DMT is aware that no biogas stream has the same properties, and that more than one technology can fit for one project. As a specialist in gas treatment technologies, we offer a wide portfolio for biogas and landfill gas desulfurization purposes. The principle of the technologies is the absorption of H₂S in a liquid and further oxidization to elemental sulfur or sulfate.
(Caustic Re-use) harnesses a chemical scrubber where H₂S is absorbed into a liquid with a high pH to enhance the absorption capacity of the solvent, and further oxidized during the aerobic treatment. Its Smart Dosing System (SDS) reduces operational expenses (OPEX) and can improve the bottom line for RNG projects.
(Bio-trickling Filter) is a biological process where H₂S is absorbed in an aqueous solution with a low pH, and biologically oxidized to sulfur/sulfate in situ.
(Biological Regeneration) is the combination of Sulfurex® CR and a bioreactor used for the biological regeneration of the caustic. In the Sulfurex® BR, H₂S is absorbed into a solvent under alkaline conditions, then further oxidized into sulfur in the bioreactor.
Sulfurex® BR Product Description
Biogas is produced by fermentation of biological waste products and is considered one of the most important renewable energies as a replacement of natural gas. Syngas is produced by gasification of a carbon containing fuel and used as an intermediate in generating synthetic natural gas. Both gases can contain hydrogen sulfide, which needs to be removed due to potential mechanical, environmental and safety reasons.
Sulfurex® BR is a desulfurization process that combines chemical desulfurization, at medium to high pH, with biological regeneration of the solvent (caustic). The system consists of a packed column, a biological reactor and a settler. Figure 1 shows a basic process flow diagram of a Sulfurex® BR process.
The biogas enters the scrubber at the bottom of the tower and flows upwards through a packed column that is approximately 12 meters in height. A caustic solution is distributed on top of the column over the packing media and falls through the packing material in a counter-current direction of the gas. The packing material inside the column ensures good contact between hydrogen sulfide and the process liquid for a maximum efficiency.
While the biogas flows through the packed column, H₂S is absorbed in the caustic solvent. The biogas leaves the column free of hydrogen sulfide at the top. The saturated process liquid is collected in the sump at the bottom of the scrubber, and flows under gravity to the bioreactor.
In the bioreactor, the hydrogen sulfide present in the liquid is biologically oxidized into elemental sulfur by Thiobacillus bacteria. The oxygen required for this biological process is supplied by an aeration system installed at the bottom of the bioreactor.
During oxidation, the caustic solution is regenerated before being reused for another washing step in the scrubber.
In the bioreactor water, nutrients and caustic are automatically refreshed for cellular growth and guarantee good operating conditions. Whenever the measured reactor fluid level is higher than the set point, part of the liquid will be discharged. The discharge stream is harmless and, generally, can be discharged without any form of post-treatment.
Under optimal conditions, 98% of the hydrogen sulfide is converted into elemental sulfur.
The elemental sulfur is separated from the process liquid in the settler, which can be integrated inside the bioreactor. The settler is fed with a small part of the effluent coming from the bioreactor. The overflowing process liquid (low TSS) flows from the settler to the bioreactor. Sulfur sludge is removed from the bottom of the settler with a high dry matter content of 5-10% mass, which can then be used as high quality fertilizer.
Sulfurex® BR is a flexible desulfurization technology that achieves low hydrogen sulfide outlet concentrations with low operational expenses (OPEX). Since the air injection takes place in the bioreactor, the technology is suitable for biogas upgrading. This technology is also suitable for high loads of sulfur, since the reduction in OPEX compensates for the higher initial investment cost as opposed to pure chemical or biological processes.