Abstract
The efficiency of hydrogen sulfide scavengers directly injected into gas streams is often compromised by short contact times due to space limitations on offshore assets. The use of static mixers is often employed to increase the efficiency of gas-liquid mixing. The performance of two commercially available hydrogen scavenger products were assessed in the laboratory utilising a specially fabricated test chamber designed to mimic a static mixer. A continuous feed of both gas and a liquid scavenger solution were mixed through a glass bead static mixer. The liquid scavenger was atomized into the gas prior to traveling through the bed. The impact of dose rate, water content, carbon dioxide and contact time were assessed on the scavenging efficiency and kinetics of two triazine chemicals used to sequester H2S from a gas stream containing 180 ppmv H2S in nitrogen, to achieve a target H2S concentrations of <10 ppmv. Efficiencies derived from the test apparatus revealed that the formulation based on the ethanolamine triazine chemistry performed significantly better than the methylamine triazine product at the two contact times of 3 and 25 seconds. The equilibration time required to reach the target concentration were significantly longer at the shorter contact time, and unachievable without the static mixer. The dosages of scavenger required to reduce the H2S concentrations from 180 ppmv to 10 ppmv were much higher than theoretical dosages. The addition of water to the scavenger mixtures was found to increase the efficiency of the ethanolamine scavenger but decrease the performance of the methylamine based triazine. The importance of atomisation of the scavenger onto the fixed bed was reinforced by the dramatic reductions in performance associated with a lack of atomisation. The presence of CO2 had no significant impact on the scavenging efficiency but had a kinetic impact and reduced the time to achieve the target concentration.
