MODELING AND SIMULATION OF CROSS-FLOW GRAIN DRYERS .2. DESIGN MODIFICATIONS

This is the second of three papers on modelling and simulation of cros sflow grain dryers. The first paper reported on the development of the so called DPM (Distributed Parameter Model). This paper extends the r esults of the first paper and studies the effects of design modificati ons on the performance of crossflow dryers. Crossflow grain dryer desi gn modifications including airflow reversal, tapered columns and tempe rature staging were studied using a Distributed Parameter Model (DPM) based simulation program in an attempt to improve drying efficiency an d grain quality. Airflow reversal across the dryer outlet or grain flo w reversal was found to reduce moisture differential by up to 65% and lowers average grain temperature up to 10-degrees-C. Tapered columns w ere found to lower the moisture differential by up to 25%. Temperature staging was found to lower average grain temperature considerably but resulted in only slight decreases in moisture differential. Simulatio ns of the dryer cooling section indicate that in most commercial appli cations the cooling section does not need to be greater than 20% of th e total column length for drying air temperatures less than 135-degree s-C. Two forms of air recycle in crossflow dryers have been studied. T hese include direct recycle of exhaust air from the cooling section to the heating section and recycle of exhaust air from the heating and c ooling sections that has been mixed with fresh air and heated. Energy savings due to direct air recycle ranged from 0 to 25%. Energy savings due to indirect air recycle ranged from 0 to 55%.