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The present study addresses limestone attrition and fragmentation associated with impact loading, a process which may occur extensively in various regions of fluidized bed (FB) combustors/gasifiers, primarily the jetting region of the bottom bed, the exit region of the riser, and the cyclone. An experimental protocol for the characterization of the propensity of limestone to undergo attrition/fragmentation by impact loading is reported. The application of the protocol is demonstrated with reference to an Italian limestone whose primary fragmentation and attrition by surface wear have already been characterized in previous studies. The experimental procedure is based on the characterization of the amount and particle size distribution of the debris generated upon the impact of samples of sorbent particles against a target. Experiments were carried out at a range of particle impact velocities between 10 and 45 m/s, consistent with jet velocities corresponding to typical pressure drops across FB gas distributors. The protocol has been applied to either raw or preprocessed limestone samples. In particular, the effect of calcination, sulfation, and calcination/recarbonation cycles on the impact damage suffered by sorbent particles has been assessed. The measurement of particle voidage and pore size distribution by mercury intrusion was also accomplished to correlate fragmentation with the structural properties of the sorbent samples. Fragmentation by impact loading of the limestone is significant. Lime displays the largest propensity to undergo impact damage, followed by the sorbent sulfated to exhaustion, the recarbonated sorbent, and the raw limestone. Fragmentation of the raw limestone and of the sulfated lime follows a pattern typical of the failure of brittle materials. The fragmentation behavior of lime and recarbonated lime better conforms to a disintegration failure mode, with an extensive generation of very fine fragments.

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In this paper weathered coal fly ash has been used in polycondensation processes aimed at the production of geopolymer-based low temperature ceramic bricks. The ash has been employed both "as received" and after drying, showing favorable reactivity in any case. Different curing conditions with a variable period at 60 °C have been tested. Samples obtained have been characterized by measuring Unconfined Compressive Strength (UCS) and by SEM observations. Good strength values have been obtained with the systems tested. Furthermore, it has been found that mechanical performance increases as the time during which samples are kept at 60 °C increases

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Among low cost or readily available raw materials, reservoir clay sediments are of interest as potential precursors in geopolymer binder manufacture. These materials come from dredging of reservoirs because periodical sediment removal is necessary in order to keep a satisfactory level of functionality. In this paper, two sediments, coming from reservoirs located in Southern Italy, have undergone preliminary characterisation by X-ray diffraction, differential thermogravimetry and Fourier transformed infrared (FTIR) spectroscopy. Then, the sediments were submitted to 1 and 2 h calcination treatments at 650 and 750°C. The effects of calcination were evaluated by means of 27Al magic angle spinning nuclear magnetic resonance and FTIR. The calcined samples were mixed with 5M NaOH solution, and the obtained mixtures were studied for reactivity by means of differential scanning calorimetry. Finally, cylindrical samples were prepared with the same mixtures and cured for 3 days at 60°C plus 4 and 25 days at room temperature. The obtained samples were subjected to unconfined compressive strength determinations in order to verify the actual occurrence of geopolymerisation. The results show that the calcined clay sediments can be suitable precursors in polycondensation reactions

Six limestones were tested for CO2 capture during calcium looping cycles in a lab-scale fluidized bed apparatus. Batch tests were carried out under alternating calcination–carbonation conditions representative of a process with calcination in an oxy-firing environment (T = 940 °C, 70% CO2). The effect of the presence of SO2 was also studied at two concentration levels: 1500 ppm SO2 during both carbonation and calcination, simulating CO2 capture from uncontrolled flue gas and regeneration in an oxy-fired calciner burning high-sulfur coal; 75 ppm SO2 during carbonation and 750 ppm SO2 during calcination, simulating CO2 capture from already desulfurized flue gas and regeneration in an oxy-fired calciner burning medium-sulfur coal. Limestone attrition processes were characterized during the tests by measuring the changes of the sorbent particle size distribution and the fines elutriation rate along conversion over repeated cycles. Results showed that for all the limestones the CO2 capture capacity decreased with the number of cycles reaching a very low asymptotic value. The combination of high bed temperature and high CO2 concentration during the calcination stage significantly enhanced particle sintering. Moderate attrition rates were experienced by the sorbent particles mostly during the first cycle. In the subsequent cycles the attrition rate progressively declined, due to the concurrent chemical–thermal treatment making the sorbent surface increasingly hard. The presence of a high SO2 concentration significantly depressed the sorbent CO2 capture capacity, because of the buildup of a compact CaSO4 layer on the particle surface. Under a lower SO2 concentration level, the effect on CO2 capture capacity was less important. In both conditions, limestone attrition was only influenced to a limited extent by SO2. The slight variations of the sorbent particle size distribution indicated that very low particle fragmentation occurred over the repeated cycles