Models of a Continuous Fertilizer Granulation Process - Control Design Application

Abstract

Abstract In solid fertilizer plants, the granulation process often places constraints on production. The process requires big and expensive machinery, and the energy consumption is relatively high because of the high temperatures and the extensive volumes of recycle material. Therefore an effective control of this process is desired. To facilitate the design of control systems without causing too much disturbance to the production, a dynamical model of the process has been developed. Systems with different types of controls have been tested by simulating. In the process that has been studied, a spherodizer granulator is used as the main piece of process equipment. Slurry is sprayed on the recycled granular material and the granules are dried. Fertilizer granules have two important product properties: moisture and granule size distribution. The moisture content of the product is highly dependent on temperatures in the granulator. First order 'black-box' models have been developed for temperature relations and a control system based on this model has been implemented and is currently in use. We have been able to develop a model which has been used in designing controls of granule size distribution. The growth of ten different granule size classes is descriped each in its own differential equation. Each equation consists of factors that describe growth of granules within its class, growth from smaller classes and to bigger classes. A factor for granule breakage can be used. The 'granule-size-model' is based on physical phenomena. Its parametres have been developed from mass balances and adjusted by means of simulation.