The process of changing from liquid to gas state

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What is it?

As the requirement for ZLD (Zero Liquid Discharge) increases, the need for technologies and solutions based around evaporation / condensation increases.

Added to this constraint, we have a duty to reduce our carbon footprint. Yet, for the evaporation of 1,000 litres of water at atmospheric pressure, over 700kWh are required.

With this in mind and consideration to be given to the specificities of the client effluent treatment project, Puretech can implement various evaporations technologies :

Mechanical Vapour Recompression

Operating under a partial vacuum (~650mbar), it operates at a temperature of approximately 80°C. The steam being produced is recompressed by  a compressor which then allows the vapour to condense and provide the energy to the incoming effluent.

Mechanical vapour recompression schematic to achieve ZLD. Especially for coolant & waste metal working fluid

The main advantages of this technology are the very low energy requirement (60kWh/m3 of effluent or less), the ability to have high capacity machine (several m3 per hour) and the small footprint in relation to the capacity. However since the effluent vapour is in direct contact with the compressor it would not be recommended for certain applications (e.g. corrosion, explosive vapours).

MHD technology

Operating at atmospheric pressure, it offers a very respectable 160kWh/m3 of energy consumption, by implementing a clever energy recovery from the condensation of the vapour formed by mean of patented plastic heat exchangers.

MHD technology principle for evaporation of corrosive effluent to achieve Zero Liquid Discharge

Being all plastic means that this technology is adapted to highly corrosive effluent. An other advantage is its simplicity and low cost components. Finally, the energy can either be gas or electricity. Based on a modular design it has the disadvantage of its benefit : Whilst scaleable, it quickly require a large footprint for higher capacity.

Vacuum Evaporator with Heat pump

Operating at a near vacuum (<50mbar) allowing an operating temperature of 35 degresC, the energy consumption is in the region of 200kWh/m3. Fully enclosed there is no emission to atmosphere unlike the two above technologies. The evaporator can be made of very noble material (PVDF, titanium) allowing its application in highly corrosive application.

Vacuum evaporator to achieve Zero Liquid Discharge and concentrate recovery

ZLD and recovery using vacuum evaporator

The low operating temperature means that thermo sensitive compounds are not damaged. Consequently this evaporator is particularly adapted for application where the concentrate is valuable and can be re-used in the process.

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Aidan Kelly | Thermo-King - Group Leader
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... by the range of industrial pollutions we can address : pH, heavy metals, cyanides, hexavalent chromium, BOD, "Hard" COD, Fat Oil & Grease, suspended solids, sulphates, phosphorous, nitrates, Ammonia, and anything you can think of to challenge us.

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