Over 200 Turboden organic Rankine cycle (ORC) plants are currently in operation or under construction in biomass applications across Europe and these systems offer considerable potential for the Southern African market, says Karen Rowe, general manager at Scion Technologies, a company that represents Turboden (part of the Pratt and Whitney Group) in South Africa.
Turboden, which is an Italian company specialising in applications of the ORC technology with biomass being one of the main focus areas, builds and implements these applications in small biomass combined heat and power (CHP) plants. These systems are very flexible and CHP can be used in different applications, such as product drying, district heating systems, pellet production factories, sawmills and tri-generation systems with absorption chillers for cold storage warehouses or other cooling applications. The energy obtained can be maximised in small decentralised power systems sized 0,6 to 6,5 MW electric, which can be built near the heat consumer. CHP applications enhance the overall economics and can be closely integrated with the comsumer needs.
How it works
These CHP systems are based on the following main components:
1. Biomass is burned in a thermal oil biomass heater.
2. Hot thermal oil is used as a heat-transfer medium, providing a number of advantages, including low pressure in the boiler, large thermal inertia, simple adaptability to load changes, automatic and safe control and operation.
3. An organic Rankine cycle (ORC) is used to convert the available heat from the thermal oil to electricity, with the condensable heat of the turbo-generator available for a number of heat users. The ORC unit is based on a closed Rankine cycle, which makes use of a suitable organic fluid as a working fluid (typically silicon oil for biomass applications).
Using the wood industry as an example, Rowe explains that waste wood from internal processes as well as for biomass can be used to feed the biomass boiler. “Instead of using fossil fuels for the production and drying processes, hot water from the ORC can be used for wood drying and other process needs. When the ORC is used in conjunction with a biomass boiler, the system can replace fossil fuel systems in district heating grids, or can be used for cold storage and refrigeration, with large environmental benefits,” says Rowe.
Advantages of the ORC system
• Simple start-stop procedures.
• Simplicity of operation.
• Low ongoing maintenance costs.
• Good partial load performance.
• High turbine efficiency.
• High availability.
• No pressure parts, therefore no requirement for a certified engineer or statutory inspections.
“The ORC is mature and reliable technology with a high level of flexibility due to the possibility of it being integrated in an existing grid or in industrial processes. It is an ideal power system for users in remote locations with access to sustainable sources of biomass, where there is inadequate access to affordable or clean sources of electricity,” concludes Rowe.
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