Thesis
Biogas purification: a novel technique using pretreated digester effluent
Washington State University
Master of Science (MS), Washington State University
2012
Handle:
https://hdl.handle.net/2376/103749
Abstract
The aim of this thesis was to determine the H2S removal efficiency of pretreated dairy effluent using a bubble column reactor. There are a few key points to this process that are unique compared with traditional chemical absorption processes: (1) the pretreated effluent is a byproduct of the anaerobic digestion (AD) and NH3 stripping process, (2) the resulting effluent, after NH3 stripping, is at high pH (> 9.7) and therefore a suitable candidate for the absorption of H2S from biogas, (3) there is no need to regenerate the alkaline absorbent, and (4) the spent absorbent can be used as a fertilizer eliminating disposal costs. The question this thesis research attempted to answer was whether or not a process, using this pretreated effluent, could be developed to selectively remove H2S over CO2 from biogas with a simple apparatus that could be integrated at digesters where low capital/ operation /maintenance is desired. Therefore, a bubble column reactor was chosen as the absorption apparatus and tested for its removal efficiency of H2S and more importantly its ability to improve the selective removal of H2S over CO2 from biogas. The selectivity for H2S could be enhanced in a bubble column by around 50% through the manipulation of the bubbles passing through the v absorbent. This manipulation can be carried out by altering the gas sparger and was investigated with two different spargers, a single inlet orifice and an airstone sparger. In addition, studies on the effect of the effluent height in the reactor and the superficial gas velocity were conducted to increase the biogas-to-effluent ratio at a high removal efficiency (95% was used as a comparative tool). Increasing the volumetric biogas to volumetric effluent ratio will allow for a continuous stripping process if a gas to liquid 21-25:1 is achieved, since this ratio is emblematic of typical digesters. Countercurrent operation was investigated and a H2S removal efficiency of roughly 84% was achieved at a gas to liquid ratio of 20:1, close to the target value of 21-25:1, thus providing evidence that this process is achievable in a lab-scale setting.
Metrics
49 File views/ downloads
22 Record Views
Details
- Title
- Biogas purification
- Creators
- Nicholas Kennedy
- Contributors
- Craig Frear (Degree Supervisor)Shulin Chen (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Biological Systems Engineering, Department of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525188701842
- Language
- English
- Resource Type
- Thesis