Procedure description Waste Water- and Process Water Treatment

The FIDI vacuum evaporator for waste water processing shows that it is possible to produce goods (e.g. in the galvanisation process) and to reduce the volume of waste water while at the same time cutting the burden on the environment.
The use of a vacuum evaporator is an advantage for the environment, and in practice results in a reduction of current or expected residue disposal costs. Vacuum evaporation technology is a process that has been used for decades by the chemical industry.

However, traditional distillation systems require extremely complex installations and very high energy costs, which is why the evaporation process is uneconomical in most cases. On the other hand, vapour compressors are obliged to operate at high temperatures, leading automatically to corrosion and encrustations on the heat exchangers in the absence of pretreatment, which again involves costs.

The structure of the FIDI vacuum evaporators is based on the tried and tested technology of the heat pump combined with a vacuum, using an innovatory arrangement on the boiling and condensation side to ensure an even more gentle distillation process, a higher yield from the water, a higher degree of concentration and a significantly lower consumption of energy as compared with other products.

1) Refrigerant compressor
2) Boiling chamber
3) Condensation chamber
4) Destillate tank
5) Venturi jet
6) Concentrate pump
(or drain tap)
7) Vacuum pump
8) Heat exchanger

As is well known, water boils at approx. 100°C; the lower the ambient pressure, the earlier water will boil and evaporate, since the air resistance is lower. Under a vacuum (residual pressure) of approx. 40 mbar, the boiling point of water is only approx. 30°C.

Boiling temperature plays a major role in chemistry, the lower it is, the lower is the risk of decomposition in the case of many products. At the same time, encrustation is considerably cut back.

A sturdy water jet pump (7) combined with a Venturi injector (5) are responsible for creating the vacuum. The required heat and cold are provided by an integrated heat pump (1) (compressor and refrigerant). The compressor (1) compresses a gas mixture (refrigerant), heating it to a temperature of approx. 70°C. The compressed gas is pumped into the coil and the heating jacket of the boiling chamber (2). This coil acts as heat exchanger. Since it is submersed in the liquid to be concentrated, it transmits practically the whole of the heat 01 the compressed gas to the liquid.

The liquid (contaminated water) in the boiling chamber (2) begins to boil when the specified temperature and the vacuum are reached. This is the first distillation effect - water from a liquid to a vapour condition. After almost all the heat has been conveyed into the boiling chamber, the refrigerant must be cooled further; this task is carried out by the air-cooled or water-cooled heat exchanger (8). After emitting its residual heat, the refrigerant is transported to the coil of the condensation chamber (3) and vaporised by means of an expansion valve inside the cooling coil.

The expansion (evaporation) of the refrigerant "generates" cold by means of the reverse compression effect. The water vapour that has formed in the boiling chamber now moves to the cold area of the condensation chamber (3), and condenses, becoming liquid when it touches the cold surface of the coil.
The liquid is sucked up by the Venturi jet (5) (vacuum cycle) from the floor of the condensation chamber (3) and conveyed to the distillate tank(4).

The vacuum cycle takes place in the distillate tank (4), and has the dual function of generating a vacuum of approx. 30-40 mbar residual pressure inside the boiling chamber and a pressure of approx. 0.2 bar inside the distillate tank (4), in order to permit the recovered distillate to be output without the use of an additional pump.

This distillate is either returned to the process or fed to the sewers after final inspection. The degree of concentration of the residues in the boiling chamber is determined by time or density measurement. After the process is complete, the concentrate can be removed from the machine automatically by a concentrate pump (6) or manually by means of a drain tap or a flap in the floor. This concentrate is either returned to the process or disposed of externally.

The refrigerant compressor (1) and its cycle is enclosed and self lubricating. Its working life corresponds with that of a normal air conditioning system or refrigerator, or even longer, given that it is rarely switched on and off.