Discussion on 600,000 tons/year methanol distillation unit
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What type of internals are currently being used in the methanol distillation towers for the newly installed large-scale methanol plants? What diameter should the tower have? Has there also been a change in the type of condenser – are evaporative condensers or finned ones being used?
The internals of a methanol distillation column can be either floating valve trays or packing. The tower diameter is related to the production scale. It can be a 3-tower system (two towers with normal energy consumption), a 4-tower system (three towers for energy savings), a 5-tower system, or a 6-tower system (high energy consumption but high quality). The design of the condenser is quite simple; a standard shell-and-tube heat exchanger can be used. Evaporative condensers are used at the top of pressure towers. It serves as both a condenser and a reboiler for the bottom of the atmospheric pressure column.
Suggestion: Use floating valves or packing for the internal components. A new type of air cooler for condensers. In shell-and-tube designs, poor water quality can lead to mud buildup, which reduces the heat exchange efficiency
When the methanol production capacity reached 600,000 tons, the diameter of the two towers increased to over 3 meters. The diameter requirements for the internal components in the pre-treatment tower and the pressure tower are not very strict, but the large diameter of the atmospheric pressure tower led to many problems. It’s not a matter of which type of internal component is suitable; rather, it’s about choosing the one that can effectively address the problem of amplification effects. Float valve towers are certainly good and usable, but when the tower diameter exceeds 4 meters, it is very difficult to calculate the 3–4 overflow issues associated with plate towers, as their mathematical models have not yet been widely adopted ； Similarly, for packing, there are a series of advantages such as high theoretical stage number, stable operation, and low pressure drop; however, it is necessary to consider whether the distributor used in conjunction with the packing can effectively ensure uniform distribution of the liquid (vapor). In short, when choosing internal components, one must respect technology and science.
What if the scale reaches 1 million tons per year?
600,000 tons per year – a large scale. Is the technology mature?
We use 4-column distillation, with structured packing developed by Tianjin University used for the internal components of the columns, and the results are good!
I believe that air coolers are superior to water coolers: firstly, they make it easier to control the pressure at the top of the tower; secondly, they prevent defective products from being produced (as there is a risk of leakage in the circulating water when water coolers are used); thirdly, air coolers are easier to inspect and maintain.
Our company has air coolers, but they don’t seem to provide good cooling in summer.
For a methanol plant with a capacity of 600,000 tons per year, the diameter of the distillation tower is relatively large. For the 5,000 t/d plant we are currently building, the diameter of the distillation columns exceeds 5 meters; the selection of tray types should be determined in collaboration with the supplier of the tray materials.
Now the three-tower process is used everywhere; the design claims to enable the production of A** methanol, but I think it’s rare for this to be achieved in practice, and even in China, few facilities are able to do so
Methanol distillation generally employs a three-column process. Foreign catalysts perform well at the initial stage of use, but it becomes difficult to meet the American AA grade standard towards the end of their useful life; it is even more difficult to achieve the AA grade standard with domestic catalysts.