Methanol Section Daily Question, April 8: Discussion on the issues related to the gas heat exchanger at the outlet of the synthesis tower
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I would like to ask all colleagues in the industry: For the mixed synthesis gas produced by the synthesis tower in your plants, does it enter the gas-gas heat exchanger from the bottom and exit from the top, or vice versa? In previous designs, liquid entered from the bottom and exited from the top, but now some factories have made modifications to use entry from the top and exit from the bottom, claiming that this can prevent some methanol from accumulating inside the heat exchanger and affecting its efficiency. Is this claim correct? This post was last edited by lanseqinghai on 2009-4-8 17:40]
Generally, it uses input from the bottom and output from the top; I’ve never seen a setup with input from the top and output from the bottom.
Our 250,000-ton methanol off-gas enters from the top of the tube side and exits from the bottom, while the gas entering the tower comes in from the bottom of the shell side and exits from the top. Our facility was built last year; it was probably designed by East China University of Science and Technology. I don’t know what the advantage of this design is either, but today I felt it was a bit wobbly on the synthesis tower. The gas-to-gas heat exchanger also vibrates a bit.
High inlet and low outlet flow rates are used to prevent excessive temperature differences that could lead to cold shock (in the shell side, the flow is from low to high), as well as to avoid the accumulation of liquid methanol inside the heat exchanger
It’s possible that such a view exists upstairs, but from a traditional perspective. It seems that in all cases, the substance enters at a low temperature and exits at a higher one. From a practical standpoint, at such high temperatures, methanol should be in gas form
The gas-to-gas heat exchangers designed by the Second Chemical Engineering Institute are usually two in number; the first one has intake at the bottom and outlet at the top； Second entry from the top, exit from the bottom ； There is one gas-to-gas heat exchanger designed by another design institute, with air intake at the top and outlet at the bottom.
Among the companies I’ve seen, there are those in which fluid flows from top to bottom and those in which it flows from bottom to top. Both types of companies are currently operating stably; as long as heat exchange can take place in counterflow with the gas entering the tower, no liquid methanol should be formed at temperatures between 250 and 90 degrees.
It’s not a proper question. The person above said that no liquid methanol would be formed, but there needs to be a scientific basis for that claim. Although the temperature is high, the pressure is also high – can it really be guaranteed that no liquid methanol will be produced?
Our company operates in a top-down manner. The gas inside the synthesis tower moves upward through the central tube, passes through the heat exchanger, enters the catalyst layer, reacts there, then goes back down to the heat exchanger for heat exchange before exiting the synthesis tower.
Ours enters from the top; the approach you mentioned does exist – it features a large air volume, an upper inlet, and high equipment safety.
It’s related to factors such as the feed rate per CAT, the T and P values in the synthesis tower, and the space velocity
Our plant uses two heat exchangers in series, with flow from bottom to top in one series and from top to bottom in the other. If it is a single heat exchanger, there should be a scientific basis for choosing that method.
The mixed gas coming out of the synthesis tower enters at the top of the heat exchanger and exits at the bottom. Because during the heat exchange process, a small amount of liquid condenses to form tiny droplets, which then fall downward due to gravity. If the directions of entry and exit are opposite, it is not conducive to heat exchange. It was what the experienced master said during the actual implementation; provided here for everyone’s reference.