BIOCONSERVACION: Integral solution for purification of biogas in WWTPs
Biogas is mainly composed by methane and carbon dioxide as a result of organic matter fermentation in the absence of air by the action of a microbial consortium (anaerobic digestion).
The composition of biogas depends entirely on the nature of the waste processed and the conditions under which takes place the anaerobic digestion. In most of the installations an energetic profitability of the biogas generated is carried out. However, biogas must be free of certain contaminants which are truly abrasive and corrosive, such as siloxanes and H2S, in order to ensure optimal performance of cogeneration engines.
The wastewater treatment plant (WWTP) of Mapocho-Trebal, located in Santiago de Chile, deals with the 30% of the overall water of the city, turning into a reference installation. Mapocho-Trebal WWTP takes advantage of the biogas energy by means of three cogeneration engines with a power of 1000 kW each. Under normal operation two of them are being used, while the third is reserved for maintenance shutdowns.
Severe regulations of the country referred to volatile organic compounds (VOCs) and nitrogen oxides emissions among others, and the requirements to achieve a free of pollutants biogas, led to the WWTP technicians to contact with BIOCONSERVACION.
Our technical department studied the case and a competitive proposal was suggested.
- Biogas purification system has two analogous lines composed by three filters in series.
- Biogas flow: 3600 m3/h.
- H2S concentration: H2S concentrations range between 40-60 ppmv. Such low concentration values come as a result of an existing pre-treatment unit. Punctually, H2S concentration peaks as high as 500 ppmv have been measured. The goal is to reduce H2S concentration levels below 1 ppmv.
- Siloxanes: an exhaustive biogas characterization revealed important concentrations of cyclic siloxanes type D3, D4 and D5 among others. D5 concentration values up to 10 mg/m3 were measured.
- Others: in addition to the aforementioned pollutants significant concentrations of mercaptans, cycle alkanes, chlorinated compounds and aromatic hydrocarbons were measured.
After an exhaust characterization of the biogas and the operating conditions, the solution proposed by BIOCONSERVACION was:
• High quality Activated Carbon for high molecular weight VOCs and siloxanes.
• High quality Bion KOH to enhance H2S removal, mercaptans and certain VOCs
BIOCONSERVACION solutions has been succesfully porved, achieved H2S levels below 1 ppmv, resulting into a biogas quality enough to be used in the cogeneration engines.
BIOCONSERVACION collaboration continues once implemented the solution and verified the result, since it has the possibility of evaluating the media state before replacement. By evaluating the remaining capacity of the media is possible to re-optimize the process for maximum profitability of the installation