Problems with coal-fired boilers

Boilers in which the gas pressure in the combustion chamber and flue of a running boiler is 200 to 400 pascals higher than atmospheric pressure are known as slightly positive pressure combustion boilers. Micro-positive pressure combustion boilers do not have an exhaust fan. It uses the pressure generated by the blower to overcome the resistance in the air ducts and flue ducts. 　　Both the combustion and heat transfer on the flue gas side in a slightly positive pressure combustion furnace take place under positive pressure. Therefore, both combustion and heat transfer can be enhanced, which is beneficial for improving boiler efficiency and reducing low-temperature corrosion. Furthermore, the reduction in flue gas specific volume allows the combustion chamber and flue ducts to be smaller, which is advantageous for manufacturing large-capacity boilers. The poor working conditions of the furnace walls in micro-positive pressure combustion furnaces, along with the high requirements for sealing, have restricted their development.

Today, balanced ventilation is generally used for boilers, with the furnace operating at a slight negative pressure; this helps to avoid excessive pressure from the blower and reduces power consumption. At the same time, the positive pressure in the furnace also causes hot flue gas to escape, reducing thermal efficiency.

Long-term positive-pressure combustion tends to cause backfire and damage the burner blades; it is generally better to maintain negative-pressure combustion

The sealing issues with micro-positive pressure boilers are quite troublesome; generally, there is a steel shell outside the furnace wall, which requires high standards for sealing, insulation, and heat retention of the furnace wall. If smoke leaks through, failure to address it promptly can lead to damage to the inner insulation layer and even to the destruction of the shell itself. We have one such boiler – it causes a lot of problems!