Weekly Topic 10.11.22, Issue 4: What are the causes of wax formation in methanol synthesis water coolers and what are the solutions?

The reason is simple: the synthesis tower produces paraffin, and the temperature in the water cooler is low; as a result, the paraffin solidifies in the latter part of the water cooler. Paraffin is a general term for hydrocarbon mixtures, and it solidifies when the temperature drops below 37 degrees. Higher pressures lead to an even higher freezing point, which is why wax formation occurs. At present, wax formation remains a challenge that has not yet been overcome in methanol synthesis; there are only differences in severity. To address this issue, the temperature of the water cooler can be increased to prevent the paraffin from solidifying there, or, in more severe cases, the process must be stopped and the wax removed using steam. You can discuss the details further; to put it simply, that’s all for now. Please add more! !

Wax formation is related to system treatment, such as the cleanliness of the synthesis tower and connected pipelines, as well as the performance of the catalyst itself. Also, the quality of the operation, whether the components are too heavy, and whether the hotspot temperature is too high. Wait...

There are several reasons for wax formation in the methanol synthesis reaction: 1. Catalyst-related issues – poor selectivity of the catalyst can lead to side reactions, and the presence of harmful impurities such as iron in the catalyst can also cause wax formation. 2. The waxing tendency is high when the temperature of the synthesis reaction is below 210 or above 260. 3. Frequent start-up and shutdowns increase the likelihood of wax formation. 4. A high CO content in the feed gas also facilitates wax formation. Method for dealing with wax formation in water coolers: Usually, the \"tropical\" operation method is employed, which involves raising the operating temperature of the methanol water cooler to melt the paraffin present therein, and then using the synthetic recycle gas to carry it into the methanol separator. This allows normal production to be maintained for a longer period of time, with thorough wax removal of the equipment and pipelines carried out during shutdown for maintenance.

There are various reasons for wax formation, but the most common cause is the selectivity of the catalyst; (untreated iron rust in new installations is also one of the main causes.) Methods to deal with wax formation: there is really no effective solution without shutting down the plant. Water cooling helps to lower the temperature, facilitating the separation of methanol, but it simultaneously causes the solidification of C8. One can only wait until the vehicle is parked to boil it in water or use steam to blow on it.

1. The hydrogen-to-carbon ratio is severely imbalanced, with large fluctuations in gas volume； 2. The unit is started and stopped frequently; what is the level of carbon monoxide in the synthesis tower during shutdown? 3. The bed temperature is not properly controlled, with large fluctuations, especially during startup and shutdown, when it enters a temperature range prone to wax formation.

I won’t go into the reasons for wax formation. To remove wax, we first stop the process gas and then fill the system with nitrogen; after that, we start the heater and activate the circulation pump to carry the wax to the separation tank. The temperature should not be too high – around 80° or less. However, modern designs seem to be equipped with dedicated steam lines for wax removal as well as drainage pipes for removing wax

It seems that the original poster’s question is about the reasons for wax formation in the water cooler, rather than those in the synthesis tower; everyone needs to make this distinction clear. There are many reasons why wax can form in the synthesis tower. We shouldn’t deviate from the topic. The way to prevent wax formation in the water cooler is to ensure that its temperature does not drop below 37 degrees. The wax in question is essentially a shorthand for hydrocarbons, which are mixtures; the lowest melting point of such waxes is 37 degrees. Therefore, the temperature of the water cooler should not be allowed to drop too low, so as to prevent wax from forming. Once wax forms, it can be removed from the system by using an alcohol-based solution followed by a filter, through which the paraffin can be cleaned out of the system.

Wax formation in the water cooler occurs when paraffin by-products are generated in the synthesis tower; these by-products solidify under cooling and stick to the tube walls. It is mainly caused by the properties of the catalyst, as well as improper temperature control and harmful substances in the fresh gas. I’ve heard of a synthetic load-reduction method: manually closing the circulation return valve to raise the water cooling temperature by 60 degrees for half an hour. This is what’s known as the tropical method. We generally use the short-stop method, by shutting off the circulating water, stopping the compressor on the circulating water side along with the steam. It is discharged through a dedicated wax drainage port. However, recently Zhengzhou University developed an online wax removal device. Since the temperature before water cooling is above 90 degrees, most of the wax is in liquid form; it is separated using a separator. The wax, which contains a high amount of methanol, can then be sent to a flash tank. If the content is low, it can be discharged directly.

It seems that everyone uses hot washing to remove paraffin from the water cooler. I’d like to ask again: what happens when the water cooling temperature rises to 70 or 80 degrees Celsius? Could the pipes expand due to heat and damage the equipment? Have your water coolers experienced any leaks?

Tube leakage in heat exchangers such as water coolers is a challenge in equipment management, as well as in chemical processing equipment; the most common cause is large temperature differences. In particular, leaks in the reboilers and condensers of the distillation section are the most common and frequent; this is likely due to the corrosiveness of methanol and the manufacturing methods used for such heat exchangers, as well as significant fluctuations in operation. Leakages in the tubes of synthetic water coolers have occurred in many chemical plants; as far as I know, four such plants have experienced this issue. There are various reasons for this: first, water remains in the tubes of the water coolers during winter, causing them to expand; second, there are large fluctuations in operating conditions during production, leading to significant changes in temperature and pressure; third, the water coolers were not manufactured in full compliance with design specifications, with inadequate welding and subsequent processing; fourth, resonance occurs between the circulating water and the process gas inside the tubes; fifth, wax formation increases the resistance in the tubes, thereby raising the pressure difference. The remaining reasons are not very clear. Personally, I believe gradually increasing the temperature of the water cooler will not affect its operation, nor will it be the main cause of leaks. This opinion is for reference only.