• Hydrogen Generation Plant,
• Used Oils Hydrofinishing Plant,
• Amine Regeneration Plant,
• Sulphur Recovery Plant,
• Sour Water Stripping Plant.

High purity hydrogen is necessary for hydrofinishing process. The hydrogen is generated in the natural gas steam reforming process. The unit processes necessary to generate hydrogen are:

The sulphur contained in the natural gas may poison the catalyst in the reforming process and that is why it is to be removed. It is performed in a reactor with a catalyst bed on which the sulphur compounds are hydrogenated and then H₂S is adsorbed. The desulphurized gas is directed to a saturator where it is saturated with water. The process gas is directed to a convection reformer, where the proper hydrogen generation reactions take place on a catalyst. The heat exchange between combustion gases and the tubes filled with a catalyst in the reformer occurs by convection. The gas leaving the reformer contains also substantial amounts of CO, which is converted in the high-temperature conversion reactor to form CO₂ and additional amounts of hydrogen are generated at the same time. The synthesis gas obtained after water condensation is directed to PSA plant (molecular sieves). The waste gas from PSA is used as fuel for the reformer burner.

The Used Oils Hydrofinishing Plant lube oil fractions or diesel oil fraction obtained from the Used Oils Distillation Plant.

The feedstock is fed to the Hydrofinishing Plant from a proper storage tank to the feedstock tank on the plant. This oil mixed with fresh compressed hydrogen and the circulating hydrogen gas is heated in the process furnace fuelled with natural gas. The reacting mixture goes through a series of de-metallization and hydrofinishing reactors filled with catalysts.

The de-metallization reactor removes the hydrofinishing catalyst poisons (e.g.: silicon and metal compounds) The inlet temperature of this reactor depends on the kind of feedstock processed and the catalyst working cycle (average temperature is: 300⁰C - 340⁰C, and the reaction pressure ca. 5.5 MPa).

After the oil and hydrogen mixture passes through the protective de-metallization reactor bed, it is directed to the hydrofinishing reactor. The post-reaction mixture goes to the hot high pressure separator where it is separated into liquid and gaseous phases.

The gaseous phase contains mainly H₂, H₂S and CH₄ and after mixing with washing water and hydrocarbon washer it is entered into the column purifying the circulating gas. The gas from the washing column is sent to high pressure amine washing using bi-ethanoloamine in order to lower the H₂S concentration in it. The purified hydrogen is returned to the process. The be-ethanoloamine stream rich in hydrogen sulphide is transferred to the Amine Regeneration Plant.

The liquid phase from the hot high-pressure separator goes to the hot low-pressure separator and after light hydrocarbons are stripped, it is directed to the steam stripper. The stripper is equipped with a condenser, a reflux tank and a reflux and it separates the liquid and gaseous distillates and water-containing hydro-refining product. The hydro-refining product is then dried in a vacuum drying column and – after cooling – is sent to the tanks as a finished product.

The sour water generated in the process is continually sent to the Sour Waters Stripping Plant.

The Sour Water Stripping Plant is stripping the gases dissolved in the sour water in order to obtain the water of such quality which is suitable for further treatment in the waste water treatment plant and gas suitable for processing in the Sulphur Recovery Plant.

Before the water is directed to the waste water treatment plant, the sour water is sent to the stripping column where ammonia and hydrogen sulphide are separated using steam.

The gaseous product which comprises stripped gases and steam is transferred to the condenser to decrease the content of steam in the sour gas and then the product is sent the Sulphur Recovery Plant.

The sulphur-containing gas from the Hydrofinishing Plant is fed to a low-pressure absorber to be purified of H₂S by washing it with the bi-ethanolamine solution. The pure gas as a fuel gas is sent to be burnt in the hydrofinishing plant furnace.

The bi-ethanolamine from the high-pressure absorber of the circulating gas from the hydrofinishing plant and from the low-pressure absorber is fed to the regeneration column where the hydrogen sulphide is stripped away. The vapours from the top of the regenerator, after cooling and partial condensation, are separated in the reflux tank into sour gas and sour water which is returned to the column as the reflux. The sour gas is transferred to the Sulphur Recovery Plant.

The amine already without the hydrogen sulphide, from the regenerator bottom – after cooling and filtration on a mechanical filter and a carbon filter is sent back to the absorption process.

The gases coming from the Amine Regeneration Plant and from the Sour Waters Stripping Plant are fed to the Sulphur Recovery Plant.

This process comprises thermal combustion, two catalytic stages for the Claus reaction, the third catalytic process of Superclaus – the direct H₂S oxidation to obtain, and thermal afterburner.

The streams containing H₂S are mixed with air and sent to be burnt. H₂S is partially burnt in the burner to form SO₂ but the main part of H₂S reacts with SO₂ to form S. The precipitating sulphur is condensed in the steam heater. At this stage 60% of the sulphur contained in the feedstock is recovered. The gas leaving the heater contains a substantial amount of H₂S and SO2. The further transformation to recover sulphur is effected in two reactors with high-reactive catalysts. Before entering each of the reactors, the stream is heated to obtain the optimum temperature for the catalytic conversion. The gas from each reactor goes to the condenser and generated S is released through a hydraulic closing to a tank. At this stage 95% of the sulphur contained originally in the feedstock is removed. To recover 98% of the sulphur the third catalytic stage (Superclaus) is necessary. The gas from the third heater is mixed with additional air in a static mixer before the entrance to the Superclausa reactor. In this reactor H₂S is selectively oxidized to S. Next the gas goes through the final condenser where the sulphur is condensed.

The residual gas contain some amount of H₂S hazardous for the environment and that is why they are sent to a thermal afterburner.