9 - Mass and Energy Balance

Abstract

It is important to look at the kiln as a thermodynamic system that interacts with the atmosphere and, as with all thermodynamic systems, determine the thermal efficiency. The basic approach to doing this is to consider the kiln as a furnace system composed of a control volume with well-defined spatial boundaries into which mass and energy enter at a certain rate and leave at another rate. Heat balance calculations are carried out when developing new rotary kiln chemical processes or when improving old ones. No thermal process would work if too much heat is released or if there is a lack of sufficient thermal energy to drive the process, in order to maintain the reaction temperature. Heat balance can only be calculated with given mass balances as the boundary conditions, hence a quantitative description of the chemical processes on the basis of physical or chemical thermodynamicsis required. While chemical thermodynamics establishes the feasibility of a particular reaction under certain reactor conditions, chemical kinetics determines the rate at which the reaction will proceed. Before establishing the global rotary kiln mass and energy balance, some fundamental concepts of thermodynamics that provide the pertinent definitions essential for the design of new rotary kiln bed processes are examined.