Reed L. Hoskinson

Fractionation of Higher Value Crop Residue Components for Conversion into Bioenergy and Industrial Products

Separation of biomass is generally done by air-based fluidized bed density separation systems. Although these separation systems are well proven for harvesting grain the techniques have not been directly applied to separating biomass subcomponents (e.g., stems, leaves, etc.). Ultimately, a single pass harvesting operation for grain and select biomass subcomponents of crop residues is desirable. Our approach is to separate the desirable straw stems from the undesirable leaves, sheaths, and nodes, since the fibrous straw stem contains much less silica and waxy cuticle layer than do the leaves and sheaths. The leaves and sheaths contain higher nutrient levels, so they would be better utilized as organic matter for soil conservation. This separation will allow straw stem utilization in existing boilers for bioenergy production or as a biomass source for numerous industrial products. We are evaluating combine harvester unit operations for biomass separation by instrumenting the internal operating units of the harvester and collecting the experimental sensor data characterizing the separation. These data will allow us to quantify the extent and quality of biomass separation that can be obtained with existing threshing and separation unit operations with a range of biomass. Secondly, from analyses of the partitioning of potassium, chloride, silica, total ash, and fines, and recovery of usable fiber among the subcomponents of the residue, we have determined that by harvesting only the stems, a higher value feedstock results.

A Single Pass Multi-component Harvester for Small Grains

In order to meet the U. S. government’s goal of supplementing the energy available from petroleum by increasing the production of energy from renewable resources, increased production of bioenergy has become one of the new goals of the United States government and our society. U.S. Executive Orders and new Federal Legislation have mandated changes in government procedures and caused reorganizations within the government to support these goals. The Biomass Research and Development Initiative is a multi-agency effort to coordinate and accelerate all U.S. Federal biobased products and bioenergy research and development. The Initiative is managed by the National Biomass Coordination Office, which is staffed by both the DOE and the USDA. One of the most readily available sources of biomass from which to produce bioenergy is an agricultural crop residue, of which straw from small grains is the most feasible residue with which to start. For the straw residue to be used its collection must be energy efficient and its removal must not impact the sustainability of the growing environment. In addition, its collection must be economically advantageous to the producer. To do all that, a single pass multi-component harvester system is most desirable. Results from our first prototype suggest that current combines probably do adequate threshing and that a separate chassis can be developed that does additional separation and that is economically feasible.

Economically Optimum Production of Both the Agricultural Biomass Feedstock and the Crop

The Report of the National Energy Policy Development Group to President George W. Bush, titled the National Energy Policy, recognized renewable and alternative energy sectors as among the fastest growing in the United States, and identified biomass as one source for renewable energy. Agricultural crop residues are a significant renewable biomass resource from which to produce not only energy but also biobased products. In 2001, American farmers harvested 68.8 million acres of corn for grain, 48.7 million acres of wheat, and 4.3 million acres of barley. The available crop residues from these acreages represent a significant amount of available and renewable biomass. But for many years, research in support of crop production methodologies has been aimed at producing the best economic return to the farmer for the grain. In most cases, the crop residue production was either ignored, or the secondary objective of the research was to reduce the residue produced. Corn stalks have become shorter and thinner. Wheat stems have shortened. Now, in support of our national policies, interest in using crop residues as a biomass feedstock has risen. With this growing interest in crop residues, economically optimum simultaneous production of both the grain and the crop residue becomes of significant interest. In our paper we discuss new strategies for grain production involving optimum variable-rate fertilization of the crop for the simultaneous production of both the grain and the crop residue biomass. This ongoing research involved a full-field test in 2002 in which the goal was economically optimized simultaneous production of wheat and straw using site-specific variable-rate fertilization. Results from the 2002 harvest suggest some improvement over using traditional uniform fertilization, but economically efficient biomass production was not accomplished. Ongoing field tests are being conducted in 2003 using information gained in the 2002 field tests.

Engineering High-Fidelity Residue Separations for Selective Harvest

Composition and pretreatment studies of corn stover and wheat stover anatomical fractions clearly show that some corn and wheat stover anatomical fractions are of higher value than others as a biofeedstock. This premise, along with soil sustainability and erosion control concerns, provides the motivation for the selective harvest concept for separating and collecting the higher value residue fractions in a combine during grain harvest. This study recognizes the analysis of anatomical fractions as theoretical feedstock quality targets, but not as practical targets for developing selective harvest technologies. Rather, practical quality targets were established that identified the residue separation requirements of a selective harvest combine. Data are presented that show that a current grain combine is not capable of achieving the fidelity of residue fractionation established by the performance targets. However, using a virtual engineering approach based on an understanding of the fluid dynamics of the air stream separation, the separation fidelity can be significantly improved without significant changes to the harvester design. A virtual engineering model of a grain combine was developed and used to perform simulations of the residue separator performance. The engineered residue separator was then built into a selective harvest test combine, and tests performed to evaluate the separation fidelity. Field tests were run both with and without the residue separator installed in the test combine, and the chaff and straw residue streams were collected during harvest of Challis soft white spring wheat. The separation fidelity accomplished both with and without the residue separator was quantified by laboratory screening analysis. The screening results showed that the engineered baffle separator did a remarkable job of effecting highfidelity separation of the straw and chaff residue streams, improving the chaff stream purity and increasing the straw stream yield.

From Prediction to Prescription: Intelligent Decision Support for Variable Rate Fertilization

We describe the use of machine learning methods in the analysis of spatial soil fertility, soil physical characteristics, and yield data, with a particular objective of determining local (field- to farm-scale) crop response patterns. For effective prescriptive use, the output of these tools is augmented with economic data and operational constraints, and recast as a rulebased decision support tool to maximize economic return in variable rate fertilization systems. We describe some of the practical issues addressed in development of one such system, including data preparation, adaptation of regression tree output for use in a rule-based expert system, and incorporation of real-world limits on system recommendations. Results from various field trials of this system are summarized.