Thermo-economic assessment of bubbling fluidized bed paddy dryers

Abstract

A thermo-economic assessment of bubbling fluidized bed paddy dryers under atmospheric conditions applying the response surface methodology (RSM) was carried out on three atmospheric bubbling fluidized bed dryers to investigate the effects of inlet air temperature, superficial air velocity and amount of paddy on exergy efficiency at the equilibrium moisture content (EMC). Furthermore, experiments were also performed in the designed cone-shaped dryer as per the experimental matrix obtained from the software design of experiments (DoE). Experimental results were utilized to develop the quadratic model and predict the exergy efficiency. The desirability approach was used to find the optimum value of 65 °C for inlet air temperature, 2.1 m/s for superficial air velocity and 3 kg of paddy with an overall desirability index of 0.996. The optimum values were experimentally tested and verified with the least error levels. The conical dryer with a larger degree of cone angle had a higher exergy efficiency. The maximal exergy efficiency of 0.41 was observed when a spiral was attached to the dryers. All dryers benefitted from a 28% increase in exergy efficiency due to the spiral. Furthermore, an economic analysis of the dryers was also carried out on the three dryers. A higher profit/year value of ($ 1171.87) was observed to be associated with dryers having a higher cone angle with a shorter payback period (0.43 years). As a result, a higher cone-angled dryer is proven to be the optimum option for drying paddy grains.