XINLI BOILER

Energy Saving Analysis of Biomass Hot Water Industrial Boiler

09 Jul, 2021

　　1.1 Biomass fuel refers to the processing of crop wastes such as straw, rice husk, sawdust and wood chips into solid fuels with a certain shape and density through biomass compression molding technology.

　　After being extruded, the density of biomass raw materials can reach 1.1~1.4 tons/m3, the energy density is equivalent to that of medium coal, and it is easy to transport and store. In the compression process, physical changes are the main factor, and its elemental composition and microstructure are basically the same as the original material. The carbon content of various biomass fuels is concentrated in the range of 35% to 42%, while the hydrogen content is relatively low, in the range of 3.82% to 5%. Extremely low. The volatile content of biomass fuel is 60% to 70%, so volatiles should be considered in the design of combustion equipment.

　　1.2 The combustion characteristics of biomass pellet fireplaces

　　After forming biomass fuel under high pressure, its density is much higher than that of the original material, and the combustion is relatively stable. Although the ignition temperature increases and the ignition performance becomes worse, it has better ignition performance than coal. Because biomass fuel is a massive fuel formed by high pressure, its structure and organizational characteristics determine the escape rate and heat transfer rate of volatile substances are greatly reduced, but it is easier than coal. Therefore, the volatility characteristic index of biomass fuel is greater than the volatility characteristic index of coal, and its combustion characteristic index is greater than that of coal. The combustion speed is moderate, and the heat emitted by the volatiles can be transferred to the heating surface in time, reducing the heat loss of exhaust smoke; at the same time, the oxygen required for volatile combustion is well matched with the diffused oxygen outside, and the combustion wave is very small. Reduce the heat loss of solid waste gas.

　　2, biomass pellet hot water boiler

　　2.1 Structure of biomass fuel hot water boiler

　　At present, there are many types of biomass-fueled hot water boilers in my country. According to the type of fuel, they can be divided into wood pellet boilers and straw pellet boilers, and they can be divided into household and commercial use according to their uses. The downdraft fixed double-grate water heater is a widely used structural form, which fully considers the combustion characteristics of biomass fuel. It is composed of door, furnace rate, furnace, heating surface, gas chamber, dust chamber and furnace wall. Main parts such as exhaust pipe, flue, chimney, etc.

　　2.2 Working process of biomass fireplace fuel hot water boiler

　　The biomass fuel of a certain particle size is added to the grate through the upper furnace door of the furnace. According to the characteristics of the fuel, the biomass is easy to burn, will burn instantly, and is burned under the guidance of the burner. Induced draft fan; The fuel residue ash and slag leaking from the upper grate continue to burn, and there is ash at the bottom of the lower furnace, which is then discharged through the ash outlet. The flue gas and part of the combustible gas formed after the fuel is burned on the upper grate pass through the fuel layer and the ash layer and enter the lower furnace to continue burning. And together with the flue gas generated by the fuel on the lower grate, it leaves the high-temperature air outlet and flows to the dust removal chamber and the convective heating surface on the back. After sufficient heat exchange, it enters the chimney and then discharges to the outside.

　　3, the principle of energy saving

　　According to the relevant combustion theory, the necessary conditions for maintaining sufficient fuel combustion are maintaining sufficient furnace temperature, proper air volume, good mixing with fuel, and sufficient combustion time and space. Therefore, according to the characteristics of biomass fuel and combustion theory, the energy-saving analysis of the boiler structure is carried out.

　　3.1 grate and hearth

　　Biomass fuel hot water boiler adopts a double-layer grate structure, that is, a water-cooled steel pipe grate is added to a certain height of the manual grate, and the elbow is directly inserted into the upper drum. On the other hand, the heat absorption area of ​​the water-cooled grate speeds up the heat transfer between the grate and the return water in the drum.

　　The fuel combustion uses the downward suction combustion method. The formed fuel is preheated and burned by the furnace door and grate on the upper part of the furnace. Under the guidance of the fan, the new fuel will not directly encounter the high temperature and overheated flue gas, thereby delaying the concentrated precipitation of volatiles and avoiding The fluctuating temperature of the furnace is in order to stabilize the combustion; at the same time, the volatiles must pass through the high-temperature oxide layer and be fully mixed with the air, thereby burning in the coke particles. After a period of combustion is completed, the fuel fragments and ash formed by the upper grate will leak into the furnace and continue to burn until it burns.

　　The double-layer grate is used to realize the gradual combustion of the straw briquette fuel, reduce the burning speed of the straw, and realize the matching of the combustion oxygen demand and the oxygen supply, thereby realizing the continuous and complete combustion of the straw briquette fuel. At the same time improve fuel utilization. Smoke removal effect.