Regarding the utilization of heat at the compressor outlet?
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I see that many process gases are directly cooled by water after compression; why isn’t this heat recovered and utilized? What is the main reason? Of course, a small number of processes have also been found to be useful. I don’t quite understand; forget the guidance from the process expert!
The key lies in the reuse after recycling, as well as the costs and investment associated with recycling. It’s not that heat needs to be recovered just because it’s present. There are also those that cannot be fully recycled. For example, the exhaust gases emitted by thermal power plants can only be recovered to a limited extent; there is also heat that is considered waste heat and has no value for recovery. Another example is the heat brought back by the cooling water in equipment coolers; this heat is mainly discharged into the atmosphere through cooling towers. It would be great if such heat could be converted into electrical energy, allowing for its widespread use.
There are just two points: 1. Technology 2. Economics
Actually, it can be recycled. The issue lies in where the recovered energy can be used, what the benefits will be, and whether there is enough space at the site, among other things. But thanks for asking; your question has prompted me to reconsider the feasibility of recovering energy from the compressor outlet
Gases have a relatively low specific heat, so the heat isn’t very high. Instead, find ways to utilize this heat; too much thermal integration can actually restrict one another.
For reciprocating compressors, the temperature of gases after compression at normal conditions generally does not exceed 140°C. Since the exergy value of these gases is limited, shell-and-tube heat exchangers can raise the temperature of the cold medium to at most 120°C℃； With other types of heat exchangers, the temperature can be raised at most to 130°C; similarly, the temperature after compression cooling is also determined by the downstream process. To determine whether heat recovery is necessary, a pinch analysis of the entire plant is required. There must be a cold source in a certain temperature range that can be heated to the appropriate temperature, thereby allowing the high-temperature gases to be cooled to a suitable level; only in this way can consumption of utility resources such as cooling water/heat transfer oil be reduced. Of course, if during the design phase the fixed investment required to add a new heat exchanger is already much greater than the operating costs, it is not economical to utilize this thermal energy.