Abstract
Investigations on exergy resources are important from the point of energy sustainability. In the presented study, an energy and exergy analysis of the operating biomass and natural gas boilers at the University of Idaho (UI) district energy plant is conducted. Exergy flows through the components of the steam cycle associated with the biomass boiler are quantified to identify major sources of exergy destruction in the district heating system. It is found that the biomass boiler has reduced energy and exergy efficiency compared to the natural gas boilers. Thermal efficiency varies from 76 to 85%, while exergy efficiency is significantly lower at 24 to 27% for all the boilers. Exergy accounting reveals that the biomass boiler and furnace account for the greatest exergy destruction, at approximately 68% of the exergy provided by the fuel. Steam use on campus represents about 6% of exergy losses while the pressure reducer is responsible for 4%.
Highlights
Fossil fuels such as coal, oil, and natural gas are by far the largest sources of energy on the planet.While there is much debate on how long fossil fuels will be available in sufficient quantities, it is known that the greenhouse gas (GHG) emissions created after combustion have negative impacts on the environment and GHG concentrations have increased substantially since the pre-industrial era [1]
Natural gas boiler 3, built in 1940, has comparable performance with the newest boiler due to the equipment upgrades introduced throughout its life
Much of the reduced exergy efficiency for both fuel types is due to the exergy destroyed during the combustion process, an unavoidable characteristic of combusting fuel
Summary
Fossil fuels such as coal, oil, and natural gas are by far the largest sources of energy on the planet.While there is much debate on how long fossil fuels will be available in sufficient quantities, it is known that the greenhouse gas (GHG) emissions created after combustion have negative impacts on the environment and GHG concentrations have increased substantially since the pre-industrial era [1]. Fossil fuels such as coal, oil, and natural gas are by far the largest sources of energy on the planet. Research into sustainable energy generation is growing, development is not yet at a point where fossil fuels can be replaced fully. Older district energy systems commonly use low pressure steam; newer designs produce hot and/or chilled water in a central location. This makes them ideal for scenarios such as industrial processes with excess waste heat or high population density locations where individual heating and cooling equipment can be eliminated
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