Improvement Scheme of High Pressure Heater Water Level Control System for 350MW Unit

Abstract: The information on the improvement plan of the water level control system of the high pressure heater of the 350MW unit is provided by the excellent manufacturers of flowmeters and flowmeters. The water level control system of two 350MW high-pressure heaters (high-pressure heaters) in the first-phase project of Huaneng Nantong Power Plant has always been difficult to put into operation and the quality of water level adjustment is not good after being put into operation. High water level and high protection. For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following is the article details of the improvement plan for the water level control system of the high-pressure heater of the 350MW unit. The water level control system of two 350MW high-pressure heaters (high-pressure heaters) in the first-phase project of Huaneng Nantong Power Plant has always been difficult to put into operation and the quality of water level adjustment is not good after being put into operation. The high water level and high protection action make the high addition unload. Therefore, it is necessary to improve and perfect the control and protection system of high water level. 1. System introduction No. 1 unit has three sets of U-tube surface vertical high-rise units No. 6, No. 7 and No. 8. According to the conventional steam extraction and water supply circuit design, No. 6, No. 7, and No. 8 high-speed plus is a large bypass for water supply. The normal drainage is step-by-step flow water, and each high plus has 1 channel of critical drainage straight-through condenser. Each Gaojia is equipped with 1 water level transmitter, 1 local water level controller (gas-assisted) and 1 water level switch. The water level transmitter is used for water level display and high/low water level alarm in the main control room. The local water level controller controls the normal trap and the emergency trap according to the high water level, and the pneumatic controller outputs (20.67～103.35) kPa control signal. The control signal controls the normal steam trap from 0 to 100% opening in the range of (20.67 to 62.21) kPa, and controls the critical steam trap from 0 to 100% in the range of (62.21 to 103.35) kPa. Under different working conditions, the switching of these two valve control modes is realized by controlling the solenoid valves on the gas path of the normal trap and the emergency trap. When the solenoid valve of the normal trap is powered, it participates in the water level adjustment and accepts the control signal of the water level controller; when the power is lost, the normal trap is closed. When the solenoid valve of the emergency trap is de-energized, it participates in the water level adjustment, and accepts the control signal of the water level controller; when the power is received, the emergency trap is closed. The control logic of No. 7 high-pressure trap is shown in Figure 1 (No. 6 and No. 8 are similar). The water level switch is used to detect the high three-value signal of the water level. When the water level reaches the high three-value, the delay is 20s, and the extraction check valve and the extraction steam shut-off valve of the high-pressure pump are closed; Take the big bypass, and all 3 high-speed plus units are released. 2. Problems (1) Water level controller Because the water level adjustment system only uses one local water level controller to control the normal steam trap and the emergency steam trap, the control characteristics of these two steam traps are different. The normal steam trap is used for the normal adjustment of high water level, which requires stable action and high precision; while the critical steam trap is used for the protection function of high water level and requires rapid response, so a water level controller is difficult to satisfy the normal steam trap and emergency Due to the different requirements of steam traps, the quality of water level adjustment is not ideal, which makes it difficult to use high additions. Moreover, the water level controller cannot withstand disturbances during operation. When disturbances occur, high water level and high protection actions often occur, affecting the stability of the unit. Economic Operation. (2) The installation position of the solenoid valve and its control logic are high. The solenoid valve of the emergency water valve is installed on the control signal gas pipeline output by the water level controller. During normal operation, the solenoid valve is powered, the control gas signal is cut off, and the emergency trap valve is closed. . The solenoid valve is de-energized when one of the following conditions occurs: 1) the water level of the current high water supply reaches a high two value; 2) the water level of the lower high water supply reaches a high three value; 3) the normal trap is closed. At this time, the control gas signal of the water level controller is sent to the positioner of the emergency trap, and the emergency trap is in the adjustment state. However, when one of the above three situations occurs, the high-pressure operation is already in a relatively emergency condition, but the output signal of the water level controller must be converted and amplified by the positioner before the critical trap is opened. In this way, the water level tends to rise rapidly, sometimes reaching the third value of the high water level and cutting off the high feed steam, or even making the high feed water bypass. What is particularly serious is that once the water level controller fails, the high-pressure water can not be drained, which will cause more serious consequences. (3) Water level switch The response of the water level switch is insensitive. After the water level high three-value switch is activated, even if the actual water level returns to normal, it cannot be restored to its original position immediately, so the high water level protection signal is sent by mistake. (4) High water level protection logic When the high water level is high, the high water inlet steam delay is cut off and the delay time for the high water feed water to go to the bypass is too long. protection and lead to water ingress to the steam turbine. 3. Improvement plan and improvement effect (1) Eliminate the pneumatic controller and realize the high water level adjustment with DCS. Change the normal steam trap and the critical flow valve to DCS control, and design their own water level regulators respectively. According to the different dynamic characteristics of normal steam traps and critical steam traps,Set the respective adjustment parameters.

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