• Boilers are provided with economizer and air pre-heaters to recover heat from the flue gases. An increase of about 20% in boiler efficiency is achieved by providing both economizer and air pre-heaters.
• Economizer alone gives only 10-12% efficiency increase, causes saving in fuel consumption 5-15 %. The feed water from the high pressure heaters enters the economizer and picks up heat from the flue gases after the low temperature super heater.
• Economizer can be classified as an inline or staggered arrangement based on the type of tube arrangement.
• For pressure of 70 Kg/cm2 or more economizer becomes a necessity.
• The tubes are arranged in parallel continuous loops.
• Feed water flows through the tubes and the flue gases outside the tubes across them. The feed water should be sufficiently pure not to cause forming of scales and cause internal corrosion and under boiler pressure.
• The temperature of the feed water entering the economizer should be high enough so that moister from the flue gases does not condense on the economizer tubes.