Abstract: A recirculation apparatus is employed to recirculate a portion of the feedwater in a vertical-tube economizer to reduce the likelihood of reverse flow and steaming at startup and/or low load. A recirculation valve, opened at low load, directs part of the water from the economizer outlet back to the inlet of the boiler feed pump via a deaerator. The recirculated water not only increases the pumping head across the economizer tube planes, but also reduces the temperature rise of the increased water flow rate passing through the economizer tubes which now enters the economizer tube bank at an elevated temperature. The reduced temperature rise in a given single pass through a tube plane consequently reduces the buoyant force which opposes the pumping head in downflowing tube planes. Additionally, the amount of water being recirculated at these light load conditions results in a total boiler feed pump flow which is well within the capacity of a given pump size without consideration of the present invention.

Abstract: A heat exchanger includes a number of fluid carrying tubes disposed in a hot gas flow path. One arrangement of heat exchanger tubes includes a plurality of finned serpentine tubes parallel to one another and connected to an inlet header and an outlet header. The present invention discloses a support for a serpentine tube arrangement and a method of construction for a non-contact heat exchanger.

Abstract: This disclosure is directed toward combined cycle power plants which include at least one gas turbine and one steam turbine thermally coupled through a heat recovery steam generator (HRSG). Exhaust gas from the gas turbine is used to heat feedwater into steam for the steam turbine. One optimum criterion is to design the HRSG so that the exit temperature of the exhaust gas is at a minimum without the occurrence of sulfur condensation on the economizer tube bundles. The allowable minimum temperature varies with the sulfur content of the fuel and, hence, it would be desirable to be able to adjust the tube surface temperature as necessary in accordance with the sulfur content of the gas turbine fuel.