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Attrition and CO2 adsorption of dry sorbents in fluidized bed
159 Studies in Surface Science and Catalysis, volume 159 Hyun-Ku Rhee, In-Sik Nam and Jong Moon Park (Editors) © 2006 Elsevier B.V. All rights reserved
549
Attrition and CO2 adsorption of dry sorbents in fluidized bed Ki Chul Choa, Eun Yong Leea, Jeong Suk Yoob, Young Hean Choung \Sang Woo Parkc and Kwang Joong Oha* a
Department of Environmental Engineering, Pusan National University, San 30 jangjeondong, Guemjeong-gu, Busan 609-735, Republic of Korea b Doosan Heavy Industries & Construction Co. Ltd., R&D Center, 555 Gwigok-dong, Changwon, Gyeongnam 641-792 , Republic of Korea c Department of Chemical Engineering, Pusan National University, 30 jangjeon-dong, Guemjeong-gu, Busan 609-735, Korea (e-mail: [email protected])
Abstract Characteristics of attrition and adsorption were investigated to remove CO2 in fluidized bed using activated carbon, activated alumina, molecular sieve 5 A and molecular sieve 13X. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and attrition indexs(AI) of molecular sieve 5A and molecular sieve 13X were higher than those of activated carbon and activated alumina. Percentage loss of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but that of activated carbon and activated alumina were 8.3% and 8.1%, respectively. Overall attrition rate constant (Ka) of activated alumina and activated carbon were lower than other sorbents. Introduction In 1997, more than 160 nations negotiated binding limitations on green house gases for developed nations in Kyoto, Japan. In Kyoto protocol, the developed nations agreed to limit their green house gas emissions relative to the levels emitted in 1990. A number of techniques have been used for separation of carbon dioxide from flue gas streams. Among these techniques, chemical absorption has been commercially operated. The chemical absorption process can control carbon dioxide with high removal efficiency, but it needs intensive energy for carbon dioxide removal and has a problem with corrosion. Therefore, fluidized bed is known as a proper process to control high volumes of flue gases, and dry sorbents can be used to cut down the operating cost, so the use of dry sorbents in a fluidized bed may remove carbon dioxide economically. However, this technique is required for developments of the fluidized bed process with dry sorbents which have low attrition and high adsorption capacity for carbon dioxide. Therefore, in this study, activated carbon, activated alumina, molecular sieve 5A, and molecular sieve 13X were used as dry sorbents to control carbon dioxide in a fluidized bed. In addition, the attrition and percentage loss of adsorption capacity of the dry sorbents were investigated.
550
Experimental Apparatus and procedure for attrition experiment. Three-hole air jets used by Gwyn on the basis of a research of Forsythe and Hertwig were used to investigate attrition of dry sorbent with fluidization. Air was supplied from a compressor, moisture and particles in the air are removed passing a trap, and air flow rate was controlled by mass flow controller (5850E, Brooks Co.). The dry sorbents after the attrition were collected, then the particle sizes of them were measured by sieves of 60, 80, and 140 mesh. Apparatus and procedure for adsorption experiment. An experimental fluidized bed reactor has a 2.5 cm in diameter and 230 cm in height, and the distributor has 32 holes and each hole was 2 mm in diameter. 200 mesh net was put on the distributor to prevent particles from falling down. The cyclone was made by standard proportion to collect fine particles. Air flow rate was controlled by a flow meter, CO2 (99.9%) flow rate was controlled by mass flow controller and then 10% CO2 inlet concentration was maintained by mixing in a mixing chamber. CO2 outlet concentration was also measured by CO2 analyzer (CD 95, Geotechnical instruments, England). Results and Discussion Fig. 1 shows that minimum fluidization velocities of activated carbon, activated alumina, molecular sieve 5A and molecular sieve 13X are 8.0 cm/s, 8.5 cm/s, 6.2 cm/s and 6.5 cm/s, respectively. Also, theoretical calculation values of minimum fluidization velocity and terminal velocity of each dry sorbent were summarized in Table 1. The remaining weight of dry sorbents with time is shown in Fig. 2. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and AI test on the basis of the weight after 5 hours shows that AIs of molecular sieve 5A and molecular sieve 13X presented 2.1~4.0 times higher than those of activated carbon and activated alumina. Therefore, the use of molecular sieve 5A and 13X in a fluidized bed can cause high maintenance cost and problems in the operating the process. 3.5 50
45
2.5 Remainingweight(g)
Pressure drop (mbar)
3.0
2.0 1.5 1.0
- - >-Activated Activated carbon carbon - • Molecular Molecular Sieve Sieve 13x 13x _. ±.Molecular Molecular Sieve SA 5A - - ».Activated Alumina Alumina
0.5
40
Activated carbon •Activated •Activated Activated alumina * Molecular Molecular sieve sieve 5A • Molecular Molecular sieve sieve 13X 13X
35
30
0.0 0
5
10 10
15 15
20
0
10
20
Table 1. minimum fluidization velocity and terminal velocity of dry sorbents Mean
40
Fig. 2. The remaining weight with time for attrition of dry sorbents.
Fig.l Minimum fluidiztion velocity for dry sorbents with gas velocity.
Dry sorbent
30
(hr) Time (h r)
Gas Velocity (cm/s)
Density
J
mf,exp.
551
Size(/™)
(g/cm3)
(cm/s)
Wen&Yu
Richardson
Activated carbon
326.0
2.79
8.0
9.4
Molecular sieve 5A
326.0
2.47
6.2
8.3
Molecular sieve 13X
326.0
2.51
6.5
Activated Alumina
326.0
2.88
8.5
Chitester
(cm/s)
10.8
13.1
191.7
9.6
11.7
177.9
8.5
9.8
11.8
179.7
9.7
11.2
13.5
195.4
Adsorbed amount (mmol/g)
4
• Before Before attrition attrition • After After attrition attrition - Percentage Percentage loss loss of adsorption adsorption capacity 15
3 10 2
5 1
0
0 Activated carbon
Activated alumina
Molecular sieve 5A
Molecular sieve 13X
Dry sorbents
Fig. 3. Percentage loss of adsorption capacity by attrition with dry sorbents.
Remaining weight (g)
20
5
Percentage loss of adsorption capacity (%)
CO2 adsorption capacities with dry sorbents before and after attrition were shown in Fig.3. We found variation of CO2 adsorption capacity during operation by examining effect of attrition on adsorption capacity. So, adsorption experiments for each sorbent fluidized for 30hours were carried out. As a result, percentage losses of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but those of activated carbon and activated alumina were 8.3% and 8.1% respectively. This is because retention time of molecular sieve 5A and molecular 13X decreased due to elutriation of particle generated from attrition. Gas velocity is an important operating condition in the fluidized bed process and it can highly affect the attrition of dry sorbents. Therefore, the weight remaining in the bed with fluidization time for gas velocity of 20.59 cm/s, 25.74 cm/s, and 30.89 cm/s was measured to estimate the attrition of dry sorbent with gas velocity. As shown in Fig. 4, attrition mainly occurred in the early stage of fluidization. The attrition rate with time decreased and the regression equations fit natural log functions. In addition, Fig. 4 shows that the attrition of dry sorbents is highly affected by gas velocity in the fluidized bed process. Table 2 summaries overall attrition rate constants (Ka) and physical properties for each dry sorbent. As shown in Table 2, Ka of activated alumina was the lower than any other sorbent, but was similar to activated carbon. However, we used activated carbon as dry sorbent to control CO2 because it is the most cost-effective among others. Table 3 summaries Ka for activated carbon. The value of Ka presented 4.032 X10"5, 9.184 X10"5,1.980 xiO"4 with each gas velocity and the value of Ka increased with increasing gas velocity. 50
45
40
• 20.59c 2059c m/s m/s • 25.74c 25.74cm/s m/s 30.89c m/s m/s
35
30 0
10
20
30
40
Time Tim e ((hr) hr )
Fig. 4. The remaining weight with time for attrition of 40/60 mesh activated carbon at different gas velocities.
Table 2. Summary of attrition rate constants for dry sorbents at gas velocity of 20.59 cm/s
552
Sorbent
BET
Pore Volume
Pore Diameter
Mean Size
Density
(nr/g)
(cm /g)
(A)
(um)
(g/cm3)
(cm2/s3)
Activated Carbon
1142
0.58
20.3
326
2.79
4.032 X1O"S
Activated
275
0.34
48.8
326
2.88
3.824 XI0' 5
Molecular Sieve 5A
394
0.31
31.6
326
2.47
7.169 X10"s
Molecular Sieve 13X
480
0.34
28.6
326
2.51
7.863 X10"5
Alumina
3
Table 3. Summary of attrition rate constants for activated carbon at different gas velocities. Gas velocity (cm/s) Ka (cmV) 20.59 25.74 30.89
4.032 X10"5 9.184 X10'5 1.980 x i 0"4
Conclusion In the fluidized bed process, attrition caused dry sorbent to be carryover. This mainly occurred in the early stage of fluidization and was highly affected by gas velocity. The amount of attrition of molecular sieve 5 A and molecular sieve 13X were larger than those of activated carbon and activated alumina. In addition, percentage losses of adsorption capacities of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, whereas those of activated carbon and activated alumina were 8.3% and 8.1%, respectively. This is because retention time of molecular sieve 5A and molecular 13X decreased due to elutriation of particle generated from attrition. Also, Ka of activated alumina and activated carbon were the lower than those of Molecular sieve 13X and 5A. Consequently, molecular sieve 5A and molecular 13X could cause high maintenance cost for dry sorbent and problems in the operation of fluidized bed process. Acknowledgement This research was supported by a grant (DA2-201) from Carbon Dioxide Reduction & Sequestration Research Center, one of the 21st Century Frontier Programs funded by the Ministry of Science and Technology of Korean government. References [1] Hoffman, J. S., Pennline, H. W.; J. Energ. & Environ. Res., U.S.A, Pittsburgh, 1(1), (2001), pp. 90-100. [2] Forsythe, W. L. and Hertwig, W. R., "Attrition characteristics of fluid cracking catalyst," Ind. Eng. Chem.,(1949),41,pp. 1200-1206. [3] Daizo Kunii, Octave Levenspiel, Fluidization Engineering second edition, (1991). [4] Lin cy, Wey My, Korean Journal of Chemical Engineering, Republic of Korea, Seoul, 22(1), (2005), pp. 154-160. [5] S. J. Son, J. S. Choi and K. Y. Choo, Korean Journal of Chemical Engineering, Republic of Korea, Seoul, 22(2), (2005), pp. 291-297. [6] S.S. Lee, J.S. Yoo, G.H. Moon, S.W. Park, D.W. Park, K.J. Oh, Am. Chem. Soc, Div. Fuel Chem. U.S.A., Washington, 48(2), (2003).
549
Attrition and CO2 adsorption of dry sorbents in fluidized bed Ki Chul Choa, Eun Yong Leea, Jeong Suk Yoob, Young Hean Choung \Sang Woo Parkc and Kwang Joong Oha* a
Department of Environmental Engineering, Pusan National University, San 30 jangjeondong, Guemjeong-gu, Busan 609-735, Republic of Korea b Doosan Heavy Industries & Construction Co. Ltd., R&D Center, 555 Gwigok-dong, Changwon, Gyeongnam 641-792 , Republic of Korea c Department of Chemical Engineering, Pusan National University, 30 jangjeon-dong, Guemjeong-gu, Busan 609-735, Korea (e-mail: [email protected])
Abstract Characteristics of attrition and adsorption were investigated to remove CO2 in fluidized bed using activated carbon, activated alumina, molecular sieve 5 A and molecular sieve 13X. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and attrition indexs(AI) of molecular sieve 5A and molecular sieve 13X were higher than those of activated carbon and activated alumina. Percentage loss of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but that of activated carbon and activated alumina were 8.3% and 8.1%, respectively. Overall attrition rate constant (Ka) of activated alumina and activated carbon were lower than other sorbents. Introduction In 1997, more than 160 nations negotiated binding limitations on green house gases for developed nations in Kyoto, Japan. In Kyoto protocol, the developed nations agreed to limit their green house gas emissions relative to the levels emitted in 1990. A number of techniques have been used for separation of carbon dioxide from flue gas streams. Among these techniques, chemical absorption has been commercially operated. The chemical absorption process can control carbon dioxide with high removal efficiency, but it needs intensive energy for carbon dioxide removal and has a problem with corrosion. Therefore, fluidized bed is known as a proper process to control high volumes of flue gases, and dry sorbents can be used to cut down the operating cost, so the use of dry sorbents in a fluidized bed may remove carbon dioxide economically. However, this technique is required for developments of the fluidized bed process with dry sorbents which have low attrition and high adsorption capacity for carbon dioxide. Therefore, in this study, activated carbon, activated alumina, molecular sieve 5A, and molecular sieve 13X were used as dry sorbents to control carbon dioxide in a fluidized bed. In addition, the attrition and percentage loss of adsorption capacity of the dry sorbents were investigated.
550
Experimental Apparatus and procedure for attrition experiment. Three-hole air jets used by Gwyn on the basis of a research of Forsythe and Hertwig were used to investigate attrition of dry sorbent with fluidization. Air was supplied from a compressor, moisture and particles in the air are removed passing a trap, and air flow rate was controlled by mass flow controller (5850E, Brooks Co.). The dry sorbents after the attrition were collected, then the particle sizes of them were measured by sieves of 60, 80, and 140 mesh. Apparatus and procedure for adsorption experiment. An experimental fluidized bed reactor has a 2.5 cm in diameter and 230 cm in height, and the distributor has 32 holes and each hole was 2 mm in diameter. 200 mesh net was put on the distributor to prevent particles from falling down. The cyclone was made by standard proportion to collect fine particles. Air flow rate was controlled by a flow meter, CO2 (99.9%) flow rate was controlled by mass flow controller and then 10% CO2 inlet concentration was maintained by mixing in a mixing chamber. CO2 outlet concentration was also measured by CO2 analyzer (CD 95, Geotechnical instruments, England). Results and Discussion Fig. 1 shows that minimum fluidization velocities of activated carbon, activated alumina, molecular sieve 5A and molecular sieve 13X are 8.0 cm/s, 8.5 cm/s, 6.2 cm/s and 6.5 cm/s, respectively. Also, theoretical calculation values of minimum fluidization velocity and terminal velocity of each dry sorbent were summarized in Table 1. The remaining weight of dry sorbents with time is shown in Fig. 2. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and AI test on the basis of the weight after 5 hours shows that AIs of molecular sieve 5A and molecular sieve 13X presented 2.1~4.0 times higher than those of activated carbon and activated alumina. Therefore, the use of molecular sieve 5A and 13X in a fluidized bed can cause high maintenance cost and problems in the operating the process. 3.5 50
45
2.5 Remainingweight(g)
Pressure drop (mbar)
3.0
2.0 1.5 1.0
- - >-Activated Activated carbon carbon - • Molecular Molecular Sieve Sieve 13x 13x _. ±.Molecular Molecular Sieve SA 5A - - ».Activated Alumina Alumina
0.5
40
Activated carbon •Activated •Activated Activated alumina * Molecular Molecular sieve sieve 5A • Molecular Molecular sieve sieve 13X 13X
35
30
0.0 0
5
10 10
15 15
20
0
10
20
Table 1. minimum fluidization velocity and terminal velocity of dry sorbents Mean
40
Fig. 2. The remaining weight with time for attrition of dry sorbents.
Fig.l Minimum fluidiztion velocity for dry sorbents with gas velocity.
Dry sorbent
30
(hr) Time (h r)
Gas Velocity (cm/s)
Density
J
mf,exp.
551
Size(/™)
(g/cm3)
(cm/s)
Wen&Yu
Richardson
Activated carbon
326.0
2.79
8.0
9.4
Molecular sieve 5A
326.0
2.47
6.2
8.3
Molecular sieve 13X
326.0
2.51
6.5
Activated Alumina
326.0
2.88
8.5
Chitester
(cm/s)
10.8
13.1
191.7
9.6
11.7
177.9
8.5
9.8
11.8
179.7
9.7
11.2
13.5
195.4
Adsorbed amount (mmol/g)
4
• Before Before attrition attrition • After After attrition attrition - Percentage Percentage loss loss of adsorption adsorption capacity 15
3 10 2
5 1
0
0 Activated carbon
Activated alumina
Molecular sieve 5A
Molecular sieve 13X
Dry sorbents
Fig. 3. Percentage loss of adsorption capacity by attrition with dry sorbents.
Remaining weight (g)
20
5
Percentage loss of adsorption capacity (%)
CO2 adsorption capacities with dry sorbents before and after attrition were shown in Fig.3. We found variation of CO2 adsorption capacity during operation by examining effect of attrition on adsorption capacity. So, adsorption experiments for each sorbent fluidized for 30hours were carried out. As a result, percentage losses of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but those of activated carbon and activated alumina were 8.3% and 8.1% respectively. This is because retention time of molecular sieve 5A and molecular 13X decreased due to elutriation of particle generated from attrition. Gas velocity is an important operating condition in the fluidized bed process and it can highly affect the attrition of dry sorbents. Therefore, the weight remaining in the bed with fluidization time for gas velocity of 20.59 cm/s, 25.74 cm/s, and 30.89 cm/s was measured to estimate the attrition of dry sorbent with gas velocity. As shown in Fig. 4, attrition mainly occurred in the early stage of fluidization. The attrition rate with time decreased and the regression equations fit natural log functions. In addition, Fig. 4 shows that the attrition of dry sorbents is highly affected by gas velocity in the fluidized bed process. Table 2 summaries overall attrition rate constants (Ka) and physical properties for each dry sorbent. As shown in Table 2, Ka of activated alumina was the lower than any other sorbent, but was similar to activated carbon. However, we used activated carbon as dry sorbent to control CO2 because it is the most cost-effective among others. Table 3 summaries Ka for activated carbon. The value of Ka presented 4.032 X10"5, 9.184 X10"5,1.980 xiO"4 with each gas velocity and the value of Ka increased with increasing gas velocity. 50
45
40
• 20.59c 2059c m/s m/s • 25.74c 25.74cm/s m/s 30.89c m/s m/s
35
30 0
10
20
30
40
Time Tim e ((hr) hr )
Fig. 4. The remaining weight with time for attrition of 40/60 mesh activated carbon at different gas velocities.
Table 2. Summary of attrition rate constants for dry sorbents at gas velocity of 20.59 cm/s
552
Sorbent
BET
Pore Volume
Pore Diameter
Mean Size
Density
(nr/g)
(cm /g)
(A)
(um)
(g/cm3)
(cm2/s3)
Activated Carbon
1142
0.58
20.3
326
2.79
4.032 X1O"S
Activated
275
0.34
48.8
326
2.88
3.824 XI0' 5
Molecular Sieve 5A
394
0.31
31.6
326
2.47
7.169 X10"s
Molecular Sieve 13X
480
0.34
28.6
326
2.51
7.863 X10"5
Alumina
3
Table 3. Summary of attrition rate constants for activated carbon at different gas velocities. Gas velocity (cm/s) Ka (cmV) 20.59 25.74 30.89
4.032 X10"5 9.184 X10'5 1.980 x i 0"4
Conclusion In the fluidized bed process, attrition caused dry sorbent to be carryover. This mainly occurred in the early stage of fluidization and was highly affected by gas velocity. The amount of attrition of molecular sieve 5 A and molecular sieve 13X were larger than those of activated carbon and activated alumina. In addition, percentage losses of adsorption capacities of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, whereas those of activated carbon and activated alumina were 8.3% and 8.1%, respectively. This is because retention time of molecular sieve 5A and molecular 13X decreased due to elutriation of particle generated from attrition. Also, Ka of activated alumina and activated carbon were the lower than those of Molecular sieve 13X and 5A. Consequently, molecular sieve 5A and molecular 13X could cause high maintenance cost for dry sorbent and problems in the operation of fluidized bed process. Acknowledgement This research was supported by a grant (DA2-201) from Carbon Dioxide Reduction & Sequestration Research Center, one of the 21st Century Frontier Programs funded by the Ministry of Science and Technology of Korean government. References [1] Hoffman, J. S., Pennline, H. W.; J. Energ. & Environ. Res., U.S.A, Pittsburgh, 1(1), (2001), pp. 90-100. [2] Forsythe, W. L. and Hertwig, W. R., "Attrition characteristics of fluid cracking catalyst," Ind. Eng. Chem.,(1949),41,pp. 1200-1206. [3] Daizo Kunii, Octave Levenspiel, Fluidization Engineering second edition, (1991). [4] Lin cy, Wey My, Korean Journal of Chemical Engineering, Republic of Korea, Seoul, 22(1), (2005), pp. 154-160. [5] S. J. Son, J. S. Choi and K. Y. Choo, Korean Journal of Chemical Engineering, Republic of Korea, Seoul, 22(2), (2005), pp. 291-297. [6] S.S. Lee, J.S. Yoo, G.H. Moon, S.W. Park, D.W. Park, K.J. Oh, Am. Chem. Soc, Div. Fuel Chem. U.S.A., Washington, 48(2), (2003).