Anaerobic Digestion to produce biogas (essentially a mixture of Methane and Carbon Dioxide) has been an established process in the sewage industry for nearly 100 years. From development in the sewage industry it has been used for solid and liquid waste treatment in industrial and municipal applications and more recently for purpose grown agricultural crops.
The overreaching advantage of Anaerobic Digestion over alternate process technologies, is that it is energy producing. The feedstocks are all organic in nature and hence the energy produced is classed as Renewable Energy.
The biogas produced can be burnt in a boiler to produce heat but nowadays the most efficient use of biogas is to utilise an engine to produce combined heat and power (CHP). Electricity and heat generation from biogas plants is now an important contribution towards greater use of renewable sources and part of the Government response to combat climate change.
Benefits of biogas CHP
- Reduced energy bills – typically saving a minimum of 10% on previous energy expenditure
- Typical return on your investment payback in 3-4 years
- Significant reductions in carbon emissions
- Maintain security of power supply
- Improve financial forecasting (energy spend) and business competitiveness
- Improve corporate ethics
Biogas to Electricity
The scope of supply of a biogas CHP installation could start at the biogas pipe work at the digester. It may contain several discrete process elements all of which may or may not be required. These are usually:
- Biogas desulphurisation
- Biogas drying
- Biogas composition analysis (CH4, O2, CO2, and H2S)
- Biogas flow (Temperature and pressure measurement)
- Biogas booster
- Standby flare
- Jacket water heat recovery
- Exhaust heat recovery by heat exchanger for Low Temperature Hot Water (LTHW), or Waste Heat Boiler (WHB) for steam production
- Exhaust stack
- Process plant connection and integration
All the above would need to be monitored and controlled with data fed back to a central control system. The degree of sophistication of an installation is usually linked with the overall size of the project. Larger size plant with significant electrical generation/biogas production will have a greater capital expenditure scope and would install more of the above elements. This would give greater gas conditioning and better process reliability.