The conversion system of the pyrite-based acid production plant is not operating properly, and the output does not meet the required standards
Thread Content
This post was last edited by lyp81 on 2018-1-5 at 11:45. I have just taken over a sulfuric acid production plant that uses pyrite as raw material, and its operating conditions are extremely poor. The conversion system is not functioning properly: the concentration of the gas entering the conversion unit is 6.5–7.5%, while the pressure drop across the first-stage catalyst bed reaches 10 kPa; the pressure drops in the other stages are relatively normal. The temperature at the inlet of the first stage is 430 degrees, while the temperature at the lower layer of the catalyst there is only 540 degrees. At the inlet of the second stage, the temperature is 460 degrees, with the temperature at the lower layer of the catalyst reaching 575 degrees. The inlet temperature of the third stage is 480 degrees, and the temperature at the lower layer of the catalyst there is 515 degrees. The inlet temperature of the fourth stage is 435 degrees, with the temperature at the lower layer of the catalyst reaching 465 degrees. The inlet temperature of the fifth stage is 450 degrees, and the temperature at the lower layer of the catalyst there is 460 degrees. The heat exchanger system also operates abnormally; the flow patterns are of type III-I and V-IV-II, with the fourth heat exchanger serving as a bypass. The temperature at the outlet of the fan is 100 degrees, 355 degrees at the outlet of the shell side of the third heat exchanger, and 205 degrees at the outlet of its tube side. The temperature at the outlet of the shell side of the first heat exchanger is 430 degrees. It is necessary to use an electric furnace intermittently to maintain the inlet temperature of the first stage. The temperature at the outlet of the shell side of the fifth heat exchanger is as high as 430 degrees, while it is 420 degrees at the outlet of its shell side. This is probably due to the use of a cooling bypass; otherwise, the inlet temperature of the fourth stage would be as high as 450 degrees. Another problematic issue is that the temperature at the outlet of the tube side of the fifth heat exchanger is as high as 320 degrees. Even with the cooling bypass in place to reduce the heat transfer in that stage, such a high temperature should not occur. A wire mesh demister is still being used at the outlet of the second absorption tower – can this tower actually perform absorption? It’s likely that the gas contains a lot of acid mist. The tail gas treatment system uses hydrogen peroxide along with electrostatic demisting to mask the problem of acid mist. This plant, with an annual production capacity of 100,000 tons, only manages to produce 240 tons per day. The most troublesome aspect is that driving after short-term parking is extremely difficult; starting from stage two, the temperature rises in both the inlet area and the catalyst layer at a very slow pace. Even with all the auxiliary heating systems turned on, it takes another 36 hours for the gas concentration to reach 7%, after which the desired operating temperature is finally attained. My preliminary analysis is: 1. The catalyst plate is caked and pulverized, resulting in severe deactivation ； 2. A replacement may cause internal leakage, resulting in a high concentration of gas in the second stage ； 3. A leak may occur during the second conversion step, resulting in higher temperatures and gas concentrations in the fourth stage. Please help analyze what other possible causes there could be and how to address them. . . It’s driving me crazy!
You need to provide as complete data as possible so that others can help analyze it; based on what you’ve said, it seems that catalyst powder fragmentation or caking is the main cause.
This post was last edited by lyp81 on 2018-1-6 at 15:21. I previously measured the sulfur dioxide concentration: it was 2.6% at the inlet after changing the shell side, and 3.53% at the outlet. Although I conducted 4 parallel tests, I still don’t trust these results. Yet even if the numbers are inaccurate, the trend should be correct—that is, the sulfur dioxide concentration at the outlet is higher than that at the inlet, which suggests that there might be an internal leak when changing the shell side.
How can this be used again? The conversion rate is low, and a large amount of hydrogen peroxide is consumed. Not only conversion, but also purification – the indicators are too poor.
The parking lot will check the shell sides of each heat exchanger, the tube banks, and the catalyst condition
In the 3+2 conversion process, there is still a significant difference in conversion temperatures. There is a problem with the catalyst in the first stage, but there is still a temperature difference; the second stage becomes the key factor now, and the conversion temperature has increased. It seems that some of the catalysts need to be replaced. Is there any issue with the way the catalysts are installed?
Catalyst loading factor 320 l/t.d
I plan to replace a section of the catalyst, as it has become too worn out. The sections following it will be screened, and then heaters No. 1 and No. 2 will be checked as well.
It’s basically a catalyst-related issue; let’s check the heat exchanger standpipe as well.
This post was last edited by in the blink of an eye on 2018-1-20 at 23:31. I have encountered this situation several times in recent years; the fundamental problem lies in the poor thermal stability of the catalyst layer, which causes the conversion reaction to occur at a later stage, resulting in the subsequent catalyst bed experiencing a high temperature. The machine must be stopped promptly to address this issue; otherwise, the subsequent bed layers will develop a memory effect due to operating at high inlet temperatures for an extended period of time! By then, even if you set the inlet temperatures at each stage of conversion to normal values, the catalyst activity will drop significantly; you will need to replace a large amount of catalyst in order to raise the conversion rate to a somewhat normal level. The setup for acid production in this system is likely not very advanced; it’s probable that none of the equipment is imported. The absorption tower even uses wire mesh, which provides almost no protection against sub-micron acid mist. It is quite normal for the outlets of the drying tower and the first absorption tower to be severely acidic, which in turn leads to corrosion and perforations in the heat exchangers downstream. (Note: I should be referring to the pipe route taking SO3; the SO2 side is the high-pressure side, and the SO2 concentration at the inlet and outlet of the high-pressure side should remain unchanged.) ）