2000 Hook-up Book

a Figure II-76 Typical Flash Steam Recovery Hook-up Thermostatic Air Vent Strainer Float & Thermostatic Steam Trap Spira-tec Loss Detector Safety Valve Flash Recovery Vessel L. P. Condensate H. P. Condensate L. P. Steam Main Drip Pan Elbow Drain to Safe Place

Condensate from high pressure loads releases steam by flash ing as it passes to the lower pressures, downstream of the high pressure traps. The mixture of steam and condensate is readi ly separated in Flash Vessels of appropriate dimensions and proportions. A supply of Low Pressure steam then becomes available for use on any application which can accept steam at this low pressure, or the separated steam may simply be taken into the LP steam mains, where it is supplemented through pressure reducing valves, for general plant use. Where the supply of flash steam may at times exceed the demand from the LP system, the surplus flash steam can be discharged through a back pressure control valve. This is set at a few psi above the normal LP steam pressure, but below the setting of the LP safety valve. See Figure II-77. The condensate leaving the flash recovery vessel is at low pres sure. Usually it is handled by a float-thermostatic steam trap and is delivered to the receiver of a condensate pump for return to the boiler house. Any residual flash steam from the low pressure condensate is vented from the pump receiver. (Figure II-78.) In some cases, pressures are sufficiently high that the flash can be taken off at an intermediate pressure and the con densate leaving the flash vessel still contains a useful amount of sensible heat. It can then be taken to a second flash vessel working at low pressure, so that the maximum heat recovery is effected. The use of two flash vessels in series, or “cascade”, means that these vessels may be installed generally as Figure II-76 and II-77. Alternatively, it may be desirable to use the recovered flash steam at a low pressure, below that in the condensate return line or perhaps the de-aerator tank. The arrangement adapt ed may then be either as Figure II-78 or as Figure II-79. This latter system uses a steam powered pump, with the bottom of the flash recovery vessel serving as the pump receiver. Power steam used by the pump is vented to the LP steam line, so that pumping is achieved at virtually zero cost and the use of unsightly or wasteful vents is avoided.

HOOK-UP DIAGRAMS

a a

Thermostatic Air Vent

Drain to Safe Place

Vent

Strainer

Pilot Operated Back Pressure Control Valve

Moisture Separator

Strainer

H. P. Steam Supply

L. P. Steam

Spira-tec Loss Detector

Pilot Operated Pressure Control Valve

Safety Valve

Drip Pan Elbow

Strainer

Float & Thermostatic Steam Trap

H. P. Condensate

Flash Recovery Vessel

H. P. Condensate

Float & Thermostatic Steam Trap

Figure II-77 Flash Steam Recovery with Live Steam Make up and Back Pressure Surplussing Valves

Strainer

L. P. Condensate

Check Valve

Spira-tec Loss Detector

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a