SIMULATION OF THE PROCESS DYNAMICS OF ALUMINA CALCINATION IN ROTATING DRUM FURNACES

Abstract

The issues of modeling processes occurred in drum-type rotary kilns in steady-state (static) modes are considered in details in the literature, unlike the processes occurred in dynamic conditions (transient modes). However, management and optimization of technological regimes require gaining information about the dynamics of those processes. The goal of the study is analysis of the process of alumina calcination. The quality indicators of the process have a significant impact on the process of aluminum electrolysis. Calcination of aluminum hydroxide is a final stage in all technologies of alumina production. We present the results of theoretical construction of mathematical models of the dynamics of heat and mass transfer processes upon heat treatment of the initial aluminum hydroxide. Three types of models are constructed under different initial conditions which describe the main regularities of the process with different degree of accuracy. Proceeding from the data of the theoretical study a methodology has been developed for experimental study of the dynamics of the process along the main control channels: "hydrate loading - flue gas temperature," "natural gas consumption - temperature in the calcination zone," and "natural gas consumption - flue gas temperature." Transfer functions and differential equations of the process were thus obtained for the studied channels. The revealed good agreement between the structures of theoretical and experimental models made it possible to formulate recommendations for the construction of a process control system for alumina calcination. The temperature in the calcination zone affects the fuel (gas) consumption and determines the quality of the resulting alumina. The flue gas temperature must be maintained at the desired level using a two-circuit system which stabilizes the aluminum hydroxide charge with correction for the flue gas temperature. The temperature in the lower head of the furnace is an integral indicator of the interaction of two flows: the flow of burning gas and the counter-moving flow of the material. This temperature in the steady state operation of the furnace is a control parameter associated with the quality of the resulting alumina. When managing gas consumption, it is also necessary to maintain an optimal fuel-air ratio to ensure complete fuel combustion with maximum efficiency.