Regarding the issue of modifying falling film evaporators, I am seeking help from experts in this field to provide answers

I have a set of four-effect falling-film evaporators for use with saline wastewater, but their performance is poor. After reviewing relevant information, it was found that falling-film four-effect evaporators are not effective in removing salts from saline wastewater; forced-circulation evaporators are more effective for treating such water quality. I’m seeking advice from experts: Is it possible to convert a falling film evaporator into a forced circulation system? If so, how would that be done? Could it work by using falling film evaporation for pre-treatment in two stages, followed by two stages of forced evaporation, and then crystallization for desalination? Collect | Invite Editor | Delete|

The difficulty in converting a falling film evaporator to a forced circulation system lies in the fact that the diameter of the tubes in existing evaporators is relatively large; forced circulation requires a very large volume of fluid flow to achieve the desired heat transfer capacity. It is possible to make such a conversion. Additionally, when using a falling film evaporator for treating brine, it becomes difficult to form a film when the salt concentration exceeds 20%, which is why forced circulation is necessary

1. The specific components are unknown; during the concentration of saline wastewater, oil layers tend to form, especially in wastewater with high concentrations. These oil layers significantly reduce the efficiency of evaporation, necessitating the use of oil separation equipment； 2. When falling film evaporation is used for salt concentration, the degree of concentration cannot be too high; it is generally applied to salts with large changes in solubility, and crystallization can be reduced after concentration ； 3. I’m not sure what equipment is included in your falling film system. When changing from a falling film to a forced circulation heat exchange system, it’s necessary to consider whether the heat exchange area is sufficient and whether the crystallization area is adequate. In fact, these factors only affect the evaporation efficiency; the system can definitely be used (my personal suggestion is to build a new system instead;P).

Hello! The basic components of the treated water include inorganic salts such as sodium chloride, sodium sulfate, sodium sulfite, ammonium chloride, and calcium carbonate, as well as trace amounts of organic solvents such as dichloroethane and methanol. Among them, sodium chloride accounts for a large proportion. The salinity of the raw water ranges from 10% to 15% ； The existing evaporator is a four-effect counter-current falling-film evaporation system with a water treatment capacity of 10 T/h; its performance at the time of initial operation was very poor, with an efficiency of around 50%. If it is possible to modify this system to use a falling-film + forced-circulation design, what approach should be adopted? Which components need to be modified in each evaporator? Is it feasible? Thank you for the reply, thank you for your support!

When you say the performance is poor, do you mean the low evaporation rate? What does efficiency of 50% mean? What is the total heating area of your set of four-effect falling-film evaporators? Did four-effect crystallization occur during the evaporation process? A two-effect falling-film + two-effect forced-circulation configuration can be adopted, with the mother liquor being returned from the third effect for further distillation.

Hello! The heat exchange area of a single falling film evaporator is roughly 280 square meters, and it should be able to handle a water flow rate of 10 tons per hour; in reality, the flow rate is less than 4 tons per hour, and the operation is unstable. There have been instances of crystallization blocking the tubes in the four-effect separator. If modifications can be made, could it be that the separator is also not suitable?

The main issue is that it does not meet the current actual operating conditions; salt production is not possible

Yes, the total heating area seems to be quite large. The problem lies in the process: first, crystallization occurs in the last two stages; falling film evaporators are not suitable for this situation, so it is necessary to convert the system to a forced circulation type, using an axial flow pump in place of the circulation pump, and the separator also needs to be adjusted ； Second, the current four-effect falling-film evaporators have a low evaporation capacity; is this related to the circulation pump? I need to see your process flow diagram and pump configuration to identify the problem.

Is it equipment structure design or process consulting?