Flat bed drying including survey results on the drying costs of various drying methods practiced in mekong delta

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FLAT BED DRYING INCLUDING SURVEY RESULTS ON THE DRYING COSTS OF VARIOUS DRYING METHODS PRACTICED IN MEKONG DELTA " SECTION 3 FLAT BED DRYING INCLUDING SURVEY RESULTS ON THE DRYING COSTS OF VARIOUS DRYING METHODS PRACTICED IN MEKONG DELTA 93 CARD Project FLAT-BED DRYER Sub-Component 2006/2007 Report Reporting period: from 15 May 2006 to 28 Feb 2007 Compiled by: Phan Hieu Hien, Ph.D. with contributions from staff of the NLU Center for Agricultural Energy and Machinery: Le Quang Vinh, Tran Thi Thanh Thuy, Tran Van Tuan, Nguyen Thanh Nghi. March 2007 94 CONTENTS CARD PROJECT, FLAT-BED DRYER SUB-COMPONENT 2006 REPORT.....96 1 INTRODUCTION.....................................................................................................96 2 INSTALLATION OF THE 8-TON FLAT-BED DRYER....................................96 3 EXPERIMENTS WITH THE 8-TON DRYER UNDER ACTUAL PRODUCTION CONDITIONS..............................................................................98 4 5 3.1 Objectives.........................................................................................................98 3.2 Materials and methods...................................................................................98 3.3 Results and discussion:.................................................................................98 3.3.1 July 2006 experiments .............................................................................98 3.3.2 March 2007 experiments..........................................................................98 FABRICATION OF A LAB (MINI) DRYER FOR EXPERIMENTING UNDER CONTROLLED CONDITIONS. ...........................................................99 4.1 Objective ..........................................................................................................99 4.2 Materials and methods...................................................................................99 4.3 Results and discussion (1-to dryer) ...........................................................104 THE PRRA SURVEY ON THE USE OF FLAT-BED DRYER AND THE COST OF VARIOUS DRYING METHODS IN THE MEKONG DELTA. ...110 5.1 Background ...................................................................................................110 5.2 Objectives.......................................................................................................110 5.3 Method...........................................................................................................110 5.4 Result and discussion....................................................................................110 5.4.1 Background data ....................................................................................110 5.4.2 Post-harvest and drying status .............................................................112 5.4.3 Conclusions............................................................................................114 6 EXTENSION MATERIALS FOR TRAINING COURSES, BASED ON THE OUTCOME OF THE SURVEY AND EXPERIMENTS .................................115 7 CONCLUSIONS AND FURTHER PROPOSALS ...........................................116 8 EVALUATION OF FARMERS’ PRACTICE .....................................................117 8.1 9 Value losses due to field drying and sun drying ..........................................117 REFERENCES ........................................................................................................118 10 APPENDIX ..............................................................................................................119 10.1 Appendix 1 : Paddy milling quality analysis (procedure by IRRI) ............119 95 CARD Project, FLAT-BED DRYER Sub-Component 2006 Report (from 15 May 2006 to 28 February 2007) 1 INTRODUCTION The sub-component of CARD Project 026/VIE-05 on the flat-bed dryer study, as specified in the contract, consists of the following activities: • Select the site and supervise the installation of an 8-ton flat-bed dryer for experiments. • Conduct experiments with the 8-ton dryer under actual production conditions. • Build a lab (mini) dryer and other needed tool for experimenting under controlled conditions. • Conduct experiments to determine the optimum drying conditions for the flat-bed dryer (with or without air reversal) using the lab mini-dryer at the Nong-Lam University or a nearby location. • Conduct a Participatory Rapid Rural Appraisal (PRRA) survey on the use of flat-bed dryer in the Mekong Delta. • Write extension materials for future training courses, based on the outcome of the survey and experiments. The above activities can be clustered into 3 groups: - The 8-ton dryer - The 1-ton dryer - Survey, training, and extension This is the final report of the above-mentioned activities, covering the period from 15 May 2006 to 28 Feb 2007. It is compiled from 2 earlier Progress Reports, and updated with most recent data and findings, thus conclusions from this report supercede the earlier reports for any discrepancies. 2 INSTALLATION OF THE 8-TON FLAT-BED DRYER Together with the Project Leader, Dr. Truong Vinh, we selected the site for installing the 8-ton flat-bed dryer; the site was Tan-Phat-A Cooperative, located in Tan-Hiep District, Kien Giang Province. At first, we intended to contract from a local dryer builder for a typical dryer in the region, adding features needed for the experiment, but no contractor was willing to meet the needs they considered too time-consuming with these added features in a miscellaneous contract for their business. So, the research team decided to build an 8-ton air-reversible dryer which is a SRA-8 design from NLU with slight modifications. The installation of the dryer was completed in mid-July 2006 (Fig.1 & 2), just in time for the wet-season harvest and for experimental purposes. 96 Figure 1: The 8-ton dryer at Tan-Phat-A Cooperative, Kien Giang Figure 2: The 8-ton dryer with the air for downward direction . 97 3 EXPERIMENTS WITH THE 8-TON DRYER UNDER ACTUAL PRODUCTION CONDITIONS. 3.1 Objectives To determine the performance of the dryer under actual production conditions, for different drying regimes. 3.2 Materials and methods The experiments were conducted in July 2006 Tan-Phat-A Cooperative, Tan-Hiep District, Kien-Giang Province. Eight experiments were done, with 2 factors under study. • Air reversal at 2 levels: a) YES , and • Drying temperature at 2 levels: a) Constant at 43 oC ; and b) At 50 oC for the first hour, and afterwards constant at 43 oC. In reality, due to the furnace configuration, the temperature rarely exceeded 50 oC, and was about 48 oC at most. b) NO Each treatment was replicated twice. However, due to severe difficulty in securing batches of the same quantity or initial moisture content, the experiments were not strictly factorial. The arrangement of factor levels is for systematic observation only. Due to different views on milling analysis, data on head rice recovery were discarded. Thus in March 2007, another set of experiment was replicated, with focus on comparing the crack and head rice recovery of 2 different drying modes, namely with and without air reversal. Sun drying on the cement drying yard with a 7-cm paddy layer, as popularly practiced by local farmers, was replicated as control treatment. The crack analysis was done at the VINACONTROL, an accredited agency in charge of certifying the rice quality for export. Each treatment was analyzed by 3 samples, each consisting of 30 grains taken at random; each paddy grain was hand-husked and examined under the magnifying glass for fissure. The head rice recovery analysis was done at the Rice Quality Laboratory of the NLU Chemical Technology Department, following procedures adopted by International Rice Research Institute (see Appendix) and the University of Queensland. 3.3 Results and discussion: 3.3.1 July 2006 experiments The experiment results are summarized in Table 1. Figures 3 and 4 show the moisture reduction curves. Remarks: - The effect of air reversal is very apparent in reducing the final moisture differential. When operated correctly, this differential is less than 2 % with air reversal, but at least 5% without air reversal. More MC differential means more rice cracking during milling. This explains why dryers installed since 2003 have been more and more of the reversible principle. - Air reversal also decreased the drying time. - The drying temperature is stable and can be kept within ± 3 oC. 3.3.2 March 2007 experiments Results are in Table 2. All 3 above observations hold with these new experiments. Data on the crack of rice upon milling show that: 98 a) Mechanical drying, whether with or without air reversal, is superior to sun drying in terms of less crack percentage or more head rice recovery. About 3- 4 % less cracking, and about 4 % more head rice recovery are main data obtained from this set of experiments. b) Mechanical drying with air reversal resulted in less Final MC differential (2.2 %) compared to without air reversal (4.6 %) c) The increase in crack percentage between mechanical drying with and without air differed by only 1 %; while judged by the head rice recovery, the difference was only 0.4 %, or almost no difference (Table 2). This was not expected in line with the above data on Final MC differential. Thus more experiments should be conducted in the future to confirm the trend. 4 FABRICATION OF A LAB (MINI) DRYER FOR EXPERIMENTING UNDER CONTROLLED CONDITIONS. 4.1 Objective To determine the performance of the 1-ton dryer under controlled conditions. 4.2 Materials and methods A lab mini-dryer of maximum capacity of 1 ton was designed and fabricated for experimenting under controlled conditions.. (Fig.5) (a) (b) Figure 5: The 1-to dryer: Airflow upward; (b) Downward reverse airflow 99 Table 1: Summary of 8 drying batches (July 2006 ) 2523-7 25-7 Date /2006 26/7 30-7 24-7 27-7 23-7 29-7 Batch Number 1 5 4 8 3 6 2 7 Temperature, oC 43 43 43 43 48 x43 48 x43 48 x43 48 x43 Air reversal Yes Yes No No Yes Yes No No Drying time, h+xx/100 10.42 6.00 10.50 8.75 10.00 3.58 5.75 11.67 Air reversal time, minute 10 15 --- --- 15 10 --- --- --- --- 60 --- --- --- --- Break-down time, minute Ave Initial MC, % 27.4 19.3 21.5 24.5 25.6 20.7 25.6 26.0 Final MC: Bottom, Max: 9.1 13.9 11.7 13.2 13.4 14.1 8.1 12.8 Final MC: Bottom, Min: 5.9 12.1 11.2 11.2 12.2 13.1 6.1 10.6 Final MC: Bottom, Ave,%: 8.2 13.4 11.6 12.0 12.7 13.6 7.6 11.3 Final MC: Top, Max: 15.5 14.9 23.1 22.7 17.3 15.2 13.0 22.6 Final MC: Top, Min: 15.2 13.3 15.2 15.5 15.8 14.4 12.2 17.8 Final MC: Top, Ave, %: 15.3 14.2 18.9 19.1 16.5 14.8 12.5 20.4 7.1 0.8 7.3 7.1 3.8 1.2 4.9 9.1 10.13 9.72 10.23 9.62 10.23 9.78 9.78 9.71 0.28 0.22 0.16 0.17 0.16 0.22 0.15 0.20 5.31 5.10 5.37 5.05 5.37 5.13 5.13 5.10 5.19 42.8 42.5 43.3 41.4 42.2 44.8 42.2 44.3 42.9 2.0 2.8 2.4 2.8 3.6 2.8 3.6 3.2 2.9 16.2 16.25 12.41 12.14 12.0 11.83 12.0 12.20 13.1 Bulk density:Before, kg/m 521 505 529 495 529 525 522 523 519 After drying, kg/m3 480 484 465 493 498 515 477 503 489 Paddy : BEFORE, kg 8338 7246 8185 7860 8805 8724 5307 9438 AFTER drying, kg 6946 6564 --- 7368 7462 7706 4599 8307 Grain depth: BEFORE, m 0.508 0.456 0.491 0.504 0.528 0.528 0.323 0.573 AFTER drying, m 0.459 0.431 --- 0.474 0.475 0.475 0.306 0.524 416.4 206.4 220.9 282.2 371.5 138.9 160.5 373.0 39.95 34.40 21.04 36.41 37.16 38.80 27.92 31.96 18.0 17.0 16.6 12.0 17.00 6.0 9.50 17.0 1.73 2.83 1.58 1.55 1.70 1.68 1.65 1.46 Final MC differential, % Air SUPERFICIAL Velocity Average , m /minute ± Std. Dev., m /minute AIR FLOW, m3/s Av. Drying temp, oC ± Std.Dev, oC Temp. Increase, oC 3 Husk consumption: Total, kg kg/ hour Diesel consump. :Total, Lit Lit/ hour 9.90 33.45 1.77 100 Table 2: SUMMARY results of March 2007 experiments: Comparison of 2 drying batches Batch 1 (46+43 oC, with air reversal). Batch 2 (46 x43 oC, WITHOUT air reversal) (46 x43 = 46 oC in first 1,5 hours, &43 oC in remaining time) Place Tan Phat A Cooperative, Ken Giang Province. Date: March 2007 Batch Number Batch 1 Batch 2 Air reversal Yes Drying temperature (oC) ± StDev No 43.3 ± 3.1 43.0 START date-time 08-03-07 10:30 10-03-07 11:30 END date-time 08-03-07 16:30 10-03-07 17:30 6.00 6.00 Drying time, h+xx/100 Air reversal time, minute ± 2.9 15 Laborer for air reversal 2 Initial MC, % (Ave ± StDev) 23.86 Final MC % (Ave ± StDev) 14.94 ± 0.71 20.41 ± 0.45 16.07 Top layer 13.92 0.31 18.23 0.75 Middle layer 16.16 1.05 16.38 0.7 Bottom layer 14.75 0.63 13.59 0.47 MC differential Top-Bottom, % MC differential Middle-Top , % 0.83 4.64 2.24 AIRFLOW (20 points) Airflow, m3/s 5.88 Superf. vel. (Ave ±StDev), m/min 11.20 5.70 ± 0.30 10.85 Rice husk consumption: kg /batch 171.2 215.2 Rice husk consumption: kg / hr 28.5 35.9 Diesel consumption, liter /h 1.70 1.75 Initial Paddy mass, kg 9276 9197 Initial Paddy Layer (Ave±StDev), mm 517.8 15.6 507.8 ± 0.37 7.5 Crack BEFORE drying, % 12.00 Differ 21.00 Differ Crack AFTER drying, % 13.75 1.75 23.75 2.75 Crack, Sun drying on Cement yard, 7-cm layer, % 17.80 5.80 26.80 5.80 Head Rice Recovery, % Head Rice %, BEFORE drying 62.72 Differ 59.12 Differ Head Rice %, AFTER drying 59.39 -3.33 56.21 -2.91 Head Rice %, Sun drying 55.58 -7.14 52.12 -7.00 Difference (Sun & Mechanical) . % -3.81 -4.09 101 BATCH 1 ( 43 oC, With air reversal ) BATCH 4 ( 43 oC, Without air reversal) Meû 1, Ñaû o gioù , 43 oC MEÛ 4 (saáy 43 oC, KHOÂNG ñaûo gioù) Döôù i 1 25 Döôù i 2 20 Döôù i 3 15 Döôù i 4 Döôù i 5 10 Treâ n 1 5 Treâ n 2 0 Treâ n 3 0 2 4 Thôø i gian saá y 6 8 10 12 30 AÅ m ñoä MC %(wb) AÅ m ñoä MC %(wb) 30 Döôùi 1 25 Döôùi 2 20 Döôùi 3 15 Döôùi 4 Döôùi 5 10 Treân 1 5 Treân 2 0 Treâ n 4 Treân 3 0 Treâ n 5 Döôù i 2 20 Döôù i 3 Döôù i 4 15 Döôù i 6 10 Treâ n 1 5 Treâ n 2 Treâ n 3 0 Thôø i gian saá y 3 4 10 12 Treân 4 Treân 5 Drying time, h 5 6 30 AÅ m ñoä MC %(wb) AÅ m ñoä MC %(wb) Döôù i 1 25 2 8 Meû 8 (saáy 43 oC, KHOÂNG ñaûo gioù) 30 1 6 BATCH 8 ( 43 oC, Without air reversal) MEÛ 5 (saá y 43 oC, COÙ ñaû o gioù ) 0 4 Thôø i gian saá y Drying time, h BATCH 5 ( 43 oC, With air reversal ) 2 Döôùi 1 25 Döôùi 2 20 Döôùi 3 15 Döôùi 4 10 Döôùi 5 Treân 1 5 Treân 2 0 Treâ n 4 Treâ n 6 Drying time, h Treân 3 0 1 2 3 4 Thôø i gian saá y 5 6 7 8 Drying time, h 9 Treân 4 Treân 5 Figure 3: Moisture reduction curves at 43 oC 102 BATCH 3 (48 oC + 43 oC, With air reversal ) BATCH 2 (48 oC + 43 oC, Without air reversal ) MEÛ 3 (saáy 50 oC + 43oC, COÙ ñaûo gioù) MEÛ 2 (saáy 50oC + 43oC, KHOÂNG ñaûo gioù) 30 Döôùi 1 25 AÅ m ñoä MC %(wb) AÅ m ñoä MC %(wb) 30 Döôùi 2 20 Döôùi 3 15 Döôùi 4 10 Döôùi 5 Treân 1 5 Treân 2 0 2 4 6 8 Thôø i gian saá y 10 12 14 Döôùi 2 20 Döôùi 3 15 Döôùi 4 10 Döôùi 5 Treân 1 5 Treân 2 0 Treân 3 0 Döôùi 1 25 Treân 3 0 Treân 4 Treân 5 Drying time, h BATCH 6 (49 oC + 43 oC, With air reversal ) BATCH 7 20 Döôùi 3 15 Döôùi 4 10 Döôùi 5 Treân 1 5 Treân 2 0 Treân 3 Thôø i gian saá y Drying time, h 5 6 Treân 4 Treân 5 Drying time, h 30 4 Treân 4 Treân 5 AÅ m ñoä MC %(wb) AÅ m ñoä MC %(wb) Döôùi 2 3 4 (48 oC + 43 oC, Without air reversal ) Döôùi 1 25 2 3 MEÛ 7 (saáy 50 oC +43 oC, KHOÂNG ñaûo gioù) 30 1 2 Thôø i gian saá y Meû 6 (saáy 50 oC +43 oC, COÙ ñaûo gioù) 0 1 Döôùi 1 25 Döôùi 2 20 Döôùi 3 15 Döôùi 4 10 Döôùi 5 Treân 1 5 Treân 2 0 Treân 3 0 2 4 Thôø i gian saá y 6 8 10 Drying time, h 12 Treân 4 Treân 5 Figure 4: Moisture reduction curves at 48 oC in the first hour, and 43 oC afterwards. 103 .The SRA-1 dryer fan was tested for the performance (Fig.6) SRA-1 FAN 40 2.0 Static Pressure, mmH2O 30 1.5 Static.Eff , % 25 20 1.0 15 10 0.5 Power, kW Stat.Pressur, mmH2O ; Efficiency, % 35 5 0 M ech. Eff, % Power kW 0.0 0.8 0.9 1.0 1.1 1.2 3 Airflow, m /s Figure 6: Fan performance of the SRA-1 dryer Originally, three factors were planned for study: − Air reversal at 2 levels: a) YES , and b) NO − Drying temperature at 2 levels: a) Constant at 43 oC ; and o b) At 50 C for the first hour, and afterwards constant at 43 oC. − Final moisture content at 2 levels: a) 14.5 % ; and b) 17.0%. Thus there would be 8 treatments, arranged in blocks, so that the initial moisture contents in each block are similar. However, in actual conditions, it was impossible to arrange for the blocks with same moisture content since the paddy belongs to the owner or the rice miller. Eight experiments would last at least 4- 8 days, thus even if the same paddy field were booked for the test, the initial MC would be different. With different input MC, the final MC at 2 levels would not make sense, at different drying rates. So we decided to conduct paired experiments, based on the first variable, namely with or without air reversal. Each pair was combined with a level of the second variable (drying temperature). Each pair draw from the same lot of paddy input, thus could be assumed as having the same initial MC. 4.3 Results and discussion (1-to dryer) The experiment results are summarized in Table 3. Figures 7 and 8 show the moisture reduction curves. 104 Table 3: Summary of 8 drying batches Nong-Lam University Center for Agr. Energy & Machinery No Drying conditions Date TESTS: drying paddy with SRA-1 dryer (CARD Project) Place : Le- Minh BRVT Rice Mill 8 drying batches Batch 1 50+43o C with Air Batch 2 Batch 3 50+43oC Without Air Reversal 43oC Without Air Reversal Batch 4 43oC with Air Batch 5 Batch 6 43oC with Air Reversal 43oC Without Air Reversal Reversal Reversal 09-16/ Dec.2006 Pers: : TTT Thuy, NV Quy Batch 7 50+43 oC with Air Batch 8 Note 50+43oC Without Air Reversal Reversal 1 Date 10 /12 /06 11 /12 /06 1112/12/06 12 /12 /06 1314/12/06 14/12/06 15/12/06 16/12/06 2 3 4 5 6 7 8 9 10 11 12 13 14 Paddy MC Before drying (%) Paddy MC After drying (%) Ave. Final MC, Top layer Ave. Final MC, Bottom layer Final MC Differential = Top - Bottom Layer thickness before drying (m) Layer thickness after drying (m) Fresh /Dried before air reversal - Top Layer Fresh /Dried after drying - Top Layer Fresh / Dry Ratio before air reversal - Bottom L. Fresh / Dry Ratio after drying - Bottom Layer Coal consumption (kg) Coal consumption (kg / hr) 24.71 13.43 18.84 12.82 0.364 0.321 1.11 1.22 1.36 1.39 22 1.93 0.243 0.230 24.35 12.62 13.9 11.8 2.1 0.248 0.208 1.11 10 2.50 1.26 18 2.25 25.97 12.49 12.8 11.0 1.8 0.405 0.361 1.19 1.29 1.41 1.45 17 1.55 21.83 12.64 13.3 11.1 2.2 0.249 0.220 1.18 27.70 13.53 13.6 11.7 1.9 0.379 0.350 1.10 1.25 1.34 1.36 20 1.74 27.35 13.35 13.6 11.4 2.2 0.261 0.230 1.07 21.10 13.65 12.9 11.2 1.7 0.246 0.219 1.14 1.20 1.23 1.25 9 0.84 1.23 1.38 8 1.23 1.13 1.20 0.00 Table 3 (continued) 105 No 18 19 20 21 22 23 24 25 26 27 28 29 30 Drying conditions Air SUPERFICIAL Velocity, Ave (m/minute) Batch Batch 2 1 50+43 50+43oC o Without C Air with Reversal Air Reversa l 11.46 0.42 Batch 3 43 oC Without Air Reversal Batch 4 43 oC with Air Reversa l Air SUPERFICIAL Velocity, Std.Dev., m/minute) Air Flow, m3 / s 0.76 > 0.80 Air flow rate (m3 /s / ton) > 1.39 1.32 Mass of Paddy Before Drying (kg) 893 572 576 606 Mass of Paddy After Drying(kg) 665 474 420 434 Mass Reduction, Actual (kg) 228 98 155 172 Mass Reduction, from MC calc.(kg) 116 39 77 52 Ratio Reduction: Actual/ MC Calc. 2.0 2.5 2.0 3.3 Drying time (hr) 11.42 4.00 8.00 10.67 Time of Air Reversal, after (hr) 7.00 7.00 Bulk Density WET, kg / m3 613 588 581 616 3 Bulk Density DRIED , kg / m 695 621 692 692 Note Batch 1 &2 for Lots of immature, tune-up green grains. Batch 3 & 3: from same input paddy Batch 5 Batch 6 43 oC with Air Reversal 43 oC Without Air Reversal Batch 7 50+43 o C with Air Batch 8 Note 50+43 oC Without Air Reversal Reversal > 0.79 > 0.80 > 0.99 > 1.43 803 560 851 586 556 381 620 486 247 179 231 100 132 90 131 62 1.9 2.0 1.8 1.6 11.50 6.50 11.00 7.20 9.00 9.00 530 535 525 588 573 608 590 666 Good grain, little impurities - Very wet paddy, forced aeration for 1.5 hr to obtain desired initial MC - Lots of immature grains & impurities -Batch 5, 6& 7: from same input paddy 106 BATCH 3 ( 43 oC, Without air reversal) BATCH 4 ( 43 oC, with Air reversal) Batch 3 ( 43 oC, Without Air Reversal ) B a tc h 4 (43 o C , with Air R e ve rs a l ) 28 28 26 24 T1 26 T2 24 T3 22 22 T4 20 T5 16 14 12 2 3 4 5 6 7 8 9 10 T4 T5 D1 D2 16 D2 D3 14 D4 12 D3 D4 D5 10 10 1 T3 18 D5 0 T2 20 D1 18 T1 0 11 12 1 2 3 4 5 6 7 8 9 10 11 12 Drying tim e , hr D rying t im e , hr Batch 6 (43 oC, Without Air Reversal ) Batch 5 (43 oC, with Air Reversal ) Batch 6 (43 o C, Witho ut Air Revers al ) Batch 5 (43 oC, with Air Reversal ) 28 28 24 22 20 18 16 14 12 10 T1 26 Moisture content, % T1 T2 T3 T4 T5 D1 D2 D3 D4 D5 26 T2 24 T3 22 T4 20 T5 18 D1 D2 16 D3 14 D4 12 D5 10 0 1 2 3 4 5 6 7 8 9 10 11 12 Drying time , hr Figure 7 : 0 1 2 3 4 5 6 7 8 9 10 11 12 Drying time, hr Moisture reduction curves at 43 oC drying temperature 107 Batch 8 (50 oC + 43 oC, WITHOUT Air Reversal Batch 7 (50 oC + 43 oC, with Air Reversal ) Batch 8 (50 oC + 43 oC, WITHOUT Air Reversal Batch 7 (50 oC + 43 oC, with Air Reversal ) 28 26 T1 26 T1 24 T2 24 T2 22 T3 20 T4 18 T5 16 D1 14 D2 12 D3 10 D4 0 1 2 3 4 5 6 7 8 9 Drying time, hr Figure 8 : 10 11 12 D5 Moisture content, % Moisture content, % 28 22 T3 20 T4 18 T5 16 D1 14 D2 12 D3 D4 10 0 1 2 3 4 5 6 7 8 9 10 11 12 D5 Drying time, hr Moisture reduction curves. at 50 oC + 43 oC drying temperature 108 The following remarks could be pointed out: - The effect of air reversal was very apparent in reducing the final moisture differential (FMD). Without air reversal this FMD was larger than 2 % point. With air reversal, it was less than 2 % point; even that the grain quantity dried was much more than the former case. - For this lab dryer, air reversal did not decrease the drying time, because for the same airflow, with less grain on the floor, the specific airflow rate (per ton) was higher in the case air was not reversed. . - The drying temperature is stable and can be kept within ± 2 oC. The above remarks do not offer much new findings; yet the tests give specific and handy data for preparing training materials on rice drying, as part of the Project activities. The problem of non-uniformity of the input materials for testing is reflected with data on the bulk density of the input (wet) as well as the output (dried) paddy (Fig..9) SRA-1, Ba-Ria VT, Dec.2006 (DRIED paddy) Bulk density, kg /m3 640 620 600 kg/ m3 580 Regression 560 540 520 18 20 22 24 26 Bulk density, kg /m3 SRA-1, Ba-Ria VT, Dec.2006 (Wet paddy) 28 700 650 600 550 500 12.0 12.5 13.0 13.5 14.0 Moisture content, % wb Moisture content, % wb (b) (a) Figure 9: Bulk density of the wet (a) and dried paddy (b) used in the tests. The learning experience from the tests have been: A balanced set of experimental data for drying treatments of even 1 ton each is difficult to obtain under actual field conditions. Perhaps, a quantity of around 20 kg each is more appropriate. Even so, cold storage room is needed for conditioning the grain for one-week-long testing. Miscellaneous equipment such as cleaner is also needed. All these rigorous procedures would give pure academic results, which in fact do not reflect the realities, as the graph on the bulk density showed. Thus in the future, an alternative ---that several drying researchers followed--- would be modeling of the drying process. This hopefully can cope with diversities in material conditions as well as ambient conditions. Another constraint was the laboratory milling equipment for milling analysis (for head rice recovery) could not be standardized for proper operation at the time. Page 109 5 THE PRRA SURVEY ON THE USE OF FLAT-BED DRYER AND THE COST OF VARIOUS DRYING METHODS IN THE MEKONG DELTA. By the terms of the contract, two other activities were conducted: The survey using the Participatory Rapid Rural Appraisal (PRRA) method on the use of flat-bed dryer in the Mekong Delta and the cost of drying; and the writing of extension materials for future training courses, based on the outcome of the survey and experiments. 5.1 Background The flat-bed dryer has been with the rice agriculture in the Mekong Delta of Viet Nam since early 1980’s. Its development over the past 25 years and its current status need to be examined in the context of the CARD Project 026/VIE-05 with focus on the cracking of paddy grains in the area. Thus a survey using the PRRA method on the use of flat-bed dryer in selected Provinces of the Mekong Delta was conducted. 5.2 Objectives - To confirm the role of flat-bed dryers in reducing post-harvest losses and in preserving rice quality. - To identify operating factors of the flat-bed dryer which contribute to the reduction of rice crack. - To identify problems with the flat-bed dryer that the CARD Project could possibly help. 5.3 Method The survey used the PRRA method, through interviewing different people class, from farmers to rice millers to governmental officials… But it also relied heavily on both available data gathered in the past 10 years by various agencies, and on personal experience of the people involved with the dryer at NLU over the past 20 years. Four Provinces were selected, namely Can-Tho City, Kien-Giang, Long-An, and Tien-Giang. The first three Provinces have sites which had been selected by the CARD Project for all related experiments, demonstrations, and extension activities. The fourth Province is adjacent to Long-An, and also planned as site for rice milling survey, so facts and data on the dryer would be relevant. Note: Can-Tho = Can-Tho City, which used to be part of Can-Tho Province, and is about half of the latter in terms of rice land. 5.4 Result and discussion 5.4.1 Background data The 4 Provinces under study have similar data in terms of climate and other agricultural features. All have the average monthly temperature of 27- 28 oC, with the average maximum of 29 oC in April and minimum of 25 oC in January. But the temperature difference between daytime and night time is more pronounced, say between 25 and 36 oC in hot months, or 23 and 33 oC in cooler months. Page 110 The rainy season in the region occurs from May to October, the remaining months are dry season (no Spring, Summer …Winter like in Northern Provinces). The annual rainfall is 1 400 mm in Long-An, and higher in Can-Tho and Kien-Giang (1 600 and 1800 mm respectively). The average annual relative humidity is 80- 82 %. This just says that is typical tropical humid climate, and not specific enough about its significance in post-harvest. Figure 10 presents average variation of a typical day of March (dry season) and of August (rainy season) in Can-Tho, which is very similar to that of other places in the Mekong Delta. Whether in rainy or dry season, the relative humidity during the night time (21h00 PM to 7h00 AM) is very high, over 90%. This is totally different with Australia, where the RH is below 70 % even in night time. The implication is the moisture re-absorption of the grain during storage. 100 90 80 70 60 50 40 30 20 10 0 42 40 38 36 34 32 30 28 26 24 22 0 3 6 9 12 15 18 21 Rel.Humidity, % Temperature, oC Temperature and Rel.Humidity, CAN-THO (average 1988- 1992) 24 Tim e of the day (12= noon ; 24 = m idnight) oC-March oC-August %RH-March %RH-August Figure 10. Weather data of a typical day in March and August, at Can-Tho Province (average 1988- 1992) Specific data pertaining to each Province are shown in Table 4. Table 4: Selected data of the 4 Provinces under survey Population (2005), million Can-Tho Kien-Giang Long-An Tien-Giang 1.14 1.65 1.41 1.70 of which % in agriculture/ rural area Rice Yearly PLANTED area, ha Rice production,. million ton 50 85 596 000 430 000 252 000 1.23 2.90 1.93 1.31 47 ≈350 % of wet-season paddy dried by machines 83 231 000 of which % harvested in rainy months Number of flat-bed dryers 76 ≈15 (10- 20) 48 1100 35 580 24 # 60 300 22 ## 12 Source: General Statistics Office, Ha-Noi, Viet Nam, http://www.gso.gov.vn/ (2005) Danida ASPS Report (2004) # Mr. Con, Office of Long An Rural Development (2006) . Page 111
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