稻穀乾燥成品率之研究與乾燥模擬相關軟體之建立

Abstract

濕榖收穫後係由農會或民間糧商收購，再統一進行乾燥。其間牽涉到交易時濕榖品質之認定問題，而如何由濕榖預測乾榖成品率，成為重要的技術指標。本研究係針對省產濕榖的物理性質(含水率、容積密度、風選除雜率、糙米重百分比)與乾榖成品率的關係進行探討。 就三年期共246批之稉稻樣本中分析結果：稉稻一期作乾榖成品率平均為82.3%，二期作則略降0.45~2.08 %，其平均夾雜率為1.12~3.26%。乾榖成品率與濕榖含水率具有顯著之線性關係(R^2=0.641)；其與濕糙米含水率間之關係則更為顯著(R^2=0.7917)。因此濕榖水分應以測定濕糙米含水率更為準確、穩定。就55批次乾燥實驗結果顯示：每小時減乾率0.58%以下，整米率可達95%以上，對於提升米質有相當大之助益。 本研究中提出”以核殼比預估成品率”新理論以計算乾燥後穀物之成品率。該理論係利用濕榖中含有糙米的飽滿稻穀為基礎，計算其經乾燥後之乾榖成品，其餘均視為夾雜物。由於飽滿之濕榖粒所含之糙米與稻殼重量比為水份之函數，經過礱榖脫殼，由濕糙米重及核殼比可推估乾榖之成品率，其誤差僅及1.6%。研究中並針對國產稻穀建立上項之關係函數，由此建立一套標準測定程序，並設計一台成品率測定裝置，可以供農會檢測人員使用。該設備採用衝擊式礱榖機構，配合脫殼、風選、秤重及測水分，使檢測工作一元化。 本研究中並針對穀物乾燥過程以MATLAB撰寫模擬程式SAPGD-2004，模擬多種穀物於乾燥過程空氣性質變化、空氣流經穀物之阻力、平衡含水率、薄層乾燥及對模式之厚層靜置式乾燥。利用此項模擬並驗證ASAE標準及文獻中若干薄層乾燥方程式之錯誤。

Rice after harvested is usually sent or sold to the nearby Farmers’ Associations or local merchants for further drying. A conversion standard based on the relationship of the wet and dry grain is thus important to precisely evaluate the dried yield rate in the process of the trade. This study examined the characteristics of local rice such as moistures, bulk density, foreign matters (FM) and brown rice weights, etc. in order to find the rice dried yield rates (DYR). Within three years, there were 246 specimens of harvested rice under testing and results showed that their DYRs was 82.3% for the 1st crop and 0.45-2.08% less for the 2nd, with their FM rates fallen within 1.12-3.26%. The DYR was fairly significant with the wet grain moisture (R^2 =0.641) and strong with the hulled grain moisture (R^2 =0.7917), which indicated that a best method of detecting the moisture of wet grain is to directly measure that of the hulled grain for the stability and accuracy. By examining 55 experiments on grain drying, it was found that the sound kernel rate of 95% could be obtained at the drying rate less than 0.58% per hour, leading a possibility to enhance the rice quality. A new theory, the wet kernel-husk ratio, was also proposed in this study to predict the quality of wet rice, on a basis of a moisture function that describes the weight ratio of sound brown rice (kernel) and the husks, which are weighed after the wet sample is hulled. The dried yield rate was then derived from a standard kernel-husk ratio of the wet rice grains by adjusting the weight of water during the drying process. The error of estimation was only 1.6%. A standard testing procedure for the prediction of dried yield rate under this theory has been worked out successfully and built in a testing machine developed in this study. The device can handle a wet sample through weighing, hulling, reweighing, moisture measuring and data-displaying in a few seconds. A simulation software based on MATLAB, SAPGD-2004, was also developed in this study for the grain drying. It provided functions for psychometric properties of moist air, the resistance of airflow through grain, equilibrium moisture content, and thin-layer and deep-bed drying, for most grains. Several discrepancies were found in ASAE Standard during verifying thin-layer drying equations with graphical simulation results.