温度对玉米秸秆成型颗粒烘焙制备生物炭及其特性的影响
|
摘要
采用低温烘焙技术制备玉米秸秆成型生物炭,可解决玉米秸秆带来的环境污染及资源浪费。研究以玉米秸秆成型颗粒为原料,利用固定床反应器,制备了不同烘焙温度(250～400℃)成型生物炭,采用元素分析、工业分析、能量产率、质量产率、机械性能、疏水性、红外光谱(Fourier transform infrared spectroscopy,FTIR)、扫描电镜(Scanning electron microscopy,SEM)、元素K含量等分析生物炭特性。随烘焙温度升高,热值增加,能量产率降低,400℃时,成型生物炭热值为21.86MJ/kg,能量产率为50.17%。成型生物炭颗粒表面裂纹增多,机械性能降低,350℃烘焙成型生物炭(CSP350)机械性能好于400℃烘焙成型生物炭(CSP400),低于成型生物质颗。烘焙生物炭疏水性提升,可贮藏于室外。成型玉米秸秆经烘焙热解发生了脱水、脱羰基、脱甲基反应,纤维素、半纤维素热解剧烈,木质素开始热解。随温度升高,其孔径呈下降趋势,比表面积增大。结果表明,玉米秸秆成型烘焙生物炭可作为优质生物燃料,适宜制备温度为300～350℃。
China is an agricultural country with huge corn planting area. According to data of the 2015 Statistical Yearbook of China, corn planting area was 37 million hectares in 2014, which produced about 225 million tons of corn stalk wastes. The large amount of corn stalk wastes are treated by incineration or landfill, resulting in serious environmental pollution and waste of resources. In order to solve these problems, curing molding, thermo-chemical conversion and biochemical conversion are used to prepare all kinds of biofuel(e.g. gas, bio-oil, and biochar). Preparation of biochar from corn straw pellets is an effective method by thermal conversion. The torrefaction is a mild pyrolysis mode between 200 and 350 ℃ which results in partial devolatilization of the solid biomass. Biochar pellets from the torrefaction technology have a considerable density, desirable hardness, and good hydrophobicity. Using biochar pellets reduces transport and investment costs for fuel storage and process feeding to greater extent than using biochar powder. Therefore, there are obvious advantages of lower equipment cost, simpler equipment system, and higher production efficiency when biomass pellets are pyrolyzed. In this paper, biochar pellets of corn straw were produced by the fixed bed pyrolysis at different temperature(250-400 ℃) at the heating rate of 10 ℃/min for a residence time of 30 min, with the N2 flow rate of 100 mL/min. Biochars were collected after the pyrolysis reaction, and their characteristics were analyzed. Characteristics of biochar pellets were analyzed by elemental analysis, proximate analysis, energy yield, mass yield, mechanical properties, hydrophobicity, FTIR, SEM and K contents. With the increase of torrefaction temperature, the O content decreased, and the C content increased. The results caused the higher heating value of biochar increased and the mass yield and energy yield decreased. At 400 ℃, the higher heating value and energy yield of biochar pellets were 21.86 MJ/kg, 50.17%, respectively. The surface cracks of biochar pellets increased and the mechanical properties were reduced. The mechanical properties of biaochar at 350 ℃(CSP350) were better than that of biaochar at 400℃(CSP400), which was lower than that the raw corn straw pellets. But the mechanical properties of biochar pellets could meet the requirement for the use of storage and transportation. Biochar pellets showed good hydrophobicity, which benefitted their storage in outsides. Moreover, biochar pellets will not decay and disperse during storage. Analysis of FTIR indicated that dehydration, decarbonylation and demethylation occurred during torrefaction process of corn straw pellets, the cellulose and hemicellulose should be basically finished, and lignin began to pyrolyze. Analysis of SEM and BET showed that the pore size decreased and the surface area increased with the increase of temperature. The K content in biochar increased from 1.68% of raw pellets to 3.12% of CSP400. This phenomenon has an adverse effect on the combustion of biochar pellets, which is easy to slag in combustion furnace. In conclusion, the results showed that biochar pellets from corn straw could be used as biofuel, and the optimum preparation temperature was 300-350 ℃.
China is an agricultural country with huge corn planting area. According to data of the 2015 Statistical Yearbook of China, corn planting area was 37 million hectares in 2014, which produced about 225 million tons of corn stalk wastes. The large amount of corn stalk wastes are treated by incineration or landfill, resulting in serious environmental pollution and waste of resources. In order to solve these problems, curing molding, thermo-chemical conversion and biochemical conversion are used to prepare all kinds of biofuel(e.g. gas, bio-oil, and biochar). Preparation of biochar from corn straw pellets is an effective method by thermal conversion. The torrefaction is a mild pyrolysis mode between 200 and 350 ℃ which results in partial devolatilization of the solid biomass. Biochar pellets from the torrefaction technology have a considerable density, desirable hardness, and good hydrophobicity. Using biochar pellets reduces transport and investment costs for fuel storage and process feeding to greater extent than using biochar powder. Therefore, there are obvious advantages of lower equipment cost, simpler equipment system, and higher production efficiency when biomass pellets are pyrolyzed. In this paper, biochar pellets of corn straw were produced by the fixed bed pyrolysis at different temperature(250-400 ℃) at the heating rate of 10 ℃/min for a residence time of 30 min, with the N2 flow rate of 100 mL/min. Biochars were collected after the pyrolysis reaction, and their characteristics were analyzed. Characteristics of biochar pellets were analyzed by elemental analysis, proximate analysis, energy yield, mass yield, mechanical properties, hydrophobicity, FTIR, SEM and K contents. With the increase of torrefaction temperature, the O content decreased, and the C content increased. The results caused the higher heating value of biochar increased and the mass yield and energy yield decreased. At 400 ℃, the higher heating value and energy yield of biochar pellets were 21.86 MJ/kg, 50.17%, respectively. The surface cracks of biochar pellets increased and the mechanical properties were reduced. The mechanical properties of biaochar at 350 ℃(CSP350) were better than that of biaochar at 400℃(CSP400), which was lower than that the raw corn straw pellets. But the mechanical properties of biochar pellets could meet the requirement for the use of storage and transportation. Biochar pellets showed good hydrophobicity, which benefitted their storage in outsides. Moreover, biochar pellets will not decay and disperse during storage. Analysis of FTIR indicated that dehydration, decarbonylation and demethylation occurred during torrefaction process of corn straw pellets, the cellulose and hemicellulose should be basically finished, and lignin began to pyrolyze. Analysis of SEM and BET showed that the pore size decreased and the surface area increased with the increase of temperature. The K content in biochar increased from 1.68% of raw pellets to 3.12% of CSP400. This phenomenon has an adverse effect on the combustion of biochar pellets, which is easy to slag in combustion furnace. In conclusion, the results showed that biochar pellets from corn straw could be used as biofuel, and the optimum preparation temperature was 300-350 ℃.
引文
[1]Avelar N V,Rezende A A P,Silva C M.Evaluation of briquettes made from textile industry solid waste[J].Renewable Energy,2016,91:417-424.
[2]Yank A,Ngadi M,Kok R.Physical properties of rice husk and bran briquettes under low pressure densification for rural applications[J].Biomass&Bioenergy,2016,84(1):22-30.
[3]Hu J J,Lei T Z,Wang Z W,et al.Economic,environmental and social assessment of briquette fuel from agricultural residues in China:A study on flat die briquetting using corn stalk[J].Energy,2014,64(1):557-566.
[4]Felfli F F,Luengo C A,Rocha J D.Torrefied briquettes:technical and economic feasibility and perspectives in the Brazilian market[J].Energy for Sustainable Development,2005,9(3):23-29.
[5]Hu Q,Shao J G,Yang H P,et al.Effects of binders on the properties of bio-char pellets[J].Applied Energy,2015,157:508-516.
[6]刘泽伟,闫思佳,夏子皓,等.温度和CO2对热解成型生物质炭孔隙结构和表面分形维数的影响[J].材料导报,2018,32(17):2925-2931.Liu Zewei,Yan Sijia,Xia Zihao,et al.Effects of temperature and CO2 on pore structure and surface fractal dimension of pyrolytic carbonization biochar briquettes[J].Materials Review,2018,32(17):2925-2931.(in Chinese with English abstract)
[7]卢辛成,蒋剑春,孟中磊,等.生物质成型炭的制备及其性能研究[J].林产化学与工业,2013,33(2):81-84.Lu Xincheng,Jiang Jianchun,Meng Zhonglei,et al.Preparation and properties of formed biomass charcoal[J].Chemistry and Industry of Forest Products,2013,33(2):81-84(in Chinese with English abstract).
[8]黄睿.热解炭化过程成型生物质与外热烟气传热的基础研究[D].昆明,昆明理工大学,2014.Huang Rui.Basic Research on Heat Transfer between Biomass and External Flue Gas during Pyrolysis Carbonization Process[D].Kunming:Kunming University of Science and Technology,2014.(in Chinese with English abstract)
[9]Zhai Y B,Wang T F,Zhu Y,et al.Production of fuel pellets via hydrothermal carbonization of food waste using molasses as a binder[J].Waste Management,2018,77:185-194.
[10]严伟,陈智豪,盛奎川.适宜炭化温度及时间改善生物质成型炭品质[J].农业工程学报,2015,31(24):245-249.Yan Wei,Chen Zhihao,Sheng Kuichuan.Carbonization temperature and time improving quality of charcoal briquettes[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(24):245-249.(in Chinese with English abstract)
[11]Basu P,Rao S,Acharya B,et al.Effect of torrefaction on the density and volume changes of coarse biomass particles[J].Canadian Journal of Chemical Engineering,2013,91(6):1040-1044.
[12]Paulauskas R,Dziugys A,Striugas N.Experimental investigation of wood pellet swelling and shrinking during pyrolysis[J].Fuel,2015,142:145-151.
[13]Ghiasi B,Kumar L,Furubayashi T,et al.Densified biocoal from woodchips:Is it better to do torrefaction before or after densification?[J].Applied Energy,2014,134:133-142.
[14]邢献军,范方宇,施苏薇,等.玉米秸秆成型颗粒烘焙工艺优化及产品质量分析[J].过程工程学报,2017,17(3):545-550.Xing Xianjun,Fan Fangyu,Shi Suwei,et al.Technology optimization of corn straw pellets torrefaction and analysis of production quality[J].The Chinese Journal of Process Engineering,2017,17(3):545-550.(in Chinese with English abstract)
[15]国家统计局.2015中国统计年鉴[M].北京:中国统计出版社,2015.
[16]Irfan M,Chen Q,Yue Y,et al.Co-production of biochar,bio-oil and syngas from halophyte grass(Achnatherum splendens L.)under three different pyrolysis temperatures[J].Bioresource Technology,2016,211:457-463.
[17]Kambo H S,Dutta A.Strength,storage,and combustion characteristics of densified lignocellulosic biomass produced via torrefaction and hydrothermal carbonization[J].Applied Energy,2014,135:182-191.
[18]孟晓晓,孙锐,袁皓,等.不同热解温度下玉米秸秆中碱金属K和Na的释放及半焦中赋存特性[J].化工学报,2017,68(4):1600-1607.Meng Xiaoxiao,Sun Rui,Yuan Hao,et al.Effect of different pyrolysis temperature on alkali metal K and Na emission and existence in semi-char[J].CIESC Journal,2017,68(4):1600-1607.(in Chinese with English abstract)
[19]Wang S R,Dai G X,Ru B,et al.Effects of torrefaction on hemicellulose structural characteristics and pyrolysis behaviors[J].Bioresource Technology,2016,218:1106-1114.
[20]Frau C,Ferrara F,Orsini A,et al.Characterization of several kinds of coal and biomass for pyrolysis and gasification[J].Fuel,2014,152:138-145.
[21]Gil M V,Oulego P,Casal M D,et al.Mechanical durability and combustion characteristics of pellets from biomass blends[J].Bioresource Technology,2010,101:8859-8867.
[22]Zornoza R,Morenobarriga F,Acosta J A,et al.Stability,nutrient availability and hydrophobicity of biochars derived from manure,crop residues,and municipal solid waste for their use as soil amendments[J].Chemosphere,2015,144:122-130.
[23]Li H,Liu X H,Legros R,et al.Pelletization of torrefied sawdust and properties of torrefied pellets[J].Applied Energy,2012,93:680-685.
[24]Chen Y,Yang H,Wang X,et al.Biomass-based pyrolytic polygeneration system on cotton stalk pyrolysis:Influence of temperature[J].Bioresource Technology,2012,107:411-418.
[25]Yang H P,Yan R,Chen H P,et al.Characteristics of hemicellulose,cellulose and lignin pyrolysis[J].Fuel,2007,86(12):1781-1788.
[26]Biagini E,Federica B A,Tognotti L.Devolatilization of biomass fuels and biomass components studied by TG/FTIRtechnique[J].Industrial&Engineering Chemistry Research,2006,45(13):4486-4493.
[27]Zhao Y,Feng D,Zhang Y,et al.Effect of pyrolysis temperature on char structure and chemical speciation of alkali and alkaline earth metallic species in biochar[J].Fuel Processing Technology,2016,141(2):54-60.
[28]王春红,白肃跃,岳鑫敏.乌拉草纤维热解及其产物挥发性有机物特性分析[J].农业工程学报,2015,31(10):249-253.Wang Chunhong,Bai Suyue,Yue Xinmin.Pyrolysis and its products volatile organic compounds characteristics of curaua fiber[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(10):249-253.(in Chinese with English abstract)
[29]卫文娟,李宝霞.温度对水葫芦热解特性的影响[J].化工进展,2013,32(9):2126-2129.Wei Wenjuan,Li Baoxia.Effects of temperature on pyrolysis characteristics of water hyacinth[J].Chemical Industry and Engineering Progress,2013,32(9):2126-2129.(in Chinese with English abstract)
[30]Garlapalli R K,Wirth B,Reza M T.Pyrolysis of hydrochar from digestate:Effect of hydrothermal carbonization and pyrolysis temperatures on pyrochar formation[J].Bioresource Technology,2016,220:168-174.
[2]Yank A,Ngadi M,Kok R.Physical properties of rice husk and bran briquettes under low pressure densification for rural applications[J].Biomass&Bioenergy,2016,84(1):22-30.
[3]Hu J J,Lei T Z,Wang Z W,et al.Economic,environmental and social assessment of briquette fuel from agricultural residues in China:A study on flat die briquetting using corn stalk[J].Energy,2014,64(1):557-566.
[4]Felfli F F,Luengo C A,Rocha J D.Torrefied briquettes:technical and economic feasibility and perspectives in the Brazilian market[J].Energy for Sustainable Development,2005,9(3):23-29.
[5]Hu Q,Shao J G,Yang H P,et al.Effects of binders on the properties of bio-char pellets[J].Applied Energy,2015,157:508-516.
[6]刘泽伟,闫思佳,夏子皓,等.温度和CO2对热解成型生物质炭孔隙结构和表面分形维数的影响[J].材料导报,2018,32(17):2925-2931.Liu Zewei,Yan Sijia,Xia Zihao,et al.Effects of temperature and CO2 on pore structure and surface fractal dimension of pyrolytic carbonization biochar briquettes[J].Materials Review,2018,32(17):2925-2931.(in Chinese with English abstract)
[7]卢辛成,蒋剑春,孟中磊,等.生物质成型炭的制备及其性能研究[J].林产化学与工业,2013,33(2):81-84.Lu Xincheng,Jiang Jianchun,Meng Zhonglei,et al.Preparation and properties of formed biomass charcoal[J].Chemistry and Industry of Forest Products,2013,33(2):81-84(in Chinese with English abstract).
[8]黄睿.热解炭化过程成型生物质与外热烟气传热的基础研究[D].昆明,昆明理工大学,2014.Huang Rui.Basic Research on Heat Transfer between Biomass and External Flue Gas during Pyrolysis Carbonization Process[D].Kunming:Kunming University of Science and Technology,2014.(in Chinese with English abstract)
[9]Zhai Y B,Wang T F,Zhu Y,et al.Production of fuel pellets via hydrothermal carbonization of food waste using molasses as a binder[J].Waste Management,2018,77:185-194.
[10]严伟,陈智豪,盛奎川.适宜炭化温度及时间改善生物质成型炭品质[J].农业工程学报,2015,31(24):245-249.Yan Wei,Chen Zhihao,Sheng Kuichuan.Carbonization temperature and time improving quality of charcoal briquettes[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(24):245-249.(in Chinese with English abstract)
[11]Basu P,Rao S,Acharya B,et al.Effect of torrefaction on the density and volume changes of coarse biomass particles[J].Canadian Journal of Chemical Engineering,2013,91(6):1040-1044.
[12]Paulauskas R,Dziugys A,Striugas N.Experimental investigation of wood pellet swelling and shrinking during pyrolysis[J].Fuel,2015,142:145-151.
[13]Ghiasi B,Kumar L,Furubayashi T,et al.Densified biocoal from woodchips:Is it better to do torrefaction before or after densification?[J].Applied Energy,2014,134:133-142.
[14]邢献军,范方宇,施苏薇,等.玉米秸秆成型颗粒烘焙工艺优化及产品质量分析[J].过程工程学报,2017,17(3):545-550.Xing Xianjun,Fan Fangyu,Shi Suwei,et al.Technology optimization of corn straw pellets torrefaction and analysis of production quality[J].The Chinese Journal of Process Engineering,2017,17(3):545-550.(in Chinese with English abstract)
[15]国家统计局.2015中国统计年鉴[M].北京:中国统计出版社,2015.
[16]Irfan M,Chen Q,Yue Y,et al.Co-production of biochar,bio-oil and syngas from halophyte grass(Achnatherum splendens L.)under three different pyrolysis temperatures[J].Bioresource Technology,2016,211:457-463.
[17]Kambo H S,Dutta A.Strength,storage,and combustion characteristics of densified lignocellulosic biomass produced via torrefaction and hydrothermal carbonization[J].Applied Energy,2014,135:182-191.
[18]孟晓晓,孙锐,袁皓,等.不同热解温度下玉米秸秆中碱金属K和Na的释放及半焦中赋存特性[J].化工学报,2017,68(4):1600-1607.Meng Xiaoxiao,Sun Rui,Yuan Hao,et al.Effect of different pyrolysis temperature on alkali metal K and Na emission and existence in semi-char[J].CIESC Journal,2017,68(4):1600-1607.(in Chinese with English abstract)
[19]Wang S R,Dai G X,Ru B,et al.Effects of torrefaction on hemicellulose structural characteristics and pyrolysis behaviors[J].Bioresource Technology,2016,218:1106-1114.
[20]Frau C,Ferrara F,Orsini A,et al.Characterization of several kinds of coal and biomass for pyrolysis and gasification[J].Fuel,2014,152:138-145.
[21]Gil M V,Oulego P,Casal M D,et al.Mechanical durability and combustion characteristics of pellets from biomass blends[J].Bioresource Technology,2010,101:8859-8867.
[22]Zornoza R,Morenobarriga F,Acosta J A,et al.Stability,nutrient availability and hydrophobicity of biochars derived from manure,crop residues,and municipal solid waste for their use as soil amendments[J].Chemosphere,2015,144:122-130.
[23]Li H,Liu X H,Legros R,et al.Pelletization of torrefied sawdust and properties of torrefied pellets[J].Applied Energy,2012,93:680-685.
[24]Chen Y,Yang H,Wang X,et al.Biomass-based pyrolytic polygeneration system on cotton stalk pyrolysis:Influence of temperature[J].Bioresource Technology,2012,107:411-418.
[25]Yang H P,Yan R,Chen H P,et al.Characteristics of hemicellulose,cellulose and lignin pyrolysis[J].Fuel,2007,86(12):1781-1788.
[26]Biagini E,Federica B A,Tognotti L.Devolatilization of biomass fuels and biomass components studied by TG/FTIRtechnique[J].Industrial&Engineering Chemistry Research,2006,45(13):4486-4493.
[27]Zhao Y,Feng D,Zhang Y,et al.Effect of pyrolysis temperature on char structure and chemical speciation of alkali and alkaline earth metallic species in biochar[J].Fuel Processing Technology,2016,141(2):54-60.
[28]王春红,白肃跃,岳鑫敏.乌拉草纤维热解及其产物挥发性有机物特性分析[J].农业工程学报,2015,31(10):249-253.Wang Chunhong,Bai Suyue,Yue Xinmin.Pyrolysis and its products volatile organic compounds characteristics of curaua fiber[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(10):249-253.(in Chinese with English abstract)
[29]卫文娟,李宝霞.温度对水葫芦热解特性的影响[J].化工进展,2013,32(9):2126-2129.Wei Wenjuan,Li Baoxia.Effects of temperature on pyrolysis characteristics of water hyacinth[J].Chemical Industry and Engineering Progress,2013,32(9):2126-2129.(in Chinese with English abstract)
[30]Garlapalli R K,Wirth B,Reza M T.Pyrolysis of hydrochar from digestate:Effect of hydrothermal carbonization and pyrolysis temperatures on pyrochar formation[J].Bioresource Technology,2016,220:168-174.