Ammonia gas and air mixed injection system for ethylene cracking furnace

Abstract

The utility model relates to the technical field of flue gas treatment, in particular to an ammonia gas and air mixed injection system for an ethylene cracking furnace. The system comprises an ammonia spraying grid mounted in an SCR denitration area, at least one heat exchange module and a catalyst bed layer, in the airflow flowing direction, the ammonia spraying grid is located in the upstream direction of the catalyst bed layer, and at least one heat exchange module is arranged between the ammonia spraying grid and the catalyst bed layer. The system is helpful for effectively capturing low-concentration nitrogen oxides in flue gas; the flue gas can be uniformly mixed with flue gas within an extremely short time and an extremely short mixing distance; the system is particularly suitable for an ethylene cracking furnace with low nitrogen oxide concentration, small flue gas amount and low flue gas flow rate and ammonia gas and air mixed gas sprayed by an ammonia spraying grid, the volume percentage of ammonia gas is smaller than 1%, low-concentration NOx can be quickly captured after turbulent flow of the heat exchange module, and the flue gas denitration treatment effect is better.

Description

Technical Field

[0001] The utility model relates to the technical field of flue gas treatment, in particular to an ammonia-air mixing injection system for an ethylene cracking furnace. Background Art

[0002] Nitrogen oxides are one of the main sources of air pollution, mainly NO and NO2, usually NO x Indicates that NO in the air x The main sources are internal combustion engine combustion, power and petrochemical industries, and the NO contained in the flue gas after combustion x Discharged into the atmosphere, in addition, waste gas is discharged from the production of nitric acid, its salts and nitrites.

[0003] Ethylene is an important starting material for the petrochemical industry and occupies a core position in the petrochemical industry chain. The upstream raw materials of ethylene are naphtha, ethane, coal and natural gas. As the scale of ethylene plants continues to expand, the heat load of cracking furnaces increases, the amount of flue gas generated by fuel combustion also increases, and the nitrogen oxides (NO x ) The total amount also increased accordingly.

[0004] At present, the ethylene cracking furnaces in operation are basically not equipped with flue gas denitrification facilities, and most of them use low-nitrogen burners to reduce nitrogen oxide emissions. Considering the factors of fuel utilization and stable combustion, low-nitrogen burners can only reduce NO x The concentration is reduced to 80-100 mg / Nm 3 level, and is close to the ultra-low emission index (50mg / Nm 3 Therefore, taking practical denitrification measures to reduce nitrogen oxide concentrations and emissions in existing ethylene cracking furnaces has become an urgent task for all refining and chemical companies.

[0005] Heating furnace and cracking furnace have small flue gas volume and NO in flue gas. x With the characteristics of low concentration and low flue gas flow rate, how can the denitrification reducing agent sprayed into the flue reduce the low concentration of NO in the flue gas? x Rapid capture has become a difficult problem in the denitrification process of this type of furnace; in addition, the cross-sectional area of ​​the temperature window area suitable for the SCR denitrification process of the heating furnace and the cracking furnace is generally rectangular, that is, the long side is much larger than the short side, so that the cross-sectional area makes it easy for the injected ammonia-air mixture to mix unevenly with the flue gas, thereby causing the NH3 / NO entering the catalyst inlet to x The molar ratio deviation is greater than 5%, resulting in low denitrification efficiency of the entire device and serious ammonia slip.

[0006] The SCR denitrification process typically uses liquid ammonia, urea, or aqueous ammonia as a denitrification reducing agent. Liquid ammonia is a widely used raw material in the petrochemical industry, and some plants produce liquid ammonia as one of their products. Therefore, the use of liquid ammonia as a reducing agent is common in heating furnaces and ethylene cracking furnaces. However, as is well known, the ammonia gas produced after evaporation of liquid ammonia needs to be mixed with dilution air and diluted to a concentration below 5% before entering the flue gas for reaction. Traditional power plant denitrification process designs typically use a dilution concentration between 2% and 5%. However, this dilution concentration is insufficient to achieve uniform ammonia injection in heating furnaces and ethylene cracking furnaces. Utility Model Content

[0007] The technical problem to be solved by the utility model is to provide an ammonia-air mixed injection system for an ethylene cracking furnace.

[0008] The technical solution of the utility model to solve the above technical problems is as follows:

[0009] The utility model provides an ammonia-air mixed injection system for an ethylene cracking furnace, wherein the ethylene cracking furnace includes an SCR denitration area; an ammonia injection grid, at least one heat exchange module, and a catalyst bed installed in the SCR denitration area; in the direction of air flow, the ammonia injection grid is located upstream of the catalyst bed, and at least one heat exchange module is provided between the ammonia injection grid and the catalyst bed.

[0010] On the basis of the above technical solution, the present invention can also be improved as follows.

[0011] Furthermore, there are at least two heat exchange modules, the ammonia injection grid is located between the two heat exchange modules, the distance between the ammonia injection grid and the heat exchange module located in its injection direction is 200-400 mm, and the distance between the ammonia injection grid and the catalyst bed is greater than 2000 mm.

[0012] Furthermore, the ammonia injection grid includes a plurality of nozzles opened toward the catalyst bed, the plurality of nozzles are connected through a plurality of distribution pipes, and the plurality of distribution pipes are connected to a feed pipe.

[0013] Furthermore, the plurality of nozzles are arranged at intervals on the plane where the ammonia injection grid is located; the diameter of the nozzle hole of each nozzle is 3 to 8 mm, and the distance between the centers of the nozzle holes of two adjacent nozzles is less than 400 mm.

[0014] Furthermore, the ammonia injection grid includes a plurality of partitions, each of which includes at least one nozzle; and each of which is provided with a concentration control valve.

[0015] Furthermore, it also includes a dilution air regulation module, an ammonia regulation module and an ammonia-air mixer; the dilution air regulation module and the ammonia regulation module are respectively connected to the ammonia-air mixer, and the dilution air regulation module is also connected to the compressed air supply device; the ammonia-air mixer is connected to the ammonia injection grid.

[0016] The beneficial effects of the utility model are:

[0017] (1) The ammonia-air mixed injection system for an ethylene cracking furnace of the present invention can further mix the ammonia-air mixed gas sprayed from the ammonia spray grid with the flue gas in the boiler under the turbulence of a heat exchange module, which helps to effectively capture low-concentration nitrogen oxides in the flue gas;

[0018] (2) The ammonia-air mixed injection system for an ethylene cracking furnace of the present invention increases the distance between the ammonia injection grid and the catalyst bed, thereby increasing the mixing distance between the ammonia-air mixed gas and the flue gas, allowing nitrogen oxides to fully react;

[0019] (3) The ammonia-air mixed injection system for the ethylene cracking furnace of the present invention can also be arranged with the ammonia injection grid to evenly inject the ammonia-air mixed gas into the SCR denitrification area, and evenly mix it with the flue gas in a very short time and a very short mixing distance;

[0020] (4) The ammonia-air mixed injection system for the ethylene cracking furnace of the present invention uses compressed air as dilution air, which can replace the dilution fan and reduce the power consumption of the project operation;

[0021] (5) The ammonia-air mixed injection system for the ethylene cracking furnace of the present invention sets the ammonia injection grid in a zone control mode, so that the cross-sectional area where the ammonia injection grid is located is divided into several areas, and a concentration control valve is set on each area, so that the outlet NO corresponding to different areas can be realized. x The valve opening is adjusted according to the concentration value, so as to control the ammonia injection amount as accurately as possible and reduce the ammonia escape concentration;

[0022] (6) The flue gas treatment system of the ethylene cracking furnace of the present invention is particularly suitable for ethylene cracking furnaces with low nitrogen oxide concentration, small flue gas volume and low flue gas flow rate. The volume percentage of ammonia in the ammonia-air mixed gas injected by the ammonia grid is less than 1%. After the turbulence of the heat exchange module, the low concentration of NO can be quickly captured. x , which makes the denitrification effect of flue gas better. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic structural diagram of an ammonia-air mixed injection system for an ethylene cracking furnace according to the present invention;

[0024] Figure 2 This is a front view of the ammonia-air mixed injection system for an ethylene cracking furnace of the present invention, including an ammonia injection grid, a heat exchange module, and a catalyst bed;

[0025] Figure 3 for Figure 2 Side view of

[0026] Figure 4 This is a front view of the ammonia injection grid in the embodiment of the ammonia-air mixed injection system for an ethylene cracking furnace of the present invention;

[0027] Figure 5 This is an ammonia-air mixed injection system for an ethylene cracking furnace of the present invention. In the embodiment, the ammonia injection grid corresponds to Figure 4 Schematic diagram of the partition structure.

[0028] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0029] 1. Dilution air adjustment module; 11. First flow meter; 12. Control valve;

[0030] 2. Ammonia regulating module; 21. Pneumatic switch valve; 22. Second flow meter; 23. Pneumatic regulating valve;

[0031] 3. Ammonia-air mixer;

[0032] 4. Ammonia injection grid; 41. Nozzle; 42. Distribution pipe; 43. Feed pipe; 44. Concentration control valve;

[0033] 100. Convection section; 200. Heat exchange module; 300. Catalyst bed. DETAILED DESCRIPTION

[0034] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0035] like Figures 1 to 5 As shown, the ammonia-air mixed injection system for an ethylene cracking furnace of the present invention includes an SCR denitration area in the boiler; the system includes an ammonia injection grid 4 installed in the SCR denitration area, at least one heat exchange module 200 and a catalyst bed 300; in the direction of air flow, the ammonia injection grid 4 is located upstream of the catalyst bed 300, and at least one heat exchange module 200 is provided between the ammonia injection grid 4 and the catalyst bed 300.

[0036] The ammonia-air mixed injection system for an ethylene cracking furnace of the present invention is equipped with an ammonia injection grid (4) within the SCR denitration zone, upstream of the catalyst bed (300). This allows the ammonia-air mixture ejected from the grid to mix with the flue gas within the boiler, where it is further mixed under the turbulence of a heat exchange module (200). This arrangement also increases the distance between the grid (4) and the catalyst bed (300), thereby increasing the mixing distance between the ammonia-air mixture and the flue gas. The placement of the grid (4) also enables the ammonia-air mixture to be evenly injected into the SCR denitration zone, mixing uniformly with the flue gas in a very short time and over a very short mixing distance.

[0037] The ammonia-air mixed injection system of the utility model is mainly suitable for ethylene cracking furnaces with low nitrogen oxide concentrations, where the flue gas volume is small and the NO in the flue gas is low. x The concentration is low. At the entrance of the SCR denitrification area, the concentration of nitrogen oxides in the flue gas is 50-200 mg / Nm 3 (dry basis, 3% oxygen), and the flue gas flow rate is low, so that the NO in the flue gas x It is generally difficult to capture NO quickly, but the above-mentioned injection system of the utility model can effectively and quickly capture NO x , thereby significantly improving the flue gas treatment effect of the ethylene cracking furnace.

[0038] Preferably, there are at least two heat exchange modules 200, the ammonia injection grid 4 is located between the two heat exchange modules 200, the distance between the ammonia injection grid 4 and the heat exchange module 200 located in its injection direction is 200-400 mm, and the distance between the ammonia injection grid 4 and the catalyst bed 300 is greater than 2000 mm.

[0039] The distance between the heat exchange modules 200 is 500-800 mm.

[0040] Preferably, the catalyst bed 300 is arranged in the temperature window area of ​​280-420°C of the boiler. A heat exchange module 200 is also installed downstream of the catalyst bed 300. The distance between the two heat exchange modules 200 is 6-7m.

[0041] Preferably, the ammonia injection grid 4 includes a plurality of nozzles 41 opened toward the catalyst bed 300, and the plurality of nozzles 41 are connected through a plurality of distribution pipes 42, and the plurality of distribution pipes 42 are connected to a feed pipe 43; the above structure enables the nozzles 41 of the ammonia injection grid 4 to be arranged at multiple points, so that the injection effect of the ammonia-air mixed gas is more uniform and efficient.

[0042] Preferably, the nozzles 41 are arranged at intervals on the plane where the ammonia injection grid 4 is located; the diameter of the nozzle hole of each nozzle 41 is 3 to 8 mm, and the distance between the centers of the nozzle holes of two adjacent nozzles 41 is less than 400 mm; the specifications and arrangement of the nozzles 41 make the sprayed ammonia-air mixture gas more uniform and can further quickly and effectively capture low-concentration NO x .

[0043] Preferably, the ammonia injection grid 4 includes a plurality of partitions, each of which includes at least one nozzle 41; each partition is provided with a concentration control valve 44. The ammonia injection grid 4 is set in a zone control mode, so that the cross-sectional area of ​​the ammonia injection grid 4 is divided into several zones, and a concentration control valve 44 is provided on each zone, so that the outlet NO corresponding to different zones can be realized. x The valve opening is adjusted according to the concentration value, so as to control the ammonia injection amount as accurately as possible and reduce the ammonia escape concentration.

[0044] Further preferably, the concentration control valve 44 can be an automatic valve or a manual valve, so that its control mode is flexible and diverse.

[0045] Further preferably, the concentration control valve 44 is an automatic valve. At the same time, multiple NO x Concentration monitor, each NO x The concentration monitor and each automatic valve can be connected to the control unit circuit to x By monitoring the concentration, the opening of each automatic valve can be remotely and automatically controlled.

[0046] The ammonia injection grid 4 of the present invention is communicated with a pipeline located outside the boiler, and the pipeline can supply ammonia-air mixed gas to the ammonia injection grid 4 .

[0047] Preferably, the pipeline connected to the ammonia injection grid 4 is specifically connected to the ammonia-air mixer 3, and the ammonia-air mixer 3 is respectively connected to the dilution air regulation module 1 and the ammonia regulation module 2, so that the dilution air and ammonia supplied by the two can be mixed in proportion in the ammonia-air mixer 3.

[0048] Further preferably, the dilution air regulating module 1 includes a first flow meter 11 and a regulating valve 12 ; the ammonia regulating module 2 includes a pneumatic switch valve 21 , a second flow meter 22 and a pneumatic regulating valve 23 .

[0049] Further preferably, the formula for mixing ammonia and air in the ammonia-air mixer 3 is:

[0050] Concentration of ammonia / air mixture = ammonia volume flow rate / (ammonia volume flow rate + dilution air volume flow rate) × 100 (%).

[0051] Preferably, in actual use, the ammonia-air mixer 3, the dilution air regulating module 1, and the ammonia regulating module 2 can all be connected to a control module circuit. The control module can be a DCS control system. The above formula is input into the DCS control system. The system receives the flow monitoring value and automatically calculates the concentration of the ammonia / air mixture. If the concentration is less than 1%, the opening of the regulating valve 12 of the dilution air regulating module 1 is increased to increase the dilution air volume, thereby ensuring that an equal amount of ammonia-air mixture is sprayed out from each area of ​​the ammonia injection grid 4.

[0052] Further preferably, the concentration of ammonia / air mixture is not greater than 1% by controlling the regulating valve 12; ammonia is sent into the ammonia injection system through a large amount of dilution air, thereby ensuring that each area of ​​the ammonia injection grid 4 has uniform and sufficient ammonia injection.

[0053] Further preferably, the dilution air regulating module 1 is also connected to the compressed air supply device; since the flue gas volume and ammonia consumption of boilers such as heating furnaces and ethylene cracking furnaces are small, the required dilution air volume is small. Therefore, compressed air is used as dilution air to replace the dilution fan, thereby reducing the power consumption of the project operation.

[0054] The system of the utility model can be used for treating flue gas from an ethylene cracking furnace, and a mixed gas containing ammonia and air is sprayed into the SCR denitration area of ​​the boiler through the ammonia spray grid 4; the volume percentage of ammonia in the mixed gas is less than or equal to 1%.

[0055] Preferably, the nozzle pressure drop of the ammonia injection grid 4 is greater than 1500 Pa, and the resistance of the ammonia injection grid 4 is lower than 60 Pa.

[0056] Preferably, in the gas entering the catalyst bed 300 , the deviation of the molar ratio of ammonia to nitrogen oxides is less than or equal to 5%.

[0057] The volume percentage of ammonia in the ammonia-air mixture injected by the ammonia injection grid 4 is less than 1%. After the turbulence of the heat exchange module 200, low-concentration NO can be quickly captured. x , which makes the denitrification effect of flue gas better.

[0058] The present invention is described below through specific embodiments.

[0059] Example

[0060] In this embodiment, the ammonia-air mixed injection system is installed in the convection section 100 of the flue of the ethylene cracking furnace. The flue has a cross-sectional dimension of 2102 x 15250 mm. The ammonia injection grid 4 in this embodiment is divided into 22 zones. The spacing between the nozzles 41 is 350 mm, and there are 264 nozzles 41 in total. The nozzle orifice diameter of each nozzle 41 is 3 mm. During ammonia injection, the pressure drop at each nozzle 41 is approximately 1800 Pa.

[0061] In this embodiment, each partition of the ammonia injection grid 4 has a main distribution pipe 42, and a manual valve is provided on the distribution pipe 42.

[0062] The specific control process of this embodiment is as follows: when the outlet NO corresponding to a partition position of the ammonia injection grid 4 x When the concentration value is too high, the outlet NO corresponding to the other partition position x If the concentration value is too small, then at the beginning of operation, the manual valve opening on the main distribution pipe 42 corresponding to a zone is adjusted to increase the amount of ammonia-air mixture, thereby making the NO in this area x A large amount of reducing agent reacts; the opening of the manual valve on the main distribution pipe 42 corresponding to another partition is adjusted to a smaller level to reduce the amount of ammonia-air mixture, thereby avoiding waste of reducing agent and serious ammonia escape.

[0063] The dilution air used in this embodiment is compressed air. The volume percentage of ammonia in the ammonia-air mixed gas is 0.5%. At the inlet of the catalyst bed 300, the deviation of the molar ratio of ammonia to nitrogen oxides is 2%.

[0064] The treated flue gas was tested at the boiler flue gas outlet and the nitrogen oxide concentration was found to be 15 mg / Nm 3 (dry basis, 3% reference oxygen), far below the environmental ultra-low emission index. x The flue gas can also be effectively treated.

[0065] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation to the present invention.

[0066] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this utility model, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0067] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0068] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0069] In the description of this utility model, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; direct connections, indirect connections through an intermediate medium, and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on the specific circumstances.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An ammonia-air mixed injection system for an ethylene cracking furnace, wherein the ethylene cracking furnace includes an SCR denitrification area; characterized in that: The invention comprises an ammonia injection grid (4), at least one heat exchange module (200) and a catalyst bed (300) installed in the SCR denitration area; in the direction of air flow, the ammonia injection grid (4) is located upstream of the catalyst bed (300), and at least one heat exchange module (200) is provided between the ammonia injection grid (4) and the catalyst bed (300).

2. The ammonia-air mixed injection system for an ethylene cracking furnace according to claim 1, characterized in that: There are at least two heat exchange modules (200), the ammonia injection grid (4) is located between the two heat exchange modules (200), the distance between the ammonia injection grid (4) and the heat exchange module (200) located in its injection direction is 200-400 mm, and the distance between the ammonia injection grid (4) and the catalyst bed (300) is greater than 2000 mm.

3. The ammonia-air mixed injection system for an ethylene cracking furnace according to claim 1, characterized in that: The ammonia injection grid (4) includes a plurality of nozzles (41) opened toward the catalyst bed (300), the plurality of nozzles (41) are connected through a plurality of distribution pipes (42), and the plurality of distribution pipes (42) are connected to a feed pipe (43).

4. The ammonia-air mixed injection system for an ethylene cracking furnace according to claim 3, characterized in that: The plurality of nozzles (41) are arranged at intervals on the plane where the ammonia spray grid (4) is located; the diameter of the spray hole of each nozzle (41) is 3 to 8 mm, and the distance between the centers of the spray holes of two adjacent nozzles (41) is less than 400 mm.

5. The ammonia-air mixed injection system for an ethylene cracking furnace according to claim 4, characterized in that: The ammonia injection grid (4) comprises a plurality of partitions, each of which comprises at least one nozzle (41); and each of which is provided with a concentration control valve (44).

6. The ammonia-air mixed injection system for an ethylene cracking furnace according to any one of claims 1 to 5, characterized in that: The invention also includes a dilution air regulating module (1), an ammonia regulating module (2) and an ammonia-air mixer (3); the dilution air regulating module (1) and the ammonia regulating module (2) are respectively connected to the ammonia-air mixer (3), and the dilution air regulating module (1) is also connected to a compressed air supply device; the ammonia-air mixer (3) is connected to the ammonia injection grid (4).

Images