Economic design criteria for cooling solid beds

Moving beds are widely employed in cooling particulate solids for process requirements. In this paper a moving cooling bed design optimization approach is developed which is based on total cost minimization and considers either capital investment (bed structure, trolleys and fans) and operating expenses (blowers operation and trolleys motion). Resorting to a previously developed heat exchange simulation model, to an optimization algorithm and to properly developed cost functions the optimal set of design variables, namely bed width, length, depth, advancement speed and cooling air flow rate, are chosen on the basis of the given set of input data, including solid inlet flow rate, temperature and physical characteristics, in order to respect the required solid exit temperature and other constraints at the minimum total cost. After outlining the adopted solution method some optimized results are shown to highlight the capabilities of the proposed approach. A sinter cooling bed of Riva/ILVA steel works in Italy is assumed as reference case study. Results show that expected savings could range around 10% to 25% of total annual cost when an optimized design is adopted.