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Four limestones were calcined in atmospheres containing moderate (∼30%) and high (∼100%) CO2 levels, and the carbonation characteristics of the quicklimes during cooling in these atmospheres were studied using thermogravimetric analysis. The carbonation rates, extents, and onset temperatures varied depending on the atmosphere and parent limestone type. Scanning electron microscopy showed that the quicklimes produced from sedimentary limestones exhibited larger pores and thicker structures, especially after calcination in the high CO2 atmosphere. The quicklimes produced from metamorphic limestones exhibited smaller pores among finer structures, with no major observed differences due to the different calcination atmospheres. However, the carbonation extents differed more in the quicklimes produced from metamorphic limestones after calcination in the different atmospheres, and their carbonation rates were also generally higher. Pore filling was observed in all carbonated quicklimes. Practically, the results indicate significant carbonation of all the tested quicklimes when cooling is conducted in atmospheres containing moderate or high levels of CO2. This has ramifications for processes where such conditions can occur, especially if excessive carbonation is unacceptable; e.g., in the cooling zone of electrified lime-based production kilns.

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.

Carbonation of quicklimes degrades their quality and can occur when process temperatures become sufficiently low. This risk can be heightened in process atmospheres containing high CO2 and steam. To assess this, carbonation experiments involving atmospheres with different CO2 concentrations and steam were performed at 700 °C on 2.5–5 mm quicklime granules derived from sedimentary and metamorphic limestones. The carbonation extents of the quicklimes derived from metamorphic limestones during the fast stage were higher, corresponding with their larger specific surface areas. However, SEM analysis revealed that these quicklimes had fine structures with relatively small pores that likely became blocked during carbonation, causing plateauing of carbonation that appeared to be mainly limited to particle surfaces. The presence of steam caused only mild enhancements in carbonation of these quicklimes. Contrastingly, the quicklimes derived from sedimentary limestones had lower specific surface areas that concurred with their thicker structures and larger pores. The carbonation extent during the initial fast stage was correspondingly lower, but carbonation progressed at a sustained rate thereafter. The resulting high carbonation extents appeared to be facilitated by the larger pore volumes available for carbonate growth, including locations inside particles. The presence of steam greatly enhanced the carbonation of these quicklimes. Overall, every quicklime exhibited high carbonation extents despite being granular-sized. Moreover, their distinctive carbonation behaviors and microstructures could be delineated by their parent limestone type. These findings should be considered when carbonation in high CO2 atmospheres may occur, e.g., during cooling in electrical lime kilns.

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.

Magnesium oxide (MgO)-based refractories are commonly used in quicklime and cement rotary kilns. At the high temperatures in the kiln burn zone, the infiltration of molten fuel ash into the refractory can occur. Subsequent chemical interactions can cause refractory wear that inflicts high maintenance costs and loss of production. To improve refractory reliability, it is necessary to increase the understanding of the interactions between fuel ash slag and refractory liner materials. Three commercially available MgO-based refractory materials were exposed to coal ash at 1200 °C and 1400 °C for between 15 and 60 min under a CO₂-rich gaseous environment. Hot slag from the coal ash infiltrated the refractories and the infiltration depths were estimated with scanning electron microscope with energy dispersive X-ray spectroscopy. Based on detailed elemental and microstructure analyses, the interactions between ash and refractory were examined. Molten silicates infiltrated the refractory through grain boundaries and pores into depths of up to 2.8 mm. Powder X-ray diffraction of the exposed refractory samples indicated that MgO grains reacted with SiO₂-containing phases to form Mg₂SiO₄. This was identified as a corrosion product whose formation was supported by thermochemical equilibrium calculations. Elevated Mg content was found in the ash residue on top of the samples, indicating the dissolution or dislocation of refractory components. In addition, phases such as MgO were identified in the ash residue.

MgO-based refractories are used in lime kilns to withstand the high temperature and chemical environment. Efforts to reduce CO₂ emissions have led to an increased interest to use bio-based fuels as alternatives to traditional fossil sources. The potential for refractory corrosion from a potassium-rich biomass ash was investigated by studying the infiltration of olive pomace ash into magnesia/spinel refractories. Refractory samples were exposed to the ash at up to 1400 °C for 15–60 min in a CO₂–rich atmosphere. Molten ash infiltrated the refractories through pores and grain boundaries to a depth of up to 9.6 mm, which was quantified with a new systematic procedure. The phase KAlO₂ was identified inside the refractories after exposure, indicating an attack of spinel components by potassium. Phases found in the ash residues also indicated the migration of refractory constituents. Thermochemical equilibrium calculations were also used to investigate the ash/refractory chemistry.

Photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS) was used to simultaneously measure the concentrations of gas phase atomic potassium (K), potassium hydroxide (KOH) and potassium chloride (KCl) in the reactor core of a 140 kWth atmospheric entrained-flow gasifier (EFG). In two gasification experiments at air-to-fuel equivalence ratio of 0.5, the EFG was first run on forest residues (FR) and then on an 80/20 mixture of FR and wheat straw (FR/WS). Combustion at air-to-fuel equivalence ratio of 1.3 was investigated for comparison. A high K(g) absorbance was observed in gasification, requiring the photofragmentation signals from KOH(g) and KCl(g) to be recorded at a fixed detuning of 7.3 cm⁻¹ from the center of the K(g) absorption profile. In combustion, the fragments recombined instantly after the UV pulse within around 10 µs, whereas in gasification, the K(g) fragment concentration first increased further for 30 µs after the UV pulse, before slowly decaying for up to hundreds of µs. According to 0D reaction kinetics simulations, this could be explained by a difference in recombination kinetics, which is dominated by oxygen reactions in combustion and by hydrogen reactions in gasification. The K species concentrations in the EFG were stable on average, but periodic short-term variations due to fuel feeding were observed, as well as a gradual increase in KOH(g) over the day as the reactor approached global equilibrium. A comparison of the average K species concentrations towards the end of each experiment showed a higher total K in the gas phase for FR/WS, with higher K(g) and KCl(g), but lower KOH(g), compared to the FR fuel. The measured values were in reasonable agreement with predictions by thermodynamic equilibrium calculations.