Ammonia injection device and design method thereof

Abstract

The present invention relates to an ammonia injection device and a design method thereof, comprising an ammonia supply source and an ammonia injection main pipe, the ammonia injection main pipe having at least two main pipe sections, the ammonia injection device also comprising an ammonia injection branch pipe group connected to each main pipe section, the ammonia injection branch pipe group comprising a first branch pipe section, a manifold, a second branch pipe section, a nozzle and a regulating valve, and the ammonia injection branch pipe groups connected to different main pipe sections: at least part of the first branch pipe section and the second branch pipe section are different, so that the opening of the regulating valve is in a linear regulation area. The present invention proposes a design method for an ammonia injection device based on the actual flue gas flow field distribution, divides the ammonia injection control zone according to the distribution gradient of the required ammonia amount, adopts differential design for the length and diameter of each section of the ammonia supply main pipe, the diameter of the branch pipe section, the number of branch pipe groups, the nozzle diameter, the regulating valve range, etc., to meet the NH3 / NO distribution uniformity requirements in actual operation, and the regulating valve opening of each branch pipe section is in a linear regulation range, thereby improving the regulation performance of the ammonia injection device.

Description

Technical Field

[0001] The invention belongs to the technical field of SCR catalysts, and in particular relates to an ammonia injection device and a design method thereof. Background Art

[0002] There are three main technical classifications of SCR ammonia injection mixing technology: grid-type AIG, mixed-type AIG and vortex mixing disk-type AIG. Regardless of the technology, in the current design and application, the deviation of actual flue gas parameters is not taken into account, and the ammonia injection pipeline is designed according to equal pipe diameter.

[0003] When the equal pipe diameter design is adopted, in order to improve the uniformity of NH3 / NO distribution, in actual operation, it is often necessary to adjust the regulating valves of the branch pipes in some areas to a smaller opening. For units with large deviations in the distribution of the flue gas flow field, the opening of individual branch pipe regulating valves even needs to be closed to less than 30% opening. When the valve opening is too small, its flow regulation performance will be significantly deteriorated, and the flow will deviate from the linear range, affecting the regulation performance of the ammonia injection grid, which is likely to cause a large fluctuation in the amount of ammonia injection in the corresponding area: when the ammonia amount is too high, the ammonia escape in this area will be too high, affecting the operation of downstream facilities; when the ammonia amount is too low, the NOx concentration in this area exceeds the standard. In order to meet the emission standards, the total amount of ammonia injection increases, and the ammonia escape in other areas increases accordingly, which also affects the operation of downstream facilities and increases the ammonia consumption. Therefore, it is necessary to change the existing design ideas and design ammonia injection devices in a targeted manner according to the actual flue gas conditions.

[0004] Referring to the patent with publication number CN109173635A, a design method for a variable diameter ammonia injection grid pipeline system is disclosed, which uses a tapered mother pipe to evenly distribute the ammonia injection amount of the ammonia injection branch pipe, but the design of the patent scheme does not consider the influence of the difference in ammonia demand in different regions and the adjustment characteristics of the ammonia injection valve on the design of the ammonia injection grid. Referring to the patent with publication number CN108722184A, a scheme using a tapered mother pipe is disclosed to evenly distribute the ammonia injection amount of the ammonia injection branch pipe, and the nozzle diameter is designed differently, but the scheme also has problems such as incomplete consideration of the actual ammonia demand distribution.

[0005] Most of the domestic denitrification devices are renovation projects. Due to the limitation of on-site space, the uniformity of the incoming flue gas distribution may be further deteriorated from the original state. The current ammonia injection device does not take into account the actual flue gas conditions, and generally adopts the equal pipe diameter design concept. The ammonia flow regulation performance is difficult to meet the actual operation needs. Summary of the invention

[0006] One object of the present invention is to provide an ammonia injection device to avoid the problem of poor ammonia injection regulation performance caused by the current equal pipe diameter design. The ammonia injection device is designed with differentiation in the diameter of the ammonia injection main pipe, the diameter and number of the ammonia injection branch pipes, the diameter and number of the nozzles, etc. according to the actual flue gas conditions. Different zones use regulating valves of corresponding ranges. After hot operation optimization and adjustment, it is ensured that the regulating valves of each zone are in

[0007] Linear opening range improves flow regulation performance and increases NH3 / NO distribution uniformity.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] An ammonia injection device comprises an ammonia source and an ammonia injection main pipe connected to the ammonia source, the ammonia injection main pipe having at least two main pipe sections, the diameter of the main pipe section decreasing from the side close to the ammonia source to the side away from the ammonia source, the ammonia injection device also comprises at least one group of ammonia injection branch pipe groups connected to each of the main pipe sections, characterized in that: the ammonia injection branch pipe group comprises a first branch pipe section connected to the main pipe section, a manifold connected to the first branch pipe section, a plurality of second branch pipe sections connected to the manifold, a plurality of nozzles connected to the second branch pipe sections and a regulating valve arranged on the first branch pipe section, and in the ammonia injection branch pipe group connected to different main pipe sections: at least some of the first branch pipe sections and the second branch pipe sections are different, so that the opening of the regulating valve is in a linear regulation area.

[0010] Preferably, the length of the main pipe section with the largest non-pipe diameter accounts for 1 / 3 to 1 / 2 of the total length of the ammonia injection main pipe.

[0011] Preferably, when a plurality of ammonia injection branch pipe groups are connected to the mother pipe section, the pipe diameters of the first branch pipe sections connected to the same mother pipe section are equal or unequal.

[0012] Preferably, the diameters of the second branch pipe sections in each of the ammonia injection branch pipe groups are equal or unequal.

[0013] Preferably, the lengths of the second branch pipe sections in each of the ammonia injection branch pipe groups are equal or unequal.

[0014] Preferably, the number of the second branch pipe sections in each of the ammonia injection branch pipe groups is equal or unequal.

[0015] Preferably, the plurality of nozzles are distributed along the depth direction of the second branch pipe section extending into the flue.

[0016] Preferably, the number of nozzles on each of the second branch pipe sections is equal or unequal.

[0017] Preferably, in each group of the ammonia injection branch pipe groups: the positions of the first nozzles in the second branch pipe section are the same or different.

[0018] Preferably, at least two mother pipe sections are provided.

[0019] Another object of the present invention is to provide a design method for an ammonia injection device, according to the actual flue gas flow field distribution, the SCR ammonia injection main pipe, branch pipe section and nozzle are differentiatedly designed to improve the uniformity of NH3 / NO distribution in actual operation, while ensuring that the opening of the ammonia injection regulating valve is in a linear range, thereby improving the regulation performance of the ammonia injection device.

[0020] In order to achieve the above object, the technical solution adopted by the present invention is:

[0021] A design method for an ammonia injection device comprises the following steps:

[0022] 1) Under different loads and typical operating conditions, test the flue gas velocity in the inlet flue and the NOx concentration distribution in the flue gas to calculate the ammonia required at each point.

[0023] 2) Divide the flue area according to the mixed gas flow gradient, and the mixed gas flow deviation in each area shall not exceed 8L / s / m 2 , and the partition area is not larger than 2m 2 , determine the number of ammonia injection branch pipe groups n, and determine the diameter dn1 of the first branch pipe section in each ammonia injection branch pipe group according to the ammonia demand in each zone, the gas flow rate requirements, and the flow adjustment range of the regulating valve, to ensure that the opening of the regulating valve under different loads is in the linear adjustment range,

[0024] 3) Determine the number of nozzles and nozzle diameter dn4 according to the amount of ammonia required in the zone.

[0025] 4) Determine the optimal tube diameter ratio β value based on CFD numerical simulation calculation. The β value includes βn1 value, βn2 value, and βn3 value, where: tube diameter ratio βn1=dn1 / Z, tube diameter ratio βn2=dn3 / dn2, tube diameter ratio βn3=dn4 / dn3, and each tube diameter ratio satisfies: βn1<0.2, βn2<0.5, βn3<0.4,

[0026] When two main pipe sections are set, Z1=1.3Z2, L1=(1~2)L2, according to the βn1 value, determine the minimum value of the diameter Z of each main pipe section, and determine the maximum value of the diameter Z of each main pipe section according to the static pressure distribution of the ammonia injection main pipe. Determine Z within the range of the minimum and maximum values.

[0027] According to βn3 and nozzle diameter dn4, determine the diameter dn3 of the second branch pipe section.

[0028] According to the βn2 value, determine the header pipe diameter dn2,

[0029] 5) Perform thermal optimization adjustment under different loads to meet the uniformity requirements of NH3 / NO distribution, so that the opening of each regulating valve is in the linear adjustment range, and the flow between the nozzles on the second branch pipe section controlled by the regulating valve is evenly distributed.

[0030] Among them: Z is the diameter of the main pipe section, dn1 is the diameter of the first branch pipe section, dn2 is the diameter of the header, dn3 is the diameter of the second branch pipe section, and dn4 is the diameter of the nozzle.

[0031] Preferably, the grid method is used to test the flue gas velocity in the inlet flue and the NOx concentration distribution in the flue gas.

[0032] Preferably, the number of the second branch pipe sections in the ammonia injection branch pipe group is determined according to the partition area.

[0033] Preferably, the gas flow rate in the ammonia injection mother pipe is not greater than 15 m / s.

[0034] Preferably, the minimum dust blocking prevention diameter of the nozzle is not less than 4 mm, and the arrangement spacing is not greater than 300 mm.

[0035] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0036] The present invention proposes an ammonia injection device design method based on the actual flue gas flow field distribution, divides the ammonia injection control zone according to the distribution gradient of the required ammonia amount, designs the length and diameter of the ammonia supply main pipe in sections, and designs the branch pipe section diameter, the number of branches, the nozzle diameter, the regulating valve range and the like in a differentiated manner to meet the NH3 / NO distribution uniformity requirement in actual operation. The opening of the regulating valve of each branch pipe section is in the linear regulation range, thereby improving the regulation performance of the ammonia injection device, and the regulation performance is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Attached Figure 1 It is a structural schematic diagram of the present invention.

[0038] In the above attached figure:

[0039] 1. Ammonia injection main pipe; 2. First branch pipe section; 3. Junction box; 4. Second branch pipe section; 5. Nozzle; 6. Regulating valve; 7. Flue. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0042] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] like Figure 1 The ammonia injection device shown includes an ammonia supply source, an ammonia injection main pipe 1, and an ammonia injection branch pipe group. The ammonia injection main pipe 1 is connected to the ammonia supply source, and the ammonia injection main pipe 1 is divided into two main pipe sections, and the diameter of the main pipe section close to the ammonia supply source is larger than the diameter of the blind end main pipe section.

[0044] At least one ammonia injection branch pipe group is connected to each mother pipe section. The ammonia injection branch pipe group includes a first branch pipe section 2 connected to the mother pipe section, a header 3 connected to the first branch pipe section 2, a plurality of second branch pipe sections 4 connected to the header 3, a plurality of nozzles 5 connected to the second branch pipe sections 2, and a regulating valve 6 arranged on the first straight pipe section 2. In the ammonia injection branch pipe groups connected to different mother pipe sections, at least some of the first branch pipe sections 2 and the second branch pipe sections 4 are different, so that the opening of the regulating valve 6 is in a linear adjustment area.

[0045] by Figure 1 For the structure: the diameter of the main pipe section 10 is larger than the diameter of the main pipe section 11, and the length L1 of the main pipe section 10 is equal to the length L2 of the main pipe section 11. The number of ammonia injection branch pipe groups is determined according to the flue gas distribution adjustment, and the figure shows 6 groups.

[0046] According to the actual flue gas parameters: the diameters of the first branch pipe sections 2 in each ammonia injection branch pipe group are equal or unequal. For example, the diameters of the first branch pipes 20, 21, 22 and 23, 24 are not equal, and finally ensure that the corresponding regulating valve stroke is in the linear adjustment range. The number of second branch pipe sections 4 in different ammonia injection branch pipe groups is equal or unequal, for example, 3 second branch pipe sections 40 are provided, and 2 second branch pipe sections 41 are provided; the lengths of the second branch pipe sections 4 in each ammonia injection branch pipe group are equal or unequal, for example, the length of the second branch pipe section 41 is less than the length of the second branch pipe section 40. Multiple nozzles 5 are distributed along the depth direction of the second branch pipe section 4 extending into the flue 7, for example, the depth of the first nozzle 52 on the second branch pipe section 42 extending into the flue is greater than the depth of the first nozzle 50 on the second branch pipe section 40 extending into the flue. The number of nozzles 5 set in the second branch pipe section 4 is equal or unequal, for example, 4 nozzles 5 are set in the second branch pipe section 40, and 3 nozzles 5 are set in the second branch pipe section 41.

[0047] The design method of the ammonia injection device in this application is described in detail below, including the following steps:

[0048] 1) Under different loads and typical operating conditions, test the flue gas velocity in the inlet flue and the NOx concentration distribution in the flue gas, and calculate the ammonia required at each corresponding point (expressed as the flow rate of ammonia-air mixed gas).

[0049] 2) Divide the flue area according to the mixed gas flow gradient, and the mixed gas flow deviation in each area shall not exceed 8L / s / m 2 , and the partition area is not larger than 2m 2 , determine the number of ammonia injection branch pipe groups n, and determine the diameter dn1 of the first branch pipe section in each ammonia injection branch pipe group according to the ammonia demand in each zone, the gas flow rate requirements in the ammonia injection pipe, and the flow adjustment range of the regulating valve, to ensure that the opening of the regulating valve under different loads is in the linear adjustment range,

[0050] 3) The minimum anti-clogging dust pipe diameter of the nozzle is not less than 4mm, and the arrangement spacing is not more than 300mm. The number of nozzles and the nozzle diameter dn4 are determined according to the ammonia demand in the partition.

[0051] 4) To ensure uniform distribution of ammonia flow in the same ammonia injection branch pipe group, the optimal pipe diameter ratio β value is determined according to CFD numerical simulation calculation. The β value includes βn1 value, βn2 value and βn3 value, among which: pipe diameter ratio βn1=dn1 / Z, pipe diameter ratio βn2=dn3 / dn2, pipe diameter ratio βn3=dn4 / dn3,

[0052] The pipe diameter ratios should satisfy: βn1<0.2, βn2<0.5, βn3<0.4,

[0053] In this embodiment, two mother pipe sections are designed, Z1=1.3Z2, L1=(1~2)L2, according to the βn1 value, the minimum value of the diameter Z of each mother pipe section of the ammonia injection mother pipe is determined, and the maximum value of the diameter Z of each mother pipe section is determined according to the static pressure distribution of the ammonia injection mother pipe. Z is determined within the range of the minimum value and the maximum value.

[0054] According to βn3 and nozzle diameter dn4, determine the diameter dn3 of the second branch pipe section.

[0055] According to the βn2 value, determine the header pipe diameter dn2,

[0056] 5) Perform thermal optimization adjustment under different loads to meet the uniformity requirements of NH3 / NO distribution, so that the opening of each regulating valve is in the linear adjustment range, and the flow between the nozzles on the second branch pipe section controlled by the same regulating valve is evenly distributed.

[0057] Above: Z is the diameter of the main pipe section, dn1 is the diameter of the first branch pipe section, dn2 is the diameter of the header, dn3 is the diameter of the second branch pipe section, and dn4 is the diameter of the nozzle.

[0058] The regulating valve opening in this embodiment is in the linear regulation range, which means that in the process of gradual increase / decrease of the regulating valve adjustment opening, the gas flow rate is also in the process of gradual increase / decrease, rather than the process of gradual increase / decrease of the regulating valve adjustment opening, the gas flow rate will not show obvious change or there will be a sudden change in the flow rate.

[0059] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for designing an ammonia injection device, the ammonia injection device comprising an ammonia source and an ammonia injection main pipe connected to the ammonia source, the ammonia injection main pipe having at least two main pipe sections, the diameter of the main pipe section decreasing from the side close to the ammonia source to the side away from the ammonia source, the ammonia injection device further comprising at least one group of ammonia injection branch pipes connected to each of the main pipe sections, characterized in that: The ammonia injection branch pipe group includes a first branch pipe section connected to the mother pipe section, a header connected to the first branch pipe section, a plurality of second branch pipe sections connected to the header, a plurality of nozzles connected to the second branch pipe sections, and a regulating valve arranged on the first branch pipe section. In the ammonia injection branch pipe groups connected to different mother pipe sections, at least some of the first branch pipe sections and the second branch pipe sections are different, so that the opening of the regulating valve is in a linear regulation area. It is characterized by comprising the following steps: 1) Under different loads and typical operating conditions, test the flue gas velocity in the inlet flue and the NOx concentration distribution in the flue gas to calculate the ammonia required at each point. 2) Divide the flue area according to the mixed gas flow gradient, and the mixed gas flow deviation in each area shall not exceed 8L / s / m 2 , and the partition area is not more than 2m 2 , determine the number of ammonia injection branch pipe groups n, and determine the diameter dn1 of the first branch pipe section in each ammonia injection branch pipe group according to the ammonia demand in each zone, the gas flow rate requirements, and the flow adjustment range of the regulating valve, to ensure that the opening of the regulating valve under different loads is in the linear adjustment range, 3) Determine the number of nozzles and nozzle diameter dn4 according to the amount of ammonia required in the partition. 4) Determine the optimal tube diameter ratio β value according to CFD numerical simulation calculation. The β value includes βn1 value, βn2 value and βn3 value, where: tube diameter ratio βn1 = dn1 / Z, tube diameter ratio βn2 = dn3 / dn2, tube diameter ratio βn3 = dn4 / dn3, and each tube diameter ratio satisfies: βn1 < 0.2, βn2 < 0.5, βn3 < 0.4, When two mother pipe sections are set, Z1=1.3Z2, L1=(1~2)L2, according to the βn1 value, determine the minimum value of the diameter Z of each mother pipe section, and according to the static pressure distribution of the ammonia injection mother pipe, determine the maximum value of the diameter Z of each mother pipe section, and determine Z within the range of the minimum and maximum values. According to βn3 and nozzle diameter dn4, determine the diameter dn3 of the second branch pipe section. According to the βn2 value, determine the header pipe diameter dn2, 5) Perform thermal optimization adjustment under different loads to meet the uniformity requirements of NH3 / NO distribution, so that the opening of each regulating valve is in the linear adjustment range, and the flow between the nozzles on the second branch pipe section controlled by the regulating valve is evenly distributed. Among them: Z is the diameter of the main pipe section, dn1 is the diameter of the first branch pipe section, dn2 is the diameter of the header, dn3 is the diameter of the second branch pipe section, and dn4 is the diameter of the nozzle.

2. The method according to claim 1, characterized in that: The grid method is used to test the flue gas velocity in the inlet flue and the NOx concentration distribution in the flue gas, and the ammonia injection control zone is divided according to the mixed gas flow gradient.

3. The method according to claim 1, characterized in that: The number of the second branch pipe sections in the ammonia injection branch pipe group is determined according to the partition area.

4. The method according to claim 1, characterized in that: The gas flow rate in the ammonia injection mother pipe is not greater than 15m / s.

5. The method according to claim 1, characterized in that: The minimum anti-dust pipe diameter of the nozzle is not less than 4mm, and the arrangement spacing is not greater than 300mm.

6. The method according to claim 1, characterized in that: The length of the main pipe section not having the maximum pipe diameter accounts for 1 / 3 to 1 / 2 of the total length of the ammonia injection main pipe.

7. The method according to claim 1, characterized in that: When a plurality of ammonia injection branch pipe groups are connected to the main pipe section, the pipe diameters of the first branch pipe sections connected to the same main pipe section are equal or unequal.

8. The method according to claim 1, characterized in that: The diameter, length and number of the second branch pipe sections in each ammonia injection branch pipe group are equal or unequal.

9. The method according to claim 1, characterized in that: The plurality of nozzles are distributed along the depth direction of the second branch pipe section extending into the flue, and the number of nozzles on each second branch pipe section is equal or unequal; the position of the first nozzle in each group of ammonia injection branch pipe groups in the second branch pipe section is the same or different.

Images