Precautions for the maintenance of vinyl chloride gas tanks
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What safety precautions should be observed when maintaining vinyl chloride gas tanks?
Safety Operating Procedures for the Vinyl Chloride Unit 1 Subject Matter and Scope 1.1 These standards specify the safety operating procedures, process control parameters, accident handling measures, and safety production techniques for various production positions in the vinyl chloride unit during startup, shutdown, and normal operation. 1.2 This standard applies to operators at various positions in the vinyl chloride production unit as well as relevant technical management personnel. 2 Production Purpose: Utilizing high-purity acetylene gas provided by the acetylene unit and qualified HCl gas from the hydrochloric acid unit, these gases are mixed, frozen, and dehydrated before being reacted in a converter (with catalytic agents) to produce crude C2H3Cl gas. This crude gas is then purified, compressed, and distilled to yield high-purity C2H3Cl monomer with a purity of over 99.9%, which is supplied to the polymerization unit. 3 Brief description of the process flow: The pure acetylene gas from the acetylene unit and the qualified HCl gas from the hydrochloric acid unit are mixed uniformly in a mixer according to a specific molecular ratio. After that, the mixture enters a graphite cooler for cooling and dehydration; fine acid mist is captured by an acid mist collector. Subsequently, it passes through a graphite preheater to be preheated, and then enters a converter where, under the catalysis of catalyst (HgCl2/C), an addition reaction occurs between the two substances, producing crude C2H3Cl and other by-product gases. The sublimated HgCl2 is absorbed by a mercury removal device, and the mixture then enters a washing tower for two rounds of washing to remove any unreacted HCl. Finally, an alkaline washing tower is used to neutralize any remaining hydrochloric acid and CO2. After purification, one stream is sent to the gas holder for storage, while another stream enters the compressor for pressurization; it is then cooled in a total condenser to become liquid. The uncondensed gas is condensed again in an exhaust gas condenser and returned to the system. The liquid crude C2H3Cl produced in both processes is sent to the low-boiling point tower, where low-boiling substances such as C2H2 and other compounds with low boiling points are vaporized off. The crude C2H3Cl at the bottom of the tower is transferred from an intermediate storage tank to the high-boiling point tower, from where pure C2H3Cl is vaporized at the top of the tower. This pure C2H3Cl is then condensed into a liquid state and stored in a monomer storage tank, thereby providing qualified monomer for use in the polymerization process at any time. 4 Safety Operating Procedures for Synthesis Processes 4.1 Purpose of Production By controlling the appropriate flow rates of C2H2 gas and HCl gas, and through mixing, freezing, dehydration, and preheating, the mixed gases undergo an addition reaction in a converter using HgCl2/c as a catalyst to produce crude C2H3Cl. After removing HgCl2 using a mercury removal device, as well as through washing with water and alkali, the product is stored in a gas tank; it is also supplied to the compression unit. 4.2 Brief description of the process flow: The pure C2H2 gas from the acetylene unit is cooled and dehydrated using a cooler. It is then mixed with HCl gas from the hydrochloric acid unit in a ratio of 1:1.05–1.10 in a mixer. After that, it passes through a graphite cooler for further dehydration and an acid mist collector to capture any acid mist. Subsequently, it enters a preheater for preheating, and then goes into a converter where, thanks to the HgCl2/C catalyst present in the tubes, an addition reaction occurs between C2H2 and HCl, resulting in the formation of C2HCl and other by-products. The heat released during the conversion process is carried away by the circulating cooling water outside the tubes. Maintain the temperature of the reaction system stable. After the reaction, the crude chloroethene gas is purified by removing HgCl2, then sent to a water washing tower and an alkali washing tower; from there, it is routed either to a gas holder or to the compression unit. 4.3 Preparations before driving 4.3.1 Check whether the liquid level in the circulating cooling water tank is at the specified level (i.e., around 2/3 of the gauge), and ensure that there is sufficient 30% NaOH in the concentrated alkali tank. 4.3.2 Check that all equipment, pipelines, and valves meet the requirements for startup, and that there are no issues with the electrical systems and instruments. 4.3.3 Check the inlet and outlet valves of each converter to ensure that the switches are in the correct position. 4.3.4 Steam should be introduced into the circulating cooling water tank to raise the water temperature to 85–90°C; at the same time, the hot water pump should be started to ensure circulation, until the temperature of the converter exceeds 80°C. 4.3.5 Contact the control room to inform the hydrochloric acid, acetylene, compression, and refrigeration teams to prepare for startup. 4.3.6 Once the temperature of the brine to be frozen reaches the required level, open the inlet and outlet valves for the brine in the graphite condenser and the acid mist collector, and inform the freezing station to supply brine at –35°C. 4.3.7 Once the alkaline solution is prepared, start the alkali pump to initiate circulation. Open the valves of the wash tower to adjust the water flow, and open the vent valve of the wash tower. 4.4 Operating the System 4.4.1 When the purity of HCl is above 90% and it contains no free chlorine, open the HCl flow control valve to introduce a certain amount of HCl gas. 4.4.2 After passing HCl for 10–15 minutes, if a sample analysis shows that the purity of HCl is greater than 92% and there is no Cl- present, notify the acetylene section to supply acetylene gas. Once the purity and pressure of acetylene meet the required specifications, slowly open the acetylene control valve to start supplying acetylene. 4.4.3 When passing acetylene, close the vent valve after water washing. Open the inlet valve of the alkali scrubber tower, and simultaneously inform the compression team to start up. 4.4.4 While ensuring that the levels of C2H2 and HCl at the converter outlet remain within the normal control range and the catalyst temperature stays below 180°C, gradually increase the acetylene flow rate in proportion until the required level is reached. 4.4.5 Acid is discharged from the bottom of the converter one hour after acetylene is introduced. 4.4.6 During normal production, if it is necessary to adjust the pressure or change the flow rate, permission must be obtained from the dispatch team, who will issue the corresponding instructions. 4.4.7 Activation of the newly installed catalyst and startup procedures: ① Open the inlet and outlet valves for the circulating hot water in the converter to heat the catalyst using circulating hot water. ②When the catalyst temperature rises above 80°C, HCl is introduced to dry and activate the catalyst. The exposure to hydrogen chloride should not be less than 10 hours. Acetylene can be introduced only when no acidic water can be discharged from the bottom of the converter. ③When using the new catalyst, the initial flux of C2H2 is 20–30 M3/h; the acetylene flux can be gradually increased as long as the reaction proceeds well and the reaction temperature remains stable at or below 150°C. Generally, new catalyst converters are operated in series after the old catalyst converter, so the flux of the old catalyst should also be allocated according to the aforementioned principles. ④When using a new catalyst, the increase in flux must not exceed 10 m3/h. 4.5 Normal shutdown procedures 4.5.1 Inform the control room, the acetylene unit, the hydrogen chloride unit, and relevant stations to make preparations for the shutdown. 4.5.2 Upon receiving the shutdown notice for the acetylene section, close the acetylene flow control valve and the main outlet valve of the alkali scrubber; open the vent valve. At this point, the converter continues to be fed with HCl for 5 minutes. 4.5.3 The main valve at the converter outlet is used to maintain system pressure. Notify the HCl unit to shut down, then close the HCl flow control valve and the inlet and outlet valves of each converter. 4.5.4 Stop the alkali pump and close the water inlet valve of the wash tower; if the shutdown lasts for more than 8 hours, close the inlet and outlet valves for the circulating water in each converter as well as stop the circulating water pump. 4.5.5 In the event of a short-term shutdown of acetylene. HCl can be continued to be passed through. The ventilation time should be determined based on specific circumstances. 4.5.6 Shutdown for catalyst replacement: ① Close the inlet and outlet valves of the converter whose catalyst needs to be replaced, as well as the inlet and outlet valves for circulating water; open the drain valve at the bottom of the converter to drain all the water outside its tubes. ②With the converter under positive pressure, use N2 to purge the residual gases inside. ③Only after a certain period of natural cooling, when the temperature inside the converter is below 60°C, can the pipes be removed. 4.6 Emergency Shutdown Procedure 4.6.1 First press the alarm bell, then close the C2H2 valve, and finally close the HCl valve; at the same time, notify other processes to perform an emergency shutdown. 4.6.2 The rest follows the general parking sequence. 4.6.3 To prevent the alarm bells from failing, the crews responsible for chloroethylene and hydrochloric acid must establish contact immediately after taking over their shifts and test the alarm bells of each other. 4.7 Process Control Parameters: Sequence Number, Parameter Name, Location for Measurement, Frequency of Measurement
1. Acetylene gas pressure: 26.6–60 Kpa (200–450 mmHg); at the work station, once per hour
2. Purity of C2H2: ≥98.5%, and ≥95% during operation; at the liquid seal point, three times every 3 hours
3. Amount of S and P in C2H2: none; at the liquid seal point, three times every 8 hours
4. HCl gas pressure: ≥26.6 KPa (200 mmHg); at the work station, once per hour
5. Purity of HCl: ≥92%; in the buffer tank, once per hour. Oxygen content: <0.2%; also measured in the buffer tank, once per hour. Chlorine content: <0.04%; also measured in the buffer tank, once per hour
6. Control of the molecular ratio C2H2:HCl: 1:1.05–1.10; at the work station, once every 2 hours
7. Temperature of the mixture at the outlet of the graphite condenser: 1# – 10±2°C, 2# – 14±2°C; at the work station, once per hour
8. Temperature of the mixture after preheating: 70–80°C; at the work station, once per hour
9. Reaction temperature: ≤180°C; at the work station, once per hour
10. Temperature at the outlet of the circulating cooling water in the converter: 95±5°C; at the work station, once per hour
11. Content of C2H2 and HCl in the syngas: <1% for C2H2, 5–15% for HCl; measured in the converter, once every 2 hours
12. Concentration of Na2CO3 in the circulating alkali solution in the scrubber tower: 8–15%, <10% in winter (<8% in winter); measured in the scrubber tower, once every 8 hours
13. Concentration of acid recovered from the water wash tank: ≤25%; measured in the acid tank, once every 8 hours
4.8 Abnormal Conditions and Handling Methods: Sequence Number, Abnormal Condition, Cause of the Abnormality, Handling Method
1. Mixer temperature rises above 50°C: ① Excessive free chlorine in HCl reacts violently with acetylene, generating heat. ① Activate the alarm to notify those responsible for HCl and C2H2 handling; immediately stop the supply of acetylene. In severe cases, introduce N2 to evacuate the area. 2. High pressure difference between the mixer and the acid mist collector. ① The graphite condenser in between freezes due to supercooling, causing blockage of the tubes. ① Stop supplying chilled brine. 3. Sudden increase in the amount of acid below the graphite condenser. ① Leaks in the tubes of the graphite condenser, allowing brine to seep into those tubes. ①Shutdown for maintenance: Excessive acid release at the lower part of preheater ① Leak in the preheater ① Shutdown for maintenance or replacement. 5 Inability to increase the flow rate of raw gas ① Insufficient pressure of the raw gas ② Blockage of the flow meter orifice plate or pressure tap tubes ③ Blockage in the mixing and dehydration system ④ Catalyst caking due to acid mist, FeCl3, FeSO4 carried in by the raw gas, or resin formation resulting from acetylene self-polymerization in the upper part of the converter ⑤ Blockage at the converter outlet caused by HgCl2 and FeCl3 ⑥ Scaling on the packing in the alkali scrubber tower ① Coordinate with the HCl or C2H2 units to increase pressure ② Clean the orifice plate or pressure tap tubes ③ Inspect or shut down for cleaning ④ Shut down for maintenance and replace the caked catalyst ⑤ Shut down to clear the blockage at the outlet ⑥ Shut down to address scaling on the packing. 6 Narrow reaction zone, high reaction temperature with a downward trend ① Cooling water temperature is too low, resulting in insufficient activation of the catalyst in the upper layers. ①Raising the water temperature or reducing the flow rate causes the converter temperature to rise sharply. ① The circulation of water is interrupted, preventing the reaction heat from being removed in a timely manner. ②The flow rate of the new catalyst is too high, causing an excessive intensity of reaction. ①Immediately increase the circulation water volume. ② Reduce the acetylene flow rate; the reaction temperature in the reaction zone shows a downward trend. ① The temperature of the circulation water is too low; ② The upper catalyst is not functioning properly. ① Increase the steam supply to the hot water tank to raise the temperature of the circulation water. ② Slightly reduce the acetylene gas flow rate. 9 The temperature of the gas after conversion is low, and no HCl gas is detected. ① The temperature of the conversion reaction drops suddenly or a large amount of by-products are formed. ① Reduce the acetylene flow rate or increase the HCl flow rate to maintain stability in temperature and molecular ratio. 10 Too much acid is released at the bottom of the converter. ① There is a leak in the tubes of the converter, allowing circulation water to seep into them. ①Shut down the converter, drain the circulating water, and then carry out maintenance. 11 Low acetylene conversion: ① Reaction temperature too low; ② Flow rate exceeds the capacity; ③ Catalyst not fully activated, or the catalyst is ineffective, or there are issues with its installation, resulting in excessive load on certain tubes; ④ Low purity of the feed gas. Solutions: ① Increase the water temperature or raise the flow rate; ② Reduce the flow rate and lower the reaction speed appropriately, and replace or reinstall the catalyst; ④ Improve the purity of the feed gas. 12 The reaction temperature generally decreases and is difficult to increase; the reaction zone widens and the conversion rate remains low. ①The catalyst has become ineffective. ①Increase the temperature as much as possible and reduce the flow rate; if this does not work, stop the system and replace it with a new catalyst. 13 The circulating hot water pump does not deliver water: ① There is a large amount of steam in the pipes or converter; ② The pump is faulty; ③ The pipes are blocked. Solutions: ① Release the steam; ② Repair the pump; ③ Clean the pipes. 4.9 Safety precautions: 4.9.1 When performing cleaning tasks while the equipment is in operation, cleaning must not be carried out while the moving parts of the equipment are rotating. Do not wear gloves when refueling; be careful for safety. Do not touch electrical switches with wet hands. Make sure the switch box remains dry when it is raining. 4.9.2 Regularly check the motor coupling guard and ensure that the motor’s grounding wire is in good condition; if any issues are found, address them immediately. 4.9.3 Cu, Hg, Ag, and their alloys shall not be used in any pipes, equipment, or instruments that come into contact with acetylene or vinyl chloride. 4.9.4 Air must be purged with N2 before driving. 4.9.5 When burning C2H2, C2H3Cl, and C2H4Cl2, use CO2 fire extinguishers or dry powder fire extinguishers; water, foam fire extinguishers, or CCl4 fire extinguishers should not be used. For electrical fires, use CCl4 fire extinguishers; water or foam extinguishers should not be used. Foam fire extinguisher for oil fires. 4.9.6 When replacing lye, protective equipment (glasses, gloves, work clothes) must be worn, and air must not be allowed to enter the production system. 4.9.7 When loading or unloading catalyst in the converter, air circulation around it must be ensured. To prevent the catalyst from harming the body, used catalysts must be collected and managed properly. Whenever the skin comes into contact with the catalyst, it must be washed with hot water. 4.9.8 When performing hot work on various equipment containing C2H3Cl, the gas remaining in the pipes and equipment must be completely displaced with N2. After the analysis meets the requirements, a \"Hot Work Permit\" must be obtained before hot work can proceed (with the C2H3Cl content being less than 0.4%), and consideration should be given to allowing explosion relief at the other end. 5 Safe Operating Procedures for Compression Processes 5.1 Purpose of Production: To compress the synthesized crude vinyl chloride gas to 0.55 MPa (gauge pressure) and send it to the distillation unit for use. Ensure safe and civilized production. 5.2 Brief description of the process flow: The crude VC gas, which comes directly from the synthesis unit or the VC gas tank, first passes through the pre-compressor cooler and pre-compressor mist catcher. After cooling and partial water removal, it enters the compressor, where it is compressed to 0.55 MPa (gauge pressure). Subsequently, it goes through the post-compressor cooler and oil separator before being sent to the distillation unit for further purification. 5.3 Preparations before driving 5.3.1 Check whether all pressure gauges, temperature gauges, valves, and oil levels in this position meet the requirements for starting the machine. 5.3.2 Open the chilled brine inlet valve of the pre-start cooler, open the cooling water inlet valve of the post-start cooler, and open the cooling water valve for the compressor cylinders. 5.3.3 Check whether the foot bolts of the compressor and motor are tightened, and whether all tools are available. 5.4 Operation: 5.4.1 Upon receiving the instruction to start up from the synthesis unit, and when the height of the gas holder is at 4 levels, open the inlet valve of the pre-machine cooler to start the machine, and inform the distillation unit to get ready for startup. 5.4.2 Open the compressor circulation valve. 5.4.3 Start the motor; once it is operating properly and the oil pressure as well as the oil leakage are normal, close the circulation valve, quickly open the outlet valve, and then slowly open the primary inlet valve. 5.4.4 Adjust the compressor according to the height of the gas tank to ensure smooth pumping and control the outlet pressure and temperature. 5.5 Normal shutdown procedure: 5.5.1 Upon receiving the shutdown instruction, coordinate with the relevant processes; then reduce the height of the gas tank to 2 bars, close the compressor inlet valve, and shut down the motor. When the motor stops running completely, close the outlet valve to the compressor and open the circulation valve. 5.5.2 Close the brine inlet valve of the pre-cooler and the water inlet valve of the post-cooler before shutting down the machine. 5.5.3 Close the coarse VC inlet valve of the cooler before shutting down the machine. 5.6 Emergency shutdown procedure: 5.6.1 Emergency shutdown measures shall be taken when the compressor suffers a serious failure or when the upstream and downstream processes affect safe production. 5.6.2 Stop the motor, close the inlet valve; the rest follows the planned shutdown procedure. 5.6.3 Notify the relevant processes that this position has been shut down. 5.7 Process control parameters: Serial number, Parameter name, Parameter value, Detection point, Frequency of detection 1. Gas tank height: 3–7 grids; Station – 1 time per hour 2. Gas outlet temperature of the pre-cooler before the compressor: 15–20°C; Station – 1 time per hour 3. Compressor inlet pressure: 33–2.66 Kpa (10–20 mmHg); Station – 1 time per hour 4. Compressor outlet pressure and outlet temperature: 0.56±0.02 Mpa, <105°C; Station – 1 time per hour 5. Compressor oil pressure: 0.05–0.1 Mpa higher than the inlet pressure; Station – 1 time per hour 6. Compressor oil level: 1–2 levels; Station – 1 time per hour 7. Temperature of the shaft seal oil tank: <60°C; Station – 1 time per hour 8. Motor temperature: <60°C; Station – 1 time per hour 9. Gas outlet temperature of the cooler after the compressor: 42–46°C; Station – 1 time per hour 5.8 Abnormal phenomena and handling methods: Serial number, Fault phenomenon, Cause of fault, Handling method 1. Low compressor outlet pressure: ① Damaged outlet valve; ② Failed piston rings. ① Stop the machine for maintenance; ② Stop the machine for maintenance. 2. Excessively high compressor exhaust temperature: High temperature of the inlet gas. Lower the temperature of the inlet gas and increase the amount of water used in the pre-cooler before the compressor. 3. Low oil pressure in the compressor: ① Damaged oil pump or leaks in the oil pump; ② Clogged oil pipes or filters; ③ Oil level too low. ① Repair the oil pump; ② Clean the oil pipes or filters; ③ Top up the oil promptly. 4. Abnormal noise from the compressor: ① Improper installation, loose anchor bolts; ② Incorrect installation of the drive wheel; ③ Parts have fallen out inside; ④ Hard objects have entered the cylinders; ⑤ Oil pump failures causing power loss or cylinder wear; ⑥ Water in the inlet gas, leakage in the cylinders or intermediate cooler, resulting in liquid accumulation in the cylinders. ① Stop the machine for inspection and repair; ② Same as above; ③ Same as above; ④ Same as above; ⑤ Same as above; ⑥ Improve water drainage from the pre-cooler and mist catcher before the machine, and stop it for inspection and repair. 5.9 Safety Precautions: 5.9.1 Strictly follow operating procedures to prevent improper operations. 5.9.2 Do not wear gloves while refueling to prevent accidents. 5.9.3 Do not touch electrical switches with wet hands to prevent electric shock. 5.9.4 During winter, when the machine is parked for an extended period of time, all excess water in the machine and the condenser should be drained to prevent freezing and cracking. If the parking period is short, the water flow can be reduced to keep it moving and avoid freezing. 5.9.5 The height of the gas tank must be strictly controlled within the specified range. 5.9.6 When hot work is required on equipment or pipelines, the residual gases within them must be completely displaced with N2. Only after the analysis is approved can a ‘Hot Work Permit’ be obtained to carry out hot work, and consideration should be given to allowing explosion relief at the other end. 5.9.7 Pipes, equipment, and instruments in contact with VC shall not be made of Cu, Hg, Ag, or their alloys. 5.9.8 Mixing explosion range of VC and air: 3.6–31% (by volume). 6 Safe operating procedures for the distillation unit. 6.1 Purpose of production: This unit is used to compress the crude vinyl chloride (VC) produced in the synthesis unit, followed by liquefaction and distillation to purify it, so that it meets the specified standards and can be used in the polymerization unit. Ensure proper management of equipment in one’s position, as well as safe and civilized production practices. 6.2 Brief description of the process flow: The crude vinyl chloride gas, after being washed with water and alkali, is compressed and then fed into a total condenser where it is liquefied. After free water is removed using a water separator, the gas enters a low-boiling-point tower for distillation, in order to remove fractions with boiling points lower than that of vinyl chloride (mainly acetylene, N₂, etc.). The low-boiling-point fractions emerge from the top of the tower and, along with the non-condensable gases from the total condenser, go into an exhaust gas condenser to recover any vinyl chloride contained therein. The non-condensable gases are vented, while the condensed liquid is separated from water via a water separator before being sent back to the low-boiling-point tower. The material from the bottom of the tower overflows into the intermediate control tank. The VC liquid exiting the intermediate storage tank enters the high-boiling tower for distillation, driven by the pressure difference between the low-boiling tower and the high-boiling tower to overcome the head difference and remove high-boiling substances. High-purity vinyl chloride gas escapes from the top of the tower, is condensed in the product condenser, and then enters the monomer storage tank. The high-boiling substances are periodically transferred from the bottom of the tower to a residue receiving tank, where the small amount of VC contained in them is vaporized using hot water in the jacket; the residue is then put into barrels for further disposal. When feeding material to the polymerization section, a monomer pump is used to transfer the monomer from the vinyl chloride storage tank to the polymerization section. 6.3 Preparations before driving 6.3.1 Check that all equipment, pipes, valves, instruments, and level gauges are in good condition and functional. 6.3.2 Open the inlet and outlet valves for brine in each condenser, inform the refrigeration team to supply refrigerated brine, and control it to the specified temperature. 6.3.3 Open the valves of the feed pipe and balance pipe in the monomer storage tank, as well as the inlet and outlet valves for the material in the total condenser and exhaust gas cooler. 6.4 Driving Operations 6.4.1 Notify the compression station to start operation. 6.4.2 The condensed crude VC, after water removal in a water separator, enters the low-boiling tower; at this point, it is necessary to accurately control the temperature of the exhaust gas condenser and the vent pressure. 6.4.3 When liquid vinyl chloride overflows from the low-boiling tower into the intermediate control tank, open the circulating hot water valve to accurately control the temperature and pressure at the bottom of the low-boiling tower. 6.4.4 When the liquid level, temperature, and pressure in the intermediate control tank are stable, open the feed control valve leading to the high-boiling tower. 6.4.5 When a liquid level forms in the bottom of the high-boiling tower and exceeds the overflow level, circulating hot water is turned on for heating to gradually raise the temperature to the specified value. 6.4.6 When VC condensate appears in the finished product condenser, activate the top condensers of the high- and low-boiling towers, and adjust the internal reflux to control the reflux ratio. 6.4.7 Strictly control the pressure difference between the bottom of the low-boiling tower and the top of the high-boiling tower, so that the VC liquid can be smoothly forced from the bottom of the low-boiling tower into the intermediate control tank and then into the high-boiling tower. 6.4.8 Strictly control the difference between the bottom pressure and the top pressure of the tower. Generally, the pressure at the bottom of the tower is 0.01–0.02 MPa higher than the pressure at the top of the tower. 6.5 Normal shutdown procedure 6.5.1 After the compression unit stops supplying air, reduce the size of the exhaust vent valve. 6.5.2 After the compression unit has been shut down for 5 minutes, close the exhaust vent valve as well as the valves at the top of the low-boiling point tower, the total condenser, and the brine inlet of the exhaust condenser. 6.5.3 Increase the temperature at the bottom of the high-boiling tower, close the equilibrium valve at the bottom of the tower to raise the system pressure, and transfer all the monomer in the bottom of the tower to the high-boiling tower. 6.5.4 After the discharge of the finished condenser stops, close the discharge valve and the balance valve. 6.5.5 The water-monomer mixture in the water separator is placed into a water collector and then heated with hot water to be recovered to the gas holder. 6.5.6 Release of high-boiling substances. For maintenance, it can be evacuated using nitrogen. 6.6 Emergency Shutdown Procedure 6.6.1 Once the compression unit stops supplying gas, close the exhaust vent valve. 6.6.2 Close the discharge valve, balance valve, and feed valve of the high-boiling tower; stop the chilled brine supply to the condensers as well as the circulating hot water in the tower bottom. 6.6.3 In the event of a prolonged stoppage, permission may be requested from the dispatcher to follow the planned shutdown procedure. 6.7 Process Control Parameters: Serial Number, Parameter Name, Parameter Value, Detection Point, Frequency of Detection 1. Chloride vinyl ether condensation temperature in the total condenser: 20±5°C; Detection point: at the workstation; Frequency: once per hour 2. Bottom temperature and bottom pressure of the low-boiling-point tower: 39–41°C and 0.5±0.02 MPa respectively; Detection point: at the workstation; Frequency: once per hour 2. Top temperature and top pressure of the low-boiling-point tower: 20±5°C and 0.5±0.02 MPa respectively; Detection point: at the workstation; Frequency: once per hour 3. Bottom temperature and bottom pressure of the high-boiling-point tower: 30±2°C and 0.3±0.03 MPa respectively; Detection point: at the workstation; Frequency: once per hour 3. Top temperature and top pressure of the high-boiling-point tower: 20±2°C and 0.32±0.02 MPa respectively; Detection point: at the workstation; Frequency: once per hour 4. Temperature of the exhaust gas condenser: 15±5°C; Detection point: at the workstation; Frequency: once per hour 5. Exhaust gas release pressure: 0.52±0.02 MPa; Detection point: at the workstation; Frequency: once per hour 6. Pressure in the monomer storage tank: 0.32±0.02 MPa; Detection point: in the monomer storage tank; Frequency: once per hour 7. VC content in the exhaust gas: ≤10%; Detection point: at the exhaust pipe; Frequency: once every 4 hours 8. Purity of the monomer: Acetylene content ≥99.99% and impurity content ≤0.0024%; Detection point: in the monomer storage tank; Frequency: once every 8 hours 6.8 Abnormal Phenomena and Handling Methods: Serial Number, Fault Phenomenon, Cause of Fault, Handling Method 1. Unstable liquid level in the tower bottom: ① Insufficient circulation water volume or water temperature; ② Insufficient exhaust gas release volume; ③ Unstable temperature of the top condenser. Handling methods: ① Control the water inflow volume and maintain a stable temperature; ② Continuously release exhaust gas to keep pressure stable. ③ Maintain stable freezing water volume and temperature. 2 The liquid level in the tower reactor is stable, but the quality of the monomer is poor. ① ① Low reflux rate of the material in the tower. ② Low evaporation rate of the material in the tower. ③ Low temperature at the bottom of the tower. ④ Low feed temperature in the low-boiling-point tower. ⑤ Too low temperature at the top of the low-boiling-point tower or in the exhaust gas condenser. ⑥ Low temperature of the circulating water, with unstable circulation volume. ⑦ Low acetylene conversion rate. ⑧ The intermediate control tank is empty. ① Increase the reflux rate. ② Raise the temperature at the bottom of the tower. ③ Raise the temperature at the bottom of the tower. ④ Appropriately reduce the amount of cooling water used in the total condenser. ⑤ Raise the temperature. ⑥ Raise the water temperature and increase the circulation volume. ⑦ Improve synthesis control. ⑧ Stabilize the liquid level in the intermediate control tank. 3. Low temperature in the exhaust gas condenser, but increased VC venting volume. ① Ice formation and blockage in the exhaust gas condenser. ② Low purity of crude vinyl chloride. ③ High temperature in the total condenser. ④ Excessive evaporation rate. ① Replace the exhaust gas condenser. ② Inform the conversion unit to identify the cause. ③ Lower the temperature of the total condenser. ④ Adjust the evaporation rate at the bottom of the tower. 4. Uneven or intermittent discharge from the product condenser. ① Blockage or malfunction of the discharge balance pipe. ② Blockages in the discharge pipes. ③ Large pressure fluctuations in the product condenser. ① Inspect and clear any blockages. ② Shut down the high-boiling-point tower for inspection. ③ Adjust the system pressure and ensure strict stability of pressure. 5. Accumulation of material in the high-boiling-point tower. ① Blockage caused by self-polymerization inside the tower. ① Replace the high-boiling-point tower and shut it down for maintenance. 6 High temperature of the total condenser: ① High temperature or low pressure of the 5℃ saline; ② Obstructions in the inlet and outlet of the saline. ① Notify the refrigeration station to adjust the saline temperature or increase the pressure; ② Check the inlet and outlet valves. 7 Leakage of chlorine vinyl into the saline: ① Leaks in the tubes of the condenser equipment. ① After checking each condenser, replace it if necessary. 6.9 Safety precautions: 6.9.1 All pipes, equipment, and instruments that come into contact with acetylene C2H2 and chlorine vinyl C2H3Cl must not be made of Cu, Hg, Ag, or their alloys. 6.9.2 Emptying must be done before driving. 6.9.3 When C2H2, C2H3Cl, and C2H4Cl2 are on fire, use CO2 extinguishers or dry powder extinguishers; water or foam extinguishers should not be used. For electrical fires, use CCl4 fire extinguishers; water or foam fire extinguishers should not be used. Foam is used to extinguish oil fires. 6.9.4 When working on equipment containing C2H3Cl, it is necessary to remove all residual gases from the equipment’s pipelines; only after the gas has been analyzed and found to be safe can a ‘Work Permit’ be obtained before starting any work. 6.9.5 All equipment shall be grounded to eliminate static electricity. 7 Environmental Protection: 7.1 Working Environment 7.1.1 Maximum allowable concentrations of harmful substances in workshop air (mg/m3): ① Vinyl chloride < 30 ② Dichloroethane < 25 ③ Hydrogen chloride < 15 ④ Mercuric chloride < 0.1 7.1.2 Noise level in workshops and work areas < 90 dB. 7.2 Sources of three wastes and treatment methods. 7.2.1 Spent activated carbon and catalysts: During high-temperature operations in the synthesis reaction of hydrogen chloride and acetylene, mercury chloride on the activated carbon sublimes and is carried away with the gases. The main methods for dealing with this issue are to use activated carbon pumps and adsorbers for gas-phase mercury removal, to replace the activated carbon and catalysts regularly, and to dispose of the spent catalysts and activated carbon externally for recycling. 7.2.2 Excess hydrogen chloride. Treatment: Excess hydrogen chloride is the largest volume of acidic wastewater generated in vinyl chloride production; water-washed foam towers and packed towers are used to remove hydrogen chloride, with 20–25% of the resulting hydrochloric acid being recycled for export. 7.2.3 Treatment of vinyl chloride off-gases: During the distillation of vinyl chloride, the non-condensable gases containing less than 10% vinyl chloride, which are discharged through the off-gas condenser, pass through an off-gas adsorption unit to have the vinyl chloride component recovered; thereafter, the inert gases are vented under pressure-controlled reduction. 7.2.4 Treatment of high-boiling dichloroethane: Intermittent distillation is used to remove vinyl chloride therefrom, and 1,1-dichloroethane is collected for export for further processing.
1. Acetylene gas pressure: 26.6–60 Kpa (200–450 mmHg); at the work station, once per hour
2. Purity of C2H2: ≥98.5%, and ≥95% during operation; at the liquid seal point, three times every 3 hours
3. Amount of S and P in C2H2: none; at the liquid seal point, three times every 8 hours
4. HCl gas pressure: ≥26.6 KPa (200 mmHg); at the work station, once per hour
5. Purity of HCl: ≥92%; in the buffer tank, once per hour. Oxygen content: <0.2%; also measured in the buffer tank, once per hour. Chlorine content: <0.04%; also measured in the buffer tank, once per hour
6. Control of the molecular ratio C2H2:HCl: 1:1.05–1.10; at the work station, once every 2 hours
7. Temperature of the mixture at the outlet of the graphite condenser: 1# – 10±2°C, 2# – 14±2°C; at the work station, once per hour
8. Temperature of the mixture after preheating: 70–80°C; at the work station, once per hour
9. Reaction temperature: ≤180°C; at the work station, once per hour
10. Temperature at the outlet of the circulating cooling water in the converter: 95±5°C; at the work station, once per hour
11. Content of C2H2 and HCl in the syngas: <1% for C2H2, 5–15% for HCl; measured in the converter, once every 2 hours
12. Concentration of Na2CO3 in the circulating alkali solution in the scrubber tower: 8–15%, <10% in winter (<8% in winter); measured in the scrubber tower, once every 8 hours
13. Concentration of acid recovered from the water wash tank: ≤25%; measured in the acid tank, once every 8 hours
4.8 Abnormal Conditions and Handling Methods: Sequence Number, Abnormal Condition, Cause of the Abnormality, Handling Method
1. Mixer temperature rises above 50°C: ① Excessive free chlorine in HCl reacts violently with acetylene, generating heat. ① Activate the alarm to notify those responsible for HCl and C2H2 handling; immediately stop the supply of acetylene. In severe cases, introduce N2 to evacuate the area. 2. High pressure difference between the mixer and the acid mist collector. ① The graphite condenser in between freezes due to supercooling, causing blockage of the tubes. ① Stop supplying chilled brine. 3. Sudden increase in the amount of acid below the graphite condenser. ① Leaks in the tubes of the graphite condenser, allowing brine to seep into those tubes. ①Shutdown for maintenance: Excessive acid release at the lower part of preheater ① Leak in the preheater ① Shutdown for maintenance or replacement. 5 Inability to increase the flow rate of raw gas ① Insufficient pressure of the raw gas ② Blockage of the flow meter orifice plate or pressure tap tubes ③ Blockage in the mixing and dehydration system ④ Catalyst caking due to acid mist, FeCl3, FeSO4 carried in by the raw gas, or resin formation resulting from acetylene self-polymerization in the upper part of the converter ⑤ Blockage at the converter outlet caused by HgCl2 and FeCl3 ⑥ Scaling on the packing in the alkali scrubber tower ① Coordinate with the HCl or C2H2 units to increase pressure ② Clean the orifice plate or pressure tap tubes ③ Inspect or shut down for cleaning ④ Shut down for maintenance and replace the caked catalyst ⑤ Shut down to clear the blockage at the outlet ⑥ Shut down to address scaling on the packing. 6 Narrow reaction zone, high reaction temperature with a downward trend ① Cooling water temperature is too low, resulting in insufficient activation of the catalyst in the upper layers. ①Raising the water temperature or reducing the flow rate causes the converter temperature to rise sharply. ① The circulation of water is interrupted, preventing the reaction heat from being removed in a timely manner. ②The flow rate of the new catalyst is too high, causing an excessive intensity of reaction. ①Immediately increase the circulation water volume. ② Reduce the acetylene flow rate; the reaction temperature in the reaction zone shows a downward trend. ① The temperature of the circulation water is too low; ② The upper catalyst is not functioning properly. ① Increase the steam supply to the hot water tank to raise the temperature of the circulation water. ② Slightly reduce the acetylene gas flow rate. 9 The temperature of the gas after conversion is low, and no HCl gas is detected. ① The temperature of the conversion reaction drops suddenly or a large amount of by-products are formed. ① Reduce the acetylene flow rate or increase the HCl flow rate to maintain stability in temperature and molecular ratio. 10 Too much acid is released at the bottom of the converter. ① There is a leak in the tubes of the converter, allowing circulation water to seep into them. ①Shut down the converter, drain the circulating water, and then carry out maintenance. 11 Low acetylene conversion: ① Reaction temperature too low; ② Flow rate exceeds the capacity; ③ Catalyst not fully activated, or the catalyst is ineffective, or there are issues with its installation, resulting in excessive load on certain tubes; ④ Low purity of the feed gas. Solutions: ① Increase the water temperature or raise the flow rate; ② Reduce the flow rate and lower the reaction speed appropriately, and replace or reinstall the catalyst; ④ Improve the purity of the feed gas. 12 The reaction temperature generally decreases and is difficult to increase; the reaction zone widens and the conversion rate remains low. ①The catalyst has become ineffective. ①Increase the temperature as much as possible and reduce the flow rate; if this does not work, stop the system and replace it with a new catalyst. 13 The circulating hot water pump does not deliver water: ① There is a large amount of steam in the pipes or converter; ② The pump is faulty; ③ The pipes are blocked. Solutions: ① Release the steam; ② Repair the pump; ③ Clean the pipes. 4.9 Safety precautions: 4.9.1 When performing cleaning tasks while the equipment is in operation, cleaning must not be carried out while the moving parts of the equipment are rotating. Do not wear gloves when refueling; be careful for safety. Do not touch electrical switches with wet hands. Make sure the switch box remains dry when it is raining. 4.9.2 Regularly check the motor coupling guard and ensure that the motor’s grounding wire is in good condition; if any issues are found, address them immediately. 4.9.3 Cu, Hg, Ag, and their alloys shall not be used in any pipes, equipment, or instruments that come into contact with acetylene or vinyl chloride. 4.9.4 Air must be purged with N2 before driving. 4.9.5 When burning C2H2, C2H3Cl, and C2H4Cl2, use CO2 fire extinguishers or dry powder fire extinguishers; water, foam fire extinguishers, or CCl4 fire extinguishers should not be used. For electrical fires, use CCl4 fire extinguishers; water or foam extinguishers should not be used. Foam fire extinguisher for oil fires. 4.9.6 When replacing lye, protective equipment (glasses, gloves, work clothes) must be worn, and air must not be allowed to enter the production system. 4.9.7 When loading or unloading catalyst in the converter, air circulation around it must be ensured. To prevent the catalyst from harming the body, used catalysts must be collected and managed properly. Whenever the skin comes into contact with the catalyst, it must be washed with hot water. 4.9.8 When performing hot work on various equipment containing C2H3Cl, the gas remaining in the pipes and equipment must be completely displaced with N2. After the analysis meets the requirements, a \"Hot Work Permit\" must be obtained before hot work can proceed (with the C2H3Cl content being less than 0.4%), and consideration should be given to allowing explosion relief at the other end. 5 Safe Operating Procedures for Compression Processes 5.1 Purpose of Production: To compress the synthesized crude vinyl chloride gas to 0.55 MPa (gauge pressure) and send it to the distillation unit for use. Ensure safe and civilized production. 5.2 Brief description of the process flow: The crude VC gas, which comes directly from the synthesis unit or the VC gas tank, first passes through the pre-compressor cooler and pre-compressor mist catcher. After cooling and partial water removal, it enters the compressor, where it is compressed to 0.55 MPa (gauge pressure). Subsequently, it goes through the post-compressor cooler and oil separator before being sent to the distillation unit for further purification. 5.3 Preparations before driving 5.3.1 Check whether all pressure gauges, temperature gauges, valves, and oil levels in this position meet the requirements for starting the machine. 5.3.2 Open the chilled brine inlet valve of the pre-start cooler, open the cooling water inlet valve of the post-start cooler, and open the cooling water valve for the compressor cylinders. 5.3.3 Check whether the foot bolts of the compressor and motor are tightened, and whether all tools are available. 5.4 Operation: 5.4.1 Upon receiving the instruction to start up from the synthesis unit, and when the height of the gas holder is at 4 levels, open the inlet valve of the pre-machine cooler to start the machine, and inform the distillation unit to get ready for startup. 5.4.2 Open the compressor circulation valve. 5.4.3 Start the motor; once it is operating properly and the oil pressure as well as the oil leakage are normal, close the circulation valve, quickly open the outlet valve, and then slowly open the primary inlet valve. 5.4.4 Adjust the compressor according to the height of the gas tank to ensure smooth pumping and control the outlet pressure and temperature. 5.5 Normal shutdown procedure: 5.5.1 Upon receiving the shutdown instruction, coordinate with the relevant processes; then reduce the height of the gas tank to 2 bars, close the compressor inlet valve, and shut down the motor. When the motor stops running completely, close the outlet valve to the compressor and open the circulation valve. 5.5.2 Close the brine inlet valve of the pre-cooler and the water inlet valve of the post-cooler before shutting down the machine. 5.5.3 Close the coarse VC inlet valve of the cooler before shutting down the machine. 5.6 Emergency shutdown procedure: 5.6.1 Emergency shutdown measures shall be taken when the compressor suffers a serious failure or when the upstream and downstream processes affect safe production. 5.6.2 Stop the motor, close the inlet valve; the rest follows the planned shutdown procedure. 5.6.3 Notify the relevant processes that this position has been shut down. 5.7 Process control parameters: Serial number, Parameter name, Parameter value, Detection point, Frequency of detection 1. Gas tank height: 3–7 grids; Station – 1 time per hour 2. Gas outlet temperature of the pre-cooler before the compressor: 15–20°C; Station – 1 time per hour 3. Compressor inlet pressure: 33–2.66 Kpa (10–20 mmHg); Station – 1 time per hour 4. Compressor outlet pressure and outlet temperature: 0.56±0.02 Mpa, <105°C; Station – 1 time per hour 5. Compressor oil pressure: 0.05–0.1 Mpa higher than the inlet pressure; Station – 1 time per hour 6. Compressor oil level: 1–2 levels; Station – 1 time per hour 7. Temperature of the shaft seal oil tank: <60°C; Station – 1 time per hour 8. Motor temperature: <60°C; Station – 1 time per hour 9. Gas outlet temperature of the cooler after the compressor: 42–46°C; Station – 1 time per hour 5.8 Abnormal phenomena and handling methods: Serial number, Fault phenomenon, Cause of fault, Handling method 1. Low compressor outlet pressure: ① Damaged outlet valve; ② Failed piston rings. ① Stop the machine for maintenance; ② Stop the machine for maintenance. 2. Excessively high compressor exhaust temperature: High temperature of the inlet gas. Lower the temperature of the inlet gas and increase the amount of water used in the pre-cooler before the compressor. 3. Low oil pressure in the compressor: ① Damaged oil pump or leaks in the oil pump; ② Clogged oil pipes or filters; ③ Oil level too low. ① Repair the oil pump; ② Clean the oil pipes or filters; ③ Top up the oil promptly. 4. Abnormal noise from the compressor: ① Improper installation, loose anchor bolts; ② Incorrect installation of the drive wheel; ③ Parts have fallen out inside; ④ Hard objects have entered the cylinders; ⑤ Oil pump failures causing power loss or cylinder wear; ⑥ Water in the inlet gas, leakage in the cylinders or intermediate cooler, resulting in liquid accumulation in the cylinders. ① Stop the machine for inspection and repair; ② Same as above; ③ Same as above; ④ Same as above; ⑤ Same as above; ⑥ Improve water drainage from the pre-cooler and mist catcher before the machine, and stop it for inspection and repair. 5.9 Safety Precautions: 5.9.1 Strictly follow operating procedures to prevent improper operations. 5.9.2 Do not wear gloves while refueling to prevent accidents. 5.9.3 Do not touch electrical switches with wet hands to prevent electric shock. 5.9.4 During winter, when the machine is parked for an extended period of time, all excess water in the machine and the condenser should be drained to prevent freezing and cracking. If the parking period is short, the water flow can be reduced to keep it moving and avoid freezing. 5.9.5 The height of the gas tank must be strictly controlled within the specified range. 5.9.6 When hot work is required on equipment or pipelines, the residual gases within them must be completely displaced with N2. Only after the analysis is approved can a ‘Hot Work Permit’ be obtained to carry out hot work, and consideration should be given to allowing explosion relief at the other end. 5.9.7 Pipes, equipment, and instruments in contact with VC shall not be made of Cu, Hg, Ag, or their alloys. 5.9.8 Mixing explosion range of VC and air: 3.6–31% (by volume). 6 Safe operating procedures for the distillation unit. 6.1 Purpose of production: This unit is used to compress the crude vinyl chloride (VC) produced in the synthesis unit, followed by liquefaction and distillation to purify it, so that it meets the specified standards and can be used in the polymerization unit. Ensure proper management of equipment in one’s position, as well as safe and civilized production practices. 6.2 Brief description of the process flow: The crude vinyl chloride gas, after being washed with water and alkali, is compressed and then fed into a total condenser where it is liquefied. After free water is removed using a water separator, the gas enters a low-boiling-point tower for distillation, in order to remove fractions with boiling points lower than that of vinyl chloride (mainly acetylene, N₂, etc.). The low-boiling-point fractions emerge from the top of the tower and, along with the non-condensable gases from the total condenser, go into an exhaust gas condenser to recover any vinyl chloride contained therein. The non-condensable gases are vented, while the condensed liquid is separated from water via a water separator before being sent back to the low-boiling-point tower. The material from the bottom of the tower overflows into the intermediate control tank. The VC liquid exiting the intermediate storage tank enters the high-boiling tower for distillation, driven by the pressure difference between the low-boiling tower and the high-boiling tower to overcome the head difference and remove high-boiling substances. High-purity vinyl chloride gas escapes from the top of the tower, is condensed in the product condenser, and then enters the monomer storage tank. The high-boiling substances are periodically transferred from the bottom of the tower to a residue receiving tank, where the small amount of VC contained in them is vaporized using hot water in the jacket; the residue is then put into barrels for further disposal. When feeding material to the polymerization section, a monomer pump is used to transfer the monomer from the vinyl chloride storage tank to the polymerization section. 6.3 Preparations before driving 6.3.1 Check that all equipment, pipes, valves, instruments, and level gauges are in good condition and functional. 6.3.2 Open the inlet and outlet valves for brine in each condenser, inform the refrigeration team to supply refrigerated brine, and control it to the specified temperature. 6.3.3 Open the valves of the feed pipe and balance pipe in the monomer storage tank, as well as the inlet and outlet valves for the material in the total condenser and exhaust gas cooler. 6.4 Driving Operations 6.4.1 Notify the compression station to start operation. 6.4.2 The condensed crude VC, after water removal in a water separator, enters the low-boiling tower; at this point, it is necessary to accurately control the temperature of the exhaust gas condenser and the vent pressure. 6.4.3 When liquid vinyl chloride overflows from the low-boiling tower into the intermediate control tank, open the circulating hot water valve to accurately control the temperature and pressure at the bottom of the low-boiling tower. 6.4.4 When the liquid level, temperature, and pressure in the intermediate control tank are stable, open the feed control valve leading to the high-boiling tower. 6.4.5 When a liquid level forms in the bottom of the high-boiling tower and exceeds the overflow level, circulating hot water is turned on for heating to gradually raise the temperature to the specified value. 6.4.6 When VC condensate appears in the finished product condenser, activate the top condensers of the high- and low-boiling towers, and adjust the internal reflux to control the reflux ratio. 6.4.7 Strictly control the pressure difference between the bottom of the low-boiling tower and the top of the high-boiling tower, so that the VC liquid can be smoothly forced from the bottom of the low-boiling tower into the intermediate control tank and then into the high-boiling tower. 6.4.8 Strictly control the difference between the bottom pressure and the top pressure of the tower. Generally, the pressure at the bottom of the tower is 0.01–0.02 MPa higher than the pressure at the top of the tower. 6.5 Normal shutdown procedure 6.5.1 After the compression unit stops supplying air, reduce the size of the exhaust vent valve. 6.5.2 After the compression unit has been shut down for 5 minutes, close the exhaust vent valve as well as the valves at the top of the low-boiling point tower, the total condenser, and the brine inlet of the exhaust condenser. 6.5.3 Increase the temperature at the bottom of the high-boiling tower, close the equilibrium valve at the bottom of the tower to raise the system pressure, and transfer all the monomer in the bottom of the tower to the high-boiling tower. 6.5.4 After the discharge of the finished condenser stops, close the discharge valve and the balance valve. 6.5.5 The water-monomer mixture in the water separator is placed into a water collector and then heated with hot water to be recovered to the gas holder. 6.5.6 Release of high-boiling substances. For maintenance, it can be evacuated using nitrogen. 6.6 Emergency Shutdown Procedure 6.6.1 Once the compression unit stops supplying gas, close the exhaust vent valve. 6.6.2 Close the discharge valve, balance valve, and feed valve of the high-boiling tower; stop the chilled brine supply to the condensers as well as the circulating hot water in the tower bottom. 6.6.3 In the event of a prolonged stoppage, permission may be requested from the dispatcher to follow the planned shutdown procedure. 6.7 Process Control Parameters: Serial Number, Parameter Name, Parameter Value, Detection Point, Frequency of Detection 1. Chloride vinyl ether condensation temperature in the total condenser: 20±5°C; Detection point: at the workstation; Frequency: once per hour 2. Bottom temperature and bottom pressure of the low-boiling-point tower: 39–41°C and 0.5±0.02 MPa respectively; Detection point: at the workstation; Frequency: once per hour 2. Top temperature and top pressure of the low-boiling-point tower: 20±5°C and 0.5±0.02 MPa respectively; Detection point: at the workstation; Frequency: once per hour 3. Bottom temperature and bottom pressure of the high-boiling-point tower: 30±2°C and 0.3±0.03 MPa respectively; Detection point: at the workstation; Frequency: once per hour 3. Top temperature and top pressure of the high-boiling-point tower: 20±2°C and 0.32±0.02 MPa respectively; Detection point: at the workstation; Frequency: once per hour 4. Temperature of the exhaust gas condenser: 15±5°C; Detection point: at the workstation; Frequency: once per hour 5. Exhaust gas release pressure: 0.52±0.02 MPa; Detection point: at the workstation; Frequency: once per hour 6. Pressure in the monomer storage tank: 0.32±0.02 MPa; Detection point: in the monomer storage tank; Frequency: once per hour 7. VC content in the exhaust gas: ≤10%; Detection point: at the exhaust pipe; Frequency: once every 4 hours 8. Purity of the monomer: Acetylene content ≥99.99% and impurity content ≤0.0024%; Detection point: in the monomer storage tank; Frequency: once every 8 hours 6.8 Abnormal Phenomena and Handling Methods: Serial Number, Fault Phenomenon, Cause of Fault, Handling Method 1. Unstable liquid level in the tower bottom: ① Insufficient circulation water volume or water temperature; ② Insufficient exhaust gas release volume; ③ Unstable temperature of the top condenser. Handling methods: ① Control the water inflow volume and maintain a stable temperature; ② Continuously release exhaust gas to keep pressure stable. ③ Maintain stable freezing water volume and temperature. 2 The liquid level in the tower reactor is stable, but the quality of the monomer is poor. ① ① Low reflux rate of the material in the tower. ② Low evaporation rate of the material in the tower. ③ Low temperature at the bottom of the tower. ④ Low feed temperature in the low-boiling-point tower. ⑤ Too low temperature at the top of the low-boiling-point tower or in the exhaust gas condenser. ⑥ Low temperature of the circulating water, with unstable circulation volume. ⑦ Low acetylene conversion rate. ⑧ The intermediate control tank is empty. ① Increase the reflux rate. ② Raise the temperature at the bottom of the tower. ③ Raise the temperature at the bottom of the tower. ④ Appropriately reduce the amount of cooling water used in the total condenser. ⑤ Raise the temperature. ⑥ Raise the water temperature and increase the circulation volume. ⑦ Improve synthesis control. ⑧ Stabilize the liquid level in the intermediate control tank. 3. Low temperature in the exhaust gas condenser, but increased VC venting volume. ① Ice formation and blockage in the exhaust gas condenser. ② Low purity of crude vinyl chloride. ③ High temperature in the total condenser. ④ Excessive evaporation rate. ① Replace the exhaust gas condenser. ② Inform the conversion unit to identify the cause. ③ Lower the temperature of the total condenser. ④ Adjust the evaporation rate at the bottom of the tower. 4. Uneven or intermittent discharge from the product condenser. ① Blockage or malfunction of the discharge balance pipe. ② Blockages in the discharge pipes. ③ Large pressure fluctuations in the product condenser. ① Inspect and clear any blockages. ② Shut down the high-boiling-point tower for inspection. ③ Adjust the system pressure and ensure strict stability of pressure. 5. Accumulation of material in the high-boiling-point tower. ① Blockage caused by self-polymerization inside the tower. ① Replace the high-boiling-point tower and shut it down for maintenance. 6 High temperature of the total condenser: ① High temperature or low pressure of the 5℃ saline; ② Obstructions in the inlet and outlet of the saline. ① Notify the refrigeration station to adjust the saline temperature or increase the pressure; ② Check the inlet and outlet valves. 7 Leakage of chlorine vinyl into the saline: ① Leaks in the tubes of the condenser equipment. ① After checking each condenser, replace it if necessary. 6.9 Safety precautions: 6.9.1 All pipes, equipment, and instruments that come into contact with acetylene C2H2 and chlorine vinyl C2H3Cl must not be made of Cu, Hg, Ag, or their alloys. 6.9.2 Emptying must be done before driving. 6.9.3 When C2H2, C2H3Cl, and C2H4Cl2 are on fire, use CO2 extinguishers or dry powder extinguishers; water or foam extinguishers should not be used. For electrical fires, use CCl4 fire extinguishers; water or foam fire extinguishers should not be used. Foam is used to extinguish oil fires. 6.9.4 When working on equipment containing C2H3Cl, it is necessary to remove all residual gases from the equipment’s pipelines; only after the gas has been analyzed and found to be safe can a ‘Work Permit’ be obtained before starting any work. 6.9.5 All equipment shall be grounded to eliminate static electricity. 7 Environmental Protection: 7.1 Working Environment 7.1.1 Maximum allowable concentrations of harmful substances in workshop air (mg/m3): ① Vinyl chloride < 30 ② Dichloroethane < 25 ③ Hydrogen chloride < 15 ④ Mercuric chloride < 0.1 7.1.2 Noise level in workshops and work areas < 90 dB. 7.2 Sources of three wastes and treatment methods. 7.2.1 Spent activated carbon and catalysts: During high-temperature operations in the synthesis reaction of hydrogen chloride and acetylene, mercury chloride on the activated carbon sublimes and is carried away with the gases. The main methods for dealing with this issue are to use activated carbon pumps and adsorbers for gas-phase mercury removal, to replace the activated carbon and catalysts regularly, and to dispose of the spent catalysts and activated carbon externally for recycling. 7.2.2 Excess hydrogen chloride. Treatment: Excess hydrogen chloride is the largest volume of acidic wastewater generated in vinyl chloride production; water-washed foam towers and packed towers are used to remove hydrogen chloride, with 20–25% of the resulting hydrochloric acid being recycled for export. 7.2.3 Treatment of vinyl chloride off-gases: During the distillation of vinyl chloride, the non-condensable gases containing less than 10% vinyl chloride, which are discharged through the off-gas condenser, pass through an off-gas adsorption unit to have the vinyl chloride component recovered; thereafter, the inert gases are vented under pressure-controlled reduction. 7.2.4 Treatment of high-boiling dichloroethane: Intermittent distillation is used to remove vinyl chloride therefrom, and 1,1-dichloroethane is collected for export for further processing.
Safety precautions to be observed during the maintenance of vinyl chloride gas tanks: 1. Ensure proper purging to meet the requirements for working with fire； 2. Disconnect the pipeline or install a blind flange to isolate it from the system ； 3. When entering the gas holder for work, follow the “eight musts” for entering containers ； 3. Operations at the top of the gas holder shall be carried out in accordance with the safety regulations for working at heights.
The big shot upstairs has already made it very clear. I would like to add a less common scenario: if the water quality used in your gas cylinders is poor, a layer of silt tends to accumulate at the bottom of the cylinders. This layer of silt often contains high concentrations of vinyl chloride gas. Be sure to clean it thoroughly before carrying out any related maintenance work.
When maintaining vinyl chloride gas tanks, two main issues need to be considered: safety issues and the quality of maintenance work. 1. Regarding safety issues, particular attention should be paid to the safety measures for working at heights and for entering gas tanks. Since the water in the dome of the gas tank as well as the sediment at its bottom contain toxic, harmful, flammable, and explosive gases, it is necessary to meet certain conditions before entering such areas. 2. Quality issues related to inspection, maintenance, and repair: The top counterweights, pulleys/columns, anti-corrosion measures, thickness measurements, lightning protection, sprinkler systems, etc., must all be thoroughly inspected and addressed to ensure the overall quality of operation.
Safety is the top priority; once internal toxic gas detection shows satisfactory results, forced air circulation is employed, with checks being conducted every half hour.
What is the required concentration of monomers in space, in mg/l?
Safety and environmental protection: lower the gas tank, isolate it from connected systems, empty the gas, use indirect displacement, install blind flanges, open and close openings at the top and bottom, implement displacement ventilation, conduct analyses and obtain necessary permits, supervise personnel entering the tank, and complete the work
It should be carried out in accordance with the tank entry permit; the analysis of hazardous gases must be determined based on one’s own process conditions. Vinyl chloride definitely needs to be tested, and it is very difficult to achieve a level below 5 ppm. Consider using a positive-pressure protective mask to remove the sediment at the bottom. Additionally, it is necessary to consider whether substances such as H2S are present.