1. Optimization of Woody biomass handling and drying
Prepared for AROWRN Workshop
Camrose, June 2017
Joy Agnew, P.Eng., Ph.D.
Research Scientist, Ag and Bioproducts, Prairie Agricultural Machinery Institute

2. Why is pami at arowrn?
PAMI: 40 year history of equipment development and evaluation
Applied Bioenergy Centre (ABC) established within PAMI in 2007 with a mandate to fill engineering gaps related to agricultural biomass utilization with a focus on:
biomass harvesting, handling and processing
supply chain optimization (from farmer to refinery) and assessment of costs related to biomass logistics
PAMI’s grain drying expertise may be useful for smaller- scale biomass drying
Involved in a partnership with St. Peter’s College and City of Humboldt to replicate AROWRN’s wastewater irrigation and biomass utilization model in Saskatchewan

3. Dedicated Woody biomass harvesting & handling
Concept 1: Biobaler, bales dry during storage, must be chipped prior to use

4. Dedicated Woody biomass harvesting & handling
Concept 2: Forage-type harvester chips in-field, stored in piles

5. Issues related to storage of freshly harvested biomass
High moisture content (>30%) can result in
Rotting
Freezing (handling issues)
Other problems

7. Biomass drying Heated air drying in batch dryers = $$
Value of biomass ~ $100 to $500 per tonne (if considered as a replacement fuel with $50/tonne CO2 carbon tax)
Cost to produce, collect, transport and store dedicated woody biomass ~$100 to $200 per tonne
If biomass is produced for another purpose (e.g.: wastewater treatment, the economics look a bit better)
Margin available for drying = minimal
Without optimization, operation of fans for woodchip drying can cost $5 to $10 per tonne or more
Without drying, value of biomass can turn into a cost to dispose

8. Low-cost, high-capacity drying option for grain
Natural air drying (NAD)
Very popular in western Canada for management of conditions during storage
Uses existing storage structure and air’s natural capacity to dry material
Requires sufficient airflow and airflow uniformity

9. Efficient nad for grain requires an understanding of
Effect of airflow rate on drying rate
Target airflow rate for grain drying is 1 cfm/bu
Expected drying rates with ideal conditions
Effect of air and grain conditions on air’s “capacity to dry”
Resistance to airflow (duct pressure) which dictates airflow rate from each specific fan type
Depends on grain depth, grain type, ducting configuration, airflow rate
Effect of ducting configuration on airflow uniformity

10. efficient nad for woody biomass requires understanding of
Effect of airflow rate on drying rate
Past work with NAD of woody residues showed that 500 to 4000 m3/hr per tonne (3 to 5 times higher than airflow rate required for NAD of grain) has resulted in 20% moisture removal in 5 to 35 days
Is there a critical airflow rate above which drying rate does not increase?
Effect of pile properties on resistance to airflow
Height, configuration, ducting
Biomass type, moisture content, % fines, porosity
Ducting configuration required for uniform airflow and ease of material handling
Effect of air temp/RH and pile conditions on air’s capacity to dry
Fan control strategies (on during day only?)
Energy balance
Is it worth fan operation?
Is use of supplemental heat justified?

11. Test bunkers
Grain drying bunkers in Humboldt (constructed in 2007)
18 inch diameter, 10 ft tall
Woodchip drying bunkers in Portage la Prairie (constructed in 2017)
24 inch diameter, 12 ft tall
Both systems include multiple sampling ports, air plenum at bottom of each bunker, internal and external temp/RH sensors, load cells for individual bunkers, loading and unloading conveyors

12. Sample of data and observable trends from grain test bunkers
Upper left: screenshot of data that is continually logged from each of 6 test bins
Upper right: plot of test bin weight loss (drying) over time and ambient temperature and absolute humidity
Lower left: plot of resistance to airflow for peas and its dependence on grain depth and airflow rate
Lower right: equilibrium moisture content chart for hard red spring wheat illustrating the effect of air temp and air RH on the air’s capacity to dry wheat (green conditions will result in wetting, red conditions will result in drying)

13. Bunker testing validated at large scale
2000 bushel bin on a hopper with rocket aeration and 5 hp in-line centrifugal fan (with various inlet restrictors to allow some control over airflow rate). Sampling probe allowed collection of samples from various grain depths and in-grain sensors logged temp and RH within the grain near sampling location.

14. Other grain storage evalutions at pami
Determining most accurate way to measure duct pressure to estimate actual airflow rate
Assessing effect of various fan control strategies on drying rate and energy consumption
Use of supplemental heating to improve drying potential in adverse weather conditions

15. Planned nad trials with woody products
Effect of airflow rate (x3) and starting moisture content (x2) on drying rate for two different materials
Trial 1: Hog fuel
Trial 2: Sawmill chips
Will continuously monitor moisture loss, resistance to airflow, in-bin temperature and RH
End goal: use info to define best practices for using NAD with woodchips (including design of ducting and fan selection) and assess overall economic viability (including capital and operating costs)
Note: NAD in piles will generate lateral airflow whereas bunkers allow for vertical airflow only, but results from bunkers may be used to answer basic questions related to NAD of woodchips

16. Woodchip drying trials will include full characterization before and after drying
Including moisture content, bulk density, porosity and particle size distribution

17. Photos “borrowed” from Martin Blank and their test bunker
Photos “borrowed” from Martin Blank and their test bunker. Silo bunkers will allow replicated evaluation of different operating parameters to help optimize design and best practices for operation (and hopefully, optimize operation of fan to minimize costs associated with biomass drying)

18. Wrap up Bunker construction for woodchip NAD completed
Instrumentation being installed and verified
Commissioning trial with hog fuel planned for July
Two trials with target materials planned for Aug-Oct
Final report will be available by January
Funding provided by
PAMI’s Applied Bioenergy Centre
Natural Resources Canada
Manitoba Biomass Energy Support Program

19. Contact Joy Agnew jagnew@pami.ca (306) 682-5033 ext. 280
Questions or comments?
Contact Joy Agnew (306) ext. 280