Pyrolysis carbonization technology is a treatment method that uses high temperature to pyrolyze organic components under anaerobic conditions and finally form solid carbon compounds. In the process of pyrolysis and carbonization, a large amount of strong acid gases such as nitrogen oxides, sulfur oxides, carbon oxides, hydrogen chloride and hydrogen fluoride will be produced. In addition to the action of high-temperature water vapor, the generated flue gas will seriously erode the lining of the carbonization furnace. Lining castables for carbonization furnaces must have good high temperature acid corrosion resistance, suitable strength, low thermal conductivity and excellent thermal shock resistance. In order to take into account the comprehensive properties of the lining castables such as strength, corrosion resistance and thermal conductivity, mullite and brown corundum are used as the main raw materials in the research, and some silicon carbide and alumina hollow spheres are introduced at the same time to prepare a kind of Carbonization furnace lining material with low thermal conductivity and strong acid corrosion resistance. In order to further improve the strength and acid resistance of the castable, according to the use conditions and performance requirements of the carbonization furnace lining, in this work, the addition amount (w) of alumina hollow spheres of 1~0.2mm is 15% and ≤0.074mm. Based on the addition of silicon carbide powder (w) of 8%, the effects of silicon powder and carbon black on the properties of acid-resistant castables for carbonization furnaces were studied.
test
1.1 Raw materials
The main raw materials used in the test are: fused mullite, density 2.71g·cm-3, particle size 8~5, 5~3, 3~1, ≤1, ≤0.074mm; density of brown corundum 3.90g·cm- 3, particle size ≤ 1, ≤ 0.08mm; silicon carbide, particle size ≤ 0.074mm; alumina hollow sphere, particle size 1~0.2mm; Silica micropowder, pure calcium aluminate cement, silica fume (≤0.074mm), carbon black powder. Admixtures include polyphosphate water reducing agent and organic fiber explosion-proof agent.
1.2 Test process and performance testing
Mix all kinds of raw materials evenly in proportion, add water and stir, and vibrate to form samples of 40mm × 40mm × 160mm and φ180mm × 30mm. After curing at room temperature for 24 hours, the molds are released. After heat preservation at 1100℃ for 3h and 1350℃ for 3h, the bulk density (YB/T5200—1993), compressive strength (GB/T5072—2008), flexural strength (GB/T3001—2007), and linear changes of the test samples were tested. rate (GB/T5988-2007). According to HG/T3210-2002, the samples were tested for acid resistance with nitric acid solution with a mass concentration of 50%.
Results and discussion
2.1 Influence of the amount of silicon powder added on the properties of acid-resistant castables for carbonization furnaces
After the samples were treated at different temperatures, with the increase of the amount of silicon powder added, the change trend of the bulk density was not consistent. The bulk density of the samples treated at 110 °C basically decreased with the increase of the amount of silicon powder added. The bulk density of the samples treated at 1100 °C decreased slightly with the increase of the amount of silicon powder added. The bulk density of the samples is significantly higher than that after the treatment at 1100 °C.
In the test plan, the same amount of silicon powder was used instead of silicon carbide powder. The density of silicon carbide is greater than that of silicon. Under the same particle size, the difference in the density of the two raw materials caused the difference in the bulk density of the sample at 110 °C. With the increase of the amount of silicon powder added, the bulk density of the sample decreased. Under the condition of 1100 ℃ treatment, the bulk density of the sample decreases slightly with the increase of the amount of silica fume added, because the silica fume is partially oxidized to form silica, and reacts with cement, silica fume and other components to form a low-melting liquid phase. , the carbon-buried reducing atmosphere under the test conditions prevented the oxidation process. The decrease in bulk density relative to the 110°C treatment was mainly due to the volatilization of bound water. After heat treatment at 1350℃, the increase of the bulk density of the sample compared with 1100℃ is mainly caused by reaction sintering. Silicon does not melt at 1350 ° C. On the one hand, its own oxidation can prevent the oxidation of silicon carbide, and may react with carbon black to form silicon carbide; on the other hand, the temperature rise causes the reaction formation process of eutectic. It is easier to perform and can promote the densification of the sample.
In terms of the online change rate, it can be seen from Figure 2 that under the condition of 1100 °C, the linear change rate of the samples with different amounts of silicon powder is not much different, and they all show a shrinking trend, indicating that the degree of reaction of the silicon powder is relatively small, and at 1350 Under the condition of ℃, it is closer to the melting point of silicon. In this process, the silicon powder undergoes an obvious reaction and sintering, which causes the bulk density of the sample to increase, the apparent porosity to gradually decrease, and the linear shrinkage rate to increase, and this effect exceeds that of kyanite molybdenum. Expansion from petrochemical reactions.
The strength of the samples treated at 110℃ at room temperature has little difference. The strength at this temperature is mainly due to the combination of the mineral phase hydrate in the calcium aluminate cement to the system phase. The cement content is the same, so the strength difference is not big. After heat treatment at 1100 ℃, the flexural strength and compressive strength of the samples showed a trend of increasing slowly with the increase of the amount of silicon powder added, indicating that the silicon powder has played a role in improving the strength at this temperature. After heat treatment at 1350℃, the strength of the sample changed obviously with the increase of the amount of silicon powder added. Especially when the amount of silicon powder added exceeds 2.5% (w), although the flexural strength of the sample increases, the compressive strength decreases compared with that after heat treatment at 1100 °C. The analysis shows that under the temperature condition of 1350 ℃, a certain content of liquid phase components has been formed in the sample, resulting in a decrease in the toughness of the castable at room temperature and an increase in brittleness, especially for the internal uneven structure of the castable, the strength is affected by various defects. , cracks and other factors become very sensitive, resulting in inconsistent trends in flexural strength and compressive strength. Considering the influence of silicon powder on flexural strength and compressive strength, the suitable amount of silicon powder added is about 2.5% (w).
in conclusion
(1) Silicon powder has little effect on the strength of acid-resistant castable samples at 110 °C. At 1100 °C, silicon powder begins to undergo oxidation reaction, and at 1350 °C, silicon powder undergoes obvious reaction and sintering, causing the bulk density of the sample to increase. , the linear shrinkage rate increases, and this effect exceeds the expansion effect produced by the kyanite mulliteization reaction. Under the test conditions, the suitable amount of silicon powder added is about 2.5% (w).
(2) At the temperature of 110 and 1100 ℃, the strength of carbon black is reduced due to the increase in the amount of water added to the acid-resistant castable. At 1350 ℃, the reaction between carbon black and silicon powder can improve the strength. effect. The addition of carbon black is beneficial to the improvement of the acid resistance of the castable, but the addition of excess carbon black will increase the porosity of the castable. According to the test results, when the addition amount of carbon black is 1.5% (w), the acid-resistant castable has suitable strength and acid resistance.
