DESIGN CONSIDERATIONS FOR DRY SCRUBBERS
Z . ,
Roy F Weston nc Bulngton Msscusetts
mnds s we evew dy scubbe desgns te utos' concens e lso ocused on second moe lkely scenio one n wc good opetons e dvesely mpcted to ceve te equed emovl ecences Bsed on cetn desgn evews two es ve been dented n wc opeton could potentlly be d vesely ected te egent eed system nd te down stem ptculte emovl system n ptcul bc ltes Snce bc ltes e moe susceptble to dy scub be opetonl upsets tn electosttc pecpttos bc ltes e o gete conce e susceptbty o bc tes to dy scubbe opeton upsets s becuse te lme egent used n te scubbe s y goscopc nd tends to become cement-lke most o wet Sould ts occu ete becuse o ncomplete dyng o te sluy wte n te scubbe (cused by nsucent lowble tempetue deentl toug te scubbe o by mpope scubbe desgn) o be cuse o ue gs tempetue t te bic te (opetng ne te dew pont) wc s lowe tn desgn ull o ptl blndng o te bc wtn te bc lte woud lkely esult [1] ectosttc pecpttos e not s ected by most o wet lme egent becuse te gs ow toug ts devce does not pss toug sml dmete poes (wc could become clogged) Howeve electosttc pecpttos coud ce educed ecency te most o wet egent "sets-up on collecto ptes nd could
s ppe pesents comments nd ecommend tons egdng conceptul desgn specctons o dy scubbes (lso known s wet/dy scubbes) o use on wste-to-enegy cltes ese ecommendtons would be used to develop mnmum cceptble desgn pmetes o equests o poposls o ul-sevce o tunkey wstetoenegy contctos e eson o pesentng tese comments nd ecommendtons s tt te utos peceve genel oveestmton wtn te wste-to-enegy ndusty s to te extent o pplcble pplc ble expeence wt te dy scubbe tecnology on wsteto-enegy cltes ese ecommendtons oweve e moe consevtve tn wt cetn ull sevce nd tukey contctos e wlng to gu ntee Upon exmnton te dy scubbe tecnology expeencebse s ctully qute lmted (s o te tme t me o wtng o ts ppe n Septembe 1987 nd te tme o espondng to evewes comments n Febuy 1988). Bsed on ts lmted expeence te utos e euctnt to consde o ecommend dy scubbe desgns tt devte sgncntly om ts expeence becuse o concen tt unsuccessul opeton wll esult Unsuccessul opeton o dy scubbe cn be dened n sevel wys Foemost s te stuton n wc te equed emov ecences e not ceved teeby potentlly esultng n clty sut down educton n tougput o equpment eplce ment Altoug ts sceno s uppemost n ou 13
cilities (no temperature measurements or other data, except for outlet HCl concentrations, have been taken for this system For these reasons, the Framingham facility is not appropriate for developing or transposing design parameters to future US systems The Marion County facility has been in operation for approximately one year Although there have been no data obtained from this facility by independent parties, the authors have been in communication with the owner/ operator and the dry scrubber equipment supplier regarding its perrmance and have incorpo rated this experience (conservatively, since the facility does not meet two of the previously-listed criteria i the development of conceptual design specications The Commerce facility does have independent party data available for its operations; however, since this facility has started up recently (approximately 3 months prior to this writing, we cannot lean too heav ily on those data for future systems Facility data that, in the authors opinion, are suit able for interpretation and for use in the design of future systems is presented in Table 1 These data best meet the criteria established (2 years in operations, independent party taking data, full scale facility, suc cessful operations, and technology equivalent to US systems, although, as described earlier, only the Mun ich facility fully satises these criteria The following observations can be made about the individual facilities presented: a The City of Commerce, Califoia facility was tested by an independent test company The facilitys test results show greater than 90% and 70% removal of HCl and S, respectively The outlet emission re sults are below 50 PPMDV at 12% CO for HCl and S City of Commerce was tested in une 1987 for compliance with the permit The inlet temperature to the scrubber is 460°F 2] b The Marion County, Oregon twotrain facility was tested by a now independent test company No inlet scrubber data were reported for HCl or S; therefore, the removal eciencies are not known The outlet emission results are below 50 ppmdv at 12% CO for HC and S The stack analysis obtained for HC demonstrated emissions at 39 and 20 ppmdv at 12% CO for boiler nos 1 and 2, respectively However, one stack analysis for S on boiler no 2 demonstrated emission at 75 ppmdv at 12 CO (Three stack analyses were obtained and averaged for S on boiler no 2 and demonstrated emission at approximately 45 ppmdv at 1% CO The inlet temperature for boiler no 2 scrubber is 383°F Marion County was tested in Oc tober 1986 for compliance with the permit [3
not be removed by rapping The remedy, if this were to occur, for an electrostatic precipitator is less costly and less time consuming than for a fabric lter because it involves surface scraping of plates, rather than whole-bag replacement W--Y X
The authors recommend that certain criteria be ad hered to regarding eerience-bases which are utilized for future designs Ideally, experience or data should be taken from a facility 2 years old or greater, to observe a variety of operating conditions; the facility should full-scale and not pilot scale; the facility's operating conditions should generally match those of the facility being designed; the data from the facility should be obtained by independent parties rather than by the facility operator; and the facility should have experienced successful operations n the event that these criteria are not fully satised, caution and con servatism should be used by persons attempting to utilize this eerience For dry scrubbers on waste-to-energy facilities, there is to the author's knowledge (at the time of this writing only one facility world-wide that meets all of the above criteria; that beng the Munich, Germany facility Other European facilities with acid gas control have wet scrubbers, dry/ dry scrubbers, retrot devices that do not qualify as wholly designed systems, or dry scrubbers that do not meet the time or the independent party criteria stated above There are several facilities, on the order of four to six, in Japan that have operated with dry scrubbers for more than 2 years; however, their experience is not relevant or transferable to US systems because the inlet temperatures to the scrubbers (a critical design parameter which is described in more etail later in this paper are typically in excess of 600°F whereas the trend in the United States is to lower this value to below 4°F n the authors opinion, this dierence in temperatures is sucient to exclude data from those facilities for S design purposes Furthermore, data taken by an independent party is available for only one of those facilities The US eerience is with facilities in: Fra mingham, Massachusetts; Marion County, Oregon; and Commerce, California Framingham has been in operation for several years; however, it does not have a designed dry scrubber and has, instead, lime slurry injection in an existing refractory-lined chamber down stream of a temperature quench water spray in the same chamber Moreover, the temperature at the point of injection is likely to be similar to the apanese fa114
TABLE 1 IDENTIFICATION O APPROPRIATE SCRUBBER DATA FOR USE IN SCRUBBER CONCEPTUA DESIGNS
Fii
Ine Te o O
let e f Pariate D O
l e tiC ( I r
ifia 8)
J
b
/ (c)
Mi : T 2
3 0/45
i, G 8)
50
35 b
65/2
Cl, Hi
-
� 95 d d 64
t h yt e b la a
i:
: : : : FF: E:
R Effici
i
-DS O-FF 2 Lis: ' OFF
E 01FF
F
Ms 'N D Inji S Fc Fi. Eic ipi
\! b Ine o i c r o 3 r n d
c The Mnih West Germany faiity was tested
state of experiene for dry srbbers on wastetoen ergy failities. It is bease there are so few failities shown that we take sh a onservative position in onept design speiations for new failities t shold be noted that several failities are presenty in the statp or testing mode These failities are Bristol onnetit; Hartford onnetit; St. roix Virgin sands; Milbry Massahsetts; London On tario; Jakson ity Missori; Dthess onty New York; and Orrington Maine We antiipate that the state of eeriene on an indstywide basis will ex pand signiantly as these failities ome on-ine and go into ongterm operations
by an independent test ompany The faility's test reslts show greater than 90% and 70% removal of H and S respetivey The otlet emission reslts are below 50 ppmdv at 12% O for H and S. Mnih was tested in Jly 98 5 months after initial operation [] There are several failities not shown in the tabe for whih independent data were taken from the srb bing systems. (The athors are awaiting reeipt of the reslts from the Biddeford Maine faility emission testing; however the reslts are not available in time for inlsion in this report) These inde several Japanese failities; Zrih Switerand; Hogdaen Sweden; and Wrbrg Germany. As stated earier the Japanese data are not inded bease of its atyp ially (to the .S.) high srbber inlet temperatres Zrih Hogdalen and Wrbrg data are not inded bease ertain key measrements (sh as gas ows O H or O onentrations) neessary for the onversion of the data to omparable nits and vaes were not reported or were not measred. The reader may be srprised at how few failities are identied in Table . However those are the fa ilities whih in the athors' opinion represent the
M
There are severa areas of oneptal design that are typially speied or reviewed. etain of the ritial ones inde residene time slrry/ gas interfae and temperatre dierential throgh the srbber Residene time aets the apabiity of the eqip ment to ahieve a dry prodt to maintain dry wals to maintain adeqate gas veloities throgh the nit 5
mately F (assumng 20°F tempeatue loss n the downsteam ductng and patculate emoval devces. Wth ths tempeatue deental (and wth othe good desgn paametes one can be easonably codent based on the dy scrubbe expeence on wastetoen egy facltes shown n Table 1 that emoval ecen ces wll be acheved that the lme sluy concentaton wll be ow enough to elably acheve pope gas/ sluy nteface wthout hgh mantenance costs that a downsteam fabic lte would not be partally o totaly blnded by wet o hygoscopc eacton poduct theeby causng hgh pessue dop hgh cost opea ton o facty shutdown and lte eplacement and that a downsteam fabic lte o electostatc pecp tato ntenal metal hadwae would not be deteo ated by cooson fom wet o hygoscopc eacton poduct The authos poston has been critczed n seveal ways: fullservce and tukey contactos have stated that we shoud ely on the guaantees to perfom that we should ely on equpment supple guaantees to pefom that we ae standng n the way of nno vaton and that the equed emoval ecences can be acheved n any event wth nceased lme sluy concentatons. u esponse s that thee ae nsucent ndusty data to justfy any devaton fom cuent successful desgns that f the contacto wshes to nnovate t should allow fo such nnovaton by nstallng had wae that coud povde vaiable deenta tempe atues (ncludng up to at least the ecommended 30F and that the contactos o the equpment suppes guaantees ae typcally measued by testng ove a mted tme period dung whch tme t could absob opeatonal poblems to pass the test. n geneal ths ssue s esolved by ncudng equp ment exblty to opeate at a tempeatue deental of at least 130F. Ths can be acheved by a ue gas bypass aound the economze by a wate sde bypass (wth appoprate tube danage aound an econo mze secton o by a steam col heate po to the dy scubbe. n all events howeve engneeing ana yss enegy pojectons and feasblty opnons should be pefomed fo the 130F tempeatue deental case and not fo lowe cases.
and to alow enough tme fo eacton to occu. Based on avaabe eeience to acheve the tcalyequed emoval ecences and outlet emssons (90% HCl and 70% S emoval and 50 ppmdv coected to 12% fo HCl and S outet emsson the authos specfy 8 sec fo an upow eacto and 18 sec fo a downow eacto. When ssung speccatons such as these contactos and equpment supples ae nvted and encouaged to povde appopiate data to justfy an excepton to the equements To date the authos have not evewed data that woud alte (.e. educe these speced etenton tmes Sluy/ gas nterface elates to the abty of the equpment to mx the eagent wth the ue gas such that chemcal eacton wl occu sucently to meet equed emoval ecences. The mxng must take place unde all easonable load condtons and slury concentatons. Ths s essentaly a state of the at athe than a state of scence theefoe one should look praly to the equpment suppes past suc cessful opeatons n wastetoenegy facltes fo com fot. Deental tempeatue though the dy scubbe s a catchall paamete that coves sevea desgn and opeatonal ssues n patcua t s assocated wth the concentaton of lme n the slurry and the dyness of the mateal as t exts the scubbe and entes the patcuate conto devce Speccatons n egad to ths paamete ceate the most contovesy n scubbe desgn evews. The eason fo ths contovesy s that cetan fulsevce and tukey contactos to obtan the hghest themal ecences possble attempt to lowe the desgn tempeatue deental though the scubbe to have moe heat extacted by the econo mze and theeby appled to steam geneaton. n the othe hand the authos beleve based on the data pesented n Tabe that thee exst no data that would justfy a lowe tempeatue deental than that ec ommended below Futhermoe the authos beeve that to easonaby acheve equed emoval ecences wth owe tempeatue deentals the opeaton of the sluy feed system and the downsteam patcuate contol devce would be jeopadzed. Speccaly wth an assumed stack tempeatue of 250°F a mnmum dy scubbe tempeatue de ental of appoxmately 30F should be equed wth a scubbefabric lte system. A scubbeelecto statc pecptato system would eque an even geate tempeatue deental because the eectostatc pe cptato does not povde secondary acd gas emoval as does a fabic lteby means of the dy excess eagent coveng the lte bags. n othe wods a scubbe eques an nlet tempeatue of appox
H
the dy scubbe desgn ssues that ae ethe ec ommended o speced to ncease elabty and op eablty ae as follows aJ f a fabc lte s n place, space and hadwae 116
should be insalled olowing he dry scrubber or dry inecion o hydraed lime; his may allow reducing he emperaure dierenial across he scrubber or herma eciency i may alow coninued operaions when he scrubber is ou o service and i may provide addiiona lime inecion capaciy in he even ha regulaions become more sringen (his use however would no apply o an elecrosaic precipiaor since his device exhibis ile acid gas remova because i eoses ony a small porion o he gas sream o he coeced lime). b ual 1% slakers or redundancy. c Space or prereamen o waer in he even ha he waer is high in carbonae (which causes scae) or oher impuriies ha woud aec operaions. d One or wo 4-hr (nominal acid gas oadings) surry anks. (e) One slurry pump per combusion rain and one sandby pump (or common sandby pump).
Redundan slurry lines per combusion rain. g ry scrubber vesse and slurry handling sysem sied or 12% o maximum acid gas oadings (o cover peak condiions and o provide a buer in he even ha he acid gas concenraion increases in he uure).
[I) Theodore, Louis and Buonicore Anthony J. Ai Pollution
Contl Equipmnt. New Jersey: Penice Ha nc
[2) Enegy Systems Associates. "Air Emissions Tests a Com merce Refuse-to-Energy Faciy May 26June 5 1987 Pepared for County Saniaion Disrcts of os Angeles. [3 Ogden Pojecs nc. "Environmena es Repor. Pre pared or Ogden Martn Sysems of Maron, nc (es dates Sep ember 22 1986 to October 8 986. 4"Air Emission ess a the Munich Nor ReuseFired Power Pan Cper Engneers and Beco Poluton Contro Cop APCA paper June 62 1985
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