Effect of Temperature and Pressureo on Moisture Diffusion Characteristics of Paddy (Cv. MTU 1075)

Abstract

Parboiling is an important and energy intensive unit operation in rice processing. Proper management of parboiling can reduce the energy requirement during parboiling and the associated cost. Soaking and steaming are the two major steps in parboiling. Soaking of paddy is usually carried out under atmospheric pressure, which takes more time. The temperature of soak water affects the rate of moisture adsorption and diffusion. The pressure during soaking and steaming also affects the process and consequently, affects the overall economics of parboiling. The hydration characteristic of paddy (Cv. MTU 1075) was studied at different conditions with the basic objective to standardize parameters for these unit operations. Soaking was carried out at four levels of soaking temperature under atmospheric pressure. Similarly hydrostatic soaking at pressure levels of 2.0, 4.0 and 6.0 kg·cm-2 was studied at a constant soak water temperature of 70°C. Steaming was carried out at 0.5, 1.0, 1.5, 2.0 and 2.5 kg·cm-2 pressure levels. The initial moisture content of paddy was varied at three levels. It was observed that the soaking temperature and pressure and steaming pressure affected the rate of moisture absorption by the grain and thus the time requirement. The diffusion coefficient was independent of initial moisture content and showed Arrhenius type relationship with temperature of soaking and steaming. The diffusion coefficient of paddy ranged between 8.939 x 10-5 to 2.678 x 10-4 cm²·min-1 for steaming under pressure, 7.01 x 10-6 to 1.399 x 10-5 cm²·min-1 for hydrostatic pressure soaking at 70°C and 1.898 x 10-6 to 1.11 x 10-5 cm²·min-1 for soaking under atmospheric pressure at different temperature. The diffusion constant was calculated as 0.01345 m²·min-1 and activation energy for moisture diffusion was 35.19 kJ·g-mol-1.

Predkuvanje je važan i energetski intenzivan postupak u preradi pirinča. Pravilan postupak može da smanji potrošnju energije i prateće troškove. Natapanje i parenje su dva glavna koraka u ovom postupku. Natapanje pirinča se obično izvodi pod atmosverskim pritiskom, što traži više vremena. Temperatura vode utiče na adsorpciju i difuziju vlage. Pritisak pri natapanju i parenju takođe utiče na process, a time i na ukupne ekonomske efekte. Karakteristike hidriranja pirinča (Cv. MTU 1075) su ispitivane pod različitim uslovima sa osnovnim ciljem da se standardizuju parametri za ove operacije. Natapanje ke izvođeno pri četiri temperature pod atmosverskim pritiskom. Hidrostatičko natapanje je izvođeno pri pritiscima od 2.0, 4.0 i 6.0 kg∙cm-2 na konstantnoj temperature od 70°C. Natapanje je izvođeno pod pritiscima od 0.5, 1.0, 1.5, 2.0 i 2.5 kg∙cm-2. Inicijalni sadržaj vlage pirinča varirao je na tri nivoa. Uočeno je da temperatura i pritisak natapanja i pritisak parenja utiču na adsorpciju vlage u zrno, a time i na vreme trajanja postupka. Koeficijent difuzije je bio nezavistan od inicijalne vlažnosti i pokazao je Arrhenius odnos sa temperaturom natapanja i parenja. Koeficijent difuzije pirinča varirao je u interval 8.939 x 10-5 do 2.678 x 10-4 cm²∙min-1 za parenje pod pritiskom, 7.01 x 10-6 do 1.399 x 10-5 cm²∙min-1 za hidrostatičko natapanje na 70°C i 1.898 x 10-6 do 1.11 x 10-5 cm²∙min-1 za natapanje pod atmosverskim pritiskom pri različitoj temperature. Izračunata vrednost difuzione konstante je bila 0.01345 m²∙min-1, a aktivaciona energija za difuziju vlage 35.19 kJ∙g-mol-1.