CEMENT KILNS
The function of the kiln in the cement industry is to first convert CaCO3
into CaO and then react Silica, Aluminum Oxide, Ferric Oxide, and Calcium Oxide
with the free lime to form clinker compounds: C3S, C2S, C3A, and C4AF.
The cement kiln uses higher temperatures to form the clinker. The process involves
gas, liquid and solid flows with heat and mass transfer, combustion of fuel,
reactions of clinker compounds and undesired chemical reactions that include sulphur, chlorine,
and Alkalies. It is important to understand these processes to
optimize the operation of the cement kiln, diagnose operational problems, increase production,
improve energy consumption, lower emissions, and increase
refractory life.
Process Model
PSL has developed a 3-D coupled computational model to predict the flow and heat
transfer in cement kilns. The model is being extended to include the pre-calciner.
The model uses block-structure body-fitted coordinates with
domain segmentation, models combustion and radiation, and incorporates the
modelling of the reactions occurring in the feed. The model includes
radiation, combustion of coke and coal, buoyancy effects, and features
complex geometry capability. Separate equations are solved for O2, N2, H2,
CO, CO2, H2O CH4, HCN, NOx, and NH3.
Issues Addressed by PSL
- Kiln efficiency
- Burner characteristics
- Refractory life
- Control of heat profile to clinker
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 plant managers in making decisions regarding kiln
refits/replacements
- Assists cement manufactures in optimizing burner and kiln designs
Model Predictions
Gas flow velocity fields, temperature distributions, heat transfer to wall
surfaces and feed, gas species (H2, O2, N2, CO, CO2, H2O, CH4, HCN, NOx, NH3) distributions,
pollutant emissions, and droplet trajectory in the cooler, kiln hood, and kiln barrel.
