01. Current status of boiler operation
1. Raw materials and proportions The raw materials used are mainly: silicon carbide with a particle size of 0.5-0mm and ≤0.074mm, ω (SiC) = 98.31%, silicon nitride with a particle size of ≤0.074mm, ω (Si3N4) = 93.26%, silicon nitride with a particle size of 0.5-0mm and ≤0.074mm, ω (SiC) = 74.42%, ω (Si3N4) = 20.26% combined with silicon carbide waste brick powder, liquid phenolic resin is used as the binder, and a small amount of additives are added.
2. Sample preparation and performance testing Pour the prepared materials into the mixer and dry mix for 1min, then add liquid phenolic resin and wet mix for 6min to make mud. The amount of binder added is determined based on the initial cone penetration of about 450mm as the evaluation standard. The amount of binder added for the three groups of samples is 26%, 31%, and 33% respectively. Then the consistency and flexural bonding strength were tested according to GB/T 22459-2008, and 50 mm×50 mm×50 mm cubic test blocks were made for antioxidant performance testing.
02. Problem handling
1. The influence of raw materials on the cone penetration of refractory cement . Under the conditions of temperature of (25±5)℃ and humidity of 20%~25%, the cone penetration of three groups of samples and the cone penetration at different times were tested according to GB/T 22459.1-2008.
After the three groups of mud were stirred at a cone penetration of about 450mm, the cone penetration changed greatly with time. The cone penetration of synthetic silicon carbide raw material and silicon carbide composite silicon nitride raw material samples A and B showed a trend of increasing first and then decreasing with time, but within 5 hours, the cone penetration value remained above 435mm, and the material construction time was relatively long. The analysis shows that there is a certain amount of water, alcohols and volatiles in the phenolic resin. The initial water and silicon carbide raw materials are not completely wetted. As time goes by, the water gradually wets the raw materials, and the cone penetration of the material increases. In addition, the volatilization of water, alcohols and volatiles will increase the viscosity of the mud, resulting in a decrease in the cone penetration. The cone penetration of sample C, which uses waste brick powder as the main raw material, basically shows a trend of gradual decrease. It may be that a small amount of alkaline substances penetrate into the bricks during use, and are gradually dissolved by water after mixing, causing the phenolic resin to solidify, thereby reducing the cone penetration of the mud.
2. The influence of raw materials on the bending bond strength of the refractory cement
The bonding specimens were heat treated at different temperatures and different atmospheres, and the bending bond strength test results after heat treatment in air environment. It can be seen that the bending bond strength of the two groups of specimens after drying at 110°C is quite different. The bonding strength of specimen A made entirely of silicon carbide raw materials exceeds 25MPa, the strength of specimen B made of silicon carbide and silicon nitride raw materials is close to 25MPa, and the strength of specimen C made of waste brick powder as the main raw material is less than 20MPa. However, the strength after drying at 180°C is not much different, all around 22MPa. Analysis shows that the bending bond strength of the mud at low temperature is mainly provided by phenolic resin, so the bending strength of the three groups of specimens is relatively high.
It can be seen that the bending bond strength of the two groups of samples at the two heat treatment temperatures is slightly higher than that of the buried carbon sample, especially when heat treated at 1300°C, the bending bond strength is increased from less than 5MPa to more than 10MPa, and the strength of sample A exceeds 14MPa. Under all heat treatment conditions, sample A has the highest bending bond strength, which may be due to the relatively small amount of binder required for the refractory cement of sample A, the fewer pores left after the volatile matter in the binder evaporates, and the sintering effect of the mud during the heat treatment process is better than that of samples B and C.
3. Effect of raw materials on the oxidation resistance of mud
In order to study the durability of silicon nitride combined with silicon carbide brick mud with different raw materials, the oxidation resistance comparison test of three groups of refractory mud samples was carried out at 800℃.
It can be seen that after oxidation at 800℃, oxide layers appeared around both groups of samples, the oxide layer thickness of sample B was the thickest, and the oxide layer thickness of samples A and C was not much different.
