Flue gas cascade cooling system and cooling method

Abstract

The invention discloses a flue gas cascade cooling system and method.The flue gas cascade cooling system comprises a spray cooling tower, a mixing tank and a plurality of spray cooling mechanisms, the spray cooling tower comprises a plurality of spray areas which are sequentially arranged at intervals in the flue gas flow direction, and the spray cooling mechanisms are connected with the spray tower; the plurality of spray cooling mechanisms and the plurality of spray areas are arranged in a one-to-one correspondence manner, so that the temperature of the flue gas sequentially cooled by the plurality of spray cooling mechanisms is reduced to a subzero temperature area, the mixing tank is provided with a mixing inlet and a mixing outlet, the mixing inlet is connected with at least one of the liquid outlets of the plurality of spray areas, and the mixing outlet is connected with at least one of the liquid outlets of the plurality of spray areas. The mixing outlet is connected with at least one of the liquid inlets of the plurality of spraying areas, so that spraying solutions discharged from the liquid outlets of the spraying areas are mixed in the mixing tank and then are introduced into the spraying areas. The flue gas cascade cooling system disclosed by the invention has good spray cooling and dust removal effects on flue gas.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas purification, and in particular to a flue gas cascade cooling system and a cooling method. Background Art

[0002] The large amount of pollutants produced by coal flue gas and incineration flue gas is one of the important factors that endanger the atmospheric environment and human health. In the relevant technology, large units have basically completed the transformation of ultra-low emissions, that is, the emission standards are: SO2≤35mg / Nm3, NOx≤50mg / Nm3, dust≤5mg / Nm3. Although the emission concentration has been controlled to a very low level, the absolute value of pollutant emissions cannot be ignored due to the huge total amount of flue gas emissions. Near-zero emissions of flue gas pollutants are still one of the ultimate goals of clean coal power and incineration.

[0003] In the related art, different spray liquids are used for flue gases of different types or temperatures. However, during the spray cooling process, the concentration of the spray liquid will gradually increase due to the full reaction with the flue gas. When it is directly sprayed with the flue gas, it will lead to poor reaction with the flue gas and gradually worse dust removal effect. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, an embodiment of the present invention provides a flue gas cascade cooling system, which has good spray cooling and dust removal effects on flue gas.

[0005] The flue gas cascade cooling system of the present invention comprises:

[0006] A spray cooling tower, the spray cooling tower comprising a plurality of spray zones arranged in sequence and at intervals along the direction of flue gas flow;

[0007] A plurality of spray cooling mechanisms, each of which is connected to the spray tower, and each of which is arranged in one-to-one correspondence with each of the spray zones, so that the temperature of the flue gas cooled by the plurality of spray cooling mechanisms in sequence drops to a sub-zero temperature zone;

[0008] A mixing tank having a mixing inlet and a mixing outlet, wherein the mixing inlet is connected to at least one of the liquid outlets of the plurality of spraying zones, and the mixing outlet is connected to at least one of the liquid inlets of the plurality of spraying zones, so that the spray solution discharged from the liquid outlet of the spraying zone is mixed in the mixing tank and then introduced into the spraying zone.

[0009] The flue gas step cooling system of the present invention can extract the relatively concentrated spray liquid after reacting with the flue gas in the spray area, mix it with a dilute solution in a mixing tank, and then pass the mixed spray liquid into the spray area for cooling to ensure sufficient reaction between the spray solution and the flue gas, thereby achieving good spray cooling and dust removal effects on the flue gas.

[0010] Optionally, the mixing tank has a cavity, and the mixing tank includes a first mixing element and a second mixing element arranged in the cavity, wherein the first mixing element and the second mixing element sequentially divide the cavity into a plurality of mixing zones along a flow direction of the spray solution.

[0011] The first mixing element is located below the mixing inlet in the height direction of the mixing tank, and the first mixing element has a through hole.

[0012] The second mixing element is a tube body, the lower end of the second mixing element is connected to the bottom wall of the mixing tank, and there is a gap between the lower bottom wall of the second mixing element and the bottom wall of the mixing tank, and there is a gap between the upper end of the second mixing element and the through hole, and the outer peripheral wall of the second mixing element and the hole wall of the through hole.

[0013] Optionally, in a plane orthogonal to the height direction of the mixing tank, the cross-sectional area of ​​the first mixing element gradually decreases in a direction from top to bottom.

[0014] Optionally, the second mixing element has a first section and a second section connected in sequence, the first section is located above the second section, and at least part of the first section passes through the through hole, and the radial dimension of the first section is smaller than the radial dimension of the second section.

[0015] Optionally, the second mixing element further includes a transition section, which is connected between the first section and the second section and is located below the through hole, and in a plane orthogonal to the height direction of the mixing tank, the cross-sectional area of ​​the transition section gradually increases from top to bottom.

[0016] Optionally, the distance from the upper end surface of the first section to the bottom wall of the mixing tank is greater than or equal to the distance from the mixing inlet to the bottom wall of the mixing tank.

[0017] Optionally, the flue gas step cooling system of the present invention further comprises a liquid extraction pipe, a first end of the liquid extraction pipe is connected to the mixing outlet, and a second section of the liquid extraction pipe is disposed in the tube cavity of the second mixing element.

[0018] Optionally, the flue gas step cooling system of the present invention further comprises a liquid extraction component having a liquid extraction inlet and a liquid extraction outlet, wherein the liquid extraction inlet is connected to the mixing outlet, and the liquid extraction outlet is connected to at least one of the liquid inlets of the plurality of spray zones.

[0019] Optionally, the multiple spray cooling mechanisms include a primary spray cooling mechanism, a secondary spray cooling mechanism, a tertiary spray cooling mechanism and a quaternary spray cooling mechanism which are spaced apart in sequence along the flow direction of the flue gas, so that the temperature of the flue gas after being cooled by the primary spray cooling mechanism, the secondary spray cooling mechanism, the tertiary spray cooling mechanism and the quaternary spray cooling mechanism is reduced to a sub-zero temperature zone.

[0020] The flue gas cascade cooling method of the present invention is used in the above-mentioned flue gas cascade cooling system, and the cooling method comprises:

[0021] After dust removal, the flue gas at 80℃~100℃ is cooled to 40℃~45℃ by the first-level spray cooling mechanism.

[0022] Then it is cooled to 30℃~35℃ through the secondary spray cooling mechanism.

[0023] Then it is cooled to 0℃~5℃ through the three-stage spray cooling mechanism.

[0024] Finally, the temperature is cooled to -20°C to -15°C through the four-stage spray cooling mechanism;

[0025] The flue gas discharged from the flue gas outlet of the spray cooling tower is subjected to low-temperature adsorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the flue gas cascade cooling system of the present invention.

[0027] Figure 2 It is a schematic cross-sectional structural diagram of a mixing tank of the flue gas cascade cooling system of the present invention.

[0028] Figure 3 It is a schematic cross-sectional structural diagram of a mixing tank of the flue gas cascade cooling system of the present invention.

[0029] Figure 4 It is a structural schematic diagram of a conveying pipeline assembly of a flue gas cascade cooling system according to an embodiment of the present invention.

[0030] Reference numerals:

[0031] Spray cooling tower 1; first-level spray cooling mechanism 11; second-level spray cooling mechanism 12; third-level spray cooling mechanism 13; fourth-level spray cooling mechanism 14; flue gas inlet 15; flue gas outlet 16;

[0032] Water cooler 2;

[0033] Medium temperature refrigerator 3;

[0034] Low temperature refrigerator 4;

[0035] Mixing tank 5; mixing inlet 50, first mixing element 51; through hole 511; second mixing element 52; first section 521; transition section 522; second section 523; liquid extraction pipe 53;

[0036] Delivery pipeline assembly 6; pipeline body 61; filter screen 62; first butterfly valve 63; water pump 64; check valve 65; second butterfly valve 66. DETAILED DESCRIPTION

[0037] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0038] The flue gas cascade cooling system according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

[0039] like Figure 1-Figure 4 As shown, the flue gas cascade cooling system of the present invention comprises: a spray cooling tower 1, a mixing tank 5 and a plurality of spray cooling mechanisms.

[0040] The spray cooling tower 1 includes a plurality of spray zones arranged in sequence along the direction of flue gas flow. The plurality of spray cooling mechanisms are all connected to the spray tower, and the plurality of spray cooling mechanisms are arranged one-to-one with the plurality of spray zones, so that the temperature of the flue gas cooled by the plurality of spray cooling mechanisms in sequence drops to the sub-zero temperature zone. The mixing tank 5 has a mixing inlet 50 and a mixing outlet, the mixing inlet is connected to at least one of the liquid outlets of the plurality of spray zones, and the mixing outlet is connected to at least one of the liquid inlets of the plurality of spray zones, so that the spray solution discharged from the liquid outlet of the spray zone is mixed in the mixing tank 5 and then passed into the spray zone.

[0041] Optionally, the plurality of spray cooling mechanisms include a primary spray cooling mechanism 11, a secondary spray cooling mechanism 12, a tertiary spray cooling mechanism 13 and a quaternary spray cooling mechanism 14 which are spaced apart in sequence along the flow direction of the flue gas, so that the temperature of the flue gas after being cooled by the primary spray cooling mechanism 11, the secondary spray cooling mechanism 12, the tertiary spray cooling mechanism 13 and the quaternary spray cooling mechanism 14 is reduced to a sub-zero temperature zone.

[0042] Specifically, Figure 1 and Figure 4 As shown, the primary spray cooling mechanism 11, the secondary spray cooling mechanism 12, the tertiary spray cooling mechanism 13 and the quaternary spray cooling mechanism 14 are sequentially arranged from bottom to top. The primary spray cooling mechanism 11 has a smoke inlet 15 for introducing smoke into the primary spray cooling mechanism 11, and the quaternary spray cooling mechanism 144 has a smoke outlet 16 for discharging the cooled smoke.

[0043] The liquid outlet of the first-stage spray cooling mechanism 11 is connected to the liquid inlet of the first-stage spray cooling mechanism 11 and the mixing inlet of the mixing tank through a pipeline, the liquid outlet of the fourth-stage spray cooling mechanism 14 is connected to the mixing inlet of the mixing tank through a pipeline, the mixing outlet of the mixing tank is connected to the liquid replenishing port of the first-stage spray cooling mechanism 11 and the spray liquid inlet of the low-temperature refrigerator 5 through a pipeline, and the spray liquid outlet of the low-temperature refrigerator 5 is connected to the liquid inlet of the fourth-stage spray cooling mechanism 14 through a pipeline.

[0044] It is understandable that, since the temperature in the four-stage spray cooling mechanism 14 is relatively low (-20°C to -15°C), a solution that does not solidify at this temperature, such as a calcium chloride solution, needs to be used in the four-stage spray cooling mechanism 14. Then, in the four-stage spray cooling mechanism 14, after the spray liquid and the flue gas undergo a heat exchange reaction, the water in the flue gas will flow out with the calcium chloride solution, diluting the calcium chloride solution.

[0045] That is to say, the spray liquid of the first-stage spray cooling mechanism 11 can also be a calcium chloride solution, that is, after the spray liquid of the first-stage spray cooling mechanism 11 reacts with the flue gas, since the temperature of the flue gas itself (80°C-100°C) is relatively high, the spray liquid of the first-stage spray cooling mechanism 11 contacts the flue gas, and it is easy to evaporate the water in the spray liquid of the first-stage spray cooling mechanism 11, so that the spray liquid of the first-stage spray cooling mechanism 11 (that is, the concentration of the calcium chloride solution) increases. Therefore, the spray liquid after heat exchange with the flue gas in the first-stage spray cooling mechanism 11 and the spray liquid after heat exchange with the flue gas in the fourth-stage spray cooling mechanism 14 are passed into a mixing tank, and the calcium chloride solution can be mixed so that the concentration of the calcium chloride solution in the mixing tank is lower than that in the first-stage spray cooling mechanism 11, so that it can be used again with the spray liquid of the first-stage spray cooling mechanism 11 and the fourth-stage spray cooling mechanism 14.

[0046] Therefore, the flue gas step cooling system of the present invention can extract the more concentrated spray liquid after reacting with the flue gas in the spray area, mix it with the dilute solution in the mixing tank, and then pass the mixed spray liquid into the spray area for cooling to ensure sufficient reaction between the spray solution and the flue gas, thereby achieving good spray cooling and dust removal effects on the flue gas.

[0047] In addition, if Figure 1 and Figure 4 As shown, the water cooler 2 and the spray liquid outlet of the secondary spray cooling mechanism 12 can be connected through a delivery pipeline assembly 6, and the delivery pipeline assembly 6 includes a pipeline body 61, and a filter 62, a first butterfly valve 63, a water pump 64, a check valve 65, and a second butterfly valve 66 arranged on and along the pipeline body 61. The first butterfly valve 63, the water pump 64, and the second butterfly valve 66 can all be opened or closed by an electric actuator (such as a motor) controller.

[0048] That is, the spray liquid outlet of the secondary spray cooling mechanism 12 can be transported in the direction from the filter screen 62 to the second butterfly valve 66 to improve the transport efficiency of the spray liquid and remove some particulate impurities contained in the spray liquid.

[0049] Preferably, two delivery pipeline assemblies 6 are provided between the secondary water cooler 23 and the spray liquid outlet of the secondary spray cooling mechanism 12, that is, the two delivery pipeline assemblies 6 are arranged in parallel to ensure that when one of the delivery pipeline assemblies 6 is blocked, the other delivery pipeline assembly 6 is started.

[0050] Of course, if Figure 1 and Figure 4 As shown, the medium-temperature refrigerator 3 and the three-stage spray cooling mechanism 13 as well as the low-temperature refrigerator 4 and the four-stage spray cooling mechanism 14 can be connected via a delivery pipeline assembly 6.

[0051] Alternatively, if Figure 2 and Figure 3 As shown, the mixing tank 5 has a cavity, and the mixing tank 5 includes a first mixing piece 51 and a second mixing piece 52 arranged in the cavity. The first mixing piece 51 and the second mixing piece 52 divide the cavity into a plurality of mixing zones in sequence along the flow direction of the spray solution. The first mixing piece 51 is located below the mixing inlet 50 in the height direction of the mixing tank 5, and the first mixing piece 51 has a through hole 511. The second mixing piece 52 is a tube body, and the lower end of the second mixing piece 52 is connected to the bottom wall of the mixing tank 5, and there is a gap between the lower bottom wall of the second mixing piece 52 and the bottom wall of the mixing tank 5, and there is a gap between the upper end of the second mixing piece 52 and the through hole 511, and the outer peripheral wall of the second mixing piece 52 and the hole wall of the through hole 511.

[0052] Specifically, Figure 2 and Figure 3 As shown, the upper surface of the first mixing element 51 and the inner cavity of the mixing tank 5 define a first mixing zone, the outer peripheral wall of the second mixing element 52 located below the through hole 511 and the inner wall of the mixing tank 5 define a second mixing zone, and the tubular cavity of the second mixing element 52 is the third mixing zone.

[0053] It should be noted that the calcium chloride solution discharged from the first-stage spray cooling mechanism 11 is passed into the first mixing zone through the mixing inlet 50, and the calcium chloride solution discharged from the fourth-stage spray cooling mechanism 14 is also passed into the first mixing zone through the mixing inlet 50, thereby mixing the calcium chloride solution with a high concentration (i.e., the calcium chloride solution discharged from the first-stage spray cooling mechanism 11) with the calcium chloride solution with a low concentration (i.e., the calcium chloride solution discharged from the fourth-stage spray cooling mechanism 14).

[0054] It can be understood that the first mixing element 51 can be an annular plate, the outer peripheral wall of which is connected to the inner wall of the mixing tank 5, and the upper end of the second mixing element 52 passes through the central hole of the annular plate (i.e., the through hole 511), so that the spray solution introduced through the mixing inlet 50 is mixed for the first time in the first mixing zone, and the mixed calcium chloride solution flows to the second mixing zone through the through hole 511, and is mixed for the second time in the second mixing zone under the action of gravity. The calcium chloride solution after mixing again flows to the third mixing zone. Since the bottom of the second mixing element 52 is connected to the cavity of the mixing tank 5 (the communicating vessel principle), the liquid level of the calcium chloride solution in the third mixing zone gradually rises, and the third mixing is achieved, so that the calcium chloride solution is fully mixed in the mixing tank 5.

[0055] Optionally, in a plane orthogonal to the height direction of the mixing tank 5, the cross-sectional area of ​​the first mixing element 51 gradually decreases from top to bottom. Figure 2 and Figure 3 As shown, the first mixing element 51 is in the shape of an "inverted frustum".

[0056] Optionally, the second mixing element 52 has a first section 521 and a second section 523 connected in sequence, the first section 521 is located above the second section 523, and at least a portion of the first section 521 passes through the through hole 511, and the radial dimension of the first section 521 is smaller than the radial dimension of the second section 523. It can be understood that the larger the radial dimension of the second section 523, the larger the capacity of the third mixing zone, so that the calcium chloride solution flows from the second mixing zone to the third mixing zone for a longer time, thereby improving the mixing effect.

[0057] Optionally, the second mixing element 52 further includes a transition section 522, which is connected between the first section 521 and the second section 523 and is located below the through hole 511. In a plane orthogonal to the height direction of the mixing tank 5, the cross-sectional area of ​​the transition section 522 gradually increases from top to bottom.

[0058] It is understandable that if Figure 2 and Figure 3 As shown, the transition section 522 is generally in the shape of a "frustum".

[0059] Optionally, the distance from the upper end surface of the first section 521 to the bottom wall of the mixing tank 5 is greater than or equal to the distance from the mixing inlet 50 to the bottom wall of the mixing tank 5. In other words, the spray solution flowing into the cavity through the mixing inlet 50 will flow to the first mixing zone under the action of gravity, thereby preventing the spray liquid from flowing from the upper port of the second mixing element 52 into the third mixing zone, so as to ensure that the spray solution can be fully mixed.

[0060] Optionally, the flue gas step cooling system of the present invention further includes a liquid extraction pipe 53 , a first end of the liquid extraction pipe 53 is connected to the mixing outlet, and a second section 523 of the liquid extraction pipe 53 is disposed in the tube cavity of the second mixing element 52 .

[0061] Optionally, the flue gas cascade cooling system of the present invention further includes a liquid extraction component (not shown in the figure), the liquid extraction component has a liquid extraction inlet and a liquid extraction outlet, the liquid extraction inlet is connected to the mixing outlet, and the liquid extraction outlet is connected to at least one of the liquid inlets of the plurality of spraying zones. It is understandable that the liquid extraction component can be a water pump to extract the mixed spray solution in the mixing tank 5.

[0062] The flue gas step cooling method of the present invention is described below.

[0063] The flue gas cascade cooling method of the present invention is used for the above-mentioned flue gas cascade cooling system, and the cooling method comprises:

[0064] After dust removal, the flue gas at 80℃~100℃ is cooled to 40℃~45℃ by the first-level spray cooling mechanism, then cooled to 30℃~35℃ by the second-level spray cooling mechanism, then cooled to 0℃~5℃ by the third-level spray cooling mechanism, and finally cooled to -20℃~-15℃ by the fourth-level spray cooling mechanism; the flue gas discharged from the flue gas outlet of the spray cooling tower is subjected to low-temperature adsorption.

[0065] It can be understood that when the flue gas enters the primary spray cooling mechanism from the flue gas inlet of the spray cooling tower, the spray liquid in the primary spray cooling mechanism can reduce the flue gas from 80℃ to 100℃ to 40℃ to 45℃, that is, the flue gas at 40℃ to 45℃ is passed from the primary spray cooling mechanism to the secondary spray cooling mechanism. Among them, the temperature of the spray liquid after heat exchange with the flue gas in the primary spray cooling mechanism is about 52℃, and the spray liquid discharged from the liquid outlet of the primary spray cooling mechanism is cooled to about 42℃ by the spray liquid discharged from the mixing tank, so as to be passed into the primary spray cooling mechanism again for heat exchange with the flue gas.

[0066] Similarly, the spray liquid in the secondary spray cooling mechanism can reduce the flue gas from 40℃~45℃ to 30℃~35℃, and the water cooler 2 can reduce the spray liquid (about 42℃) discharged from the liquid outlet of the secondary spray cooling mechanism to about 32℃, so that it can be passed into the secondary spray cooling mechanism again for heat exchange with the flue gas; the spray liquid in the tertiary spray cooling mechanism can reduce the flue gas from 30℃~35℃ to 0℃~5℃, and the medium-temperature refrigerator 3 can reduce the spray liquid (about 12℃) discharged from the liquid outlet of the tertiary spray cooling mechanism to about 2℃, so that it can be passed into the tertiary spray cooling mechanism again for heat exchange with the flue gas; the spray liquid in the quaternary spray cooling mechanism can reduce the flue gas from 0℃~5℃ to -20℃~-15℃, and the low-temperature refrigerator 4 can reduce the spray liquid (about 8℃) discharged from the liquid outlet of the quaternary spray cooling mechanism to about -18℃, so that it can be passed into the quaternary spray cooling mechanism again for heat exchange with the flue gas.

[0067] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0068] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0069] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0070] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0071] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0072] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A flue gas cascade cooling system, characterized in that: include: A spray cooling tower, the spray cooling tower comprising a plurality of spray zones arranged in sequence and at intervals along the direction of flue gas flow; A plurality of spray cooling mechanisms, each of which is connected to the spray tower, and each of which is arranged in one-to-one correspondence with each of the spray zones, so that the temperature of the flue gas cooled by the plurality of spray cooling mechanisms in sequence drops to a sub-zero temperature zone; A mixing tank having a mixing inlet and a mixing outlet, wherein the mixing inlet is connected to at least one of the liquid outlets of the plurality of spraying zones, and the mixing outlet is connected to at least one of the liquid inlets of the plurality of spraying zones, so that the spray solution discharged from the liquid outlet of the spraying zone is mixed in the mixing tank and then introduced into the spraying zone.

2. The flue gas cascade cooling system according to claim 1, characterized in that: The mixing tank has a cavity, and includes a first mixing element and a second mixing element disposed in the cavity, wherein the first mixing element and the second mixing element sequentially divide the cavity into a plurality of mixing zones along the flow direction of the spray solution. The first mixing element is located below the mixing inlet in the height direction of the mixing tank, and the first mixing element has a through hole. The second mixing element is a tube body, the lower end of the second mixing element is connected to the bottom wall of the mixing tank, and there is a gap between the lower bottom wall of the second mixing element and the bottom wall of the mixing tank, and there is a gap between the upper end of the second mixing element and the through hole, and the outer peripheral wall of the second mixing element and the hole wall of the through hole.

3. The flue gas cascade cooling system according to claim 2, characterized in that: In a plane orthogonal to the height direction of the mixing tank, the cross-sectional area of ​​the first mixing element gradually decreases from top to bottom.

4. The flue gas cascade cooling system according to claim 2, characterized in that: The second mixing element comprises a first section and a second section connected in sequence, the first section is located above the second section, and at least a portion of the first section passes through the through hole, and a radial dimension of the first section is smaller than a radial dimension of the second section.

5. The flue gas cascade cooling system according to claim 4, characterized in that: The second mixing element also includes a transition section, which is connected between the first section and the second section and is located below the through hole. In a plane orthogonal to the height direction of the mixing tank, the cross-sectional area of ​​the transition section gradually increases from top to bottom.

6. The flue gas cascade cooling system according to claim 5, characterized in that: The distance from the upper end surface of the first section to the bottom wall of the mixing tank is greater than or equal to the distance from the mixing inlet to the bottom wall of the mixing tank.

7. The flue gas cascade cooling system according to any one of claims 2 to 5, characterized in that: It also includes a liquid extraction tube, a first end of which is connected to the mixing outlet, and a second section of which is placed in the tube cavity of the second mixing element.

8. The flue gas cascade cooling system according to claim 7, characterized in that: It also includes a liquid pumping component, which has a liquid pumping inlet and a liquid pumping outlet. The liquid pumping inlet is connected to the mixing outlet, and the liquid pumping outlet is connected to at least one of the liquid inlets of the plurality of spraying areas.

9. The flue gas cascade cooling system according to claim 8, characterized in that: The multiple spray cooling mechanisms include a primary spray cooling mechanism, a secondary spray cooling mechanism, a tertiary spray cooling mechanism and a quaternary spray cooling mechanism which are distributed in sequence along the flue gas flow direction, so that the temperature of the flue gas after being cooled by the primary spray cooling mechanism, the secondary spray cooling mechanism, the tertiary spray cooling mechanism and the quaternary spray cooling mechanism is reduced to a sub-zero temperature zone.

10. A flue gas step cooling method, characterized in that: The cooling method is used for the flue gas cascade cooling system according to claim 9, and the cooling method comprises: After dust removal, the flue gas at 80℃~100℃ is cooled to 40℃~45℃ by the first-level spray cooling mechanism. Then it is cooled to 30℃~35℃ through the secondary spray cooling mechanism. Then it is cooled to 0℃~5℃ through the three-stage spray cooling mechanism. Finally, the temperature is cooled to -20°C to -15°C through the four-stage spray cooling mechanism; The flue gas discharged from the flue gas outlet of the spray cooling tower is subjected to low-temperature adsorption.

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