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    Home > Active Ingredient News > Drugs Articles > Cause analysis and improvement of gas regulating valve jamming

    Cause analysis and improvement of gas regulating valve jamming

    • Last Update: 2014-02-12
    • Source: Internet
    • Author: User
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    Once there was a problem with the regulating valve The process personnel often find out from the DCS monitoring screen that the command of the control valve does not correspond to the feedback value The thermal instrument personnel and the instrument personnel check that the signal, circuit and all are normal Then the mechanical maintenance personnel separate the pneumatic actuator from the valve body parts Without the butterfly valve plate, the signal sent out is consistent with the mechanical position of the actuator The treatment method of the mechanical personnel is mainly to spray rust remover at the packing gland for lubrication, manually add the pipe tongs to the shaft for force cooperation and repeated activities In case of severe jamming, gas welding shall be used to bake the shaft sleeve In case of severe jamming, boiler shall be shut down and manhole shall be opened on the pipeline Hammer shall be used to knock the valve plate Instrument personnel shall cooperate to add air source pressure of pneumatic actuator and manually control the valve positioner on site , to assist in forced valve movement, but the above measures can only solve the problem for a while, the symptoms will not be cured, and the valve will continue to be inflexible or jammed after 2-3 months of use 2 Cause analysis we summarize the experience of using the control valve for many years After careful research, we conclude that the causes of the jam of the control valve are as follows 2.1 improper installation At present, most of them are installed vertically and vertically on the horizontal pipeline (the valve plate shaft is vertical and horizontal) This method is to ensure that the actuator is on the upper part of the gas pipeline, but the rear shaft of the valve is at the bottom of the pipeline, and the moisture and impurities in the gas pipeline will fall or accumulate on the rear bearing, filling the gap day by day, causing corrosion to block the valve shaft 2.2 it is found that the gap between the shaft sleeve of the drive shaft of the valve plate and the valve body is filled with some foreign matters, with sludge, water, rust and other scaling Moreover, the length of the original designed shaft sleeve is too large, and the front and rear shaft sleeve parts of the control valve bear the friction force of the valve shaft rotating back and forth With the extension of the operation time, the dust in the gas and the rusty impurities in the pipeline are easy to enter the shaft sleeve gap, increase their own rotation resistance, and the gradually accumulated mixture will fill the gap, solidify the valve shaft, shaft sleeve and valve body, and hinder the valve shaft The flexible rotation of 2.3 gas corrosion At present, all the blast furnace gas pipelines in domestic steel plants are seriously corroded The gas pipelines suffer from strong corrosion, which is mainly reflected in the hole corrosion and cracking of compensators, gas leakage on pipelines, valves on pipelines, pressure reducing valves and other components that can not be operated normally due to corrosion The corrosiveness of blast furnace gas brings serious potential safety hazards to equipment operation and gas pipelines 。 Our gas pipeline also has the phenomenon of local corrosion, air leakage and water dripping at the bellows of compensator, so it can be seen that the impact on the valve is also very serious In order to analyze the gas corrosion, we take coal gas samples from the two gas pipelines of the power plant for analysis and test Table 1 Composition Analysis of blast furnace gas% Vol High temperature H2, Co, H2O and so on also have considerable corrosion on steel Because of the water content in the gas, especially the power generation system is generally at the back or end of the whole gas pipe network, there is a large number of condensate in the pipeline After testing, the pH value of condensate in the gas pipeline of NISCO power plant is about 5-6, and the conductivity is 2762 μ s / cm In addition, there are a large number of iron ions, chloride ions and sulfate ions Ions Some data show that Cl - and SO42 - induce stress corrosion As far as the corrosion form of gas pipeline and equipment is concerned, it is mainly non-uniform corrosion Its specific manifestations are: (1) corrosion under scale, also known as crevice corrosion; (2) spot corrosion; (3) spot corrosion; (4) wear corrosion; (5) stress corrosion The existence of condensate has certain corrosiveness to the pipeline, the higher the conductivity, the faster the corrosion rate The dirty and corrosive characteristics of the gas medium are the main causes of the valve jamming 2.4 improper use due to the fact that the gas regulating valve is not put into closed-loop automatic regulation operation at present, the valve depends on the opening set by the operator through DCS for regulation, sometimes the load is relatively stable, the valve plate is in a fixed angle for a long time, it is not often active, and it is easy to make the action of the valve inflexible 3 Improvement measure 3.1 the installation mode is changed from vertical installation to horizontal installation Avoid impurities, moisture and dirt in the medium to deposit into the shaft sleeve gap under the action of gravity 3.2 to reduce the acid of gas, because the acid of gas is harmful to the whole gas pipeline system, large valves, compensators, etc., it has attracted the attention of senior leaders of the company The company has adopted the method of adding alkali liquor to the gas pipeline at the entrance of TRT for neutralization After sampling and analyzing the condensed water in the gas pipeline of power generation, it is found that its pH value is about 6 3.3 improve the shaft sleeve with unreasonable design, shorten the shaft sleeve size, reduce the length of the front shaft sleeve from 400 to 200, and the length of the rear shaft sleeve from 800 to 200 The material is made of stainless steel According to JB / t1759-2010, it is changed into castable copper alloy with the brand of zcusn10pb1 Even if there is slight scaling in the gap, the friction will be reduced by 1 / 2 to 3 / 4 due to the greatly reduced length of the shaft sleeve, and the valve is relatively easy to operate At the same time, this improvement proposal is also provided to the supplier free of charge When submitting such valve spare parts later, the manufacturer is required to make them according to our requirements During the maintenance and inspection, it was also found that the packing gland on the upper part of the valve shaft was too tight, and some packing gland screws were broken due to excessive torque When the gland is reprocessed by machining, the gap shall be increased properly, and the gap shall be filled with butter to prevent gas leakage 3.4 in terms of process, improve the process specification, require the stoker personnel to carry out activity test on all gas regulating valves in each shift, and record the instructions and feedback values in a form, so as to prevent the valve plate from being fixed in a certain opening for a long time, resulting in scaling, solidification and axle hugging 3.5 in terms of maintenance strategy, the standby control valve adopts the method of replacement and rotation maintenance, that is, once there is a chance to shut down the boiler, according to the activity test of the process personnel, find out the valve with serious jamming Zui and replace it After the offline regulating valve is disassembled for maintenance and improvement, lubrication and maintenance shall be reserved to save the shutdown time 3.6 in terms of lubrication and maintenance, the packing gland of the gas regulating valve in online operation, oil lubrication at the front and rear axles, spot inspection of the equipment and timely understanding of the operation status of the equipment shall be conducted every month The instrument and control personnel shall do a good job in rainproof and anti-corrosion of the control part (valve positioner) equipment, regularly check the air source pressure, check whether the connection part of each air source is blocked or leaked, and check the quality of compressed air In addition, increase the pressure of compressed air source and increase the output force of the actuator The instrument personnel stabilize the pressure at about 0.5MPa by adjusting the pressure reducing valve in front of the positioner Every time there is an opportunity to shut down the boiler for overhaul, arrange to clean up the mud, impurities and debris in the pipeline, so as to reduce wear and corrosion 4 The effect of implementation is to make the operators pay attention to the operation state of the control valve at all times by making and modifying the process procedure, so as to achieve the purpose of managing the equipment by all the staff, which is actually an attempt of the state maintenance mode After the improvement, the maintenance quantity is reduced, and the maintenance period is extended from 2-3 months to 6-8 months on average The labor intensity of maintenance workers is greatly reduced The key is to ensure the flexibility and reliability of the control valve and provide equipment guarantee for the safe and stable operation of the boiler This solution can also be extended to other large valves on the gas pipeline.
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