A Small-Scale Pneumatic Conveying Dryer of Rough Rice

Abstract

This article studies the possibility of reducing the high initial moisture content of wet rough rice using a small-scale low-cost pneumatic conveying dryer as a first stage dryer. The parameters investigated are final moisture content, surface temperature of rough rice, head rice yield, drying rate, power consumption per unit mass of evaporated water, and physical characteristics of rice. Parametric effects of the following variables are examined: velocity of drying air from 20 to 30 m/s, feed rate of rough rice from 150 to 350 kg/h, initial moisture content from 22 to 26% (wet basis), and drying air temperature from 35 to 70 C. From the experimental results, it is found that this drying method can be used for fresh rough rice with an initial moisture content of over 24% (wet basis). The drying process is able to lead to very rapid drying without any grain quality problems such as cracks in the rice kernel. The moisture content can be reduced to approximately 18% (wet basis) or about 5-6% of the initial moisture content within 3-4 s. The optimal drying air temperature is in the range of 50 to 60 C. A comparison of pneumatic conveying drying data obtained from the present study with fluidized bed drying data reported in the open literature is also discussed.

Comparative Evaluation of Hot-Air and Superheated-Steam Impinging Stream Drying as Novel Alternatives for Paddy Drying

“…[1,[4][5][6] Kaensup et al, [1] for example, investigated the use of pneumatic drying for paddy and found that the moisture content of paddy could be rapidly decreased, especially at a higher inlet air temperature. Nevertheless, pneumatic drying suffers from some drawbacks; in particular, in terms of excessive cracks and discoloration of dried paddy kernels.…”

“…Paddy may be dried in two stages; the first stage involves fast drying, while drying in the second stage must be slower to avoid excessive kernel breakage. Many drying techniques can be used for first-stage drying, including pneumatic drying, [1] fluidized bed drying, [2] and superheated-steam fluidized bed drying. [3] Ambient air ventilation may be used to dry paddy in the second stage.…”

Modeling Identification and Control of an Air Preheating Furnace of a Pneumatic Conveying and Drying Process

“…because of its simplicity in construction, efficiency in terms of operations, and environmental and economical aspects as compared to other conveying and drying units. 9,11,14 The drying operation in these units is characterized by a coherent flow of a preheated gas−grain mix, in which grains are dehydrated or dried by the preheated air during transportation through the air duct, and thereafter the grains are separated according to size by some cyclone systems. There has been enormous research work in the broad area of pneumatic conveying and powder technology.…”

“…The applications of pneumatic conveying and drying systems are wide in various industries, such as for pulverized coal and ash handling in power plants, , sawdust for pellet production, calcinations of gypsum, , cement production, , and food and pharmaceutical product processing. , Especially in the food industries, pneumatic conveying and drying has become very popular for batch production or the processing of agro-based food products such as wheat, corn, turmeric, tea, and coffee etc. because of its simplicity in construction, efficiency in terms of operations, and environmental and economical aspects as compared to other conveying and drying units. ,, …”

“…The drying operation in these units is characterized by a coherent flow of a preheated gas–grain mix, in which grains are dehydrated or dried by the preheated air during transportation through the air duct, and thereafter the grains are separated according to size by some cyclone systems. There has been enormous research work in the broad area of pneumatic conveying and powder technology. − In convective drying, air temperature, relative humidity, and velocity have a significant effect on the drying kinetics and quality of food products. − Since the preheating of air before mixing with wet material improves the overall performance, reducing energy consumption and drying time, most pneumatic convective dryers use an air preheater. In a majority of the applications, the outlet air temperature of the air preheater is dynamically controlled according to the airflow rate, as required for the sustained conveyance of materials and moisture content of the input raw material, so that the moisture content of the final product remains within the desired limits; however, the airflow rate is mainly governed by the inlet wet material flow rate and moisture content.…”