Reducing energy costs during solvent regeneration at the tar deasphalting unit

Abstract

For propane tar deasphalting units, a rather high energy intensity of the technological process is characteristic. In order to reduce it, an assessment was made of the possibility of reducing the steam consumption during the regeneration of propane from asphalt solution. The study was carried out using a Honeywell UniSim Design modeling system, in which a model of a propane tar deasphalting unit was formed. The Peng-Robinson method was used as a mathematical package for calculating the thermodynamic properties of the components of the fractions. The component composition of the feedstock is represented by oil fractions with boiling points from 405 to 616 °C. When carrying out a computational experiment, the following values of technological parameters were used: the tar consumption was 38.9 t / h, the ratio (propane: raw material) was (6.4: 1), the yield of deasphalted oil was about 30 wt%. The performed analysis of a typical scheme for the regeneration of propane from asphalt solution showed that in the process stream supplied to the feed of the stripping column K-6, there is already a sufficiently large amount of a vapor phase consisting practically of propane and traces of oil fractions. To efficiently use the energy of the flow without attracting additional energy costs, it is advisable to separate the gas and liquid phases before they enter the column K-6, that is, to include an additional separator in the technological scheme before it. The performed computational experiment showed that in the proposed version of the technological scheme, the steam consumption required for the release of propane decreases by 17.5%, which, accordingly, for the subsequent devices of the scheme, reduces the amount of water discharged into the sewage system. Optimization of technological modes of the stripping column K-6 provides a clear separation of propane, in the flow of which the content of bitumen fractions is 0.03 mol%, which makes it possible in industrial conditions to return the flow of propane to the feed of the extraction column. The proposed technological solution for propane recovery can be used in the processes of one- and two-stage tar deasphalting.