A boiler economizer, also known as a flue gas heat recovery unit, is a piece of equipment installed on the stack of a boiler to improve efficiency. It is a heat exchanger designed to recover heat that would otherwise be wasted, typically from the stack exhaust. The recovered heat is transferred to a fluid, such as boiler feedwater, makeup water, or process water, which effectively uses that amount of heat. The fluid using the heat must be at a lower temperature than the flue gas. Economizers can be installed during a new boiler installation or retrofitted on an existing system. They work by lowering the consumption of fuel for a given steam demand, reducing thermal stress in the boiler, and adding heat transfer surface area to the boiler system. By recovering waste heat, an economizer can often reduce fuel requirements by 5% to 10% and pay for itself in less than 2 years.
Economizers serve two main functions: saving energy and improving the water temperature going into the boiler to reduce thermal shock when there is a feed system. They can increase boiler efficiency by 10-12% and reduce fuel consumption and cost.
There are two types of economizers: non-condensing and condensing. Non-condensing economizers are the most common and typically raise the overall efficiency by 2% to 4%. Condensing economizers capture much more heat and can raise the overall boiler efficiency by 10% to 15% .
In summary, a boiler economizer is a valuable component of a boiler system that helps to improve efficiency, reduce fuel consumption, and lower thermal stress in the boiler, ultimately leading to cost savings and environmental benefits.
