Pilot scale production of novel calcium sulfoaluminate cement clinkers and development of thermal model

Pilot scale trials were successfully performed on the production of novel calcium sulfoaluminate (CSA) cement clinker in a direct natural gas heated rotary kiln at the IBU-tec facility in Germany. A raw meal throughput of ∼25 kg/h was fed to the rotary kiln heated by co-combustion of natural gas and elemental sulfur, with the latter serving as both fuel substitute and reactant, to partially or wholly replace gypsum as the source of sulfur in CSA production. A well-mixed heat transfer kiln model was developed to predict the overall kiln heat flux and gas temperature profiles, to account for gaseous radiative properties. The predicted gas temperature inside the kiln varied from 1566 K in the flame zone to 1019 K at the feed zone, with peak temperature approaching 1724 K. The combined emissivity of the CO2 and H2O gas mixture varied between 0.13 and 0.2 at these temperatures for partial pressure ratio PH2O/PCO2 of 1.7. The trial kiln has a low thermal efficiency of 3% of the total supplied energy. The simplistic model provided approximate performance predictions for the KDO kiln and also for different kiln sizes and can help to establish the effects of operating parameters on heat transfer trends

The use of micro-XRD for the study of glaze color decorations

The compounds responsible for the colours and decorations in glass and glazed ceramics include: colouring agents (transition metal ions), pigments (micro-and nano-precipitates of compounds that either do not dissolve or recrystallize in the glassy matrix) and opacifiers (microcrystalline compounds with high light scattering capability). Their composition, structure and range of stability are highly dependent not only on the composition but also on the procedures followed to obtain them. Chemical composition of the colorants and crystallites may be obtained by means of SEM-EDX and WDX. Synchrotron Radiation micro-X-ray Diffraction has a small beam size adequate (10 to 50 microns footprint size) to obtain the structural information of crystalline compounds and high brilliance, optimal for determining the crystallites even when present in low amounts. In addition, in glass decorations the crystallites often appear forming thin layers (from 10 to 100 micrometers thick) and they show a depth dependent composition and crystal structure. Their nature and distribution across the glass/glazes decorations gives direct information on the technology of production and stability and may be related to the color and appearance. A selection of glass and glaze coloring agents and decorations are studied by means of SR-micro- XRD and SEM-EDX including: manganese brown, antimony yellow, red copper lusters and cobalt blue. The selection includes Medieval (Islamic, and Hispano Moresque) and renaissance tin glazed ceramics from the 10th to the 17th century AD

Thermodynamic data for cement clinkering

The proportions of cement clinker phases produced by the pyro-processing of a raw-material mix are often predicted through the Bogue equations, established in the 1930s; however, the Bogue approach is limited in its applicability. This presents a challenge as the cement industry is seeking innovative and more environmentally friendly cement clinker formulations and production processes. These often go beyond the limitations of the Bogue equations and more flexible approaches are required. Modern thermodynamic calculations allow this flexibility but rely on databases not freely available and often specialised for other applications. The title paper reviews the thermodynamic data for stoichiometric clinker phases and presents a new dataset. The dataset is validated and its application demonstrated by case studies. Electronic CSV files containing the data which can be parsed for use with existing Gibbs energy minimisation solvers/software is distributed with this article as supplementary material

One-dimensional steady-state thermal model for rotary kilns used in the manufacture of cement

Rotary kilns are used extensively in the cement industry to convert raw meal into cement clinker. In order to optimise the operation of cement kilns, computationally efficient thermal models are required. In this work, the development of a one-dimensional thermal model for kilns is explored. To simplify the model, the kiln is assumed to be well mixed in the transverse direction. A simultaneous mass and energy balance is solved based on a steady-state approximation. Existing semi-empirical models for heat transfer in the kiln are implemented and critically evaluated. The resulting one-dimensional model is capable of predicting axial temperature profiles in the rotary kiln which agree well with the available experimental data found in the literature. The model presented here extends from previous published models by considering a full enthalpy balance for the gas in the kiln. This allows the model to be used in a fully predictive manner, taking into account the temperature-dependent thermodynamic, transport, and radiative properties of the gas phase

Advances in clinkering technology of calcium sulfoaluminate cement

A new method for producing calcium sulfoaluminate (CS¯A) clinkers is described. Sulfur is introduced from the gas phase as sulfur dioxide and oxygen and reacts with solids during clinkerisation. In this paper, the laboratory experiments are described and thermodynamic calculations are presented. The sulfur-containing phases ye'elimite and ternesite were stabilised together with belite to produce clinkers with various mineralogies. The influences of temperature and sulfur dioxide partial pressure were analysed and their effect on the formation of undesirable anhydrite and gehlenite was examined. The process by which a potentially hazardous waste material such as sulfur can be used as raw material, and possibly as fuel, to form CS¯A cements, is shown to be successful

Phase compatibility in the system CaO–SiO₂–Al₂O₃–SO₃–FE₂O₃ and the effect of partial pressure on the phase stability

The compatibility of phases within the CaO–SiO2–Al2O3–SO3–Fe2O3 system is revisited. The influence of the SO2 partial pressure on the formation of phases and the stability of phase assemblages is addressed by means of new experimental methods (performed under controlled atmospheres) and thermodynamic calculations. Existing data from the literature are compiled and compared with the results obtained from this work. The results obtained are linked to real clinker formulations, and practical implications are discussed