In most industrial or commercial heating processes, a large amount of the heat energy that is produced through fuel combustion is underutilized and wasted in the exhaust gas streams. For boilers and dryers, the typical fuel utilization efficiency is 80% (plus or minus 5%).
Wasting 20% of the fuel that is fired is inefficient and extremely costly. Very large quantities of this unused energy are recoverable and reusable.
Now, by recovering heat from the boiler exhaust gas it is feasible to take the heating duty of one of the processes and provide that heating duty from recovered waste heat, rather than steam. By reducing the steam consumption, the amount of fuel required by the boilers is reduced which creates a dollar savings incentive and a commensurate reduction in emissions is also achieved.
Boiler make up water is an easy example: when a process loses steam (direct injection, blowdown, etc.) the boiler plant must make up for this lost water by adding in fresh water. Traditionally this water would be added to the deaerator cold, or blended in with condensate return. By pre-heating this make up water using the energy in the exhaust gas, less fuel will be used in the boiler to heat the cold water and a savings is created.
With the implementation of economizer fuel saving was achieved. Higher temperature can be achieved with no extra amount of fuel used. The carbon dioxide gas emission was studied to be reduced due to the reduction in natural gas fuel consumption.