Low-temperature methanol washing process control

The magnitude of the tower pressure difference can reflect the operating condition of the tower; if the pressure difference is higher than the design value, it indicates an increase in the tower’s resistance, an increased load on the tower, or problems with the tray system； If the resistance is low, under normal load conditions, there may be a problem with the internals of the tower

1. What information can the pressure difference display inside the tower provide? The information displayed by the pressure difference in the tower indicates the level of production load and the flow pattern of the liquid within the tower. The situation of the trays in the tower internals. 2. How to save energy. That is, to make efficient use of the system’s cooling capacity – how can the system’s temperature be reduced in the shortest possible time when starting up or during temperature adjustments? Please share your experiences and opinions. Steam flow rate to the reboiler of the thermal regeneration tower – as long as the reboiler is capable of providing the heat required by the thermal regeneration tower ； The ammonia cooler should be put into use at the initial stage of establishing the cycle; if the water content of methanol in the system is not high, a water separation tower may not be necessary, and it can be installed only when introducing gas. 3 Recently, the COS levels in the low-temperature methanol wash unit where I work have been exceeding the specified limits. I was wondering: since our desulfurization and decarbonization processes are primarily aimed at removing CO2 and H2S, could the issue of high COS levels be related to inadequate sulfur hydrolysis? (What do I think are the reasons? 1. Insufficient pressure: Designed for 3.2 MPA but operating at 2.6 – 2.2. 2. High water content, 1-2%. 3. There is no ammonia tower in the system. But the absorption tower has a pre-washing section. Does ammonia affect absorption? ) Note: The cooling capacity of the system is quite satisfactory. Please analyze which factor is the most important; if there are other factors, I would appreciate it if the teacher could provide guidance. If the COS level is too high in low-temperature methanol washing, first check whether the shift system is functioning properly; under normal circumstances, the shift process converts COS into H2S. If the transformation is fine, then it might be that the flow rate of the pre-washed methanol is insufficient. 4. What are the standard levels of methanol and ammonia after birth? The ammonia content in methanol after regeneration is generally less than 50PPM

1. The magnitude of the pressure difference in the tower can reflect its operating condition; this pressure difference changes when the load varies. During normal production, if the tower’s pressure difference changes, it indicates that there is an excessive amount of liquid accumulated on the tray? If there are foreign objects blocking the passage, they should be removed promptly. 2. What about energy-saving measures! The main goal is to minimize the system’s heat loss; during operation, the system is first cooled and then put into use in the hot area, which reduces the amount of methanol that needs to circulate and thus lowers the load on the reboiler. If the COS level is too high, it indicates that the conversion process was not effective – after all, COS is present in trace amounts, and at the temperature of the conversion furnace, almost all of it should be converted into hydrogen sulfide. It’s possible that the hydrogen sulfide content in the gas fed into the system is low, so COS or CS2 is being fed in instead! 4. The ammonia content varies from plant to plant; Zhenhai Refining & Chemical ensures that the ammonia content in methanol is between 100 and 200

3 Recently, the COS levels in the low-temperature methanol wash unit where I work have been exceeding the specified limits. I was wondering: since our desulfurization and decarbonization processes are primarily aimed at removing CO2 and H2S, could the issue of high COS levels be related to inadequate sulfur hydrolysis? (What do I think are the reasons? 1. Insufficient pressure: Designed for 3.2 MPA but operating at 2.6 – 2.2. 2. High water content, 1-2%. 3. There is no ammonia tower in the system. But the absorption tower has a pre-washing section. Does ammonia affect absorption? ) Note: The cooling capacity of the system is quite satisfactory. Please analyze which factor is the most important; if there are other factors, I would appreciate it if the teacher could provide guidance. First of all, not all COS will be converted into H2S during the conversion process, especially in the conversion plus gas blending process ； Methanol has a higher absorption capacity for COS than CO2, and this effect is minor. If the level of COS exceeds the permissible limit, what about CO2 and H2S in the syngas – do their levels also exceed the limits? ； A water content of 1-2% has little impact on absorption; it mainly affects corrosion!

We have never detected H2S again, while C02 levels sometimes exceed the limit. But with an appropriate hydrogen-to-carbon ratio, it hardly ever exceeds the limit~ Currently, the main issue we face is COS; there’s not much of a problem with CS2

What process do you use? Are the NH3 content and COS levels in methanol excessive?

In my opinion, the main issue is decarbonization; could it be that the temperature used for removing COS is too high? Under normal circumstances, the lower the temperature within the specified range, the better for the absorption of COS. It seems that the heat exchange efficiency is not good enough. It is also possible that the COS content in the lean solution is high.

On the 7th floor, we use the process developed by Dalian University of Technology; there is a pre-washing section in the absorption tower, which I consider to be equivalent to an ammonia tower. The methanol from this section is sent to the methanol-water separation tower for regeneration. The performance of the regeneration tower has been checked many times, and there are no issues. On the 8th floor, our absorption tower consists of 5 sections: a pre-washing section, a desulfurization section, and a decarburization section. I’m not sure what the names of the first two sections should be; in any case, they are also used for decarburization. The temperature of methanol entering each section reaches -31 degrees Celsius. I don’t think it’s a temperature issue. Regarding the regeneration problem, the temperature in our regeneration tower is around 91 degrees, but the pressure is set relatively low, at 0.03 MPA

The process design pressure is 3.3, but the actual operating pressure ranges between 2.1 and 2.3.

The ammonia content in methanol after regeneration should be kept within 5 g/L!

The design pressure for you is 3.3 MPa; why is the actual operating pressure only 2.1–2.3 MPa? Pressure is the main factor affecting absorption; if the pressure is too low, a larger volume of circulation is required, which results in higher cooling demands for the system and increased energy consumption! Perhaps the pressure is too low, resulting in an extremely high absorption efficiency of COS and thus exceeding the limits! Also, as mentioned above, it’s possible that the COS content in the gas is already high, and the circulation volume in the desulfurization section is insufficient! Additionally, I would like to ask: can the pressure in your regeneration tower reach 0.03 MPa and the temperature reach 91 degrees? Have you analyzed the sulfur content in the lean methanol at the bottom of your regeneration tower?

I’m a bit confused about precise desulfurization now; could everyone give me some advice? Thank you!