An ammonia injection mixer and a flue gas denitrification system

Abstract

The present invention discloses an ammonia injection mixer and flue gas denitrification system. The ammonia injection mixer is installed in a flue and includes multiple ammonia injection mixing units. The ammonia injection mixing units include: two or more reducers, each of which is a tubular structure with a narrow middle and thick ends, and the area between the reducers is sealed to form a cavity; an ammonia inlet pipe; a coil installed in the reducer, one end of which is connected to the ammonia inlet pipe and the other end is connected to the cavity; an ammonia distribution pipe, one end of which is connected to the cavity and the other end is connected to several branch pipes and extends to the flue gas inlet end of each reducer; and an ammonia nozzle. The ammonia injection mixer of the present invention is improved in structure and function, integrating ammonia injection and mixing functions, solving the problem of ammonia nozzle blockage in the ammonia injection pipe, and significantly reducing the installation height. It is suitable for denitrification renovation of old boilers and construction of new denitrification equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas denitration, and in particular to an ammonia injection mixer and a flue gas denitration system. Background Art

[0002] Among the existing flue gas denitrification methods, the most widely used one at home and abroad is the selective catalytic reduction (SCR) technology. The main principle of SCR technology is to inject the reducing agent ammonia into the flue gas at 280℃~450℃ and mix it evenly. Under the action of the catalyst, NH3 reduces NO in the flue gas to x Reduce to non-toxic and pollution-free nitrogen and water, thereby removing NO from the mixed gas x purpose.

[0003] GB / T 34339-2017 "Ammonia Injection Mixing System for Denitrification of Coal-fired Flue Gas" divides the ammonia injection mixing system into an ammonia injection grid (AIG) and an ammonia injection static mixer. The AIG is defined as an injection device that injects ammonia into the flue in the form of a grid pipe, including ammonia injection pipes, nozzles, supports and accessories; the ammonia injection static mixer is defined as a device that uses certain fixed components to change the flow state of ammonia and flue gas to achieve full mixing, thereby achieving a higher NH3 / NO x Mixing efficiency. Typical ammonia injection static mixers include vortex, swirl, longitudinal vortex, and V-shaped structures. In existing ammonia injection mixing systems, the ammonia injection grid and static mixer must be installed at a certain height within the flue to ensure effective ammonia mixing. However, the limited free installation height and space in older, long-operated boilers make existing ammonia injection grids and static mixers difficult to adapt for denitrification retrofits.

[0004] During the operation of the SCR denitrification device, the nozzle of the ammonia injection pipe often becomes clogged, causing the uniformity of the ammonia-nitrogen molar ratio distribution at the catalyst inlet of the SCR reactor to deteriorate, and local ammonia escape to increase, resulting in serious blockage or leakage of downstream equipment such as the air preheater or economizer, threatening the safe and economical operation of the boiler / device; if there is a wet desulfurization device downstream, it will cause problems such as unqualified gypsum products or excessive ammonia nitrogen in the desulfurization wastewater; the escaped ammonia discharged into the atmosphere will cause secondary pollution.

[0005] CN113083013A discloses a method and system for preventing blockage in ammonia injection grids used in urea-to-ammonia processes, using steam to purge the ammonia injection pipelines. CN212942296U discloses a blockage-resistant ammonia injection device for coal-fired power plant denitrification systems that uses compressed air to prevent nozzle blockage. However, these solutions, which employ purge lines on ammonia injection pipes to address nozzle blockage, typically involve numerous nozzles on each ammonia injection pipe (or branch pipe). During the purge, steam / compressed air typically enters the flue through unobstructed nozzles, preventing the obstruction of blocked nozzles.

[0006] There are two main causes of nozzle blockage: fly ash and salt buildup. Flue gas contains a high concentration of dust (fly ash), which can easily accumulate around the nozzle edges and form bridges, clogging the nozzles. Furthermore, accumulated dust on the flue duct or components above the nozzles can collapse and clog the nozzles. Flue gas contains SO₃, which the injected ammonia reacts with to form ammonium bisulfate (ABS). ABS exists in three forms: gaseous, molten, and solid. The SCR reaction temperature is typically above 300°C, at which point ABS is in a gaseous state. Its melting point is 147°C. Once melted, ABS is extremely viscous, acidic, and hygroscopic. At temperatures between 147°C and 260°C, ABS forms a highly viscous liquid salt. Before ammonia is sprayed into the flue, it is generally mixed with dilution air to reduce its concentration to below the explosion limit. The dilution air is air at room temperature. When the temperature of ammonia and air mixed and sprayed into the flue falls into the temperature range of 147-260°C or even lower than this temperature range, the generated ammonium bisulfate easily adheres to the vicinity of the nozzle and continues to adhere to the dust in the flue gas. Over time, the nozzle will gradually be clogged by the generated ammonium salt and its mixture with dust.

[0007] To solve the problem of nozzle blockage caused by salt deposition, the dilution air is usually heated. There are two main heating methods. One is heating through equipment installed outside the flue, including electric heating (such as CN111672319A, CN204307517U), steam heating (such as CN210544284U, CN213160221U), natural gas combustion heating (CN208115468U), etc., but the above heating methods have high energy consumption; the other is heating through equipment installed in the flue, which can effectively utilize the flue gas heat to achieve the purpose of energy saving and consumption reduction. CN104941446A discloses an anti-blocking device for an ammonia injection grid used in an SCR denitration system. By installing a heater in the flue at the inlet of the denitration reactor, the dilution air is heated and then sprayed into the flue. CN111054211A discloses a heating device for a denitration dilution air system. A heating device for heating the dilution air is installed in the flue at the outlet of the economizer or in the flue at the inlet of the low-temperature superheater, and the heat of the high-temperature flue gas is used as a heat source for heating the dilution air. CN204672138U discloses a dilution air heating device for a flue gas denitration system. By installing a heating coil at the outlet of the reactor, the dilution air is heated. The above-mentioned equipment for heating the dilution air in the flue requires a certain installation height. However, the free installation height / space in old boilers that have been in operation for many years is limited, making it difficult to meet the requirements of the denitration transformation of the old boilers.

[0008] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0009] In response to the shortcomings of the existing technology, the present invention provides an ammonia spray mixer and a flue gas denitrification system. The ammonia spray mixer is improved in structure and function, integrating ammonia spray and mixing functions, solving the problem of ammonia nozzle blockage in the ammonia spray pipe, and greatly reducing the installation height. It is suitable for denitrification modification of old boilers and new denitrification equipment.

[0010] The ammonia spray mixer of the present invention is arranged in a flue and includes a plurality of ammonia spray mixing units, wherein the ammonia spray mixing units include:

[0011] Two or more reducers are arranged along the cross section of the flue. The reducers are tubular structures that are thin in the middle and thick at both ends. The area between the reducers is closed to form a cavity. One end of the reducer is the flue gas inlet end, and the other end is the flue gas outlet end.

[0012] Ammonia inlet pipe, used to introduce ammonia / ammonia-air mixture into the ammonia injection mixing unit;

[0013] The coil is arranged in the reducer, one end of which is connected to the ammonia inlet pipe and the other end is connected to the cavity, and is used to introduce the ammonia / ammonia-air mixture from the ammonia inlet pipe into the cavity;

[0014] An ammonia distribution pipe, one end of which is connected to the cavity and the other end is connected to a plurality of branch pipes and extends to the flue gas inlet end of each reducer, preferably 2 to 16 branch pipes, and the flue gas inlet end of each reducer corresponds to at least one branch pipe, and preferably the number of branch pipes corresponding to the flue gas inlet end of each reducer is the same;

[0015] An ammonia nozzle is installed at the end of each branch pipe, and the direction of the ammonia nozzle is the same as the direction of the flue gas flow.

[0016] It should be further explained that two adjacent ammonia injection mixing units may not be connected to each other, or their cavities may be connected to each other through a connecting pipe.

[0017] Furthermore, in the above technical solution, the reducer is preferably a Lafayette tube structure or a Venturi structure.

[0018] Furthermore, in the above technical solution, the reducer is a Rafael tube structure, including a reducing section and an expanding section, and the cross-sections of the lower end face of the reducing section and the upper end face of the expanding section include circular, elliptical, square, and rectangular shapes.

[0019] Furthermore, in the above technical solution, the reducer is a Venturi structure, including a reduced diameter section, a straight pipe section and an expanded diameter section. The shapes of the reduced diameter section and the expanded diameter section can be a trapezoid, a quadrangular cone, a truncated cone, a geometric body with an upper circle and a lower section, or an upper section and a lower circle.

[0020] Furthermore, in the above technical solution, the lower end surface of the reduced diameter section of the reducer is connected to an inlet straight pipe section for rectifying the flue gas entering the reducer.

[0021] Furthermore, in the above technical solution, the upper end surface of the expanded diameter section of the reducer is connected to an outlet straight pipe section for rectifying the flue gas leaving the reducer.

[0022] Furthermore, in the above technical solution, the coil can adopt types including corrugated tubes, finned tubes, spiral grooved tubes, convergent tubes, swirl tubes, pin-fin tubes, etc. as needed, and various turbulent elements such as spiral coils, rings, sheets, balls, etc. can be inserted into the coil to enhance the heat transfer effect between the gas inside and outside the coil; turbulent elements and / or guide elements can also be set outside the coil to enhance the mixing effect of the gas in the ammonia injection mixing unit.

[0023] Furthermore, in the above technical solution, the coil is a spiral coil, which is distributed axially along the reducer and is at a certain distance from the inner wall of the reducer, generally 10~200mm. The distance between two adjacent spiral coils in the axial direction of the reducer is generally 10~200mm. The distance between any two adjacent spiral coils can be the same or different, and is preferably arranged equidistantly.

[0024] Furthermore, in the above technical solution, connecting pieces are provided between the spiral coils, and the connecting pieces and the spiral coils are sealed to completely divide the space of the reducer into an intermediate channel and at least one annular channel.

[0025] Furthermore, in the above technical solution, a spiral coil is also provided in the inlet straight pipe section or / and in the inlet straight pipe section.

[0026] Furthermore, in the above technical solution, the ammonia nozzle is arranged on the central axis of the reducing pipe.

[0027] Furthermore, in the above technical solution, a dust blocking element is provided above the ammonia nozzle to block dust falling from above the ammonia nozzle to avoid clogging the ammonia nozzle.

[0028] Furthermore, in the above technical solution, the dust shielding element is a floating part. When gas is ejected from the ammonia nozzle, the dust shielding element floats up and away from the ammonia nozzle under the blowing action of the gas. When no gas is ejected from the ammonia nozzle, the dust shielding element falls down under the action of its own gravity and blocks the ammonia nozzle.

[0029] Furthermore, in the above technical solution, a protective element is provided above the reducer or the outlet straight pipe section to protect the coil located therebelow and to play a turbulent role, thereby enhancing the mixing of ammonia and flue gas.

[0030] According to a second aspect of the present invention, the present invention provides a flue gas denitrification system, comprising:

[0031] An ammonia injection assembly includes an ammonia injection main pipe on which a main pipe flow regulating valve is provided; a plurality of ammonia injection main pipes are connected to the ammonia injection main pipe and are connected to the cavity of the ammonia injection mixing unit through the ammonia inlet pipe;

[0032] An ammonia injection mixer according to any one of the above technical solutions;

[0033] The denitration unit is arranged downstream of the ammonia injection mixer and includes at least one layer of denitration catalyst.

[0034] Furthermore, in the above technical solution, an ammonia-air mixer is provided on the ammonia injection main pipe or the ammonia injection mother pipe, and the ammonia-air mixer is connected to the dilution air pipeline to mix ammonia with dilution air so that the ammonia concentration in the ammonia-air mixture injected into the flue is far away from its explosion limit.

[0035] Furthermore, in the above technical solution, the dilution air line is branched 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 through the flue, the valve on the dilution air branch pipe is in an open state, so that the ammonia nozzle always has gas ejected to avoid clogging of the ammonia nozzle.

[0036] Furthermore, in the above technical solution, a guide assembly and a rectifying grid are arranged between the flue gas denitrification ammonia injection mixer and the first layer of denitrification catalyst. The guide assembly is arranged at the bend of the flue to divert the upward flue gas to enter the denitrification unit downward; the rectifying grid is arranged on the upper part of the first layer of catalyst along the direction of flue gas flow, and is used to rectify the flue gas passing through the denitrification catalyst.

[0037] The working process of the ammonia spray mixer of the present invention is as follows: ammonia or ammonia-air mixture enters the coil from the ammonia inlet pipe, exchanges heat with the flue gas flowing through the reducer, and then enters the cavity. It is then sprayed from the ammonia nozzle into the reducer through the ammonia distribution pipe through the branch pipe and mixed with the flue gas flowing through the reducer. Furthermore, when a protective element is provided above the reducer, the flue gas and ammonia will form a vortex on the back side of the protective element when passing through the protective element, thereby enhancing the mixing of the ammonia and flue gas; further, when a dust barrier element is provided above the ammonia nozzle, the flow velocity and direction of the ammonia or ammonia-air mixture gas ejected from the ammonia nozzle will change after passing through the dust barrier element, which is beneficial to the dispersion of ammonia in the flue gas and enhances the mixing of ammonia and flue gas; further, when the dust barrier element is a floating part, the smaller the flow rate of the ammonia or ammonia-air mixture gas, the closer the distance between the dust barrier element and the ammonia nozzle, and the larger the cross-sectional area of the ammonia or ammonia-air mixture gas diffused after passing through the dust barrier element, thereby ensuring the mixing effect with the flue gas when the flue gas volume is low and the flow rate of the ammonia or ammonia-air mixture gas is low at low load of the boiler.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. Conventional flue gas SCR denitrification flue requires an ammonia spray grid and an ammonia spray static mixer. This application integrates the functions of the two and adopts an ammonia spray mixer, which significantly reduces the required installation height in the flue. It is especially suitable for the denitrification transformation of old boilers that have been in operation for many years. At the same time, the weight of the equipment required to be 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, so the required investment is also reduced, which significantly increases its market competitiveness. This equipment can also be used in new flue gas denitrification equipment.

[0040] 2. In the ammonia spray mixer of the present invention, a coil is provided in the reducer, and the flue gas is used to directly heat the ammonia / ammonia-air mixture in the coil, so that the temperature of the heated ammonia / ammonia-air mixture is higher than the dew point of ammonium bisulfate and away from the temperature range where ammonium bisulfate becomes liquid salt, effectively preventing the formation of liquid ammonium bisulfate, avoiding the deposition of ammonium bisulfate, and adhering fly ash to block the ammonia nozzle, solving the problem of salt accumulation and blockage of the ammonia nozzle; further, an ash blocking element is provided above the ammonia nozzle, which can block the dust falling above the nozzle and avoid clogging the ammonia nozzle; further, when the ash blocking element adopts a floating part, after the boiler or device is shut down, the denitrification system is deactivated, and the ash blocking element falls to block the ammonia nozzle. At this time, when the dust in the flue is cleaned or the flue vibration causes dust to fall, the ammonia nozzle can be effectively prevented from being blocked by dust. The present invention adopts the above-mentioned measures to avoid scaling and clogging of the ammonia injection nozzle, which can effectively ensure that the ammonia injection nozzle is always in normal working condition, and further ensure the precise control of ammonia injection in the flue gas SCR denitrification system, thereby ensuring the uniformity of the distribution of the ammonia-nitrogen molar ratio, avoiding local ammonia escape, and thus avoiding the occurrence of leakage or blockage of downstream air preheaters or economizers and other equipment, unqualified gypsum products or excessive ammonia and nitrogen in desulfurization wastewater, and escaped ammonia entering the atmosphere to cause secondary pollution, thereby effectively extending the operation cycle of the device.

[0041] 3. The coil of the present invention enhances the mixing effect of the flue gas and ammonia in the ammonia injection mixing unit; further, the spiral coil divides the reducer into one or more annular areas and an intermediate central area in the radial direction, so that the mixed gas is more evenly distributed in the radial direction, and the uniformity of the gas in the radial direction is increased, which is more conducive to the uniform mixing of ammonia and ammonia; further, connecting plates are provided between the spiral coils in the vertical direction, and the space of the reducer is completely divided into an intermediate channel and at least one annular channel. On the one hand, the mixed gas can be rectified in the same channel to make its flow direction and flow velocity more uniform and consistent; on the other hand, the up and down vibration of the spiral coil in the circumferential direction under the impact of the mixed gas can be eliminated, thereby avoiding damage to the spiral coil and helping to extend the service life of the spiral coil.

[0042] 4. In the present invention, a protective element is provided above the reducer or the outlet straight pipe section, which mainly plays three roles: first, it is used to protect the coil located below it to avoid damage to the coil, especially during equipment transportation, installation and maintenance, to avoid damage to the coil by impact. During installation and maintenance, the protective element can play a supporting role, and people can step on it to complete equipment installation and maintenance work; second, it plays a turbulent role. When the flue gas passes through the protective element, a turbulent flow is generated, and a vortex is generated on the back of the protective element, further strengthening the mixing of ammonia and flue gas; third, it plays an ash blocking role. Large pieces of ash located in the flue above the ammonia spray mixer or on the internal components are vibrated or disturbed and fall onto the protective element first, thereby preventing the ash from adhering to the coil, reducing the heat exchange efficiency and clogging the ammonia nozzle below.

[0043] 5. In the present invention, the dilution air used for ammonia is divided into two routes. The dilution air in the dilution air main line is used to dilute the ammonia concentration to below the explosion limit, and the dilution air in the dilution air branch line is used to prevent the ammonia nozzle from being blocked. As long as there is flue gas in the flue, there will be dilution air in the dilution air branch line, so gas will pass through the ammonia branch pipe and the ammonia nozzle. When the NOx concentration in the flue gas is lower than the emission standard and the SCR denitrification system does not spray ammonia, it can effectively ensure that the ammonia nozzle is not blocked by dust in the flue gas. Combined with the ash blocking element, it can prevent nozzle blockage from the perspective of equipment structure and from the perspective of process operation, thereby avoiding a series of problems caused by nozzle blockage.

[0044] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and to implement it according to the contents of the specification, and to make the above and other purposes, technical features and advantages of the present invention easier to understand, one or more preferred embodiments are listed below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a front view of an ammonia injection mixing unit structure (Venturi structure) of the present invention.

[0046] Figure 2 for Figure 1 Left view of the structure of the ammonia injection mixing unit.

[0047] Figure 3 for Figure 1 Top view of the structure of the ammonia injection mixing unit.

[0048] Figure 4 This is a front view of an ammonia injection mixing unit structure (Rafale tube structure) of the present invention.

[0049] Figure 5 for Figure 4 Left view of the structure of the ammonia injection mixing unit.

[0050] Figure 6 for Figure 4 Top view of the structure of the ammonia injection mixing unit.

[0051] Figure 7 for Figure 4 Bottom view of the inlet straight pipe section structure of the ammonia injection mixing unit.

[0052] Figure 8 This is a front view of an ammonia injection mixing unit structure (Venturi structure) of the present invention.

[0053] Figure 9 for Figure 8 Left view of the structure of the ammonia injection mixing unit.

[0054] Figure 10 for Figure 8 Top view of the structure of the ammonia injection mixing unit.

[0055] Figure 11 for Figure 8 Top view of the expanded diameter section and outlet straight pipe section of the ammonia injection mixing unit.

[0056] Figure 12 for Figure 8 Bottom view of the inlet straight pipe section of the ammonia injection mixing unit (heating pipe omitted).

[0057] Figure 13 This is a schematic diagram of a flue gas denitrification and ammonia injection mixing system according to the present invention.

[0058] Figure 14 This is a top view of the structure of an ammonia injection mixer of a flue gas denitrification ammonia injection mixing system of the present invention.

[0059] Figure 15 This is a top view of the structure of an ammonia injection mixer of a flue gas denitrification ammonia injection mixing system of the present invention.

[0060] Description of main reference numerals:

[0061] 10-reducing pipe, 10A-reducing section, 10B-straight pipe section, 10C-expanding section, 10D-inlet straight pipe section, 10E-outlet straight pipe section, 10F-protective element, 10G-fixing bracket, 10H-sieve hole, 10I-fixing piece;

[0062] 11- ammonia inlet pipe, 12- ammonia nozzle, 13- ammonia distribution pipe, 14- ash retaining element, 15A- fixing rod, 15B- limiting member, 16- cavity, 17- coil, 18- branch pipe, 19- connecting piece;

[0063] 31- ammonia injection main pipe, 32- ammonia injection main pipe, 33- ammonia-air mixer, 34- dilution air line, 34A- dilution air main pipe, 34B- dilution air branch pipe, 35- main pipe flow control valve, 36- branch pipe flow control valve;

[0064] 100- ammonia injection mixer, 200- flue, 400- flow guide assembly, 500- rectifier grid, 600- denitrification unit, 601- denitrification catalyst. DETAILED DESCRIPTION

[0065] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0066] Unless expressly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising” will be understood to include the stated elements or components but not to exclude other elements or components.

[0067] In this document, for ease of description, spatially relative terms such as "below," "beneath," "below," "above," "above," etc. may be used to describe the relationship of one element or feature to another element or feature in the accompanying drawings. It should be understood that the spatially relative terms are intended to encompass different orientations of the object in use or operation in addition to the orientation depicted in the drawings. For example, if the object in the drawings is turned over, the element described as being "below" or "beneath" other elements or features will be oriented "above" the elements or features. Therefore, the exemplary term "below" can include both below and above. Objects may also have other orientations (rotated 90 degrees or other orientations) and the spatially relative terms used herein should be interpreted accordingly.

[0068] In this document, the terms "first", "second", etc. are used to distinguish two different elements or parts, and are not used to limit specific positions or relative relationships. In other words, in some embodiments, the terms "first", "second", etc. can also be interchangeable with each other.

[0069] According to the first aspect of the present invention, Figure 1-13As shown, the present invention provides an ammonia injection mixer 100, which is arranged in a flue 200 and consists of a plurality of ammonia injection mixing units, each of which includes: two or more reducers 10, the reducers 10 being arranged along the cross section of the flue 200, the area between the reducers 10 being sealed to form a cavity 16; one end of the reducer 10 being a flue gas inlet end, and the other end being a flue gas outlet end; an ammonia inlet pipe 11 for introducing ammonia / ammonia-air mixed gas into the ammonia injection mixing unit; a coil 17, which is arranged in the reducer 10, one end of which is connected to the ammonia inlet pipe 11, and the other end is connected to the flue gas outlet end; The cavity 16 is used to introduce the ammonia / ammonia-air mixture from the ammonia inlet pipe 11 into the cavity 16; the ammonia distribution pipe 13, one end of which is connected to the cavity 16, and the other end is connected to a plurality of branch pipes 10J and extends to the flue gas inlet end of each reducer 10, preferably 2 to 16 branch pipes 10J, and the flue gas inlet end of each reducer 10 corresponds to at least one branch pipe 10J, and preferably the number of branch pipes 10J corresponding to the flue gas inlet end of each reducer 10 is the same; the ammonia nozzle 12 is installed at the end of each branch pipe 10J, and the direction of the ammonia nozzle 12 is the same as the direction of the flue gas flow.

[0070] It should be further explained that two adjacent ammonia injection mixing units may not be connected to each other, or their cavities 16 may be connected to each other through a connecting pipe.

[0071] Furthermore, the reducer 10 is preferably a Rafael tube structure (such as Figure 4-7 as shown) or a Venturi structure (as Figure 1-3 , 8-11).

[0072] Further, if Figure 4-7 As shown, the reducer 10 is a Rafael tube structure, including a reducing section 10A and an expanding section 10C. The cross-sectional shapes of the lower end surface of the reducing section 10A and the upper end surface of the expanding section 10C include circular, elliptical, square, and rectangular, but the present invention is not limited thereto.

[0073] Further, if Figure 1-3 As shown in Figures 8-11, the reducer 10 is a Venturi structure, including 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 can be a trapezoid, a quadrangular cone, a truncated cone, a geometric body with an upper circle and a lower bottom, or an upper circle and a lower bottom, but the present invention is not limited thereto.

[0074] Further, if Figure 4-5 As shown, the lower end surface of the reduced diameter section 10A of the reducer 10 is connected to an inlet straight pipe section 10D for rectifying the flue gas entering the reducer 10 .

[0075] Further, if Figure 8-9 As shown, the upper end surface of the expanded diameter section 10C of the reducer 10 is connected to an outlet straight pipe section 10E for rectifying the flue gas leaving the reducer 10 .

[0076] Furthermore, the ammonia nozzle 12 is provided in the diameter-reducing section 10A (e.g. Figure 1-2 As shown) or inlet straight pipe section 10D (as shown Figure 4-5 , 8-9).

[0077] Furthermore, in the above technical solution, coil 17 can be a bellows, finned tube, spirally grooved tube, convergent-divergent tube, swirl tube, pin-fin tube, or other type of coil 17 as needed. Various flow-disturbing elements, such as spiral coils, spiral sheets, rings, sheets, and balls, can be inserted into coil 17 to enhance heat transfer between the gases inside and outside the spiral coil. Flow-disturbing elements and / or flow-guiding elements can also be provided outside the spiral coil to enhance gas mixing within the ammonia injection mixing unit. The aforementioned heat exchange and mixing enhancement methods are well known to those skilled in the art and will not be elaborated upon here.

[0078] Further, if Figure 4-6 As shown in Figures 8-11, the coil 17 is a spiral coil, which is distributed axially along the reducer 10 and is at a certain distance from the inner wall of the reducer 10, generally 10 to 200 mm. The distance between two adjacent spiral coils in the axial direction of the reducer 10 is generally 10 to 200 mm. The distance between any two adjacent spiral coils can be the same or different, and is preferably arranged at equal intervals.

[0079] Further, if Figure 8-9 As shown in Figures 11, connecting pieces 19 are provided between the coils 17 in the vertical direction. The connecting pieces 19 and the coils 17 are sealed to completely divide the space within the diameter-reducing section 10A and / or the diameter-expanding section 10C into an intermediate channel and at least one annular channel.

[0080] Further, if Figure 8-9 As shown, a spiral coil is also provided in the inlet straight pipe section 10D or / and in the inlet straight pipe section 10D.

[0081] Further, if Figure 1-2 As shown in Figures 4-5 and 8-9, a dust blocking element 14 is provided above the ammonia nozzle 12 to block dust falling from above the ammonia nozzle 12 and avoid clogging the ammonia nozzle 12.

[0082] Further, if Figure 4-5 As shown in Figures 8-9, the dust blocking element 14 is a floating component. When gas is ejected from the ammonia nozzle 12, the dust blocking element 14 floats up and away from the ammonia nozzle 12 under the blowing action of the gas. When no gas is ejected from the ammonia nozzle 12, the dust blocking element 14 falls down under the action of its own gravity to block the ammonia nozzle 12.

[0083] Further, if Figure 8-10As shown, a protective element 10F is provided above the reducer 10 or the outlet straight pipe section 10E to protect the coil 17 located below it and to provide a flow disturbance, thereby enhancing the mixing of ammonia and flue gas. Preferably, but not limiting, the protective element 10F can be a sphere, ellipsoid, hemisphere, cone, torus, or protective sheet. The shape of the protective sheet can be circular, rectangular, square, star-shaped, plum blossom-shaped, herringbone-shaped, polygonal, or the like. For example, Figures 8-10 The protective element 10F shown is a spoiler, which is square and covered with mesh holes 10H.

[0084] According to a second aspect of the present invention, the present invention provides a flue gas denitrification system, comprising: an ammonia injection assembly, which includes an ammonia injection main pipe 32, on which a main pipe flow regulating valve 35 is provided; a plurality of ammonia injection mother pipes 31, which are connected to the ammonia injection main pipe 32 and connected to the coil 17 through the ammonia inlet pipe 11 of the ammonia injection mixing unit; an ammonia injection mixer 100 according to any one of the above technical solutions; and a denitrification unit 600, which is arranged downstream of the ammonia injection mixer 100 and includes at least one layer of denitrification catalyst 601.

[0085] Further, if Figure 13-15 As shown, an ammonia-air mixer 33 is provided on the ammonia injection main pipe 32 or the ammonia injection main pipe 31. The ammonia-air mixer 33 is connected to the dilution air pipeline 34 and is used to mix ammonia with dilution air so that the ammonia concentration in the ammonia-air mixture injected into the flue 200 is far away from its explosion limit.

[0086] Further, if Figure 15 As shown, the dilution air 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 through the flue 200, the valve on the dilution air branch pipe 34B is in an open state, so that the ammonia nozzle 12 always has gas ejected to avoid clogging of the ammonia nozzle 12.

[0087] Further, if Figure 13 As shown, a guide assembly 400 and a rectifying grid 500 are arranged between the flue gas denitration ammonia injection mixer 100 and the first layer of denitration catalyst 601. The guide assembly 400 is arranged at the turning point of the flue 200, and is used to divert the upward flue gas to enter the denitration unit 600 downward; the rectifying grid 500 is arranged on the upper part of the first layer of catalyst along the flue gas flow direction, and is used to rectify the flue gas passing through the denitration catalyst 601.

[0088] The working process of the ammonia injection mixer of the present invention is as follows: ammonia or ammonia-air mixture enters the coil 17 through the ammonia inlet pipe 11, exchanges heat with the flue gas flowing through the reducer 10, and then enters the cavity 16. It is then sprayed into the reducer 10 from the ammonia nozzle 12 through the ammonia distribution pipe 13 through the branch pipe 18, and mixed with the flue gas flowing through the reducer 10. Furthermore, when a protective element 10F is provided above the reducer 10, the flue gas and ammonia will form a vortex on the back side of the protective element 10F when passing through the protective element 10F, thereby strengthening the mixing of the ammonia and flue gas; further, when a dust barrier element 14 is provided above the ammonia nozzle 12, the flow velocity and direction of the ammonia or ammonia-air mixture gas ejected from the ammonia nozzle 12 and passing through the dust barrier element 14 will change, which is beneficial to the dispersion of ammonia in the flue gas and strengthens the mixing of ammonia and flue gas; further, when the dust barrier element 14 is a floating part, the smaller the flow rate of the ammonia or ammonia-air mixture gas, the closer the distance between the dust barrier element 14 and the ammonia nozzle 12, and the larger the cross-sectional area of the ammonia or ammonia-air mixture gas diffused after passing through the dust barrier element 14, thereby ensuring the mixing effect with the flue gas when the flue gas volume is low and the flow rate of the ammonia or ammonia-air mixture gas is low at low load of the boiler.

[0089] Example 1

[0090] like Figures 1-3 As shown, the ammonia spray mixing unit of the present invention is composed of two venturi-structured reducers 10. The reducers 10 consist of a reduced diameter section 10A, a straight section 10B, and an expanded diameter section 10C. Both the reduced diameter section 10A and the expanded diameter section 10C are in the shape of a regular quadrangular pyramid. The area between the two reducers 10 is enclosed to form a cavity 16. Coils 17 are disposed within the reducers 10. The ammonia spray mixing unit is equipped with a total of 12 coils 17, located within the reduced diameter sections 10A and the expanded diameter sections 10C of the reducers 10. An ammonia inlet pipe 11 and an ammonia distribution pipe 13 are disposed within the cavity 16. The ammonia distribution pipe 13 communicates with the cavity 16 and extends to the centerline of the two reducers 10. An ammonia nozzle 12 is disposed at its distal end. An umbrella-shaped dust barrier 14 is disposed above the ammonia nozzle 12. The dust barrier 14 is secured to the ammonia nozzle 12 by a fixing rod 15A.

[0091] A pulverized coal furnace was retrofitted for denitrification. The installation height required for a conventional ammonia injection grid and static mixer was 1.2 m, while the installation height required for the ammonia injection mixer composed of the ammonia injection mixing unit of this embodiment was only 0.5 m, significantly reducing the installation height. After one year of operation, the furnace was shut down for maintenance. None of the ammonia nozzles 12 of the ammonia injection mixer of this embodiment were clogged. In contrast, six ammonia nozzles of another pulverized coal furnace of the same size were clogged.

[0092] Example 2

[0093] like Figure 4-7As shown, the ammonia injection and mixing unit of the present invention is composed of four reducers 10 with a Laval tube structure. Each reducer 10 consists of a reduced diameter section 10A and an expanded diameter section 10C. The lower and upper ends of the reduced diameter sections 10A and 10C are rectangular. The lower end of the reduced diameter section 10A of the reducer 10 is connected to an inlet straight pipe section 10D. Each reducer 10 is equipped with a spiral coil. The coils are arranged symmetrically around the centerline of the reduced and expanded diameter sections 10A and 10C of the reducer 10, with a distance of 20 mm from the inner wall of the reducer 10. The distance between adjacent coils along the axial direction of the reducer 10 is 20 mm. An ammonia distribution pipe 13 communicates with the cavity 16 and extends to the centerline of the four reducers 10. An ammonia nozzle 12 is located at its end. The dust blocking element 14 is a floating element in the shape of a jujube pit. 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 from the ammonia nozzle 12 .

[0094] Example 3

[0095] like Figure 8-12 As shown, the ammonia injection mixing unit of the present invention is composed of 6 venturi-structured reducers 10, the lower end face of the reduced diameter section 10A of the reducer 10 is connected to the inlet straight pipe section 10D, and the expanded diameter section 10C of the reducer 10 is connected to the outlet straight pipe section 10E.

[0096] Each reducer 10 has a coil 17 (spiral coil) installed within its inlet straight section 10D and reduced diameter section 10A. This coil 17 communicates with the coils 17 within the inlet straight section 10D and reduced diameter section 10A of the adjacent reducer 10. Each reducer 10 also has a coil 17 installed within its expanding diameter section 10C and outlet straight section 10E. This coil 17 communicates with the coils 17 within the expanding diameter section 10C and outlet straight section 10E of the adjacent reducer 10. The coils 17 are arranged symmetrically in a spiral pattern around the centerline of the reducing and expanding diameter sections 10A, 10C, and 10E of the reducer 10. The shape formed by this spiral arrangement is identical to that of the reducing and expanding diameter sections 10A, 10C, and 10E. A connecting piece 19 is provided between the coils 17 in the vertical direction. The connecting piece 19 and the coils 17 are sealed to completely divide the space within the reduced diameter section 10A and the expanded diameter section 10C and the expanded diameter section 10C and the outlet straight pipe section 10E into an intermediate channel and an annular channel.

[0097] Ammonia distribution pipe 13 connects to cavity 16 and extends to the centerline of the six reducers 10. Ammonia nozzle 12 is located at its end. A spherical floating dust block 14 is located above ammonia nozzle 12. A limiter 15B is also provided on ammonia nozzle 12 to prevent dust block 14 from being blown off by the gas sprayed from ammonia nozzle 12.

[0098] A protection element 10F is provided above the outlet straight pipe section 10E. The protection element 10F is a square spoiler provided with a plurality of sieve holes 10H. The protection element 10F is fixed to the baffle by two fixing brackets 10G.

[0099] Example 4

[0100] This embodiment is an embodiment of the flue gas denitrification system of the present invention. Figure 13-14 As shown, for example, this embodiment adopts the ammonia injection mixing unit of Example 2, and an ammonia injection mixer 100, a guide component 400, a rectifying grid 500, and a denitrification unit 600 are arranged in sequence along the flue gas flow direction, and a three-layer denitrification catalyst 600 is arranged in the denitrification unit 600.

[0101] The ammonia injection mixer 100 is composed of three ammonia injection mixing units arranged side by side. The ammonia inlet pipe 11 of each ammonia injection mixing unit is connected to the ammonia injection main pipe 31. The three ammonia injection main pipes 31 are connected to the ammonia injection main pipe 32. The ammonia injection main pipe 32 is provided with a main pipe flow regulating valve 35 and an ammonia-air mixer 33. The ammonia-air mixer 33 is connected to the dilution air line 34. For example, a branch pipe flow regulating valve 36 is provided on the ammonia injection main pipe 31, but the present invention is not limited to this.

[0102] It should be noted that the embodiment of the flue gas denitrification ammonia injection mixing system can apply any of the above ammonia injection mixers.

[0103] A coal-fired boiler underwent denitrification retrofit. The installation height required for a conventional ammonia injection grid and static mixer was 1.6 m, while the installation height required for the ammonia injection mixer composed of the ammonia injection mixing unit of this embodiment was only 0.7 m, significantly reducing the installation height. The flue gas of this embodiment was desulfurized using a sodium-alkali flue gas desulfurization process, and the ammonia nitrogen content in the desulfurization wastewater was less than 5 mg / L. In contrast, another coal-fired boiler of the same size also used a sodium-alkali flue gas desulfurization process, and the ammonia nitrogen content in the desulfurization wastewater was 30-80 mg / L. After one and a half years of operation and shutdown for maintenance, none of the ammonia nozzles 12 of the ammonia injection mixer of this embodiment were clogged. In contrast, eight ammonia nozzles of another coal-fired boiler of the same size were clogged.

[0104] Example 5

[0105] This embodiment is an embodiment of the flue gas denitrification system of the present invention. Figure 13 、 15 As shown, for example, this embodiment adopts the ammonia spray mixing unit shown in Example 3, and the ammonia spray mixer 100 is composed of 5 ammonia spray mixing units arranged side by side. The 5 ammonia spray mother pipes 31 are connected to the ammonia spray main pipe 32, and the dilution air line 34 is branched into a dilution air main pipe 34A and 5 dilution air branch pipes 34B.

[0106] It should be noted that the embodiment of the flue gas denitrification ammonia injection mixing system can apply any of the above ammonia injection mixers.

[0107] A boiler underwent denitration retrofit. The installation height required for a conventional ammonia injection grid and static mixer was 2.5 m, while the installation height required for the ammonia injection mixer composed of the ammonia injection mixing unit of this embodiment was only 1.2 m, significantly reducing the installation height. The ammonia slip of this embodiment was <3 ppm, compared to <8 ppm for another boiler of the same size. After one and a half years of operation and shutdown for maintenance, none of the ammonia nozzles 12 of the ammonia injection mixer of this embodiment were clogged, compared to six clogged ammonia nozzles of another coal-fired boiler of the same size.

Claims

1. An ammonia spray mixer, which is arranged in a flue, characterized in that: It includes multiple ammonia spraying and mixing units, and the ammonia spraying and mixing units include: Two or more reducers are arranged along the cross section of the flue. The reducers are tubular structures that are thin in the middle and thick at both ends. The area between the reducers is closed to form a cavity. One end of the reducer is the flue gas inlet end, and the other end is the flue gas outlet end. Ammonia inlet pipe, used to introduce ammonia / ammonia-air mixture into the ammonia injection mixing unit; The coil is arranged in the reducer, one end of which is connected to the ammonia inlet pipe and the other end is connected to the cavity, and is used to introduce the ammonia / ammonia-air mixture from the ammonia inlet pipe into the cavity; An ammonia distribution pipe, one end of which is connected to the cavity, and the other end of which is connected to a plurality of branch pipes and extends to the flue gas inlet end of each reducer, wherein the flue gas inlet end of each reducer corresponds to at least one branch pipe; An ammonia nozzle is installed at the end of each branch pipe, and the direction of the ammonia nozzle is the same as the direction of the flue gas flow.

2. The ammonia injection mixer according to claim 1, characterized in that: Two adjacent ammonia spray mixing units are not connected to each other or their cavities are connected to each other through a connecting pipe.

3. The ammonia injection mixer according to claim 1, characterized in that: The number of branch pipes corresponding to the flue gas inlet end of each reducer is the same.

4. The ammonia injection mixer according to claim 1, characterized in that: The reducer is a Lafarge tube structure or a Venturi structure.

5. The ammonia injection mixer according to claim 4, characterized in that: The reducer is a Rafael tube structure, including a reducing section and an expanding section. The cross-sections of the lower end face of the reducing section and the upper end face of the expanding section are circular, elliptical, square or rectangular.

6. The ammonia injection mixer according to claim 4, characterized in that: The reducer is a Venturi structure, including a reduced diameter section, a straight pipe section and an expanded diameter section. The shapes of the reduced diameter section and the expanded diameter section are trapezoidal, quadrangular, truncated, or geometric bodies with an upper circle and a lower bottom or an upper circle and a lower bottom.

7. The ammonia injection mixer according to claim 5 or 6, characterized in that: The lower end surface of the reduced diameter section of the reducer is connected with an inlet straight pipe section, which is used to rectify the flue gas entering the reducer.

8. The ammonia injection mixer according to claim 5 or 6, characterized in that: The upper end surface of the expanded diameter section of the reducer is connected with an outlet straight pipe section, which is used to rectify the flue gas leaving the reducer.

9. The ammonia injection mixer according to claim 1, characterized in that: The coil adopts one or more of corrugated tubes, finned tubes, spiral grooved tubes, convergent-divergent tubes, swirl tubes or pin-fin tubes.

10. The ammonia injection mixer according to claim 1, characterized in that: A turbulent element is inserted into the coil to enhance the heat transfer effect between the gas inside and outside the coil.

11. The ammonia injection mixer according to claim 1, characterized in that: A turbulent element and / or a flow guide element is arranged outside the coil to enhance the mixing effect of the gas in the ammonia injection mixing unit.

12. The ammonia injection mixer according to claim 1, characterized in that: The coil is a spiral coil, which is distributed axially along the reducer and a certain distance away from the inner wall of the reducer. The distance between two adjacent spiral coils along the axial direction of the reducer is 10-200 mm, and the distance between any two adjacent spiral coils is the same or different.

13. The ammonia injection mixer according to claim 12, characterized in that: Connecting pieces are provided between the spiral coils, and the connecting pieces and the spiral coils are sealed, so as to completely divide the space of the reducer into an intermediate channel and at least one annular channel.

14. The ammonia injection mixer according to claim 1, characterized in that: The ammonia nozzle is arranged on the central axis of the reducing pipe.

15. The ammonia injection mixer according to claim 1, characterized in that: An ash blocking element is provided above the ammonia nozzle.

16. The ammonia injection mixer according to claim 15, characterized in that: The ash blocking element is a floating part. When the ammonia nozzle has gas ejected, the ash blocking element floats up and away from the ammonia nozzle under the blowing action of the gas. When the ammonia nozzle does not eject gas, the ash blocking element falls under the action of its own gravity and blocks the ammonia nozzle.

17. The ammonia injection mixer according to claim 1, characterized in that: A protective element is provided above the reducer to protect the coil located below it and to act as a flow turbulent to enhance the mixing of ammonia and flue gas.

18. A flue gas denitrification system comprising: An ammonia injection assembly includes an ammonia injection main pipe on which a main pipe flow regulating valve is provided; A plurality of ammonia injection main pipes, which are connected to the ammonia injection main pipe and are connected to its cavity through the ammonia inlet pipe of the ammonia injection mixing unit; an ammonia injection mixer according to any one of claims 1 to 17; a denitration unit, which is arranged downstream of the ammonia injection mixer and includes at least one layer of denitration catalyst.

19. The flue gas denitrification system according to claim 18, characterized in that: An ammonia-air mixer is provided on the ammonia injection main pipe or the ammonia injection mother pipe. The ammonia-air mixer is connected to the dilution air pipeline and is used to mix ammonia with dilution air so that the ammonia concentration in the ammonia-air mixture injected into the flue is far away from its explosion limit.

20. The flue gas denitrification system according to claim 19, characterized in that: The dilution air pipeline is divided 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 through the flue, the valve on the dilution air branch pipe is in the open state, so that the ammonia nozzle always has gas ejected to avoid clogging of the ammonia nozzle.

21. The flue gas denitrification system according to claim 18, characterized in that: A guide assembly and a rectifying grid are arranged between the flue gas denitrification ammonia injection mixer and the first layer of denitrification catalyst. The guide assembly is arranged at the bend of the flue to divert the upward flue gas to enter the denitrification unit downward; the rectifying grid is arranged on the upper part of the first layer of catalyst along the direction of flue gas flow, and is used to rectify the flue gas passing through the denitrification catalyst.

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