Boiler/Burner Combustion Air Supply Requirements and Maintenance

There are several important components of a boiler/burner combustion air system that must be considered in order to properly operate and maintain a boiler/burner. Among these components are Secondary air, Overfire air, Pressure jet burners, and the proper venting system. In addition, boilers located above sea level must include a 3.5% correction factor to account for the less dense air.

Overfire air

Spring is a common time for many plants to conduct annual boiler/burner maintenance and tune-ups. This is done to ensure that boilers are operating as efficiently as possible throughout the seasons. Boiler/Burner combustion is a complex process that relies on fuel, heat, and air. Air consists mainly of oxygen and nitrogen, but it also contains other gases. In order for combustion to occur efficiently, fresh air is necessary.

Boiler/Burner combustion air requirements vary from manufacturer to manufacturer. Most manufacturers refer to the NFPA 54 standard for combustion air requirements. This standard calls for a combustion air opening with a free area of 0.33 to 1 square inch per kBtu/hr input. This specification applies to power burner boilers, furnaces, and water heaters.

The combustion air supplied to the burner is either overfire air or underfire air. The former is usually drawn from a common air duct or from a separate source. It is injected into the flame zone at a higher pressure than underfire air and may require a booster fan.

Secondary air

A boiler/burner combustion system requires adequate secondary air supply to maintain the proper combustion temperature. In order to meet these requirements, the combustion system must be positioned in an area with adequate free air supply. This is not possible if the combustion system is located inside a confined space. In such situations, an outside combustion air duct shall be installed.

The air flow rate varies with the type of coal and boiler. This makes it difficult to control the air flow rate. Also, the heat output of the fuel and starting and tripping of the pulverizing system change the oxygen concentration in the flue gas.

Proper combustion requires the right balance between Primary and Secondary air. Secondary air is typically two times as dense as Primary air. Therefore, it is important to monitor the primary and secondary air in order to maintain the stoichiometric ratio.

Pressure jet burners

A pressure jet burner is a gas or oil combustion device for boilers. Its combustion intensity varies from seven to fifteen bar and depends on the design of the burner and the boiler load. It can use diesel, heavy oil, or combination fuel. The burner is suitable for high-volume applications, and can be mounted directly on the boiler.

A pressure jet burner uses pressure of the fuel oil to generate a rotating spray. The fuel flows through the centre passage of the burner through a swirl plate that converts pressure energy into tangential velocity. Another type of boiler burner utilizes centrifugal force. It consists of a heat-resistant steel cup fixed to the end of a shaft. The shaft rotates at a high speed, which forces the fuel to flow.

Flow rate and atomisation rate are dependent on the flow rate of the fuel from the burner to the nozzle. The lower the flow rate, the greater the atomization. The atomization rate is also affected by the nozzle size. The nozzle size can be interchanged depending on the fuel flow rate and boiler load.

Proper venting system

Proper venting is vital to the efficiency of your boiler/burner. A venting system should prevent corrosive, explosive, or flammable vapors from being carried by the combustion air. Use a corrosion guide to determine the corrosiveness of the gasses that will be emitted during the combustion process. Also, ensure that the air intake is not too cold, which could lead to damage.

The proper ventilation system must be designed to meet federal and local regulations regarding the airflow into a boiler/burner combustion chamber. In general, a combustion air opening must have a surface area of at least 1 square inch per thousand BTU/hr. In order to meet these requirements, a ventilation system should be equipped with mechanical fans that increase the movement of supply air into the boiler room.

The most common type of venting system for boiler/burner combustion is a Category I system, which allows heated flue products to rise in the air. Unlike Category II systems, Category I vent pipe should only extend vertically from the boiler vent connection. It is recommended to limit the horizontal length of flue pipe to one-half feet, as any longer than this could lead to draft problems.