Nearly every person has already had some experiences with vacuum in his life – by using a vacuum cleaner for cleaning their home. Vacuum (from Latin vacuum = emptiness, empty room) itself is every pressure below the atmospheric pressure of 1013 mbar(abs). Even the Greek philosophers were already thinking about the term “vacuum”.
However, the history of physical vacuum R&D goes back to the 17th century. Nowadays, there are different increments of vacuum ranging from low vacuum, fine vacuum, high vacuum, ultra-high vacuum, extreme ultra-high vacuum to ideal vacuum. econ uses low vacuum (1013 – 1 mbar(abs)) in its VacuDry® plant design in order to reduce the effective boiling temperature of the evaporating contaminants of industrial waste streams. This kind of process is also known as vacuum distillation.
A reduction of boiling points has two benefits. First of all, lower heating temperatures and with it less energy are required in order to clean up industrial waste. For example, in the field of drill cuttings treatment drilling fluids can be recovered at lower temperatures, the thermic stress is lower and therefore the recycle rate of the drilling oil is higher.
The second benefit is the range of industrial waste, which can be treated in the VacuDry® plants. Under atmospheric pressure the maximum evaporating temperature would be limited to approx. 350 °C. By applying vacuum (~50 mbar(abs)) on the vacuum dryers the effective evaporating temperature increases to 450 °C, although the heating temperature is still the same. This e.g. results in better clean up rates of mercury contaminated soil and increases the treatment range to e.g. tank cleaning sludge or sludge from oil lagoons.
Another benefit of vacuum is process safety. During an explosion the pressure increases to values ten times bigger than the pressure at the beginning of the explosion. If the initial pressure is lowered because of vacuum, the maximum pressure in case of an explosion is also lowered. 100 mbar(abs) increase to 1000 mbar(abs), which is atmospheric pressure. In addition, the possibility of an explosion is reduced under vacuum as well.
Vacuum also increases the environmental safety of the VacuDry® plants. In case of a leakage, process media will not exceed into the surrounding atmosphere. Instead, surrounding atmosphere will be sucked into the plant. This strong argument for process safety can be quoted whenever it comes to plant authorisation according to environmental law.
The selection of the appropriate vacuum generation system depends on the properties of the input material. econ industries usually uses dry working screw vacuum pumps for generating the vacuum in its VacuDry® plants. However, also other principles like steam injector vacuum pumps or oil lubricated rotary slide vacuum pumps are possible.
By contrast, vacuum in combination with high temperatures also put some challenges on the plant design. Every connection – no matter if static or moving – within the vacuum area of the plant must be tight against vacuum and every vessel must withstand lowered pressure as well as high temperatures. The answers for these challenges are special designed vacuum slide valves, floating stuffing box bearings and vacuum dryers.