Abstract: Biomass liquefaction includes bio-chemical production of fuel ethanol and thermochemical production of bio-oil. The thermal chemical method can be divided into rapid pyrolysis liquefaction and pressurized liquefaction. Various rapid pyrolysis liquefaction processes, such as rotary cone reactors, entrained bed reactors, circulating fluidized bed reactors, vortex reactors, vacuum pyrolytic reactors and the like, which are currently reaching the scale of industrial demonstration, The plasma liquefaction process in the laboratory stage is discussed. The characteristics of each process and the main problems are discussed. It is pointed out that the circulating fluidized bed process has a high heating and heat transfer rate, and the processing capacity can reach a higher scale and is currently utilized Most, liquid highest rate of technology. Liquid liquefaction of biomass liquefaction has broad prospects in our country. It is suggested that the development of fuel ethanol production by cellulase enzymatic saccharification and fermentation and the development of new technology of thermo-chemical bio-oil refining should be strengthened so as to reduce the production cost and increase the cost of fossil fuels Competitiveness. Key words: biomass; liquefaction; pyrolysis; fuel Key words: AResearch progress in liquefaction technologies of biomass CHANG Jie (Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, 510070, China) Abstract: Liquefaction of biomass presemental biochemical conversion for fuel ethanol and themochemical conversion for bio-oil, which include fast pyrolysis processes of biomass for liquid fuel, such as rotating cone reactor, entrained flow reactor, circulating fluid bed reactor , vortex reactor and vacuum hearth reactor, which are at the commercial demonstration stage, as well as plasma jet flow reactor which is at laboratory stage, were emphatically introduced. The features and problems of each process were discussed and compared. heat transfer could be obtained in the circulating fluid bed process; also larger scale ofolving amount of feed It said that circulating fluid bed process, which can get the highest liquid yield among the above processes, is extensively used in the liquefaction of biomass. Liquefaction of biomass for liquid fuel is a promising technology in China. In order to lower the production cost and improve the rivalrousness of biomass fuel to fossil fuel, research and development in the following technologies, simultaneous saccharification and fermentation of cellulose to ethanol by enzyme, and new refining process of bio-oil produced by thermochemical conversion to higher quality China's primary energy consumption second only to the United States to become the world's second largest consumer of energy, however, imports of crude oil in 2000 reached 70 million t. The shortage of liquid fuels has seriously threatened China's energy and economic security. Therefore, China has proposed a strategic development plan for vigorously developing new and renewable energies and optimizing energy structure [1-2]. Biomass is the only renewable energy that can be converted into liquid fuels. Converting biomass into liquid fuels not only can make up for the shortage of fossil fuels, but also help to protect the ecological environment. Biomass includes a variety of fast-growing energy plants, agricultural waste, forestry waste, aquatic plants and a variety of organic waste. China's abundant biomass resources, the theoretical annual output of 50 billion t [3], the development of biomass liquefaction alternative fossil fuels have enormous potential for resources. Biomass energy technologies include gasification, direct combustion power generation, solidification and liquefaction. At present, the first three technologies have reached a relatively mature stage of commercialization, and biomass liquefaction is still in the research, development and demonstration stages [4]. From the product points, biomass liquefaction can be divided into the preparation of liquid fuel (ethanol and bio-oil, etc.) and the preparation of chemicals. As preparation of chemicals requires more complex product separation and purification process, high technical requirements, and high cost, at home and abroad are still in the laboratory research stage, there are many literatures on the thermal conversion and catalytic conversion of refined chemical reaction conditions, the catalyst , Reaction mechanism and purification methods were reported in detail [4-8]. The author will mainly introduce the technology and research progress of liquid liquefaction from biomass liquefaction. From the process, biomass liquefaction can be divided into biochemical and thermochemical methods. Biochemical method mainly refers to the use of hydrolysis, fermentation and other means of biomass into fuel ethanol. Thermochemical methods include rapid pyrolysis liquefaction and pressurized catalytic liquefaction. A biochemical production of fuel ethanol biomass fuel ethanol production of raw materials are mainly surplus grain, energy crops and crop stalks and so on. The use of starch and other raw materials for food production of ethanol is a very mature technology of traditional technology. Production of fuel ethanol from grain Although the cost is high and the price is not competitive with petroleum fuels, due to the increase in grain output in recent years, a large amount of grain has been accumulated in China. In 2002, the Chinese government formulated a policy of producing fuel ethanol for grain by aging , A certain percentage of fuel ethanol added to gasoline as a motor fuel, has been demonstrated in Henan and Jilin provinces. The application of fuel ethanol at home and abroad proves that it can make the engine in good technical condition, improve the bad emission and have obvious environmental benefits. However, even if the surplus grain in our country is converted into ethanol at a rate of 30 million tons at the time of the great harvest, it can produce 10 million tons of ethanol and only 1/10 of the crude oil gap in 2000. And as the population in China continues to grow, food is hard to come by A lot of surplus appears. Therefore, Chen grain is an unreliable source of energy [2]. The United States and Brazil use large amounts of domestic-produced corn and sugar cane, respectively, to produce ethanol as vehicle fuel. Since 1975, Brazil has launched the world's largest fuel ethanol development plan to get rid of its dependency on oil. By 1991, Brazil had produced 13 billion liters of fuel ethanol. Since 1991, the United States has to pay a huge subsidy of 700 million U.S. dollars each year [2, 3, 8] in order to maintain the annual output of 5 billion liters of corn. In order to make up for the lack of food, many countries have carried out research and development on the technology of sweet sorghum and cassava making ethanol. For example, the implementation of the project of "winning sweet sorghum from ethanol" made by China's "10th Five-year National Hi-Tech Research and Development Program (863 Program) Industrial pilot demonstration project will be established to provide technical support for the conversion of biomass to liquid fuels [9]. From the perspective of supply of raw materials and social and economic benefits, the production of ethanol from agricultural and forestry wastes containing higher cellulose is an ideal process route. Biomass fuel ethanol is the technology of hydrolyzing lignocellulose to produce glucose and then fermenting glucose to produce fuel ethanol. Cellulose hydrolysis can only proceed significantly in the presence of a catalyst. Commonly used catalysts are inorganic acids and cellulases, whereby an acid hydrolysis process and an enzymatic hydrolysis process, respectively, are formed. China has carried out many research work in this area. For example, East China University of Science and Technology carried out a hydrolysis process using dilute hydrochloric acid and ferrous chloride as catalyst and a simultaneous fermentation of hydrolyzate glucose and xylose at a conversion rate of over 70% [10] . The Institute of Process Engineering, Chinese Academy of Sciences, supported by the national research project, carried out research on the cellulase enzymatic decomposition of saccharified ethanol by solid state fermentation and laid the foundation for the development of cellulosic ethanol technology [11-12]. Researchers represented by the National Renewable Energy Laboratory (NREL) in the United States have carried out a great deal of research work in recent years. For example, yeast strains capable of fermenting five carbon sugars are obtained through the transgenic technology, and simultaneous saccharification and fermentation processes are developed. And built a number of pilot plants with a certain scale. However, due to the breakthrough of key technologies, production costs have remained high [13-15]. Cellulosic ethanol technology can achieve technological breakthroughs in the coming decades will have very good prospects for development. 2 Thermochemical Production of bio-oil fuel Biomass thermochemical liquefaction technology according to its principle can be divided into rapid pyrolysis liquefaction and pressurized liquefaction, two kinds of technology have more than 20 years of development history. 2.1 Rapid pyrolysis liquefaction The rapid pyrolysis liquefaction of biomass is a technique developed on the basis of traditional pyrolysis. Compared with traditional pyrolysis, superheated heating rate (102 ~ 104K / s), ultra-short residence time ~ 3s) and moderate pyrolysis temperature, the organic polymer molecules in biomass can be rapidly broken into short-chain molecules under the condition of isolating air, and the coke and product gas are minimized to obtain the maximum liquid product. This liquid product, known as bio-oil, is a dark brown viscous liquid with a caloric value of 20-22 MJ / kg, which can be used directly as a fuel or refined to become a fossil fuel substitute. Therefore, with the gradual reduction of fossil fuel resources, the research on rapid pyrolysis liquefaction of biomass has aroused widespread international interest. Since 1980, great progress has been made in biomass rapid pyrolysis technology, making it one of the most promising biomass liquefaction technologies. More than 10 research groups from the United States, Canada, Finland, Italy, Sweden, Britain and other countries organized more than 10 years of research and development work, focusing on the development potential of the process, the technical and economic feasibility and the cooperation between participating countries Of the technical exchanges conducted a survey that the biomass rapid pyrolysis technology to obtain more energy and more benefits than other technologies [16]. All countries in the world through the reactor design, manufacture and control of process conditions, the development of various types of rapid pyrolysis process. Several representative processes are described below [16-22]. The parameters such as the scale and liquid yield of each device are listed in Table 1, and the schematics of each process are shown in [16,18,21]. (1) The Twente rotating cone process developed by the University of Twente in the Netherlands, without carrier gas, not only greatly reduces the volume of the apparatus, but also reduces the condenser load and has high liquefaction efficiency. Biomass particles are added into the bottom of the rotating cone together with the inert heat carrier, and rapid pyrolysis reaction takes place along the helical cone of the conical wall. However, the biggest disadvantage of biomass particles is the small scale of production and high energy consumption [16-17]. China's Shenyang Agricultural University in 1995 from the Netherlands BTG Group, the introduction of a scale of 10 kg / h device, the German pine powder as raw material, the reaction temperature is 600 ℃, the feed rate of 34.8kg / h, the liquid yield 58.6% [18]. (2) The entrained flow reactor developed by Georgia Institute of Technology (GIT) introduces propane and air into the combustion zone at the bottom of the reaction tube according to the stoichiometric ratio. The high temperature combustion gas rapidly heats and decomposes the biomass, The shortcomings of this device are the drawbacks that limit its use when the feedstock volume is 15 kg / h and the reaction temperature is 745 ° C, yielding 58% of the liquid product but requiring a large amount of high temperature combustion gas and producing a large amount of non-condensable gases of low calorific value [ 19-20]. (3) Circulating fluid bed reactor developed by the Ensyn Engineers Association of Canada Bastardo, Italy, has built a demonstration plant of 650 kg / h and can produce poplar flour as raw material at a reaction temperature of 550 ° C 65% of liquid product. The device has the advantages of compact equipment, short residence time of vapor phase, preventing secondary cracking of pyrolysis steam and consequently higher liquid yield. However, its main disadvantage is the need for carrier gas to fluidize the heat carrier and biomass within the equipment. Ensyn also installed a 20 kg / h small-scale installation in Finland [21-22]. The University of Waterloo in Canada developed an approximate flash pyrolysis process (WFPP) with a unit size of 5 to 250 kg / h and a maximum liquid yield of 75% [16,22]. China's Guangzhou Institute of Energy (GIEC) also independently developed a biomass circulating fluidized bed liquefaction small devices, quartz sand as a circulating medium, wood flour feed rate of 5kg / h, the reaction temperature is about 500 ℃, available 63% liquid yield [23]. (4) The National Renewable Energy Laboratory (NREL) developed a vortex reactor with a reaction tube length of 0.7 m and a tube diameter of 0.13 m. The biomass particles were accelerated by nitrogen to 1200 m / s and fed into the reactor from the tangential line Tube, produces a layer of bio-oil in the tube wall and is rapidly evaporated. The largest unit currently built is 20 kg / h, with a liquid yield of up to 5% at a wall temperature of 625 ° C [18,24]. (5) Unlike several other atmospheric operated reactors, the multiple hearth reactor developed by Laval University in Canada operates at a negative pressure of 1 kPa and the reaction feedstock is fed from the top , The temperature of bed top is 200 ℃ and the temperature of bottom is 400 ℃. Because of the short residence time of pyrolysis steam, the secondary cracking is greatly reduced. When the content of sawdust is 30kg / h, the liquid yield is 65%. The disadvantage is the need for high-power vacuum pumps, high prices, energy consumption, amplification difficulties [18,20,25]. In summary, the CFB process is the most widely used and rapidly evaluated technique for rapid biomass pyrolysis. The process has a high heating and heat transfer rate, and throughput can reach a higher scale, the current view, the liquid obtained in the highest yield. The rapid pyrolysis of hot plasma liquefaction is a recent new method of biomass liquefaction, which uses hot plasma to heat biomass particles to rapidly warm up, and then rapidly separated and condensed to obtain a liquid product. This is carried out by our Shandong Institute of Engineering Aspects of the experimental study [26]. Table 1 6 kinds of rapid pyrolysis device typical test results comparison
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