Determination of the optimum feed water temperature at the inlet to the fire-tube steam boiler equipped with a non-boiling economizer

In the heat balance of fire-tube steam boiler units, the losses of thermal energy with waste combustion products are the largest. The installation of non-boiling economizers for the purpose of utilizing the heat energy of flue gases in industrial boilers based on fire-tube boiler units is a common practice. At the same time, insufficient attention is paid to the analysis of the temperature regime of feed water at the economizer outlet, before it is fed into the fire-tube boiler, and its influence on the boiler unit efficiency. The article investigates the change in the efficiency of medium-capacity fire-tube steam boiler units depending on the feedwater temperature when using non-boiling economizers. Carbon steel fire-tube boilers with non-boiling economisers provide increased fuel efficiency, if the boiler operating parameters are considered. In particular, the following conditions must be met to achieve maximum thermal efficiency. The temperature of the feed water after the deaerator before entering the economiser should be reduced from 105 °C to 65 °C. Deeper cooling of the feed water after the deaerator leads to condensation of water vapour contained in the flue gases on the steel heating surfaces of the economiser and, as a result, to their destruction due to corrosion. Cooling the feed water to a temperature above 65 °C leads to a decrease in the fuel efficiency of boilers (Fig. 3 - curves 2, 3). The feed water at the outlet of the economiser should be heated to a temperature in the range of 65...105 °C. The maximum efficiency corresponds to the feed water outlet temperature of 85-90 °C. Heating the feed water to a temperature above 105 °C is impractical, since the increase in the boiler heat balance component q2 exceeds the increase in Δη, which leads to a decrease in boiler efficiency. Heating the feed water to a temperature of less than 65 °C ensures the boiler operation in the condensation mode, which is undesirable for the heating surface of a carbon steel boiler due to corrosion processes.