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

Abstract

An investigation was conducted on impinging stream drying of moist paddy using hot air and superheated steam as the drying media. Drying experiments were divided into two parts: namely, one-pass and two-pass drying. The volumetric water evaporation rate, volumetric heat transfer coefficient, and specific energy consumption of the drying system at various conditions were assessed; in the case of superheated-steam drying, the effect of steam recycle was also assessed. The quality of dried paddy was evaluated in terms of color, head rice yield, and degree of starch gelatinization. In the case of one-pass drying, an increase in the drying temperature led to a significant increase in the volumetric water evaporation rate and volumetric heat transfer coefficient. On the other hand, in the case of two-pass drying, an increase in the drying temperature led to a significant decrease in the volumetric heat transfer coefficient; the volumetric water evaporation rate was not significantly affected, however. The specific energy consumption decreased with an increase in the drying temperature. At the same temperature, using superheated steam as the drying medium led to lower specific energy consumption; higher level of steam recycle also led to more energy conservation. The color of the dried paddy was not affected by the change in the drying temperature; superheated-steam-dried paddy was redder and more yellow than the hot-air-dried paddy. An increase in the drying temperature led to decreased percentage of head rice yield. Superheated-steam drying helped enhance the level of starch gelatinization in comparison with hot-air drying at the same temperature. Nevertheless, drying at the highest tested temperature led to a lower level of starch gelatinization.

Sustainable Dewatering of Industrial Sludges in Sludge Treatment Reed Beds: Experiences from Pilot and Full-Scale Studies under Different Climates

“…On the other hand, the dewatering of biological or alum sludge through mechanical processes results in a solids content that does not usually exceed 15-20% [43,62,64]. Thermal processes can deliver higher solids contents, but the high energy required for these systems makes them often not financially feasible and also technically challenging [64,65]. The high organic solids content in feed industrial sludge leads to lower ds content and anaerobic conditions in the residual sludge layer.…”

Rapid Drying of High-Moisture Paddy Using a Pneumatic Dryer with Corrugated-Surface Drying Column

“…This is because the time that the drying material stays in the dryer is very short [6]. To increase the amount of moisture reduction, the time that the drying material spends in the dryer should be extended; thus, the drying material should be dried for more than one drying pass [6,[11][12][13]. With the use of this drying concept, a partially dried material is again fed into the dryer for further drying.…”

A Review of Dehydration of Various Industrial Sludges

“…The metal-hydroxide sludge produced by metal-finishing and steel industries is generally hazardous; drying this sludge reduces its volume and, therefore, its handling and disposal costs. [11][12][13] Some industrial sludges are classified as hazardous or toxic wastes in national or local environmental regulations (e.g., U.S. regulations promulgated under RCRA). Others may be classified as hazardous wastes because they Correspondence: Tolga Tunçal, Namık Kemal University, Ç orlu Engineering Faculty, Environmental Engineering Department, Ç orlu, Tekirdag, Turkey; E-mail: ttuncal@nku.edu.tr Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/ldrt.…”