Sulphur compounds in the fuels generate toxic and cancer causing pollutants when they are combusted. Even they create the life span of the catalyst used in petrochemical and chemical industrial reactors. One of the easy and simple ways to remove sulphur from them can be achieved by hydrotreating process.
In this process, hydrogen is allowed to react with sulphur compounds present in the process gas (naphtha) to form into hydrogen sulphide compound and H2S is distilled out from the naphtha continuously.Even diesel oil and kerosene can be desulfurized by this method. The main disadvantage of this technique is that it consumes more energy than the Zinc bed adsorption technique.
Brief description of naphtha hydrodesulfurization process:
Organic sulphur compounds in this form of thiophenes and mercaptans are not at all favorable in chemical reactors of petrochemical industries. Raw naphtha may contain sulphur about 200-300 ppm and vary based on refinery conditions. By catalytic reaction, hydrogen reacts with mercaptans like compound and takes out the sulfur bond in the compounds. Resulting H2S is easily distilled out using distillation column. Oxygen and nitrogen is aerated from naphtha in deaerator and passed to the packed bed reactor through effluent heat exchangers and fire heater to obtain the temperature of 380oC if the operating pressure is 29-30 kg/cm2.
The outlet of reactor is cooled by the effluent plate type heat exchangers and fed to separator. Unreacted hydrogen is recycled and remaining treated naphtha is fed to distillation column to remove H2S gas. This technique yields naphtha with sulphur content less than 0.5ppm. H2S is a corrosive compound, to protect the equipments anti corrosion solution is fed at top of the distillation column by a dosage pump.
Equipments involved in naphtha hydrodesulfurization continuous process flowsheet model:
- Distillation column
- Packed bed reactor
- Fired heater
- Plate and frame heat exchanger
- shell and tube heat exhanger