Emergency shutdown procedures and key points for urea production by CO2 stripping?

There are many types of emergency shutdowns: cutting off the circulating water, shutting down power supply, cutting off instrument air, stopping the carbon dioxide supply, tripping the high-pressure pump, and so on. Which type is the author referring to?

Don’t you have any operating procedures? You should take a close look at them; they’re things that need to be memorized by heart.

If one is proficient with this system, solutions can be found for any abnormal situation. What is readily available may not be easily digested and absorbed.

3. Emergency shutdown: An emergency shutdown shall be initiated in any of the following situations: a sudden drop in the steam supply to the thermal power plant to below 2.5 MPa; interruption of the power supply to instruments and instrument air; failure of the CO2 compressor; power outages; interruption of cooling water supply; or significant leaks of NH3, ammonium methoxide, etc., resulting in an unclear situation at the site that makes it impossible to shut down the system normally. All such cases shall be treated as emergency shutdowns. (1) Emergency shutdown procedure: (a) Press the emergency shutdown button to stop the CO2 compressor, the ammonium methane pump, and the ammonia pump; the control room shall close the quick shut-off valves HV204 and HV206, the pump room staff shall close the main CO2 valve and open the upstream shut-off valve PV204, while the circulation station staff shall close the main ammonia valve. (b) Immediately and quickly shut off HV201 and PV904, turn off TV901, TV902, and LV203; open HV901 to reduce the pressure in PIC904 to 0.55 MPa, and open HV203 for venting for 10 minutes to prevent backflow in the synthesis system. (c) Immediately notify the shift operator to open the shell-side steam valve of 202C, manually open PV213/2, and raise PIC213 to around 0.5–0.55 MPa. (d) After confirming that the bottom discharge pipe of 203C is unobstructed for the cyclic position, open the bottom discharge valve of 203C. (e) Open HV902 and HV903, and inform the circulation team to send water via the bypass line and supply steam to the jacket. (f) The steam system should be put into circulation immediately to break the vacuum, and the process should be switched to water flushing and discharge; meanwhile, the desorption and hydrolysis systems should have their load reduced. (g) Notify to start the 301J cycle, maintain the water addition volume for 301C/CA, and maintain the level of 302EF using the discharge method. (h) When there is no liquid level in LIC203, manually close LV203 and shut off PV301. (i) The synthesis system can be sealed in the tower for 12 hours. (j) Notify the personnel on duty to flush the relevant pipelines. (2) For shutdowns caused by power outages, it is also necessary to: (a) start 901J and 902J as soon as possible using the emergency power supply. (b) Quickly shut down PV704, initiate evaporation shutdown, flush with water, and discharge. (c) For 301J inlet, water is added; to 706J inlet, condensate is added to 301C/CA to dilute the process medium. The discharge from 302EF remains unchanged, and condensate is added from 706J inlet to both 708C and the pipeline from 708C to 301C to carry out dilution. (d) Once power is restored, start all pumps except the NH3 pump and 705J immediately. (3) Shutdowns caused by steam shutdown must also: (a) shut off PV213/2, PV205, FV704, FV703, and open PV204 to keep PIC204 above the high-pressure system pressure; as appropriate, close the main 3.5 MPa steam inlet valve and open the steam line drain. (b) Close the upstream and downstream shut-off valves of LV901 and LV903, and close valve 902F to the high-pressure water supply valve. (c) Immediately stop evaporation and break the vacuum, and switch to water flushing and discharge. (d) Stop 903J or close the cooling water valve of 902C, or drain part of the high-pressure water from 203C to prevent excessive condensation in 203C. (4) In the case of an emergency shutdown caused by a lack of instrument air, the relevant valves can be quickly closed when there is still 0.14 MPa of instrument air available. (a) For the circulating position, keep the HV202 shut-off valve slightly open for about 0.5 to 1.0 hour before closing it completely; immediately inform the pump station to close the LV203 shut-off valve in order to seal the high-pressure system. (b) The circulation system is shut down and flushed clean. (c) Notify the shift on duty to immediately close the FV704 and FV705 (FO) isolation valves. (d) Evaporation to break vacuum and allow fluid flow: The evaporation system is equipped with four jet pumps and four shut-off valves (it is best to directly close the PV704 shut-off valve and open the air intake valve in order to completely break the vacuum in stages 1 and 2). The personnel responsible for the evaporation process should be informed to open FV401 using a handwheel; once fluid starts flowing through the system, they should immediately close the PV401 and TV402 shut-off valves. After the evaporation system has been thoroughly flushed, it can be shut down. Once the instrument air is restored, the discharge process for the synthesis system can begin. (5) Disruption of cooling water: Once the cooling water is interrupted, it will inevitably cause the CO2 compressor to shut down. (a) The control room promptly closed the HV204 quick shut-off valve and instructed the pump room crew to close the CO2 inlet main valve. (b) The master controller shuts off HV201 and PIC904. (c) The circulating station quickly opens the HV901 shut-off valve to reduce PIC904 to 0.55 MPa. (d) While shutting down HV204, inform the pump room staff to stop the ammonia pump; once it has stopped, shut down HV206 and inform the circulation team to close the ammonia angle valve on the fourth floor. (e) Stop the methylammonium pump to stop circulation. (f) Notify the pump room to open the PV204 isolation valve (this will allow pressure to be maintained in the CO2 at the bottom of tower 201C). After the CO2 compressor starts, it is vented through the PIC204 to maintain a certain pressure. (g) Other matters follow the emergency shutdown steps “(c)～(j)”. (6) Emergency shutdown caused by a large-scale leak of liquid ammonia: (a) Once a large-scale leak of liquid ammonia occurs, first press the emergency shutdown button to stop the ammonia pump, the CO2 compressor, and the methylammonium pump; the control system shall then close the HV204 and HV206 quick shut-off valves. (b) In the event of a large leak in the pump body or at the outlet pipe of the ammonia pump, the personnel on duty at the circulation station should put on protective equipment, close the outlet valve of the ammonia buffer tank, while the personnel at the pump room should close the inlet valve of the ammonia pump. In the event of a major leak in the ammonia buffer tank (103F), close the inlet valve to 103F on the second floor, and the operator in the pump room shall close the inlet valve of the ammonia pump. (c) If the on-site conditions are harsh, notify the dispatcher to close the first urine ammonia inlet valve and open the second one. (d) The pump room operator closes the CO2 main valve and opens the PV204 isolation valve; the circulation room operator closes the ammonia angle valve. (e) Other matters follow the emergency shutdown steps “(b)～(j)”.