Selection of the evaporating agent of the partial topping tower

The operation of the primary oil refining unit significantly affects the technical and economic indicators of the oil refinery. One of the most common options for the technological scheme of the installation provides for partial topping of oil in column K-1 with its further fractionation in the main atmospheric and vacuum columns. The separation of the gasoline fraction in the K-1 column is possible using various evaporating agents - water vapor, the reflux of the main atmospheric column, kerosene or diesel fractions. The paper evaluates the possibility of using the C1 ? C4 gas fraction obtained from delayed coking and gas fractionation units as an evaporating agent on column K-1, as well as after separating the gas-liquid flow from the top of column K-1. The studies were carried out using the Honeywell UniSim Design modeling system. To calculate the thermodynamic properties of the components of the fractions, the Peng-Robinson method was chosen. The calculations were carried out when considering two different oils as raw materials, which have significantly different contents of gas and gasoline (end boiling point 180 ° C) fractions in them. In the crude oil-1, their potential amount is 0.204 of the total volume, and in the oil-2 stream - 0.065. The operation of a typical column for partial topping of oil is simulated, containing 22 trays (contact device efficiency 0.7), feedstock is fed to 13 (the main amount of 479 t / h) and 18 trays (10 t / h) with a temperature of 232 ? and a pressure of 517.1 kPa, the pressure of the top and the bottom of the column is 280 and 294.2 kPa, respectively. The active specifications, according to which the Honeywell UniSim Design environment ensures the convergence of the calculation processes, are reflux R = 0.1 and a fixed withdrawal of distillate (17% of the potential content in oil), which is 15300 kg / h for crude oil-1 and 5000 kg / h when using raw oil-2. The flow rate of evaporating agents supplied to the bottom of the apparatus was 6000 kg / h. When calculating columns with different evaporating agents, the achieved estimates of the content in the distillate of the gasoline fraction with the end-boiling point of 180 ° C were evaluated and compared. Calculations have shown the possibility of using the C1 ? C4 gas fraction as an evaporating agent, which, in terms of its thermophysical parameters, occupies an intermediate value between the use of water vapor on the one hand and the use of a gasoline or kerosene-gas oil fraction on the other.