Waste heat is recovered from hot waste gases by employing recuperators. These are basically of two types:
Metallic and ceramic:
Ceramic recuperators are more common and popular for high temperature applications.
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Economisers are also used for heating boiler feed water in many industries. This is a typical heat recovery device.
An economiser improves the efficiency by reducing the flue gas temperature at exit from the boiler and increasing the feed water temperature.
One per cent reduction in the fuel consumption takes place with every 6°C increase in the feed water.
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Waste heat boiler is also employed to recover heat. It can generate steam with the heat in the exhaust gases from an engine, turbine, or process streams. These are used in medium and large process industries for increasing the efficiency of energy.
The following are some of the some examples of recycling which result in energy saving:
1. Recycling of waste paper reduces the steam requirement for pulping the raw materials.
2. In glass industry, the broken glass is mixed with batch of raw material for recycling. In this process the energy requirement for melting is reduced.
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3. Recycling of rejected castings, scrap materials such as gates, risers etc. in the melting furnace.
4. In the sugar industry, the exhaust steam (at pressures around 1 kg/ sq.cm.) from the turbines is used for evaporators, juice heaters and other process equipment.
5. In the rice milling operations, black liquor in paper industry, hydrocarbon effluents in paint industry, waste heat is also available in the form of combustible fuels out of process rejections/rejects.
It reduces the demand for commercial fuels, if waste fuels are burnt to provide heat for process needs.
In this lesson, we have studied a number of ways in which energy, which is a precious thing these days, can be saved. Suggestions and tips given should be implemented to save energy.