Operating Procedures for Urea Carbon Dioxide Compressor Post

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Operating Procedures for Carbon Dioxide Compressor 1. Main Tasks of the Position: The responsibility of this position is to take the CO2 gas with a purity of 98.5% and an oxygen content of 0.5% (v), which has been obtained through decarburization, remove water from it using a droplet separator, and then use a compressor to increase its pressure to 20.59 MPa at a temperature of 125°C, before sending it to the urea synthesis tower. Maintain the operating conditions in accordance with the process specifications; be responsible for the startup, normal shutdown, emergency shutdown, as well as routine operation and maintenance of the compressor system, and keep proper records. 2. External Communications 2.1. Communication with the control room for urea and synthetic ammonia regarding the start-up, shutdown, gas supply, or gas isolation. 2.2. Contact the electrician regarding power supply during startup and the current and voltage conditions during normal operation. 2.3. Coordinate with the pump room staff to supply gas to the urea synthesis tower. 2.4. Communicate with the shift leader and the control room staff to inform them of any changes in gas flow and the operating status of the compressors, and make corresponding adjustments. 2.5. Contact the instrument technician for the maintenance and calibration of the instruments. 3. Process parameters: Inlet pressure of Stage 1: 0.01–0.06 MPa; Exhaust pressure of Stage 1: 0.10–0.33 MPa; Exhaust pressure of Stage 2: 0.6–1.15 MPa; Exhaust pressure of Stage 3: 2.0–3.10 MPa for Unit 1 and Unit 2, 2.0–3.55 MPa for Unit 3; Exhaust pressure of Stage 4: 6.0–8.1 MPa; Exhaust pressure of Stage 5: 19.3–20.59 MPa. Inlet temperature of Stage 1: 25–45°C; Exhaust temperature of Stage 1: 100–115°C; Exhaust temperature of Stage 2: 110–125°C; Exhaust temperature of Stage 3: 110–125°C; Exhaust temperature of Stage 4: 100–115°C; Exhaust temperature of Stage 5: 110–125°C. Circulating oil pressure: 0.25–0.6 MPa; Circulating oil temperature: 20–40°C; Cooling water pressure: 0.2–0.45 MPa; Temperature of cooling water inlet: ≤35°C; Temperature of main bearings: 30–60°C; Inlet temperature of Stage 5: 35–40°C; Current of the main motor: as specified by the rated current of the main motor. 4. Operating procedures: 4.1. Preparations before startup: 1.1.1. Check that all reports, tools, equipment, fire-fighting facilities, and protective gear are available and in good condition ； 1.1.2. Thoroughly inspect the equipment, pipes, valves, and all connection flanges to ensure they are in good condition ； 1.1.3. Contact the instrument technician to check whether the instrument signals and interlocks are sensitive and functioning properly ； 1.1.4. Contact an electrician for inspection before restoring power ； 1.1.5. Contact the dispatch team to supply cooling water, open the main inlet and outlet valves for the compressors, and direct water to each cooler to check the return water condition ； 1.1.6. Contact the synthesis control room to supply qualified CO2 gas, and use the vent valve on the compressor inlet main pipe to control the inlet pressure at 0.02~0.05 MPa. 1.1.7. Check the valves that should be opened: the inlet valve for Section 1, the valve for each return line, the valve for each of the five return lines, the vent valve for Section 5, the oil-water discharge valves for each section, the valves at the base of each pressure gauge, the inlet and outlet valves for the coolers in each section, the inlet and outlet valves for the cylinder jackets in each section, the inlet and outlet valves for the oil coolers, and the on-site drain valves for each section. Valve to be closed: Section 5 outlet valve. 1.2. Driving 1.2.1. Activating the lubrication system 1.2.1.1. Starting the circulating oil system ⑴ Check the oil quality, oil tank level, and oil level control; keep the temperature of the circulating oil between 20~40°C, and adjust the cooling water according to the oil temperature ； ⑵Start the circulating oil pump and adjust the oil pressure to the specified range. 1.2.1.2. Starting cylinder lubrication system ⑴ Check the oil quality and the oil level in the filler; the oil level should be at 4/5. Rotate the filler by hand to verify that oil is reaching all relevant points ； ⑵Start the oil injection pump, inspect the pump, check the oil injection status, and adjust the oil volume. 1.2.2. Cranking: Stop the circulating oil pump, switch the cranking handle to the “forward cranking” position, start the oil pump and the cranking motor. Crank the compressor for a few rotations to check whether all its components are functioning properly. Once everything is normal, stop the cranking motor and the oil pump, move the cranking device to the “start” position, and verify that it is disengaged. 1.2.3. Start the host 1.2.3.1. Contact the electrician to adjust the excitation current to the rated value. 1.2.3.2. After obtaining the scheduler’s approval, start the host and check whether all operating components are functioning properly. Also, examine the temperature rise of the lubricating oil and the bearing shells; only after everything is in order can pressure be applied. 1.2.4. Pressurization: Starting from the low-pressure section, sequentially close the oil and water discharge valves of each section, close the vent valve of section 5, and close the three-to-one valve; then slowly reduce the flow rate of the five-to-one valve in order to allow the pressure in each section to rise gradually. Adjust the inlet vent valve based on the pressure in the CO2 main pipe, and use the one-to-one valve to regulate the load. Once the pressure at the five-output port reaches 20 MPa, use the vent valve of section 5, the five-to-one valve, and the inlet vent valve to control the pressure in each section. Check the operation of the equipment and adjust the amount of cooling water according to the temperature in each section. 1.2.5. Gas supply: After receiving the signal to supply or stop supplying gas, open the five-stage outlet valves and gradually close the vent valve, thereby sending CO2 to the area in front of the urea synthesis tower valves. When starting the machine for the first time, it is necessary to constantly monitor the pressure changes at the five outlet stages to prevent overpressure. The vent valve can only be closed after the pressure reaches 20 MPa and once it has been confirmed by the central control system or the pump room that feeding has been successful. 1.3. Parking 1.3.1. After receiving the parking instruction, slightly open the fifth-stage vent valve while closing the fifth-stage outlet valve, maintaining the CO2 outlet pressure at around 20 MPa to prevent overpressure or backflow of material. 1.3.2. Pressure relief: First, slightly open the return valve to reduce the pressure, while monitoring the inlet pressure; use the vent valve on the inlet manifold to control the pressure in the manifold. Open the circuit valve, pay attention to the compression ratio, and allow the pressure to drop slowly. After all the pressures in each section have been released, open the oil and water release valves for each section to discharge the oil and water using the remaining pressure. 1.3.3. Stop the main machine according to the instructions from the shift leader and the control room. 1.3.4. Close the main intake valve and the valves of each circuit; close the vent valve as appropriate. Stop the oil feed pump 5 minutes after the main unit stops operating; stop the circulation oil pump and turn off the cooling water half an hour later. In winter, drain all water accumulated in the coolers and cylinder jackets to prevent the equipment from being damaged by freezing. 1.4. Shutdown 4.4.1 Prepare the standby unit in accordance with the normal startup procedure. 4.4.2 Contact the synthesis control room and pay attention to the regeneration pressure. Open the circuit valves for each section fully, close the vent valve, start the standby unit, close the oil and water discharge valves for each section, and slowly close valve 3-1. Pay attention to maintaining the pressure in the inlet main pipe; increase the pressure gradually using valve 5-1. Try to avoid releasing CO2. Once the exhaust pressure at section 5 reaches 20 MPa, open the outlet valve of the standby unit. Turn on the main machine at 5 revolutions per minute, and turn on the valve and set the standby machine to 1 revolution per minute. Once the main machine is running at 5 revolutions per minute, switch to mode 5, and shut down the main machine following the standard shutdown procedures. Adjust the load of the standby machine according to instructions from the central control system. 1.5. Emergency Stop 1.5.1. An emergency stop should be initiated in the following situations: (1) Loss of water supply, power supply, fuel supply, air supply, or automatic tripping ； ⑵Major mechanical or electrical accidents ； ⑶Fire and explosion ； ⑷Severe overpressure. 1.5.2. Emergency shutdown procedures 1.5.2.1. Shut down the main machine. 1.5.2.2. First close the five-stage outlet valves, then open the five-stage vent valves to relieve pressure in each circuit, and use the remaining pressure to discharge oil and water. 1.5.2.3. Others shall be treated as normal shutdowns. 2. Common accidents, causes, and handling methods
Phenomenon, Cause, Handling Method
1. Excessive pressure at a certain outlet section
(1) Leakage in the inlet/outlet valve of the next section
(2) Inadequate cooling at the outlet
(3) Wear of the cylinder piston rings
(4) Blockage by impurities at the gas outlet
(1) Shut down and replace the valve
(2) Improve cooling efficiency
(3) Shut down and replace the piston rings
(4) Shut down and remove impurities

2. Abnormally low discharge pressure at a certain section
(1) Fault in the inlet/outlet valve of this section
(2) Wear of piston rings causing leakage in this section
(3) Leakage in the exhaust path of this section
(1) Shut down and replace the valve
(2) Shut down and replace the piston rings
(3) Shut down for repair

3. Abnormally high exhaust temperature at a certain section
(1) Fault in the inlet valve of this section
(2) Poor cooling effect in the preceding section
(3) Damaged piston rings in this section
(4) Too low pressure in the preceding section
(1) Shut down and replace the valve
(2) Improve cooling efficiency in the preceding section
(3) Shut down and replace the piston rings
(4) Identify the cause and address it

4. Abnormally high bearing temperature at a certain section
(1) Insufficient supply of circulating oil
(2) Excessively high oil temperature
(3) Too small bearing clearance or presence of impurities
(4) Degraded lubricating oil
(5) Incorrect type of lubricating oil used
(1) Shut down and check the oil supply system
(2) Clean the filter and increase the water flow
(3) Shut down to adjust the clearance and remove impurities
(4) Replace the lubricating oil
(5) Replace the lubricating oil

5. Abnormal noises in the cylinder
(1) Liquid entering the cylinder
(2) Loose fastening nuts of the piston
(3) Loose valves
(4) Foreign objects in the cylinder
(1) Shut down for repair
(2) Shut down for repair
(3) Shut down to repair the valve
(4) Shut down for repair

6. Abnormal noises in the machine body
(1) Knocking sound in the main shaft bearings (excessive clearance or loose nuts)
(2) Knocking sound in the connecting rod bearing shells (excessive clearance at connection points)
(3) Foreign objects inside the machine body
(4) Wear of the connecting rod small-end bearings
(1) Shut down for repair
(2) Shut down for repair
(3) Shut down for repair
(4) Shut down for repair

7. Drop in circulating oil pressure
(1) Clogged filter
(2) Leakage or improper adjustment of the return valve
(3) Fault in the oil pump
(4) Fault in the safety valve
(5) Low oil level
(1) Clean the filter
(2) Eliminate leakage and readjust
(3) Shut down to repair the oil pump
(4) Shut down for repair
(5) Add more circulating oil

9. Excessively high circulating oil temperature
(1) Insufficient cooling water or high water temperature
(2) Poor cooling effect of the oil cooler
(1) Increase cooling water volume and lower water pressure
(2) Clean the oil cooler

10. Abnormal noises in the circulating oil pump
(1) Air being drawn into the oil pump
(2) Wear of the oil pump bearing gears
(3) Misalignment of the drive gear
(1) Immediately transfer oil to raise the oil level
(2) Shut down for repair
(3) Shut down for repair

11. Water in the lubricating oil
(1) Leakage in the oil cooler
(2) Water present in the raw oil
(3) Leakage into the oil through the stuffing box
(4) Cooling water leaking into the lubricating oil through the stuffing box
(1) Repair the oil cooler and change the oil
(2) Replace with qualified lubricating oil
(3) Reduce water vapor content in CO2 and change the oil
(4) Shut down for repair and change the oil

12. Oil injector not supplying oil
(1) Wear of the plunger and large clearance in the plunger sleeve
(2) Too low oil level
(3) Clogged filter screen or oil pipe
(4) Air entering through the plunger sleeve or air in the cylinder
(5) Improper oil volume adjustment
(1) Replace the components
(2) Add oil to raise the level
(3) Clean the filter screen and remove debris from the oil circuit
(4) Filter
(5) Adjust the position of the screw

13. Excessive pressure at the outlet of section 5
(1) Blocked outlet pipe or closed outlet valve
(2) Excessive pressure in the synthesis tower
(3) Faulty pressure gauge
(4) Damaged check valve
(1) Clear the outlet pipe and open the valve
(2) Notify the control room of excessive pressure in this section
(3) Contact the instrumentation team to replace the pressure gauge
(4) Shut down for repair

14. Decreased temperature in the balance pipes of sections 4 and 5
(1) Wear of piston rings
(1) Shut down and replace the piston rings