Heat recovery from moving cooling beds: transient modeling by dynamic simulation

Abstract

Heat recovery from moving beds of solid particulate that have to be cooled for process requirements is usually carried out by one or more hoods collecting the cooling air fed underneath the bed. However, in many process plants the bed operation is characterized by continuous variations of solid inlet temperature and flow rate. As a consequence, the design of the heat recovery plant is usually performed by assuming a hypothetical steady-state operation and resorting to mean values of the process parameters. Sizing optimization of the air capturing hoods becomes difficult to perform under such circumstances, resulting in poor performances of the whole heat recovery plant from the economical standpoint. Furthermore, control system design appears particularly critical especially for more complex heat recovery schemes. With the aim to make a contribution towards the modeling of the real-time behaviour of the cooling bed, in this paper a dynamic simulation approach has been developed based on two-dimensional schematization and on time-dependent convective-conductive heat transfer. The model enables the transient analysis of the cooling bed operation and could be used as a useful tool in control and optimal design studies. In this work reference has been made to the cooling section of an iron-ore sintering bed of the Ilva steelworks in Taranto for operating conditions definition and model verification.