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Ferrachel II® Iron Chelate Process
The process is recommended for reduction of high hydrogen sulfide concentrations (>1000ppmv) to concentrations of less than 100ppmv. To achieve hydrogen sulfide concentrations in the <4ppmv, a second stage consisting of a dry scrubbing catalyst will be required.
The process consists in passing the hydrogen sulfide charged biogas through a series of mass transfer towers where the proprietary iron chelate liquor will interact with the hydrogen sulfide and remove it from the gas phase.
The spent liquor is then processed in a liquor regeneration tower where the iron chelate liquor is regenerated and the sulfur precipitated as elemental sulfur which will then be separated by filtration.
The process operates at atmospheric pressure, at ambient temperature and has no liquid discharge. The only process discharge is the sulfur cake which has a certain humidity content.
The process operates continuously and only requires a periodical inspection and cleaning of some internal components to ensure optimum efficiency and performance.
Dry Scrubbing Catalyst (DSC) Process
The DSC process is based on the property of iron sponge to convert to iron pyrite in the presence of hydrogen sulfide.
To enhance the reactivity of the active product as well as the activity of the whole pellets and not only the external surface, the active media is enhanced by certain additives defined as catalysts.
The process consists in passing the hydrogen sulfide charged biogas through a tower filled with the required amount of active media to ensure the required hydrogen sulfide outlet concentration level as well as the expected life of the media.
Once spent, the media will be disposed of in a regular solid waste landfill for non hazardous waste.
Generally, two towers are installed with inter connecting piping and valving to operate each tower in a lead or lag mode. This features allows for the optimal use of the desulfurization media and minimize the operating cost of the desulfurization process.
Biogas Dry Desulfurization process using activated carbon.
Iron based desulfurization media has low cost and high desulfurization capacity as its main advantage, however the chemical reaction occurring during the capture of hydrogen sulfide tends to agglomerate the media pellets in larger chunks which render the spent media removal a time consuming chore. For this reason the tendency for landfill gas and biogas desulfurization has been to use activated carbon as the favored desulfurization media.
AirScience’s AST-AC/S01 is a high performance desulfurization activated carbon specifically made for biogas/landfill gas applications with high sulfur capture capacity. That media requires a relative humidity range of 60% to 80%, a temperature range of 30°C (86°F) to 40°C (104°F) and an oxygen to sulfur ratio of 3 to 1 for optimum performance.
Tests performed on AirScience supplied activated carbon desulfurization system have demonstrated outlet concentrations of less than 2 ppmv after one year of operation with an average H2S inlet concentration of 6,000 ppmv.
AirScience Desulfurization System
AirScience Technologies offers two desulfurization processes. The Ferrachel II® Iron chelate process for high gas flows and high inlet hydrogen sulfide concentrations. Dry scrubbing catalyst for low inlet hydrogen sulfide concentrations. In cases where hydrogen sulfide concentrations of less than 100 ppmv are required, a dry scrubbing catalyst stage is required.