A stepped heat recovery type pallet grate for pellet roasting

Abstract

The utility model relates to the pelletizing technical field, concretely relates to a kind of pelletizing and calcining are used in step heat recovery type trolley grate bar;The present application is by built-in heat recovery channel and step utilization structure, realize the efficient capture and grading recovery of different temperature section waste heat, improve energy utilization, reduce unit product energy consumption;Meanwhile it also optimizes grate bar body material, improves structural design, improves the thermal fatigue resistance, wear resistance and corrosion resistance of grate bar, prolongs its service life, reduces the frequency of replacement downtime, reduces maintenance cost;In addition, the ventilation structure and airflow passage layout of grate bar are optimized, the contact area and uniformity of airflow and pellets are enhanced, the heat exchange efficiency is improved, and the pelletizing quality is stable;Secondly, through the heat recovery interface, the grate bar becomes the core component of the heat recovery system, realizes the integration function of "load ventilation heat recovery", adapts to the low-carbon upgrading of pelletizing process, and helps the steel industry to achieve the emission reduction target.

Description

Technical Field

[0001] This utility model relates to the field of pellet roasting technology, and in particular to a stepped waste heat recovery type trolley grate for pellet roasting. Background Technology

[0002] In the pellet production process, pellet roasting is a crucial step. Existing bogie grates, as core components of roasting equipment (especially belt roasters), play a vital role. Their main functions include carrying the pellets and completing drying, preheating, roasting, and cooling processes as the bogie moves. Simultaneously, as airflow channels, they allow hot flue gas (roasting section) or cooling air (cooling section) to pass through the grates and exchange heat with the pellets, achieving heating or cooling. Existing bogie grates are designed primarily to meet basic load-bearing, permeability, and high-temperature resistance requirements. Materials typically include heat-resistant steel (such as CrNi alloys), and structures are mainly straight, grooved, or comb-tooth types, with a focus on wear resistance, thermal fatigue resistance, and structural strength. These designs, to a certain extent, ensure the normal operation of the pellet roasting process, providing fundamental support for pellet production.

[0003] However, the core problems of existing pellet roasting trolley grate bars are the lack of waste heat recovery, short lifespan, low thermal efficiency, and single function, which cannot meet the requirements of modern metallurgical industry for energy conservation, consumption reduction, quality improvement and efficiency enhancement. Utility Model Content

[0004] The purpose of this utility model is to provide a stepped waste heat recovery trolley grate for pellet roasting, which aims to solve the core problems of existing trolley grate for pellet roasting, namely, lack of waste heat recovery, short lifespan, low thermal efficiency and single function, which cannot meet the requirements of modern metallurgical industry for energy saving, consumption reduction and quality improvement.

[0005] To achieve the above objectives, this utility model employs a stepped waste heat recovery trolley grate for pellet roasting, comprising a grate body, with multiple nested waste heat recovery channels arranged on the inner side of the grate body. The inner channel is close to the bearing surface of the grate body, the middle channel is connected to the high-temperature flue gas duct of the roasting equipment, and the outer channel is connected to the hot air duct of the cooling section. The surface of the grate body is provided with guide grooves along the airflow direction. A heat insulation layer is provided between the grate body and the trolley, and connecting structures are provided at both ends of the grate body.

[0006] The grate body is made of a high-temperature resistant and high-strength alloy material. The grate body is designed to be flat, and the surface is covered with regularly arranged air vents. The diameter and spacing of the air vents can be designed according to the particle size of the pellets and the airflow distribution requirements.

[0007] Among them, the multi-layered nested waste heat recovery channels are all closed circulation pipeline structures, and the interior of each channel is filled with a high-efficiency heat-conducting medium.

[0008] The insulation layer is made of a high-efficiency insulation material.

[0009] The connection structure consists of bolts and pins. The grate bar body is firmly connected to the trolley frame via bolts and pins, and the connection between the grate bar body and the trolley frame is sealed with a sealing material.

[0010] This invention relates to a tiered waste heat recovery trolley grate for pellet roasting. By designing a built-in waste heat recovery channel and a tiered utilization structure, this invention achieves efficient capture and graded recovery of waste heat at different temperature ranges (e.g., high-temperature waste heat is used to preheat combustion air, medium-temperature waste heat is used to preheat raw materials, and low-temperature waste heat is used for heating or auxiliary drying), thereby improving energy utilization and reducing energy consumption per unit product. Simultaneously, by optimizing the grate material (e.g., using a composite of high-temperature resistant alloy and heat-insulating coating) and improving the structural design (e.g., adding heat dissipation fins and reducing stress concentration points), the invention enhances the grate's resistance to thermal fatigue, wear resistance, and corrosion resistance, extending its service life (targeting over 12 months), reducing downtime for replacement, and lowering maintenance costs. Furthermore, by optimizing the grate's permeable structure (e.g., variable diameter holes and guide channels), the invention further improves its energy efficiency and reduces energy consumption per unit product. The invention utilizes a unique design and airflow channel layout to enhance the contact area and uniformity between the airflow and the pellets, thereby improving heat exchange efficiency (aiming for over 75%) and ensuring stable pellet roasting quality (e.g., strength deviation controlled within 5%). Secondly, through waste heat recovery interfaces (such as structures connected to pipes and heat exchangers), the grate becomes a core component of the waste heat recovery system, achieving an integrated function of "carrying, permeable, and waste heat recovery." This adapts to the low-carbon upgrade of the pellet roasting process, contributing to the achievement of emission reduction targets in the steel industry. Finally, the core objective of this invention is to simultaneously achieve cascaded waste heat recovery, extended lifespan, improved thermal efficiency, and functional integration through innovative design. This addresses the technical bottlenecks of existing trolley grate ... Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of the internal structure of the stepped waste heat recovery trolley grate for pellet roasting according to this utility model.

[0013] 1-Grate body, 2-Nested waste heat recovery channel, 3-Guide groove, 4-Insulation layer, 5-Connecting structure. Detailed Implementation

[0014] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this utility model, and should not be construed as limiting this utility model.

[0015] Please see Figure 1 This utility model provides a stepped waste heat recovery trolley grate for pellet roasting, including a grate body 1. The inner side of the grate body 1 is provided with a multi-layer nested waste heat recovery channel 2, with the inner channel close to the bearing surface of the grate body 1, the middle channel connected to the high-temperature flue gas duct of the roasting equipment, and the outer channel connected to the hot air duct of the cooling section. The surface of the grate body 1 is provided with a guide groove 3 along the airflow direction. A heat insulation layer 4 is provided between the grate body 1 and the trolley. Both ends of the grate body 1 are provided with a connecting structure 5.

[0016] In this embodiment, the multi-layered nested waste heat recovery channels 2 are nested within the grate body 1 and are tightly connected to the grate body 1 by welding or mechanical sealing to ensure that the heat transfer medium circulates within the channels without leakage. The inner channel is close to the bearing surface of the grate body 1 and is mainly used to recover the sensible heat of the high-temperature pellets. The middle channel is connected to the high-temperature flue gas duct of the roasting equipment to recover the waste heat of the high-temperature flue gas. The outer channel is connected to the hot air duct of the cooling section to utilize the waste heat of the cooling hot air. The guide groove 3 is directly processed or welded to the surface of the grate body 1 and is integral with the grate body 1. The heat insulation layer 4 is laid between the grate body 1 and the trolley and is kept in a stable position by adhesive or mechanical fixing. The grate body 1 is rigidly connected to the trolley frame through the connecting structure 5 to ensure the stability of the grate during the operation of the trolley.

[0017] Furthermore, the grate body 1 is made of a high-temperature resistant and high-strength alloy material. The grate body 1 is designed to be flat, and the surface is distributed with regularly arranged air vents. The diameter and spacing of the air vents can be designed according to the particle size of the pellets and the airflow distribution requirements.

[0018] In this embodiment, the alloy material is a heat-resistant alloy steel of chromium, nickel and molybdenum to ensure stability and reliability under high temperature (1000-1300℃), high load and complex chemical environment. At the same time, the diameter of the vent hole can be designed to be 8-12mm and the hole spacing is 15-20mm.

[0019] Furthermore, the multi-layered nested waste heat recovery channels 2 are all closed circulation pipeline structures, and the interior of each channel is filled with a highly efficient heat-conducting medium.

[0020] In this embodiment, the high-efficiency heat-conducting medium is a low-melting-point metal alloy or high-thermal-conductivity ceramic particles to enhance heat transfer efficiency. In addition, the multi-layer nested waste heat recovery channels 2 are made of copper tubes with an inner diameter of 15 mm, arranged in a serpentine pattern, accounting for 10% of the cross-sectional area of ​​the grate body 1; the middle layer channel is made of stainless steel tubes with an inner diameter of 20 mm, spaced 10 mm apart from the inner layer channel, and arranged around the inner layer channel; the outer layer channel is made of nickel-based alloy tubes with an inner diameter of 25 mm, 15 mm away from the middle layer channel, and is also arranged around the inner layer channel; heat collection tubes are connected to both ends of each layer channel to realize the circulation of the heat-conducting medium.

[0021] Furthermore, the heat insulation layer 4 is a high-efficiency heat insulation material.

[0022] In this embodiment, the thickness of the high-efficiency heat insulation material is 5mm, the thermal conductivity is less than 0.02W / (m·K), and it is laid at the contact point between the grate body 1 and the trolley. The high-efficiency heat insulation material is ceramic fiber or aerogel, so as to reduce the heat conduction from the grate to the trolley, reduce the temperature of the trolley body, extend the service life of the trolley, and reduce heat loss.

[0023] Furthermore, the connecting structure 5 consists of bolts and pins, and the grate body 1 is firmly connected to the trolley frame by bolts and pins, and the connection between the grate body 1 and the trolley frame is made of sealing material.

[0024] In this embodiment, L-shaped connecting ears are provided at both ends of the grate body 1, which are fastened to the trolley frame by M16 high-temperature bolts. The connection is sealed with a high-temperature resistant rubber sealing ring, and the rubber can withstand temperatures up to 1200℃.

[0025] The working principles of each stage in this invention are as follows:

[0026] 1. Waste heat recovery stage: When the pellets are roasted on the grate, the sensible heat of the high-temperature pellets is first transferred to the inner waste heat recovery channel through the grate body 1, heating the heat transfer medium in the channel; at the same time, the high-temperature flue gas discharged from the roasting section enters the middle waste heat recovery channel through the pipeline, and the hot air from the cooling section enters the outer waste heat recovery channel, heating the heat transfer medium in the corresponding channel respectively.

[0027] 2. Waste Heat Cascade Utilization Stage: The heated heat transfer medium circulates within the channels, transferring heat to different waste heat utilization stages. Heat recovered in the high-temperature section (inner channel) can be used to preheat combustion air, improving combustion efficiency. Heat in the medium-temperature section (middle channel) can be used to preheat green pellets entering the calcination system, reducing energy consumption for green pellet heating. Heat in the low-temperature section (outer channel) can be used for factory heating or other auxiliary production processes. Through this cascade utilization method, efficient recovery and rational distribution of waste heat are achieved.

[0028] 3. Heat exchange and pellet roasting stage: Under the guidance of the guide trough 3, hot flue gas or cooling air passes evenly through the air vents on the surface of the grate bar and exchanges heat with the pellet layer; the hot flue gas provides the heat required for roasting the pellets, causing them to undergo physical and chemical reactions and achieve consolidation; the cooling air carries away the heat from the pellets, cooling them to a suitable temperature; throughout the process, the heat insulation structure effectively reduces the loss of heat to the trolley and the surrounding environment, ensuring that the heat is mainly used for the roasting of the pellets and the recovery of waste heat.

[0029] Regarding material selection and optimization in this utility model: in addition to the high-temperature resistant alloy material used for the grate body 1, the pipe material of the waste heat recovery channel is selected as stainless steel or nickel-based alloy with high temperature resistance, corrosion resistance and good thermal conductivity; the materials of the guide groove 3 and the insulation layer 4 need to have good high temperature resistance, wear resistance and heat insulation performance to adapt to the harsh working environment; in the material manufacturing process, advanced casting, forging or powder metallurgy processes can be adopted to optimize the microstructure of the material and further improve the comprehensive performance of the material; for example, the material of the grate body 1 is heat-treated to adjust its metallographic structure and enhance its resistance to thermal fatigue. Through the above technical solutions, the cascade waste heat recovery trolley grate for pellet roasting realizes efficient recovery and cascade utilization of waste heat, while improving the quality of pellet roasting and the stability of equipment operation, providing a strong guarantee for energy saving, consumption reduction and quality improvement in pellet production.

[0030] This utility model also provides two embodiments, as follows:

[0031] Example 1:

[0032] Structural Composition: The grate body 1 is cast from heat-resistant alloy steel containing 25% chromium (Cr), 20% nickel (Ni), and 5% molybdenum (Mo). The body is flat, 1200mm long, 150mm wide, and 30mm thick. The upper surface is uniformly distributed with circular vent holes of 10mm diameter and 18mm spacing, achieving an opening rate of 25%. Waste Heat Recovery Channels: The inner channel is made of copper tubing with an inner diameter of 15mm, arranged in a serpentine pattern, and occupies 10% of the cross-sectional area of ​​the grate body 1. The middle channel uses stainless steel tubing with an inner diameter of 20mm, spaced 10mm from the inner channel and arranged around it. The outer channel uses nickel-based alloy tubing with an inner diameter of 25mm, 15mm from the middle channel, also arranged around it. Heat collection tubes are connected to both ends of each channel to achieve heat transfer medium circulation. Flow guiding and heat insulation structure: Flow guiding grooves 3, 5mm deep and 8mm wide, are formed on the upper surface of the grate bars along the airflow direction, spaced 20mm apart. A 5mm thick aerogel heat insulation layer 4 is laid at the contact point between the grate bars and the trolley, with a thermal conductivity of less than 0.02W / (m·K). Connection and fixing components: L-shaped connecting ears are provided at both ends of the grate bars, which are fastened to the trolley frame with M16 high-temperature bolts. The connection is sealed with a high-temperature resistant rubber sealing ring, with the rubber capable of withstanding temperatures up to 1200℃.

[0033] Working Principle: Waste Heat Recovery: During pellet roasting, the sensible heat of the high-temperature pellets causes the temperature of the inner channel heat-conducting medium (low-melting-point bismuth-tin alloy, melting point 138℃) to rise rapidly. High-temperature flue gas at approximately 1000℃ enters the middle channel to heat the heat-conducting medium, while hot air at approximately 500℃ in the cooling section heats the outer channel medium. Waste Heat Cascade Utilization: The high-temperature inner channel heat-conducting medium enters the heat exchanger through heat collection pipes, transferring heat to the combustion air and raising its temperature by 300℃. The heat from the middle channel heat-conducting medium is used to preheat the green pellets, raising their temperature from room temperature to 200℃. The heat from the outer channel medium provides heating for the factory during winter, maintaining the indoor temperature above 18℃. Heat Exchange and Pellet Roasting: Guided by the guide channel 3, the hot flue gas or cooling air passes evenly through the vents and exchanges heat with the pellets. The hot flue gas provides heat, and the cooling air removes heat. The insulation layer 4 effectively reduces heat transfer to the trolley, lowering the trolley surface temperature by 80℃.

[0034] Effects and benefits: Waste heat recovery efficiency is significantly improved, reducing energy consumption in the pellet roasting process by 18%. The service life of the grate bars is extended to 15 months, and maintenance costs are reduced by 40%. The standard deviation of pellet strength is reduced from 8 MPa to 5 MPa, and quality stability is significantly improved.

[0035] Example 2:

[0036] Structural Composition: The grate body 1 is upgraded to a heat-resistant alloy steel containing 28% Cr, 22% Ni, and 6% Mo, with trace amounts of rare earth elements, improving high-temperature performance. The body thickness is reduced to 25mm, reducing weight while enhancing heat conduction. The vent holes are changed to tapered holes, wider at the top and narrower at the bottom (12mm diameter at the top, 8mm diameter at the bottom), improving airflow distribution. Waste Heat Recovery Channels: The inner channel adopts a microchannel structure, with a channel width of 2mm and a depth of 3mm, increasing the heat exchange area. The pipe diameters of the middle and outer channels remain unchanged, but internally reinforced heat transfer tubes are used, with an internal rib height of 2mm and a helix angle of 30°. Flow Guiding and Insulation Structure: The flow guide groove 3 is changed to a wave shape, with a wave height of 6mm and a wavelength of 25mm, further enhancing airflow turbulence. The insulation layer 4 is replaced with a ceramic fiber and aerogel composite insulation material, 6mm thick, with a thermal conductivity as low as 0.018W / (m·K). Connection and fixing components: The connecting lugs have been changed to a dovetail groove structure, making the connection with the trolley more secure and facilitating installation and disassembly. The sealing material uses ceramic-based sealant, which is heat resistant up to 1300℃.

[0037] Working principle: In terms of waste heat recovery, the inner layer of the microchannel rapidly absorbs the sensible heat of the pellets, while the enhanced heat transfer tubes improve the heat exchange efficiency between the middle and outer layers and the flue gas and hot air. In the cascade utilization of waste heat, the inner layer heat-conducting medium raises the temperature of the combustion air to 350℃; the middle layer preheats the green pellets to 250℃; and the outer layer heat, in addition to providing heating, is used for preheating the pellets before drying, reducing the pellet moisture content by 1%. During heat exchange, the corrugated guide channel 3 ensures more uniform airflow dispersion, and the composite insulation material further reduces heat loss, lowering the trolley temperature by 100℃.

[0038] Effects and benefits: Waste heat recovery efficiency is increased to 70%, and energy consumption is reduced by 25%. The service life of the grate bars is extended to 18 months, and maintenance costs are reduced by 50%. The compressive strength of the pellets is increased by 10%, the quality of the finished pellets is better, and over-burning and under-burning phenomena are basically eliminated.

[0039] As can be seen from the above examples, the stepped waste heat recovery trolley grate for pellet roasting, under different structural designs, can effectively achieve the goals of waste heat recovery, extending grate life, and improving pellet quality, and has good application prospects.

[0040] In this invention, the stepped waste heat recovery trolley grate for pellet roasting has several advantages over existing technologies, including high efficiency in waste heat recovery, extended equipment lifespan, improved pellet quality, and improved production environment, as detailed below:

[0041] Firstly, it improves energy efficiency: Through a unique cascaded waste heat recovery design, it can effectively recover the sensible heat of high-temperature pellets, the waste heat of high-temperature flue gas, and the waste heat of hot air in the cooling section during the pellet roasting process. The recovered waste heat is used to preheat combustion air and raw materials, reducing energy consumption, lowering the amount of fuel such as coal gas used, and improving the overall energy utilization rate of the pellet roasting process. Secondly, it extends the service life of the grate bars: The material and structure of the grate bars have been optimized, enhancing their resistance to thermal fatigue, wear resistance, and corrosion resistance. For example, using a composite material of high-temperature resistant alloy and heat-insulating coating can reduce high-temperature damage to the grate bars, and adding heat dissipation fins can lower the grate bar temperature and reduce thermal stress concentration, thereby extending the service life of the grate bars, reducing replacement frequency, lowering maintenance costs and downtime, and improving production continuity.

[0042] Secondly, improving the quality of pellet roasting: A well-designed grate structure and airflow channel layout allow hot flue gas or cooling air to pass through the pellets more evenly, enhancing the contact area and uniformity between the airflow and the pellets, and improving heat exchange efficiency. This helps to ensure more uniform heating or cooling of the pellets, reducing localized over- or under-burning, improving the strength and chemical stability of the pellets, and ultimately enhancing product quality.

[0043] Thirdly, it reduces production and operating costs: Improved energy efficiency directly reduces fuel costs, and extended grate lifespan lowers spare parts replacement and maintenance costs. Reduced downtime also increases production efficiency, indirectly reducing production costs and improving the company's economic benefits. It also improves the operating environment: Effective waste heat recovery reduces the dissipation of high-temperature waste heat into the surrounding environment, lowering the ambient temperature around the roasting equipment, improving the working environment for operators, reducing labor intensity, and enhancing work safety.

[0044] Fourth, it adapts to energy-saving process upgrades: the grate can work in conjunction with the waste heat recovery system to become an important part of the pellet roasting energy-saving process. It can meet the requirements of new energy-saving processes such as cascade utilization of waste heat for power generation and preheated air recycling, which helps enterprises adapt to the development trend of low-carbon emission reduction in the steel industry and enhance their competitiveness.

[0045] The above-disclosed embodiments are merely preferred embodiments of the present utility model and should not be construed as limiting the scope of the present utility model. Those skilled in the art can understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present utility model are still within the scope of the utility model.

Claims

1. A stepped waste heat recovery type trolley grate for pellet roasting, characterized in that, The device includes a grate body, on the inner side of which is provided a multi-layer nested waste heat recovery channel. The inner channel is close to the bearing surface of the grate body, the middle channel is connected to the high-temperature flue gas duct of the roasting equipment, and the outer channel is connected to the hot air duct of the cooling section. The surface of the grate body is provided with a guide groove along the airflow direction. A heat insulation layer is provided between the grate body and the trolley. Both ends of the grate body are provided with a connecting structure.

2. The stepped waste heat recovery trolley grate for pellet roasting as described in claim 1, characterized in that, The grate body is made of high-temperature resistant and high-strength alloy material. The grate body is designed to be flat, and the surface is distributed with regularly arranged air vents. The diameter and spacing of the air vents can be designed according to the particle size of the pellets and the airflow distribution requirements.

3. The stepped waste heat recovery trolley grate for pellet roasting as described in claim 2, characterized in that, All the nested waste heat recovery channels described above are closed circulation pipeline structures, and the interior of each channel is filled with a highly efficient heat-conducting medium.

4. The stepped waste heat recovery trolley grate for pellet roasting as described in claim 3, characterized in that, The insulation layer is made of high-efficiency insulation material.

5. The stepped waste heat recovery trolley grate for pellet roasting as described in claim 4, characterized in that, The connection structure consists of bolts and pins. The grate bar body is firmly connected to the trolley frame by bolts and pins, and the connection between the grate bar body and the trolley frame is sealed with a sealing material.

Images