Aeration vs NAD vs NAD+heating vs Heated Air Drying

Aeration vs NAD vs NAD+heating vs Heated Air Drying SEPTEMBER, 2018 @JoyAgnew3 @PAMI_Machinery

General grain drying principles Effect of adding heat on air s capacity to dry grain Sources of heat, sizing of heaters, cost of heating Best management practices for use of supplemental heating Knowledge gaps related to use of supplemental heat Options and equipment for heated air (batch and continuous) dryers Applying Technology for Agriculture

Hot/wet grain may spoil during storage Risk of spoilage depends on BOTH temperature and moisture content Cereals and pulses will look moldy, clumpy Oilseeds will look/smell burnt or ashy (sometimes clumpy as well)

Note: Oilseeds are considered dry at 10% and most cereals are considered dry at ~14% Source: Dr Noel White, AAFC, as posted on Canadian Grain Commission website http://www.grainscanada.gc.ca/storage-entrepose/ssg-de-eng.htm

Blow air through it Aeration = temperature control Reduces temp and evens out temperature profile Low airflow rates (0.1 cfm/bu) Natural air drying (NAD) = moisture and temperature control Supplemental heating can improve drying efficiency Mid airflow rates (1 cfm/bu) Heated air drying = moisture control Cooling cycle cools the grain after drying High airflow rates (~20 cfm/bu)

Air s ability to hold water depends on its temperature Time of day Temp Water holding capacity Relative humidity Actual water in air Capacity to take up water Noon 30ºC 30 g 50% 15 g 15 g Evening 10ºC 8 g 75% 6 g 2 g Air is technically drier in the evening but it s capacity to hold water is higher during the day!

Warm air Air @ noon (60% RH) Water holding capacity Cool air Air @ midnight (70% RH) Warms up Water holding capacity

EMC of air for wheat (using modified Henderson model) Temp Relative Humidity (%) ⁰C 35 40 45 50 55 60 65 70 75 80 85-2 11.5 12.2 13.0 13.7 14.5 15.3 16.0 16.9 17.7 18.7 19.8 2 11.1 11.9 12.6 13.4 14.1 14.9 15.6 16.4 17.3 18.2 19.3 5 10.9 11.7 12.4 13.1 13.8 14.6 15.3 16.1 17.0 17.9 19.0 8 10.7 11.5 12.2 12.9 13.6 14.3 15.1 15.8 16.7 17.6 18.7 10 10.6 11.3 12.0 12.7 13.4 14.2 14.9 15.7 16.5 17.4 18.5 13 10.4 11.1 11.8 12.5 13.2 13.9 14.6 15.4 16.2 17.1 18.2 15 10.3 11.0 11.7 12.4 13.1 13.8 14.5 15.2 16.1 17.0 18.0 18 10.1 10.8 11.5 12.2 12.9 13.6 14.3 15.0 15.8 16.7 17.7 22 9.9 10.6 11.3 11.9 12.6 13.3 14.0 14.7 15.5 16.4 17.4 26 9.7 10.4 11.1 11.7 12.4 13.0 13.7 14.4 15.2 16.1 17.1 28 9.6 10.3 11.0 11.6 12.3 12.9 13.6 14.3 15.1 15.9 16.9

Good drying weather requires a temp above 10 C and RH less than 70% Average daily temp in the Prairies drops below 10 C in mid to late September, during peak harvest season Supplemental heating can extend good drying weather to late November Applying Technology for Agriculture

Heated air drying uses high temperatures (as high as 75 C) and very high airflow rates (up to 20 cfm/bushel) Supplemental heating allows producers to extend season of good drying weather (up to 20 C) Typical NAD airflow rates still used (1 cfm/bu) Do NOT use supplemental heating unless the fan can achieve an airflow rate of at least 1 cfm/bu

New Air RH (decimal) Applying Technology for Agriculture 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0-10 deg C, 80% 10 deg C, 70% 15 deg C, 100% 0 20 40 60 80 100 New Air Temperature ( C) The more heat the better.but only to a point.

The key is to increase temperature of air (and thus it s capacity to hold moisture) WITHOUT adding water to the air Applying Technology for Agriculture

Increases the air s capacity to dry Useful for NAD only (not aeration) Accelerates the process or prolongs the drying season Sources of heat Electricity Propane Natural gas Biomass combustion Conductive heating (DryAir)

Electric and conductive heating = dry heating Electricity for heat + fan not always possible Conductive/hydronic systems not as commonly used Natural gas and propane = direct fired Flame is directly used to heat air By-product of combustion is water and CO 2 Burning propane generates 93 lb H 2 O per million btu (40 kg H 2 O per GJ) How much water is added per hour for a target airflow rate of 5000 cfm and target temp increase of 10 C using propane? Approx 7 lb/hr How does the amount of water added compare to the amount of water in (and removed from) the grain? Approx 45,000 lb in 5,000 bu of tough wheat Approx 150 lb/hr being removed

Capacity of heater depends on desired temperature change and airflow rate (size of bin) Heater Capacity (W) = temperature change C x airflow rate L x 1.28 s Heater Capacity W = temperature change C x airflow rate cfm x 0.6 Heater Capacity BTU = temperature change C x airflow rate cfm x 2.05 h Conversions: 1 btu/h = 0.293 W 1000 cfm = 472 L/s Temp change of 10 C = temp change of 18 F 1 W = 1 J/s 1 GJ is roughly equivalent to a million BTU Note: calculated heater capacity does NOT account for heat transfer losses (which can be as high as 50%, depending on configuration)

Example 1: Determine the heater capacity required to raise temperature by 10 C in a 5,000 bu bin with a target airflow rate of 1 cfm/bu Heater capacity = 10 x 5,000 x 0.6 = 30,000 W (or 30 kw) Heater capacity = 10 x 5,000 x 2.05 = 102,500 btu/hr Example 2: Determine the estimated rise in temperature that can be achieved if you have a 20 kw heater and an airflow rate of 2,000 L/s Temp rise = 20,000/2,000/1.28 = 7.8 C

Energy costs (valid as of January, 2017) Fuel Cost Cost ($/GJ) Natural gas $0.1387/m 3 $3.91 Electricity $0.053/kW-hr $14.81 Propane $0.49/L $19.37 To increase air temp by 10 C for a 5000 cfm system, it will cost between 50 cents and $3 per hour in fuel, depending on fuel type and efficiency of heat transfer system. For context, electricity to run a 10 hp fan will cost ~ $0.75/hr

Heat can be added upstream or downstream of the fan Upstream heating Easier to implement Suitable for retrofitting Can be transferred among bins Flame can be pulled in to the fan/motor and cause damage or result in fire risk Downstream heating More energy efficient Doesn t expose the motor/blade of the fan to increased temperature Heater must be installed when fan is installed Applying Technology for Agriculture

8. Heat coil assembly 9. Air tube 10. Aeration fan 11. Plenum 12. Intake air 13. Heated air 14. Saturated air 1. Central heating module 2. Hydronic water heater 3. Pump and controls 4. Circulation manifold 5. Flexible circulation line 6. Fixed insulated circulation lines 7. Quick coupler circulation hook-up From: Dryair.ca

Pros Extends harvest and drying window, increasing harvest efficiency Helps maintain grain quality (compared to no drying). Suitable for drying seed grain or sensitive grain (compared to heated air drying). Lower cost and less management than heated air drying Cons Added capital and operating cost (compared to NAD) High probability of overdrying bottom layers of grain (requires mixing or turning bin to achieve uniform grain) Installation of heater requires inspection and approval from appropriate regulating body

1. Only use a certified heater that is designed for use with grain storage fans for safety reasons 2. Ensure adequate airflow rate (minimum 1 cfm/bu) or there is risk of overheating the grain Low airflow rates may not have enough energy to fully remove moisture from the bin 3. Limit air temperature increase to 15 C or less Higher temp increases results in high fuel costs, reduced heat transfer efficiency, increased chance of overdrying, and increased chance of freezing/sticking at edge of bin For every temperature increase of 10 C, the RH of the air is cut in half 4. Do not exceed an inlet (after heater) temperature of 30 C Even though higher temp = more drying capacity, you do not want to overheat the grain Airflow rates of 0.75 to 1 cfm/bu can keep up with moderate drying rates, but not with high drying rates associated with high (>30 C) Applying Technology for Agriculture

5. As much as possible, maintain a CONSISTENT air temperature going into the bin 6. Ensure adequate ventilation in the headspace, consider use of active ventilation in the headspace 7. Target temp increase, airflow rate, and heat exchanger losses need to be considered when sizing a heater 8. Direct fired systems do add water to the air, but the amount of water is relatively insignificant compared to the water in the grain

9. Consider turning the grain partway through drying to distribute over-dry grain at bottom 10. Grain MUST BE turned and cooled to less than 15 C after drying Cooling will also remove some moisture, so drying may be complete when moisture is within 1% of target 11. Monitor grain conditions with in-bin cables during drying

Economics: when does it make sense to invest in heating equipment & fuel? Only in bad harvest years? Every year? Wider harvest window = higher grades, fewer harvest losses? Expected drying rates depending on airflow rate and temp increase Minimum airflow rate to minimize risk of damage when using supplemental heat

Required headspace ventilation depending on depth of headspace, airflow rate, moisture removal rate, etc. Recommended/allowable temperature increase when ambient air is below -10 C Upstream vs downstream heat addition Technology for better control of air temperature going into the bin Equipment options for high capacity fan + heater + generator? Applying Technology for Agriculture

Claim: 5000+ cfm @ 40+ in H 2 O (approx. 80-90 hp) Applying Technology for Agriculture

Single fan batch or continuous 300 to 1,100 bu/hr for 5% removal Dual fan batch or continuous 1,500 to 2,500 bu/hr for 5% removal Note: actual drying capacity will depend on ambient air conditions (temp and RH), grain type, and grain moisture content

Crossflow column tower drier 800 to 7,000 bu/hr Mixed flow tower drier 800 to 7,000 bu/hr Note: actual drying capacity will depend on ambient air conditions (temp and RH), grain type, and grain moisture content

Maximum temperature depends on seed type Grain mixing = more uniform drying Grain must be cooled before storage Energy savings up to 20% if dryaeration or other cooling strategies employed Hot grain removed from drier when ~2% above dry, then evaporative cooling results in dry product Cooling in a dedicated cooling bin rather than the drier can increase capacity of drier Drawbacks of cooling outside of drier Requires more grain handling and handling equipment Potential for condensation is high Potential for damage if hot grain is cooled too quickly or with air that is too cold Applying Technology for Agriculture

Description Drying timeframe ** Estimated operating cost** When to use Heated air drying Batch or continuous process, dedicated equipment, high energy requirement Hours 20 to 30 cents/bu When grain is more than 5-10% over target moisture content When large volumes of grain must be dried quickly NAD In-bin drying, using ambient air Weeks (to months) 3 to 5 cents/bu When grain is a few points over target moisture content Early in harvest season when average temp is >10 C NAD + heat In-bin drying, using warmed ambient air, moderate energy requirement Days (up to a week) 6 to 10 cents/bu When grain is a few points over target moisture content When relatively small volumes of grain must be dried quickly Later in the harvest season when average temp is <10 C Assuming propane heat, 5% moisture removal, 5000 bu, 1 cfm/bu for NAD and NAD+heat, 7 days for NAD, 3 days of NAD+heat with 2 days of just NAD

Higher air temp = greater capacity to dry Higher airflow rate = more efficient moisture removal NAD, NAD+heat and heated air drying options all require understanding and management Grain conditions need to be monitored (particularly when drying with heat) Take home message grain storage and aeration requires proper monitoring and management. Better understanding = better management decisions