In collaboration with KWR and Biogasplus, AquaMinerals has over the past two years conducted extensive research into the removal of H2S from biogas through the use of iron pellets. H2S is undesirable in biogas – it is poisonous, malodorous and very corrosive for the installation. Moreover, strict requirements apply to its injection into the natural gas network and, in many cases, the H2S needs to be removed. The research was conducted in the context of the TKI programme of the Ministry of Economic Affairs, and the results are very positive.
The application of granular ferric (hydr)oxide in the gas phase has a number of benefits: (a) less iron is required: only the sulphide in the gas phase is bound; (b) phosphorus remains available for recovery from the digestate; and (c) (saturated) granular ferric (hydr)oxide can be easily replaced and collected.
The pellets were produced by Biogasplus using ferric (hydr)oxide from drinking water production processes. The small granules were manufactured with an additive to make them more robust; they were subsequently dried, ground and sieved. They were then loaded with H2S in a laboratory. The removal was so effective that, in the initial tests, no saturation point was measured and the tests therefore failed. The research showed that the granulate has a maximum adsorption capacity of 160 mg H2S per gram. The first saturation point was measured following the adsorption of about 110 mg H2S per gram of granulate.
In addition the sulphur-loaded material spontaneously regenerates when it comes into contact with the outside air. In principle this is a positive effect – after all, it means the granulate lasts longer – but the regeneration process has to take place under controlled conditions. We’ll be looking at this in subsequent research.