Vacuum evaporators, also know as wastewater evaporators, are one of the most effective technologies for the minimization and treatment of industrial wastewater. The technology is clean, safe, very versatile and has a very low management cost. In many cases, it can also lead to a treatment system with zero discharge.
Vacuum evaporation is one of the most competitive and efficient techniques for treating aqueous effluents when conventional techniques are not effective or feasible. It transforms waste effluent into two streams, one of concentrated waste and another of high quality water. The evaporators work under vacuum, so the boiling temperature of the liquid effluent is lower; thus saving energy and improving efficiency.
Wastewater evaporators are a key technology for implementing a zero discharge system, where waste effluent is transformed into solid waste and high quality water, all of which can be reused.
Depending on their different uses or geographical criteria, vacuum evaporators receive different names: e.g. vacuum distillers, vacuum concentrators, water evaporators or industrial evaporators.
The Condorchem Envitech Vacuum Evaporator range covers the three main types of equipment, which have a robust and simple operation, occupy little space and constitute clean and safe technology. In addition, all equipment is highly automated, requiring minimal supervision.
The following can be found for the effluent heating system:
Operation of this system is based on the refrigeration cycle of gas contained in a closed loop. The refrigeration gas is compressed by a compressor, as a result of which its temperature and pressure increase. It then circulates through the heat exchanger of the evaporator itself, heating the feed. As the system operates under vacuum, the boiling temperature is around 40 ºC.
The refrigeration liquid leaves the evaporator’s exchanger and is decompressed and cooled using an expansion valve. Passage through a second heat exchanger (the condenser) causes the vapor formed in the evaporator to condense and its temperature to increase immediately prior to passing through the compressor again, thus repeating the cycle.
The same refrigeration fluid allows the feed to be evaporated and the vapor generated to be condensed, therefore the system does not require any other heating or refrigeration source. This means that the process is highly advantageous from an economic and management viewpoint.
This technology is based on recovery of the heat of condensation of the distillate as a heat source for evaporating the feed. To this end, the temperature of the vapor generated upon evaporation is increased by mechanical compression.
Upon passing through the exchanger of the evaporator itself, this compressed, and therefore superheated, vapor has two effects: (1) it heats the liquid to be evaporated and (2) it condenses, thereby reducing the need for a refrigeration fluid.
This technology comprises a series of mutually connected evaporators in which the vacuum steadily increases from first to last. This means that, in principle, the boiling temperature decreases, thus allowing the vapor generated in an evaporator (or effect) to be used as heating fluid in the following effect.
Its main advantage with respect to a single evaporator is the saving in both heating fluid and refrigeration fluid. This is one of the economically most competitive options for treating high flows.
Vacuum evaporation is a simple process of high energy efficiency, i.e. low energy consumption and it is practically maintenance free. Normally, evaporation is preceded by other concentration technologies, such as reverse osmosis, for treating large volumes of waste water.
The basic operation is very simple and is based on bringing the effluent to its boiling point, which is around 40°C when working under vacuum conditions. When the effluent begins to boil in the evaporator boiler tank, the steam condenses and is withdrawn from the system as more effluent is fed into the boiler tank. The effluent must be preheated before being fed for the evaporation process to continue. The technology used to pre-heat the effluent before reaching the tank constitutes the main difference between the different types of vacuum evaporator.
Treated water (distilled) that has been extracted from the liquid waste is of high quality and can be recycled in the plant for various applications (e.g. production and refrigeration); thus reducing the consumption of drinking water.
The application of evaporation technologies for treating industrial liquid waste where it is produced has a series of advantages. Firstly, the waste can be minimized by concentration, thus significantly reducing its management cost. In some cases, it is possible to evaluate the concentrate itself for possible re-use in the same process or in alternative applications. Minimization at the point of origin also reduces the need for storage of large volumes of hazardous waste in industrial sites, and reduces the risk of spills caused by accidents during the transport of liquid waste. Finally, it contributes to a reduction in greenhouse gas emissions produced when transporting the waste.