Introduction The steam turbine of Huadian Yizheng Thermal Power Co., Ltd. is produced by Shanghai Steam Turbine Co., Ltd. The model is LZCC81-7.65/2.3/1.3/0.6. It is a sub-high pressure, single-cylinder, single-shaft, double-pressure, double-extraction condensing steam turbine. The shaft seal system of the steam turbine is equipped with 1 shaft seal heater and 2 magnetic float level gauges. It adopts a one-use and one standby operation mode to extract the non-condensable gas in the shaft seal heater and form a negative pressure in the shaft seal heater. Pressure, so that the shaft seal return steam and valve stem leakage can enter the shaft seal heater to heat the condensed water, and maintain a slight negative pressure operation (about -5kpa).
1 Basic situation The arrangement of the drain pipeline of the magnetic float level gauge is shown in the figure. In the normal operation of the unit, one of the maglev level gauges is in operation, and the other maglev level gauge is in standby. The water discharge of the two maglev level gauges has always been in direct drainage mode, that is, before the maglev level gauge is started. Directly discharge to the atmosphere, collect water with a suitable container, and operate manually, which not only takes a long time, but also easily causes water accumulation on the ground. Due to the unreasonable design, during the periodical switching of the two maglev level gauges, the backup maglev level gauge will trip after it is started. After investigation, the cause is determined by the fact that there is too much water in the fan casing, resulting in excessive starting current. Large, thermal coupling action, causing startup failure. To complete the switch, the internal negative pressure environment must be destroyed, and the inlet baffle must be closed before the water can be released. The operation volume is large, and it is difficult to release the water when the inlet baffle is not tight. And in the normal operation of the unit, if the operating maglev level gauge trips, after the backup fan is connected, due to internal water accumulation, it will also cause start-up failure and affect the reliability of the equipment.
2 In response to this situation, the transformation plan combines the on-site layout of the shaft seal heater and its fan, looks for the design drawings and nameplate parameters, and from the actual point of view of operation, ensures the reliability of the maglev level gauge before and during operation of the unit. For sex, the following three transformation plans are proposed:
■ 2.1
Solution 1 On the basis of retaining the original water discharge pipe, add a continuous water discharge pipe to the inlet pipe of the magnetic float level gauge. Figure 2 shows the modification plan 1 of the hydrophobic pipeline of the magnetic float level gauge. The solution is to lead a drain pipe from the original pressureless drain pipe at the bottom of the maglev level gauge to the main inlet pipe of the fan. The position of the main inlet pipe of the maglev level gauge is slightly higher than the drain pipe at the bottom of the fan by 90mm on site. That is to say, there is a certain height difference, but the inlet pipe of the fan is slightly negative pressure (1Kpa=10.2 cm water column). If there is water at the bottom of the fan, under the negative pressure of the system (-5Kpa), it can be During operation, ensure that the drain at the bottom of the standby fan impeller is drained by the negative pressure in the shaft seal heater so that the fan does not accumulate water, but when the unit is started for the first time, the maglev level gauge still needs to be artificially removed from the fan. Operation exhausted.
■ 2.2
Option 2 On the basis of retaining the original drain pipe, add a new drain pipe to the pressure sampling point of the shaft seal heater (pressure transmitter/pressure switch). The modification plan 2 of the hydrophobic pipeline of the magnetic float level gauge is shown. In this scheme, the pressure sampling on both sides of the shaft seal heater is connected to the steam side of the heater at one end, and connected to the meter at the other end. Due to the problem of the sampling tube site layout, the sampling point is 5.5m, and the transmitter/pressure The switch is arranged at the 1m position, the pressure sampling condensing elbow is arranged horizontally, and the meter is not equipped with a sewage outlet, there is water in the meter during operation, and the accurate value in the shaft seal heater has not been correctly displayed. Observe on the spot that the water discharge pipe at the bottom of the fan is 70mm higher than the pressure sampling pipe, so you can add a water discharge pipe to the front of the pressure sampling pipe, and the pressure sampling pipe will be transformed into an upper arched condensing elbow, and the highest point is slightly higher than the maglev The drain on the bottom of the sub-level gauge comes out. When the fan is out of operation, due to the height difference, the condensed water inside the enclosure can flow to the shaft seal heater. When the unit starts the fan operation, because the steam side of the shaft seal heater is under negative pressure, the drain at the bottom of the fan impeller can pass through the shaft. The negative pressure inside the heater is pumped clean. On this basis, because the pressure sampling tube has also undergone the transformation of the upper arch condensing elbow, there will be no water accumulation at the meter, and the value can be displayed correctly.
■ 2.3
Scheme 3 On the basis of retaining the original water discharge pipe, add a water discharge pipe to the connection of the shaft seal heater drain to the single-stage water seal. The improvement plan 3 of the hydrophobic pipeline of the magnetic float level gauge is shown. The shaft seal heater drain must pass through a single-stage water seal before returning to the condenser. Its function is to maintain the drain water level of the shaft seal heater and maintain the vacuum in the condenser. It increases the resistance of the drain backwater. , The shaft seal heater drains through the water seal, and then returns to the steam side of the condenser. Connecting a drain at the junction of the shaft seal heater drain to the single-stage water seal can effectively drain the water stored at the bottom of the fan and at the same time recover the water. For the unit startup and normal operation, ensure that there is nothing in the magnetic float level gauge. Stagnant water.
■ 2.4 Conclusion
After analyzing and comparing the three schemes, scheme one requires manual operation when the unit is started, which is relatively inconvenient; scheme three can achieve the goal, but the engineering quantity is the largest among the three schemes, while the technical transformation engineering quantity of scheme two is relatively small. It can solve the problem of poor drainage of the magnetic float level gauge, reduce the workload of the operators, and improve the reliability of the equipment without affecting the standby of the equipment. Therefore, the use of Option 2 to transform the steam turbine magnetic float level gauge drain pipeline can achieve the desired effect.
3 Scheme implementation After repeated demonstrations of the above schemes, taking advantage of the opportunity of mid-repair of #3/4 unit in April, scheme 2 was adopted to transform the drain pipe of #4 machine magnetic float level gauge. Since there are few on-site changes, it is only necessary to increase A valve and a 1m long pipeline will be completed within half a day, as shown in 5 after the site modification.
4 Concluding remarks After the above-mentioned scheme is adopted, the maglev level gauge is manually drained when the unit is started and the equipment is switched to confirm that there is no internal water in the standby state, and the operator does not need to manually drain the water to ensure the maglev level. The meter is always in a reliable standby state, the workload is greatly reduced, and multiple repeated switching tests are performed during the actual start-up and operation of the unit, and all can be reliably started, the reliability of the equipment is greatly improved, and the amount of operation of the operators is also reduced. , Observing the meter measurement, the displayed value is no different from the historical value. The meter also shows normal at the moment when the magnetic float level meter starts and stops. The modification of the pressure sampling tube of the meter has no effect on the meter. It is understood that most power plants use direct drainage at the bottom of the magnetic float level gauge, and there is no separate drainage pipeline. Manual operation is required for each start. This modification method can provide a reference for other power plants.
Post time: 07-01-22