[Q&A Question 151] 2016.09.18
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【Q&A Question 151】September 18, 2016: What happens when pressure is transmitted from the cold high-pressure separator to the cold low-pressure separator? How to handle it? The answer key will be available after responding; scoring is based on answering the key points. (1) Turn off the drain valve, and contact the operator to adjust the control valve; ask the operator to set the valve opening to 0%, 50%, and 100% respectively for tracking verification. (2) Open the downstream valve fully. (3) Set a certain opening degree for the control valve and open the virtual lock of the upstream valve until there is fluctuation in the indication. (4) Slowly open the upstream valve while slowly closing the branch line valve, aiming for minimal fluctuations, until the branch line is fully closed and the upstream valve is fully open. (5) Adjust the opening degree of the control valve to keep the controlled parameter within the specified range. Answer: Phenomenon: (1) The liquid level in the cold high-pressure separator decreases ； (2) The pressure in the cold low-pressure separator rises rapidly ； (3) System pressure drops. Actions to take: (1) Immediately switch the liquid control of the cold high-pressure separator to manual control, and contact the field operator to shut off the feed to the cold low-pressure separator; once the liquid level in the cold high-pressure separator rises, regulate it to be within the normal range. (2) Immediately reduce the pressure in the cold low-pressure separator to the normal operating parameters. (3) Contact the instrumentation team to check the cause of the hydraulic control failure and carry out repairs. .
Connecting a high-pressure system to a low-pressure one is extremely dangerous, as it can lead to situations such as the activation of the low-pressure safety valve. Generally, high-pressure systems are equipped with emergency shut-off interlock controls, which ensures a high level of safety. However, in the event of pressure crossover, the emergency shut-off valve and the hydraulic control valve must be manually closed immediately. Low-pressure control is usually set to automatic mode, with the valves opening fully to release pressure when it rises too high
Phenomenon: The liquid level in the cold high-pressure separator is too low; the liquid level in the cold low-pressure separator rises suddenly, the pressure reading of the cold low-pressure separator increases, as does the pressure reading of the low-pressure gas desulfurization tower. In severe cases, the safety valve activates, and even after it activates, the pressure does not decrease； The pressure in the reaction system drops, and the inlet flow rate of the recycle hydrogen compressor fluctuates severely ； Vibration is severe in the pipeline between the cold high separator and the cold low separator. It is a very dangerous accident with a low probability of occurrence, but once it happens, pay attention to controlling four aspects: 1. Shut down the high-pressure liquid control shut-off valve. 2. Low-pressure relief. 3. Closely monitor the low-pressure level. 4. The safety of personnel comes first.
Phenomenon: (1) Drop in liquid level of the cold high-pressure separator； (2) The pressure in the cold low-pressure separator rises rapidly ； (3) System pressure drops. Actions to take: (1) Immediately switch the liquid control of the cold high-pressure separator to manual control, and contact the field operator to shut off the feed to the cold low-pressure separator; once the liquid level in the cold high-pressure separator rises, regulate it to be within the normal range. (2) Immediately reduce the pressure in the cold low-pressure separator to the normal operating parameters. (3) Contact the instrumentation team to check the cause of the hydraulic control failure and carry out repairs.
Phenomenon: The liquid level in the cold high-pressure separator is too low; the liquid level in the cold low-pressure separator rises suddenly, the pressure reading of the cold low-pressure separator increases, as does the pressure reading of the low-pressure gas desulfurization tower. In severe cases, the safety valve activates, and even after it activates, the pressure does not decrease； The pressure in the reaction system drops, and the inlet flow rate of the recycle hydrogen compressor fluctuates severely ； Vibration is severe in the pipeline between the cold high separator and the cold low separator. Processing: 1. Close the high-pressure hydraulic cut-off valve. 2. Low-pressure relief. 3. Closely monitor the low-pressure level. 4. The safety of personnel comes first.
The cold high-pressure liquid level drops rapidly, even to zero, while the pressure in the cold high-pressure system rises, to the point that the safety valve activates!
Phenomenon: The liquid level in the cold high-pressure separator is too low; the liquid level in the cold low-pressure separator rises suddenly, the pressure reading of the cold low-pressure separator increases, as does the pressure reading of the low-pressure gas desulfurization tower. In severe cases, the safety valve activates, and even after it activates, the pressure does not decrease； The pressure in the reaction system drops, and the inlet flow rate of the recycle hydrogen compressor fluctuates severely ； Vibration is severe in the pipeline between the cold high separator and the cold low separator. Handling: Quickly switch the control of the high-pressure liquid regulating valve to manual mode and close the regulating valve completely; if necessary, close the manual valve in front of the regulating valve. Quickly open the pressure-controlled valve for the low-pressure side, and if needed, open the bypass valve as well. Once the pressure has dropped, adjust everything back to normal operating conditions. Contact the instrumentation team to check the high-level liquid control valve; determine whether the high-level liquid level transmission is malfunctioning
Due to the excessively low high-level liquid level caused by the instrument (three-out-of-two failure), the low-level liquid level rose suddenly. Automatic level control has failed; the control valve is now operated manually. The actual liquid level is verified on-site, and adjustments are made based on this actual level to prevent the liquid level from being too high or too low.
(1) Turn off the drain valve, and contact the operator to adjust the control valve; ask the operator to set the valve opening to 0%, 50%, and 100% respectively for tracking verification. (2) Open the downstream valve fully. (3) Set a certain opening degree for the control valve and open the virtual lock of the upstream valve until there is fluctuation in the indication. (4) Slowly open the upstream valve while slowly closing the branch line valve, aiming for minimal fluctuations, until the branch line is fully closed and the upstream valve is fully open. (5) Adjust the opening degree of the control valve to keep the controlled parameter within the specified range. Answer: Phenomenon: (1) The liquid level in the cold high-pressure separator decreases ； (2) The pressure in the cold low-pressure separator rises rapidly ； (3) System pressure drops. Actions to take: (1) Immediately switch the liquid control of the cold high-pressure separator to manual control, and contact the field operator to shut off the feed to the cold low-pressure separator; once the liquid level in the cold high-pressure separator rises, regulate it to be within the normal range. (2) Immediately reduce the pressure in the cold low-pressure separator to the normal operating parameters. (3) Contact the instrumentation team to check the cause of the hydraulic control failure and carry out repairs. .
Connecting a high-pressure system to a low-pressure one is extremely dangerous, as it can lead to situations such as the activation of the low-pressure safety valve. Generally, high-pressure systems are equipped with emergency shut-off interlock controls, which ensures a high level of safety. However, in the event of pressure crossover, the emergency shut-off valve and the hydraulic control valve must be manually closed immediately. Low-pressure control is usually set to automatic mode, with the valves opening fully to release pressure when it rises too high