Effect of pre-calcination for modified CaO-based sorbents on multiple carbonation/calcination cycles

In the present work,the effect of pre-calcination on carbonation conversion and cyclic stability of modi fied CaObased sorbent was investigated by thermogravimetric analyzer(TGA).The modi fied CaO-based sorbents with CaAc_2 as precursor were respectively doped with different elements(Mg,Al,Ce,Zr and La).The speci fic surface area,pore volume and pore size distribution were tested by N_2 isothermal adsorption measurements.The phase compositions of sorbents were characterized by X-ray diffraction(XRD).The results showed that the cyclic stabilities of the sorbents were improved by pre-calcination.The pre-calcination was conducted at 900°C for 5 h in air by the muf fle furnace.With pre-calcination,the cyclic stabilities of sorbents could be as high as 96% after 22 cycles,such as CaO-Al,CaO-Ce and CaO-La.After contact with air,the carbonation conversions of spent sorbents with pre-calcination suddenly increased by about one-sixth due to the change of channel structure by hydration.Both the cyclic stability of sorbent and the durability of reactivation were related to the structural stability of sample,especially the stability of mesopores between 2 nm and 5.5 nm.The present work also provided an easy and low-cost method for reactivating the spent CaO-based sorbents.

A Short Communication on Refractories as Kiln Lining along Various Thermal Zones in Pre-calcining Cement Rotary Kiln

Modern cement rotary kiln is often large in size while rotating in high speed. Thermal condition within a rotary kiln is rather complex, exerting severe thermal and chemical attack on refractory of its kiln lining. In the present paper, the cause that leads to refractory failure was analyzed; requirements for refractory to overcome such failure was discussed. Composites and properties of different refractories most often used as kiln lining were assessed, including magnesia - chrome bricks, magnesia spinel bricks, dolomite bricks, silicon carbide muUite bricks and castables etc. Recommendation was made for refractories with suitable composites and properties to be used as kiln lining in each specific zone to best counteract the severe thermal conditions. A cost-effective configura- tion was presented to assemble kiln lining for rotary kiln＇s different zones in line with the regulation at JC/ T 2196-2013 ＂Specifications of refractory for cement rotary kiln＂. Chromite-free refractories with property of high endurance to thermal attack and corrosion are required to be used in modern Pre-calcining cement rotary kilns.