Bioenergy, while environmentally cleaner and more sustainable than fossil fuels, has historically been too energy intensive to produce — a big negative from an economic perspective.
However, recent bioenergy research from the University of Minnesota on combining solar thermal energy with biomass gasification for producing a natural gas substitute indicates a cost-competitive economic model may now work.
According to ScienceDaily, a new University of Minnesota study examining the financial viability of solar-heated biomass gasification technologies that produce a natural gas substitute product concludes that combining these renewable resources can make economic sense, even in the face of historically low natural gas pricing.
Here are the specifics on production economics: In traditional biomass gasification, 20% to 30% of the biomass feedstock is burned to produce heat for the process. But if the required thermal energy is supplied from a concentrated solar source, all of the biomass can be converted into useful synthesis gas.
A financial feasibility metric was developed to determine the break-even price of natural gas at which the produced syngas could be sold at a profit. Study results suggest that solar-heated biomass gasification systems could break even at natural gas prices of $4.04-$10.90 per gigajoule (metric standard for energy content is joules), depending on configuration.
According to the Biomass Energy Centre (BEC), gasification gases are known as ‘producer gas’ or product gas. Source material used to produce these gases include virgin wood, energy crops (currently corn, ie, ethanol), agricultural residue, and industrial waste and co-products.
In 2011, the widespread planting of corn to produce ethanol was blamed for creating severe food shortages worldwide — with 44 million people falling below the poverty lines due to an increase in food prices, according to 2010 World Bank estimates. As a result, World Bank president Robert Zoellick called for the world to “put food first” — first, that is, over biofuels, which, for example, make up 40% of US corn usage, an example of the issues facing the biofuel industry.
Depending on the feedstock, the precise characteristics of the gas will depend on the gasification parameters, including temperature and also what oxidizers are used. If the oxidizer is air, in which the producer gas will also contain nitrogen (N2), or steam or oxygen, reports the BEC, reporting gasification dates back to the 19th century.
Gasification is not a new technology, it was originally developed in the 1800s and is the processes used to make town gas for lighting and cooking. Small-scale gasifiers were also used to power internal combustion engine vehicles during fuel shortages during the Second World War.
Uses for gasification technology:
- Heating water in central heating, district heating or process heating applications
- Steam for electricity generation or motive force
- As part of systems producing electricity or motive force
- Transport using an internal combustion engine
“While the cost of adding solar energy generation to a biomass gasification facility can approach one-third of a plant’s total capital costs, other equipment required in traditional plants can be avoided and the amount of syngas produced per ton of biomass — a major variable cost of production — increases significantly,” said senior author and former University of Minnesota College of Food, Agricultural and Natural Resource Sciences student Tom Nickerson.
“With average US natural gas prices at $4.80 per gigajoule in 2014, two of the four configurations modeled were economically competitive,” said co-author Timothy Smith, director of the NorthStar Initiative for Sustainable Enterprise, IonE resident fellow and CFANS faculty member.
Though government incentives could significantly reduce the risks associated with volatile energy markets, demonstrating that the gap isn’t insurmountable is an important step toward environmentally preferred energy solutions. “Utilizing solar technologies to get more energy out of each acre of biomass reduces the impacts to the landscapes producing it,” Smith added.
No commercial plants currently exist, but the technologies modelled in this study are being developed at the Solar Energy Laboratory at the University of Minnesota under the direction of Jane Davidson and lead research scientist Brandon Hathaway of the College of Science and Engineering.
“Our novel approach to gasification has demonstrated its benefits at the bench scale, and testing with our 3 kW prototype is ongoing in the University of Minnesota’s High Flux Solar Simulator,” said Hathaway.
“We hope to find industry partners to join us in the next steps as we scale up the process and move towards testing on-sun,” Davidson added.
Photo credit: Modern biogas plant in Holland via Shutterstock
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