Technical discussion: On the use of vacuum evaporation for salt production from concentrated seawater
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This post was last edited by hesonchang214 on 2011-1-25 at 17:47. I have been working on evaporation calculations related to vacuum salt production from brine recently. As land prices in coastal areas rise, the area of many salt pans is shrinking. To address this issue, our teacher wants to conduct a research project on salt production using vacuum methods with concentrated seawater. It is still a long way from industrialization, but I hope to conduct some calculations on this issue. Here are the relevant parameters: The concentrated seawater has a specific gravity of 15 Bé; its components are sodium chloride at 129.93%, sodium ions at 51.25%, chloride ions at 92.37%, magnesium ions at 6.127%, and water at 950.58%. The density is 1.1151. When it becomes saturated brine, its specific gravity is 25 Bé; the components then are sodium chloride at 251.06%, sodium ions at 99.03%, chloride ions at 179.1%, magnesium ions at 11.93%, and water at 896.27%. The density in this case is 1.2088. At a specific gravity of 30 Bé, the components are sodium chloride at 132.37%, sodium ions at 53.12%, chloride ions at 191, magnesium ions at 47%, and water at 897; the density is 1.2625. The production capacity is 1 million tons per year. The amount of steam used is 3 kilograms at 133 degrees Celsius. The temperature of the raw brine is 40 degrees Celsius. My initial idea is to first concentrate the concentrated seawater (15 Bé) using five-effect evaporation to turn it into saturated brine (25 Bé), employing a co-current evaporation process. Salt is used without hesitation in this process, with only a small amount of calcium sulfate precipitating. Then, the saturated brine is subjected to four-effect evaporation for salt precipitation until a Bézier degree of 30 is achieved, using a process with parallel feed, countercurrent flow, and salt discharge from the last effect. Since the steam output of the first effect is only three kilograms, the boiling point rises too much in the case of concentrated solutions; it’s unlikely that a five-effect system will be useful in such situations. What I would like to ask is: 1. Do you think my approach/method is feasible? 2. I chose to proceed through two evaporation steps; if we were to directly evaporate from 15 degrees Baume to 30 degrees Baume, wouldn’t the load on the evaporator be too high? I originally thought of using one evaporation step, but later I realized that this would place too much load on the evaporation tank. 3. I ran into difficulties in my calculations, as my raw brine cannot reach boiling point even after preheating; therefore, it is not possible to calculate the evaporation area using the usual method based on boiling point feeding. Because under normal conditions, feed is added at the boiling point in the flow direction, it is possible to determine the concentration in each stage by assuming a relationship between evaporation in each stage; once the boiling point elevation is determined, the effective temperature difference can be calculated, and then the calculation can be carried out using the method of equal areas. But I don’t know how to assume the evaporation rate and calculate the area right now. I hope there are experts here who can answer my questions above. Or if you have any other questions or ideas, feel free to share them. Learn from each other and make progress~ Strongly request to pin it~~~`
This method is feasible, but the two-evaporation system you use should result in considerable consumption. I guess by then you’ll lose so much that you won’t even be able to see your home. Unless you have some other equipment, such as one that can produce bromine compounds. A vacuum salt production system can be used directly; a preheater is added before the four-effect evaporation process. In the first and second effects, the solution is concentrated to a saturated state, salt precipitates out in the third effect, and the salt is removed in the fourth effect. Four-effect secondary steam condenser with atmospheric condensation, evacuated.
The last edit to this post was made by hesonchang214 on 2011-1-25 at 18:06. Reply to 2# zhongnanchem: I’ve thought about this as well, but I believe the load on the evaporator would be too high; the amount of water that needs to be evaporated in the range of 15 to 25 degrees Bé is much greater than during the subsequent salt precipitation stage. There must be other forms of production as well; it’s definitely not profitable to rely solely on salt!
The production of fresh water as a result of this process is a significant benefit; I think it might be better to separate evaporation from heating.
The poster has already mentioned in the title the issue of the shrinking area available for salt production facilities; therefore, the process design should also take into account this space constraint. Improving the quality and efficiency of salt production represents two conflicting aspects. From this perspective, I agree with the suggestion from the second floor