Distillation column problems
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One of our deep cryogenic distillation columns fails to achieve the required purity level for the product at the top of the column under its designed operating conditions. The operation can barely be maintained when the feed temperature remains more than 10 degrees below the design temperature for an extended period. This tower has no reboiler, with low-temperature liquid reflux at the top. The feed is introduced at the bottom of the tower; currently, the temperature of the feed at the tower is -153 degrees Celsius, while the temperature of the liquid at the bottom of the tower reaches -166 degrees Celsius. Can it be determined now that there is a problem with the tower packing/top distributor? The low-temperature liquid resulting from reflux at the top of the tower does not reach phase equilibrium on the packing and therefore reaches the bottom of the tower, which is why the temperature there is low (My understanding is that in a typical distillation column, the feed temperature is usually the same as the temperature at the feed location; the temperature increases as one goes downward.) Could anyone please give me some guidance? ?
I don’t know what the product of this distillation tower is. If the cryogenic air separation tower is used as a reference, it may be possible to analyze the existing problems more directly by referring to the changes in purity at various parts of the material, for reference purposes.
This depends on whether the energy and material flow of the distillation tower are within the design parameters; a systematic investigation is required
The system’s heat balance hasn’t been calculated; the feed temperature is very low, and there is cryogenic cooling at the top. There is no heat source within the system, so the cold energy from that cryogenic cooling will be carried down to the bottom of the tower via the reflux liquid. A possible solution is to remove the insulation from the bottom of the tower so that heat can be obtained through heat exchange with air. What is used for cryogenic cooling at the top of your distillation column? Is it liquid nitrogen?
Liquid high-pressure carbon monoxide for tower top reflux, -176 degrees Celsius. The feed to the syngas tower is a gas-liquid mixture of CO, CH4, and H2, while the product at the top of the tower is crude syngas (CO+H2); this tower is primarily used to remove CH4. My understanding is that this tower does not have a stripping section; if the low-temperature CO at the top of the tower affects the temperature at the bottom of the tower, could this indicate a problem with the packing or distributor? The temperature at the bottom of the tower can’t possibly be lower than the feed temperature.
Are you sure this is called a distillation tower and not a washing tower? Following the distillation model, the analysis direction is reversed; the wash tower controls the temperature of the trays, without paying attention to the bottom of the tower. There is reflux liquid flowing down; the temperature of this reflux liquid affects the temperature at the bottom of the tower, and the feed also has an impact. It depends on which factor has a greater effect. I’ve worked in large chemical plants only occasionally, and this type of process is something I’ve heard of for the first time. You can consider the low-temperature methanol washing process, which uses methanol to wash and absorb H2S and CO2; methanol functions in this context as a washing liquid for CO
If it’s the scrubber you mentioned, where heat is released after absorption, then shouldn’t the temperature of the liquid in the tower bottom be high? Is it even less logical? Puzzled
This post was last edited by Qingchengjun on 2020-5-27 at 11:51. You still haven’t even reached the basics of this way of thinking. The mindset in engineering is not a qualitative one that focuses on how various factors affect things, but rather a quantitative mindset that takes numbers into account. For example, driving is faster than walking, but when it comes to going to a store across the street to buy something, taking into account the practical issues of picking up and parking the car, walking might be faster than driving. When looking at a problem, it’s necessary to consider practical aspects; numbers can help illustrate this. If CO’s temperature is -176°C, there is still a margin before the temperature rises to -153°C during adsorption. It’s completely reasonable for the temperature at the bottom of the tower to be below -153°C – this needs to be calculated
I simulated it using software, and the temperature at the bottom of the tower indeed doesn’t drop that low. If the design involves feeding at the most economical location (where the feed temperature is equal to that of the feed plate), then as the low-temperature reflux liquid moves downward through each layer of the packing, material and energy balance should be achieved; therefore, the temperature of the liquid at the bottom of the tower shouldn’t be so low, right?
“If the design provides for feeding at the most economical location (with the feed temperature being the same as that at the feed plate), such a thing does not exist; wash towers are fed from the bottom. I don’t know how you simulated it. It seems like you don’t even understand the process; I suggest you learn about the low-temperature methanol washing process before coming back to this topic
Bro, the low-temperature methanol washing you mentioned is a method that utilizes the high solubility of acidic gases in low-temperature methanol to separate them. Part of this tar, after being regenerated by CO gasification, still serves as the overhead product. Separation is achieved by taking advantage of the differences in the volatility of various components, so it still belongs to a distillation tower, right? ? :lol