【Q&A Question 120】2016.08.18

Reasons for liquid carryover in circulating hydrogen: 1. High temperature of the medium in the liquid separation tank； 2. Excessively high liquid level in the liquid separation tank: Hazard – Circulating hydrogen carrying liquid can cause liquid slugging, damaging components such as the blades of centrifuges and air valves in reciprocating machines. Solution: 1. If the temperature of the medium is high, increase the operation of air cooling or water cooling systems to lower the temperature of the medium in the liquid separation tank ； 2. Lower the liquid level in the separation tank to a reasonable level.

(1) When the circulating hydrogen is diverted from the desulfurization tower, the main reasons for liquid entrainment in the circulating hydrogen are poor gas-liquid separation in the cold high-pressure section and excessive gas flow rate, as well as excessively high liquid levels and temperatures in that section. (2) When the circulating hydrogen desulfurization tower is not shut off, the main reason for liquid entrainment in the circulating hydrogen is an excessive amount of circulating hydrogen, which leads to the entrainment of mist ； Or the circulating hydrogen desulfurization tower is not operated properly, resulting in significant pressure fluctuations. Hazard: Since liquids are incompressible, introducing a liquid into a compressor exerts a strong impact on the impeller and the compressor casing, resulting in damage to these components. Treatment: (1) Strengthen the condensate drainage from the compressor inlet separator tank ； (2) Reduce the circulation volume of recycled hydrogen ； (3) Reduce the cold high-pressure liquid level and temperature ； (4) Strengthen the operation of the circulating hydrogen desulfurization tower to maintain stable pressure.

I. Cause: The high liquid level or the foam breaker failing results in oil being carried in the circulating hydrogen； In units equipped with a circulating hydrogen desulfurization system, liquid carryover is caused by either an excessively high liquid level in the desulfurization tower or amine foam formation resulting from hydrocarbons in the circulating hydrogen. II. Hazards: Liquid carried in the circulating hydrogen can easily cause liquid slugging in the circulating hydrogen compressor, leading to damage to the compressor. III. Solutions: 1. Try to reduce the temperature of the high-pressure separator. 2. Keep the liquid level in the high-pressure separator from rising too high. 3. Drain the liquid from the circulating hydrogen buffer tank in a timely manner. 4. Slightly reduce the processing capacity of the plant. 5. Calibrate the level measurement devices in the high-pressure separator and the circulating hydrogen buffer tank to ensure accurate readings

The amount of recycled hydrogen entering C101 is too high, resulting in liquid foam entrainment； The liquid level in C101 is too high; the operating temperature is high ； Hazard: Since liquids are incompressible, introducing a liquid into a compressor can damage the blades ； Processing: ； (1) Strengthen the drainage of the liquid separation tank at the compressor inlet and the liquid separation package on the inlet line ； (2) Appropriately reduce the amount of recycle hydrogen fed to C101 ； (3) Appropriately lower the C101 liquid level and temperature ； (4) In the event of an accident such as a loss of instrument air, make sure to properly control C101 ；

Excessive amount of circulating hydrogen leads to foam entrainment； The liquid level is too high, and the operating temperature is high ； Treatment: (1) Strengthen the condensate drainage from the compressor inlet separator tank and the inlet line separator ； (2) Appropriately reduce the amount of recycle hydrogen fed to C101 ； (3) Appropriately lower the C101 liquid level and temperature ； (4) In the event of an accident such as a loss of instrument air, make sure to properly control C101 ；

The temperature of the recycled hydrogen is high, causing liquid to enter the desulfurization tower for recycled hydrogen； Compressor interlock shutdown

The reason is that the amount of recycled hydrogen entering C101 is too high, resulting in foam entrainment； The liquid level in C101 is too high, and the operating temperature is high. Hazard: Since liquids are incompressible, when liquid enters the compressor it exerts a strong impact on the impeller and the compressor housing, leading to damage to these components. Actions to take: (1) Strengthen the drainage of condensate from the compressor inlet separator tank and the inlet line separators. (2) Slightly reduce the amount of recycle hydrogen fed to C101. (3) Slightly lower the liquid level and temperature in C101. (4) In the event of an accident such as a loss of instrument air, pay close attention to controlling the liquid level in C101 to prevent it from rising too high.

The amount of recycled hydrogen entering C101 is too high, resulting in liquid foam entrainment； The liquid level in C101 is too high; the operating temperature is high ； Hazard: Since liquids are incompressible, introducing a liquid into a compressor can damage the blades ； Processing: ； (1) Strengthen the drainage of the liquid separation tank at the compressor inlet and the liquid separation package on the inlet line ； (2) Appropriately reduce the amount of recycle hydrogen fed to C101 ； (3) Appropriately lower the C101 liquid level and temperature ； (4) In the event of an accident such as a loss of instrument air, make sure to properly control C101 ； 9. What is the function of the anti-surge line in the circulating hydrogen compressor? ； The circulating hydrogen compressor is a centrifugal compressor. When the amount of circulating hydrogen entering C101 is too large, it leads to the entrainment of liquid droplets, resulting in a high liquid level in C101 and elevated operating temperatures. Hazard: Since liquids are incompressible, the presence of liquid in the compressor can cause severe impact on the impeller and the compressor casing, leading to damage to these components. Actions to take: (1) Strengthen the drainage of condensate from the compressor inlet separator tank and the inlet line separators. (2) Slightly reduce the amount of recycle hydrogen fed to C101. (3) Slightly lower the liquid level and temperature in C101. (4) In the event of an accident such as a loss of instrument air, pay close attention to controlling the liquid level in C101 to prevent it from rising too high.

Reason: The high level of the liquid phase or the failure of the foam breaker cause the circulating hydrogen to carry oil. In units equipped with a circulating hydrogen desulfurization system, the presence of liquid is caused by an excessive liquid level in the desulfurization tower or by the circulating hydrogen itself; abnormal foaming can also lead to the presence of liquid. Harm: Liquid in the circulating hydrogen can cause the circulating hydrogen compressor to smoke; in severe cases, it can lead to vibration of the compressor and forced shutdown, as well as an increase in system pressure. When circulating hydrogen contains liquid, the following phenomena occur: ① The liquid level in the liquid separation tank at the inlet of the circulating hydrogen compressor is too high; when circulating hydrogen contains liquid, the flow rate of the circulating hydrogen compressor fluctuates, and in severe cases this can lead to vibration of the compressor and its shutdown due to failure. ②System pressure fluctuates. Treatment: ① Increase the pressure relief valve from the hydrogen circulation machine inlet buffer tank to the cold low-pressure separator, and quickly adjust the liquid level in the inlet liquid separation tank to normal. ②Suspend the circulation of the slurry in the cyclohydrogen desulfurization tower if necessary. Check whether the mixing steam at the inlet of the cyclohydrogen compressor is enabled. After excluding the above factors, if circulating hydrogen still contains liquid, the possibility of a failed defoamer screen should be considered; in emergency situations, shutdown procedures should be followed.

What are the reasons for liquid entrainment in circulating hydrogen? What are the harms? How to address this: There are several possible reasons: 1. Excessively high inlet temperature of the recycle hydrogen; 2. Excessively high liquid level in the recycle hydrogen desulfurization tower; 3. Excessively high liquid level in the recycle hydrogen liquid separation tank; 4. Foaming of the solvent; 5. Failure of the foam removal screens at the tops of the towers and containers. It is important to check whether the heating steam pipeline at the inlet of the recycle hydrogen compressor is in use. The presence of liquid in the recycle hydrogen can lead to liquid slugging in the compressor, resulting in damage to the compressor. Solutions: 1. Try to reduce the temperature of the high-pressure separator. 2. Keep the liquid level in the high-pressure separator from rising too high. 3. Drain the liquid from the recycle hydrogen buffer tank in a timely manner. 4. Slightly reduce the processing capacity of the plant. 5. Calibrate the level measurement devices in the high-pressure separator and the recycle hydrogen buffer tank to ensure accurate readings