Flue gas denitration ammonia injection mixer and denitration system

Abstract

The application discloses a flue gas denitration ammonia injection mixer and a denitration system. The mixer is arranged in a flue and comprises a plurality of ammonia injection mixing assemblies arranged side by side. The ammonia injection mixing assembly comprises two or more variable-diameter pipes arranged side by side, and a hollow structure formed by sealing the area between the variable-diameter pipes. The variable-diameter pipe is a tubular structure with a thin middle and thick ends. An ammonia gas distribution pipe is in communication with the hollow structure at one end and extends to the flue gas inlet end of each variable-diameter pipe at the other end, and is in communication with a plurality of branch pipes, with the flue gas inlet end of each variable-diameter pipe corresponding to at least one branch pipe. An ammonia gas nozzle is arranged at the end of each branch pipe. The ammonia injection mixer of the application overcomes the problems of the prior art, such as the fact that the ammonia injection mixing system cannot be applied to the denitration reconstruction of old boilers due to the large installation height, the blockage of the nozzle of the ammonia injection pipe leading to the increase of ammonia escape and the blockage of downstream equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flue gas denitration technology, and particularly relates to a flue gas denitration ammonia injection mixer and a denitration system. BACKGROUND

[0002] Among the existing flue gas denitration methods, the most widely used at home and abroad at present is the selective catalytic reduction (SCR) technology. The main principle of the SCR technology is to inject a reducing agent ammonia into flue gas at 280 DEG C to 450 DEG C and mix it uniformly, under the action of a catalyst, NH3 reduces NOx in the flue gas into non-toxic and non-polluting nitrogen and water, thereby achieving the purpose of removing NOx from the mixed gas.

[0003] GB / T34339-2017 "Flue Gas Denitration Ammonia Injection Mixing System" divides the ammonia injection mixing system into an ammonia injection grid (AIG) and an ammonia injection static mixer. The definition of the AIG is a spraying device in the form of a grid pipeline for injecting ammonia into a flue, including an ammonia injection pipeline, a nozzle, a support and accessories. The definition of the ammonia injection static mixer is a device that uses certain fixed components to change the flow state of ammonia and flue gas so as to achieve full mixing, thereby obtaining higher NH3 / NOx mixing efficiency. Typical ammonia injection static mixers have vortex, swirl, longitudinal vortex and V-shaped structural forms. In the existing ammonia injection mixing system, the ammonia injection grid and the ammonia injection static mixer need a certain installation height in the flue to ensure the ammonia injection mixing effect. However, the idle installation height / space in the old boiler that has been in operation for many years is limited, and the existing ammonia injection grid and ammonia injection static mixer are difficult to be applied to the denitration modification thereof.

[0004] During the operation of the SCR denitration device, the nozzle of the ammonia injection pipe often gets blocked, which causes the poor uniformity of the ammonia nitrogen molar ratio distribution at the inlet of the catalyst of the SCR reactor, the increase of local ammonia escape, and the leakage or serious blockage of the downstream air preheater or coal economizer and other equipment, thereby threatening the safe and economic operation of the boiler / device. If there is a wet flue gas desulfurization device downstream, it will cause the unqualified gypsum product or the excessive ammonia nitrogen in the desulfurization wastewater. The escaped ammonia discharged into the atmosphere will cause secondary pollution.

[0005] The reasons for the nozzle blockage caused by dust mainly include two aspects: one is that the dust accumulates and forms a bridge at the edge of the ammonia nozzle to block the nozzle, and the other is that the dust accumulated on the flue or components above the ammonia nozzle collapses and falls to block the nozzle. In recent years, affected by factors such as the slowing down of economic growth and the increasing pressure of environmental protection, the utilization hours of coal-fired units, heating furnaces, incinerators and waste heat boilers have been continuously reduced, and they have been in long-term low-load operation. As a result, the flue gas volume is reduced, the ammonia injection volume is also reduced, and the ammonia injection volume is also greatly reduced. At this time, the dust is more likely to accumulate and form a bridge at the edge of the nozzle, and even fall into the nozzle.

[0006] CN113083013A discloses a method and system for preventing ammonia injection grid from being blocked in urea ammonia production process, which uses steam to purge the ammonia injection pipeline; CN212942296U discloses a blocking prevention type ammonia injection device for a coal-fired power plant denitration system, which uses compressed air purging to prevent the nozzle from being blocked. However, the above-mentioned scheme of setting a purging pipeline on the ammonia injection pipe to solve the nozzle blockage problem cannot blow open the blocked nozzle because the steam / compressed air basically enters the flue through the unblocked nozzles when the purging pipeline is purged.

[0007] The information disclosed in this BACKGROUND section is only for the purpose of increasing the understanding of the general background of the application and should not be taken as admitting that the information forms the prior art that is already known to those of ordinary skill in the art. SUMMARY

[0008] In view of the deficiencies of the prior art, the purpose of the present application is to provide a flue gas denitration ammonia injection mixer and a denitration system to overcome the problems of the prior art, such as the large installation height of the ammonia injection mixing system which cannot be applied to the denitration modification of old boilers, the blockage of the nozzles of the ammonia injection pipe which leads to an increase in ammonia escape and causes blockage of downstream equipment, etc.

[0009] The present application provides a flue gas denitration ammonia injection mixer, which is arranged in a flue and comprises a plurality of ammonia injection mixing assemblies arranged side by side.

[0010] The ammonia injection mixing assembly comprises two or more variable diameter pipes arranged in the vertical direction of the flue cross section, and the area between the variable diameter pipes is closed to form a hollow structure; the variable diameter pipes are tubular structures with thin middle and thick ends; one end of the variable diameter pipe is a flue gas inlet end, and the other end is a flue gas outlet end.

[0011] An ammonia gas inlet pipe is connected to the hollow structure for introducing ammonia gas into the hollow structure.

[0012] An ammonia gas distribution pipe is connected to the hollow structure at one end and extends to the flue gas inlet end of each variable diameter pipe at the other end, and is connected to a plurality of branch pipes, preferably 2-16 branch pipes; the flue gas inlet end of each variable diameter pipe corresponds to at least one branch pipe, and preferably the number of branch pipes corresponding to the flue gas inlet end of each variable diameter pipe is the same.

[0013] An ammonia gas nozzle is installed at the end of each branch pipe, and the direction of the ammonia gas nozzle is the same as the flow direction of the flue gas.

[0014] It should be further noted that the adjacent two ammonia injection mixing assemblies can be not connected to each other, or the hollow structures of the two ammonia injection mixing assemblies can be connected to each other through a connecting pipe.

[0015] Further, in the above technical solution, the variable diameter pipe is preferably a Laval pipe structure or a Venturi structure.

[0016] Further, in the above technical solution, the variable-diameter pipe is a Laval pipe structure, including a reduced-diameter section and an expanded-diameter section, and the cross-sectional shape of the lower end surface of the reduced-diameter section and the upper end surface of the expanded-diameter section includes a circle, an ellipse, a square, and a rectangle.

[0017] Further, in the above technical solution, the variable-diameter pipe is a Venturi structure, including a reduced-diameter section, a straight pipe section, and an expanded-diameter section, and the shapes of the reduced-diameter section and the expanded-diameter section include a hollow trapezoidal body, a quadrangular frustum body, a circular frustum body, and a geometric body with a circular upper part and a square lower part or a square upper part and a circular lower part.

[0018] Further, in the above technical solution, the lower end surface of the reduced-diameter section of the variable-diameter pipe is connected with an inlet straight pipe section for rectifying the flue gas entering the variable-diameter pipe.

[0019] Further, in the above technical solution, the upper end surface of the expanded-diameter section of the variable-diameter pipe is connected with an outlet straight pipe section for rectifying the flue gas leaving the variable-diameter pipe.

[0020] Further, in the above technical solution, a turbulence element is arranged above the expanded-diameter section or the outlet straight pipe section of the variable-diameter pipe for forming a vortex on the back surface of the turbulence element to strengthen the mixing of ammonia gas and flue gas.

[0021] In the flue gas denitration ammonia injection mixer of the present application, a dust blocking element is preferably arranged above the ammonia gas nozzle to shield the falling dust above the ammonia gas nozzle and avoid blocking the ammonia gas nozzle.

[0022] Further, the dust blocking element is a floating element, which floats away from the ammonia gas nozzle under the blowing action of the gas when the ammonia gas nozzle sprays gas, and falls to shield the ammonia gas nozzle under the action of its own gravity when the ammonia gas nozzle does not spray gas.

[0023] According to a second aspect of the present application, the present application provides a flue gas denitration ammonia injection mixing system, comprising:

[0024] an ammonia injection assembly, which includes an ammonia injection main pipe provided with a main pipe flow adjusting valve;

[0025] a plurality of ammonia injection sub-pipes connected with the ammonia injection main pipe and connected with the hollow structure through the ammonia gas inlet pipe of the ammonia injection mixing assembly;

[0026] the ammonia injection mixer of any one of the above technical solutions;

[0027] a denitration unit arranged downstream of the ammonia injection mixer, including at least one layer of denitration catalyst.

[0028] Further, in the above technical solution, an ammonia-air mixer is arranged on the ammonia injection main pipe or the ammonia injection sub-pipe, the ammonia-air mixer is connected with a dilution air pipe line, and is used to mix ammonia gas with dilution air to make the ammonia concentration in the ammonia-air mixed gas sprayed into the flue far away from the explosion limit.

[0029] Further, in the technical scheme, the dilution air pipeline branch is a dilution air main pipe and a dilution air branch pipe, the dilution air in the dilution air main pipe is used for diluting the ammonia gas concentration to below the explosion limit; as long as the flue gas flows through the flue, the valve on the dilution air branch pipe is in an open state, so that the ammonia gas nozzle always has gas sprayed out, and the ammonia gas nozzle is prevented from being blocked.

[0030] Further, in the technical scheme, a flow guide component and a flow rectifying grid are arranged between the flue gas denitration ammonia injection mixer and the first layer of denitration catalyst, the flow guide component is arranged at a turning position of the flue, and is used for turning the upward flue gas to downward flue gas entering the denitration unit; the flow rectifying grid is arranged at the upper part of the first layer of catalyst along the flue gas flow direction, and is used for rectifying the flue gas passing through the denitration catalyst.

[0031] The working process of the flue gas denitration ammonia injection mixer of the present application includes the following contents: ammonia gas or ammonia-air mixed gas enters the hollow structure through the ammonia gas inlet pipe, and then is sprayed into the reducing pipe from the ammonia gas nozzle through the branch pipe from the ammonia gas distribution pipe, and is mixed with the flue gas flowing through the reducing pipe; further, when the upper part of the reducing pipe is provided with a flow disturbing element, the flue gas and the ammonia gas pass through the flow disturbing element, and vortexes are formed at the back of the flow disturbing element, thereby strengthening the mixing of the ammonia gas and the flue gas; further, when the upper part of the ammonia gas nozzle is provided with a dust blocking element, the flow velocity and flow direction of the ammonia gas or ammonia-air mixed gas sprayed out from the ammonia gas nozzle are changed after passing through the dust blocking element, which is beneficial to the dispersion of the ammonia gas in the flue gas and strengthens the mixing of the ammonia gas and the flue gas; further, when the dust blocking element is a floating element, the smaller the flow of the ammonia gas or ammonia-air mixed gas, the closer the distance between the dust blocking element and the ammonia gas nozzle, and the larger the cross-sectional area of the diffusion of the ammonia gas or ammonia-air mixed gas after passing through the dust blocking element, thereby ensuring the mixing effect with the flue gas when the flue gas amount is low and the flow of the ammonia gas or ammonia-air mixed gas is low at low load of the boiler.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] 1. The conventional flue gas SCR denitration flue needs to be provided with an ammonia injection grid and an ammonia injection static mixer, but the present application only needs to be provided with an ammonia injection mixer, thereby significantly reducing the required installation height in the flue, and is particularly suitable for denitration modification of old boilers that have been operated for many years; the ammonia injection mixer of the present application replaces the conventional ammonia injection grid and ammonia injection static mixer, the required equipment weight added in the flue is greatly reduced, at the same time, the boiler foundation and frame do not need to be modified or only need to be reinforced, and is particularly suitable for denitration modification of old boilers that have been operated for many years, at the same time, the required investment is also reduced, thereby significantly increasing the market competitiveness.

[0034] 2、The present application is provided with a dust blocking element above the ammonia nozzle, which can block the dust falling above the nozzle to avoid blocking the ammonia nozzle; further, when the boiler or device is stopped, the denitration system is stopped, the dust blocking element falls to block the ammonia nozzle, at this time, the dust in the flue can be effectively prevented from blocking the ammonia nozzle when the dust falls due to cleaning or flue vibration. The present application adopts the above measures to avoid the scaling and blocking of the ammonia nozzle, which can effectively ensure that the ammonia nozzle is always in a normal working state, thereby ensuring the precise control of the partitioned ammonia injection of the flue gas SCR denitration system, ensuring the uniformity of the ammonia nitrogen molar ratio distribution in each ammonia injection partition, avoiding local ammonia escape, thereby avoiding problems such as leakage or blocking of downstream air preheaters or coal economizers, unqualified gypsum products, ammonia nitrogen exceeding standard in desulfurization wastewater, and secondary pollution caused by escaped ammonia entering the atmosphere, and effectively prolonging the operation cycle of the device.

[0035] 3、In the present application, the dilution air for ammonia is divided into two paths, the dilution air in the main dilution air pipeline is used to dilute the ammonia concentration to below the explosion limit, and the dilution air in the branch dilution air pipeline is used to prevent the ammonia nozzle from being blocked. As long as there is flue gas in the flue, there is dilution air in the branch dilution air pipeline, so the ammonia injection branch and the ammonia nozzle are both passed through by gas. In the case that the flue gas NOx concentration is lower than the emission standard and the SCR denitration system does not inject ammonia, the ammonia nozzle can be effectively prevented from being blocked by dust in the flue gas. Combined with the dust blocking element or / and the flow disturbing element, both the nozzle blocking from the equipment structure and the nozzle blocking from the process operation can be avoided, thereby avoiding a series of problems caused by nozzle blocking.

[0036] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application and can be implemented according to the content of the specification, at the same time, in order to make the above and other purposes, technical features and advantages of the present application more easily understood, one or more preferred embodiments are listed below, and are described in detail as follows with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a front view of a structure of a ammonia injection mixing assembly (venturi structure) of the present application.

[0038] Figure 2 It is a front view of a structure of a ammonia injection mixing assembly (venturi structure) of the present application. Figure 1 It is a front view of a structure of a ammonia injection mixing assembly (venturi structure) of the present application.

[0039] Figure 3 It is a front view of a structure of a ammonia injection mixing assembly (venturi structure) of the present application. Figure 1 It is a front view of a structure of a ammonia injection mixing assembly (venturi structure) of the present application.

[0040] Figure 4 It is a front view of a structure of a ammonia injection mixing assembly (venturi structure) of the present application. Figure 1 It is a front view of a structure of a ammonia injection mixing assembly (venturi structure) of the present application.

[0041] Figure 5Front view of a structure of an ammonia injection mixing assembly (Laval tube structure) of the present application.

[0042] Figure 6 For Figure 5 Structure left view of the ammonia injection mixing assembly.

[0043] Figure 7 For Figure 5 Structure top view of the ammonia injection mixing assembly.

[0044] Figure 8 For Figure 5 Structure bottom view of the ammonia injection mixing assembly.

[0045] Figure 9 Front view of a structure of an ammonia injection mixing assembly (Venturi structure) of the present application.

[0046] Figure 10 For Figure 9 Structure left view of the ammonia injection mixing assembly.

[0047] Figure 11 For Figure 9 Structure top view of the ammonia injection mixing assembly.

[0048] Figure 12 For Figure 9 Structure bottom view of the ammonia injection mixing assembly.

[0049] Figure 13 Schematic diagram of a flue gas denitration ammonia injection mixing system of the present application.

[0050] Figure 14 Front view of a structure of an ammonia injection mixer of the flue gas denitration ammonia injection mixing system of the present application (Laval tube structure).

[0051] Figure 15 Front view of a structure of an ammonia injection mixer of the flue gas denitration ammonia injection mixing system of the present application (Venturi structure).

[0052] Explanation of main reference numerals:

[0053] 10 - reducer, 10A - reduced diameter section, 10B - straight pipe section, 10C - expanded diameter section, 10D - inlet straight pipe section, 10E - outlet straight pipe section, 10F - turbulence element, 10G - fixed support, 10H - screen hole;

[0054] 11 - ammonia inlet pipe, 12 - ammonia nozzle, 13 - ammonia distribution pipe, 14 - dust blocking element, 15A - fixed rod, 15B - limiting piece, 16 - hollow structure, 17 - branch pipe;

[0055] 31 - ammonia injection main, 32 - ammonia injection header, 33 - ammonia air mixer, 34 - dilution air line, 34A - dilution air main, 34B - dilution air branch, 35 - header flow regulating valve, 36 - branch flow regulating valve;

[0056] 100 - ammonia injection mixer, 200 - flue, 400 - flow guide assembly, 500 - rectifier grid, 600 - denitration unit, 601 - denitration catalyst. DETAILED DESCRIPTION

[0057] The specific embodiments of the present application will now be described in detail with reference to the accompanying drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the application, are given by way of illustration only, since various changes and modifications within the spirit and scope of the application will become apparent to those skilled in the art from this detailed description.

[0058] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an overly literal sense unless expressly so defined herein.

[0059] In this document, relational terms such as "first" and "second", and the like, can be used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. The use of the terms "first" and "second" does not imply that these elements must be in a given order - both elements could be first, depending on the context in which they are used.

[0060] The spatially relative terms "under", "below", "lower", "over", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. For example, if a device described is turned over in use, a

[0061] The terms "first", "second", and the like, herein do not imply a specific order, unless otherwise specified. In other words, a first element or feature before a second element or feature can mean that the first element or feature occurs before the second element or feature, or that the second element or feature occurs before the first element or feature.

[0062] As Figures 1-15As shown, the present application provides a flue gas denitration ammonia injection mixer 100, which is arranged in a flue 200, comprising a plurality of side-by-side ammonia injection mixing assemblies; the ammonia injection mixing assembly comprises: two or more side-by-side variable diameter pipes 10, the area between the variable diameter pipes 10 is closed to form a hollow structure 16; the variable diameter pipe 10 is a tubular structure with thin middle and thick ends; one end of the variable diameter pipe 10 is a flue gas inlet end, and the other end is a flue gas outlet end; an ammonia gas inlet pipe 11 which communicates with the hollow structure 16 for introducing ammonia gas into the hollow structure 16; an ammonia gas distribution pipe 13, one end of which communicates with the hollow structure 16, and the other end extends to the flue gas inlet end of each variable diameter pipe 10, and communicates with a plurality of branch pipes 17, preferably 2-16, and the flue gas inlet end of each variable diameter pipe 10 corresponds to at least one branch pipe 17, and preferably the number of branch pipes 17 corresponding to the flue gas inlet end of each variable diameter pipe 10 is the same; an ammonia gas nozzle 12 installed at the end of each branch pipe 17, and the direction of the ammonia gas nozzle 12 is the same as the flow direction of the flue gas.

[0063] It should be further pointed out that the adjacent two ammonia injection mixing assemblies can be disconnected from each other, or the hollow structures 16 can be connected to each other through connecting pipes, which is not embodied in the drawings and examples.

[0064] Further, in one or more exemplary embodiments of the present application, the variable diameter pipe 10 is preferably a Laval pipe structure or a Venturi structure.

[0065] Further, as shown in Figures 5-8 , the variable diameter pipe 10 is a Laval pipe structure, comprising a reduced diameter section 10A and an expanded diameter section 10C, and the cross-sectional shape of the lower end surface of the reduced diameter section 10A and the upper end surface of the expanded diameter section 10C can be circular, oval, square, rectangular, but the present application is not limited thereto.

[0066] Further, as shown in Figures 1-4 , 9-12, the variable diameter pipe 10 is a Venturi structure, comprising a reduced diameter section 10A, a straight pipe section 10B and an expanded diameter section 10C, and the shapes of the reduced diameter section 10A and the expanded diameter section 10C can be hollow trapezoidal bodies, four-prism bodies, circular truncated cone bodies, geometric bodies with upper circle and lower square or upper square and lower circle, but the present application is not limited thereto.

[0067] Further, as shown in Figures 5-6 , 9-10, the lower end surface of the reduced diameter section 10A of the variable diameter pipe 10 is connected with an inlet straight pipe section 10D for straightening the flue gas entering the variable diameter pipe 10, especially the flow direction of the flue gas in the local area downstream of the flue elbow and the flue variable diameter section will be chaotic, and the inlet straight pipe section 10D helps to straighten the flue gas and make its flow consistent.

[0068] Further, as shown in Figures 9-10As shown, the upper end face of the expanding section 10C of the reducing pipe 10 is connected with an outlet straight pipe section 10E, which is used to rectify the flue gas leaving the reducing pipe 10.

[0069] Further, as shown, the upper end face of the expanding section 10C of the reducing pipe 10 is connected with an outlet straight pipe section 10E, which is used to rectify the flue gas leaving the reducing pipe 10. Figures 5-12 Figures 5-8 Further, as shown, the upper end face of the expanding section 10C of the reducing pipe 10 is connected with an outlet straight pipe section 10E, which is used to rectify the flue gas leaving the reducing pipe 10. Figures 9-12 Further, as shown, the upper end face of the expanding section 10C of the reducing pipe 10 is connected with an outlet straight pipe section 10E, which is used to rectify the flue gas leaving the reducing pipe 10.

[0070] Figures 1-12 Further, as shown, the upper end face of the expanding section 10C of the reducing pipe 10 is connected with an outlet straight pipe section 10E, which is used to rectify the flue gas leaving the reducing pipe 10.

[0071] Further, as shown, the upper end face of the expanding section 10C of the reducing pipe 10 is connected with an outlet straight pipe section 10E, which is used to rectify the flue gas leaving the reducing pipe 10. Figures 5-12 Further, as shown, the upper end face of the expanding section 10C of the reducing pipe 10 is connected with an outlet straight pipe section 10E, which is used to rectify the flue gas leaving the reducing pipe 10.

[0072] According to the second aspect of the present application, the present application provides a flue gas denitration ammonia injection mixing system, comprising:

[0073] an ammonia injection assembly, which comprises an ammonia injection header 32, on which a header flow regulating valve 35 is arranged; a plurality of ammonia injection sub-pipes 31,

[0074] which are in communication with the ammonia injection header 32 and in communication with the hollow structure 16 through the ammonia gas inlet pipe 11 of the ammonia injection mixing assembly; the ammonia injection mixer 100 of any one of the above technical solutions; a denitration unit 600, which is arranged downstream of the ammonia injection mixer 100 and comprises at least one layer of denitration catalyst 601.

[0075] Figures 14-15 Further, as shown, the ammonia injection header 32 or the ammonia injection sub-pipe 31 is provided with an ammonia-air mixer 33, which is connected with a dilution air pipe line, used to mix the ammonia gas with the dilution air, so that the ammonia concentration in the ammonia-air mixed gas injected into the flue 200 is far away from the explosion limit.

[0076] Further, as shown, the dilution air pipe line 34 is branched into a dilution air main pipe 34A and a dilution air branch pipe 34B, the dilution air in the dilution air main pipe 34A is used to dilute the ammonia concentration to below the explosion limit; as long as there is flue gas flowing in the flue 200, the valve on the dilution air branch pipe 34B is in an open state, so that the ammonia gas nozzle 12 always has gas spouting, avoiding the blockage of the ammonia gas nozzle 12. Figure 15 Further, as shown, the dilution air pipe line 34 is branched into a dilution air main pipe 34A and a dilution air branch pipe 34B, the dilution air in the dilution air main pipe 34A is used to dilute the ammonia concentration to below the explosion limit; as long as there is flue gas flowing in the flue 200, the valve on the dilution air branch pipe 34B is in an open state, so that the ammonia gas nozzle 12 always has gas spouting, avoiding the blockage of the ammonia gas nozzle 12.​​​

[0077] Further, as shown in Figure 13 The ammonia injection and mixing device for flue gas denitration is provided with a flow guide assembly 400 and a flow rectifying grid 500 between the ammonia injection and mixing device 100 and the first layer of denitration catalyst 601. The flow guide assembly 400 is arranged at the turning position of the flue gas duct 200, and is used to turn the upward flue gas into downward flue gas entering the denitration unit 600. The flow rectifying grid 500 is arranged at the upper part of the first layer of catalyst 601 along the flue gas flow direction, and is used to rectify the flue gas passing through the denitration catalyst 601.

[0078] The working process of the ammonia injection and mixing device for flue gas denitration includes the following contents: ammonia or ammonia-air mixed gas enters the hollow structure 16 through the ammonia inlet pipe 11, and then is injected into the variable diameter pipe 10 through the ammonia injection nozzle 12 via the branch pipe 17 and the ammonia distribution pipe 13, and is mixed with the flue gas flowing through the variable diameter pipe 10. Further, when the upper part of the variable diameter pipe 10 is provided with the flow disturbing element 10F, the flue gas and the ammonia pass through the flow disturbing element 10F, and a vortex is formed at the back of the flow disturbing element 10F, thereby strengthening the mixing of the ammonia and the flue gas. Further, when the upper part of the ammonia injection nozzle 12 is provided with the dust blocking element 14, the flow rate and flow direction of the ammonia or ammonia-air mixed gas change after the ammonia or ammonia-air mixed gas is injected out of the ammonia injection nozzle 12 and passes through the dust blocking element 14, which is beneficial to the dispersion of the ammonia in the flue gas and strengthens the mixing of the ammonia and the flue gas. Further, when the dust blocking element 14 is a floating element, the smaller the flow of the ammonia or ammonia-air mixed gas, the closer the distance between the dust blocking element 14 and the ammonia injection nozzle, and the larger the cross-sectional area of the diffusion of the ammonia or ammonia-air mixed gas after passing through the dust blocking element 14, so that the mixing effect of the ammonia or ammonia-air mixed gas and the flue gas can be ensured when the flue gas amount is low and the flow of the ammonia or ammonia-air mixed gas is low at low load of the boiler.

[0079] Example 1

[0080] As shown in Figures 1-4 The ammonia injection and mixing assembly of the present application is composed of two Venturi structure variable diameter pipes 10 arranged side by side, the variable diameter pipe 10 is composed of a reduced diameter section 10A, a straight pipe section 10B and an expanded diameter section 10C, the shapes of the reduced diameter section 10A and the expanded diameter section 10C are both regular quadrangular frustum bodies; the area between the two variable diameter pipes 10 is closed to form a hollow structure 16, the hollow structure 16 is provided with an ammonia inlet pipe 11 and an ammonia distribution pipe 13, the ammonia distribution pipe 13 is in communication with the hollow structure 16 and two branch pipes 17, and the end of each branch pipe 17 is provided with an ammonia injection nozzle 12. The upper part of the ammonia injection nozzle 12 is provided with a dust blocking element 14, the dust blocking element 14 is in the shape of an umbrella cap and is fixed to the ammonia injection nozzle 12 by a fixed rod 15A.

[0081] A coal-fired boiler is modified for denitration, the installation height required for the ammonia injection grid and static mixer of other conventional ammonia injection grid and static mixer is 1.5 m, the installation height required for the ammonia injection mixer composed of the ammonia injection mixing assembly of the embodiment is only 0.6 m, the installation height is greatly reduced; after one year of operation, the boiler is shut down for maintenance, none of the ammonia nozzles 12 of the ammonia injection mixer of the embodiment is blocked, in contrast, 7 ammonia nozzles of another coal-fired boiler of the same scale are blocked.

[0082] Embodiment 2

[0083] As shown in Figures 5-8 , the ammonia injection mixing assembly of the application is composed of four variable-diameter pipes 10 arranged side by side, the variable-diameter pipe 10 is composed of a reduced-diameter section 10A and an enlarged-diameter section 10C, the lower end surface of the reduced-diameter section 10A and the upper end surface of the reduced-diameter section 10A are rectangular, the ammonia distribution pipe 13 is connected with four branch pipes 17, and the end of each branch pipe 17 is provided with an ammonia nozzle 12. The lower end surface of the reduced-diameter section 10A of the variable-diameter pipe 10 is connected with an inlet straight pipe section 10D, the enlarged-diameter section 10C of the variable-diameter pipe 10 is provided with a turbulence element 10F above, the turbulence element 10F is a rectangular turbulence plate, and the turbulence element 10F is fixed on the variable-diameter pipe 10 by two fixed supports 10G. The dust blocking element 14 is a floating element in the shape of a jujube seed, a limiting element 15B is provided on the ammonia nozzle 12 to prevent the dust blocking element 14 from being blown off by the gas sprayed by the ammonia nozzle 12. The rest is the same as Embodiment 1.

[0084] A coal-fired boiler is modified for denitration, the installation height required for the ammonia injection grid and static mixer of other conventional ammonia injection grid and static mixer is 1.5 m, the installation height required for the ammonia injection mixer composed of the ammonia injection mixing assembly of the embodiment is only 0.6 m, the installation height is greatly reduced; after one year of operation, the boiler is shut down for maintenance, none of the ammonia nozzles 12 of the ammonia injection mixer of the embodiment is blocked, in contrast, 7 ammonia nozzles of another coal-fired boiler of the same scale are blocked.

[0085] Embodiment 3

[0086] As shown in Figures 9-12As shown, the ammonia injection mixing assembly of the present application is composed of six venturi structure reducing pipes 10 arranged side by side, the lower end surface of the reduced section 10A of the reducing pipe 10 is connected with an inlet straight pipe section 10D, the expanded section 10C of the reducing pipe 10 is connected with an outlet straight pipe section 10E, a turbulence element 10F is arranged above the outlet straight pipe section 10E, the turbulence element 10F is a square turbulence vane provided with a plurality of screen holes 10H, and the turbulence element 10F is fixed on the outlet straight pipe section 10E through two fixing supports 10G. A dust blocking element 14 is arranged above the ammonia nozzle 12, which is a spherical floating element, and a limiting element 15B is arranged on the ammonia nozzle 12 to prevent the dust blocking element 14 from being blown off by the gas sprayed by the ammonia nozzle 12. The rest is the same as example 1.

[0087] The installation height required by the ammonia injection grid and the static mixer of other conventional ammonia injection systems is 2.0 m, the installation height required by the ammonia injection mixer composed of the ammonia injection mixing assembly of the present example is only 1.0 m, the installation height is greatly reduced; the ammonia escape of the present example is <3 ppm, in comparison, the ammonia escape of another coal-fired boiler of the same scale is <7 ppm; after one year and eight months of operation, the ammonia gas nozzle 12 of the ammonia injection mixer of the present example is not blocked, in comparison, 7 ammonia gas nozzles of another coal-fired boiler of the same scale are blocked.

[0088] Example 4

[0089] The present example is an example of a flue gas denitration ammonia injection mixing system of the present application, as shown in Figures 13-14 , as an example, the present example adopts Figures 5-8 the ammonia injection mixing assembly shown, which is sequentially provided with an ammonia injection mixer 100, a flow guide assembly 400, a rectifying grid 500, and a denitration unit 600, and three layers of denitration catalysts 600 are arranged in the denitration unit 600.

[0090] The ammonia injection mixer 100 is composed of three ammonia injection mixing assemblies arranged side by side, the ammonia inlet pipe 11 of each ammonia injection mixing assembly is in communication with the ammonia injection main pipe 31, the three ammonia injection main pipes 31 are in communication with the ammonia injection main pipe 32, the main pipe flow regulating valve 35 and the ammonia-air mixer 33 are arranged on the ammonia injection main pipe 32, the ammonia-air mixer 33 is connected with the dilution air pipe line 34, and as an example, the branch pipe flow regulating valve 36 is arranged on the ammonia injection main pipe 31, but the present application is not limited thereto.

[0091] It should be noted that the flue gas denitration ammonia injection mixing system example can apply any one of the above ammonia injection mixers.

[0092] The installation height of the ammonia injection grid and the static mixer required by the conventional ammonia injection system is 2.5 m, while the installation height of the ammonia injection mixer composed of the ammonia injection mixing assembly of the embodiment is only 1.2 m, and the installation height is greatly reduced. The ammonia escape of the embodiment is <2 ppm, and the ammonia escape of another coal-fired boiler of the same scale is <6 ppm. After one and a half years of operation and shutdown for maintenance, none of the ammonia nozzles 12 of the ammonia injection mixer of the embodiment is blocked, and in contrast, five ammonia nozzles of another coal-fired boiler of the same scale are blocked.

[0093] Embodiment 5

[0094] This embodiment is an embodiment of the flue gas denitration ammonia injection mixing system of the application, as shown in Figure 13 , 15 , the embodiment uses the ammonia injection mixing assembly shown in Figures 9-12 , the ammonia injection mixer 100 is composed of five ammonia injection mixing assemblies arranged side by side, the five ammonia injection main pipes 31 are connected to the ammonia injection main pipe 32, the dilution air pipe line 34 is branched into the dilution air main pipe 34A and the five dilution air branch pipes 34B, and the rest is the same as Embodiment 4.

[0095] It should be noted that the flue gas denitration ammonia injection mixing system embodiment can use any of the above ammonia injection mixers.

[0096] The foregoing description of specific exemplary embodiments of the application is intended for purposes of illustration and example only. These descriptions are not intended to limit the application to the precise form disclosed, and obviously many modifications, equivalents and alternatives are intended to be within the scope of the application. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application, and to allow others skilled in the art to understand the application for various embodiments with various modifications as are suited to the particular use contemplated. Any simple modification, equivalent change and modification made to the above exemplary embodiments shall fall within the scope of the application.

Claims

1. A flue gas denitration ammonia injection mixer characterized by: The mixer is arranged in the flue and comprises a plurality of parallelly arranged ammonia injection mixing assemblies; The ammonia injection mixing assembly comprises: two or more variable diameter pipes arranged along the vertical direction of the flue cross section, the area between the variable diameter pipes being closed to form a hollow structure; the variable diameter pipe is a tubular structure with a thin middle and thick ends; one end of the variable diameter pipe is a flue gas inlet end, and the other end is a flue gas outlet end; an ammonia gas inlet pipe which is connected to the hollow structure and used to introduce ammonia gas into the hollow structure; an ammonia gas distribution pipe which is connected to the hollow structure at one end and extends to the flue gas inlet end of each variable diameter pipe and is connected to a plurality of branch pipes, the flue gas inlet end of each variable diameter pipe corresponding to at least one branch pipe; an ammonia gas nozzle which is installed at the end of each branch pipe, the ammonia gas nozzle having the same direction as the flue gas flow; a dust blocking element which is arranged above the ammonia gas nozzle and used to block the dust falling above the ammonia gas nozzle to avoid blocking the ammonia gas nozzle; the dust blocking element is a floating element, and when the ammonia gas nozzle sprays gas, the dust blocking element floats away from the ammonia gas nozzle under the blowing action of the gas, and when the ammonia gas nozzle does not spray gas, the dust blocking element falls to block the ammonia gas nozzle under the action of its own gravity.

2. The flue gas De-NOx ammonia injection mixer of claim 1, wherein: The ammonia gas distribution pipe is connected to 2-16 branch pipes; the number of branch pipes corresponding to the flue gas inlet end of each variable diameter pipe is the same.

3. The flue gas De-NOx ammonia injection mixer of claim 1, wherein: The two adjacent ammonia injection mixing assemblies are not connected to each other or are connected to each other through a connecting pipe.

4. The flue gas De-NOx ammonia injection mixer of claim 1, wherein: The variable diameter pipe is a Laval pipe structure or a Venturi structure.

5. The flue gas De-NOx ammonia injection mixer of claim 1 wherein: The variable diameter pipe is a Laval pipe structure comprising a reduced diameter section and an enlarged diameter section; the variable diameter pipe is a Venturi structure comprising a reduced diameter section, a straight pipe section and an enlarged diameter section.

6. The flue gas De-NOx ammonia injection mixer of claim 5, wherein: The lower end surface of the reduced diameter section of the variable diameter pipe is connected to an inlet straight pipe section for straightening the flue gas entering the variable diameter pipe.

7. The flue gas De-NOx ammonia injection mixer of claim 5 wherein: The upper end surface of the enlarged diameter section of the variable diameter pipe is connected to an outlet straight pipe section for straightening the flue gas leaving the variable diameter pipe.

8. The flue gas De-NOx ammonia injection mixer of claim 1, wherein: A turbulence element is arranged in the variable diameter pipe for forming a vortex on the back of the turbulence element to strengthen the mixing of ammonia gas and flue gas.

9. A flue gas denitration ammonia injection mixing system characterized by It comprises: The ammonia injection assembly comprises an ammonia injection main pipe on which a main pipe flow regulating valve is arranged; A plurality of ammonia injection branch pipes are connected to the ammonia injection main pipe and connected to the hollow structure through the ammonia gas inlet pipe of the ammonia injection mixing assembly; the flue gas denitration ammonia injection mixer of any one of claims 1-8; a denitration unit arranged downstream of the flue gas denitration ammonia injection mixer and comprising at least one layer of denitration catalyst.

10. The flue gas denitration ammonia injection mixing system according to claim 9, characterized in that: An ammonia-air mixer is arranged on the ammonia injection main pipe or the ammonia injection branch pipe, the ammonia-air mixer is connected to a dilution air pipe line, and the ammonia-air mixer is used to mix ammonia gas and dilution air to make the ammonia concentration in the ammonia-air mixed gas injected into the flue far away from the explosion limit.

11. The flue gas denitration ammonia injection mixing system according to claim 10, characterized in that: The dilution air pipe line branches into a dilution air main pipe and a dilution air branch pipe, the dilution air in the dilution air main pipe is used to dilute the ammonia concentration to below the explosion limit; as long as there is flue gas flowing in the flue, the valve on the dilution air branch pipe is in an open state, so that the ammonia gas nozzle always sprays gas to avoid blocking the ammonia gas nozzle.

12. The flue gas denitration ammonia injection mixing system according to claim 9, characterized in that: A flow guide assembly and a straightening grid are arranged between the flue gas denitration ammonia injection mixer and the first layer of denitration catalyst, the flow guide assembly is arranged at the turning place of the flue to turn the upward flue gas into downward flue gas entering the denitration unit, and the straightening grid is arranged above the first layer of catalyst along the flue gas flow direction to straighten the flue gas passing through the denitration catalyst.

Images