1 Introduction to anti-corrosion magnetic flap level gauge device
1.1 Principle of anti-corrosion magnetic flap level gauge The anti-corrosion magnetic flap level gauge uses the principle of absorption and uses high-concentration triethylene glycol (hereinafter referred to as lean liquid) as an absorbent to contact natural gas, so that water is absorbed by the solvent, thereby achieving the purpose of dehydration . After absorbing water, the triethylene glycol (hereinafter referred to as rich liquid) is heated to evaporate the water in the rich liquid to become the lean liquid and be recycled repeatedly.
1.2 Anti-corrosion magnetic flap level gauge system Anti-corrosion magnetic flap level gauge device is divided into natural gas dehydration system, glycol regeneration system, instrument air system, fuel gas system and power supply system according to functions. The process is as follows:
(1) Natural gas system: feed gas (hereinafter referred to as wet gas) into the station → filter separator → absorption tower → dry gas/lean liquid heat exchanger → product gas (hereinafter referred to as dry gas) out of the station.
(2) Glycol regeneration system: absorption tower (rich liquid) → rectification column heat exchange & rarr; flash tank & rarr; mechanical filter & rarr; activated carbon filter & rarr; buffer tank & rarr; rectification column & rarr; reboiler (Lean liquid) →Buffer tank→Cooler→Circulating pump→Absorption tower.
(3) Instrument air system: wet air→filter→air compressor→air dryer→instrument wind tank→all pneumatic instruments.
(4) Fuel gas system: sour natural gas → throttling & rarr; desulfurization tower & rarr; throttling & rarr; metering & rarr; boiler, burning furnace.
(5) Power supply system: mains → transformer → online uninterruptible power supply system (UPS) → power supply equipment.
2 The risk of the operation of the anticorrosive magnetic flap level gauge device
2.1 Risk of overpressure
(1) The entrance and exit valves are abnormally closed. The anti-corrosion magnetic flap level gauge device adopts automatic control for the entry and exit control valves and the flow, liquid level and temperature adjustments. When the inlet and outlet valves are closed abnormally, the upstream pressure will be excessively high, and the upstream single well will be suppressed or shut in.
(2) The entry and exit pipes are blocked. If the blockage is not removed in time or the operation of the device is stopped, the upstream pressure may be excessively high.
(3) The level adjustment system is faulty. The anti-corrosion magnetic flap level gauge device controls the level of TEG at the bottom of the absorption tower and the bottom of the flash tank, and at the same time realizes the liquid seal to prevent the low pressure (absorption tower liquid level regulating valve) and the low pressure from the normal pressure. (Flash tank level regulating valve). The liquid level regulating system consists of a liquid level gauge, a liquid level regulating valve and a liquid level regulating valve bypass valve.
① When the liquid level control valve fails or the bypass valve of the control valve leaks, the sum of the leakage of the bypass valve and the throughput of the control valve is greater than the inflow, and the liquid level of the absorption tower and valve steamer is too low, causing the absorption tower to flash vaporize The liquid seal of the tank was broken, and the channeling pressure caused the regeneration vessel to explode with super high pressure.
②False liquid level. For the level gauge involved in the control, due to glycol foaming or transmission failure, the displayed value is higher than the actual liquid level and higher than the setting value of the regulating valve. The control system always gives a valve opening signal. When the outflow of the regulating valve is greater than The inflow of the absorption tower will eventually cause the liquid level to be too low, the liquid seal is broken and the pressure is channeled.
(4) The circulation pump is faulty. The circulation pump ensures that the entire device circulates. If the TEG circulating pump fails, the TEG pumped into the absorption tower is reduced, and the absorption tower liquid level regulating valve is not closed in time, and the absorption tower liquid level is too low, which can cause medium and low pressure channeling.
(5) The safety valve does not operate. When the entry and exit valves are abnormally closed or the medium and low pressure blow-by pressure exceeds the safety valve take-off pressure, the safety valve does not operate, or the relief speed is less than the overpressure speed, resulting in excessively high equipment pressure.
(6) The instrument control system fails. The instrument control system is mainly used for on-site data acquisition, monitoring and control of operating conditions. Under normal production conditions, the operator issues instructions from the upper system, arrives at the RTU, and issues instructions from the RTU to realize the opening and closing of the valve. When the RTU switching failure or the communication interruption of each module occurs due to equipment aging and other reasons, there will be failures such as on-site valve failure, out of control adjustment, etc. Failure to deal with it in time may cause accidents such as overpressure and explosion.
(7) Power supply system and instrument wind failure. The power supply system functions to provide power to the TEG control system, power equipment, and various valves. The instrument air system provides the power source for various pneumatic valves. According to different control principles, after power loss or instrument wind interruption, some of the on-site valves are opened or some closed. No matter which power supply or instrument wind fails, it will affect the operation of the device. In severe cases, accidents such as overpressure and channel pressure will occur.
2.2 Fire risk The incinerator mainly burns the steam distilled from the rectification and the hydrocarbon gas flashed from the flash tank. A large amount of TEG enters the burning furnace, flows out to the equipment area along the burner and the air distribution port and burns, causing a fire. The reasons that cause TEG to enter the burning furnace are:
(1) The packing of the rectification column is blocked. After the blockage, the flow of TEG is blocked. Under the condition of constant circulation, the excess TEG enters the burning furnace through the steam line at the top of the rectifying column.
(2) Glycol foaming and deterioration. Because the raw material gas contains gas field water, heavy hydrocarbons and other impurities, the filler becomes dirty, and the glycol in the rectification column is foamed. After foaming, the quality is lighter and easier to be carried by water vapor into the burning furnace.
(3) The saturated water content of the gas field water entering the device or the natural gas is too high, resulting in a low glycol concentration, and the vapor pressure is too high during glycol regeneration, forming a gas seal on the upper part of the rectification column.
(4) The pipeline from the rectifying column to the burning furnace is partially blocked, and the reflux is too large after the water vapor condenses, forming a water seal.
(5) The liquid level of the flash tank is too high, and a large amount of TEG enters the burning furnace through the upper flash steam pipeline. 2.3 Glycol loss
2.3.1 Impact of improper operation
(1) When the device is started, natural gas is introduced before the tray is sealed by liquid, and the gas rises through the overflow pipe and bubble cap. At this time, the TEG is pumped into the absorption tower, and the liquid is difficult to seal the overflow pipe, and is carried into the downstream natural gas pipeline by the airflow, which increases TEG loss.
(2) When increasing the treatment capacity of the absorption tower, an instantaneous increase in the gas volume will increase the pressure drop through the tray, break the liquid seal and take the glycol out of the tray, impact the mist trap and increase the glycol loss.
(3) The processing capacity of the absorption tower exceeds the upper limit, and the air flow velocity is too fast, and a large amount of TEG is carried to the downstream gas pipeline, causing TEG loss.
2.3.2 Trays and bubble caps are not tightly sealed. Trays and bubble caps are not tightly sealed. The TEG is not liquid-sealed in the shape of the trays and is carried downstream by the airflow during production.
2.3.3 Blocking of trays or packings Blocking of trays or packings causes excessive pressure difference in the absorption tower, breaks the liquid seal, and brings the TEG downstream.
2.4 Equipment damage Since the gas field water in the feed gas contains a large amount of inorganic salts, during the heating process of the reboiler, the water in the glycol is evaporated, and inorganic salts are precipitated from the glycol. After the precipitation of the inorganic salt, it precipitates at the bottom of the reboiler. When there is more precipitation, the fire tube of the reboiler is deformed due to extrusion. The second is to deposit in the pipeline and block the glycol circulation pipeline. The third is the accumulation of salt scale on the surface of the fire tube, which reduces the heat transfer performance of the fire tube, causing local high temperature in the fire tube, and in severe cases, causing the fire tube to perforate.
2.5 Risk of Environmental Pollution The hydrocarbons and sulfides contained in the regenerated tail gas of the anticorrosive magnetic flap level gauge device are burned into the atmosphere after being burned in the incinerator. To achieve complete combustion, the furnace reaction temperature must be above 600°C. When the fuel gas pressure is insufficient or the exhaust gas volume is greater than the furnace capacity, the sulfide and hydrocarbons cannot completely react, and the exhaust gas does not meet the standard and pollutes the environment.
3 Risk control measures
3.1 Daily operation management
(1) During normal operation of the dehydration device, attention should be paid to the prevention of abnormal conditions and to strengthen patrol inspections. Through indoor status and parameter monitoring; outdoor patrol inspection through watching, smelling, and listening, observe the equipment pressure difference, liquid level, and mechanical and electrical equipment working conditions and judge whether the production is normal.
(2) Strengthen quality management. One is to strengthen sewage discharge at all levels to reduce gas field water entering the device. The second is to strengthen the filtration, by monitoring the filter separator, activity, mechanical filter pressure difference, timely replacement of filter elements, to ensure the quality of raw gas and TEG. The third is to strengthen the pigging operation control to prevent a large amount of free water from entering the dehydration device.
(3) Regularly charge and discharge the UPS; replace the UPS battery according to the battery usage; regularly run the generator on a sports car with load to ensure the normal operation of the backup power supply in the event of a mains power failure.
(4) Maintain and operate the equipment in accordance with the management system, and extend the service life and maintenance period of the equipment as much as possible.
3.2 Do a good job in overhaul management
(1) According to the key equipment of dehydration equipment such as absorption tower and buffer tank, according to the operating conditions, combined with temperament, overhaul once every 2-3 years.
(2) The TEG circulating pump and air compressor run 24 hours a day, and the seals and inlet and outlet valves are vulnerable parts. It is recommended to overhaul once a year.
(3) In order to ensure the normal operation of the dehydration unit, the generator is on standby for 24 hours. In addition to the need to strengthen daily maintenance, the unit will be fully maintained on a regular basis according to the operating time.
(4) In addition to the regular inspection and maintenance of on-site instruments and meters, the automatic control system specifically collects and analyzes the abnormal problems and phenomena in the control system, and implements major modifications in a timely manner.
(5) Ensure that the quality of overhaul meets management and operation requirements.
3.3 Establish a complete equipment ledger Establish a corresponding file for each equipment. Establish equipment maintenance records, including failure time, maintenance time content, failure reason, etc.
3.4 Strengthen personnel training
(1) Strengthen the training of well equipment maintenance. Let employees master the main technical parameters, operation steps, precautions, handling of common faults, etc. of equipment operation.
(2) Strengthen emergency response training. Improve employees’ emergency response and handling capabilities under conditions such as leakage, and reduce personnel and economic losses.
4 Conclusion
Although there are various risks during the operation of TEG, effective control measures can effectively reduce or avoid operational risks. To ensure the safe and stable operation of the anticorrosive magnetic flap level gauge device, daily management should be strengthened to ensure safe production.
Post time: 06-01-22