Heat recovery for large scale boilers

 

A common large scale or industrial use of heat recovery technology is to install it on boilers. Boilers work by converting the energy in a fuel for the purpose of heating water. The fuel is burned and the resulting heat gets transferred to water.

During this process, the excess gas produced by the burning of the fuel leaves the boiler through a flue or chimney. Many boilers are inefficient, however, as some of the heat produced by burning the fuel can be lost through the flue, sometimes as much as 20%. 

Heat recovery systems can serve to minimise heat lost in this way. The heat contained in flue gases can be harnessed through the use of what are known as ‘boiler flue economisers’. These economisers are retrofitted to the flue itself, where they capture the flue gas in heat exchanger tubes.

The un-heated water then passes over the heat exchanger tubes before it reaches the boiler, which means that less fuel needs to be used by the boiler to bring the water up to temperature, as the water has been preheated. This reduces the effect of what is known as ‘thermal shock’, which is caused by big differences in temperature.

This form of heat recovery may be suitable for a range of boiler types, though the exact configuration of the system will vary between installations. There is one type of boiler that may not be suitable for flue gas heat recovery, however. ‘Condensing boilers’ are highly efficient as they already involve heat recovery, whereby the flue gases are used to preheat the cold water before it enters the boiler, thus reducing the work the boiler has to do. Domestic boilers are not usually suitable for the retrofitting of heat recovery technology.

As well as being suitable for oil, gas and CHP, it is also possible to combine heat recovery systems with other green or low-carbon technologies, such as wood chip boilers, onto which a flue economiser can be fitted. What’s more, specialist commercial premises may have other sources of waste heat which can be exploited, such as the exhaust air sections of certain industrial processes.

Heat recovery installation companies will be able to advise you on the type boiler you have and the suitability of a heat recovery system. These companies may undertake a feasibility study to better determine your site’s potential for heat recovery.

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