Refinery equipment

On the road to cleaner diesel

As limits on sulphur in fuels have tightened over the years to fight pollution, Shell has steadily improved refining equipment to produce cleaner diesel.

All crude oil contains some sulphur. To remove it, refineries combine partially refined oil with hydrogen under high pressure and pour the mixture over catalysts to convert sulphur into hydrogen sulphide. It is then absorbed by solvents and separated from the oil.

To help meet ever-tighter standards, Shell researchers redesigned equipment inside refinery reactors, the large steel vessels where catalytic reactions occur. The changes also made reactors more reliable and helped improve catalyst efficiency, lowering costs.

In earlier designs, the oil trickled down from small pipes held by a horizontal plate in the top of the vessel, coming into contact with 80-90% of the catalysts. However, that approach would have made it prohibitively expensive to meet new standards in Europe and the United States – which allow only traces of sulphur – because the catalysts would have needed frequent changing. As a solution, Shell developed a distributor with nozzles that spray the oil uniformly so that it comes in contact with 100% of the catalysts. The new design extends the catalysts’ life, reducing both the amount of catalysts needed over time and the number of costly shutdowns required to replace them.

Shell also installed equipment lower down in the reactor to inhibit overheating, which can shorten catalyst life. Cool hydrogen is introduced into horizontal disk-shaped plates inside the vessel to keep the temperature below 400°C (752°F). Both the cooling disks and nozzles are compact designs, leaving more room for catalysts inside the reactors. Shell carried out over 200 projects over the past 15 years to upgrade refinery units or build new ones with these designs. More than two in three were third-party plants.