How is the temperature of the two-stage furnace controlled?
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50,000 tons of synthetic ammonia; a major shutdown for maintenance was carried out in December. When operations resumed in January, the temperature in the second-stage furnace exceeded the allowed limits. There are no changes in the other data. The specific data are as follows: Conversion load, Temperature in Stage 1, Methane in Stage 1, Air volume in Stage 2, Air temperature, Combustion chamber temperature, Temperature in the middle layer, Outlet temperature, Methane in Stage 2. Before shutdown: 4200, 735, 13.5%, 5900, 520, 980, 880, 865, 0.65%. After shutdown: 4150, 715, 13.5%, 5800, 515, 1060, 870, 860, 0.9%. The catalyst in Stage 1 was replaced during maintenance. So the temperature is controlled at 715 degrees, but the temperature in the combustion chamber of the second-stage furnace reaches 1060 degrees. Our target is 1050. The instrument calibrates the thermocouple temperature multiple times. The display is normal. Please, experts, analyze where exactly the temperature is high ? ? ? ? ? :L :L :L
Is there any change in steam volume, that is, a change in the water-to-carbon ratio? What about pressure? Today, while we were operating the plant, the inlet temperature was 200 degrees, and the temperature of the bed layer was 170 degrees; there was no change for an hour. It wasn’t until the space velocity was increased that the temperatures started to rise. Ammonia synthesis is very complex!!!!
Both the converted water-carbon ratio and pressure are similar to those before shutdown. There isn’t much change. Including the air pressure and temperature in the second-stage furnace. I just don’t know why the temperature in the combustion chamber rises by 80 degrees. And the methane content in the emissions has increased a bit too? ? ? ?
Are there any changes in the steam protection before and after parking? What are the changes in the fuel gas pressure and the negative pressure in the furnace?
In terms of gas volume, the amount of gas decreases by 50; together with the amounts of steam and air, the total decrease is 200. From one segment, the water-carbon ratio is slightly higher after parking compared to before parking. From the second section, methane levels increase slightly, with a slightly higher water-to-carbon ratio ； The temperature difference between the combustion chamber and the middle section of the converter increases. From these two points, it can be seen that an increase in pressure, a decrease in air velocity, or an increase in the pressure difference between the front and back can reduce pressure regulation.
1. For the catalyst replacement in the first reactor, I’m not sure whether the catalyst being used contains sulfur; this could be the cause of poisoning in the second reactor.
2. There is an issue with the temperature indication – the thermocouple cannot be calibrated, so it needs to be replaced. Since the temperature in the second reactor is high, the methane content should be low; therefore, I suspect there is a problem with the temperature reading.
3. Is there any risk of water infiltration, poor flow, poisoning, or sintering of the catalyst in the second reactor? This kind of situation tends to occur during startup and shutdown. If the temperature is correct and the methane at the outlet of the first reactor is normal, then there is a problem with the catalyst in the second reactor
2. There is an issue with the temperature indication – the thermocouple cannot be calibrated, so it needs to be replaced. Since the temperature in the second reactor is high, the methane content should be low; therefore, I suspect there is a problem with the temperature reading.
3. Is there any risk of water infiltration, poor flow, poisoning, or sintering of the catalyst in the second reactor? This kind of situation tends to occur during startup and shutdown. If the temperature is correct and the methane at the outlet of the first reactor is normal, then there is a problem with the catalyst in the second reactor
Check the outlet temperature of Section 1 carefully; it’s most likely that the temperature shown for that section is too low. After all, 715 degrees cannot correspond to 13.5% residual methane, while the temperature distribution in Section 2 is more in line with the levels of residual methane. It might be an analytical issue.
\ Since our protection steam does not have a flow meter, by comparing the amount of secondary air added and the temperature of that secondary air before and after shutdown, the ratio of protection steam volume remains the same. Comparing gas pressure and negative pressure before and after shutdown, the gas pressure remains the same, while the negative pressure is slightly higher than before shutdown. In terms of furnace temperature, it is still below that before shutdown.
However, the pressure difference in our two-stage furnace is still a bit lower than before it was shut down. The pressure difference across the two stages was 0.9 MPa before shutdown, and it is now 0.6 MPa after shutdown. I don’t think it’s a pressure-related issue. Including a comparison before and after the inlet pressure, there is not much change.
Stage 1 of the catalyst contains a small amount of sulfur; according to the catalyst reduction process at elevated temperatures, the temperature in Stage 1 furnace is raised to 740 degrees to allow sulfur to be released steadily, until the sulfur content at the analysis outlet meets the specified standards. Then, the temperature in Stage 2 furnace is increased to around 900 degrees. The sulfur content in the export product meets the specifications. I think there might be a problem with the combustion chamber. Is it broken? Since I’m not very familiar with equipment and instruments, I’m just making an estimate. For example, could the deterioration and detachment of the refractory materials in the combustion chamber cause temperature changes? ? ? ? Are there any experts in this field? Explain it.
If it falls off above and covers the catalyst, it causes airflow deviation; this is a problem! If the lining is damaged, then there’s a problem with the temperature of your furnace wall – and it’s a serious problem! Has there been any change in the jacket water? Temperature, flow rate! After finding a way to confirm that one section of the furnace is functioning properly, gradually narrow down the scope of the problem. You also need to consider the burners and distributors in the second section of the furnace, as these can also cause uneven flow
Based solely on the data provided by the poster, it’s not possible to draw any conclusions; there are various possibilities, including catalyst issues or problems with the internals of the two-stage furnace. If the data was obtained under stable operating conditions, it is likely that the issue has little to do with the space velocity or pressure, and the possibility of catalyst poisoning is also low. It would be best to share a diagram of the internal structure of the two-stage furnace so that everyone can conduct a more in-depth analysis
By strictly comparing the process gas composition (on a wet basis) at the outlet of the first furnace before and after the major maintenance, did the gas composition at the outlet of the first furnace change?
Try adding about 5% water vapor to the air tube.
Based on the data, the outlet temperature of the second-stage furnace has increased, as has the methane content at the outlet. It seems there is a problem with the gas distribution within the second-stage furnace; gas is taking a shortcut. It would be advisable to check the catalyst or replace it. The decrease in pressure difference also illustrates this issue; a book on ammonia synthesis discusses this problem.