FLSmidth (Denmark)

The Dense Discrete Phase Model, DDPM, was used to investigate erosion, caused by the impacts of solid particles, in an industrial cyclone preheater by application of Oka's erosion model. The model predictions of flow pattern and temperature profile were validated by measurements in an industrial cyclone preheater. Then, the erosion model was tested against the results in a lab-scale cyclone reported in the literature. Furthermore, the erosion patterns in the industrial cyclone preheater were predicted by the model. The predicted results were qualitatively matching with the erosion observed in the cyclone. In addition, parametric studies on key operating conditions were performed and the impacts on erosion as well as pressure drop and heat transfer rate were evaluated. The results indicate that gas flow rate and inlet temperature have the greatest influence on erosion. The erosion rate is largely unaffected by solid flow rate and particle size in the studied range.

A hybrid multiphase model (Dense Discrete Phase Model, DDPM) coupled with a k-ω sst turbulence model, which includes gas–solid heat exchange was developed for the simulation of industrial-scale cyclone preheaters operating under high solid loadings. The model results are validated by experimental measurements from an industrial cyclone preheater with a diameter of 1.6 m, with respect to the pressure drop, gas and particle exit temperature, local gas velocity profiles, measured using the LDA, and gas temperature profiles, measured using thermocouple and FTIR. Reasonable agreement between the data from experiments and simulations was obtained. In addition, the major trends, such as changes in the pressure drop, overall heat transfer rate, and flow pattern, caused by the changes in the operating parameters can be captured accurately by the model.

This work investigates the initial (short-term) deposit formation in a cement calciner co-fired with coal and SRF (Solid Recovered Fuel). The main objective was to evaluate and compare the tendencies of deposit formation (i.e. material deposition rate and composition) at different locations (heights) in the calciner system, during different operation conditions. A steel probe was used to collect initial deposits from four different sampling locations: i) in the kiln riser (two sampling locations), ii) in the mid calciner, and, iii) at the outlet from the bottom stage preheater cyclone (C5). After an exposure time of the probe between 1 and 20 min, the collected deposit samples were weighted and characterized by SEM-EDX, ICP-OES/IC, and XRD. Plant operation data, measured gas temperatures, as well as gas phase composition data (i.e. KCl(g) and SO2(g)), supported the evaluation of deposit formation. Due to high particle flux (up to approx. 61,000 kg/(m2·h) in the riser duct), the average net deposit formation rate was around 500 kg/(m2·h) for 1 min exposure time, decreasing to <100 kg/(m2·h) for exposure times ≥4 min (due to spontaneous shedding and erosion). The deposits contained primarily five crystalline phases (CaO, CaCO3, Ca(OH)2, KCl, and SiO2), which is in general consistence with the composition of the admitted preheated raw meal (C4 meal) at measurement locations, with a slight enrichment in KCl, suggesting some condensation of volatile elements from the high-temperature gas phase on the surface of the somewhat colder deposit particles. Further, the deposit samples obtained in the kiln riser had a higher degree of calcination (higher proportion of CaO as compared to CaCO3) as compared to the admitted C4 meal, suggesting carry-over of dust from the kiln feed pipe, or fast calcination of the riser meal due to high temperature.The collected short-term deposits differ significantly from long-term (mature) deposits, which have previously been collected from the site, in terms of chemical and physical properties. Compared to short-term deposits, which had a content of KCl in the range of approx. 3–5 wt%, the content of KCl in the mature deposits increased substantially from around 2 wt% in samples from the kiln riser area to a level of >20 wt% in the calciner and C5 cyclone area, implying significant accumulation of KCl caused by volatile circulation and condensation from the hot gas on surfaces with locally lower temperatures. The most prevalent crystalline phases in the mature deposits were KCl, CaCO3, and the mineral spurrite (Ca5(SiO4)2CO3). The presence of spurrite implied that SiO2 reacts with CaCO3, or with CaO and gaseous CO2, to form spurrite during long-term deposit build-up and maturation.Overall, the results from this work suggest that the short-term deposit formation in the cement calciner is dominated by impaction. The composition of the short-term deposits is quite similar to the composition of the entrained C4 meal particles; while the build-up of mature deposits is influenced greatly by local temperature gradients and long-term fluctuations. I.e. in zones with locally lower temperatures, such as cold area of calciner walls (< ∼850 °C), heterogeneous condensation and/or thermophoresis of KCl from the high-temperature flue gas is facilitated.

The corrosion resistance of two high chrome wear facings, manganese cold workable steel and heat treated white cast iron, was investigated. The addition of Cl− to the aqueous solution unexpectedly improves the corrosion resistance. Tribocorrosion experiments show that the current density increases but with magnitudes of no importance in industrial vertical roller mill applications. However, these corrosion magnitudes might show significant material losses in other industrial applications such as marine industries including oil drilling. The investigated wear part materials are not specifically designed to withstand abrasive marine conditions; however, the applied scientific approach might be used on such materials.

During combustion of alternative fuels in the material inlet end of cement rotary kilns, local reducing conditions may occur and cause reductive decomposition of sulfates from calcined cement raw materials. Decomposition of sulfates is problematic because it increases the gas-phase SO2 concentration, which may cause deposit formation in the kiln system. In this study, the release of sulfur from calcined cement raw materials under both oxidizing and reducing conditions is investigated. The investigations include thermodynamic equilibrium calculations in the temperature interval of 800–1500 °C and experiments in a tube furnace reactor in the temperature interval of 900–1100 °C. The investigated conditions resemble actual conditions in the material inlet end of cement rotary kilns. It was found that the sulfates CaSO4, K2SO4, and Na2SO4 were all stable under oxidizing conditions but began to decompose under reducing conditions. Particularly, CaSO4 was sensitive to reducing conditions. The sulfur release was most significant if the gas atmosphere frequently shifted between oxidizing and reducing conditions. An increasing temperature from 900 to 1100 °C under alternating oxidizing and reducing conditions was also observed to increase the sulfur release from the calcined raw materials by a factor of 3, from 14 to 48%.