Techno-economic evaluation of quality improvement of heavy gas oil with different processes

• Investigation of hydrotreating of heavy gas oil is in one-stage and two-stage.
• Conditions for removing of sulphur and aromatics were not coincided in one-stage.
• Conditions for removing of sulphur and aromatics were coincided in two-stage.
• Hydrotreatment ensured high reduction in CO, HC and PM emissions.
• Emission estimation can be used to benchmark process alternatives.

Nowadays, high quality diesel fuels can only be produced by the hydrotreatment of various refinery streams. Preparing catalytic experiments and process engineering calculations are inevitable for selecting the most technically and economically appropriate process. There is limited information in the free literature about the complex approach of hydrotreating processes that deal with both the catalytic and process issues. This paper summarizes the results of an engineering study to evaluate the techno-economic feasibility of different types of hydrotreating processes for producing high quality gas oil blending components from heavy gas oil fraction. Hydrotreatment of feed in one-stage on nickel(Ni) molybdenum(Mo)/alumina and in two-stage on NiMo/alumina followed by on platinum(Pt) palladium(Pd)/zeolite catalysts were investigated. In one stage hydroprocessing sulphur and polyaromatic contents of the products met the requirements of the standard only if strict process parameters were applied (temperature > 370 °C and Liquid Hourly Space Velocity < 1.5 h−1) which resulted in operation problems and product loss, moreover the advantageous process parameters of hydrodesulphurization and hydrodearomatization did not coincide. In two-stage hydrotreating results showed that the advantageous process parameters for reduction of sulphur and aromatics coincided. Advantageous process parameters to produce gas oil of quality meeting the requirement of the standard were determined. Based on the experimental results model for both alternatives was prepared, and heat and material balances were determined. By applying two step hydrotreating, the yield of gas oil having low sulphur and aromatic content was 6.2% higher than that obtained in one step. Heat exchanger network analysis and sizing of main equipments were accomplished. Operating and investment costs were estimated for both processes, which showed that all the cost elements were higher for the two-stage process. But it provides the following advantages in comparison to one-stage process: higher yield of gas oil, better product quality allowing the application of low value hydrocarbon streams in higher quantity at the blending, the lower density of products would be the source of extra profit due to diesel fuels are sold on volume basis at the petrol stations. Estimation of emission potential of feed and products was prepared, too. This showed that the hydrotreating of heavy gas oil contributes to significant reduction in emission of particulate matter, hydrocarbons and carbon monoxide, but the effect on the emission of nitrogen oxides was scarce. Product of two-stage process provided considerably greater decrease in carbon monoxide and hydrocarbon emissions comparing to the one-stage alternative (52% vs. 14% and 54% vs. 14%). Consequently, the estimation of emission potential of hydrotreated products can be used as one of the parameters for selecting between various process alternatives.