DPT’s methanol synthesis technology

The area of ​​the heat exchanger is too small, and the amount of steam generated is small; the circulation volume is too large, there is a lot of ineffective gas, a large amount of heat is taken away by the circulation machine, the water cooling load is heavy, the system operation is uneconomical, the alcohol content at the outlet of the synthesis tower is low, the amount of methanol returned at the entrance of the synthesis tower is large, and the system output is low.

In fact, the outlet temperature of the synthesis tower mentioned on the first floor is the average temperature of the gas, that is, the initial gas outlet temperature is 260 degrees, and the final gas outlet temperature is 280 degrees. Because the temperature of the steam produced is only 220 degrees, it means that the temperature of the gas on the cold side of the catalyst is about 230 degrees. Calculated this way (conservative estimate), the temperature of the gas on the hot side of the catalyst (hot spot temperature) will exceed 300 degrees. Domestic copper-based catalysts must not be able to withstand such high temperatures, or have a service life.* * Shortened, but can JMC’s catalyst be used? It’s also a Cu-Zn-Al catalyst.

I hope everyone will actively participate in the discussion.

As far as domestic catalysts are concerned, they are definitely not able to adapt to this kind of technology. I think that with such high energy consumption, the monool factory will definitely not consider this process now, and the equipment cannot be installed. DN1000mm high-pressure pipelines, let alone such a large cycle machine. However, there are really few introductions to this technology now.

Shenhua 5500MTPD uses DPT's methanol synthesis technology and catalyst. Two synthesis towers and two synthesis loops are connected in series. DPT uses a radial tower. However, the gas flow direction of its radial tower is different from that of Casali, which is from the inside to the outside. This is inconsistent with the shrinkage of the methanol synthesis reaction gas volume. Because like DPT, the flow rate in the center is extremely high, and the flow rate at the bed outlet is very low. Is this method causing the outlet gas temperature of the synthesis tower to be too high? As a result, the methanol concentration at the outlet is too low?

Everyone is also welcome to participate in the discussion on the following post: Selection of million tons/a methanol synthesis reactor http://bbs.hcbbs.com/thread-42199-1-1.html

The gas flows divergently from the inside to the outside, and the flow rate changes vary several times, making it difficult to ensure uniform distribution. In addition, especially after the radial reactor is enlarged and the height of the catalyst layer increases, the stacking density of the upper and lower catalysts is different, resulting in different flow resistance, which also affects the distribution of gas in the catalyst layer. As for the lower steam production pressure, it is mainly because the internal parts are arranged in annular tubes, and the number of tubes is smaller than that of the cold surface compared with the row tubes. Under the effective heat exchange surface, the heat transfer K is basically unchanged. In order to ensure that the reaction heat can be removed, the heat transfer temperature difference must be increased, that is, the water side heat transfer temperature is reduced, that is, the steam production pressure is reduced to achieve the purpose of heat transfer. This is also the reason why it is difficult to increase the steam production pressure in the early stage of domestic shell and tube reactors and domestic catalysts.

The analysis above makes sense. However, the problem of density difference caused by shrinkage after heating and reduction and settlement after operation should be an issue that must be considered and has been considered by patentees specializing in radial reactors. Domestic shell and tube reactors should be of the tubular type, and there should be no problem of insufficient specific cold surface. The example cited above does not seem to prove its point.

Everyone needs to sit down and discuss the issue of large methanol. Enterprises, design institutes, and research institutes need to sit together to communicate face to face and brainstorm, and there will be a perfect design.

What do you mean? With such a low one-way conversion rate, why should you consider it? Just don’t use it.

I don’t know the two loops, how many stages and times they are separated, the alcohol content at the outlet of the first tower, and the alcohol content at the inlet of the second tower.

I think the process gas flows from the inside out. When it just enters the catalyst bed, the methanol content in the process gas is very low and has no inhibition ability, so the speed is faster.； When the gas reaches the end of the bed, the higher methanol content will inhibit the reaction, so slowing down the speed can improve the conversion rate. The conversion rate of DAVY is indeed a bit low, and the amount of cycles is very large. . . Moreover, the temperature inside the furnace is also very high. The normal outlet temperature is 283

Going from the inside out, in addition to the slightly larger resistance drop, another problem is that the pressure shell always operates at a relatively high temperature.； This is different from going in from the outside in. The pressure enclosure operates at relatively low temperatures. I don’t know how DPT explains this gas flow arrangement. A normal outlet temperature is 283 degrees. Under normal circumstances, for an isothermal tower, the outlet temperature should not be the hot spot temperature, that is, the hot spot temperature should be higher. In this case, the impurities in the crude methanol make it difficult to predict the life of the catalyst. But it also shows that JMC’s catalyst is indeed powerful, and I estimate that the catalyst upstairs will always rely on it in the future. :L

Why is the resistance of this kind of tower with air flowing from the inside out high? Is it compared with the synthetic tower that goes from the outside in, or with the axial synthetic tower? There won’t be many impurities in crude methanol, because the main side reactions that produce impurities are exothermic reactions, and the heat is greater than that of synthesizing methanol, so in theory, side reactions will be suppressed. I wonder if this will be the case in real production? I just briefly learned some DAVY craftsmanship. I really don’t know why DAVY is designed like this, but I can ask.

For the post posted by the poster, you can analyze it from the following points:: 1. DPT uses fully radial reactor technology. The low concentration of methanol at the outlet is caused by the high circulation ratio. The high circulation ratio is due to the insufficient heat transfer capacity of the reactor. The reaction heat must be moved out of the reactor in time through a large circulation volume. It is learned from the literature that the specific cold surface of this reactor is 20-30m2/m3, while the Lurgi shell-and-tube type is 100m2/m3, which is a large gap. 2. Due to insufficient heat transfer capacity, the catalyst layer temperature difference is relatively large. As for the initial reaction temperature of 260°C, it is based on the use of foreign catalysts. Compared with domestic catalysts, foreign catalysts have better high-temperature activity and can still operate at high temperatures of 300°C. However, domestic catalysts have good low-temperature activity, high-temperature activity drops quickly, high by-products, and shortened service life. 3. The by-product steam pressure is low. This is also because the reactor is too small compared to the cold surface. The heat transfer temperature difference must be increased to increase the heat transfer amount. The by-product steam pressure may not reach 2.2MPa in the early stage. The lowest steam production pressure I know is 1.9MPa. 4. The use of fully radial reactors is beneficial to the large-scale methanol, but it is difficult to control the gas distribution from the inside out. The large methanol solution proposed by David in China in recent years adopts a water-cooled air-cooling process and reduces the cycle to ~2.5. The water-cooling tower adopts the shell-and-tube type commonly used in China, and the air-cooling tower adopts TC C single-tube counterflow cooling tube tower. My personal analysis is that the reason why David uses a shell-and-tube tower instead of a full radial tower is mainly because of its insufficient heat transfer capacity. Both towers are axial and lose the advantage of low resistance of full radial towers. In addition, the DPT water-cooling and air-cooling process has two more gas-to-gas heat exchangers than the Lurgi technology.

This post was last edited by tomlhq on 2009-7-14 18:11. There are more than two gas-to-gas heat exchangers. , the whole thing is two loops. I have recently read information on several foreign second-hand methanol plants. They all use ICI technology and were put into production in the 1990s, but they still use cold-shock methanol synthesis towers. The amount of circulation is really huge. Baotou MTO is already a lot better. I feel that ICI's technology is still strong in natural gas steam reforming, and I cannot praise the methanol synthesis technology. Rucci is relatively strong overall, but has gone downhill in recent years. Making a two-wash plan is completely wrong. Low-temperature methanol washing and liquid nitrogen washing are done separately, the logistics are not compatible, and the depth is not the same. It is really difficult to reassure people.