Waste heat from industrial plants

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. 

Another applieation for turboexpanders is in power reeovery from various heat sourees utilizing the Rankine eyele. The heat sourees presently being eonsidered for large seale power plants inelude geothermal and oeean-thermal energy, while small systems are direeted at solar heat, waste heat from reaetor proeesses, gas turbine exhaust and many other industrial waste heat sourees. Some of these systems are diseussed below in greater detail. 

District heating systems can use the waste heat from electric generation and industrial plants that would be released to the air or to nearby water supplies. Some estimates suggest that district heating could save as much as one billion barrels of oil per year in the United States. 

The experiments have proved that membrane distillation can be applied for radioactive wastewater treatment. In one-stage installation the membrane retained all radionuclides and decontamination factors were higher than those obtained by other membrane methods. The distillate obtained in the process was pure water, which could be recycled or safely discharged into the environment. It seems the process can overcome various problems of evaporation such as corrosion, scaling, or foaming. There is no entrainment of droplets, which cause the contamination of condensate from thin-film evaporator. Operation at low evaporation temperature can decrease the volatility of some volatile nuclides present in the waste, such as tritium or some forms of iodine and ruthenium. The process is especially economic for the plants, which can utilize waste heat, e.g., plants operating in power and nuclear industry. 

Cogeneration Process whereby waste heat from a thermoelectric power plant is used as space heating for contiguous industries. 

Thermal power plant is more commonly associated with very large central power stations. The capital cost for thermal power plant, in terms of cost per installed kilowatt of electrical generating capacity, rises sharply for outputs of less than some 15 MW. It is for this reason that thermal power plant is not usually considered for industrial applications unless it is the combined cycle or combined heat and power modes. However, for cases where the fuel is of very low cost (for example, a waste product from a process such as wood waste), then the thermal power plant, depending on output, can offer an excellent choice, as its higher initial capital cost can be offset against lower running costs. This section introduces the thermal power cycle for electrical generation only. 

There are a few other kinds of industrial plants. An air-lift tower fermenter was developed by ICI for the production of single-cell protein from methanol which employs an external loop for heat removal. Trickle beds for the treatment of waste waters employ packing structures or packing elements of 4-6 cm dia and porosities above 50%. Microbial films are formed on the packing that react with the organic substrate and the air as the liquid flows down and the air up. 

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