Condensate Pumps

Condensate pumps take their suction from the condenser hot well and discharge either to the deaerating heater in open feedwater systems (refer to Figure 3) or to the suction of the

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FIGURE 27 Recommended thermal insulation of a boiler feed pump (Flowserve Corporation)

boiler-feed pumps in closed systems (refer to Figure 6). These pumps, therefore, operate with a very low pressure at their suction. The available NPSH is obtained by the submergence between the water level in the condenser hot well and the centerline of the condensate pump first-stage impeller. Because it is desirable to locate the condenser hot well as low as possible and avoid the use of a condensate pump pit, the available NPSH is generally extremely low, on the order of 2 to 4 ft (0.6 to 1.2 m). The exception to this occurs when vertical-can condensate pumps are used because these can be installed below ground and higher values of submergence can be obtained. Frictional losses on the suction side must be kept to an absolute minimum. The piping connection from the hot well to the pump should therefore be as direct as possible and of ample size and should have a minimum of fittings.

Because of the low available NPSH, condensate pumps operate at relatively low speeds, ranging from 1750 rpm in the low range of capacities to 880 rpm.

It is customary to provide a liberal excess capacity margin above the full-load steam condensing flow to take care of the heater drains that may be dumped into the condenser hot well if the heater drain pumps are taken out of service for any reason.

Types of Condensate Pumps Both horizontal and vertical condensate pumps are used.

Depending on the total head required, horizontal pumps may be either single-stage or multistage. Plants constructed in the 1950s and before utilized horizontally split multistage pumps mounted at the lowest plant level, near the bottom of the condenser. As required condensate flows increased in later years, the common installation incorporated vertical can-type multistage pumps (Figure 30). Combined cycle plants utilize vertical turbine-type multistage condensate pumps (Figure 31). The vertical turbine-type pump is of medium-duty construction and lower in cost than the can-type pump shown in Figure 30.

Figure 32 shows a single-suction, single-stage pump with an axially split casing used for heads up to about 100 ft (30 m). It is designed to have discharge pressure on the stuffing box. The suction opening in the lower half of the casing keeps the suction line at floor level. An oversize vent at the highest point of the suction chamber permits the escape of all entrained vapors, which will be vented back to the condenser and removed by the air-removal apparatus.

Multistage pumps are used for higher heads. A two-stage pump is shown in Figure 33, with the impellers facing in opposite directions for axial balance. By turning the impeller

BOILER FEED PUMP INJECTION CONTROL (CONSTANT DRAIN TEMPERATURE) ELECTRO-PNEUMATIC SYSTEM

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Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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