What is the source of water in methanol from Dalian low-temperature methanol washing?

It depends on the stage. Take the initial startup process as an example: after cleaning the equipment and activating the water system, if the water in the system isn’t removed properly or if the system isn’t dried thoroughly (depending on the drying method used), this can result in an excessively high water content in the system. In some cases, the water content exceeds 5%, but during our initial startups it never exceeded 2%. During normal operation, the main source of water in the system is the shift gas, which comes from the ammonia washing tower. Another source is water that gets into the system due to improper operation of the water-water separation tower; we have examples of this.

Hello, could you tell me about the specific methods you use for drying? Thank you

After normal production, the sources of water content in the system are: 1. Converted gas； 2. Washing water for the exhaust gas scrubber tower ； 3. If the water content remains above the limit and it is determined that the causes are not the two mentioned above, then there is a possibility of leakage in one of the heat exchangers in E11 (the reboiler of the regeneration tower), E15 (the reboiler of the methanol-water separation tower), or E12 (the water cooler at the top of the regeneration tower)! ! In the case of initial driving, apart from the reasons mentioned above, the main cause is that the system has not been properly dried after water circulation

Common drying methods used in the system include: 1. Methanol circulation to remove moisture； 2. Nitrogen drying ； Nitrogen drying is generally used; if time permits, the drying process should be carried out for as long as possible, so that there will be less water remaining in the system!

According to the process flow, it is mainly the moisture in the feed gas; the water is separated out in tank V01

Under different circumstances, the source of water varies. Generally speaking, there are specified requirements regarding the percentage of water content in the feed gas. During operation, there may be heat exchangers that leak water, or issues with the proper control of the operating conditions in the water separation tower, among many other reasons. What the original poster mentioned is just one of these factors.

The water present in methanol is mainly water introduced from the process gas; the water that enters the water separation tower comes from the methanol vapor at the top of the tower, and this water then enters the methanol circulation system. Stabilizing the temperature of the methanol water separation tower is essential for maintaining a stable water content in the system. An excessive amount of water in methanol is usually caused by poor operation of the water separation tower or leaks in the reboiler. The water pressure in the water cooler is not high enough to allow water to enter the system. The methods used for drying include: 1) establishing a methanol circulation system and using the methanol water separation tower to purify the methanol; 2) using nitrogen to dry it out

This can be divided into the following two cases: First, during the testing phase, if the water accumulated from washing equipment and pipes with water or chemicals is not completely drained, this water will end up dissolving in the circulating methanol after methanol is introduced into the system, thereby increasing its concentration. (When the system is initially filled with methanol, only pure methanol is used, unless...)； II. During normal production, 1) the moisture in the shift gas, 2) the moisture carried over after passing through the ammonia scrubber, 3) unstable operation of the water separation system leading to a continuous increase in the water content in the circulating methanol (note that this is a continuous increase), 4) leaks in the water cooler at the top outlet of the thermal regeneration tower, which result in an increased water content in the reflux methanol and thus an increased water content throughout the entire system (specifically applicable to the Lurgi process). All of the above are common reasons; my apologies

I recently had a conversation with Professor Zhang Shuwei from Dalian University of Technology. According to him, the system water content in some of the originally designed devices was above the acceptable level, which resulted in the methanol distilled in Tower 5 containing a significant amount of water. As a result, they have now optimized the design of Tower 5 and also improved the design of its trays

We also used the technology from Dalian University of Technology; it hasn’t been put into operation yet. How should we make corrections?

Introducing the feed gas is one aspect. There’s also what was said upstairs. After the water interconnection. When dried with nitrogen. Not thorough. Caused

I think another issue is that when methanol is added to the system, the water content in the methanol is too high, which results in a high water content in the circulating methanol

There are many reasons for the high water content in the system: 1. During the initial startup, the moisture is not completely dried, and pipes in hard-to-reach areas are not blown dry. It is important to check the pipe layout to identify any areas where drainage channels need to be added. 2. Improper operation of the methanol-water separation tower may be due to inaccurate temperature readings or inappropriate pressure settings. 3. Possibility of leakage in the circulating water heat exchanger. 4. When methanol is added, the methanol is not fully analyzed for water content; a high level of water in the methanol is also possible. 5. It is also possible for the transformed gas to contain water.

Water vapor carried in the transformed gas, leaks from the methanol regeneration unit, and a decrease in the efficiency of the methanol-water separation tower all contribute to the introduction of water into the system

Reason: 1. Water presence in the shifted gas: Since the shifted gas coming from the carbon monoxide shift unit enters the shift reactor with medium-pressure steam as a reactant and to regulate the temperature, the gas exiting the reactor is necessarily saturated water gas or semi-saturated water gas. Moreover, after passing through the gas cooling section, it is also washed with phenol water, so it contains phenol water as well. To enter the low-temperature methanol washing section, one must first go into the water washing tower, where the material is washed with circulating water and phenol-water; this adds more water again! 2. Raw gas already contains water, and in the gas treatment section water is also used or washing with water is carried out, so it still contains some water.

Personally, I think all of the above make sense. However, it seems that the current bottleneck lies in the pure water separation tower: the circulation volume of methanol has increased, as has the volume of process gas, and the amount of water entering the system has also increased, yet the processing capacity of the pure water separation tower does not seem to have increased much. I wonder if anyone has calculated this, but it seems that the amount of water introduced into the system and the amount of water that exits it are not in balance. Moreover, the amount of methanol injected into the system doesn’t change much either. I really don’t understand what these design firms are doing these days; is there anyone who takes this seriously?

The methanol-water separation tower was designed with a certain margin, providing some operational flexibility. For HAIYOU on the 17th floor, if the methanol-water separation tower in your plant does not have sufficient processing capacity, you can describe the specific situation, and we will help analyze and find a solution.