The Vapor of Thermal Deaerators as a Factor of their Energy Efficiency

Abstract

The effect of the vapor of thermal deaerators on the energy efficiency of these heat-and-mass transfer apparatus and the thermal power plant as a whole is considered. Problems of reducing the vapor flow rate and its use in design and operation of Russian thermal power plants are neglected. Unjustified fuel losses in thermal deaerators of poor design and the lack of control over the vapor and its recovery are exemplified. The theoretical vapor flow rates necessary for different flow patterns of deaerated water and desorbing agent in deaerators are determined. A significant advantage in the energy efficiency of the countercurrent design over the once-through design is demonstrated. It is shown that the standardized specific vapor flow rates for thermal deaerators of different types are justified inadequately. The possibility of effective deaeration of water at a specific vapor flow rate that is substantially lower than the standard one and very close to the theoretically necessary value is proved based on experimental data. It is demonstrated that there is a wide margin to improve the energy efficiency of thermal power plants by rationally using the vapor heat of thermal deaerators. A necessary condition for increasing the energy efficiency of thermal power plants is shown to be the recovery of the vapor heat and mass of thermal deaerators. To this end, the vapor coolers should be made of corrosion-resistant materials and the vapor condensate should be used in the water-steam cycle of the power plant. Another important way to improve the efficiency is to maintain the vapor flow rate consistent with the operating mode of the deaerator, which can most effectively be done by monitoring the residual content of corrosive gases in the deaerated water. A schematic of a deaeration plant with the vapor flow rate controlled by monitoring the residual oxygen content in the deaerated water is proposed. The vapor flow rate in such a plant is kept necessary and sufficient to maintain the rated desorption efficiency of dissolved oxygen in all thermohydraulic deaeration modes, thus preventing the operation of the deaerators at insufficient or excessive vapor flow rate.