What type of circulation do most horizontal gas flow HRSG boilers use?

Most horizontal gas flow Heat Recovery Steam Generators (HRSG) utilize natural circulation. In these systems, the flow of water or steam is driven primarily by the temperature difference in the fluid due to heating. As water is heated, it becomes less dense and rises, while cooler, denser water sinks, creating a natural convective flow. This method is particularly efficient in HRSGs due to the design and operational characteristics of these boilers.

Natural circulation is favored in HRSG applications because it enhances the safety and reliability of the system. It reduces the need for additional pumping mechanisms, which can introduce complexities and maintenance requirements. Since the flow is driven by thermal buoyancy, it also tends to be more energy-efficient, as there are no external devices consuming electrical energy to circulate the water or steam.

This operational principle contrasts with other circulation types like forced, controlled, or positive circulation, which involve mechanical pumps or specific control systems to manage fluid movement. Such alternatives may be more suited to different types of boiler systems where precise control of water flow is necessary, or where high pressures and temperatures are involved that may hinder effective natural circulation.