Anti-corrosion tubular heat exchanger for recycling flue gas waste heat of papermaking alkali furnace

Abstract

The utility model relates to an anti-corrosion tubular heat exchanger for flue gas waste heat recovery of a papermaking alkali furnace, and belongs to the technical field of heat exchange. Comprising a heat exchange tube bundle, the heat exchange tube bundle is arranged in a shell, the heat exchange tube bundle is composed of a plurality of polyphenylene sulfide composite tubes, the polyphenylene sulfide composite tubes take polyphenylene sulfide as a matrix and are compounded with high-heat-conductivity filler, and the axial heat conductivity coefficient is not lower than 11 W / (m.K); tube plates are arranged at the two ends of the shell respectively, and the two ends of the heat exchange tube bundle are fixedly connected to the tube plates respectively. Liquid tube boxes are arranged on the outer sides of the tube plates respectively and communicated with the heat exchange tube bundles. The excellent tolerance of the PPS material to corrosive media such as sulfuric acid, alkali liquor and salt is reserved, and the axial heat conductivity coefficient of the composite pipe is remarkably improved through the high-heat-conductivity filler, so that the heat exchange efficiency is remarkably improved.

Description

Technical Field

[0001] This utility model relates to a corrosion-resistant tubular heat exchanger for waste heat recovery from flue gas in papermaking alkali furnaces, belonging to the field of heat exchange technology. Background Technology

[0002] In alkali recovery systems for papermaking and pulping, the flue gas temperature from alkali furnaces typically ranges from 120°C to 180°C, containing a significant amount of recoverable low- to medium-temperature waste heat. Current recovery methods often employ tubular heat exchangers: while metal heat exchange tubes (such as carbon steel and stainless steel) have good thermal conductivity, they are highly susceptible to corrosion by sulfuric acid (low-temperature dew point corrosion) in the flue gas, resulting in a short lifespan; and while fluoroplastic heat exchange tubes (such as PTFE) are corrosion-resistant, their thermal conductivity is extremely low (typically below 0.5 W / (m·K)), leading to low heat exchange efficiency and bulky equipment. Furthermore, fly ash, unburned carbon particles, and alkaline sodium salts in the flue gas easily cause ash accumulation and blockage, further affecting heat exchange efficiency and system resistance.

[0003] To address the aforementioned problems, existing technical solutions have proposed various improvement measures. For example, Chinese Patent Publication No. CN202547453U discloses a low-temperature flue gas waste heat recovery heat exchanger, including a shell, heat exchange tubes installed inside the shell, a water manifold at the inlet of the heat exchange tubes, a water inlet pipe connected to the water manifold, and the water inlet pipe connected to the heat exchange tubes. The cooling medium inside the heat exchange tubes is led out through the water inlet pipe. The water manifold is designed to regulate the tube wall temperature, making it fluctuate within ±12℃ of the temperature at which the corrosion rate is lowest, thereby reducing corrosion. However, the temperature control method requires high system adjustment accuracy, which is difficult to maintain stably in actual operation.

[0004] Therefore, how to simultaneously solve multiple problems in the waste heat recovery process of papermaking alkali furnaces, such as efficient heat exchange, long-term corrosion resistance, resistance to ash accumulation and blockage, and convenient maintenance, remains a critical technical bottleneck that urgently needs to be overcome. Developing a new type of heat exchanger that overcomes the corrosion defects of traditional metal tubes, avoids the low efficiency of fluoroplastic tubes, and combines simple structure, reliable operation, and convenient maintenance is of significant practical importance and application value for improving the energy efficiency of alkali recovery systems and reducing operation and maintenance costs. Summary of the Invention

[0005] The purpose of this utility model is to overcome the shortcomings of the existing technology and address the problems of easy corrosion of metal heat exchange tubes and low efficiency of fluoroplastic heat exchange tubes. It provides a corrosion-resistant tubular heat exchanger for waste heat recovery of flue gas from papermaking alkali furnaces. It is specially designed for deep waste heat recovery of flue gas from papermaking alkali furnaces. It has a reasonable structural design, high heat exchange efficiency, strong corrosion resistance, low operating resistance and convenient maintenance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The application discloses a corrosion-resistant tubular heat exchanger for recovering waste heat of alkali furnace flue gas in papermaking, which comprises a heat exchange tube bundle arranged in a shell, wherein the heat exchange tube bundle is composed of a plurality of polyphenylene sulfide composite tubes, the polyphenylene sulfide composite tube is composed of polyphenylene sulfide as a base body and high-thermal-conductivity fillers, and the axial thermal conductivity coefficient of the polyphenylene sulfide composite tube is not less than 11 W / (m*K); the shell is respectively provided with a tube plate at two ends; the two ends of the heat exchange tube bundle are respectively fixedly connected to the tube plates; and the outer sides of the tube plates are respectively provided with liquid tube boxes which are communicated with the heat exchange tube bundle.

[0008] The polyphenylene sulfide composite tube is used as the heat exchange tube bundle, the excellent resistance of PPS material to corrosive media such as sulfuric acid, lye and salt is retained, the hidden troubles of low-temperature acid dew point corrosion and chemical corrosion of alkali furnace flue gas are completely eliminated, and the service life of the equipment is greatly prolonged; the axial thermal conductivity coefficient of the polyphenylene sulfide composite tube is not less than 11 W / (m*K) through the high-thermal-conductivity fillers, which is more than one order of magnitude higher than that of a traditional fluoroplastic heat exchange tube (the thermal conductivity coefficient is less than 0.5 W / (m*K)), the heat exchange efficiency is significantly improved, and the industry pain point that corrosion resistance and high-efficiency heat exchange cannot be achieved simultaneously is solved. The combined structure of the shell, the tube plate and the liquid tube box provides independent and sealed flow channels for flue gas and working medium, and fluid leakage is avoided; the connection mode that the heat exchange tube bundle is fixed to the tube plate guarantees the structural stability, can resist the washing and temperature fluctuation (80-180 DEG C) of alkali furnace flue gas, and ensures stable operation of the equipment in a harsh industrial environment.

[0009] Here, the specific formula of the polyphenylene sulfide composite tube that is composed of polyphenylene sulfide as a base body and high-thermal-conductivity fillers is prior art, for example, a high-thermal-conductivity reinforced polyphenylene sulfide composite material and a preparation method thereof are disclosed in Chinese Patent Publication No. CN112322039A, and the thermal conductivity coefficient can reach 15 W / (m*K).

[0010] Preferably, the outer diameter of the polyphenylene sulfide composite tube is 20-40 mm, and the wall thickness is 2-3 mm.

[0011] The specification design guarantees sufficient heat transfer area of a single tube, ensures that the pipeline has good mechanical strength, rigidity and wear resistance, can resist long-term washing of fly ash in alkali furnace flue gas, avoids pipeline deformation or damage, balances heat exchange performance and structural durability, and reasonably designed outer diameter and wall thickness form appropriate flue gas flow gaps between the tube bundles, so that the flue gas flow gaps are neither too small to cause ash accumulation and blockage nor too large to reduce flue gas washing intensity, the smoothness of shell-side flue gas flow is guaranteed, and the long-term heat exchange efficiency is stable.

[0012] Preferably, the heat exchange tube bundle is arranged in the tube plate and fixed, and the two ends of the heat exchange tube bundle extend into the liquid tube box; the liquid tube box is provided with a working medium inlet and a working medium outlet.

[0013] The heat exchange tube bundle extends to the inside of the liquid header at both ends, so that the working medium (desalted water) can be evenly distributed to each composite tube in the header, avoiding differences in heat exchange efficiency caused by uneven single tube flow, ensuring that all heat exchange tubes can fully participate in heat exchange, and improving the overall heat exchange efficiency of the heat exchanger. The working medium inlet and outlet on the liquid header provide standardized interfaces for external pipeline connections, facilitating the construction of a closed circulation system, ensuring continuous and stable circulation of the working medium, achieving continuous recovery of waste heat, and adapting to industrial-scale application scenarios.

[0014] Preferably, an O-ring is arranged between the polyphenylene sulfide composite tube and the tube hole of the tube sheet, and the outer wall of the polyphenylene sulfide composite tube is in interference fit with the O-ring to form an elastic sealing connection.

[0015] The interference fit elastic sealing structure of the outer wall of the PPS composite tube and the O-ring can effectively block the mutual leakage of the flue gas in the shell side and the working medium in the tube side, has high tolerance to processing and installation errors, adapts to temperature changes during equipment operation, and has much higher sealing stability than traditional welding or expansion joint structures. The non-welded detachable connection method allows individual heat exchange tubes to be independently detached and replaced without affecting the normal operation of other tube bundles, without the need for hot work or large tools, shortens the maintenance downtime, and reduces the labor and time costs of equipment operation and maintenance.

[0016] Preferably, the shell is internally provided with a baffle.

[0017] The baffle guides the flow direction of the flue gas from axial flow to transverse scouring of the heat exchange tube bundle, enhances the degree of turbulent flow of the flue gas, breaks the heat transfer boundary layer near the tube wall, greatly improves the heat transfer coefficient of the flue gas and the tube wall, and significantly improves the heat exchange efficiency. The turbulent flue gas can effectively scour the tube wall, reducing the deposition of fly ash, unburned carbon particles, and alkaline sodium salt on the tube wall; at the same time, the flow guiding effect of the baffle avoids local retention of the flue gas, reduces the risk of ash deposition, maintains stable system resistance, and prolongs the continuous operation cycle of the equipment.

[0018] Preferably, the liquid header forms a closed circulation system with the external pipeline, and the working medium circulating in the closed circulation system is desalted water.

[0019] The closed circulation design allows the working medium to be recycled, continuously absorbs waste heat from the flue gas, avoids waste of the working medium, and maximizes the recovery of waste heat; the heated desalted water can be used to preheat boiler feed water, process water, or regional heating, achieving step-by-step utilization of energy and improving the overall energy utilization rate of the plant. Desalted water has stable chemical properties and is non-corrosive, which can avoid corrosion and damage of the working medium to the tube side (PPS composite tube) and the header, further prolonging the service life of the core components of the heat exchanger; at the same time, closed circulation reduces the contact of the working medium with the outside world, reducing the risk of pipeline blockage caused by impurities. After absorbing the waste heat of the flue gas, the desalted water is heated and can be used to preheat boiler feed water, process water, or regional heating, achieving step-by-step utilization of energy.

[0020] Preferably, the heat exchange tube bundle is arranged in a square array or a staggered triangular array on the tube sheet.

[0021] To address the varying characteristics of alkali furnace flue gas, such as dust content and viscosity, different heat exchanger arrangements can be selected: square in-line (easier to clean) or triangular staggered (higher heat exchange efficiency). This allows the heat exchanger to adapt to diverse industrial scenarios and enhances product applicability. Square in-line arrangements facilitate the removal of ash accumulation between tube bundles using mechanical cleaning or high-pressure water washing, reducing cleaning difficulty. Triangular staggered arrangements allow for the placement of more heat exchange tubes within the same shell space or enhance flue gas turbulence, further improving heat exchange efficiency. Users can choose precisely based on their actual needs.

[0022] Preferably, the housing is provided with a flue gas inlet and a flue gas outlet.

[0023] The placement of the flue gas inlet and outlet allows the flue gas from the tail end of the alkali furnace to smoothly enter the shell (shell side), fully contact the heat exchange tube bundle, and then exit, forming a complete flue gas flow path and providing the necessary conditions for waste heat transfer. The structural design of the inlet and outlet conforms to industrial pipeline connection standards, facilitating connection with existing equipment such as alkali furnace exhaust pipes and chimneys. Installation is convenient, requiring no major modifications to the existing system and reducing project implementation costs.

[0024] Preferably, the high thermal conductivity filler is an inorganic non-metallic filler.

[0025] Inorganic non-metallic fillers (such as graphite and carbon fiber) possess excellent thermal conductivity, effectively improving the axial thermal efficiency of PPS composite tubes and ensuring that the thermal conductivity of the composite tubes consistently meets the requirement of not less than 11 W / (m·K), thus guaranteeing heat exchange performance. The inorganic non-metallic fillers exhibit strong compatibility with the PPS matrix, preventing separation or degradation due to temperature changes or media contact. Furthermore, their corrosion resistance and high-temperature resistance match those of the PPS material, ensuring the overall weather resistance of the composite tubes and guaranteeing long-term stable operation of the equipment under conditions of high corrosion and temperature fluctuations caused by alkali furnace flue gas.

[0026] The corrosion-resistant tubular heat exchanger for waste heat recovery from flue gas in papermaking alkali furnaces, as described in this utility model, has the following advantages:

[0027] 1. Achieving a perfect balance between high-efficiency heat exchange and long-term corrosion resistance: By using PPS composite tubes modified with high thermal conductivity, the thermal conductivity (≥11W / (m·K)) is more than an order of magnitude higher than that of traditional fluoroplastic heat exchange tubes, significantly improving heat exchange efficiency. Simultaneously, the PPS material itself exhibits excellent corrosion resistance to sulfuric acid, alkali solutions, salts, and organic solvents, completely eliminating the risks of low-temperature acid dew point corrosion and chemical corrosion, thus greatly extending the service life of the equipment.

[0028] 2. Modular design, very low maintenance cost: unique "tube sheet-O ring" elastic sealing structure, instead of traditional welding or expansion, to achieve the modular installation of heat exchange tubes. Any single pipe damage can be quickly replaced individually, without large tools or fire operation, short maintenance downtime, significantly reducing the overall maintenance cost.

[0029] 3. Excellent anti-fouling and self-cleaning ability: PPS material surface energy is low, smooth and self-lubricating, and the ash, viscous sodium salt and other substances in the flue gas are not easy to adhere and accumulate. Combined with the optimized flue gas flow channel design, the problem of ash accumulation and blockage is effectively alleviated, and the heat exchange efficiency and system resistance can be kept high for a long time.

[0030] 4. Temperature resistance and reliable operation: the selected reinforced PPS composite material can be used continuously at a temperature of more than 200℃ for a long time, and can be used at a higher temperature for a short time, fully meeting the working condition requirements of the flue gas temperature fluctuation (usually 80℃-180℃) of the alkali furnace tail, ensuring the safe and stable operation of the heat exchanger in harsh industrial environment.

[0031] 5. Significant energy saving and environmental protection benefits: the utility model can deeply cool the alkali furnace exhaust gas temperature from the conventional 130℃ or so to 80℃ or even lower, fully recovers low-grade waste heat, and improves the overall energy utilization rate of the whole plant. At the same time of creating direct economic benefits, reducing greenhouse gas emissions and thermal pollution, it meets the development direction of green manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is an external structure schematic view of the anti-corrosion tube type heat exchanger for waste heat recovery of papermaking alkali furnace flue gas.

[0033] Figure 2 It is a partial enlarged structure schematic view of the connection part of the polyphenylene sulfide composite pipe and the tube sheet.

[0034] Figure 3 It is a structure schematic view of the anti-corrosion tube type heat exchanger for waste heat recovery of papermaking alkali furnace flue gas along the tube sheet direction.

[0035] In the figure: 1, shell; 2, flue gas inlet; 3, flue gas outlet; 4, tube sheet; 401, front tube sheet; 402, rear tube sheet; 5, heat exchange tube bundle; 6, water inlet pipe box; 7, water outlet pipe box; 8, working medium inlet; 9, working medium outlet; 10, O-shaped sealing ring. DETAILED DESCRIPTION

[0036] The specific implementation of the utility model will be described in further detail below in combination with the drawings and examples.

[0037] As Figure 1As shown, the heat exchanger body in this embodiment is a horizontally arranged rectangular cross-section shell 1. The flue gas flows in from the flue gas inlet 2 on the left side, flows to the right through the shell side (the internal space of the shell), and finally is discharged from the flue gas outlet 3 on the right side. Two tube sheets (front tube sheet 401, rear tube sheet 402) are fastened and sealed with the shell 1 at both ends through flanges to ensure the sealing of the shell side. A plurality of PPS composite tubes form the heat exchange tube bundle 5, which is fixed at both ends on the two tube sheets to form the tube side (the space inside the tube); the left end of the PPS composite tube is opened into the water inlet pipe box 6, and the right end is opened into the water outlet pipe box 7. The lower part of the water inlet pipe box 6 is provided with a working medium inlet 8, and the upper part of the water outlet pipe box 7 is provided with a working medium outlet 9, so as to realize the distribution and collection of the working medium.

[0038] As shown in Figure 2 , the sealing structure of the PPS composite tube and the tube sheet 4 is that a rectangular or trapezoidal annular groove is formed in the machining hole of the tube sheet 4, and a high-temperature-resistant and corrosion-resistant O-shaped sealing ring 10 (made of perfluoroether rubber material) is placed in the groove. When the PPS composite tube penetrates into the tube hole, its outer diameter is slightly larger than the inner diameter of the sealing ring, and a continuous radial sealing force is generated by interference compression, effectively preventing mutual leakage between the shell side flue gas and the tube side working medium. This structure has high tolerance to processing and installation errors, reliable sealing, and is easy to disassemble and assemble.

[0039] A plurality of horizontal baffles are installed in the shell 1, the baffles are provided with holes for the heat exchange tube bundle 5 to pass through, and the edges of the baffles are left with a gap with the inner wall of the shell to guide the flow direction of the flue gas, enhance the turbulence degree of the flue gas, improve the heat exchange efficiency and reduce the ash accumulation. The heat exchange tube bundle 5 can be arranged in a triangular staggered manner, taking into account the heat exchange efficiency and the convenience of ash removal; the specification of the PPS composite tube is selected to be 30mm in outer diameter and 2.5mm in wall thickness, ensuring the structural strength and heat transfer effect.

[0040] As shown in Figure 3 , the arrangement of the heat exchange tube bundle 5 adopts square in-line arrangement, achieving the balance and optimization of "convenient ash removal, stable operation, and low maintenance cost". Its advantages are highly consistent with the core design goal of the utility model (long-term corrosion prevention, convenient maintenance, and energy-efficient), especially suitable for industrial scenes with high dust content in flue gas and frequent ash removal needs, and complementary to the triangular staggered arrangement (focusing on improving heat exchange efficiency), meeting the individualized adaptation needs under different flue gas characteristics.

[0041] The working process is as follows: low-temperature desalted water (working medium) is pumped into the water inlet pipe box 6 by the working medium inlet 8, is distributed to the pipe passages of the PPS composite pipes, and flows from left to right; about 130℃ alkali furnace tail flue gas enters the heat exchanger shell passage from the flue gas inlet 2, and is guided by the baffle to transversely wash the outer wall of the PPS composite pipe. The heat of the flue gas is efficiently transferred to the desalted water in the pipe through the high-thermal-conductivity PPS composite pipe wall, and the heated desalted water (temperature can reach above 70℃) is collected in the water outlet pipe box 7 and is transported to the heat application point (such as the deaerator) through the working medium outlet 9; the flue gas is cooled to about 80℃ and is discharged into the chimney from the flue gas outlet 3.

[0042] In this process, the excellent corrosion resistance of the PPS material guarantees that the pipe wall is not damaged when long-term contacting with the acidic condensed liquid, the high-thermal-conductivity characteristic ensures efficient heat transfer, the smooth surface effectively inhibits dust accumulation, and the O-shaped sealing ring 10 sealing structure provides reliable guarantee for stable operation of the equipment, and the alkali furnace flue gas waste heat is deeply recovered and the long-term stable operation of the equipment is realized.

[0043] The above examples are only used to more clearly illustrate the technical solutions of the present application, and are not intended to limit the protection scope thereof. Those skilled in the art can adjust and modify the structure of the present application according to actual needs, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

[0044] The above only describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above examples. Any technical solution falling within the idea of the present application belongs to the protection scope of the present application. It should be noted that, for ordinary skilled persons in the technical field, some improvements and decorations without departing from the principles of the present application shall be considered to fall within the protection scope of the present application.

Claims

1. A corrosion-resistant tubular heat exchanger for waste heat recovery from flue gas in papermaking alkali furnaces, comprising a heat exchange tube bundle (5), wherein the heat exchange tube bundle (5) is disposed within a shell (1), characterized in that, The heat exchange tube bundle (5) is composed of multiple polyphenylene sulfide composite tubes. The polyphenylene sulfide composite tubes are based on polyphenylene sulfide and are composited with high thermal conductivity fillers. The axial thermal conductivity is not less than 11 W / (m·K). The shell (1) is provided with tube sheets (4) at both ends. The two ends of the heat exchange tube bundle (5) are fixedly connected to the tube sheets (4). Liquid tube boxes are provided on the outside of the tube sheets (4). The liquid tube boxes are connected to the heat exchange tube bundle (5).

2. The corrosion-resistant tubular heat exchanger for waste heat recovery from papermaking alkali furnace flue gas according to claim 1, characterized in that, The outer diameter of the polyphenylene sulfide composite tube is 20mm to 40mm, and the wall thickness is 2mm to 3mm.

3. The corrosion-resistant tubular heat exchanger for waste heat recovery from papermaking alkali furnace flue gas according to claim 1, characterized in that, The heat exchange tube bundle (5) is inserted through the tube sheet (4) and fixed, with both ends extending into the liquid tube box; the liquid tube box is provided with a working fluid inlet (8) and a working fluid outlet (9).

4. A corrosion-resistant tubular heat exchanger for waste heat recovery from flue gas in papermaking alkali furnaces according to claim 3, characterized in that, An O-ring (10) is provided between the polyphenylene sulfide composite tube and the tube hole of the tube sheet, and the outer wall of the polyphenylene sulfide composite tube is interference-fitted with the O-ring (10).

5. A corrosion-resistant tubular heat exchanger for waste heat recovery from flue gas in papermaking alkali furnaces according to claim 1, characterized in that, The housing (1) is equipped with a baffle plate inside.

6. A corrosion-resistant tubular heat exchanger for waste heat recovery from flue gas in papermaking alkali furnaces according to claim 1, characterized in that, The liquid tank and external pipelines form a closed-loop circulation system, and the working fluid flowing in the closed-loop circulation system is demineralized water.

7. A corrosion-resistant tubular heat exchanger for waste heat recovery from flue gas in papermaking alkali furnaces according to claim 1, characterized in that, The heat exchange tube bundle (5) is arranged in a square in sequence or a triangular staggered arrangement on the tube sheet (4).

8. A corrosion-resistant tubular heat exchanger for waste heat recovery from flue gas in papermaking alkali furnaces according to claim 1, characterized in that, The housing (1) is provided with a flue gas inlet (2) and a flue gas outlet (3).

9. A corrosion-resistant tubular heat exchanger for waste heat recovery from flue gas in papermaking alkali furnaces according to claim 1, characterized in that, The high thermal conductivity filler is an inorganic non-metallic filler.

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