BRDI Waste to Wisdom: Remote Power Generation and Summer Testing

BRDI-2-webSERC continues work on the BRDI Waste to Wisdom project, a three-year, multidisciplinary project to study pathways to convert forest residuals – or slash piles – into valuable energy and agricultural products at processing sites near timber harvest locations. Many of the potential processing sites do not have access to electricity, so SERC has been analyzing various methods to power this industrial equipment in remote locations. With help from the Environmental Resources Engineering capstone design course, SERC completed a technical and economic feasibility analysis comparing various remote power generation technologies, including waste heat recovery, biomass gasification, solar photovoltaic, and others. The results from this paper study indicate that a biomass gasifier is likely to outperform the other technologies in terms of mobility, cost, reliability, and environmental impact. After presenting these finding to the U.S. Department of Energy, the funding agency for this project, we procured a mobile, 20 kW biomass gasifier (similar to the one in the photo above) from All Power Labs in Berkeley, CA. Once it arrives, we will begin a series of tests to evaluate whether its performance will meet the requirements to operate in the demanding conditions of a forest-landing site.

With the gasifier being fabricated and a torrefier and a briquetter being prepared for shipment, it’s shaping up to be an exciting and eventful spring and summer of biomass fieldwork. SERC will lead the effort to test the torrefier, briquetter, and gasifier generator set at a forest-landing site in Big Lagoon, CA. We will measure the performance characteristics of each machine with a variety of biomass feedstocks recovered from timber harvest operations here in northern California. In addition to testing these machines individually, their synergy in an integrated system will be evaluated by connecting them together. For example, we will conduct experiments to densify torrefied biomass and to evaluate whether the gasifier generator set can reliably provide electricity to the other machines. Having these three commercial-scale technologies at a single site provides a unique testing and demonstration experience.

To prepare for this fieldwork, we have been busy developing the testing matrices, procuring feedstocks, detailing our instrumentation plans, preparing our data analysis tools, and coordinating associated logistical issues. The entire BRDI team is looking forward to a productive season of data collection and analysis that will help address the key issues posing a barrier to recovery and utilization of forest residual waste.

Aqueous Phase Reformation

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.

Stand-Alone Torrefaction Update

As we reported previously, SERC is collaborating with Renewable Fuel Technologies (RFT) to assess performance of RFT’s biomass torrefier. The torrefier converts wood waste from logging or forest thinning, roasting it to make a renewable energy product that can replace coal in power plants. The testing is funded by a grant from the California Energy Commission. The goal of the assessment is to determine whether waste heat from the torrefier can be used to make the device self-powered for off-grid use at timber harvest sites. Such use could make recovery of waste material at these sites more cost-effective.

This past fall, SERC engineers made multiple trips to RFT’s abrication and testing facility in Hayward, CA. We first procured about three tons of tanoak wood chips in Humboldt County and delivered them to RFT. Tanoak is of special interest because it is abundant in northwest California but considered of low value as a timber species.

TorrSolids-adj

An array of torrefied wood chips shows the effects of varying temperature and processing time. The raw biomass is shown in the column on the right.

We next performed a series of test runs with RFT engineers, in which we varied the moisture content of the feedstock, operating temperature, and residence time of the material in the roaster. We collected operating data such as temperatures, material flow rates, and electric power use during each run. In addition, we collected samples of the raw wood chips used for each run as well as the solid, liquid, and gas outputs from the process for later laboratory analysis. All of these data allowed us to perform a rigorous energy and mass balance for the process, key to determining the feasibility of stand-alone operation.

Our tentative conclusion is that such operation may be feasible, though the design may need further modification to reduce heat loss to the surroundings. We are now working to prepare our final report to the Energy Commission.