ATR designs and supplies evaporator units of borosilicate glass from laboratory and pilot plant size right upto complete production plants. During thermal treatment, heat- sensitive products can suffer considerable losses of quality, the degree of which depends essentially on the treatment time and the temperature level.
Units for gentle evaporation of heat-sensitive substances must therefore meet two main requirements:
Operation in vacuo allows the working temperature to be lowered. A short residence time of the medium us most advantageously achieved in film-forming apparatus designed for vacuum operation. An effect on the boiling point due to the hydrostatic height of the liquid is avoided in this case. In addition to the proven falling-film evaporator with free-flowing liquid film, ATR offers borosilicate glass thin-layer evaporators in this field
The use of the thin-layer evaporator is advisable particularly for difficult evaporation problems, for example the working-up of the extract solution from solids extraction by the Soxhlet principle or for treating liquids of high viscosity. For example in the case of vitamins, hormones, enzymes or aroma substances, chemical changes having an adverse effect on the product quality can be avoided.
The wiper system produces a thin, thoroughly mixed product film on the evaporator surface. Depending on the feed rate, the viscosity and the speed of rotation, the thickness of the film is 0.1mm to 2 mm. This results in a short residence time for the medium, with the narrow residence time spectrum, within the working range of the evaporator. At the same time only very small temperature and concentration gradients arise in the thoroughly mixed film, that is to say the liquid vaporises immediately after it has absorbed the energy. In addition due to the turbulence in the bow wave in front of the wiper (peripheral speeds of upto 2.8 m/sec) and due to the continuous circulation, the heat transfer is improved. The light volatile substance does not need to reach the film surface by mechanical circulation, and the evaporator wall is kept largely free of deposits and encrustation.
In the chemical and pharmaceutical industries, circulation evaporators form part of the standard equipment for thermal separation of materials. ATR supplies circulation evaporators with Glass coil heat exchangers, basket type or bayonet –type heaters of corrosion resistant metals, block heat exchangers and annular- grove heat exchangers of graphite and with Glass shell and tube heat exchangers especially for use as heaters.
Different types of construction of the circulation evaporator allow adaptation to the process requirements, and the type most frequently encountered is a shell and tube heat exchanger with circulation. Due to the thermos-syphon effect (natural circulation) or by means of a centrifugal pump (forced circulation), a turbulent fluid flow along the evaporator surface is produced. This flow is a necessary condition for good heat transfer between the heating medium and the product to be evaporated. Depending on the type of heating, two different types of Glass shell and tube heat exchangers of glass can be supplied.
Heating with low pressure steam or heat transfer oil, a heater with a glass shell and PTFE tube plates was developed, based on the shell and tube heat exchangers proven over many years. The external diameter of the evaporator tubes is 14mm. To improve the heat transfer in operation with heat transfer oil, baffle segments are provided in the shell space.
Heating with saturated steam (6 bar max.), a heater with a steel shell and steel/PFA tube plates is available. The evaporator tubes of 20mm external diameter are sealed in the tube plates by pressure-tight gland packing. Baffles in the shell space are not envisaged for this type. In both cases, the product flows through the tubes, and the tube length is 1000mm as standard. The small volume of this arrangement results in a correspondingly short residence time of the product in circulation and thus meets any important requirement for the mild treatment of temperature-sensitive substances.
Circulation Evaporators are standard equipment in the chemical and pharmaceutical industries for the thermal separation of materials. ATR designs and supplies circulation evaporators with Glass shell and tube heat exchangers, basket type or bayonet-type heaters of corrosion-resistant metals and block heat exchangers and annular-grove heat exchangers made of graphite.
Different design types of circulation evaporators allow adjustment to the process requirements. A turbulent fluid flow along the evaporator surface is generated due to the thermosiphon effect (natural circulation) or by means of a centrifugal pump (forced circulation). This flow is a prerequisite for good heat transfer between the heating medium and the product which is to be vaporised.
The circulation evaporators are individually designed in accordance with the applicable operating conditions. This comprises both the sizing and the selection of suitable heating materials, for example stainless steel, titanium or tantalum.