The longitudinal drum boiler is classified as what type of combustion gas pass boiler?

The longitudinal drum boiler is classified as a three-pass combustion gas pass boiler. This classification is based on the flow of the combustion gases through the boiler. In a three-pass boiler, the flue gases travel through the boiler in three distinct passes before exiting into the atmosphere.

In the first pass, the hot gases flow from the furnace to the rear of the boiler, transferring heat to the water or steam in the drum. The second pass involves the gases moving back towards the front of the boiler below the water level, which aids in heat transfer by utilizing the heat remaining in the flue gases. Finally, in the third pass, the gases travel through the economizer section, which improves efficiency by capturing additional waste heat for preheating the feedwater.

This design allows for efficient heat recovery, minimizing the energy lost and improving the overall efficiency of the boiler system. Therefore, the classification of the longitudinal drum boiler as a three-pass boiler accurately reflects its operational characteristics and heat exchange efficiency.