What are the functions of the primary air and secondary air in a burner?

A Adjustment of primary air volume: To ensure optimal operating conditions and high thermal efficiency for the boiler, it is necessary to adjust the primary air volume in a timely manner during operation, in response to changes in coal quality and load. At the same time, the air supply should be adjusted appropriately based on the fuel combustion, temperature changes in the bottom fluidized bed, and the differential pressure across the material layer. If the air supply is too low, the fuel cannot burn fully; over time, there is also a risk of coking ； Excessive air flow will also lower the bed temperature; it will likewise prevent the fuel from burning fully, resulting in increased heat losses through exhaust gases. It should also be emphasized that when starting up a cold furnace, the minimum flow rate of air required for fluidization should be adjusted appropriately based on the actual particle size of the bed material and the results of tests conducted in cold conditions, in order to prevent low-temperature coking. During low-load operation, the primary air flow rate must not be below the minimum value; otherwise, coking and flameout may occur. B Adjustment of secondary air volume: The basic principles for introducing and adjusting the secondary air volume are as follows: primary air is used to adjust fluidization, furnace temperature, and bed pressure difference, while secondary air is used to control the total air volume. When the total air volume is insufficient, the secondary air dampers can be gradually opened to introduce secondary air; it is generally appropriate to do this at a load of around 40 t/h. As the boiler load increases, the amount of secondary air also increases. When the rated evaporation rate is reached, the ratio of primary to secondary air is approximately 50%. At this point, the oxygen level behind the superheater is still kept at around 3-5%. It should be noted that the introduction of secondary air must be carried out gradually and slowly, in accordance with the increasing load and furnace temperature; it is absolutely avoidable to introduce it rapidly in large quantities. Since the boiler has just been put into operation at this time, the heat intensity inside the furnace is still very low and the combustion in the system is not stable enough. Introducing a large amount of secondary air with a low temperature rapidly will inevitably cause significant fluctuations in the furnace temperature, posing many difficulties for operational adjustments; if not controlled properly, it can lead to flameout.

First, let’s clarify the concepts: the primary and secondary air are not part of the burner’s components. The primary air is supplied by a primary fan and is used to carry coal powder into the furnace. The secondary air is provided by a secondary fan; it serves to supply the additional air needed for combustion. After being distributed by the large air box, this air is blown into the furnace in layers. Generally, the secondary air accounts for 60% of the total air volume in the boiler

It has been discussed before; please refer to http://bbs.hcbbs.com/thread-205545-1-1.html

Repeated post – just do a search; this topic comes up almost every few days~~~ And it’s mentioned in the books as well~~~~

Harbin Institute of Technology Press publishes materials that provide detailed explanations on things such as the first, second, and third stage winds; the content is thorough and authoritative.