Researchers at SERC are studying alternative pathways for biomass energy to displace fossil fuels in existing high-efficiency power plants. Chemical reactions can harness waste heat to convert biomass into a hydrogen-rich syngas, displacing fossil fuel consumption. Modeling work at SERC estimates that integrated systems can produce between 5% and 100% of a power plant’s fuel requirement from biomass, depending on the quality of the waste heat resource. If applied to internal combustion engine power plants, blending hydrogen-rich syngas with natural gas additionally reduces untreated nitrogen oxide (NOx) emissions by up to 95% and increases engine efficiency by up to 25%.
Over the past year, SERC’s Dr. David Vernon led a research team to study aqueous phase reformation (APR) of plant-derived sugars to produce a hydrogen-rich syngas. This project, funded by the California Energy Commission, investigated the potential to use this low temperature reformation process to recover waste heat from natural gas power plants. SERC engineers designed, built, and tested a benchtop chemical reactor to convert aqueous sorbitol (C6H14O6) into an energy-rich gas consisting of hydrogen, carbon dioxide, and methane. Sorbitol, a sugar alcohol, was selected as the feedstock because it is easily produced from glucose, a biomass derivative, and reforming sorbitol produces hydrogen at a faster rate than reforming glucose.
Testing was completed in April. Our results showed that APR is able to convert up to 94% of the input sorbitol into a hydrogen-rich gaseous fuel. By synthesizing our own catalysts at SERC, we were able to produce a gas containing 64% hydrogen by volume. Furthermore, the output liquid and gas were found to contain 46% more chemical energy than the input feedstock.
Based on these promising results, we conclude that it is feasible to use APR in waste heat recovery applications. We have applied for additional funding to continue this work. Next, we plan to use crude glycerol, a byproduct of biodiesel production, as the feedstock. Our economic models predict that converting crude glycerol will significantly reduce the lifecycle costs of the system, making this process more cost competitive than other waste heat recovery technologies such as organic Rankine cycles.
I’ve been leading a new area of research aimed at offsetting natural gas consumption with hydrogen produced from biomass-derived sugars or waste glycerol from biodiesel production. The process utilizes waste heat in the exhaust from internal-combustion-engine power plants to drive chemical reactions that produce hydrogen. The hydrogen can then be blended with the primary natural gas fuel in order to enhance combustion. Hydrogen-enriched combustion can increase efficiency by up to 20% and reduce emissions of NOx by more than 95%.
The current project is focused on understanding the use of catalysts in aqueous phase reformation (APR) processes to speed up chemical reactions so that medium-temperature waste heat can be used to reform a wide range of plant based feedstocks.
Mark Severy recently graduated with a M.S. in Environmental Resources Engineering from HSU. His thesis modeled the waste heat resources available from large internal-combustion-engine power plants like the one at the Humboldt Bay Generating Station. His work demonstrates that, depending on engine type and operating conditions, there is sufficient waste heat to replace a significant portion of the natural gas with hydrogen produced from waste glycerol left over from biodiesel production. His work also shows that water vaporization in APR can consume a significant portion of the recovered waste heat. By raising the APR pressure, this water vaporization could be reduced. We are currently applying for grants to experimentally investigate high-pressure APR.
Waste heat from engine exhaust is used to convert the feedstock into hydrogen rich gas. The hydrogen produced in the reformer will be mixed with natural gas and air in the combustion engine to increase efficiency and reduce emissions.
A $95,000 California Energy Commission (CEC) grant enables SERC, in partnership with Renewable Fuel Technologies (RFT) of San Mateo, to continue experiments aimed at converting slash from logging and fuel reduction efforts into energy dense bio-coal. RFT has developed a pilot-scale, one ton per day torrefier which produces bio-coal from timber waste by heating biomass to 300°C in the absence of air. Bio-coal can be co-fired in a power plant with standard fuels such as coal or wood chips to generate renewable electricity.
This new project involves measuring the energy and mass balances in RFT’s pilot-scale unit. These measurements will aid in designing the torrefier for mobile, stand-alone operation and optimizing the technology for commercial use. Mobility is considered crucial if torrefier technology is to become commercially viable. A good deal of forest debris lies in remote, difficult to reach locations, generating high logistics overhead. By making biomass three times as energy dense, the mobile torrefier would provide a far more economical approach as well as a major incentive to commercial conversion of timber waste into very low carbon renewable energy.
The CEC also awarded SERC Faculty Research Associate Dr. David Vernon $94,993 to examine the use of sugars from biomass to offset fossil fuel use, increase efficiency and reduce emissions in combustion processes. This work uses plant-derived sugars in chemical reactions that consume waste heat to produce a hydrogen-rich gas that can be mixed with traditional fuels to promote more complete combustion. This process has the potential to replace up to 50% of the fossil fuel and to increase efficiency by as much as 25%. It could also reduce emissions of NOx by over 95% while maintaining or reducing emission levels of other pollutants. If successful, the technology developed from this work could be retrofit onto existing gas turbines and engines in power plants and gas pipeline compressor stations without requiring costly modifications to the existing systems.
Graduate Student Assistants Mark Severy and Billy Karis (left) and Faculty Research Associate David Vernon test aqueous phase reformation reactions.
Specifically, this project explores the use of aqueous phase reformation reactions that directly process sugars and operate at lower temperatures than the gas phase reformation reactions that are being investigated for waste heat recovery elsewhere. Sugars can be produced from virtually any cellulosic biomass, including waste resources such as forestry slash, lumber mill waste, crop residues, portions of municipal solid waste, yard waste, etc. By operating at lower temperatures, aqueous phase reformation has the potential to recover significantly more waste heat compared to gas phase reformation reactions.