How Refineries Remove H2S from Fuel Gas

In the process of converting crude oil to liquid transportation fuels, a wide variety of gases are produced. These are referred to as fuel gas. Before that fuel gas is combusted in refinery process heaters or boilers, H2S (hydrogen sulfide) must be removed. The most common method is to contact the fuel gas with amine.

Lean Amine and Rich Amine

When amine is low in sulfur, it is called lean amine. When it has absorbed a significant amount of H2S, it becomes rich amine. Amine regeneration is the process of converting rich amine back to lean amine so it can be circulated again to remove more H2S.

How Regeneration Works

The process is straightforward. Rich amine is heated inside a trayed vessel. The heat breaks the sulfur-amine bonds and generates H2S gas. The H2S exits from the top of the vessel, and the regenerated lean amine exits from the bottom.

Why Zero H2S Isn't the Target

Lean amine is routinely sampled and its residual H2S is monitored. It might seem like the goal would be lean amine with zero H2S, but that's not the case. Targeting zero H2S would require an impractical amount of heat, and hot lean amine with no residual H2S is actually a corrosion concern. At the same time, too much H2S in the lean amine leads to poor performance in the absorbers.

The result is that lean amine H2S loading targets are established, a range that minimizes corrosion while keeping H2S removal effective.

Controlling the Regenerator

Operators hit that target by adjusting the heat applied in the regenerator, which is controlled by modifying steam flow to the reboiler. One common control method is a steam-to-feed ratio, expressed in pounds of steam per barrel of amine feed.

A known steam-to-feed range is established that reliably produces lean amine within the target H2S loading. The console operator adjusts within that range based on samples. Deviating from the accepted range typically requires additional levels of approval.

The advantage of a steam-to-feed ratio is that it handles variable flow automatically. Amine flow rates can shift quickly, and the control scheme responds by increasing or decreasing steam proportionally, keeping the regenerator on target without constant manual intervention.