Discussion on the option of increasing the low-temperature economizer’s capacity to absorb heat from the boiler exhaust gases down to below the dew point temperature

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Discussion on a scheme to increase the heat absorbed by the low-temperature economizer from the boiler exhaust gases to below the dew point temperature. The phenomenon of low-temperature dew formation in the exhaust gases forces thermal power plants to raise the boiler exhaust temperature above the dew point, sacrificing 7–11% in heat loss and fuel costs in order to maintain continuous operation of the boiler. With rising coal prices, it is necessary (and feasible) to find ways to make further use of the heat from boiler exhaust gases in order to reduce heat losses and lower operating costs. To this end, I suggest that we conduct research and discussions to develop feasible technical solutions to achieve the above objectives; I urge all colleagues to participate actively and offer their ideas and support. First, I would like to present my preliminary proposal for discussion among all of you – installing a low-temperature economizer is a relatively cost-effective solution. The advantages of using a low-temperature economizer are as follows: (1) Material selection. Components exposed to flue gas are manufactured from acid-resistant stainless steel (1Cr18Ni9, 1Cr18Ni9Ti). The low-temperature economizer overcomes the dew point limitation by capturing and utilizing the latent heat of vaporization in the flue gas as well as the heat from the flue gas at lower temperatures; based on current fuel and steel prices, it is economically viable. (2) Cooling water. Thermal system make-up water, condensate water, thermal system make-up water + condensate water, raw water, domestic hot water. (3) Installation location. In the case of electrostatic precipitators or fiber filter dust collectors, the low-temperature economizer is installed behind the induced draft fan ； In the case of a water bath dust collector, the low-temperature economizer is installed in front of the dust collector. (4) Clean off dust accumulation. Special hooks are used to hang the heated surface tubes on the front and rear box plates, with no other supports. The dust removal device consists of two dust removal plates, a motor, screws and nuts, bearings, and an automatic controller. The two ash removal plates are drilled with many holes; their diameter is slightly larger than that of the tubes on the heat-exposing surface, and their pitch is the same as that of the tubes on the heat-exposing surface. The two dust removal plates are separated by an appropriate distance and welded to each other to form a rectangle with a certain degree of stiffness. The motor rotates either periodically or continuously; through screws and nuts, it drives the ash-clearing plate to slide along the tubes of the heated surface, forcing the accumulated ash into motion so that it can be carried away by the flowing flue gas.