Large fluctuations in temperature

It’s probably just the circulation volume that has changed; has it increased? Another aspect is adjusting the cold shock; specifically, it depends on the distribution of temperature levels and the internal components of the tower. In the case of methanol synthesis, it is also necessary to consider how changes in operating conditions such as the temperature of the methanol tower affect the quality of the product, and whether there are any issues with trace elements. Our plant has encountered similar situations.

1. Are there any fluctuations in the amount of gas supplied to the previous section and in the minor parameters as well? It’s essential to ensure stability in these two aspects. 2. There are variations in the circulation volume; the cold bypass line isn’t functioning properly, and it’s not possible to find a new equilibrium point in a short time. 3. For the circulation machine that has stopped operating, it’s necessary to check whether the inlet and outlet valves are properly closed. If it’s not certain that these valves are fully closed, then the bypass valve can be closed to prevent gas from escaping through that route. 4. For the circulation machine that has just started operating, it’s important to check whether the gas valves are damaged or blocked by foreign objects, and whether the bypass valve is closed, in order to prevent unstable gas flow from this machine. In such situations, the operator can raise the bed temperature to its upper limit (a slight increase in temperature isn’t a big problem, but a significant drop in temperature can be serious). The opening degree of all valves (whether they are cold shock valves or bypass valves for circulation machines) should not be too large. I think that as long as the minor parameters don’t increase, a new equilibrium point can be found quite quickly.

It must be a problem with the circulation volume adjustment. 1. When adjusting the circulation volume, there is a certain delay in the reaction of the temperature in the synthesis tower; especially when the temperature is unstable, the reference for adjustment is inaccurate, so the variation in circulation volume should not be large. 2. When methane levels are low, the reaction rate in the synthesis tower is high; improper adjustment of the circulation rate can lead to greater fluctuations in tower temperature. 3. The liquid level of ammonia at the second stage should be checked to prevent intermittent carryover of liquid ammonia.

First, it is necessary to check the cause of the circulation machine – whether its air injection is unstable. Second, observe any changes in the methane content; it should neither be too low nor too high. Third, check if there are any changes in the pressure drop in the synthesis tower; if the pressure drop corresponds with changes in temperature, then carefully examine the hydrogen-to-nitrogen ratio.

If the trace amount is normal, it must be ammonia that is present in that zone.

The tower in our company should be of the same type; we also use counter-current reactors there. The temperature in such towers can change quite easily, so considerable experience is required to operate them properly. Once, during operation of the counter-current reactor, the circulation rate decreased, causing the temperature to rise from 504 degrees to over 530 degrees. The valve controlling the flow was opened a bit too much and wasn’t closed in time, as a result the temperature dropped sharply from 530 degrees to 470 degrees...............................It seems that the main reasons are the small size of the tower, the limited area available for using the catalyst, or its aging. There are also some unreasonable aspects in the design of this tower! We usually focus on checking the inlet and outlet temperatures of the reactor bed, as well as the temperature at the hot spots. But once the inlet and outlet temperatures of the reactor bed remain stable, the temperatures at the hot spots will generally also stay stable!!!

The temperatures dropped sharply at 1, 2, and 4 o’clock; this was likely due to the fact that when the circulation machine was about to be brought online, the shortcut for pre-shutdown mode wasn’t activated, while the shortcut for operating the machine normally was closed. As a result, the circulation rate increased suddenly, causing the temperature to drop. Later, when the shortcut for pre-shutdown mode was activated, the circulation rate decreased and the temperature rose, leading to temperature fluctuations. 2. Check whether there is any change in the amount of air being supplied; a slight variation is normal. Also, verify that no other toxic gases are entering the tower, and that there is no water or oil present. 3. Inspect the circulation pump to see if there are any issues with the inlet and outlet valves, and check whether its flow rate is stable. Also, ensure that the inlet and outlet valves of the pump that has been shut down are properly closed, with no internal leaks. 4. When adjusting the tower temperature, is cooling shock adjusted frequently? In situations with large temperature fluctuations, it is generally necessary to adjust based on the temperature at zero meters – this value is located at the very top of the catalyst layer and changes rapidly; its fluctuations can indicate the changes throughout the entire catalyst layer. Additionally, it is best not to use a cold shock valve to regulate the temperature at such times; instead, it is preferable to use the circulation rate for adjustment. After making adjustments, the catalyst layer needs some time to respond, as changes do not occur immediately; therefore, adjustments should not be made too quickly. 5. Check whether the ammonia content entering the tower is normal, and whether the hydrogen-to-nitrogen ratio is normal. It’s just my personal opinion; please feel free to correct me. This post was last edited by snowdfr on 2009-3-9 10:56.]

The flow rate is too high, or the original machine’s branch was open; it was turned off after being reversed

The circulation rate is low, and the amount of circulation is insufficient; cooling air is used to regulate the temperature, which results in unstable temperatures with large fluctuations. The temperature becomes even more unstable when the flow rate of the cooling air is high, showing great sensitivity.

It is clear that unstable circulation volume during the machine switching process causes fluctuations in tower temperature. The most sensitive points are areas at zero meters and other hot spots; unstable circulation volume, coupled with inadequate adjustment through auxiliary systems, leads to such fluctuations. Once the adjustment process after switching is stabilized, the tower temperature will gradually return to normal. It is necessary to improve the plans for adjusting the machine during switching in order to minimize the fluctuations caused by it.