【Q&A Question 006】2017.01.06
Thread Content
This post was last edited by 955559 on 2017-7-21 13:20. [Q&A Question No. 006] January 6, 2017: What is the phenomenon of a high-pressure separator being connected in series with a low-pressure separator, and how to deal with it? The reference answers will be visible after responding; points are awarded by identifying the key points. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) Phenomena: 1. The high-level liquid level drops, causing the system pressure to decrease. 2. The liquid level in the stripping tower rises suddenly; the otherwise stable operation curve becomes unstable due to delayed adjustments. 3. The pressure in the stripping tower increases, and in severe cases the safety valve opens; even after this, the pressure does not decrease. Handling: 1. Immediately switch high-pressure operation to manual mode, close the on-site manual valve, and cut off the feed to the stripping tower; once the liquid level at high pressure returns to normal, keep it within a reasonable range. 2. Immediately reduce the low pressure to the normal operating pressure. 3. Contact the instrumentation team to inspect and repair the hydraulic control valve. 4. Operate the distillation unit smoothly. Summary thread of Q&A questions for 2017 (updates ongoing): http://bbs.hcbbs.com/thread-1657793-1-1.html Summary thread of daily questions for 2017 (updates ongoing): http://bbs.hcbbs.com/thread-1657794-1-1.html Summary thread of Q&A questions for 2016 (already updated): http://bbs.hcbbs.com/thread-1597792-1-1.html New Normal Cup – 2016 HaiChuan Top 10 Selection – Please recommend candidates: http://bbs.hcbbs.com/thread-1654112-1-1.html Third-phase evaluation for outstanding management members at HaiChuan: http://bbs.hcbbs.com/thread-1655902-1-1.html (Source: HaiChuan Chemical Industry Forum)
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 operates, 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. Treatment: 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
1. Cut off the area where pressure leakage occurs and identify the cause of it； 2. Pressure relief for overpressure vessels: In the event of pressure transmission, the emergency shut-off valve and the hydraulic control valve should be manually closed immediately. Low-pressure control is usually set to automatic mode, while the valves will open fully to relieve 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 operates, 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. Treatment: 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
Phenomena: 1. The high-level liquid level drops, and the system pressure decreases. 2. The liquid level in the stripping tower rises suddenly; the otherwise stable operating curve becomes unstable due to delayed adjustments. 3. The pressure in the stripping tower increases, and in severe cases the safety valve opens; even after this, the pressure does not decrease. Handling: 1. Immediately switch high-pressure operation to manual mode, close the on-site manual valve, and cut off the feed to the stripping tower; once the liquid level at high pressure returns to normal, keep it within a reasonable range. 2. Immediately reduce the low-pressure level to the normal operating pressure. 3. Contact the instrumentation team to inspect and repair the hydraulic control valve. 4. Operate the distillation unit smoothly.
Series pressure phenomenon: The liquid level in the high-pressure separator is too low, the liquid level in the low-pressure separator rises suddenly, the pressure reading in the low-pressure separator increases; in severe cases, the safety valve activates, and even after it does so, the pressure does not decrease； The pressure in the reaction system drops, and the flow rate at the compressor inlet fluctuates severely ； Vibration is severe in the pipeline between the high-pressure separator and the low-pressure separator. Handling of series pressure phenomenon: Quickly close the high-pressure control valve completely; if necessary, close the manual valve before the control valve. Quickly open the pressure control valve for low pressure, and if needed, open the bypass valve. Once the pressure has dropped, adjust it to normal operating levels. Check the high-level liquid control valve to see if the high-level liquid level transmission is malfunctioning.
The pressure at low levels rises rapidly, the safety valve may activate, and the liquid level at low levels drops. If the operator on site detects this, they should promptly close the valve that regulates flow from high pressure to low pressure; if the valve cannot be closed, the operator outside should go to the site to close the valves upstream and downstream
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.
Phenomenon: Pressure to achieve high scores decreases, while pressure to achieve low scores increases； The system pressure drops too quickly ； Fluctuations in feed rate ； Low-pressure safety valve trips ； Treatment: Set off a fire at a high distance for pressure relief ；
As the pressure at low levels increases, immediately shut off the valve that regulates high pressure to low pressure to achieve emergency pressure relief
The high-pressure pressure drops rapidly, while the low-pressure pressure rises quickly; the low-pressure safety valve opens, causing surging in the turbine. The valves that regulate the flow from high pressure to low pressure, as well as the safety valves, are closed, allowing for rapid pressure release at low pressure. The turbine’s surging protection mechanism is activated