Experimental simulation of a cross flow drying column Sangeeta Mukhopadhyay and Terry J. Siebenmorgen Pre-heating/ tempering bins Dryer Introduction Storage bins Storage bins On-farm rice drying facility On farm dryer Green rice (inlet) Green rice (inlet) Pre-heating bin Drying column Fan Burner Exhaust Drying column Hot air plenum Dry rice (outlet) Research Gap Rice lots are routinely dried in on-farm dryers as well as commercial dryers; in both cases, the thickness of the rice bed is approx. 12-15. Limited research on the impact of various drying-air conditions on head rice yield, as a function of drying-bed thickness. Overall goal - Generating data for a simulation model Objective Quantify the impact of various drying air conditions [temperature/relative humidity (Tda/RHda) and airflow rate (Q)] on head rice yield (HRY), with distance from the hot air plenum () for a stationary bed of rice. 1
From on farm dryer to laboratory set up Drying air leaving the drying bed Materials and Methods Drying air entering the drying bed Line of symmetry Laboratory set up Drying cylinders 8 in 2.4 in Cylinder 6 Screened bottom 14 in Heated air Cylinder 1 Hot-air plenum (on side wall) Screen Crimped end Controlled environment chamber Take a look inside Cylinder 6 Temperature/ relative humidity Cylinder 1 Airflow rate Fan Chamber 2
Experimental design six cylinder drying tests Factors: 1. Cultivar [CL XL745] 2. Initial moisture content (IMC) [18.5% (wb)] 3. Drying condition i. Drying-air conditions [122 F/18% RH, 131 F/15% RH, and 140 F/12% RH] - Drying-air temperature (T da ) - Relative humidity of the drying air (RH da ) ii. Air-flow rate of the drying air (Q) [34, 41, and 47 cfm/ft 2 ] iii.drying duration [50 min] Responses: 1. Head rice yield (HRY) 2. Moisture content after tempering (MC after tempering) Full Factorial design: 1 cultivar X 1 IMC X 3 drying-air conditions X 3 air-flow rates X 1 drying duration X 3 replications = 27 runs Experimental procedure Hybrid, long-grain cultivar CL XL745 at 18.5% (wb) HMC Cleaning Storing at 39 F (4 C) Equilibrating to room temperature for 24 h before conducting a drying run Conducting the drying run at set conditions Tempering of contents of individual cylinders at the T da for that run for 2 h Experimental procedure (contd.) Measuring MC of rice in each bag Gently conditioning the contents of each bag to 12.5% MC Results and Discussion six cylinder drying tests Milling analyses Report head rice yield 122 F 34 cfm/ft 2 131 F 41 cfm/ft 2 34 cfm/ft 2 41 cfm/ft 2 47 cfm/ft 2 140 F 122 F 131 F 140 F 47 cfm/ft 2 3
The full picture HRY The full picture MC after tempering Take home messages T da Q HRY and Both effects were more prominent in cylinders adjacent to the hot-air plenum. Question How do the drying air conditions impact rice that is near the hot air plenum (), in terms of head rice yield? Single cylinder drying work the idea! Cylinder 6 Single cylinder drying Cylinder 1 4
Experimental design single cylinder drying tests Factors: 1. Cultivar [XL753] 2. Initial moisture content (IMC) [17.5% (wb)] 3. Drying condition i. Drying-air conditions - Drying-air temperature (T da ) - Relative humidity of the drying air (RH da ) ii. Air-flow rate of the drying air (Q) [88 cfm/ft 2 ] 113 F/25% RH, 122 F/18% RH, 131 F/15% RH, 140 F/12% RH, 149 F/9% RH. 4. Final moisture content (targets) [16.5%, 15.5%, 14.5%, 13.5%, and 12.5% (wb)] Responses: 1. Head rice yield (HRY) 2. Moisture content after tempering (MC after tempering) Full Factorial design: 1 cultivar X 1 IMC X 5 drying-air conditions X 1 air-flow rate X 5 final moisture contents X 2 replications = 50 runs Controlled environment chamber Airflow rate Fan Chamber Load-cell assembly Temperature/ relative humidity Inside Experimental procedure Hook (connected to the load-cell assembly) Hybrid, long-grain cultivar XL753 at 17.5% (wb) HMC Cleaning Drying cylinder Storing at 39 F (4 C) Equilibrating to room temperature for 24 h before conducting a drying run Conducting the drying run at set conditions for the pre-selected duration Tempering of contents at the T da for that run for 2 h Experimental procedure (contd.) Control Hybrid, long-grain cultivar XL753 at 17.5% (wb) HMC Measuring MC of rice in each bag Gently conditioning the contents of each bag to 12 ± 0.5% MC (wb) Milling analyses Report head rice yield Cleaning Storing at 39 F (4 C) Equilibrating to room temperature for 24 h before conducting a drying run Gently conditioning to 12 ± 0.5% MC (wb) Milling analyses Report head rice yield (HRY) of CONTROL 5
Results and Discussion Drying curves Moisture content (% wb) 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Drying curves 0 100 200 300 400 500 Duration (min) 113 F/25% RH 122 F/18% RH 131 F/15% RH 140 F/12% RH 149 F/9% RH Drying durations to attain desired Final MC Predicted Duration (min) MC (% wb) 113 F/25%RH 122 F/18%RH 131 F/15%RH 140 F/12%RH 149 F/9%RH 16.5 33 15 13 12 9 15.5 67 27 24 22 18 14.5 105 47 36 32 27 13.5 149 71 50 43 38 12.5 200 99 68 56 51 Preliminary Results Head rice yield Future Work HRY of CONTROL = 49.2% 113 F/25% RH 122 F/18% RH 131 F/15% RH 140 F/12% RH 149 F/9% RH At each drying air condition, how much HRY reduction can be allowed adjacent to the without causing substantial HRY reduction in the entire bed? Simulation model on what happens inside the drying column with regards to HRY reduction? Effect of drying air temperature on other rice quality parameters? Type of fissures formed? Effect of air flow rate? 6
Acknowledgements Arkansas Rice Research and Promotion Board and University of Arkansas Rice Processing Program Industry Alliance Group for the financial support of this project Patrick Farias Thank you 7