Design method of nozzle arrangement for urea direct injection pyrolysis technology in transition flue of gas turbine

Abstract

The invention discloses a nozzle arrangement design method for a urea direct injection pyrolysis technology in a transition flue of a gas turbine, comprising the following steps: 1) establishing a solid geometric model of a flue of equal dimensions; 2) determining the number of nozzles, and determining various arrangements of the nozzles under the number of nozzles; 3) simulating the ammonia distribution of an inlet cross section of an SCR system under various arrangements of the nozzles under the premise that the total urea flow rate, flue gas parameters and flue gas flow rate are the same, and adjusting the flow rate of each nozzle at the same time, so as to obtain the variation law of the ammonia distribution of the inlet cross section of the SCR system with the nozzle arrangement and the flow rate of each nozzle; 4) according to the variation law of the ammonia distribution of the inlet cross section of the SCR system with the nozzle arrangement and the flow rate of each nozzle, determining the optimal nozzle arrangement and the corresponding nozzle flow rate under the current number of nozzles, so as to make the ammonia distribution of the inlet cross section of the SCR system uniform. The method can design and determine the arrangement of the nozzles, the number of the nozzles and the flow rate of each nozzle.

Description

Technical Field

[0001] The invention relates to a nozzle arrangement design method, in particular to a nozzle arrangement design method for a urea direct injection pyrolysis technology for a transition flue of a combustion engine. Background Art

[0002] As people's environmental awareness increases, the control of air pollution has become particularly important. Among them, nitrogen oxides are the main component of air pollution, and the denitrification treatment of flue gas from coal-fired boilers has received widespread attention. In recent years, the denitrification technology transformation of coal-fired boilers has been basically completed, and the denitrification technology transformation of flue gas from gas turbines is also imminent. At present, in the flue gas denitrification technology, the selective catalytic reduction (SCR) denitrification process has been widely used. In this process, urea is used as a reducing agent and is pyrolyzed or hydrolyzed to produce ammonia, which is sprayed into the flue. After ammonia is evenly mixed with nitrogen oxides in the flue gas, it flows through the SCR catalyst system. Under the catalytic action of the catalyst, nitrogen oxides are removed.

[0003] In the transition flue at the turbine outlet, the flue gas temperature is about 500°C, reaching the temperature required for urea thermal decomposition. Urea is sprayed into this flue, and the heat of the flue gas is used to thermally decompose the urea. As the flue gas flows, the urea is fully mixed with the nitrogen oxides in the flue gas, thereby reducing the nitrogen oxide content and ammonia escape in the flue gas.

[0004] Transition flues are mostly circular flues, and the rationality of the nozzle layout directly affects the uniformity of ammonia in the flue. The number of nozzles and the flow rate of each nozzle also have a great influence on the ammonia distribution in the flue, so it is necessary to design the nozzle layout, the number of nozzles and the flow rate of each nozzle. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a nozzle arrangement design method for urea direct injection pyrolysis technology in the transition flue of a gas turbine, which can design and determine the nozzle arrangement, the number of nozzles and the flow rate of each nozzle.

[0006] To achieve the above-mentioned purpose, the nozzle arrangement design method of the gas turbine transition flue urea direct injection pyrolysis technology of the present invention comprises the following steps:

[0007] 1) Establish a solid geometric model of the flue with equal dimensions;

[0008] 2) In the solid geometric model of the flue with equal dimensions, determine the number of nozzles, and determine various arrangements of the nozzles under the number of nozzles;

[0009] 3) Under the premise of the same total urea flow, flue gas parameters and flue gas flow, the ammonia distribution at the inlet cross section of the SCR system under various nozzle arrangements is simulated, and the flow rate of each nozzle is adjusted at the same time, and the change law of ammonia distribution at the inlet cross section of the SCR system with the nozzle arrangement and the flow rate of each nozzle is obtained;

[0010] 4) According to the variation law of ammonia distribution at the inlet section of the SCR system with the nozzle arrangement and the flow rate of each nozzle, determine the optimal nozzle arrangement and the corresponding nozzle flow rate under the current number of nozzles, so that the ammonia distribution at the inlet section of the SCR system is uniform;

[0011] 5) Change the number of nozzles and repeat steps 2) to 4) to obtain the optimal arrangement of nozzles and the corresponding nozzle flow rate under different numbers of nozzles.

[0012] The specific operations of step 1) are:

[0013] The dimensions of the flue and the SCR system are determined, and a solid geometric model of equal dimensions of the flue is established using the modeling software Gambit, and the solid geometric model of equal dimensions is meshed.

[0014] The specific operations of step 2) are:

[0015] In the solid geometric model of the flue with equal size, the computational fluid dynamics software FLUENT is used for simulation to determine the number of nozzles and various arrangements of the nozzles under this number of nozzles.

[0016] When the flue is a circular flue, the regular n-gon method is used to evenly arrange the nozzles on the vertices of the regular n-gon, and the center of the regular n-gon determines the number of nozzles according to the size of the circular flue.

[0017] When the flue is a rectangular flue, the rectangular flue is divided into n small rectangular sections with equal cross-sectional areas, and a nozzle is installed at the center of each small rectangular section.

[0018] In FLUENT software, the number of nozzles is determined by the number of injections added.

[0019] The present invention has the following beneficial effects:

[0020] The nozzle arrangement design method of the gas turbine transition flue urea direct injection pyrolysis technology described in the present invention adopts software simulation to determine the optimal nozzle arrangement and corresponding nozzle flow rate under different nozzle numbers during specific operation, so that the ammonia distribution at the inlet cross section of the SCR system is uniform, ensuring that ammonia and nitrogen oxides are fully mixed and uniform, thereby improving the denitrification efficiency of the system and reducing ammonia escape. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of an arrangement of eight nozzles on a circular transition flue cross section;

[0022] Figure 2 It is a schematic diagram of another arrangement of 8 nozzles on the circular transition flue cross section;

[0023] Figure 3 Schematic diagram of the arrangement of 15 nozzles on the rectangular transition flue cross section. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only an embodiment of a part of the present invention, not all embodiments, and is not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0025] The accompanying drawings show schematic diagrams of structures according to embodiments disclosed in the present invention. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0026] refer to Figure 1 , Figure 2 and Figure 3 The nozzle arrangement design method of the urea direct injection pyrolysis technology for the transition flue of a gas turbine of the present invention comprises the following steps: establishing a geometric model of the transition flue of a gas turbine and the flue of a preheating boiler, performing numerical simulation calculations based on FLUENT software, and dividing the transition flue of the gas turbine into n imaginary cross-sectional areas, wherein n is greater than or equal to 7. By setting different numbers of nozzles and the flow rate of urea solution of the nozzles, under the same boundary conditions, the ammonia distribution and velocity distribution size of the inlet cross section of the SCR system are obtained, and the nozzle flow rate of the corresponding flue gas is adjusted according to the unevenness of the ammonia distribution, so that the ammonia distribution of the inlet cross section of the SCR system tends to be uniform, ensuring that ammonia and nitrogen oxides are fully mixed and uniform, so as to improve the denitration efficiency of the system and reduce ammonia slip.

[0027] The specific steps include:

[0028] 1) Establish flue model

[0029] Determine the size of the flue and the SCR system, use the modeling software Gambit to establish an equal-sized solid geometric model of the flue, and mesh the equal-sized solid geometric model;

[0030] 2) In the equal-size solid geometry model of the flue, the computational fluid dynamics software FLUENT is used for simulation to determine the number of nozzles, and various arrangements of the nozzles are determined under the number of nozzles. When the flue is a circular flue, the regular n-gon method can be used to evenly arrange the nozzles on the vertices of the regular n-gon. The center of the regular n-gon increases the number of nozzles according to the size of the circular flue, and the equal-size solid geometry models of different nozzle arrangements are analyzed; when the flue is a rectangular flue, the rectangular flue is divided into n small rectangular sections with equal cross-sectional areas, and a nozzle is installed at the center of each small rectangular section;

[0031] It should be noted that in FLUENT software, the number of nozzles is determined by the number of injections added.

[0032] 3) Under the premise that the total urea flow rate, flue gas parameters and flue gas flow rate are the same, the ammonia distribution at the inlet cross section of the SCR system is simulated under various nozzle arrangements, and the flow rate of each nozzle is adjusted at the same time, and the change law of ammonia distribution at the inlet cross section of the SCR system with the nozzle arrangement and the flow rate of each nozzle is obtained;

[0033] 4) According to the variation of ammonia distribution at the inlet section of the SCR system with the nozzle arrangement and the flow rate of each nozzle, determine the optimal nozzle arrangement and corresponding nozzle flow rate under the current number of nozzles, so that ammonia and nitrogen oxides are evenly mixed;

[0034] 5) Change the number of nozzles, and repeat steps 2) to 4) to determine the best nozzle arrangement and corresponding nozzle flow rate under the number of nozzles, and obtain the best nozzle arrangement and corresponding nozzle flow rate under different numbers of nozzles.

[0035] The specific operations of step 2) are:

[0036] Import the mesh file of the solid model of the flue and other dimensions obtained in step 1) into the FLUENT software, select the standard k-ε model as the turbulence model, set the boundary conditions as follows: set the flue gas inlet as the velocity inlet boundary condition, the outlet as the pressure outlet boundary condition, and the wall as the adiabatic no-slip wall surface, where the standard k-ε model:

[0037]

[0038]

[0039] Where ρ is density, t is time, k is turbulent kinetic energy, ε is dissipation rate, G k is the generation term of turbulent kinetic energy k caused by the mean velocity gradient, G b is the generation term of turbulent kinetic energy k caused by buoyancy, μ t is the turbulent dynamic viscosity, μ is the laminar dynamic viscosity, Y M is the contribution of pulsation expansion in compressible turbulence, C 1ε , C 2ε , C 3ε is an empirical constant, σ k and σ ε are the Prandtl numbers corresponding to the turbulent kinetic energy k and the dissipation rate ε, respectively.

[0040] It should be noted that the present invention adopts FLUENT software to determine the arrangement mode of the urea solution nozzles in the transition flue of the gas turbine, the number of nozzles and the flow rate of each nozzle, so that the ammonia gas at the inlet cross section of the SCR system is evenly distributed, and the relative standard deviation value is within 3%, thereby saving urea consumption and reducing ammonia slip.

Claims

1. A nozzle arrangement design method for urea direct injection pyrolysis technology in a gas turbine transition flue, characterized in that: The following steps are involved: 1) Establish a solid geometric model of the flue with equal dimensions; 2) In the solid geometric model of the flue with equal dimensions, determine the number of nozzles, and determine various arrangements of the nozzles under the number of nozzles; 3) Under the premise of the same total urea flow, flue gas parameters and flue gas flow, the ammonia distribution at the inlet cross section of the SCR system under various nozzle arrangements is simulated, and the flow rate of each nozzle is adjusted at the same time, and the change law of ammonia distribution at the inlet cross section of the SCR system with the nozzle arrangement and the flow rate of each nozzle is obtained; 4) According to the variation law of ammonia distribution at the inlet section of the SCR system with the nozzle arrangement and the flow rate of each nozzle, determine the optimal nozzle arrangement and the corresponding nozzle flow rate under the current number of nozzles, so that the ammonia distribution at the inlet section of the SCR system is uniform; 5) Changing the number of nozzles, and repeating steps 2) to 4) to obtain the optimal arrangement of nozzles and the corresponding nozzle flow rates under different numbers of nozzles; The specific operations of step 1) are: Determine the size of the flue and the SCR system, use the modeling software Gambit to establish an equal-size solid geometric model of the flue, and mesh the equal-size solid geometric model; The specific operations of step 2) are: In the solid geometric model of the flue with equal size, the computational fluid dynamics software FLUENT is used for simulation to determine the number of nozzles and various arrangements of the nozzles under this number of nozzles.

2. The nozzle arrangement design method for urea direct injection pyrolysis technology for a gas turbine transition flue according to claim 1 is characterized in that: When the flue is a circular flue, the regular n-gon method is used to evenly arrange the nozzles on the vertices of the regular n-gon, and the center of the regular n-gon determines the number of nozzles according to the size of the circular flue.

3. The nozzle arrangement design method for urea direct injection pyrolysis technology for a gas turbine transition flue according to claim 1 is characterized in that: When the flue is a rectangular flue, the rectangular flue is divided into n small rectangular sections with equal cross-sectional areas, and a nozzle is installed at the center of each small rectangular section.

4. The nozzle arrangement design method for urea direct injection pyrolysis technology for a gas turbine transition flue according to claim 1 is characterized in that: In FLUENT software, the number of nozzles is determined by the number of injections added.

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