BOILER FLUE GAS ECONOMISER

The capturing waste heat from boiler hot flue gas to preheat feed water to improve boiler efficiency. Typically, the flue gases leaving a modern 3-pass shell boiler are at temperatures of 200 to 300 oC. Thus, there is a potential to recover heat from these gases. The flue gas exit temperature from a boiler is usually maintained at a minimum of 200oC, so that the sulphur oxides in the flue gas do not condense and cause corrosion in heat transfer surfaces. When a clean fuel such as natural gas, LPG or gas oil is used, the economy of heat recovery must be worked out, as the flue gas temperature may be well below 200 oC. The potential for energy savings depends on the type of boiler installed and the fuel used. For a typically older model shell boiler, with a flue gas exit temperature of 260 oC, an economizer could be used to reduce it to 200 oC, increasing the feed water temperature by 15 oC. Increase in overall thermal efficiency would be in the order of 3 percent. For a modern 3-pass shell boiler firing na