Abstract : After a 300MW subcritical heating unit is put into operation, the valve is abnormally closed during operation and the valve stem is damaged, causing internal and external leakage of the valve. This has seriously affected the safe and economic operation of the unit. The author proposed several improvements to the problem by disassembling the valve structure and solving the problem.
Key words: fixed row valve; keyway; moment;
1 Equipment Overview A 300MW subcritical heating unit, the boiler maximum continuous evaporation of 1025t / h, the burner is arranged in four corners, a single furnace balance ventilation, solid slag, semi-outdoor layout, all-steel frame âˆ-type drum furnace. Boiler Water Wall Lower Boxes Fixed Electric Gates Model Number: 1.25"-A105-CL2500, Total 24 Pieces; Fixed Row Motorized Total Gate Models: 2"-A105-CL2500, Total 4 Pieces; With Valve Fitting Mechanical Rotor The electric actuator (rotork), model: 10A-10F-B, torque 34N? m, matching gearbox IB4 (6:1) 6, a total of 28. Due to the unreasonable structural design of the fixed row electric cut-off valve and improper selection of the actuator, the valve is in an abnormally closed state and the valve stem is damaged during operation. The internal and external leakage of the valve exceeds 2/3 within half a year of the unit operation, which may not only cause the unit to stop operation. The occurrence of accidents also poses a serious threat to human life and safety.
2 Cause Analysis 2.1 Valve stem guide keyway design is unreasonable.
The fixed row electric stop valve guide button is installed on the valve stem. When the valve is opened and closed, the valve stem guide button moves through the guide keyway inside the pressure blue. The pressure blue keyway restricts the valve stem to move up and down, but cannot rotate.
Decontamination overhaul found that this type of valve guide key cut into the valve stem graphite seal about 3-5mm (Figure 1). The reason is that the length of the relative position of the bottom sealing surface to the valve stem keyway is less than the distance from the bottom sealing surface to the top surface of the pressure packing, and the graphite waveform sealing packing is under compression during operation. Due to the unreasonable design of the part, the valve is about to close tightly, the guide key cuts into the seal packing, because the seal packing has a reaction force upwards on the valve rod guide key, which causes the electric actuator to require more torque to make it Effectively sealed with the bottom.
2.2 Indentation guided keyway processing defects Through the dismantling inspection, found that part of the valve pressure contact with the stem and the valve stem scratches, accounting for about 1/3 of the valve stem circumference, length in the range of 20-35mm (Figure 4). The main reason is that when the valve is assembled in the factory or the personnel in the power construction spot inspection, the clearance between the pressure blue and the valve stem is not properly adjusted, resulting in the pressure force on the unilateral side of the pressure force being too large, resulting in a firm contact between the pressure blue and the valve stem, and during the switching process. Blue and valve stem direct contact full stroke scratches. In the process of valve switching, the actuator force acts on the trapezoidal thread to drive the valve stem to move up and down under the keyway. The side of the valve stem is in direct contact with the guideway groove edges and corners. Because of the sharpness of the guideway groove, the valve stem is axially grooved. Invasive strokes are scratched.
2.3 improper selection of electric actuators fixed row of electric cut-off valve actuator manufacturers to provide assembly torque and valve torque comparison table: (Table 1)
The fixed row electric stop valve requires a torque of 107 N·m, the actuator is equipped with a torque of 173 N·m, the final electric actuator is equipped with a gear box type 10AB4/IB4 (6:1), and the “6:1†is the gear box to the electric actuator. The magnification ratio. The final row of electric actuator electric actuator selection torque: 34N? m, fixed row electric stop valve matched with mechanical Rotork type, 10A-10F-B, torque 34N·m, ie mechanical Rotork actuator actual output torque 34N·m × 6=204N·m.
2. The torque value of the selected electric device should be 1.1 to 1.3 times the valve's operating torque value.
It can be seen from the above table that the actuator torque of the 1.25" (32mm) stop valve should be 450N·m, and the torque of the 2" (50.8mm) stop valve should be 600N·m. From the above analysis, it can be seen that the selection of electric actuators for the currently scheduled row of electric globe valves is quite different from the recommended torque in the Valve Design Manual.
3 Solution 3.1 Valve stem keyway, guide key and pressure blue guide keyway transformation 3.1.1 The valve stem with serious damage will be provided with the keyway position moved upward by 8mm when ordered newly, as shown in the figure below:
3.1.2 The valve stem does not need to be replaced, and the guide key is modified as shown in the following figure:
3.2 Replacement The original valve reducer IB4 (6:1) is not replaced and the electric actuator is reselected. The minimum torque of the 1.25" stop valve electric actuator should be selected to be 81N·m, and the minimum torque of the 2" globe valve actuator should be selected to be 108N·m. According to the product sample provided by Rotork, combined with the practical application of field conditions, the preliminary All the selections are IQ20 intelligent adjustable actuators, which can meet the torque requirements and ensure the valve switching time requirements.
4 Summary Through the above-mentioned transformation, the internal and external leakage defects of the fixed-row electric shut-off valve are basically solved, and the loss of steam and water and pressure loss are reduced, which ensures the safety and economy of the machine operation group.
Key words: fixed row valve; keyway; moment;
1 Equipment Overview A 300MW subcritical heating unit, the boiler maximum continuous evaporation of 1025t / h, the burner is arranged in four corners, a single furnace balance ventilation, solid slag, semi-outdoor layout, all-steel frame âˆ-type drum furnace. Boiler Water Wall Lower Boxes Fixed Electric Gates Model Number: 1.25"-A105-CL2500, Total 24 Pieces; Fixed Row Motorized Total Gate Models: 2"-A105-CL2500, Total 4 Pieces; With Valve Fitting Mechanical Rotor The electric actuator (rotork), model: 10A-10F-B, torque 34N? m, matching gearbox IB4 (6:1) 6, a total of 28. Due to the unreasonable structural design of the fixed row electric cut-off valve and improper selection of the actuator, the valve is in an abnormally closed state and the valve stem is damaged during operation. The internal and external leakage of the valve exceeds 2/3 within half a year of the unit operation, which may not only cause the unit to stop operation. The occurrence of accidents also poses a serious threat to human life and safety.
2 Cause Analysis 2.1 Valve stem guide keyway design is unreasonable.
The fixed row electric stop valve guide button is installed on the valve stem. When the valve is opened and closed, the valve stem guide button moves through the guide keyway inside the pressure blue. The pressure blue keyway restricts the valve stem to move up and down, but cannot rotate.
Decontamination overhaul found that this type of valve guide key cut into the valve stem graphite seal about 3-5mm (Figure 1). The reason is that the length of the relative position of the bottom sealing surface to the valve stem keyway is less than the distance from the bottom sealing surface to the top surface of the pressure packing, and the graphite waveform sealing packing is under compression during operation. Due to the unreasonable design of the part, the valve is about to close tightly, the guide key cuts into the seal packing, because the seal packing has a reaction force upwards on the valve rod guide key, which causes the electric actuator to require more torque to make it Effectively sealed with the bottom.
2.2 Indentation guided keyway processing defects Through the dismantling inspection, found that part of the valve pressure contact with the stem and the valve stem scratches, accounting for about 1/3 of the valve stem circumference, length in the range of 20-35mm (Figure 4). The main reason is that when the valve is assembled in the factory or the personnel in the power construction spot inspection, the clearance between the pressure blue and the valve stem is not properly adjusted, resulting in the pressure force on the unilateral side of the pressure force being too large, resulting in a firm contact between the pressure blue and the valve stem, and during the switching process. Blue and valve stem direct contact full stroke scratches. In the process of valve switching, the actuator force acts on the trapezoidal thread to drive the valve stem to move up and down under the keyway. The side of the valve stem is in direct contact with the guideway groove edges and corners. Because of the sharpness of the guideway groove, the valve stem is axially grooved. Invasive strokes are scratched.
2.3 improper selection of electric actuators fixed row of electric cut-off valve actuator manufacturers to provide assembly torque and valve torque comparison table: (Table 1)
The fixed row electric stop valve requires a torque of 107 N·m, the actuator is equipped with a torque of 173 N·m, the final electric actuator is equipped with a gear box type 10AB4/IB4 (6:1), and the “6:1†is the gear box to the electric actuator. The magnification ratio. The final row of electric actuator electric actuator selection torque: 34N? m, fixed row electric stop valve matched with mechanical Rotork type, 10A-10F-B, torque 34N·m, ie mechanical Rotork actuator actual output torque 34N·m × 6=204N·m.
2. The torque value of the selected electric device should be 1.1 to 1.3 times the valve's operating torque value.
It can be seen from the above table that the actuator torque of the 1.25" (32mm) stop valve should be 450N·m, and the torque of the 2" (50.8mm) stop valve should be 600N·m. From the above analysis, it can be seen that the selection of electric actuators for the currently scheduled row of electric globe valves is quite different from the recommended torque in the Valve Design Manual.
3 Solution 3.1 Valve stem keyway, guide key and pressure blue guide keyway transformation 3.1.1 The valve stem with serious damage will be provided with the keyway position moved upward by 8mm when ordered newly, as shown in the figure below:
3.1.2 The valve stem does not need to be replaced, and the guide key is modified as shown in the following figure:
3.2 Replacement The original valve reducer IB4 (6:1) is not replaced and the electric actuator is reselected. The minimum torque of the 1.25" stop valve electric actuator should be selected to be 81N·m, and the minimum torque of the 2" globe valve actuator should be selected to be 108N·m. According to the product sample provided by Rotork, combined with the practical application of field conditions, the preliminary All the selections are IQ20 intelligent adjustable actuators, which can meet the torque requirements and ensure the valve switching time requirements.
4 Summary Through the above-mentioned transformation, the internal and external leakage defects of the fixed-row electric shut-off valve are basically solved, and the loss of steam and water and pressure loss are reduced, which ensures the safety and economy of the machine operation group.
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