مقایسه فرآیند خشک کردن و کیفیت تبدیل در خشک‌کن‌های گردش مجدد و رایج شلتوک

مصرف بالای انرژی و غیر یکنواختی خشک شدن شلتوک در خشک‌کن‌های خوابیده رایج می‌باشد که شانس شکستگی دانه در مراحل تبدیل برنج را بالا می‌برد. به‌کارگیری خشک‌کن‌های جدید می‌تواند مشکلات ذکر شده را حل نماید. در این مقاله عملکرد یک دستگاه خشک‌کن ایستاده گردش مجدد شلتوک با یک خشک‌کن رایج برنج (خشک‌کن خوابیده) برای خشک کردن شلتوک رقم طارم مقایسه شد. در هر دو خشک‌کن شاخص‌های زمان خشک کردن شلتوک، روند تغییرات رطوبت شلتوک و انرژی ویژه مصرفی تبخیرآب شلتوک بررسی شد. همچنین تاثیر کاربرد هرکدام از خشک‌کن‌ها نیز بر روی شاخص‌های کیفی راندمان تبدیل، درصد شکستگی برنج سفید، درجه سفیدی برنج و کیفیت پخت برنج (درصد افزایش طول بعد از پخت) بررسی شد. نتایج تحقیق نشان داد که کاربرد خشک‌کن ایستاده گردش مجدد، موجب کاهش 54.12 درصدی زمان و مصرف انرژی در خشک کردن شلتوک شد. در خشک‌کن‌های ایستاده مقدار انرژی لازم برای تبخیر یک کیلوگرم آب از شلتوک mj3.9 به‌دست آمد که 76.25 درصد کمتر از خشک‌کن‌های خوابیده رایج بود. کاربرد خشک‌کن‌های ایستاده نسبت به خشک‌کن‌های زمینی تاثیر معنی‌داری بر راندمان تبدیل شلتوک نداشت، امّا مقدار شکستگی برنج را 5 درصد کاهش داد. درجه سفیدی برنج خشک شده در خشک‌کن خوابیده 2.4 درصد نسبت به برنج خشک شده در خشک‌کن ایستاده بیشتر بود و خشک کردن شلتوک با خشک‌کن‌های خوابیده رایج موجب افزایش 6.2 درصدی نسبت افزایش طول (ری کردن) برنج پس از پخت شد.

Comparison of the Paddy Drying Process and Milling Quality between Recirculating and Conventional Batch Type Dryers

Introduction ;High energy consumption and nonuniformity drying in conventional batch type dryer are the common problems in paddy dying industry. Nonuniformity drying causes to kernel breaking chance in the milling process. Using new dryers with better performance can solve the drying problem and energy saving. In this research, the operation of a recirculating batch dryer was compared with a fixed bed batch dryer (conventional dryer) for paddy drying.;Materials and Methods ;This research was done in a paddy milling factory in Ferydonkenar and deputy of Rice Research Institute of Iran, in Amol, Mazandaran province. Both recirculating dryer and conventional batch type dryer were made by Khazar Electric Company in Amol Iran and they had 5 tonnes capacity. In the recirculating dryer, ambient air was warmed in the furnace and blown to drying zone inside of grain bin. Natural Gas (NG) was used for air warming in dryers. Warm air absorbed paddy moisture and pushed away from the dryer. Drying temperature ranges for recirculating dryer and conventional dryer was 4850 °C and 3852°C, respectively. The paddy variety was one of the Iranian rice varieties as Tarom and initial moisture content of grains was 21% (w.b), it was decreased using drying to 89% (w.b) for milling process. Paddy moisture content was measured each 60120 min by SUNCUE TD6 portable  moisture testerTaiwan. Energy consumption calculated by fuel and electrical energy summation in each experiment. Natural Gas and electrical power consumption were measured by Gas and electric counters respectively.;Drying time, paddy moisture change trend and energy consumption were investigated for paddy drying in each dryers. Also, milling ratio, breaking percent, whitening degree, and elongation rate after cooking were studied after the milling process for rice dried using national standard methods and deputy of Rice Research Institute facilities in Amol. Experimental samples were 150 g and husker (SATAKE THU35B), a whitener (SATAKE TMU05) and KETT C100 were used for husking, whitening and whiteness degree, respectively. All Experiments were done with three replication and data analyzed using T student method in 5% probability.  ;Results and Discussion;Results showed that recirculating dryer caused to reduce 54.12 percent in drying time and energy saving in paddy drying in compare with conventional paddy dryers. The trend of moisture content changes was longer and overdrying occurred in lower layers in conventional batch type dryer compared to recirculating dryer. Paddy drying was 20 hours more in batch type than the recirculating dryer. It caused wasting time and energy consumption. Specific energy consumption for water evaporating in the recirculating batch dryer was 3.9 MJ/kg water and it was 76.25 percent less than fixed bed batch dryer.   After the drying process in both dryers, paddy moisture content was in range 89 percent (% w.b). Using recirculating dryer did not have a significant effect on milling yield but it had a significant effect on broken rice. Broken rice decreased by 5 percent after the milling process when paddy dried by recirculating. Uniformity of layers drying and normal heat stress in rice kernels in recirculating dryer reduced broken rice in the milling process. Whiteness degree of rice dried using fixed bed dryer was 2.4 percent more than the recirculating batch dryer. Also, rice dried had more elongation rate about 6.2 percent after cooking when paddy dried by conventional dryer.  ;Conclusions ;Results of this paper showed that using of recirculating dryer would decrease time and modify energy consumption in paddy drying. The costs of installation for the recirculating batch dryer was about 5.3 times more than fixed bed batch dryer. It seems too expensive at first but considering energy and timesaving in the drying process and suitable effect on decreasing grain breakage in paddy milling, using of the recirculating batch dryer is recommendable in rice milling factories.