GAS RNG SYSTEMS offers two desulfurization processes. The Ferrachel II® Iron chelate process applies to high gas flows and high inlet hydrogen sulfide concentrations, while the dry scrubbing catalyst is used for low inlet hydrogen sulfide concentrations. In cases where hydrogen sulfide concentrations of less than 100 ppmv are required, the dry scrubbing catalyst stage is required.
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FERRACHEL II® IRON CHELATE PROCESS
This process is recommended for reduction of high hydrogen sulfide concentrations (>1000ppmv) to concentrations of less than 100ppmv.
The desulfurization process consists of passing the hydrogen sulfide charged biogas through a series of mass transfer towers where our proprietary iron chelate solution interacts with the hydrogen sulfide and removes it from the gas phase.
The spent liquid is then processed in a regeneration tower where it is reoxidized and the sulfur precipitates as elemental sulfur, which is separated by filtration.
This process operates at atmospheric pressure, at ambient temperature, and the only process discharge is the elemental sulfur cake.
The desulfurization equipment operates continuously and only requires periodical inspection and cleaning of some internal components to ensure optimum efficiency and performance.
To achieve hydrogen sulfide concentrations in the <4ppmv range, a second stage consisting of a dry scrubbing catalyst is required.
ACTIVATED CARBON PROCESS
Typically, desulfurization via dry scrubbing is achieved with an iron based catalyst. The main advantages of using iron based desulfurization media are its low cost and high desulfurization capacity. However, the chemical reaction occurring during the capture of hydrogen sulfide tends to agglomerate the media pellets into larger chunks, which renders spent media removal a time consuming chore. For this reason, landfill gas and biogas desulfurization has been trending towards the use of activated carbon as the desulfurization media.
AirScience’s AST-AC/S01 is a high performance desulfurization activated carbon specifically made for biogas and landfill gas applications. This 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 our activated carbon desulfurization systems have demonstrated outlet concentrations of less than 2 ppmv after one year of operation with an average H2S inlet concentration of 6,000 ppmv.