CN103150433A - Modeling method for coupling numerical value of cracking reaction in furnace tube and combustion of industrial dichloroethane cracking furnace chamber - Google Patents

Abstract

The invention provides a modeling method for a coupling numerical value of cracking reaction in a furnace tube and combustion of an industrial dichloroethane cracking furnace chamber. According to the method, the dichloroethane cracking furnace is divided into a furnace chamber model and a furnace tube model during modeling, and grids are divided on the furnace chamber and the furnace tube. The furnace chamber takes an outer tube wall temperature given by the furnace tube model as a boundary condition, important furnace chamber parameter distribution of the furnace chamber flue gas temperature, the speed, the component concentration and the like is calculated by a combustion model, a flowing model and a heat transmission model; the furnace tube takes a furnace tube heat flux calculated by the furnace chamber as a boundary condition, and process temperature, pressure and concentration distribution in a tube length direction is calculated through a cracking reaction model in the tube and taking mass conservation, momentum conservation, energy conservation relations in the tube, so that analyses of important economic targets of the dichloroethane cracking conversion rate, the selectivity, the unit consumption and the like under current operation conditions are facilitated, and guidance of filed process optimization is facilitated. The modeling method is applicable to various high-temperature cracking furnaces and has a wide adaptability.

Description

The Coupled Numerical modeling method of cracking reaction in industry dichloroethane cracking furnace hearth combustion and boiler tube

Technical field

The present invention relates to a kind of process apparatus modeling method, the Coupled Numerical modeling method of cracking reaction in especially a kind of industrial dichloroethane cracking furnace hearth combustion and boiler tube.

Background technology

Dichloroethane cracking furnace is the core cell of vinyl chloride process units and with can the rich and influential family, design and the operant level of whole TOWER OUTLET IN VINYL CHLORIDE UNIT benefit and pyrolysis furnace are closely bound up, and the key that vinyl chloride process units economic benefit promotes is high level design and operating conditions how to optimize pyrolysis furnace.From external a complete set of the introduction, the introduction of advanced and mature TOWER OUTLET IN VINYL CHLORIDE UNIT provides higher starting point for the VC in China industrial expansion mostly for the most of ethylene dichloride cracking techniques of China and device at present.But China's ethylene dichloride cracking operation level totally lags behind advanced international standard, ethylene dichloride cracking low conversion rate, and selectivity is low, and unit consumption is high.And the patent business makes China not deep enough to the grasp of ethylene dichloride cracking technology mechanism to the maintaining secrecy of gordian technique, and technical merit is difficult to obtain substantive breakthroughs.Domestic clear not to cracking furnace interior material Fluid Flow in A, heat transfer, mass transfer, chemical reaction understanding, lack enough theory supports, make when the design of the transformation of pyrolysis furnace and Cracking furnace made at home, be mainly the foreign imitation technology, there is no theoretical foundation, often make transformation and design improper, perhaps when cracking stock and operating conditions change, can only the dependence experience determine operating parameter, so designing and operating with certain blindness, device potential is not fully exerted.Therefore the Introduced From Abroad complete set technology is also imitated transformation simply, and does not notice that from basic, the technical innovation basis, VC in China cracking production technology will always lag behind world lead level so, lack competitiveness in the world.

In order to grasp the operation mechanism of dichloroethane cracking furnace comprehensively, grasp the thermal coupling relation between burner hearth and boiler tube, understanding is to the dichloroethane cracking furnace cycle of operation, the key parameter that the important performance indexes such as ethylene dichloride cracking conversion ratio, selectivity, unit consumption cause material impact carries out modelling by mechanism to dichloroethane cracking furnace and seems particularly important.The research and development of dichloroethane cracking furnace mathematical model in the past lay stress in the dynamic (dynamical) description of cracking reaction, influencing each other with cracking reaction and between flowing and conducting heat do not taken into account, the reaction tube inner fluid flowed done very large simplification with diabatic process.In the modeling effort of burner hearth, it is mainly the simulation to the radiant heat transfer process, their radiant heat transfer processes in the method that adopts Luo Bai-Yi Wansifa, Bie Luokangfa, field method etc. to simplify is calculated burner hearth, not to fuel combustion mechanism process simulation, but simply utilize the rate of heat release of fuel to estimate composition and the temperature of flue gas, but also burning and the impact of flow of flue gas process on conducting heat have been ignored.

Along with computer computation ability is unprecedented soaring, the Fluid Mechanics Computation of complicated and time consumption (Computational Fluid Dynamics, be called for short CFD) become the important method that relates to the every field of Fluid Flow in A in solution, as machine-building, the numerous areas such as chemical industry.CFD is a hydromechanical branch, utilizes detailed method for numerical simulation to substitute the Analytic Method nonlinear partial differential equation, has solved the insurmountable problem of many theoretical fluid mechanics.flowing in most engineering problem engineerings, conduct heat, the non-linear momentum of mass transfer and course of reaction, heat, quality and component converged equations can utilize CFD to carry out discretize to it and process, the field (velocity field of original physical quantity continuous in volume coordinate, the temperature field, concentration field etc.), set with the variate-value on a lot of discrete points replaces, and set up Algebraic Equation set about field variable Relations Among on these discrete points, sealing discrete equation group under the known boundaries condition, carry out numerical solution, to obtain the approximate solution of Physical Quantity Field, provide each physical quantity (as: speed in whole research system, temperature and concentration etc.) distribution.Accurately flow, the details of the processes such as heat transfer, mass transfer and reaction.The CFD of narrow sense Study of Fluid flow phenomenon still along with the development of other each research fields (as: burning, radiation and chemical reaction etc.), makes the feeler of CFD stretch longer and longer, and coverage rate is also more and more wider.As in chemical field, the reaction model of describing chemical reaction can be combined with flow model and carry out reactor simulation; Reaction and mobility status in the equipment such as effective analogue reactor.Therefore, theoretically, every occasion that has Fluid Flow in A, the CFD method can effectively play a role.So the CFD technology is incorporated in the modelling by mechanism of dichloroethane cracking furnace, will helps clearer understanding dichloroethane cracking furnace thorax boiler tube thermal coupling, the important informations such as Flow Field Distribution.This will be further the Design ﹠ reform of ethane cracking furnace, and the exploitation of Optimum Operation and new technology provides strong theory and Data support, thereby can provide technical support for dichloroethane cracking furnace production domesticization and old transformation.

Summary of the invention

in order to solve the deficiency of above-mentioned existing model, the present invention has systematically analyzed flow of matter in the dichloroethane cracking furnace reaction tube comprehensively, conduct heat, flow in mass transfer and cracking reaction and burner hearth, conduct heat, the complex process such as mass transfer and combustion reaction, analyzed simultaneously strong coupling between these complex processes, based on hydromechanical turbulent flow model, radiation heat-transfer model, combustion model and cracking reaction kinetic model, burning diabatic process in transmission and cracking reaction process and burner hearth in the pyrolysis furnace reaction tube is coupled, designed the Coupled Numerical modeling method of cracking reaction in a kind of industrial dichloroethane cracking furnace hearth combustion and boiler tube.

Model of the present invention is comprised of burner hearth model and boiler tube model, and wherein: in the burner hearth model, the mixability of based on fuel and air adopts full premixed; The one-level series connection combustion model of simplifying is adopted in the burning of fuel gas; Turbulent flow-chemical reaction interaction model---whirlpool dissipation model is adopted in the combustion chemistry reaction; The burner hearth flow of flue gas adopts the Reynolds average model, and adopts the k-ε two-equation model sealing turbulent flow item wherein of standard; Burner hearth gas radiation heat transfer model adopts the discrete coordinates model, and adopts how grey gas weighted model to calculate the gas radiation characteristic.In the boiler tube model, adopt the cracking reaction of the ethylene dichloride one-level series connection of simplifying; The Process Gas flow model is consistent with the flow of flue gas model.The iteration variable of burner hearth model and boiler tube model coupled simulation is selected furnace tube outer wall temperature and thermoflux.In thus can burner hearth, flue-gas temperature, speed, concentration of component distribute, boiler tube inside and outside wall Temperature Distribution, in boiler tube heat flux distribution and pipe, pyrolysis gas temperature, speed, concentration of component distribute, thereby more accurately understand the dichloroethane cracking furnace intrinsic characteristic, support for the operation optimization of pyrolysis furnace, technological transformation, new technological design etc. provide theoretical.

A kind of industrial dichloroethane cracking furnace burner hearth and boiler tube Coupled Numerical modeling method comprise the following steps:

Step 1: determine dichloroethane cracking furnace burner hearth boiler tube size to be simulated, carry out the grid division for burner hearth and boiler tube; Determine boundary condition according to technological parameter, comprising: the fuel gas inlet flow of burner on sidewall, air inlet flow and reaction tube inlet gas flow and temperature, furnace wall heat loss factor, burner hearth exhanst gas outlet pressure and boiler tube pyrolysis gas top hole pressure;

Step 2: set up the burner hearth model:

Step 2.1: in burner hearth, the flow of flue gas model adopts and sets up closed model based on the standard k-ε two-equation model of Reynolds average equation;

Step 2.2: burner hearth fuel gas adopts one-level series connection combustion reaction model, and during burning, flow model adopts finite rate/whirlpool dissipation model;

Step 2.3: in burner hearth, radiation heat-transfer model adopts the discrete coordinates model, and the burner hearth flue gas adopts how grey gas weighted model to calculate its radiation characteristic;

Step 3: set up the boiler tube model:

Step 3.1: in boiler tube, the ethylene dichloride cracking reaction adopts one-level cascade reaction model, and cracking reaction dynamics meets Allan Li Wusi formula;

Step 3.2: the parameter of determining gas density in the boiler tube model, thermal capacitance, viscosity, coefficient of heat conductivity and coefficient of diffusion computing formula;

Step 4: have starting condition and the boundary condition that obtains in serious thermal coupling relation and step 1 based on burner hearth and boiler tube, furnace tube outer wall temperature and boiler tube thermoflux mutual iteration coupling variable during as burner hearth model and boiler tube model numerical solution, carry out the loop iteration of burner hearth and boiler tube model, until the model convergence obtains model and relates to each value of consult volume.

Further, carry out grid for burner hearth and boiler tube in described step 1 and divide, burner region in burner hearth, boiler tube district adopts tetrahedron element to be used for grid division; Other zones of burner hearth adopt hexahedral elements to be used for grid division; In the boiler tube model, boiler tube straight tube wall adopts hexahedral element to come grid division; Bend pipe adopts mixture dividing elements grid.

Further, in described step 2, step 3, boiler tube and burner hearth wall surface are considered as non-slippage border; In viscous sublayer, adopt Standard law of wall to approach flowing and heat exchange of real process near wall; Thermal boundary on the burner hearth wall is given the thermoflux boundary condition by thermal loss; Boiler tube wall border adopts self-defining function to be assigned to tube wall, and in the boiler tube model, furnace tube outer wall thermoflux self-defining function is defined as Q (x)=a ₁+ b ₁x+c ₁x ²+ d ₁x ³+ e ₁x ⁴+ f ₁x ⁵, in the burner hearth model, furnace tube outer wall temperature self-defining function is defined as T (x)=a ₂+ b ₂x+c ₂x ²+ d ₂x ³+ e ₂x ⁴+ f ₂x ⁵, a wherein ₁, b ₁, c ₁, d ₁, e ₁, f ₁, a ₂, b ₂, c ₂, d ₂, e ₂, f ₂For treating the parameter of match, x is along boiler tube coordinate radially; Q is thermoflux, and T is the furnace tube outer wall temperature;

Further, in described step 2.2, one-level series connection combustion model is:

$C_x{H}_y+(\frac{x}{2}+\frac{y}{4})O_2=\mathrm{xCO}+\frac{y}{2}{H}_{2}O$

$\mathrm{CO}+\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="O"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">O</figure-callout>}}_2={\mathrm{<figure-callout\; id="2"\; label="CO"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">CO</figure-callout>}}_2;$

Use finite-rate model, chemical source item is calculated with the Arrhenius formula:

$R_i=M_{w,i}\underset{r=1}{\overset{N_R}{\mathrm{\&Sigma;}}}{\hat{R}}_{i,r}$

M _w,iBe the molecular weight of component i, N _RBe reactional equation number, R _iBe the clean throughput rate of the component i that is caused by chemical reaction,

Be the product of i kind material in r reaction

Life/decomposition rate, its expression formula is: ${\hat{R}}_{i,r}=\mathrm{\&Gamma;}(v_{i,r}^{\&prime;\&prime;}-v_{i,r}^{\&prime;})\left(k_{f,r}\underset{j=1}{\overset{N}{\mathrm{\&Pi;}}}{\left[C_{j,r}\right]}^{({\mathrm{\&eta;}}_{j,r}^{\&prime;}+{\mathrm{\&eta;}}_{j,r}^{\&prime;\&prime;})}\right)$

The wherein clean impact of Γ third body on reaction rate, ν ' _i,r, ν " _i,rBe stoichiometric coefficient, k _f,rThe forward reaction rate constant, C _j,rBe volumetric molar concentration, η ' _j,r, η " _j,rBe the speed index, N is for participating in the sum of reactive material;

Use the whirlpool dissipation model, the generation speed R of material k in reaction r _i,kBy less one in lower formula two:

$R_{i,k}=\min [v_{i,k}^{\&prime;}{M}_{w,i}\mathrm{A\&rho;}\frac{\mathrm{\&epsiv;}}{k}\min \left(\frac{Y_R}{v_{R,k}^{\&prime;}{M}_{w,R}}\right),v_{i,k}^{\&prime;}{M}_{w,i}\mathrm{AB\&rho;}\frac{\mathrm{\&epsiv;}}{k}\frac{{\mathrm{\&Sigma;}}_P{Y}_P}{{\mathrm{\&Sigma;}}_j^N{v}_{j,k}^{\&prime;\&prime;}{M}_{w,j}}]$

ν ' wherein _i,k, ν ' _R,k, ν " _j,kBe stoichiometric coefficient, M _w,i, M _w,R, M _w,jBe molecular weight, A, B are experience factor, the ρ gas density,

Be Lenard-Jones potential energy parameter, Y _R, Y _PBe mass fraction of product.

Further, set up the mathematical model of sealing in step 2.1 based on the standard k-ε two-equation model of averaged Navier-Stokes equation, the dissipative shock wave of quality, momentum, tubulence energy, tubulence energy, energy and component transport equation are as shown in the formula expression:

Continuity equation: $\frac{\&PartialD;}{{\&PartialD;x}_i}\left(\mathrm{\&rho;}{U}_i\right)=0$

The equation of momentum: $\frac{\&PartialD;}{\&PartialD;x_j}\left(\mathrm{\&rho;}{U}_i{U}_j\right)=\frac{\&PartialD;p_{\mathrm{eff}}}{\&PartialD;x_i}+\frac{\&PartialD;}{{\&PartialD;x}_j}\left[{\mathrm{\&mu;}}_{\mathrm{eff}}(\frac{{\&PartialD;U}_i}{{\&PartialD;x}_j}+\frac{{\&PartialD;U}_j}{{\&PartialD;x}_i}-\frac{2}{3}{\mathrm{\&delta;}}_{\mathrm{ij}}\frac{{\&PartialD;U}_l}{{\&PartialD;x}_l})\right]$

The k-equation: $\frac{\&PartialD;}{{\&PartialD;x}_i}\left(\mathrm{\&rho;k}{U}_i\right)=\frac{\&PartialD;}{{\&PartialD;x}_j}\left[(\mathrm{\&mu;}+\frac{{\mathrm{\&mu;}}_t}{{\mathrm{\&sigma;}}_k})\frac{\&PartialD;k}{{\&PartialD;x}_j}\right]+G_k-\mathrm{\&rho;\&epsiv;}$

ε-equation: $\frac{\&PartialD;}{{\&PartialD;x}_i}\left(\mathrm{\&rho;\&epsiv;}{U}_i\right)=\frac{\&PartialD;}{{\&PartialD;x}_j}\left[(\mathrm{\&mu;}+\frac{{\mathrm{\&mu;}}_t}{{\mathrm{\&sigma;}}_{\mathrm{\&epsiv;}}})\frac{\&PartialD;\mathrm{\&epsiv;}}{\&PartialD;x_j}\right]+\frac{\mathrm{\&epsiv;}}{k}(C_{1\mathrm{\&epsiv;}}{G}_k-{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">C</figure-callout>}}_{2\mathrm{\&epsiv;}}\mathrm{\&rho;\&epsiv;})$

Energy equation:

$\frac{\&PartialD;}{{\&PartialD;x}_i}\left[U_i(\mathrm{\&rho;E}+p)\right]=\frac{\&PartialD;}{{\&PartialD;x}_j}(k_{\mathrm{eff}}\frac{\&PartialD;T}{{\&PartialD;x}_j}-\underset{j}{\mathrm{\&Sigma;}}{h}_j{\stackrel{\&RightArrow;}{J}}_j+U_i{\mathrm{\&mu;}}_{\mathrm{eff}}[(\frac{{\&PartialD;U}_j}{{\&PartialD;x}_i}+\frac{{\&PartialD;U}_i}{{\&PartialD;x}_j})-\frac{2}{3}\frac{{\&PartialD;U}_l}{{\&PartialD;x}_l}{\mathrm{\&delta;}}_{\mathrm{ij}}\left]\right)+S_h$

The component transport equation: $\frac{\&PartialD;{\mathrm{\&rho;U}}_j{Y}_i}{{\&PartialD;x}_j}=\frac{\&PartialD;}{\&PartialD;x_j}\left[(\mathrm{\&rho;}{D}_{i,m}+\frac{{\mathrm{\&mu;}}_t}{{\mathrm{Sc}}_t})\frac{{\&PartialD;Y}_i}{\&PartialD;x_j}\right]+R_i$

U wherein _i, U _j, U _lBe i, j, the speed component of k direction, x _i, x _j, x _lBe i, j, the coordinate of k direction, ρ are gas density, p _effBe effective pressure, μ _effBe virtual viscosity, δ _ijBe Kronecker function, k is tubulence energy, and μ is the viscosity of gas molecule, μ _tBe turbulent viscosity, G _kBe the generation item of tubulence energy, ε is the dissipative shock wave of tubulence energy, S _hBe the source item in energy equation, C _μ, C _{1 ε}, C _{2 ε}, σ _k, σ _εBe standard k-ε model parameter, E is the gross energy of unit mass, and p is pressure, k _effConductivity,

Be the diffusion flux of component, h _jBe the enthalpy of component j, Y _jBe the massfraction of component j, D _i,mBe the mass diffuse coefficient of component i in potpourri, Sc _tBe turbulent Schmidt number, R _iBe the clean generation rate of the component i that is caused by chemical reaction.

Further, in step 2.3, radiation heat-transfer model adopts the discrete coordinates model, and its mathematic(al) representation is:

$\&dtri;\&CenterDot;\left(I(\stackrel{\&RightArrow;}{r},\stackrel{\&RightArrow;}{s})\stackrel{\&RightArrow;}{s}\right)+(\mathrm{\&alpha;}+{\mathrm{\&sigma;}}_s)I(\stackrel{\&RightArrow;}{r},\stackrel{\&RightArrow;}{s})=\mathrm{\&alpha;}{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">n</figure-callout>}}^2\frac{\mathrm{\&sigma;}{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">T</figure-callout>}}^4}{\mathrm{\&pi;}}+\frac{{\mathrm{\&sigma;}}_{\mathrm{<figure-callout\; id="4"\; label="s"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">s</figure-callout>}}}{4\mathrm{\&pi;}}{\&Integral;}_0^{4\mathrm{\&pi;}}I(\stackrel{\&RightArrow;}{r},{\stackrel{\&RightArrow;}{s}}^{\&prime;})\mathrm{\&Phi;}(\stackrel{\&RightArrow;}{s}\&CenterDot;{\stackrel{\&RightArrow;}{s}}^{\&prime;})d{\mathrm{\&Omega;}}^{\&prime;};$

Wherein I is radiation intensity,

Be position vector,

Be direction vector, α is absorption coefficient, σ _sBe scattering coefficient, n is refractive index, and σ is the Stefan-Boltzmann constant, and T is that flue-gas temperature Φ is phase function, and Ω ' is solid angle;

In burner hearth, the how grey gas weighted model of flue gas employing calculates the radiation characteristic of flue gas, this model handle

The blackness approximate processing of real gas is the weighted sum of some grey channel black degree: $\mathrm{\&epsiv;}=\underset{i=0}{\overset{I}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{\mathrm{\&epsiv;},i}\left(T\right)(1-e^{-k_i\mathrm{ps}})$

α wherein _{ε, i}The emissivity weight factor of the virtual ash gas of i kind, the total adsorption coefficient of flue gas can be expressed as:

Work as s〉10 ^-4m, $\mathrm{\&alpha;}=-\frac{\ln (1-\mathrm{\&epsiv;})}{s};$ When s≤10 ^-4m， $\mathrm{\&alpha;}=\underset{i=0}{\overset{I}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{\mathrm{\&epsiv;},i}{k}_{i}p.$

Further, step 3.1 ethylene dichloride pyrolysis gas one-level series connection cracking reaction is

Its dynamics meets Allan Li Wusi formula, and chemical reaction rate is expressed from the next:

${\hat{R}}_{i,r}=\mathrm{\&Gamma;}(v_{i,r}^{\&prime;\&prime;}-v_{i,r}^{\&prime;})\left(k_{f,r}\underset{j=1}{\overset{N}{\mathrm{\&Pi;}}}\right[C_{j,r}]{\mathrm{\&eta;}}_{j,r}^{\&prime;}-k_{b,r}\underset{j=1}{\overset{N}{\mathrm{\&Pi;}}}[C_{j,r}\left]{\mathrm{\&eta;}}_{j,r}^{\&prime;\&prime;}\right)$

Wherein

Be the generation/decomposition rate of i kind material in r reaction, ν ' _i,r, ν " _i,rBe stoichiometric coefficient, η ' _j,r, η " _j,rBe reaction velocity index, k _f,rBe forward reaction rate constant, k _b,rBe backward reaction rate constant, C _j,rVolumetric molar concentration for component j.

Further, the burner hearth model condition of convergence is that the burner hearth model obtains on one group of new tube wall thermoflux and compares with thermoflux on the front tube wall that once calculates and reach default precision.

Further, the boiler tube model condition of convergence is that the boiler tube model obtains one group of new pipe surface temperature and compares with the front furnace tube outer wall temperature that once calculates and reach default precision.

The invention provides the Coupled Numerical modeling method of cracking reaction in a kind of industrial dichloroethane cracking furnace hearth combustion and boiler tube, the method is divided into dichloroethane cracking furnace burner hearth model and boiler tube model in modeling, and respectively to burner hearth boiler tube grid division.Burner hearth as boundary condition, utilizes combustion model with the tube wall temperature of boiler tube model, flow model, and heat transfer model calculates chamber flue gas temperature, speed, the important burner hearth parameter distribution such as concentration of component; The boiler tube thermoflux that boiler tube calculates take burner hearth is as boundary condition, utilize cracking reaction model in pipe, consider the mass conservation in pipe, momentum conservation, energy conservation relation calculates the Process Gas temperature along the pipe range direction, pressure, CONCENTRATION DISTRIBUTION, thereby under favourable analysis current operation condition, ethylene dichloride cracking conversion ratio, selectivity, the principal economic indicators such as unit consumption are conducive to the guide field process optimization.And this modeling method is applicable to all kinds of high-temperature cracking furnaces, and adaptability is widely arranged.

Description of drawings

Fig. 1 dichloroethane cracking furnace grid is divided figure.

Fig. 2 dichloroethane cracking furnace burner hearth boiler tube coupling iterative block diagram.

Fig. 3 burner hearth flow of flue gas velocity field distribution plan (y=0.0485m)

Fig. 4 chamber flue gas temperature field pattern (y=0.0485m)

O2 concentration profile (y=0.0485m) in Fig. 5 burner hearth flue gas

Fig. 6 burner hearth CO concentration in flue gas distribution plan (y=0.0485m)

CO2 concentration profile (y=0.0485m) in Fig. 7 burner hearth flue gas

Fig. 8 boiler tube thermoflux is along boiler tube length direction distribution plan

In Fig. 9 boiler tube, the pyrolysis gas temperature is along boiler tube length direction distribution plan

In Figure 10 boiler tube, the pyrolysis gas flow velocity is along boiler tube length direction distribution plan

In Figure 11 boiler tube, the pyrolysis gas pressure distribution is along boiler tube length direction distribution plan

In Figure 12 boiler tube, the pyrolysis gas molar flow is along boiler tube length direction distribution plan

Embodiment

Complete dichloroethane cracking furnace comprises convection section and radiation section, convection section section Main Function is that radiation section is sent in the ethylene dichloride preheating of liquid state and vaporization, the high-temperature flue gas dichloroethane that radiation section further utilizes fuel combustion to discharge, and making it that cracking reaction occur rapidly, vinyl chloride and accessory substance form pyrolysis gas.Therefore the present invention mainly considers the radiation section with cracking reaction, and it is certain to suppose to enter radiation section ethylene dichloride vapor (steam) temperature.Although in pyrolysis furnace, the heat transmission is coupled various physics, the chemical process that occurs in burner hearth and boiler tube closely, on research object, both are relatively independent.Therefore, consider from the angle of modeling, can set up respectively burner hearth mathematical model and boiler tube mathematical model.The interphase in burner hearth and boiler tube two spaces is furnace tube outer wall, and burner hearth model and boiler tube model can get up to form the mathematical model of a complete pyrolysis furnace radiation section by the temperature of the thermoflux on the pipe outer wall with two model simultaneous.

The burner hearth mathematical model

Ejection that fuel and air are respectively arranged from sidewall in the dichloroethane cracking furnace burner hearth, and burning rapidly, from academicly being the Fluid Flow in A with chemical reaction.From this definition, burning is the transfer reaction process of a complexity, and therefore, as long as can be somebody's turn to do the chemical reaction process that flows by accurate description, in burner hearth, the distribution of each physical quantity in furnace cavity just can clearly show.Utilize the CFD method, at first burner hearth can should describe flowing in burner hearth, then considers chemical reaction and radiation, convection heat transfer' heat-transfer by convection on the basis of flowing.But in fact do not have strict precedence relationship between these several persons, but reciprocal causation, influence each other: Fluid Flow in A affects the CONCENTRATION DISTRIBUTION of component, thereby affect chemical reaction, the variation of chemical reaction can have influence on heat transfer again, heat transfer go back to and can affect mobile, these process interdependences, inseparable ceding territory is coupled.Therefore, these several persons' mutual relationship should organism be revealed in the foundation of burner hearth mathematical model.Carefully dissect this physics of burning, chemical process, it also can decompose, and each subprocess after decomposition can be described with several like this mathematical models: (1) Fluid Flow in A model, and key is turbulence model; (2) mass transfer model of each component is mainly considered the impact of combustion chemistry reaction rate; (3) heat TRANSFER MODEL comprises convection heat transfer' heat-transfer by convection and radiant heat transfer, and wherein key is radiation heat-transfer model.

(1) Fluid Flow in A model

In the pyrolysis furnace burner hearth, suppose that flow of flue gas embodies with turbulent model, therefore describe flow of flue gas in the Reynolds average conservation equation with turbulent transport item hypothesis, so that the Simultaneous Equations sealing.Because the burner of installing in the pyrolysis furnace burner hearth sprays fuel at a high speed, the heat release of burning in burner hearth, the flue gas flow rate of formation is very fast, so flowing in burner hearth is in turbulence state, its flowing law more complicated basically.Existing more influential turbulent model has: zero equation model, single equation model, two-equation model, algebraic stress model and reynolds stress model and other be the journey model in many ways.In these models, use more generally two-equation model.Forefathers' result of study shows, algebraic stress model and reynolds stress model are optimum, but implements the most difficultly, requires also high to computing power; K-ε pattern is two-equation model, have advantages of applied widely, precision is high, it is relatively easy to find the solution.Therefore the present invention selects the mathematical model of setting up sealing based on the standard k-ε two-equation model of averaged Navier-Stokes (RANS) equation.The dissipative shock wave of quality, momentum, tubulence energy, tubulence energy, energy and component transport equation are as shown in the formula expression:

Continuity equation: $\frac{\&PartialD;}{{\&PartialD;x}_i}\left(\mathrm{\&rho;}{U}_i\right)=0$

The equation of momentum: $\frac{\&PartialD;}{{\&PartialD;x}_j}\left(\mathrm{\&rho;}{U}_i{U}_j\right)=\frac{{\&PartialD;p}_{\mathrm{eff}}}{{\&PartialD;x}_i}+\frac{\&PartialD;}{{\&PartialD;x}_j}\left[{\mathrm{\&mu;}}_{\mathrm{eff}}(\frac{\&PartialD;U_i}{{\&PartialD;x}_j}+\frac{{\&PartialD;U}_j}{{\&PartialD;x}_i}-\frac{2}{3}{\mathrm{\&delta;}}_{\mathrm{ij}}\frac{{\&PartialD;U}_l}{{\&PartialD;x}_l})\right]$

The k-equation: $\frac{\&PartialD;}{{\&PartialD;x}_i}\left(\mathrm{\&rho;k}{U}_i\right)=\frac{\&PartialD;}{{\&PartialD;x}_j}\left[(\mathrm{\&mu;}+\frac{{\mathrm{\&mu;}}_t}{{\mathrm{\&sigma;}}_k})\frac{\&PartialD;k}{{\&PartialD;x}_j}\right]+G_k-\mathrm{\&rho;\&epsiv;}$

ε-equation: $\frac{\&PartialD;}{{\&PartialD;x}_i}\left(\mathrm{\&rho;\&epsiv;}{U}_i\right)=\frac{\&PartialD;}{{\&PartialD;x}_j}\left[(\mathrm{\&mu;}+\frac{{\mathrm{\&mu;}}_t}{{\mathrm{\&sigma;}}_{\mathrm{\&epsiv;}}})\frac{\&PartialD;\mathrm{\&epsiv;}}{{\&PartialD;x}_j}\right]+\frac{\mathrm{\&epsiv;}}{k}(C_{1\mathrm{\&epsiv;}}{G}_k-{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">C</figure-callout>}}_{2\mathrm{\&epsiv;}}\mathrm{\&rho;\&epsiv;})$

Energy equation: $\frac{\&PartialD;}{{\&PartialD;x}_i}\left[U_i(\mathrm{\&rho;E}+p)\right]=\frac{\&PartialD;}{{\&PartialD;x}_j}(k_{\mathrm{eff}}\frac{\&PartialD;T}{{\&PartialD;x}_j}-\underset{j}{\mathrm{\&Sigma;}}{h}_j{\stackrel{\&RightArrow;}{J}}_j+U_i{\mathrm{\&mu;}}_{\mathrm{eff}}[(\frac{{\&PartialD;U}_j}{{\&PartialD;x}_i}+\frac{{\&PartialD;U}_i}{{\&PartialD;x}_j})-\frac{2}{3}\frac{{\&PartialD;U}_l}{{\&PartialD;x}_l}{\mathrm{\&delta;}}_{\mathrm{ij}}\left]\right)+S_h$

The component transport equation: $\frac{\&PartialD;\mathrm{\&rho;}{U}_j{Y}_i}{{\&PartialD;x}_j}=\frac{\&PartialD;}{{\&PartialD;x}_j}\left[(\mathrm{\&rho;}{D}_{i,m}+\frac{{\mathrm{\&mu;}}_t}{{\mathrm{Sc}}_t})\frac{\&PartialD;Y_i}{{\&PartialD;x}_j}\right]+R_i$

Wherein $p_{\mathrm{eff}}=p+\frac{2}{3}\mathrm{\&rho;k},$ ${\mathrm{\&mu;}}_{\mathrm{eff}}=\mathrm{\&mu;}+{\mathrm{\&mu;}}_t,$ ${\mathrm{\&mu;}}_t=\mathrm{\&rho;}{C}_{\mathrm{\&mu;}}\frac{k^2}{\mathrm{\&epsiv;}},$ ${\mathrm{\&delta;}}_{\mathrm{ij}}=\left\{\begin{array}{c}1(i=j)\\ 0(i\&NotEqual;j)\end{array}\right.,$ $G_k={\mathrm{\&mu;}}_t[(\frac{{\&PartialD;\mathrm{\&mu;}}_i}{{\&PartialD;x}_j}+\frac{{\&PartialD;\mathrm{\&mu;}}_j}{{\&PartialD;x}_i})-\frac{2}{3}\frac{{\&PartialD;\mathrm{\&mu;}}_l}{{\&PartialD;x}_l}{\mathrm{\&delta;}}_{\mathrm{ij}}]\frac{{\&PartialD;u}_i}{{\&PartialD;x}_j},k_{\mathrm{eff}}=k+k_t,$ $E=h-\frac{p}{\mathrm{\&rho;}}+\frac{{\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">U</figure-callout>}}^2}{2}$ $h=\underset{j}{\mathrm{\&Sigma;}}{Y}_j{h}_j,$ $h_j={\&Integral;}_{T_{\mathrm{ref}}}^T{c}_{p,j}\mathrm{dT},$ $D_{i,m}=\frac{1-X_i}{\underset{j,j\&NotEqual;i}{\mathrm{\&Sigma;}}(X_j/D_{\mathrm{ij}})},$ ${\mathrm{Sc}}_t=\frac{{\mathrm{\&mu;}}_t}{\mathrm{\&rho;}{D}_t}.$ Standard k-ε model parameter value is C _μ=0.09, σ _k=1.0, σ _ε=1.3, C _{1 ε}=1.44 and C _{2 ε}=1.92.For the calculating of component enthalpy, T _refBe made as 298.15K.

(2) combustion model

The industrial dichloroethane cracking furnace of setting up at present all adopts burner on sidewall heat supply combustion mode.The object that the present invention simulates is the dichloroethane cracking furnace of a Mitsui device, adopts equally the burner on sidewall heat supply, and pyrolysis furnace furnace wall both sides are respectively equipped with totally 136 of two row's premixed type burners, and namely fuel and air are pre-mixed to spray afterwards and burn.

Fuel and air spray from nozzle, form high-speed jet, and rapid reaction, and it is the burning that the whirlpool dissipation model is described the wall burner that the present invention adopts turbulent flow-chemical reaction interaction model.In finite-rate model, chemical source item is calculated with the Arrhenius formula, and the clean source item of the chemical reaction of chemical substance i is by there being the N of its participation _RThe Arrhenius reaction source of individual chemical reaction and calculate:

$R_i=M_{w,i}\underset{r=1}{\overset{N_R}{\mathrm{\&Sigma;}}}{\hat{R}}_{i,r}$

M wherein _w,iThe molecular weight of i kind material,

Be the generation/decomposition rate of i kind material in r reaction, its expression formula is:

${\hat{R}}_{i,r}=\mathrm{\&Gamma;}(v_{i,r}^{\&prime;\&prime;}-v_{i,r}^{\&prime;})\left(k_{f,r}\underset{j=1}{\overset{N}{\mathrm{\&Pi;}}}{\left[C_{j,r}\right]}^{({\mathrm{\&eta;}}_{j,r}^{\&prime;}+{\mathrm{\&eta;}}_{j,r}^{\&prime;\&prime;})}\right)$

In the dissipation model of whirlpool, the generation speed R of material k in reaction r _i,kBy in following two expression formulas less one provide:

$R_{i,k}=v_{i,k}^{\&prime;}{M}_{w,i}\mathrm{A\&rho;}\frac{\mathrm{\&epsiv;}}{k}\min \left(\frac{Y_R}{v_{R,k}^{\&prime;}{M}_{w,R}}\right)$

$R_{i,k}=v_{i,k}^{\&prime;}{M}_{w,i}\mathrm{AB\&rho;}\frac{\mathrm{\&epsiv;}}{k}\frac{{\mathrm{\&Sigma;}}_P{Y}_P}{{\mathrm{\&Sigma;}}_j^N{v}_{j,k}^{\&prime;\&prime;}{M}_{w,j}}$

In this model, this device dichloroethane cracking furnace fuel gas adopts liquefied petroleum gas (LPG) (LPG), and principal ingredient comprises C ₃H ₈/ C ₄H ₆/ C ₄H ₈/ C ₄H ₁₀The present invention adopts the combustion reaction model of one-level series connection.

C ₃H ₈+3.5O ₂→3CO+4H ₂O

C ₄H ₆+3.5O ₂→4CO+3H ₂O

C ₄H ₈+4O ₂→4CO+4H ₂O

C ₄H ₁₀+4.5O ₂→4CO+5H ₂O

CO+0.5O ₂→CO ₂

(3) radiation model

Go for the medium of any optical depth due to the discrete coordinates model, not only can Calculation of Gas and particle between radiation heat transfer, and allow to use grey band model to calculate non-gray radiation, not only considered the impact of scattering, and allow to occur mirror-reflection and the radiation in translucent medium, be particularly suitable for having the problem of local heat source.In addition, because the discrete coordinates algorithm is simple, reliable, calculated amount is little, so be applied widely.The radiation heat-transfer model of this patent is used discrete coordinates model (Discrete Ordinates), find the solution the radiation transfer equation that the discrete solid angle of limited quantity is sent, identical with the appropriate number of direction in the number of radiation transfer equation and space coordinates, its mathematic(al) representation is:

$\&dtri;\&CenterDot;\left(I(\stackrel{\&RightArrow;}{r},\stackrel{\&RightArrow;}{s})\stackrel{\&RightArrow;}{s}\right)+(\mathrm{\&alpha;}+{\mathrm{\&sigma;}}_s)I(\stackrel{\&RightArrow;}{r},\stackrel{\&RightArrow;}{s})=\mathrm{\&alpha;}{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">n</figure-callout>}}^2\frac{\mathrm{\&sigma;}{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="HDA00002892144900041.png"\; state="\{\{state\}\}">T</figure-callout>}}^4}{\mathrm{\&pi;}}+\frac{{\mathrm{\&sigma;}}_s}{4\mathrm{\&pi;}}{\&Integral;}_0^{4\mathrm{\&pi;}}I(\stackrel{\&RightArrow;}{r},{\stackrel{\&RightArrow;}{s}}^{\&prime;})\mathrm{\&Phi;}(\stackrel{\&RightArrow;}{s},{\stackrel{\&RightArrow;}{s}}^{\&prime;})d{\mathrm{\&Omega;}}^{\&prime;}$

A large amount of flue gases have been full of in burner hearth, these flue gases (CO especially, CO ₂And H ₂O) to participate in radiant heat transfer.In these flue gases, CO ₂And H ₂O has different absorption wide-bands.This simulation adopts how grey gas weighted model (WSGGM) to calculate the radiation characteristic of flue gas.This model is divided into the blackness of real gas the weighted sum of some grey channel black degree, and expression formula is as follows:

$\mathrm{\&epsiv;}=\underset{i=0}{\overset{I}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{\mathrm{\&epsiv;},i}\left(T\right)(1-e^{-k_i\mathrm{ps}})$

For open region, due to its higher spectral absorption, the absorption coefficient of i=0 component is made as 0, and the weighted value of its absorption coefficient is:

${\mathrm{\&alpha;}}_{\mathrm{\&epsiv;},0}=1-\underset{i=1}{\overset{I}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{\mathrm{\&epsiv;},i}$

Depend on a of temperature _{ε, i}Can be by any approximation to function (match), but generally adopt following form:

${\mathrm{\&alpha;}}_{\mathrm{\&epsiv;},i}=\underset{j=1}{\overset{J}{\mathrm{\&Sigma;}}}{b}_{\mathrm{\&epsiv;},i,j}{T}^{j-1}$

The total adsorption coefficient of mixed gas is calculated as follows:

Work as s〉10 ^-4m， $\mathrm{\&alpha;}=-\frac{\ln (1-\mathrm{\&epsiv;})}{s};$ When s≤10 ^-4m， $\mathrm{\&alpha;}=\underset{i=0}{\overset{I}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{\mathrm{\&epsiv;},i}{k}_{i}p.$

The boiler tube mathematical model

In reaction tube, cracking stock is also carrying out complicated cracking reaction when carrying out Fluid Flow in A, heat transfer and mass transfer.From transmittance process, boiler tube and burner hearth are all the Fluid Flow in As with chemical reaction, and unique difference is to have lacked a radiant heat transfer process in pipe.From the angle of chemical reaction, although in pipe, the combustion reaction mechanisms in cracking reaction mechanism and the burner hearth of raw material is different, the equation that both needs are found the solution is similar, is all to find the solution composition equation.Therefore, equation and burner hearth that in pipe, each model relates to are basic identical, have just lacked a radiant heat transfer equation.

(1) cracking reaction kinetic model

For ethylene dichloride cracking reaction process, process with one-level cascade reaction model:

(2) transfer reaction mathematical model in the pipe

Use when in one-level cascade reaction model computer tube, component distributes, CFD need to find the solution the component process, the most important thing is the source item in definite equation, and this source item has just embodied the impact of chemical reaction.Cracking reaction dynamics meets Allan Li Wusi formula, and therefore, chemical reaction rate is expressed from the next:

${\hat{R}}_{i,r}=\mathrm{\&Gamma;}(v_{i,r}^{\&prime;\&prime;}-v_{i,r}^{\&prime;})\left(k_{f,r}\underset{j=1}{\overset{N}{\mathrm{\&Pi;}}}\right[C_{j,r}]{\mathrm{\&eta;}}_{j,r}^{\&prime;}-k_{b,r}\underset{j=1}{\overset{N}{\mathrm{\&Pi;}}}[C_{j,r}\left]{\mathrm{\&eta;}}_{j,r}^{\&prime;\&prime;}\right)$

In the CFD simulation, claim that also this formula is finite-rate model (FRC).During transfer reaction process in computer tube, except will calculating these 4 composition equations, equally also will find the solution above-mentioned fluid flow equation and energy equation, its form is the same with equation form in burner hearth, therefore repeat no more, adds up to totally 11 equations.At last, make these partial differential equation that the solution of deciding is arranged, just necessary given corresponding boundary condition seals whole system of equations.

(3) material property

In the reaction tube mathematical model, gas physical property such as density, thermal capacitance, viscosity, coefficient of heat conductivity and coefficient of diffusion are calculated by following formula.

Reaction tube internal procedure gas is under high-temperature low-pressure, and mixed gas density is calculated by the Ideal-Gas Equation.

$\mathrm{\&rho;}=\frac{p}{\mathrm{RT\&Sigma;}\frac{Y_i}{M_i}}$

Single component viscosity is calculated by kinetic theory: ${\mathrm{\&mu;}}_i=2.67\&times;{10}^{-6}\frac{\sqrt{M_{i}T}}{{\mathrm{\&sigma;}}_i{\mathrm{\&Omega;}}_{\mathrm{\&mu;i}}},$ Wherein, ${\mathrm{\&Omega;}}_{\mathrm{\&mu;i}}={\mathrm{\&Omega;}}_{\mathrm{\&mu;i}}\left(\frac{T}{{(\mathrm{\&epsiv;}/k)}_i}\right)$ Cracking mixed gas viscosity is drawn by the viscosity formula weighting technique of one-component:

Wherein,

Single-component gas thermal capacitance: C _pi=A _i+ B _iT+C _iT ²+ D _iT ³, mixed gas thermal capacitance:

In formula, A _i, B _i, C _i, D _iThermal capacitance design factor for component i.

The single component coefficient of heat conductivity is calculated by kinetic theory:

Mixed gas coefficient of heat conductivity:

Coefficient of diffusion between two components is calculated by kinetic theory: Wherein, ${\mathrm{\&Omega;}}_D={\mathrm{\&Omega;}}_D\left(\frac{T}{{(\mathrm{\&epsiv;}/k)}_{\mathrm{ij}}}\right),$ ${(\mathrm{\&epsiv;}/k)}_{\mathrm{ij}}=\sqrt{{(\mathrm{\&epsiv;}/k)}_i{(\mathrm{\&epsiv;}/k)}_j},$ ${\mathrm{\&sigma;}}_{\mathrm{ij}}=\frac{1}{2}({\mathrm{\&sigma;}}_i+{\mathrm{\&sigma;}}_j).$ Can obtain the coefficient of diffusion of mixed gas thus: $D_{i,m}=\frac{1-X_i}{{\mathrm{\&Sigma;}}_{j,j\&NotEqual;i}{X}_j/D_{i,j}}.$

Ethylene dichloride burner hearth and boiler tube coupled simulation

Grid is divided

Due to the symmetry of dichloroethane cracking furnace, in order to reduce the CFD calculated amount, along Width, only have the dichloroethane cracking furnace of half to be used for simulation.The grid of burner hearth is divided: tetrahedron element is used for dividing the grid in burner region, boiler tube district; Hexahedral element is used for dividing other regional grids of burner hearth.The grid of boiler tube is divided: hexahedral element is used for dividing the grid of boiler tube wall; The mixture unit is used for dividing the grid of boiler tube coupling part.The grid of burner hearth and boiler tube is divided as shown in Figure 1:

Boundary condition

(1) inlet boundary condition: determine the fuel gas inlet flow of burner on sidewall according to technological parameter, air inlet flow and reaction tube inlet gas flow and temperature.

(2) wall boundary condition: reaction tube and furnace wall wall all adopt without the slippage hypothesis, and namely on wall, the value of each physical quantity is 0; Flow in viscous sublayer near wall and adopt the Standard law of wall approximate processing with heat exchange; Thermal boundary on the burner hearth wall is given the thermoflux boundary condition by thermal loss; The temperature of factory's actual condition, the preliminary hypothesis of operating experience is adopted on furnace wall surface temperature border, is assigned to tube wall, specifically can carry out assignment by self-defining function (UDF), and furnace tube outer wall thermoflux UDF function definition is: Q (x)=a ₁+ b ₁x+c ₁x ²+ d ₁x ³+ e ₁x ⁴+ f ₁x ⁵, in the burner hearth model, furnace tube outer wall temperature UDF is defined as T (x)=a ₂+ b ₂x+c ₂x ²+ d ₂x ³+ e ₂x ⁴+ f ₂x ⁵

(3) export boundary condition: determine pyrolysis furnace burner hearth exhanst gas outlet pressure and boiler tube pyrolysis gas top hole pressure according to process conditions.

Coupled simulation is found the solution

By at Fluid Mechanics Computation platform Ansys14.0(fluent) set up respectively the transfer reaction mathematical model in above-mentioned burner hearth and pipe.But, we say that this two covers mathematics model is not isolated the existence, are coupled but connect each other, and " tie " of this contact is namely temperature and the thermoflux of tube wall, therefore must both are coupled together to calculate by thermal boundary just can obtain final result, and specific algorithm is as follows:

(1) the present invention selects one group of pipe surface temperature of actual measurement as initial value, assign it to the tube wall border in the burner hearth model, calculate thus burning and the flow process of burner hearth fuel gas, obtain thus the one group of thermoflux data that distributes on one group of checking boiler tube length direction.These group thermoflux data are with comparing with the front thermoflux data that once calculate, if both differences have reached the precision of appointment.

(2) thermoflux that calculates in (1) is assigned to the tube wall border of the pipe inner model of foundation, by calculating cracking process in furnace tube heat transfer and pipe, obtains one group of new pipe surface temperature.(3) one group of new pipe surface temperature and the front furnace tube outer wall temperature that once calculates that calculates in (2) compared, if both differences have reached the precision (it is less than 1 ℃ that the present invention gets precision) of appointment, calculating stops, otherwise, iteration is continued in repeating step (1), (2), until satisfy computational accuracy.

Dichloroethane cracking furnace hearth combustion heat transfer model is found the solution flow process as shown in Figure 2 with the interior transfer reaction model coupling of pipe.

Interpretation of result

Determine boundary condition, the degree of freedom that sealing CFD calculates through the CFD simulation, can obtain the detailed distribution situation of significant variable in burner hearth and boiler tube.Fig. 3 has provided respectively burner hearth velocity of flue gas field, temperature field, CO on the tangent plane on furnace chamber width y=0.0485m direction, O2, CO2 distribution of concentration to Fig. 7.Fig. 8-Figure 12 has provided respectively boiler tube thermoflux, the interior pyrolysis gas temperature of pipe, has managed pyrolysis gas pressure in interior pyrolysis gas flow velocity, pipe, has managed each component composition of interior pyrolysis gas along the distribution curve of boiler tube length direction.By table 1 data analysis as seen, critical data and field measurement data error that the simulation of this CFD method provides are less, this shows that to utilize above-mentioned CFD method very accurate to the dichloroethane cracking furnace modeling.

Table 1CFD modeling and one dimension modeling method critical data contrast table

The appendix symbol table

The A empirical constant

The B empirical constant

C _j,rThe volumetric molar concentration of component j in reaction r, kgmol/m ³

C _piThe thermal capacitance of one-component i, J/kg/K

D _i,mThe mass diffuse coefficient of component i in potpourri, m ²/ s

D _ijComponent i is the binary quality coefficient of diffusion in j, m ²/ s

D _tDue to the effective mass coefficient of diffusion that turbulent flow causes, m ²/ s

The gross energy of E unit mass, J/kg

G _kThe generation item of tubulence energy, J/m ³/ s

The h sensible enthalpy, J/kg

h _jThe enthalpy of component j, J/kg

The I radiation intensity, J/m ²/ s

The diffusion flux of component, kg/m ²/ s

The k tubulence energy, m ²/ s ^-2

k _effEffective conductivity, W/m/K

k _f,rThe forward rate constant of reaction r, 1/s

k _b,rThe reverse rate constant of reaction r, 1/s

k _iThe absorption coefficient of i kind ash gas, 1/m

k _tThe turbulent flow coefficient of heat conductivity, W/m/K

M _w,iThe molecular weight of component i, g/mol

The n refractive index

Chemical species number in the N system

The partial pressure sum of p pressure and all absorption gases, Pa

p _effEffective pressure, Pa

Position vector

The R ideal gas constant, R=8.314J/mol/K

R _iBy the clean generation rate of component i that chemical reaction causes, gmol/m ³/ s

R _jThe reaction rate that j participates in, kmol/m/s

Direction vector

The scattering direction vector

The s path

Sc _tThe turbulent Schmidt number amount

S _hSource item in energy equation, J/m ³/ s

T local temperature and oil gas temperature, K

U _i, U _j, U _lI, j, the speed component of k direction, m/s

x _i, x _j, x _lI, j, the coordinate of k direction, m

X _iThe mole fraction of component i

Y _jThe massfraction of component j

Y _PThe massfraction of product P

Y _RThe massfraction of reactant R

The α absorption coefficient, 1/m and dependence p _tThe transforming factor of unit

α _{ε, i}The emissivity weight factor of the virtual ash gas of i kind

δ _ijKronecker function

The dissipative shock wave of ε tubulence energy, m ²/ s ³And emissivity

ε/k Lenard-Jones potential energy parameter, K

The viscosity of μ gas molecule, kg/m/s

μ _effVirtual viscosity, kg/m/s

μ _tTurbulent viscosity, kg/m/s

The ρ gas density, kg/m ³

The clean impact of Γ third body on reaction rate

ν _i' _{, r}The stoichiometric coefficient of reactant i in reaction r

ν _i' _,' _rThe stoichiometric coefficient of product i in reaction r

η _{J ', r}The speed index of reactant j in reaction r

The speed index of product j in reaction r

σ Stefan-Boltzmann constant, σ=5.672 * 10 ^-8W/m ²K ⁴

σ _iThe Leonard of component i-Jones's collision diameter, angstrom

σ _SScattering coefficient, 1/m

The Φ phase function

Ω ' solid angle

Ω _DThe diffusion collision integral

Ω _{μ i}The viscosity collision integral number of times of component i

The above is only illustrative, but not is restricted person.Any spirit and category that does not break away from the present invention, and to its equivalent modifications of carrying out or change, all should be contained in rear attached claim.

Claims (9)

1. an industrial dichloroethane cracking furnace burner hearth and boiler tube Coupled Numerical modeling method, is characterized in that, comprises the following steps:

Step 1: determine dichloroethane cracking furnace burner hearth boiler tube size to be simulated, carry out the grid division for burner hearth and boiler tube; Determine boundary condition according to technological parameter, comprising: the fuel gas inlet flow of burner on sidewall, air inlet flow and reaction tube inlet gas flow and temperature, furnace wall heat loss factor, burner hearth exhanst gas outlet pressure and boiler tube pyrolysis gas top hole pressure;

Step 2: set up the burner hearth model:

Step 2.1: in burner hearth, the flow of flue gas model adopts and sets up closed model based on the standard k-ε two-equation model of Reynolds average equation;

Step 2.2: burner hearth fuel gas adopts one-level series connection combustion reaction model, and during burning, flow model adopts finite rate/whirlpool dissipation model;

Step 2.3: in burner hearth, radiation heat-transfer model adopts the discrete coordinates model, and the burner hearth flue gas adopts how grey gas weighted model to calculate its radiation characteristic;

Step 3: set up the boiler tube model:

Step 3.1: in boiler tube, the ethylene dichloride cracking reaction adopts one-level cascade reaction model, and cracking reaction dynamics meets Allan Li Wusi formula;

Step 3.2: the parameter of determining gas density in the boiler tube model, thermal capacitance, viscosity, coefficient of heat conductivity and coefficient of diffusion computing formula;

Step 4: have starting condition and the boundary condition that obtains in serious thermal coupling relation and step 1 based on burner hearth and boiler tube, furnace tube outer wall temperature and boiler tube thermoflux mutual iteration coupling variable during as burner hearth model and boiler tube model numerical solution, carry out the loop iteration of burner hearth and boiler tube model, until the model convergence obtains model and relates to each parameter.

2. a kind of industrial dichloroethane cracking furnace burner hearth and the boiler tube Coupled Numerical modeling method described according to claim 1, it is characterized in that, carry out grid for burner hearth and boiler tube in described step 1 and divide, burner region in burner hearth, boiler tube district adopts tetrahedron element to be used for grid division; Other zones of burner hearth adopt hexahedral elements to be used for grid division; In the boiler tube model, boiler tube straight tube wall adopts hexahedral element to come grid division; Bend pipe adopts mixture dividing elements grid.

3. the Coupled Numerical modeling method of cracking reaction in a kind of industrial dichloroethane cracking furnace hearth combustion described according to claim 1 and boiler tube, is characterized in that, in described step 2, step 3, boiler tube and burner hearth wall surface are considered as non-slippage border; In viscous sublayer, adopt Standard law of wall to approach flowing and heat exchange of real process near wall; Thermal boundary on the burner hearth wall is given the thermoflux boundary condition by thermal loss; Boiler tube wall border adopts self-defining function to be assigned to tube wall, and in the boiler tube model, furnace tube outer wall thermoflux self-defining function is defined as Q (x)=a ₁+ b ₁x+c ₁x ²+ d ₁x ³+ e ₁x ⁴+ f ₁x ⁵, in the burner hearth model, furnace tube outer wall temperature self-defining function is defined as T (x)=a ₂+ b ₂x+c ₂x ²+ d ₂x ³+ e ₂x ⁴+ f ₂x ⁵, a wherein ₁, b ₁, c ₁, d ₁, e ₁, f ₁, a ₂, b ₂, c ₂, d ₂, e ₂, f ₂For treating the parameter of match, x is along boiler tube coordinate radially; Q is thermoflux, and T is the furnace tube outer wall temperature.

4. the Coupled Numerical modeling method of cracking reaction in a kind of industrial dichloroethane cracking furnace hearth combustion described according to claim 1 and boiler tube, is characterized in that, in described step 2.2, one-level series connection combustion model is:

Use finite-rate model, chemical source item is calculated with the Arrhenius formula:

M _w,iBe the molecular weight of component i, N _RBe reactional equation number, R _iBe the clean throughput rate of the component i that is caused by chemical reaction,

Be the generation/decomposition rate of i kind material in r reaction, its expression formula is:

The wherein clean impact of Γ third body on reaction rate, ν ' _i,r, ν " _i,rBe stoichiometric coefficient, k _f,rThe forward reaction rate constant, C _j,rBe volumetric molar concentration, η ' _j,r, η " _j,rBe the speed index, N is for participating in the sum of reactive material;

Use the whirlpool dissipation model, the generation speed R of material k in reaction r _i,kBy less one in lower formula two:

ν ' wherein _i,k, ν ' _R,k, ν " _j,kBe stoichiometric coefficient, M _w,i, M _w,R, M _w,jBe molecular weight, A, B are experience factor, the ρ gas density,

Be Lenard-Jones potential energy parameter, Y _R, Y _PBe mass fraction of product.

5. the Coupled Numerical modeling method of cracking reaction in a kind of industrial dichloroethane cracking furnace hearth combustion described according to claim 1 and boiler tube, it is characterized in that, set up the mathematical model of sealing in step 2.1 based on the standard k-ε two-equation model of averaged Navier-Stokes equation, the dissipative shock wave of quality, momentum, tubulence energy, tubulence energy, energy and component transport equation are as shown in the formula expression:

Continuity equation:

The equation of momentum:

The k-equation:

ε-equation:

Energy equation:

The component transport equation:

U wherein _i, U _j, U _lBe i, j, the speed component of k direction, x _i, x _j, x _lBe i, j, the coordinate of k direction, ρ are gas density, p _effBe effective pressure, μ _effBe virtual viscosity, δ _ijBe Kronecker function, k is tubulence energy, and μ is the viscosity of gas molecule, μ _tBe turbulent viscosity, G _kBe the generation item of tubulence energy, ε is the dissipative shock wave of tubulence energy, S _hBe the source item in energy equation, C _μ, C _{1 ε}, C _{2 ε}, σ _k, σ _εBe standard k-ε model parameter, E is the gross energy of unit mass, and p is pressure, k _effConductivity,

Be the diffusion flux of component, h _jBe the enthalpy of component j, Y _jBe the massfraction of component j, D _i,mBe the mass diffuse coefficient of component i in potpourri,

Be turbulent Schmidt number, R _iBe the clean generation rate of the component i that is caused by chemical reaction.

6. the Coupled Numerical modeling method of cracking reaction in a kind of industrial dichloroethane cracking furnace hearth combustion described according to claim 1 and boiler tube, is characterized in that, in step 2.3, radiation heat-transfer model adopts the discrete coordinates model, and its mathematic(al) representation is:

Wherein I is radiation intensity,

Be position vector,

Be direction vector, α is absorption coefficient, σ _sBe scattering coefficient, n is refractive index, and σ is the Stefan-Boltzmann constant, and T is that flue-gas temperature Φ is phase function, and Ω ' is solid angle;

In burner hearth, the how grey gas weighted model of flue gas employing calculates the radiation characteristic of flue gas, this model handle

The blackness approximate processing of real gas is the weighted sum of some grey channel black degree:

α wherein _{ε, i}The emissivity weight factor of the virtual ash gas of i kind, the total adsorption coefficient of flue gas can be expressed as:

When s＞10 ^-4m，

When s≤10 ^-4m，

7. the Coupled Numerical modeling method of cracking reaction in a kind of industrial dichloroethane cracking furnace hearth combustion described according to claim 1 and boiler tube, is characterized in that, step 3.1 ethylene dichloride pyrolysis gas one-level series connection cracking reaction is

Its dynamics meets Allan Li Wusi formula, and chemical reaction rate is expressed from the next:

Wherein

Be the generation/decomposition rate of i kind material in r reaction, ν ' _i,r, ν " _{I, r}Be stoichiometric coefficient, η ' _j,r, η " _j,rBe reaction velocity index, k _f,rBe forward reaction rate constant, k _b,rBe backward reaction rate constant, C _j,rVolumetric molar concentration for component j.

8. the Coupled Numerical modeling method of cracking reaction in a kind of industrial dichloroethane cracking furnace hearth combustion according to claim 1 and boiler tube, it is characterized in that, the burner hearth model condition of convergence is that the burner hearth model obtains on one group of new tube wall thermoflux and compares with thermoflux on the front tube wall that once calculates and reach default precision.

9. the Coupled Numerical modeling method of cracking reaction in a kind of industrial dichloroethane cracking furnace hearth combustion according to claim 1 and boiler tube, it is characterized in that, the boiler tube model condition of convergence is that the boiler tube model obtains one group of new pipe surface temperature and compares with the front furnace tube outer wall temperature that once calculates and reach default precision.

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