12.1 Introduction

In this lecture, we present a brief overview of the refinery supporting processes.

If we analyze the petroleum refinery, other than hydrocarbon balances, two other components balances need to be considered.

These are sulphur and hydrogen.

It is a fact that the refinery has good number of hydrotreaters which needs to be fed with hydrogen to generate the H₂S. This hydrogen is primarily generated from the catalytic reforming unit.

Now the question that are posed in the refinery are

• 
  • How to handle H₂S for following environmental legislations.

• How to purify the reformer H₂ gas stream to meet the required inlet specifications in various hydrotreaters, hydrocracking and isomerisation units.

• How to produce H₂ additionally, as the reformer off gas may not be able to meet the H₂ demands in various hydrotreaters.

When the above question is answered, in due course, we get the two major supporting processes.

• • Hydrogen production and purification process.

• Sulfur recovery process.

We first discuss hydrogen production and purification process followed with the sulphur recovery process.

 

12.2 Hydrogen production

Hydrogen can be produced in many ways namely.

• • Partial oxidation of heavy ends.

• Steam reforming of various product stocks.

• Methane steam reforming.

Amongst these, methane steam reforming is more famous for hydrogen production.

Depending upon the process, the hydrogen production consists of four basic reactions.

• • Reforming: Here, methane reacts with water molecules to form CO and H₂ at about 20 bar and 800°C. The reaction is endothermic.

• CO shift reaction: In this reaction, CO is converted to CO₂ and H₂ by reacting with water. The reaction is usually carried out on a catalyst. There are two types of shift reactions namely high temperature shift or low temperature shift. In the high temperature shift, the reaction is carried out on iron oxide or chromia catalyst at about 350 – 550°C. In the low temperature shift, the reaction is carried out at 200 – 250°C using copper or zinc oxide on alumina.

• Gas purification: The CO₂ is separated by passing the product gases through amine scrubber.

• Methanation: The remaining CO₂ and CO are converted back to methane using nickel-alumina catalyst in a reversible reaction scheme at 400°C.