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Finite element analysis of stress on 7m coke oven door body

Finite element analysis of stress on 7m coke oven door body

Abstract: Using ANSYS finite element analysis software to conduct stress analysis on the 7m coke oven door body will help improve problems that arise in the oven door structure, materials and manufacturing process. In particular, improvements in the structural design of stress concentration areas have high practical application value in reducing the probability of coke oven door damage. The analysis results provide scientific reference data and theoretical basis for the design and manufacturing of coke oven doors.

Keywords: coke oven door; finite element; model; stress analysis

In recent years, due to factors such as increased demand for coke, reconstruction and upgrading of coke ovens, reduction of construction land, and environmental pollution, coke ovens have become increasingly large-scale. As one of the main components of the coke oven, the oven door plays an important role in sealing flue gas and tar. It is also one of the key equipment of the entire coke oven. If its design is unreasonable, flue gas and tar leakage in the coke oven may easily occur, which not only harms the health of on-site personnel, but also seriously pollutes the environment.

1 Design selection of 7m coke oven door

The traditional coke oven door design method is the analogy method, that is, based on the size of the furnace and experience, the design is carried out with reference to the structure of coke oven doors of similar furnace types. The main problems arising from this approach are as follows:

1) Local high stress areas appear in the coke oven door during use, causing damage to the coke oven door;

2) The safety factor of the coke oven door is over-amplified during the design process, causing material waste and increasing unnecessary costs.

“Development of furnace protective iron parts and coke oven door structures for ultra-large-volume coke ovens” is a sub-topic of the 863 Program key project “New Generation of Efficient and Clean Coking Process Equipment and Technology Development”. It is also a 7m coke oven door project jointly developed by our company and MCC Coke Refractory. In order to solve the above design problems, finite element analysis was applied to the design of the 7m coke oven door body, and its structure was rationally designed and improved to improve strength, stiffness and stability. The method adopted is: ① Establish a UG three-dimensional geometric model of the coke oven door body. ②Use ANSYS finite element analysis software to conduct stress and deformation analysis to determine whether the deformation of the coke oven door body is within a reasonable range and the location of the stress concentration point, so as to guide the design.

2 Model establishment

2.1 Establishment of geometric model

First, the coke oven door body is designed using the analogy method based on experience, and its three-dimensional geometric model is established using the computer-aided design software UG NX4.0, as shown in Figure 1.

Figure 1 Geometry of the coke oven door body

2.2 Establishment of mechanical model

The main force on the coke oven door body comes from the spring box-pressing cylinder (required for sealing), rollers (supporting the body) and other forces. Under working conditions, the supporting rollers mainly play the role of supporting the main body and have little effect on the deformation and stress of the coke oven door body, so they are ignored in the calculation. The pair of forces of the spring box and the pressing cylinder has the greatest impact on the coke oven door, and the deformation and damage of the coke oven door are basically caused by this. Therefore, the main force on the coke oven door body can be simplified into the spring box-pressure cylinder action force and reaction force, and the force mode is static pressure.

There are 2 spring boxes on the coke oven door body. There are 3 kinds of springs in each spring box to exert force. Calculated based on the working pressure, the resultant force is   . There are 74 pressure cylinders with different pressures. There is a spring in each cylinder to exert force. Calculated according to the working pressure fj of each spring, the resultant force is . The coke oven door body is generally in a balanced state, that is: F = 2 × F. The force diagram is shown in Figure 2.

Figure 2 Mechanical model of coke oven door body

3 Force finite element analysis and calculation results

3.1 Unit selection and meshing

Import the UG 3D model of the furnace door body into ANSYS in solid format. Materials, yield strength, tensile strength, elastic modulus, Poisson’s ratio and other properties are shown in Table 1.

Table 1 Furnace door body material list

Properties Material Yield strength Tensile strength Modulus of elasticity Poisson’s ratio
value RuT340 257MPa 336MPa 158000MPa 0.28

The element type is defined as an 8-node SOLID45 tetrahedral element, and a level 6 free mesh is used to divide the coke oven door body. The cell division results of the spring box part are shown in Figure 3.

Figure 3 Partial cell division of spring box

3.2 Load handling

1) Constraint processing. According to the assembly relationship of the coke oven door and the on-site usage conditions, the two spring boxes are regarded as fixed, and constraints in the X, Y, and Z directions are imposed on their bottom surfaces, and the displacement is set to zero.

2) Load handling. The 74 pressing cylinders are regarded as loads. The loading pressure on the nth pressing cylinder is fn, the direction is upward, and the pressure is static pressure. The total force can be obtained as  .

3.3 Stress analysis of coke oven door body

1) According to the calculation of the first strength theory, the stress distribution pattern of the coke oven door body is shown in Figure 4. It can be seen that the stress gradually increases from around the coke oven door body to the direction of the two spring boxes. Large stress is mainly concentrated on the spring box and its surroundings. This area is a high stress area and can easily cause damage to the coke oven door.

Figure 4 Stress distribution in the spring box part

2) The stress on the inside of the spring box is greater than the stress on the outside, and the stress on the bottom is greater than the stress on the side wall. The junction area between the bottom and the side wall, especially the inside, has the largest stress, which is about 68MPa. This area is a high stress concentration area.

3.4 Analysis of deformation of coke oven door body

Different from the stress distribution, the deformation gradually increases from the periphery of the coke oven door body to the middle, as shown in Figure 5. The two sides deform downward and the middle deforms upward, and the maximum deformation amount in the center is 1.29mm. Therefore, the pressure on the spring in the cylinder should be appropriately increased in the end areas on both sides.

Figure 5 Deformation of the coke oven door body

4 Result analysis

1) Based on the above analysis results, when modifying the structural design, the transition radius of the bottom and side walls of the spring box is appropriately increased. When the force calculation is performed again, the stress value decreases and the degree of concentration also decreases.

2) From the above analysis results, the design of the coke oven door is generally conservative and has a large safety factor. However, the actual environment in which the coke oven door is located is relatively complex and is greatly affected by environmental factors such as rapid cooling, rapid heating, and slight impact. Therefore, it is reasonable to choose a higher safety factor. 3) The deformation of the coke oven door is <1.5mm, and the normal deformation of the spring is >20mm. The deformation of the coke oven door is 7.5% of the spring, which has a small impact. It does not affect the service life of the spring and has little impact on the overall coke oven door.

5 Conclusion

1) The finite element analysis method was used to conduct a structural analysis of the 7m coke oven door body, which provides scientific reference data for judging whether the design structure of the oven door is reasonable.

2) The finite element analysis method can make timely improvements to problems that arise in the coke oven door structure, materials and manufacturing process. In particular, the improvement of the structural design of stress concentration areas has high practical application value in reducing the probability of damage to the coke oven door.

 

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coke ovens
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