The Applied Basic Research Of Biomass Boiler With Gasification And Combustion

Human use of biomass energy is the earliest and largest, the most direct one's energy, second only to coal, and oil and gas, the fourth in the world's total energy consumption of the energy, in the entire energy system occupies an important position. The advantages of biomass energy are renewable, wide range of the source and non-polluting and so on. With the increasing depletion of fossil fuels and growing environmental problems, bio-energy technology research and development has become one of the world's major topical issues by the government and scientists around the world attention. China is a country with a large population and a rapid economic development national, 21 century will be faced with the economic growth and environmental protection of the double pressure. Therefore changes in energy production and consumption patterns, the development and utilization of renewable biomass energy and other clean energy resources to the establishment of sustainable energy systems, to promote national economic development and environmental protection is of great significance.Biomass fuels can be divided into gaseous fuels, liquid fuels and curing fuel.From the technical and economic side, the most feasibility of bio-energy technologies is the use of curing - that is, straw densification briquette fuel technologies. However, biomass energy use in China started late, as a new type of fuel, its combustion characteristics of the theoretical and experimental research is still at the initial stage. The key question of Constraints of its application is not corresponding combustion equipment. The purpose of this paper is based on straw densification briquette fuel combustion theory, research and develops of well-designed combustion equipment and heat transfer equipment, sought to provide some theoretical basis for the future of biomass fuel combustion equipment design, operation and technology. The main contents of the thesis are as f o11ows:1.In this paper, corn stalks come for the northeastern region, firstly, did experimental study of infrastructure.①Biomass fuel industry analysis and elemental analysis results showed that Biomass fuel contains large quantities of volatile,hydrogen and oxygen, which makes biomass fuels ignite easily. However, carbon content is only about 50% of coal, burned very quickly and heat value is lower. Most of the sulfur content of less than 0.2%, less combustion pollutants can save desulfurization devices, reduce the cost of combustion equipment is conducive to environmental protection.②Straw densification briquette fuel experiments show that biomass heating-hot molding is directly related to temperature and pressure. The pressure in the range of 15～46MPa, and the temperature in the range of 160～200℃can meet the requirements.③draw biomass TG-DTG curve through the experimental analysis, identify the three stages of combustion. Dehydration drying stage of the fuel, escape and combustion stage of volatile, stage of coke combustion. Experiments show that ignition temperature of straw densification briquette fuel is low and the time is shot, ignition performance is much higher than that of coal, and rate of burn out is high.④Trough simulating straw densification briquette fuel combustion process in the furnace, find out corn straw densification briquette fuel have more serious slag tendency. In order to enable the safe operation of boilers, the maximum temperature of fuel level should be below of 1000℃. As biomass fuel contains a large amount of alkali metal elements, resulting in low melting point and easy ash slag. Tube wall surface roughness, fuel layer thickness distribution large or uneven and poor operating condition of boiler will increase the rate of fuel slag.2.Through analysis of the mechanism of biomass gasification, the use of biomass gasification technology make corn straw densification briquette fuel incomplete combustion in hypoxic conditions to produce CO, H2 and CnHm such as combustible gases, then combustible gases mixed with air for complete combustion, that is the realization of direct utilization of fired gas heat. It was found that under suction gasification reactor ignited more easily. After several rounds of prototype experiments, the basic combustion shape of biomass gasification has been determined. Under suction gasification reactor was used. There are parts of the structure of combustion, Solid-phase combustion chamber, gas chamber and the combustion of ash dust chamber. Developed specifically biomass boiler for experiment, and analysised thermal and emission characteristics of the boiler. Experiments show that When the furnace excess air ratio of exportα= 1.5, furnace temperature is high, CO concentration is the smallest, flue gas temperature is low, flue gas heat lose and incomplete combustion heat loss is the smallest, thermal efficiency of boiler is the highest, at this point furnace achieve the best operating conditions. However, continue to increase the furnace export excess air ratio, will absorb the furnace temperature, not conductive to burning reaction, increase CO concentration in flue gas, rise the exhaust gas temperature and reduce the thermal efficiency of boiler. As the furnace temperature is always lower than 1000℃, main Nox of flue gas is fuel type Nox. Because content of nitrogen and sulfur in biomass fuels is low, Nox concentration of flue gas in less than coal, SO2 concentration is very low or not detected by detection apparatus. This is the one of the important causes why biomass particle shape fuel can reduce environmental pollution.3.Use mathematical software simulates performance of burning biomass gasification boiler.①the increase of furnace export excess air ratio, will cause the volume and temperature of flue gas to increase, resulting in lower thermal efficiency of boiler. As more air you give, completely burn the fuel becomes more, and the thickness of the fuel will increase. Heat released from fuel combustion so that the sharp rise in temperature is expected, and to worsen the ventilation grate. Ultimately affect the safe operation of boiler. The furnace excess air ratio of exports increased will increase convective heat transfer coefficient and heat. But due to the increase of the volume of flue gas, in the convection heating surface structure of the same conditions, then increase the speed of gas outside the tube. Units as a result of the flue cross-section of the kinetic energy of the fly ash with the heating surface and the wear volume of flue gas is directly proportional to the speed of the three parties, which makes the metal heating surfaces susceptible to wear, impact the safe operation of boilers. Furnace excess air ratio changes in exports will be caused by a variety of resistance changes in the furnace, the greater excess air ratio, the greater wind resistance and the greater mechanical and electrical consumption.②Grate area is the main geometric parameters of industrial boiler. Under the conditions of exports excess air coefficientα=1.5 in the furnace, simulation results show that the smaller grate area, heat load becomes greater, in industrial boilers, grate combustion equipment area is the geometric characteristics of the main parameters,the export in the furnace excess air coefficientα=1.5 in conditions , the performance simulation results show that the smaller the area of grate, grate area the greater the heat load, fuel thickness the greater the level of fuel to run the ventilation resistance and increased power consumption, heat loss incomplete combustion increased, so that to reduce the thermal efficiency of boilers.③Exports in the furnace excess air coefficientα=1.5 condition, the first horizontal convection relative pitch control for the s1/d less, so that flue gas flow rate increases, the heat transfer coefficient increases, and the root tube substantially reduced the number to reduce the cost of the boiler. However, flue gas flow rate is too large, so that severe wear tube,flue gas flow rate is too small prone to fouling and the convection heating surface should be noted that the best determination of flue gas velocity. Relative pitch control for horizontal s1/d decreases, so that flue gas-side flow resistance increased, the increase in fan power consumption to run, therefore, the relative pitch of a horizontal tube boilers must be designed to meet both the needs of convective heat transfer as well as to meet the economic needs.④Performance simulation results show that the incomplete combustion with increased heat loss, has not been completely burn ash particles may be removed from the furnace will be in the form of fly ash together with the escaping gas, so that the thermal efficiency of boilers obvious lower. Mechanical incomplete combustion heat loss increases, means that the fuel burning on the grate situation deteriorate, the boiler heating surface of heat transfer situation has declined, the total resistance of the furnace is also on the rise, thus increasing the mechanical and electrical consumption of the wind.4.According to biomass fuel combustion particles forming theory and analysis of combustion characteristics, combined with the experimental boilers heat and emission characteristics, as well as the results of mathematical simulation, research and development of a biomass combustion boiler which suitable for densification briquette fuel of a new generation of fuel burning equipment and heat transfer equipment, that is, the integration of biomass gasification combustion boiler heat exchanger. Introduced and has been applied in practical engineering of WSS2.8-80/60-SW-type combustion of biomass gasification boiler working principle and structure. Relevant departments of thermal and environmental test results show that the furnace thermal efficiency more than 80%, reasonable structure, stable, adequate efforts and environmental protection are in line with national standards.