A three-coil gas flue gas turbulent heat exchange device and method

Abstract

A three-coil gas flue gas turbulent heat exchange device and method of the present invention. The device takes a burner, an inner layer disc tube, a middle layer disc tube, and an outer layer flat coil tube as the main body, and adopts a three-layer coil design of inner, middle, and outer layers. The smooth tube coils of the inner and middle layers are arranged in a staggered manner to form a radiation-closed furnace chamber. The outer layer uses a flat coil tube to cool and condense the flue gas, effectively improving the thermal efficiency of the boiler. While cooling and condensing the flue gas, the viscous resistance of the flue gas is increased, so that the flow state of the flue gas changes from turbulent flow to laminar flow, increasing the heat transfer coefficient and enhancing the flue gas cooling and condensing ability. Moreover, the inner layer disc tube and the middle layer disc tube are arranged in a staggered manner to form a radiation-closed furnace chamber. According to the radiation fourth power law, the flue gas discharged from the burner can absorb a large amount of radiant heat. Compared with the current one-pass flat coil heat exchange wall in service, the manufacturing process is simpler, the heat exchange coil is more compact, and the cost is lower.

Description

Technical Field

[0001] The present invention relates to the technical field of enhanced heat transfer and energy conservation, and specifically to a three-coil gas flue gas turbulent heat exchange device and method. Background Art

[0002] Natural gas, as a clean and environment-friendly high-quality energy source, is being widely used. Gas coil boilers, as energy-saving and environmental protection products, are also required by the future development trend. The currently used gas coil boilers have the following problems: First, the two heat exchange coils are independently arranged and stacked together. During operation, only a single coil exchanges heat, resulting in low thermal efficiency and inability to make full use of the energy. Second, both the inner and outer layer coils are flat coils. The manufacturing process of the hydraulically formed flat coils is complex. It is necessary to roll and weld steel plates into round tubes, then cold-work the round tubes to be extruded into flat tubes with an oblong cross-section, cold-work the straight flat tubes into coils, and finally perform stress relief annealing to obtain the finished coil units. During the coil processing, the cold working deformation is large, and there are residual stresses and lattice defects. The processing process is cumbersome and the yield is low. To reduce the gap between the coils, it is necessary to increase the number of coil turns, which greatly increases the total heat exchange area of the coils and the weight of the boiler. Third, in the case of special requirements for the heat exchange amount, the traditional gas coil boilers have a large heat exchanger volume, large flue gas and air resistance, high initial investment and operating costs, and the flue gas temperature cannot meet the requirements, making it difficult to apply.

[0003] In addition, for every 1 m 3 of natural gas (about 85% methane), there are about 2.1 - 2.3 m 3 of latent heat steam in the combustion products. Calculated according to the calorific value of natural gas of 8000 - 8500 kcal per cubic meter and the latent heat of water vapor of 2257 kj / kg at 0.1 MPa and 100 °C, the latent heat loss of steam in the lower calorific value accounts for about 9.57% of the total heat of natural gas combustion. However, this part of the heat has not been fully utilized in the current boilers, resulting in a high demand for natural gas in gas boilers, causing huge energy losses. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a three-coil gas flue gas turbulent heat exchange device and method, which has a simple structure and reasonable design, effectively improves the thermal efficiency of the boiler, can dilute harmful substances in the flue gas at the same time, reduce the gas consumption, lower the price and operating costs of the coil gas boiler, save energy, reduce emissions, reduce costs, and promote the development of the coil gas boiler technology.

[0005] The present invention is realized through the following technical solutions:

[0006] A three-coil gas flue gas turbulent heat exchange device includes a housing, an inner layer circular coil, a middle layer circular coil, and an outer layer flat coil coaxially arranged in the housing, and a burner inserted along the axis at the upper end of the housing;

[0007] A smoke exhaust port is connected and arranged at the lower end of the outer shell, an upper cover plate is arranged at the upper end, and a lower cover plate is arranged inside; the upper and lower ends of the inner-layer disc tube, the middle-layer disc tube, and the outer-layer flat coil tube are hermetically arranged with the upper and lower cover plates respectively;

[0008] The heat exchange tubes of the inner-layer disc tube and the middle-layer disc tube are arranged in a staggered manner to form a radiation-closed furnace; an inner-middle coil tube gap is formed between the inner-layer disc tube and the middle-layer disc tube; both ends of the inner-layer disc tube and the middle-layer disc tube are respectively connected to an inner header;

[0009] The inner side of the outer-layer flat coil tube is intermittently arranged with the middle-layer disc tube, and the outer side is arranged with a gap from the inner wall of the outer shell to form a near-wall surface flue gas channel, and a flat coil tube gap is directly arranged between adjacent heat exchange tubes; the near-wall surface flue gas channel is communicated with the smoke exhaust port; both ends of the outer-layer flat coil tube are respectively connected to an outer header; the flat coil tube gap is smaller than the inner-middle coil tube gap;

[0010] The outer header return water inlet of the outer header is arranged outside the outer shell as the return water inlet of the heat exchange device, the outer header outlet is connected to the inlet of the inner header, and the inner header return water outlet of the inner header is arranged outside the outer shell as the return water outlet of the heat exchange device.

[0011] Preferably, the inner-layer disc tube and the middle-layer disc tube have the same pitch, the same pipe diameter, and the same wall thickness; the pitch of the inner-layer disc tube and the middle-layer disc tube is 40 mm - 64 mm, the pipe diameter is 24 mm - 44 mm, and the wall thickness is 1.5 mm - 3 mm; the helix radius of the inner-layer disc tube is 320 mm - 580 mm, and the helix radius of the middle-layer disc tube is 370 mm - 650 mm; the inner-layer disc tube and the middle-layer disc tube form two rows of staggered furnace water-cooled walls with the same transverse pitch as the pitch and a longitudinal pitch smaller than the pitch; both the inner-layer disc tube and the middle-layer disc tube adopt a multi-tube circle parallel structure, and a parallel structure is also adopted between the inner-layer disc tube and the middle-layer disc tube.

[0012] Preferably, the cross-section of the burner is circular, the diameter is 60 mm - 350 mm, and the length is 450 mm - 780 mm; a contact space of 45 mm to 950 mm is reserved between the outer surface of the burner and the inner surface of the inner-layer disc tube.

[0013] Preferably, the inner header is arranged between the middle-layer disc tube and the outer-layer flat coil tube; when the two ends of the round tubes of the inner-layer disc tube are turned 90 degrees outward, they gradually become elliptical tubes and extend out from the gap between the two circles of the middle-layer disc tube to be connected to the inner header; the two ends of the round tubes of the middle-layer disc tube are turned 90 degrees outward and connected to the inner header.

[0014] Preferably, the outer header is arranged on the outer wall surface of the outer shell, and both ends of the outer-layer flat coil tube are respectively connected to the outer header through 90-degree elbows; the inner-layer disc tube, the middle-layer disc tube, and the outer-layer flat coil tube form water inlets and outlets on the same plane.

[0015] Preferably, the outer shell includes a furnace body section arranged in a cylindrical shape and a reduced-diameter section arranged in an inverted conical shape; a lower cover plate is arranged between the furnace body section and the reduced-diameter section, and refractory mud is wrapped on the lower cover plate; the inner-layer disc tube, the middle-layer disc tube, and the outer-layer flat coil tube are supported on the lower cover plate and arranged inside the furnace body section; the near-wall surface flue gas passage is connected to the smoke exhaust port through the reduced-diameter section.

[0016] Preferably, the inner-layer disc tube, the middle-layer disc tube, and the outer-layer flat coil tube are respectively provided with 1 to 40 coil units, and the number of tube turns of each coil unit is 1 to 50 turns; the upper and lower coil units of the outer-layer flat coil tube are stacked, and positioning gaskets, positioning comb teeth, or bulging protrusions are arranged in the gaps between the coil units for positioning.

[0017] Preferably, the return water inlet of the outer header is arranged at the upper end of the outer header and communicates with the outer water inlet cavity, an elbow is arranged to communicate the outer water outlet cavity with the lower end of the outer header, and the elbow communicates with the inlet arranged at the lower end of the inner header; the inlet of the inner header communicates with the inner water inlet cavity, the return water outlet of the inner header is communicated with the inner water outlet cavity through a bent pipe passing through the outer shell, and the connecting end of the bent pipe is arranged at the lower end of the inner header;

[0018] The cooling water in the outer-layer flat coil tube all enters from the top and exits from the bottom, and the cooling water in the inner-layer disc tube and the middle-layer disc tube all enters from the bottom and exits from the top.

[0019] A three-coil gas flue gas turbulent heat exchange method, based on the heat exchange device described in any one of the above, includes,

[0020] The first-pass cooling and condensation of flue gas; the flue gas discharged from the burner first flows through the gap between the inner and middle coils, absorbs radiant heat, the flue gas flows through the gap of the disc tube, passes through the inner-layer disc tube and the middle-layer disc tube in sequence, increases the viscous resistance of the flue gas, and changes the turbulent flue gas at the burner outlet from turbulent flow to laminar flow, mainly absorbing radiant heat and convective heat;

[0021] The second-pass cooling and condensation of flue gas; after the laminar flue gas flows through the gap of the flat coil tube for second-pass cooling and condensation of the flue gas, it flows along the near-wall surface flue gas passage, converges, and is discharged into the smoke exhaust port.

[0022] Preferably, the inlet flue gas temperature of the first-pass cooling and condensation of flue gas is 950 - 1200 °C, and the outlet flue gas temperature is about 360 - 420 °C; the inlet flue gas temperature of the second-pass cooling and condensation of flue gas is 330 - 390 °C, and the outlet flue gas temperature can be reduced to 30 - 47 °C.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] The present invention relates to a three - coil gas flue gas turbulent heat exchange device, which takes a burner, an inner - layer disc tube, a middle - layer disc tube and an outer - layer flat coil as the main body. It adopts a three - layer coil design for the inner, middle and outer layers. The smooth - tube coils in the inner and middle layers are arranged in a staggered manner to form a radiation - enclosed furnace. The outer layer uses a flat coil to cool and condense the flue gas, effectively improving the thermal efficiency of the boiler. While cooling and condensing the flue gas, it increases the viscous resistance of the flue gas, realizes the transformation of the flue gas flow state from turbulent flow to laminar flow, increases the heat transfer coefficient, and enhances the flue gas cooling and condensing ability. Moreover, the inner - layer disc tube and the middle - layer disc tube are arranged in a staggered manner to form a radiation - enclosed furnace. According to the Stefan - Boltzmann law, it can greatly absorb the radiant heat of the flue gas discharged from the burner. Compared with the current one - pass flat - coil heat - exchange wall in service, the manufacturing process is simpler, the heat - exchange coils are more compact, and the cost is lower.

[0025] Furthermore, in the present invention, a return - water loop is set according to the heat - exchange return. In the first return, the inner - layer disc tube is connected to the inner - layer header through a variable - diameter design. In the second return, the outer - layer flat coil is connected to the outer - layer header through a 90 - degree elbow. In the return - water system, the return water first enters the outer - layer header, flows in from the top and out from the bottom, then enters the inner - layer header from the bottom, and then flows out from the bottom of the inner - layer header for system recycling or as process water for other units. The reasonable design of the return - water system makes the whole device have a lower return - water resistance, improves the utilization rate of water resources, and effectively saves water resources.

[0026] The present invention relates to a three - coil gas flue gas turbulent heat - exchange method. Through the two - return heat exchange set, in the first return, it absorbs the radiant heat and convective heat of the flue gas, and increases the viscous resistance of the flue gas to realize the transformation of the flow state from turbulent flow to laminar flow, greatly reducing the flue - gas temperature. In the second return, a parallel structure of flat coils with extremely small gaps is set to deeply cool and condense the flue gas, increase the heat - transfer coefficient, and enhance the cooling and condensing ability. It can reduce the exhaust - gas temperature to 30 - 47 °C, contributing to energy conservation and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a sectional view of the overall structure of the device described in the embodiment of the present invention.

[0028] Figure 2a It is an axonometric view of the structure of the inner - layer disc tube described in the embodiment of the present invention.

[0029] Figure 2b It is a top view of the structure of the inner - layer disc tube described in the embodiment of the present invention.

[0030] Figure 3 It is a schematic diagram of the structure of the outer - layer flat coil described in the embodiment of the present invention.

[0031] Figure 4 It is a schematic diagram of the structure of the inner - layer header described in the embodiment of the present invention.

[0032] Figure 5Schematic diagram of the outer header structure according to the embodiment of the present invention.

[0033] In the figure: outer header return water inlet 1, outer header 2, burner closure 3, burner 4, flat coil pipe interface 5, outer header interface 6, inner disc pipe interface 7, inner header inner layer interface 8, middle disc pipe interface 9, inner header middle layer interface 10, inner header 11, outer flat coil pipe 12, flat coil pipe gap 13, positioning gasket 14, near-wall surface flue gas passage 15, inner disc pipe 16, inner disc pipe reduced diameter pipe orifice 16-1, middle disc pipe 17, inner and middle coil pipe gap 18, inner header return water outlet 19, elbow 20, refractory mud 21, smoke exhaust port 22, outer shell 23. Detailed implementation manners

[0034] The present invention will be further described in detail below with reference to specific embodiments, which are explanations of the present invention rather than limitations.

[0035] A three-coil gas flue gas turbulent heat exchange device of the present invention is a compact and efficient three-coil gas boiler device with an inner and outer three-layer design. The smooth tube coils in the inner two layers are arranged in a staggered manner to form a radiation-closed furnace. The outer layer is provided with flat coil pipes to cool and condense the flue gas, effectively improving the thermal efficiency of the heat exchange device, achieving the purposes of saving energy, reducing emissions, and reducing costs.

[0036] Specifically, as Figure 1 shown, the present invention includes an outer header return water inlet 1, an outer header 2, a burner closure 3, a burner 4, a flat coil pipe interface 5, an outer header interface 6, an inner disc pipe interface 7, an inner header inner layer interface 8, a middle disc pipe interface 9, an inner header middle layer interface 10, an inner header 11, an outer flat coil pipe 12, a flat coil pipe gap 13, a positioning gasket 14, a near-wall surface flue gas passage 15, an inner disc pipe 16, an inner disc pipe reduced diameter pipe orifice 16-1, a middle disc pipe 17, an inner and middle coil pipe gap 18, an inner header return water outlet 19, an elbow 20, refractory mud 21, a smoke exhaust port 22 and an outer shell 23.

[0037] Among them, the flue gas discharged from the burner 4 first flows through the inner-middle coil pipe gap 18 formed by the staggered arrangement of the inner-layer disc pipe 16 and the middle-layer disc pipe 17, that is, the furnace water-cooled wall gap, to absorb radiant heat. The flue gas flows through the furnace water-cooled wall gap between the diameters of the heat exchange pipes, greatly reducing the temperature at the flue gas inlet of the outer-layer flat coil pipe 12, and reducing the inertial force of the turbulent flue gas at the burner outlet and increasing the viscous resistance, realizing the transition of the flow state from turbulent flow to laminar flow; then it flows through the flat coil pipe gap 13 of the outer-layer flat coil pipe 12 to cool and condense the flue gas in a second return, enhancing both the cooling and condensation capacity and the heat transfer coefficient, and requiring a smaller number of turns and total area of the outer-layer coil pipes, effectively saving consumables. In this preferred example, the burner 4 provided is a cylindrical fully premixed burner, arranged at the center of the outer shell 23, with a burner diameter of 100 mm and a length of about 685 mm, which is easy to burn low-calorific-value gas and has less incomplete combustion of gas, saving gas resources. A lower cover plate wrapped with refractory mud 21 is provided at the bottom of the furnace body section. The flue gas passes through the inner, middle, and outer three-layer coil pipes in sequence, flows along the outer wall surface of the outer-layer flat coil pipe 12 in the near-wall flue gas passage 15, converges to the reduced-diameter section below the refractory mud 21, and is discharged into the smoke exhaust port 22.

[0038] The three-coil-pipe gas flue gas turbulent heat exchange device described in the present invention adopts a design of inner, middle, and outer three-layer coil pipes. The inner wall surfaces of the inner-layer disc pipe 16 and the middle-layer disc pipe 17, together with the upper cover plate and the rear cover plate, form a closed furnace to absorb the radiant heat and convective heat of the flue gas. The outer-layer flat coil pipe 12 deeply cools and condenses the flue gas. The flue gas exchanges heat in a second return through the three-layer coil pipes in sequence and flows to the smoke exhaust port 22 along the near-wall flue gas passage 15 of the shell.

[0039] Such as Figure 1As shown, the inner-layer disc tube 16 and the middle-layer disc tube 17 are two layers of disc tubes, arranged in staggered rows. The inner-layer disc tube 16 and the middle-layer disc tube 17 have the same pitch, the same pipe diameter, and the same wall thickness. According to the installed capacity and actual situation, the coil pitch of the coil tube can be 40 mm - 64 mm, the pipe diameter can be 24 mm - 44 mm, and the wall thickness can be 1.5 mm - 3 mm; the helix radius of the inner-layer disc tube 16 can be 320 mm - 580 mm, and the helix radius of the middle-layer disc tube 17 can be 370 mm - 650 mm; the inner-layer disc tube 16 and the middle-layer disc tube 17 form two rows of staggered furnace water-cooled walls with the same transverse pitch as the pitch and a longitudinal pitch smaller than the pitch; both the inner-layer disc tube 16 and the middle-layer disc tube 17 adopt a multi-tube loop parallel structure, and a parallel structure is also adopted between the inner-layer disc tube 16 and the middle-layer disc tube 17. The circular cross-section burner 4 has a diameter of 60 mm - 350 mm and a length of 450 mm - 780 mm, which is easy to burn low-calorific-value gas, and there is less incomplete combustion of the gas, saving gas resources. The burner 4 is arranged at the center of the furnace, matching the inner and middle-layer disc tubes to ensure the uniform distribution of the flue gas along the circumference. A contact space of 45 mm - 950 mm is reserved between the outer surface of the circular cross-section burner 4 and the inner surface of the inner-layer disc tube 16 to prevent the flame from directly flushing the inner surface of the inner-layer disc tube 16, resulting in incomplete combustion and carbon deposition, and reducing the heat exchange efficiency of the coil tube.

[0040] According to the difference in the power of the heat exchange device, the inner-layer disc tube 16, the middle-layer disc tube 17, and the outer-layer flat coil tube 12 are respectively provided with 1 - 40 coil units, and the number of tube loops in each coil unit is 1 - 50 loops. The upper and lower coil units of the outer-layer flat coil tube 12 are stacked, and positioning gaskets 14, positioning comb teeth, or bulging protrusions are arranged in the gaps between the coil units for positioning.

[0041] The return water inlet 1 of the outer header is arranged at the upper end of the outer header 2 and communicates with the outer water inlet chamber. The outer water outlet chamber is communicated with the lower end of the outer header 2 through an elbow 20, and the elbow 20 is communicated with the inlet arranged at the lower end of the inner header 11; the inlet of the inner header 11 is communicated with the inner water inlet chamber, and the return water outlet 19 of the inner header passes through a bent pipe passing through the outer shell 23 and is communicated with the inner water outlet chamber, and the connecting end of the bent pipe is arranged at the lower end of the inner header 11;

[0042] The cooling water in the outer-layer flat coil tube 12 all enters from the top and exits from the bottom, and the cooling water in the inner-layer disc tube 16 and the middle-layer disc tube 17 all enters from the bottom and exits from the top.

[0043] The working medium first enters the outer header 2 from the upper left corner. It flows downward along the outer water inlet cavity on the left side of the outer header 2. The outer header interface 6 is connected to the 90-degree elbow of the outer flat coil 12, evenly distributing the working medium to all the outer flat coils 12. The working medium absorbs the heat of the flue gas inside the outer flat coil 12 and flows downward and converges into the outer water outlet cavity on the right side of the outer header 2. The working medium in the right outer water outlet header flows downward to the bottom and is connected to the bottom of the right header of the inner header 11 through the elbow 20, and then is distributed to the inner disc tube 16 and the middle disc tube 17 by the inner header 11 to absorb the radiant heat and convective heat of the flue gas. Finally, it converges into the inner water outlet cavity on the left side of the inner header 11 and flows out of the boiler from the bottom of the left inner water outlet cavity through the inner header return water outlet 19. The working medium can be recycled or used as the process water of other units. The reasonable design of the return water system makes the whole device have a lower return water resistance. Among them, the flow rate of the boiler working medium in the inner disc tube 16 shall not be lower than 0.5 m / s, the flow rate in the middle disc tube 17 shall not be lower than 0.42 m / s, and the flow rate in the outer flat coil 12 shall not be lower than 0.3 m / s.

[0044] A method for turbulent heat transfer of three-coil gas flue gas in the present invention uses the above heat exchange device and includes two-pass cooling and condensation.

[0045] The first-pass cooling and condensation of the flue gas: The flue gas discharged from the burner 4 first flows through the inner and middle coil gaps 18 to absorb radiant heat. The flue gas flows through the gaps of the disc tubes, passes through the inner disc tube 16 and the middle disc tube 17 in sequence, increasing the viscous resistance of the flue gas, and changing the turbulent flue gas at the burner outlet from turbulent flow to laminar flow, mainly absorbing radiant heat and convective heat.

[0046] The second-pass cooling and condensation of the flue gas: After the laminar flue gas flows through the flat coil gap 13 for second-pass cooling and condensation of the flue gas, it flows along the near-wall flue gas channel 15, converges and is discharged into the smoke exhaust port 22.

[0047] Among them, the inlet flue gas temperature of the first-pass cooling and condensation of the flue gas is 950 - 1200 °C, and the outlet flue gas temperature is about 360 - 420 °C; the inlet flue gas temperature of the second-pass cooling and condensation of the flue gas is 330 - 390 °C, and the outlet flue gas temperature can be reduced to 30 - 47 °C.

[0048] In this preferred example, such as Figure 2a and Figure 2bAs shown, the diameter of the helix where the center of the inner disc tube is located is 400 mm, the pitch is 50 mm, the tube diameter is 32 mm, the wall thickness is 2 mm, and there are 16 turns in total; the diameter of the helix where the center of the middle disc tube is located is 460 mm, the pitch is 50 mm, the tube diameter is 32 mm, the wall thickness is 2 mm, and there are 16 turns in total; the inner disc tube 16 and the middle disc tube 17 form two rows of staggered furnace water walls with a transverse pitch of 50 mm and a longitudinal pitch of 30 mm, absorbing radiant heat. The flue gas flows through the gap of the tube diameter, that is, the inner and middle coil pipe gap 18. The flue gas inlet temperature is about 1050 °C, and the outlet flue gas temperature is 390 °C. To reduce the water-side flow velocity, both the inner layer and the middle layer adopt a 4-tube coil parallel structure, and the inner disc tube 16 and the middle disc tube 17 are also connected in parallel. The whole is equivalent to an 8-tube coil structure, with a water-side flow velocity of 1.7 m / s, a flue gas-side flow velocity of 3.52 m / s, a heat transfer coefficient of 44.5 W, and a resistance of about 20 Pa. The disc tube of the inner disc tube 16 is connected to the inner header 11, but the transverse pitch of the tube is only 50 mm, and the inner tube cannot extend out, as Figure 2a and Figure 2b shown, design the variable-diameter nozzle 16-1 of the inner disc tube. When the circular tube of the inner disc tube turns 90 degrees outward, it gradually becomes an elliptical tube. The short axis is in the vertical direction, and the long axis is equal to the original diameter. It extends out from the gap between the diameters of the two middle tubes and is connected to the inner header 11.

[0049] As Figure 3 shown, in this preferred example, the designed diameter of the helix where the center of the outer flat coil tube 12 is located is 680 mm, the pitch is 27.3 mm, the flat tube gap is 0.8 mm, and there are 32 turns in total. Every 4 turns is a unit, and there are 8 units in parallel; the wall thickness of the flat tube is 2.3 mm, the total width is 80 mm, the height is 26.5 mm, and the fillet radius is 13 mm; the inlet flue gas temperature of the flat coil tube 12 is 360 °C. Since the smaller flat coil tube gap 13 is set to 0.8 mm, the convective heat transfer coefficient of the second-pass flat coil tube is greatly increased. After heat exchange through the flat coil tube gap 13, the outlet flue gas temperature can be reduced to 47 °C. Taking 140 °C as the boundary, when it is above 140 °C, the condensation amount is extremely small, and according to convective heat transfer calculation, the flue gas flow velocity is 12 m / s, and the heat transfer coefficient is 141 W; between 140 °C and 47 °C, a large amount of water vapor begins to condense, the flue gas flow velocity is 6.7 m / s, and the average heat transfer coefficient can reach 231 W. The outer flat coil tube 12 is welded to both ends of the coil with a 90-degree elbow to form inlet and outlet ports with the end faces in the same plane. Considering that the 90-degree elbow occupies part of the space, each coil unit is 3.92 turns, and 0.08 turns are vacated as the area occupied by the elbow; the upper and lower coil units are stacked together, and the gaps between the coil units are positioned by positioning gaskets 14; as Figure 5 shown, the water in all flat coil tubes enters from the top and exits from the bottom. The ports on the left half are all water inlets, and the right half are water outlets. In this preferred example, the outer flat coil tube 12 adopts a flat coil tube of Jidun.

[0050] AsFigure 1 As shown, the inner header 11 is arranged between the outer flat coil 12 and the middle disc tube 17. As Figure 4 shown, in this preferred embodiment, the water in the outer flat coil 12 enters the right inner water inlet chamber of the inner header 11 from the bottom, and distributes the water to 8 disc tubes; the water in the 8 disc tubes flows upward along the coil and converges in the left inner water outlet chamber, and flows out of the boiler from the bottom of the left inner water outlet chamber through the inner header return water outlet 19. The inner header 11 is respectively provided with an inner interface 8 and a middle interface 10, which are connected to the inner disc tube reducer nozzle 16-1 through the inner interface 8 and connected to the middle disc tube 17 through the middle interface 10. The specific shape of the inner header 11 can be adjusted according to the process, but the water flow velocity does not exceed 2.5 m / s. The inner water inlet chamber and the inner water outlet chamber are formed by the inner header 11 separated by a partition.

[0051] As Figure 1 and Figure 5 shown, the system return water first enters the outer header 2 from the upper left corner. It flows downward along the outer water inlet chamber on the left side of the outer header 2. The outer header interface 6 is connected to the 90-degree elbow of the outer flat coil 12, and evenly distributes the working medium to 8 flat coils. The working medium absorbs the heat of the flue gas inside the outer flat coil 12 and flows downward and converges into the outer water outlet chamber on the right side of the outer header 2. The working medium in the right outer water outlet header flows downward to the bottom, is connected to the bottom of the right header of the inner header 11 through the elbow 20, and then is distributed to the inner disc tube 16 and the middle disc tube 17 in the inner header 11 to absorb the radiant heat and convective heat of the flue gas. Finally, it converges in the left inner water outlet chamber of the inner header 11 and flows out of the boiler from the bottom of the left inner water outlet chamber through the inner header return water outlet 19, and can be recycled or used as the process water of other units. The reasonable design of the return water system makes the whole device have a lower return water resistance; among them, the flow velocity of the boiler working medium in the inner disc tube 16 shall not be lower than 0.5 m / s, the flow velocity in the middle disc tube 17 shall not be lower than 0.42 m / s, and the flow velocity in the outer flat coil 12 shall not be lower than 0.3 m / s. Both ends of the outer flat coil 12 pass through the outer shell through 90-degree elbows and are connected to the outer header interface 6 on the outer header 2. The outer water inlet chamber and the outer water outlet chamber are formed by the outer header 2 separated by a partition. The outer flat coil 12 is arranged outside the outer shell 23, and the outer wall surface thereof is 60 mm away from the outer wall surface of the outer shell 23. The diameter of the helix where the center of the flat coil is located is 680 mm, the pitch is 27.3 mm, the flat tube gap is 0.8 mm, there are 32 turns in total, every 4 turns is a unit, and there are 8 units in parallel; the wall thickness of the flat tube is 2.3 mm, the total width is 80 mm, the height is 26.5 mm, and the fillet radius is 13 mm.

[0052] The described outer shell 23 includes a furnace body section arranged in a cylindrical shape and a reduced-diameter section arranged in an inverted conical shape; a lower cover plate is arranged between the furnace body section and the reduced-diameter section, and refractory mud 21 is wrapped on the lower cover plate; the inner-layer disc tube 16, the middle-layer disc tube 17 and the outer-layer flat coil tube 12 are supported on the lower cover plate and arranged inside the furnace body section; the near-wall surface flue gas channel 15 is connected to the smoke exhaust port 22 through the reduced-diameter section; the upper and lower ends of the inner-layer disc tube 16, the middle-layer disc tube 17 and the outer-layer flat coil tube 12 are hermetically arranged with the upper and lower cover plates respectively; specifically, the gaps between the upper and lower ends of each layer of coil tube and the upper and lower cover plates are filled and sealed. The gaps between the inlets and outlets of each coil tube also need to be filled to prevent the formation of a flue gas corridor and aggravate the wear of the pipe wall. In this preferred example, the diameter of the outer shell 23 is 800 mm, the total height of the furnace body part is 1000 mm, the designed power of the boiler is 700 kW, the total weight of the boiler body is about 396 Kg, and 316L material is used.

[0053] In the device of the present invention, the boiler body is composed of upper and lower cover plates with refractory materials internally applied, inner and middle double-layer disc tubes, outer-layer flat coil tubes and an outer shell. The upper cover plate fixes the burner, and the circular cross-section burner matches the disc tube to ensure the uniform distribution of flue gas along the circumference. The flue gas flows through the gaps of the disc tube, increasing the viscous resistance of the flue gas and realizing the transformation of the flue gas flow state from turbulent flow to laminar flow, so that the flue gas is deeply cooled and condensed, and the outlet flue gas temperature can be reduced to below 47°C. The boiler return water is distributed from the outer header to all outer-layer flat coil tube units, and after absorbing heat in one pass, it is introduced into the inner header and then distributed to the inner and middle double-layer disc tubes for cooling and condensing the flue gas in the second pass. The three-coil tube gas flue gas turbulent heat exchange device has a compact structure, low return water resistance and strong cooling and condensing ability.

Claims

1. A three-coil gas flue gas turbulent heat exchange device, characterized in that, it includes a housing (23), an inner layer disc tube (16), a middle layer disc tube (17) and an outer layer flat coil tube (12) coaxially arranged in the housing (23), and a burner (4) inserted along the axis at the upper end of the housing (23); a smoke exhaust port (22) is communicatively provided at the lower end of the housing (23), an upper cover plate is provided at the upper end, and a lower cover plate is provided inside; the upper and lower ends of the inner layer disc tube (16), the middle layer disc tube (17) and the outer layer flat coil tube (12) are hermetically provided with the upper and lower cover plates respectively; the heat exchange tubes of the inner layer disc tube (16) and the middle layer disc tube (17) are arranged in a staggered manner to form a radiation-closed furnace; an inner-middle coil gap (18) is formed between the inner layer disc tube (16) and the middle layer disc tube (17); both ends of the inner layer disc tube (16) and the middle layer disc tube (17) are respectively connected to an inner layer header (11); the inner side of the outer layer flat coil tube (12) is intermittently arranged with the middle layer disc tube (17), and the outer side is arranged with a gap with the inner wall of the housing (23) to form a near-wall surface flue gas channel (15), and a flat coil gap (13) is directly arranged between adjacent heat exchange tubes; the near-wall surface flue gas channel (15) is communicated with the smoke exhaust port (22); both ends of the outer layer flat coil tube (12) are respectively connected to an outer layer header (2); the flat coil gap (13) is smaller than the inner-middle coil gap (18); the outer layer header return water inlet (1) of the outer layer header (2) is arranged outside the housing (23) as the return water inlet of the heat exchange device, the outlet of the outer layer header (2) is connected to the inlet of the inner layer header (11), and the inner layer header return water outlet (19) of the inner layer header (11) is arranged outside the housing (23) as the return water outlet of the heat exchange device.

2. A three-coil gas flue gas turbulent heat exchange device according to claim 1, characterized in that, the inner layer disc tube (16) and the middle layer disc tube (17) have the same pitch, the same pipe diameter and the same wall thickness; the pitch of the inner layer disc tube (16) and the middle layer disc tube (17) is 40 mm - 64 mm, the pipe diameter is 24 mm - 44 mm, and the wall thickness is 1.5 mm - 3 mm; the helix radius of the inner layer disc tube (16) is 320 mm - 580 mm, and the helix radius of the middle layer disc tube (17) is 370 mm - 650 mm; the inner layer disc tube (16) and the middle layer disc tube (17) form two rows of staggered furnace water-cooled walls with the same transverse pitch as the pitch and a longitudinal pitch smaller than the pitch; the inner layer disc tube (16) and the middle layer disc tube (17) each adopt a multi-tube circle parallel structure, and the inner layer disc tube (16) and the middle layer disc tube (17) also adopt a parallel structure.

3. A three-coil gas flue gas turbulent heat exchange device according to claim 1, characterized in that, the cross-section of the burner (4) is circular, with a diameter of 60 mm - 350 mm and a length of 450 mm - 780 mm; there is a contact space of 45 mm - 950 mm reserved between the outer surface of the burner (4) and the inner surface of the inner layer disc tube (16).

4. A three-coil gas flue gas turbulent heat exchange device according to claim 1, It is characterized in that The inner header (11) is arranged between the middle-layer disc tubes (17) and the outer-layer flat coil tubes (12); when the two ends of the inner-layer disc tubes (16) turn 90 degrees outward, the round tubes gradually become elliptical tubes and extend out from the gaps between the two circles of middle-layer disc tubes (17) to be connected with the inner header (11); the two ends of the middle-layer disc tubes (17) turn 90 degrees outward and are connected with the inner header (11).

5. A three-coil gas-fired flue gas turbulent heat exchange device according to claim 1 It is characterized in that The outer header (2) is arranged on the outer wall surface of the outer shell (23), and the two ends of the outer-layer flat coil tubes (12) are respectively connected with the outer header (2) through 90-degree elbows; the inner-layer disc tubes (16), the middle-layer disc tubes (17) and the outer-layer flat coil tubes (12) form water inlets and outlets on the same plane.

6. A three-coil gas-fired flue gas turbulent heat exchange device according to claim 1 It is characterized in that The outer shell (23) includes a furnace body section arranged in a cylindrical shape and a reduced-diameter section arranged in an inverted conical shape; a lower cover plate is arranged between the furnace body section and the reduced-diameter section, and refractory mud (21) is wrapped on the lower cover plate; the inner-layer disc tubes (16), the middle-layer disc tubes (17) and the outer-layer flat coil tubes (12) are supported on the lower cover plate and arranged in the furnace body section; the near-wall surface flue gas channel (15) is connected to the smoke exhaust port (22) through the reduced-diameter section.

7. A three-coil gas-fired flue gas turbulent heat exchange device according to claim 1 It is characterized in that The inner-layer disc tubes (16), the middle-layer disc tubes (17) and the outer-layer flat coil tubes (12) are respectively provided with 1 to 40 coil units, and the number of tube turns of each coil unit is 1 to 50 turns; the upper and lower coil units of the outer-layer flat coil tubes (12) are stacked, and positioning gaskets (14), positioning comb teeth or bulge protrusions are arranged in the gaps between the coil units for positioning.

8. A three-coil gas-fired flue gas turbulent heat exchange device according to claim 1 It is characterized in that The return water inlet (1) of the outer header is arranged at the upper end of the outer header (2) and communicated with the outer water inlet cavity, the outer water outlet cavity is communicated with the lower end of the outer header (2) through an elbow (20), and the elbow (20) is communicated with the inlet arranged at the lower end of the inner header (11); the inlet of the inner header (11) is communicated with the inner water inlet cavity, and the return water outlet (19) of the inner header passes through a bent pipe of the outer shell (23) and is communicated with the inner water outlet cavity, and the connecting end of the bent pipe is arranged at the lower end of the inner header (11); The cooling water in the outer-layer flat coil tubes (12) all enters from the top and exits from the bottom, and the cooling water in the inner-layer disc tubes (16) and the middle-layer disc tubes (17) all enters from the bottom and exits from the top.

9. A three-coil gas-fired flue gas turbulent heat exchange method It is characterized in that Based on the heat exchange device according to any one of claims 1-8 Including The first-pass cooling and condensation of flue gas; the flue gas discharged from the burner (4) first flows through the gap between the inner and middle coils (18), absorbs radiant heat, the flue gas flows through the gap of the disc tubes, and successively passes through the inner-layer disc tubes (16) and the middle-layer disc tubes (17), increasing the flue gas viscous resistance, so that the turbulent flue gas at the burner outlet changes from turbulence to laminar flow, mainly absorbing radiant heat and convective heat; Two-pass cooling and condensation of flue gas; after the laminar flue gas flows through the gap (13) of the flat coil to cool and condense the flue gas in two passes, it flows along the near-wall flue gas channel (15), converges and is discharged into the smoke exhaust port (22).

10. A three-coil gas flue gas turbulent heat transfer method according to claim 9, characterized in that for the one-pass cooling and condensation of flue gas, the inlet flue gas temperature is 950 - 1200 °C, and the outlet flue gas temperature is about 360 - 420 °C; for the two-pass cooling and condensation of flue gas, the inlet flue gas temperature is 330 - 390 °C, and the outlet flue gas temperature can be reduced to 30 - 47 °C.

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