Abstract: In order to explore the mechanism of corrosion of refractory materials for waste incinerators by alkali metal compounds, three castables of mullite, corundum and chromium corundum were subjected to corrosion tests at 800, 1000, 1200 and 1350 ℃ for 30 hours by the alkali vapor method. Compare the physical properties and alkali corrosion resistance of the three castables before and after erosion at different temperatures. The results show that: 1) At 800℃, the strength of mullite, corundum and chromium corundum castables eroded by K₂CO₃ is higher than the strength before erosion, and the corundum castables have the highest strength after erosion. Mullite and corundum castables Its alkali corrosion resistance is better than that of chromium corundum castable. 2) When the temperature is 1000, 1200 and 1350 ℃, the compressive strength of mullite, corundum and chromium corundum castables after being eroded by K₂CO₃ all decrease, but the compressive strength of chromium corundum castable before and after alkali corrosion resistance is higher than that of Mo For Lai Shi and corundum castables, chromium corundum castables have better alkali corrosion resistance.
With the continuous increase of the world’s population and rapid economic development, the amount of urban garbage and industrial waste has increased dramatically. The existence of garbage not only takes up a lot of space, but also causes serious pollution to the earth’s environment and endangers the living environment of human beings, animals and plants. Incineration is more commonly used in garbage disposal. In the waste incinerator, because the waste to be incinerated is a heterogeneous mixture of different composition, its type and heat are very different. For this reason, the physical and chemical properties of the lining of the waste incinerator need to be adapted to the operational requirements of different stages. The working temperature of garbage incinerators generally does not exceed 1400°C, but the complex working environment (such as gas erosion, metal in garbage, etc., at high temperatures on the inside of the furnace body abrasion, impact, etc.) requires the refractory lining to have the following characteristics: Good wear resistance; good volume stability and acid and alkali resistance; good thermal shock; good corrosion resistance; good high temperature strength and heat insulation. Therefore, in order to explore the mechanism of corrosion of refractory materials for waste incinerators by alkali metal compounds, in this work, the physical resistance of three castables of mullite, corundum and chromium corundum before and after corrosion at different temperatures was studied by using the alkali resistance test method. Performance, phase composition and microstructure, explore the corrosion behavior of three refractory castables against K₂CO₃.
Test
1.1 Raw materials
The main raw materials used in the test are: fused mullite particles and fine powder (particle size: 5～3, 3～1, ≤1, ≤0.045mm, w(Al₂O₃)≥75.3%, w(SiO2)≥24.1%), Fused white corundum particles and fine powder (particle size of 5～3, 3～1, ≤1, ≤0.045mm, w(Al₂O₃)≥99.4%), fused chromium oxide particles and fine powder (particle size of 5～3, 3～1, ≤1, ≤0.045mm, w(Cr₂O₃)≥99.5%), active α-Al₂O₃ fine powder (d50=2.41μm, w(Al₂O₃)≥99.6%), the binder is calcium aluminate cement (Secar71) , Water reducing agent is FS10+FW10.
1.2 Anti-alkali corrosion test
Weigh each raw material, dry mix for 1 min in NRJ-411A cement sand mixer, and add water to wet mix for 3 min. The mixed material is vibrated into a 40mm×40mm×160mm spline on the HCZT vibration table, cured at room temperature for 24h, demolded, dried at 110°C for 24h, and kept at 800, 1000, 1200 and 1350°C in an electric furnace for 3h Heat treatment. Refer to GB/T14983-1994 refractory alkali resistance test method: spread a layer of 5cm thick mixed reagent (mass ratio of potassium carbonate powder and charcoal powder with a mass ratio of 1:1) on the bottom of the sagger, and heat it up. Place the sample on the reagent, and then spread the reagent so that the sample is completely buried in the mixed reagent, cover the cover, seal the edge with fire mud, and heat up to 800 in the electric furnace at a speed of 2℃·min⁻¹. , 1000, 1200 and 1350℃ for 30h.
1.3 Performance testing
According to GB/T5072-2008 and GB/T2997-2000, the normal temperature compressive strength, apparent porosity and bulk density of the samples before and after the alkali corrosion test were tested respectively, and the strength change rate [(normal temperature compressive strength after corrosion-before corrosion Compressive strength at room temperature) ÷ Compressive strength at room temperature before corrosion × 100%]. The sample was analyzed by X-ray diffractometer (XPertProMPD), the microstructure of the sample was analyzed by scanning electron microscope (EVO-18), and EDS analysis was performed on each point in the figure.
Results and discussion
2.1 Comparison of physical properties before and after erosion
With the increase of temperature, the volume density of mullite castable is gradually reduced after being corroded, and the apparent porosity gradually increases. At 800℃, the volume density of corundum and chromium corundum castables increases after being eroded, and the apparent porosity decreases; but at 1000, 1200 and 1350℃, the volume density after being corroded gradually decreases, and the apparent porosity gradually increases. .
The strength change rates of mullite and chromium corundum castables at 800°C are both positive, and the strength after erosion is higher than that before erosion; when the temperature is 1000, 1200 and 1350°C, the strength change rates are all negative. The intensity gradually decreases. The strength change rate of corundum castable is positive at 800 and 1000℃, and the strength after erosion is higher than that before erosion; at 1200 and 1350℃, the strength change rate is both negative, and the strength gradually decreases.
2.2 Phase composition
With the increase of temperature, the main phases of mullite samples are mullite and corundum, the main phases of corundum samples are corundum, and the main phases of chromium corundum samples are corundum and Cr₂O₃, indicating the three types of casting There is no change in the main phases after the erosion of the material. At 800℃, the corresponding products KAlSiO₄, β-Al₂O₃ and K2CrO₄ after the three castables of mullite, corundum and chromium corundum react with alkali, but the diffraction peak intensity is relatively low, the amount of formation is small, and the alkali corrosion of the material is not obvious ; With the increase of temperature, the diffraction peaks of KAlSiO₄ and β-Al₂O₃ gradually increase, indicating that the corrosion degree of K₂CO₃ on mullite and corundum castables increases with the increase of temperature, among which β-Al₂O₃, KAlSiO₄ and K₂CrO₄ phases are at 1350 The diffraction peaks at ℃ are all higher, and the amount of formation is large, while the diffraction peaks of the main phase are significantly reduced, indicating that the three castables are seriously corroded by alkali at 1350 ℃.
in conclusion
(1) At 800°C, the strength change rate of mullite, corundum and chromium corundum castable samples after corrosion is positive, and the strength after corrosion is higher than that before corrosion; at 1000, 1200 and 1350°C, The chromium corundum castable sample has high strength after corrosion, and the strength change rate is smaller than that of mullite and corundum castable.
(2) At 800℃, the alkali corrosion resistance of mullite and corundum castable is better than that of chromium corundum castable; when the temperature is higher than 800℃, the alkali corrosion resistance of chromium corundum castable is better.
