1. Melting phenomenon: Melting phenomenon is an important problem faced by refractory materials. When the working temperature exceeds its refractoriness, melting will inevitably occur. This melting phenomenon often occurs in high-temperature parts such as the furnace wall, furnace top and reaction chamber top near the natural gas ignition point.
In order to eliminate this phenomenon, we have made strict requirements on the temperature of the reaction chamber. The results show that operation at the required temperature is relatively stable and safe. At the same time, we also found that if the operation control is not careful, heat will accumulate in some areas of the combustion chamber, thereby increasing the risk of melting.
This phenomenon poses a severe challenge to our refractory materials, because excessive temperature will directly affect the refractory performance and service life of the material. Therefore, during the design and operation process, we must fully consider the relationship between the combustion point and temperature to ensure that the refractory materials can work normally within their refractoriness range, thereby avoiding the occurrence of melting phenomenon and ensuring the stable operation of the reactor.
2. Chemical erosion: Chemical erosion refers to a series of complex chemical reactions between refractory materials and materials, acidic gases, dust, exhaust gases and other materials in the furnace. These reactions include gas-solid reactions, liquid-solid reactions, and gas-liquid reactions, which together constitute the chemical challenges faced by refractory materials in the furnace environment.
When the working temperature of refractory materials approaches or exceeds their refractoriness, the chemical attack of acidic substances on them will be significantly enhanced. This is because the activity of substances increases in high temperature environments, and the rate and intensity of chemical reactions will increase accordingly. At this time, the substances in the reactor are more likely to react with refractory materials, causing changes in their structure and performance, thereby shortening their service life.
In order to meet this challenge, we need to have a deep understanding of the mechanisms and influencing factors of various chemical attacks in order to make more reasonable decisions in material selection and furnace environment control. At the same time, optimizing the composition and structural design of refractory materials to improve their ability to resist chemical attack is also the key to ensuring the stability of the furnace environment and extending the service life of refractory materials.
3. Mechanical action: The impact of mechanical action on refractory materials cannot be ignored. In the working layer, when the temperature of the refractory material is higher than its load softening temperature, the mechanical strength of the material will drop significantly and become extremely susceptible to external forces. At this time, the mechanical force of the rotating stirring in the furnace is like a heavy blow, which is constantly applied to the refractory of the entire furnace body, causing it to gradually deform, crack or even break. This mechanical loss will seriously affect the service life of the refractory and the normal operation of the furnace.
Therefore, we need to pay close attention to the working temperature of the refractory to ensure that it does not exceed the load softening temperature, and prevent the mechanical equipment from being shut down for a long time and then restarted, so as to reduce the loss caused by mechanical action. At the same time, choosing refractory materials with high strength and high wear resistance is also an effective way to reduce mechanical loss. Through these measures, we can better protect the refractory materials, ensure the stable operation of the furnace and extend the service life.
4. Peeling and cracking: Peeling and cracking are serious problems that refractory materials are prone to under certain conditions. When refractory materials are subjected to rapid temperature changes or uneven heat loads, significant thermal stress will be generated inside them. If this thermal stress exceeds the structural strength limit of the material, it will cause local damage to the material, manifested as peeling or cracking.
Especially when the furnace is restarted after a long shutdown, due to the huge temperature difference between the inside and outside of the furnace, the refractory materials are prone to expansion and cracking under the state of overheating. In addition, opening the furnace door for a long time during operation will cause a large amount of cold air to enter, which will also cause cracks of varying degrees in the corresponding areas. Due to long-term production operations, the peeling and cracking of refractory materials are also particularly obvious.
In order to avoid such problems, we not only need to carefully select and design refractory materials, but also need to strictly control the process management of the operation. At the same time, reasonable heating and cooling is more important to reduce the thermal stress of refractory materials, extend their service life, and ensure the safe and stable operation of the furnace.
Specific reasons for the damage of reactor refractory materials
1. The long-term low negative pressure in the combustion chamber will have a significant impact on the refractory materials in the combustion chamber of the reactor. Due to the low negative pressure, the heat from the combustion of natural gas cannot flow quickly, and the heat borne by the refractory materials in the combustion chamber of the reactor increases significantly, resulting in a large amount of natural gas consumption. This consumption not only causes an increase in consumption, accelerates the aging and damage of local refractory materials, but may also cause more serious problems such as collapse.
Specifically, the temperature of the combustion chamber may accumulate heat after combustion due to the low negative pressure, which will have a negative impact on the performance of the refractory materials at the top of the combustion chamber. What is more serious is that long-term overheating and excessive consumption of refractory materials may increase the risk of burning through the joint area between the combustion chamber and the dome, thereby threatening the safe operation of the entire reactor.
Therefore, we must strictly control the negative pressure of the combustion chamber, eliminate positive pressure operation, and ensure that it is within a reasonable range to reduce the pressure of the combustion chamber refractory materials and reduce the consumption rate, thereby maintaining the stability and safety of the reactor. This requires us to remain highly vigilant during operation, adjust the frequency of the induced draft fan in time, and ensure that the negative pressure of the combustion chamber is within a reasonable range to cope with various possible situations.
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2. Irregular operation and misoperation will cause a series of serious problems. Due to the long-term high temperature state of the reactor production, the characteristics of the refractory silicon carbide bricks in the reactor, the silicon carbide bricks are prohibited from rapid cooling and heating, and the rake and abnormal handling of the furnace conditions during the production cycle will cause cracks to varying degrees. Irregular operation in production will aggravate this phenomenon, which will damage the entire reactor top body. As the crack gap increases, the combustion chamber and the reaction chamber will cross gas with each other, which will destroy the negative pressure balance in the Mannheim reactor and affect the overall operation efficiency of the reactor.
Therefore, we must standardize and strictly control operations such as raking and cleaning to ensure that the damage caused by the operation is minimized and the service life is extended. At the same time, it is also necessary to standardize the selection and use of raw materials, reasonable feed ratio, etc., to reduce the frequent raking in the furnace caused by imbalance of raw materials and ratios, and reduce the safety hazards caused by external reasons. Only in this way can we ensure the safe and stable operation of the reactor and improve production efficiency.
3. When the reactor is restarted after a long-term shutdown, the furnace body is very likely to expand and crack. This is because the furnace body cools and shrinks during the shutdown period, and during the re-heating process, the material expands due to temperature changes, thereby generating stress. If this stress exceeds the bearing capacity of the material, it will cause cracking. Especially in the case of frequent start-stop and too fast heating, the expansion of various materials in the furnace body due to temperature changes is not consistent, and the resulting cracking phenomenon will be more obvious.
This cracking not only affects the structural integrity of the furnace body, but may also cause the risk of collapse in some areas. Therefore, when the reactor is heated up after a long-term shutdown or frequently started and stopped, it is necessary to strictly follow the heating curve control. Once the cracking phenomenon is found, the impact caused cannot be compensated.
Selection of refractory materials for reactor body
The reactor body consists of an insulation layer (red bricks for the furnace wall), a heat-insulating layer, a heat-preserving layer and a working layer. The production process is in a complex environment of high temperature, corrosion and heat dissipation. The damage of the furnace lining increases energy consumption and production costs. Therefore, optimizing the furnace lining structure is an important direction for energy saving in the reactor.
1. Application of reactor combustion chamber expansion. This method is to increase the height of the combustion chamber, use the increased space layer to increase the flow rate of the combustion hot gas, and reduce the heat accumulation caused by the poor flow of flue gas. On the basis of the original combustion chamber cavity height, the furnace wall height is increased for furnace body masonry, the overall height of the combustion chamber is increased, and the overall space of the combustion chamber is increased. Through the increase in space, the high-temperature gas in the combustion chamber can flow quickly. Thereby, the phenomenon of local overheating of refractory materials caused by poor flow of high-temperature flue gas is alleviated to a certain extent.
2. In the production process of the reactor, silicon carbide bricks are the key masonry materials. The SiC content in the selected silicon carbide bricks is between 80% and 85%, mainly based on the excellent physical and chemical properties of silicon carbide bricks. Silicon carbide bricks have high thermal conductivity and corrosion resistance, which enables them to remain stable in the high temperature environment of the reactor and are not easy to melt or deform. At the same time, its excellent corrosion resistance ensures that the corrosion effect of acidic gas during the production process is minimized. In addition, silicon carbide bricks can still maintain high strength under high thermal conductivity, effectively support the furnace structure, and prevent the furnace body from collapsing due to material softening. More importantly, silicon carbide bricks are not easily attacked by acidic gases, which greatly reduces the corrosion rate of the furnace body and extends the service life of the furnace body. These advantages make silicon carbide bricks an ideal choice for the Mannheim reactor.
4. During the masonry process of the Mannheim reactor, refractory materials need to be carefully selected to ensure the stability and durability of the furnace body. Among them, commonly used refractory materials include silicon carbide bricks, modified high-alumina bricks, high-alumina bricks and other refractory materials. The Al2O3 content in modified high-alumina bricks is above 75%, while the Al2O3 content in high-alumina bricks is about 45%. When building furnace walls, furnace bottoms, combustion chambers and domes, we must choose different masonry materials according to different refractory materials. Under high temperature, the masonry materials and refractory materials fuse with each other, thereby improving the integrity of the reactor. However, in the process of continuous production and use, these fusions will slowly form small cracks. These gaps become channels for the penetration of sulfuric acid, acid gas and solid-liquid reaction materials, allowing them to penetrate into the bottom of the reactor and even into the combustion chamber, which in turn leads to the occurrence of furnace bed arching, flue acid infiltration, exhaust system equipment corrosion and other phenomena.
In addition, silicon carbide bricks have excellent corrosion resistance. Its corrosion resistance has been significantly improved, and it can still maintain volume stability at high temperatures of up to about 1000℃, showing excellent high-temperature strength. This makes silicon carbide bricks an indispensable and important material in the masonry of the Mannheim reactor.
Summary and Suggestions
The damage of reactor refractory materials is the result of the combined effect of multiple factors. In order to extend the service life of refractory materials, it is necessary to comprehensively consider multiple aspects such as material selection, construction technology, operation and maintenance. Protection measures for key parts are also helpful to extend the use of the reactor. For example, the measure of laying an insulation layer in the area with the most concentrated flames in the combustion chamber can alleviate the impact of heat on the furnace structure to a certain extent. As an industry practitioner with many years of refractory experience, when we select refractory materials for Mannheim reactors, we should fully consider their resistance to high temperature and chemical corrosion; during the construction process, we should strictly follow the specifications to ensure the construction quality; in daily use, we should strengthen operation and maintenance management to reduce unnecessary damage. Only in this way can we ensure the long-term stable operation of Mannheim reactors and improve the production efficiency and economic benefits of enterprises.
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