Does gaseous ammonia have an effect on the shift catalyst?
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A few days ago, a leak was detected in the tubes of the synthetic intermediate-pressure reactor at our plant; some of the synthetic cycle gas entered the shift system along with the steam. Currently, the steam input to the conversion system is high; the low-temperature rise is 10 degrees lower than before, and the temperature for medium conversion is excellent. Today, through the analysis of the transformation rate, reactions with low variation perform poorly. Some of the technicians in our plant believe that synthetic ammonia has an impact on the shift catalyst, reducing its activity. The reason for this is that in the past, when water was introduced into the system, our plant would add ammonia to it in order to neutralize the acidity of that water; at that time, a large amount of shift steam was used. I believe that during the parking and maintenance process of the boiler, water vapor entered the low-voltage transformation system, resulting in reverse sulfidation. I checked the catalyst promotion materials from Hubei Shuangxiong Catalyst Factory from 10 years ago: for the XB303Q catalyst, small amounts of ammonia, HCN, and benzene have no effect on it. And now we are using the dual-hero SB303Q. Let’s discuss whether gaseous ammonia has an impact on medium-temperature and low-temperature catalysts Talk about your reasons.
Maintenance of the catalyst during normal operation of SB303Q: Proper maintenance of the catalyst throughout its use ensures its service life and performance. The following points should be noted during use: ① The oxygen content in semi-water gas must be kept below 0.5%; excessive oxygen levels can cause sulfation of the catalyst, leading to its deactivation. ②Avoid internal leakage in the heat exchanger, as it is a major cause of abnormal catalyst deactivation. Oxygen and oily impurities in semi-water gas enter the low-temperature shift converter, causing permanent deactivation of the catalyst. ③If there is a sudden decrease in load during the production process, the steam supply should be immediately reduced or cut off; otherwise, an excessively high steam-to-gas ratio in the short term can cause resulfidation. ④Strict precautions must be taken to prevent water from entering the catalyst bed, especially with new catalysts. Backflow of hot water from within the water heater or the hot water tower, or incomplete separation of water droplets in the humidifier, can cause water to enter the catalyst bed, leading to a rapid drop in bed temperature and catalyst deactivation. ⑤Avoid contamination by impurities, which include compressor oil residues that enter with the airflow, solid dusts, especially dust from Fe–Cr-based high-activity catalysts, and scale resulting from poor water purification. These impurities adhere to the surface of the catalyst, covering the active components, blocking the catalyst’s micropores, and reducing its specific surface area, thereby lowering the catalyst’s activity. You say: Now, the amount of steam supplied to the system is high; the low temperature rise is 10 degrees lower than before. It’s possible that the increased amount of steam is causing re-sulfidation! By reducing catalyst activity, the temperature rise is lowered!
The carrier of the low-temperature shift catalyst is alumina, and ammonia can react with alumina. For medium-temperature shift catalysts, the carrier is iron oxide, and ammonia has little effect on the medium-temperature shift reaction.