【Q&A Question 011】2017.01.11
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This post was last edited by 955559 on 2017-7-21 at 13:02. [Q&A Question No. 011] 2017.01.11: What are the causes of pressure differential fluctuations in hydrogen systems and how to address them? 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.) ) Causes of pressure differential fluctuations: ① Changes in hydrogen purity ② Fluctuations in the flow rate of circulating hydrogen ③ Changes in the amount of feed oil processed, or changes in its composition – becoming lighter or heavier, or containing water ④ Local crushing or coking of the catalyst ⑤ Scaling at the reactor inlet or blockage and coking in the outlet filter ⑥ Deviation of the gas flow within the reactor or leakage/short circuits in the heat exchangers. 7. Scaling in heat exchangers 8. Blockage of ammonium salts in coolers. Treatment methods: ① The purity of the hydrogen to be used should be greater than 90%. ② Keep the hydrogen-to-oil ratio within an appropriate range. ③ Maintain the space velocity within the specified limits; regularly dehydrate the raw oil buffer tank. ④ Shut down the system to regenerate, sieve, or replace the catalyst. ⑤ Shut down the system to clean the fouling baskets and outlet filters. ⑥ Shut down the system for treatment. ⑦ Shut down the system for cleaning. ⑧ Increase the amount of water supplied. Summary thread of Q&A questions from 2017 (updates ongoing): http://bbs.hcbbs.com/thread-1657793-1-1.html Summary thread of daily questions from 2017 (updates ongoing): http://bbs.hcbbs.com/thread-1657794-1-1.html Summary thread of Q&A questions from 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)
Fluctuations in feed volume, fluctuations in circulating hydrogen volume, fluctuations in reaction pressure, internal leakage in the pressure difference line valves, localized carbon deposition on the catalyst, etc. – Treatment: maintain stable operation, identify the causes; if catalyst replacement is necessary, shutdown is required
Changes in feed volume and feed properties, water content in the feed, excessive crystallization of ammonium salts, uneven flow within the bed layer, internal leaks in the heat exchanger, fluctuations in the temperature at the furnace outlet. Solutions: control the feed volume stably, improve dehydration of the raw material tanks, switch to alternative raw materials, increase the amount of water used, stabilize the temperature at the furnace outlet, and shut down the system to replace the heat exchanger
Fluctuations in the amount of new hydrogen, fluctuations in the high-pressure liquid level, and malfunction of the pressure-controlled valve for waste hydrogen discharge
There are many impurities, and the feed is unstable. Solution: Stabilize the feed rate and enhance feed backwashing
Circulating hydrogen volume, cold hydrogen volume, changes in feedstock properties, changes in bed temperature rise, and so on
Reasons for pressure difference fluctuations in the hydrogen system: 1) Changes in hydrogen purity. 2) Fluctuations in circulating hydrogen flow rate. 3) Changes in the processing volume of the crude oil, or changes in its composition such as it becoming lighter or heavier, or containing water. 4) Local crushing or coking of the catalyst. 5) Clogging or coking of the fouling basket distributor at the reactor inlet or the outlet filter screen. 6) Flow deviation in the reactor or short circuit due to heat exchanger leakage. 7) Heat exchanger scaling. 8) Ammonium salt blockage in the cooler. Treatment method: 1) Required purity of hydrogen. 2) Control the hydrogen-to-oil ratio at 240:1. 3) Keep the space velocity within the specified range for the process; the initial boiling point and dry point of the feedstock must meet the required criteria, and the feedstock buffer tank should be dehydrated regularly. 4) Stop operation, sieve the catalyst for regeneration or replace the catalyst. 5) Stop operation, regenerate the catalyst by removing the catalyst, and clean the scaling basket and outlet filter screen. 6) Shutdown handling. 7) Shutdown cleaning. 8) Increase the water injection volume.
1. Ammonium salt crystallization occurs in the low-temperature zone; first, it is necessary to determine the location of the pressure difference distribution. 2. It should be considered whether the backwash filter has failed, by observing whether the number of backwash cycles has decreased. Generally, there are two sets of backwashing, with one set being switched off. 3. Measure the pressure difference across each section of the bed; if the pressure difference in the lower section is high, it is very likely that the crushing of the bed material has worsened. If it is at the upper level, there are various reasons, but whenever the pressure drop across the bed increases, the only option is to shut down operations and reinstall the catalyst.
The amount of circulating hydrogen is unstable, the feed rate fluctuates greatly, there are blockages in certain parts of the system, and there are instrument failures
The reasons for high pressure differences include: the reactor bed, salt formation due to air cooling, and instrument issues. For the bed, catalyst coking should be considered; in the case of salt formation, water injection is necessary; as for instruments, calibration is required
Fluctuations in processing capacity, fluctuations in the amount of recycled hydrogen, failure of surge valves, incorrect readings from instruments, changes in pressure drop across the catalyst bed, changes in the properties of the feedstock