Principle: Alkali Bio-desulfurization (BD-II) is a proven biological process with many projects for the removal of hydrogen sulfide from biogas that produce elemental sulfur. The process is divided into three sections including the absorption section, the bioreactor section and the sulfur sedimentation section. The absorption tower uses a packed absorption tower. Inside the absorption tower, an acid-base neutralization reaction occurs, where the H2S in the biogas is absorbed and dissolved into the desulfurization liquid, and it then reacts with the alkali. The H2S rich liquid (rich liquid) reacts with O2 in the bioreactor tank under the action of sulfur bacteria, producing elemental sulfur. The alkaline liquid is regenerated and recycled for reuse.
Process: In the first section, H2S rich biogas enters the packed absorption tower and gets in contact with alkaline wash solution (lean solution). The wash solution is sprayed down evenly over the packing from the top of the tower to ensure proper contact between the solution and the biogas. The H2S is absorbed into the solution. The purified gas leaves the absorber at the top of the tower.
The main material for the tower is glass fiber reinforced plastics /SS304.
The second stage is the bioreactor. The H2S rich liquid (rich liquid) accumulates in the bottom of the absorber tower then flow by itself into the enters the bioreactor. In the bioreactor, air is injected into the system to help the sulfur bacteria convert the sulfide into elemental sulfur via aeration device. The wash solution is regenerated and can be pumped back to the absorption tower again for a new process cycle. To maintain biological activity, additional nutrients are needed.
The third stage is the sulfur sedimentation section. A part of the wash solution is pumped to the settler. The element sulfur is concentrated here and discharged the system as sulfur sludge. The overflow in the settler is reused in the process.