Fig. 31-34 Reciprocating Engine Pump Drives Applied in Flood Control Station. Source: Fairbanks Morse Engine Div.

Gas turbine drives are generally used only for very large capacity remote pumping applications. Figure 31-35 shows a two-shaft design applied in a pumping application requiring 10,000 hp (7,500 kW).

Pumps are generally not pre-packaged with prime movers because applications and equipment types are too diverse. There are three basic drive configurations: a single prime mover drive, a hybrid setup using one pump and two drivers on a shaft, and a hybrid setup using two driver/pump sets.

Fig. 31-35 Two-Shaft Gas Turbine Featured in Large Pumping Application. Source: Solar Turbines

It may also be less costly to purchase a hybrid unit rather than two entirely separate pump/driver sets. Dualshaft, or common single-shaft, pumps, which allow operation from two different types of drivers, are often used in prime mover drive applications. An electric motor can be included along with a prime mover drive, such as a backpressure steam turbine. In the case of the failure of one driver, the other driver can easily take over. The electric drive could also be used when back-pressure steam loads are insufficient, or during inexpensive off-peak rate periods. When two pumps are desired to provide increased reliability, a hybrid system may be appropriate.

Boiler feedwater pumps are a particularly attractive back-pressure turbine application. As feedwater flow is reduced, turbine steam flow and available back-pressure steam are also reduced. Turbine discharge is used for feed-water heating, which varies in direct proportion to feed-water flow. Because feedwater pumps are critical for plant operation, multiple pumps or drivers are usually installed. Often, hybrid systems are used, with one or more electric motors and prime movers.

Figure 31-36 shows a boiler feed pump driven by a steam turbine. The 26 hp (19 kW) turbine serves a 40,000 lbm/h (18,000 kg/h) steam boiler and operates at 3,553 rpm, with an inlet steam condition of 195 psig (14.5 bar) dry saturated steam. Turbine exhaust steam at 5 psig (1.4 bar) feeds a deaerator tank.

Figure 31-37 shows a 375 hp (280 kW) vertical turbine pump driven by a gas-fired reciprocating engine. This system is part of four pumping stations that move water through 14 miles (22.5 kilometers) of pipeline from a desert to a New Mexico municipality. The pump specification required variable speed operation to meet the following head-capacity requirements:

• 1,600 gpm at 380 ft of head (6,056 L/m at 11.3 bar)

• 2,900 gpm at 410 ft of head (10,977 L/m at 12.3 bar)

• 2,550 gpm at 490 ft of head (9,652 L/m at 14.6 bar)

• 2,070 gpm at 552 ft of head (7,835 L/m at 16.5 bar) The system design called for maximum efficiency to be obtained when pumping 2,900 gpm (10,977 L/m) at 410 ft of head (12.3 bar) operating under a maximum ambient temperature condition of 100°F (38°C) at an elevation of about 6,000 ft (1,829 m). An exhaust silencer was also required, designed to maintain a 60 dba sound emission level at a distance of 25 ft (7.6 m). Figure 31-38 shows the performance curves for the featured engine over the range of operating speeds.

Fig. 31-36 26 hp Steam Turbine-Driven Boiler Feed Pump. Source: UTC Sikorsky Aircraft

The driver is a turbocharged and intercooled, lean combustion, eight cylinder, four cycle, natural gas-fired engine with an 11:1 compression ratio. Operation is between 1,400 and 1,750 rpm to deliver between 205 and 375 hp (153 to 280 kW). Dimensions are 7.9 ft (2.4 m) long by 4.5 ft (1.4 m) wide by 5.6 ft (1.7 m) high, with a dry weight of 7,200 lbm (3,300 kg) and a piston displacement of 1,462 cubic inches (24 L). The engine is equipped with a 24 volt dc starting and charging system and necessary controls for automatic operation.

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