Numerical analysis of the thermal profile inside the wall of a rotary cement kiln

The present study aimed to evaluate the temperature profile along the inside of the wall of a clinker kiln from a cement industry. The problem was modeled by the equation of transient heat conduction in cylindrical coordinates, considering radial symmetry. Being the wall composed of different materials, even adopting constant physical properties, there is no analytical solution to the problem. The method of the lines was used, being the radial and axial directions discretized by finite differences and the resulting system of ordinary differential equations integrated in time until obtaining the temperature field in steady state. The obtained field was compatible with heat transfer fundamentals and presented a good fit in relation to industrial data. The main limitations of the modeling performed in this study include the fact that the gases and solids contained in the kiln have not been modeled, and the variation in thicknesses of the layers of the kiln wall has not been considered. The program developed in this study can be used to evaluate the performance of different refractories or to infer the refractory wear level from experimental kiln surface temperature profiles.

Aerodynamic control of a diffusion flame to optimize materials' transition in a rotary cement kiln

The aim of this work is to deepen the understanding of the aerodynamics of a diffusion flame in a rotary cement kiln. The kiln is a rotary with a cylindrical shaped, long and equipped with a burner, and it is the seat of a diffusion flame with an axisymmetric turbulent jet. The kiln has a capacity of 8,000 Nm3 to 13,000 Nm3 of natural gas and primary air at T = 25 °C which interacts with a secondary hot air volume at T = 800 °C. The aerodynamic modelling of the furnace is achieved using the turbulence model RNG k–ε, which is able to handle the turbulence and capture the vortex shedding process. The Ansys/Fluent code, based on the finite volume approach to solve the Reynolds averaged Navier-Stokes (RANS), was used in this study. The interactions between turbulence and diffusion flame were handled by the PDF (Probability Density Function) approach. The numerical simulations have been validated by experiments from the kiln considered. Based on the findings obtained, it is concluded that the recirculation zone seems of paramount importance when combustion is taken into account because the reverse flow improves the flame stability and affects the combustion efficiency. In addition, limiting the secondary air flow through the furnace is major to improve combustion and avoid disturbing the advancement of the material along the kiln.

Hercynite spinel effectson the technological featuresof MCZ composite brick used for RCK lining

Magnesia-calcium zirconate (MCZ) composite brickswere recently used in the transition zones of cement kilnsbecause they are environment-friendly and hard-wearing towards cement clinker phases at high temperatures. Modifiers such as hercynite spinel (FA: FeO·Al2O3) can be added in small amounts to enhance elasticity, coatability, and load bearing of the brick structure. In the current study, different amounts (2, 4 and 6 wt. %) of hercynite spinelwere added to the MCZ composite clinkermade from Egyptian magnesite and zirconia (9,8 wt. %)then densification parameters, cold compressive strength (CCS), attacking by cement clinker components (CCC), and other technical characteristics of the formedbricks were explored. The maximum strength was gotten by 2,00 wt. % FA spinel addition,where excessive micro-cracks and glassy phase were the limiting factors for further added spinel. The penetration depth of the cement clinker components into MCZ‒FA bricks was downsized as FA spinel was added and further reduction occurred as FA increased. Furthermore, the coating character and the thermal shock cycles of the bricks were greatly improved as FA spinelraised to 6,00 wt. %. Those bricks with different FA spinel ratios can be put forward for lining different zones in the rotary cement kiln where different affinities for coating formations occur. Ill. 8. Ref. 31. Tab. 3.

Hybrid Eulerian Multiphase-Dense Discrete Phase Model Approach for Numerical Simulation of Dense Particle-Laden Turbulent Flows Within Vertical Multi-Stage Cyclone Heat Exchanger

This article describes a CFD engineering application developed to investigate numerically the multiphase, non-isothermal, turbulent flow physics within the suspension preheater of a dry-process rotary cement kiln. The multi–stage cyclone preheater is a counter-current heat exchanger. We used the CFD flow solver ANSYS-Fluent R18.1. to accomplish this task. The hybrid Eulerian multiphase-dense discrete phase model is a coupled Eulerian-Lagrangian technique. The primary carrier-phase is treated as a continuum by solving the Navier-Stokes equations, while the secondary discrete dispersed-phase is solved by tracking the particle parcels through the calculated flow field. The multiphase turbulence of the carrier-phase is modeled using the Reynolds stress transport model. The dispersed-phase interactions are modeled through the specific collisions models provided by the kinetic theory of granular flow and/or discrete element method. The Eulerian multiphase-DDPM method provided a quiet stable solution for a medium/high mass loading (solid to gas mass ratio 0.89:1). The four-stage cyclone suspension preheater is analyzed for its operating performance i.e. overall pressure drop and global collection efficiency of cyclone stages, calcination degree at bottom cyclone stage, flue gas temperature at 1st. cyclone stage and availability to get more insight of very complex multi-phase flow patterns within this equipment. The set of industrial measurements, collected during a heat and mass balance of a dry process rotary cement kiln, were used to verify and to validate part of the simulation results.