Structural design of grate bars for waste incineration grate
Grate sheet design requirements
In order to ensure the stable operation of the incinerator, in the design of the grate sheet, it is not only ensured that the material of the grate sheet has high temperature heat resistance, corrosion resistance, and wear resistance, but also structurally improves the design requirements of combustion air, reduces the slag leakage rate, and avoids as much as possible. Partial wear and burnout need to be designed in terms of structure and material.
1 Structural design
(1) Grate ventilation rate. The grate ventilation rate is equal to the ratio of the total area of ​​the ventilation holes on the grate surface to the entire grate area. The grate piece is a high-temperature working part, and the working conditions are quite harsh. Especially the reciprocating grate pieces work at high temperature for a long time. Although the grate piece and the combustion layer are separated by a layer of "ash pad", which can shield part of the heat, the surface temperature of the grate piece can still reach above 600-700℃. For safe and reliable work of the grate, effective air cooling must be adopted; the reciprocating incinerator uses the grate to ensure that the garbage moves and burns evenly on the grate, and the air passes through the grate and the garbage from the bottom to the top from the air chamber under the grate. layer to provide sufficient oxygen for waste combustion.
Therefore, there should be uniform ventilation channels on the grate sheet, which is the so-called ventilation rate requirement. When designing the grate sheet, it is necessary to consider how to control and reduce slag leakage and improve the utilization rate of combustible substances. Under normal circumstances, the ventilation channel width of the reciprocating grate in the drying section is controlled within 4mm, the ventilation channel width in the combustion area is controlled within 3mm, and the ventilation width in the ember section is slightly smaller, which can not only effectively control slag leakage, but also greatly reduce slag leakage. Improve combustion efficiency.
Many relevant materials believe that the ventilation rate of the reciprocating grate should be 3% to 6%. Of course, the larger the ventilation rate, the larger the ventilation channel section, the smaller the air perforation speed, and the smaller the flow resistance. Affected by factors such as slag leakage and grate sheet strength, the ventilation rate reaches 2% to 4%, which belongs to the high pressure loss grate, and the actual use effect is very good. In general, the air intake of the grate sheet needs to comprehensively consider important factors such as ventilation rate, slag leakage rate, and combustion efficiency.
(2) The cooling degree of the grate. The cooling degree of the grate is equal to the ratio of the total area of the grate fins to the total area of the grate. The grate sheet mainly relies on air convection to cool the grate sheet, thereby reducing the temperature of the grate sheet. The outline of a common grate sheet is shown in Figure 2.
Figure 2 Outline drawing of the grate sheet
The design of grate fins is not only a consideration of structural strength, but also a consideration of forced cooling. According to the current experience value, the cooling degree is generally designed to be greater than 2 under the premise of satisfying the strength design of the grate sheet itself. In addition, if the low calorific value exceeds 8260kJ/kg, consider using a water-cooled grate to further enhance the forced cooling effect.
(3) The fixed form of the grate piece. The grate pieces are installed in various forms, usually in the form of tail fixing. Some manufacturers design bolts or hooks at the bottom or both sides of the grate sheet to fix it to prevent the grate sheet from lifting. There are various connection forms between the movable grate piece and the movable grate piece, and the fixed grate piece and the fixed piece And eccentric wear, but the maintenance and disassembly is inconvenient, the gap is easy to assemble, disassemble and maintain, and it is easy for foreign objects to get stuck, the gap becomes larger, and eccentric wear occurs, which leads to the early replacement of the grate pieces. The fixed form of the grate sheet should ensure that the reciprocating motion of the grate sheet is not easy to be stuck and tilted, and a certain maintenance convenience should be reserved.
(4) Aided design tools. The grate piece usually has a long service time, and the general design life is more than 5 years. If the development and design of the new type of grate piece adopts the actual furnace verification method, not only the cycle is too long, but also it brings uncertainty to the engineering application, which is not conducive to the development and design of the product.
Therefore, before engineering application, it is necessary to use auxiliary design software for analysis. Commonly used computer-aided engineering (CAE) software such as ANSYS is used for thermal stress analysis to optimize the structural strength design of the grate pieces; through computational fluid dynamics (CFD) ( computational fluid dynam-ics) such as FLUENT for fluid analysis to optimize parameters such as ventilation rate and cooling degree of grate sheets.
Through CFD software such as FLUENT, the ventilation rate simulation calculation of the side of the grate sheet or the grate sheet itself can be used to realize the optimization calculation of the pressure loss and flow rate of the grate sheet, and provide the convection heat transfer boundary conditions for the thermal stress analysis of the grate sheet. The theoretical calculation provides the design basis.
Through CAE software such as ANSYS, the structure of the grate sheet is analyzed, and the simulation calculation is performed in terms of structural strength and heat transfer. Through the coupling of heat transfer and structural stress analysis, the large-scale thermal stress concentration in the grate sheet can be avoided, thereby providing the optimization of the structure of the grate sheet. Design Basis. Through the application of auxiliary design software, the structural form of the grate sheet is optimized, the product design cycle is reduced, the structural stability and reliability of the grate sheet are improved, and the cost of product development and design is reduced.
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