Compared with fossil energy, biomass energy has the advantages of renewable and low pollution, so it has received universal attention and has become one of the development directions of new energy. Biomass energy is mainly through direct combustion, gasification,
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Compared with fossil energy, biomass energy has the advantages of renewable and low pollution, so it has received universal attention and has become one of the development directions of new energy. Biomass energy is mainly utilized by direct combustion, gasification, liquefaction and anaerobic fermentation. Biomass is a high-quality fuel because of its high volatile content, high carbon activity, low N and S content, low ash content, and zero CO2 emissions during combustion in the life cycle. Biomass combustion technology can be divided into biomass molding fuel (pressed by pellet machine or straw briquetting machine) combustion technology, biomass bun burning technology, biomass powder burning technology and biomass gas combustion according to its different forms. Technology, etc., in terms of China's basic national conditions and biomass utilization level, biomass combustion technology is undoubtedly one of the most simple and feasible ways to use biomass resources efficiently.
1 Combustion characteristics of biomass fuel
Biomass as a fuel has many differences compared to coal, the differences are listed in Table 1. It can be seen from Table 1 that the volatile matter of biomass is much higher than that of coal, the ash content and carbon content are much smaller than that of coal, and its calorific value is less than that of coal. The fuel characteristics of biomass determine its combustion has certain characteristics.
Fuel type C/% O/% H/% S/% A/% V/% Density/cm-3
Biomass fuel 38～50 30～44 5～6 0.10～0.20 4～14 65～70 0.47～0.64
Coal 55～90 3～20 3～5 0.40～0.60 5～25 7～38 0.80～1.00 The combustion process of biomass fuel is mainly divided into two independent stages: the precipitation of volatile matter, the combustion and the burning and burning of residual coke. The characteristics of its combustion process are:
(1) The biomass has a large moisture content, and the combustion requires a higher drying temperature and a longer drying time, and the generated flue gas volume is larger, and the exhaust heat loss is higher;
(2) The density of biomass fuel is small, the structure is relatively loose, the windward area is large, and it is easy to be blown up, and the proportion of suspended smoldering is large;
(3) Due to the low calorific value of biomass, the temperature field in the furnace is low, and the stable combustion of the structure is difficult;
(4) Due to the high volatile content of biomass and low ignition temperature of fuel, the volatile matter generally precipitates at a temperature of 250 ° C ~ 350 ° C and begins to burn intensely. If the air supply is insufficient, the fuel will increase. Incomplete combustion loss;
(5) After the volatilization analysis, the coke particles are slow to burn and difficult to burn due to the difficulty of ash wrapping and air infiltration. If no necessary measures are taken, more residual carbon remains in the ash. Increase mechanical incomplete combustion losses.
It can be seen that the design and operation mode of biomass combustion equipment should be selected from the combustion characteristics of different types of biomass to ensure the economics and reliability of biomass combustion equipment operation and improve the efficiency of biomass development and utilization.
2 different forms of biomass burning technology
2.1 Biomass Forming Fuel Combustion Technology
Biomass forming fuel is a method of pressurizing biomass waste such as straw, rice husk, sawdust, and wood chips by mechanical means (usually used mechanical equipment is a pellet machine or a straw briquetting machine) to make the original loose and amorphous raw materials. It is compressed into a solid shaped fuel with a certain shape and high density, which has the advantages of small volume, high density, convenient storage and transportation, stable combustion, long cycle, high combustion efficiency, and low content of pollutants in ash and flue gas.
In the 1930s, the United States began to study compression molding fuel technology and combustion technology, and developed a screw compressor and corresponding combustion equipment. In the 1930s, Japan began to study mechanical piston molding technology to treat waste materials, 1 954 In the late 1970s, many countries in Western Europe such as Finland, Belgium, France, Germany, Italy and other countries began to pay attention to the research of compression molding technology and combustion technology. Molding machine and supporting combustion equipment; In the 1980s, in addition to Japan, Thailand, India, the Philippines, South Korea, and Malaysia have established a number of solidification and carbonization production plants, and have developed related combustion equipment. By the 1990s, biomass-forming fuel combustion equipment in Japan, the United States, and some European countries had been finalized and industrialized, and had been widely applied in the fields of heating, heating, drying, and power generation. However, compared with China, these foreign combustion equipments have the disadvantages of high price, single fuel consumption, easy slagging, high power consumption, etc., and are not suitable for introduction to China.
Since the introduction of the spiral propelling straw forming machine in the 1980s, the research and development of China's biomass compression molding technology has been more than 20 years old. So far, China has developed a variety of molding machines such as mechanical stamping machines, piston forming machines, hydraulic forming machines, and roll forming machines. However, the development of corresponding dedicated biomass forming fuel combustion equipment is still rare. Some units use biomass-forming fuels, blindly changing the original coal-fired combustion equipment to biomass-forming fuel combustion equipment without clarifying the combustion characteristics of biomass-forming fuels. The reformed combustion equipment still has unreasonable phenomena such as air flow field distribution, furnace temperature field distribution, concentration field distribution, excess air coefficient size, and heating surface arrangement, which seriously affects the normal speed and normal condition of biomass forming fuel combustion. The reformed combustion equipment has problems such as low thermal efficiency, high content of pollutants in the exhaust gas, and easy slagging.
In 2003, Henan Agricultural University proposed the theory of biomass-forming fuel combustion, and developed a double-layer grate biomass-forming fuel boiler. The combustion equipment adopts a double-layer grate structure, which is printed on a certain height of the hand-fired grate and a water-cooled steel grate. The upper furnace door of the double-layer grate is normally opened for fuel supply and air supply; the middle furnace door is used for adjusting the combustion of the fuel on the lower grate and removing ash, which is only opened during ignition and cleaning; the lower furnace door It is used for ash discharge and supply a small amount of air. It is slightly opened during normal operation, and the opening degree depends on the combustion condition on the grate. The space above the upper grate is equivalent to the wind chamber, the space between the upper and lower grate is the furnace, and the exhaust wall is provided on the rear wall. The flue gas outlet should not be too high, so as to avoid the short circuit of the flue gas, affecting the combustion of the combustible gas and the flame filling the furnace, but it should not be too low to ensure the necessary ash layer thickness (100mm ~ 200mm). This kind of combustion method realizes the stepwise combustion of biomass forming fuel, alleviates the burning speed of biomass, achieves the matching of combustion oxygen demand and oxygen supply, and makes the biomass forming fuel stable, continuous and complete combustion, and plays a role of smoke elimination and dust removal. .
2.2 Biomass Bundling Technology
Many member states of the European Union are rich in renewable energy, and biomass straw burning technology is developing rapidly. The development of biomass bale burning technology in Denmark, Belgium and France is the most mature. The United States, Japan and other countries have also developed biomass bunling technology, and formed a series of products, which have been promoted and applied in some areas. Denmark has a variety of small, medium and large balers that can produce a variety of types of biomass straw bales to suit different levels of combustion equipment. The biomass boiler model is also relatively complete, mainly including the following three boiler systems:
1) System using flake bales as fuel
The whole grasshopper was cut into pieces by a hydraulic slicer and then pushed into the boiler by a piston conveyor. Before slicing, the bales are lifted to a position perpendicular to the hydrotome and then sliced ​​from the bottom of the bales.
2) System for continuously burning whole bales
Instead of shredding the bales, such boilers are arranged in a row and continuously pushed into the furnace. First, the crane places the bales in a bin, which is pushed into the channel by a hydraulically driven piston conveyor, and then the bales are pushed to the burners on the furnace wall. The straw releases volatiles here and is completely ignited by a large amount of secondary air. At this time, the bales were still pushed forward, and the unburned straw and the generated ash fell on the water-cooled grate and finally burned.
Sanmenxia Futong New Energy sells biomass molding machinery such as pellet machine, straw pellet machine, wood pellet machine, straw briquetting machine.
Information from: Current status and prospects of different forms of biomass burning technology (1) http://
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