Geothermal efficiency

The flashed steam method is less efficient and its requirements for steam properties—cleanliness, high temperature, and high pressure— are usually unavailable in most geothermal fields. The situation is different with the binary cycle system, which is quite efficient and widely used. This wet system involves the transfer of heat from the hot well stream into a more manageable boiling fluid to generate power through a turboexpander. 

Some geothermal power plants use a combination of flash and binai y cycles to increase the efficiency of electricity production. An initial flash creates steam that drives a turbine then the binai y cycle is run, using either the hot water remaining after the initial flash or the hot exliaust from the turbine. 

Project delineates between cleaner new gas technologies and polluting old natural gas technologies—and reserves a third cleanest category for energy efficiency/conservation, solar, wind, and geothermal (but not hydro or biomass). 

The salt- and Cu2+-catalysed condensation of peptides provides a very simple polymerisation reaction with remarkable efficiency at 80°C. The proposed mechanism is shown in Figure 8.17 for the dimerisation of glycine. The presence of Cu2+ is important in this process and is unlikely to be present in the geothermal vent environment but it does require only small quantities of O2 to oxidise copper. A better condensation reaction would be autocatalytic and provide a template for future generations - in short, a genetic code. 

In some European cities, waste heat from fossil fuel electric power plants is used for district heating with an overall energy efficiency of 85%. These plants were not originally constructed as cogenerating units. Waste heat from industrial process plants can also be used. Geothermal sources are used to provide heat for district heating systems in Iceland and Boise, Idaho. 

Solid Oxide Electrolysers (SOE) are in development for steam electrolysis. As electrolysis is an endothermic process, a supply of waste heat can be used beneficially to reduce the electrolyzer voltage, and thus increase its electrical efficiency. Combination with nuclear power generation and geothermal heat sources is often encountered in development programs for SOE. 

Much of this chapter has been concerned with various modifications to the simple Rankine cycle at high temperature. In the following five sections, the Rankine cycle that makes possible use of energy sources at low temperature, such as solar, geothermal, ocean thermal, solar pond, and waste heat, will be discussed. Because of the small temperature range available, only a simple Rankine cycle can be used and the cycle efficiency will be low. This is not critical economically, because the fuel is free. 

A proposal is made to use a geothermal supply of hot water at 1500 kPa and 180°C to operate a steam turbine. The high-pressure water is throttled into a flash evaporator chamber, which forms liquid and vapor at a lower pressure of 400 kPa. The liquid is discarded while the saturated vapor feeds the turbine and exits at lOkPa. Cooling water is available at 15°C. Find the turbine power per unit geothermal hot-water mass flow rate. The turbine efficiency is 88%. Find the power produced by the geothermal power plant, and find the optimized flash pressure that will give the most turbine power per unit geothermal hot water mass flow rate. 

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