Journal of Southeast University(English Edition)Vo1.31,No.2,PP.215—219 June 2015 ISSN 1003--7985 Effect of sulfation during carbonation on CO2 capture in calcium looping cycle Wang Chunbo Liu Hongcai Chen Liang Lufei Jia Yewen Tan ● ’ ・ 一 ‘ 一 ( School of Energy and Power Engineering,North China Electric Power University,Baoding 07 1003,China) ( CanmetENERGY,Natural Resources Canada,1 Haanel Drive,Ottawa,Ontario,Canada K1 A 1 M1) Abstract:Two Canadian limestones wim different properties nd overa 900℃for calcination in a rich atmosphere of were tested to determine the effect of SO,during the carbonation of sorbent on the CO capture performance in Ca. 1ooping.When the reaction gas is mixed、Ⅳith S02,the carbonation ratio of the sorbent is always lower than that without SO1 for each cycle under the same condiifons.and the sulfation ratio increases almost linearly wiht the increase in the cycle times.At 650℃.there is little difference in the carbonation ratio of the sorbent during the first four cycles for hte two carbonation time.5 and 10 min at 0.18%SO,.The indirect sulfation reaction that OCCurS simultaneously with the carbonation of Cat is responsible for the degradation of the sorbent for CO,crd口ture,and the carbonation duration is not the main factor that affects the ability ofthe sorbent.680℃is hte best carbonation temperature among the three tested temperatures and the highest carbonation ratio can be obtained.A1so.the sulfation ratio is the highest.111e probable cause is the different effects oftemperature on the carbonation rate and sulfation rate. A higher SO,concentration will decrease the carbonation ratio clearly,but the decrease in the carbonation capability of the sorbent is not proportional to the increase of the S concentration in flue gases. Key words:Ca.based sorbent; carbonation; sulfation; looping;CO2 capture doi:10.3969/j.issn.1003—7985.2015.O2.010 C atelcmiupmer altouorpe inpog sits- caonmb emusetriognin Cg Ote2 cchanpotluorgey .I for ht ighhas— experienced the fastest developing pace due to the strong similarities and synergies with existing combustion tech. nology in circulating fluidized beds,including recent oxy— ifred CFB development ….Both carbonation and calcina— tion reactions are carded out at very high temperatures, raound 650℃for carbonation. Cat+CO2--*CaCO3 (1) Receired 2Ol5 1 7. Biography:Wang Chunbo(1973一),male,doctor,professor,hdwchb @126.corn. Foundafion iteIllS'-The National Natural Science Foundation of China (No.51276064),the Natural Science Foundation of Beijing City(No. 3132028). Citation:Wang Chunbo,Liu Hongcal,Chen Liang,et a1.Effect of sul— fafion dunng carbonation on CO2 capture in calcium looping cycle[J】. Journal of Southeast University(English Ediiton),2015,3l(2):215— 219-Idoi:10.3969/j.issn.1003—7985.2015.02.010】 CO2, CaCO3一Ca0+Cat (2) However,there is some SO.in coal fired flue gases. Limestone has great potential for capturing sulphur diox- ide,despite SO2 concentrations being two orders of mag— nitude lower than that Of C0 .The desulphurization of the combustion flHe gases is achieved via the following reaction under the atmospheric conditions: Cat十SO2+1/202_+CaS04 (3) which is USUally called the indirect sulfation of limestone. In combustion systems where the partial pressure of CO2 is high enough that CaCO3 is not calcined to Cat, hte removal of SO,can be realized via direct sulfation, i.e..direct reaction of hte gaseous SO,with calcium car. bonate in the presence of O : CaCO3+SO2+1/202-*CaSt4+CO2 (4) Sulfation is irreversible under typica1 FBC conditions. although it proceeds at a much slower rate than carbona— tion.As sulfation proceeds,the CaSO formed leads to pore blockage due to the high volume per unit mass OCCU— pied by the primary sulfation product compared to the cal— cine .Pore closure mainly occurs on the surface of the particles,obstructing direct contact with the interior cal— cine /-1o1.Since the pore of Cat will be blocked and the CaSO product layer will be resistant to CO.diffusion on the surface of the sorbents,the SO,wil1 bring a negative effect on the C0 capture for this process.Ryu et a1. ” suggested that the presence of SO leads to the fast deteri. oration of limestone CO,capture,mainly due to the com— petition between carbonation and both sulfation reactions. Basinas et a1. found that the sorbents sulphated via the an reacted core mode converted more available calcium, but this adversely affected the reversibility of cyclic CO, caDmre.The reversibility strongly deteriorated when a higher total pressure was combined with increasing SO, partial pressure.The eflfect of the presence of SO was a1. so studied by Coppola et al .Results showed that the presence of S02 in the flue gas signiifcantly decreased the sorbent CO.capacity.most likely because of the forma. tion of an impervious CaSt4 layer at the periphery of the 216 Wang Chunbo,Liu Hongcai,Chen Liang,Lufei Jia,and Yewen Tan particleI 16]. effects.Also,a high SO2concentration of 0.1 8%was As tested,the CO2 capture capacity for all sorbents calcined in CO,in the presence of SO was effectively tested,aiming to find how much negative effect of SO2 exists only in the carbonation stage on the Ca—sorbents utilization. eliminated after 2 to 3 cycles.These results suggest that the presence of S0 must be avoided if the object is CO2 capture from flue gas… In this study,the sul— .1 Experimental Procedure Two limestones,Massieci and Kelly Rock,were used for the test.Prior to the sorption test,both limestones were milled and sieved to ensure the particle size ranging fation following the carbonation of CaO is tested.The effect factors,such as the carbonation temperature, S0,concentration etc,are tested.Especially the influ— ence of duration is tested,which is hoped to obtain the best balance between C02 capture and SO2 negative from 250 to 425 LLm for all the tests performed.The main components of the sorbents are presented in Tab.1. % Tab.I The component of the two limestones TherMax 700 TGA was used for testing.The tempera- ture and the weight of the sample were recorded continu— ously,and the flow rate was kept at 50 mL/min for both calcination and carbonation. The initial calcination of the 1imestone occurred under the non—isothermal conditions as he temperature was raised ftrom room temperature to 1oo 9O /u0 ∞B §0 80 70 850℃.The samples were then maintained at this temper— ature or fa suficifent time r5 rain)to ensure complete cal— cination,and then it was cooled down to the carbonation temperature.Pure nitrogen was used for the calcination process in all cases. When the furnace temperature 6O 50 0 50 100 150 200 t/rnin 250 300 350 reached the set carbonation temperature,the gas was switched to the mixed gases containing SO,for specified duration.After carbonation duration,the inlet gas was then switched back to pure nitrogen,and it was heated to Fig.1 Effect of SO2 on the conversion of Massieci limestone in Ca—looping at 650℃ same degree of decomposition for every cycle although the ability of capture CO,always decreases with the in. crease in the cycle times.However,when the reaction gas contains 0.01 8%SO .the final conversion degree in— creases with the increase in the cycles’times.For exam. 850℃in N。.Tl1e cyclic process was repeated 8 times. The testing conditions are shown in Tab.2. Tab.2 Testing conditions ple,for the first cycle,the conversion degree is 56.8% nd it is 65.8%afor the 8th cycle.The only reason for this is that CaSO4 is formed during CaO carbonation,and this will degrade the capability of the sorbent for captu. ring CO2. 2.2 Effect of duration on conversion of carbonation and sulfation 2 Results and Discussion 2.1 Effect of SO2 on carbonation kinetics and conversion Massieci limestone is chosen for testing the effect of SO,on the carbonation first,and the carbonation temper— To obtain a good carbonation utilization of sorbent,a suitable carbonation duration should be evaluated.The car— bonation duration of 5 and 10 min are tested,and the tes— ting conditions are the SalTle as those in Fig.1(see Fig.2). As shown in Fig.2(a),the difference in the carbona— tion ratio between the two carbonation durations,5 and .ature is 650℃.For comparison,the carbonation in 15% C0,and 85%N,(without S0,)was also tested.The car— 10 min are not obvious for all the eight cyclesA1so.a bonation duration for both tests is 5 min.as shown in Fig.1. The most common characteristic shown in Fig.1 is that when the reaction gas is without SO,,the limestone ca1. similar tendency occurs for the sulfation ratio of sorbents or the tfwo durations,as shown in Fig.2(b1.For exalTl— ple,11.65%for 10 min and 10.29%for 5 min at the 8th cycle.It seems that a longer carbonation duration(5 and cined to CaO completely,and this can be found from the 10 min)will not greatly decrease the carbonation ratio. Effect of sulfation during carbonation on CO2 capture in calcium looping cycle 217 tics of sorbent at temperatures of 620,650 and 680℃, respectively,and the SO2 concentration is 0.1 8%. (a (a) Cycles (b) Fig.2 The carbonation and sulfation ratio of Massieci lime- stone at 5,10 min carbonation duration.(a)Carbonation ratio; (b)Sulfation ratio To verify this further,the carbonation ratio under the (b) Fig.4 Effect of carbonation temperature on carbonation and conditions without SO2 in reaction gases are tested,as shown in Fig.3. Fig.3 shows that there is little difference in the carbon. ation ratios between the two durations.It can be specula— sulfation ratios of Massieci limestone in 0.18%SO2 mixed ga— ses.(a)Carbonation ratio;(b)Sulfation ratio As shown in Fig.4fa)。for the 5 min carbonation dura. ted that the difference in carbonation ratios between the tion.the best carbonation is obtained at 680℃,then at min duration.the carbonation ratio is higher at 680℃ two durations(see Fig.2)is mainly caused by SO2 rather 650℃.and the worst is at 620℃.F0r the tests of 10 than carbonation duration.Since the sulfation reaction oc- curing after 5 min is direct sulfation which is very slow at than that at 650℃.It shows that temperature is an im— bent.and 680℃is the best carbonation temperature among the three testing temperatures.However,as an negative influence on carbonation.the sulfation ratio is 650℃.it will not produce seriously adverse effects on portant factor that determines the carbonation of the sor— the carbonation of CaO even after a longer carbonation duration.So,the carbonation duration is not an influen— tial factor that affects the ability of the sorbent at 650℃ in the calcium looping cycles. the highest at 680℃,as shown in Fig.4(b).Since the sulfation reaction of sorbent can retard the carbonation of he sorbent,the highestt sulfation ratio of sorbent should result in the lowest carbonation ratio.A probable reason or this phenomenon is tfhat the increase in the carbonation ratio caused by the increasing temperature is greater than he negattive effect caused by sulfation reaction.Alhough tsulfation will be enhanced by high temperatures,the car— bonation improvement will be more obvious. №.3 c… 。…iec㈨…e wi t 2 s ∞ 嘣 …咖 商… 卜SO at 650℃ Donauon ann SUllallon As known from Fig.1,0.18%SO2 will bring a nega— 2.3 Effect of temperature on conversion of carbona- tion and sulfation Fig.4 shows the carbonation and sulfation characteris— tive effect on the capability of sorbent for CO2 capture. For the low sulphur content coal,the SO2 concentration in lue gasf is less than0.18%,and the effect of a relatively 2l8 Wang Chunbo,Liu Hongcm,Chen Ling,Lufei Jiaa,and Yewen Tan low concentration SO2 is investigated.The mixed gas in 0.18%S0 mixed gases.The sulfation occurred along with the carbonation of sorbent brings more negative with 0.09%SO2 is used for the next test at the carbona- tion temperature of 650℃(see Fig.5). fa) Cycles (b) Fig.5 Carbonation and sulfation ratio vs cycles in 0.09%and 0.18%SO2 mixed gases.(a)Carbonation ratio;(b)Sulfation ratio It can be seen from Fig.5(a)that a higher concentra— tion of SO,will greatly decrease the carbonation ratio,es— pecially from the second cycle.For example,the carbon— ation ratio is 18.33%at 0.09%SO and only 13.06%at 0.18%SO for the 8th cycle。and the difference is 5.27%.However.the relative sulfation ratio difference is greater than that of the carbonation ratio。as shown in Fig.5(b).For example,the sulfaion ratio is 10.29%for 0.18%SO.and only 2.47%ofr 0.09%SO at the 8th cycle.It shows that the decrease in the carbonation caOa. bility of the sorbent caused by SO2 is not proportional to hte increase of the SO.concentration in flue gases,and e— yen a little CaSO product formed in the carbonation will lead to a decrease in the capability of the sorbent for CO, capture. 2.5 E ct of diiferent limestones Another limestone,Kelly Rock limestone,was tested to check if the phenomena occurring above are only appli— cable to one speciifc limestone.For comparison,the car— bonation in 15%CO and 85%N at the carbonation tem。 perature of650℃is also tested f see Fig.61.As shown in Fig.6.when the reaction gases are mixed with 0.18% SO ,the carbonation ratio of the sorbent is always lower than that without SO,for each cycle.For example,the carbonation ratio is 23%without SO and only l1.17% effect with more looping cycles,just like htat of Massieci limestone.Also,the sulfation ratio of sorbent increases with the cycles almost linearly,from the first cycle of 1.5l%up to 11.71%of the 8th cycle. (a) g Cycles (b) Fig.6 Carbonation and sulfation ratio of Kelly Rock limestone at 5 min carbonation duration.(a)Carbonation ratio;(b)Sulfation ratio 3 Conclusion When reaction gases are mixed wim 0.18%SO..the carbonation ratio of the sorbent is always lower than that without SO for each cycle.The carbonation ratio of the sorbent decreased with cycles whether with SO,or not, but a fast decrease occurred when the reaction gases con— tained SO .Sulfation of the sorbent occurred during car— bonation will bring more negative effect with more loo. ping cycles.The difference in carbonation ratios between hte sorbent at 5 and 10 min durations at650 oC is not very clear,which shows a long duration will not bring great effect on the carbonation at 650℃and in 0.18%S0 . Sulfation that occurred simultaneously with the carbona. tion of CaO is responsible for the degradation of the sor— bent for CO capture.680℃is the optimal carbonation temperature among the three temperatures.However,the sulfation ratio is also the highest at this temperature.A probable cause for this is that the eflfect of temperature on carbonation is stronger than that of sulfation for this kind Of sOrbent.The negative effect will be increased witIl more SO。,and the decrease in the carbonation capability Effect of sulfation dunng carbonation on CO2 capture in calcium looping cycle 219 of the sorbent by SO2 is not proportional to the increase of the SO2 concentration in flue gases. l。707—1743. [9】Cheng L M,Chen B,Liu N,et a1.Effect of characteris— tic of sorbents on their sulfur capture capability at a fluid. References 【1】Lasheras A,Str6 ̄e J,Galloy A,et a1.Carbonate loo— ping process simulation using a 1 D fiuidized bed model ized bed condition【J]., eZ,2Oo4,83(7/8):925—932. 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Process Technology,2005,86(16): 碳酸化过程中硫化反应对钙基吸收剂循环捕集CO2的影响 王春波 刘洪才 陈 亮 Lufei Jia Yewen Tan ( 华北电力大学能源动力与机械工程学院,保定071003) ( CanmetENERGY,Naturla Resources Canada,1 Haanel Drive,Ottawa,Ontario,Canada K1A 1MI) 摘要:采用2种不同特性的加拿大石灰石来研究钙基吸收剂循环煅烧碳酸化捕集CO:过程中硫化反应对碳 酸化反应的影响.当反应气氛中有SO 时,每次循环中钙的碳酸化转化率都要低于没有SO:的循环,而且钙 的硫酸化转化率几乎随着循环次数线性增长.在650℃,0.18%SO 的环境中,对5和10 min这2种碳酸化 时间而言,前4次循环的碳酸化转化率几乎没有区别.与碳酸化过程同时发生的间接硫化反应是导致吸收 剂捕集CO,能力下降的原因,而碳酸化时间并不是影响吸收剂脱碳的主要影响因素.在所测试的3个温度 中,680℃是最佳碳酸化温度,在此温度下碳酸化转化率最高,而此温度下硫化转化率最大,则可能是由于温 度对碳酸化和硫化反应速率的作用不同而造成的.碳酸化转化率随SO,浓度的增加而减小,但两者之间并 不是线性关系. 关键词:钙基吸收剂;碳酸化;硫化;循环;CO 捕集 中图分类号:TK16