New publication: measuring residence time distributions in screw conveyor reactors

Charles Chamberlin, David Carter, and Arne Jacobson recently authored an article on measuring residence time distributions of wood chips in a screw conveyor reactor. A screw conveyor or auger makes use of a rotating helical blade inside of a tube or trough to move wood chips, sawdust, flour, or other granular materials through a reactor — such as a dryer, heater, cooler, gasifier, or torrefier. How much change in the materials takes place in such reactors depends on the average residence time and how variable that residence time is.

Internal view of a screw conveyor.

The screw conveyor in this Norris Thermal Technologies torrefier moves the woods chips from the inlet (on the left) to the outlet (on the right). The rate of rotation controls the residence time within the reactor. The reactor cover has been removed to show the screw.

This paper compares three alternative methods for measuring the residence time distribution of wood chips in a screw conveyor reactor using experimental results from a pilot scale torrefier:

  • addition of material to an empty reactor (step-up),
  • halting addition of material to a reactor under steady flow, (step-down), and
  • addition of a pulse of labelled material (i.e., a tracer) to a reactor under steady flow.

We found that all three methods yield residence time distributions that are approximately symmetrical and bell-shaped, but the distribution estimated from the pulse input of tracer exhibited a long trailing tail that was not detectable in either the step-up or step-down results. Second, we demonstrated that a normal probability plot provided a useful way to display and analyze the distributions obtained in the tracer experiments. Finally, we observed that all three methods yielded mean residence times that consistently differed from the nominal values, with the step-up method averaging 8% shorter, the pulse addition of tracer averaging 7% longer, and the step-down averaging 60% longer.

The article appeared in the August 2018 issue of Fuel Processing Technology and is available to download here in pdf.

Student research developments: summer 2018

This summer, thirteen students contributed to Schatz Center research projects in smart grids, bioenergy, wind, and off-grid energy access.

SMART GRIDS

Craig Mitchell provided construction observation at the Solar+ installation, tracking the canopy weight in real-time and serving as an onsite liaison between contractors and the Schatz microgrid team. As part of his observation, Craig recorded the installation’s actual daily labor and equipment requirements, to better define the needs for similar projects in the future. He is currently developing a hardware design toolkit that documents lessons learned in the Solar+ installation.

Solar+ students standing outside the Schatz Center

Solar+ student team: (l to r) Craig Mitchell, Thalia Quinn, Ellen Thompson and Rene DeWees

Thalia Quinn, Ellen Thompson and René DeWees have been developing a model to assess the current and future costs of building microgrids that integrate solar, battery storage, and fast EV charging. This model will help define which sites are good candidates for investment, and identify future research and development opportunities. This summer, the team conducted a detailed literature review to assess current and forecasted cost data: Thalia focused on battery storage, Ellen on electric vehicle charging infrastructure, and René on solar PV. They are now refining their cost model and generating a convenience store survey, to understand how current site owners view microgrids and to better assess installation opportunities.

Smart grid design is also evolving to take advantage of demand response technologies. As part of a collaboration with GE & Southern California Edison, Anh Bui developed an algorithm using Python code for estimating the tension between shifting a customer load to benefit the grid versus shifting a load to reduce their bill. Anh also helped with the installation of our new Schatz Solar Array in September.

Anh Bui tightens a solar module on the Schatz Center roof

Anh Bui installs a module for the new Schatz Solar Array

BIOENERGY

This summer, Sabrinna Rios Romero quantified decay rates for the post-harvest residues of seven agricultural crops: corn, wheat, rice, cotton, almond, walnut and grape. These decay rates will allow us to better assess the greenhouse gas (GHG) emission implications of leaving residues in field versus converting them into electricity. This fall, Sabrinna is surveying state foresters to clarify the fate of forest residues — i.e. whether they are piled, burned, or scattered in the field — information which will allow us to more accurately assess emissions following forest harvest. She has also been analyzing biomass samples using a bomb calorimeter and a thermogravimetric analyzer, to measure the performance of a gasifier system.

Cassidy Barrientos conducted a literature review that characterized GHG emissions from wood chip storage (e.g. chip piles at a power plant). Decomposition during storage — and the resulting emissions — are an area that have not been well-quantified, and may represent an important source of greenhouse gases. In September, Cassidy and Schatz Faculty Research Associate Sintana Vergara presented a poster, “Characterizing greenhouse gas emissions from wood chip storage,” and gave an oral presentation “Waste not: Improving the efficiency of using forestry residues as an energy resource” at the ARI Principal Investigator’s Meeting in Sacramento.

Cassidy Barrientos in front of her poster at the ARI conference

Cassidy Barrientos at the ARI Principal Investigator’s Meeting

Max Blasdel continued his ongoing work for the California Biopower Impacts Project. Max is characterizing the field decomposition of woody biomass residues left behind by forestry operations. His efforts comprise a key component of the business-as-usual case used to evaluate the net climate impacts of biomass removal for electricity generation. Max’s project research will form the basis for his master’s thesis in the Natural Resources program here at Humboldt State.

WIND ENERGY

Karsten Hayes developed an initial cost model (using Python and R) for north coast California offshore wind energy. The model includes associated storage needs, and integrates high-resolution offshore wind resource data from the National Renewable Energy Laboratory with load data for Humboldt County and California, drawn from Pacific Gas & Electric and the California Independent System Operator (CAISO).

OFF-GRID ENERGY ACCESS

Eli Wallach and Chih-Wei Hsu developed a method to estimate the number of fossil fuel generators used in low- and middle-income countries, how much electricity they generate, and how much fuel they consume. Their work supports a larger effort to estimate the economic, environmental and health impacts of fossil fuel generator systems used as a primary or backup source of electricity. To inform their assumptions and approach, they drew from multiple sources of data, including dozens of nationally representative household and business surveys. These data helped them understand the intensity of generator use at the country level, and in which sectors they are being utilized (i.e. commercial, residential). Eli and Chih-Wei’s fuel consumption estimates for over 130 countries are currently being utilized to update a widely used air quality and climate impacts model maintained by project collaborators at the International Institute of Applied Systems Analysis.

Schatz fellow Anamika Singh worked this summer with a team led by Dr. Amol Phadke at Lawrence Berkeley National Laboratory. Her research, which included collaboration with Dr. Phadke and Dr. Nikit Abhyankar, focused on identifying the parity price at which renewable energy technologies become feasible for heavy industries in India. Read more in our Fall 2018 From the Fellows report…

Chih-Wei and Anamika also helped with our Schatz Solar Array installation in September.

Tanya Garcia worked in the Schatz Center’s off-grid solar lab this summer, conducting solar product tests — including durability (drop and ingress), safety, and truth in advertising (light output, max power, full battery run time, etc.). She developed communications templates for the test lab network and edited specifications sheets to clarify product test policies. Tanya also helped test an open source electricity monitor, the EmonPi, and provided energy outreach activities for university and K-12 groups. Tanya is continuing her work in the off-grid solar lab this fall.

Tanya Garcia unpacks a solar module in the Schatz courtyard

Tanya Garcia prepares to test a solar module

Biochar Quality Assessment Project

Biochar has the potential to provide environmental and economic benefits to California’s agricultural sector through improved water retention [1], carbon sequestration [2], and reduced nutrient leaching [3], but realization of this potential is currently impeded by an information market failure [4]. In August, the Schatz Center was awarded a new project from the Agricultural Research Institute (ARI) to study the biochar market and evaluate how physical characteristics of different biochars relate to their market price. The outcomes from this project will help biochar producers understand how to price their product based on its characteristics, and it will help consumers identify the quality of different biochars using informed knowledge and price signals.

Two cupped hands hold (a) woody biomass and (b) biochar.

Woody biomass before and after biochar conversion

The current market size for biochar is estimated around 400,000 tons per year for gardening and landscaping — but it is poised to quickly grow into much larger agricultural sector opportunities where biochar could gain an estimated 2% of the soil amendment market [5]. To achieve this growth, improved information about available biochar products is needed. Currently, many sellers may not receive the full value for their product, and consumers do not know the characteristics of the biochar they are considering for purchase because quality assessment protocols have not been widely adopted. This project aims to understand this market failure and help close the information gap between producers, distributors, and buyers by measuring the characteristics of a dozen biochar products and interviewing stakeholders about desirable properties. By improving the maturity of the biochar market, this project will help California farmers save water and improve crop yield by appropriate, context-specific biochar applications.

As the first step in this project, Mark Severy attended the U.S. Biochar Initiative 2018 Conference in Wilmington, Delaware to deliver a presentation and connect with key stakeholders. The presentation, Biochar Quality and Market Assessment: Comparing Physical Properties to Market Value, provided an overview of the current state of the biochar market and demonstrated how price is not always reflective of quantitative, measured physical characteristics. Mark connected with many biochar producers who are willing to participate in interviews and contribute samples for testing and analysis.

This work will continue by collecting samples of biochar and conducting measurements to quantify their chemical, physical, and agricultural properties. Before and after the tests, interviews with biochar suppliers and end users will be used to understand how they evaluate the use value of biochar in each context. Results will be disseminated through a webinar and technical report when the project concludes in early 2020.

  1. Abel, Stefan, Andre Peters, Steffen Trinks, Horst Schonsky, Michael Facklam, and Gerd Wessolek. “Impact of biochar and hydrochar addition on water retention and water repellency of sandy soil.” Geoderma 202 (2013): 183-191. doi: 10.1016/j.geoderma.2013.03.003
  2. Brassard, Patrick, Stephane Godbout, and Vijaya Raghavan. “Soil biochar amendment as a climate change mitigation tool: Key parameters and mechanisms involved.” Journal of environmental management 181 (2016): 484-497. doi: 10.1016/j.jenvman.2016.06.063
  3. Laird, David, Pierce Fleming, Baiqun Wang, Robert Horton, and Douglas Karlen. “Biochar impact on nutrient leaching from a Midwestern agricultural soil.” Geoderma 158, no. 3 (2010): 436-442. doi: 10.1016/j.geoderma.2010.05.012
  4. Groot, Harry, Jeff Howe, Jim Bowyer, Ed Pepke, Richard, A. Levins, and Kathryn Fernholz. “Biochar as an innovative wood product: A look at barriers to realization of its full potential.” Dovetails Partners, Inc. (2017) Accessed August 27 2018
  5. Sasatani, Daisuke and Ivan Eastin. “Demand curve estimation of locally produced woody biomass products.” Applied Engineering in Agriculture 34, no. 1 (2018): 145-155. doi: 10.13031/aea.12392

Woody biomass poster & presentation given at the annual ARI meeting

In September, Sintana Vergara and Cassidy Barrientos presented on bioenergy and biomass emissions at the annual CSU Agricultural Research Institute (ARI) meeting in Sacramento.

Sintana presented ongoing research on the environmental implications of using residual woody biomass — a timber industry byproduct — as an energy resource, specifically within California. Ongoing work to develop a Life Cycle Assessment (LCA) for evaluating the climate change implications of mobilizing woody biomass for electricity production has uncovered a potentially significant source of greenhouse gas emissions: storage of woody biomass. Current work, funded by ARI, is now focused on characterizing these emissions.

Cassidy assisted with Sintana’s talk, and also presented a poster synthesizing what we know about greenhouse gas emissions from woody biomass. This poster presented a literature review of published studies that directly measured carbon dioxide (CO2) and methane (CH4) emissions from woody biomass stockpiles.

A jpeg of the linked pdf poster

Schatz Energy Spring/Summer Newsletter

Our print (and pdf) newsletter is just off the press, with features & updates on:

  • the Redwood Coast Airport (ACV) microgrid
  • breaking ground on Solar+ at the Blue Lake Rancheria
  • the California Biopower Impact project
  • our recent publications on biomass conversion technologies
  • the May dedication of the West Wing addition, and
  • HSU’s first EV charging station, unveiled at the Schatz Center…

… Plus a recap of our spring education and outreach programs, faculty and fellowship news, and recent conference presentations.

Two middle school students hold solar modules and fans in the sun


Students explore solar circuits at the 2018 Redwood Environmental Education Fair

Evaluation of biomass conversion technologies: new publication released

We recently completed work on the Waste to Wisdom project that examined the entire supply chain of converting forest waste residues into bioenergy and wood products. The Center’s role was to evaluate equipment that produces biochar, torrefied biomass, electricity, or densified wood briquettes using forest residues as the input feedstock. Collaborators from Humboldt State’s Forestry Department analyzed the upstream collection of forest biomass, and experts from the U.S. Forest Service conducted a lifecycle assessment and economic analysis of the supply chain.

SEM biochar image

SEM biochar image (taken at the HSU CNRS Core Facility)


Data collected by the Schatz Center during field tests of biomass conversion equipment were used to:

  • identify optimal process conditions,
  • specify feedstock limitations,
  • measure emissions,
  • evaluate product quality, and
  • recommend design improvements to equipment manufacturers.

Results and conclusions from the entire project are presented in a special issue of Applied Engineering for Agriculture, published in February 2018. Four principal investigators, including Schatz Center Director Arne Jacobson, summarized the project’s objectives and major conclusions in the introduction article to the special issue. Engineers from Schatz authored four papers, on biochar production, torrefaction and briquetting, and gasification of forest residues:

Collaborators at the U.S. Forest Service and the Consortium for Research and Renewable Industrial Materials (CORRIM) used the results collected from testing activities to conduct economic and environmental life cycle analyses of biomass conversion technologies. Field measurements from the Waste to Wisdom project will also be included in our current California Biopower Impacts project, which is evaluating the environmental impacts associated with utilization of forest-derived woody biomass for electricity generation.

This work could not have been completed without close collaboration between our primary industry partners: Biochar Solutions, Inc., Norris Thermal Technologies, and Pellet Fuels Institute, who provided the testing equipment. Other partners that provided key support include the Green Diamond Resource Company, the Redwood Forest Foundation, Inc. (RFFI), All Power Labs, Bear Mountain Forest Products, Colorado Biochar Resources, Pueblo Wood Products, California Redwood Company, North Coast Air Quality Management District, RUF Briquetting Systems, and OMNI Test Labs.

Stack of three briquettes; different colors represent combinations of temperature and time.
Forest residues were converted into torrefied briquettes in the demonstration-scale torrefaction plant. The perceptible differences in color and density reflect combinations of reaction temperature and residence time.

Schatz Energy in brief: climate-smart infrastructure and sustainable bioenergy

The Union of Concerned Scientists just released a new white paper on “climate-smart” infrastructure in California, citing the Blue Lake Rancheria (BLR) microgrid as a prime example of infrastructure built to safely sustain communities during climate change.

The Roundtable on Sustainable Biomaterials (RSB) adopted a revised Standard for Advanced Fuels this month at the delegate meeting in Vancouver, Canada. Kevin Fingerman (second from left below) is an RSB board member, and is the principal investigator on the California Biopower Impact Project here at the Schatz Center.

California Biopower Impact Project: creating a Life Cycle Assessment for bioenergy systems

The Schatz Center recently began work on the California Biopower Impact (CBI) Project, supported by a three-year $1,000,000 grant from the California Energy Commission. Our project will investigate the impacts associated with utilization of forest-derived woody biomass and agricultural residues for electricity generation. If managed properly, bioenergy could support sustainable forest management activities while also advancing California’s Renewables Portfolio Standard goals. However, there are also legitimate concerns surrounding the climate, air quality, soil fertility, and ecosystem health implications of improperly managed bioenergy systems. Before biomass energy can be responsibly pursued as a means to achieve forest management and renewable energy goals, additional research is needed to firmly establish the climate impact and broader environmental performance of forest and agricultural bioenergy.

Our central effort under the CBI Project will be the creation of a Life Cycle Assessment (LCA) greenhouse gas emissions accounting tool that will allow stakeholders in California to evaluate the impacts of different bioenergy policy and technology pathways in the state. Along with greenhouse gas balances, the project team will address additional critical environmental impacts that can be associated with bioenergy – including altered risk or severity of wildfire, soil fertility and carbon stock reduction, changes to air quality, and potential impact on habitats and biodiversity.

Pile of small branches


Woody biomass

Key study areas and outputs:

  • Assessment and mapping of net recoverable biomass that could be utilized for electricity generation. This analysis will focus on agricultural residues as well as forestry residues and fire reduction thinning material per the California Governor’s state of emergency brought on by the record numbers of drought and beetle- killed trees in the Sierra Nevada range.
  • Conduct a landscape-level probabilistic assessment of the fire risk implications of sustainable forest harvesting. Fire behavior under future climate scenarios will be simulated using the Pacific Northwest variant of the USDA Forest Vegetation Simulator (FVS) in combination with the Fires and Fuels Extension and Climate Extension modules.
  • Develop and demonstrate the California Residual Biomass-to-electricity Carbon Accounting Tool (CaRBCAT). This tool will improve on existing frameworks representing California’s unique bioeconomy context, offering improved spatial resolution, rigorously characterizing uncertainty, and offering a high degree of specification regarding supply chain characteristics. Users will be able to specify harvest practices, feedstock collection and handling methods, post-harvest treatments, feedstock management pathways, conversion technologies, and other characteristics.
  • Characterize and report on key environmental impacts of residual biomass mobilization such as changes to soil nutrient balance and carbon stock, air quality effects from altered black carbon and criteria air pollutant emission profiles, and impacts to biodiversity.
  • Assess potential to offset some harvest and supply chain costs through payments for ecosystem services and similar environmental market schemes.
  • Identify best management practices to improve bioelectricity system net GHG balance as well as to optimize performance with respect to fire risk, soil health, air quality, and habitat conservation. Develop and disseminate science-based policy recommendations that support implementation of these practices in bioelectricity supply chains.
Kevin Fingerman headshot


Kevin Fingerman, CBI Project Principal Investigator

Kevin Fingerman is a Schatz Center Faculty Research Associate and an Assistant Professor of Environmental Science & Management at Humboldt State University. His research employs life cycle assessment and simulation modeling tools to evaluate the broad-based impacts of bioenergy and transportation energy systems. He has also worked extensively on the water/energy nexus and on bioenergy policy.

Kevin serves on the board of directors of the Roundtable on Sustainable Biomaterials and, prior to joining HSU, he worked in Rome for the United Nations Food and Agriculture Organization. He holds MS and PhD degrees from UC Berkeley’s Energy & Resources Group.

Biomass Utilization Feasibility Study for the Karuk Tribe of California

The Schatz Center is assisting the Karuk Community Development Corporation (KCDC) with a biomass utilization feasibility study. The Karuk Tribe of California (KTOC) has aboriginal territory encompassing the Klamath River and Salmon River watersheds in Northern California. These lands are heavily forested and have been adversely impacted by postcolonial land use practices like timber production and wildfire suppression. Large, destructive wildfires have become an annual occurrence in and around Karuk territory, and there is widespread agreement among land managers that forest practices in the region need to change. The KTOC is leading this change through eco-cultural revitalization efforts that involve putting beneficial fire back on the land and restoration of traditional oak woodlands. Within this context, there is a role for utilization of biomass residuals that are removed through mechanical treatment. The Schatz Center is evaluating economic development opportunities for the KCDC to utilize forest residuals.

The overall goal of the project is to determine the feasibility of using local, renewable biomass resources that are available to the KTOC to generate power, heat, or products, while creating jobs, fostering environmental stewardship, and providing benefits to the Tribe’s economy. The objectives of this project are to determine the resource availability, identify technologies that could be implemented, and calculate the financial viability of potential projects.

This project is currently active and is funded by US Department of Interior Indian Affairs Energy and Mineral Development Program. We expect to complete the project by the second quarter of 2018.

Improving a Biochar Production System in Mendocino County

by Kyle Palmer and Mark Severy

For the past three years, the Redwood Forest Foundation, Inc. (RFFI) has produced biochar from small-diameter tanoak trees collected from thinning operations in Mendocino County’s Usal Forest. The Usal Forest ecosystem was disrupted by industrial logging operations throughout the 20th century. Tanoak’s rapid regrowth dominated canopy light, and interfered with redwood repopulation. RFFI is selectively removing tanoak to create the natural space that redwood needs to flourish, and converting the tanoak into biochar to help fund their restoration work.

Biochar, a blackened, solid biomass produced at temperatures above 500°C in the absence of oxygen, is used primarily as a soil amendment to increase water holding capacity, reduce nutrient leaching, and improve conditions for microbial life. (Learn more about biochar on the Waste to Wisdom site.)

RFFI’s biochar production operation has balanced on the edge of technical and economic feasibility due to the high moisture content of the tanoak feedstock and the labor costs required to operate the machine. In 2016, the Schatz Energy Research Center addressed moisture content by installing a biomass drying system that uses waste heat from the biochar machine. This year, the Schatz Center is working to reduce labor hours while improving safety and productivity, by automating key processes on the machine.

A SEM photo shows the porosity of biochar


The highly porous structure of biochar is shown through scanning electron microscopy (SEM) at 600x magnification. This SEM image was taken by Murielle Manka and Marty Reed, using the Humboldt State CNRS Core Research Facility’s FEI Quanta 250 ESEM. The Quanta was obtained in 2012 via a Major Research Instrumentation grant from the National Science Foundation.

In July and August, research engineers Kyle Palmer, Andy Eggink and student research assistant Murielle Manka evaluated baseline labor hours, biochar production rate, and biochar quality produced with the existing system. Throughout these tests, real-time data were collected for gas flow, composition, and electric power demand to help develop the control schemes. Monitoring and automation equipment are currently being installed and performance improvements will be validated in the coming months.

The preliminary results from this study were presented in early September by Murielle Manka and Schatz Director Arne Jacobson at the Agricultural Research Institute’s (ARI) principal investigator’s meeting in Sacramento. Validation test results analyzed this autumn will quantify benefits of the automation system, including any reductions in labor, increases in throughput, and changes in biochar quality.

This material is based upon work supported by California State University Agricultural Research Institute and a grant from the U.S. Department of Energy under the Biomass Research and Development Initiative program: Award Number DE-EE0006297.


Murielle Manka and Arne Jacobson present biochar testing results


Murielle Manka and Arne Jacobson at the September 2017 ARI meeting in Sacramento