Side by the river
Abstract: In recent years, due to the burning of traditional fuels such as coal and petroleum, the energy security and environmental problems are becoming more and more serious.With the increasing importance of the state and the need of the transformation of related enterprises, biomass energy has become the key to solve the above problems of energy. Biomass energy is stored by plants through the photosynthesis and solar energy inside the body, compared with fossil fuels, with a large yield, a wide range of distribution, the use of more, low nitrogen and sulfur content, ash content is small, low calorific value The objective is to review the current research status of biomass pellet boilers at home and abroad, to explore the deepening direction and research prospects of biomass pellet boilers, and to refine the existing academic And engineering problems, sort out the next step of research and development ideas.The paper put forward the problems to be solved in the field of biomass pellet boiler and the key contents for further study for readers' reference.
According to the 2006 China Energy Development Report, about 90% of global energy consumption comes from fossil fuels, 10% of nuclear power and hydropower, while the main energy consumed by China is coal and oil. Due to the fossil fuels including coal gold and petroleum Heavy use, exacerbating global warming and other environmental issues.If the energy security and environmental issues are not properly resolved, by 2050, China's standard coal consumption will be three times in 2005, the CO 2Emission will also increase 2.5 times.Therefore, looking for a safe and reliable new energy is the urgent problem to be solved at this stage.
Biomass energy is a plant that absorbs solar, water and CO through photosynthesis 2, Generate O 2And carbohydrates, and will be stored in plants as an energy source.Compared with fossil fuels, biomass has the following characteristics: large amount of storage, wide range of raw material distribution and utilization methods; low N and S content in biomass , Ash content is small, the combustion process NO x, SO xLow emissions with dust; CO absorbed by biomass fuel during formation 2Approximate CO emissions from combustion 2, CO 2The net emissions are approximately zero; due to the high water content of biomass fuels, its pyrolysis and combustion characteristics are relatively poor; biomass energy is a renewable energy source. Therefore, boilers that generate high-efficiency combustion of particulate matter in the boiler industry are already A major trend in the development of the boiler industry.
1 Status quo and existing problems at home and abroad
In the 1950s, in response to the characteristics of biomass fuels and combustion methods, Japan took the lead in the development of rod-shaped fuel molding machines and related combustion equipment. In the late 1970s, the United States developed special wood pellets for the characteristics of wood pellets. Fuel combustion equipment. Based on research in the United States and Japan, Sweden, Finland, Denmark, and other countries have developed particle-forming machines and combustion equipment for biomass-based particulate fuels. Currently, research on biomass-fuel-burning equipment in developed countries is relatively mature. , And further upgrade according to industry needs, to achieve industrialization in the field of heating heating and power generation.
At this stage, in the field of biomass particle fuel combustion, China has focused its research on the combustion characteristics of fuel, but it has not yet established the theory and related standards that will be the system. The research on biomass fuel combustion equipment is still in its infancy.
Based on tests such as thermal performance test, air flow field test, temperature field test and furnace gas concentration field test, Liu Shengyong independently designed single and double grate fired biomass combustion equipment and its performance indicators. Equipment, Liu Shengyong studied the air flow field, concentration field, temperature field and other parameters, which laid a theoretical foundation for the further development of China's biomass fuel combustion equipment.
Tian Yishui, et al.According to the biological characteristics of straw itself, based on the structure of double combustion chamber in the front and back of the furnace, a straw direct combustion hot water boiler combustion chamber was designed.The double combustion chamber was separated by a fire arch, , High-temperature flue gas mixed with each other, and extend the straw burning time in the combustion chamber, improve fuel burn.
Zhai Xuemin In-depth study of the combustion mechanism of bagasse, using a separate closed-hearth combustion chamber and radiation heating surface structure designed for the bagasse, rice husks, twigs, bark and other biomass fuel combustion boilers. Furnace structure is not only conducive to the fuel combustion process, but also has enough heating surface, to meet the dual requirements of combustion and heat transfer.At the same time, the furnace is provided with herringbone arch before and after, to improve the radiation of high temperature flue gas to promote the bagasse fuel Burning speed and combustion stability.
In view of the combustion characteristics of sawdust, twigs, bark, wood flour and other wastes, HE Yu-heng designed a layer-fired boiler with water-cooled wall tubes in the furnace based on the theory of negative pressure combustion to enhance the internal temperature of the furnace and promote the fuel such as sawdust Of the full combustion.At the same time, the furnace has explosion-proof door, to avoid the combustion of wood chips and other combustion deflagration phenomenon.
Although the biomass pellet fuel industry in our country started relatively lately, its development speed is relatively fast and the relevant combustion technologies are relatively mature. However, the development of combustion equipment for biomass pellet fuel can not keep up with the pace of industrial development and there are many problems to be solved problem:
1) The degree of automation of existing combustion equipment is low.At present, the feeding system of domestic biomass pellet fuel combustion equipment mostly adopts artificial or semi-automatic feeding, which has high production and maintenance costs and greatly hinders the promotion of biomass pellet fuel and At the same time, the ventilation of small combustion equipment is still dominated by natural ventilation, which reduces the degree of combustion of the fuel and increases the emission of pollutants.
2) The structural characteristics of coal-fired boilers do not apply to the combustion characteristics of biomass pellet fuel, since biomass pellet fuel is converted from plants and has high water content and low calorific value, which is burned in coal-fired boilers The larger the flue gas volume, the higher the exhaust heat loss.High heat loss will lead to a substantial reduction in the furnace temperature, directly affecting the fuel combustion efficiency.At the same time, the biomass particles with high volatile content, precipitation speed, speed up the fuel Burning rate and air consumption, the structural characteristics of the coal-fired boiler will directly affect the amount of air supplied to the furnace, reduce the combustion of biomass pellet fuel and reduce the combustion efficiency.
3) High ash deposition rate and severe slagging phenomenon The straw biomass biomass fuel has a high Si content and a deformation temperature of about 750-1000 ° C. Meanwhile, the ash deposition rate of straw fuel is higher than that of wood pellet fuel, resulting in The former has many sediments such as fouling, etc. A large amount of alkaline components and chlorides are usually present in fouling, which may cause the hazards of fouling and slagging, which will affect the thermal performance and safety of the combustion equipment. Therefore, the design of biomass pellet fuel Burning equipment design process to fully consider the deposition of sediment and other clean-up issues.
4) Chlorine corrosion leads to a decrease in the life of the combustion equipment Stalk Biomass Pellet fuel has a high content of alkali metals and chlorine In the fuel combustion process, as the flue gas temperature decreases, the alkali and alkali metal chlorides in the fly ash Condensation and release of chloride on the surface of particles or heat exchangers Chloride has a strong oxidizing power and the corrosion rate is further increased under high temperature leasing, resulting in a faster metal loss rate and a lower heat transfer efficiency.In the partially corroded area , Even the local metal surface loss of heat transfer performance.Therefore, straw-based particulate fuel than wood pellets fuel more likely to damage the equipment, equipment, material requirements more stringent.
2 biomass pellet steam boiler development trend
Foreign biomass pellet fuel combustion equipment with low emissions, high combustion efficiency, high degree of automation advantages, and has been in the heating, power generation and other fields to achieve industrial applications.In contrast, China's biomass pellet fuel combustion equipment is still In research and development stage, there are serious problems of fouling and slagging, poor fuel adaptability, high pollutant discharge and low degree of automation.
With the improvement of energy security and environmental issues in our country and the further development of biomass pellet fuel industry, the application of biomass pellet fuel will be more and more widely.Therefore, in combination with biomass pellet fuel combustion technology, The combustion equipment adapted to the national conditions of our country is a big research focus in the field of biomass particles in our country at this stage. The main research directions are as follows:
1) For the existing equipment, there is a problem that it is easy to burn the hopper, and the structure of the hopper is avoided by optimizing the product structure.
2) In view of the existing equipment, there is a problem that biomass pellet fuel has high exhaust heat loss during combustion and biomass fuel combustion is not sufficient, and the intake mode is optimized to increase the intake air temperature.
3) Aiming at the serious problems of fouling and slagging of the existing combustion equipment, the key structure of the combustion equipment is optimized to reduce the degree of fouling and slagging and improve the fuel adaptability.
4) Aiming at the problems of low degree of automation of existing combustion equipment, automatic feeding system and real-time monitoring system are designed, and pollutant control technology is introduced to monitor changes of internal temperature and gas concentration in the combustion equipment, adjust combustion parameters and reduce pollutants Emissions, improve combustion efficiency.
references
'1' Geng Chunmei, Chen Jianhua, Wang Xinhua. Comparison of Emissions Characteristics of Biomass Boiler and Coal-fired Boiler Particles J '. Environmental Science Research, 2013.6, 26 (2).
'2' Liu Shengyong, Liu Xiaowei, Wang Sen, et al. Development of a Type II Biomass Briquette Boiler [J] .Journal of Agricultural Engineering, 2007, (12): 100-104.
'3' LU Juan, HOU Shu-lin, ZHAO Li-xin, et al.Research progress on biomass pellet fuel combustion equipment 'J'. Renewable energy, 2009, 27 (6): 90-95.
'4' Ren Minna.Experimental Study on Ignition and Combustion Characteristics of Typical Biomass Pellet Fuel 'D' .Shandong Architecture University, 2012.
'5' Huang Bo.Experimental Study on the Combustion Characteristics of Biomass Molding Fuels for Furnace 'D'. Central South University, 2011.
'6' Sun Kang, Chen Chao, Xu Yu, et al. Design and Experimental Research on Stove Burning Fuel Boiler (J). Chemical Industry and Industry, 2014, (6): 93-99.
'7' Zheng Kaixuan .4t / h biomass molding fuel fired furnace hearth and grate design and research 'D'. Henan Agricultural University, 2013.
