cr2032 button battery.Research status and development of biomass pyrolysis and gasification technology

　　Research status and development of biomass pyrolysis and gasification technology

　　With the advent of the new century, mankind is facing the dual pressures of economic growth and environmental protection. Changing the way energy is produced and consumed, using modern technology to develop and utilize renewable energy including biomass energy, is crucial to establishing a sustainable development of energy. It is of great significance to promote social and economic development, improve the ecological environment and get rid of dependence on fossil energy.

　　1Biomass energy resources

　　Biomass energy has always been one of the important energy sources for human survival, including energy trees, energy crops, aquatic plants, various organic wastes, etc. They are renewable energy resources converted through photosynthesis of plants. Organic storage of solar energy. Biomass energy is the most common renewable energy source on earth, with a huge amount. In terms of its energy equivalent, it ranks fourth after coal, oil, and natural gas. Biomass energy in a broad sense includes all energy that uses biomass as a carrier and is renewable. It is estimated that the annual heat equivalent of water and terrestrial biomass production on the earth is about 3×1021J, which is 10 times the current total energy consumption in the world. my country's biomass energy resources are quite abundant. The resources of various agricultural wastes (such as straw, etc.) alone amount to 308 million tons of standard coal per year, and the amount of fuelwood resources is 130 million tons of standard coal. Including feces, urban garbage, etc., The total resources are estimated to reach more than 650 million tons of standard coal, which is equivalent to about half of the country's total energy consumption in 1995.

　　At present, biomass energy occupies an important position in the world's energy structure. Biomass energy accounts for 14% of the world's energy consumption, and developing countries account for more than 40%. According to United Nations survey data, 42% of energy consumption in Southeast Asian countries comes from biomass, and African countries account for 58%. In rural areas, which account for 70% of my country's population, the main energy source is biomass energy. The total annual energy consumption of direct burning of straw and firewood in rural areas of my country is 264 million tons of standard coal, accounting for 79.3% of rural energy consumption. The annual consumption of biomass energy reaches 610 million tons, accounting for 27% of the country's total energy consumption.

　　In developed countries, the use of biomass as energy mostly adopts high-input, high-output methods to build large-scale biomass energy conversion projects to convert traditional biomass energy into modern energy utilization. For example, in 1992, there were about 1,000 power plants using wood gasification in the United States, with an operating capacity of 6.5 million kilowatts and an annual power generation of 4.2 billion kilowatt hours. The power generation cost was 4-6 cents per kilowatt hour, and the investment per kilowatt was US$2,000-3,000. , 40% of California's electricity supply comes from biomass power generation. Currently, the biomass power industry has become the second largest renewable energy source in the United States after hydropower. The use of biomass converted into modern energy accounts for 40%, 16% and 10% of basic energy consumption in the United States, Sweden and Austria respectively. In EU countries, biomass energy accounts for 59.6% of all new and renewable energy (including hydropower) developed and utilized.

　　2. Disadvantages and countermeasures caused by the traditional biomass utilization model

　　In rural areas of my country, the traditional way of energy consumption still relies on cooking as the basic requirement, with crop straw and firewood as the main resources. Most of them are directly burned in kang stoves, with low conversion efficiency and serious energy loss. On the other hand, since about 80% of rural energy consumption comes from biomass energy, the disordered use and waste of biomass resources not only directly leads to air pollution, but also seriously damages the ecological environment. In our country, the soil organic content of the Northeastern Plains, which used to be very fertile, has dropped from 5-9% to 2%; the national forest coverage has dropped to 13%, only half of the world average; the area of soil erosion has also dropped from 1.5 million in the 1950s. The square kilometers expanded to 3.67 million square kilometers.

　　Therefore, for biomass energy utilization technology, the core content of development and research is to achieve clean combustion and efficient utilization of biomass fuel and develop various energy conversion and utilization technologies of biomass.

　　3 Categories of Biomass Technology

　　Biomass energy utilization technologies are generally divided into several categories: direct combustion technology, physical and chemical conversion technology, biochemical conversion technology, liquefaction technology and solid waste technology (see Figure 1).

　　4Basic theory of biomass gasification

　　The gasification of solid fuel is the process of using oxygen or oxygen-containing substances in the air as a gasification agent to oxidize the carbon in the solid fuel into combustible gas. Different raw materials and blown gases (air, oxygen or water vapor) are used, so The composition of the combustible gas produced also varies. Among them, the technology of using air and water vapor as gasification agents at the same time to obtain mixed gas is the most widely used. The current fixed bed biomass gasification system basically adopts this gasification method.

　　In the gasification process, fuel basically goes through four stages: oxidation, reduction, carbonization and drying. The main reaction formula is:

　　Solid fuel gasification is a multi-phase reaction process between gas (oxygen) and solid (carbon). The reaction mechanism between carbon and oxygen is still a controversial issue. There are three main types of gasification reaction mechanisms. theory:

　　(1) Reduction theory, it is believed that the reaction of carbon and oxygen first generates CO2, and the existence of CO is due to the reduction of CO2 by the carbon in the fuel.

　　(2) Carbon monoxide theory holds that CO is the primary product of the reaction between carbon and oxygen, and CO is further oxidized to generate CO2.

　　(3) Complex theory, it is believed that carbon and oxygen first form a CXOY complex. Due to different conditions such as temperature, this complex decomposes into CO2 and CO in different proportions, so CO2 and CO are formed at the same time.

　　5 Overview of biomass gasification technology

　　Pyrolysis gasification is a thermochemical reaction technology that converts low-grade solid biomass into high-grade combustible gas through thermochemical reactions in the gasification device. Since the advent of the world's first upper-suction gas furnace in 1839, gasification technology has a history of more than 160 years. However, large-scale application of biomass pyrolysis gasification technology began in the 1930s and 1940s. During World War II, small gasification devices for internal combustion engines were widely used to solve the shortage of petroleum fuel. Since the early 1970s, affected by the oil crisis, this technology has undergone new developments. In the early 1940s, charcoal and wood blocks were used as fuel to drive civil vehicles through gasification in some areas of my country. From the 1950s to the early 1960s, some urban and rural areas in my country used wood fuel gasification to drive internal combustion engines, replacing diesel and gasoline. , used to drive cars and lift water power generation equipment. Now, as a supplementary energy source to fossil energy, it has attracted more attention from various countries.

　　Foreign biomass gasification devices are generally large-scale, highly automated, and have complex processes. They mainly focus on power generation and heat supply. For example, the fixed-bed wet upstream gasification device designed and developed by Moore Canada Ltd. The fluidized bed gasification device designed and manufactured by Canada's Omnifuel Gasification System Limitred, the carbonized gasification wood gas generation system designed and manufactured by American Standard Solid Fuels Inc, and the German Imbert Energy The company (Imbert Energietechnik GMBH) designs and manufactures downward gasifier-internal combustion engine generator system, etc., with gasification efficiency up to 60%-90% and combustible gas calorific value 1.7-2.5×104kJ/m3. At present, the leading countries in this field include Sweden, the United States, Italy, Germany, etc. The United States has made breakthroughs in biomass pyrolysis and gasification technology in recent years. It has developed a complete set of biomass comprehensive gasification device-gas turbine power generation system, providing a model for large-scale power generation.

　　Starting from the early 1980s, after nearly 20 years of efforts, my country's biomass gasification technology has also become increasingly perfect. my country's self-developed centralized gas supply and household gasification furnace products have entered the practical testing and demonstration stage, forming multiple series of furnace types that can meet the gasification requirements of a variety of materials. They are widely used in production, daily life energy use, and power generation. , drying, heating and other fields have been utilized. For example, the ND series of biomass gasifiers developed by the Chinese Academy of Agricultural Mechanization Sciences, among which the ND-600 gasifier has been in production for a long time and has achieved certain benefits; the rice husk gasifier produced in Wujiang County, Jiangsu The furnace uses the scraps from the rice mill to drive the generator set, with a power of 160 kilowatts, which has reached the practical stage;

　　6 my country’s existing biomass gasification technology

　　At present, the biomass pyrolysis and gasification technology used in my country mainly includes three process forms: fixed bed, fluidized bed and direct distillation pyrolysis. Fixed bed processes generally use air as the gasification agent. This type of process, whether it is an upward suction type, a down suction type or a flat suction type air flow method, has a simple equipment structure, is easy to operate, and can realize a variety of biomass raw materials. It has the characteristics of pyrolysis and gasification and low investment. However, the calorific value of the biomass gas obtained is low, generally only 5000KJ/Nm3, and the tar content in the biomass gas is high (see Table 2), which can easily cause pipeline blockage. Analyzing the reasons, there are two main aspects: first, due to the limitations of the process route, air is often used as the gasification agent, and the nitrogen content in the obtained biomass gas is high, usually around 50%; second, due to some inaccuracies of the biomass raw materials Factors that are conducive to gasification, such as high volatile content of biomass raw materials and relatively low fixed carbon content, result in high tar content in the biomass gas obtained. Moreover, biomass raw materials have small bulk density and so on.

　　In response to these shortcomings, the Key Laboratory of Rural Energy of Yunnan Normal University proposed a biomass pyrolysis and complete gasification technology using steam as the gasification agent. This technology can greatly increase the calorific value of biomass gas, and the experimental calorific value reaches The gas production rate has reached more than 8300KJ/Nm3 and the gas production rate has reached more than 1.20m3/kg, and there is still potential for improvement.

　　The biomass gas obtained by the fluidized bed process has a high calorific value, up to about 12,000KJ/Nm3, and the gas yield and gasification efficiency have reached about 0.95 and 63% respectively. However, the process equipment is complex and the operation is difficult to master.

　　In 1998, the LZ series biomass direct thermal cracking device developed by Dalian Environmental Science Research Institute can obtain cracked gas with a calorific value of 14651KJ/m3 and a gas production rate of 0.35m3/kg. The main product of this device is carbon, and pyrolysis produces Material gas is a by-product, and the cost of gas depends on the sales of carbon.

　　7Conclusion

　　In summary, biomass gasification technology is becoming increasingly mature, and the application technology of biomass gasification systems has attracted more and more attention. The main hot spots are gasification drying, gasification power generation, household gas centralized supply and household gas. Chemical stoves and other four aspects.

　　my country is rich in biomass resources, and biomass gasification technology is of great significance in making full use of these resources, alleviating energy tension, improving energy quality, improving environmental quality, and improving people's living standards. Therefore, there is broad scope for vigorously developing biomass gasification technology. Prospects.

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