Energy-saving heat storage element and rotary air preheater
By employing Venturi tubes and phase change materials in the rotary air preheater, the problem of heat storage element blockage was solved, heat exchange efficiency and temperature stability were improved, production costs were reduced, and equipment service life was extended.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NINGXIA HUANENGDA ENVIRONMENTAL PROTECTION TECH DEV CO LTD
- Filing Date
- 2026-04-13
- Publication Date
- 2026-06-09
AI Technical Summary
The heat storage elements of existing three-compartment rotary air preheaters are prone to blockage due to changes in coal quality, especially in the medium-temperature and low-temperature sections, where the heat exchange efficiency decreases, the cleaning frequency increases, and replacements become more frequent.
The heat storage elements employ different heat transfer structures. The high-temperature section uses Venturi tubes and phase change materials, the medium-temperature section has a waveform structure, and the low-temperature section is the same as the high-temperature section. The gaps between the Venturi tubes in the high-temperature and low-temperature sections are filled with phase change materials. Combined with the contraction and expansion design of the Venturi tubes, the airflow velocity and heat exchange time are optimized. Graphite powder or copper powder is added to the phase change materials to improve thermal conductivity.
It effectively prevents clogging, improves heat exchange efficiency, reduces production costs, extends cleaning and replacement frequency, enhances temperature stability, and reduces ash accumulation.
Smart Images
Figure CN122170686A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of rotary air preheaters, and more particularly to an energy-saving thermal storage element and a rotary air preheater. Background Technology
[0002] The three-compartment rotary air preheater is the most widely used heat exchange equipment for flue gas waste heat recovery in large power plant boilers. Its heat storage elements are arranged in either a three-layer or two-layer structure; the heat storage elements are generally corrugated and come in various types, including DNF, KH, DU, HS8, and HC. The three-compartment, three-layer element arrangement, and HS8 corrugated rotary air preheater are the most widely used. It has advantages such as compact structure, light weight, high heat exchange efficiency, and flexible and convenient layout. However, with changes in coal quality, such as increased ash and sulfur content, the heat storage elements in the medium-temperature section are prone to blockage due to decreased flue gas pressure; the heat storage units in the low-temperature section are prone to blockage due to ash condensation. This leads to problems such as decreased heat exchange efficiency, increased cleaning frequency, and frequent replacement of heat storage elements. Summary of the Invention
[0003] In view of this, this application proposes an energy-saving heat storage element that is not prone to clogging and has high-efficiency heat exchange.
[0004] This application also proposes a rotary air preheater with energy-saving heat storage elements.
[0005] An energy-saving heat storage element comprises, from top to bottom: The high-temperature section is provided with a plurality of Venturi tubes distributed therefrom, and the gaps between the Venturi tubes are filled with phase change material. The intermediate temperature range, wherein the intermediate temperature range has a waveform structure; The low-temperature section has the same structure as the high-temperature section.
[0006] This application utilizes different heat transfer structures based on the temperature gradient within the rotary air preheater: 500–800℃ in the high-temperature section, 300–600℃ in the medium-temperature section, and 100–350℃ in the low-temperature section. This achieves efficient heat exchange while mitigating blockage issues in the medium- and low-temperature sections. Venturi tubes and phase change materials (PCMs) are employed in the high- and low-temperature sections. Due to their variable cross-section and curved walls, Venturi tubes offer higher heat transfer efficiency than direct-flow channels and are less prone to dust accumulation. The gaps between the Venturi tubes are filled with PCMs, which can store and release more heat, thereby enhancing heat transfer, especially in the low-temperature section. Due to their better temperature stability, the tube wall temperature can be maintained above the dew point, reducing the likelihood of dust accumulation and blockage. Furthermore, the cured PCMs enhance the overall rigidity of the Venturi tube array, reducing thermal deformation. Corrugated plates are used in the medium-temperature section to ensure heat transfer efficiency while improving thermal stability and reducing production costs.
[0007] The linear velocity of the rotary air preheater rotor increases with the radius, leading to insufficient heat transfer in the inner ring and excessive heat transfer in the outer ring. Therefore, preferably, the high-temperature or low-temperature section is radially divided into an inner ring region, a middle ring region, and an outer ring region, with the gap between the Venturi tubes in the inner ring region, middle ring region, and outer ring region gradually increasing. Increasing the gap of the outer ring Venturi tubes can reduce the airflow velocity and prolong the heat transfer time; decreasing the gap of the inner ring can increase the airflow velocity and enhance the heat transfer intensity, thereby making the radial heat transfer more uniform.
[0008] Preferably, the radial range of the inner ring region is r / R<0.5, where r is the outer diameter of the inner ring, R is the radius of the heat storage element, and the venturi tube contraction ratio of the inner ring region is 1:0.7~0.8, and the expansion ratio is 1:1.3~1.5.
[0009] Preferably, the radial range of the middle ring region is 0.5≤r / R<0.8, where r is the outer diameter of the middle ring, R is the radius of the heat storage element, and the venturi tube of the middle ring region has a contraction ratio of 1:0.6~0.7 and an expansion ratio of 1:1.4~1.6.
[0010] Preferably, the radial range of the outer ring region is r / R≥0.8, where r is the outer diameter of the outer ring, R is the radius of the heat storage element, and the Venturi tube of the outer ring region has a contraction ratio of 1:0.5~0.6 and an expansion ratio of 1:1.5~1.7.
[0011] The above-mentioned venturi tube's contraction ratio, expansion ratio, and throat diameter are set based on heat exchange efficiency and pressure loss considerations. The specific parameters are determined according to the actual operating results.
[0012] Preferably, the phase change material has a filling rate of 70-80%.
[0013] When phase change materials melt, their volume expansion rate is about 5% to 10%. Reserving 20% to 30% expansion space can prevent structural deformation or damage. At the same time, it can ensure sufficient contact between the phase change material and the Venturi tube, while avoiding the increase in thermal resistance caused by excessive filling.
[0014] Preferably, the phase change material contains 10% to 15% graphite powder or copper powder to improve its thermal conductivity. Specifically, the graphite powder or copper powder can form a continuous thermal conductivity path in the phase change material, thereby improving the thermal conductivity of the phase change material. This ultimately improves the heat exchange efficiency of the phase change material and accelerates the charging and discharging rate of the heat storage element.
[0015] The high-temperature section involves high ambient temperatures, requiring the phase change material to possess excellent thermal stability to prevent decomposition or deterioration under prolonged high temperatures. Preferably, the phase change material in the high-temperature section is a metal-based alloy or a nitrate eutectic salt. Metal-based alloys offer excellent thermal conductivity but are more expensive, while nitrate eutectic salts are less expensive but have poorer thermal conductivity; the choice depends on the specific operating conditions.
[0016] Preferably, the phase change material in the low-temperature section is a paraffin-based composite material. The low-temperature section is prone to low-temperature corrosion, and the paraffin-based composite material has good insulation properties, which can prevent electrochemical corrosion.
[0017] A rotary air preheater includes the aforementioned heat storage element. In addition, the conventional structure of a rotary air preheater includes a fixed cylindrical outer shell, flue gas duct, sealing system, and transmission device, wherein the sealing system includes radial seals, axial seals, and circumferential seals. The Venturi tube structure of the heat storage element in this application can form a local negative pressure zone, which, in conjunction with the radial and axial seals of the air preheater, can reduce the air leakage rate.
[0018] The technical advantages of this application are as follows: The high-temperature and low-temperature sections employ a Venturi tube design, different from the traditional waveform structure. Furthermore, phase change material is filled in the gaps between the Venturi tubes to store energy. Compared to the waveform structure, airflow in the high-temperature section is smoother and less prone to blockage, while the pressure upon entering the mid-temperature section is reduced, significantly improving the blockage problem in the mid-temperature section. This application retains the waveform structure in the mid-temperature section, reducing manufacturing costs while improving heat exchange efficiency. In the low-temperature section, the combination of Venturi tubes and phase change material maintains the tube wall temperature above the dew point, effectively suppressing ash condensation caused by low temperatures. Attached Figure Description
[0019] Figure 1 A schematic diagram of the energy-saving heat storage element of this application; Figure 2 This is a regional division diagram of the high-temperature or low-temperature heat storage element in this application.
[0020] Explanation of reference numerals in the attached diagram: High temperature section 1, Venturi tube 11, Phase change material 12, Medium temperature section 2, Low temperature section 3, Inner ring region 31, Middle ring region 32, Outer ring region 33. Detailed Implementation
[0021] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.
[0022] It should be noted that the gap between the Venturi tubes 11 and other parameters of the Venturi tubes 11 in this application are determined according to the heat exchange effect. Figure 1 and Figure 2 The figures provided in this application are for the purpose of facilitating understanding by those skilled in the art and do not represent actual parameters.
[0023] Example 1 Please refer to Figure 1In this embodiment, the energy-saving heat storage element includes, from top to bottom: High-temperature section 1, wherein a plurality of Venturi tubes 11 are evenly distributed in the high-temperature section 1, and the gaps between the Venturi tubes 11 are filled with phase change material 12; The intermediate temperature section 2 has a waveform structure; the intermediate temperature section 2 is a heat storage structure currently used in this field. A waveform structure refers to a structure with a waveform cross-section, and the longitudinal cross-section of the waveform structure is a rectangular channel for easy processing.
[0024] Low-temperature section 3 has the same structure as high-temperature section 1.
[0025] Example 2 Please refer to Figure 2 In this embodiment, based on embodiment 1, the high temperature segment 1 or the low temperature segment 3 is divided into an inner ring region 31, a middle ring region 32 and an outer ring region 33.
[0026] Among them, in high temperature segment 1: The preferred material for the venturi tube 11 in the inner ring region 31 is zirconia-coated stainless steel (Cr25Ni20). The inner ring has the highest temperature, reaching 700-800℃, and the zirconia coating can withstand high temperatures of 1000℃. At the same time, the zirconia coating has high hardness and high resistance to fly ash abrasion. In addition, the zirconia coating has a moderate thermal conductivity, which can be used in conjunction with the phase change material 12 for efficient heat exchange.
[0027] The preferred material for the Venturi tube 11 in the central region 32 is Corten steel (09CuPCrNi-A). The temperature in the central region 32 is moderate, reaching 500-700℃, and the high-temperature corrosion resistance of Corten steel meets the requirements. At the same time, Corten steel has a high thermal conductivity, which can improve the charging and discharging rate of the phase change material 12. In addition, Corten steel has a low cost and good economic efficiency.
[0028] The preferred material for the Venturi tube 11 in the outer ring region 33 is enamel-lined steel plate. The temperature in the outer ring region 33 is relatively low, reaching 500-600℃, and the enamel-lined steel plate has good corrosion resistance; at the same time, the enamel layer is insulating, which can slow down electrochemical corrosion; the cost of enamel-lined steel plate is lower than that of Corten steel, making it suitable for large-area applications.
[0029] In low temperature range 3: The preferred material for the Venturi tube 11 is enamel-lined steel plate or 304 stainless steel. The low-temperature section 3 is prone to ammonium bisulfate corrosion, and enamel-lined steel plate or 304 stainless steel offers better corrosion resistance. Simultaneously, enamel-lined steel plate or 304 stainless steel has moderate thermal conductivity, which, combined with the paraffin-based phase change material 12, can significantly improve heat exchange efficiency. Furthermore, enamel-lined steel plate is less expensive, and 304 stainless steel has better weldability.
[0030] It should be noted that the linear velocity of the rotary air preheater rotor increases linearly with the radius. The gap between the Venturi tubes 11 needs to be matched inversely to the flow velocity distribution, i.e., a smaller gap in the inner ring and a larger gap in the outer ring, to ensure uniform radial heat transfer. Simultaneously, the contraction-expansion structure of the Venturi tubes 11 creates localized negative pressure zones. Excessive gaps lead to increased air leakage, while insufficient gaps increase flow resistance. A balance must be struck between air leakage and resistance. In a preferred embodiment, the gap between the Venturi tubes 11 in the inner ring region 31 is preferably 10–15 mm; the gap in the middle ring region 32 is preferably 15–20 mm; and the gap in the outer ring region 33 is preferably 0–25 mm.
[0031] Example 3 Based on Example 2, this embodiment further defines the range of the inner ring region 31 and the structure of the Venturi tube 11. Specifically, the radial range of the inner ring region 31 is r / R<0.5, where r is the outer diameter of the inner ring and R is the radius of the heat storage element. The contraction ratio of the Venturi tube 11 in the inner ring region 31 is 1:0.7~0.8, and the expansion ratio is 1:1.3~1.5.
[0032] Example 4 Based on Example 2, this embodiment further defines the range of the middle ring region 32 and the structure of the venturi tube 11. Specifically, the radial range of the middle ring region 32 is 0.5≤r / R<0.8, where r is the outer diameter of the middle ring and R is the radius of the heat storage element. The venturi tube 11 of the middle ring region 32 has a contraction ratio of 1:0.6~0.7 and an expansion ratio of 1:1.4~1.6.
[0033] Example 5 This embodiment further defines the range of the outer ring region 33 and the structure of the Venturi tube 11 based on embodiment 2. Specifically, the radial range of the outer ring region 33 is r / R≥0.8, where r is the outer diameter of the outer ring and R is the radius of the heat storage element. The Venturi tube 11 of the outer ring region 33 has a contraction ratio of 1:0.5~0.6 and an expansion ratio of 1:1.5~1.7.
[0034] Example 6 This embodiment further limits the filler of the phase change material 12 based on embodiment 1, that is, the filling rate of the phase change material 12 is 70-80%.
[0035] In a preferred embodiment, when the gap between the Venturi tubes 11 is 10-15 mm, the phase change material 12 has a filling rate of 75%-80%, with a reserved expansion space of 20%-25%; when the gap between the Venturi tubes 11 is 15-20 mm, the filling rate is 70%-75%, with a reserved expansion space of 25%-30%; when the gap between the Venturi tubes 11 is 20-25 mm, the filling rate is 70%-75%, with a reserved expansion space of 25%-30%.
[0036] Example 7 In this embodiment, based on Example 1, 10% to 15% of graphite powder or copper powder is added to the phase change material 12 to improve the thermal conductivity of the phase change material 12.
[0037] Example 8 This embodiment defines the phase change material 12 in the high-temperature section 1 based on embodiment 1, namely, the phase change material 12 is a metal-based alloy or a nitrate eutectic salt.
[0038] Metal-based alloys may be selected, but are not limited to, aluminum-silicon alloys (Al-12Si), aluminum-copper alloys (Al-25Cu), and magnesium-aluminum alloys (Mg-30Al).
[0039] Nitrate eutectic salts may be selected, but are not limited to, sodium nitrate-potassium nitrate (NaNO3-KNO3), potassium nitrate-lithium nitrate (KNO3-LiNO3), and sodium nitrate-calcium nitrate (NaNO3-Ca(NO3)2).
[0040] The specific materials can be selected based on the actual operating conditions.
[0041] Example 9 This embodiment defines the phase change material 12 in the low-temperature section 3 based on embodiment 1, that is, the phase change material 12 is a paraffin-based composite material.
[0042] Paraffin-based composite materials can be selected from, but are not limited to, pure paraffin, paraffin-graphite composite materials, paraffin-expanded graphite composite materials, paraffin-metal powder composite materials, paraffin-ceramic powder composite materials, and paraffin-polymer composite materials.
[0043] Among them, pure paraffin has high latent heat of phase change and low cost, but low thermal conductivity and slow thermal response speed. It is suitable for the outer ring region 33 of the low temperature range, where the temperature is low and the requirement for thermal response speed is not high, so its high latent heat density can be fully utilized.
[0044] The paraffin-graphite composite material is made by adding 10% to 15% graphite powder to pure paraffin, which significantly improves the thermal conductivity of the phase change material 12 while slightly reducing the latent heat of phase change. It is suitable for the inner ring region 31 of the low-temperature section 3, where the temperature is moderate and a high heat exchange efficiency is required, and the thermal conductivity enhancement effect of graphite powder is significant.
[0045] The expanded graphite in the paraffin-expanded graphite composite material has a porous structure, which can adsorb paraffin to form a composite phase change material 12. This can significantly improve the thermal conductivity of the phase change material 12, making it suitable for the inner ring region 31 of the low-temperature section 3, where the temperature is high and a rapid thermal response is required.
[0046] Paraffin-metal powder composites are made by adding 10%–15% copper or aluminum powder, or other highly conductive metal powders, to pure paraffin. This significantly improves the thermal conductivity of the phase change material 12, but reduces the latent heat of phase change to some extent. It is suitable for the low-temperature, easily corroded region 3, where ammonium bisulfate corrosion is prone to occur. The metal powders can improve the material's electrical conductivity and prevent electrochemical corrosion.
[0047] Paraffin-ceramic powder composites are made by adding 10%–15% of highly conductive ceramic powders such as alumina or boron nitride to pure paraffin, thereby improving the thermal conductivity of the phase change material and reducing the latent heat of phase change, as well as the volume expansion rate. This makes them suitable for the low-temperature range and high-temperature range, where high temperatures require good thermal stability and resistance to volume expansion.
[0048] Paraffin-polymer composites are made by adding 10% to 20% of polymers such as polyethylene or polypropylene to pure paraffin, thereby reducing the volume expansion rate of phase change material 12 and improving mechanical strength. They are suitable for areas with significant vibration, such as the low-temperature section 3, where rotor vibration is substantial and requires good mechanical strength and resistance to volume expansion.
[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.
Claims
1. An energy-saving heat storage element, characterized in that: From top to bottom, including: High temperature section (1), wherein a plurality of venturi tubes (11) are distributed in the high temperature section (1), and the gaps between the venturi tubes (11) are filled with phase change material (12). The intermediate temperature section (2) has a waveform structure. Low temperature section (3) has the same structure as high temperature section (1).
2. The energy-saving heat storage element as described in claim 1, characterized in that: The high-temperature section (1) or low-temperature section (3) is radially divided into an inner ring region (31), a middle ring region (32), and an outer ring region (33), and the gap between the Venturi tubes in the inner ring region (31), the middle ring region (32), and the outer ring region (33) gradually increases.
3. The energy-saving heat storage element as described in claim 2, characterized in that: The radial range of the inner ring region (31) is r / R<0.5, where r is the outer diameter of the inner ring and R is the radius of the heat storage element. The Venturi tube (11) of the inner ring region (31) has a shrinkage ratio of 1:0.7~0.8 and an expansion ratio of 1:1.3~1.
5.
4. The energy-saving heat storage element as described in claim 2, characterized in that: The radial range of the middle ring region (32) is 0.5≤r / R<0.8, where r is the outer diameter of the middle ring and R is the radius of the heat storage element. The Venturi tube (11) of the middle ring region (32) has a shrinkage ratio of 1:0.6~0.7 and an expansion ratio of 1:1.4~1.
6.
5. The energy-saving heat storage element as described in claim 2, characterized in that: The radial range of the outer ring region (33) is r / R≥0.8, where r is the outer diameter of the outer ring and R is the radius of the heat storage element. The Venturi tube (11) of the outer ring region (33) has a shrinkage ratio of 1:0.5~0.6 and an expansion ratio of 1:1.5~1.
7.
6. The energy-saving heat storage element as described in claim 1, characterized in that: The phase change material (12) has a filling rate of 70-80%.
7. The energy-saving heat storage element as described in claim 1, characterized in that: The phase change material (12) contains 10% to 15% graphite powder or copper powder.
8. The energy-saving heat storage element as described in claim 1, characterized in that: The phase change material (12) of the high-temperature section (1) is a metal-based alloy or a nitrate eutectic salt.
9. The energy-saving heat storage element as described in claim 1, characterized in that: The phase change material (12) of the low-temperature section (3) is a paraffin-based composite material.
10. A rotary air preheater, characterized in that: It includes the energy-saving heat storage element as described in any one of claims 1 to 9.