Problems with the low-methane process in ammonia synthesis
Thread Content
During normal operation initially, we set the gas supply pressure at 6.25 MPA; when supplying gas, it is set at 3.0 MPA. Is it necessary to raise the pressure to 5.0 MPA before supplying gas to the low-pressure methane system? And when connecting the low-pressure methane system, should the pressure for C01 be set at 5.0 MPA or 3.0 MPA? The outlet pressure of the lean methanol pump is 7.9 MPA.
This post was last edited by XJBXPP on 2021-2-22 09:00. The pressure can be either high or low, but the changing pressure must be higher than the low-pressure level. After reducing the pressure, increase it to the operating pressure.
A methanol circulation should be established before introducing gas at low pressure; if the pressure of low-pressure methanol is 3.0 MPA during gas introduction, will the large pressure difference before and after the valve leading to tower C01 cause any damage to the equipment and valves?
Before introducing gas, nitrogen should be used to pressurize the system, in order to minimize the pressure difference between the converter and the low-pressure section. After that, the process gas is used to equalize the pressures; once equilibrium is achieved, the valves are opened to allow gas to flow in. At this point, the converter is operating at a low load and normally, so the pressure should not be increased arbitrarily, as this could make it difficult to operate the valves. Once the gas flow is stable, the pressures in the purification and conversion sections can be gradually increased to the design values. As for the pump issue, it’s normal for there to be a pressure difference before and after the valve of a centrifugal pump
The pressure can be increased gradually; keep an eye on it at any time
During gas introduction, the load on the methanol-poor pump is not high; methanol remains in liquid form even after its pressure is reduced from 7.9 to 3.0, so it poses no harm to the valve equipment. (Personal opinion)
It is best to perform low-pressure gas introduction; after that, increase the pressure to make it equal to the pressure used in low-temperature washing. This serves as a way to equalize the pressures, and then proceed with the low-temperature washing process
The principles for boosting gas pressure are more or less the same; what matters most is the manufacturing process and the actual conditions of the equipment
If conditions permit, it is recommended to increase the low methane pressure as much as possible, provided that the pressure required for gas transformation is met. Firstly, when the system approaches its operating pressure, the operating pressures of the various pumps also approach normal levels, which prevents the need to adjust both the pressure and the flow rate later on； Second, during gas introduction, the pressure difference between the two devices is too large, resulting in a long equalization time; such a large pressure difference also causes damage to the valves ； Third ； The system pressure being close to the operating pressure helps the purified gas meet the standards more quickly.
In my opinion, after changing the gas guide, the pressure should be increased, or the pressure should be raised while connecting the gas. The gas connection pressure for the low-pressure methanol unit should not be too low; otherwise, the pressure difference between the lean methanol stream and the absorption tower will be too large, which is detrimental to the equipment.
The last edit to this post was made by ningzi521 on 2021-9-7 at 16:03. 1. Based on the actual conditions of one’s own installation, considering potential equipment damage, it is possible to change the frequency of the lean methanol pump. 2. Concerned about the pressure difference issue: doesn’t your low-pressure washing system have a pressure control valve or a valve at the boundary of the output section?