APPLICATION OF POLISH CALCIUM SORBENTS IN CARBONATE LOOPING

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1 Physicochem. Probl. Miner. Process. 49(), 203, 20 Physicochemicl Problems of Minerl Processing ISSN (print) ISSN (online) Received April 3, 202; reviewed; ccepted June 5, 202 APPLICATION OF POLISH CALCIUM SORBENTS IN CARBONATE LOOPING Michlin KOTYCZKA-MORANSKA, Grzegorz TOMASZEWICZ Institute for Chemicl Processing of Col, Zmkow 4-80 Zbrze, Abstrct: The purpose of this work ws the investigtion of behviour of three Polish CO-bsed sorbents during clcium looping cycles. All investigtions were conducted with Netzsch STA 409PG Luxx thermogrvimetric nlyser. Smples weighing m s = 0.0() mg were plced in n Al 2 O 3 crucible. The clcium looping processes were performed t two crbontion tempertures (650 C nd 680 C) nd three clcintion tempertures (880, 900 nd 920 C). Additionlly, clcintion-crbontion cycles with different gs flows were explored. We investigted the influence of CO 2 concentrtion nd totl gs flow on crbontion conversion. Keywords: clcium looping, CO2 cpture, CO-bsed sorbents Introduction The emission of CO 2 from fossil fuel combustion is the mjor contributor to nthropogenic greenhouse gs emissions. During the lst severl yers, CO-bsed sorbents hve been intensively investigted for their possible pplictions in CO 2 cpture. Among the vrious options for the seprtion of CO 2 from flue gses, hightemperture CO 2 bsorption by minerl sorbents such s C-sorbents ppers promising. The min rection in this process is the crbontion rection: CO + CO 2 = CCO 3 + het. () The sorbent cn be regenerted vi clcintion, which entils heting the crbonte until it decomposes into CO nd CO 2. In this process, pure CO 2 is obtined for sequestrtion. The regenerted sorbent cn then undergo nother round of crbontion. This process is bsed on looping cycle in which the two rections, crbontion nd clcintion, re lternted. The crbontion rection is exothermic, wheres clcintion rection is endothermic. Crbontion is chrcterised by rpid initil rte nd very slow finl rection rte. Clcintion is rpid process tht occurs over wide

2 2 M. Kotyczk-Mornsk, G. Tomszewicz temperture rnge (Blmey et l., 200). Thus, the crrying cpcity of the sorbent is the number of moles of CO 2 rected in the period of fst rection rte with respect to tht of the rection stoichiometry for complete conversion of CO to CCO 3. The min disdvntge of CO-bsed sorbents is the decy of ctivity with n incresing number of cycles. This decy trend ws summrised by Abndes nd Alvrez (2003) s the following first-order formul: N N m w w X f ( f ) f (2) where X N is the crbontion conversion in the Nth cycle, nd f m nd f w re empiricl prmeters. The optiml vlues of these prmeters were clculted from dt series found in the literture s f m = 0.77 nd f w = 0.7. This eqution ws fitted to crbontion/clcintion dt from over 50 cycles, nd n excellent regression coefficient of pproximtely 0.99 ws obtined, indicting tht fresh sorbent is needed in the clcium looping process due to its dectivtion, which increses the cost of the process. For this reson, it is necessry to mitigte nturl sorbent dectivtion (Li, 20). The lrgest devition from the optimum vlue given by eqution 2 is found in processes where in considerble sintering ws observed, nd the dectivtion rte of the sorbents incresed ccordingly. Fennell et l. (2007) found tht eqution 2 does not describe sorbent ctivity in fluidised bed environment becuse incresing the clcintion period reduces f m. This prmeter cn be interpreted s residul rectivity. Mess et l. (999) observed tht sorbent prticles remined cpble of forming C- CO 3 lyer despite undergoing numerous cycles. For this reson, the term f m nd eqution 2 re more pplicble in systems where ttrition nd fribility re less significnt. An lterntive formul ws developed by Wng nd Anthony for crbontion conversion ctivity (Wng nd Anthony, 2005): ( k ) (3) N N N where k is proportionlity coefficient, nd N is the ctivity of the sorbent in the Nth cycle. These uthors reported tht ctivity decy depends on the ctivity of the sorbent in the (N ) cycle. Their formul describes the dt quite well with k = The disdvntge of this formul is its limittion in N, becoming useless when N is lrge. As n lterntive for lrge N, Wng nd Anthony (2005) proposed eqution (4): N kn. (4) In this eqution, the prmeter k is the rte of decy of sorbent ctivity. This eqution is reminiscent of the formul for ctlyst dectivtion by sintering s function of time t:

3 Appliction of Polish clcium sorbents in crbonte looping 3 N kt. (5) Eqution (5) suggests tht sintering is the cuse of decy. The eqution proposed by Wng nd Anthony does not include residul rectivity. Grs nd Abndes (2006) developed Eq. 4 to ccount for the residul ctivity: N kn 00 (6) where is the residul ctivity, with vlue of pproximtely 7%. This eqution is useful for dt for up to pproximtely 500 cycles, where Another formul ws subsequently proposed by Lysikov et l. (2007): N ( kn) 00 (7) where is the residul ctivity, nd is prmeter tht depends on the sintering mechnism. This formul is especilly useful for synthetic sorbents but requires n dditionl prmeter. Wng nd Anthony (2007) lter proposed formul tht includes residul rectivity: [ k( )] 00 (8) N N N which, for lrge number of cycles, reduces to the following: N ( ) e k N 00. (9) This eqution lso describes decy behviour in systems where sintering occurs. There re numerous equtions in the literture tht cn fit experimentl dt, but there is no redy correltion between their prmeters, sorbent chrcteristic nd process conditions. Therefore, the finl sorbent cpcity fter n infinite number of cycles is not predictble. This sitution demonstrtes tht the influence of different process prmeters on sorbent ctivity requires dditionl investigtion. Mnovic nd Anthony (2008) exmined the influence of temperture on sorbent ctivity using the sme tempertures for clcintion nd crbontion nd found tht sorbent sintering is msked t higher tempertures by enhnced crbontion due to incresed CO 2 diffusion through the CCO 3 lyer. These uthors concluded tht long crbontion period led to fster loss of sorbent ctivity nd further showed tht longer clcintion period

4 4 M. Kotyczk-Mornsk, G. Tomszewicz increses sorbent conversion. Their results stnd in contrst to those presented by Grs nd Abndes (2006) nd Lysikov (2007), who reported tht clcintion time is not n importnt prmeter. The im of this work ws to determine the crbontion/clcintion process prmeters tht llow for the most efficient use of the sorbent in clcium looping instlltion. For this purpose, we studied the influence on sorbent ctivity of prmeters such s crbontion nd clcintion tempertures, the CO 2 /CO rtio in the rector nd the choice of minerl sorbent. Experimentl system We investigted three nturl Polish minerl sorbents: limestone from Cztkowice nd dolomites from Siewierz nd Sndomierz. All investigtions were conducted in n STA 409PG Luxx thermogrvimetric nlyser (Netzsch). Smples of mss m s = 0.0() mg were plced in n Al 2 O 3 crucible. The mesurements were conducted t vrious crbontion nd clcintion tempertures, gs flows nd CO 2 concentrtions. Results nd discussion Figure presents comprison of these three minerl sorbents during ten clcintion/crbontion cycles. Fig.. Comprison of three minerl sorbents during ten clcintion/crbontion cycles All the mesurements were conducted under the sme conditions: crbontion t 650 C, clcintion t 900 C nd CO 2 flow of 25 cm 3 /min during crbontion. The simple comprison of the two dolomites shows tht the dolomite from Sndomierz

5 Appliction of Polish clcium sorbents in crbonte looping 5 displys worse sorbent properties becuse the period of fst rection rte during the crbontion process is less thn tht of the dolomite from Siewierz. Therefore, we used the dolomite from Siewierz nd the limestone from Cztkowice in our subsequent investigtions. The first stge of our mesurements involved conducting crbontion/clcintion cycles t different crbontion tempertures. We investigted two tempertures: 650 C nd 680 C. These tempertures were chosen becuse their ppliction in clcium looping instlltion cn be economiclly justified. Furthermore, we chose not to pply higher temperture during crbontion to prevent sorbent sintering (Mnovic nd Anthony, 2008). Figure 2 presents the results for the limestone from Cztkowice. The clcintion temperture ws 900 C, nd the gs flows consisted of 25 cm 3 /min CO 2 plus 25 cm 3 /min N 2 during crbontion nd 25ml/min N 2 during clcintion. We observed no difference between the results for this sorbent t these two tempertures. Fig. 2. Comprison of crbontion conversion of limestone for two crbontion tempertures The second prt of our study consisted of investigting the influence of clcintion temperture on sorbent ctivity. For the limestone, we compred three clcintion tempertures: 880, 900 nd 920 C. The cycles were performed t crbontion temperture of 650 C nd the gs mixtures consisted of 25 cm 3 /min CO 2 plus 25 cm 3 /min N 2 during crbontion nd 25 cm 3 /min N 2 during clcintion.

6 6 M. Kotyczk-Mornsk, G. Tomszewicz Fig. 3. Comprison of the crbontion conversion of limestone t three clcintion tempertures Figure 3 presents comprison of the crbontion conversion for limestone t the three studied tempertures. There ws no difference observed between crbontion conversions t 880 C nd 900 C, but crbontion conversion ws lower t 920 C. These results re in ccordnce with the results presented by Mnovic nd Anthony (2008), who reported tht smples cycled t higher temperture were more sintered nd, hence, less ctive. However, the clcintion temperture in n industril rector should be t lest 900 C to chieve clcintion yielding concentrted CO 2 strem. Thus, it ppers pproprite to conduct further investigtions t clcintion temperture of 900 C nd crbontion temperture of 650 C.The second investigted sorbent ws the dolomite from Siewierz. We conducted mesurements in the sme wy s for the limestone, nd the results were the sme s for the limestone. Regrding the first vrible (crbontion temperture), there ws no difference between the results obtined with crbontions t 650 C nd 680 C. In processes with different clcintion tempertures, the results were lso similr to the limestone results. The worst crbontion conversion ws obtined for clcintion conducted t 920 C. The lst prt of our investigtion consisted of clcintion/crbontion processes conducted using severl different gs flows with vrious CO 2 concentrtions. These mesurements were ll conducted t clcintion temperture of 900 C nd crbontion temperture of 650 C. Figure 4 presents the dt obtined in four limestone clcintion/crbontion cycles conducted with four different gs flows during crbontion (24, 50, 00 or 50 ml/min) with constnt CO 2 concentrtion (50%). The prtil gs flows re lso presented in this figure. Nitrogen ws used s purge gs t constnt flow rte in ech process (2, 25, 50, or 75 cm 3 /min).we observed tht the crbontion conversion is better t lower gs flows thn with the lrgest gs flow (50 cm 3 /min). The influence of CO 2 concentrtion on crbontion conversion ws lso investigted. Three process-

7 Appliction of Polish clcium sorbents in crbonte looping 7 es with different CO 2 concentrtions (25, 50 or 75%) but constnt totl gs flow during crbontion (00 cm 3 /min) were evluted with the limestone. Fig. 4. Comprison of crbontion conversion of limestone for four gs flows: N 2 75 cm 3 /min/co 2 75 cm 3 /min; N 2 50 cm 3 /min/co 2 50 cm 3 /min; N 2 25 cm 3 /min/co 2 25 cm 3 /min; Ο N 2 2 cm 3 /min/co 2 2 cm 3 /min Fig. 5. Comprison of crbontion conversion of limestone for three CO 2 concentrtions with the sme gs flow: N 2 25 cm 3 /min/co 2 75 cm 3 /min; N 2 50 cm 3 /min/co 2 50 cm 3 /min; N 2 25 cm 3 /min/co 2 75 cm 3 /min The dt presented in Fig. 5 show tht the crbontion conversion is slightly lower t 75% CO 2 thn t the other CO 2 concentrtions. This result my be relted to the fct tht n tmosphere of concentrted CO 2 lso mplifies sintering, consequently reducing the sorbent ctivity with n incresing number of rection cycles. This phenomenon cn lso be observed in Fig. 6.

8 8 M. Kotyczk-Mornsk, G. Tomszewicz Fig. 6. Crbontion conversion of limestone for three CO 2 concentrtions (purge gs flow 25 cm 3 /min) This grph presents the reltion between CO 2 concentrtion nd crbontion conversion during the first cycle. In these processes, the purge gs flow ws constnt (25 cm 3 /min), nd CO 2 concentrtion ws vried (50, 67 nd 75%). The sme types of mesurements were performed for the dolomite, nd in both cses (constnt CO 2 concentrtion nd constnt totl gs flow), there were no differences between the dt obtined. Figure 7 presents the dt collected t constnt totl gs flow; here, it cn be observed tht dolomite ctivity does not depend on CO 2 concentrtion in this rnge. Fig.7. Comprison of crbontion conversion of dolomite for three CO 2 concentrtions with the sme gs flow: N 2 25 cm 3 /min/co 2 75 cm 3 /min; N 2 50 cm 3 /min/co 2 50 cm 3 /min; N 2 25 cm 3 /min/co 2 75 cm 3 /min Becuse the CO 2 concentrtion in typicl flue gs is pproximtely 20%, we decided tht the best dt for further nlysis were those obtined t 20% CO 2. Figure 8

9 Appliction of Polish clcium sorbents in crbonte looping 9 presents comprison of our dt for limestone nd dolomite in 0 crbontion/clcintion cycles with three curves representing reltions found in the literture (Eqs (2), (3), (8)).We observed tht the ctivity of dolomite is slightly higher thn tht of limestone. All these equtions describe crbontion conversion for limestone. As stted in the introduction, Eq. 2 does not consider sorbent sintering, nd this eqution did not describe our dt. Furthermore, the eqution developed by Wng nd Anthony (Eq. (3); 2005) did not describe our dt, but fter the introduction of the fctor for residul rectivity (Eq. (8)), corresponded to our dt quite well. Fig. 8. Comprison of dt obtined for limestone nd dolomite in 0 crbontion/clcintion cycles with the reltions found in the literture Conclusions The purpose of our work ws to determine the best prmeters for clcium looping processes conducted with Polish minerl sorbents. We investigted three minerl sorbents: one limestone nd two types of dolomite. We excluded one type of dolomite erly in our experiments due to its wek crbontion conversion. The two other sorbents were investigted t vrious crbontion nd clcintion tempertures nd t different CO 2 concentrtions nd gs flows. We found tht the best process prmeters for our sorbents re clcintion temperture of 900 C nd crbontion temperture of 650 C. Additionlly, we observed tht there ws no difference in crbontion conversion for dolomite in the rnge 25 75% CO 2, nd higher ctivity decy occurs with limestone t high CO 2 concentrtions. We lso found tht the ctivity decy of the limestone from Cztkowice is well described by the eqution developed by Wng nd Anthony (Eq. 8). This reltion is useful becuse it llows for the clcultion of sorbent ctivity in clcium looping instlltion fter N cycles.

10 20 M. Kotyczk-Mornsk, G. Tomszewicz Acknowledgements This reserch ws conducted in the frmework of the Development of col gsifiction technology for high-efficiency production of fuels nd energy project, Tsk No. 3 of the Strtegic Progrmme for Reserch nd Development: Advnced energy genertion technologies funded by the Ntionl Centre for Reserch nd Development, Polnd. References ABANADES J., ALVAREZ D., 2003, Conversion Limits in the Rection of CO 2 with Lime, Energy & Fuels, 7, BLAMEY J., ANTHONY E., WANG J., FENNELL P., 200, The clcium looping cycle for lrge-scle CO 2 cpture, Progress in Energy nd Combustion Science, 36, FENNELL P., PACCIANI R., DENNIS J., DAVIDSON J., HAYHURST A., 2007, The effects of repeted cycles of clcintion nd crbontion on vriety of different limestones, s mesured in hot fluidized bed of snd, Energy & Fuels;2, GRASA G., ABANADES J., 2006, CO 2 cpture cpcity of CO in long series of crbontion/clcintion cycles, Industril & Engineering Chemistry Reserch, 45, LI Y., ZHAO Ch., CHEN H., REN Q., LUNBO D., 20, CO 2 cpture efficiently nd energy requirement nlysis of power plnt using modified clcium-bsed sorbent looping cycle, Energy 36, LYSIKOV A., SALANOV A., OKUNEV A., 2007, Chnge of CO 2 crrying cpcity of CO in isotherml recrbontion decomposition cycles, Industril & Engineering Chemistry Reserch 46, MANOVIC V., ANTHONY E., 2008, Prmetric study on the CO 2 cpture cpcity of CO-bsed sorbents in looping cycles, Energy & Fuels, 22, MESS D., SAROFIM A., LONGWELL J., 999, Product lyer diffusion during the rection of clcium oxide with crbon dioxide, Energy & Fuels, 3, WANG J., ANTHONY E., 2005, On the decy behvior of the CO 2 bsorption cpcity of CO-bsed sorbents, Industril & Engineering Chemistry Reserch, 44, WANG J., ANTHONY E., 2007, A common decy behvior in cyclic processes, Chemicl Engineering Communictions, 94,