While the food that fuels us is grown more or less as we need it, our machines are mostly powered by fuels that don’t get replaced as we use them up. This is a major reason for interest in one method of supplying energy: growing crops for fuel as well as food. Although people have done this at least since they started cultivating trees for firewood, the production rate of biofuels has greatly increased in the last several years—“five times, from less than 20 billion litres/year in 2001 to over 100 billion litres/year in 2011” according to a report”[SciTech Connect] prepared for the United Nations Committee on World Food Security. Yet the current and potential demand are even greater. Researchers continue to investigate the biological production of fuels that not only provide about the same power per unit as hydrocarbons like oil, coal, and natural gas, but are similarly convenient to handle. The reports described below, all available through the U. S. Department of Energy’s SciTech Connect, present a sample of the most recent of these investigations that the Department of Energy has sponsored, along with the investigation described in the United Nations report just quoted.
The report “Development of the University of Washington Biofuels and Biobased Chemical Process Laboratory”[SciTech Connect] briefly mentions several such projects, but its main point is to report on the use of a Department of Energy grant that was given for the design and construction of the equipment used in these projects. This equipment, a reactor in which microorganisms carry out chemical reactions[Wikipedia] and ancillary devices like a high-pressure boiler and a fermenter, has supported
The reactor produces pretreated biomass with “exceptional uniformity” and low concentrations of substances that inhibit chemical reactions. It has been used to develop technologies for improving the efficacy of steam explosion pretreatment, including
Figure 1: Equipment at the University of Washington Biofuels and Biobased Chemical Process Laboratory and one of its uses. Top left: high-pressure steam reactor and dedicated boiler. Top right: fermenter. Bottom left: poplar wood chips pretreated in the steam reactor. Bottom middle and bottom right: biomass suitable for biofuel production formed from poplar chips. (From “Development of the University of Washington Biofuels and Biobased Chemical Process Laboratory”[SciTech Connect], pp. 3 and 4 of 5.)
Other reports focus on research projects and results. For instance, the “Brown Grease to Biodiesel Demonstration Project Report”[SciTech Connect] from the San Francisco Public Utilities Commission describes their investigation of residual grease as an energy source, which at present not only goes largely to waste but, when handled as a waste product, causes several problems.
Ordinarily, residual grease concentrates in wastewater drainage from restaurants (“trap waste”) and accumulates in municipal wastewater collection systems. If left in the wastewater, the grease can lead to increased corrosion and pipe blockages that can cause wastewater overflows. At wastewater treatment facilities, residual grease can impair the operation of preliminary treatment equipment, which only removes part of it from the wastewater. In secondary treatment processes, residual grease increases the demand for treatment materials such as oxygen. When disposed of in landfills, if the grease decays before landfill capping, it releases the greenhouse gas methane into the air. So the San Francisco Public Utilities Commission tested the feasibility of recovering energy from residual grease in the form of methane or biodiesel[Wikipedia], a biofuel that can be put directly to use in standard diesel engines.
The test involved demonstrating a facility[Wikipedia] designed to receive 10-12 thousand gallons of raw trap waste per day from private trap waste hauling companies and recover, from those thousands of gallons, 300 gallons of brown grease per day. The side streams produced during this recovery were codigested with wastewater sludge in a wastewater treatment facility’s anaerobic digestors[Wikipedia] (in which materials are biodegraded by microorganisms), where the side streams’ effect on the digestion was compared with baseline data. The brown grease itself was used as feedstock in a demonstration biodiesel conversion facility to produce 240 gallons of biodiesel per day, and the side streams from this process were also codigested with wastewater sludge. Potential toxicity and/or changes in biogas production in the wastewater facility’s anaerobic digestors were determined from tests on the side streams from both the grease recovery and the biodiesel production.
Figure 2. Left: Brown grease recovery demonstration facility. Right: Biodiesel conversion facility. (From “Brown Grease to Biodiesel Demonstration Project Report”[SciTech Connect], pp. 6 and 13.)
As the report indicates, the experiment was only partially successful. While the biodiesel conversion process appeared to work, and the dewatering process’ side streams saved natural gas costs by augmenting digester gas production from 10.3 to 16 standard cubic feet[Wikipedia] per pound of volatile solids destroyed, the biodiesel production process “was subject to numerous operational issues and ancillary equipment part failures during the demonstration period”. The grease recovery rate over a 6-month period was found to range from 21% to 54%, which was below the 60%+ rate required to recover 300 gallons of brown grease per day. And although the grease recovery system used technology similar to that of the wastewater treatment facility, making it relatively easy for the facility’s operators to manage, the biodiesel facility required numerous raw materials that raised safety concerns and contained more specialized equipment that required more specialized personnel for operation. So although the idea was validated that wastewater treatment plants can serve to recover brown grease, there wasn’t enough operational data to evaluate and validate the system performance for a business case study based on this technology.
In a different project, one byproduct of biodiesel production, glycerol (C3O3H8), was itself investigated as an additional replacement fuel. This project, described in the report “Crude Glycerol as Cost-Effective Fuel for Combined Heat and Power to Replace Fossil Fuels”[SciTech Connect], was conducted by researchers at North Carolina State University, Alcoa Technical Center, and Applied Combustion Technologies.
One of the project’s aims was to develop a system that can reliably and repeatedly combust glycerol and analyze the combustor’s emissions. Glycerol, as the project report notes, “presents several difficulties to its use as a fuel”. The report goes on to describe some of the difficulties and how they were resolved by the combustor that the investigators designed:
“The spray burner utilizes a high-swirl stabilized turbulent jet diffusion flame in order to effectively combust glycerol. The difficulties associated with high viscosity fuels include fluid handling and achieving adequate atomization. The burner uses an air-atomizing nozzle specifically designed for high viscosity fuels and is commercially available. The low energy density and high autoignition temperature[Wikipedia] present a coupled problem in which the total heat released and the heat release rate are not sufficient to raise the temperature of the fresh, unburned droplets high enough to sustain combustion if there are significant heat loses or short residence times [of the droplets in the burner]. This is addressed by utilizing very high swirls and a hot, insulated combustion chamber. The chamber is preheated using a traditional hydrocarbon fuel until steady state is achieved and then the fuel supply is switched to pure glycerol. The high thermal feedback of the hot chamber coupled with the increased residence time and mixing with hot combustion products due to the swirl allow adequate time for the glycerol droplets to evaporate, combust, and release heat back into the system to sustain combustion.” (Pp. 4-5.)
The investigators accordingly found that the burner they developed could completely combust glycerol within “a relatively wide range of operating conditions” without emitting excessive amounts of acrolein (C3H4O)[Wikipedia] or any other volatile organic compound while producing significantly less NOx[Wikipedia] (nitric oxide[Wikipedia] and nitrogen dioxide[Wikipedia]) than the combustion of more traditional fuels does. On the other hand, they found that glycerol combustion produces high concentration of particulate matter comparable to that of unfiltered coal combustion, so practical application of glycerol burning will require exploring ash mitigation techniques.
Figure 3. Left: Laboratory-scale glycerol burner described in the report “Crude Glycerol as Cost-Effective Fuel for Combined Heat and Power to Replace Fossil Fuels”[SciTech Connect]. Right: Cross sectional view of flow paths within burner with axial (A), tangential (B), and atomizing (C) air flows. (Pp. 5, 22.)
The other major aim of this project, to develop a commercialization strategy for using glycerol as a fuel replacement, resulted in a 30-month plan for scaling up the burner into a pre-pilot scale system and initial plans for a pilot demonstration plant[Wikipedia; Wikipedia] to definitively assess the system’s merits and make final design adjustments. Applied Combustion Technologies intends to have, after the demonstration, a system ready to be built and sold in large volume. The investigators’ commercial analysis showed that the ideal customers for energy from crude glycerol are “biodiesel producers who are located in remote regions, where the cost of energy is higher and the cost of crude glycerol is lowest” (p. i).
“Lipids [fatty acids[Wikipedia] and their derivatives] are present in many forms and play various roles within an algal cell[Wikipedia]…. The ability to identify and accurately quantify the fatty acid content of these lipids as well as free fatty acids is essential to evaluating fuel potential and establishing a comprehensive compositional analysis of algae.” This is a quote from a report from the National Renewable Energy Laboratory (NREL) that gives directions for doing just that: “Determination of Total Lipids as Fatty Acid Methyl Esters (FAME) by in situ Transesterification: Laboratory Analytical Procedure (LAP)”[SciTech Connect]. The procedure “first solubilizes the lipids and then frees the fatty acids by transferring a methyl group [-CH3] from methanol [CH3OH] onto the -acyl[Wikipedia] chains of the lipids”, which produces methyl esters of the fatty acids plus free glycerol. The esters are then extracted and reacted with a fatty acid that doesn’t naturally occur in algae; this fatty acid is used to quantify the methyl ester content on a gas chromatograph[Wikipedia], thus allowing evaluation of the fuel potential of the algae from which the original lipids were taken.
Reports like “Algal Lipid Extraction and Upgrading to Hydrocarbons Technology Pathway”[SciTech Connect] and “Whole Algae Hydrothermal Liquefaction Technology Pathway”[SciTech Connect] mention how microalgae[Wikipedia] could “make sizeable contributions to renewable fuel mandates”, noting that this is “particularly due to their rapid growth rates and other favorable cultivation characteristics relative to terrestrial biomass feedstocks.” There are multiple possible methods of actually making fuel from algae that could realize this potential. Each of these methods may involve overcoming technical barriers to be competitive with petroleum-derived hydrocarbon fuels, and will incur costs to execute. To identify the barriers and reduce the costs, the National Renewable Energy Laboratory and the Pacific Northwest National Laboratory (PNNL) are studying different processes for converting algal and other biomass into fuels. The two reports just quoted are among those that describe details of the processes NREL and PNNL are studying, their analyses of the processes, the “data from recent pilot- and bench-scale demonstrations, collaborative industrial and academic partners, and published literature and patents” used in the analyses, and data gaps that the researchers have identified.
Among the key findings from the “Algal Lipid Extraction and Upgrading to Hydrocarbons Technology Pathway” study:
The other study quoted, “Whole Algae Hydrothermal Liquefaction Technology Pathway”, focused on using whole wet algae as a feedstock for making fuel by hydrothermal liquefaction—i.e., liquid production within a hot liquid medium[NABC]. This study’s key findings included the following:
Figure 4: Process block diagrams for different methods of producing hydrocarbon biofuels from algae. Top: process modeled in “Algal Lipid Extraction and Upgrading to Hydrocarbons Technology Pathway”[SciTech Connect] (p. 1). Bottom: process modeled in “Whole Algae Hydrothermal Liquefaction Technology Pathway”[SciTech Connect] (p. 1).
To provide guidance on the cost of hydrothermal liquefaction reactor systems and highlight where research could lead to project-cost reductions, researchers for Harris Group, Inc. were commissioned to provide hydrothermal liquefaction reactor designs for NREL and the National Advanced Biofuels Consortium (NABC). (NABC is an industry-university-national lab partnership led by NREL and PNNL to develop cost-effective processes to produce biofuels compatible with today’s transportation infrastructure.[NABC]) Five designs are described in their report “Production of Advanced Biofuels via Liquefaction - Hydrothermal Liquefaction Reactor Design: April 5, 2013”[SciTech Connect] to address three primary challenges: maximizing heat integration, managing the potential for poor heat transfer from the reactor effluent to the reactor feed due to potential high viscosities in the feed streams, and minimizing cost of the reactor system itself given the very high pressures required.
The designs differed in their heating methods, placement of bio-oil/water separation, and amount of dry solids content pumped to the reactor. If the design assumptions are accurate, the “Case D” design, which pumps a feed with a high dry-solids content to the reactor, is the most economical design of the five for commercializing hydrothermal liquefaction; different alternatives would be more effective if different assumptions prove mistaken.
“Case D-L would be suitable if the bio-oil/process water separation were not feasible at high temperatures. Furthermore, if pumping high solids material is not possible, either Case A, or a hybrid between Case A and Case D that would accommodate the maximum allowable solids content in the feed pumps could be utilized. Extensive heat integration, as illustrated by Cases B and B-L, is not cost-effective unless experiments show that the in-service heat transfer coefficients are much higher than those estimated herein.” (P. 8-1.)
The designers also considered a “Case C” early on, which included a continuously stirred tank reactor to address a plugging problem found in the small laboratory-bench system. However, the designers decided this case was infeasible, since a continuously stirred tank reactor that was big and strong enough for a commercial-scale system would be very expensive, and they expected that the larger piping sizes that a commercial system would have anyway should prevent the plugging problem even without a continuously stirred tank reactor.
The designers’ sensitivity analysis[Wikipedia] indicated that future research should focus on increasing how many reactor-volumes of feedstock the reactor can treat per hour[Wikipedia], assessing the pumpability of streams with high solids content, experimentally determining heat flux rates[Wikipedia], and determining whether the system’s unit for separating solids, water, bio-oil, and reactor gas can be operated at reactor temperature and pressure.
The reports described so far are about equipment and processes for making fuels from biological material. The Pennsylvania State University reports “Identifying Genes Controlling Ferulate Cross-Linking Formation in Grass Cell Walls”[SciTech Connect] and “Modification of Lignin by Protein Cross-linking to Facilitate Production of Biofuels from Poplar”[SciTech Connect] are instead about projects to genetically engineer plants so they’ll be easier to produce fuels from.
One impediment is that plants normally form cross-links[Wikipedia] in the molecules of their cell walls, which can make those molecules harder to break down. Reducing the number of cross-links does reduce the cell walls’ structural strength[Wikipedia] and can alter the plant’s pathogen resistance[SciTech Connect, p. 1], but if changes aren’t too great, so that the plant can still grow and mature until harvest, the chemical breakdown of the plant’s cell walls would be easier and the biofuel yield greater. The first project has resulted in mutants of Brachypodium distachyon grass[Wikipedia] that have such desirable characteristics, but the genes whose mutation produces these characteristics have not been identified. The project’s long-term goal is to identify and isolate the genes that govern the cross-link formation, which could be of great importance in controlling the cross-linking process.
The second project involves poplars[Wikipedia] instead of grass and focuses particularly on the cell-wall material lignin[Wikipedia]. While the difficulty of breaking lignin down chemically is a limiting factor in converting lignin into fuel, it is also difficult to reduce a plant’s lignin content and composition without compromising the plant’s health and vigor. Accordingly, in this project a different approach to the cross-link problem was taken. Instead of genetically altering poplars to build their cell walls from a substance that has fewer cross-links than lignin, the poplars were altered to produce lignin with cross-links made of different, more easily decomposed material. The resulting lines of poplars had the same form and lignin content as wild poplars, though some lines had different elastic properties. The report also describes what the researchers found from examining the altered poplars’ cross-linking mechanism and gene expression.
Things done today affect the likelihood—and even the possibility—of other things happening tomorrow, but when the connections between today’s actions and tomorrow’s results are more complex or obscure, our unaided minds are less able to figure out what to expect. Ways to help us think through the complexity to possible and likely consequences of different choices can be very important to us when those consequences are significant. As the report “Biomass Scenario Model Scenario Library: Definitions, Construction, and Description”[SciTech Connect] says, “Exploring the multifaceted and at times counterintuitive dynamics of large systems can elucidate unforeseen interactions and inform strategy.” The Biomass Scenario Model of this report’s title, funded by the Department of Energy, helps people explore how the biofuels industry may develop, a process with the kind of complexity and consequentiality that makes it worthwhile to study through a mathematical model. This report from NREL and Lexidyne, LLC, and its companion “Biomass Scenario Model Documentation: Data and References”[SciTech Connect], each describe different aspects of the model.
The “Data and References” report describes the data used in the model:
“The Biomass Scenario Model (BSM) has been carefully validated and calibrated against the available data, with data gaps filled in using expert opinion and internally consistent assumed values. Most of the main data sources that feed into the model are recognized as baseline values by the industry. There are over 12,000 total input values in the BSM2, contained in 506 distinct variables. Of the 506, any variable may be arrayed by one or two dimensions (e.g., contain subscripts) and/or be represented as a graph, with the ability to describe how values on the y-axis will respond depending on how the x-axis is defined.” (P. 1.)
Figure 5. High-level schematic showing the elements of the biofuel supply chain modeled in the Biomass Scenario Model. (From “Biomass Scenario Model Scenario Library: Definitions, Construction, and Description”[SciTech Connect], p. 1.)
The “Scenario Library: Definitions, Construction, and Description” report, which notes that the model “can be used to explore many aspects of the industry” (p. iii), describes a set of reference scenarios representing different hypothetical futures.
“Development of a “baseline” or “reference” case is a common practice for users of a given model because such cases provide a stable reference point for comparative analyses and for modifications to the model. Because the future is uncertain with regard to biofuel policies and because the BSM has so many biofuel pathways modeled, developing a single reference case is challenging. Instead, we designed a series of scenarios that are comprised of biofuel incentives. Each scenario represents a potential means to achieve a certain goal for the biofuels industry. These scenarios may be used as analyses by themselves or as the initial model conditions for other directed analysis. For example, analysts could use one or more scenarios as the base conditions to explore an analysis of oil price volatility.” (Pp. 3-4.)
Another report from NREL, “Effects of Deployment Investment on the Growth of the Biofuels Industry”[SciTech Connect], describes a use of the Biomass Scenario Model to estimate the effects of private and public investments in biorefineries that convert biomass to biofuels. As the report notes, exactly what set of investments will most cost-effectively advance the maturity of any conversion-technology pathway, such as the ones illustrated in Figure 6, is unknown; “[i]n some cases, whether or not the pathway itself will ultimately be technically and financially successful is also unknown.”
Figure 6. “The Biomass Scenario Model considers multiple conversion pathways; line formats show that there are multiple possibilities for integrating biomass-derived products.” (“Effects of Deployment Investment on the Growth of the Biofuels Industry”[SciTech Connect], p. 5.)
Results from the Biomass Scenario Model show that “[d]eployment investments substantially accelerate industrial development under certain conditions … . The size of the effect … depends heavily on other conditions, such as incentives, baseline scheduled biorefinery investments, and techno-economics. The deployment investment effects … include accelerated industrial learning, biorefinery construction, and biofuel production in the targeted pathways.” When additional deployment investment was combined with a production incentive, the model indicated that biorefinery construction and biofuels production would increase sharply. As the authors state, “While simulation results cannot precisely predict real-world events, these results suggest that deployment investments can accelerate industrial development if conditions are sufficiently favorable.”
The authors note plans and possibilities for improving the analysis, which include accounting for other conditions that could affect growth of the biofuels industry, such as “overall economic growth, petroleum price, growth of other non-petroleum transportation fuels, capacity for construction of biorefineries and other chemical industry facilities, ease of industrial learning within and among biomass to biofuels conversion technology pathways, ethanol blending policy, and incentive policies that target various parts of the biofuels industry with production, point of use, capital, or other incentives.” Accounting for these in the model “could help target incremental investment where it is most effective.”
Refineries dedicated to biofuels are thus expected to be important for the long term, but the biofuels industry’s immediate growth potential is affected by the availability of refineries currently used for other fuels. As noted in a report from Pacific Northwest National Laboratory, “the production of both gasoline and diesel biofuels will employ biomass conversion methods that produce wide boiling range intermediate oils requiring treatment similar to conventional refining processes (i.e. fluid catalytic cracking, hydrocracking, and hydrotreating).” To meet U.S. biofuel objectives over the coming decade while reducing overall capital demands, “it is widely recognized that leveraging existing U.S. petroleum refining infrastructure is key”. The match between this demand and the supply of existing U.S. refinery locations, capacities, and conversion capabilities is the subject of the report, entitled “Initial Assessment of U.S. Refineries for Purposes of Potential Bio-Based Oil Insertions”[SciTech Connect]. While the conversion and hydrotreating facilities in existing refineries appear adequate, the authors identified several concerns, including:
The authors recommend further enhancing the assessment to address gaps in the current analysis, improving the chemical understanding of intermediates and fuels and how they affect refinery operations and final-product performance, and enabling a partnership between refiners, biofuel producers, and technology developers.
Figure 7. Top: refineries in the first 48 states and Puerto Rico listed in the Energy Information Administration’s database, categorized by biofuel processing potential. Middle: U.S. refinery sites with the highest estimated biofuel production volumes. Bottom: projected total biofuel production by state in billions of gallons per year (bgy). (From “Initial Assessment of U.S. Refineries for Purposes of Potential Bio-Based Oil Insertions”[SciTech Connect], pp. 8, 10, 9.)
“Most models only consider biomass in either the power or fuels market. If one looks at the results of such models, the biomass availability and utilization could easily be double-counted because competition from the other sector is not considered. Double-counting could lead to unwarranted conclusions and decisions; thus studies that include multiple sectors are needed.” So notes a report in the Transportation Energy Futures Series[DoE], “Projected Biomass Utilization for Fuels and Power in a Mature Market”[SciTech Connect, p. 76], from National Renewable Energy Laboratory. In fact, biomass is not only useful for producing fuel or power, but as feedstock for chemical products. Accordingly, researchers carrying out the Transportation Energy Futures project developed a simple tool for modeling an equilibrium market, in which the market sets prices such that supply meets demand, and applied the tool to the biomass market with its competing demands for fuel, power, and chemical products. According to the report, market equilibrium analyses indicate the likely performance of a mature commodity market, so comparison between equilibrium-market models and market expansion models can ensure that driving forces in the expansion models are headed toward equilibrium, though the equilibrium models don’t provide insights into interim technology development or the merits of policy options (p. 2).
The model developed includes mathematical relations between domestic supplies and corresponding prices of forest residues, short-rotation woody crops, agricultural residues, grassy energy crops, corn for ethanol and butanol production, soybeans for biodiesel, and algae for diesel. The model also includes domestic markets for biomass-based energy (electricity, gasoline, diesel, jet fuel, and ship fuel oil (aka bunker fuel[Wikipedia])), greenhouse gas emissions, and petroleum use. The model is, however, limited by not including or accounting for imports, exports, and the effects of substitute fuels on fuel prices due to a lack of relevant information or insight. Given these limitations, provisional conclusions include the following:
Not only can different demands for biomass-based products compete with each other, there is potential for unintended competition for land and water, particularly in two countries which, in response to the two oil price hikes in the 1970s, developed biofuels ethanol markets and biofuel production sectors: the United States, using corn, and Brazil, using sugar cane.[SciTech Connect, p. 28] The efficiency of land and water use in both countries with respect to their ethanol systems, and the potential for unintended competition for land and water in both countries, are addressed in a poster[SciTech Connect] from NREL presented at the December 2012 meeting of the American Geophysical Union. From their review of literature on the subject and meta-analysis, the researchers conclude that
The group mentioned at the beginning of this article, the United Nations Committee on World Food Security, has a name that indicates an interaction even more significant than those considered in the reports just described—the interaction between the production of the fuel that powers much of the work we depend on and the production of the food we live on.
Because of the way both biofuel and food production require some of the same resources for different end uses, the biofuel and food industries have complex interactions of their own that affect the security of the world’s food supply. The aforementioned report to the UN committee, “Biofuels and Food Security. A report by the High Level Panel of Experts on Food Security and Nutrition”[SciTech Connect], describes the nature of the complexity:
“Analysing the relationships between biofuels and food security is especially challenging. It is at the intersection of some major global issues: energy, food, land use, and development. Biofuel production and the policies used to support its development can relate both positively and negatively with each of the four dimensions of food security – availability, access, utilization (nutrition) and stability. An appreciation of the relationships and causal impact and feedback links between biofuels and food security requires assessments at both global and local levels. It must also be situated within a dynamic perspective, given the fast changing developments, the complex and not necessarily instantaneous relationship between the drivers of biofuels’ rise and the (positive and negative) impacts on food security, and the need for projections of the future. Such an approach requires making assumptions on various parameters, ranging from the role of bioenergy, to the evolution of techniques, and to potential impacts at global and local levels.” (P. 11.)
Among the considerations reported are the effects of government policies on biofuel markets, competition for land and how new technology affects it, and the relative roles of biofuels versus other factors on food-price increases. The report ends with several conclusions, including (p. 107):
The panel recommended (pp. 17-19) that “[g]overnments should adopt the principle: biofuels shall not compromise food security and therefore should be managed so that food access or the resources necessary for the production of food, principally land, biodiversity, water and labour are not put at risk” and that “governments adopt a coordinated food security and energy security strategy.”
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Last updated on Monday 07 July 2014