CFD Modeling of Multi-Fuel Suspension Co-Combustion and Calcination Processes Within a DDF Precalciner of Cement Kiln

Abstract The paper reports a CFD engineering application for modeling the thermal-fluid dynamics and thermochemical conversion processes, which govern the conventional air-fossil fuel firing or multi-fuel co-processing, responsible for thermal sustain of raw material calcination process, within a dry process cement kiln. We simulate a Dual-Combustion and Denitration Furnace (DDF) precalciner, which co-combusts in suspension the petroleum coke (primary fuel) with alternative fuels (e.g., the pre-dried sewage sludge and/or the animal meat and bonemeal). CFD software package ANSYS Fluent R18.2 is used to build CFD reactive model and to perform the numerical simulations. The Eulerian–Lagrangian approach is usually employed for modeling turbulent multiphase reacting flows. Few turbulence and radiation heat transfer models are compared, to identify pros and cons of each model applicability and to determine which model is most suitable. The Discrete Phase Model (DPM), in Lagrangian framework, is employed for tracking petcoke/alternative fuels and limestone particle clouds. CFD analysis provides valuable insights into the DDF precalciner performance e.g., combustion and calcination characteristics, in-furnace NOx control strategy by combustion aerodynamics optimization (particularly the effect of Tertiary Air tangential inlet, which creates swirl and induces several local flow recirculation zones). The major predicted results e.g., exit degree of calcination, fuel burnout, gas species concentration fields etc., are quite well captured and validated against control system continuously logged operation data and the measurements collected by newly installed instrumentation.