Understanding grain pneumatic conveying in seeding equipment
Date: Dec 31, 2022
Term: April 1, 2019 to Dec 31, 2022
Status: Completed
Researcher: Hubert Landry, Ian Paulson, PAMI, Scott Noble, Donald Bergstrom, University of Saskatchewan
SaskCanola Investment: Equal match to MB CAP - $93,725
Total Project Cost: $187,450
Funding Partners: Governments of Manitoba and Canada through the Canadian Agricultural Partnership, Saskatchewan Canola Development Commission, Prairie Agricultural Machinery Institute (in-kind).
Grower Benefits
Simple but careful maintenance of air drill pneumatic conveying components and systems is important.
Consistent secondary hose lengths are important to system performance. Follow the manufacturer suggested hose routings unless actual performance data suggests otherwise.
Wherever possible, severe bends should be minimized in both primary and secondary hoses, and replace damaged or kinked hoses immediately. Secondary hoses should maintain a downward slope.
The most appropriate fan speed is the one suggested by the manufacturer.
Full-scale testing of pneumatic conveying of canola seed through the air drill did not result in a reduction in germination from the control sample, and no variations in samples taken across the air drill were evident.
Project Summary
Air drills, which continue to be a popular choice for seeding many of the crops grown in the prairies, rely on a pneumatic conveying system and the passive division of seed through well-mixed, two-phase or gas-solid flows. Many factors are known to influence the distribution consistency of passive division, however there are information gaps pertaining to the relationships between air velocity, seed distribution, and seed injury in air seeders. There is a need to better understand the role of air speed and distribution distance on the performance of a pneumatic delivery system, which can impact both equipment design decisions and farm-level operation, maintenance and profitability.
This three-year project represented a multi-year effort in measuring air drill distribution performance, both in the laboratory and at field-scale, in addition to simulating various configurations of pneumatic conveying systems. The first objective was to determine the effect of air velocities, air hose lengths and routing geometries, and/or tool bar angles on the seed distribution coefficient of variance (CV) and germination of canola in a pneumatic seeding system. Another objective was to develop and validate numerical models, specifically coupled computational fluid dynamics (CFD) - discrete element method (DEM) models to track machine-seed interactions in the pneumatic conveying system.
The project included a literature review related to experimental testing and numerical modeling of pneumatic conveying research. A second component tested a full-scale pneumatic seeding system to quantify seed damage, seed distribution consistency, and air flow behaviour. Air flow measurements were taken with and without seed being conveyed. Three different fan speed treatments were used, 2,200, 2,800, and 3,400 RPM. Seed germination was also measured after the experiments were completed to characterize possible germination effects from pneumatic conveying; samples were grouped by distributor and fan speed treatment. Finally, numerical models were developed to predict both the airflow behaviour and the seed distribution performance of several configurations of pneumatic conveying systems.
The results of the project ultimately highlighted the importance of simple but careful maintenance of air drill pneumatic conveying components and systems with existing machines. Using consistent secondary hose lengths are important to system performance, along with maintaining downward sloping secondary hoses. Longer secondary hoses tended to receive less seed in both measured and simulated datasets; this is illustrated in the simulation results from two primary hoses shown in Figure 1.
Figure 1. The simulated seed mass fraction through the secondary hoses of primary 4 (P4) and 6 (P6) of the modeled full-scale drill, at a fan speed of 2200 RPM.
Follow the manufacturer suggested hose routings unless actual performance data suggests otherwise. Severe bends should be minimized in both primary and secondary hoses wherever possible, and avoid introducing sharp bends close to the entry of a J-tube elbow when replacing primary hoses. The impact of sharp primary hose bends is shown in the simulation results in Figure 2`. Replace damaged or kinked hoses immediately and use the hose fastening/restraint schemes suggested by manufacturers.
Figure 2. A detailed view of the flow behaviour through the sharp bend in a upstream of the entry to the distributor J-tube.
The results also showed that using the manufacturer-suggested fan speed provided the most consistent distribution of seed across the air drill. Increased fan speed reduced distribution consistency. The coefficient of variation across the whole drill increased from 11.0% at the lowest fan speed tested to 12.5% at the highest fan speed. While imbalanced, the air and seed mass distribution pattern was generally consistent across the range of fan speeds tested. The overall conclusion was that the most appropriate fan speed is the one suggested by the manufacturer, unless drill-specific information suggests otherwise. Interestingly, air and speed distribution patterns differed from each other (i.e. more air through a given secondary hose did not guarantee more seed). Full-scale testing of pneumatic conveying of canola seed through the air drill did not result in a reduction in germination from the control sample, and no variations in samples taken across the air drill were evident.
Overall, many factors are known to influence the distribution consistency of passive division, including distributor geometry, fan speed, primary and secondary hose lengths and routings, and machine orientation while in operation. The project results point to opportunities for improved design of these systems in the future.
Full Report PDF: Understanding grain pneumatic conveying in seeding equipment
Other References to this Research Project
University of Saskatchewan Mechanical Engineering Department – graduate student funding and supervision, and lab testing facility contributions