Late last spring, the BRDI team began acquiring testing apparatus and field equipment needed for torrefaction, drying, and briquetting of biomass at a test site located on Green Diamond property at Big Lagoon. The area, a demolished mill site, consisted of dilapidated cement, old iron railings, and overgrown shrubs. Drawings had already been prepared for electrical lines, equipment placement, and emergency evacuation locations for the test site, so site set up proceeded quickly.
From right to left: the torrefier trailer, the biomass drying unit, and the homemade chip screener used to sift feedstocks to acceptable chip sizes.
The torrifier was a pilot unit custom-built by Norris Thermal Technologies (NTT) and hauled on a trailer over 2000 miles from Indiana. This was the largest piece of equipment on site and was the main focus for our summer testing of feedstocks at various temperatures and dwell times. NTT also provided a drying unit, which was purchased by BRDI for future biochar field-testing. This is the same type of drying unit used in many industries, including food and agriculture. BRDI’s application of the dryer was unique in that it used waste heat from the torrifier to dry the feedstocks to varying degrees of moisture content. The team found that moisture content in the woodchips, hard to control due to the combination of summer rains, early fog, and blazing mid day heat, had a significant impact on torrefaction. Moisture content in samples also affected the briquetting of the woodchips. Dry feedstocks of small particle sizes were observed to form dense briquettes of uniform size. Briquettes made of larger wet chips tended to crumble easily, and if the moisture content was high, the bricks expanded and deformed. In addition, because water is incompressible, too much moisture could damage the process mold and hydraulic pistons used to densify the woodchips into briquettes.
The summer testing team from left to right: Yaad Rana, Andy Eggink, David Carter, Greg Pfotenhauer, Kyle Palmer, Anna Partridge, and Marc Marshall.
Overall, testing was successful and the BRDI team has a plethora of samples to analyze in the lab. An exciting year is expected, as analysis is performed in preparation for continued testing using full-scale equipment next summer.
SERC 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.
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.
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.
The newly-installed air-measurement devices.
In September, Greg Chapman and I made our second trip to Renewable Fuel Technologies (RFT) to continue work on measuring the energy and mass balances of RFT’s pilot-scale torrefier. The one-ton-per-day torrefier produces a charcoal-like product called bio-coal from wood waste by heating biomass to 300°C in the absence of air. The bio-coal can then be co-fired in a power plant with standard fuels such as coal or wood chips to generate renewable electricity. SERC’s measurements of the device will aid in designing the torrefier for mobile, stand-alone operation and optimizing the technology for commercial use in converting timber waste into very low carbon renewable energy. This work is funded by the California Energy Commission.
The newly-installed torrgas sample condenser.
During this visit, we installed new instrumentation on the pilot-scale torrefier to measure power, air and gas flows. Greg also designed, built, and installed a condenser to sample the condensable portion of the gas by-product of the torrefaction process, called torrgas, which is used to generate heat as a key part of RFT’s efficient design. An initial test run of the system using the new instrumentation was successful, and planning is now underway to procure and transport several tons of wood chips to RFT, which will be used in a series of torrefaction experiments under varying conditions to collect detailed data on the operating characteristics of the system.
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.
Unprocessed wood chips (front) and the same feedstock after torrefaction. Photo credit Kellie Brown, HSU Photographer.
SERC is continuing its work with Renewable Fuel Technologies (RFT) on torrefaction. Torrefaction is the process of heating biomass to 250 – 300 degrees Celcius in the absence of oxygen.
The resulting product, referred to by RFT as “BioCoal,” has a higher energy density and is easier to pelletize than raw biomass. It is also hydrophobic, meaning it does not absorb water. These properties make BioCoal easier and less costly to store and transport compared to raw biomass. BioCoal can be used as a feedstock for liquid biofuels or co-fired in a coal power plant, thus replacing fossil fuels with a renewable energy source.
Biomass energy VIPs gather around the torrefier at SERC. Photo credit Kellie Brown, HSU Photographer.
SERC’s recently launched collaboration with biomass energy startup Renewable Fuel Technologies (RFT) reached an important milestone on April 7, when a group of U.S. Forest Service officials, professional foresters, and biomass specialists from across the country convened at SERC for a Torrefaction Research, Development, and Commercialization Meeting.
The meeting included a demonstration of RFT’s prototype wood torrefier that had been recently moved to SERC. Many of the meeting participants, including RFT’s technical and business leadership team, braved late-season storms and a major landslide to make the trek up from the Bay Area.