Heat exchanger temperature rise and coking
Thread Content
Organic wastewater flows through the shell side of the heat exchanger; the organic compounds in this wastewater are mainly phenolic substances. An acidic environment is required for this process. During heat exchange, when the temperature rises to a certain level, viscous coking substances similar to those shown in the diagram will form. Such coking substances adhere to the outer wall of the heat exchange tubes, resulting in a significant reduction in the heat exchange efficiency of the heat exchanger, and eventually it may become almost unable to perform heat exchange at all. Various cleaning methods were tried on site, such as acid cleaning, alkali cleaning, and steam purging, but with little noticeable effect. Regarding the above description, there are the following main issues for which I seek advice from fellow sailors: 1. How can this type of coking substance be avoided during the heat exchange process? 2. If coking cannot be avoided, how can effective cleaning be carried out?
Is the temperature control unreasonable? ? Try other heating methods to create a smaller temperature difference on both sides.
It’s of no use if the temperature difference is small; the heat exchangers are connected in series across multiple stages. Once a certain temperature is reached, coking occurs. When the heat exchanger becomes clogged and stops functioning, this problem affects the next stage of heat exchangers in the lower temperature range, causing those heat exchangers to start coking as well
If it is determined by the properties of the medium, coking will inevitably occur at a certain temperature, and you must heat it to that temperature. Then do not use a heat exchanger; instead, use double-tube or other kettle-type heating methods. Start with the lower possibility of coking and blockages.
Can increasing the water volume reduce the concentration?
This post was last edited by Baoji Chaosheng Titanium Industry on 2018-6-4 at 11:54. I believe that the main substances in wastewater are phenol and other impurities; when heated to a certain temperature, secondary polymerization reactions occur, resulting in coking. Samples can be taken for verification in the laboratory. Specific solution: It is necessary to determine what the coking substances are, what the impurities in the wastewater consist of, and what the mechanisms behind their formation are; only then can an optimal solution be proposed. I hope those who have experienced this situation can provide an answer!
The process route can only use heat exchangers; according to you, if the medium remains unchanged, coking is inevitable. Actually, we don’t have much hope of avoiding coking now; it would be sufficient if it can be cleaned thoroughly. Relatively speaking, this is more feasible.
It can be determined that this is not due to crystal precipitation, so it should have nothing to do with concentration.
We also think it is due to secondary polymerization; we have tried to change the working conditions of the medium, but effective solutions have not been found yet. For now, this can only serve as an alternative option, in the hope that breakthroughs can be achieved in the future.
It’s just a way to reduce the concentration by increasing the water content, thereby lowering the likelihood of coking (many substances tend to coke more as their concentration increases, and the higher the temperature, the more likely coking is; since it’s not possible to lower the temperature, reducing the concentration is the only option). This also helps to increase the flow rate (which in effect reduces the residence time, and that should also be beneficial). Also, is your material transported in shells? If so, try changing it to a pipeline.
Could it work like this: first determine the temperature at which coking occurs, and then find ways to avoid it through process modifications – for example, changing the heating method when that temperature is reached and using direct heating; after that, filter out the coking substances and proceed to the next stage. Analyze again what these coking substances are; if chemical methods don’t work, use physical methods, such as applying high-pressure water jets to clear them away