What classification does the HRT boiler fall under regarding passes?

The HRT (Horizontal Return Tubular) boiler is classified as a two-pass boiler. This classification pertains to the flow path of the flue gases through the boiler. In a two-pass design, the flue gases travel through the combustion chamber, then pass through tubes that run back and forth, ultimately exiting the boiler. This configuration improves the heat transfer efficiency owing to the increased surface area available for the heat exchange, allowing the water to absorb more heat as it passes through the tubes.

The two-pass design also enhances the overall efficiency of the boiler by allowing for better utilization of the heat in the flue gases before they are discharged. By contrast, a single-pass configuration would have the gases flow through the boiler only once without any return, which would typically result in lower efficiency. Similarly, a three-pass design would involve the flue gases making three passes through the system, usually in larger or more specialized boilers. The classification of "no pass" does not apply as it indicates a non-existent flow path, which is not the case for the HRT boiler.

Understanding this classification is crucial for assessing the operational efficiency and design principles of different boiler types within the scope of power engineering.