Abstract: An evaporator for a heat recovery steam generator has two horizontal steam drums of moderate size, one located slightly higher than the other. It also includes a coil having tubes located in the flow of a hot gas. The lower drum communicates with the inlets of the tubes for the coil. The outlets of the tubes communicate with the upper drum. A drain line connects the bottom of the upper drum with the lower region of the lower drum, so that water will flow from the upper drum to the lower drum. Water, which is primarily in the liquid phase, enters the lower drum through an inlet line and mixes with water from the upper drum. The mixture flows through into the coil. Here some of it transforms into saturated steam while the rest remains as saturated water. The saturated steam and saturated water flow into the upper drum where the steam escapes and the water flows back into the lower drum to recirculate through the coil.

Abstract: A heat recovery steam generator that includes a first steam drum for receiving a flow of water and steam from an evaporator. The first steam drum is adapted to provide the flow of water and steam to a second steam drum. The second steam drum is in fluid communication with the first steam drum and receives the flow of water and steam from the first steam drum and separates steam from the flow of water and steam to form a separated steam. There is a steam flow outlet positioned in the second steam drum, the steam flow outlet adapted to release the separated steam from the second steam drum.