CN115238451A - Flue urea pyrolysis numerical simulation method - Google Patents
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Abstract
The invention discloses a flue urea pyrolysis numerical simulation method, which comprises the steps of establishing a flue geometric model; establishing a numerical simulation model of the flue; setting a boundary condition and a convergence condition of the numerical simulation model; and carrying out simulation calculation on the numerical simulation model according to the boundary condition and the convergence condition to obtain a simulation calculation result. The flue urea pyrolysis numerical simulation method can improve the thermal decomposition efficiency of urea in the flue and the denitration efficiency of a system.
Description
Technical Field
The invention relates to the technical field of flue gas denitration, in particular to a flue urea pyrolysis numerical simulation method.
Background
In the flue gas denitration technology, a Selective Catalytic Reduction (SCR) denitration process is widely applied, urea is used as a reducing agent to be pyrolyzed or hydrolyzed to prepare ammonia gas to be sprayed into a flue, the ammonia gas is uniformly mixed with nitrogen oxides in flue gas and then flows through an SCR catalyst system, and the nitrogen oxides are removed under the catalytic action of a catalyst.
And urea is sprayed into the transition flue at the outlet of the gas turbine, the urea is pyrolyzed by utilizing the heat of the flue gas and is fully and uniformly mixed with the nitrogen oxides in the flue gas along with the flow of the flue gas, so that the content of the nitrogen oxides in the flue gas and the escape amount of ammonia are reduced.
Flue temperature, urea injection parameters and a nozzle arrangement mode influence the distribution of ammonia in a flue and the pyrolysis efficiency of urea, and the operation and the efficiency of a pyrolysis system are influenced due to inaccurate parameter setting caused by the fact that the parameters are adjusted by experience in most of related technologies.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, the embodiment of the invention provides a flue urea pyrolysis numerical simulation method, which can improve the thermal decomposition efficiency of urea in a flue and the denitration efficiency of a system.
The numerical simulation method for the pyrolysis of the urea in the flue comprises the following steps: establishing a geometric model of the flue; establishing a numerical simulation model of the flue; setting boundary conditions and convergence conditions of the numerical simulation model; and carrying out simulation calculation on the numerical simulation model according to the boundary condition and the convergence condition to obtain a simulation calculation result.
The flue urea pyrolysis numerical simulation method provided by the embodiment of the invention can improve the thermal decomposition efficiency of urea in a flue and the denitration efficiency of a system.
In some embodiments, the numerical simulation model comprises a urea solution evaporation model comprising a liquid phase model and a gas phase model.
In some embodiments, the liquid phase model is:
in the formula: yu is the mass fraction of urea, t is the time, m vap Is urea liquid drop evaporation materialAmount, m d The gas phase model is the urea droplet mass:
in the formula: m is d Is the urea droplet mass, m vap For the urea droplet evaporation mass, c p.d Is the specific heat of the droplet; cp (p) .vap.ref Is the specific heat of the gas phase after evaporation, t is the time, D d Is the droplet diameter; g.ref gas phase density after evaporation, g.ref diffusion coefficient, sh ·
Is a value of Schwood number, B M Is the sbert number, tg is the gas temperature, td is the droplet temperature, and hvap is the vapor phase enthalpy after evaporation.
In some embodiments, the numerical simulation model further includes a urea discrete phase model formed by coupling urea liquid with a urea gas phase according to lagrangian sitting.
In some embodiments, the numerical simulation model further comprises a urea dynamics model, the kinetic equation of which comprises:
water is evaporated from the urea solution mist:
CO (NH 2) 2. XH2O (solution) → CO (NH) 2 ) 2 (solid or gas) + xH 2 O，
Pyrolysis of urea into ammonia and isocyanic acid
CO(NH 2 ) 2 (solid or gas) → HNCO (gas) + NH 3 (gas) is added into the mixture,
isocyanic acid is hydrolyzed to generate ammonia gas
HNCO (gas) + H 2 O (gas) → NH 3 (gas) + CO 2 (gas).
In some embodiments, the numerical simulation model further comprises a reactor model, the reactor model being an ideal hybrid reactor model.
In some embodiments, the reactor model includes a mass control equation and an energy control equation, the mass control equation being:
in the formula: m-mass flow rate of reactant/g.s -1 ，Y k -the mass fraction of the kth component,
-mass fraction at the inlet of the kth component reactor, W k Production Rate/mol (m) of the kth component 3 ·s) -1 ，W k The molar mass of the kth component/g.mol -1 V-reactor volume/m 3 ，
The energy control equation is:
in the formula: h is k Specific enthalpy of the kth component/J.g -1 ；
Specific enthalpy at the inlet of the kth component reactor/J.g -1 (ii) a Heat removal Rate/J.s of Q reactor -1 。
In some embodiments, the boundary condition comprises at least one of a flue gas flow rate, a flue gas temperature, a flue gas total pressure average value, a urea solution concentration, a urea solution flow rate or a urea particle size, and the convergence condition is that a continuity value and a component concentration residual are less than 10 -6 。
In some embodiments, the flow rate of the flue gas is 40-70 m/s, the temperature of the flue gas is 350-700 ℃, the total pressure average value of the flue gas is 2000-4000 Pa, the concentration of the urea solution is 10-50%, the flow rate of the urea solution is 1-20 kg/h, and the particle size of the urea particles is 10-120 microns.
In some embodiments, the numerical simulation method for urea pyrolysis in flue further comprises comparing the numerical simulation result with the experimental result, and if the error value between the numerical simulation result and the experimental result is greater than 10%, adjusting parameters of boundary conditions, and/or adjusting parameters of a geometric model and performing numerical simulation calculation again.
Drawings
Fig. 1 is a schematic diagram of a flue urea pyrolysis model in a flue urea pyrolysis numerical simulation method according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a reactor model in a flue urea pyrolysis numerical simulation method according to an embodiment of the invention.
FIG. 3 is a graph of urea pyrolysis products over time at different temperatures for a flue urea pyrolysis numerical simulation method of an embodiment of the present invention.
FIG. 4 is a urea pyrolysis efficiency-flue gas temperature-residence time relationship curve of a flue urea pyrolysis numerical simulation method according to an embodiment of the invention.
FIG. 5 is a flue geometric model of a flue urea pyrolysis numerical simulation method according to an embodiment of the present invention.
FIG. 6 is a schematic diagram of a urea particle moving track in a flue by a flue urea pyrolysis numerical simulation method according to an embodiment of the invention.
FIG. 7 is a flue gas flow diagram of a flue urea pyrolysis numerical simulation method according to an embodiment of the present invention.
FIG. 8 is a urea volume concentration distribution cloud chart of a flue urea pyrolysis numerical simulation method according to an embodiment of the invention.
FIG. 9 shows NH of a flue urea pyrolysis numerical simulation method according to an embodiment of the present invention 3 A volume concentration distribution cloud.
FIG. 10 is a HNCO volume concentration distribution cloud chart of the flue urea pyrolysis numerical simulation method in the embodiment of the invention.
FIG. 11 is a schematic diagram of a urea particle travel track in a flue of a flue urea pyrolysis numerical simulation method according to another embodiment of the invention.
FIG. 12 is a flue gas flow diagram of a flue urea pyrolysis numerical simulation method according to another embodiment of the present invention.
FIG. 13 is a urea volume concentration distribution cloud of a flue urea pyrolysis numerical simulation method according to another embodiment of the invention.
FIG. 14 is NH of a flue urea pyrolysis numerical simulation method according to another embodiment of the present invention 3 A volume concentration distribution cloud.
FIG. 15 is a HNCO volume concentration distribution cloud chart of a flue urea pyrolysis numerical simulation method according to another embodiment of the invention.
FIG. 16 is a method for arranging nozzles in a flue urea pyrolysis numerical simulation method according to an embodiment of the present invention.
FIG. 17 is a flow chart of a flue urea pyrolysis numerical simulation method of an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The numerical simulation method for the urea pyrolysis of the flue comprises the step of establishing a geometric model of the flue.
For example, a flue geometry model may be established based on actual dimensions of the gas turbine outlet flue, the waste heat boiler, and the boiler internal heat exchange module.
As shown in fig. 16, the arrangement of the nozzles in the flue is as shown in fig. 16, and the black circles shown in fig. 16 are the nozzles.
Establishing a numerical simulation model of the flue, setting boundary conditions and convergence conditions of the numerical simulation model, and carrying out simulation calculation on the numerical simulation model according to the boundary conditions and the convergence conditions to obtain a simulation calculation result.
According to the flue urea pyrolysis numerical simulation method provided by the embodiment of the invention, the optimal urea pyrolysis parameters are determined by performing numerical simulation on the urea pyrolysis process in the flue, and the thermal decomposition efficiency of urea in the flue and the denitration efficiency of a system can be improved by depending on experience judgment in the related technology.
In some embodiments, the numerical simulation model includes a urea solution evaporation model including a liquid phase model and a gas phase model.
It should be noted that, the phase transition process also exists in the process of the urea solution transitioning from the liquid phase to the gas phase, and it is assumed that the evaporation latent heat enthalpy value on the surface of the urea solution droplet is consistent with the evaporation enthalpy value on the surface of the pure water droplet, and the experimental measurement proves that there is no obvious difference between the urea solution droplet and the pure water.
In some embodiments, the liquid phase model is:
in the formula: yu is the mass fraction of urea, t is the time, m vap Is the evaporation mass of the urea droplets, m d The gas phase model is the urea droplet mass:
in the formula: m is d Is the mass of urea droplets, m vap Is the evaporation mass of the urea droplets, c p.d Is the specific heat of the droplet; c. C p.vap.ref Is the gas phase specific heat after evaporation, t is the time, D d Is the droplet diameter; ref gas phase density after evaporation, Γ g.ref diffusion coefficient, sh ·
Is a value of Schwood number, B M Is the sbert number, tg is the gas temperature, td is the droplet temperature, and hvap is the vapor phase enthalpy after evaporation.
The liquid phase model and the gas phase model in the flue urea pyrolysis numerical simulation method can predict the heating and evaporating process of urea solution liquid drops, reduce the calculated amount of numerical simulation and improve the efficiency and the accuracy of the numerical simulation.
It should be noted that urea melts at 133 ℃ and further starts to thermally decompose into NH 3 And HNCO, completely hot at 152 ℃Decomposition to NH 3 And HNCO. The urea thermal decomposition path is that solid (liquid) urea is firstly evaporated into gas phase NH 2 CONH 2 Then the gas phase urea is decomposed into NH 3 And HNC0, decomposition model as shown in fig. 1, the thermal decomposition of urea is limited by kinetic parameters, so that urea remains in the solid state (molten liquid state) for a period of time, and gaseous urea is not stable in a high temperature environment, assuming the conversion of gaseous urea to NH 3 And HNCO, a fast reaction process relative to the urea evaporation process. The HNCO hydrolysis reaction equation is a gas phase homogeneous reaction.
In some embodiments, the numerical simulation model further includes a urea discrete phase model formed by coupling urea liquid and urea gas phases according to lagrangian sitting.
It should be noted that the urea solution droplet is processed in the gas phase by adopting a tracking mode under a Lagrange coordinate system, meanwhile, due to the interaction between gas phase turbulence and the particle phase, the particle phase is considered to conform to a random orbit model, so that the instantaneous flow velocity of fluid at each point on the orbit is always utilized when the particle orbit is calculated by integration, the turbulence diffusion is defined by a vortex dissipation model, and the momentum, the mass and the heat of urea are considered between the urea droplet and the gas phase coupling.
In some embodiments, the numerical simulation model further comprises a urea dynamics model, the kinetic equation of the urea dynamics model comprising:
water is evaporated from the urea solution mist droplets:
CO (NH 2) 2. XH20 (solution) → CO (NH) 2 ) 2 (solid or gas) + xH 2 O，
Pyrolysis of urea into ammonia and isocyanic acid
CO(NH 2 ) 2 (solid or gas) → HNCO (gas) + NH 3 (gas) is added into the mixture,
isocyanic acid is hydrolyzed to generate ammonia gas
HNCO (gas) + H 2 O (gas) → NH 3 (gas) + CO 2 (qi).
In some embodiments, the numerical simulation model further comprises a reactor model, the reactor model being an ideal hybrid reactor model.
Specifically, as shown in fig. 2, the reactor model is an open 0-dimensional reactor, and the reactor inlet for the reactants and the reactor outlet for the products are provided, so that the reactor model is assumed that the mass, energy and momentum of each reactant in the reactor are fully and ideally distributed.
The reactor model assumes that the reactants are dispersed completely and uniformly in the reactor immediately after entering the reactor, and if the reactants are not a single pure substance but a mixture of a plurality of components, all the components are dispersed sufficiently and uniformly immediately to achieve the effect of sufficient mixing, so that the components in the reactor are in an ideal mixing state.
According to the flue urea pyrolysis numerical simulation method provided by the embodiment of the invention, based on the characteristic that each reaction physics in the reactor model is mixed, the reaction process in the model reactor is not influenced by mixing factors but is completely controlled by the chemical reaction rate, and the accuracy of the numerical simulation result is improved.
In some embodiments, the reactor model includes a mass control equation and an energy control equation, the mass control equation being:
in the formula: m-mass flow rate of reactant/g.s -1 ，Y k -the mass fraction of the kth component,
-mass fraction at the inlet of the kth component reactor, w k Production rate of kth component/mol (m) 3 ·s) -1 ，W k The molar mass of the kth component/g.mol -1 V-reactor volume/m 3 ，
The energy control equation is:
in the formula: h is a total of k Specific enthalpy of the kth component/J.g -1 ；
Specific enthalpy at the inlet of the kth component reactor/J.g -1 (ii) a Heat removal Rate/J.s of Q reactor -1 。
In some embodiments, the boundary condition comprises at least one of a flue gas flow rate, a flue gas temperature, a flue gas total pressure average value, a urea solution concentration, a urea solution flow rate or a urea particle size, and the convergence condition is that a continuity value and a component concentration residual are less than 10 -6 。
It should be noted that, when the numerical simulation calculation is performed on the reactor model, the urea particle size and the flue gas temperature do not need to be calculated, so that the simulation calculation process is simplified, and the efficiency of the simulation calculation is improved.
In some embodiments, the flow rate of the flue gas is 40-70 m/s, the temperature of the flue gas is 350-700 ℃, the total pressure average value of the flue gas is 2000-4000 Pa, the concentration of the urea solution is 10-50%, the flow rate of the urea solution is 1-20 kg/h, and the particle size of the urea particles is 10-120 microns.
For example, the flow rate of flue gas is 40m/s, 50m/s, 55m/s, 60m/s, 65m/s and 70m/s, the temperature of flue gas can be 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃ and 700 ℃, the total pressure average value of flue gas is 2000Pa, 2500Pa, 3000Pa and 4000Pa, the concentration of urea solution is 10%, 20%, 30%, 40% and 50%, the flow rate of urea solution is 1kg/h, 5kg/h, 10kg/h, 12.5kg/h, 15kg/h and 20kg/h, and the particle size of urea particles is 10 microns, 20 microns, 30 microns, 50 microns, 70 microns, 100 microns, 110 microns and 120 microns.
In some embodiments, the flue urea pyrolysis numerical simulation method further comprises comparing the numerical simulation result with the experimental result, and if the error value between the numerical simulation result and the experimental result is greater than 10%, adjusting the parameters of the boundary condition and performing the numerical simulation calculation again.
It should be noted that, by comparing the numerical simulation result with the actual measurement experiment result, if the error between the numerical simulation result and the experiment result is less than 10%, the numerical simulation result is used as an industrial application parameter, and if the error between a plurality of numerical simulation results and the experiment result exceeds 10%, the parameter selection of the boundary condition is adjusted, and/or the geometric model parameter is adjusted and the numerical simulation calculation is performed again.
For example, the boundary condition parameters can be individually selected and re-simulated, or the geometric model parameters can be individually adjusted and the numerical simulation calculation can be re-performed, for example, by adjusting the meshing of the geometric model or adjusting the size parameters of the geometric model or adjusting the scale parameters of the geometric model, or the boundary condition parameters can be adjusted and the geometric model parameters can be adjusted by the same staff and the numerical simulation calculation can be re-performed.
According to the flue urea pyrolysis numerical simulation method disclosed by the embodiment of the invention, the numerical simulation result is compared with the experimental result, and the parameters in the numerical simulation are adjusted in time, so that the accuracy of the numerical simulation is improved, and the thermal decomposition efficiency of urea and the denitration efficiency of a system are improved in industrial application.
The numerical simulation results of the flue urea pyrolysis numerical simulation method according to the embodiment of the present invention are described below with reference to fig. 3, 4, and 6 to 10.
As shown in fig. 3, the urea pyrolysis products at flue gas temperatures of 300 c, 350 c and 400 c are plotted against time, and it can be seen from the graph that the volume fraction of urea rapidly decreases and the volume fractions of isocyanic acid and ammonia rapidly increase as the residence time increases at 300 c, 350 c and 400 c. The retention time is between 0.1s and 0.4s, the volume fraction of the urea is reduced to a larger extent, and the volume fractions of the isocyanic acid and the ammonia gas are increased to a larger extent. After 0.4s, the urea volume fraction slowly decreased and the isocyanic acid and ammonia gas volume fractions slowly increased. It can also be seen that the volume fractions of isocyanic acid and ammonia gas are equal, which indicates that after urea is pyrolyzed to form isocyanic acid and ammonia gas, isocyanic acid does not undergo hydrolysis reaction to form ammonia gas within 1.7s of reaction time.
The curves of the urea pyrolysis products at the flue gas temperatures of 450 ℃ and 500 ℃ over time show that at 450 ℃ and 500 ℃ the urea volume fraction decreases rapidly and the isocyanic acid and ammonia volume fractions increase rapidly with increasing residence time. The retention time is between 0.1s and 0.3s, the volume fraction of the urea is reduced to a larger extent, and the volume fractions of the isocyanic acid and the ammonia are increased to a larger extent. After 0.3s, the urea volume fraction slowly decreased and the isocyanic acid and ammonia gas volume fractions slowly increased. It can also be seen that the volume fractions of isocyanic acid and ammonia gas are equal, which indicates that after urea is pyrolyzed to form isocyanic acid and ammonia gas, isocyanic acid does not undergo hydrolysis reaction to form ammonia gas within 1.7s of reaction time.
The time profile of the products of the urea pyrolysis at a flue gas temperature of 650 c shows that at 650 c the volume fraction of urea decreases rapidly and the volume fractions of isocyanic acid and ammonia increase rapidly with increasing residence time. The retention time is between 0.1s and 0.2s, the volume fraction of the urea is reduced to a larger extent, and the volume fractions of the isocyanic acid and the ammonia gas are increased to a larger extent. After 0.2s, the urea volume fraction slowly decreased and the isocyanic acid and ammonia gas volume fractions slowly increased. It can also be seen that the volume fractions of isocyanic acid and ammonia gas are equal, which indicates that after urea is pyrolyzed to form isocyanic acid and ammonia gas, isocyanic acid does not undergo hydrolysis reaction to form ammonia gas within 1.7s of reaction time.
As shown in fig. 4, the urea pyrolysis efficiency increases with increasing flue gas temperature (from 300 ℃ to 650 ℃); increasing with increasing residence time. When the residence time is more than 0.5s, the urea pyrolysis efficiency exceeds 95 percent, and in the residence time of 1.7s, isocyanic acid generated by urea pyrolysis does not generate hydrolysis reaction with water in the flue gas.
As shown in fig. 6 to fig. 10, the system is in a full load condition, which is calculated according to a winter pure condensation 100% (maximum output of the unit), and at this time, the flue gas temperature is 611 ℃, and the flue gas components are set according to actual flue gas components.
The urea solution which can be sprayed is heated by high-temperature flue gas, the water in the urea solution is evaporated after being sprayed into the flue for 3 m, and the concentration of gaseous urea is gradually reduced along with the flow of the flue gasAnd NH 3 And the concentration of HNCO was gradually increased. And the statistics of the relative standard deviation of the urea conversion rate and the product concentration of the main section under the full working condition are shown in table 1:
table 1: statistics of urea conversion rate and relative standard deviation of product concentration of main cross section under full working condition
As can be seen from Table 1, the urea conversion reached 99.5% NH at the catalyst inlet 3 And the concentration of HNCO was low relative to standard deviation.
The numerical simulation results of the flue urea pyrolysis numerical simulation method according to another embodiment of the present invention will be described below with reference to fig. 11 to 15.
It should be noted that, as shown in fig. 11 to fig. 15, the system is in a low-load condition, the low-load condition is calculated according to a winter pure condensation 30% condition, at this time, the flue gas temperature is 479.9 ℃, and the flue gas components are set according to actual flue gas components.
The water in the urea solution is evaporated after being sprayed into the flue for a distance of 3 m, the concentration of the gaseous urea is gradually reduced along with the flow of the flue gas, and the concentrations of NH3 and HNCO are gradually increased. And the statistics of the relative standard deviation of the urea conversion rate and the product concentration of the main section under the low working condition are shown in table 2:
table 2: low-load main section urea conversion rate and product concentration relative standard deviation statistics
From Table 2 it can be seen that the urea conversion reached 99.6% NH at the catalyst inlet 3 And the concentration of HNCO was low relative to standard deviation.
Simulation results show that in the range of 300-650 ℃, when the retention time reaches more than 0.5s, the pyrolysis efficiency of the urea is more than 95%. And in the retention time of 1.7s, the isocyanic acid generated by the pyrolysis of the urea does not have a hydrolysis reaction with water in the flue gas.
The numerical simulation method is used for researching the direct injection pyrolysis process of the urea in the flue at the outlet of the combustion engine, the simulation result shows that under the working conditions of full load and 30% pure condensation in winter of the combustion engine, the urea conversion rate at the inlet of the catalyst reaches 99.5%, and when the urea pyrolysis spray gun is inserted into the flue and arranged according to the equal-area method, NH is arranged on the cross section of the inlet of the catalyst 3 And the concentration of HNCO was low relative to standard deviation.
In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, but are not intended to indicate or imply that the device or element so referred to must have a particular orientation, be constructed in a particular orientation, and be operated in a particular manner, and are not to be construed as limiting the invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; may be mechanically coupled, may be electrically coupled or may be in communication with each other; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood according to specific situations by those of ordinary skill in the art.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In the present disclosure, the terms "one embodiment," "some embodiments," "an example," "a specific example," or "some examples" and the like mean that a specific feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are exemplary and not to be construed as limiting the present invention, and that changes, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A flue urea pyrolysis numerical simulation method is characterized by comprising the following steps:
establishing a geometric model of the flue;
establishing a numerical simulation model of the flue;
setting the boundary condition and the convergence condition of the numerical simulation model;
and carrying out simulation calculation on the numerical simulation model according to the boundary condition and the convergence condition to obtain a simulation calculation result.
2. The numerical flue urea pyrolysis simulation method of claim 1, wherein the numerical simulation model comprises a urea solution evaporation model comprising a liquid phase model and a gas phase model.
3. The numerical simulation method for flue urea pyrolysis according to claim 2, wherein the liquid phase model is:
in the formula: yu is the mass fraction of urea, t is the time, m vap M is the evaporation mass of the urea droplets d The mass of the urea droplets is the mass of the urea droplets,
the gas phase model is as follows:
in the formula: m is d Is the mass of urea droplets, m vap For the urea droplet evaporation mass, c p.d Is the specific heat of the droplet; c. C p.vap.ref Is the specific heat of the gas phase after evaporation, t is the time, D d Is the droplet diameter; ρ g.ref, gas phase density after evaporation, Γ g.ref, diffusion coefficient, sh, sjowed number, B M Is the number of Sclbins, tg is the gas temperature, td is the droplet temperatureAnd hvap is the vapor phase enthalpy after evaporation.
4. The flue urea pyrolysis numerical simulation method of claim 1, wherein the numerical simulation model further comprises a urea discrete phase model formed by coupling urea liquid and urea gas phases according to the Lagrangian method.
5. The numerical simulation method of flue urea pyrolysis of claim 1, wherein the numerical simulation model further comprises a urea dynamics model, and the kinetic equation of the urea dynamics model comprises:
water is evaporated from the urea solution mist droplets:
CO (NH 2) 2. XH2O (solution) → CO (NH) 2 ) 2 (solid or gas) + xH 2 O，
Pyrolysis of urea into ammonia and isocyanic acid
CO(NH 2 ) 2 (solid or gas) → HNCO (gas) + NH 3 (gas) is added into the mixture,
isocyanic acid is hydrolyzed to generate ammonia gas
HNCO (gas) + H 2 O (gas) → NH 3 (gas) + CO 2 (gas).
6. The numerical flue urea pyrolysis simulation method of claim 1, wherein the numerical simulation model further comprises a reactor model, the reactor model being an ideal mixing reactor model.
7. The numerical simulation method for flue urea pyrolysis of claim 6, wherein the reactor model comprises a quality control equation and an energy control equation, and the quality control equation is as follows:
in the formula: m-mass flow rate of reactant/g.s -1 ，Y k The kth speciesThe mass fraction of the components is as follows,
mass fraction at the inlet of a kth component reactor, W k Production Rate/mol (m) of the kth component 3 ·s) -1 ，W k The molar mass of the kth component/g.mol -1 V-reactor volume/m 3 ，
The energy control equation is:
in the formula: h is k Specific enthalpy of the kth component/J.g -1 ；
Specific enthalpy at the inlet of the kth component reactor/J.g -1 (ii) a Heat removal Rate/J.s of Q-reactor -1 。
8. The numerical simulation method for flue urea pyrolysis as claimed in any one of claims 1 to 7, wherein the boundary condition includes at least one of flue gas flow velocity, flue gas temperature, flue gas total pressure average value, urea solution concentration, urea solution flow rate or urea particle size, and the convergence condition is that the residual error between continuity value and component concentration is less than 10 -6 。
9. The numerical simulation method for urea pyrolysis in the flue according to claim 8, wherein the flow velocity of the flue gas is 40-70 m/s, the temperature of the flue gas is 350-700 ℃, the total pressure average value of the flue gas is 2000-4000 Pa, the concentration of the urea solution is 10-50%, the flow rate of the urea solution is 1-20 kg/h, and the particle size of the urea particles is 10-120 microns.
10. The numerical flue urea pyrolysis simulation method of claim 1, further comprising comparing the numerical simulation result with an experimental result, and if an error value between the numerical simulation result and the experimental result is greater than 10%, adjusting parameters of boundary conditions, and/or adjusting parameters of a geometric model and performing numerical simulation calculation again.
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| CN113941251A (en) * | 2021-11-08 | 2022-01-18 | 西安热工研究院有限公司 | Flue gas denitration flow field simulation checking method and system |
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