What characteristic do controlled circulation HRSGs provide regarding circulation?

Controlled circulation heat recovery steam generators (HRSGs) are designed to manage the flow of water and steam within the system actively. When these systems are in operation, they utilize pumps to create a positive circulation of the working fluid, which is essential for efficient heat transfer and overall system performance.

This positive circulation means that once the pump is engaged, water flows continuously through the evaporator sections, ensuring that heat is effectively absorbed from the combustion gases. By maintaining a controlled flow rate, the system can optimize the evaporation process and enhance steam generation under varying operational conditions. This characteristic differentiates controlled circulation HRSGs from natural circulation systems, where fluid movement is driven solely by density differences, which can be less reliable.

Furthermore, the use of pumps enables better management of pressures and temperatures, contributing to the efficiency and reliability of the power generation process. Hence, the characteristic of having positive circulation once the pump starts is critical for the effective function of controlled circulation HRSGs.