Interaction of High Al₂O₃ Refractories with Alkaline Salts Containing Potassium and Sodium in Biomass and Waste Combustion

Abstract

Utilization of challenging fuels, such as biomass residues and waste-derived fuels, may lead to problems with refractory corrosion. Alkalis and chlorine in such fuels can lead to the formation of low melting deposits and slags on the refractory lining of boilers during combustion. This may cause excessive wear, possibly limiting the service lifetime of the refractories. In this work, the attack of alkali salts to high alumina refractories was studied. The refractory was exposed to four pure salts (K2CO3, K2SO4, Na2CO3, and Na2SO4) and one synthetic ash (K2CO3–KCl). The refractory was exposed to the salts at 700, 800, and 900 °C for 168 h. The penetration of potassium into the refractory was determined from horizontal line scan analyses of the sample cross section using scanning electron microscopy with energy-dispersive X-ray analysis. Detailed information on alkali infiltration was obtained by using the Xphase spectral imaging software. Additionally, X-ray diffraction analyses were made on cross sections of the refractory before and after exposure to detect new compounds. Even at the lowest temperature, K2CO3 formed low melting compounds with the refractory, resulting in accelerated deterioration. The main new phases formed were kalsilite, kaliophilite, and leucite. Thermodynamic calculations showed that the initiating step in the corrosion could be the reaction between free silica in the refractory and potassium, even at 700 °C. Similar refractory deterioration was caused by the KCl–K2CO3 mixture. Exposure to Na2CO3 led to the formation of nepheline and sodium aluminum silicate. Sodium and potassium sulfate did not show any major corrosive effects; however, at 900 °C Na2SO4 melt penetrated deep into the refractory.

Corn-Stalk Chemical Looping Combustion Using tert-Butanol Waste Solution

“…Comparing the detailed X c for II-S and III-S, we observed that X c for II-S is higher than that X c for II-S and III-S under each Ω. The enhancement of X c for II-S may result from the OC-catalyzed gasification of corn stalk, since OC usually acts as an efficient catalyst during steam-reforming reactions. − In addition, corn-stalk contains metallic elements, like K, Ca, Al, etc, which can alter the properties of OC to avoid its agglomeration during the reduction process and hence promoting the CLC efficiency. ,, …”

“…34−36 In addition, corn-stalk contains metallic elements, like K, Ca, Al, etc, which can alter the properties of OC to avoid its agglomeration during the reduction process and hence promoting the CLC efficiency. 26,37,38 For both II-S and III-S, 1.8 can be hailed the relatively optimized Ω for the CLC reactions, which is only a quantitatively conclusion. Actually, the detailed reaction mechanism for the CLC processes of corn stalk and tertbutanol solution would be rather complex.…”

Analysis of the Structure and Durability of Refractory Castables Impregnated with Sodium Silicate Glass

“…According to the Na 2 O−Al 2 O 3 −SiO 2 phase diagram [35], liquid sodium silicate can further react to form albite (NaAlSi 3 O 8 ) and nepheline (NaAlSiO 4 ). Additionally, it was found [36] that Al 2 O 3 can influence viscous glass melting temperature and its viscosity; therefore, the melting temperature and viscosity values of formed glass on the surface of the sample tend to increase [37].…”

Analysis of the Formed Protective Layer Inhibiting Alkali Corrosion in Aluminosilicate Refractory Castables

“…Alkali metal ions penetrate most easily into the matrix of material [11], accumulate in the matrix, and only then react with the aggregates [12]. This process takes place due to the higher porosity of the matrix compared to the aggregate and usually a higher content of various impurities (Na 2 O, TiO 2 , and other compounds) [13].…”