KilnSimu – Rotary Kiln Simulator

KilnSimu is used in several industries. Though the technology of rotating drums has been available for over 100 years, it has not been replaced, but remains in active use in many of its traditional applications. The rotary drum provides an effi cient means for both heat and mass transfer in the processing of slurries and other condensed mixtures.

Pigment and cement manufacturing industries are using rotary drums for the thermal treatment of various materials. In the chemical recovery of kraft pulping rotary drums are applied for lime recycling. Other uses are in themanufacture of oxides (aluminium, zinc, lead), reduction of ores and in waste incineration. Currently KilnSimu has customers in Finland, Japan and Italy.

There is increasing interest in the complex chemistry of rotary drums, as many of the raw materials as well as the fuels used as heat sources vary in their chemical composition. This variation may lead to undesired emissions in the off gas or maintenance problems of the kiln. One common problem in lime kiln is the formation of rings due to alkali compounds. An additional challenge is created by the structure of the kilns. Due to the rotating cylindrical steel cover, the monitoring of the kiln interior is difficult. Due to long residence times, which may exceed 10 hours in continuous operation, undesired chemical pathways should be avoided. Thus it is often benefi cial to use a reliable simulation model to depict and control their internal processes.

Most kilns operate in the counter-current mode, i.e., the condensed material is fed into the kiln from the cold ‘feed end’, and is then processed to reacted product by heat transfer from the surrounding hot gas, which is introduced into the kiln from its hot ‘burner end’. The final material product is removed from the hot end. A fraction of exit gas can be circulated back to the hot end to improve the heat transfer efficiency. As a heat source, a fuel burner operating with the primary air is typically used. In KilnSimu the rotary kiln is divided into number of axial calculation zones, in which the radial temperatures of material
bed and gas fl ows and inner and outer wall of the kiln are assumed constant. The volume elements of material bed and gas in the zones are described as open thermodynamic systems, which transform mass and heat with each other. The chemical composition of the volume elements are calculated by thermodynamics, yet taking into account the time-dependent mass and heat transfer between the elements and their surroundings. The kinetics of the material bed reactions are incorporated by dividing
the solid phases into reactive and inert subsystems by using experimental reaction rates. The bed and gas flows of the kiln are calculated in a successive manner until all the energy and mass balances converge to an accurate solution.

Key benefits
The simulation yields axial temperature profi les for the bed, the gas and the inner and outer walls. In addition, axial phase compositions of the bed and gas flows are calculated. Results can be used to optimise fuel consumptions with different material feed capacities and to study the effect of using various fuels. Other uses are optimising the gas circulation and other energy factors including the kiln geometry. KilnSimu is also well suited for kiln scale-up.