KilnSimu

KilnSimu is a standalone software that can be used for thermodynamic modelling rotary drum furnaces. While it relies on the calculation routines of ChemApp, it is user-friendly and specialized to one specific application.


KilnSimu – ROTARY KILN SIMULATION PROGRAM

The rotary kiln is concurrently used in several industries. The rotary drum provides an efficient means for both heat and mass transfer in the processing of slurries and other condensed mixtures. Pigment and cement manufacturing industries among others are using rotary drums for the thermal treatments of various materials. In the chemical recovery of kraft pulping rotary drums are applied for lime recycling. Other uses include manufacture of oxides (aluminium, zinc, lead), reduction of ores and waste incineration.

There is increasing interest in the complex chemistry of the 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. On the other hand, if the operational conditions of the kilns remain sufficiently stable, their remote control and a centralised maintenance for several kilns can be achieved. Such arrangements may lead to significant savings in the operation cost of a production site.

Most kilns operate in the counter-current mode, that is, 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. As a heat source, a fuel burner operating with the primary air is typically used. In KilnSimu there can be any number of feed flows at any positions – but there must always be at least one bed feed at the ‘feed end’ and one gas feed at the ‘burner end’ of the kiln. If kiln operates in co-current mode then the ‘burner end’ and the ‘feed end’ coincides and the gas flow direction is reversed.

In KilnSimu the rotary kiln is divided into number of axial calculation zones, in which the radial temperatures of material bed and gas flows 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 thermo-dynamic systems, which transform mass and heat with each other. The equilibrium states of the volume elements are calculated by minimizing their Gibbs energy and by taking into account the mass and heat transfer between the elements and their surroundings. The time dependent solid state reactions in the material bed are taken into account by dividing the solid phases into reactive and inert subsystems according to Arrhenius based reaction rate equations. The bed and gas flows of the kiln are calculated in a successive manner until all the energy and mass balances converge to accurate solution. The radial movement of the bed depends on the holdup of the kiln, its angular velocity and the properties of the bed. 

The simulation yields axial temperature profiles for the bed, the gas and the inner and outer walls. In addition, axial phase compositions of the bed and gas flows are calculated. Figures on the left and below show typical results for precalcined cement kiln. They show accumulation of sulfur and chlorides (introduced by the the coal fuel) in the kiln and the cyclones. In general the results can be used to optimize fuel consumptions with different material feed capacities and to study the effect of using various fuels. Other uses are optimizing the gas circulation and other energy factors including the kiln geometry KilnSimu is also well suited for kiln scale-up.

With KilnSimu it is also possible to build and simulate a flowsheet containing several different kinds of unit operations commonly used with rotary kiln. These are: Cooler, Calciner, Cyclone, Mixer and Splitter. Cooler is a grate kiln where air is blown from the bottom of the cooler through the grates and the bed in a cross current fashion. Calciner is a vertical riser duct where the bed is fluidized with gas. The Cooler and the Calciner are also divided into number of control volumes in a similar way as in the rotary kiln. Cyclone, Mixer and Splitter are simple flow separation, mixing and splitting unit operations where the temperature of the outlet flow can be solved from an energy balance. With these unit opearations it is possible to simulate a for example NSP cement process containing several cyclones, calciner, rotary kiln and clinker cooler). All unit operations, their parameters like geometries and feed flows and the flowsheet connections are defined in Excel worksheet tables. There is also a separate GUI for KilnSimu implemented with ExtendSim simulation software. 

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