Step 1: Understanding the Concept:
Parboiling is a process where paddy (rice in its husk) is soaked, steamed, and then dried before milling. The drying step is crucial and requires a specific type of dryer that can handle large volumes of moist, sticky grain and provide uniform drying. The question asks to identify the dryer commonly used for this purpose.
Step 2: Detailed Explanation:
Let's analyze the different types of dryers:
(A) LSU dryer: "LSU" stands for Louisiana State University, where this dryer was developed. The LSU dryer is a continuous-flow, mixing-type dryer. It consists of a vertical chamber with alternating rows of inverted V-shaped air channels (ducts) for air inlet and outlet. The grain flows downwards by gravity, mixing as it moves around these ducts. This design ensures continuous mixing of the grain, leading to very uniform drying. Because of its ability to provide gentle and uniform drying for large quantities of grain, it is the most widely used and recommended type of dryer for modern rice mills, especially for parboiled paddy.
(B) Sack dryer: In this method, grains are held in sacks, and heated air is blown through them. It is a simple, low-capacity batch method, not suitable for the large volumes in a commercial parboiling plant.
(C) Vacuum dryer: This dryer operates under reduced pressure, which lowers the boiling point of water, allowing for drying at low temperatures. It is expensive and used for heat-sensitive materials like pharmaceuticals or high-value foods, not for bulk commodities like paddy.
(D) Bin dryer: This involves drying grain in a large storage bin by blowing air through it over a long period (in-storage drying). It's a slow, low-temperature process, not typically used for the primary drying of freshly parboiled paddy which has very high moisture content.
Step 3: Final Answer:
The LSU dryer is the standard and most suitable type of dryer for the commercial drying of parboiled paddy due to its continuous, mixing-flow design that ensures uniformity. Therefore, option (A) is the correct answer.