1. Field of the Invention
The present invention relates to a technology for recovering heat of flue gas from a boiler.
2. Description of the Related Art
It is known to recover heat of flue gas from a coal burning boiler. Specifically, the heat of the flue gas is recovered before discharging the flue gas.
FIG. 19 is a schematic of a conventional heat recovery equipment disclosed in Japanese Patent Application Laid-open No. H11-179147. In the conventional heat recovery equipment, untreated flue gas A1 discharged from a coal burning boiler 1 is introduced first into heat recovery equipment of an air heater (AH) 2, where heat is recovered from the flue gas A1, and air B to be supplied to the boiler 1 is heated with the recovered heat. As a result of recovery of the heat from the flue gas A1, the temperature of the flue gas A1 drops down to 120° C. to 160° C.
The flue gas A1 is then introduced into a heat extractor unit 3a of a non-leakage gas-gas heater (GGH). The non-leakage gas-gas heater recovers heat from the flue gas A1, as a result of which the temperature of the flue gas A1 drops down to about 80° C. to 110° C. The flue gas A1 is then introduced into a dry electrostatic precipitator (ESP) 4. The dry ESP 4 removes a substantial amount of particulate matter from the flue gas A1 and outputs the flue gas A1 as flue gas A2.
The flue gas A2 is then introduced into a soot mixture desulfurization unit 5. The soot mixture desulfurization unit 5 absorbs sulfur dioxide and collects particulate matter from the flue gas A2 thereby removing the sulfur dioxide and the particulate matter to output the flue gas A2 as flue gas A3.
The flue gas A3 output from the desulfurization unit 5 is at a temperature of about 50° C. The flue gas A3 is heated by a heat medium 6, which is heated with the heat recovered from the flue gas A1, in a reheating unit 3b of the GGH to a temperature (about 90° C. to 100° C.) desirable for emitting into the air, and discharged from a stack 7 into the air.
However, the conventional equipment does not make fully effective use of heat. It is, therefore, desired to further improve heat efficiency of the equipment and also to improve, for example, power generation efficiency of power generation equipment.
Furthermore, to use the waste heat in the power generation equipment, a heat extractor unit is required to have high reliability. However, a heat extractor unit capable of stably recovering heat at low cost has not been developed. The reheating unit 3b provided in a rear side of the desulfurization unit 5 as shown in FIG. 19 is, in particular, in a severe corrosion environment caused by an SO3 fume remaining in the flue gas. It is, therefore, necessary to take measures for preventing corrosion.
Furthermore, in the conventional technology, steel balls (of about 8 millimeters to 10 millimeters in diameter) are constantly dropped to remove soot adhering to a surface of a tube of the heat extractor unit. The tube is, therefore, disadvantageously low in durability.