農試型循環式稻穀乾燥機之研究與試造

Abstract

1. 展循環式乾燥機，使乾燥中稻穀自動循環，一次乾燥量1.5~3噸，動力110V, 1-2HP馬達，適合個別農家、碾米廠或共同經營使用。其乾燥性能可兼用於搶救及一般乾燥，結構力求簡化適用以降低生產成本。 2. 結構： (1) 稻穀輸送控制系統：①採用星槽式滾筒配合螺旋輸送器，控制流量較確實，但構造複雜，星槽易受斷穗或石礫等阻塞，又如穀粒外層黏有水膜和後期快乾時稻穀流量不一致，且係間歇性漏穀，故升降機負荷忽大忽小，易造成阻塞。②採用星槽式滾筒配合斜向導板，構造較上項簡單，但仍有如上缺點，又具有旁側壓力，故濕穀流動更為不易，此型較適合於四方形或圓形乾燥箱使用。③採用螺旋輸送控制器，流量控制精確，結構簡單，較適合長方形乾燥箱者，其螺旋形狀必須變化螺葉節距、或螺葉直徑、或兩者皆變化以免前後段流量不均，同時螺葉之上應設一左右調節板，以調節螺旋轉向出入口的進穀量。 (2) 穀箱上層穀粒均分器，使用斜板式構造簡單，但因受到角度的影響，故較適合於四方或圓形乾燥箱；而螺旋式均分器做長方形方向的分配較確實，但因係成線狀漏穀，故乾燥箱寬度較大時應設補助裝置，俾使向橫方向分散。 (3) 進風管及排風管：進風管及排風管的位置、形狀等乃關係乾燥性能的重要因素之一，兩者愈近則熱風經過穀層時間愈短，較易浪費熱效益；反之，較遠時熱效率雖可提高，但較易產生胴裂，同時，高含水率稻穀易生回潮現象。而其對乾燥性能的影響尚有含水率、熱風量、熱風溫度、循環量、及大氣條件等的複雜相關，故欲確定一個固定的形式較為困難。研究過程中首先採用進風管於下，排風管於上，後來採用進、排風管於同一層，最後再改為如圖十二所示進排風管同層，但進風管分兩道，並可調節，以適應範圍較廣的穀量乾燥。 (4) 升穀機：使用杓瓢式提運機(Bucket elevator)較適合，但其揚穀量應注意滾筒的間歇性漏谷，高低含水率穀的流動差異性等安全係數，又皮帶以外層橡膠內層帆布者較能適應水份的影響及各種負荷的變化，以防打滑及阻塞。 3. 各機種乾燥性能： (1) 含水率23→13%，乾燥後重胴裂5%，蓬萊稻。 (2) 含水率23→13%，乾燥後重胴裂10%，蓬萊稻。 (3) 含水率23→13%，乾燥後重胴裂5%，秈稻及在來稻。 4. 乾燥成本：含水率23%~13%間每公斤在0.23~0.60元之間。 若使用得宜，乾燥成本低於靜置平箱型，然尚高於南部晴天用人工曝曬，但差額可以與每年的雨季損失相抵，同時可配合聯台收擭機一貫機械作業。 5. 搶救性乾燥：秈稻含水率由35%乾到13%，乾燥速度隨著乾燥時間（或含水率）呈直線下降：（乾燥溫度50~60℃) (1) 乾燥到17％時，穀溫超過35℃，而重胴裂增加3~4％。 (2) 含水率28％以下，排氣濕度開始離開飽和狀態。 (3) 乾燥速度宜再研究促其提高。 6. 含水率23~13%，蓬萊稻，乾燥速度在0.5~1.2％間時，乾燥速度與重胴裂的關係式： Y=0.1187x+0.551 Y:當天重胴裂增加數(%) X：乾燥速度(%/hr) This is an automatic circulation dryer developed under this project. The capacity of this dryer is 1.5 to 3 tons equiped with an electric motor of 110V and 1 to 2 HP. This dryer is suitable for individual farm household, rice mills orcooperative farms. One of the function of this dryer is for quick drying during rainy season, the other is for general purpose. The structure of this dryer is simple, so that the production cost can be reduced. 2. Structure (1) Grain flow control system (a) Metering rolls like a star in section and a screw elevator are adopted. This kind of combination of flow control system performed very well. However, the structure is very complicated and the star type rolls will be clogged easily by broken rice panicles and small stones mixed with the rice grains. In the meantime, since the flow speed of wet grains in the very beginning and in the end of the process are different a lot, and the grain f low are moved intermittently during the process. Hence, the elevator is easily stopped. (b) The star type metering rolls and a declined collecting board are adopted. The structure of this system is simple than the previous one, however, this combination has the same defects mentioned above. Since there are considerable side pressures on the board, the wet grain flow will not be moved so easily on the board. This system is suitable for the square or column type grain dryer. (c) Screw elevator control system is adopted. The flow control of this system is very accurate and simple in structure. This system is suitable for rectangle type grain dryer. A variable screw pitch or a variable diameter of the screw or both are needed, so that a uniform grain flow will be achieved in the front as well as in the rear of the whole system. In the meantime, an adjusted plate is needed to be attached to both of the front and the rear of the system so as to control the grain quantity in the inlet and in the outlet of the dryer. (2) Grain distributor in the upper of the bin There are two kinds of grain distributors, one is the declined board type which is suitable for square or round type bin. The other kind of distributor is the screw type which is suitable for the rectangle type bin. Since the screw type distributor can only spread the grains linearly, therefore, an auxiliary attachment is needed when the short side of the bin is not so short. (3) The inlet and the outlet of heat flow The relative position and pattern of the inlet and the outlet of heat flow are very important factors for drying functions of the dryer. When the inlet and the outlet are nearly in the same level, the heat flow will pass the grain in a very short time, and the heat flow will be lost a lot, on the contrary, when there is a considevable height between the inlet and the outlet, the heat efficiency will be high, however, the broken rice will be increased also, moreover, the grains will become wet again when rice grains are high moistured. It is difficult to map a definite pattern of them because these factors such as the moisture content of grains, the quantity and the temperature of heat flow, circulation quantity of grains and the atmosphere conditions can effect the whole result. We arrange that the inlet is below the outlet in the very beginning, then we set the inlet and the outlet in the same level latter, finally, we set the inlet and the outlet in the same level, but the inlet is divided into two parts which can be adjusted freely as indicated in picture 12. This final arrangement can be met the necessity when the cereal capacity is varied. (4) Grain elevator The bucket elevator is very suitable for this dryer. However the capacity of this elevator should be met the character of intermittent flow of the star type roller, and different flow speeds of grains with different moisture content. The belt of the elevator is better made of rubber outside and cloth inside so to met the wet condition and various loads. This arrangement can prevent slippage and stoppage. 3. Drying function (1) Moisture content 23-13%, heavy broken rice 5% after drying, ponlai rice. (2) Moisture content 23-13%, heavy broken rice 10% after drying, ponlai rice. (3) Moisture content 23-13%, heavy broken rice 5% after drying, native variety. 4. Drying cost: The grain drying cost is NT $ 0.23-0.60 per Kg (rice moisture content 23-13%). The drying cost will be lower than the horizontal box type dryer if this grain dryer is properly used. However the cost of drying of this dryer will be still higher than the solar drying in southern Taiwan. The excess cost of drying between this dryer and the solar drying is almost equal to the grain loss each year during the rainy season. Moreover, this grain dryer can be operated together with the rice combine in the same time.