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Refractory liner bricks in the hot zone of rotary lime kilns can sustain wear and corrosion during contact with fuel ashes and quicklime (QL), a product composed mainly of CaO. The effects on a MgO-based refractory after exposure at 1400 °C for 96 h to olive pomace ash (OPA) and coal ash (CA), with and without QL, were investigated. Exposure of the refractory to only OPA caused slag intrusion with no ash deposits remaining on top, while CaMgSiO4 (monticellite) was also identified as a new phase. When exposed to only CA, the refractory exhibited dissolution into the molten slag and 0.5–2 mm cracks were found on the surface interfacing the ash. Mg2SiO4 (forsterite) and CaMgSiO4 were identified as new formed phases. Exposure of the refractory to OPA + QL and CA + QL caused less slag intrusion and substantial amounts of ash/QL deposit remained afterwards. No new phases were identified. The differences in interactions between the exposure materials and refractory were supported by thermochemical equilibrium analysis. Apparent Ca-Si–rich or Ca-rich melts were found in all the exposed samples, but potassium (K) was found to be depleted in all samples, including those involving OPA, which was rich in K. Furthermore, with the exception of exposure to only CA, the other exposures caused the cold crushing strength (CCS) of the refractory to increase compared to its original value. This was attributed to the sintering of the refractory microstructure. The CCS of the refractory decreased after exposure to only CA. The findings of this study enhance understanding of how CA and OPA impact MgO refractories in lime kilns, supporting initiatives aiming at reducing fossil fuel use. The results are encouraging and motivate further investigation.

Oxy-fuel biomass combustion can facilitate carbon capture in heat and power plants and enable negative carbon dioxide (CO₂) emissions. We demonstrate oxy-fuel combustion (OFC) of softwood powder in a 100-kW atmospheric down-fired pulverized combustor run at a global oxidizer-fuel equivalence ratio of around 1.25. The simulated oxidizer was varied between oxygen (O₂)/CO₂ mixtures of 23/77, 30/70, 40/60 and 54/46, and artificial air. The concentrations of the main gaseous potassium (K) species: atomic K, potassium hydroxide (KOH) and potassium chloride (KCl), were measured at two positions in the reactor core using photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS). Major species were quantified by TDLAS in the reactor core and with Fourier transform infrared spectroscopy and mass spectrometry at the exhaust. Flue gas particles were collected at the exhaust employing a low-pressure impactor and analyzed by X-ray powder diffraction and scanning electron microscopy. The measured individual K species concentrations in the reactor core agreed with predictions by thermodynamic equilibrium calculations (TEC) within one order of magnitude and the sum of K in the gas phase agreed within a factor of three for all cases. Atomic K was underpredicted, while the dominating KOH and KCl were slightly overpredicted. The ratios of measured to predicted total K were similar in artificial air and OFC, but the distributions of the individual species differed at the upper reactor position. The gaseous K species and fine particle concentrations in the flue gas were directly proportional to the O₂ content in the oxidizer. The crystalline phase compositions of the coarse mode particles were rich in K- and calcium-containing species. The fine mode particles, which contained most of the K, consisted mainly of K₂SO₄ (94%) and K₃Na(SO₄)₂, which is in excellent agreement with TECs of gas phase condensation. As supported by the solid phase analysis, complete sulfation of K species was achieved for all studied cases. A CO₂ purity (dry) of up to 94% was achieved for OFC.

In the future, cement clinker formation is likely to take place in high temperatures and high carbon dioxide atmospheres in carbon-neutral production processes as part of, for example, electrified processes. The aim of this study was thus to compare the volatilisation of minor and trace elements during cement clinker formation in a high carbon dioxide atmosphere and a conventional combustion atmosphere. Raw meal samples were exposed, at high temperature, to the two different atmospheres, with elemental analysis performed before and after. For both atmospheres, the minor elements potassium and sulfur, and the trace elements rubidium, lead, thallium, caesium, cadmium and mercury were highly volatile. For most of the analysed elements, no difference was observed between the two atmospheres. However, volatilisation of potassium, sodium and sulfur was lower in the high carbon dioxide atmosphere. It is suggested that this should be further studied in relation to the molar ratio of sulfur to alkalis in the clinker and the effect on clinker quality.

Quicklime, rich in CaO(s), is generated by calcining limestone at high temperatures. Parallel-flow regenerative lime kilns are the most energy-effective industrial method available today. To prevent major disruptions in such kilns, a high raw material quality is necessary. Under some conditions, impurity-enriched material may adhere to limestone pebbles and enter the kiln. In this study, limestone and corresponding quicklime were analyzed to evaluate the extent and composition of surface impurities and assess the effect on quicklime product quality, here defined as free CaO. This was performed by sampling and analyzing limestone, quarry clay, laboratory-produced quicklime, and industrially produced quicklime with XRF, SEM/EDX, and XRD; interpretations were supported by thermodynamic equilibrium calculations. In the laboratory-produced quicklime, the surface impurities reacted with calcium forming Larnite, Gehlenite, Åkermanite and Merwinite, reducing the quicklime quality. The results showed that the limestone surface layer comprised 1.2 wt.-% of the total mass but possessed 4 wt.-% of the total impurities. The effect on industrially produced quicklime quality was lower; this indicated that the limestone surface impurities were removed while the material moved through the kiln. Multicomponent chemical equilibrium calculations showed that the quarry clay was expected to be fully melted at 1170 °C, possibly leading to operational problems.

Quicklime is produced through the thermal processing of limestone in industrial kilns. During quarry operations, fine particulate quarry dust adheres to limestone lump surfaces, increasing the bulk concentration of impurities in limestone products. During thermal processing in a kiln, impurities such as Si, Mg, Al, Fe, and Mn react with Ca, reducing quicklime product quality. Which reactant phases are formed, and the extent to which these result in a reduction in quality, has not been extensively investigated. The present study investigated as-received and manually washed limestone product samples from two operational quarries using elemental compositions and a developed predictive multi-component chemical equilibrium model to obtain global phase diagrams for 1000–1500 °C, corresponding to the high-temperature zone of a lime kiln, identifying phases expected to be formed in quicklime during thermal processing. The results suggest that impurities found on the surface of the lime kiln limestone feed reduce the main quality parameter of the quicklime products, i.e., calcium oxide, CaO (s), content by 0.8–1.5 wt.% for the investigated materials. The results also show that, in addition to the effect of impurities, the quantity of CaO (s) varies greatly with temperature. More impurities result in more variation and a greater need for accurate temperature control of the kiln, where keeping the temperature below approximately 1300 °C, that of Hatrurite formation, is necessary for a product with higher CaO (s).

Research infrastructure MAXS offers state-of-the-art X-ray diffraction, totalX-ray scattering, and X-ray reflectometry with several sample environments foradvanced material characterization to users from academy, industry, or public sectors. The platform also offers a comprehensive data evaluation environment with access to extensive reference databases for data collected at MAXS or elsewhere, including compatibility with data from synchrotron light sources.

The available instruments are two independent Bruker D8Advance systems with the possibility to choose from three X-ray wavelengths, X-ray profile, detector configuration with two detector types, and a broad selection of sample stages to match the needs of an experiment. The users can define what they need from an experiment and the instrument can be configured accordingly. An important feature is the automatic sample changer, increasing the sample throughput.

Data evaluation environment is provided locally at MAXS at two workstations, but also via network for internal users permitting local installation within Umeå University. Up to 20 users can simultaneously use the evaluation software with local installations of the crystallographic open database (COD) making it readily accessible for both research and education.