As the cellulosic ethanol industry continues to develop, improvements to the harvesting practices for corn stover and other feedstocks will be vital to reducing production costs. Once at full capacity, the biorefinery in this study will produce 114 million liters (25 million gallon) per year and will require an expected 700,000 large square corn stover bales on an annual basis. This represents a large fleet of harvest equipment, machinery operators, and management teams to ensure the required feedstock is secured during the fall harvest season. Many previous studies have evaluated the machinery requirements and costs for harvesting feedstock for commercial biorefineries but have done so using small-scale operations data. As the size of the supply chain, the level of complexity increases as machinery and labor are spread out over a large area. Observing the operations of a large scale facility will provide a more detailed view of individual field operations.
For a multi-pass harvest system, the in-field operations will typically include a
windrowing or raking of stover material. In this activity, the corn stover is collected from the field and placed into a windrowed path for the baler to collect. A baler will collect the
material and densify the material into a large square bale. These two operations are coupled together as the baler operation is dependent upon the material windrowed by the shredder. Once the bales have been produced, a bale collection system will bring the bales to a field edge location for short term storage or transportation to either the biorefinery or a long term storage facility.
These in-field operations are part of a much larger supply chain process that encompasses all activities from the production of the grain harvest to the final conversion of cellulosic material at the biorefinery. Each stage can operate independently of one another but it is
critical to consider the impact that one stage will have on another. The physical properties of the baled material, such as density, length, moisture content, and ash content, will determine how the material is handled during the transportation, storage, and processing stages.
The harvesting practices for a near commercial scale harvest operation were evaluated to determine Key Performance Indicators (KPI’s) in order to improve machinery productivity and efficiency. Data was collected from harvest machinery in order to assess the
performance of individual harvest crews across an entire season. The information collected was used to identify areas of potential improvement within the supply chain. The primary metrics identified included machinery productivity, machinery season productive time, and bale density. Increasing the productivity of equipment will help to reduce costs for the harvest supply chain, specifically for fuel and labor. Harvest crews demonstrated the ability to reduce machinery idle time below 10% and increase productivity to over 80% for an entire harvest season. A higher machine productivity will increase the material throughput of individual machines. Knowing the total material throughput is important, especially for matching the number of required windrowers and balers for the harvest season. Having the improper balance of machinery will cause bottlenecks within the supply chain as machines wait for operations to complete. As the machine productivity is increased, total machinery required for the season can be reduced. Increasing the usage of individual machines will reduce costs for the supply chain as the capital cost of equipment is reduced. This is a critical factor, especially as the size of biorefineries increase and will require a larger fleet of equipment.
Bale densities of 187 kg m-3 (11.7 lb ft-3) were achieved during the 2015 harvest season and represented a significant improvement over previous seasons. The relationship between
material moisture content, baler chamber pressure, and operator settings was observed through multiple seasons to establish guidelines for baling based on field conditions. While the 2015 harvest season represented an improvement over previous seasons, it appears unlikely that future densities will continue to increase as the season was especially dry and unlikely to be repeated.
The use of the KPI metrics, along with preseason training sessions, in-season data review, and post-season evaluation all worked together to implement a lean process to the supply chain. The continual collection and reporting of data regarding machine productivity and bale quality allowed machine operators to evaluate performance and recognize areas of potential improvement. The post-season review sessions identified larger, systematic improvements to the supply chain process.
4.1. Future work
The KPI metrics developed in this study helped to identify areas of potential
improvement for biomass harvesting. As biorefineries continue to reach full scale capacity, it will be necessary to maximize machinery productivity and feedstock quality in order to reduce costs. It has been identified that increasing the total season production time of individual machinery will be critical to reducing overall machinery requirements.
With the current multi-pass configuration, three separate passes are required through the field to windrow, bale, and collect the material. The use of alternative harvest methods could potentially be used to reduce the total equipment. One method that has been identified is single-pass harvesting of corn stover, a process where the baling operation is combined with the grain harvest process. The separate windrowing and baling operations are eliminated as stover from the grain harvester is collected by the baler. This process can help to reduce ash
content as the material is collected from the grain harvester without coming into contact with the ground. However, the single-pass system can potentially increase moisture content of the bales as the stover drying time is reduced. Another potential alternative harvest systems could integrate the windrowing and baling into a single operation. Similar to the single-pass bale system, the material is windrowed and baled within a single-pass, eliminating equipment and labor from the harvest process. Continued research in these alternative harvest systems will be required to determine effectiveness and potential cost savings for the supply chain.
Future research work will also need to address the transportation and storage stages of the supply chain. Management of biomass storage will be a critical factor in maximizing value of feedstock material. The material coming out of the field can potentially have a wide range of densities and moisture content. The moisture content of harvest material impacts the ability of feedstock to be stored for long periods of time. Additional research will be required for determining proper management of material based on moisture content. It may be necessary to develop multiple paths where material is stored at field edge, placed in a long term storage facility, or transported directly to the processing plant depending on the
characteristics of harvested feedstock.
As the cellulosic biofuels industry continues to develop it will be important to advance the harvesting methods by improving the existing multi-pass harvest systems and also by developing alternative harvest strategies that reduce the equipment needs. Future research can build the results of this dissertation to increase machinery productivity. The strategies for using KPI metrics can be applied to other areas of the supply chain, such as
transportation, and also to harvest of other feedstock materials. Corn stover has been
material density and improving machinery performance can be used across multiple feedstock supply chains.
APPENDIX. 2014 & 2015 CREW SURVEY RESULTS 2014 Crew Survey Results