Liquid Turbines

Liquid turbines are familiar as water-powered electricity generators. There are three main types of rotor:

• Pelton wheel-used with limited supply of high pressure water.

• Francis type-used with large supply of high pressure water.

• Kaplan type-used with large supply of low pressure water.

It is rare to find any of these designs used in the process industries, though there are certainly opportunities in some high pressure plants for a Pelton wheel application. Most liquid turbines in the process industries are essentially pumps running backwards to recover pressure energy. A typical arrangement is shown in Figure 8.10.

The power recovered is a roughly a function of (flow rate)3 and so even a small reduction in flow drops power recovered dramatically. Since it is necessary to control the upstream pressure, it is better to undersize the turbine and control flow or upstream pressure using a by-pass control valve. Figure 8.10 shows a split range control-the inlet to the hydraulic turbine being normally full open except during start-up or when running at low plant rate. The over-run clutch allows the hydraulic turbine to idle when not in use, rather than absorb power from the motor. The motor should be rated to drive the charge pump with the turbine out of commission.

Liquid turbines can be used in refrigeration systems in place of the more conventional Joule-Thompson (JT) valves. In most cases these are used to generate electricity and thus remove extra energy from the refrigerant. Depending on the size of the installation and the refrigerant used, there can be net system energy savings of up to 15%.

recovery turbine pump

Figure 8.10 Power recovery train.

recovery turbine pump

Figure 8.10 Power recovery train.

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