Energy, recovery from pump turbines

As more membrane-cell plants come on line, the use of dual pipelines between wells and plant will become more conunon. Saturated brine from the wells will be pumped to the plant and depleted brine pumped back for resaturation. When there is a high point or a substantial difference in elevation between the two sites, much of the pumping energy, at least in one direction, will be expended in lifting the brine. This creates an opportunity to use an energy-recovery turbine to assist at least one of the pumps. 

A closed circuit of propane is employed for indirect recovery of power from the thermal energy of the hot pyrolyzate of an ethylene plant. The propane is evaporated at 500 psig, and then expanded to 100°F and 190 psig in a turbine where the power is recovered. Then the propane is condensed and pumped back to the evaporator to complete the cycle. Since expansion turbines are expensive machines even in small sizes, the process is not economical on the scale of this example, but may be on a much larger scale. 

Energy to drive the process is provided by the R-113 vapor compressor, which pumps heat from the lower temperature of the fin cooler to the higher temperature of the final heaters. Most of this energy is removed in the R-113 condenser as heat to cooling water. Because the heat-pump circuit operates between temperatures of 100 to 200°C, some energy is recovered in the power-recovery turbine. 

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