The search and treatment of the causes of condenser leakage

2018-04-18 15:51:42 157

The factors that affect the vacuum of the steam turbine are complex, including the tightness of the condenser, the heat transfer characteristic of the condenser, the heat load of the condenser, the interruption of air or siphon on the top of the circulating water outlet, the cleaning coefficient, the insufficient force of the vacuum pump, the large leakage of the high middle pressure drainage system, the cooling water, the circulating water flow and the inlet water temperature. The characteristics of the cooling water system. Among them, the tightness of the condenser is particularly important for maintaining the vacuum of the steam turbine, but its aberration has become one of the frequent faults in the operation of the steam turbine.

First, there are mainly several leaks in tightness.

(1) abrupt interruption of steam supply for shaft seal or low steam pressure of shaft seal. At this point, a large amount of air will leak into the condenser, and the vacuum will drop rapidly. The fault characteristics are as follows: the condenser terminal differential increases, the condensate supercooling degree increases, and the rotor causes negative differential expansion due to rapid cooling.

(2) the rupture of the vacuum system piping, such as the condenser copper tube, the last stage of the low copper tube, and so on. The main fault features are: the rise of the water level of the condenser, the increase of the end difference, the increase of the supercooling and the conductivity of the condensate, the increase of the outlet pressure of the condensing pump, the increase of the electric current of the condensing pump and the sharp drop of the vacuum.

(3) the leakage of the throat expansion joint of the condenser. In operation, due to the influence of temperature, pressure and vibration, the expansion joint weld of condenser throat is often cracked and leaked. The leak is concealed here, and helium leak detection is not easy to find. Irrigation and leak detection should be adopted at this time.

(4) leakage of joint surface of low pressure cylinder and flange of safety door. The main reasons are as follows: (1) there are problems in the manufacturing, repairing and installation of the cylinder, the tight joint surface of the cylinder flange or the existence of residual stress, and the leakage of steam after the unit is put into operation. In the process of starting and stopping of the unit, the load is too fast, the cylinder interlayer and the flange heating device are not used properly; after the shutdown, the heat insulation of the cylinder is broken too early or after the maintenance is not good, the cylinder temperature drops too quickly or the cylinder enters the cold steam and cold water and so on, so that the temperature difference between the inner and outer walls of the cylinder and the inner and outer walls of the flange is too large and causes up and down. When the cylinder joint surface is not well fitted, the gap is generated locally, and a large number of air enters the exhaust chamber, resulting in a decrease in vacuum.

(5) leakage of the throat of the condenser of the high pressure expansion vessel. Because of the negative pressure in the condenser, the outside air leaks into the throat of the condenser through the high pressure expanding vessel and causes the vacuum degree of the condenser to drop.

(6) the shaft seal system of the steam turbine is not adjusted. The steam pressure of the shaft seal can not be adjusted correspondingly with the change of the load, causing air to enter the steam side of the condenser and reduce its vacuum degree. The size of the gland seal and the integrity of the seal are also important factors that cause shaft seal leakage.

(7) the structure of the shaft seal system is not perfect. Only the half part shaft seal on the shaft seal sleeve of the single and single shaft seal system has no inlet and outlet pipe, only the lower half axle seal sleeve has the inlet and outlet pipes, the upper half axle seal pressure is low, the lower half axle seal pressure is high, the pressure of the upper and lower shaft seal is uneven, which affects the sealing effect of the shaft seal.

(8) the shaft seal of the turbine is not reasonable. When the unit is running, the shaft seal of the main engine is self sealing and automatic tracking through high and low pressure, while the shaft seal of the small steam turbine is introduced directly from the auxiliary steam for the front and rear axle seal, and the rear axle seal resistance is unequal. So the pressure of the front and rear air supply is difficult to adjust and automatically adjust and track, resulting in the leakage of air in the front and rear axle seal of the small machine. In addition, if the steam pressure of the shaft seal is too low or the shaft seal of the small steam turbine is too large to open the valve, the air will enter the condenser directly through the steam return gate and affect the vacuum.

(9) leakage of air pump, low inlet valve, drain door and other kind of leakage, such as leakage of medium pressure drainage system, leakage of valve hole door and throat joint of condenser steam side, valve leakage of air pumping system, and drainage of drainage U shaped water seal of exhaust pipe, etc.

Two, selection of leak point search method

1. fire candle method and soap foam method can only be used to determine a large number of leakage points, and it is time-consuming, laborious, and poor accuracy. It is to determine the leakage position by observing the flicker of the candle. In addition, the fire method threatens the safety of hydrogen cooled generating units, and is not suitable for leakage detection of condenser vacuum in our factory.

The deficiency of the 2. halogen leak detection method is that the response time is long, and the sensitive components of the leak detector are prone to toxic effects, such as halogen gas with high concentration for a long time.

The 3. ultrasonic leak detection method has the advantages of fast speed, timely response and convenient detection, but it requires the inspector to have rich experience and exclude complex background ultrasound, and its precision is only equivalent to the foam leak detection method.

4. helium mass spectrometer leak detector is reliable and sensitive, but it also has its limitations. In the case of unknown vacuum leakage, it is necessary to remove the valve sleeve and flange. It has a large amount of work, and sometimes it is difficult to obtain the expected effect.