Maintenance methods and steps of main valves in power plants

Maintenance methods and steps of main valves in power plants

Power plant valves are mainly used on the pipelines of various systems in the power plant to cut off or connect the pipeline medium. Taking the valve of the WODE power plant of Germany, a commonly used brand in the world, as an example, the main valves used in thermal power generation according to their functions can be divided into three categories: closing, control, and safety protection. Such as power plant desulfurization system, ash removal system, suitable for the transportation of water, steam, ash slurry, dry powder and other media. Compared with other valve products, the power plant valve is characterized by high temperature and high pressure, unique self-sealing design, the higher the pressure, the more reliable the sealing. Due to the special performance and technical characteristics and special working conditions, the product has also formed characteristics that cannot be replaced by other products.

safety protection

1. Extraction check valve

A check valve is a valve used to prevent backflow of media in pipes and equipment. The steam extraction check valve is set on each extraction pipe of the external heater of the extraction steam regenerative system in the steam turbine unit. The steam is poured back into the turbine, causing the turbine to overspeed to avoid accidents.

During the normal operation of the unit, the check valve plate remains in the normally open position due to the action of the extraction steam pressure. When the unit is load-rejected and shut down, the extraction steam pressure drops sharply, and the valve plate quickly returns to the seat by its own weight, closing the valve, thereby preventing the steam stored in the heater and the pipeline from returning to the steam turbine to achieve the function of protection.

The preparations before the maintenance of the extraction check valve are as follows:

After the equipment is out of service and the protection and power supply and air source are cut off, loosen the air inlet and outlet joints of the air control seat, remove the pin connecting the piston rod of the control seat with the check valve lever, and loosen the control seat. After fixing the bolts, remove the control seat and place it quantitatively. Then, do the following work.

1. Valve disintegration

(1) First, mark the matching of the cover head and the valve body with a marker pen, etc., then loosen the cover head bolt and remove the cover head.

(2) Remove the bearing, oil retaining ring and lever on the connecting side of the lever shaft and the pneumatic control seat, and place them in a fixed position.

(3) Loosen the large sealing cover nut and remove the large pressure ring.

(4) After the matching marks are made, loosen the fixing bolts of the large bracket, remove the large bracket, and place it in a fixed position.

(5) Remove the lever shaft and bushing and place them in a fixed position.

(6) Remove the small bracket and accessories on the side of the rocker arm shaft and place them in a fixed position.

(7) Loosen the fixing nut on the small pressure ring, remove the small pressure ring, and place it quantitatively.

(8) After making the matching mark, loosen the fixing bolts on the flange cover, remove the flange cover, and place it in a fixed position.

(9) Remove the rocker arm and valve core and place them in a fixed position.

(10) Take out the rocker arm and valve core and place them in a fixed position.

2. Valve cleaning and inspection

(1) Check the valve line on the valve core and valve body. There should be no grooves, air holes and traces across the sealing surface that affect the sealing performance on the valve line, and the contact should be uninterrupted throughout the circumference. If defects affecting the sealing performance are found, grinding and other treatments should be carried out.

(2) Check the connection between the valve butterfly and the rocker arm. The gap between the adjustment gasket and the rocker arm should be between 1 and 1.2mm, which should not be too large or too small, otherwise it should be adjusted. The connection between the tightening nut of the valve butterfly and the rocker arm should be firm, the welding point of the positioning should be complete and no cracks, and the gap between the valve butterfly shaft and the rocker arm ring should meet the requirements.

(3) Check that the clearance between the lever shaft, rocker shaft and the size bushing and seeding arm should meet the requirements, and the surface of each shaft and the inner wall surface of the bushing should be smooth and free of dents.

(4) Check the packing in the large sealing cover and the flange cover, they should be complete, if damaged, they should be replaced.

(5) Check that the sealing surface of the valve cover head and valve body should be complete, and there should be no grooves, sand holes and penetration scratches that affect the sealing effect.

(6) Clean and inspect the sealing surface of the joint between the bracket, the flange cover and the valve shell, and the old gaskets adhering to the sealing surface should be cleaned and shoveled away. The sealing surface should be free of defects that affect the sealing effect.

(7) All keys and keyways should be cleaned up, and good connections should be ensured.

3. Valve installation

Before the valve is installed, the surfaces of each shaft and bushing should be rubbed with molybdenum disulfide powder until shiny. The assembly and restoration should be carried out in the reverse order of disassembly according to the assembly marks. During the assembly and restoration process, the following points should be paid attention to:

(1) After the valve butterfly is connected to the rocker arm, the thickness of the adjustment gasket can be adjusted to ensure that the rotation angle of the valve butterfly switch meets the angle required by the manufacturer. After that, the fixing nut should be spot welded with the valve butterfly firmly.

(2) When the lever shaft, the rocker arm shaft and the rocker arm are assembled, there should be a clearance of 1-1.20mm between the lever shaft and the rocker arm end, the adjusting washer of the rocker arm shaft and the rocker arm end.

(3) When assembling and tightening the bracket and flange cover connecting the outer side of the rocker shaft and the lever shaft with the valve shell, pay attention to keeping the two shafts concentric to prevent the valve butterfly switch from being inactive or jammed.

(4) In the process of compressing the packing at both ends, it should be ensured that each axis (lever axis, rocker arm axis) is active and not jammed.

(5) All gaskets should be renewed.

4. Disassembly of the control seat

(1) After marking the assembly between the upper cover of the control seat and the cylinder block, and between the cylinder block and the base, remove the short bolts in the fastening studs between the upper cylinder and the base, and place them in a fixed position.

(2) Loosen the nuts of the two long fastening bolts at the same time or separately, all require slow progress (alternate when loosening separately), until loosening, and place the bolts in a fixed position.

(3) Separate the upper cover of the control seat, the cylinder block and the base, take out the piston, door rod and spring, and place them in a fixed position.

(4) Remove the cotter pin and the hexagonal grooved nut, separate the piston rod from the piston, and place them in a fixed position.

(5) Inspection and cleaning of the control seat.

Check that the inner wall of the piston cylinder should be smooth.

Check the cylindrical compression spring and record the length of the spring in the free state for comparison with previous (rear) overhauls.

Check that the piston rod and piston surface should be smooth.

Check that the sealing surface at the connection between the upper cover, the cylinder block and the base should be in good condition and clean up.

(6) Reinstallation of the control seat. The assembly and reassembly of the control seat is carried out in the reverse steps of disassembly, and the following points should be paid attention to:

All sealing O-rings should be replaced with new ones, and the temperature-resistant rubber and type sealing rings should be replaced;

The inner wall of the cylinder and the surface of the piston should be coated with silicone grease to ensure lubrication;

After the pneumatic control seat is installed, use compressed air to check the empty stroke of the piston rod, which should meet the requirements of the manufacturer, and the movement of the piston rod should be active and continuous without jamming.

(7) Overall verification. Fix the control seat on the valve body, connect it with the lever of the valve, connect the compressed air connector, and carry out the overall verification. Require:

After being assembled with the extraction check valve, the stroke of the compressed air switch should conform to the stroke specified by the manufacturer.

During the switching process, the overall action should be continuous and active without jamming.

The opening indication of the valve should be verified correctly, and the action switch should be verified together with the thermal control. The display of ON and OFF matches the actual position indication of the valve, and the calibration is over.

2. Trap valve

1 Introduction

The steam turbine drainage system is an important part of the steam turbine thermal system, especially the steam turbine body, main steam, reheat steam and high and medium pressure valves, feed pump steam turbine new steam drainage and other important drainage valves. It can be drained normally in time, and when the unit is in normal operation, the valve is required to be reliably isolated without leakage. If these traps leak, the impact on the efficiency of the unit is very obvious.

In view of this, some important drain valves are imported valves, and their structural type is a two-position shut-off valve operated by air. The globe valve has the advantages of simple structure, good sealing performance and easy maintenance. The globe valve is equipped with a pneumatic control mechanism, which makes the valve operate quickly and has a sensitive response, which can better meet the requirements of the automatic control of the unit.

2. Overhaul of steam trap

Since the valve is composed of two parts, the operating mechanism and the valve body, the disintegration is carried out in two steps.

(1) Dismantling of the operating mechanism.

Remove the compressed air pipe intake joint, solenoid valve, action switch and other peripheral components connected with the pneumatic control mechanism, and place them in a fixed position.

Remove the manual operating device of the operating mechanism and place it in a fixed position.

Loosen all the spring-loaded bolts on the top of the operating mechanism.

Loosen the fastening bolts at the connection between the operating mechanism and the valve stem, and move the fastening ring slightly upwards.

Loosen the connecting bolts on the Huff lock block that fixes the operating seat on the valve body, remove the two lock blocks respectively, connect the two lock blocks with bolts and place them in a fixed position.

Loosen the connecting nut between the valve stem and the operating mechanism with a wrench until the operating mechanism is disengaged from the valve body, and the operating mechanism is placed in a fixed position.

(2) Disassembly of the valve body.

Use an Allen wrench to loosen and remove the fastening bolts on one side of the bonnet, screw in the fastening bolts from the other side from the thread, and place a piece of iron with a thickness of about 1mm in the middle slot where the bonnet is fastened. Plate (diameter: 35 ~ 40), tighten the fastening bolts with an Allen wrench, and further open the slot of the valve cover to increase the gap.

Use a special wrench (or rubber clapper) to turn (or knock) the door cover, so that the door cover rotates counterclockwise until it is unscrewed and removed, and placed in a fixed position.

Tap the outside of the packing gland with a red copper rod until it is loose, and then take out the packing gland.

Take out the door rod and door core, and place them in a fixed position.

(3) Check. After the valve is completely disassembled, the sealing surface and other parts of the valve should be inspected.

Valve line inspection on valve seat and door core: Visual inspection The valve line seal should be in full contact, and there should be no defects such as grooves and blow damage that affect the seal.

The sealing surfaces between the valve stem, valve casing and packing gland should be in good contact.

The inlet and outlet of the valve should be free of foreign matter and impurities.

(4) Maintenance treatment.

If the valve line is damaged by blowing, the valve line in the valve core and valve seat should be treated differently: the valve line on the valve core should be turned out on the lathe at the original angle; the valve line on the valve seat should be repaired by special The tool scrapes the cemented carbide sealing surface in the valve seat, and the amount of scraping is about 0.05-0.08mm each time, and the amount of scraping is determined according to the actual situation of the valve line defect. After observing that the sealing surface is free of dents, finely grind the valve wire with abrasive paste. After the valve line is polished, evenly apply blue oil (or red powder) to the sealing surface of the door core, fix it with a special sleeve, and send it to the valve seat for sealing contact test. The sealing surface should be in uniform and uninterrupted contact around the entire circumference.

If the packing in the stuffing box is non-flexible graphite packing, it should be replaced with flexible graphite packing. The original flexible graphite packing should be checked for damage, and if damaged, it should be renewed.

The sealing surface on the door rod (contact with the packing) should be bright and free of rust, and the self-sealing surface in the valve seat and the lower part of the stuffing box should be polished clean.

The surface of the connecting thread on the top of the door rod should be clean and the connection should be flexible.

The threaded connection of the packing compression sleeve should be cleaned so that it can move freely. In order to ensure that it can be easily adjusted during the normal operation of the unit.

(5) Reinstallation. After the cleaning and inspection work is completed, all the connecting threads are coated with anti-seize paint, and then the valve can be reassembled. Reassembly is carried out in the reverse order of the disassembly procedure.

(6) Adjustments and matters needing attention.

After the operating mechanism is connected with the valve stem, the lower limit of the valve (close direction) is adjusted at the beginning. When the door rod thread is screwed into the connecting nut of the operating mechanism, connect the compressed air directly to the air inlet of the operating mechanism, switch the valve on and off, and adjust the connecting nut until the valve is fully closed, where the operating seat and the valve body are connected. There is a gap of 3 to 5mm in the lower part of the At this point, the preliminary adjustment is over (the Huff lock block is not installed at this time).

Open the valve by pneumatic control, after the control seat frame is tightly connected with the valve body, install the Hada lock block and tighten the fastening bolts.

Pneumatic control switches the valve on and off, and adjusts the opening indicator of the valve so that the position of the pointer of the valve matches the actual switch position of the valve.

After the solenoid valve, action switch and other peripheral equipment are installed, adjust and verify the switch signal indication together with the thermal control professional to confirm that the opening and closing directions are correct, and the adjustment is completed.

3. Control valve

The regulating valve of WODE in Germany is used to regulate the flow of the medium in the equipment and the pipe. Its working principle mainly depends on changing the flow channel area between the valve core and the valve seat to achieve the purpose of regulating the flow. The structure has multi-stage throttling, Rotary cylinder type, sleeve plunger type, flat gate type and cage type, etc. Large thermal power plants have complex systems and high requirements for media regulation, so regulating valves are widely used in steam and water systems of the unit. also keep improving.

1. Valve disintegration

(1) Remove the compressed air pipe joints, solenoid valves, etc. connected to the pneumatic control mechanism.

(2) Loosen the nut connecting the transmission rod of the operating mechanism and the valve door rod, and loosen the door rod until it is disengaged from the transmission rod.

(3) Loosen the nut of the control device bracket on the upper end of the valve cover, lift out the air control device, and place it in a fixed position.

(4) Loosen the valve cover head bolt, take out the cover head together with the door rod, and place it in a fixed position.

(5) Loosen the gland bolts, pull out the door rod and door core from the cover head, and place them in a fixed position.

(6) Take out the sleeve in the valve body and the split valve seat and sealing gasket on the valve seat, and place them in a fixed position.

2. Clean up and check

(1) Check the valve core and the valve line on the valve seat, they should be in good condition, and there is no defect that affects the sealing effect. If there is a slight defect, use the grinding method to eliminate it; if there is a deep blow damage or pit, it should be repaired by lathe processing; if the valve line is seriously damaged and cannot be repaired, the spare parts should be replaced.

(2) Check that the sealing section of the valve stem should be clean.

(3) There should be no accumulation and adhesion of oxides and other impurities around the window of the inspection sleeve, if any, it should be cleaned.

(4) Check the sealing surface between the valve line and the valve seat on the valve seat. It should be smooth and complete, without dents, blisters and penetrating scratches that affect the sealing performance.

(5) Check that the sealing surface between the bonnet and the valve body should be complete.

(6) Check the inside of the valve body, especially the inner wall of the outlet side, there should be no obvious blow damage and thinning.

(7) Check the packing in the packing chamber and replace it if damaged.

(8) All sealing surfaces should be cleaned.

3. Reinstall

Reassembly is carried out in the reverse order of disassembly. When reassembling, pay attention to the following points:

(1) All gaskets should be replaced with new ones.

(2) After the sleeve is installed, the sealing surface of the upper end should be basically kept at the same height as the sealing surface of the valve body to ensure the sealing effect of the cover head and the valve seat.

(3) When the control seat is connected with the valve body, the nut of the transmission door rod should be tightened to facilitate adjustment.

4. Adjustment

After the valve is installed in place, install the peripheral accessories such as air control joints in place, and adjust the valve together with the relevant thermal control personnel.

(1) Connect the compressed air, adjust the valve stem to the closed position, then operate the control device to fully open the valve, adjust the door stem to the closing direction by 2-3mm, and then connect the valve stem to the air control device. Tighten the nut.

(2) Adjust the valve to the closed position, adjust the opening indicator of the valve to the zero position, and then operate the valve switch several times to confirm that the valve is fully switched and the switching process is continuous and active. If there is no jamming phenomenon, the limit adjustment ends.

(3) Adjust the positioning plate of the action switch so that the action of the action switch is correct when the valve is fully opened and closed.

4. Butterfly valve of circulating water system

(I. Overview

Due to the large amount of cooling water required by the thermal power plant, the diameter of the circulating water system is also quite large. The nominal diameter of the circulating water mother pipe of the 300MW unit is DN2600, and the nominal diameter of the circulating water inlet and outlet valves of the main condenser The diameter is DN1800. Butterfly valve has become the opening and closing and regulating valve of low-pressure large-diameter pipeline system because of its compact structure, small footprint and good sealing performance.

The working pressure of the DN1800 butterfly valve of the corresponding domestic model DF47DH-1.0 is ≤1.0MPa, and it is suitable for water with a temperature ≤50℃. The valve and the pipeline are connected by flange, adopt the secondary reduction device, and the valve is arranged vertically. The butterfly valve is mainly composed of a valve body with a positioning block, a butterfly plate, an upper and lower valve shaft and a transmission device.

The working principle is: the motor drives the valve stem to rotate, and then drives the valve shaft and the butterfly valve to rotate within a 90° range relative to the valve body to achieve the purpose of controlling flow and opening and closing.

Because most of the isolation valves of the circulating jellyfish pipe are arranged in the outdoor valve wells, the working environment in the valve wells is very poor, and there is a lot of water and gas, which makes the control circuit of the electric device fail, and the limit of the valve is ineffective, causing the valve to switch too far. In actual use, the electric device should be replaced with an outdoor type to ensure reliable switching and adjustment of the valve in harsh environments.

(2) Maintenance of circulating water butterfly valve

Before the system is isolated, the appearance of the valve can be checked: first, the water trapped in the valve well is lightened. Then, check the tightness of the connecting flange of the valve (at this time, the pipeline should be filled with water and have pressure), and the flange of the valve should be connected tightly without leakage.

After the system is reliably isolated, the valve can be serviced. The repair steps are as follows:

(1) First of all, it should be confirmed that the stored water in the pipeline has been cleared.

(2) Open the valve electrically to the fully open position, and pull the power off.

(3) The staff enters the pipeline through the condenser manhole door (sufficient lighting should be ensured) to check the sealing surface of the valve. At this time, there should be no special person to supervise outside the manhole door, and they should contact in time and not leave. The lighting in the pipeline should use 12V running lights or explosion-proof power supply to ensure the safety of personnel.

(4) If it is found that the valve sealing ring is seriously damaged, the sealing ring should be replaced. First, prepare the spare parts of the same type of sealing ring, then remove the bead screw of the original sealing ring, remove the bead, take out the damaged sealing ring, install the spare sealing ring in place, and refit the sealing ring bead and bolts.

After the sealing ring is checked without damage and the valve is well sealed, the valve can be powered on to check the high and low limits of the valve. At this time, personnel should stay in the pipeline to observe the action of the valve limit (especially the low limit). If the valve limit is not accurate, it should be re-calibrated.

(5) Check the limit position of the valve. After the switch is normal, the personnel are evacuated and the tools are taken out, the manhole door is installed, and the valve inspection is completed.

Five, vacuum butterfly valve

(I. Overview

The exhaust steam of the 300MW feed pump steam turbine is directly connected to the main engine condenser through the exhaust steam pipeline. In order to ensure the reliable isolation of the feed pump steam turbine during the operation of the main engine, an isolation valve is set in the exhaust steam pipe. Due to the large diameter of the exhaust pipe and the vacuum state, the electric vacuum butterfly valve is selected.

Due to the importance of its location, the sealing of the valve must be good, otherwise it will cause the vacuum of the unit to drop and the economy to decrease.

The steps for adding water are:

(1) After confirming that the exhaust valve is closed in place, open the exhaust valve on the upper part of the valve.

(2) Open the sealing water inlet valve at the lower part of the valve and add water to the chambers of the two sealing valves. When the exhaust pipe overflows, close the exhaust valve to keep the sealing water pressure in the chamber.

(2) Maintenance of vacuum butterfly valve

After the unit has been out of service and the valve has the maintenance conditions, the maintenance work of the vacuum butterfly valve can be started. The maintenance work steps are as follows:

(1) Open the manhole door beside the valve.

(2) Open the valve electrically to the fully open position.

(3) Relevant staff shall enter the pipeline to check the valve under the condition of ensuring sufficient lighting. At this time, there should be a special person outside the manhole door to supervise and contact at any time, and not to leave. If running lights are used, the voltage should be 12V, and the transformer for running lights should be placed outside the pipes.

(4) Check the double sealing surface of the valve and the sealing ring on the valve plate. If the sealing ring is seriously damaged during the use of the valve and affects the sealing of the valve, the spare sealing ring should be replaced in time.

(5) After checking that the valve seal is in good condition, check the valve switch stroke and high and low limit. At this time, the staff in the pipeline should carefully monitor and check, and after confirming that the normal limit action of the valve electric switch is correct, take out the workers, utensils and other items in the pipeline, evacuate the personnel, and install the manhole door.