Pumping Applications

In many pumping applications, the liquid remains at a high pressure after it has completed its cycle. It is often economically desirable to recover some of the energy, which will otherwise have to be dissipated when the liquid is brought back to a lower pressure. Instead of running the liquid through a pressure-reducing valve to destroy the energy, a hydraulic turbine may be installed. This turbine can therefore assist in driving the process pumps. There are many such applications in use. Among these are the use of turbine-driven pumps in gas-cleaning operations. Here the solutions from scrubber towers are passed through turbines that in turn drive pumps. Some of the solutions involved in such a process are water saturated with carbon dioxide at a temperature of 40 to 70°F (4 to 21°C) and potassium carbonate containing dissolved carbon dioxide at a specific gravity of 1.31. A liquid at the much lower specific gravity of 0.84 has been used in power-recovery turbines in a glycol-ethylene hydration process.

One of the oldest applications of turbine-driven pumps was for fire-fighting equipment in mills having a natural head of water. The large volume of low head water was routed through a hydraulic turbine that drove the pump to pressurize a sprinkler system or provide high-pressure water to the fire-hose connections. Today, hydraulic turbines are used to drive pumps that generate fire-fighting foam.

At thermal power plants, cooling water returning from the cooling towers has been used to drive a hydraulic turbine directly connected to a pump that provides part of the cooling water. Naturally, in such an application, the power from the turbine alone is not enough to maintain the pumping system. Therefore an auxiliary power source is also required.

Turbines using oil pressure have been employed at thermal power plants. Large steam turbines obtain bearing oil and control oil pressure from a main feed pump that is directly connected to the steam turbine shaft. A small amount of the oil at this high pressure is used for the relay control, with the majority of the oil going to the bearings at a lower pressure. To reduce the oil pressure from that required by the relays to that needed by the bearings, the oil is passed through a turbine driving a booster pump that pressurizes the oil at the intake of the main pump. At locations with high flood levels, it is preferable to locate pumps and electrical equipment above flood level. Some recent steam power plant installations have used the return from the condenser to the river (normally an appreciable drop in head) to drive a hydraulic turbine, which in turn may assist in driving the condensate pumps. Also, effluent from sewage treatment plants may have a significant discharge head.

It is often economical to use a small volume of water at a high head to move a large volume of water at a low head. Of course, the reverse application can also be accomplished. The former procedure is employed at hydroelectric projects where it is necessary to operate fishways to enable migrating fish to continue traveling upstream over the dam. The large volume of water is used both to attract the fish to the fish flume and to transport the fish to the fish ladders. An example of such an installation can be seen in Figure 1.

Turbines have also been used to start large pumping units when the hydraulic conditions are suitable. The impulse turbine, which develops maximum torque at zero speed, is especially useful for this application. The power required on such a starting turbine would be less than the power required on a starting motor to do the same job. Many electric controls can be eliminated when starting with a turbine. An illustration of this application is shown in Figure 2.

Desalinization plants have been built wherein salt is removed from seawater by pumping it through a membrane at high pressure. Only pure water goes through the membrane, with most of the sea water being used to carry away the salt. This excess high-pressure sea water is then put through a power-recovery turbine that helps to drive the high-pressure pumps.

FIGURE 1 Turbine-driven fishway pumps. High head, low volume Francis-type turbine drives a low head, highvolume propeller pump at Rocky Reach, Washington.
FIGURE 2 Impulse runner used to start a large pump. Left to right: Francis turbine, generator motor, starting impulse turbine, and two-stage double-suction storage pump (Adapted from Voith Publication 1429, J. M. Voith GmbH, Heidenheim, Germany).

It is often desirable to have the turbine and pump running at different speeds, and this has been accomplished by means of a variable-speed coupling between turbine and pump. Reliable low-speed gear increasers or reducers of up to 35,000 hp (26,000 kW) are being built by many manufacturers. In applications such as starting a pump by means of a turbine, a mechanism may be needed to disengage the turbine after the pump has been started, in order to minimize windage and friction. Disengaging couplings may be hydraulic or mechanical and may be actuated when the unit is stationary or rotating, depending on the application. However, it is possible to allow the turbine to spin in air with the pump after the pump has been started. Figure 3 is an illustration of a turbine-drive pump arrangement.

Survival Treasure

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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