| Condenser is one of the important auxiliary facilities of condensing steam turbine in power plant. Except the steam turbine exhaust, the condenser also receives a variety of drains. For the small generating unit, there is no difficulty in accepting the drains, but as the power of the steam unit increases dramatically, the appearance of the critical and supercritical units, especially the extensive development of once-through boiler and nuclear power unit, the parameter of the drains is increasing, and as a result, new problems appeared. Therefore, the new study of drains drained to condenser is of great importance and great value.Based on the understanding of the condenser principle and the analysis of condenser heat-transfer character, this paper analyze the drains and the drain systems comprehensively, including the source and the classification.According to the balance principle of heat transfer under stable conditions, this paper establish the static mathematical model about the influence of drains on vacuum, based on the flow and heat-transfer character analysis above. The model can be used for analyzing the influence on condenser by drains qualitatively and quantitatively. According to the conservation of mass and energy, the working process of condenser is expressed with differential coefficient, the dynamic mathematical model of influence on vacuum by drains is also established, which can be used for researching the dynamic response of vacuum when the drains get into the condenser.Applying the static model established to the condenser of a 300 MW unit and a 600 MW unit, this paper discover the regulation that the vacuum changing with the flow and enthalpy of the drains by calculating. That is: when the flow is constant, with the increase of the enthalpy, the whole heat-transfer coefficient is nearly unchanged, the terminal temperature and the pressure increased; when the enthalpy is constant, with the increase of the temperature, the conclusion is similar to the conclusion above. With the drain draining into the condenser, the vacuum is decreased, and as a result affecting the economic of the unit.Applying the dynamic model established to the condenser referred above, this paper make dynamic response curve by calculating. From the curve, we can see: when the flow is constant, the changing rate of the vacuum is increased with the increase of the enthalpy; and when the enthalpy is constant, the rate is increased with the increase of the flow. As the self-balance performance of the condensing systerm and the flow and enthalpy are limited, the drain rarely causes the deterioration of the condenser vacuum.Through the model, we can see: besides the influence on the security of the condenser in the draining process, the drain can influence the economic of the unit to a certain extent. Therefore, it is not reasonable for the drain drained into the condenser directly or through the expanding device indirectly. For the drain: source should be considered first. Then, choose reasonable position and drain back to the main pipeline of the regenerative system, in accordance with the parameters of the drain. It can decrease the exergy in the heat-transfer process because of the irreversibility, also, decrease the influence on the condenser vacuum.This paper also introduces two important drains: bypass steam and low-pressure heater drain. Applying the Dynamic model to the bypass steam, dynamic response curve about the condenser vacuum, when the load rejected and bypass steam input, is made. Before inputting bypass steam, the vacuum decreased; after it, the vacuum increased, and finally reached a new balance. In the new balance, the vacuum decreased because of the heat load increase. Through the curve, a better understanding of the vacuum changing process, resulting from the bypass steam, can be obtained; By applying the static model to the low-pressure heater drain of the regeneration system, the influence on the economy can be analyzed, from the point of vacuum.
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