XINLI BOILER

Influence of Biomass Pellets Fuel Characteristics on Boiler

16 Nov, 2021

　　The influence of fuel characteristics on the boiler is mainly reflected in: the difficulty of ignition, the stability of combustion, the characteristics of slagging and bonding, ash formation and the mass concentration distribution of ash in the furnace, combustion efficiency, pollutant emission, heating surface layout, and crushing The selection of the system, the selection of auxiliary equipment.

　　Biomass biomass combustion process: first, fuel particles are heated and dried by the high-temperature bed material; then fuel pyrolysis and volatile matter combustion; then some particles will expand and one-stage crushing; finally, coke combustion and accompanied by abrasion Phenomenon.

　　Biomass pellet fuel is particularly flammable, and the combustion of volatile matter is completed in a short time (about 3s). The main stage of semi-coke combustion is 8-10s after the fuel enters the furnace, and the basic burn-out of semi-coke takes 45-50s. Therefore, the combustion process of biomass in the furnace and the combustion process of coal have significant differences in the occurrence time and combustion process. .

1. The influence of ash content

　　Biomass requires a large amount of bed material particles to circulate in the circulation loop, so that the heat distribution is more uniform, the heat transfer is faster, and the combustion is more complete.

2. The effect on combustion

　　The increase of the ash mass fraction increases the boiler material circulation and reduces the furnace combustion temperature, especially for biomass boilers that use medium temperature separation. Using a biomass boiler with medium temperature separation, the return temperature is generally around 620℃, and when the ash content increases greatly, the return temperature will be lower than 550℃, which will cause the furnace temperature to drop rapidly, sometimes even causing Fire accident in the furnace.

3. Impact on load

　　The mass concentration of ash in the flue gas has a great influence on the heat transfer coefficient of the biomass boiler furnace. When the mass concentration of ash increases, the convective and radiative heat transfer coefficients of the water wall will increase. Therefore, the ash mass concentration is used as the adjustment load and the bed temperature. The method is widely used.

4. The impact on the material layer

　　It is very important to maintain the relative stability of the bed height during the operation of the biomass boiler. If the bed is too high or too low, it will affect the fluidization quality and cause coking.

5. Influence on the layout of the heated surface of the tail

　　The fuel ash mass fraction affects the mass concentration of fly ash in the flue gas, thereby affecting the ash accumulation and wear on the heated surface of the tail. Due to the impact of the amount of ash carried by the biomass pellet fuel, the tail economizer has serious ash accumulation, so the economizer structure is changed from the original staggered arrangement to the in-line arrangement.

　　In order to minimize the adverse effects of changes in the ash content in the fuel, when the fuel contains a lot of ash, the bottom slag method is generally adopted. When the biomass pellet fuel contains less ash, the ash content of its own cannot meet the requirements of bed material circulation, so bed material generally needs to be added during operation. The added bed material becomes the main body of the circulating material, and should not be easily worn, such as quartz sand, river sand, etc.