Conference Agenda

There is increasing interest in Ontario about the impact of grain dryer sound emissions on neighbours as rural populations increase. Predicting the sound levels at particular distances from a dryer is complicated because different types of dryers produce different amounts of sound, and grain dryers are partially or fully surrounded by other structures, most commonly large steel grain storage bins. Prior studies by the research team measured sound levels in the areas around multiple Ontario grain dryers. However, since actual sites are complex, it is difficult to use measured data at one site to accurately predict sound conditions at a different site. Acoustic modelling software provides an opportunity to simulate specific sites as well as general configurations of dryers and structures to get insights needed to provide general guidelines for sound propagation at grain dryers and to model how different mitigations (like barriers or operational changes) would impact sound levels at neighbouring locations. This study used SoundPLAN software to trial three different sound propagation models (ISO 9613-2, CnossosEU and Nord 2000) to predict sound level distribution around actual grain dryers. Simulation accuracy was quantified using the degree of agreement with measured sound levels collected by the research team at four different grain drying sites in southern Ontario. It was found that error levels of less than 5 dB(A) could be consistently achieved using the more accurate CnossosEU model. Specific recommendations for simulating sound propagation from grain dryers and similar agricultural facilities will be reviewed.

New approaches to energy supply for low temperature grain drying have the potential to reduce energy costs, improve grain quality and yield climate benefits. Current options for drying grain using alternative energy sources are few, necessitating the development of new dryers optimized for this type of drying. This research project is studying a full-scale prototype of an electrically-powered air source heat pump, horizontal flow, low temperature batch dryer. Initial drying experiments have been completed in the prototype dryer with corn. The initial tests quantified the energy intensity and energy consumption of corn drying in the prototype dryer. Further analysis of the efficiency of the dryer will be included in future research and used to inform refinement of the prototype dryer design. Supporting lab-scale experiments have also been conducted to replicate drying processes to predict likely drying efficiency with other grains in a range of operating conditions. These lab tests provide supplemental data under controlled conditions to analyze how different variables impact the drying process. Tests of multiple drying iterations were conducted with cycles of rehydrated and dried grain. The low temperature drying cycles were shown to have negligible impact on grain germination rates. This ongoing research using full-scale field studies and laboratory experiments has already provided insights into the potential benefits of low temperature drying at a larger scale, which may include reduced greenhouse gas emissions, and lower and less variable energy costs than conventional high temperature drying with fossil fuels.

The main objective of this research was to develop a numerical model to simulate the transport phenomena involved in grain drying processes in mixed-flow grain dryers by coupling the discrete element method (DEM) and computational fluid dynamics (CFD), and utilize the proposed model for the design assessment and optimization of mixed-low grain dryers. The proposed model was validated against experimental literature data in terms of grain temperature and moisture content distribution, as well as grain movement and airflow pattern. Close agreements were achieved between simulated results of the coupled CFD-DEM model and published experimental data, with an average difference of 4.3% for grain temperature and 2.5% for grain moisture content. Using empirical models in the literature, risks of germination reduction and fissure (stress cracking) of grain kernels during drying was predicted based on the grain conditions simulated by the coupled CFD-DEM model. The proposed model provides a versatile numerical tool to assess the performance of mixed-flow grain dryers by quantify the uniformness of grain moisture content and temperature, as well as the risk of germination reduction and stress cracking of grain kernels. The model was applied to assessment of different duct designs and layouts in mixed-flow grain dryers. It was found that the air ducts with 60-degree angles resulted in the best drying performance among the five layouts that were simulated. The best layout had the ratio of vertical distance to duct height of 1.35 and the ratio of horizontal distance to duct width of 1.5.

Drying is essential for grain corn production to preserve harvested goods in high humidity. Current processes rely on fossil fueled heat sources, greatly contributing to their global warming potential (GWP) through greenhouse gas (GHG) emissions. A proposed solution for improving grain drying is the use of electric air source heat pumps (HPs) which are proven to increase efficiency while decreasing GHG emissions. This study uses a life cycle assessment to justify the environmental feasibility of transitioning from fossil fuels to HPs. The project boundaries included the manufacturing of heating units to sufficiently dry corn. Different electricity sources were assessed. For Ontario, a GWP reduction of more than 22.5 times was achieved by using HPs over fossil fuel heaters. For other provinces, 100% natural gas, and 100% coal sourced electricity, reductions in GWP over fossil fuel dryers were shown. The effect of the coefficient of performance (COP) on the GWP was studied. Assuming higher COP resulted in lower GWP: a COP of 9.5 had 2.4 times smaller GWP than a COP of 3.5. However, the COP of 3.5 still achieved 15.4 and 13.0 times less GWP than using natural gas and propane heaters respectively. The HP construction contributed significantly to its overall GWP (13.8%). The working fluid (R134a) was a major contributor to GWP (15.0%) but could be mitigated by choosing a cleaner working fluid (e.g. R1234z(E)). In summary, using electric HPs in Ontario grain drying appears to be an environmentally feasible substitute for propane and natural gas heaters.

Drying stands as a pivotal process in manufacturing, essential for removing moisture from materials. However, its energy-intensive nature leads to substantial energy consumption, accounting for more than 12% of total industry energy usage. Moreover, conventional thermal drying systems exhibit low energetic performance, contributing to environmental harm. The study aimed to introduce and compare three novel exergy-based real-time control schemes for manipulating and adjusting the recycle ratio of outflow air in dryers to enhance energetic and exergetic performance. The control schemes developed in the study include Scheme I, based on the thermophysical exergy efficiency, Scheme II, which considers the outflow wet exergy rate below a constant threshold value and Scheme III, which incorporates a varying threshold value for the outflow wet exergy rate. The drying process for poplar wood chips involved examining two drying air temperatures (55-70 ºC) and two air volume flow rates (360‒450 m3/h). Additionally, the total exergy of air exhaust from the drying chamber was also fractionated into thermophysical and wet exergies for further assessing the effect of the recycle fraction. The study found that the universal exergetic efficiency of the drying chamber varied from 30.2% to 95.5%, and the overall functional exergetic efficiency of the drying system suggested that implementing developed control schemes could enhance the functional exergetic efficiency of the dryers. This study revealed that control scheme III, demonstrating the highest improvement of up to 75%, could be implemented on industrial dryers to improve the energetic performance and environmental sustainability by recovering exergy from outflow air.

Atmospheric Freeze Drying (AFD) has emerged as a promising alternative to the conventional freeze-drying method (VFD). This technology is characterized by its ability to operate under atmospheric conditions, offers lower energy consumption, continuous processing, and cost-effectiveness, especially in cold climates where natural cooling can be exploited. Despite its advantages, AFD faces challenges such as prolonged drying times and potential product shrinkage, which are addressed through innovative hybrid techniques, incorporating thermal or mechanical energy inputs to enhance drying efficiency. This literature review presented a comprehensive analysis of recent advancements in AFD technology by examining both the fundamental principles underlying the process and innovative approaches designed to improve its efficiency. The investigation of AFD fundamentals demonstrated the importance of vapor partial pressure gradients and external factors such as boundary layer effects in enhancing the drying process. Hybrid approaches, such as heat pumps, vortex tubes, expanders, ultrasonic and microwave assistance, adsorbent usage, and fluidization, have shown significant savings in energy consumption and improvements in product quality. Additionally, this review examined the influence of process parameters such as drying temperature, air velocity, and sample characteristics on drying kinetics and product attributes, offering insights into optimal process conditions. Finally, the review explored modeling approaches, including diffusion models and the Uniformly Retreating Ice Front (URIF) model to provide a comprehensive understanding of drying kinetics, facilitating the optimization of drying processes. Despite the promising advancements, this review emphasized the need for ongoing research to and extend the applicability of advanced AFD technologies across various industrial sectors.

With rising concerns on sustainability, fuel sourcing for continuous dryers is shifting towards natural gas and propane, however, carbon dioxide (CO2) emission is inevitable, subject to levies. The continuous drying process, reliant on electrical energy along with fuel, results in a total emission of 0.209 tonnes (t) of CO2 equivalent/Gigajoule. The levy is expected to increase at $15/year until 2030 capping at $170/tCO2e on the top of the actual fuel cost. To address these issues, a three-year (2021-2023) on-farm study was conducted with 5 different dryers in Alberta. The initial grain moisture of 15 to 23% wet basis (wb) was dried at 49-93.3℃ with discharge rates of 10,402-51,709 kg/h (385-1800 bu/h). Actual energy was calculated with weather-normalized fuel and electricity consumption. Results showed that levies were 47% (average) higher than fuel costs for any dryer. Double-flow dryer emitted the lowest emission with the lowest cost due to its air-recirculation system. Approximately 20% cost increment was observed per point of initial moisture decrease from 23 to 18% wb. However, a 32% cost increase was observed from 17 to 15% wb. This showed that grain moisture below 17% wb should not be dried in high-temperature dryers unless waste heat is reused for operations to promote drying sustainability.

Drying and storage at sub-zero temperatures affects the quality of stored grains and oilseeds. This review explored the efficacy of sub-zero temperatures in prolonging the viability of food grains and oilseeds. Seed survival mechanisms, particularly the formation of intracellular glasses, play a crucial role in preserving biological structures in seeds. The focus was primarily on orthodox seeds, which are characteristic of most agricultural crops and known for their desiccation tolerance at sub-zero temperature conditions. Drying at these low temperatures along with a high airflow inhibits ice crystal formation and slows down metabolic processes. This property eventually helps in prolonging the seed survival. The review also discussed the varying moisture content thresholds for different seeds and the risk of spoilage and maintaining nutritional quality. Additionally, the review highlighted the environmental benefits of this approach, aligning with the objectives of sustainable agriculture by minimizing emissions and maximizing resource efficiency.