Vaporization Plants and Evaporation Plants
Ebner plans, designs and builds evaporation- and vaporization plants for concentration of solutions, inorganic and organic substances. Evaporation- and vaporization plants may be operated under overpressure, normal pressure or vacuum.
• circulation evaporators with or without forced circulation
• falling film evaporators
• vapor compression evaporators
• flash evaporators
Substances which are evaporated in Ebner plants
• ammonium rhodanide solution
• ammonium sulfate solution
• aluminat liquor
• aluminium sulfate solution
• calcium chloride solution
• cellophane bath
• filament fiber spinbath
• iron sulfate solution
• mixed bath
• normal fiber spinbath
• oil mixtures
• pickling baths
• polynosic fiber spinbath
• potash magnesia solution
• sodium carbonate solution
• sodium chloride solution
• sodium sulfate solution
• sodium sulfite solution
• special fiber spinbath
• titanium dioxide solution
• waste waters
• zinc chloride solution
In circulation evaporators the solution to be evaporated circulates in each stage through one or several heaters which are usually located outside the evaporator and are designed as tubular heat exchangers or plate heat exchangers. The circulation is effected either by the thermo syphon effect (natural circulation) or by outside effect, i.e. circulation pumps or air circulation (forced circulation).
In order to reduce the steam cost, especially at large evaporation capacities, circulation evaporators are also designed multi-stage.
Falling film evaporation
Compared to circulation evaporators falling film evaporators preferably find application at evaporation of heat-sensitive solutions and solutions which are not susceptible to incrustation. In falling film evaporators the solution flows downwards. In the head of the evaporator the solution is evenly distributed through a proper device over each heating tube and is led on the inner surface of each tube and flows as a thin liquid film downwards. The tubes are heated with steam and the evaporation takes place. The vapour and the solution run in parallel flow downwards. The concentrated solution and the vapour are separated in the vapour chamber in the bottom by means of separators of special design.
Falling film evaporators may be designed single-stage or multi-stage.
Vapour compression finds application as well.
Today the flash evaporator is the most cost-effective type of evaporator regarding the operation cost.
Unlike conventional circulation evaporators each stage of which has its own heater circuit, the flash evaporator has several stages and heaters which are installed circulatory; however the investment cost are quite considerable and this type of evaporator is suited for operation capacities of more than abt. 5 t/h.
The solution may be fed into any stage of the evaporator and also drained from any stage, i.e. in EBNER plants the outlet temperature is allowed to be higher than the inlet temperature. The specific steam consumption of flash evaporation plants is low. The consumption depends on both, the number of stages and the total temperature drop in the evaporator stages.
Vapour compression evaporation
If the temperature difference between the heating medium and the solution to be evaporated shall be low in order to avoid an overheating of the solution, the plants should be operated with vapour compression. Depending on the cost ratio between steam and electric power, the following methods may be applied:
Thermal vapour compression:
A steam ejector sucks in a part of the vapour which develops during evaporation, compresses it by the aid of live steam to a higher pressure and temperature and leads it back into the heater of the evaporator to serve as heating steam. Thus the heating steam consumption can be reduced under the steam consumption of a two-stage circulation evaporation plant.
Mechanical vapour compression:
If the cost of electric power are lower than the cost for the production of steam it is advisable to operate the vapour compression by means of electric power. A mechanical turbo compressor does the compression work. In this case live steam is only needed for starting of the plant. Besides single-stage radial compressors also multi-stage machines and axial compressors may find application.
Vapour compression may also be applied in multi-stage evaporation plants and evaporation crystallization plants.
Evaporation plant for radioactive contaminated waste water
At dismantling of a nuclear power station the contaminated equipment is hackled and after that decontaminated. In general this is achieved by means of washing the components thoroughly. In doing so, radioactive contaminated waste water comes into existence which is treated in an evaporation plant. At present Ebner plans, supplies and installs such a plant for a nuclear power station located in Germany being dismantled currently. The purpose of the evaporation plant is to clean the waste waters to such an extent that a re-use or a delivery of the distillate to the discharge system is possible in compliance with the regulations. The waste water volume is reduced up to a minimum; this results in a considerable decrease of the disposal costs. The waste waters are stored in raw water tanks and evaporated in the evaporation unit after pre-treatment. In this case the salts and solids contained in the waste water are thickened to a concentrate by extraction of water. The concentrate is fed from the evaporator into concentrate tanks and subsequently delivered to the drying unit for further treatment. After drying the residue is stored in disposal sites either for intermediate or final storage. The evaporated vapours are led through drop separators and re-cleaned in a column since an high econtamination value (10 ) in the vapour respectively in the distillate must be kept. In the following the condensation of the vapours takes place in a surface condenser by means of cooling water. The distillate is fed into the distillate tank and re-used as flushing water or supplied to the discharge system after an analysis has been made and the release has been given.
The plant is projected for continuous operation. For the design of the plant great importance was attached to highest level of operational reliability and high degree of automation.