High temperature hydrogen sulfide adsorption on activated carbon I. Effects of gas composition and metal addition

Transcription

1 PERGAMON Crbon 38 (000) High temperture hydrogen sulfide dsorption on ctivted crbon I. Effects of gs composition nd metl ddition M.P. Cl *, B.W. Strickler, A.A. Lizzio, b c New Mexico Tech, Dept. Env. Engr., 801 Leroy Plce, Socorro, NM 87801, USA b Mlcolm Pirnie, Inc., 104 Corporte Prk Drive, Box 751, White Plins, NY , USA c Illinois Stte Geologicl Survey, 615 E. Pebody Dr., Chmpign, IL 6180, USA Received 30 Mrch 1999; ccepted 30 October 1999 Abstrct Vrious types of ctivted crbon sorbents were evluted for their bility to remove H S from simulted col gs strem t temperture of 5508C. The bility of ctivted crbon to remove H S t elevted temperture ws exmined s function of crbon surfce chemistry (oxidtion, therml desorption, nd metl ddition), nd gs composition. A sorbent prepred by stem ctivtion, HNO oxidtion nd impregnted with Zn, nd tested in gs strem contining 0.5% H S, 3 50% CO nd 49.5% N, hd the gretest H S dsorption cpcity. Addition of H, CO, nd H O to the inlet gs strem reduced H S brekthrough time nd H S dsorption cpcity. A Zn impregnted ctivted crbon, when tested using simulted col gs contining 0.5% HS, 49.5% N, 13% H, 8.5% HO, 1% CO, nd 7.5% CO, hd brekthrough time of 75 min, which ws less thn 5 percent of the length of brekthrough for screening experiments performed with simplified gs mixture of 0.5% H S, 50% CO, nd 49.5% N. Keywords: A. Activted crbon; B. Gsifiction, Surfce tretment; C. Adsorption 000 Elsevier Science Ltd. All rights reserved. 1. Introduction The gs mixture produced is predomintely hydrogen (H ) nd crbon monoxide (CO), both of which hve high While col gsifiction hs been round for mny yers, heting vlue. In ddition to the high heting vlue gses the interest in col gsifiction for commercil power produced during gsifiction, there re numerous other genertion hs just recently been revived. The current gses tht re produced, including crbon dioxide (CO ), interest in col gsifiction predomintely concerns the methne (CH 4), hydrogen sulfide (HS), crbonyl sulfide ppliction of col gsifiction to the Integrted Gsific- (COS), nd wter (HO). Commercil gsifiers re genertion Combined Cycle (IGCC) process. Over the pst 15 lly clssified s one of two types: Oxygen-blown or yers, the col gsifiction combined cycle method of ir-blown. Typicl gs compositions of n O-blown power genertion hs progressed from the reserch lbor- gsifier re (in vol %) 7.7% H, 39.4% CO, 13.1% CO, tory to the threshold of widespred commercil ppliction 18.4% HO, 1.1% HS, nd 0.0% N []. Typicl gs [1]. compositions of n ir-blown gsifier re (in vol %) 14.% Rther thn burning col directly, s in trditionl col-fired power plnt, the gsifiction process begins by 49.8% N [3]. converting col into combustible gs. In the gsifiction process, col rects with stem nd oxygen (O ) or ir. *Corresponding uthor. Tel.: ; fx: E-mil ddress: mcl@nmt.edu (M.P. Cl) / 00/ $ see front mtter 000 Elsevier Science Ltd. All rights reserved. PII: S (00) H, 3.1% CO, 5.8% CO, 6.6% H O, 0.5% H S, nd One dvntge of col gsifiction over other forms of electric power genertion is the lrge supply of col vilble within the United Sttes. Col currently supplies 56% of the electricity in the U.S. nd remining col reserves could power the U.S. for hundreds of more yers [1]. Environmentl benefits of col gsifiction compred

2 1758 M.P. Cl et l. / Crbon 38 (000) to other mens of power genertion re extremely im-.1% pyritic sulfur, 1.1% orgnic sulfur, nd 6.7% high portnt considering the incresing concern with CO s temperture sh. greenhouse gs nd incresingly stringent nitrogen oxides IBC-10 ws ground nd sieved to prticle size of (NO x) nd sulfur dioxide (SO ) regultions. Environmen mesh ( mm) nd then stem cti- tl dvntges of the IGCC process compred to trditionl vted. Activted crbon smples were prepred from the col-fired combustion include very low NOx nd SO size-grded ( mesh) IBC-10 col. Most sorbents emissions nd lower CO emissions. prepred for this study were prepred using stem The IGCC process is n innovtive electric power ctivtion method. The steps of stem or physicl ctivgenertion technology tht combines modern col gsific- tion were preoxidtion, pyrolysis, nd then stem ctivtion with gs turbine nd stem turbine power genertion tion in 5 cm dimeter fluidized-bed rector (FBR) t technologies; hence, the nme combined cycle. Hot fuel Illinois Stte Geologicl Survey (ISGS) fcilities. The gs produced by gsifying col is clened nd then burned FBR is 55 cm long, type 304 stinless steel pipe with in gs turbine to produce electric power. Het recovered porous hstlloy gs distributor plte locted 15 cm from from the gs turbine s exhust produces stem tht turns the bottom of the rector. The FBR ws heted by 7.5 cm the stem turbine to produce more electricity. Require- dimeter, 60 W split-tube furnce controlled by PID ments for col gs clening systems re bsed upon controller. Smple temperture ws monitored with typeerosion nd corrosion protection for turbines nd environ- K thermocouple plced in the middle of the smple bed mentl emission limits. Prticulte mteril must be re- [6]. moved to prevent erosion of the bldes of the gs turbine. During the first step of stem ctivtion, btch of 150 Sulfur products tht must be removed from the col gs g of col ws preoxidized with ir t 58C for h in the include HS, CS, nd COS, but HS is the gretest FBR t totl gs flow rte of 4 l/ min. Initilly, during corrosion concern. preoxidtion, ir ws periodiclly diluted in hlf using N. In the pst, the typicl method for sulfur removl in Reducing the oxygen concentrtion ws necessry to IGCC systems ws cold gs clenup t tempertures of prevent temperture increse due to n exothermic C. Cold gs clenup typiclly uses wet scrubbing rection between oxygen nd col. Preoxidtion ws or cid gs tretment to remove sulfur. If HS cn be performed to minimize col cking nd gglomertion removed while the gs is still hot ( C), then there during pyrolysis. Next, the smple ws pyrolyzed t 458C is gin in overll process therml efficiency ( 3%). for 1 h in 4 l/ min N. Pyrolysis continued for bout 30 Current IGCC plnts operte with n efficiency of bout min while temperture ws incresed to 858C. Once the 43% compred to mximum of 35% for conventionl temperture leveled t 858C, the col ws ctivted using col-fired power plnts. With improved gs turbine tech- stem by replcing the N flow with 50% HO/50% N nology nd high temperture col gs clenup, efficiencies mixture. HO for the stem mixture ws supplied either by exceeding 50% re possible [4]. bubbling N through flsk contining unfiltered H O t Much reserch hs been devoted to developing regener- 88C or by dding HO to heted N strem with ble metl-bsed sorbents to efficiently remove H S from peristltic pump (Cole Plmer model [ ). Stem col gsifiction strems t high temperture, but until ctivtion t 858C continued in the FBR for 4 h. The recently no one hs exmined the use of crbon-bsed smple ws cooled to room temperture (38C) in N. sorbents for the sme purpose. The use of ctivted crbon About 70 g of ctivted crbon ws typiclly produced s hot gs clenup sorbent in n IGCC system is novel reserch re nd it ws the focus of this study. The overll objective of this study ws to evlute the potentil of crbon-bsed sorbents to remove HS from hot col gsifiction gs strems. from the originl 150 g col, for yield of 45%. Surfce res were mesured fter the production of ech btch of ctivted crbon to confirm proper ctivtion... Chemicl ctivtion A smll number of smples were prepred by chemicl ctivtion with zinc chloride (ZnCl ). Typiclly, g. Mterils ZnCl ws dissolved in beker of l H O. About 50gof mesh col ws dded to the beker, for.1. Preprtion of stem ctivted crbon sorbents ZnCl to col mss rtio of The solution ws continuously stirred nd heted t C until ll liquid All smples in this study were prepred from Illinois evported. After physicl mixing nd cooling, the smple No. col. The col ws from stockpile nmed IBC-10, ws oven dried t 108C for pproximtely 16 h. The which is prt of the Illinois Bsin Smple Progrm [5], nd smple ws then plced in tube furnce for pyrolysis- IBC-10 is bituminous col from mine in western ctivtion. Smples were heted in tube furnce (Lin- Illinois. On weight percentge bsis, IBC-10 consists of dberg type 59344) t C for 1 3 h in l/min N. 39.9% voltile mteril, 53.% fixed crbon, 8.6% oxygen, After cooling in N to 308C, the smple ws wshed with

3 M.P. Cl et l. / Crbon 38 (000) deionized HO to remove ny excess chloride nd the ph which were controlled by Tyln mss flow controllers of the rinse solution ws verified to be bout neutrl. (MFC). Gs cylinders used were technicl grde CO, Resulting smple surfce res were checked to determine ultr high purity (UHP) N, nd 1% HS by volume in N. degree of ctivtion. Severl reserchers hve more exten- Clibrtions for the MFCs were performed for ll gses sively studied ZnCl ctivtion nd the reder is referred to used. the literture for more informtion [7 9]. The experimentl pprtus used for HS dsorption experiments consisted of qurtz rector fixed-bed d-.3. Oxidtion of crbon sorbents sorption unit followed by qudrupole mss spectrometer (MS). During typicl brekthrough curve experiment, 5.5 After stem ctivtion, most smples were oxidized with g of ctivted crbon ws loded into the fixed-bed qurtz queous nitric cid (HNO 3) tretment. Typiclly, 35 g of rector, which creted bed length of pproximtely 5.5 stem ctivted smple ws dded to 0.35 l 45% HNO3 by cm. Smples were dried while being heted in N t 108C mss solution nd heted to 908C for.5 h. A reflux for 30 min with the bottom of the rector open to llow 3 column ws used to prevent excessive HNO3 loss. The moisture to escpe. Smples were heted in 00 cm / min reson for oxidizing the stem ctivted crbon smples N until constnt temperture (usully 5508C) ws with HNO3 ws to crete more crbon oxygen (C O) mintined. complexes. In some cses, oxidized smples were ther- Rectnt gses were dded to the qurtz rector using mlly desorbed of C O complexes in N to 958C or compressed gs cylinders, or in the cse of HO, syringe metls were dded to oxidized smples. When highly pump (Cole-Prmer 74900) ws used to inject liquid H O into preheted gs strem. Once the gs strem, con- tining vrying mounts of H, CO, CO, HO, HS, nd N, ws djusted to desired concentrtions, n H S d- oxidized ctivted crbon smple is thermlly desorbed, the number of ctive crbon sites is gretly incresed, which my enhnce H S dsorption. Other reserchers hve more extensively studied oxidtion of col-derived ctivted crbons [10]. sorption experiment ws strted. The MS mesured the concentrtion of HS in the effluent gs exiting the fixedbed rector, nd recorded signl every minute. By.4. Metl ddition to crbon sorbents mesuring the influent nd effluent H S gs concentrtion, the gs flow rte, nd brekthrough time, the mss of H S After HNO3 oxidtion, portion of the stem ctivted removed (dsorbed) cn be clculted from the HS sorbents ws impregnted with selected metls to improve brekthrough curve. Rector temperture ws held constnt HS dsorption performnce. Metl (Zn, or Cu) cette t 5508C for most experiments nd totl gs flow rte ws ws used s the source of metl in ll cses. Metls were 3 00 cm /min. The spce velocity (SV), which is defined dded to the crbon surfce by n queous ion-exchnge s volumetric gs flow rte divided by volume of smple (IE) process. Typiclly for IE, 0.5 g of zinc cette 1 bed, for ll dsorption experiments ws h. [Zn(CH3O ) ] ws dded to 0.5 l deionized HO nd The composition (vol %) of the simulted col gs mixed. About 10 g of oxidized crbon smple were dded strem ws 0.5% HS, 50% N, 13% H, 8.5% HO, 1% nd the mixture ws continuously stirred for 1.5 h t 38C. CO, nd 7.5% CO This mixture corresponds to typicl The smple ws filtered once nd rinsed with deionized col gs generted t n ir blown IGCC plnt. Severl HO, nd then ir dried. dsorption experiments were performed with different permuttions of the gs mixtures to determine the effect of ech gs on the HS dsorption cpcity nd brekthrough 3. Experimentl time. The outlet gs concentrtion ws gin mesured using the MS nd totl sulfur dsorbed on the crbon Mesurement of HS brekthrough curves t bsed sorbents ws mesured fter ech dsorption experimbient pressure ment. HS dsorption experiments were performed t the ISGS using 1. cm inner dimeter qurtz rector with fritted plte. Teflon fittings nd tubing were used t lower tempertures where fittings were required to insure n inert 3.. Mesurement of physicl nd chemicl properties of prepred sorbents experimentl system. Periodiclly, blnk dsorption experi- Single-point BET surfce res for prepred ctivted ments were performed t ctul experimentl conditions crbon smples were mesured using N t 77 K nd using n empty qurtz rector. Outlet concentrtions from Monosorb flow pprtus (Quntchrome Corportion). the empty qurtz rector were compred to outlet concentrtions from bypss line. This experiment confirmed tht the experimentl system ws inert with respect to HS. Compressed gs cylinders provided the inlet gses, Ech smple ws mesured twice, nd the ccurcy of the Quntchrome Monosorb ws checked periodiclly with stndrd mterils. The surfce res for some of the smples were lso determined using five-point isotherm

4 1760 M.P. Cl et l. / Crbon 38 (000) Quntchrome dsorption pprtus, nd then compred to smples rnged from 50 to 510 m / g, nd ZnCl chemi- the single-point mesurements. clly ctivted smples rnged from 400 to 1030 m / g. Temperture progrmmed desorption (TPD) ws used to Smple surfce res were tested before nd fter H S quntify the oxygen content of the oxidized smples. dsorption nd results showed surfce res remining Typiclly, 0.6 g of HNO3 oxidized smple ws plced in constnt (within 5%), except for some metl impregnted.5 cm dimeter, type 304 stinless steel rector with chrs. Ion exchnge (IE) metl impregntion did not hstlloy porous plte. Smples were heted in 0.5 l/ min significntly chnge the surfce res for most smples, N from 58C to 958C t rte of 108C/min. Chemiclly nd s long s the smples hd surfce re greter thn bound oxygen evolved s CO nd CO, nd were continu- bout 100 m / g, H S dsorption performnce did not ously monitored with stedy-stte infrred nlyzer pper to be dependent on sorbent surfce re. (Rosemount Model 880). Surfce oxygen content ws Temperture progrmmed desorption (TPD) ws used to clculted bsed upon the mount of CO nd CO re- quntify the oxygen content of HNO3 oxidized crbon- lesed. Quntifiction of smple oxygen content ws bsed sorbents. TPD results showed tht HNO oxidized 3 necessry to correlte surfce oxygen content with HS smples hd surfce oxygen content between 10 nd 15% dsorption cpcity. by weight, nd stem ctivted smples hd surfce Metl content of zinc nd copper impregnted crbon- oxygen content between nd 4% by weight. bsed sorbents (by IE method) nd zinc chloride ctivted Metl content of Zn- nd Cu-impregnted ctivted crbon smples ws determined using tomic bsorption crbon smples (by IE) nd ZnCl ctivted smples ws (AA) spectrometry. Crbon-bsed smples were dissolved determined using tomic bsorption (AA) spectrometry. Zn in hydrofluoric cid qu regi before nlysis. Mesure- content of the impregnted sorbents (by IE) ws found to ments were mde using tomic bsorption spectrophotome- be between 0.83 nd 3.3% by weight. The 3.3% Zn by ter (Perkin-Elmer Model 306) using the settings recom- weight smple hd Zn content of 0.03% by weight fter mended by the mnufcturer. Clibrtion curves were heting to 958C in N. Cu content of the Cu-impregnted clculted for ech set of nlyses using stndrd solu- crbon-bsed smple (by IE) ws found to be 1.03% by tions. Prcticl determintion limits were 5 ppm Cu nd weight. Zn content of the chemiclly ZnCl ctivted.5 ppm Zn by mss. crbon smples ws found to be between 0.5 nd 0.7% by After dsorption nd regenertion experiments, totl weight. After completing HS dsorption experiments for dsorbed sulfur ws determined by elementl nlysis of vrious smples, the tretment nd impregntion techthe ctivted crbon using solid-stte infrred detector niques were compred nd then ltered to improve H S (LECO SC-3). Smples were combusted in n oxygen dsorption. Chrcteriztions for few exmples of repretmosphere where the sulfur oxidized to SO nd ws then senttive ctivted crbon smples before HS dsorption mesured with solid-stte infrred detector. Mesured re shown in Tble 1. SO ws then converted to totl percentge of sulfur. Sulfur content of smples before nd fter HS dsorption 4.. HS dsorption experiments with HS/N /CO inlet experiments ws mesured in order to clculte the totl gs strem sulfur dsorbed nd ws then compred to the clculted vlue for the dsorbed sulfur from the brekthrough Initil HS (screening) dsorption experiments were curves. Smples were nlyzed for sulfur before nd fter performed to nrrow the lrge number of prepred crbonregenertion experiments to determine the effectiveness of bsed sorbents down to two or three of the best performing different regenertion methods. sorbents. Prt of the gol of these experiments ws to understnd HS dsorption with crbon-bsed sorbents nd to exmine the effects of smple surfce oxygen nd metl 4. Results nd discussion ddition on HS dsorption. A few nottionl definitions need to be clrified for the 4.1. Prepred ctivted crbon smples brekthrough curve experiments nd smple identifiction. All inlet nd outlet gs concentrtions re in percent by Physicl nd chemicl properties of most prepred volume. The term brekthrough is used throughout this ctivted crbon smples were chrcterized before the pper nd refers to predetermined HS outlet condition smples were used for HS dsorption experiments. Acti- when certin concentrtion of HS hs not been removed vted crbon smples were nlyzed for surfce re, by the crbon bed or HS hs broken through. Brekoxygen, nd metl content so tht properties of the smples through in ll HS dsorption experiments is defined s before HS dsorption experiments could be correlted to 00 ppmv HS outlet concentrtion, which is common their dsorption performnce [11]. N-BET surfce res stndrd t IGCC plnts. Brekthrough time is the time for most prepred smples were mesured using N t 77 tht the outlet gs HS concentrtion reches 00 ppmv. In K. Surfce res of stem ctivted smples (S) were in the the brekthrough figures, S represents stem ctivted, O rnge of 460 to 700 m / g, metl impregnted crbon represents HNO3 oxidized, nd D represents thermlly

5 M.P. Cl et l. / Crbon 38 (000) Tble 1 Representtive ctivted crbon smple chrcteriztion for HS dsorption experiments Activted crbon Oxygen Metl Surfce re smple description [wt %] [wt %] [m / g] S S 1 O S 1 O 1 D S 1 O1Cu by IE S 1 O1Zn by IE ZnCl, 1.0 col:0.5 ZnCl weight rtio before ctivtion Note: S5stem ctivted, O5HNO oxidized, D5thermlly desorbed in N t 958C, IE5metl dded by ion-exchnge. 3 desorbed in N t 958C. Lines representing HS outlet outlet gs concentrtion down to very low levels (,0 concentrtion versus time in brekthrough plots were ppmv). smoothed once using grphing softwre. A few HS dsorption experiments were performed with vried mounts of CO present in the inlet gs strem. All 4.3. Effect of sorbent oxygen content on HS dsorption three brekthrough experiments shown in Fig. were performed with stem ctivted crbons using the sme Experiments were performed with crbon smples of experimentl conditions. Brekthrough time decresed controlled surfce oxygen contents rnging from 0 to 15% from 60 min to 90 min nd then to 40 min s the inlet oxygen by weight (Fig. 1). As suggested from previous CO concentrtion decresed from 50% to 10% nd then literture nd our initil experimentl results, the more to 0% by volume, respectively. These results suggest tht oxygen present on smple s surfce, the greter the interction between the CO gs nd solid C sites enhnces sorbent s cpcity for HS [11,1]. This grees with the HS dsorption. One possible explntion of this phenomtheory tht sulfur toms rect in substitution rection enon is tht CO prtilly gsifies C sites nd forms C O with C O surfce complexes to form C S complexes. complexes. This rection is n intermedite step of gsifi- Although the thermlly desorbed sorbent (S 1 O 1 D) hd ction of crbon which is known to occur bove 8008C reltively fst brekthrough time, the desorbed smple [13]. It ws determined, by monitoring the concentrtions did dsorb some sulfur, which indicted dsorption by of outlet gs compounds during HS dsorption experiunsturted bonds or ctive sites on the crbon surfce. A ments, tht CO or CO rected with HS in the gs phse stem ctivted smple (S) performed lmost s well s in the presence of ctivted crbon to form gseous COS. HNO oxidized crbon (S 1 O), but did not polish the H S COS ws only formed when the crbon ws nerly 3 Fig. 1. Effect of smple oxygen content on HS brekthrough Fig.. Effect of CO inlet gs concentrtion on HS brekthrough time. Gs composition: 0.5% HS, 50% CO, blnce N. T5 time. Gs composition: 0.5% HS, 0 50% CO, blnce N. 5508C. P51 tm. T55508C. P51 tm.

6 176 M.P. Cl et l. / Crbon 38 (000) sturted with HS, nd COS ws not formed in blnk runs when crbon sorbent ws not present. Zn nd Cu, which re metls known to chemiclly dsorb pprecible mounts of HS, were dded to the crbon-bsed sorbents using IE impregntion, nd chemicl ctivtion. Brekthrough curves for four metl-impregnted crbon sorbents t the sme experimentl conditions re shown in Fig. 3. Activted crbon impregnted with Zn by IE performed the best with brekthrough time of 380 min. The good performnce of the Zn-impregnted sorbent cn be prtilly ttributed to the smple hving Zn content over 3% by weight. A Cu-impregnted sorbent lso performed well. The ZnCl chemiclly ctivted sorbent performed resonbly well considering tht the ZnCl chemicl ctivtion technique ws rther crude nd ws not s thoroughly investigted s the other metl ddition techniques. HS dsorption screening experiments with the qurtz rector system re summrized in Fig. 4 nd Tble. Fig. 4. HS brekthrough times for vrious screening experi- Adding Zn to HNO3 oxidized ctivted crbon (S 1 O1 ments. Gs composition: 0.5% HS, 50% CO, blnce N. Zn) improved the HS dsorption performnce. Stem T55508C. P51 tm. ctivted (S) nd HNO3 oxidized (S 1 O) smples did not perform s well s Zn-impregnted (S 1 O1Zn), but did hve good brekthrough times compred to Clgon Crbon nlyze the performnce of crbon-bsed smples. It is CenturE. CenturE is commercil sorbent with ct- importnt to know how much sulfur sorbent will remove lytic properties nd it is used for HS removl t mbient before reching brekthrough (00 ppmv outlet HS). tempertures, but did not perform well in our tests t Adsorption cpcity of hot gs clenup sorbents deter- 5508C. A stem ctivted (S) smple prepred in this study mines how much sorbent is needed t n IGCC plnt, hd brekthrough time more thn six times tht of which is n importnt design nd economic considertion. CenturE. Zn-impregnted ctivted crbon (S 1 O 1Zn) dsorbed Tble displys the sulfur contents for the four smples pproximtely 10% sulfur by weight t 00 ppmv brekwith brekthrough curves shown in Fig. 4. Sulfur testing through, nd stem ctivted smple (S) dsorbed bout fter HS dsorption experiments is nother method to 5.3% sulfur by weight fter 60 min t 00 ppmv brekthrough, nd 6.1% sulfur fter 300 min. It should be noted tht these sulfur lodings were for screening experiments with simplified inlet gs nd did not use complete simulted col gs. The mount of sulfur dsorbed cn lso be clculted using mss blnce on the inlet nd outlet H S concentrtions. Results of sulfur content mesurements, using the combustion technique described in Section 3., typiclly differed from the results of sulfur content clculted from the brekthrough curves by 10 5%. Mesured sulfur contents were consistently higher thn the clculted sulfur contents. It is unknown why this consistent error occurred Effect of CO, CO, H, nd H O in inlet gs strem on H S dsorption By vrying the inlet gs composition, effects of individul gses on HS dsorption with crbon-bsed sorbents cn be determined. For simplicity, initil dsorption experiments used inlet gs strems consisting of Fig. 3. H S brekthrough times for ctivted crbon smples fter only HS, CO, nd N. Since col gsifiction strems metl ddition (Cu nd Zn). Gs composition: 0.5% H S, 50% lso contin CO, H, nd HO, it ws importnt to CO, blnce N. T55508C. P51 tm. exmine the effects of these gses. Concentrtions of gses

7 M.P. Cl et l. / Crbon 38 (000) Tble Amount of sulfur dded to selected crbon-bsed sorbent smples during HS brekthrough experiments Smple description % Sulfur Totl dsorption Brekthrough time to dded [wt%] time [min] 00 ppmv [min] S S 1 O S 1 O1Zn Clgon Crbon CenturE Note: S5stem ctivted, O5HNO 3 oxidized, Zn dded to smple by ion-exchnge. used for this set of experiments were similr to those found sorbent, but tht time ws only hlf of the brekthrough t n ir-blown IGCC plnt. It is importnt to note tht the time for the experiment with 50% CO. sme btch of stem ctivted, HNO3 oxidized, Zn-impregnted (by IE) ctivted crbon ws used for ll gs Addition of CO to inlet gs strem effect experiments. By using the sme ctivted crbon for Addition of CO to the inlet gs strem hd detrimentl ll experiments, the only vrible ws the inlet gs. effect on brekthrough time (Fig. 6). Adding CO to the Informtion gined in these prmetric gs studies my inlet gs decresed brekthrough time from 160 min for n led to useful informtion tht could be used to design inlet gs of just 0.5% HS nd 99.5% N to 100 min for n better ctivted crbons for high temperture HS d- inlet gs of 0.5% HS, 0% CO, nd 79.5% N. The sorption. negtive effects of CO ddition my be becuse CO reduces oxidized sites on the crbon surfce, forming CO, nd thereby limiting H S dsorption, but further study is Addition of CO to inlet gs strem needed to confirm this hypothesis. Despite the positive As seen with the stem ctivted crbon (Fig. ), effects of hving CO in the inlet gs s shown in previous decresing the concentrtion of CO hd negtive impct experiments, the ddition of 7.5% CO to the 0% CO on brekthrough time of the Zn-impregnted smple (Fig. mixture did not chnge the 100 min brekthrough time. 5). The S 1 O1Zn sorbent, with 0% CO in the inlet gs, Adding H to the inlet gs decresed brekthrough time still hd significnt brekthrough time of 160 min further from 100 min for n inlet gs of 0.5% H S, 0% compred to 40 min for the stem ctivted crbon (S) CO, nd 79.5% N to 60 min for n inlet gs of 0.5% H S, with 0% CO in Fig.. This shows the effect of oxygen 0% CO, 13% H, nd 66.5% N. The initil elevtion in nd Zn on H S dsorption. Addition of 7.5% CO in- H S concentrtion seen in Fig. 6 for the gs strem cresed brekthrough time to 00 min on the S 1 O1Zn Fig. 6. Effect of CO inlet gs concentrtion on H S brekthrough Fig. 5. Effect of CO on H S brekthrough time of zinc im- time of zinc impregnted (S 1 O1Zn by IE) ctivted crbons. pregnted (S 1 O1Zn by IE) ctivted crbons. Gs composition: Gs composition: 0.5% H S, 0 0% CO, 0 7.5% CO, 0 13% 0.5% H S, 0 50% CO, blnce N. T55508C. P51 tm. H, blnce N. T55508C. P51 tm.

8 1764 M.P. Cl et l. / Crbon 38 (000) contining H is believed to be cused by the introduction of H into the system nd is discussed in more detil in Section Addition of H to inlet gs strem Addition of H to the inlet gs strem ws found to hve the most negtive effect of ll inlet gses on brekthrough time (Fig. 7). Brekthrough time decresed from 160 min for n inlet gs of 0.5% H S nd 99.5% N to bout 65 min for n inlet gs of 0.5% HS, 13% H, nd 86.5% N. Adding 7.5% CO or 0% CO hd lmost no effect on brekthrough time. This shows tht the effects of H dominte over the effects of CO nd CO for HS dsorption with crbon-bsed sorbents t the concentrtions tested in these experiments. An initil increse in the HS outlet concentrtion shown in Fig. 7 is believed to be cused by introduction of H into the system, which cused smll mount of preexisting sulfur (,1% of sulfur by weight) on the ctivted crbon smple to be Fig. 8. Effect of HO inlet gs concentrtion on HS brekremoved s HS. This initil phenomenon ws seen in through time of zinc impregnted (S 1 O1Zn by IE) ctivted other experiments nd ws not considered true brek- crbons. Gs composition: % HS, 0 50% CO, 0 7.5% through. H O, blnce N. T55508C. P51 tm Addition of HO to inlet gs strem Addition of HO to the inlet gs hd negtive effect on HS dsorption hd excess CO ( 50%) present in the brekthrough time, but the effect ws not s severe s it ws for CO or H ddition (Fig. 8). Brekthrough time for hve excess CO. Zn-impregnted smples with n inlet gs of 0.5% H S, inlet gs, wheres the other gs effects experiments did not 50% CO, nd 49.5% N ws 400 min, but decresed to 4.5. H S dsorption with H S/H /CO/CO /H O/N in 00 min for the experiment with n inlet gs of 0.46% inlet gs strem HS, 7.5% HO, 46% CO, nd 46% N. It should be noted tht the experiments nlyzing the effects of H O on H S dsorption experiments with simulted col gs strems were performed. Gs composition used to simulte n O blown IGCC plnt ws 0.5% HS, 13% H, 1% CO, 7.5% CO, 8.5% HO, nd 49.5% N by volume. Effect on HS dsorption of the simulted col gs versus the simple mixture used for screening experiments is shown in Fig. 9. All three experiments shown in Fig. 9 were performed with Zn-impregnted crbon (by IE). Brekthrough time decresed from 400 min for the screening gs mixture to min for the complete col gs mixture. 5. Summry nd conclusions Fig. 7. Effect of H inlet gs concentrtion on HS brekthrough time of zinc impregnted (S 1 O1Zn by IE) ctivted crbons. Gs composition: 0.5% HS, 0 0% CO, 0 7.5% CO, 0 13% H, blnce N. T55508C. P51 tm. Crbon-bsed sorbents mde from bituminous col were exmined for their bility to dsorb HS from high-temperture simulted col gs strems. Currently, the leding sorbents for this ppliction re metl-bsed sorbents, such s zinc titnte nd copper nd mngnese oxides. These metl-bsed sorbents, while effective t tempertures round 5508C, lose much ctivity when the gs rection temperture is lowered much below 5508C. Metl-bsed sorbents re lso expensive, costing between $15 nd 30/kg. Crbon-bsed sorbents hve the potentil to be

9 M.P. Cl et l. / Crbon 38 (000) Doctor Sntosh Gngwl of the Reserch Tringle Institute (Reserch Tringle Prk, NC) for their technicl ssistnce. References [1] U.S. Deprtment of Energy. Clen Col Technology: The New Col Er, DOE/ FE-017P, [] Swisher JH, Yng J, Gupt RP. Attrition-resistnt zinc titnte sorbent for sulfur. Ind Eng Chem Res 1995;34(4): [3] Khre GP, Delzer GA, Kubicek DH, Greenwood GJ. Hot Gs Desulfuriztion with Phillips Z-Sorb Sorbent in Moving Bed nd Fluidized Bed Rectors. Environ Prog 1995;14(3): [4] vn der Hm AGJ, Venderbosch RH, Prins W, vn Swi WPM. In: NATO/ASI Course on High-temperture Desulfuriztion, Kusdsi, Turkey, July, [5] Illinois Deprtment of Nturl Resources. Illinois bsin col Fig. 9. Comprison of HS brekthrough time for zinc impregsmple progrm. Illinois stte geologicl survey, Chmpign, nted (S 1 O1Zn by IE) ctivted crbons with different inlet gs IL, compositions. Gs composition: 0.5% H S, 0 1% CO, 0 7.5% [6] DeBrr JA. The role of free sites in the removl of SO from CO, 0 13% H, 0 8.5% HO, blnce N. T55508C. P51 tm. simulted flue gses by ctivted chr, Urbn-Chmpign: University of Illinois, 1995, M.S. Thesis. less expensive hot gs clenup sorbent nd they retin their [7] Cturl F, Molin-Sbio M, Rodriguez-Reinoso F. Prepr- ctivity s the rection temperture is lowered. While more tion of ctivted crbon by chemicl ctivtion with ZnCl. reserch still needs to be done to determine the vibility of Crbon 1991;9(7): crbon-bsed sorbents for hot gs clenup, zinc-impregfrom col by chemicl nd physicl ctivtion. Crbon [8] Ahmdpour A, Do DD. The preprtion of ctive crbons nted crbon sorbents show much promise nd hve 1996;34(4): brekthrough times pproching those of the best metl- [9] Ibrr JV, Moliner R, Plcios JM. Ctlytic effects of zinc bsed sorbents. Prt II of this study will exmine the chloride in the pyrolysis of Spnish high sulphur cols. Fuel effects of gs temperture nd gs pressure on H S 1991;70:77 3. dsorption cpcity nd it exmines methods of sorbent [10] Lizzio AA, DeBrr JA. Effect of surfce re nd chemiregenertion. sorbed oxygen on the SO dsorption cpcity of ctivted chr. Fuel 1996;75(13):1515. [11] Strickler BW. High temperture removl of hydrogen sulfide Acknowledgements from col gsifiction strems with crbon-bsed sorbents, Urbn-Chmpign: University of Illinois, 1998, M.S. Thesis. The uthors would like to cknowledge the Illinois [1] Puri BR, Hzr RS. Crbon sulphur complexes on chrcol. Clen Col Institute nd the University of Illinois Reserch Crbon 1971;9: Bord for funding this reserch project. The uthors would [13] Wlker PL, Rusinko F, Austin LG. In: Wlker PL, editor, lso like to thnk Doctor Mrk Rood of the University of Chemistry nd physics of crbon, vol., New York: Dekker, Illinois t Urbn-Chmpign, Doctor John Lytle nd 1966, p. 75. Gwen Donnls of the Illinois Stte Geologicl Survey, nd