Waste heat utilization
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I would like to ask the engineers here: in the usual process design processes, such as in the petrochemical industry, coal chemical industry, ammonia synthesis industry, papermaking industry, brewing industry, food industry, and so on, in which processes do these industries generate large amounts of waste heat (flue gas, steam, hot water, etc.)? Apart from these industries, any industry encountered in daily life can be mentioned; I would like to research and design some energy-saving solutions.
What can be used or recycled basically has little left that can be developed; what remains is material that is difficult to recycle and counts as waste heat, and the amount of such waste is actually quite significant.
Hot flue gas from the hot air furnace: discharge temperature of 140°C, hot air circulation volume: 50,000 m3/h; discharge volume: 5,000–10,000 m3/h (not yet determined). We plan to use this as a heat source for mist drying. The current calculations regarding the discharge volume are not clear, and that’s why we’re reaching out to you. Do you need any additional data?
Many new processes have not taken this into account yet. Furthermore, any disruptive changes in the fundamental aspects of the entire process, such as reaction principles and separation principles, will lead to inefficient use of energy.
The key question here is how large the input-output space is; in other words, whether it is worth it. For example, in a company’s cooling tower, fans expel hot air with low heat content into the atmosphere; the volume of such air is large, but its thermal value is low. Similarly, for this type of \"waste heat\" as well, it is necessary to carefully assess whether it has any value that can be utilized.
In the fine chemical industry, a lot of heat is also wasted, as it is often overlooked due to the low amount of heat involved and the high costs associated with recovery. In fact, if all this small amount of heat were collected, the total heat generated over a year would be quite significant
Mainly, what parameters are required for the application after heat recovery. I’m not familiar with the mist drying process; could you give me some information on it?
Typically, the exit temperature of spray drying is around 110°C; the hot flue gas enters at 140°C and exits at 110°C, resulting in a temperature difference of only 30°C. Using a drying heat source with a capacity of 5,000–10,000 m3/h, the amount of water that can be evaporated is approximately (5,000–10,000 m3/h) / 1.38 * 1.005 * 30 / 4.18 / 640 = 40–80 kg/h of water, which represents little practical value.
Venting the torch represents a waste of heat that everyone is aware of; why not work on addressing this issue?
Here, we use the convection chamber of the fueling furnace to recover the waste heat from flue gases, and we employ flash tanks to generate steam from steam condensate!