Power recovery from liquid streams efficiency

Valves are often used to reduce the pressure of a gas or liquid process stream. By replacing the valve with a turbine, called an expander, turboexpander, or expansion turbine in the case of a gas and a liquid expander or radial-infiow, power-recovery turbine in the case of a liquid, power can be recovered for use elsewhere. Power recovery from gases is far more common than from liquids because for a given change in pressure and mass flow rate, far more power can be recovered from a gas than from a liquid because of the lower density of the gas. Equations for f.o.b. purchase costs of power recovery devices are included in Table 16.32 in terms of horsepower that can be extracted. Typical efficiencies are 75-85% for gases and 50-60% for liquids. Condensation of gases in expanders up to 20% can be tolerated, but vapor evolution from liquid expansion requires a special design. Whenever more than 100 Hp for a gas and more than 150 Hp for a liquid can be extracted, a power recovery device should be considered. 

The power loss from a process liquid stream going through a pressure letdown valve could be significant. If a power expander is considered to replace the letdown valve, equation (8.1) could be used to estimate the power recovery potential, and a typical power generation efficiency for a liquid expander is 75%. 

Dust Filter. The cloth or bag dust filter is the oldest and often the most reliable of the many methods for removing dusts from an air stream. Among their advantages are high (often 99+%) collection efficiency, moderate pressure drop and power consumption, recovery of the dust in a dry and often reusable form, and no water to saturate the exhaust gases as when a wet scrubber is used. There are also numerous disadvantages maintenance for bag replacement can be expensive as well as a sometimes unpleasant task these filters are suitable only for low to moderate temperature use they cannot be used where liquid condensation may occur they may be hazardous with combustible and explosive dusts and they are bulky, requiring considerable installation space. 

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See also in sourсe #XX -- [ , , , , , , , , , , , , , , , , , ]

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