Lime Kiln Combustion CFD Simulation by ANSYS Fluent, Tutorial

The present problem simulates the combustion process of methane gas in a vertical lime kiln using ANSYS Fluent software. We perform this CFD project and investigate it by CFD analysis.

The present model is designed in three dimensions using Design Modeler software. The model is a semi-designed vertical furnace due to its symmetrical geometric structure and to reduce the computational cost.

The model has four fuel inlets in the middle of the side surface of the lime kiln and one fuel inlet in the center of the furnace and has a primary air inlet in the center of the lime kiln, and a secondary air inlet in the lower part of the furnace, and an outlet for products in the lower part of the furnace.

Furthermore, a particular outlet for discharging gases in the upper part of the furnace is considered.

The meshing of this present model has been generated by Ansys Meshing software. The element number is 2219550.

CFD Methodology

The present problem simulates the combustion process of methane gas in a vertical lime kiln using ANSYS Fluent software. The construction of a vertical lime kiln consists of two main parts, including the combustion zone and the preheating zone.

The fuel and air enter the building from the middle of the lime kiln and form a combustion reaction. As a result of the chemical reaction of combustion, a significant amount of heat is produced, increasing the temperature inside the lime kiln.

On the other hand, some calcium carbonate enters the lime kiln from the upper part. This calcium carbonate or limestone reacts separately by receiving heat from the combustion of the desired fuel and carbon dioxide production.

As a result, it can produce calcium oxide or the same as quicklime and separate it from carbon dioxide. In this project, only the occurrence of the chemical reaction of burning inside a lime kiln is investigated.

The combustion reaction defined in the model consists of performing a chemical reaction between air and methane. Thus, the species transport model and the volumetric sub-model can simulate the combustion.

In the middle part of the lime kiln and from four side inputs, the flow, including 0.9 methane (CH4) and 0.1 nitrogen (N2), enters the lime kiln with speed equal to 1.357 m/s and a temperature equal to 300 K.

Simultaneously, an initial airflow and a fuel flow enter the furnace from the central area in the middle of the lime kiln.

There are also two outputs for the model; Thus, the reaction products are discharged from the outlet at the bottom of the vertical lime kiln at atmospheric pressure, and the excess gases produced are sucked into the outside space by a suction fan.

In addition, porous materials have been used inside the lime kiln. The porous area is made of aluminum with a porosity coefficient of 0.3 and has an inertial resistance equal to 907.4 1/m and a viscous resistance equal to 1100000 1/m2.

Moreover, the standard k-epsilon model and energy equation are used to solve the turbulent fluid equations and calculate temperature change within the domain.

Lime Kiln Combustion CFD Simulation Conclusion

At the end of the solution process, two-dimensional and three-dimensional contours related to pressure, temperature, velocity, and mass fraction O2, CH4, H2O, CO2, N2, and CaCO3 were obtained.

The resulting images show that the reaction products, including carbon dioxide and water vapor, are produced due to the combustion reaction between the reactants (methane fuel and airflow). Significant heat is also generated when a combustion reaction occurs.

The heat generated by the combustion reaction can contribute to the dissociation of calcium carbonate or limestone and the production of quicklime.