JAERI-Conf DESIGN OF A STEAM REFORMING SYSTEM TO BE CONNECTED TO THE HTTR

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1 JARI-Cnf DSIGN F A STAM RFRMING SYSTM T B NNCTD T TH HTTR K. Hada, T. Nishihara, T. Shibata and S. Shizawa Japan Atmi nergy Researh Institute Japan ABSTRACT Tp pririty bjetive fr develping the first heat utilizatin system t be nneted t the HTTR is t demnstrate tehnial feasibility f a nulear press heat utilizatin system fr prdutin f hydrgen fr the first time in the wrld. Majr issues t be reslved fr upling the heat utilizatin system t the HTTR are l)t develp safety philsphy fr reasnably and reliably ensuring safety f the nulear reatr, 2)t develp ntrl design nept fr the ttal system f the nulear reatr and heat utilizatin system beause thermal dynamis f endthermi hemial reatr t be heated by nulear heat is muh different frm the nulear reatr, 3)t develp helium-heated mpnents and 4)t develp enhaned hydrgen prdutin tehnligies fr ahieving mpetitiveness t a fssil-fired plant. A steam refrming hydrgen prdutin system was studied as ne f the first pririty andidates fr an HTTR-heat utilizatin system due t matured tehnlgy in fssil-fired plants and sine tehnial slutins demnstrated by the upling f the steam refrming system t the HTTR will ntribute t all ther hydrgen prdutin systems. Basi design philsphy fr the HTTR-steam refrming system is that the steam refrming plant dwnstream f an intermediate sendary helium lp is designed at the same safety level as fssil-fired plants and therefre the sendary helium lp was seleted as a safety barrier t the HTTR nulear reatr. JARI has been nduting several studies t develp a framewrk f the HTTR-steam refrming system. Key design ahievements were as fllws. 1) Hydrgen prdutin perfrmane was imprved t ahieve the mpetitiveness t the fssil-fired by applying new nepts f steam refrmer and ptimizing heat and material balane nditins f the system. 2) A natural nvetin type f steam generatr was allated dwnstream the steam refrmer in the sendary helium lp t ahieve suffiient system ntrllability with amdating the large differene in thermal dynamis as mentined abve, and t frm the safety barrier by the sendary helium lp. 3) Basi safety design riteria fr fire and explsin riginated at the steam refrming plant were develped

2 JARI-Cnf Intrdutin Cnsumptin f a huge amunt f fssil fuels resulted frm human ativities sine the industrial revlutin, in additin t defrestatin, auses an enhaned glbal warming. In rder t relax the glbal warming issue and t sustain ur future develpment, new energy resure/arrier r energy tehnlgy t meet the fllwing requirements may be needed t develp as early as pssible; 1) freedm frm resure nstraint, espeially stable and unlimited supply f resure, 2) envirnmentally friendly energy use, 3) high effiieny energy use, and 4) nentrated energy use fr industries. Suh an energy tehnlgy inludes t refrm fssil fuels t new energy arrier. Hydrgen is ne f key energy arriers t meet the abve requirements. The Ministry f Internatinal Trade and Industry has started the New Sunshine Prgram(R&D Prgram n nergy and nvirnmental Tehnlgies) in April 1993, with fusing n develpment f hydrgen prdutin and utilizatin tehnlgy[1], A High Temperature Gas-led Reatr(HTGR) supplies a high temperature nulear heat enabling us t attain a high effiieny heat utilizatin withut any emissin f 2 gas. Therefre, hydrgen prdutin by the use f nulear heat generated frm an HTGR as a heat sure has the high pssibility t meet the abve requirements. JARI has been studying a pssibility f develping nulear-heated hydrgen prdutin tehnlgies and f demnstrating tehnial feasibility f nulear-heated hydrgen prdutin at an engineering testing HTGR, alled HTTR(High Temperature engineering Test Reatr) sine 199. A steam-methane refrming system is under study as a hydrgen prdutin system t be nneted t the HTTR due t its advantages as desribed belw: 1) It is highly pssible t uple it t the HTTR in the early 2's beause a fssil-fired steam refrming f natural gas r naphta is an enmial and mature tehnlgy fr prdutin f hydrgen. 2) Tehnial slutins demnstrated by upling the steam refrming system t the HTTR will ntribute t ther nulear-heated hydrgen prdutin systems. 3) The nulear-heated steam refrming is a pratiable means fr prduing hydrgen by pre- mbustin remval f 2 frm hydrarbn resures suh as natural gas and al and has great ptential as a means t failitate the transitin frm fssil fuels t future hydrgen energy systems[2j. At a preliminary design nduted frm fisal 199 thrugh 1995, JARI has develped a framewrk f the HTTR-steam refrming system. Key design ahievements were as fllws. 1) By applying a new nept f steam refrmer heated by helium gas frm nulear reatr(preisely, frm IHX) and by ptimizing arrangement f helium-heated mpnents and related heat and material balane nditins f (he system, hydrgen prdutin perfrmane was imprved t ahieve the mpetitiveness t the fssil-fired. 2) A natural nvetin type f steam generatr was allated dwnstream the steam refrmer in the sendary helium lp t ahieve suffiient system ntrllability with amdating a large differnee in thermal dynamis between nulear reatr and steam refrmer, and t frm a safety barrier at the sendary helium lp. -23-

JARI-Cnf 96-1 3) Basi safety design riteria fr fire and axplsin riginated at the steam refrming plant were develped.

3 JARI-Cnf ) Basi safety design riteria fr fire and axplsin riginated at the steam refrming plant were develped. In the next fisal year, JARI is planning t start a neptual design in nsignment f the Siene and Tehnlgy Ageny, aiming at a start f test fr develping nulearheated hydrgen prdutin tehnlgies by the steam refrming press at the HTTR in fisal 22. In the fllwing, key tehnlgies t be develped fr upling an HTGR and hydrgen prdutin system are disussed first, and then design philsphy and nept f the HTTR-steam refrming system fr prviding the apability t develp these tehnlgies are prpsed. Finally, ahievements f design studies s far are presented. 2. Design philsphy and basi nept f HTTR-steam refrming system The first HTGR in Japan, namely HTTR, is under nstrutin at the arai Researh stablishment f JARI. Key tehnlgies fr assuring reasnable reliability and safety f an HTGR at malfuntin r aident f the HTGR itself have been develped thrugh a design and nstrutin f the HTTR. Fr upling a press heat utilizatin system fr prdutin f hydrgen t an HTGR, the fllwing key tehnlgies remain t be develped. 1) nhaned hydrgen prdutin t ahieve its mpetitiveness t an enmial fssil - fired hydrgen prdutin plant. 2) Helium-heated mpnents, espeially helium-heated endthermi hemial reatr: A ht helium gas whih prvides the nulear generated heat t an endthermi reatr is pressurized t l the nulear reatr re. A heat exhanger type f hemial reatr is suitable t ntain the pressurized helium. 3) Cntrl f the ttal system nneting an HTGR t a press heat utilizatin system with an endthermi hemial reatr whih has a quite different thermal dynamis frm an HTGR reatr: In an HTGR re, a nulear generated heat is transfrmed t a sensible heat f helium gas, the reatr lant, resulting in a prprtinal relatinship f reatr pwer and helium temperature. n the ther hand, in an endthermi hemial reatr where an endthermi reatin urs fr prdutin f hydrgen, a heat input enugh t ause the reatin dramatially inreases with inreasing reatin temperature due t the Arrenhius type temperature dependene f reatin rate. A new ntrl tehnlgy needs t be develped t balane suh a quite differene in thermal dynamis between the nulear reatr and the hemial reatr. 4) Safety measures fr ensuring reasnable reliability and safety f HTGR against malfuntin r failure f a hydrgen prdutin system: A higher prbability f malfiintin r failure f a hydrgen prdutin system than a pwer generatin system is expeted t result frm a severe envirnment f hemial reatrs fr prdutin f hydrgen. A safety measures needs t prevent frequent reatr srams triggered by suh a malfuntin r failure fr ensuring a reasnable reliability and safety f an HTGR. 5) Safety measures against a fire/explsin aused by a mbustible/explsive gas in strage at a hydrgen prdutin system beause f integratin arrangement f an HTGR and hydrgen prdutin system: Tw different ptential rigins f fire/explsin shuld be taken int aunt. ne rigin is the hydrgen prdutin system utside the nulear reatr building and the ther is the inside f the reatr building if it is pssible t frm a rute f explsive gas ingress frm hemial reatr with the explsive gas feed t the inside f the reatr -231-

4 JARI-Cnf 96-1 building. 6) Safety measures fr transprtatin f fissin prduts released frm the reatr t the prdut hydrgen at a nrmal peratin and fr preventing unntrlled release f fissin prduts t envirnment at a aident f the steam refrming system. Tritium has a pssibility t be transprted frm the reatr t the prdut hydrgen thrugh a ht tube walls f helium-heated heat exhangers suh as a helium-t-helium intermediate heat exhanger(ihx) and an endthermi hemial reatr in servie at a high temperature. Tritium nentratin f the prdut hydrgen shuld be limited as lw as reasnably ahievable. The tp -pririty bjetive fr upling a steam refrming hydrgen prdutin system t the HTTR is t develp these tehnlgies and then t demnstrate tehnial feasibility f a nulear press heat utilizatin system fr prdutin f hydrgen fr the first time in the wrld. Taking int nsideratin the imprtane f the bjetive, the authrs have defined the fllwing design philsphy fr establishing a design nept f the HTTR-steam refrming system fr prviding the apability t develp thse key tehnlgies. 1) Tehinial slutins demnstrated by upling the steam refrming system t the HTTR shuld ntribute t all ther hydrgen prdutin systems. 2) The steam refrming system is designed at the same safety level as a fssil-fired plant under a strit requirement f assuring the safety and reliability as a nulear reatr sytem. 3) Simpliity and peratr friendly methdlgies are pursued. Several design studies have been nduted t develp a design nept f the HTTRsteam refrming system fr develping the key tehnlgies f an HTGR-hydrgen prdutin system under the design philsphy. Finally, the authrs prpse the fllwing basi design nept whih inrprates new ideas f passive safety features. 1) An innvative design nept f helium-heated steam refrmer is develped t imprve hydrgen prdutin perfrmane, with ptimizing heat and material balane nditins f the whle steam refrming system. 2) A steam generatr is installed in the helium lp(the sendary helium lp fr the HTTR) fr prviding the stable ntrllability against any disturbane triggered in the steam refrming system. 3) A passive safety barrier as shwn in Table 1, separating the HTTR reatr and the steam refrming system, is adpted t ensure the reatr safety passively against any transient r aident triggered at the steam refrming system. 4) Tritium transprtatin is limited as lw as reasnably ahievable primarily by purifiatin systems f the reatr lant helium and the sendary helium whih flws in the intermediate ling lp(named the sendary helium lp) separating the reatr ling lp and the steam refrming lp. Bth f IHX and a pair f islatin valves in the sendary helium lp prvide a safety barrier fr preventing unntrlled release f fissin prduts at the aident f sendary helium pipe rupture arding t the HTTR safety design guideline. The detail f the design nept fr the items 1) t 3) is presented in the fllwing hapter. 3. Design nept f HTTR-steam refrming system arrangement and key system mpnents The steam refrming system is arranged t nnet t the IHX as shematially illustrated in Fig. 1. A ut-away view f the whle ttal system is shwn in Fig. 2. The HTTR reatr supplies nulear generated heat f 3MW t parallel-laded M heat exhangers in

5 JARI-Cnf 96-1 the reatr ling lp, namely the IHX f 1MW at the rated heat exhanging rate and a pressurized water ler f the remaining 2MW. The thermal energy f 1MW transferal at the IHX t the sendary helium lp is utilized fr prdutin f hydrgen. Heat and material balane nditins at the IHX are given in Table 2 fr the maximum sendary helium temperature f 95 C at the utlet f IHX. Due t a heat lss alng a sendary helium piping frm the IHX t a steam refrmer, the sendary helium temperature is redued t 88 C at the inlet f the refrmer fr the IHX utlet temperature f 95 C. JARI has been nduting several design studies t develp a design nept f the HTTR-steam refrming system under the bundary nditins as defined abve. 3.1 Imprvement f hydrgen prdutin perfrmane In the HTTR-steam refrming system, the sendary helium at the temperature f 88 C and at the high pressure f 4MPa flws int a heat exhanger type f steam refrmer, and supplies the thermal energy enugh t ause a steam refrming reatin t a refrming press gas flwing inside atalyst tubes. With a nventinal type f heat exhanger and fr similar press gas feed nditins t a fssil-fired plant, lwer hydrgen prdutin perfrmane f the HTTR-steam refrming system is predited than a fssil-fired system. A mparisn f peratinal nditins between HTTR- and fssil-fired refrming system is shwn in Table 3. Sine a hydrgen prdutin rate is expressed as the prdut f a refrming press gas feed rate and a refrming rate, the fllwing imprvements are fund t prvide higher hydrgen prdutin perfrmane. 1) Inreasing heat input t the refrming press gas whih flws in atalyst tubes 2) Inreasing a reatin temperature, that is a press gas temperature at the utlet f atalyst zne in the atalyst tube 3) ptimizing refrming gas mpsitin s as t enhane the refrming rate Redutin in press gas pressure is ne f effetive imprvements, but depends n the helium pressure. Survey f imprved types f heat exhangers and an analytial study n enhanement f hydrgen prdutin rate lead t the prpsal shwn in Fig. 3. The prpsed type f helium-heated refrmer as shwn in Fig. 4 and its ptimized perating nditins has the pssibility t attain a mpetitive hydrgen prdutin perfrmane( by mparing a thermal energy utilizatin, 78% is mpetitive t 8-85% fr a fssil-fired plant). These imprvements are appliable nt nly t HTGR-steam refrming system but als t ther HTGR-hydrgen prdutin systems beause a heat exhanger type f endthermi hemial reatr is an essential tehnlgy fr prdutin f hydrgen by utilizing the nulear heat. 3.2 Steam generatr in the sendary helium lp fr stable ntrllability and as a safety barrier The authrs have fund that installatin f a steam generatr(sg) at the dwnstream f the steam refrmer in the sendary lp prvides the stable ntrllability fr any disturbane at the steam refrmer due t a larde apaity f heat sink. Fr example, fr suh a thermal transient that a helium temperature at the steam refrmer utlet and then at the SG inlet ges up by a disturbane in the refrming press gas feed line, a helium temperature at the SG utlet an remain nstant at the saturatin temperature f steam. A transient analysis result is shwn in Fig. 5 fr a stepwise derease in press gas flw rate by 2%. System arrangement is shwn in Fig. 6. This is phenminlgially explained that an inreased heat input t SG due t inreasing SG inlet helium temperature is pssible t result in nly an inreased steam quality at the saturatin temperature due t biling, but nt

6 JARl-Cnf 96-1 in an inreased steam temperature. Suh an advantage fsg is utilized t prevent a reatr sram due t a malfuntin r aident at the steam refrming system and therefre the sendary helium lp with SG an be funtined as a safety barrier as mentined abve. Fr preventing a reatr sram due t a lss f water feed t SG by a lss-f-n-site~pwer aident at the refrming system and by a malfuntin f feed water flw rate ntrl system fr example, a natural nvetin type f SG with a suffiient apaity f water hldup and with a passive SG ling system is seleted as the safety barrier SG and is nw under design t speify 1 a reasnable safety requirements and reasnable nfiguratin. A mparisn f system arrangement amng andidate nulear-heated hydrgen prdutin presses has revealed that the tehnial slutin t ahieve stable ntrllability and t meet the safety requirement t the steam refrming system f designing it at the same safety level f a fssil-fired plant ntributes t ther hydrgen prdutin systems. Ardingly, the arrangement f the HTTR-steam refrming system is speified as shwn in Fig Safety barrier agaist fire I explsin Safety barrier (funtinal r physial) is required t assure the safety f nulear system and publi. In the HTTR-steam refrming system has a ptential pssibility f tw types f rigins f fire/explsin, namely utside f the nulear reatr building(rib) and inside f the R/B. The safety design nept is shematially illustrated in Fig. 7. Against the fire/explsin utside the RIB, it is reasnable t assure safety integrity f safety-related items as the nulear system against a ptential fire/explsin beause a lw pssibility f fire/'explsin shuld be assumed. Hwever, against fire/explsin inside the R/B, it is the priniple t take a safety measures t prevent urrene f fire/explsin. In detail, the sendary helium piping system is designed t prevent the frmatin f rute f explsive gas ingress frm the steam refrmer int the RIB. Fr the HTTR-steam refrming system, a pssibility f pipe rupture f the sendary helium lp des nt seem t mpletely exlude and therefre, the basi design nept is t limit ingress amunt f explsive gas within an allwable limit t prevent any hazard t safety-related items suh as the reatr ntainment vessel. A mbinatin f the CIV islatin valves and emergengy shut-ff valve in the press gas feed line is effetive t restrit the amunt f ingress gas. 4. Cnluding remarks Based n the defined design philsphy, the authrs have nduted design studies t develp a design nept f the HTTR-steam refrming system. The framewrk f the system arrangement and the helium-heated steam refrmer nept have been speified fr ahieving a mpetitive hydrgen prdutin perfrmane t a fssil-fired plant and fr ensuring a stable ntrllability and safety barrier. A heat transfer enhanement, an inreased heat input t the press gas and thers ntribute t a mpetitive hydrgen prdutin perfrmane, in detail, the thermal energy utilizatin f arund S%. A steam generatr is designed t install at the dwnstream f the steam refrmer in the sendary helium lp, prviding the stable ntrllability and the safety barrier against malfuntins r aidents in the press gas and feed water lines. A safety design nept is develped fr explsin/fire due t explsive gas, taking

7 JARl-Cnf 96-1 int aunt differene f safety requirements depending upn the rigins f fire/explsin. These tehnial slutins will ntribute t ther hydrgen prdutin systems. In nsignment f the Siene and Tehnlgy Ageny, JARIis plannning t establish the design nept f the HTTR-steam refrming system and the related R&Ds, aiming at a start f test peratin f the steam refrming system in fisal 22. Referenes [1] C. Watanabe, "MITI's new mprehensive apprah t energy and envirnmental tehnlgies: the New Sunshine Prgram", presented at the 7th Japanese-Frenh xpert Meeting n nergy and nvirnmental Tehnlgies, May 31-June 1, 1993, Tky, Japan. [2] Y.Mri et al, "Pre-mbutin remval f arbn dixide frm natural gas pwer plants and the transitin t hydrgen energy systems", J. f nergy Resures Tehnlgy, vl.!14(sept. 1992), p Table 1 Passive safety barrier fr ensuring the reatr safety against transient/aident triggered at the steam refrming system Transient/ aident Safety barrier Thermal-hydrauli transients triggered at the steam refrming system Physial barrier f the sendary helium lp installing a natural nvetin type f steam generatr fr preventing a reatr sram Fire and explsin aident riginated utside the HTTR reatr building Within the reatr building Funtinal barrier f safe distane fr preventing damage at the reatr building and mpnents imprtant t safety Physial barrier f the sendary helium lp and emergeny shut-ff valves (r islatin valve) fr preventing urrene f explsin r fr preventing damage at mpnets imprtant t safety -235-

8 JARI-Cnf 96-1 abl X X x: 4 > w IZZ ' a rr4 X X x: 4 * " :er Heat and materiai bale and key de;sign pairam S 4-' t ted heat exhangin DC imary heliurr CL P P in en 4 * JX> 4 ' Z3 3 inl Temperature at thi. 4 > _ C -4-* Pressure al x: CVJ 4 ' Mass flw r ussndary hellium desig"5 (fr the maximum allwable t.ture the utlet Cu a u en P in ) P in T e inl e at thi Temperatur _ the inle w CL sz.71 en flw r w t 11 ent ai ndtul tubelneat Cunte r-ur heliall y wu f shell -and- 1ger. H 1 K ) W X) 4-' I W CTJ 4 ' "t nditin f he 't P L m ) m iperaturi h B l 'w 29MPa n pressure 'w X X x: 3 thr ressure drp um fl 't in ) «a) a 15 SI t u 2 5 a _ '$< l t t CL ri ry heliium CL t CL.21 in helium idary Table 3 Cmparisn f peratinal nditins and perfrmane f steam refrmers Refrmer type Fssil-fired Helium-heated withut imprvements Imprved helium-heated Press gas pressure 1~3MPa depending upn final prduts >Helium pressure P Me f 4.MPa Balaned presure (^ Ri ) B^4.5MPaatthe inlet f steam refrmer Maximum press gas temperature 85~9 C ^75 C 8 C Maximum heat flux t atalyst zne 5-8 kw/rrf 1~2kW/m' 4kW/m Thermal energy utilizatin f steam refrmer 8-85% (~5%)* 78% 2 emissin frm heat sure fr heat sure pwer 3t- 2 /h/ (*) Based n JARTs design data /1MW -236-

9 JAISRI-Cnf 96-1 Cling twer Auxiliary water/air ler Reatr ntainment vessel Pressurized water/air ler Heat utilizatin plant : Sendary helium piping system Sendary helium 95"C,4.IMPa 1 IHX : Helium/helium intermediale heat exhanger PPWC". Primary pressurized water ler ACS : Auxiliary ling subsystem VCS : Vessel ling subsystem Fig. 1 Simplified diagram f the HTTR plant with a heat utilizatin system. Reatr building Steam refrming system AuxiIlary water/air ler Pressurized water/air ler Steam refrmer Strage tanks Caxial duble-walled piping system nneting a heat utiiizatin plant \ Intermediate heat exhanger (IHX) Reatr pressure vessel (RPV) Reatr ntainment vessel (C/V) Fig.2 Cutaway drawing f the HTTR-steam refrming system

10 JARI-Cnf 96-1 mal energy atin f 78% pat seamie yst tubes t» [ Th ydr man nts f i perf 2 <n w uti -C 1 s nput ^_ x: C ' b ming " ati tili 3 >. UJ u ibes redr _j t >, r " " "S. ) f*^ 3 " ) C _ 3 3. liu - "3 L_ 1 rr 6MW 2MW 1 vi.5 "5 *-> it 1- "-, t f L. it D> C C iza. C sit D. _ 3. d 11 /> «? g-a fl 3 HI g).> ~ III V) LJJ ^ I a. a a) ) T3 I. J8 X) t t 3 p. w "(D 4 > a. LL UJ6-238-

11 JARI-Cnf ' T 1 let 1 h- ) _ w 'g[ ZJ 4 ' C C n 1 1 <D 5) D helii fl CL ajn}bj9dlu9i Lumjau, Ajepuas pue 5 -i- w CT3 W 2 is 5 2 g r u 4^ Iff I ff +- *= C r in r.s>"s -5' w D. XJ S r n_ d w m > * ( _ <5^ r T^ *- ** t *\ ZJ "'^ f~> Z5CP a +-> t CC x r r i_ +-> t 13 la i

12 JARI-Cnf 96-1 Steam refrming hydrgen prdutin system HTTR (3MW) H,,}j J Super heater (SH) >f - (1.2MW) Pressurized water ler (2MW) Steam refrmer (SR) (3. 6MW) Steam generatr (SG) (3. 3MW) Sendary helium Feed water Fig.6 Flw sheme f the HTTR-steam refrming hydrgen prdutin system. Safe Distane Sendary He Piping mergeny shut ff valve C/V R/B I/V IHX SR SG Cntinment Vessel Reatr Building Islatin Valve Intermediate Heat xhanger Steam Stem Refrmer Generatr Fig.7 Safety design nept against fire and explsin. H 2I,- -24-

Heat Transfer and Friction Characteristics of Heat Exchanger Under Lignite Fly-Ash

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