LIME KILNS
The function of the lime kiln is to convert CaCO3 back into CaO for reuse in
the causticizing process. The lime kiln involves complicated processes,
including flow, heat and mass transfer, combustion of fuel, drying of lime
mud, and calcining of CaCO3. It is important to understand these processes to
optimise the operation of the lime kiln, diagnose operational problems,
improve energy consumption, increase production, lower emissions, increase
refractory life, and reduce instabilities.
Process Model
The UBC modelling group in collaboration with PSL is currently working to
complete a 3-D steady-state computational model to predict the flow and heat
transfer in a lime kiln for application in the cement and pulp and paper
industries. The model uses block-structure body-fitted coordinates with
domain segmentation, models combustion and radiation, and incorporates the
modelling of the non-Newtonian lime mud. Currently, the model includes
radiation, combustion of natural gas and oil, buoyancy effects, and features
complex geometry capability. Separate equations are solved for O2, N2, H2,
CO, CO2, H2O and CH4. Previous applications include modelling the flow, heat
transfer, and combustion in the lime kiln, and to analyze the influence on the
flame of secondary flows from the hood and the primary air from the
burner.
Issues Addressed by PSL
- Kiln efficiency
- Burner characteristics
- Refractory life
- Dams and rings
- Stable operation
- Flame shape
Advantage and Benefits
- The model provides comprehensive information throughout the entire kiln
at relatively low cost.
- Can evaluate "what if" scenarios to improve operation
- Supplements operator knowledge of lime kiln operations
- Assists mill managers in making decisions regarding kiln
refits/replacements
- Assists manufactures in optimizing burner and kiln designs
Model Predictions
Gas flow velocity fields Temperature distributions and heat transfer to wall
surfaces and mud Gas species (H2, O2, N2, CO, CO2, H2O, CH4) distributions
Pollutant emissions (NOx) Oil or solid fuel combustion and droplet trajectory.
