Importance

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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. Owing to their moderate sizes, the drums can withstand high pressures without having excessive wall thickness, and this enables the evaporator to be set into operation with minimal or no hold points. Yet the two drums provide a retention time—and the protection that it provides—of a single large capacity drum having substantial wall thickness.

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First Claim