Heat exchanger for biomass boilers

Abstract

The utility model discloses a kind of heat exchangers for biomass boiler, solve the problem of poor adaptability of heat exchanger structure in prior art, low heat recovery efficiency.The utility model heat exchanger for biomass boiler, heat exchanger is connected on the flue of biomass boiler, including shell, spiral heat exchange tube is equipped in shell, the import pipe and outlet pipe of spiral heat exchange tube are all extended shell, shell includes integrally-formed setting upper cylinder portion and lower conical hopper portion, first outlet is equipped in upper cylinder portion top, second outlet is equipped in lower conical hopper portion bottom, upper cylinder portion upper portion side wall is equipped with gas inlet.The utility model uses spiral heat exchange tube, prolongs the residence time of hot airflow in heat exchanger, reduces exhaust loss, to reach the effect of high-efficiency waste heat recovery.

Description

Technical Field

[0001] This utility model relates to the field of heat exchanger technology, and in particular to a heat exchanger for a biomass boiler. Background Technology

[0002] Heat exchangers, as crucial energy conversion devices for exchanging heat from flue gas in biomass boilers, significantly impact the overall efficiency of these boilers and are essential for reducing energy consumption and increasing economic benefits. Biomass boilers are clean energy heating devices that use agricultural and forestry waste (straw, rice husks, sawdust, etc.) as fuel. However, due to the high volatile matter, high alkali metal (K, Na) and high chlorine (Cl) content of biomass fuels, as well as their low ash melting point, existing heat exchanger structures have poor adaptability. Existing technologies, such as the Chinese patent with authorization announcement number CN209639566U, disclose a waste heat recovery heat exchanger for gas-fired, oil-fired, and biomass boilers. This exchanger utilizes guide vanes and baffles to immediately disperse and fill the hot air buffer tank when hot air is sprayed onto the guide vanes, improving the uniformity of hot air distribution and preventing excessive temperature differences at the edges of the buffer tank. Furthermore, it uses flue gas to flush the heat exchange tubes, heating the soft water circulating within the tubes from room temperature (20°C) to 60°C-90°C before it enters the boiler, increasing boiler thermal efficiency by 8°C-13°C and reducing combustion consumption. However, this heat exchanger suffers from problems such as rapid ash accumulation, slow heat transfer, and frequent ash cleaning, which negatively impacts the heat recovery efficiency of biomass boiler flue gas. Utility Model Content

[0003] To address the shortcomings in the aforementioned background technology, this utility model proposes a heat exchanger for biomass boilers, which solves the problems of poor structural adaptability and low heat recovery efficiency in existing heat exchangers.

[0004] The technical solution of this utility model is implemented as follows: A heat exchanger for a biomass boiler is connected to the flue of the biomass boiler. The heat exchanger includes a shell, inside which a spiral heat exchange tube is installed. The inlet and outlet pipes of the spiral heat exchange tube extend out of the shell. The shell includes an integrally formed upper cylindrical section and a lower conical hopper section. A first outlet is located at the top of the upper cylindrical section, and a second outlet is located at the bottom of the lower conical hopper section. An air inlet is located on the upper side wall of the upper cylindrical section. The spiral heat exchange tube + upper cylindrical / lower conical hopper design allows ash particles in the high-alkali biomass flue gas to be "thrown out while exchanging heat," eliminating the need for boiler shutdown and ash cleaning, saving on corrosion-resistant alloys, while simultaneously increasing the heat exchange area and improving heat recovery efficiency.

[0005] Further preferably, the spiral heat exchange tube is arranged between the upper cylindrical section and the lower conical hopper section. This allows for sufficient heat exchange with the hot flue gas and also guides the ash and slag in the flue gas to the second outlet, reducing ash and slag accumulation while ensuring heat exchange efficiency.

[0006] Further optimization involves using spiral heat exchange tubes with a larger diameter at the top and a smaller diameter at the bottom, and a certain taper, which facilitates slag removal.

[0007] Further optimization involves ensuring that the taper of the spiral heat exchange tube is the same as that of the lower conical hopper; this reduces the vortex zone and prevents secondary dust re-entrainment.

[0008] Further optimization involves 15° taper for both the spiral heat exchange tubes and the lower conical bucket. The 15° taper spiral tube arrangement results in vortices in the internal flow field that positively impact the heat exchange effect inside the heat exchanger. Additionally, the 15° taper heat pipe arrangement allows the hot flue gas to make more thorough contact with the heat pipes as it flows from the bottom of the heat exchanger to the exhaust port. The vertically staggered arrangement also ensures more thorough contact with the heat pipes during the hot gas exhaust process.

[0009] Further optimization involves extending the inlet tube of the spiral heat exchanger tube from the lower conical hopper and the outlet tube from the upper cylindrical section. The dual counter-current flow design of flue gas and water, with a higher temperature at the top and lower at the bottom of the tube, reduces flue gas adhesion to the wall and simultaneously improves heat exchange efficiency.

[0010] Further optimized, the upper cylindrical section is equipped with an exhaust pipe, the top of which extends out of the shell to form a first outlet. The exhaust pipe is coaxially arranged with the upper cylindrical section, and an annular cavity is formed between the exhaust pipe and the upper cylindrical section. The arc shape allows the high-temperature flue gas to enter the shell in a spiral motion, changing from linear motion to rotational motion, thus increasing the heat exchange area, while also allowing the gas to flow out smoothly after heat exchange.

[0011] Further optimized, the side wall of the upper cylindrical section is provided with a rectangular air inlet pipe, which is tangentially arranged to the upper cylindrical section. The outlet of the rectangular air inlet pipe is connected to the annular cavity, and the inlet of the rectangular air inlet pipe forms an air inlet. The rectangular air inlet pipe is flush with the top surface of the upper cylindrical section. The tangential arrangement of the rectangular air inlet pipe prevents the airflow from making a sharp 90° turn, greatly reducing system resistance and facilitating the rotational separation of ash and slag.

[0012] The beneficial effects of this invention are as follows: This invention uses a spiral heat exchange tube, which extends the residence time of the hot airflow in the heat exchanger and reduces exhaust losses, thereby achieving efficient waste heat recovery. Furthermore, the spiral heat exchange tube design combined with an upper cylindrical / lower conical hopper allows ash particles to "fall" and separate during the hot airflow heat exchange process, eliminating the need for furnace shutdown and ash cleaning, saving on corrosion-resistant alloys, while simultaneously increasing the heat exchange area and improving heat recovery efficiency.

[0013] This utility model features a spiral heat exchanger tube with a 15° taper. The 15° taper of the spiral tube arrangement causes vortices in the internal flow field, which positively impacts the heat exchange effect inside the heat exchanger. Furthermore, the 15° taper allows the hot flue gas to make more thorough contact with the heat pipes as it flows from the bottom of the heat exchanger to the exhaust port. The vertically staggered arrangement also ensures more thorough contact with the heat pipes during hot gas exhaust. In addition, the taper of the spiral heat exchanger tube is the same as the taper of the lower conical hopper, forming a parallel flow channel, reducing the vortex area of ​​ash particles, and preventing secondary ash particle re-entrainment.

[0014] As the core equipment of the entire boiler system, the heat exchanger of this utility model can improve the energy efficiency of industrial production processes and reduce energy consumption through effective heat exchange, thus having a significant impact on energy conservation and consumption reduction. Attached Figure Description

[0015] To more clearly illustrate the embodiments of this utility model, the drawings used in the description of the embodiments 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.

[0016] Figure 1 This is a schematic diagram of the structure of the present invention in Embodiment 1; Figure 2 This is a perspective view of the present invention in Embodiment 2; Figure 3 This is the velocity contour plot of the YZ section when the taper of the spiral heat exchanger tube is 15°.

[0017] Figure 4 This is a vector diagram of the temperature distribution across the YZ section of a spiral heat exchanger tube with a taper of 15°. Detailed Implementation

[0018] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0019] Example 1, such as Figure 1As shown, a heat exchanger for a biomass boiler is connected to the flue of the biomass boiler. Biomass fuel is burned inside the biomass boiler, and hot gas enters the heat exchanger through the flue. The heat exchanger includes a shell 1, inside which a spiral heat exchange tube 2 is installed. The inlet pipe 21 and outlet pipe 22 of the spiral heat exchange tube 2 extend out of the shell 1 to facilitate the flow of the medium. In this embodiment, water is used as the medium in the spiral heat exchange tube. The shell 1 includes an integrally formed upper cylindrical part 11 and a lower conical bucket part 12. The top of the upper cylindrical part 11 has a first outlet 13 for discharging the gas after heat exchange. The bottom of the lower conical bucket part 12 has a second outlet 15 for discharging soot or ash. The upper side wall of the upper cylindrical part 11 has an air inlet 14 for the entry of hot gas. Hot air enters the heat exchanger through a tangential inlet. Before entering the heat exchanger, the hot air flows in a straight line along the inlet, impacts the inner wall of the upper cylindrical section of the heat exchanger, and then rotates. It then moves downwards along the inner wall of the upper cylindrical section cavity in a spiral path. After being heat-exchanged by the cold fluid flowing through the spiral tube, the hot air rises again along the spiral path and exits from the first outlet. The heat-exchanged water is then transported to the indoor radiators. The purpose of designing the spiral heat exchange tube in this embodiment is to extend the residence time of the hot air in the heat exchanger, reduce exhaust losses, and achieve efficient waste heat recovery. In addition, the design of the spiral heat exchange tube + upper cylindrical / lower conical hopper allows ash particles to "throw off" and separate during the heat exchange process, eliminating the need for furnace shutdown and ash cleaning, saving on corrosion-resistant alloys, while increasing the heat exchange area and improving heat recovery efficiency.

[0020] In this preferred embodiment, the spiral heat exchange tube 2 is arranged between the upper cylindrical portion 11 and the lower conical hopper portion 12; as shown... Figure 3 As shown, there are many hot air vortices here, increasing the heat exchange area. As a preferred solution, the spiral heat exchange tube 2 has a larger diameter at the top and a smaller diameter at the bottom, and has a certain taper. That is, the spiral heat exchange tube itself is also made into an inverted cone shape with a "thicker at the top and thinner at the bottom", and the coiled area covers 30-50% below the "cylinder-cone" junction line. This can upgrade the previously mentioned "ash particle throwing-falling" to a "ash particle throwing-falling-guided flow" three-linkage, so that after the ash particles are thrown out, they can also be accelerated to slide to the bottom along the cone, thus avoiding ash accumulation.

[0021] Example 2, as Figure 2 As shown, a heat exchanger for a biomass boiler is further optimized based on Example 1. In this example, the taper of the spiral heat exchange tube 2 is the same as the taper of the lower conical bucket 12. That is, the taper of the spiral heat exchange tube is made to be completely at the same angle as the lower conical bucket, which is equivalent to laying a layer of heat-conducting "spiral slide" "parallel" on the inner surface of the conical bucket. This can compress the interaction of the three phases of ash, flue gas, and tube into a "conformal flow channel". The main flue gas flow generates forced swirling at the outer edge of the spiral tube, while the ash layer attached to the wall is not radially entrained because the cone angle is the same, resulting in fewer ash particle vortex areas and avoiding secondary ash particle re-entrainment.

[0022] In this embodiment, preferably, the taper of the spiral heat exchange tube 2 and the taper of the lower conical bucket 12 are both 15°. The 15° taper spiral tube arrangement causes eddies generated in the internal flow field, which has a positive impact on the heat exchange effect inside the heat exchanger. In addition, the 15° taper heat pipe arrangement allows the hot flue gas to make more full contact with the heat pipe when flowing from the bottom of the heat exchanger to the exhaust port. The vertically staggered arrangement also allows for more full contact with the heat pipe during the hot gas exhaust process.

[0023] In this preferred embodiment, the inlet pipe 21 of the spiral heat exchanger tube 2 extends out of the lower conical bucket 12, and the outlet pipe 22 of the spiral heat exchanger tube 2 extends out of the upper cylindrical part 11. This design, with water outlet at the top and water inlet at the bottom, creates a double gradient of completely counter-current and gravity-driven flow with the direction of hot air and ash movement. The tube wall temperature is higher at the top and lower at the bottom, reducing the flue gas adhesion rate. Some of the hot air "floats" on the upper part of the spiral, forming a natural secondary circulation; this increases the heat exchange area and improves heat exchange efficiency.

[0024] Example 3, as Figure 4 As shown, a heat exchanger for a biomass boiler is further optimized based on embodiment 1 or 2. In this embodiment, an exhaust pipe 3 is provided inside the upper cylindrical part 11, and the top of the exhaust pipe 3 extends out of the shell 1 to form a first outlet 13, which serves to guide the exhaust flow. The exhaust pipe 3 is coaxially arranged with the upper cylindrical part 11, and an annular cavity is formed between the exhaust pipe 3 and the upper cylindrical part 11. The "exhaust pipe" is made into a sleeve coaxial with the upper cylinder, instantly designing the upper cylindrical part into a two-stage structure of "outer ring in, inner core out" cyclone-settling-reseparation. A rectangular air inlet pipe 4 is provided on the side wall of the upper cylindrical part 11. The rectangular air inlet pipe 4 is tangentially arranged with the upper cylindrical part 11. The outlet of the rectangular air inlet pipe 4 is connected to the annular cavity, and the inlet of the rectangular air inlet pipe 4 forms an air inlet 14. The annular cavity works in conjunction with the rectangular intake pipe 4, utilizing the cyclone separation principle to facilitate the separation of ash and slag. Furthermore, the hot air forms a turbine, increasing the heat exchange area. The central exhaust pipe acts as a "pressure stabilizer," eliminating the top swirling vortex, reducing system resistance, and facilitating smooth exhaust. The rectangular intake pipe 4 is flush with the top surface of the upper cylindrical section 11, preventing the hot air from forming a turbine within the annular cavity.

[0025] Biomass fuel is burned in a biomass boiler. Hot gas enters the rectangular inlet pipe of the heat exchanger through a flue. The hot gas flows into the heat exchanger along the tangential inlet. Before entering the heat exchanger, the hot gas moves in a straight line along the inlet, impacts the inner wall of the upper cylindrical section of the heat exchanger, and then changes to a rotating motion. It then moves downward along the inner wall of the upper cylindrical section of the cavity in a spiral path. After being heat-exchanged by the cold fluid flowing through the spiral tube, the hot gas rises along the spiral path and is discharged from the first outlet. The heat-exchanged water is then transported to the indoor radiators. The purpose of designing the spiral heat exchange tube in this embodiment is to extend the residence time of the hot gas in the heat exchanger, reduce exhaust losses, and achieve the effect of efficient waste heat recovery.

[0026] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A heat exchanger for a biomass boiler, wherein the heat exchanger is connected to the flue of the biomass boiler, characterized in that: Includes a shell (1), inside which is a spiral heat exchange tube (2), the inlet pipe (21) and outlet pipe (22) of the spiral heat exchange tube (2) both extend out of the shell (1), the shell (1) includes an integrally formed upper cylindrical part (11) and a lower conical bucket part (12), the top of the upper cylindrical part (11) is provided with a first outlet (13), the bottom of the lower conical bucket part (12) is provided with a second outlet (15), and the upper side wall of the upper cylindrical part (11) is provided with an air inlet (14).

2. The heat exchanger for a biomass boiler according to claim 1, characterized in that: The spiral heat exchange tube (2) is arranged between the upper cylindrical part (11) and the lower conical bucket part (12).

3. The heat exchanger for a biomass boiler according to claim 1 or 2, characterized in that: The spiral heat exchange tube (2) has a larger diameter at the top and a smaller diameter at the bottom, and has a certain taper.

4. The heat exchanger for a biomass boiler according to claim 3, characterized in that: The taper of the spiral heat exchange tube (2) is the same as that of the lower conical bucket (12).

5. The heat exchanger for a biomass boiler according to claim 4, characterized in that: The taper of the spiral heat exchange tube (2) and the taper of the lower conical bucket (12) are both 15°.

6. The heat exchanger for a biomass boiler according to claim 5, characterized in that: The inlet pipe (21) of the spiral heat exchanger (2) extends out of the lower conical bucket (12), and the outlet pipe (22) of the spiral heat exchanger (2) extends out of the upper cylindrical part (11).

7. The heat exchanger for a biomass boiler according to claim 1, 2, 5, or 6, characterized in that: An air outlet (3) is provided inside the upper cylindrical part (11), and the top of the air outlet (3) extends out of the shell (1) to form the first outlet (13).

8. The heat exchanger for a biomass boiler according to claim 7, characterized in that: The air outlet pipe (3) is coaxially arranged with the upper cylindrical part (11), and an annular cavity is formed between the air outlet pipe (3) and the upper cylindrical part (11).

9. The heat exchanger for a biomass boiler according to claim 8, characterized in that: The upper cylindrical part (11) has a rectangular air inlet pipe (4) on its side wall. The rectangular air inlet pipe (4) is tangential to the upper cylindrical part (11). The outlet of the rectangular air inlet pipe (4) is connected to the annular cavity, and the inlet of the rectangular air inlet pipe (4) forms an air inlet (14).

10. The heat exchanger for a biomass boiler according to claim 9, characterized in that: The rectangular air intake pipe (4) is flush with the top surface of the upper cylindrical part (11).

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