One of the main problems of the malfunction of biogas plants is due to the high concentration of H2S in the biogas. For the moment, the technologies used have been essentially: powdered iron oxides included in the digesters (with high operating costs); biological treatment systems (with a high investment cost and acid effluent to manage); chemical washes (with very high operating and frequent maintenance costs) and static carbon or iron oxide filters (with very high operating costs).
Low-cost, high-efficiency technology
AIRDEP (the company SUEZ works with in Spain) has developed a new technology with a very low installation and operating cost.
Essentially, the new technology consists on a gas scrubbing tower to desulfurize the biogas and a soda regeneration process. The tower is composed of filling material that favours a close contact between the washing liquid (soda) and the biogas and, in this way, the hydrogen sulfide (H2S) present in the biogas is eliminated.
Once the washing liquid has passed through the absorption tower (also taking the H2S from the biogas), it reaches the rear tank where oxidation occurs through oxygenation. In this tank, the recovery of the previously used soda is produced, which is recirculated again to the first absorption stage. From this second stage, sulfur is obtained in elemental form, not dangerous and revaluable.
Its main advantages are:
- Very high H2S scrubbing efficiency
- Optimal system for very high H2S concentrations in biogas
- Very low OPEX
- It does not present clogging problems like other systems, and therefore, its maintenance is easier.