shwn in Figure 1 were cmprehensively instrumented t measure temperatures, pressures and flwrates t enable the perfrmance f the unit t be evaluated V Flw-rate measurement emperature measurement P Pressure measurement Header tank Deaeratr Exhaust gas Dry blast cling unit Display cabinet Expansin tank V Generatr Chilled fluid pump Absrptin Chiller V Generatr jacket Fluid receiver P Ht fluid pump Cling cil Micrturbine pwer generatr HX Figure 1: Schematic diagram f test facility using il as the heat transfer medium between the micrturbine and absrptin refrigeratin system he CHP mdule is based n a Bwman 8 kwe recuperated micrturbine generatin package MG8RC-G with in-built biler heat exchanger (exhaust heat recvery heat exchanger he micrturbine cnsists f a single stage radial cmpressr, single radial turbine within an annular cmbustr and a permanent magnet rtr (alternatr all n the same rtr shaft Other systems in the engine bay include the fuel management system and the lubricatin/cling system Heat recvery frm the exhaust gases is perfrmed in a stainless steel flue-gas/liquid heat exchanger he heat recvery fluid is Diphyl-H high perfrmance synthetic heat transfer fluid that can perate at temperatures up t 34 C he absrptin refrigeratin system emplyed is a packaged gas fired ROBUR ACF-6LB chiller he perfrmance f the unit in its gas fired frmat, was established frm tests in the labratry Fr brine flw

3 temperatures between 11 C and +3 C, the refrigeratin capacity f the unit was fund t vary frm 85 kw t 15 kw and the COP frm 32 t 57 (assu et al 28 be used in a trigeneratin arrangement the generatr f the absrptin unit was mdified t be heated by the heat transfer fluid that flws in a lp between the micrturbine exhaust heat recvery heat exchanger and the absrptin refrigeratin system generatr as shwn in Figure 1 he mdificatin included the replacement f the gas burner with a heat transfer jacket arund the generatr as shwn in Figure 2 he jacket design and heat transfer fluid flw arund it were ptimised using Cmputatinal Fluid Dynamics (CFD Original direct gas fired generatr (Rbur, 27 Generatr Mdified generatr with heat transfer fluid jacket system 455e+2 453e+2 Figure 2: Design mdificatin f the absrptin chiller t perate with heat recvered frm the exhaust gases f the micrturbine 451e+2 449e+2 447e+2 445e+2 443e+2 441e+2 439e+2 437e+2 435e+2 433e+2 431e+2 429e+2 427e+2 425e+2 423e+2 421e+2 419e+2 417e+2 415e+2 in 18 C m 9 kg/s emperature scale in K ut 169 C Design f heat transfer jacket using CFD MEHODOLOGY AND ES RESULS ests were perfrmed at different brine temperatures at the refrigeratin system evapratr and heat transfer fluid temperatures at the generatr Brine delivery temperatures ranged between -14 t -23 C he micrturbine perated at full lad with 1% recuperatin ests at different heat transfer fluid temperatures between 187 and 217 C were perfrmed by changing the pwer utput f the micrturbine frm 1 t 8 kw whilst the brine flw temperature was maintained at -8 C he fllwing parameters were recrded: pwer utput, fuel cnsumptin and exhaust gas temperature f the micrturbine; temperatures, pressures and flwrates f the brine and heat transfer fluid; pressures and temperatures at varius pints f the refrigeratin cycle f the absrptin chiller; pwer cnsumptin f the heat transfer fluid pump and absrptin refrigeratin system brine pump hese parameters were used t determine the COP f the refrigeratin system, the electrical generatin efficiency f the micrturbine system and the verall efficiency f the system perating in a cmbined refrigeratin and pwer mde (CRP and cmbined refrigeratin, heating and pwer mde (trigeneratin Equatins 1 t 5 were used fr the calculatins as fllws: Qc mb Cpb( bi b COP [1] Q m Cp ( g i Including the pwer cnsumptin f the heat transfer fluid pump the system COP is given by, COP s Q g Qc + W pump mb Cpb( bi b m Cp ( + W i pump [2]

4 We 36 We η e x 1 (% [3] W f 1 V CV We 36( We η CRP x 1 (% [4] W f 1 V CV We + Qh 36( We + Qh η RI x 1 (% [5] W f 1 V CV he results f a start up test fr the il fired unit are shwn in Figure 3 he Figure shws the variatin f the heat transfer fluid (HF temperature and the brine temperature entering and leaving the evapratr with time It can be seen that at start up f the gas turbine unit the HF temperature increased almst linearly and reaches 15 C apprximately 15 minutes frm start up he absrptin unit started t prduce refrigeratin at this pint with average HF temperature arund the generatr f 145 C and average generatr surface temperature 1345 C he HF temperature cntinued t rise reaching a maximum f apprximately 21 C apprximately 75 minutes frm start up HF temperature ( C HF in generatr jacket Brine in evapratr HF ut generatr jacket Brine ut evapratr -15 1:48 11: : : : : : : : : : : ime (minutes ime (minutes ime Figure 3: emperature prfile f HF and brine f the plant at 8 kw pwer utput and ambient temperature 9-11 C he perfrmance f the absrptin unit, in its gas fired frmat, was established frm tests in the labratry Fr brine flw temperatures between 11 C and +3 C, the refrigeratin capacity varied frm 85 kw t 15 kw and the COP frm 32 t 57 (assu et al, 28 he mdified unit perfrms as well if nt better than the gas fired unit At brine flw temperature f 8 C bth units have a refrigeratin capacity f 12 kw If the heat transfer fluid pump pwer is taken int cnsideratin, bth units will have a COP f arund 53 he influence f the HF and brine delivery temperature n the perfrmance f the absrptin refrigeratin unit is shwn in Figure 4 It can be seen that as the HF temperature increases the refrigeratin capacity f the absrptin refrigeratin system increases frm arund 1 kw at a HF temperature f 167 C t 13 kw at HF temperature f 217 C he COP f the system initially increases reaching maximum at HF temperature f 195 C, and then begins t reduce Maximum refrigeratin system COP f 73 is achieved at HF temperature f 195 C at a brine flw temperature f -8 C he verall system COP which includes the HF pump pwer fllws clsely the variatin f the refrigeratin system COP, reaching a maximum f 6 at HF temperature f 195 C Figure 4 als shws that the refrigeratin capacity f the absrptin system is nt influenced by the brine delivery temperature he brine temperature, hwever, has an influence n the system COP which Brine temperature ( C

5 increases as the brine delivery temperature reduces, reaching a plateau at a brine delivery temperature f -4 C Cling capacity Heat recvered COP COPs Cling capacity Heat recvered COP COPs Cling capacity r heat recvered (kw HF temperature 211 C Ambient 9 t 11 C Delivery brine temperature ( C COP Cling capacity r heat recvered (kw Brine temperature -8 C Ambient 11 t 13 C Oil HF temperature temperature entering at generatr generatr inlet jacket ( C ( C COP Figure 4: Perfrmance f absrptin refrigeratin unit at different brine delivery and HF temperatures RIGENERAION SYSEM ARRANGEMEN he heat required by the absrptin chiller used in the tests was much lwer than the heat available in the exhaust gases f the micrturbine establish the refrigeratin and heating ptential f the trigeneratin plant a spreadsheet based simulatin was perfrmed using the perfrmance parameters and characteristics established frm the experimental prgramme A prpsed trigeneratin system arrangement fr fd retail applicatins is illustrated in Figure 5 he system is based n an 8 kw e recuperated micrturbine with tw identical biler heat exchangers installed in series his cnfiguratin can minimise cmplexity in regulating the exhaust gas flw and prvides cnstant HF temperature t the absrptin refrigeratin system It can be seen that the system can generate 45 kw f refrigeratin and 93 KW f heat fr space and dmestic ht water heating Figure 6 shws the influence f the HF flw rate n the perfrmance f the refrigeratin system assuming full lad peratin f the micrturbine, a return HF temperature f 189 C and ambient temperature f 12 C he heat recvered frm the exhaust gases increases slightly with HF temperature as well as the refrigeratin capacity f the absrptin refrigeratin system at the expense thugh f increased HF pump pwer he influence f the HF flwrate n the system efficiency is shwn in Figure 7 It can be seen that the HF flwrate has little impact n the verall perfrmance f the system he pwer generatin, refrigeratin, heating and verall system efficiency remain fairly cnstant ver a wide range f HF flw rate frm 25 t 65 kg/s he verall efficiency f the system is 75% Cling efficiency f the trigeneratin plant can be imprved up t 19% when the temperature f the HF entering generatr is set at abut 18 C, but it can reduce the verall efficiency f the plant Fr ptimum efficiency and savings, the plant capacity needs t be designed in accrdance with simultaneus demand f cling, heating and electricity

6 Fd retail industry Fuel (Natural Gas 2916 kw f Imprted electricity Flue gases 83 kg/s 93 C Micrturbine pwer generatin 277 C Ht gas 8 kw e HX2 HX1 9 C Dmestic heating & ht water Ht water 11 kg/s 7 C Ht gas 23 C 2 C Ht il 25 kg/s 189 C 62 kw t Absrptin Chiller tal kw e required 93 kw t Medium temperature refrigeratin 45 kw c Electric cntrl bard Lighting, small pwer, ther electrical appliances and lw temperature refrigeratin Assumptins: - HF-transprt heat lsses 7 W/m (steel pipe 8 mm and HF-circuit length 2 m - HX 1 HX 2 are 2-2 shell and ciled tube heat exchanger with heat transfers area 12 m 2 - HX 1 and HX 2 are installed adjacent t each ther, heat lsses in HX and duct is nt cnsidered - emperature drp in the ht water system cnsidered 2 K and ambient temperature 12 C Figure 5: Estimated capacity f a trigeneratin plant utilizing an 8 kw micrturbine pwer generatin fr fd retail industry 21 Gas ut HX1 Heat recvered HF ut HX1 Cling capacity 12 8 Overall Electrical Heating Cling emperature f Gas r HF ( C Heat Cling r cling capacity capacity r heat (kw Efficiency f the plant (% Mass flwrate f HF (kg/s Mass flwrate f HF (kg/s Figure 6: Heat recvered fr generating cling in the trigeneratin plant Figure 7: Efficiency f the trigeneratin plant at different HF mass flwrate CONCLUSIONS A cmmercially available gas fired ammnia-water absrptin refrigeratin system has been redesigned t perate in a trigeneratin arrangement in cnjunctin with a micrturbine based CHP system he system utilises a heat transfer fluid fr heat transfer between the CHP exhaust gas heat recvery system and the generatr f the absrptin system

7 Best absrptin refrigeratin system perfrmance was btained with a HF temperature t the generatr f 195 C Based n the perfrmance characteristics established in the labratry the maximum refrigeratin capacity f an 8 kwe micrturbine based trigeneratin system was fund t be 45 kw he verall efficiency f such a system was determined t be 75% System imprvements can be achieved by using a higher efficiency CHP system and ptimising the heat transfer circuit t reduce the pump pwer cnsumptin ACKNOWLEDGEMEN he authrs acknwledge the financial supprt received frm the Fd echnlgy Unit f DEFRA fr this prject and the cntributin f the industrial cllabratrs: Bnd Retail Services Ltd, Apex Air Cnditining, Bwman Pwer and Dug Marritt Assciates Ltd NOMENCLAURE Symbl Descriptin Symbl Descriptin CFD Cmputatinal fluid dynamics Q c Cling capacity (kw CHP Cmbined heat and pwer Q g Heat recvered in generatr (kw COP Cefficient f perfrmance Q h Heating capacity (kw COPs COP system with HF pump pwer i, emperature f HF in and ut ( C cnsidered V Fuel flwrate (m 3 /hr Cp b Specific heat f brine (kj/kgk bi, b emperature f brine in and ut ( C Cp Specific heat f HF (kj/kgk W e Electrical pwer generatin (kw CRP Cmbined refrigeratin and pwer W f Energy cnsumptin rate f fuel (kw CV Calric value f fuel (MJ/m 3 W pump Pump pwer (kw HX Heat exchanger η e Electrical efficiency (% HF Heat transfer fluid η RI Overall efficiency f the trigeneratin m b, m Mass flwrate f brine and HF (kg/s plant (% REFERENCES 1 Alalzadeh-Azar A A, Slayzak S J and Ryan J P, Evaluatin f Cling, Heating and Pwer (CHP fr Office Buildings, ASHRAE ransactins, Sympsia, 22, pp Artecni A, Brandni C, and Plnara F, Distributed generatin and trigeneratin: Energy saving pprtunities in Italian supermarket sectr, Applied hermal Engineering 29, 29, DI, Meeting the Energy Challenge, A White Paper n Energy, 343 pgs 27, 4 Flrides G A, Kalgiru S A, assu S A and Wrbel L C, Mdelling and simulatin f an absrptin slar cling system fr Cyprus, Slar Energy, 22, 72, 1, Rbur, Gas fired absrptin chiller fr cling medium-large area: installatin, use and maintenance manual, 7th ed, 27, 6 Rssa J A, Matelli J A and Bazz E, An experimental investigatin f an ammnia-water absrptin system assciated t a micr-turbine, In: Prceedings f the Internatinal Cnference n ECOS, 27, Padva, Italy 7 Sugiartha N, Chaer I, assu S A and Marritt D, Assessment f a micr-gas turbine based trigeneratin system in a supermarket, In: Prceedings f the Internatinal Cnference n FEC, 26, Jakarta, Indnesia, ISSN assu S A, Chaer I, Sugiartha N, Ge Y and Marritt D, Applicatin f tri-generatin systems t the fd retail industry, Energy Cnversin and Management 48, 27, assu S A, Chaer I, Sugiartha N, Marritt D and Suamir IN, rigeneratin a slutin t efficient use f energy in the fd industry, In: Prceedings f the Institute f Refrigeratin, sessin 27-28, Prc Inst R /1-16