Low-temperature catalyst
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The low-temperature shift catalyst in our plant was replaced after a 50% capacity expansion and renovation on October 2005. After it had been in operation for over half a year, an increase in the CO content at the outlet was observed. The company sent personnel to investigate the cause; there were no issues with the process operations, natural gas, or process steam. It was only through further analysis that chlorine ions in the outlet condensate were identified as the reason for the reduced activity of the low-temperature shift catalyst and the resulting increase in CO content at the outlet. I hope everyone can help analyze the sources of these chloride ions and the corresponding countermeasures. This post was last edited by snowdfr on 2009-2-28 09:10]
Chloride ions mainly come from process water, air, and feed gas. The demineralization units in medium and large-scale ammonia plants can effectively remove inorganic chlorides, but it is difficult to remove organic chlorides. Coastal ammonia plants are particularly vulnerable to the effects of chlorine, as seawater contains high levels of chloride ions ； Water in rivers often contains organochlorines as well, due to residual pesticides ； Heavy oil; naphtha also contains a small amount of chlorine ； Light oil may contain up to 15 MI/M3 of chloroalkyl groups. Liquefied natural gas or liquefied petroleum gas stored in caves contains trace amounts of hydrogen chloride. Our factory uses multi-functional towers to remove chloride ions, and there are now many dechlorinating agents available in China that can effectively remove chloride ions.
It is important to note that this has also happened in our factory: new catalysts exceeded the specified limits after a few months, and analysis revealed that chloride ions were the cause. As little as 0.001 mg/L of chloride ions can cause the microcrystals to increase in size from 100 angstroms to 10,000 angstroms, resulting in catalyst deactivation.
Main sources of chloride ions: added steam and chilled water
If it is to be sourced from desalinated water, carefully check the CL ion content of that desalinated water.
Pay special attention to checking the sources of water and water vapor in the conversion system; in most cases like this, it is caused by excessive levels of CL- in the process water supplied by the water treatment system.
I’m not sure what catalyst model you are using. Our company uses coal as raw material, along with B303Q cobalt-molybdenum-based fully low-temperature conversion catalysts; the medium-temperature type was upgraded to a fully low-temperature type in 1997. Reasons for catalyst deactivation: 1. Prolonged operation at high temperatures causes changes in the crystal phase, a reduction in specific surface area, and a decrease in activity ； 2. When water enters, the soluble components in the catalyst dissolve in water, resulting in loss. If, after parking the vehicle and starting it up again, the bed temperature is not raised above the dew point using an electric heater, water vapor will condense, causing the catalyst to stick together and thus affecting its activity ； The condensate water in front of the furnace was not drained before it was integrated into the system ； Water is poured into the converter ； Dry gas was not used for purging before long-term parking ； The steam purifier and pipes have water in them. 3. The catalyst becomes clogged and agglomerated, causing gas to flow unevenly. 4. Air enters during the period after sulfidation is completed and while the plant is shut down, either because no dry gas or nitrogen is used to maintain pressure and thus air gets in, or because a large amount of nitrogen is used, and the oxygen present in that nitrogen reacts with the catalyst. Furthermore, the oxygen content in the feed gas is high. 5. Anti-sulfidation reaction. 6. Issues with the sulfidation quality of the catalyst. 7. Oil contamination enters the bed layer. Internal leakage in heat exchanger ； The booster pump has oil in it ； The heat exchanger was not cleaned during maintenance ； The bottom of the pot was not cleaned before loading the catalyst ； Steam with misty water ； The system water contains a high amount of contaminants ； Chlorine content in feed gas, steam, or water ； Water leakage, etc.
As the catalyst is used for an extended period, its activity decreases, and it is normal for the output to be high. But it’s abnormal for the catalyst used by the original poster to show adverse reactions so quickly; high chloride ion levels are mainly due to saturated water vapor. The poster should improve control over the water content in the steam, and strictly regulate the composition of the gases. Only in this way can the service life and cycle of the catalyst be ensured!
Here is a discussion on chloride ion poisoning of conversion catalysts, which can be referenced: http://bbs.hcbbs.com/thread-393613-1-7.html