XINLI BOILER

Introduce in detail the method of biomass boiler combustion adjustment

30 Jul, 2021

　　1. The combustion process of biomass on the vibrating grate

　　The combustion of biomass can usually be divided into three stages, namely, the preheating and ignition stage, the volatile combustion stage, and the char combustion stage. The combustion process of biomass on the grate is divided into a preheating drying zone, a combustion zone and a burnout zone, which can correspond to the high, middle and low ends of the vibrating grate. According to the combustion characteristics of each zone, the air volume required by each zone is different. The air volume in the preheating drying zone and burnout zone is less, and the air volume in the combustion zone is larger. The combustion of fuel particles in biomass boilers can be divided into two types: the large particles are burned on the grate, and during the pneumatic spreading process, the small particles are suspended and burned in the upper space of the grate.

　　2. Conditions for complete combustion of biomass on the grate

　　The sign of good combustion in the biomass boiler is that it is as close to complete combustion as possible without slagging in the furnace, while ensuring a faster combustion speed and obtaining a high combustion efficiency.

　　(1) Sufficient supply and suitable air volume

　　If the excess air coefficient is too small, that is, the air supply is insufficient, it will increase the solid incomplete combustion heat loss q4 and the combustible gas incomplete combustion heat loss q3, which will reduce the combustion efficiency; if the excess air coefficient is too large, the furnace temperature will be reduced. Increase incomplete combustion heat loss. The good excess air coefficient makes the sum of q2+q3+q4 very small.

　　(2) Increase furnace temperature appropriately

　　According to Arrhenius’ law, the combustion reaction rate has an exponential relationship with temperature. On the premise of ensuring that the furnace does not form slag, try to increase the furnace temperature as much as possible.

　　(3) Good disturbance and mixing in the furnace

　　In the fire and combustion stage, it is necessary to ensure the full mixing of air and fuel, and in the burnout stage, it is necessary to strengthen the disturbance mixing.

　　(4) The fuel has ample residence time on the grate and in the furnace

　　(5) Maintain a reasonable flame front position. The flame front should be located in the area between the grate and the middle grate, and the flame is full of the grate.

　　3. Combustion adjustment method of biomass boiler

　　(1) Adjust the vibration frequency and vibration period of the biomass boiler (vibration time and stop time)

　　The vibration frequency of the grate is generally not adjusted with the change of the load. The good vibration frequency is determined by observing the thickness of the ash deposit at the ash baffle of the low-end grate. When the particle size, moisture, and load of the fuel change, only the vibration time and stop time are adjusted, and the vibration frequency is generally not adjusted.

　　The frequency of the grate should be determined by the following two factors: one is the thickness of the ash deposit at the ash baffle of the low-end grate, which should be maintained at 5-10cm; the other is that the furnace cannot be made at a specific vibration frequency. The negative pressure changes drastically; the third is to detect the carbon content of the ash slag exported from the No. 1 slag conveyor. The normal carbon content should be 5-10%. (In the enkoping power plant, under normal circumstances, the carbon content of fly ash is 1 to 2%; the carbon content of ash slag is 5 to 10%.). According to the adjustment test, the frequency of the vibrating grate should be 40～45 Hz.

　　The vibration time of the grate determines the walking speed of the fuel particles on the grate (or the stroke of the fuel on the grate in each vibration period). The longer the vibration time, the stronger the ability to destroy the coke and slag, but the turning inside the material layer The performance is poor, and the walking speed is accelerated; the stop time of the grate determines the residence time of the fuel particles on the grate in large cases.