Italian Limestone Research Articles

Influence of Fluidised Bed Inventory on the Performance of Limestone Sorbent in Calcium Looping for Thermochemical Energy Storage

This research work deals with the application of the calcium looping concept for thermochemical energy storage. Experiments were carried out in a lab-scale fluidised bed reactor, which was electrically heated. An Italian limestone (98.5% CaCO3, 420–590 μm) was present in the bed alone, or in combination with silica sand/silicon carbide (this last material was chosen as per its high absorption capacity in the solar spectrum). Calcium looping tests (20 calcination/carbonation cycles) were carried out under operating conditions resembling the “closed-loop” scheme (calcination at 950 °C, carbonation at 850 °C, fluidising atmosphere composed of pure CO2 in both cases). Carbonation degree, particle size distribution, and particle bulk density were measured as cycles progressed, together with the application of a model equation to relate carbonation degree to the number of cycles. Mutual relationships between the nature of the bed material and possible interactions, the degree of CaO carbonation, the generation of fragments, and changes in particle density and porosity are critically discussed. An investigation of the segregation behaviour of the bed material has been carried out through tests in a devoted fluidisation column, equipped with a needle-type capacitive probe (to measure solid concentration).

Elemental abundances and isotopic composition of Italian limestones: Glimpses into the evolution of the Tethys

Biogenic limestones from three sections (north, central, and south) across peninsular Italy have been analysed for major and trace elements and Nd, Pb, and Sr isotopic ratios. These data are used to monitor the evolution of the Tethys Ocean from the Triassic through to the Miocene. Limestones’ major, trace, and REE elements contents are consistent with their formation in seawater with little sign of crustal, volcanic, or hydrothermal input. V/Cr and Ce/Ce* ratios indicate their deposition in oxygenated waters. Rb-Sr-Ba discrimination diagram, consistent with the immobile trace element distribution, indicates that limestone deposition took place in either marginal or open ocean environments. Ages based on stratigraphy are in good agreement with the chronostratigraphic Sr curves implying that the Tethys ocean, throughout its history, was in contact with the open, global, ocean system. Although the isotopic values of Sr and Nd are relatively restricted, Pb is extremely variable and highly radiogenic. High Pb isotope ratios characterise limestones deposited during the rifting of the southern Tethyan ocean in the Lower Jurassic and in the Lower Cretaceous, suggesting stronger crustal inputs in small basins. The weighted average, present-day, isotope values (AIL = average Italian limestone) for the Italian limestones, excluding anomalous samples, are 87Sr/86Sr = 0.70785, 143Nd/144Nd = 0.51227, and 206Pb/204Pb = 18.94, 207Pb/204Pb = 15.69, 208Pb/204Pb = 38.66. These values are useful in monitoring the fate of limestones during orogenesis and the role that they may have played in magma genesis.

Performance of limestone‐based sorbent for sorption‐enhanced gasification in dual interconnected fluidized bed reactors

AbstractA possibility to carry out sorption‐enhanced gasification (SEG) is represented by its integration with the calcium looping concept in dual interconnected fluidized beds (DIFB). This article is focused on the sorbent CO2 uptake performance and attrition/fragmentation tendency when operating conditions simulating those of a DIFB‐SEG process are adopted. Experiments were carried out on a commercial Italian limestone in a laboratory‐scale DIFB reactor. Carbonation was carried out in a range of test conditions, including variable temperature (600–700°C) and absence/presence of steam (10% by volume); CO2 concentration was set at 10% by volume. The characterization is extended by investigating the behavior of preprocessed DIFB‐SEG samples on impact fragmentation tests, conducted in an ex situ apparatus. Tests were carried out for impact velocities in the range 17–45 m/s. Results were discussed considering both the impact velocity value and the operating conditions under which the sample was preprocessed in the fluidized bed.

Production of the Roman Cement in Italy: characterization of a raw material used in Tuscany between 19th and 20th century and its comparison with a commercialized French stone material

ABSTRACTAn experimental approach in order to investigate the possibility that some Italian limestones were used for the production of Roman Cement is proposed. Three types of Pietra Alberese, a marly limestone used since Roman times for the production of “lime” in Tuscany (Italy), were selected. By burning of these stones, specimens of binders were realized. The characteristics of these binders were compared with the binder obtained by burning a French marly limestone commercially used for the production of Roman Cement.All samples of carbonate stones were preliminarily characterized from the chemical, mineralogical, and petrographic point of view. The colorimetric coordinates were measured on both rock samples and hardened binder samples. The analysis carried out shows that Pietra Alberese with an high content of clay minerals develops a similar microstructure with respect to that developed by the French marly limestone used for the production of Roman Cement.

An experimental characterization of Calcium Looping integrated with concentrated solar power

Carbon Capture and Sequestration (CCS) and renewable energy sources are both essential to mitigate the CO2 emissions in the near future. Calcium Looping (CaL) is an important post-combustion carbon capture technology that has reached the maturity of the pilot plant stage. On the other side Concentrated Solar Power (CSP) is a fast-growing renewable technology in which solar energy, concentrated up to several MWm−2, can be used to produce electricity or to drive an endothermic chemical reaction. The integration between a CSP system and a CaL cycle, in order to use a renewable source to supply the energy required by the calciner, would strongly improve the performance of the CaL process by overcoming some of its main drawbacks. However, the role that highly concentrated radiation can have on the sorbent properties in the CaL cycle is still matter of investigation. In this study, the CaL-CSP integrated process is experimentally investigated through the use of a directly irradiated Fluidized Bed (FB) reactor. Simulated concentrated solar radiation featured a peak flux on the FB surface of approximately 3MWm−2 and a total power of about 3kWth. Several calcination and carbonation tests have been performed on samples of a commercial Italian limestone, in order to establish the evolution of the sorbent capacity of CO2 capture at increasing number of cycles. The properties of the limestone samples were further investigated by means of microstructural characterization. The comparison between results obtained with and without the use of the solar concentrated flux to thermally sustain calcination provides useful information on the potential of solar driven CaL and on the measure to overcome some of its potential limitations.

The effect of steam on CO2 uptake and sorbent attrition in fluidised bed calcium looping: The influence of process conditions and sorbent properties

Calcium looping was investigated with a focus on the effect of exposure to steam during calcination and/or carbonation stages. Experiments were carried out using an Italian limestone in a lab-scale fluidised bed reactor. Calcium looping cycles were performed at temperatures of 940 and 650 °C and in atmospheres containing 70 and 15% CO2 for calcination and carbonation stages, respectively. When present, steam accounted for 10% of the fluidising gas. CO2 concentration in the flue gas was continuously monitored for the evaluation of the CO2 capture capacity in each carbonation stage. The rate of fines generation by attrition during iterated carbonation and calcination stages was measured by collection of elutriated fines in filters at the exhaust. The extent of fragmentation was characterised by analysis of the particle size distribution of in-bed sorbent fragments after each calcination and carbonation stage. Porosimetric analyses on selected samples complemented the overall characterisation. Results of this investigation were compared with those obtained in a previous study on a different (more reactive) limestone sorbent with the aim of outlining a general mechanistic frame of the mutual relationships among the exposure to steam, sorbent microstructural features, CO2 capture capacity and attrition. The propensity to attrition and fragmentation was specifically scrutinised, as it has been largely unexplored in the literature under operating conditions relevant to calcium looping.

Propuesta de reconstrucción virtual y material por anastilosis de los restos arqueológicos del patio del palacio renacentista del Embajador Vich en Valencia, España

<p>Ambassador Vich’s palace in Valencia (1526-1858) was one of the first examples of renaissance architecture in Spain. After its demolition, part of the courtyard’s marbles was conserved, gathered, after a century and a half of pilgrimage in a unifying intervention in the Museum of Fine Arts of San Pío V in 2006. The recovery of the spatial, composite and material essence of the monument remains incomplete, as the cornices and frames that decorated the surrounding lower gallery are missing; archaeological remains made with grey Italian limestone, Pietra Serena, which together with the white Carrara marble, created the typical two-colour of these, such “Brunelleschian” composite games. The virtual anastylosis allows a proposal to be launched for the material recovery of the emblematic monument, favouring as such the correct reading of the same.</p>

The influence of reactivation by hydration of spent SO 2 sorbents on their impact fragmentation in fluidized bed combustors

The relationship between calcination/sulphation and attrition/fragmentation of calcium-based SO 2 sorbents in fluidized bed (FB) combustors has long been recognized, but only recently did attrition by impact receive due consideration. There is limited available information in the literature on the propensity of exhausted calcium-based sorbents to undergo high-velocity impact fragmentation after they have been reactivated by steam or water hydration. The present study addresses the relationship between hydration-induced reactivation of spent Ca-based sorbents and attrition by impact loading. The sorbent used in this work (a high-calcium Italian limestone) was pre-processed (sulphation at 850 °C in a lab-scale FB, water hydration for 3 h at 25 °C in a thermostatic bath, steam hydration for 3 h at 250 °C in a tubular reactor, dehydration at 850 °C in the FB) and subjected to impact tests in a purposely designed impact test rig, operated with particle impact velocities ranging from 4 to 45 m s −1. The particle size distribution of the debris was worked out to define a fragmentation index and a probability density function of the size of generated fragments. The effect of hydration/reactivation of spent sorbent on propensity to undergo impact fragmentation was assessed, and results are discussed in the light of a mechanistic framework. It was observed that the prevailing particle breakage pattern was splitting/chipping for water-reactivated samples, disintegration for steam-reactivated samples. Characterization of sorbent microstructure by porosimetry and microscopic investigation on the reactivated samples highlighted a clear relationship between the extent of fragmentation and the cumulative specific volume of mesopores.

Comparison of magnetic hysteresis parameters of unremagnetized and remagnetized limestones

For white magnetite‐bearing Mesozoic pelagic limestones from Italy which carry a “primary” magnetization, the values of Mrs/Ms and Hcr/Hc generally lie in the pseudo‐single domain (PSD) field of the Day et al. (1977) plot. The logarithmic plot of Mrs/Ms against Hcr/Hc gives a straight line (R = 0.814) with slope and intercept close to the empirical mixing line of Parry (1982) for single domain (SD) and multidomain (MD) magnetite. For one of the white pelagic limestone formations (Maiolica Formation), samples with hysteresis ratios closer to the MD field display increased paramagnetic susceptibility and are from the upper part of the formation characterized by increased detrital clay. We therefore associate the increased MD magnetite with increased detrital influx. For pinkish and reddish varieties of the Italian pelagic limestones, the presence of hematite is manifest by high saturation fields, a wide range of Hcr/Hc, and “wasp‐waisted” hysteresis loops attributed to the mixing of magnetite and high‐coercivity authigenic hematite. The hysteresis ratios for a collection of Paleozoic and Mesozoic remagnetized magnetite‐bearing limestones from Britain, Nevada, Alaska and the Appalachians lie mainly outside the PSD field and appear to follow a power law trend. Following Jackson et al. (1993), the high values of Hcr/Hc and the characteristically “wasp‐waisted” hysteresis loops can be interpreted in terms of a fine‐grained subspherical high‐coercivity SD magnetite mixed with a high proportion of superparamagnetic magnetite. The slope and intercept of the power law relationship for Mrs/Ms and Hcr/Hc in the remagnetized limestones are distinct from those observed for the Italian limestones, and may provide a means of fingerprinting magnetite of “primary” as opposed to diagenetic origin.

Sulphur dioxide reactivity of carbonate rocks: 3. Influence of porosity and purity of sorbents

Comparative data are reported on the sulphur dioxide reactivity of 12 Italian limestones, which are possible sorbents for large-scale fluidized-bed combustors. Physical characterization of the limestones was carried out using different techniques such as X-ray diffraction, i.r. spectrophotometry, N 2 adsorption and mercury porosimetry. SO 2 reactivity, as determined using a fixed bed quartz reactor ( T = 850 °C, SO 2 = 6200 ppm) ranged from 17 to 57 wt% CaO conversion. It has been proposed that the performance of desulphurization sorbents, through the dependence on the physical and chemical characteristics, can be forecast by a simple linear semi-empirical equation.