[Q&A Question 101] 2018.04.11

(1) Drop in cold high-pressure liquid level； (2) The cold low-pressure force rises rapidly ； (3) System pressure drops.

(1) Drop in cold high-pressure liquid level； (2) The cold low-pressure force rises rapidly ； (3) System pressure drops.

Phenomenon: (1) Sudden rise in low-pressure； (2) Severe vibration in the pressure reduction pipeline ； (3) Drop in the level of the high-density liquid ； (4) System pressure drops. Treatment: (1) Immediately switch from high-pressure hydraulic control to manual control and shut off the pressure relief valve ； (2) Immediately reduce the low pressure to normal pressure ； (3) Inspect the high-pressure liquid control valve.

(1) Accident phenomena: 1. The level of the cold low-pressure fraction drops, pressure rises rapidly, and the safety valve may activate; 2. The pressure in the reaction system shows a downward trend, and there are abnormal noises as well as significant vibrations in the outlet pipeline of the cold high-pressure fraction. 3. The liquid level and pressure in the low-pressure gas desulfurization tower fluctuate greatly, which may lead to the carryover of amine solution ； 4. Increased flow of low-pressure gas to the desulfurization tower ； 5. The feed flow rate to the hydrogen sulfide stripping tower increases. (2) Cause of the accident: 1. Low liquid level in the cold high-pressure section led to gas from the cold high-pressure section leaking into the cold low-pressure section. 2. Fault in the cold high-level liquid level indicator. (3) Main steps for accident handling: 1. Interlock confirmation: Close the bottom liquid level cut-off valve of the cold high-pressure separator. For Reaction System A 1, change the cold high-pressure control valve to manual mode and reduce the opening degree of the hydraulic control valve. 2. Open the high-pressure vent manual valve at the top of the heat low-pressure section to reduce pressure. 3. Monitor the pressure and gas flow in the hot low-temp fractionator, cold low-temp fractionator, and low-temp gas desulfurization tower, and reduce the pressure in the hot low-temp fractionator to normal levels. 4. Check whether the cold low-pressure safety valve has activated; if it has, switch to the backup safety valve and arrange for the activated safety valve to have its setting adjusted again. 5. The level and pressure control valves of the low-pressure gas desulfurization tower shall be switched to manual operation; if liquid is present in the gas, enhance liquid removal in the low-pressure gas coalescer. 6. After the hot high-pressure liquid level returns to normal, reset the bottom cut-off valve of the hot high-pressure section. Open the bottom level control valve of the hot high-pressure section to regulate the liquid level in it. 7. If false readings from the liquid level gauge at the bottom of the high-temperature fractionator cause high pressure to bleed into low pressure, and once the pressure in the low-temperature fractionator returns to normal, contact the instrumentation team to calibrate the liquid level control valve. 8. Check whether the safety valve at the top of the low-pressure gas desulfurization tower has activated; if it has, switch to the backup safety valve and re-pressurize the activated safety valve. 9. Check whether there is liquid in the low-pressure flare tank inside the unit, and drain it promptly. 10. Resume normal production. B fractionation system 1. Change the pressure and level control valves to manual control, ensure proper operation, and maintain stability in the temperature at the outlet of the heating furnace ； Adjust the top reflux flow to ensure that the top temperature does not exceed the limit, thereby guaranteeing the quality of the fractionated product. After the operation stabilizes, switch all valves that were switched to manual control back to automatic control. C Absorption stabilization system: 1. Maintain the liquid level and pressure of the absorption stabilization system to ensure normal production. D Desulfurization System 1: Maintain stable pressure and liquid level to ensure normal production.

(1) Drop in cold high-pressure liquid level； (2) The cold low-pressure force rises rapidly ； (3) System pressure drops. Handling: (1) Immediately switch the cold high-pressure liquid level control from automatic to manual control, and go to the site to close the manual valve for feeding cold low-pressure fluid; once the liquid level in the cold high-pressure section rises, adjust it to stay within the normal range. (2) Immediately reduce the cold low-pressure to the normal operating parameters. (3) Contact the instrumentation team to check the cause of the hydraulic control failure and carry out repairs.

The phenomenon of cold high-pressure streams shifting to cold low-pressure streams: ① The level of cold low-pressure fluid rises suddenly; the previously stable operation curve becomes unstable due to delayed adjustments, resulting in a significant increase in the valve opening. ②The low-temperature pressure indication rises; in severe cases, the safety valve opens, yet the pressure does not decrease even after that. ③System pressure drops; the cold high-pressure liquid level is empty. Treatment method: ① Immediately switch the cold high-pressure liquid level control to manual operation, close the stop valve to cut off the feed to the cold low-pressure section, and wait until the liquid level in the cold high-pressure section rises to a normal range. ②Immediately reduce the cold low-pressure to the normal operating pressure. ③Contact the instrument technician to check the cause of the fault in the hydraulic control valve and repair it. ④Stabilize and balance the operation of the fractional distillation system.

As the cold low-level liquid level drops, the pressure rises rapidly, and the safety valve may activate. Treatment: Reduce the valve opening from high to low.

Answer: Phenomenon: (1) The liquid level in the cold high-pressure section drops； (2) The cold low-pressure force rises rapidly ； (3) System pressure drops. Handling: (1) Immediately switch the cold high-pressure liquid level control from automatic to manual control, and go to the site to close the manual valve for feeding cold low-pressure fluid; once the liquid level in the cold high-pressure section rises, adjust it to stay within the normal range. (2) Immediately reduce the cold low-pressure to the normal operating parameters. (3) Contact the instrumentation team to check the cause of the hydraulic control failure and carry out repairs.

Cold low-pressure stranding: an excessive liquid level may cause the cold low-pressure tank to become full. Shut off the cold high and low cut-off valves to address the pressure surge issue.