Keith E. Webster

Physicochemical properties of bio-oil and biochar produced by fast pyrolysis of stored single-pass corn stover and cobs.

Short harvest window of corn (Zea mays) stover necessitates its storage before utilization; however, there is not enough work towards exploring the fast pyrolysis behavior of stored biomass. This study investigated the yields and the physicochemical properties (proximate and ultimate analyses, higher heating values and acidity) of the fast pyrolysis products obtained from single-pass stover and cobs stored either inside a metal building or anaerobically within plastic wraps. Biomass samples were pyrolyzed in a 183 cm long and 2.1cm inner diameter free-fall fast pyrolysis reactor. Yields of bio-oil, biochar and non-condensable gases from different biomass samples were in the ranges of 45-55, 25-37 and 11-17 wt.%, respectively, with the highest bio-oil yield from the ensiled single-pass stover. Bio-oils generated from ensiled single-pass cobs and ensiled single-pass stover were, respectively, the most and the least acidic with the modified acid numbers of 95.0 and 65.2 mg g(-1), respectively.

Productivity and Logistical Analysis of Single-Pass Stover Collection Harvest Systems

A modified biomass combine was used in field experiments focused on measuring the productivity of single-pass bulk harvest and single-pass bale harvest systems. These harvesting machines were outfitted with ISOBUS data loggers to track overall in-field performance data. Testing of machine productivity was conducted at .7 ton/ac (1.6 Mg/ha), 1.5 ton/ac (3.4 Mg/ha), and 2.4 ton/ac (5.4 Mg/ha) for each system. The combine was also tested in a conventional configuration to provide baseline productivity data. Testing revealed significant impacts of the harvesting system on overall machine productivity and highlight the need for additional machine development to support the collection and harvest of biomass residues and grain.

Corn Stover Densification Methods and their Large-Scale Logistical Impacts—Preliminary Analysis

The bulk density of corn stover poses a major obstruction to its large scale acceptance as a biomass feedstock. The loose bulk density of corn stover is low enough to create large inefficiencies during the harvest, transport, and storage phases of production. Overall production costs of stover could be reduced if a densification method were developed that provided adequate bulk density at a low specific energy during the harvest phase of production. So far, stover densification has been accomplished either by baling, grinding, or briquetting processes. Baling faces a logistical challenge with the handling cost of an individual bale, grinding systems don’t achieve high enough bulk densities alone, and briquetting systems generally require stover preprocessing (grinding), and the addition of heat energy. All of these factors for each system drive up the unit cost of corn stover production.

Technical Note: Durability Analysis of Large Corn Stover Briquettes

Densification of agricultural residues is a key step in a cost-effective, large-scale, biomass feedstock supply system. Lab-scale densification systems exist which can produce large-scale densified corn stover briquettes that measure between 220 and 420 mm in length and with an average bulk density of 190 kg/m3 (dry particle density of 460 kg/m3). MOG (material other than grain ) and pure cob briquettes produced similar lengths and dry particle densities of 424 kg/m3 and 421 kg/m3, respectively. Durability testing, utilizing a modified form of ASABE S269.4 (ASABE Standards, 2007) was conducted to determine the overall product quality associated with these densified briquettes. This publication describes experiments which quantified the durability or briquettes produced with different material types (corn stover, MOG, the chaff from a conventional corn harvest, and pure cobs) and material particle sizes (produced from a combine chopper, MOG, and a hammer mill with a 19-mm screen opening size). The durability rating varied with each of the main effect test parameters and produced a maximum 46% durability rating using pure cobs directly from a combine without additional size reduction. The durability rating was quite low for corn stover and MOG briquettes, and it was improved for pure cob briquettes. Biomass preprocessing in a hammermill significantly reduced durability due to a lack of fiber interaction throughout the large briquette.

Single-pass baling productivity and grain logistics analysis

Corn stover harvest in Iowa was studied using a single-pass combine and baler configuration over the last three years. The combine experienced a productivity loss from pulling a baler through the field of 6-10% depending on field conditions and speed. The additional biomass harvested by the combine lowered productivity depending upon the harvest rate and yield of the biomass. At the 1.4 ton rate in 2011 fall harvest the average maximum productivity loss was 25-30%. The loss was experienced in experiments without factoring in grain logistics. A model was developed to look at the field logistics of the grain cart to and from a single-pass combine when unloading on the go. The model showed that only a 16% loss in actual productivity when compared to a conventional combine which unloaded on the go as well.