Lesson 10 Overview

PRESENTER: Now, this is the last kind or the fourth kind of processes found in a petroleum refinery, the supporting process. Interestingly enough, you will see that we also make a product here, another product that the refinery could sell, a byproduct, if you will, to make revenue for the refinery. So supporting processes make sure that the refinery could actually run.

It's not a huge chemical conversion process, if you will, that have to do with making the desirable hydrocarbons. But the principal supporting process is acid gas recovery and sulfur recovery or acid gas removal and sulfur recovery. What is acid gas? Well, H2S is the principal acid gas that is produced in a refinery from the hydro treatment processes.

Remember, we remove sulfur from the fuels, from the fractions of crude oil as hydrogen sulfide. Hydrogen sulfide is an acidic gas. So it needs to be removed from the rest of the gases, typically, methane, ethane, that come with hydrogen sulfide to the recovery or the removal acid gas removal process.

And we use a basic solvent to capture the acid gas, particularly hydrogen sulfide. So it's essentially an acid based interaction. We can use ethanolamine as a base in a solvent extraction process and in a liquid extraction process to remove high H2S, hydrogen sulfide, from methane, ethane, other hydrocarbons that are not acidic. You will see that we also have some carbon dioxide that is found along with H2S. That's also an acidic gas that tends to be separated with hydrogen sulfide party by solvent extraction and this basic solvent.

So once H2S is captured or removed using the solvent extraction process, now we need to convert that into a sellable product. I know people always think that here is a point we could recover hydrogen for reuse. Hydrogen, being such a valuable material. But unfortunately, that is not possible.

We need to burn hydrogen into water waste pretty much, hydrogen, so that we can recover sulfur as an elemental sulfur, in a solid or liquid form, that is sold to a chemical industry, chemical manufacturing industry. You know that the basic material, the primary chemical that is made from sulfur for the chemical industry is sulfuric acid manufacturing. So you use sulfur, elemental sulfur, produced in refineries in large quantities to make sulfuric acid, which is a very important raw material, a reactant in many chemical processes.

So instead of mining for sulfur, as was done in the early days, now sulfur, a large fraction of sulfur, almost 2/3 of sulfur used in sulfuric acid manufacturing, comes from petroleum refineries as a byproduct. Why is that? Because the crude oil that is refined in then these refineries becoming more sour or higher sulfur content, that should be removed because we would like cleaner fuels by environmental regulations.

So dirtier crude oil means higher sulfur crude oil coming in. And we need cleaner fuels because increasingly strict environmental regulations on the sulfur content, particularly on diesel fuel. And that gives us large quantities of sulfur recovered in the supporting processes. There are two back to back processes, as you will see, Claus and SCOT, to remove elemental sulfur and sell it as a byproduct from the refinery.

The last process we will talk about, and as a supporting process, is of course wastewater treatment. Water and steam are used in huge quantities. There is no process in petroleum refining that steam or water is not used. And of course, a refinery generates a lot of wastewater.

There are different extents of contamination. There is actually steam or water that comes into direct contact with the hydrocarbons or crude oil. Those are the most heavily polluted water. They should be treated separately.

One very important point to make, in order to have the best water treatment process, the key is segregation of the waste streams. You don't want to mix the waste water coming from, say, distillation with the stormwater. That is also contaminated because it runs through the surfaces of the refinery that may be contaminated with oil or other species. So we need to keep these streams segregated in the wastewater treatment process.

And we should also make some wise decisions about water use. For example, for desalting, you don't really need to use fresh water. You can use wastewater that is contaminated with hydrocarbons, but doesn't contain salt to remove salt from crude oil, the very first process before the distillation.