Effect of Strong Basic Oxide（ Li2O,Na2O,K2O and BaO）on Property of CaO-Based Flux

It is found that strong basic oxides including Li2O,Na2O,K2O and BaO,which are used to replace a part of CaO in CaO-based fluxes,can lower the melting point and the viscosity and enhance the dephosphorizing ability. The mechanism was analysed and the addition of Li2O to CaO based fluxes was recommended.

Modification of CaO-based sorbents prepared from calcium acetate for CO_2 capture at high temperature

CaO-based sorbent is considered to be a promising candidate for capturing CO_2 at high temperature. However,the adsorption capacity of CaO decreases sharply with the increase of the carbonation/calcination cycles. In this study, CaO was derived from calcium acetate(CaAc_2), which was doped with different elements(Mg, Al,Ce, Zr and La) to improve the cyclic stability. The carbonation conversion and cyclic stability of sorbents were tested by thermogravimetric analyzer(TGA). The sorbents were characterized by N_2 isothermal adsorption measurements, scanning electron microscopy(SEM) and X-ray diffraction(XRD). The results showed that the cyclic stabilities of all modified sorbents were improved by doping elements, while the carbonation conversions of sorbents in the 1st cycle were not increased by doping different elements. After 22 cycles, the cyclic stabilities of CaO–Al, CaO–Ce and CaO–La were above 96.2%. After 110 cycles, the cyclic stability of CaO–Al was still as high as 87.1%. Furthermore, the carbonation conversion was closely related to the critical time and specific surface area.

CO_(2) capture by double metal modified CaO-based sorbents from pyrolysis gases

High-temperature pyrolysis technology can effectively solve the problem of municipal solid waste pollution.However,the pyrolysis gas contains a large amount of CO_(2),which would adversely affect the subsequent utilization.To address this problem,a novel method of co-precipitation modification with Ca,Mg and Zr metals was proposed to improve the CO_(2)capture performance.X-ray diffraction(XRD)patterns and energy dispersive X-ray spectroscopy analysis showed that the two inert supports MgO and CaZrO_(3)were uniformly distributed in the modified calcium-based sorbents.In addition,the XRD results indicated that CaZrO_(3)was produced by the reaction of ZrO_(2)and CaO at high temperatures.The effects of doping ratios,adsorption temperature,calcination temperature,CO_(2)concentration and calcination atmosphere on the adsorption capacity and cycle stability of the modified calcium-based sorbent were studied.The modified calcium-based sorbent achieved the best CO_(2)capture performance when the doping ratio was 10:1:1 with carbonation at 700℃ under 20%CO_(2)/80%N_(2)atmosphere and calcination at 900℃ under100%N_(2)atmosphere.After ten cycles,the average carbonation conversion rate of Ca-10 sorbent was 72%.Finally,the modified calcium-based sorbents successfully reduced the CO_(2)concentration of the pyrolysis gas from 37%to 5%.

Influence of CaO-based expansive agent,superabsorbent polymers and curing temperature on pore structure evolution of early-age cement paste

Cracks easily generate in concrete at early age owing to the shrinkage deformation.CaO-based expansion agent(CEA)and superabsorbent polymers(SAP)have been extensively used for the mitigation of concrete shrinkage.The macroscopic properties of concrete are highly determined by the microstructure.In this study,the influence of CEA and SAP addition on the pore structure evolution of cement paste under different curing temperatures was evaluated via low-field nuclear magnetic resonance spectroscopy.Test results indicated that,in cement paste,a higher CEA content led to a higher porosity and a larger most probable pore diameter(MPPD).Meanwhile,SAP addition increased the porosity and MPPD of CEA cement paste at early age but decreased them after 7 d,and a higher SAP content always brought a higher porosity and MPPD.Furthermore,the addition of SAP led to a lower porosity and MPPD of CEA cement paste than that of plain cement paste after 14 d.Moreover,the porosity and MPPD of CEA cement paste decreased first and subsequently increased as the curing temperature raised.

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.

Effect of B_2O_3 on Melting Temperature of CaO-Based Ladle Refining Slag

B2O3 is selected as fluxing agent of CaO-based ladle refining slag to decrease the melting temperature as well as to improve the speed of slag forming and the refining efficiency. The effects of B2O3 on the melting temperature of two series of refining slags including the low basicity slags （the mass ratio of CaO/SiO2 is 3--4） and the high basicity slags （the mass ratio of CaO/SiO2 is 5--8.75） were investigated. The slag melting temperature was meas- ured using the hemisphere method. The results indicate that the fluxing action of B2O3 is better than that of CaF2 and A1203. For the CaO-based refining slag with low basicity, the melting temperature is decreased effectively when B2O3 is used to substitute for equal mass of CaF2, Al2O3 and SiO2, respectively. For the CaO-based refining slag with high basicity, when CaF2 is substituted by B2 03, the melting temperature can be decreased remarkably. Espe- cially, when the mass ratios of CaO/Al2O3 and CaO/SiO2 are in the range of 1.1--4.0 and 5.25--8. 0, respectively, the slag melting temperature is lower than 1 300 ℃. Therefore, the 132 03-containing refining slags with high ratios of CaO/Al2O3 and CaO/SiO2 have ultra low melting temperature.

Effects of Shale and CaO Incorporation on Mechanical Properties and Autogenous Deformation of Early-age Concrete

The pre-soaked shale employed as an internal curing agent and CaO employed as expansion agent were incorporated into concrete to investigate their effects on the mechanical properties and autogenous deformation of early-age concrete.We have conducted the relevant tests for setting time,mechanical properties,internal relative humidity and autogenous deformation of early-age concrete with shale or/and CaO incorporation.The results indicate that the set behavior is delayed by shale addition but is accelerated with CaO.The shale addition firstly enhances and subsequently decreases the strength,but CEA addition has a weakening effect.Additionally,shale or/and CaO incorporation deteriorates the elastic modulus.The shale and CaO incorporation significantly improve the internal relative humidity of concrete.The internal curing efficacy of shale could synergistically mitigate the autogenous shrinkage,that is,could enhance the expansion of CaO and then greatly reduce the contraction,which is significantly beneficial to impede the shrinkage-introduced cracks of early-age concrete.

Vacuum Treatment for Simultaneous Desulphurization and Dephosphorization of Hot Metal and Molten Steel

The vacuum treatment for simultaneous desulphurization and dephosphorization of hot metal and molten steel with pre-melted CaO-based slag was carried out.For pre-treatment of hot metal,both desulphurization and dephosphorization are improved with the increase of CaO in slag,but deteriorated with the increase of CaF2 in slag.The average desulphurization and dephosphorization rate is 68.83 % and 78.46 %,respectively.For molten steel,the substitution of BaO for CaO in slag has minor effect on simultaneous desulphurization and dephosphorization.The desulphurization and dephosphorization rate is higher than 90% and 50% respectively with the lowest final sulfur and phosphorus mass percent being 0.001 2% and 0.010%,respectively.The overall effect of simultaneous desulphurization and dephosphorization of molten steel is better than that of hot metal.

High-temperature CO_(2) sorbents with citrate and stearate intercalated Ca-Al hydrotalcite-like as precursor

CO_(2),one of the main components of greenhouse gases,increased rapidly because of the growing use of fossil fuels.And CaO sorbents possess the capability to be used in capture of CO_(2) at high temperature.In the work,Ca-Al complex oxides derived from citrate and stearate intercalated layered double hydroxides were fabricated and their CO_(2) adsorption capacity was compared with that from CO_(3)^(2-)intercalated layered double hydroxides.The results presented that the sorbents(Ca/Al=5)with Ca-Al-citrate layered double hydroxides as precursors performed best and displayed remarkable CO_(2) capture capacity of 52.0%(mass)at the carbonization temperature of 600℃without distinct recession during cycling adsorption/desorption tests.The excellent CO_(2) adsorption capacity of the sorbent was ascribed to its smaller crystallite size of calcinated particles,optimized pore size distribution as well as homogeneous distributed Ca and Al in the sorbent.