Yearly Archives: 2024

Mar 25, 2024

Chrome Corundum Brick Refractory Material for Coal Water Slurry Gasification Furnace

Gasifier slag mainly contains various oxides such as CaO, SiO2, MgO, AL2O3 and Fe2O3. Oxides Compared with various metal oxides in slag, Cr2O3 has the smallest solubility, indicating that Cr2O3 has a certain ability to resist slag erosion. On the other hand, Cr2O3 can react with AL2O3, Fe2O3, and MgO in the slag and transform it into composite spinel. Forming a dense protective layer can effectively prevent further erosion of slag. Therefore, the corrosion resistance can be improved by increasing the proportion of Cr2O3.

Selection of Refractory Materials for Coal Water Slurry Gasifier

The working conditions of coal water slurry pressurized gasification technology are relatively harsh. First, the combustion chamber temperature in the gasification furnace reaches a maximum temperature of over 1400°C, and the operating pressure reaches a maximum of 8.7MPa. Secondly, the strong reducing atmosphere and high-temperature environment existing in the gasifier will cause erosion to the refractory materials lining the gasifier. Finally, the discharge of liquid molten slagging is accompanied by high-speed erosion of solid, liquid, and gas phases, and there are drastic changes in temperature and pressure during startup and shutdown. Meeting the above working conditions requires high-quality gasifier refractory materials.

The temperature in the gasification furnace is generally higher than the melting point of the slag, so the slag in the furnace exists in liquid form. As the high-speed airflow flows down along the inner wall of the furnace, part of the liquid slag is deposited on the furnace wall, and the other part is discharged from the slag port. Because the liquid slag not only washes away the refractory material of the furnace lining, it also reacts chemically with the furnace lining, thereby eroding the furnace lining. Therefore, furnace lining refractory materials are required to have high erosion resistance and erosion resistance. Due to the high temperature and high-pressure working environment in the furnace, refractory materials are required to have excellent high-temperature creep resistance. High-temperature creep resistance is an important evaluation index of refractory materials. Excellent high-temperature creep resistance can ensure that the refractory materials used in furnace linings will not suffer skin damage during a long period of use.

To sum up, the refractory bricks in the furnace need to meet the following performance requirements. Excellent resistance to slag erosion, high thermal strength, and excellent high-temperature volume stability. Therefore, according to the characteristics of the working conditions in the gasifier, the selection of refractory bricks includes five types of materials: fire-facing bricks, backing bricks, insulation bricks, chrome steel jade castables, and compressible fiber layers.

Refractory Layer Erosion Facing Bricks

Due to the large dihedral angle of Cr2O3, there is no wetting effect with coal slag, which can minimize the erosion and penetration of slag. At the same time, because coal slag can directly contact the fire surface, the performance requirements for refractory materials are the most stringent. Therefore, the fire surface bricks of the coal-water slurry gasifier must use high-performance 90 chromium aluminum zirconium bricks, commonly known as high chromium bricks. Preparation process of high chromium bricks. It is mainly made of fused Cr2O3 synthetic material with a purity of not less than 99%, and then adds a certain amount of ultra-fine powder, and goes through processes such as mixing, shaping, and firing in a high-temperature shuttle kiln. The physical and chemical properties of high-chromium bricks are characterized by high volume density, low porosity, high-pressure resistance at normal temperature, and low content of impurities such as iron oxide and silicon oxide. It has the advantages of good thermal stability and high-temperature corrosion resistance.

Permanent Layer Chrome Corundum Brick

Behind the fire-facing brick is the backing brick. Chrome corundum bricks have high strength at room temperature and excellent resistance to corrosive gas erosion. It mainly plays the role of supporting the fire-facing refractory material, and can also resist the erosion of corrosive gases under high-temperature conditions.

Thermal Insulation Bricks

The backing brick is followed by the insulation brick, and alumina hollow ball bricks are generally used as insulation bricks. It has low thermal conductivity and a good thermal insulation effect, which can effectively reduce the heat loss of the gasifier and reduce energy consumption. At the same time, alumina hollow ball bricks have high strength under normal and high-temperature conditions. The material is light has very low impurity content, and has excellent corrosion resistance and thermal stress resistance.

Chrome Corundum Castable

Chrome corundum castable is mainly used for the spherical top and cone bottom parts of gasification furnaces. It has the advantages of good integrity and easy construction. Especially when it comes to the construction of complex structures, using chrome corundum castables is not only convenient and fast, but also saves man-hours. In addition, chromium corundum castables have strong resistance to gas erosion, high volume density, and good air tightness. Therefore, the service life of the gasification furnace can be greatly increased.

Insulation Cotton Layer

Due to its small bulk density and low thermal conductivity, the compressible fiber layer has excellent thermal insulation properties. At the same time, it can effectively reduce the radial expansion of the inner refractory material under high-temperature conditions. On the other hand, compressed fiber layers are very convenient to construct and can save manufacturing costs.

Rongsheng Refractory Materials Manufacturer is a powerful manufacturer of refractory materials production and sales. Our refractory products have been sold to more than 100 countries and regions around the world. There are many application cases for our chrome corundum brick products, and all of them have achieved good use effects. Contact us for a free refractory lining solution and quote.

Jan 24, 2024

Carbon and Graphite Refractory Materials for Metallurgical Industrial Furnaces

Carbon and graphite can constitute refractory materials or serve as important raw materials for refractory materials, mainly based on their following properties.

• (1) Graphite has high heat resistance, and the maximum temperature can reach 3850°C. Graphite has small mass loss in ultra-high temperature arcs.
• (2) Graphite has high chemical stability and is not easy to react with other inorganic materials and molten metals. It is also difficult to be wetted by oxide slag and has strong penetration resistance.
• (3) The thermal conductivity of graphite is large, but it decreases as the temperature increases. Even at extremely high temperatures, it is in an adiabatic state.
• (4) Graphite has an anisotropic structure and a small linear expansion coefficient. Therefore, it has good thermal shock resistance.

Application Development of Carbon and Graphite Refractory Materials in Blast Furnace Lining

Carbon and graphite refractories have been used in iron-making blast furnaces for a long time and have continued to develop with the development of iron-making blast furnaces. For example, Germany began using carbon bricks in blast furnaces in 1920. Subsequently (in the 1940s and 1950s), various countries competed to use carbon bricks in blast furnaces. Nowadays, large blast furnaces in the world are built with carbon bricks (charcoal blocks) from the furnace bottom, hearth to furnace belly, and other parts. Some blast furnaces are built to the furnace shaft and even the taphole. With the adoption of water-cooled furnace walls, the interior of the blast furnace bell is also built with carbon bricks.

Early carbon bricks mainly used metallurgical coke as the main raw material, asphalt as the binding agent, and were produced by extrusion molding. However, this kind of carbon brick often suffers from local abnormal erosion during use. For this reason, the metallurgical coke was changed to roasted anthracite coke with good resistance to molten iron erosion to improve the performance. However, although roasted anthracite char has the advantage of good resistance to molten iron erosion, it has the disadvantage of poor alkali resistance due to its high ash content. To overcome this shortcoming of roasted anthracite coke, artificial graphite is also used.

In order to reduce the damage of carbon bricks caused by molten iron seeping into the pores, various improvements have been made to carbon bricks.

• (1) To improve the corrosion resistance of molten iron, alumina is added to the ingredients.
• (2) To reduce the pore size, metallic silicon is added to the ingredients. During firing, the reaction generates whiskers, which refine the pores and prevent the intrusion (infiltration) of molten iron.
• (3) To improve the cooling effect, the graphite blending ratio is increased.
• (4) Change the binding agent from asphalt to resin to improve the high-temperature strength.
• (5) By adding SiC, the pores are made fine and the intrusion of molten iron is prevented.
• (6) At the bottom of the furnace, to improve the cooling effect, graphite bricks and C-SiC bricks with high thermal conductivity are used on the outside of the furnace.

The largest user of carbon and graphite refractory materials is the metallurgical industry, which is mainly used for lining refractory materials in blast furnaces (carbon and graphite refractory materials for blast furnaces), ferroalloys, metal refining (including electric furnaces and iron furnaces), etc. Among them, the usage of blast furnaces exceeds 70% (75% in Japan). In steelmaking electric furnaces, the use of artificial graphite bricks in harsh parts can extend the service life. In addition, carbon bricks are used as refractory materials for lining electric furnaces when producing phosphorus and soluble phosphate fertilizers.

Carbon and Graphite Refractory Materials are Used as Lining Materials for Non-Ferrous Metal Smelting Furnaces

Widely used carbonaceous and graphite refractory materials are amorphous carbon bricks, partially graphite or semi-graphite carbon bricks, and graphite bricks. At the same time, graphite crucibles and carbon amorphous refractory materials are also used in large industries.

In addition, carbonaceous and graphite refractory materials are also used as refractory materials for the lining of non-ferrous metal smelting furnaces. For example, carbon and graphite refractory trees are widely used in aluminum electrolytic cell linings. Typically, aluminum electrolytic cells are rectangular steel shells lined with carbon bricks. There is a carbon anode suspended in the electrolytic cell, and the bottom of the carbon cell is the cathode. Aluminum electrolytic cell cathode materials, need to have good electrical conductivity and be able to resist the erosion of cryolite, NaF, and liquid aluminum at high temperatures (900~1000°C). Therefore, carbonaceous materials are generally used as cathodes in aluminum electrolytic cells.

The damage to the carbonaceous material at the bottom of the aluminum electrolytic cell is mainly due to the infiltration of Na. Followed by the erosion of cryolite (completed through the following reaction):

3NaF·AlF3+Al═3Na+4AlF3

It has now been confirmed that Na penetration decreases with increasing degree of graphitization of the carbon cathode. Therefore, the cathode material of aluminum electrolytic cells is developing from the original amorphous carbon brick to semi-graphitized brick or graphitized carbon brick. At the same time, a layer of coating is applied on the surface of the carbon cathode that has good wettability with liquid aluminum but is infusible or refractory to liquid aluminum and cryolite and has good conductivity. For example, TiB2 or coatings containing TiB2 powder.

Since oxygen is precipitated from the carbon anode, the carbon anode oxidizes quickly and suffers large losses. In order to enable continuous production, it is necessary to continuously add anode paste to the top of the self-baking anode, which is composed of pitch coke or petroleum coke and coal pitch. It is completed by direct current conduction through the anode and heat generated between the electrodes. In addition to self-baked anodes, prebaked anode processes have also been developed.

In the past, carbon bricks have been used for the side walls of aluminum electrolytic cells. However, due to damage to the side wall carbon bricks, the service life of the aluminum electrolytic cell was reduced and its normal operation was affected. In order to prevent the side wall carbon bricks from being damaged by oxidation, SiC refractory materials (bricks) were used to build the side walls. These include high aluminum or alumina combined with SiC refractory materials, silicon nitride combined with SiC refractory materials, Si2N2O combined with SiC refractory materials, Sialon combined with SiC refractory materials, and self-bonded SiC refractory materials. SiC does not react with Na3AlF6, AlF3, NaF or CaF2. Among them, silicon nitride combined with SiC refractory materials has high resistance to cryolite erosion, good oxidation resistance, high strength, and high resistance. This can not only extend the life of the electrolytic cell and reduce leakage, but also greatly reduce the thickness of the side wall lining and expand the volume of the electrolytic cell.

RS Refractory Material Manufacturer is a powerful refractory material manufacturer. We are engaged in the production and sales of refractory products. If you need to purchase refractory lining materials or would like to find a suitable refractory lining material solution, please contact us. We have extensive experience in projects where carbon and graphite refractory materials are used in metallurgical industrial furnaces, and carbon and graphite refractory materials are used as lining materials for non-ferrous metal smelting furnaces. Free quote at email inquiry@refractoriesmaterials.com.