Biomass bale & propane hybrid grain drying

Objectives:

• Design a hybrid biomass and propane retrofit system specifically for on-farm grain dryers.
• Test and analyze design performance; develop design feasibility requirements for Ontario farmers.
• Analyze the life cycle economics and economic feasibility of on-farm grain drying with a biomass-propane hybrid system.

Impacts:

• Ontario farmers who currently dry grain with propane will be less exposed to risk from volatility in propane price and supply if a practical / reliable biomass and propane hybrid system can be developed.
• Combusting baled residue for drying grain will create a new market opportunity for crop residue.
• The retrofit system offers farmers low capital costs and simplicity by adapting existing dryers and using whole unprocessed biomass bales.

• Compared to energy from propane, the same amount of energy from sustainably removable crop residue is approximately ¼ the cost.

Scientific Summary:

Propane and natural gas are undoubtedly the most common methods for fueling grain driers in the province. Propane is popular in many areas because it has far greater accessibility than natural gas (only 20% of rural Ontario has access to natural gas utilities). However, the consumer price of propane is determined by local distributors, allowing for large price fluctuations. Natural gas prices are more consistent over time as they are regulated by the Ontario Energy Board. Natural gas is also relatively cheap. For example, propane at 45 cents/liter costs four times more per unit of energy than natural gas at 17 cents/cubic meter. For farmers without access to natural gas, development of an alternative to propane is an economic priority.

Crop residue plays an important part in maintaining soil organic matter (SOM) levels, nutrient cycles, and other services for soil life. When removing crop residue, a break-even cost which accounts for the value of nutrients, labour, and competing uses of the residue must be accounted for. A second consideration is the amount of residue that must be left in the field to maintain the SOM. It is understood that soil texture and management practises can greatly affect SOM behaviour. For example, planting a cover crop after removing wheat straw could offset the negative impact on soil health. Research at the Elora Research Station suggests that the minimum annual residue required to maintain SOM is 4,502 kg/ac/year. Residue produced in excess of this can be removed from the field without having significant impact on SOM. This is known as sustainably removable crop residue (SRR) and could potentially be used to fuel grain drying. There is now an opportunity to assess the life cycle economics of using crop residue for on-farm grain drying.

In North America there are very few examples of grain dryers fueled with biomass. Market research has shown there are three suppliers in Canada promising biomass furnaces suitable for grain drying: Mabre Air Systems, Säätötuli Canada, and Triple Green Products. These systems are all similar in that each one requires biomass in the form of chips, pellets, or finely shredded material. This is a problem for crop residue as it requires specialized equipment to prepare and store biomass. Since baling crop residue is the most common method of collection in Ontario, burning whole bales would improve feasibility for many Ontario farmers. Presently there is no whole bale burner readily available in the Canadian market.

This project proposed to design a furnace specifically designed for grain drying applications. A retrofit system was designed that uses readily available baled crop residue and incorporated existing propane-fueled equipment to create a hybrid system capable of continuous and reliable operation. The project also broke new ground by offering a full lifecycle assessment of biomass-fueled grain drying in Ontario.

Results

Experimental procedure. This iterative process, where each test performed increased in scale, revealed areas where improvements could be made before the next test. This continued until the system was ready to be used as a grain dryer. 4,400 bu of wet corn were successfully dried during testing in the fall of 2024.

Grain drying system performance. This was evaluated using the data gathered from the array of sensors revealing that the overall efficiency was low. Mechanical issues were reflected in the data showing the importance of continuous agitation and limiting the number of times the door is opened.

Design feasibility. The prototype was limited in its core function of producing heat; however, an improved design that is informed from the limitations of this protype should yield more feasible results.

Lifecycle Economics. When compared to a propane burner, the cost of energy is less for straw. Therefore, there is a utilization point where the biomass furnace costs less to run, despite its high initial cost.

Grain Drying / System Performance:

Theoretical Maximum Heat Power Produced: 226,000 W. Calculated by determining how much energy content there is in each bale and multiplying by the number of bales.

Heat Power Transferred from Furnace to Heat Exchanger: 59,587.82 W. Calculated using the temperature increase from atmospheric temperature to the average temperature measured at the inlet of the heat exchanger hot side, the mass flow rate of the combustion air, and the specific heat capacity of air under those conditions.

Heating Power Transferred Inside the Heat Exchanger: 53,344.59 W. Calculated using the average temperature decrease from the heat exchanger hot side inlet to the heat exchanger hot side outlet, the mass flow rate of the combustion air and the specific heat capacity of air under those conditions.

Heating Power Delivered to the Drier: 49,144.76 W. Calculated by determining how much heat was used to dry 4,400 bushels of corn from 18.5% moisture down to 15% over the duration of the experiment.

Heat Transfer Efficiency from Furnace to Heat Exchanger: 89.5%. This describes how well the heat was transferred from the furnace to the heat exchanger.

Heat Exchanger Number of Transfer Units: 0.789. This result describes a moderate number of transfer units. A low number would be less than 0.3 and a high number would be anything above 2. This is used to compare the performance of different heat exchangers.

Heat Exchanger Efficiency: 92.1% This result describes the effectiveness of the heat exchanger to extract heat from the hot side and move it to the cold side. This result is high and reveals that this design worked very well under these conditions.

Overall System Energy Efficiency: 21.7%. This result describes the effectiveness of the system as a whole in its ability to harvest heat from the bales and use it to dry grain.

Conclusions:

Overall, the design of the heat exchanger met its requirements. The heat exchanger was able to conduct heat at a high rate of efficiency into the drying air stream. Although the heat supplied to the heat exchanger was lower than required to achieve high temperature drying, the data and observations show that this heat exchange design should be capable of handling more heat. Results showed that the exhaust gas and the drying air reach an equilibrium at approximately the same temperature throughout the experiment. This shows that the heat exchanger is not operating at its full capacity because if the exhaust temperature would be higher than the drying air, then the heat exchanger would be undersized.

The design of this furnace was not up to the task of reliably and completely burning whole round bales. It was observed that poor bale agitation was the largest factor causing limited heat production. Each time the door was opened to manually agitate the bale, or add a new bale, it was seen that the temperature of the flue gas quickly increased. Shortly, thereafter, the temperature would begin to drop until the door was open again to agitate. This is indicative of ash smothering out the fire surrounding the bale. It was seen that as the rate of combustion decreases, so does the temperature. If this was an oxygen issue, then the fire would eventually reach a combustion rate equilibrium, which was not observed. Other factors causing the furnace to not meet its design requirements include jamming of the bale conveyor and poor ash removal. The bale conveyor was a complex component that was supposed to be able to accomplish many of the internal combustion chamber functions. The main functions that failed included bale agitation and moving ash out of the combustion chamber. Since it was not able to complete either of these tasks, the design of the conveyor is not a feasible solution for solving the problem of burning whole bales. Many other components require modification in order to function better, as previously mentioned. This furnace design overall was not successful. However, this does not necessarily reflect on the feasibility of burning whole round bales as a heat source. Using the lessons learned from this protype, it is likely that a different design would be capable of burning whole bales. Agitation of the ash layer and reliable bale advancement are key areas of concern. The trial data showed that straw is more economical per unit of energy than propane. Analysis of the lifecycle costs shows that incentives will be needed for general adoption in order to offset the high initial cost of the furnace. This research benefits Ontario’s Grain Farmers by providing a built and tested prototype as a first step towards a more refined whole bale furnace.

This furnace was designed for the unique requirements of grain drying, which any future design must continue to specifically address. Future research on this biomass hybrid grain dryer will be necessary before commercialization of a product for farmers can be made available. Next steps would be to develop a second furnace prototype using different and more reliable methods for bale agitation and ash removal. Drawing the combustion air through the furnace under negative pressure instead of pushing air through under positive pressure may also improve the design. Investigating a gravity fed combustion chamber design may also provide good research outcomes in the future.

External Funding Partners:

None.

Project Related Publications:

None.