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CO2 Recovery Pilot Plant
Studies in Surface Science and Catalysis 153 S.-E. Park, J.-S. Chang and K.-W. Lee (Editors) ©2004 Published by ElsevierB.V.
397
CO 2 Recovery Pilot Plant Kyoung Ryong Jang*, Jun Han Kim, Jae Goo Shim, Young Mo Ahn and Hee Moon Eum Radiation and Environment Group, Korea Electric Power Research Institute, 103-16 Munjidong, Yuseong-gu, Daejeon 305-380, South Korea
The pilot plant in this study was using the recycle separation process adopted the absorption and stripping. Recovery of CO2, one of the main parameters, was experimented at different temperatures and flow rates of flue gas and absorbent, Monoethanolamine(MEA). When the temperature of flue gas was increased by 10°C from 30 °C to 40 °C, CO2 recovery ratio was decreased by around 5%. When the flow rate of flue gas was increased to 690m3/hr, equivalent to 120% of design value of pilot plant, CO2 recovery ratio was decreased by around 15%. CO2 recovery ratio was maintained stably at both 15wt% and 25wt% of MEA concentration over 2.5 m /hr of MEA flow rate. 1. INTRODUCTION It is well known that global warming caused by increase of greenhouse gas like CO2 and CH4 in the air gives many ill effects to the earth. IPCC joint-established in 1988 by UN Environmental Plan(UNEP) and World Meteorology Organization(WMO) with the aim of preparing countermeasures for global climate change, predicted uprise of geo-surface temperature by 1.0-3.5 °C and of sea level by 15 ~ 95 cm in the report on Global Climate Change in July, 1997 [1]. To keep current energy system effectively and abate CO2, the unavoidable byproduct from industrial activities, it is essential to develop related technologies. Around the world, many researches to seek for the solution to reduce CO2 are under way, but yet such an effective method as not to affect industrial productivity has not developed. Of the CO2 abatement methods under research, it is known that chemical absorption process is suitable when CO2 concentration in flue gas is comparatively low(about 10% or so) as thermal power plants emit. CO2 separation process using chemical absorption
* Corresponding author. Tel. : +82-42-865-5480 ; Fax : +82-42-865-5504 E-mail address : [email protected]
398
has some problems, for example, deterioration of absorbent, corrosion of equipment, and high energy consumption. So many researchers have tried to solve this obstacles developing new style of absorbents [2]. In this study with the long term goal of being a commercialization of CO2 absorptionseparation technology, a pilot plant with the capacity of 2 ton CCVday using chemical absorption process was constructed to separate CO2 from flue gas of a thermal power plant. MEA(Monoethanolamine) was used as an absorbent and evaluated of its absorption characteristics in a series of experiments giving some kinds of variations like temperature and flow rate of MEA, temperature and rate of flue gas, and MEA concentrations [3-4]. 2. EXPERIMENTAL 2.1 Experimental pilot plant The pilot plant used in the study was followed by the general recycle separation process adopted the absorption and stripping. And this unit was constructed near unit 5 of Seoul Thermal Power Plant in order to use the real flue gas (Fig. 1). Absorber is 18.8m high and 0.46m in diameter, and stripper is 16.7m high and 0.34m in diameter, of which capacity is equivalent to treat 2 ton CO2 per day. Describing the process, flue gas was injected to the bottom of the absorber by blower and then reacted with MEA, while treated flue gas was discharged to the existing stack through the top of absorber. MEA was injected to the top of the absorber to react with flue gas. MEA solution after reaction with CO2 (rich amine) was collected in the bottom of the absorber, and then pumped to the top of the stripper, where it was separated into MEA and CO2. Separated CO2 can be either converted into various high value-added compounds or transferred for storage. CO2 separated MEA solution (lean amine) passed through the heat exchanger and the filter, and recycled into the absorber to react with CO2 again. A certain amount of packing materials was filled in the absorber to allow CO2 and MEA to contact effectively as well as to increase the residence time. Stripper was also filled with packing materials so as to make easy separation as a washing zone. This was done by heating the solution at the reboiler located on the bottom of the stripper. Cooling equipment was installed in front of the absorber to maintain the proper experimental temperatures. Control system is installed for adjusting the main accessories and equipments, and whose remote indicators were enable to monitor and control through computer. 2.2 Experimental method MEA, the CO2 absorbent, its concentration was adjusted to the experimental condition by adding pure water. Flue gas used in the study was real and made from the thermal power plant. CO2 concentration of the flue gas streamed into the pilot plant was analyzed as a real
399
time by ND-IR typed analyzer before entering the absorber, after reacting with MEA inside the absorber. CO2 recovery ratios were calculated from the differences. And also MEA solution before and after reaction were sampled and analyzed to check the loading values for lean and rich amine by the acid-base neutralization titration method.
Fig. 1. Schematic diagram of pilot plant.
3. RESULTS AND DISCUSSION 3.1. Effects of MEA temperature and flow rate Fig. 2 shows CO2 recovery ratios to MEA temperature and MEA flow rate at 15% wt MEA concentration. The lower was the temperature of MEA, the higher was the CO2 recovery ratio. It is highly estimated that it is caused that the reaction of CO2 with MEA is an exothermic process which the reaction was active at low temperature. CO2 loadings of lean and rich amine to flow rates of MEA were like Fig. 3. This shows the highest CO2 loading was around 0.66 at the flue rate of 2.0m3/hr. But the optimum of loading is needed to control less than 0.6 because it is known that corrosivity increase as loading goes higher[5-6]. CO2 loading means CO2 moles absorbed per 1 mole MEA. Generally CO2 loading of rich amine is the loading of residual MEA after reaction with CO2 in the absorber, and CO2 loading of lean amine is a value after MEA was separated from CO2 in the stripper. As for rich amine, MEA, which is the primary amine, reacts theoretically with 0.5-1.0 mole CO2 per 1 mole MEA, according to final products, either carbamate or bicarbonate[7-10].
400
Fig. 2. CO2 recovery ratios on MEA flow rate and temperature.
Fig. 3. CO2 loading of lean and rich amine on MEA flow rate and temperature.
401
3.2 Effects of flue gas temperature and flow rate Temperature and flow rate of flue gas are the fundamental parameters which should be obtained when designing and operating the pilot plant. So the effects of CO2 recovery ratio from those two parameters were checked. These experiments had been done at the gas volume between 570m3/hr and 690m3/hr. Fig. 4 shows the CO2 recovery ratios to flow rates of flue gas at the temperature of flue gas 40 °C. And this also does CO2 recovery ratios were more than 90% until flue gas flow rate went to 640m3/hr. And CO2 loadings didn't change a lot compared to the changes of CO2 recovery ratio.
Fig. 4. CO2 recovery ratio and loading on flow rate of flue gas at 40 °C.
Fig. 5 shows CO2 recovery ratios on flue gas flow rate and temperatures, 30°Cand 40 °C. In the above experiments about CO2 recovery ratio to the different MEA temperature, the change between the two items was not so big. But in this experiment, when the flue gas temperature was increased to 40 °C, CO2 recovery ratio was decreased very sharply, and when the flue gas flow rate was increased, CO2 recovery ratio was decreased also a lot. It is possible to assume that the quantity of flue gas flow rate gave bigger effects to the process more than MEA concentration did.
402
Fig. 5. CO2 recovery ratio on flow rate of flue gas at 3 0 °C and 40 "C.
3.3. Effects of MEA concentration Absorbent has more economic advantages when it absorbs CO2 gas more at the similar operation conditions. In this experiment, CO2 recovery ratio and amine loading were examined at various MEA concentrations, 10wt%, 15wt%, and 25wt%. As in Fig. 6, 15wt% and 25wt% MEA concentration showed more than 90% of CO2 recovery ratio over 2.5m3/hr of MEA flow rate. At the 10wt% MEA, CO2 recovery ratio had much lower values compared to the other MEA concentrations, but this ratio was gotten over 95% especially when MEA flow rate was increased to far over 3.0 m /hr. CO2 loadings of lean amine and rich amine at various concentrations are presented in Fig. 7. MEA concentration of 10wt% and 15wt% showed similar pattern to the variation of loading. At 2.0 m3/hr of MEA flow rate, CO2 loading of rich amine went over 0.65 which regarded as higher value for the corrosion. And 25wt% MEA showed the most stable results in CO2 loading to flow rate.
403
Fig. 6. CO2 recovery ratio on MEA flow rate and concentration.
Fig. 7. CO2 loading of lean- and rich-amine on MEA flow rate and concentration.
4. CONCLUSIONS Using a pilot plant for absorption and separation of CO2, a series of experiments with real flue
404
gas from a thermal power plant were carried out and the conclusions are as follows. 1) Recovery of CO2 was experimented at different temperatures and flow rates of flue gas and absorbent, MEA. When the temperature of flue gas was increased by 10°C from 30 °C to 40 °C, CO2 recovery ratio was decreased by around 5%. When the flow rate of flue gas was increased to 690m3/hr, equivalent to 120% of design value of pilot plant, CO2 recovery ratios was decreased by around 15%. As for MEA, the absorbent, when its temperature was varied to 40 °C, 45 °C, and 50 °C, CO2 recovery ratios decreased in proportion to flow rate. This means that temperature and flow rate of flue gas, rather than those of MEA, give more effects to CO2 recovery ratios. 2) More than 95% of CO2 recovery ratio was maintained stably at both 15wt% and 25wt% of MEA concentration over 2.5 m3/hr of MEA flow rate. On the other hand, it didn't reach 95% until MEA flow rate became over 3.0 m3/hr, at 10wt% MEA concentration. As for CO2 loadings, all the concentrations didn't give good values at the standpoint of corrosion problem below 2.5m3/hr of MEA flow. And about the 25wt% of MEA concentration, lean amine had a too high CO2 loading which shows low CO2 absorption. So all things considered, the optimal MEA concentration and flow rate is 15wt% and 3.0m /hr, respectively, considering both CO2 recovery ratio and loading value. ACKNOWLEDGMENTS This work was supported by Korea Energy Management Corporation R&D headquarter, Grant 2000-C-CD02-P-01, and by Korea Electric Power Corporation. REFERENCES 1. IPCC, The Regional Impacts of Climate Change : An Assessment of Vulnerability, (1997). 2. Chakma, A. and Tontiwachwuthikul, P., Greenhouse Gas Control Technologies, (1999) 35. 3. Kohl, A. L. and Riesenfied, F. C , Gulf Publishing Co., Houston, (1979) 28. 4. Mimura, T., Simayoshi, H., Suda, T., Iijima, M. and Mituoka, S., Energy Convers. Mgmt, 38(1997)s57. 5. Veawab, A., Tontiwachwuthikul, P. and Bhole, S. D., Ind. Eng. Chem. Res., 36(1) (1997) 264. 6. Mimura, T., Shimojo, S., Kagaku Kogaku Ronbunshu, 21(3) (1995) 478. 7. Caplow, M., J. Am. Chem. Soc, 90 (1968) 6795. 8. Danckwerts, P. V., Chem. Eng. Sci., 34 (1979) 443. 9. Xu, S., Wang, Y. W., Otto, F. D., and Mather, A. E., Chem. Eng. Sci., 51 (1996) 841. 10. Sharma, M. M., Trans. Faraday Soc, 61 (1965) 681.
397
CO 2 Recovery Pilot Plant Kyoung Ryong Jang*, Jun Han Kim, Jae Goo Shim, Young Mo Ahn and Hee Moon Eum Radiation and Environment Group, Korea Electric Power Research Institute, 103-16 Munjidong, Yuseong-gu, Daejeon 305-380, South Korea
The pilot plant in this study was using the recycle separation process adopted the absorption and stripping. Recovery of CO2, one of the main parameters, was experimented at different temperatures and flow rates of flue gas and absorbent, Monoethanolamine(MEA). When the temperature of flue gas was increased by 10°C from 30 °C to 40 °C, CO2 recovery ratio was decreased by around 5%. When the flow rate of flue gas was increased to 690m3/hr, equivalent to 120% of design value of pilot plant, CO2 recovery ratio was decreased by around 15%. CO2 recovery ratio was maintained stably at both 15wt% and 25wt% of MEA concentration over 2.5 m /hr of MEA flow rate. 1. INTRODUCTION It is well known that global warming caused by increase of greenhouse gas like CO2 and CH4 in the air gives many ill effects to the earth. IPCC joint-established in 1988 by UN Environmental Plan(UNEP) and World Meteorology Organization(WMO) with the aim of preparing countermeasures for global climate change, predicted uprise of geo-surface temperature by 1.0-3.5 °C and of sea level by 15 ~ 95 cm in the report on Global Climate Change in July, 1997 [1]. To keep current energy system effectively and abate CO2, the unavoidable byproduct from industrial activities, it is essential to develop related technologies. Around the world, many researches to seek for the solution to reduce CO2 are under way, but yet such an effective method as not to affect industrial productivity has not developed. Of the CO2 abatement methods under research, it is known that chemical absorption process is suitable when CO2 concentration in flue gas is comparatively low(about 10% or so) as thermal power plants emit. CO2 separation process using chemical absorption
* Corresponding author. Tel. : +82-42-865-5480 ; Fax : +82-42-865-5504 E-mail address : [email protected]
398
has some problems, for example, deterioration of absorbent, corrosion of equipment, and high energy consumption. So many researchers have tried to solve this obstacles developing new style of absorbents [2]. In this study with the long term goal of being a commercialization of CO2 absorptionseparation technology, a pilot plant with the capacity of 2 ton CCVday using chemical absorption process was constructed to separate CO2 from flue gas of a thermal power plant. MEA(Monoethanolamine) was used as an absorbent and evaluated of its absorption characteristics in a series of experiments giving some kinds of variations like temperature and flow rate of MEA, temperature and rate of flue gas, and MEA concentrations [3-4]. 2. EXPERIMENTAL 2.1 Experimental pilot plant The pilot plant used in the study was followed by the general recycle separation process adopted the absorption and stripping. And this unit was constructed near unit 5 of Seoul Thermal Power Plant in order to use the real flue gas (Fig. 1). Absorber is 18.8m high and 0.46m in diameter, and stripper is 16.7m high and 0.34m in diameter, of which capacity is equivalent to treat 2 ton CO2 per day. Describing the process, flue gas was injected to the bottom of the absorber by blower and then reacted with MEA, while treated flue gas was discharged to the existing stack through the top of absorber. MEA was injected to the top of the absorber to react with flue gas. MEA solution after reaction with CO2 (rich amine) was collected in the bottom of the absorber, and then pumped to the top of the stripper, where it was separated into MEA and CO2. Separated CO2 can be either converted into various high value-added compounds or transferred for storage. CO2 separated MEA solution (lean amine) passed through the heat exchanger and the filter, and recycled into the absorber to react with CO2 again. A certain amount of packing materials was filled in the absorber to allow CO2 and MEA to contact effectively as well as to increase the residence time. Stripper was also filled with packing materials so as to make easy separation as a washing zone. This was done by heating the solution at the reboiler located on the bottom of the stripper. Cooling equipment was installed in front of the absorber to maintain the proper experimental temperatures. Control system is installed for adjusting the main accessories and equipments, and whose remote indicators were enable to monitor and control through computer. 2.2 Experimental method MEA, the CO2 absorbent, its concentration was adjusted to the experimental condition by adding pure water. Flue gas used in the study was real and made from the thermal power plant. CO2 concentration of the flue gas streamed into the pilot plant was analyzed as a real
399
time by ND-IR typed analyzer before entering the absorber, after reacting with MEA inside the absorber. CO2 recovery ratios were calculated from the differences. And also MEA solution before and after reaction were sampled and analyzed to check the loading values for lean and rich amine by the acid-base neutralization titration method.
Fig. 1. Schematic diagram of pilot plant.
3. RESULTS AND DISCUSSION 3.1. Effects of MEA temperature and flow rate Fig. 2 shows CO2 recovery ratios to MEA temperature and MEA flow rate at 15% wt MEA concentration. The lower was the temperature of MEA, the higher was the CO2 recovery ratio. It is highly estimated that it is caused that the reaction of CO2 with MEA is an exothermic process which the reaction was active at low temperature. CO2 loadings of lean and rich amine to flow rates of MEA were like Fig. 3. This shows the highest CO2 loading was around 0.66 at the flue rate of 2.0m3/hr. But the optimum of loading is needed to control less than 0.6 because it is known that corrosivity increase as loading goes higher[5-6]. CO2 loading means CO2 moles absorbed per 1 mole MEA. Generally CO2 loading of rich amine is the loading of residual MEA after reaction with CO2 in the absorber, and CO2 loading of lean amine is a value after MEA was separated from CO2 in the stripper. As for rich amine, MEA, which is the primary amine, reacts theoretically with 0.5-1.0 mole CO2 per 1 mole MEA, according to final products, either carbamate or bicarbonate[7-10].
400
Fig. 2. CO2 recovery ratios on MEA flow rate and temperature.
Fig. 3. CO2 loading of lean and rich amine on MEA flow rate and temperature.
401
3.2 Effects of flue gas temperature and flow rate Temperature and flow rate of flue gas are the fundamental parameters which should be obtained when designing and operating the pilot plant. So the effects of CO2 recovery ratio from those two parameters were checked. These experiments had been done at the gas volume between 570m3/hr and 690m3/hr. Fig. 4 shows the CO2 recovery ratios to flow rates of flue gas at the temperature of flue gas 40 °C. And this also does CO2 recovery ratios were more than 90% until flue gas flow rate went to 640m3/hr. And CO2 loadings didn't change a lot compared to the changes of CO2 recovery ratio.
Fig. 4. CO2 recovery ratio and loading on flow rate of flue gas at 40 °C.
Fig. 5 shows CO2 recovery ratios on flue gas flow rate and temperatures, 30°Cand 40 °C. In the above experiments about CO2 recovery ratio to the different MEA temperature, the change between the two items was not so big. But in this experiment, when the flue gas temperature was increased to 40 °C, CO2 recovery ratio was decreased very sharply, and when the flue gas flow rate was increased, CO2 recovery ratio was decreased also a lot. It is possible to assume that the quantity of flue gas flow rate gave bigger effects to the process more than MEA concentration did.
402
Fig. 5. CO2 recovery ratio on flow rate of flue gas at 3 0 °C and 40 "C.
3.3. Effects of MEA concentration Absorbent has more economic advantages when it absorbs CO2 gas more at the similar operation conditions. In this experiment, CO2 recovery ratio and amine loading were examined at various MEA concentrations, 10wt%, 15wt%, and 25wt%. As in Fig. 6, 15wt% and 25wt% MEA concentration showed more than 90% of CO2 recovery ratio over 2.5m3/hr of MEA flow rate. At the 10wt% MEA, CO2 recovery ratio had much lower values compared to the other MEA concentrations, but this ratio was gotten over 95% especially when MEA flow rate was increased to far over 3.0 m /hr. CO2 loadings of lean amine and rich amine at various concentrations are presented in Fig. 7. MEA concentration of 10wt% and 15wt% showed similar pattern to the variation of loading. At 2.0 m3/hr of MEA flow rate, CO2 loading of rich amine went over 0.65 which regarded as higher value for the corrosion. And 25wt% MEA showed the most stable results in CO2 loading to flow rate.
403
Fig. 6. CO2 recovery ratio on MEA flow rate and concentration.
Fig. 7. CO2 loading of lean- and rich-amine on MEA flow rate and concentration.
4. CONCLUSIONS Using a pilot plant for absorption and separation of CO2, a series of experiments with real flue
404
gas from a thermal power plant were carried out and the conclusions are as follows. 1) Recovery of CO2 was experimented at different temperatures and flow rates of flue gas and absorbent, MEA. When the temperature of flue gas was increased by 10°C from 30 °C to 40 °C, CO2 recovery ratio was decreased by around 5%. When the flow rate of flue gas was increased to 690m3/hr, equivalent to 120% of design value of pilot plant, CO2 recovery ratios was decreased by around 15%. As for MEA, the absorbent, when its temperature was varied to 40 °C, 45 °C, and 50 °C, CO2 recovery ratios decreased in proportion to flow rate. This means that temperature and flow rate of flue gas, rather than those of MEA, give more effects to CO2 recovery ratios. 2) More than 95% of CO2 recovery ratio was maintained stably at both 15wt% and 25wt% of MEA concentration over 2.5 m3/hr of MEA flow rate. On the other hand, it didn't reach 95% until MEA flow rate became over 3.0 m3/hr, at 10wt% MEA concentration. As for CO2 loadings, all the concentrations didn't give good values at the standpoint of corrosion problem below 2.5m3/hr of MEA flow. And about the 25wt% of MEA concentration, lean amine had a too high CO2 loading which shows low CO2 absorption. So all things considered, the optimal MEA concentration and flow rate is 15wt% and 3.0m /hr, respectively, considering both CO2 recovery ratio and loading value. ACKNOWLEDGMENTS This work was supported by Korea Energy Management Corporation R&D headquarter, Grant 2000-C-CD02-P-01, and by Korea Electric Power Corporation. REFERENCES 1. IPCC, The Regional Impacts of Climate Change : An Assessment of Vulnerability, (1997). 2. Chakma, A. and Tontiwachwuthikul, P., Greenhouse Gas Control Technologies, (1999) 35. 3. Kohl, A. L. and Riesenfied, F. C , Gulf Publishing Co., Houston, (1979) 28. 4. Mimura, T., Simayoshi, H., Suda, T., Iijima, M. and Mituoka, S., Energy Convers. Mgmt, 38(1997)s57. 5. Veawab, A., Tontiwachwuthikul, P. and Bhole, S. D., Ind. Eng. Chem. Res., 36(1) (1997) 264. 6. Mimura, T., Shimojo, S., Kagaku Kogaku Ronbunshu, 21(3) (1995) 478. 7. Caplow, M., J. Am. Chem. Soc, 90 (1968) 6795. 8. Danckwerts, P. V., Chem. Eng. Sci., 34 (1979) 443. 9. Xu, S., Wang, Y. W., Otto, F. D., and Mather, A. E., Chem. Eng. Sci., 51 (1996) 841. 10. Sharma, M. M., Trans. Faraday Soc, 61 (1965) 681.