Hydrogen sulfide is generally a minor gaseous constituent found in crude, gas and water. It is produced through the breaking down of organic sulfur compounds by sulfate-reducing bacteria (SRBs). Research studies have also found that certain acidic fracking fluids react with certain rock formations under high pressure to generate H2S.
Once H2S testing has been performed (see blog posts on sampling and testing), it is necessary to mitigate its impacts and bring the crude oil to the desired specifications. There are mechanical/operational (physical), biological and chemical mitigation techniques from which engineers choose according to crude characteristics, H2S concentration, economic considerations, and other variables. Hydrogen sulfide is not found in isolation but together with methane, hydrogen and higher hydrocarbons, and traces of nitrogen-, oxygen-, calcium-, and metal- containing species which complicate the selection of the most suitable H2S mitigation technique.
Managing H2S is a challenge at every stage of hydrocarbon production. Whether it is downstream, midstream or upstream, H2S mitigation techniques are implemented in order to preserve the environment, take care of workers, avoid corrosion and bad smells, and protect the value of refined products and physical assets. Even crude that has already been treated, might produce more H2S, as SRBs continue to digest the oil. Testing and treatment needs to be performed across the different stages of the production line.
Mechanical/operational H2S mitigation techniques
When natural gas is produced as a byproduct of oil extraction, operators will often vent or flare the gas. Flaring is the practice of burning gas that is deemed uneconomical to collect. Flaring is also used to burn gases that would otherwise present a safety problem. It is common to flare natural gas that contains hydrogen sulfide, in order to convert the highly toxic hydrogen sulfide gas into less toxic compounds. Venting is the direct release of methane gas to the atmosphere. During oil development, gas may vent to the atmosphere. The solids and fluids from the well go to the pits, while the gases are allowed to escape to the atmosphere, or they are flared.
Physically, stripping is less common alternative to remove H2S. The oil industry may use a nitrogen stripping system to remove the H2S. Nitrogen is an inert gas that prevents the flammable gases from igniting and thus eliminates the risk of explosion. Once the H2S has been stripped from the crude oil, it is usually flared. This process tends to create 5-10% barrel losses as other light compounds are stripped from the crude. This process is energy intensive and time consuming as it occurs in batches.
Membrane technology could offer a solution for the nitrogen transportation hassle that some sour crude treatment facilities require. In this case, compressed air is pushed through a set of polymer fibers or the membrane. As the compressed air moves through the membrane, the nitrogen molecules are separated from the other molecules.
Biological H2S mitigation techniques
These are used for water in wastewater treatment plants but not for crude oil at the moment.
Chemical H2S mitigation techniques
Additives to treat H2S in crude oil are very diverse and work in different forms. The reduction in concentration of hydrogen sulfide might follow the absorption route, such as alkanolamine, ammonia solution and alkaline salt solutions; and oxidation of H2S using iron oxide, activated carbon or a Claus process.
H2S mitigation technologies are not mutually exclusive and a combination of techniques might be used. On Table 1, we show the different chemical additives that are commonly used for H2S removal in crude oil.
|Chemical Family||Chemical||Stability of Reaction (elevated temperature and lower pH)||Sector: Upstream (U), Midstream (M), Downstream (D)||Comments|
|Proprietary Materials||Pro3®||Non-Reversible||U, M, D||Non amine H2S scavenger|
|ProM®||Non-Reversible||U, M, D||Non amine H2S and mercaptan scavenger|
|Enviro-Scrub®||Non-Reversible||U, M, D||Proprietary Triazine|
|Alkanolamines||DEA, DGA, DIPA, MDEA||Reversible||M, D||The amine salts formed easily dissociate when thermally stressed, re-releasing H2S into the vapor space.|
|Triazine||MMA-Triazine||Non-Reversible||D||Preferred product for refinery applications. Commodity. Fouling and corrosion in refineries.|
|MEA-Triazine||Non-Reversible||U, M, D||Not recommended for crude. MEA will partition to the water and condense in the tower overhead early in the condensation profile, rendering MEA salts more likely to accumulate - i.e. more corrosive|
|Aldehyde||Glyoxal||Non-Reversible||M, D||Slow reaction time, corrosive to carbon steel.|
|Formaldehyde/ Formalin||Non-Reversible||Banned||Handling issues and carcinogen.|
|Aldehyde (Acrolein)||Non-Reversible||Fast reaction kinetics and water soluble reaction by-product. Highly volatile and extreme respiratory irritant. Slow reaction.|
|Nitrogen containing polymer||Polymeric Amine||Reversible||U, M, D||Heavier nitrogen compound used in the formulation polymeric reaction product expected to stayu in the bottoms of the atmospheric distillation column.|
|Imine||Non-Reversible||U||Boiling point over 260◦C. No overhead crude problem.|
|Alkaline Hydroxides||Sodium hydroxide and potassium hydroxide||Reversible||D||Caustic increases sodium level, increases fouling, catalyst poisoning and sludge generation.|
|Metal Based (inorganic and organic)||FeCl3, Fe2O3, ZnCl2, Zn2O3, CuCO3, Zn carboxylate, Fe carboxylate||Non-Reversible||D||Sludge generation, fouling of equipment, emulsion stabilizer, corrosivity from chloride salts.|
Table 1.- Chemical Additives for H2S Removal in Crude Oil
H2S is present along the hydrocarbon production line. Figure 1 shows where in the upstream operations H2S scavengers are used as well as the places where H2S is found.
Figure 1.- Points where H2S scavengers are used in oil/condensate production operations.
Midstream operations link the upstream and downstream entities, and mostly include resource transportation and storage services for resources, such as pipelines and gathering systems. H2S scavengers are used for cargo treatment, before introducing the oil in pipelines and when it is being removed from storage units. It is key to meet H2S specs in order to transport crude oil and gas via pipeline.
Downstream operations are oil and gas processes that occur after the production phase such as refineries, petrochemical plants and retail outlets. Figure 2 shows the points in the downstream operations where H2S scavengers are used.
Figure 2.- Points where H2S scavengers are used in refinery operations.
Whether your needs to mitigate H2S are upstream, midstream or downstream, we at Q2 Technologies can help you treat your crude oil and get more bang for your money. We are reliable suppliers of EnviroScrub®, a triazine based scavenger, that will bring your oil to specs. Similarly, we have our high performance non-triazine Pro3® scavenger and mercaptan scavenger ProM® to provide you with the best solutions for your H2S challenges. Contact us today to discuss how we can serve you.