Optimization of the thermal substitution rate – Part 2

Kiln burner

2 Tertiary air joining the calciner

3 Illustration of air-through precalciner riser duct [dimensions in mm]

4 Grid arrangements used for calciner
MI-CFD model

5 Lower petcoke burner location and its orientation

6 Velocity vectors and upward component of velocity

7 Illustration of the flow inside the riser duct

8 Petcoke particle and hot meal particle trajectories – colours indicate residence times in seconds

9 Mixing of CO₂ released by char combustion

10 Oxygen concentration [kg/kg] (cut off at 6 % O₂)

11 Temperature distribution inside the precalciner riser duct chamber [in C°]

12 Increased height of an inclined in-line precalciner by 3 m

13 Petcoke particles’ residence time in the riser duct (a = Base case, b = extended riser duct with lower burner location) [in sec.]

14 Higher momentum burner’s petcoke particle trajectories

1 Kiln hood, kiln burner and kiln layout [dimensions in mm]

2 Kiln burner configuration

3 Computational domain of kiln, kiln hood and kiln burner

4 Temperature profile [in °C] (Temperature at oven exit = 1077°C)

5 Oxygen concentrations [in mass %]
(O₂ concentration at oven exit = 5,75%)

6 Velocity vector field with magnitude
[in m/s]

Cement plant

7 Kiln bed temperature along the kiln length [in °C/m]

8 Major species of formed clinker

9 Typical temperature profile of gas phase

10 Burner injection locations of biosolids and SRF

11 Particle trajectories of a simulation with an achieved fuel mix of 90% TSR (SRF 45%, BS 45% and natural gas 10%)

12 Particle trajectories of a simulation with an achieved fuel mix of 75% TSR (SRF 75%, natural gas 25%)

13 Predicted clinker composition of its major constituents (SRF 45%, BS 45% and natural gas 10%)

14 Predicted clinker composition of its major constituents (SRF 75%, natural gas 25%)

By means of MI-CFD modeling, improvements to AFR thermal substitution rates (TSR) can be easily validated. Case study II shows, how natural gas can be replaced by alternative fuels.

The first part of the article in issue 5/2012 dealt with the basics and case study I. It was shown, how MI-CFD modelling can be used to understand the thermo-fluid dynamics of a calciner. In Part II a second case study and suggestions for the utilization of AFR are presented.

Case study II

The second case study is selected from a natural gas fired plant operating at 40 % heat input in the kiln burner and 60 % in the calciner. The client wanted to replace natural gas by waste derived fuels, i.e., Solid Recovered Fuel (SRF) and biosolids in both calciner and kiln burners. A brief summary of the...