How to select materials for methanol heat exchangers
Thread Content
Methanol at 62.5 degrees Celsius flows in the shell side, while cooling water at 29.25 degrees Celsius flows in the tube side. What materials should be used for the cylinder and the tubes?
At normal temperature and pressure, there are no special requirements regarding the material used for methanol; plastics, carbon steel, stainless steel, and copper can all be used. I have used all of these materials, and none of them presented any problems!
Our company uses carbon steel for both the shell side and tube side
In recent years, there has been an extraordinary boom in methanol projects, with a particular emphasis on those related to coal chemical industry. The methanol reactor, also known as the methanol synthesis tower, is one of the key equipment in methanol production facilities. Its operating conditions are special; although the constant-temperature tubular synthesis tower is a type of fixed-tube-sheet heat exchanger, the synthesis reaction taking place inside its tubes is a highly exothermic process. In the process calculations, the value of the average temperature difference between the tube side and the shell side is quite important. Therefore, for such equipment, it is crucial to choose materials suitable for both the tube side and the shell side – in addition to considering strength and corrosion resistance, it is also important that the linear expansion coefficients of these materials be similar. Domestic methanol projects: For methanol synthesis towers with an annual production capacity of 100,000 tons, the material selection is as follows – cylinder: 13MnNiMoNbR; head: 15CrMoR; reaction tubes: S31803 (2205) or S31500 ； For cylinders with a weight of over 100,000 tons, the material used is 20MnMoNi55; for the end caps, 15CrMoR is used. The reaction tubes are made of S31803 or S31500, or both the cylinders and end caps can be fabricated from SA387Gr.11CL2. The reaction tubes are made of double-direction steel; domestic suppliers include Shanghai Iron and Steel Plant No. 5 and Changshu Huaxin, with grades such as 00Cr18Ni5Mo3Si2 and 00Cr22Ni5Mo3N. The quality of this steel is satisfactory, and it has been widely used in recent years.
Carbon steel material can be used. Economical and practical
In the long term, it is best to use stainless steel (A304 steel) for both the pipes and the housing; carbon steel tends to rust, which affects product quality and can lead to leaks.
Hehe, stainless steel is certainly better than carbon steel, but what about the price?
Methanol has little corrosivity, but it is flammable and explosive; it is advisable to use 16MnR for the shell, 20G for the heat exchange tubes, and design the heat exchanger as a Class III pressure vessel.
We use carbon steel for the methanol condenser in our setup, and the operating conditions are almost exactly the same as those listed by the original poster. I’ve been using it for 8 years now, and there are no problems.
Why are 20g heat exchange tubes used for cooling water instead of 16Mn tubes?
The 4th floor has a more comprehensive explanation. There are no special requirements for methanol production. Selection can be made according to pressure, temperature, and medium in accordance with the HG20582 standard.
For ordinary pressure vessels, materials can be selected in accordance with the GB151 standard.
That’s true, but there are no strict regulations regarding these materials; the price of the heat exchangers on the 4th floor is quite high. It’s hard to decide – you decide on the corrosivity of the cooling water, and the same goes for methanol! Is 16Mn still okay?