POWER FROM BIOGAS: A distillery generates 10 to 14 times the volume of alcohol distilled as spent wash, with an average COD of 1,10,000 to 1,20,000 mg/Ltr and BOD of 50,000 to 60,000 mg/Ltr respectively. From this spent wash biogas is generated in a suitable bio-methanation reactor through anaerobic digestion by 60 to 70% COD destruction. This biogas contains about 50 to 60% methane.
The present practice is to burn the biogas directly into a low pressure boiler (with a working pressure of 10 to 21 Kg/cm2) with a substitute/supplement fuel, i.e. bagasse/rice husk, and produce steam. This steam is used in a power turbine to produce some power, with the exhaust steam being used for the process.
In this case the internal process requirement of power and steam are met by drawing some extra power either from the grid or from diesel generators.
This procedure has a serious drawback of low cycle efficiency, and the high percentage of H2S in the biogas resulting in corrosion in the boiler tubes and other auxiliaries. Besides, this also results in high SO2 ppm in the stack gas.
ALTERNATIVE SCENARIA: HIGH EFFICIENCY POWER - STEAM ROUTE:
With availability of new technology of H2S scrubbing, biogas can be made practically free of H2S, which makes it suitable for directly burning in gas engines to produce electricity. In this case the process steam requirements are met by using the existing boiler with additional bagasse/rice husk and generate incidental power through this steam. Thus, by burning clean biogas in a gas engine there is a net increase in the salable / recoverable electric energy over the biogas-boiler-turbine route.
As an additional benefit, with the increased efficiency of the power cycle, substantial amounts of carbon credits are also generated, adding to the revenue stream.
Although electricity generation using biogas in gas engines has been tried in the past, but due to the presence of highly corrosive H2S in the biogas, the experience was found to be uneconomical due to fast corrosion of engine parts.
We propose to put an efficient and proven biological H2S scrubbing system along with the gas engine and accessories.
In 2008, Digital Utilities formed a new company “DU Digital Processes Pvt Ltd” and entered into an agreement with M/s Biogasclean of Denmark (www.biogasclean.com) for microbiological scrubbing of H2S from biogas without the use of chemicals.
In collaboration with Eaga (energy India Pvt Ltd (a subsidiary of Eaga plc, U.K.) a leading consultancy and service delivery organization, DU Digital Processes Pvt Ltd provides CDM project facilitation services as well as carbon advisory services for such projects. These initiatives will lead to generation of carbon assets for power generation projects using biogas.
DU Digital Processes Pvt Ltd offers end-to-end solutions for power generation projects using biogas in the following areas:
- Engineering procurement & construction on a turn-key basis.
- Facilitation of carbon credits under the Clean Development Mechanism (CDM)