Synthetic Ammonia Overhaul Diary
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This post was last edited by chen3jun on 2010-9-15 08:56. On Tuesday, September 14, 2010, the weather was clear. It was the first day of the major maintenance, and the production manager asked me to go to the ammonia synthesis plant to provide support. Once the plant manager of the branch factory is located, the first task is to transfer the desulfurization fluid from the regeneration tank to the desulfurization tower, so that the regeneration tank can be replaced. Since the inlet pipe of the desulfurization tower is at a low position, first find a maintenance worker to install a blind flange on the inlet pipe. When I changed positions, I ran into my mentor, who instructed me to ； The conversion catalyst is cooled to 350 degrees using steam at 4:30, and after four hours a compressor is started to introduce air (by disconnecting one inlet line). At present, stages one and two have been passivated (at 170 degrees), while stage three is in the process of being passivated (at 480 degrees). During the first and second stages of passivation, the temperature at point 8 (the lowest point in the second stage) increased sharply, reaching up to 610 degrees. The synthesis catalyst also has a compressor running during passivation; there is no temperature rise at low pressures, and now the pressure has been increased to 220 kilograms. The temperature of the synthetic bed is 150, with no temperature rise. Since it was a early-shift stop, the driver had been up all night; after arranging the maintenance tasks, he went back to rest. I went to the compressor room and saw that the compressor used for feeding the synthesis process was running at 60 pressure and in vent mode; I quickly turned off the venting function and switched it to full synthesis mode. The pressure rose to 250, and the piston rod in section six was smoking. Immediately synthesize and open the large tower, then vent it to keep the pressure around 200. Checking the catalyst temperature, there is a slight rise. The circulating oxygen content was measured every half hour, with values of 0.4%, 1.2%, 4.7%, 8.5%, 11.2%, 16.4%, 16.4%, and 16.4% respectively. By 12:25 p.m., the oxygen content did not increase at three consecutive measurements, and the bed temperature dropped to 60 degrees. It was determined that the deactivation of the synthesis catalyst had occurred; accordingly, the compressor and the circulation pump were shut down, the system was depressurized, and it was prepared for maintenance. The temperatures at points 9 and 10 of the medium-voltage stage have dropped to 200 degrees, while point 11 is at 480 degrees and is in the process of passivation; at this stage, oxygen is being introduced in the low-voltage stage, and the temperature rise is normal. At 3:00 p.m., the supervisor came to the production area again, complaining that ； The phone kept ringing while I was resting at home, so I couldn’t get any rest at all. It seems there’s no way to rest during the day. Let me go home and rest first; I’ll take his place in the evening. The master is getting old, and it’s becoming difficult for him to work night shifts; I’ll likely have to take over those night shifts during maintenance periods.
Wednesday, September 15, 2010 – Sunny weather. Started work at 0:00; switched two compressors on to use air for cooling. At most of the temperature measurement points in the medium-low transformation section, the temperature is below 130 degrees, but the two lowest temperature measurement points in the third stage of the medium transformation section are at 380 degrees, and the cooling rate is very slow. It seems that some of the catalysts in this section have not been properly deactivated. I don’t understand why the operator stopped the boiler – it’s not possible to cool down by using just two compressors to remove air from the system. So, the boiler was started. More than ten minutes passed, yet the steam pressure did not increase. Upon checking the boiler room, it was found that the temperature was incorrect: the temperature at the upper part was too high, while the temperature at the lower part did not rise. When the furnace was opened, scabs could be seen, and there were quite a few of them. The boiler supervisor brought in steel bars and hammers to try and break away the scabs, but there were so many of them and they were so large that they couldn’t be broken apart under high temperatures. Now, with no workers available, it’s likely that it will be daylight before those scabs can be removed. Thus, the boiler was instructed to be shut down and then cooled down with air. The medium-pressure section utilizes the residual steam pressure, causing the temperature to drop more rapidly; by morning, the temperature in the first stage of the medium-pressure section was 90 degrees, 110 degrees in the second stage, 190 degrees in the third stage, and 80 degrees in the low-pressure section. At this rate, it might take another ten to twenty hours to bring the temperature down; we might even have to work a long night shift!
Take your time; although the maintenance period is tough, it’s the best time to learn things.
The synthetic catalysts on the upper floor, as well as the medium- and low-temperature shift catalysts, have been put through air passivation – what is the effect? The medium-temperature range goes up to 610 degrees, which is too high. It would be best if LZ could summarize the plan formulation and process evaluation after work is completed, for everyone to share. Should the catalyst be used after it becomes deactivated?
Will the major repair at the company’s headquarters result in a long shutdown? If it’s within about a week, it is actually still possible to carry out maintenance without the catalysts for synthesis and transformation becoming deactivated. During maintenance, nitrogen (or another inert gas) can be introduced into the synthesis tower or shift reactor to maintain a slight positive pressure. Parking for maintenance, with catalyst passivation protection, is of course the best approach. However, both the passivation process and the activation process up to the time of operation result in long periods of downtime, which in turn increases production costs.
Participating in a major overhaul is an excellent opportunity for those involved in chemical processing to significantly improve their technical skills. Every detail during such an overhaul is crucial, as it allows for a deeper understanding of the equipment’s structure, enabling more confident operation in the future. Next is to summarize, by recording the problems encountered during the process as well as the knowledge gained, and then reflecting on them gradually after the major repair is completed. I hope the original poster persists!
Thursday, September 16, 2010 – Clear weather. We started removing the catalyst today. It’s easy to remove the synthetic catalyst; a crane can be used to lift out the internal components along with the catalyst. The temperature of the catalyst is very low, and it doesn’t react when exposed to air, which indicates that the passivation process was successful this time. Removing the transformation catalyst is the most difficult task. The medium-temperature conversion section is divided into three groups, while the low-temperature conversion section has one group; each group consists of eight people. The temperature inside the medium-temperature conversion furnace is around 500–600 degrees, and it’s not possible to stay there for more than a few minutes – once you come out, your skin turns red. After being at the factory for over a decade, it’s the first time that I haven’t been assigned to work on the converter. My supervisor gave me a sketch showing the insertion depth of the thermocouples in the synthesis tower; I used CAD to create an accurate version of it, and that’s all there is to do for today’s work. By the afternoon, all the catalysts had been removed, and the floating bridge in Section 2 collapsed. Someone was arranged to clean the pot bottom in the evening.
This post was last edited and replied to by 654262293 on 2010-9-17 at 13:29. Reply to 7# chen3jun: OP, does it require someone to be inside in order to replace the catalyst? Isn’t it done from the outside through the discharge hole? Has the catalyst become caked?
This post was last edited by jjhgdd on 2010-9-17 at 17:40. What is the OP’s job? How can I help at the ammonia synthesis plant? Aren’t you working in ammonia synthesis?
Friday, September 17, 2010 – Clear sky. Because the second section of the medium-pressure reactor collapsed, it was very difficult to clean the bottom of the reactor; it took until noon today to finish that task. Welding work to repair the bottom of the medium-pressure reactor began this afternoon. The synthesis unit is used to remove ammonia and oil residues. The oil-containing internal components were taken out; the circulation gas, the oil-containing internal components, and the packing were all covered in a lot of oil. Diesel was poured over them and then ignited. It has been decided to use Hubei Shuangjian for the conversion; the catalyst used in medium-scale conversions is 2,000 yuan per ton cheaper than those used by Shuangxiong. I’m not too confident about the quality of the catalysts. I heard that Yihua also used Shuangjian’s products, and they still haven’t paid the full amount owed – it seems as though their performance isn’t good. The manufacturer has sent over a simple heating and reduction plan; perhaps experts will be sent over tomorrow or the day after, and the specific heating and reduction plan can be determined then.
There are some companies these days, well, they keep claiming to build a system based on integrity, but they always delay paying for goods that belong to others; they try to delay payment as long as possible and avoid it whenever they can, :-)