techniques of waste heat recovery Essay

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Techniques of Waste Heat Recovery
Waste heat recovery is being more used more and more often today as it is becoming more effective, due to increasing energy prices, technological developments and a decrease in equipment costs. Heat recovery can be classified into three main strategies: recycling energy back into the process, recovering the energy for other onsite use and using it to generate electricity in combined heat and power systems. Once the system has been made as efficient as possible before using waste heat recovery, passive strategies are used. These have no significant input for operation except for auxiliary equipment such as pumps and fans. The last case is active strategies, which require some input of energy to upgrade
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It is capable of operating at 300ºC with around 70% heat recovery capability. They are used where cross contamination between gas streams must be prevented in applications such as ovens and steam boilers.
Run around coil exchangers
These are quite similar in principle to the heat pipe exchanger. The heat from the hot fluid is transferred to the colder fluid via an intermediate fluid. One coil of this closed loop is installed in the hot stream; the other in the cold stream and the circulation is maintained by means of a pump. This application is used when the hot and cold fluids are located far away from each other and not easily accessible.
Economizers
Used in boiler systems an economizer is used to pre-heat the boiler water or combustion air using the flue gas, in low to medium temperatures. These are used in domestic cases as well as in large factories. They can increase the net thermal efficiency of a boiler by up to 15%.
Waste heat recovery boilers
They are ordinary water tube boilers in which the hot exhaust gases pass over a number of parallel tubes containing water. The water is vaporized in the tubes and collected in a steam drum from which it is drawn out for use as heating or processing steam.
Shell and tube heat exchangers
If the medium containing waste heat is a liquid or a vapor and is needed to heat another liquid both paths must be sealed to contain the pressures of the respective fluids. The shell contains the tube
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