What is the principle of ratio between level 1 and level 2 winds?

Do you think that operating a boiler is just a matter of increasing or decreasing the amount of fuel? Or do you think you understand the issues related to operation and adjustment after operating the boiler for a few days? Can you discuss on paper with the vague theories you learned from your teachers? Operating a boiler may be very easy, but truly learning it is really difficult!

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Primary air fan of circulating fluidized bed boiler

What are the principles of the ratio between primary and secondary air?

The general principles of the ratio of primary air to secondary air are as follows: primary air controls the temperature of the furnace and secondary air adjusts the oxygen content.
  • When the load is less than 35%, the primary air volume is kept unchanged to ensure that it does not exceed or approach complete boiling, at this time, the primary air is usually between 15-30%.
  • When the load exceeds this value, the primary and secondary air volumes are increased according to the degree of boiling, furnace temperature, and corresponding oxygen content.
  • When the load has increased to 65% or more, the primary air volume basically stops changing. Then, based on changes in oxygen and furnace temperature, the secondary air volume is continuously increased until the corresponding air flow rate reaches maximum evaporation.
Under the premise of appropriate furnace temperature, the speed of secondary air should be increased as much as possible and the speed of primary air should be reduced, which is beneficial for staged combustion of circulating fluidized bed boilers, and also beneficial for reducing NOx and SOx emissions.

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Secondary air fan of circulating fluidized bed boiler

The air-fuel ratio is more difficult to adjust, but it's nothing compared to the ratio of primary and secondary air!

Adjusting the air ratio is quite complicated (the ratio of primary and secondary air, the ratio of air above and below, the ratio of pre- and post-air), but the ratio of primary and secondary air is very easy to implement, and the amount of primary air can be increased or decreased appropriately according to changes in furnace temperature, with the premise of ensuring a minimum air flow rate for boiling and not much variation.

  1. In circulating fluidized bed boilers, the main task of the primary fan is to introduce air into the air box and pass through the furnace bed to boil the fuel in the furnace. Primary fluidized air is the main heat carrier for heating and entering the furnace. The magnitude of the primary air velocity determines the boiling degree of the material and adjusts the temperature in the furnace. Primary air is also the air source for blowing materials, so the largest amount of primary air in circulating fluidized bed boilers, accounting for more than 60% of total consumption.
  2. The main purpose of the secondary fan of the circulating fluidized bed boiler is to supply oxygen for combustion in the furnace and enhance fuel mixing. Due to the large proportion of the secondary air volume in the circulating fluidized bed boiler, the demand for secondary air accounts for only about 40% of the total air volume. The pressure of the secondary air is also lower than that of the primary air, so the power of the secondary fan is smaller than that of the primary fan.
  3. The general principle of primary and secondary air is: primary air controls the furnace temperature and secondary air controls the oxygen content. At the same time, the negative pressure value of the operation door is controlled by adjusting the exhaust fan.
  4. The design of each boiler is different, the ratio of primary and secondary air is not the same, and the ratio needs to be adjusted according to specific design requirements, and the air flow ratio of the boiler cannot be adjusted based on the experience of others. To reduce the amount of NOx generated during boiler operation, try to ensure that the fuel is boiling in the furnace by means of primary air.

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Air supplement fan for combustion chamber