a comparison bewteen co2 gasification of various
A COMPARISON BEWTEEN CO2 GASIFICATION OF VARIOUS BIOMASS CHARS AND CO2 GASIFICATION OF COAL CHAR F. YANG *, Y. HU *a, F. ZHOU*, D. CHEN* *Thermal & Environment Engineering Institute, School of Mechanical Engineering, Tongji University, Shanghai, 200092 China a Corresponding author: [email protected]
SUMMARY: In this paper, municipal solid waste(MSW), sewage sludge (SS) and rice straw (RS) were pyrolyzed under N2 atmosphere and at a temperature of 550 and 600 ºC, and then the produced biochars were used for gasification with CO2. The effects of preparation temperature of biomass char, gasification temperature and the ratio of CO2 to C (CO2/C) on the product composition and product yield were studied. The CO2 gasification with coal char was conducted as a baseline for comparison. The CO2 gasification kinetics of the various biomass chars and coal char were determined under CO2 flow in a Thermogravimetric analysis (TGA). The experimental results revealed that gasification behaviours of biomass chars were better than that of coal char, showing as the following order: MSW char > RS char > SS char > coal char. The pyrolysis temperature at which biomass chars were prepared has a clear influence on their gasification behaviours, and 550 ºC is recommended. The gasification temperature has a significant effect on the gasification, and the CO yield was increased with gasification temperature. Considering the energy consumption and CO yield, the recommended gasification temperature for the biomass chars is 900 ºC. With the increase of CO2 / C, the conversion rate of char increases. The optimum value of CO2 / C depends on the material from which the char was derived. The activation energies of CO2 gasification calculated from the TGA data based on the most fitted reaction models showed the following order: coal char> RS char> SS char> MSW char. The CO2 gasification with the biomass char is easier than coal char, which is consistent with the experimental results. The MSW char is probably the best feedstock for CO2 gasification.
1. INTRODUCTION The output of waste, such as municipal solid waste, sewage sludge and agricultural waste, was increased by population growth and economic development. The potential environmental and human health impacts caused the handling and disposal of the ever increasing quantities of these wastes to be the matter of great concern in societies and importance. Cropland application, ocean dumping or landfill disposal are limited, due to the uptake capacity of the soil, high cost of disposal, and potential pollution. For these reasons, incineration has become one of
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
the most promising disposal technique as it can drastically reduce the volume of waste and result in energy recovery. However, Incineration of solid wastes also produces hazardous air pollutants, requiring expensive pollutant reduction units(Jindarom et al., 2007). As an alternative, gasification of wastes is a flexible way to make clean and high efficient utilization of waste, which could transform different kinds of waste into syngas for use of supplying of heat, generation of electricity and production of chemical materials. However, the high content of tar in the syngas produced from the direct waste gaification restrict its wide commercialization. Furthermore, a two-stage process, whose basic principle is to separate the pyrolysis zone from the gasification zone, has been proposed as a method that can significantly reduce tar contents in product gas(Khalil et al., 2009). Air/oxygen, steam and CO2 are commonly selected as a gasifiying agents according to the requirements for the end products quality for different downstream applications(Sansaniwal et al., 2017). The idea of recycling of CO2 stream by directly or indirectly using carbon dioxide from flue gases as a feedstock to produce chemicals, such as synthesis gas, has attracted much interest, because not only could it mitigate greenhouse gas emissions, but also generate new opportunities for the chemical industries(Hurley et al., 2010). The use of carbon dioxide as a gasifying agent yielded a higher concentration of CO and high heating value of the producer gas. However, the chemical reactions involved in the process may require more completion time and the process may be slowness. Many scholars have studied the gasification of biomass char, but most studies are focused on biomass char derived from high temperature (>800 °C) pyrolysis of biomass(Li et al., 2017; Scott et al., 2005; Vamvuka et al., 2012; Xu et al., 2016). However, Min et al. and Morin et al. (Min et al., 2011; Morin et al., 2016) found that the reactivity of CO2 gasification of biomass char decreased with the increase in the pyrolysis temperature. In the research of Xu(Xu, 2017), it was found that the gasification gas yield, carbon conversion efficiency, gasification efficiency and tar yield of gasification of sludge char were gradually decreased with the increase of preparation temperature, and become stable when preparation temperature reached 450 °C. When the preparation temperature of sludge char was above 550 °C, tar in the produced gas of gasification was not detected. Therefore, in this paper, municipal solid waste(MSW), sewage sludge (SS) and rice straw (RS) were pyrolyzed under N2 atmosphere and at a middle temperature of 550 and 600 ºC , and then the produced bio-chars were used for gasification with CO2. The aim of this work was to investigate the possibility of exploitation of various waste materials to energetic uses, combining the recycling of CO2 streams to mitigate greenhouse gas emissions.The effects of preparation temperature of biomass char, gasification temperature and the equivalence ratio (ER) of CO2 to C (CO2/C) on the product composition, low heating value and yield were studied. The CO2 gasification using a coal char, which was commercially used to produce CO by CO2 gasification, was also conducted and taken as a baseline for comparison. The CO2 gasification kinetics of the various biomass chars and coal char were determined under CO2 flow in a Thermogravimetric analysis (TGA).
2. MATERIAL AND METHODS 2.1 Materials Municipal solid waste sample was collected from the local factory, and metals and glass were removed. The initial moisture content is 30.6 wt. %. Dewatered sewage sludge was
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
sampled from an urban wastewater treatment plant with the improved anaerobic–anoxic–oxic process treatment in Shanghai and the moisture content of raw sludge was 83.8 wt. %. Rice straw came from a local cropland, and its moisture content is 10.6 wt. %. The materials were air-dried, homogenized, milled and sieved to a particle size of coal char. 2) The lower pyrolysis temperature at 550 ºC is recommended. 3) The CO yield of char was increased with gasification temperature. Considering the energy consumption and CO yield, the recommended gasification temperature for the biomass chars is 900 ºC. 4) With the increase of CO2 / C, the conversion rate of char increases. The optimum value of CO2 / C depends on the material from which the char was derived. 5) The activation energies of CO2 gasification obtained from the TGA data showed the following
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
order: coal char> RS char> SS char> MSW char. 6)The MSW char is recommoned as the best feedstock for CO2 gasification.
AKNOWLEDGEMENTS The study was supported by Major Projects of China National Water Pollution Control and Treatment Science and Technology (Grant No. 2017ZX07202005) and the China National 863 Plan project (Grant No. 2012AA063504).
REFERENCES Chen F., Hu Y., Dou X., Chen D., Dai X.(2015). Chemical forms of heavy metals in pyrolytic char of heavy metal-implanted sewage sludge and their impacts on leaching behaviors. J. Anal. Appl. Pyrol. 116:152-160. Chen H., Li B., Yang H., Yang G., Zhang S.( 2008). Experimental investigation of biomass gasification in a fluidized bed reactor. Energ. Fuel. 22(5):3493-3498. Hu J.( 2007). Study on CO2 gasification reactivity of coal char by TGA.: Northwest University. 81 p. Hurley S., Li H., Xu C. C.(2010). Effects of impregnated metal ions on air/CO2-gasification of woody biomass. Bioresource Technol. 101(23):9301-9307. Jindarom C., Meeyoo V., Kitiyanan B., Rirksomboon T., Rangsunvigit P.(2007). Surface characterization and dye adsorptive capacities of char obtained from pyrolysis/gasification of sewage sludge. Chem. Eng. J. 133(1–3):239-246. Khalil R., Várhegyi G., Jäschke S., Grønli M. G., Hustad J.(2009). CO2 Gasification of Biomass Chars: A Kinetic Study. Energ. Fuel. 23(1):94-100. Li R., Zhang J., Wang G., Ning X., Wang H., Wang P.(2017). Study on CO2 gasification reactivity of biomass char derived from high-temperature rapid pyrolysis. Appl. Therm. Eng. 121:1022-1031. Min F., Zhang M., Zhang Y., Cao Y., Pan W.(2011). An experimental investigation into the gasification reactivity and structure of agricultural waste chars. J. Anal. Appl. Pyrol. 92(1):250257. Morin M., Pecate S., Hemati M., Kara Y.(2016). Pyrolysis of biomass in a batch fluidized bed reactor: Effect of the pyrolysis conditions and the nature of the biomass on the physicochemical properties and the reactivity of char. J. Anal. Appl. Pyrol. 122:511-523. Nilsson S., Gómez-Barea A., Cano D. F.(2012). Gasification reactivity of char from dried sewage sludge in a fluidized bed. Fuel 92(1):346-353. Nowicki L., Antecka A., Bedyk T., Stolarek P., Ledakowicz S.(2011). The kinetics of gasification of char derived from sewage sludge. J. Therm. Anal. Calorim. 104(2):693-700. Nowicki L., Markowski M.(2015). Gasification of pyrolysis chars from sewage sludge. FUEL 143:476-483. Sansaniwal S. K., Rosen M. A., Tyagi S. K.(2017). Global challenges in the sustainable development of biomass gasification: An overview. Renewable and Sustainable Energy Reviews 80:23-43. Scott S. A., Davidson J. F., Dennis J. S., Fennell P. S., Hayhurst A. N.(2005). The rate of gasification by CO2 of chars from waste. P. Combust. Inst. 30(2):2151-2159. Vamvuka D., Karouki E., Sfakiotakis S., Salatino P.(2012). Gasification of Waste Biomass Chars by Carbon Dioxide via Thermogravimetry-Effect of Catalysts. Combust. Sci. Technol.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
184:64-77. Xiao R., Chen X., Wang F., Yu G.(2010). Pyrolysis pretreatment of biomass for entrained-flow gasification. Appl. Energ. 87(1):149-155. Xu R., Zhang J., Wang G., Zuo H., Zhang P., Shao J.(2016). Gasification behaviors and kinetic study on biomass chars in CO2 condition. Chemical Engineering Research and Design 107:3442. Xu Y.(2017). Study on Characteristics of Sludge Char Gasification and Catalytic Tar Oxidation Reforming., Shanghai: Tongji University.
SUMMARY: In this paper, municipal solid waste(MSW), sewage sludge (SS) and rice straw (RS) were pyrolyzed under N2 atmosphere and at a temperature of 550 and 600 ºC, and then the produced biochars were used for gasification with CO2. The effects of preparation temperature of biomass char, gasification temperature and the ratio of CO2 to C (CO2/C) on the product composition and product yield were studied. The CO2 gasification with coal char was conducted as a baseline for comparison. The CO2 gasification kinetics of the various biomass chars and coal char were determined under CO2 flow in a Thermogravimetric analysis (TGA). The experimental results revealed that gasification behaviours of biomass chars were better than that of coal char, showing as the following order: MSW char > RS char > SS char > coal char. The pyrolysis temperature at which biomass chars were prepared has a clear influence on their gasification behaviours, and 550 ºC is recommended. The gasification temperature has a significant effect on the gasification, and the CO yield was increased with gasification temperature. Considering the energy consumption and CO yield, the recommended gasification temperature for the biomass chars is 900 ºC. With the increase of CO2 / C, the conversion rate of char increases. The optimum value of CO2 / C depends on the material from which the char was derived. The activation energies of CO2 gasification calculated from the TGA data based on the most fitted reaction models showed the following order: coal char> RS char> SS char> MSW char. The CO2 gasification with the biomass char is easier than coal char, which is consistent with the experimental results. The MSW char is probably the best feedstock for CO2 gasification.
1. INTRODUCTION The output of waste, such as municipal solid waste, sewage sludge and agricultural waste, was increased by population growth and economic development. The potential environmental and human health impacts caused the handling and disposal of the ever increasing quantities of these wastes to be the matter of great concern in societies and importance. Cropland application, ocean dumping or landfill disposal are limited, due to the uptake capacity of the soil, high cost of disposal, and potential pollution. For these reasons, incineration has become one of
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
the most promising disposal technique as it can drastically reduce the volume of waste and result in energy recovery. However, Incineration of solid wastes also produces hazardous air pollutants, requiring expensive pollutant reduction units(Jindarom et al., 2007). As an alternative, gasification of wastes is a flexible way to make clean and high efficient utilization of waste, which could transform different kinds of waste into syngas for use of supplying of heat, generation of electricity and production of chemical materials. However, the high content of tar in the syngas produced from the direct waste gaification restrict its wide commercialization. Furthermore, a two-stage process, whose basic principle is to separate the pyrolysis zone from the gasification zone, has been proposed as a method that can significantly reduce tar contents in product gas(Khalil et al., 2009). Air/oxygen, steam and CO2 are commonly selected as a gasifiying agents according to the requirements for the end products quality for different downstream applications(Sansaniwal et al., 2017). The idea of recycling of CO2 stream by directly or indirectly using carbon dioxide from flue gases as a feedstock to produce chemicals, such as synthesis gas, has attracted much interest, because not only could it mitigate greenhouse gas emissions, but also generate new opportunities for the chemical industries(Hurley et al., 2010). The use of carbon dioxide as a gasifying agent yielded a higher concentration of CO and high heating value of the producer gas. However, the chemical reactions involved in the process may require more completion time and the process may be slowness. Many scholars have studied the gasification of biomass char, but most studies are focused on biomass char derived from high temperature (>800 °C) pyrolysis of biomass(Li et al., 2017; Scott et al., 2005; Vamvuka et al., 2012; Xu et al., 2016). However, Min et al. and Morin et al. (Min et al., 2011; Morin et al., 2016) found that the reactivity of CO2 gasification of biomass char decreased with the increase in the pyrolysis temperature. In the research of Xu(Xu, 2017), it was found that the gasification gas yield, carbon conversion efficiency, gasification efficiency and tar yield of gasification of sludge char were gradually decreased with the increase of preparation temperature, and become stable when preparation temperature reached 450 °C. When the preparation temperature of sludge char was above 550 °C, tar in the produced gas of gasification was not detected. Therefore, in this paper, municipal solid waste(MSW), sewage sludge (SS) and rice straw (RS) were pyrolyzed under N2 atmosphere and at a middle temperature of 550 and 600 ºC , and then the produced bio-chars were used for gasification with CO2. The aim of this work was to investigate the possibility of exploitation of various waste materials to energetic uses, combining the recycling of CO2 streams to mitigate greenhouse gas emissions.The effects of preparation temperature of biomass char, gasification temperature and the equivalence ratio (ER) of CO2 to C (CO2/C) on the product composition, low heating value and yield were studied. The CO2 gasification using a coal char, which was commercially used to produce CO by CO2 gasification, was also conducted and taken as a baseline for comparison. The CO2 gasification kinetics of the various biomass chars and coal char were determined under CO2 flow in a Thermogravimetric analysis (TGA).
2. MATERIAL AND METHODS 2.1 Materials Municipal solid waste sample was collected from the local factory, and metals and glass were removed. The initial moisture content is 30.6 wt. %. Dewatered sewage sludge was
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
sampled from an urban wastewater treatment plant with the improved anaerobic–anoxic–oxic process treatment in Shanghai and the moisture content of raw sludge was 83.8 wt. %. Rice straw came from a local cropland, and its moisture content is 10.6 wt. %. The materials were air-dried, homogenized, milled and sieved to a particle size of coal char. 2) The lower pyrolysis temperature at 550 ºC is recommended. 3) The CO yield of char was increased with gasification temperature. Considering the energy consumption and CO yield, the recommended gasification temperature for the biomass chars is 900 ºC. 4) With the increase of CO2 / C, the conversion rate of char increases. The optimum value of CO2 / C depends on the material from which the char was derived. 5) The activation energies of CO2 gasification obtained from the TGA data showed the following
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
order: coal char> RS char> SS char> MSW char. 6)The MSW char is recommoned as the best feedstock for CO2 gasification.
AKNOWLEDGEMENTS The study was supported by Major Projects of China National Water Pollution Control and Treatment Science and Technology (Grant No. 2017ZX07202005) and the China National 863 Plan project (Grant No. 2012AA063504).
REFERENCES Chen F., Hu Y., Dou X., Chen D., Dai X.(2015). Chemical forms of heavy metals in pyrolytic char of heavy metal-implanted sewage sludge and their impacts on leaching behaviors. J. Anal. Appl. Pyrol. 116:152-160. Chen H., Li B., Yang H., Yang G., Zhang S.( 2008). Experimental investigation of biomass gasification in a fluidized bed reactor. Energ. Fuel. 22(5):3493-3498. Hu J.( 2007). Study on CO2 gasification reactivity of coal char by TGA.: Northwest University. 81 p. Hurley S., Li H., Xu C. C.(2010). Effects of impregnated metal ions on air/CO2-gasification of woody biomass. Bioresource Technol. 101(23):9301-9307. Jindarom C., Meeyoo V., Kitiyanan B., Rirksomboon T., Rangsunvigit P.(2007). Surface characterization and dye adsorptive capacities of char obtained from pyrolysis/gasification of sewage sludge. Chem. Eng. J. 133(1–3):239-246. Khalil R., Várhegyi G., Jäschke S., Grønli M. G., Hustad J.(2009). CO2 Gasification of Biomass Chars: A Kinetic Study. Energ. Fuel. 23(1):94-100. Li R., Zhang J., Wang G., Ning X., Wang H., Wang P.(2017). Study on CO2 gasification reactivity of biomass char derived from high-temperature rapid pyrolysis. Appl. Therm. Eng. 121:1022-1031. Min F., Zhang M., Zhang Y., Cao Y., Pan W.(2011). An experimental investigation into the gasification reactivity and structure of agricultural waste chars. J. Anal. Appl. Pyrol. 92(1):250257. Morin M., Pecate S., Hemati M., Kara Y.(2016). Pyrolysis of biomass in a batch fluidized bed reactor: Effect of the pyrolysis conditions and the nature of the biomass on the physicochemical properties and the reactivity of char. J. Anal. Appl. Pyrol. 122:511-523. Nilsson S., Gómez-Barea A., Cano D. F.(2012). Gasification reactivity of char from dried sewage sludge in a fluidized bed. Fuel 92(1):346-353. Nowicki L., Antecka A., Bedyk T., Stolarek P., Ledakowicz S.(2011). The kinetics of gasification of char derived from sewage sludge. J. Therm. Anal. Calorim. 104(2):693-700. Nowicki L., Markowski M.(2015). Gasification of pyrolysis chars from sewage sludge. FUEL 143:476-483. Sansaniwal S. K., Rosen M. A., Tyagi S. K.(2017). Global challenges in the sustainable development of biomass gasification: An overview. Renewable and Sustainable Energy Reviews 80:23-43. Scott S. A., Davidson J. F., Dennis J. S., Fennell P. S., Hayhurst A. N.(2005). The rate of gasification by CO2 of chars from waste. P. Combust. Inst. 30(2):2151-2159. Vamvuka D., Karouki E., Sfakiotakis S., Salatino P.(2012). Gasification of Waste Biomass Chars by Carbon Dioxide via Thermogravimetry-Effect of Catalysts. Combust. Sci. Technol.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
184:64-77. Xiao R., Chen X., Wang F., Yu G.(2010). Pyrolysis pretreatment of biomass for entrained-flow gasification. Appl. Energ. 87(1):149-155. Xu R., Zhang J., Wang G., Zuo H., Zhang P., Shao J.(2016). Gasification behaviors and kinetic study on biomass chars in CO2 condition. Chemical Engineering Research and Design 107:3442. Xu Y.(2017). Study on Characteristics of Sludge Char Gasification and Catalytic Tar Oxidation Reforming., Shanghai: Tongji University.
