When fuel is combusted in an engine or turbine, only 40–50% of the energy is used with the remainder expended as ‘waste’ heat. Cogeneration, however, harnesses this excess heat, redirecting it for heating or cooling purposes. Overall efficiency for cogeneration plants can be greater than 80%.
Electricity can be generated from a fuel, usually natural gas, in a turbine or large engine. If a turbine is used, the exhaust gases can be redirected to operate ovens or dryers, or into a heat recovery steam generator (HRSG). This steam can in turn generate more electricity, while also being extracted for other processes. If an engine is used, energy can be captured from the exhaust gases to heat water or raise low-pressure steam, while water from a closed-loop cooling system can be used for heating duties around a site or building. This repurposing of ‘waste’ heat is highly efficient.
Sectors and common applications
- Manufacturing subsectors, including paper, food, small-scale electricity generation, chemical processing
- Oil and gas production and processing facilities
- HVAC systems in buildings
Energy saving across sectors is 9 PJ (2014 estimate).
|1. Energy saving potential|
|1.1 Level of energy efficiency||15/15|
|1.2 Market prospect||2/10|
|1.3 Energy saving potential||7/10|
|2. Technical practicality|
|2.1 Innovative or advanced nature||15/25|
|3. Economic characteristics|
|3.1 Investment per unit energy||10/10|
|3.2 Payback period||10/10|
|3.3 % of Industry $ gross added value||4/5|
|4. Social characteristics||3/5|
Borg Manufacturing Pty Ltd, a maker of melamine panels, operates a gas-fired cogeneration plant. Exhaust gas from the plant is ducted to the mixing chamber of a dryer where it is blended with flue gas from a hot gas generator and ambient air. The mix of flue gases and air dries the panel fibres by direct contact when transported in the airstream of the dryer. Ongoing development of this project has confirmed its viability in terms of financial benefits and greenhouse emissions, with completion expected in mid-2016.
Food Investments Pty Ltd installed a natural gas-fired cogeneration plant to provide both electricity and process steam to the facility. Energy efficiency is achieved through the use of ‘waste’ heat from the exhaust of a generator to produce steam in a boiler. By using natural gas to produce electricity, and waste heat to produce steam, it’s estimated the cogeneration system will reduce greenhouse gas emissions by 39 714 tCO2e per year.
Other companies that have identified cogeneration energy savings can be found in the EEO opportunities register on EEX, and include:
- Kimberly-Clark Australia Pty Ltd
- Mars Australia Pty Ltd
- Nyrstar Australia Pty Ltd
- Simplot Australia Pty Ltd
For more information, see: