What are the conditions for venting gas in low-temperature methanol washing?

This post was last edited by qy576100527 on 2017-8-1 23:23: 1) The system establishes a circulation of methanol solution. 2) The system temperature drops below -20 degrees ； 3) The methanol thermal regeneration tower and the methanol-water separation tower are operating normally ； 4) Methanol spraying should be started half an hour in advance ； 5) The nitrogen stripping system is operating normally ； 6) The shift ammonia washing tower is operating normally, with venting at the exit of the shift system. 7) Slowly open the system bypass to equalize the system pressure, after which air can be introduced into the system.

1. The methanol process system has passed nitrogen purging, with O2 ≤ 0.5%. The nitrogen pressure in each tower was adjusted to the required level; the pressure at the outlet of the purification unit was set at 4.5 MPa, while that of the flash tank was set at 1.0 MPa. Automatic control was activated after setting the pressure at the outlets of the two towers at 0.15 MPa. Automatic control was also enabled after setting the pressure at the exhaust gas outlet at 0.07 MPa, and at the outlets of the four towers at 0.20 MPa. The methanol circulation system was established, and the propylene cryocooler and reboiler were put into operation. Methanol: the temperature is reduced to below -18°C. 2. Spray methanol should be activated half an hour before gas introduction; the amount of methanol sprayed must be adjusted to the design value of 1.66 m3/h. The liquid level in the separation tank at the inlet of the purified gas is set at 30% to enable automatic control. 3. Confirm that all pressure control valves for venting and flare routing are set to automatic control ； 4. Confirm operation at 70% load with a methanol circulation rate of 70% ； 5. The water content in the circulating methanol is below 1% ； 6. Commissioning of nitrogen stripping with three towers ； 7. The temperature of the lean methanol before entering the tower is reduced to below -18°C ； 8. Towers 4, 5, and 6 are all operating stably; the liquid level at the bottom of Tower 6 is automatically controlled to direct wastewater to the sewage treatment system ； II. Gas introduction: 1. Adjust the pressure at the outlet of the purified gas to 5.5 MPa; close the HPN2 pipeline leading to the washing tower. Contact the control room and use a bypass valve adjacent to the gas supply valve to slowly fill one of the towers with gas. Once the pressures before and after the boundary valve become similar, gradually open the main gas supply valve and close the bypass valve ； 2. Slowly open the purge gas outlet vent valve to stabilize the pressure in Tower 1. Once all the N2 gas in Tower 1 has been replaced by the feed gas, the purge gas outlet vent valve can be gradually opened further, until the shift unit automatically closes its own vent valve, with the purge gas outlet vent valve then taking over automatic control of the venting process. Note: Do not introduce gas too quickly at the beginning, to prevent a large amount of N2 in the tower from flowing into the flare line and causing the flare to go out; moreover, an excessive flow rate of gas may also cause the tray to be overturned ； 3. During the gas guiding process, by checking the opening degrees of each PV valve, close the temporary N2 filling valves (the two); after they are closed, open the intermediate drain valve for venting ； 4. Adjust the FV opening of one tower to ensure even distribution of the two streams of solution going to the flash tanks, so that the H2S content in the exhaust gas does not exceed the specified limits ； 5. Control the temperature and pressure of the system properly; when guiding gas, some control valves need to be set to the manual mode for adjustment, and only after stabilization can they be switched to automatic control. III. Gas Supply 1. Supply H2 and CO recycle gas. Once all the feed gas has been introduced and the system has stabilized and started cooling down, the recycle gas compressor can be activated to send the gas to the shift reaction unit, where useful gases such as H2 can be recovered. Circulating air pressure: The compressor suction pressure is automatically maintained at a constant level by the pressure control valve at the outlet of the rich tumor flash tank. 3. Supplying purified gas: When the levels of CO2 and H2S in the purified gas meet the process requirements, contact the dispatch team to supply the gas to subsequent processes. Slowly open the air supply valve to introduce pressure into the subsequent process. During the gas guiding process, the set value of the purge gas outlet vent valve can be appropriately increased; once the purge gas outlet vent valves are all closed, the gas guiding is complete. 4. When the hydrogen sulfide content analyzed meets the requirements, the acidic gases can be sent for sulfur recovery outside the plant.

1. The minimum system methanol circulation rate operates stably. 2. The temperature of methanol entering the washing tower is around -20°C. 3. The regeneration system is now functioning properly. 4. The methanol/water separation system is operating normally. 5. Methanol spraying and nitrogen stripping have been in operation for over half an hour. 6. The ammonia washing tower has been put into operation and is working properly.