Cascade flue gas waste heat deep recycling system for iron ore sintering

Abstract

The invention relates to the field of iron ore sintering, and discloses a stepped flue gas waste heat deep recycling system for the iron ore sintering process, which comprises an iron ore sintering system, a first-stage solid particle power generation system, a second-stage plate heat exchanger power generation system, a third-stage organic Rankine cycle power generation system and a fourth-stage plate heat exchanger heat exchange system, the invention further discloses a novel bubbling heat exchange plate structural design. The structure synergistically strengthens turbulence and heat exchange area on microcosmic and macroscopic scales, so that the heat exchanger still keeps extremely high heat transfer efficiency under the working condition of low temperature difference, and waste heat is recycled to the maximum extent.

Description

Technical Field

[0001] This invention relates to the field of iron ore sintering, and in particular to a cascade flue gas waste heat recovery and utilization system for iron ore sintering. Background Technology

[0002] Iron ore sintering, as a key pre-process in blast furnace ironmaking, plays an irreplaceable role in steel production. This process binds and solidifies iron ore powder, fuel, and flux at high temperatures to produce sinter with suitable strength and metallurgical properties, providing ideal furnace charge for the blast furnace. Statistics show that sinter typically accounts for over 75% of the blast furnace charge structure. This significant proportion clearly demonstrates that the sintering process dominates the raw material preparation stage in the steel industry, and its techno-economic efficiency and energy utilization efficiency have a profound impact on energy conservation and emission reduction throughout the entire process.

[0003] The iron ore sintering process mainly includes three stages: batching and granulation, feeding and ignition sintering, and sinter processing. This high-temperature physicochemical process not only consumes a large amount of solid fuel but also generates a considerable amount of medium- and high-temperature flue gas, with outlet flue gas temperatures reaching 400-500℃, characterized by large flow rates and high calorific value. Currently, this valuable waste heat resource is not systematically recovered at most production sites and is directly emitted into the atmosphere, causing significant energy waste and environmental thermal pollution. If it can be efficiently recovered and converted into electricity or process heat, it is expected to significantly reduce the energy intensity of the sintering process and improve overall energy utilization efficiency.

[0004] Although relatively mature technical experience has been accumulated in the field of industrial waste heat recovery, and medium- and high-temperature waste heat power generation technology has been widely used in industries such as boilers, cement, and chemicals, research on the systematic and in-depth recovery of waste heat from iron ore sintering flue gas is still relatively weak.

[0005] Based on the above background, this study proposes a cascade flue gas waste heat recovery and utilization system for the iron ore sintering process. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a cascade flue gas waste heat recovery and utilization system for iron ore sintering.

[0007] This invention is achieved through the following technical solution:

[0008] A cascade flue gas waste heat recovery and utilization system for iron ore sintering process includes an iron ore sintering system, a primary solid particle power generation system, a secondary plate heat exchanger power generation system, a tertiary organic Rankine cycle power generation system, and a quaternary plate heat exchanger heat exchange system, as well as a novel bubbling heat exchange plate structure design.

[0009] The iron ore sintering system includes steps such as batching, mixing, granulation, feeding, and sintering. The sintering process will generate waste heat flue gas at 400-500℃.

[0010] Furthermore, the waste heat flue gas generated by the iron ore sintering system will be removed by a dust removal system and then evacuated by an induced draft fan.

[0011] Furthermore, the flue gas from iron ore sintering, after passing through dust removal and an induced draft fan, enters the primary solid particle power generation system. The primary solid particle power generation system includes a primary heat exchanger, a high-temperature solid particle storage tank, a low-temperature solid particle storage tank, a secondary heat exchanger, a primary steam turbine, a primary generator, and valves. The flue gas extracted from the iron ore sintering system heats the low-temperature solid particles in the primary heat exchanger, after which the low-temperature solid particles enter the high-temperature solid particle storage tank. The high-temperature solid particles are extracted through valves, undergo heat exchange in the secondary heat exchanger, and the resulting steam is then used by the primary steam turbine and primary generator to generate electricity. The generated electricity is used in the iron ore sintering system.

[0012] Furthermore, after passing through the primary solid particle power generation system, the flue gas temperature decreases to 330-370℃ before entering the secondary plate heat exchanger power generation system. The secondary plate heat exchanger power generation system includes a tertiary heat exchanger, a secondary steam turbine, a secondary generator, and valves. The flue gas undergoes heat exchange in the tertiary heat exchanger, generating steam which is then used by the secondary steam turbine and secondary generator to generate electricity. The generated electricity is used in the iron ore sintering system.

[0013] Furthermore, after passing through the two-stage plate heat exchanger power generation system, the flue gas temperature drops to 150-190℃ and enters the three-stage organic Rankine cycle power generation system. The three-stage organic Rankine cycle power generation system includes a four-stage heat exchanger, a three-stage steam turbine, a three-stage generator, a condenser, a liquid storage tank, and a working fluid pump. The flue gas undergoes heat exchange in the four-stage heat exchanger, generating steam which is then used by the three-stage steam turbine and the three-stage generator to generate electricity. The generated electricity is used in the iron ore sintering system.

[0014] Furthermore, after passing through the three-stage organic Rankine cycle power generation system, the flue gas temperature drops to 80-100°C and enters the four-stage plate heat exchanger power generation system. The four-stage plate heat exchanger power generation system includes five heat exchangers and valves. The flue gas completes heat exchange in the five-stage heat exchanger, and the generated hot water is used for heating at the user end.

[0015] The novel bubbling plate heat exchanger is characterized by comprising:

[0016] The heat exchanger has upper and lower end plates, with the heat exchange plate area located between the upper and lower short end plates;

[0017] A heat exchanger base for fixing and supporting a plate heat exchanger;

[0018] A novel bubbling heat exchange plate is used for heat exchange between working fluids.

[0019] The novel bubbling heat exchange plate is characterized by comprising:

[0020] Fluid inlet and outlet areas are located at the same end of the plate;

[0021] The flue gas flow zone is located on one side of the plate bubble protrusion. As a flue gas flow area, the flue gas flow zone is composed of protruding heat exchange bubbles. The heat exchange bubbles are tilted at a certain angle, and the overall tilt angle of the bubble area is "V" shaped.

[0022] The heat exchange medium flow zone is located on the side of the plate bubble recess and includes four liquid flow channels to increase the heat exchange flow of the liquid.

[0023] The heat exchange bubbles are arranged at three different angles, and each bubble is the same size and height. Raised "X" ridges are designed on the bubbles, intersecting each other, and the height of these raised "X" ridges is lower than the height of the bubbles.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) This invention focuses on the research field of waste heat utilization of iron ore sintering flue gas, establishes the deep recovery of high-temperature flue gas generated in iron ore sintering as the research objective, and provides a complete systematic solution. Through multi-stage heat exchange and process synergy, the waste heat of sintering flue gas is extracted and efficiently converted step by step, thereby improving the energy utilization efficiency of the entire sintering process, reducing carbon emissions, and providing a feasible technical path for the green and low-carbon transformation of the steel industry.

[0026] (2) By integrating four technologies—molten salt thermal energy storage power generation, conventional waste heat boiler power generation, organic Rankine cycle power generation, and plate heat exchanger heating—in series according to flue gas temperature from high to low, this invention constructs a complete cascade energy recovery system. This design ensures that the waste heat from the flue gas in each temperature range is matched with the most suitable energy conversion method, systematically solving the problem of low efficiency of a single recovery mode, realizing the complete utilization of thermal energy from high-grade to near-environmental grade, while producing high-value electricity and hot water.

[0027] (3) To address the bottleneck of low-temperature waste heat recovery in the final stage, a new type of plate heat exchanger plate was invented. This structure synergistically enhances turbulence and heat transfer area at both the micro and macro scales, enabling the heat exchanger to maintain extremely high heat transfer efficiency under low temperature difference conditions, thereby maximizing the recovery of waste heat. Attached Figure Description

[0028] Figure 1This is a flowchart of the present invention.

[0029] Figure 2 This is a schematic diagram of the system of the present invention.

[0030] Figure 3 This is a schematic diagram of the structure of the novel bubble plate heat exchanger of the present invention.

[0031] Figure 4 Front view of the new type of bubbling heat exchange plate;

[0032] Figure 5 This is a front view of the heat exchange bubbling unit;

[0033] Figure 6 This is a side view of the heat exchange bubbling unit;

[0034] Figure 7 This is a schematic diagram showing the flow direction of the working fluid in a novel bubbling heat exchange plate.

[0035] Labeling Explanation: 11. Iron ore sintering system; 12. Dust collector; 13. Exhaust fan; 21. Primary plate heat exchanger; 22. High-temperature solid particle storage tank; 23. Low-temperature solid particle storage tank; 24. Valve; 25. Valve; 26. Valve; 27. Secondary plate heat exchanger; 28. Primary steam turbine; 29. ​​Primary generator; 31. Tertiary plate heat exchanger; 32. Valve; 33. Secondary steam turbine; 34. Secondary generator; 41. Quaternary heat exchanger; 42. Tertiary steam turbine; 43. Liquid storage tank; 44. Condenser; 45. Working fluid pump; 46. Tertiary generator; 51. Fifth stage heat exchanger; 52. Valve; 53. User end; 61. Lower end plate of heat exchanger; 62. Upper end plate of heat exchanger; 63. Heat exchanger base; 64. New type of bubbling heat exchange plate. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1

[0038] like Figure 1 This embodiment provides a gradient flue gas waste heat recovery and utilization system for iron ore sintering. The system includes an iron ore sintering system, a primary solid particle power generation system, a secondary plate heat exchanger power generation system, a tertiary organic Rankine cycle power generation system, and a quaternary plate heat exchanger heat exchange system. These systems are coupled to achieve cascaded utilization of the high-temperature waste heat flue gas generated during the iron ore sintering process.

[0039] The high-temperature flue gas is generated in the iron ore sintering system. The temperature of the generated high-temperature flue gas is 400℃. After being cleaned by the dust collector 12, the high-temperature flue gas is led to the primary solid particle power generation system by the induced draft fan 13.

[0040] The primary solid particle power generation system includes a primary heat exchanger 21, a high-temperature solid particle storage tank 22, a low-temperature solid particle storage tank 23, a secondary heat exchanger 27, a primary steam turbine 28, a primary generator 29, and valves. Flue gas extracted from the iron ore sintering system heats the low-temperature solid particles in the primary heat exchanger 21, after which the particles enter the high-temperature solid particle storage tank 22. The high-temperature solid particles are extracted through valve 24 and undergo heat exchange in the secondary heat exchanger 27. The resulting steam then powers the primary steam turbine 28 and the primary generator 29 to generate electricity. The generated power is used in the iron ore sintering system.

[0041] After passing through the primary solid particle power generation system, the flue gas temperature drops to 330°C and enters the secondary plate heat exchanger power generation system. The secondary plate heat exchanger power generation system includes a tertiary heat exchanger 31, a secondary steam turbine 33, a secondary generator 34, and valves 32. The flue gas undergoes heat exchange in the tertiary heat exchanger 31, generating steam which is then used by the secondary steam turbine 33 and the secondary generator 34 to generate electricity, which is then used in the iron ore sintering system.

[0042] After passing through the two-stage plate heat exchanger power generation system, the flue gas temperature drops to 150°C and enters the three-stage organic Rankine cycle power generation system. The three-stage organic Rankine cycle power generation system includes a four-stage heat exchanger 41, a three-stage steam turbine 42, a three-stage generator 46, a condenser 44, a liquid storage tank 43, and a working fluid pump 45. The flue gas undergoes heat exchange in the four-stage heat exchanger 41, generating steam which is then used by the three-stage steam turbine 42 and the three-stage generator 46 to generate electricity. The generated electricity is used in the iron ore sintering system.

[0043] After passing through the three-stage organic Rankine cycle power generation system, the flue gas temperature drops to 80°C and enters the four-stage plate heat exchanger power generation system. The four-stage plate heat exchanger power generation system includes a five-stage heat exchanger 51 and valves 52. The flue gas completes heat exchange in the five-stage heat exchanger, and the generated hot water is used for heating at the user end 53.

[0044] Example 2

[0045] like Figure 1 This embodiment provides a gradient flue gas waste heat recovery and utilization system for iron ore sintering. The system includes an iron ore sintering system, a primary solid particle power generation system, a secondary plate heat exchanger power generation system, a tertiary organic Rankine cycle power generation system, and a quaternary plate heat exchanger heat exchange system. These systems are coupled to achieve cascaded utilization of the high-temperature waste heat flue gas generated during the iron ore sintering process.

[0046] The high-temperature flue gas is generated in the iron ore sintering system. The temperature of the generated high-temperature flue gas is 450°C. After being cleaned by the dust collector 12, the high-temperature flue gas is led to the primary solid particle power generation system by the induced draft fan 13.

[0047] The primary solid particle power generation system includes a primary heat exchanger 21, a high-temperature solid particle storage tank 22, a low-temperature solid particle storage tank 23, a secondary heat exchanger 27, a primary steam turbine 28, a primary generator 29, and valves. Flue gas extracted from the iron ore sintering system heats the low-temperature solid particles in the primary heat exchanger 21, after which the particles enter the high-temperature solid particle storage tank 22. The high-temperature solid particles are extracted through valve 24 and undergo heat exchange in the secondary heat exchanger 27. The resulting steam then powers the primary steam turbine 28 and the primary generator 29 to generate electricity. The generated power is used in the iron ore sintering system.

[0048] After passing through the primary solid particle power generation system, the flue gas temperature drops to 350°C and enters the secondary plate heat exchanger power generation system. The secondary plate heat exchanger power generation system includes a tertiary heat exchanger 31, a secondary steam turbine 33, a secondary generator 34, and valves 32. The flue gas undergoes heat exchange in the tertiary heat exchanger 31, generating steam which is then used by the secondary steam turbine 33 and the secondary generator 34 to generate electricity. The generated electricity is used in the iron ore sintering system.

[0049] After passing through the two-stage plate heat exchanger power generation system, the flue gas temperature drops to 170°C and enters the three-stage organic Rankine cycle power generation system. The three-stage organic Rankine cycle power generation system includes a four-stage heat exchanger 41, a three-stage steam turbine 42, a three-stage generator 46, a condenser 44, a liquid storage tank 43, and a working fluid pump 45. The flue gas undergoes heat exchange in the four-stage heat exchanger 41, generating steam which is then used by the three-stage steam turbine 42 and the three-stage generator 46 to generate electricity. The generated electricity is used in the iron ore sintering system.

[0050] After passing through the three-stage organic Rankine cycle power generation system, the flue gas temperature drops to 90°C and enters the four-stage plate heat exchanger power generation system. The four-stage plate heat exchanger power generation system includes a five-stage heat exchanger 51 and valves 52. The flue gas completes heat exchange in the five-stage heat exchanger, and the generated hot water is used for heating at the user end 53.

[0051] Example 3

[0052] like Figure 1 This embodiment provides a gradient flue gas waste heat recovery and utilization system for iron ore sintering. The system includes an iron ore sintering system, a primary solid particle power generation system, a secondary plate heat exchanger power generation system, a tertiary organic Rankine cycle power generation system, and a quaternary plate heat exchanger heat exchange system. These systems are coupled to achieve cascaded utilization of the high-temperature waste heat flue gas generated during the iron ore sintering process.

[0053] The high-temperature flue gas is generated in the iron ore sintering system. The temperature of the generated high-temperature flue gas is 500℃. After being cleaned by the dust collector 12, the high-temperature flue gas is led to the primary solid particle power generation system by the induced draft fan 13.

[0054] The primary solid particle power generation system includes a primary heat exchanger 21, a high-temperature solid particle storage tank 22, a low-temperature solid particle storage tank 23, a secondary heat exchanger 27, a primary steam turbine 28, a primary generator 29, and valves. Flue gas extracted from the iron ore sintering system heats the low-temperature solid particles in the primary heat exchanger 21, after which the particles enter the high-temperature solid particle storage tank 22. The high-temperature solid particles are extracted through valve 24 and undergo heat exchange in the secondary heat exchanger 27. The resulting steam then powers the primary steam turbine 28 and the primary generator 29 to generate electricity. The generated power is used in the iron ore sintering system.

[0055] After passing through the primary solid particulate power generation system, the flue gas temperature drops to 370°C and enters the secondary plate heat exchanger power generation system. The secondary plate heat exchanger power generation system includes a tertiary heat exchanger 31, a secondary steam turbine 33, a secondary generator 34, and valves 32.

[0056] The flue gas undergoes heat exchange in the three-stage heat exchanger 31, generating steam which is then used to generate electricity via the two-stage steam turbine 33 and the two-stage generator 34. The generated electricity is used in the iron ore sintering system.

[0057] After passing through the two-stage plate heat exchanger power generation system, the flue gas temperature drops to 190°C and enters the three-stage organic Rankine cycle power generation system. The three-stage organic Rankine cycle power generation system includes a four-stage heat exchanger 41, a three-stage steam turbine 42, a three-stage generator 46, a condenser 44, a liquid storage tank 43, and a working fluid pump 45. The flue gas undergoes heat exchange in the four-stage heat exchanger 41, generating steam which is then used by the three-stage steam turbine 42 and the three-stage generator 46 to generate electricity. The generated electricity is used in the iron ore sintering system.

[0058] After passing through the three-stage organic Rankine cycle power generation system, the flue gas temperature drops to 100°C and enters the four-stage plate heat exchanger power generation system. The four-stage plate heat exchanger power generation system includes a five-stage heat exchanger 51 and valves 52. The flue gas completes heat exchange in the five-stage heat exchanger, and the generated hot water is used for heating at the user end 53.

[0059] like Figure 2 This embodiment provides a novel bubbling plate heat exchanger, which includes a lower end plate 61, an upper end plate 62, a base 63, and novel bubbling heat exchange plates 64.

[0060] like Figure 3This is a schematic diagram illustrating the fluid flow direction in a novel bubbling heat exchange plate. The high-temperature flue gas flow area is located on the bulging side of the plate, flowing in perpendicular to the longitudinal direction of the plate. The heat exchange medium flow area is located on the concave side of the bubbling plate, with the inlet and outlet of the heat exchange medium on the same side as the plate. The fluid flows through four channels to complete the heat exchange process with the high-temperature flue gas.

[0061] like Figure 4 This embodiment provides a novel bubbling heat exchange plate. The heat exchanger plate includes a fluid inlet / outlet area, a flue gas flow area, and a working fluid flow area. The flue gas flow area is located on the raised side of the plate and is composed of raised heat exchange bubbles. The working fluid flow area is located on the recessed side of the plate. The liquid flow area includes four liquid channels to increase the heat exchange flow of the liquid. In this example, the size of the bubbling heat exchange area is 1038*590mm, with 21 bubbles in the horizontal direction and 20 bubbles in the vertical direction. Along the flow direction of the working fluid, the widths of the four channels are 5, 4, 4, and 5 bubbles, respectively. The heat exchange bubbles are tilted at a certain angle, with the first two channels tilting to the right and the last two channels tilting to the left, making the entire bubbling area form a "V" shape.

[0062] like Figure 5 This embodiment provides a novel heat exchange bubble shape, with the bubbles exhibiting three different tilt angles. The bubbles tilt left and right at 45° angles, and are elliptical in shape, with a major axis of 15mm and a minor axis of 9mm. A certain height of "X"-shaped ridges converges on the bubble, with a width of 5mm. The longitudinal spacing between each bubble is 52mm, and the transverse spacing is 28mm. Figure 6 The height of the bubble is 3.75 mm, the height of the "X" shaped edge is lower than the height of the bubble, and the thickness of the plate is 0.8 mm.

[0063] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A cascade flue gas waste heat recovery and utilization system for iron ore sintering, characterized in that, It includes an iron ore sintering system (11), a primary solid particle power generation system, a secondary plate heat exchanger power generation system, a tertiary organic Rankine cycle power generation system and a quaternary plate heat exchanger heat exchange system connected in sequence. The iron ore sintering system (11) is used to generate high-temperature flue gas; The primary solid particle power generation system includes a primary plate heat exchanger (21), a high-temperature solid particle storage tank (22), a low-temperature solid particle storage tank (23), and a secondary plate heat exchanger (27), which are used to recover the high-temperature section waste heat of the high-temperature flue gas and generate electricity. The secondary plate heat exchanger power generation system includes a tertiary plate heat exchanger (31) for recovering the waste heat of the medium and high temperature section of the flue gas after heat exchange in the primary solid particle power generation system and generating electricity. The three-stage organic Rankine cycle power generation system includes a four-stage heat exchanger (41) for recovering the waste heat of the flue gas in the medium and low temperature section after heat exchange in the two-stage plate heat exchanger power generation system and generating electricity. The four-stage plate heat exchanger system includes a five-stage heat exchanger (51) for recovering the low-temperature waste heat of the flue gas after heat exchange in the three-stage organic Rankine cycle power generation system to generate heat.

2. The system according to claim 1, characterized in that, The flue gas outlet of the iron ore sintering system (11) is connected in sequence to a dust collector (12) and an induced draft fan (13), and the outlet of the induced draft fan (13) is connected to the inlet of the first-stage plate heat exchanger (21) of the first-stage solid particle power generation system.

3. The system according to claim 1, characterized in that, The primary solid particle power generation system also includes a primary steam turbine (28) and a primary generator (29); the solid particle side outlet of the primary plate heat exchanger (21) is connected to the inlet of the high-temperature solid particle storage tank (22), the outlet of the high-temperature solid particle storage tank (22) is connected to the solid particle side inlet of the secondary plate heat exchanger (27) through a valve (24), the steam outlet of the secondary plate heat exchanger (27) is connected to the inlet of the primary steam turbine (28), the primary steam turbine (28) is connected to the primary generator (29), the solid particle side outlet of the secondary plate heat exchanger (27) is connected to the inlet of the low-temperature solid particle storage tank (23), and the outlet of the low-temperature solid particle storage tank (23) is connected to the solid particle side inlet of the primary plate heat exchanger (21) through valves (25, 26).

4. The system according to claim 1, characterized in that, The secondary plate heat exchanger power generation system also includes a secondary steam turbine (33) and a secondary generator (34); the steam outlet of the tertiary plate heat exchanger (31) is connected to the inlet of the secondary steam turbine (33), and the secondary steam turbine (33) is connected to the secondary generator (34).

5. The system according to claim 1, characterized in that, The three-stage organic Rankine cycle power generation system also includes a three-stage steam turbine (42), a three-stage generator (46), a condenser (44), a liquid storage tank (43), and a working fluid pump (45); the organic working fluid steam outlet of the four-stage heat exchanger (41) is connected to the inlet of the three-stage steam turbine (42), the three-stage steam turbine (42) is connected to the three-stage generator (46), the outlet of the three-stage steam turbine (42) is connected to the inlet of the condenser (44), the outlet of the condenser (44) is connected to the inlet of the liquid storage tank (43), and the outlet of the liquid storage tank (43) is connected to the organic working fluid inlet of the four-stage heat exchanger (41) through the working fluid pump (45).

6. The system according to claim 1, characterized in that, The fifth-stage heat exchanger (51) of the four-stage plate heat exchanger system is a new type of bubbling plate heat exchanger.

7. A plate heat exchanger for use in any one of claims 1-6, characterized in that, It includes an upper end plate (62) of the heat exchanger, a lower end plate (61) of the heat exchanger, a heat exchanger base (63) and a novel bubbling heat exchange plate (64) disposed between the upper end plate (62) and the lower end plate (61).

8. The plate heat exchanger according to claim 7, characterized in that, The novel bubbling heat exchange plate (64) includes: The fluid inlet and outlet areas are located at the same end of the plate; The flue gas flow zone, located on the side of the plate bubble protrusion, is composed of multiple inclined heat exchange bubbles; The heat exchange medium flow zone, located on the side below the bubbling depression of the plate, is divided into multiple flow channels.

9. The plate heat exchanger according to claim 8, characterized in that, Along the flow direction of the heat exchange medium, the tilt direction of the heat exchange bubbles changes, so that the bubble area is arranged in a "V" shape.

10. The plate heat exchanger according to claim 8 or 9, characterized in that, The heat exchange bubble is provided with a raised "X" shaped ridge, the height of which is lower than the height of the heat exchange bubble 7.

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