Several commonly used wear-resistant lining materials for coal drop pipes in coal transportation systems

In the coal transportation system of thermal power plants, the coal drop pipe is the main conveying and connecting component connecting each transfer station, the screening and crushing room, and the conveying, storage, transfer, screening, and crushing equipment of each layer in the main building. It includes both downpipes, coal drop hoppers, and diversion troughs, etc. These components are constantly scoured and collided by the raw coal flow during the operation of the coal transportation system, which can easily cause wear, corrosion, leakage, etc. of the wall plate material, and Due to the wear and corrosion of the coal drop pipe, it is easy to cause the coal flow to stick and block in the coal drop pipe, which seriously affects the normal operation of the coal transportation system and pollutes the environment of the coal transportation system. To solve these problems, lining the coal falling pipe with wear-resistant lining is a common method.

Introduction of several commonly used coal falling pipe wear-resistant liners

16Mn belongs to the series of low-alloy steel plates, 16Mn is the old national brand name, and now the corresponding grade is Q345. It is one of the most commonly used and widely used materials for the lining of coal drop pipes in the coal transportation system of thermal power plants. Its price is comparable to that of ordinary carbon steel. It is almost the same, but the wear resistance is much higher than that of ordinary carbon steel. At the same time, it is easy to process and the material is easy to replace. It is widely used in the non-impact surface of coal drop pipes in thermal power plants. However, due to the limited performance of the 16Mn material, the coefficient of friction is relatively large, and the hardness is relatively low. When the coal flow is directly scoured, the service cycle is short. The ordinary carbon steel and 16Mn steel lined with 16-20mm in the former pipeline and coal hopper are generally worn out in a few months, and the shorter one is only 3 months [1]. The lining plate has to be replaced, but due to the high cost performance, easy processing, and convenient loading and unloading characteristics of 16Mn, it is still one of the commonly used wear-resistant materials in the lining design of the coal drop pipe in the current coal transportation system.

Wear-resistant cast iron is generally divided into ordinary white cast iron, nickel hard cast iron (Ni-Hard) and low-chromium, medium-chromium, and high-chromium cast iron [2]. It is widely used in the power industry, and the lining plates used in the coal drop pipe of the coal transportation system are mainly ordinary white cast iron and high chromium cast iron.

Ordinary white cast iron has been used for a long time in my country, and it is also a widely used wear-resistant material. For example, ordinary white cast iron is used in the plowshares in agriculture. Its advantages are low price, but its disadvantages are also obvious: brittle texture, not impact-resistant, generally due to technological reasons, this cast iron has a large plate thickness when used as a lining plate. In the 20th century, Jilin Thermal Power Plant used ordinary white cast iron in the coal transportation system as the lining plate of the coal drop pipe. The thickness of the lining plate reached 40mm. The overall weight of the coal drop pipe was very heavy, which increased the load and construction cost of the building. At the same time, it is very inconvenient to install and maintain. In addition, when the lining plate is connected with countersunk bolts, the connection will be corroded after a period of operation, so that the lining plate cannot be replaced. Rarely used in design.

High-chromium cast iron is white cast iron with a chromium content of more than 12%. It has good hardness, corrosion resistance and oxidation resistance, and has better toughness than white cast iron, so it is a good wear-resistant material. High content, so the market price of high-chromium cast iron is higher, mainly used in the building materials and power industry grinding ball, crusher hammer and blast furnace lining plate below 800 ℃. Due to the better wear resistance of high chromium cast iron, it is currently used in coal drop pipes in coal transportation systems in thermal power plants.

In order to obtain higher hardness, an appropriate amount of rare earth composite modifier is added to the rare earth wear-resistant cast steel, so as to inoculate the steel to improve the comprehensive mechanical properties of the material, especially the impact toughness. The hardness of this cast steel is close to that of ordinary steel, but the hardness can be very high after quenching and air cooling. At present, rare earth wear-resistant cast steel is used to make the lining plate of the ball mill and the ring hammer of the ring hammer crusher. Good results have been achieved in the pulverizing system. Some data show that the wear resistance of the former is nearly 2 times that of the latter by using rare earth wear-resistant cast steel for the lining plate of the ball mill and Mn13. In the past, the carbon steel plate with a thickness of 16mm was worn through in only half a year, but it can be extended to 1.5 to 2 years after switching to rare earth wear-resistant cast steel.

Rare earth wear-resistant cast steel has good wear resistance, and the price is not higher than that of high manganese steel. Therefore, many domestic thermal power plants currently use rare earth wear-resistant cast steel as the lining plate for the coal drop pipe of the coal transportation system, and the use effect is good.

Stainless steel is divided into austenitic stainless steel, martensitic stainless steel and ferritic stainless steel. The stainless steel generally used as a wear-resistant liner is martensitic stainless steel. Stainless steel has many advantages as a wear-resistant liner, mainly including: high water absorption and thermal expansion coefficient, impact resistance, smooth surface, which is conducive to material flow. Therefore, stainless steel plate is the most used material for the silo in the coal transportation system of the thermal power plant and the lining of the coal bunker in front of the circulating fluidized bed boiler. However, the disadvantages of stainless steel are also obvious: its own hardness is low, the wear resistance effect is average, the installation is inconvenient, and the cost is high. Especially in the current thermal power project, in addition to the advantages of impact resistance compared with other materials, the overall cost performance of stainless steel is not high. Therefore, it is not suitable to be used in large quantities in the lining of coal drop pipes. In the case of using stainless steel as the backing plate.

Low hardness, general wear resistance, inconvenient installation and high cost. Especially in the current thermal power project, in addition to the advantages of impact resistance compared with other materials, the overall cost performance of stainless steel is not high. Therefore, it is not suitable to be used in large quantities in the lining of coal drop pipes. In the case of using stainless steel as the backing plate.

Surfacing wear-resistant composite steel plate is composed of two parts: ordinary mother plate base material and anti-wear layer. It uses Q235 or Q345 steel plate as the mother plate, and uses submerged arc automatic welding to surfacing high-chromium wear-resistant surfacing flux-cored welding wire on the surface. On the mother board, a surfacing anti-wear layer is formed. Generally, the chemical composition of the surfacing layer has a carbon content of 4% to 5% and a chromium content of up to 25% to 30%. The anti-wear layer generally accounts for 1/3 to 2 of the total thickness. /3. The main feature of the material is good wear resistance and impact resistance, and the macro hardness can reach 50-60HRC. According to some data, through the wear comparison test, the wear resistance of wear-resistant composite steel plate is more than 20 times higher than that of low carbon steel, more than 5 times higher than that of stainless steel and high manganese steel, and 1.5 to 2.5 times higher than that of as-cast high chromium cast iron [ 4].

Because the material of the wear-resistant composite steel plate is low carbon steel, the overall material can be easily cut like ordinary steel plates, bent or curled, welded and punched, and processed into various wear-resistant parts, which is more convenient to use.

The main disadvantages of this material are: (1) The content of chromium in the surfacing welding material is high, and cracks are easily formed between the anti-wear layer and the substrate during surfacing, which makes the wear-resistant layer easy to fall off during subsequent processing or use, and it is difficult to cause trouble. to anti-wear effect. (2) The hardness of the surfacing layer of the material is too high, the processing cost is high, and the chromium content in the material is high. These factors make the market price of surfacing wear-resistant composite steel plates high.

Although there are the above shortcomings, the comprehensive performance of wear-resistant composite steel plate is still good, so it is used by some domestic power plants in the coal drop pipe of the coal transportation system.

The ceramic composite materials commonly used in coal drop pipes of coal transportation systems in thermal power plants are currently mainly enamel linings and three-in-one wear-resistant ceramic composite linings.

The enamel lining plate is fired at high temperature on the surface of the metal steel plate. The enamel is a kind of ceramic composite material. The enamel is firmly combined with the substrate, and its penetration and adhesion properties are good. Grinding, smooth, insulating and other characteristics. The general metal substrate is ordinary carbon steel, and the thickness of the steel plate can be selected according to the actual requirements of the project. In the coal drop pipe system of thermal power plants, the general substrate thickness is not less than 6mm. Because the surface finish of the enamel lining plate is high, it can also correctly solve the problem of sticking and blocking of the coal drop pipe while being wear-resistant. For example, in the fifth phase expansion project of Guodian Luanhe Power Plant, all the linings of the coal drop pipe system are made of wear-resistant enamel, and the lining plates of the coal drop pipe (bucket) in the first phase of Nanyang Thermal Power Project are made of 8mm thick enamel surface wear-resistant Lining plate, all the inner lining of the coal drop pipe system of Guodian Zhumadian Thermal Power Plant are also 10mm wear-resistant enamel lining plate.

The three-in-one wear-resistant ceramic composite liner is a combination product of ceramic, rubber and steel plate. The special ceramic sheet and rubber are directly vulcanized on the steel plate with bolts to make a three-in-one structure (ceramic + rubber + steel plate). It is directly fixed with the wall of the coal drop pipe (bucket) by bolts. The ceramic block is small, usually hemispherical or square. At the same time, the rubber absorbs the impact energy, and the noise reduction effect is remarkable. The metal base plate and the connecting parts are not in contact with the material, so as to avoid corrosion and wear. In addition, the three-in-one wear-resistant ceramic composite liner is easy to replace. Therefore, the three-in-one wear-resistant ceramic composite lining plate is currently widely used in domestic power plants. For example, all the coal falling pipes (coal falling buckets) in the cogeneration expansion project of Guodian Lanzhou Thermal Power Co., Ltd. are three-in-one wear-resistant Ceramic composite liner (ceramic 10mm + rubber 6mm + steel plate 6mm).

However, there are also reports that the three-in-one wear-resistant ceramic composite lining plate has ceramic falling off and overturning during use. After the ceramics at the local position falls off, the coal drop pipe at that place is seriously worn and coal leakage occurs; after the ceramic sheet is turned over, the coal drop tube appears The reduction of the flow area causes the clogging of the coal drop pipe.

UHMW-PE for short, is a thermoplastic engineering plastic with a molecular weight of more than 1.5 million. It has self-lubrication, wear resistance, non-adhesion, impact resistance, and excellent corrosion resistance to acid and alkali. It is widely used in coal bunker, silo and other parts of steel, electric power, coal, cement, mining and other industries. In recent years, it is also often used as a lining in the coal drop pipe system of the coal transportation system of the power plant.

However, the reason why the ultra-high molecular weight polyethylene plate is wear-resistant is that the frictional resistance between the polyethylene plate and the material is reduced, and the friction coefficient between the polyethylene plate and the coal is only 1/3 to 1/4 of that of the steel plate [5]. In addition, the hardness of the ultra-high molecular weight polyethylene plate is low, and a sharp object can be used to make a deep imprint, and it cannot withstand the impact of block materials. The wear resistance effect on objects without sharp corners is obvious, such as powder It is more suitable for the conveying lining plate of shaped objects, the lining of the raw coal bunker in front of the furnace, and the ash discharge pipe of the power plant. It can replace stainless steel within a certain range and improve economic benefits.

There are a large number of large coal blocks, gangue and other sharp-angled block materials in the material transportation process of the coal transportation system, and the impact resistance of the inner wall of the coal drop pipe is relatively high. The feedback on the situation of polymer polyethylene board as lining board is not very good. Of course, in addition to the material shortcomings of the UHMWPE board mentioned above, there are many counterfeit and shoddy products of this type of material on the market, some of which are simply ordinary plastic boards, which are prone to accidents such as burning and falling off. Therefore, try not to use ultra-high molecular weight polyethylene plate as the lining plate in the coal drop pipe system of the coal transportation system of the thermal power plant.

Calendered microcrystalline liner is a new type of wear-resistant liner, which is a new high-tech industrial protective material with high strength and high corrosion resistance, which is formed by melting, rolling, crystallization and annealing with various slag as the main raw material. Building decoration materials. Its wear resistance is 7 to 8 times higher than that of manganese steel, 15 to 20 times higher than that of cast iron, and its corrosion resistance is 10 to 25 times higher than that of stainless steel and rubber. Feedback from the usage information, this material lining board has obvious effect in the concrete silo. Based on some data, it can be seen that the rolled microcrystalline lining plate is better used as the lining plate in the coal unloading ditch, dumper room, boiler raw coal hopper and other parts of the coal transportation system of the thermal power plant. However, there is currently no specific information on the use of the coal drop pipe. Considering that this material is not easy to replace, careful consideration should be given to the use of rolled microcrystalline linings in the coal drop pipe system.

In addition to the wear-resistant lining materials commonly used in the coal handling system of thermal power plants mentioned above, there are many new high-strength wear-resistant steel plates in the world, such as: HARDOX series produced in Oclund, Sweden, 400V in Dillingen, Germany and 500V, XAR400, XAR450, XAR500 series of ThyssenKrupp in Germany, JFE-EH360, EH400 and EH500 in Japan, NM series produced by Wugang and Wuhan Iron and Steel in China, NM360, NM400, NM450, NM500 wear-resistant steel plates, etc. [ 6]. The price of these new high-strength wear-resistant steels is relatively reasonable, especially the market price of domestic NM series steel plates is reasonable compared with the prices of several lining plates introduced earlier. Taking NM400 as an example, the price per ton is only 7,600 yuan. Around, NM500 is about 8100 yuan per ton.

These newly developed high-strength wear-resistant steels are currently mainly used in vehicles, ships, mining equipment, metallurgy, construction machinery and cement equipment. Liners are made of these new wear-resistant steel materials. However, with the planning of large-capacity units in China, a large number of coal drop pipe lining materials will inevitably be required. On the basis of comprehensive consideration of economy and technology, it is recommended to try to use these new types of resistant coal drop pipe linings in the coal transportation system of thermal power plants. Grinding steel plates to reduce operating costs of power plants.

Through the introduction of several commonly used lining materials for coal drop pipes in coal transportation systems of thermal power plants, it can be known that there are many varieties of wear-resistant lining materials used in domestic coal transportation systems, there are many choices, and the cost performance is different. vary. Therefore, each power plant should collect data as much as possible when selecting coal drop pipe liner materials, and if conditions permit, they can visit other power plants with similar working conditions to obtain the use of coal drop pipe liner in the coal transportation system of these power plants. According to its own working conditions, make corresponding choices. For example, when conveying coal with small particle size or grinding surface with basically no impact, ultra-high molecular weight polyethylene material liner can be used; the material is hard, large in particle size and strong in impact. Parts, try to use rare earth wear-resistant cast steel. In the parts that are easy to stick to the coal and block the coal, stainless steel can be used as the lining material.

In short, when selecting the lining plate of the coal drop pipe of the coal handling system of the thermal power plant, the wear resistance and service life of the lining plate should be considered, as well as the price of the lining plate material and the economic situation of the power plant itself. Collect actual data, learn from each other’s strengths to make up for one’s shortcomings, and conduct a comprehensive technical and economic analysis, so as to select a more suitable material for the coal drop pipe lining plate of the coal transportation system.