The issue of steam consumption for water evaporation
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The current concentration of calcium chloride is around 200 g/L, and it is desired to evaporate and concentrate it to obtain calcium chloride dihydrate with a concentration of 70%. How should the amount of steam required (at 230 degrees) be calculated? What is the relationship between theoretical calculations and actual production?
Theoretically, the steam consumption can be calculated based on the heat transfer process. In practice, it depends on whether it is single-effect or multi-effect evaporation; multi-effect evaporation is more complicated, so it is recommended to consult the chapter on evaporation in the principles of chemical engineering
This issue relates to the evaporation process; first, it is necessary to standardize the units of concentration, with weight percent concentration being commonly used, which enables mass balance calculations. If the concentration of the feed liquid is x0, the flow rate (or processing volume) of the feed liquid is F, and the concentration of the resulting liquid is x1, then the amount of water evaporated is D = F * (1 – x0/x1). The theoretical value of steam consumption, W, is slightly higher than the amount of water evaporated, D. This is because the temperature of the heating steam is always higher than the evaporation temperature, and there is a difference in their latent heats of vaporization; in addition, heat losses mean that the actual steam consumption is even higher. This applies to single-effect evaporation, with W/D ranging roughly between 1.05 and 1.10. Regarding the evaporation issue of calcium chloride mentioned by the original poster, the concentration of the resulting solution is already quite high; when 230-degree steam is used, the difference in its latent heat of vaporization becomes even greater, which leads to an increased consumption of steam. The specific details depend on the specific evaporator used.
There are books dedicated to this topic; you can look them up. One should not take things out of context
First, calculate the amount of water that evaporates; the steam consumption can be estimated by taking 1.2 times the amount of water that evaporates.
Using the units before and after the agreement, the amount of water that needs to be evaporated is calculated, and this value is then simply converted into the required amount of steam. Of course, a coefficient must be multiplied in, as there are heat losses involved