Thermal power plants (TPPs) operate technological systems for the steam condensate return from remote external consumers. In such systems, it is necessary to protect the metal from corrosion. This will allow ful-filling the regulatory requirements for the concentration of iron compounds in the condensate entering the power plant. Such systems do not use thermal deaerators operated by using heating steam. The aim of the undertaken study is to assess the efficiency of superheated water deaerator use in such conditions, in par-ticular cavitation-jet deaerators. It means determining the effect of a new element of the system – the de-aerator – on the normalized chemical parameters of the returned condensate. A mathematical model of superheated water deaerators is used. The employed model is based on the theory of similarity of heat and mass transfer processes. The methodology for calculating the corrosion rate of return condensate pipelines was used, as well as experimental data on medium pressure TPPs. The efficiency of cavitation-jet deaerators in condensate return systems of external consumers has been estimated. A mathematical description of the system has been developed, which allows determining the required performance of deaerators and the required ratio of water recirculation through them in each mode. Recommendations for effective practical applications of the proposed technical solution have been developed considering the actual conditions at thermal power plants. It is advisable to install a deaerator according to the recirculation scheme through the condensate collection tank. This scheme, compared to a sequential scheme, enables to reduce capital costs and ensure that the deaerator operates in the highest efficiency mode. The choice of the nominal capacity of deaerators should be carried out taking into account the graphs of the change in the flow rate of incoming condensate and the concentration of dissolved oxygen in it during the day. In most operating modes of the system, it is possible to ensure compliance with the regulatory requirements for the mass concentration of corrosion products in the condensate returned to the TPP. The obtained results can be used in the design of new and improving the efficiency of existing TPPs that supply steam to external consumers.
The results obtained from combined numerical and experimental investigations of the water decar bonization process carried out in atmospheric pressure deaerators without subjecting water to steam bubbling in the deaerator tank are presented. More exact values of the hydrocarbonate thermal decomposition rate have been obtained, and the hypothesis about a change of the process governing mechanism in shifting to low total alkalinity values of deaerated water has been proven in the course of these investigations. A procedure for pre dicting the indicators characterizing the water decarbonization efficiency in using deaerators is proposed based on the obtained study results. The developed procedure features the maximally possible accuracy that can be achieved at the metrological characteristics of the standard alkalinity measurement methods.
In cavitation-jet deaerators, the process of desorption of dissolved gases proceeds when boiling overheated water is directed in the form of a swirling vortex flow into the rarefaction zone. The removal of gases is carried out from the cavitation pocket formed along the flow axis. Such deaerators are characterized by relatively low efficiency. However, their small dimensions and the ability to work without supplying a heating coolant make them useful in cases where effective deaerators of other types cannot be applied by weight and size characteristics or temperature conditions. The expansion of the scope of practical application of cavitation-jet deaerators is hampered by the lack of appropriate mathematical description that would allow solving the problems of their schematic and constructive improvement. One of the main tasks in this case is to calculate the static pressure field of the liquid phase in the deaerator core. There are no ready-made solutions to this problem in the framework of previous studies. Thus, it is relevant from scientific and practical viewpoint to develop a simulation model of active zone of cavitation-jet deaerator, which allows determining the hydrodynamic characteristics of water flows and gas-vapor mixture when the elements, the mode of water supply and drainage evaporation change. Modeling the hydrodynamic situation in the active zone of cavitation-jet deaerator is based on the numerical solution for the Navier-Stokes equations and the continuity equation. These equations are written in the Reynolds decomposition. In this case, the standard k- turbulence model is used to obtain a preliminary solution, which is then refined during the transition to the SST turbulence model. The model is implemented by means of a software package for calculating fluid flows FlowVision. For the first time, a simulation model of the active zone of cavitation-jet deaerator was developed, which made it possible to determine the hydrodynamic characteristics of water flows and gas mixture when the elements design, the mode of water supply and drainage evaporation change. The field of static pressures of liquid phase in the active zone of cavitation-jet deaerator is determined. The results obtained do not contradict the published data describing the operation of cavitation-jet deaerators. In particular, they confirm an increase in the probability of deaerator overflow when gas exhaust is turned on. The results also prove the presence of a significant dependence of the deaeration efficiency on the hydraulic resistance of the evaporation suction tract. Based on the results obtained, a mathematical model of the deaeration process under the considered conditions can be developed.
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