Types of Distillation Process Onboard

Distillation is the onboard ship process to produce freshwater from the seawater. There are two types of distillation process onboard. The process involved is evaporation and condensation. We will get the distilled water by evaporating the seawater through mainly two processes. Either using the boiling or using the flash process. By doing the evaporation, we can reduce the amount of solid that dissolved in the seawater. Also, the onboard machinery using for this process is the evaporator.

Boiling Process: Types of distillation process onboard

It is one of the types of distillation process onboard. By using the heating coil, we can boil the seawater and also by reducing the pressure of evaporating the shell. Also, the boiling process will carry out at 60 degree Celsius temperature. The first step of this process is that the seawater for the ship uses will move to the condenser. And the outlet of the condenser is attached to the evaporating chamber and the water will supply to the evaporating chamber. Also, note down that the evaporating chamber has low pressure. And the main engine jacket cooling water or steam will be passing through the heater coil of the chamber.

Then the seawater in there will start boiling. After this, the steam produced will be passing through the demister. Also, his demister will help to prevent the entry of the water particles. Then the steam will move to the condenser where the steam will condense to pure freshwater. And we can take out the freshwater by using a distillate pump. Also, there will be a flow controlling valve fit on the system to regulate the seawater feed.

In the feed water, more than half of the feed will convert to freshwater. And the remaining will take away with all accumulated salts. For that, there is a brine ejector and an air ejector is fitted. Also, it will remove all accumulated brine and air if present.

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Flash Process: Types of distillation process onboard

It is one of the types of distillation process onboard. The flash process is like we will admit the liquid with some amount of sensible heat and pressure to the low-pressure chamber. And the time we admitting the air, the liquid will suddenly convert to steam. the process does not have boiling. The process is called a flash process. The process is taking place by considering the sensible heat, pressure f water, pressure of the chamber. The main element of the process is admitting the water into a low-pressure chamber.

For the two-stage evaporators, At the first stage, the seawater will go to the condenser and to the preheater through the feed pump. After this, the seawater which is preheated will supply to the first stage of the flash process. And from there, some amount of seawater will flash off. There will be a demister to prevent the water particle in the steam and then it will condense.

Also, the seawater which is in hot condition will move to the second stage of the flash process. The chamber has very low pressure so that more amount of water will flash off. After this, the steam will pass to the demister and it will condense. Also, then we can take out distilled water by using the distillate pump. The accumulated salt in the second stage of the process will take away by using the brine pump. Also, we are using a preheater to heat the water using hot steam. There will be an air ejector using to maintain the chamber with low pressure.

Credits: Chief MAKOi / YouTube

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There will be scale formation on the heating surface that affect the evaporating process. And this scale formation will be according to the brine density, rate of flow and temperature of operation. Because of this, we need more requirements to produce a high quantity of freshwater. Also, we can reduce the amount of scale formation by cold shocking, frequent heating and cooling of the tubes. Also, we can remove the scale formed by chemical treatment also by manual cleaning. And at the time of cleaning, the system must be in a shut-off condition.

Conclusion: Hope you got the idea about the distillation process of the seawater on board ship. Comment your opinion below.

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