Simultaneous CO_(2) capture and thermochemical heat storage by modified carbide slag in coupled calcium looping and CaO/Ca(OH)2 cycles

The simultaneous CO_(2) capture and heat storage performances of the modified carbide slag with byproduct of biodiesel were investigated in the process coupled calcium looping and CaO/Ca(OH)2 thermochemical heat storage using air as the heat transfer fluid.The modified carbide slag with by-product of biodiesel exhibits superior CO_(2) capture and heat storage capacities in the coupled calcium looping and heat storage cycles.The hydration conversion and heat storage density of the modified carbide slag after 30 heat storage cycles are 0.65 mol·mol^(-1) and 1.14 GJ·t^(-1),respectively,which are 1.6 times as high as those of calcined carbide slag.The negative effect of CO_(2) in air as the heat storage fluid on the heat storage capacity of the modified carbide slag is overcome by introducing CO_(2) capture cycles.In addition,the CO_(2) capture reactivity of the modified carbide slag after the multiple calcium looping cycles is enhanced by the introduction of heat storage cycles.By introducing 10 heat storage cycles after the 10th and 15th CO_(2) capture cycles,the CO_(2) capture capacities of the modified carbide slag are subsequently improved by 32%and 43%,respectively.The porous and loose structure of modified carbide slag reduces the diffusion resistances of CO_(2) and steam in the material in the coupled process.The formed CaCO_(3)in the modified carbide slag as a result of air as the heat transfer fluid in heat storage cycles decomposes to regenerate CaO in calcium looping cycles,which improves heat storage capacity.Therefore,the modified carbide slag with by-product of biodiesel seems promising in the coupled calcium looping and CaO/Ca(OH)_(2) heat storage cycles.

NO removal performance of CO in carbonation stage of calcium looping for CO_(2) capture

Calcium looping realizes CO_(2)capture via the cyclic calcination/carbonation of CaO.The combustion of fuel supplies energy for the calciner.It is unavoidable that some unburned char in the calciner flows into the carbonator,generating CO due to the hypoxic atmosphere in the carbonator.CO can reduce NO in the flue gases from coal-fired power plants.In this work,NO removal performance of CO in the carbonation stage of calcium looping for CO_(2)capture was investigated in a bubbling fluidized bed reactor.The effects of carbonation temperature,CO concentration,CO_(2)capture,type of CaO,number of CO_(2)capture cycles and presence of char on NO removal by CO in carbonation stage of calcium looping were discussed.CaO possesses an efficient catalytic effect on NO removal by CO.High temperature and high CO concentration lead to high NO removal efficiency of CO in the presence of CaO.Taking account of better NO removal and CO_(2)capture,the optimal carbonation temperature is 650℃.The carbonation of CaO reduces the catalytic activity of CaO for NO removal by CO due to the formation of CaCO_(3).Besides,the catalytic performance of CaO on NO removal by CO gradually decreases with the number of CO_(2)capture cycles.This is because the sintering of CaO leads to the fusion of CaO grains and blockage of pores in CaO,hindering the diffusion of NO and CO.The high CaO content and porous structure of calcium-based sorbents are beneficial for NO removal by CO.The presence of char promotes NO removal by CO in the carbonator.CO_(2)/NO removal efficiencies can reach above 90%.The efficient simultaneous NO and CO_(2)removal by CO and CaO in the carbonation step of the calcium looping seems promising.

Calcium looping heat storage performance and mechanical property of CaO-based pellets under fluidization

The CaO-based pellets were fabricated using extrusion-spheronization method for calcium looping thermochemical heat storage under the fluidization.The effects of adhesive,biomass-based pore-forming agent,binder and particle size on the heat storage performance and mechanical property of the CaObased pellets were investigated in a bubbling fluidized bed reactor.The addition of 2%(mass)polyvinylpyrrolidone as an adhesive not only helps granulate,but also improves the heat storage capacity of the pellets.All biomass-templated CaO-based pellets display higher heat storage capacity than biomass-free pellets,indicating that the biomass-based pore-forming agent is beneficial for heat storage under the fluidization.Especially,bagasse-templated pellets show the highest heat storage conversion of 0.61 after 10 cycles.Moreover,Al_(2)O_(3)as a binder for the pellets helps obtain high mechanical strength.The CaO-based pellets doped with 10%(mass)bagasse and 5%(mass)Al_(2)O_(3)reach the highest heat storage density of 1621 kJ·kg^(-1) after 30 cycles and the highest crushing strength of 4.98 N.The microstructure of the bagasse-templated pellets appears more porous than that of biomass-free pellets.The bagassetemplated CaO-based pellets doped with Al_(2)O_(3)seem promising for thermochemical heat storage under the fluidization,owing to the enhanced heat storage capacity,excellent mechanical strength,and simplicity of the synthesis procedure.

Experimental analysis on calcination and carbonation process in calcium looping for CO_(2) capture: study case of cement plants in Indonesia

Carbon dioxide(CO_(2))is the main contributor to greenhouse gases that affect global warming.The industrial sector is the third largest producer of CO_(2) and the cement industry is one of the industries that consistently produces the most significant CO_(2) emissions.The cement industry produces 5-8% of global CO_(2) emissions.Several methods for reducing specific CO_(2) emissions have been reported in the cement industry,including calcium looping,which uses the reversible reaction between calcination[calcium carbonate(CaCO_(3))decomposition]and carbonation[CO_(2) capture by calcium oxide(CaO)].This work investigates calcium looping employing limestone obtained directly from several cement factories in Indonesia to observe the carbon-absorption characteristics of limestone from different mining locations.The experiment was carried out using a tube furnace equipped with a controlled atmospheric condition that functions as a calciner and a carbonator.X-ray diffraction and scanning electron microscopy with energy-dispersive x-ray spec-troscopy characterization were conducted to analyse the changes in the experimental samples.The results demonstrated that the reactor configuration was capable of performing the calcination process,which converted CaCO_(3) to calcium hydroxide[Ca(OH)_(2)],as well as the carbonation process,which captured carbon and converted it back to CaCO_(3).Parametric analysis was performed on both reactions,including pressure,temperature,duration,particle size and reaction atmosphere.The results show that the limestone obtained from all sites can be used as the sorbents for the calcium-looping process with an average reactivity of 59.01%.Limestone from cement plants in various parts of Indonesia has the potential to be used as carbon sorbents in calcium-looping technology.With a similar CO_(2) concentration as the flue gas of 16.67%,the experimental results show that Bayah limestone has the maximum reactivity,as shown by the highest carbon-content addition of 12.15 wt% and has the highest CO_(2)-capture capability up to>75% per mole of Ca(OH)_(2) as a sorbent.Similar levels of the ability to capture CO_(2) per mole of Ca(OH)_(2) can be found in other limestones,ranging from 14.85% to 34.07%.The results show a promising performance of raw limestones from different mining sites,allowing further study and observation of the possibility of CO_(2) emission reduction in the sustainable cement-production process.

Towards carbon neutrality of calcium carbide-based acetylene production with sustainable biomass resources

Acetylene is produced from the reaction between calcium carbide(CaC_(2))and water,while the production of CaC_(2) generates significant amount of carbon dioxide not only because it is an energy-intensive process but also the raw material for CaC_(2) synthesis is from coal.Here,a comprehensive biomass-to-acetylene process was constructed that integrated several units including biomass pyrolysis,oxygen-thermal CaC_(2) fabrication and calcium looping.For comparison,a coal-to-acetylene process was also established by using coal as feedstock.The carbon efficiency,energy efficiency and environmental impacts of the bio-based calcium carbide acetylene(BCCA)and coal-based calcium carbide acetylene(CCCA)processes were systematically analyzed.Moreover,the environmental impacts were further evaluated by applying thermal integration at system level and energy substitution in CaC_(2) furnace.Even though the BCCA process showed lower carbon efficiency and energy efficiency than that of the CCCA process,life cycle assessment demonstrated the BCCA(1.873 kgCO_(2eq) kg-prod^(-1))a lower carbon footprint process which is 0.366 kgCO_(2eq) kg-prod^(-1) lower compared to the CCCA process.With sustainable energy(biomass power)substitution in CaC_(2) furnace,an even lower GWP value of 1.377 kgCO_(2eq) kg-prod^(-1) can be achieved in BCCA process.This work performed a systematic analysis on integrating biomass into industrial acetylene production,and revealed the positive role of biomass as raw material(carbon)and energy supplier.

Enhancement of CO_(2) capture and microstructure evolution of the spent calcium-based sorbent by the self-reactivation process

The effect of self-reactivation on the CO_(2) capture capacity of the spent calcium based sorbent was investigated in a dual-fixed bed reactor.The sampled sorbents from the dual-fixed bed reactor were sent for XRD,SEM and N_2 adsorption analysis to explain the self-reactivation mechanism.The results show that the CaO in the spent sorbent discharged from the calciner absorbs the vapor in the air to form Ca(OH)_(2) and further Ca(OH)_(2)·2 H_(2) O under environmental conditions,during which process the CO_(2) capture capacity of the spent sorbent can be self-reactivated.The microstructure of the spent sorbent is improved by the self-reactivation process,resulting in more porous microstructure,higher BET surface area and pore volume.Compared with the calcined spent sorbent that has experienced 20 cycles,the pore volume and BET surface area are increased by 6.69 times and 56.3% after self-reactivation when φ=170%.The improved microstructure makes it easier for the CO_(2) diffusion and carbonation reaction in the sorbent.Therefore,the CO_(2) capture capacity of the spent sorbent is enhanced by self-reactivation process.A self-reactivation process coupled with calcium looping process was proposed to reuse the discharged spent calcium based sorbent from the calciner.Higher average carbonation conversion and CO_(2) capture efficiency can be achieved when self-reactivated spent sorbent is used as supplementary sorbent in the calciner rather than fresh CaCO_(3) under the same conditions.

Experimental study of the effect of friction phenomena on actual and calculated inventory in a small-scale CFB riser

Accurate information concerning riser inventory in a fluidized bed is required in some applications such as the calcium looping process, because it is related to the CO2 capture efficiency of the system. In a circulating fluidized bed （CFB）, the riser inventory is normally calculated from the riser pressure drop; however, the friction and the acceleration phenomena may have a significant influence on the total riser pressure drop. Therefore, deviation may occur in the calculation from the actual mass. For this reason the magnitude of the friction and the acceleration pressure drop in the entire riser is studied in small-scale risers. Two series of studies were performed： the first one in a scaled cold model riser of the 10 kWth facility, and the second one in the 10 kWth fluidized bed riser under process conditions. The velocities were chosen to comply with the fluidization regimes suitable for the calcium looping process, namely, the turbulent and the fast. In cold-model experiments in a low-velocity turbulent fluidization regime, the actual weight （static pressure drop） of the particles is observed more than the weight calculated from a recorded pressure drop. This phenomenon is also repeated in pilot plant conditions. In the cold-model setup, the friction and acceleration pressure drop became apparent in the fast fluidization regime, and increased as the gas velocity rose. Within calcium looping conditions in the pilot plant operation, the static pressure drop was observed more than the recorded pressure drop. Therefore, as a conservative approach, the influence of friction pressure drop may be neglected while calculating the solid inventory of the riser. The concept of transit inventory is introduced as a fraction of total inventory, which lies in freefall zones of the CFB system, This fraction increases as gas velocity rises.

Prediction of sorption enhanced steam methane reforming products from machine learning based soft-sensor models

Carbon dioxide-abated hydrogen can be synthesised via various processes,one of which is sorption enhanced steam methane reforming(SE-SMR),which produces separated streams of high purity H_(2) and CO_(2).Properties of hydrogen and the sorbent material hinder the ability to rapidly upscale SE-SMR,therefore the use of artificial intelligence models is useful in order to assist scale up.Advantages of a data driven soft-sensor model over ther-modynamic simulations,is the ability to obtain real time information dependent on actual process conditions.In this study,two soft sensor models have been developed and used to predict and estimate variables that would otherwise be difficult direct measured.Both artificial neural networks and the random forest models were devel-oped as soft sensor prediction models.They were shown to provide good predictions for gas concentrations in the reformer and regenerator reactors of the SE-SMR process using temperature,pressure,steam to carbon ratio and sorbent to carbon ratio as input process features.Both models were very accurate with high R^(2) values,all above 98%.However,the random forest model was more precise in the predictions,with consistently higher R^(2) values and lower mean absolute error(0.002-0.014)compared to the neural network model(0.005-0.024).