The chemical composition of refractory materials is one of the most basic characteristics of refractory materials. Generally, the chemical composition of refractory materials is divided into two parts according to the content of the components and their functions:
(1) The basic components that account for the absolute majority and play a decisive role in their performance – the main components.
(2) The subordinate components that account for a small amount – the secondary components. The secondary components are impurities accompanying the raw materials or additives (additives) specially added during the production process to achieve a certain purpose.
Main Component
The main component is the component that constitutes the refractory matrix in the refractory material and is the basis of the characteristics of the refractory material. Its nature and quantity play a decisive role in the properties of the material. The main component can be an oxide or a non-oxide. Therefore, the refractory material can be composed of refractory oxides, or a refractory oxide and carbon or other non-oxides, or it can be composed entirely of refractory non-oxides. Oxide refractory materials can be divided into three categories according to the chemical properties of their main component oxides: acidic, neutral and alkaline.
(1) Acidic refractory materials. This type of material contains a considerable amount of free SiO₂. The most acidic refractory material is siliceous refractory material, which is composed of almost 94% to 97% free SiO₂. Clayey refractory materials have a relatively low content of free SiO₂ and are weakly acidic. Semi-siliceous refractory materials are in between.
(2) Neutral refractory materials. High-alumina refractories (with a mass fraction of Al2O3 above 45%) are acidic and tend to be neutral, while chromium refractories are alkaline and tend to be neutral.
(3) Alkaline refractories contain a considerable amount of MgO and CaO. Magnesia and dolomite refractories are strongly alkaline, while chromium-magnesium and forsterite refractories and spinel refractories are weakly alkaline.
This classification is of great significance for understanding the chemical properties of refractories and judging the chemical reactions between refractories and between refractories and contact materials during use.
Impurities
The raw materials for refractory materials are mostly natural minerals, so they often contain a certain amount of impurities. These impurities can reduce certain properties of the refractory. For example, the main component of magnesia refractories is MgO, while other oxides such as silicon oxide and iron oxide are impurities. The higher the impurity content, the greater the amount of liquid phase formed at high temperatures.
Impurities in refractory materials directly affect the material’s high-temperature properties, such as refractoriness, load deflection temperature, corrosion resistance, and high-temperature strength. On the other hand, impurities can lower the firing temperature of the product, promoting sintering.
At high temperatures, andalusite transforms into mullite and a free SiO2 glass phase. In the Al2O3-SiO2 system, mullite is chemically stable, so refractories containing andalusite are also chemically stable.
Additives
In the production or use of refractory materials, especially amorphous refractory materials, a small amount of additives is added to improve the physical properties, molding or construction performance (operation performance) and use performance of refractory materials. The amount of additives added varies with their properties and functions, ranging from a few ten-thousandths to a few percent of the total amount of refractory materials.
Additives are divided into the following categories according to their purpose and function:
(1) Changing rheological properties: including water reducers (dispersants), plasticizers, gelling agents, degumming agents, etc.
(2) Adjusting the setting and hardening speed: including accelerators, retarders, etc.
(3) Adjusting the internal structure: including foaming agents (air entraining agents), defoamers, shrinkage inhibitors, expansion agents, etc.
(4) Maintaining the construction performance of materials: including inhibitors (anti-swelling agents), preservatives, antifreeze agents, etc.
(5) Improving the use performance: including sintering aids, mineralizers, quick-drying agents, stabilizers, etc.
These added components, except those that can be burned off, remain in the material’s chemical composition.
Chemical composition analysis allows the purity and properties of a product or raw material to be determined based on the types and quantities of the components present. Phase diagrams can also be used to roughly estimate the product’s mineralogical composition and other relevant properties.
Carbon black is mainly an aggregate of approximately spherical particles of elemental carbon melted and combined. Today, it is mainly produced by oil furnace process, which can produce carbon black of different varieties and different particle sizes.
Brief Introduction of Carbon Black Production Process
Most of the production of carbon black uses an oil furnace. Usually, the oil furnace process uses a cylindrical reactor similar to a large oil burner, which consists of 4 zones (or chambers), namely the combustion zone (chamber), throttling ring (chamber), reaction zone (chamber), and quenching zone (chamber).
The preheated air and the burning raw materials added in the combustion zone provide the high temperature required for the production process, and it is also the starting point of the channel for the raw materials to enter the reaction zone. The throttling ring separates the combustion zone and the reaction zone, and at the same time increases the gas velocity entering the reaction zone. The reaction zone forms carbon black, and the particle size, shape, and hardness of the carbon black are controlled by temperature, gas velocity, and different “seed” materials introduced with the raw materials.
The quenching zone uses water to sharply reduce the temperature, thereby ending the reaction in the furnace. The operating temperature varies during the entire reaction process of the reactor. The heating operation starts from the front end of the combustion zone, and the temperature increases towards the throttling ring. The temperature is highest and the speed is fastest at the throttling ring. In the reaction zone, the temperature drops slightly, and the speed becomes quite slow. The reaction time is changed by spraying cooling water at different positions along the cooling zone, that is, the temperature is lowered by rapid water spraying.
In addition, when the type of carbon black changes, there will usually be drastic temperature fluctuations. When the position of the cooling zone changes, it will also cause a sharp change in temperature. Such a sharp temperature change will cause the refractory bricks to peel off and be damaged. The size of carbon black particles is limited by the size, structure, temperature of the furnace and the length of time they stay in the reaction zone before cooling. The bottom operating temperature and the position of the first water spray depend on the grade of carbon black.
Selection of Refractory Materials for Reactors
The most ideal refractory materials for carbon black reactors should have the advantages of high refractoriness, good thermal shock stability, high density, low porosity, high temperature corrosion resistance, and strong erosion. Most carbon black reactor linings are built with Al2O3-SiO2 refractory bricks, among which high alumina bricks or clay refractory bricks are used for the lining. Different grades of refractory materials need to be used for lining when the operating temperature range is different. The lining of the reactor operating in the low temperature range (1550-1750℃) is generally built with mullite corundum bricks. Sometimes high-purity high-alumina bricks are used for the cooling zone.
The lining of the reactor operating in the high temperature range (1750-1925℃) is usually built in sections. On the hot surface of the combustion zone, 90% A1203-10% SiO2 refractory bricks are generally used for lining. In the high-temperature throttling ring and the hot surface of the reactor, 99% A1203 corundum bricks and chrome corundum bricks with good thermal shock resistance are used for masonry. In the ultra-high temperature range (greater than 1925℃, i.e. 2000-2100℃), zirconium chrome bricks are used for masonry.
(1) Al2O3-SiO2 refractory materials.
In the SiO2-Al2O3 series of refractory materials, when W (Al2O3)>90%, it is called corundum brick. When pure SiO2 and Al2O3 materials are used to produce corundum bricks, the temperature at which the liquid phase appears is 1840℃. The physical properties and performance of corundum bricks produced by traditional processes cannot reach a very ideal level, and their thermal shock resistance is poor. Now, by using pure raw materials and in-situ forming bonding technology, the physical properties and performance of corundum have been greatly improved, and the variety is increasing. Among them, the original mullite combined with 90% Al2O3 corundum bricks and special Al2O3, combined with 94% Al2O3, and even 98% Al2O3 corundum bricks have been developed one after another.
Rongsheng Corundum Bricks
These special corundum refractory bricks have lower porosity, higher density, greater strength, and outstanding thermal shock resistance than traditional corundum refractory bricks of the same material. The 50mm×50mm×76mm sample was kept at 1200℃ for 10min, water cooled for 2min, and placed in the air to dry for 8min as one cycle, which was more than 40 times. The traditional refractory bricks are only 2-7 times, and even the traditional mullite corundum bricks are only 10-15 times. Special mullite combined with corundum bricks are mainly used in low-temperature carbon black reactors, or in the cooling zone of high-temperature carbon black reactors. The actual use structure shows that when used in the combustion and restriction zones, the special mullite combined with 90% Al2O3 combined corundum bricks (95%-98% Al2O3) are mainly used in the reaction zone with harsh conditions in the carbon black reactor, and its use temperature limit can reach 2000℃.
(2) Al2O3-Cr2O3 refractory materials
a. Al2O3-Cr2O3 materials used above 1800℃
In order to be suitable for the lining of the combustion chamber and other parts of the carbon black reactor with a temperature exceeding 1800℃, and to have good corrosion resistance and high thermal shock resistance. The usual practice is to add a certain amount of industrial Cr2O3 powder to the corundum brick to improve its high-temperature performance.
Its high temperature flexural strength increases with the increase of Cr2O3 content. The research results show that the thermal shock resistance and wear resistance of this type of refractory brick are also improved with the increase of Cr2O3 content.
When Al2O3-Cr2O3 (10% Cr2O3) refractory castables are used as the working lining of the combustion chamber, throat, and reaction section of the carbon black reactor that are not in contact with high-temperature gas, it can ensure the safe operation of the carbon black reactor under operating conditions above 1800℃.
b. Cr2O3-Al2O3 materials used under ultra-high temperature conditions
Under the condition of temperature exceeding 1925℃, i.e. 2000-2100℃, corundum bricks are no longer competent. For example, the operating temperature of the hard carbon black reaction furnace used to manufacture low rolling friction tires is as high as 2100℃. Under such conditions, it is necessary to develop better quality refractory bricks to adapt to the ultra-high temperature conditions.
High-Quality Alumina Chrome Bricks from Rongsheng Factory
Research and development of performance requirements for lining refractory materials used under ultra-high temperature conditions of carbon black reactors:
① High refractoriness to avoid melting and allow higher operating temperatures;
② Good thermal shock stability to reduce cracking and spalling damage;
③ Low porosity (high density) to improve corrosion/erosion resistance.
Based on the research results of carbon black lining refractory bricks and the existing experience of using chrome alumina corundum bricks under high temperature conditions (1750-1925℃), the lining refractory bricks for carbon black reactors used under ultra-high temperature conditions should be selected from the Cr2O3-Al2O3 system.
When chrome corundum bricks with high Cr2O3 content are used as refractory materials for the lining of carbon black reactors, the service life can be extended under high temperature operating conditions. The normal operation of the reactor can also be ensured under ultra-high temperature operating conditions. In addition, the actual use results show that the service life is extended when the flow limiting chamber using high-temperature ash or high-vanadium combustion oil and the flow limiting chamber caused by intermittent high temperature melting are using Cr2O3-Al2O3 refractory bricks with high Cr2O3 content combined by solid solution. And the operating temperature in the carbon black reactor can be increased by 150-170℃ compared with the previous limit temperature.
Usually, because chrome corundum bricks with high Cr2O3 content are very expensive, they are only used in carbon black reactors operating at about 2100℃ (i.e., generating hard carbon black), and a comprehensive masonry scheme is adopted. That is, using 70% Cr2O3 and 25% Al2O3 refractory bricks to build the highest temperature, and using 20% Cr2O3 and 25% Al2O3 bricks to build the low temperature, better results can be obtained.
(3) ZrO2 refractory materials
Pure ZrO2 is extracted from zirconium-containing ores. High-purity ZrO2 is white powder with a high melting point and high density. Its mullite hardness is 6.5, its thermal conductivity is low, and its thermal expansion coefficient is large (25-1500℃, α=9.4×10-6/℃). Moreover, it has a weak relationship with temperature and good chemical stability. The high-temperature vapor pressure at 2000-2300℃ is very low, the evaporation rate is not high, and the decomposition pressure is also low. Therefore, ZrO2 refractory materials are an important type of refractory bricks for high-temperature furnace linings.
Rongsheng Magnesite Brick
(4) High-purity MgO bricks
High-purity magnesia bricks are structural materials for high-temperature furnace linings, and their operating temperature can reach 2200°C. However, under such conditions, such as when used in ultra-high temperature environments in carbon black reactors, the purity and performance of high-purity magnesia bricks need to be carefully balanced.
Refractory bricks (including magnesia bricks) are not only resistant to high temperatures and corrosion (erosion), but must also be as stable as possible during use. It is generally believed that the purity of magnesia and the porosity and periclase grain size in terms of physical properties are key parameters for improving the service life of high-purity magnesia bricks.
The MgO content in magnesia is an important indicator of magnesia quality, but the MgO content alone is not enough as an evaluation criterion. The relative content of impurities, especially those that easily form melts under high temperature conditions, is also important. Among the impurity components, B2O3 and SiO2 are the first, followed by A12O3, Fe2O3, MnO and CaO. Their influence depends not only on their content, but also on the Ca0/SiO2 ratio to evaluate the influence of each component on the quality of magnesia sand. It is usually hoped that the magnesia sand has a high CaO and SiO2 ratio in order to obtain the best high-temperature performance.
Magnesia bricks used in ultra-high temperature environments require high purity because high-purity magnesia bricks have high temperature strength. The high temperature flexural strength of magnesia bricks tends to decrease slowly with the MgO content from 90% to 98%, but when the MgO content exceeds 98%, it suddenly increases. When the MgO content increases to more than 99%, its high temperature strength can be significantly improved. In this case, the influence of impurity types has become insignificant. Because, in this case, the impurities exist in isolation at the junction (corner) of periclase grains. Therefore, the MgO-MgO direct bonding organization is well developed, the high temperature strength is large, the material has high wear resistance, and strong corrosion (erosion) resistance.
In the sulfur reactor, the H2S combustion furnace has a higher operating temperature and is one of the single equipment with the highest design temperature. In its design, in order to improve the recovery rate of sulfur, the method of preheating the raw gas and air is generally used to increase the furnace temperature. At present, the operating temperature of the reactor has been increased from 1050°C to 1450°C. Coupled with the combustion support of alkane gas, the furnace temperature may reach 1600°C. Therefore, it is a great challenge to the refractory materials built in the furnace.
The production of sulfur currently uses the Claus process to recover sulfur from acid gas containing H2S. This production process is common in coal gasification or petrochemical industries, because H2S is the main by-product in the production of such industries. The process principle is to use the partial combustion method in the sulfur recovery device, that is, introduce all the acid gas into the combustion furnace, and distribute the air according to the complete combustion of hydrocarbons and the complete combustion of 1/3 H2S to generate SO2. For H2S, the reaction results in that about 65% (mass fraction) of H2S in the furnace is converted into S vapor, 1/3 of the remaining 35% (mass fraction) of H2S is burned into SO2, and 2/3 remains unchanged. Among them, 65% of the S vapor generated by the reaction is condensed and captured in the waste heat boiler, while the remaining H2S and SO2 reacted in the furnace react under the action of the catalyst in the converter to further generate S. In order to react uniformly and prevent impact on the hot end of the waste heat boiler, a flower wall is built in the middle of the furnace. The main medium in the furnace is H2S + SO2 + high-temperature gas containing S vapor. The operating pressure is not greater than 0.05MPa, and the operating temperature is not greater than 1450°C. Made of refractory materials, thickness 400mm.
H2S Reaction Furnace Structure Diagram
Difficulties in Selecting Refractory Materials for Masonry Reactors Producing Sulfur
(1) The furnace temperature is high. The working temperature is 1100~1450℃, which is a furnace with a higher working temperature. Under occasional operating conditions, the furnace temperature may reach 1600°C or higher.
(2) There are various corrosive components such as H2O, H2S, SO3, SO2 and S vapor in the furnace. H2S has reducing properties. As a result, there are strict restrictions on certain impurity components in furnace lining materials.
(3) Acid gas combustion furnace has no heating surface inside the furnace. Any large fluctuation during combustion means a thermal shock to the furnace lining, which requires the furnace lining to have good thermal shock resistance.
(4) The combustion furnace has strict requirements on wall temperature and requires the furnace lining material to have good thermal conductivity.
Selection of Several Domestic Mainstream Refractory Materials
2.1 Corundum castable material material
At the earliest, corundum castable linings were commonly used as lining materials for acid gas reactors in sulfur recovery units at home and abroad. The reason is that the corundum castable lining not only has a higher fire resistance temperature but also has better wear resistance. However, due to its poor thermal shock resistance, problems such as peeling and falling off may occur within a short period of time, and it will be gradually eliminated over time.
2.2 High alumina brick + corundum brick material
The lining material of the original acid gas combustion furnace is high alumina brick + corundum brick. The brick joints are one of the weakest links. Damage to the brick joints often leads to overall deformation and collapse of the masonry. On the other hand, high alumina bricks and corundum bricks are difficult to process and manufacture, difficult to fit into some special-shaped parts, and the cost is also high.
2.3 Steel fiber castable material
Steel fiber castables have achieved good results in catalytic converters and other applications due to their good fire resistance. However, in the case of acid gas combustion furnace, this material is prone to problems such as agglomeration and deep cracks.
Castable combined with ramming makes a very good high-temperature-resistant lining. The composition (mass fraction) of ramming material is 85% AL2O3+15%SiO2. Has the following salient features:
①High temperature resistance (up to 1800℃) and high strength.
②The furnace wall support is hanging type, which is not easy to deform or fall off.
③The insulation layer is constructed by pouring, and the working layer is constructed by pounding. It can be made into any shape (especially in special shapes) and is easy to construct. Its combined structure is dense and solid, with no gaps in the walls.
④When the lining is supported by anchors, the furnace wall can withstand peeling and protrusion, making maintenance easy.
⑤The lining material has good peeling resistance and will not embed foreign matter.
⑥Short oven time, fast and economical construction
To purchase high-quality refractory lining materials, please contact us. We can provide high-quality refractory products and customer service.
The sulfur-making combustion furnace is one of the core equipment of the sulfur recovery unit, where 60%-70% of the hydrogen sulfide is converted into elemental sulfur. It controls the process of converting 1/3 of hydrogen sulfide into sulfur dioxide and complete combustion with ammonia and hydrocarbons. It can be said to be the heart of the combined device. Therefore, the operation of the sulfur combustion furnace directly affects the sulfur recovery rate and sulfur dioxide emissions. One of the most direct factors affecting the performance of a sulfur furnace is the refractory lining of the furnace. The originally designed refractory layer was made of large corundum mullite bricks, and the thermal insulation layer was made of lightweight insulating castables. However, in the early stages of operation, the outer walls of the sulfur furnaces experienced varying degrees of over-temperature and even red heat.
The sulfur recovery and sulfur production system adopts the partial combustion method to introduce all the raw gas into the sulfur production combustion furnace. In the sulfur-making furnace, the air distribution ratio is strictly controlled according to the amount of oxygen required for complete combustion of 1/3 of hydrogen sulfide, ammonia, and hydrocarbons. The amount of sulfur dioxide generated after hydrogen sulfide is burned satisfies H2S/SO2 to be close to 2. About 60% to 70% of hydrogen sulfide and sulfur dioxide react at high temperatures in the furnace to form gaseous sulfur. The operation of the sulfur-making combustion furnace directly determines the sulfur recovery rate of the entire sulfur-making system and whether the exhaust emissions meet the standards. The components of raw sour gas are relatively complex, including H2S, CO2, H20, NH3, H2 hydrocarbons, etc. The chemical reactions that occur in the furnace are also relatively complex.
Refractory Materials for Sulfur Making Furnaces
Conditions that Lining Refractory Materials Should Meet when Designing Sulfur Furnaces
Conditions that lining refractory materials should meet when designing sulfur furnaces. Able to withstand higher temperatures, the operating temperature of the sulfur furnace furnace is 1250~1400℃, which may reach 1600℃ under abnormal conditions. Since the supply of raw materials is unstable and most of them are corrosive, they must have strong corrosion resistance. There is no heating surface in the furnace, and the lining must have stable thermal shock resistance. It has stable thermal conductivity and the furnace wall temperature can be controlled to ≤300℃. For furnaces with excessively large diameters, the lining should have good high-temperature stability. It has a long service life and meets the requirements of full load and long-cycle operation. Has good volume stability. Masonry is convenient and the construction period is short.
Thickness of Refractory Material Lining Sulfur Furnace
The total thickness of the lining refractory material of the sulfur-making combustion furnace is designed to be 400mm. The refractory lining in the upper 1/2 part of the front cone section adopts a double-layer lining structure, 200mm alumina hollow ball castable + 200mm corundum refractory plastic. The acid gas inlet distribution ring bricks have a four-layer lining structure, namely 100mm lightweight insulating castable + 150mm corundum castable + 150 corundum mullite bricks + acid gas inlet distribution ring bricks. The rest of the structure is a double-layer lining structure, that is, 220mm corundum refractory plastic + 180mm lightweight heat-insulating castable. The anchoring system consists of anchor bricks with C-shaped hooks and V-shaped nails. The flower wall tiles, annular channel ring tiles, and acid gas inlet distribution ring tiles are all made of corundum mullite bricks. The anchor bricks are arranged on 2/3 of the furnace, and the center distance between adjacent anchor bricks is 400mm.
Construction of Lining Refractory Materials for Sulfur-Making Combustion Furnace
Construction method: The insulation layer is constructed by manual pounding. Use a forced mixer to mix the materials, and add water in strict accordance with the mix ratio. The mixing time is generally about 3 minutes, subject to uniform color. The mixed materials should be used within 10 minutes. It is strictly forbidden to add water to the hardened materials for reuse. The construction joints of the two layers of insulation should be staggered by more than 100mm. The insulation layer should be maintained in moisture, and the second layer of insulation or refractory plastic can be constructed only after at least 24 hours. When the entire ramming construction is completed, remove the formwork and trim the lining surface to the designed thickness. The expansion joint should be cut according to the drawing requirements, generally 60mm deep and 2-3mm wide. Horizontal and vertical expansion joints should be left at the junction of the furnace roof and furnace wall, and the joints should be filled with fiber cotton. After the lining has been trimmed, vent holes should be punched to allow moisture in the material to escape. Before and during the drying process, steam, water, oil and other impurities are not allowed to corrode the plastic. Corundum bricks should be cured naturally after being laid wet, and contact with water is strictly prohibited. The original expansion joint is widened to about 3mm, and then filled with zirconium-containing fiber blankets. The flower wall tiles and acid gas inlet distribution ring bricks are laid wet, with staggered joints, and the mortar fullness is greater than 90%. Refractory plastic is a pre-mixed and pre-pressed blank material. When using it, you only need to pound it tightly without stirring or adding binders. The construction is simple and the on-site operating conditions are good. At the same time, because plastic is a gas-thermohard material, no maintenance is required. The construction period is short and suitable for rapid repair operations of the lining. The lining structure has good thermal shock resistance and resistance to thermal stress. However, the continuity and consistency of construction must be ensured.
To purchase high-quality refractory lining products, please choose a competent manufacturer and seller of refractory materials. For example, Rongsheng Refractory Material Manufacturer. Rongsheng’s refractory products have been sold to more than 100 countries and regions around the world. Our refractory products have reliable product quality and our comprehensive customer service ensures the long life and efficient operation of the refractory lining. Contact us for a free quote.
The gas penetrates into the refractory bricks from the furnace space, accompanied by a series of physical and chemical processes. This depends on the gas composition, refractory brick composition and temperature. As refractory materials interact with gases, most will lose mechanical strength, thermal shock resistance, and in some cases even refractory resistance.
Chemical Reactions between Refractory Materials and Various Gases
(1) Interaction with water vapor and CO2
Calcium-containing refractory bricks are destroyed due to hydration of water vapor at normal temperatures. The hydration of CuO and MgO increases the volume almost 2 times, causing the bricks to spread out. Hydration products are decomposed at approximately 800°C. It can be seen that hydration will not occur above this temperature. Materials based on alkaline earth metal aluminates, gallates and indiums that improve the stability against water vapor and CO2. In the formula of MO-R2O3, M—Ca, Sr, Ba; R—Al, Ga, In.
(2) Interaction with alkali vapor
Alkali (K2O, Na2O) vapor combines with mullite and metakaolinite to form nepheline K2O·A12O3·2SiO2 and nepheline Na2O·Al2O3·2SiO2. As the reaction proceeds, the volume increases and some parts of the brick simultaneously peel off. The stability of refractory materials against alkali vapor increases in the following order: clay bricks (Al2O3 42%), high alumina bricks (mullite, Al2O3 70%), clay-bonded silicon carbide bricks, corundum bricks, self-bonded silicon carbide bricks, Nitride bonded silicon carbide bricks. According to the relationship between aluminum silicate refractory materials, lithium alkali corrodes the most, followed by sodium, and potassium less. This is related to the lowest melting temperature of lithium alkali and is consistent with the decreasing sequence of K2>Na>Li atomic radius.
(3) Interact with chlorine gas
Chlorine reacts with many refractory oxides to produce fusible or volatile compounds, and its vaporization causes the strength of refractory bricks to decrease. Chlorine destroys refractory materials similar to hydrogen. Perclase refractory materials are the least stable to chlorine (MgCl2 melts and volatilizes at 712°C), while high alumina bricks and corundum bricks are the most stable. It was found that at 950°C, in contact with chlorine for 72 hours, the strength of magnesite bricks and chromium magnesia bricks was reduced by 100%, clay bricks by 24%, silica bricks by 13% and high alumina bricks by 5%.
(4) Interaction with hydrocarbons
The hydrocarbons methane, ethane and natural gas, like CO, deposit carbon black in the presence of catalysts. They have a wider activation temperature range than carbon monoxide to precipitate carbon black, indicating the decomposition temperature of these hydrocarbons.
(5) “Oxidation-reduction” atmosphere
Carbon and silicon carbide refractory materials are oxidized at high temperatures in an oxidizing atmosphere. The carbon graphite brick medium has some slowdown in oxidation rate. The oxidation of silicon carbide refractory materials proceeds from the surface, and a SiO2 film is formed at the same time to prevent further oxidation. Due to the oxidation of the inner layer of carbonized carbon, the bricks will be damaged due to expansion during oxidation. Refractory bricks containing chromite are reduced at high temperatures in a reducing atmosphere. Magnesia-chromium and chromium-magnesite bricks are also reduced, and at temperatures exceeding 1600°C, there is a significant loss of strength and they become brittle.
(6)Interaction with sulfur dioxide gas
All types of magnesia bricks interact with sulfur dioxide gas SO2. MgSO4 is formed in the range of 400 to 900°C, and it decomposes at 1124°C. By further increasing the temperature, the periclase bricks are resintered by the activated form of magnesium oxide formed when the sulfide decomposes.
(7) Interaction with hydrogen
In aluminum silicate refractory materials, hydrogen is used to reduce oxides such as Na2O, TiO2, MgO, SiO2, etc. The hydrogen decomposes mullite to form corundum and silicon monoxide. In hydrogen medium, high alumina bricks and corundum bricks containing Al2O3≥85% have stable properties. Siliceous bricks are destroyed due to the rapid degradation of silica at 1200°C in a hydrogen medium.
(8) The corrosive effect of carbon monoxide
The most widespread and corrosive gas corrosive is carbon monoxide. Its corrosive effect lies in the reduction of refractory oxides and the precipitation of carbon black.
Refractory repair methods for blast furnace hearth-side walls. When high temperature occurs on the side wall of the blast furnace hearth, it needs to be solved by pressing in the side wall of the hearth. For high-temperature conditions on the side walls of the blast furnace hearth, it is first necessary to determine whether the cause is thinning of the lining or wind channeling from the back of the brick lining. Only when it is determined that there is back-channeling wind, it is necessary to press in. The pressed parts generally need to be determined by detecting the temperature changes of each part.
Repairing Blast Furnace Hearth Side Walls with Refractory Materials
Refractory Repair of Blast Furnace Hearth-Side Wall
Generally, the pressed material is carbonaceous mud similar to the hearth brick lining material, or other non-hydraulic materials. For the press-fitting of the furnace side wall, there are three main forms depending on the structure of the furnace lining.
The first is the furnace lining structure using large carbon bricks. Because of this structure, there is usually a layer of carbonaceous ramming material between the large carbon bricks and the furnace shell or cooling stave. High temperatures in the hearth are often caused by gaps in the carbon ramming material layer, allowing high-temperature gas to pass through. Therefore, the key point of press-in grouting is to fill and seal these gaps with press-in material. At this time, the grouting position should be to use the reserved holes on the furnace shell or drill holes in the parts where the cooling wall can penetrate, and send the pressed material to the carbon ramming material layer.
The second is for the furnace lining structure using small carbon bricks. However, during design and construction, the carbon bricks are built close to the furnace shell or cooling stave. But in fact, due to various reasons such as manufacturing and installation accuracy, there is inevitably a gap between the carbon bricks and the furnace shell or cooling stave. At this time, the grouting method is the same as the first one.
The third type refers specifically to the furnace side wall having a cooling stave structure. When the surface temperatures of the furnace lining and the furnace shell rise simultaneously, it indicates that the gap between the cooling stave and the furnace shell has become a hot coal gas flow channel. At this time, it is necessary to grout the lining of the furnace while also grouting the space between the cooling stave and the furnace shell. The key to this grouting is to find the gas channel to determine the location of the drill hole. The depth of the drill hole must ensure that it penetrates the furnace shell without damaging the cooling wall. In this case, the pressed material can be selected from carbonaceous mud or other non-aqueous pressed materials based on actual conditions such as temperature and historical records.
For the press-in of the furnace side wall, the press-in point is generally determined by arrangement and blocking.
Repair of refractory lining materials, and design of refractory materials for high-temperature industrial furnace insulation layers. Rongsheng Refractory Materials Manufacturer is a refractory material manufacturer with rich experience in the production and sales of refractory materials. The quality of our refractory products is guaranteed and ready for shipment at any time. And our comprehensive customer service also protects the rights and interests of our customers.
What is refractory cement? What are the precautions in the use of refractory cement? Rongsheng REFRACTORY CEMENT FACTORY will provide you with high-quality refractory inorganic binders, including refractory cement, aluminum dihydrogen phosphate, etc. Next, we will introduce the use nature of refractory cement in refractory materials.
Refractory Cement
What is refractory cement?
Cement with refractoriness not less than 1580℃. The different compositions can be divided into aluminate refractory cement, low calcium aluminate refractory cement, calcium magnesium aluminate cement, and dolomite refractory cement.
Historical data show that with the discovery and understanding of the heat resistance of calcium aluminate, the yield of calcium aluminate in Europe in 1913 had a rapid increase. In the 1920s, indestructible refractory casting materials began to take their own steps of development. In the late 1980s and 1990s, new pouring techniques gradually emerged. The pump and flow gating technology with low cement castables is introduced. Then came wet spray or jet technology. In these technological changes, refractory cement was produced.
Refractory cement is also called aluminate cement. Aluminate cement is made of bauxite and limestone as raw materials, calcined with calcium aluminate as the main component, the alumina content of about 50% of clinker, and then grinding into hydraulic cementitious materials. Aluminate cement is often yellow or brown, but also gray. The main mineral composition of aluminate cement is calcium aluminate and another aluminate, and a small amount of dicalcium silicate.
Refractory Cement for Refractory Materials
The use nature of refractory cement in refractories
Aluminate cement is a kind of binder (permanent binder) that can be combined at room temperature and high temperature. The refractoriness of amorphous refractories is very important. In general, the higher the Fe2O3 in cement, the lower its fire resistance. The type and content of calcium aluminate affect the fire resistance of cement. Practice shows that ordinary high aluminum cement is used at less than 1300℃, high aluminum cement (bauxite cement) is used at less than 1500℃, and low calcium high aluminum cement (high aluminum cement) is used at higher than 1600℃ temperature.
Aluminate cement often refers to calcium aluminate as the main component of cement. Calcium aluminate cement is the basic binder of amorphous refractories, especially cast refractories. The properties of aluminate cement mainly depend on its mineral composition. The main mineral composition of aluminate cement, calcium aluminate (CA), has a high hydrohard activity, the setting is not fast but hardening is very rapid, and the hardening time is not more than one day. It is the main source of the strength of high aluminum cement, especially the early strength. Calcium dialuminate (CA2) has a slow hydration hardening, low strength in the early stage, and high strength in the later stage. Dodecalcium heptaaluminate (C12A7) has the characteristics of quick hydration and rapid condensation, but the strength is not high. In ordinary high alumina cement containing inclusions, impurities affect the hardening effect of the cement and its strength.
Calcium aluminate cement contains these 5 kinds of calcium aluminate minerals, which will be along with the hydration reaction and show an intense heating phenomenon. The temperature of common high-alumina cement (53~55% A12O3) reaches the peak after 5~8h, reaching 80~90℃. The temperature of advanced high alumina cement containing 70% A12O3 reaches the peak value after 10~12h and that of 80% A12O3 after 8~10h. The temperature is 80C and 70C respectively.
The heating temperature and the time to reach the highest temperature of single castable of different kinds of high aluminum cement are determined by the heating characteristics and content of calcium aluminate. Therefore, the calorific value of high aluminum cement will also change due to the different calcium aluminate contents. If too much high aluminum cement containing C12A or CAF as the main component is added to the cast refractory, it will cause cracks and surface spalling due to intense evaporation of water in the castable hardening body due to concentrated heat. Therefore, the choice of cement dosage and quality is very important.
Precautions for the use of refractory cement
At a room temperature of 350 degrees, it is most likely to cause local bursting, and special attention should be paid to slow baking. If there is still a lot of steam bubbling up after 350 degrees of insulation, the heating rate should still be slowed down.
in the condition of poor ventilation, water is not easy to discharge, to appropriately extend the holding time.
When baking with heavy oil, it is necessary to strictly prevent heavy oil from spraying on the surface of the furnace lining to prevent local bursts.
When using wood to bake, direct contact with the flame often causes local heating to be too rapid, which should be protected.
the newly poured refractory cement, at least after 3d can be baked.
the cooling of refractory cement furnace lining should also be slow to avoid forced ventilation.
The aluminum melting furnace is an important piece of equipment in the aluminum processing industry, and the refractory lining, especially the non-stick aluminum castable used in the aluminum melting pool, plays a vital role in its normal operation at high temperatures. Liquid aluminum is lively and has a low viscosity. Therefore, the refractory materials in the molten pool that are in direct contact with molten aluminum are most severely damaged by molten aluminum erosion. Its quality and life will directly affect the quality of the product and the life of the aluminum melting furnace. So What’s the Best Proportion of Non-Stick Aluminum Castable for Aluminum Melting Pool?
Non-Stick Aluminum Castable
The Best Proportion of Non-Stick Aluminum Castable for Aluminum Melting Pool
Recently, it is time to repair the aluminum melting furnace and purchase refractory lining materials. Among them, in order to prepare non-stick aluminum castable for an aluminum melting pool with excellent resistance to aluminum melt corrosion. High alumina bauxite (8~5, 5~3, 3~1, and ≤1mm) is often used as aggregate, and fine mullite powder, α-AL2O3 powder, silica fume, barium sulfate, and high alumina cement are used as powder materials. After many times of running-in between refractory manufacturers and customers, The Best Proportion of Non-Stick Aluminum Castable for Aluminum Melting Pool. the best ratio of powder was finally obtained. The content of silica fume, anti-erosion agent, barium sulfate, and cement are 3%, 3%, 4%, and 4% respectively.
Analysis of the Influence of Fine Powder on the Corrosion Resistance of Castables for Molten Aluminum Pool
The erosion of the non-stick aluminum castable by the aluminum melt first occurs in the matrix. Therefore, in order to improve the corrosion resistance of non-stick aluminum castable for the aluminum melting furnace. In this experiment, in addition to using high alumina bauxite as aggregate, the influence of fine powder in the matrix composition on the corrosion resistance of the castable for the aluminum melting pool was also studied.
The raw material in the experiment is high alumina bauxite (8~5, 5~3, 3~1, and ≤1mm). The fine powder includes mullite fine powder (≤0.088mm), barium sulfate fine powder (≤0.045mm), α-AL2O3 fine powder (d=5μm), silica fume (≤1μm), high alumina cement, and anti-erosion agent. The basic ratio of the main raw materials is 71.71% high alumina bauxite, 5.29%-19.29% mullite fine powder, 5% α-AL2O3 powder, and the remaining matrix materials are silica fume, anti-erosion agent, barium sulfate, and cement. The anti-erosion performance of the materials after the ratio is analyzed as follows.
(1) With the addition of silica fume and the increase of its addition, the corrosion resistance of the sample gradually improves. This is because the particle size of silica fume is extremely small and can be filled in the voids formed by the coarse aggregate to densify the sample. As a result, the apparent porosity of the sample is reduced, and the passage of aluminum melt into the sample is reduced. In addition, the high proportion of silica fume has high reactivity, and it can promote the sintering of the sample matrix material at high temperatures so that the sample is densified and the strength of the sample is improved. The strength of the sample affects the ability of the castable to resist the stress caused by the metamorphic layer, and the stress change makes the corrosion caused by the appearance of cracks and cracks propagation intensified. It can be seen that the incorporation of silica fume can increase the strength of the non-stick aluminum castable while also improving the corrosion resistance of the sample.
(2) When the mixing amount of barium sulfate is 2%, the corrosion resistance of the sample can be increased from scratch to nearly double, and the corrosion resistance becomes excellent. It shows that the addition of barium sulfate can significantly improve the corrosion resistance of aluminum melt.
(3) With the increase of cement content, the corrosion resistance of aluminum melt of the sample has a tendency to decrease first and then increase. This is because the cement hydration increases the water requirement of the sample, and the dehydration of the hydration product at high temperature causes the internal structure of the sample to become loose, which weakens the structure and reduces the corrosion resistance of the sample. When the cement content continues to increase by more than 6%, the introduction of CaO into the matrix increases the amount of liquid phase at high temperatures. The surface tension of the liquid phase shortens the distance between the particles and promotes the internal densification of the sample. Thereby improving the aluminum melt corrosion resistance of the sample.
Summary:Non-stick aluminum castables are used for molten aluminum pools based on materials such as silica fume, corrosion inhibitor, barium sulfate and cement. The main factor that has an obvious influence on the corrosion performance of aluminum alloy melt is barium sulfate, and as the content increases, the corrosion resistance improves. Within a certain range, with the increase of the amount of silica fume incorporated, the corrosion resistance of the castable is improved. However, if the added amount of anti-corrosion agent and cement is controlled within a certain range, it can play a better anti-melt erosion effect.
Rongsheng is an experienced refractory material manufacturer and sales company. Rongsheng’s monolithic refractory production line has an annual output of 80,000 tons. Customers who purchase monolithic refractories from Rongsheng manufacturers each year have both new turnkey projects and furnace refractory lining repair projects. From the customer’s purchasing experience, they have not only experienced experiments with high-priced unsuitable refractory lining products, but also low-priced refractory lining materials that are not well used. Through various searches, the Rongsheng refractory manufacturer was finally selected. The product quality is qualified and the customer service is good. Formally because of this, Rongsheng continues to accumulate experience in the matching of customer projects and refractory materials, striving to provide customers with high-quality refractory products. Save production costs for customers and improve economic benefits. To choose high-quality refractory castables products, such as non-stick aluminum castables for aluminum melting furnaces, please contact us. We will provide you with unshaped refractory products that best suit your production needs according to your specific project needs.
Alumina Bubble Bricks belongs to a kind of ultra-high temperature material energy-saving insulation material. It uses alumina hollow spheres and alumina powder as the main raw materials, combined with other binders, and fired at a high temperature of 1750 degrees. As a refractory manufacturer, why are alumina hollow ball bricks widely used? Why recommend alumina hollow ball bricks to customers? This will start with the performance of Alumina Bubble Bricks.
Alumina Bubble Brick
The Manufacturing Process of Alumina Bubble Bricks
Alumina Bubble Brick is a new type of high-temperature insulation material, which is made by smelting and blowing industrial alumina in an electric furnace. With alumina hollow spheres as the main body, it can be made into products of various shapes, with a higher use temperature of 1800°C. The mechanical strength of the product is high, which is several times that of the general lightweight product, and the bulk density is only one-half of the corundum product. Among them, the alumina powder is produced by using reliable industrial alumina as the raw material, using a new high-temperature inverted flame kiln and a scientific calcination process. Manual selection, clear classification, fewer impurities, high conversion rate, stable shrinkage rate, and good consistency.
High-Quality Alumina Bubble Bricks for Sale
The Performance of Alumina Bubble Bricks
Alumina hollow ball and its products are a kind of light refractory material with excellent high-temperature resistance and energy saving, and it is very stable to use in various atmospheres. Especially it is used in the high-temperature furnace at 1800℃. Hollow balls can be used as high-temperature, ultra-high-temperature insulation fillers, high-temperature refractory concrete lightweight aggregates, high-temperature castables, etc. Hollow ball bricks can be used for high-temperature energy-saving (>30%) inverted flame kilns, shuttle kilns, molybdenum wire furnaces, tungsten rod furnaces, induction furnaces, nitriding furnaces, etc. Obvious effects will be achieved for reducing the weight of the furnace body, transforming the structure, saving materials, and saving energy.
The specific advantages of alumina bubble bricks are as follows.
The operating temperature is high, up to 1750 degrees. Good thermal stability, the small change rate of the re-burning line, longer use.
Optimize the structure and reduce the weight of the furnace body. The high-temperature-resistant materials currently used are heavy bricks with a bulk density of 2.6-3.0g/cm. The alumina hollow ball brick is only 1.1~1.5g/cm, the same volume of one cubic meter, the use of alumina hollow ball brick can reduce the weight of 1.1-1.9 tons.
Save materials. To reach the same operating temperature, the price of heavy bricks is equivalent to that of Alumina Bubble Bricks, and considerable refractory materials are required for insulation. If alumina hollow ball bricks are used, 1.1-1.9 tons of heavy bricks can be saved per cubic meter, and 80% of refractory insulation materials can be saved.
Save energy. Alumina hollow spheres have obvious thermal insulation properties, low thermal conductivity, and can play a very good thermal insulation effect. Reduce heat dissipation and improve thermal efficiency, thereby saving energy. The energy-saving effect can reach more than 30%.
Obviously, the excellent energy-saving effect of alumina hollow spheres makes it more competitive as a lightweight refractory material. Buyers of kiln lining materials will definitely prefer such superior refractory products. Therefore, not only refractory manufacturers recommend everyone to buy Alumina Bubble Bricks, but also its own advantages that make it so widely used. Alumina Bubble Bricks are widely used, for example, in high temperature and ultra-high temperature furnaces such as petrochemical industrial gasifiers, carbon black industrial reactors, metallurgical industrial induction furnaces. And they have achieved very good energy-saving effects.
For more refractory materials products, please contact us: inquiry@global-refractory.com.
What are the names of refractory materials? The question itself is inaccurate. For example, there are many kinds of cars, such as cars, vans, off-road vehicles, trucks, and so on. And there are many cars with different brands or shapes in various fields, but they are collectively called cars. Various refractory bricks or castables are collectively referred to as refractory materials. It cannot be specified which type or types of refractory bricks and castables. Because of the different fields of use, the refractory materials used in thermal equipment are also different.
Rongsheng Refractory Bricks Products
Refractory materials are divided into shaped products and unshaped products in terms of shape and are divided into three categories: ordinary, high-grade, and special-grade in temperature. The chemical properties are divided into acidic, neutral, and alkaline. Refractory insulation bricks and lightweight thermal insulation castables are called thermal insulation or thermal insulation refractory materials. No matter which method is used to define, they are called refractory materials.
Common acid-resistant bricks, oxide ceramics, refractory insulation bricks, acid-resistant refractory bricks, refractory slurries, refractory castables, lightweight thermal insulation castables, etc. Someone among them raised the question: How many names are there for the above refractory materials? He also cited a similar answer to refractory insulation bricks, also called insulation bricks.
There are many names for different refractory materials, and they are very complicated. And many materials are called differently because of different regions. For people who understand refractory materials and those who do not understand refractory materials, because they have different understandings of the same kind of refractory materials, there may be different names. For example, a common mullite insulation brick. Some people call it K23 fire brick and K28 fire brick; others call it JM23 insulation brick and JM28 insulation brick. There are others called SK32, SK34, SK36, SK37, SK38 refractory bricks, and so on. What they said is the same type of insulation brick products, and there may be slight differences in specific indicators. Therefore, as a refractory manufacturer and seller, no matter what the name of the refractory product is, we first need to confirm with the customer the application furnace type, use position and use temperature of the product that the customer needs. According to the customer’s specific needs, we will provide the customer with refractory materials that meet his thermal furnace equipment production needs.
Rongsheng Refractory Bricks Manufacturer
What are the thermal properties in refractories?
From the point of view of definition, inorganic non-metallic materials with refractoriness greater than 1580 ℃ are called refractory materials. Refractories are part of the material industry, and they are named after they are used in thermal kilns. So what are the thermal properties in refractories?
(1) Thermal expansion
The thermal expansion of refractory materials refers to the length change of the product during heating.
The expansion (or contraction) of refractory materials as the temperature changes in use will seriously affect the size, tightness, and structure of the thermal equipment masonry, and even damage the masonry. In addition, the thermal expansion of refractory materials can also reflect the thermal stress distribution and size of the product after being heated, crystal transformation and phase transformation, the generation of microcracks, and thermal shock resistance.
(2) Thermal conductivity
Under the condition of the unit temperature gradient, the heat flow rate per unit area of the material is defined as the thermal conductivity of the refractory material.
In actual production, the general thermal equipment needs to consider the amount of heat loss after passing through the refractory, and it is necessary to calculate the insulation effect of the insulating refractory. In some muffle furnaces and coke ovens, the partition walls of refractory materials are also required to have higher thermal conductivity. Therefore, the thermal conductivity of refractory materials is one of the key considerations in the design of thermal kiln lining. The pores in the refractory product have a great influence on the thermal conductivity. Within the temperature limit, for the porosity within a certain range, the greater the porosity, the smaller the thermal conductivity, and the better the thermal insulation effect.
