- Boiler Economizer Definition: A boiler economizer is a device that preheats fluid to reduce energy consumption and improve boiler efficiency.
- Function: It captures residual heat from flue gases to warm the inlet water before it enters the boiler.
- Construction: The economizer consists of horizontal inlet and outlet pipes connected by vertical pipes where heat transfer occurs.
- Heat Recovery Process: As water moves through vertical pipes, it absorbs heat from flue gases, making the boiler more efficient.
- Soot Management: A scraper mechanism removes soot from the vertical pipes to maintain effective heat transfer.
What Does an Economizer Do in a Boiler
A boiler economizer (also called an economizer) is a heat exchanger in the flue-gas path. It takes remaining enthalpy from gas that has already left the evaporator and puts that heat into the incoming feedwater. The steam boiler’s furnace then burns less fuel to raise the same steam.
After the superheater and evaporator, flue gas still holds useful heat, often a few hundred degrees Celsius. If that gas goes straight to the stack, the heat is lost. An economizer intercepts it and warms feedwater. The name comes from the fuel saved.
Construction and Working Principle of Boiler Economizer
The drawing below is the old Green cast-iron type, patented in 1845. Cold feedwater enters a horizontal header at the bottom. A second header sits at the top.
Vertical water tubes join the two headers. An outlet valve on the top header sends the warmed water toward the boiler. Flue gas flows around the outside of those tubes, not through their bores. Modern plant economizers are usually steel coils or finned tubes in the rear gas pass, with sootblowers instead of scrapers.
Water rises inside the vertical tubes and picks up heat from the gas on the outside. It then leaves the top header warmer than it entered, so the boiler has less work to do.
Ash and soot settle on the gas-side surface of the tubes. A thick layer acts as insulation and cuts heat transfer. Designers also watch stack temperature so acid in the gas does not condense on cold metal.
On the Green unit, a scraper on each vertical tube travels up and down on a chain and pulley. Soot falls into a chamber at the bottom and is raked out. The scraper gear is the mark of this old boiler economizer. A modern steel bank is cleaned with sootblowers.
