Condenser is a kind of heat exchanger that condenses the exhaust steam of steam turbine into water, also known as water recombiner. Condenser is mainly used in steam turbine power plant, which is divided into water condenser and air condenser. The water-cooled surface condenser is mainly composed of shell, tube bundle, hot well and water chamber. The exhaust steam of the steam turbine enters the shell through the throat, condenses into water on the cooling tube bundle and collects in the hot well, which is pumped out by the condensate pump. The cooling water (also known as circulating water) enters the cooling tube bundle from the inlet water chamber and is discharged from the outlet water chamber. This paper wants to introduce how to choose the vacuum system in the condenser system.
Condenser is one of the important auxiliaries in power plant, which is mainly used in power plant of steam turbine. In addition to condensing the exhaust steam of the steam turbine into water for reuse of the boiler, the condenser can also establish and maintain a vacuum at the exhaust of the steam turbine.
The condenser is composed of modules, water chamber, upper and lower exhaust neck, hot well, expansion tank, return water pipe, water outlet device, low pressure bypass and other components. After the water chamber and module are assembled in the factory and pass the hydrostatic test, they shall be disassembled and delivered separately. The water chamber of the condenser is mainly composed of shell, large connecting pipe, square flange, round flange, etc., and there are eight water chambers in the condenser.
Generation and influence of gas in water chamber of condenser
In the space of water chamber of condenser, there are a lot of gases dissolved in cooling water. Because the temperature of cooling water increases after heat exchange of condenser, and the pressure of circulating cooling water is lower than atmospheric pressure due to siphon effect, resulting in the decrease of the solubility of gases in cooling water, there must be some gas precipitation, and the separated gas can not be discharged into the atmosphere through the valve, so the separated gas can be It can accumulate at the top of the water chamber or the highest point of the circulating water outlet pipe to cause the main pipe phenomenon. When the volume of gas accumulates to a certain amount, it is likely to form a gas resistance, which will seriously affect the normal flow of circulating cooling water, thus reducing the heat exchange and cooling effect of the condenser, leading to the rise of the back pressure of the turbine and the increase of the heat consumption. In serious cases, the siphon of the circulating water system will be damaged and the water of the condenser will be cut off, finally forcing the unit to stop, thus reducing the economy and safety of the unit operation.
Purpose of setting vacuum system in water chamber of condenser
1. When the unit is started, the air on the water side can be drawn out quickly to make the condenser fill water quickly to meet the siphon requirements.
2. During the operation of the unit, the circulating water shall be continuously pumped out to separate the air due to the temperature rise and pressure drop, so as to keep the condenser operating at an effective siphon height and reduce the head of the circulating water pump.
How to select the parameters of vacuum pump used in water chamber of condenser
The amount of saturated air contained in the circulating cooling water is related to the temperature and pressure of the water respectively. The amount of air in the cooling water can be determined according to the air solubility curve in the water at various absolute pressures and corresponding temperatures.
The lower the water temperature, the more saturated air there is in the water; the lower the pressure (the higher the vacuum), the easier the air in the water will be separated. In the condenser, the temperature of circulating water increases with the cooling water flow, and the siphon effect is that the pressure drops gradually. The air in the cooling water is released freely. If the released air is not discharged in time, it will affect the siphon height of the water chamber, so that the upper tube bundle of the condenser cannot enter the water, thus reducing the effective heat exchange area of the condenser and reducing the truth of the condenser The air degree reduces the output of the steam turbine.