What are the levels of hydrogen sulfide and total sulfur in the exhaust gas after hydrogenation reduction in the sulfur recovery unit, following absorption with MDEA?

I’m not entirely sure; it has a lot to do with your total sulfur content and the absorption capacity of the lean liquid!

The hydrogen sulfide level is basically around 20 ppm, while the total sulfur content is below 50 ppm; this depends on the efficiency of amine solution absorption, as well as the effects of the sulfur and hydrogenation reactions that take place earlier.

This value can vary, depending on the flue gas emission standards, which in turn determine the amount of amine solution needed and the efficiency of absorption. If the emission standard is 200 mg/Nm3, the H2S concentration after absorption will be around 160 ppmv.

Hydrogen sulfide levels are very low, but the total sulfur content must be at least 50 ppm; there is some sulfur that cannot be absorbed

Our design criterion is that the sum of these two values should be less than 1 g/L; companies that operate efficiently can achieve a value of 0.5 g/L.

It depends on the absorption effect. The absorption efficiency depends mainly on the absorption temperature, the amine solution concentration, and its purity. Then, the exhaust composition needs to be considered; CO2 affects absorption, and the extent of this effect depends on the selectivity of the amine solution. The COS amine solution cannot absorb it; this amount depends on whether the feedstock contains hydrocarbons and CO2, as well as the catalyst’s hydrolysis capacity. If the above conditions remain constant, there are significant differences among amine solutions from different manufacturers, with domestic products being considerably inferior to imported ones. Based on my experience, with domestic agents, the H2S level in the purified gas is likely to be between 100-200 ppm, while with imported agents it’s probably 10-30 ppm; for COS, the level is likely to be 10-50 ppm. It can also be inferred by using the flue gas.