Air volume issue of the circulation machine
Thread Content
Dear teachers: I have designed a 2D10-6/280-300 type nitrogen-hydrogen circulation compressor for a chemical plant. The customer already has two 2.4-cubic-meter circulation compressors; when the new unit was put into operation, there was no significant difference in the system parameters compared to those of the existing two units. The customer suspects that the air handling capacity of the new unit does not meet the design specifications. May I ask, sir, is it really due to insufficient air volume of the machine, or is the circulating air volume affected by the entire synthesis system? If the circulating gas volume is higher than before, where are the main indicators reflected? Ammonia production volume or system pressure, etc.? Urgent! ! ! ! ! ! ! ! ! ! ! This machine was designed based on an 8-stage circulation machine from another manufacturer, and calculations suggest that there should be no major issues. The valve differs little from the reference machine; only the lift is changed from 1.8 to 1.5.
A insufficient circulation volume affects the temperature of the synthesis tower first; it is necessary to activate the auxiliary lines of the tower or increase the cooling capacity in order to maintain the tower’s temperature. Only then can it be considered as an insufficient circulation volume. Such a situation leads to an increase in system pressure and a decrease in the production of synthetic ammonia. If two 2.4 cubic meter circulation machines are used, it may be possible to meet the temperature requirements of the synthesis tower without using a heat exchanger, and in such a case it cannot be said that there is an insufficient circulation volume. When 6 cubic meter circulation machines are used, some of the gas might take a shortcut; in this case, the effects of using these two types of circulation machines are the same.
First, it is necessary to ensure that there are no changes in the gas composition, including the hydrogen-to-nitrogen ratio and the amount of inert gases. Secondly, it can be seen that operating conditions such as the ammonia cooling temperature and the amount of make-up gas have not changed either. Only in this way can a comparative analysis be conducted. When the air velocity increases, the temperature of the reactor bed is the first to be affected; in order to maintain this bed temperature, the cold bypass flow is certainly reduced. The pressure in the circuit will definitely drop, but this needs to be considered in conjunction with the inert gas content. There will be no significant change in ammonia production. Because if the amount of air supplied doesn’t change, it’s only the pressure in the circuit that decreases, while the actual volume of air circulated remains more or less the same. (It can be calculated using the gas equation of state)
The amount of circulating gas is closely related to the entire synthesis system. With the supplementary air volume remaining constant, the amount of circulating air must be adjusted according to the temperature of the catalyst layer. If the circulating air volumes from the two original circulators were sufficient to control the catalyst layer temperature, then even when switching to the current 6-cubic-meter circulator, whose air supply capacity is greater than that of the two original units, the circulating air volume will not reach the designed value. Furthermore, as the catalyst ages, its activity declines, the hydrogen-to-nitrogen ratio becomes unbalanced, the content of inert gases increases, the catalyst becomes poisoned, the ammonia concentration entering the tower is high, and the cooling effect is poor (high ammonia cooling temperature and high water cooling outlet temperature), all of which lead to a reduction in the circulation rate
If the air inflation volume of the circulation machine is high, the production volume should increase significantly, and it should be difficult to control the hotspot temperature. The air consumption of the entire synthesis system is also much higher. Of course, if the methane volume is still controlled as before, the pressure in the entire synthesis system will increase significantly. It can be seen from the motor current. However, if the piping is not designed properly, it is normal for the inflation capacity of several machines to decrease.
Thank you to all the teachers! Today I learned that, in the same system, operating a 2.4-cubic-meter and a 6-cubic-meter circulation pump together reduces the pressure in the synthesis system by 15–20 kilograms, whereas operating only the 6-cubic-meter circulation pump results in no significant change. This phenomenon seems to indicate a problem with the compressor itself. I’m frustrated!