Evaporation

Mechanical vapour compression (MVC) or mechanical vapour recompression (MVR) reduces vapour consumption, replaced by a source of electrical energy, resulting in a very low operating cost compared to a multiple effect operation.

The vapour produced by the evaporator is sent to a MVC installation, to be compressed and heated up.

It is then resent to the evaporator to the outside of the tubes to be used as a heating steam. In this process, the evaporator is also used as the condenser for the vapour evaporation.

The main advantage of the Mechanical Vapour Compression technology is its low operating costs.

Energy consumption per tonne of evaporated water:

• MVC: ~ 15 kW.h / hr electric   
• Single effect: ~ 630 kW thermal   
• Triple effect: ~ 230 kW thermal   
• Six fold effect: ~ 115 kW thermal   

Cost reduction

• Vapour consumption almost zero
• Low consumption of cooling water
• More compact layout, compared to a multiple effect evaporator (a MVC evaporator is composed of a single evaporation body and a compressor)   
  
  

Simplicity, responsiveness and flexibility of operation

The compressor is driven by a frequency inverter, which enables the implementation capacity to be finely and quickly adjusted from 30% to 100% of the maximum capacity.

Adaptation to production constraints

The MVC/MVR technology makes it possible for several compressors to be used in series in order to respond to constraints (significant boiling delay, decrease in exchange surface, etc).

Reliability

If properly sized and installed, MVC/MVR processes are very reliable. We have been using this technology for over 20 years, maintenance costs are extremely low on the compressors we use.

To ensure this reliability, we anticipate:

• A largely sized separator, which allows maximum separation of evaporation vapour and avoids provoking product droplets in the MVC, in order to ensure the fan's lifespan.
• Among our facilities, in addition to the separator, a vapour scrubber cleans the evaporation vapours and helps deconcentrate any remaining product droplets to preserve the blower mechanism. It also helps in countering foaming.
• On the outlet of the scrubber, a mist eliminator prevents possible droplets
• Many additional securities to monitor and ensure the proper functioning of the installation: levels, temperatures, vibrations, etc.   
  
  

This technology is particularly suitable for viscous and sensitive liquids, having a substantial proportion of dry matter. It is reserved for processes which require a small amount of evaporation compared to the inflow.

The process

The liquid is sent to a separator at a lower pressure than the product's boiling temperature. With this process, a rapid decrease in temperature of the product and water evaporation could be obtained.

No clogging

Flash-cooling produces partial water evaporation without putting the product in contact with an exchange surface or another element likely to transmit energy. There are no clogging problems.

An additional method

With flash-cooling, evaporation takes place and the product is cooled. In addition to another evaporator, it is often used to finish the concentration and reduce the temperature of the concentrated product.

The forced circulation evaporator comprises a heat exchanger, a separator and a circulation pump.

The product is sent to the exchanger where it is heated and then sent to the separator. After evaporation, the liquid portion is pumped again to be resent to the exchanger.

The forced circulation evaporator is great for the following applications:

Insensitive to clogging

The circulating pump ensures high speed in the exchange tubes, reduces the amount of deposits on the walls and prevents evaporation, thus the risk of over-concentration.

Suitable for use with suspended materials

For products close to crystallisation, unlike the falling film evaporator, the forced circulation evaporator can work with suspended particles or the presence of crystals, without obstructing the exchange tubes.

Financial impact

The initial investment and the footprint of these facilities is higher than in the case of a falling film evaporator, which will often be preferred.

The falling film evaporation technology has several economic and industrial benefits. The capacity of these units can range from 10 k/hr to more than 100 t/hr.

Smaller footprint

Falling film evaporators are installed vertically installed and have a small footprint. In addition, the separator can be easily integrated into the evaporator to further reduce the floor area used.

Low residence time

The product flows by gravity in the exchange tubes by creating a thin liquid film on the inner walls. By varying the liquid's speed, it is possible to control the thickness of this liquid film and thus reduce the product's residence time.

Reduced operating cost

Pumping costs per tonne treated with a falling film evaporator are much lower than those for a forced circulation evaporator.

Reduced investment

The construction cost of a falling film evaporator is lower, notably due to a compact design (separator and scrubber in a single block) and the absence of structural costs.

Low foaming

The falling film evaporator is great for products sensitive to foaming.

Greater sensitivity to clogging

The falling film technology is more sensitive to clogging, especially compared to forced circulation evaporation.

It is not recommended on the clogging products, close to crystallization or viscous.

The multiple effect evaporation processes can optimise the energy efficiency of facilities through the recycling of vapour.

Functioning

The vapour supplied during the first effect produces the vapour at a lower pressure. These vapours are then used in a second effect as a vapour heating steam.

The number of effects vary and can go right up to 8. The number of effects is chosen according to the investment and operating cost.

The vapours at the outlet of the last effect should be condensed.

Suitable for any type of evaporator

The multiple effect evaporator can be made up of falling film, forced or flash-cooling circulation evaporators.

Application

This technology is great when the cost of vapour is low.