Vacuum distillation
Wherein the vacuum distillation is a distillation, at reduced pressure (vacuum) is performed. Thus, the boiling temperature of the fluids to be separated is reduced. The vacuum distillation represents a gentle separation process so that materials can be separated, which would decompose at elevated temperatures (eg, extraction of herbal essences ). It has been used for example in separating long-chain hydrocarbons in the petroleum refining.
Distillation parts
In the vacuum distillation, a distinction between the vacuum products and vacuum distillates. It must also be made between continuous ( oil) and discontinuous mode of operation. Must Like the atmospheric distillation methods, nor between the simple vacuum distillation ( DC method, usually discontinuous, vacuum distillate overhead, possibly trappable in several fractions ) and vacuum rectification ( countercurrent process, discontinuous and continuous) are differentiated. The vacuum bottoms is the part that under the given conditions ( temperature, pressure) does not evaporate (see below). The vacuum distillate is - similar to the "simple" atmospheric distillation - taken off as overhead product. In continuous processes, the vacuum distillates are withdrawn as side cuts ( fractions) (as in the continuous atmospheric rectification). Vacuum columns usually contain so-called structured packings as internals, no trays.
Vacuum distillation in the processing of petroleum
The oil processing used in the atmospheric distillation temperatures of 370 ° C. A further increase in temperature would lead to decomposition ( cracking) of the constituents of crude oil. The bottoms from the atmospheric column, the atmospheric residue (English: Long Residue, LR) is, therefore, a vacuum distillation (actually a continuous fractionating vacuum rectification ) and is there in vacuum gas oil (s ) and vacuum residue (English: Short Residue, SR ) divided. The vacuum distillation ( rough vacuum, 10-30 mbar ) are - compared with the atmospheric distillation - at slightly elevated temperature. The vacuum gas oil (VGO) is normally supplied to an FCC unit or a hydrocracker (HCU ), where light hydrocarbons can be produced. The vacuum residue is used directly as bitumen, heavy mixed up to heavy oil or fuel oil or also cracked in thermal cracking plants to light hydrocarbons. The vacuum residue may appear in a deasphalting unit (English: Solvent Deasphalting, SDA) and extracted into the components deasphalted oil (English: deasphalted oil, DAO) and asphalt (English: asphalt ) to be separated.
A vacuum fractional distillation with a plurality of ( narrow ) the fractions is used in the production of so-called base oils for the production of lubricating oils.
Mild vacuum ( 300-500 mbar) in the separation of heavy boiling Naftakomponenten (eg C8/C9-Trennung ) used to lower the temperature level in the distillation process. This can energetically more favorable heat transfer media are used (eg, medium-pressure steam / ca. Instead of 20 bar high pressure steam / ca. 40 bar).