Drying modelling and experimentation of Assam black tea (Camellia sinensis) with producer gas as a fuel

Thin layer drying kinetics of fermented tea (Camellia sinensis) was investigated at air temperatures (80, 90,100, 110) °C and velocities (0.50, 0.65, 075) m s−1 respectively using a producer gas furnace tea dryer. The tea samples weight, dry and wet bulb temperatures and air velocities were recorded continuously during each experiment. The black tea drying data were fitted to different semi-theoretical models such as Lewis, Page, Modified Page, Henderson and Pabis and Two Term, etc. The modified Page model gave better prediction of thin layer drying kinetics of black tea followed by Lewis model. The diffusivity constant (Do = 0.746 × 10−3 m2 s−1) and activation energy (Ea = 52.104 kJ mol−1) were computed from linear regression analysis. The modified Page model gave drying rate constant (k = 25.91 × 10−4 s−1) and exponent (n = 1) at 100 °C air temperature. Both air temperatures and velocities have influence to enhance drying rate constant (k) and exponent (n) in Page and Modified Page models. The energy consumption was found as 19.01 MJ kg−1 of made tea (3% w.b.) based on calorific value of producer gas (HHV = 4.39 MJ Nm−3). Specific energy consumption of the dryer was approximately 6.274 MJ kg−1 of water removed.