Regarding the issue of increasing pressure and reducing temperature

OP, increasing the system pressure so frequently right at the beginning of using the catalyst is not a good idea in my opinion. 23% CH4, and even after filling the cycle machine, the hotspot temperature still doesn’t rise – which is certainly a good thing, indicating very high activity (the fact that this didn’t happen before shows that it’s better than before). Think about it: if you don’t control the pressure more to save energy when the activity level is high, you won’t be able to do so once the activity level drops. It is recommended to increase the CH4 content gradually; 25–27% is acceptable, and the system pressure will rise slightly as a result. Combining this with lowering the temperature to zero meters ensures that the hotspot meets the requirements. If CH4 rises to 24% and the content of CH4 in the make-up gas is 2%, the original venting ratio was 1:11.5; now it is 1:12, resulting in significant savings.

I also think that increasing the pressure isn’t a good idea, but some forum members suggest doing so; I’m not sure why, and I’d like to hear their opinions. Our supplemental methane level is between 0.4–0.8%, while the circulating methane level is between 23–28. Increasing methane levels again will lower the partial pressures of hydrogen and nitrogen, affecting the yield.

First, congratulations to the original poster – the difficulty in controlling the temperature of the synthesis tower indicates that the catalyst has been well reduced. Normal production and catalyst heating reduction are different, and should be treated separately. 1. The method employed in the reduction phase, which involves adjusting the composition of the gas fed into the tower without reducing the voltage in order to increase pressure, aims to control excessive temperatures in the upper layers by increasing the circulation rate over a short period of time, while simultaneously transferring heat to the lower layers so as to achieve thorough reduction of the catalysts there. Of course, electrically reduced furnaces and cold shock methods can also be used to control the upper-layer temperature, but compared to the former, this prolongs the reduction time and increases the consumption associated with the reduction process. 2. During normal production, the gas composition should be controlled appropriately; the concentration of inert gases should not be too high (23% is sufficient), as too high a level will reduce the partial pressure of the active components and lead to a decrease in the synthesis rate. The approach of controlling the tower temperature by suppressing the synthesis reaction with deteriorated gas components and increasing the circulation volume under high pressure is not advisable. Consequently, the system pressure should be as low as possible; this reduces the back pressure on the compressor and thus lowers the power consumption of the circulation pump. The circulation volume is insufficient; in my understanding, this makes it impossible to control the tower temperature. You can try to resolve the issue using the following methods: 1. Check the circulation pump for leaks in the air valves, to ensure that there are no blockages or internal leaks, and to verify that the piston rings are intact (check from the easiest to the more difficult items). 2. Adjust the operating methods according to the characteristics of the tower internals, and ensure proper coordination among the main line, secondary line, cooling flow, and circulation rate. I hope it will be of some help to you.

Using pressure changes to cool down is probably incorrect； Increasing the pressure facilitates the progress of the synthesis reaction; therefore, raising the pressure will only lead to an increase in the catalyst temperature, with the temperature at the upper layer certainly rising as well. When the circulation volume is insufficient, temperature adjustment should be carried out by activating a bypass line while ensuring an adequate circulation volume; a cold shock line can also be used to lower the temperature of the lower layer, thereby reducing the inlet temperature of the catalyst layer. Does the cold shock mode have a function to switch between cool and warm air? If so, try switching to cool air. Can the steam pressure of the waste boiler be reduced? If so, to the lowest possible level. If that still doesn’t work, the only option is to increase the methane content further. At present, the reaction is proceeding well, and even a decrease in the partial pressures of hydrogen and nitrogen does not affect the yield.

Our chill air system doesn’t have a hot/cold mode switch; the temperature is around 165 degrees. Currently, we have turned down the main valves a bit in order to control the temperature. Our waste boiler steam is in the steam pipeline network, and it seems that the pressure cannot be reduced.

First, I’d like to thank the original poster. The leaders have inspected the entire system, from the circulation machine to the synthesis tower; they are more anxious about this than anyone else. Our fertilizer sells well, with customers constantly approaching us to buy it. Our tower is part of the new system; it’s in its initial operational phase, so there are still many aspects that need to be explored

If the problems with the circulation pump itself can be ruled out, and various control measures have been applied during the operation of the synthesis tower, then it may not be an issue of insufficient circulation volume. Here are some suggestions for reference: 1. The ammonia synthesis output is determined by two factors, namely the circulation volume and the net ammonia amount. In the design of the internal components of the synthesis tower, the primary consideration is the net ammonia yield, that is, the one-pass conversion rate. This requires that the design of these internal components take into account the proper arrangement of adiabatic sections, cold tube sections, distributors, and heat exchangers, in order to achieve a high synthesis rate. Secondly, consider increasing the circulation rate. In other words, there may be issues with the design of the internal components of the synthesis tower. 2. As it is the initial startup of the system, there is no historical data available for reference. This requires considering whether the amount configured for the circulation machine is insufficient. 3. If the stable operation of the system and full load can be achieved by altering the soft environment (such as closing the main valve, increasing the bypass line, adding cooling effects, etc.), then do so. Of course it’s the best. If that doesn’t work, then considering modifications to the process pipeline is necessary; for example, adding a cold bypass line that can be switched in depending on the conditions of the synthesis reaction.

Thank you for the suggestion, OP. Our current ammonia purity is far from the designed value. I think the possible reasons are cold shock and the excessive opening of the side lines, which dilutes the ammonia concentration; this is also a drawback of the internals in cold-shock type synthesis towers, resulting in low ammonia purity； Also, it’s possible that it is currently operating at half capacity, so the difference should be somewhat greater compared to full capacity. As for whether the interior design is reasonable, that’s hard to say. Is the configuration of the circulation machines appropriate? The design institute said that 3 circulation machines would be sufficient during the design phase, but now that 4 machines are in use, it is still not enough. After checking, there is no issue with the air injection volume of the circulation machine; it’s not clear where the problem lies. Changing the pipes will likely require a major maintenance session. Right now it’s a time to boost production, as it’s still better to keep manufacturing than to stop operations. This post was last edited by snowdfr on 2009-4-21 at 15:26

It’s possible that a short circuit is indeed occurring: an extremely low ammonia level together with a very high circulation rate indicate this, and there is a high likelihood of leakage in the two-in-two-out packing; the probability of leakage is estimated to be over 80%.

Calculated using the formula ammonia production = 0.758 * total gas flow into the tower * (ammonia output from the tower – ammonia input to the tower) / (100 + ammonia output from the tower), the actual ammonia production differs from the theoretical value by about one ton. It’s also hard to tell right now whether there is leakage in the two-in-two-out packing; the temperature at the outlet is around 260 degrees, while the specified value is 330 degrees. The tower is currently operating at half capacity, and since it’s a new tower, it’s not clear what performance levels can be achieved. Therefore, it’s impossible to determine whether there is leakage just by looking at the temperature. I wonder if there are any other ways to determine whether the two-in-two-out packing is leaking

Even if one more circulator is added, the payment line still needs to be activated, and the main valve must be closed; the system should thus form a loop. The ammonia content at the outlet is much lower than the specified design value, and the temperature at the second outlet is 70 degrees lower than the design value; it is likely that gas from the secondary inlet has leaked into the secondary outlet, which reduced the ammonia content at the outlet as well as the temperature of the gas. Others (cold transfer ； In a heat exchange loop, there will be no issues such as excessively low ammonia content at the outlet or a outlet temperature that is 70 degrees lower. Moreover, the newly activated catalyst shows good performance, with CH4 levels above 23. It should be a filler leakage with two inlets and two outlets. This post was last edited by snowdfr on 2009-4-23 19:42]

50% design load – supplementary air volume; all four circulators are operating at full capacity (they only turn on when the designed supplementary air volume is reached); all four cold gas feed lines (as mentioned in the original post) are also in use. The main valve leading to the tower is reduced in size to ensure an appropriate amount of cold gas is supplied, with the CH4 circulation rate being 23–28%. Symptoms: 1) The bed temperature cannot be reduced, resulting in overheating； 2) Although the gas replenishment load is low, the net ammonia value is much lower than the design value ； 3) The outlet temperature of Tower 2 is only 260°C, which is lower than the design value of 330°C, and is consistent with the design value at the waste heat boiler outlet ； Analysis: Floors 10 and 12 believe that there is internal leakage in the sealing packing between the inlet and outlet; unreacted cold air from the inlet leaks into the reaction hot air at the exit of the heat exchanger inside the tower. My opinion: The reasons you analyzed are consistent with the phenomena. Additionally, the temperature of the unreacted gas at the exchanger outside the tower is low, and the temperature at zero meters may exceed the limit. To maintain production, can we find a way to reduce the pressure difference between inlet and outlet in order to decrease leakage? This post was last edited by snowdfr on 2009-4-23 19:49]

In response to the questions from the friends above, it doesn’t seem to be a leakage issue with the packing. At a pressure of 15.0 MPa, the outlet temperature is 260 degrees; at a pressure of 19.0 MPa, the temperature has risen to over 290 degrees. Our tower is designed for a pressure of 32 MPa, and I believe that when it’s operating at full capacity, the temperature should not be lower than the design value.

As a supplementary point, the ammonia net value also increases as the load rises. Also, in response to the friend on floor 12: closing the main valve is not meant to direct gas through the return circuit; rather, it reduces the amount of gas flowing in the main line, and the amount of gas flowing in the cold bypass line is increased accordingly to achieve a cooling effect. Both the circulator and the system shortcuts are closed, so the gas should not flow through the loop. There’s also the friend on floor 13; we haven’t turned on all 4 of our cold gas supplies, as we want to ensure a more appropriate temperature distribution in the catalyst layer. If it’s turned all the way on, there are no means of adjustment left at all. :) :)

There is no problem with the formula for calculating ammonia production； If the ammonia content at the exit of the tower is calculated based on the analysis values, then whether there is a leak in the packing or not, the result should be consistent with the actual ammonia production volume; an error of 1 ton is caused by the actual gas delivery volume of the circulation machine not reaching the nominal value. Using this method, it is not possible to determine whether there is a leak in the packing ； The ammonia content at the tower outlet should be calculated based on the reaction amount derived from the catalyst temperature rise.

The ammonia content at the exit of the tower should be calculated based on the amount of reaction corresponding to the temperature rise of the catalyst. Could the original poster provide the formula?

Due to the presence of cold shock gas, it is indeed difficult to calculate the catalyst temperature rise； First, it is necessary to calculate the amount of cooling air for each section; this can be estimated using the exit temperature of the previous section and the temperature difference at the inlet of that section, with the same specific heat value applied. The amount of air entering the main line is calculated by subtracting the sum of the cooling air amounts for all sections from the total amount of air ； After calculating each air intake volume, the intake air temperature is determined based on the weighted average of temperature and air volume ； The catalyst temperature rise is the temperature at the bottom layer of the catalyst minus the intake air temperature.

Give it a thumbs up: I wonder if the synthesis process at LZU factory is running normally now. I also spent a few years working in synthesis, so I’d like to know how things are for you there; let’s learn from each other.

This post was last edited by chen3jun on 2009-5-11 02:04. How does the original poster achieve pressure control? Add supplemental air? In that case, the bed temperature will definitely rise. If pressure is increased by lowering the ammonia cooling temperature or increasing the inert gas content, then the bed temperature will decrease. If the circulation volume is high yet the temperature still does not drop, it is necessary to consider whether the circulator is performing virtual work. It is necessary to check the packing of the circulation pump, as well as the packing of the tee at the bottom of the synthesis tower and that of the circulation heater. At the beginning of use, due to the high activity of the catalyst, the pressure is low, the actual space velocity is low, and it is difficult to control the temperature; in such cases, the content of inert gases is generally increased.

I’m sorry; I wasn’t able to access the forum these past two days due to internet issues. I’m responding to your question now. We increase pressure by adding supplementary gas, and we achieve an increase in volume by shutting off the main pipeline to reduce temperature. The ammonia cooling temperature is consistently maintained between -6 and -8, which is within the normal range. Based on the total circulation volume entering the tower, compared to the displacement generated by the circulator, it is less likely that the circulator performs virtual work. 20# chen3jun