CN103148506B - Secondary air distribution method and system for pulverized coal boiler with swirling combustion of front-back hedging - Google Patents

Abstract

The invention discloses a secondary air distribution method for a pulverized coal boiler with swirling combustion of front-back hedging. The method comprises the steps of establishing a mesh structure model of the boiler; according to the mesh structure model, establishing a mathematical model of each process formed during the pulverized coal combustion; according to the established mathematical model, simulating the process of the pulverized coal combustion; obtaining the proportion of an air volume with complete combustion in a total secondary air volume when the temperature field distribution in the boiler meets a preset index; and when the boiler is in operation, executing air distribution of the second air for the boiler according to the proportion of the air volume with complete combustion in the total secondary air volume. In addition, the invention further discloses a secondary air distribution system for the pulverized coal boiler with swirling combustion of front-back hedging. According to the method and the system provided by the invention, the problem that the accuracy caused by manual air distribution is not high to lead to unstable combustion inside the boiler is overcome, and the combustion efficiency of the boiler is improved. Meanwhile, the contaminants which are produced during the combustion process are greatly reduced.

Description

Before and after to liquidate the Secondary Air air distribution method and system of swirl flow combustion pulverized-coal fired boiler

Technical field

Liquidate before and after the present invention relates to swirl flow combustion pulverized-coal fired boiler technical field, particularly relates to the liquidate Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler and a kind of front and back, a kind of front and back and to liquidate the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler.

Background technology

The energy resource structure of China within the long term still based on coal.Because a large amount of fire coal is used to generating, the NO discharged _x(nitrogen oxide) accounts for the significant proportion of national total displacement, causes serious destruction to environment.Therefore, the NO in boiler combustion process _xdischarge capacity should reduce as far as possible.Because coal in China is for a long time by exhaustive exploitation, coal reserve starts to manifest deficiency, and pressure appears in coal supply.Therefore, at reduction NO _xwhile discharge, how to allow the burning of fuel-efficient, boiler combustion efficiency is improved, a major issue of Ye Shi power plant care.

In thermal power generation, boiler operatiopn quality is closely connected with Furnace Aerodynamic Field situation.Good Furnace Aerodynamic Field not only can ensure that boiler safety reliably runs, and in turn ensure that the economy of power plant.Burner is the key equipment affecting Furnace Aerodynamic Field, and dissimilar burner generates different aerodynamic fields in stove.Burner is divided into two kinds: DC burner and turbulent burner.DC burner is generally applied to Process In A Tangential Firing, is applicable to Pump for Medium and Small Power Generating Set; And turbulent burner is generally applied to the swirl flow combustion boiler that liquidates, be applied to Large-scale machine set.Compared with DC burner, the aspects such as the steady combustion of turbulent burner is good, combustion economization is high, gas temperature windage is little, unit maximization have unique advantage, but NO _xgrowing amount is higher, and some unit does not still reach discharging standards.Turbulent burner mixes strongly with air-flow due to coal dust, and the excessive oxygen of the temperature rise that fluid field in furnace is too fast and local, makes coal dust firing intensity higher, cause nitrogen oxide to generate in a large number.

In the actual motion of power plant, realize low NO by the mode changing Secondary Air partition _xdischarging and improving efficiency of combustion is a kind of important means.At present carry out according to artificial experience for the liquidate common practices of Secondary Air air distribution of swirl flow combustion pulverized-coal fired boiler of front and back, because the degree of accuracy of artificial experience is not high, cause stove combustion unstable sometimes, burner outlet is caused to be burned, or local heating's face coking, also can cause boiler extinguishment time serious, the security and the economy that reduce power plant reduce; In addition, current way cannot configure rational Secondary Air to boiler, thus have impact on the efficiency of combustion of boiler; And the mode of artificial air distribution can cause and produce a large amount of pollutants in combustion, causes very large destruction to environment.

Summary of the invention

Based on this, the invention provides the liquidate Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler and a kind of front and back, a kind of front and back and to liquidate the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler.

Front and back liquidate the Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler, comprise the following steps:

Liquidate according to front and back the design parameter of swirl flow combustion pulverized-coal fired boiler, according to the structure in turbulent burner, furnace hopper region, burner region, burner upper area and pendant superheater region, sets up the gridding structural model of described boiler;

According to described gridding structural model, set up the Mathematical Modeling of gas-phase turbulent flow process, gas-solid two flow process, radiant heat transfer process, Volatile process, coke combustion and the NO_x formation process that coal dust firing is formed;

Described Mathematical Modeling according to setting up is simulated process of coal combustion, obtains after-flame air quantity when thermo parameters method in described boiler meets pre-set level and accounts for the ratio of total secondary air flow;

When described boiler operatiopn, the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler; Wherein, when in described boiler, thermo parameters method meets pre-set level, after-flame air quantity accounts for the ratio of total secondary air flow is a number range, chooses the proportional numerical value that after-flame air quantity accounts for total secondary air flow, described boiler is carried out to the air distribution of Secondary Air in this number range.

Compared with general technology, the Mathematical Modeling that the Secondary Air air distribution method establishment of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention is corresponding with each physical and chemical processes that coal dust firing is formed, adopt the method for numerical simulation to obtain after-flame air quantity when thermo parameters method in described boiler meets pre-set level and account for the ratio of total secondary air flow, and the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler.The present invention is consuming time short in numerical simulation, assesses the cost low, and the regulation and control at implementation procedure Zhong Buxu power plant scene coordinate, and analog result has good visuality.Overcome the degree of accuracy that artificial air distribution produces not high, easily can cause the problem of stove combustion instability, improve the efficiency of combustion of boiler, can greatly reduce the pollutant produced in combustion process simultaneously.

Front and back liquidate the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler, configuration model module, Mathematical Models module, analog module and air distribution module;

Described configuration model module, for the design parameter of the swirl flow combustion pulverized-coal fired boiler that liquidates according to front and back, according to the structure in turbulent burner, furnace hopper region, burner region, burner upper area and pendant superheater region, set up the gridding structural model of described boiler;

Described Mathematical Models module, for according to described gridding structural model, set up the Mathematical Modeling of gas-phase turbulent flow process, gas-solid two flow process, radiant heat transfer process, Volatile process, coke combustion and the NO_x formation process that coal dust firing is formed;

Described analog module, for simulating process of coal combustion according to the described Mathematical Modeling set up, obtaining after-flame air quantity when thermo parameters method in described boiler meets pre-set level and accounting for the ratio of total secondary air flow;

Described air distribution module, for when described boiler operatiopn, the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler; Wherein, when in described boiler, thermo parameters method meets pre-set level, after-flame air quantity accounts for the ratio of total secondary air flow is a number range, described air distribution module is used in this number range, choose the proportional numerical value that after-flame air quantity accounts for total secondary air flow, described boiler is carried out to the air distribution of Secondary Air.

Compared with general technology, the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention sets up the Mathematical Modeling corresponding with each physical and chemical processes that coal dust firing is formed, adopt the method for numerical simulation to obtain after-flame air quantity when thermo parameters method in described boiler meets pre-set level and account for the ratio of total secondary air flow, and the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler.The present invention is consuming time short in numerical simulation, assesses the cost low, and the regulation and control at implementation procedure Zhong Buxu power plant scene coordinate, and analog result has good visuality.Overcome the degree of accuracy that artificial air distribution produces not high, easily can cause the problem of stove combustion instability, improve the efficiency of combustion of boiler, can greatly reduce the pollutant produced in combustion process simultaneously.

Accompanying drawing explanation

Fig. 1 is the schematic flow sheet of Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention;

Fig. 2 is boiler structure front view;

Fig. 3 is boiler structure front view;

Fig. 4 is turbulent burner structural representation;

Fig. 5 is the stress and strain model area schematic of boiler;

Fig. 6 is the curve map that different operating mode lower hearth horizontal cross-sections cigarette temperature changes with furnace height;

Fig. 7 is different operating mode lower hearth outlets flue-gas temperature curve maps;

Fig. 8 is the structural representation of Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention.

Detailed description of the invention

For further setting forth the technological means that the present invention takes and the effect obtained, below in conjunction with accompanying drawing and preferred embodiment, to technical scheme of the present invention, carry out clear and complete description.

Referring to Fig. 1, is the schematic flow sheet of the Secondary Air air distribution method of the swirl flow combustion pulverized-coal fired boiler that liquidates before and after the present invention.Liquidate before and after the present invention the Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler, comprises the following steps:

S101 liquidates according to front and back the design parameter of swirl flow combustion pulverized-coal fired boiler, according to the structure in turbulent burner, furnace hopper region, burner region, burner upper area and pendant superheater region, sets up the gridding structural model of described boiler;

S102, according to described gridding structural model, sets up the Mathematical Modeling of gas-phase turbulent flow process, gas-solid two flow process, radiant heat transfer process, Volatile process, coke combustion and the NO_x formation process that coal dust firing is formed;

S103 simulates process of coal combustion according to the described Mathematical Modeling set up, and obtains after-flame air quantity when thermo parameters method in described boiler meets pre-set level and accounts for the ratio of total secondary air flow;

S104 is when described boiler operatiopn, and the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler.

For DG2060/26.15-II2 type boiler, according to the actual operating data of power plant, set up the Mathematical Modeling of whole burner hearth.On the basis ensureing coal dust smooth combustion and safe operation of the boiler, change the swirl strength of the inside and outside Secondary Air of turbulent burner, burner is carried out to the cold-stat e simulation of full hearth region, draw the adjustable extent of inside and outside secondary wind swirl intensity; Under the prerequisite of safe operation of the boiler, namely improve boiler combustion efficiency, ensure NO again _xdischarge capacity is in critical field.

As one of them embodiment, in the step of the described gridding structural model setting up described boiler, described design parameter comprises that furnace width, furnace height, ceiling flex point absolute altitude, horizontal flue are dark, the spacing of the number of turbulent burner, adjacent turbulent burner, the boundary condition of burner hearth entrance and the boundary condition of furnace outlet.

The complete network structure chart of boiler can be set up like this, and the accuracy of modeling can be ensured according to setting parameter modeling.

In step S101, modeling is carried out to whole boiler.To power plant 660MW boiler BMCR (BoilerMaximum Continuous Rate, boiler maximum continuous rating) operating mode carries out modeling, when building model, turbulent burner, burner hearth, pendant superheater and enter, the condition such as export boundary condition is boiler design parameter.

For Shanwei, Guangdong Province power plant DG2060/26.15-II2 type boiler, this power plant is equiped with the coal-fired turbine LP rotors of 2 660MW.Boiler is ultra supercritical parameter, transformation Once-through Boiler, opposed firing mode (vortex burner), solid deslagging, single burner hearth, single reheat, balanced draft, outdoor layout, all steel framework, full suspention, п type structure.Boiler main wants limiting size in table 1.

Table 1 boiler main wants limiting size

Title	Unit	Data
			Furnace width	mm	22162.4
Furnace depth	mm	15456.8
			Ceiling flex point absolute altitude	mm	72500
Horizontal flue is dark	mm	5486.4

Upper furnace arranges steam, pendant superheater and high temperature superheater; Horizontal flue is made up of water-cooling wall extension and rear Yan Jing extension, internal placement high temperature reheater; Enclosure wall superheater is provided with above wall after rear vertical shaft; Before rear vertical shaft, flue is provided with low-temperature reheater, and rear pass is provided with low temperature superheater and economizer successively.Boiler structure front view, boiler structure front view and boiler primary operating parameter are shown in Fig. 2, Fig. 3 and table 2 respectively.

Table 2 boiler primary operating parameter

Title	Unit	BMCR operating mode
			Furnace outlet excess air coefficient	-	1.14
Primary air flow	Kg/s	137
			Secondary air flow (not containing burnout degree)	Kg/s	385.6
After-flame air quantity	Kg/s	111.2
			Primary air ratio	％	21.62

Secondary air ratio	％	78.38
			Burner First air temperature	℃	77
Burner Secondary Air temperature	℃	335
			Burner First air wind speed	m/s	22.4
Burner inner second air wind speed	m/s	35.2
			Burner outer second air wind speed	m/s	36.4
Burnt wind direct current wind wind speed	m/s	43.3
			Burnt wind Whirl deposite tank wind speed	m/s	30.8

As shown in Figure 4, combustion air is divided into four parts to turbulent burner structure by coal burner: centre wind, First air, inner second air and outer second air.Wherein, centre wind and First air are direct current, and inside and outside Secondary Air is eddy flow, and inner second air is designed to axial rotational flow blade, outer second air is designed to tangential swirl blade.

This model is Opposite Firing Boiler, and comprise whole burner hearth and 36 mutually isostructural turbulent burners, front-back wall arranges 3 layers respectively, and every layer has 6 burners and the spacing of adjacent burners is identical.

Whole model meshes adds up to about 2,270,000, according to the design feature of model, adopt the method for independent grid division, burner hearth is divided into 5 regions, is respectively: turbulent burner, furnace hopper region, burner region, burner upper area and pendant superheater region.In the process divided, model all adopts structured grid, turbulent burner and hearth combustor region are suitably encrypted, in order to improve the precision of calculating, the joint face of each burner outlet and burner hearth is set to interface, prevents the mesh quality in two two faces and mesh shape from differing greatly and causing error.

Because turbulent burner structure is comparatively complicated, by centre wind during grid division, First air, inside and outside secondary air channel divides separately.Furnace hopper region affects less on the flowing of fluid field in furnace and coal dust firing, and therefore this area grid is comparatively loose.Burner region is the main region of coal dust firing, and is connected with turbulent burner, and coupling part grid difference should not be too large, and therefore burner region adopts the grid configuration that close centre, two ends is dredged.The stress and strain model area schematic of boiler is shown in Fig. 5.The setting in model coordinate direction can be found out, X-axis positive direction is along burner hearth front wall to Hou Qiang direction, Y-axis positive direction is along furnace height direction, Z axis positive direction is along the left wall of burner hearth to You Qiang direction, because the numerical simulation that the present invention is all is all that same foundation carries out, the coordinate direction that therefore the present invention is all is all unified.

The entrance of burner hearth is mainly divided into three parts: turbulent burner, side burnout degree, burnout degree, the entry condition of each several part is obtained by actual operating data.Each porch turbulence intensity is comparatively strong, and therefore turbulence intensity is set as 10%.The line size of each entrance represents by water conservancy equivalent diameter, and hydraulic equivalent diameter computing formula is:

$D_H=\frac{4A}{S}$

In above formula: D _hfor water conservancy equivalent diameter; A is wetted perimeter area; S is wetted perimeter diameter; Burner inlet boundary condition is in table 3.

Outlet and wall boundary condition: in actual motion, under furnace outlet is in the state into tiny structure, therefore in simulation, furnace outlet adopts pressure export type, and outlet pressure is set as-200pa.Be set to by furnace heating surface without the static wall of slippage, owing to carrying out cold-stat e simulation, main result is velocity field in stove, uncorrelated with wall surface temperature, and therefore wall surface temperature adopts default setting, namely 77 DEG C.

Table 3 burner inlet boundary condition

In step s 102, the combustion process of coal dust is a comparatively complicated process, although this process is complicated, still observes three large basic law of conservation, that is: mass conservation law, the law of conservation of momentum and laws of conservation of energy in process.Wherein relate to radiant heat transfer and NO in gas-phase turbulent flow, gas-solid two flowing, pulverized coal particle heating, the burning of coal dust Volatile, volatile matter and coke, stove _xthe process such as generation and reduction, this chapter, for subject study object, establishes the Mathematical Modeling needed for each process, and model is as follows.

(1) governing equation

Numerical simulation coal dust firing is a three-dimensional steady-flow process, follows mass-conservation equation, momentum conservation equation and energy conservation equation, and for arbitrary chemical constituent M, the mass-conservation equation of its component is:

$\frac{\∂p}{\∂t}+\frac{\∂\mathrm{\ρ}{\stackrel{\‾}{u}}_i}{{\∂x}_i}=S_m$

Momentum conservation equation:

$\frac{\∂\left(\mathrm{\ρ}{\stackrel{\‾}{u}}_i\right)}{\∂t}+\frac{\∂}{{\∂x}_j}\left(\mathrm{\ρ}{\stackrel{\‾}{u}}_i{\stackrel{\‾}{u}}_j\right)=\frac{\∂}{\∂x_j}[\mathrm{\μ}\frac{\∂{\stackrel{\‾}{u}}_i}{{\∂x}_j}-\mathrm{\ρ}\stackrel{\‾}{u_i^{\′}{u}_j^{\′}}]-\frac{\∂p}{{\∂x}_i}+{\mathrm{\ρg}}_i$

Energy conservation equation:

$\frac{\∂\left(\mathrm{\ρ}{c}_p\stackrel{\‾}{T}\right)}{\∂t}+\frac{\∂}{{\∂x}_j}\left(\mathrm{\ρ}{c}_p\stackrel{\‾}{u_{j}T}\right)=\frac{\∂}{{\∂x}_j}[\mathrm{\λ}\frac{\∂\stackrel{\‾}{T}}{{\∂x}_j}-{\mathrm{\ρc}}_p\stackrel{\‾}{u_j^{\′}{T}^{\′}}]+S_f+S_R$

State equation:

$\mathrm{\ρ}=\mathrm{\ρ}(p,\stackrel{\‾}{T})$

In above-mentioned formula: S _m, S _f, S _rrepresent source phase; for the average speed in reference axis x, y, z three directions; U' is the fluctuation velocity in reference axis x, y, z three directions; for mean temperature; g _ifor i direction gravitational acceleration component; μ is the coefficient of kinetic viscosity caused by molecular thermalmotion; ρ is density; P is pressure.

(2) vapor phase stream movable model

During simulation gas-phase turbulent flow, use two-equation turbulence model to may be used for simulating comparatively complicated fluid flowing, and simulate effect is better, on limited computer resource basis, amount of calculation is less, therefore comparatively general in the application.

Two-equation turbulence model is divided into by fluid-flow mode difference: standard k-ε model, RNG k-ε model and realizable k-ε model.Standard k-ε model is applicable to the general flowing being applied to fluid, and RNG k-ε model is applicable to being applied to the flowing that rotating machinery produces, realizable k-ε model be applicable to being applied to fluid the flow field problem such as rotating jet, backflow,

Object of the present invention comprises the flowing of turbulent burner and opposite-flushing type boiler furnace gas thereof, the phenomenon such as rotating jet and backflow is there will be in fluid flowing, therefore turbulence model selects the realizablek-ε model with swirling modification, consider the impact of swirl flow, can simulate swirling two-phase flows.

$\frac{\∂\left(\mathrm{\ρk}\right)}{\∂t}+\frac{\∂\left(\mathrm{\ρ}{\mathrm{ku}}_i\right)}{{\∂x}_i}=\frac{\∂}{{\∂x}_j}[(\mathrm{\μ}+\frac{{\mathrm{\μ}}_t}{{\mathrm{\σ}}_k})\frac{\∂k}{{\∂x}_j}+G_k-\mathrm{\ρ\ϵ}$

$\frac{\∂\left(\mathrm{\ρ\ϵ}\right)}{\∂t}+\frac{\∂\left(\mathrm{\ρ\ϵ}{u}_i\right)}{{\∂x}_i}=\frac{\∂}{{\∂x}_j}(\mathrm{\μ}+\frac{{\mathrm{\μ}}_t}{{\mathrm{\σ}}_{\mathrm{\ϵ}}})+\mathrm{\ρ}{C}_1\mathrm{S\ϵ}-\mathrm{\ρ}{C}_2\frac{{\mathrm{\ϵ}}^2}{k+\sqrt{\mathrm{v\ϵ}}}$

$C_1=\max [0.43,\frac{\mathrm{\η}}{\mathrm{\η}+5}]$

η＝Sk/ε

In above-mentioned formula: k is turbulent flow energy; ε is dissipative shock wave; μ _tfor coefficient of eddy viscosity; σ _kand σ _εthe turbulent prandtl number of turbulent flow energy and dissipative shock wave thereof respectively; G _krepresent that the turbulent flow caused due to average velocity gradient can produce item; C ₂for constant; S is mean strain rate; V is molecular motion viscosity.

(3) Dual-Phrase Distribution of Gas olid movable model

Turbulent burner is the entrance of air, is also the entrance of coal dust, therefore needs to consider gas-solid phase flow model.In process of coal combustion, the randomness impact of fluid turbulent on pulverized coal particle needs to consider, therefore the orbiting motion of pulverized coal particle adopts Stochastic Separated Flow Model.The equation of motion of pulverized coal particle is as follows:

$\frac{{\mathrm{du}}_p}{\mathrm{dt}}=F_D(u-u_p)+\frac{g_x({\mathrm{\ρ}}_p-\mathrm{\ρ})}{{\mathrm{\ρ}}_p}+F_x$

In above formula: F _d(u-u _p) tractive force suffered by particle units quality; U is gaseous substance speed; ρ _pfor grain density; ρ is gaseous substance density; F _xthe summation of other power suffered by particle.

(4) radiation patterns

Furnace heat transfer mainly contains radiant heat transfer and heat convection, and because in-furnace temperature is higher, heat convection only accounts for the very little part of total heat exchange amount, and negligible, therefore furnace heat transfer can see radiant heat transfer process as.For coal dust firing, this model have employed P-1 radiation patterns.

Radiant heat flux:

$q_r=-\frac{1}{3(a+{\mathrm{\σ}}_s)-{\mathrm{C\σ}}_s}\▿G$

In above formula: C is linear each diversity phase function coefficient; A is absorption coefficient; σ _sfor scattering coefficient; G is incident radiation;

Introduce parameter Γ:

$\mathrm{\Γ}=\frac{1}{3(a+{\mathrm{\σ}}_s)-C{\mathrm{\σ}}_s}$

Radiant heat flux formula can be converted into:

q _r＝-Γ▽G

The Boltzman transport equation Boltzmann of G is:

-▽(Γ▽G)-aG+4aσT ⁴＝0

In above formula: σ is this Boltzmann's constant;

Merge two formulas, obtain following formula:

-▽q _r＝aG-4aσT ⁴

By-▽ q _rbring energy equation into, thus obtain the calorie source caused by radiation.

(5) Volatile model

Coal dust decomposes is a complicated process, and thermal decomposition product temperature influence is comparatively large, selects appropriate Volatile model, can improve the accuracy of coal dust firing numerical simulation.Volatile of the present invention adopts two step competitive precipitation models, and reactional equation is:

$\frac{\mathrm{dV}}{\mathrm{dt}}=\frac{{\mathrm{dV}}_1+{\mathrm{dV}}_2}{\mathrm{dt}}(a_1{K}_1+a_2{K}_2)$

$\frac{\mathrm{dC}}{\mathrm{dt}}=-(K_1+K_2)C$

In formula: a ₁, a ₂for coefficient, determined by experiment; C is the ratio of unconverted coal in residual carbon; K ₁, K ₂for constant;

When temperature is lower, first formula plays a major role, and when temperature is higher, second formula plays a major role.

(6) coke combustion model

Coke is the remainder of coal dust after fugitive constituent is separated out, coal dust is when temperature is less than 1000 DEG C, burning velocity depends mainly on chemical reaction kinetics factor, after temperature is greater than 1400 DEG C, burning depends mainly on the diffusion velocity of O2, therefore coke burning herein adopts power/diffusing surface rate process model, and coke burning global rate constant is:

$k=\frac{1}{1/k_s+1/k_d}$

k _s＝A _cT ^Nexp[-E _c/(RT)]

k _d＝φShD ₀/δ _p

In formula: k _sfor kinetic constant; k _dfor volume diffusion constant; A _cfor pre-exponential factor; E _cfor activation energy; φ is the chemical equivalent factor; Sh is particle mass tranfer coefficient; D ₀for diffusion coefficient; δ _pfor particle diameter.

(7) NOx generation model

In stove combustion process, the ratio that the growing amount of NOx accounts for the total growing amount of gas phase is very little, the generation reduction reaction process of NOx can not have an impact substantially to the result of calculation of temperature field in furnace, velocity field and each material concentration field substantially, therefore the present invention adopts the method for post processing to the simulation of NOx, namely first thermal simulation is carried out to whole burner hearth, utilize the fluid field in furnace after calculating convergence to carry out the generation-reduction reaction of NOx.Research shows, the NOx result that profit obtains in this way and actual conditions meet better, therefore demonstrate the reasonability adopting NOx generation model.The present invention have ignored Quick-type NOx, adopts Desoete mechanism model, thinks that fugitive constituent N is first converted into intermediate product NH3 and HCN, and then reaction generates NOx further, and char N directly reacts generation NOx.

As one of them embodiment, after the step of described founding mathematical models, comprise the step adopting hot test to verify the described Mathematical Modeling set up:

Hot test is carried out to described boiler, obtains hot test result;

Adopt described Mathematical Modeling to carry out thermal simulation to described boiler, obtain thermal simulation result;

Described thermal simulation result and described hot test result are compared, verifies whether described Mathematical Modeling meets default capabilities.

The Mathematical Modeling set up is verified, the accuracy of model before numerical simulation can be guaranteed.When only meeting default capabilities, just carry out numerical simulation, avoid the unnecessary wasting of resources.

As one of them embodiment, if the gap between described thermal simulation result and described hot test result is less than or equal to preset difference value, then judge that described Mathematical Modeling meets default capabilities.

Judge that Mathematical Modeling meets default capabilities by preset difference value, deterministic process is had quantize standard, improve efficiency.

In step s 103, on BMCR design conditions basis, the ratio of total secondary air flow is accounted for by changing after-flame air quantity, the aerodynamic field of breeze airflow in regulating stove, fuel is made to be in " oxygen-enriched combusting " or " fuel-rich combustion " stage, by the mutation analysis to stove combustion situation, and the generation of NOx and emission behaviour, in research stove, velocity field, temperature field are on the impact of stove combustion, provide foundation for realizing low NOx drainage technological transformation.

The present invention transforms as follows on the basis of former design conditions: on the basis that furnace outlet excess air coefficient, total secondary air flow, secondary wind swirl intensity are constant, reduce the inside and outside Secondary Air air quantity of burner respectively, the air quantity reduced on average is increased to the air quantity of burnout degree, and the ratio making after-flame air quantity account for total secondary air flow changes.Set three operating modes, detail parameters is in table 4.

The each duty parameter of table 4

Along with the increase of after-flame air quantity ratio, the inside and outside Secondary Air air quantity of burner region burner reduces, the swirling eddy speed sprayed in stove reduces, burner outlet total airflow momentum is reduced, coal dust can not well be full of whole burner hearth, and burner hearth center coal dust amount reduces gradually, increases gradually in stove near front-back wall region coal dust amount, stove combustion central area is while rising, and wall is close forwards, backwards gradually.

Fig. 6 be different burnout degree air distribution than time, the flue-gas temperature curve map that burner hearth horizontal cross-section flue gas mean temperature changes with furnace height.As can be seen from the figure, before and after burnout degree cross section (i.e. y=35.4m), respectively there is a peak value in cross section flue gas mean temperature, peak is all positioned at furnace height 30-35m areas adjacent, and this region is coal dust firing central area in stove.Burner region excess air coefficient a drops in the process of 0.78 by 1.05, the position of stove combustion central area also changes accordingly, correspondingly appear at the region near 31m, 32m, 33m, 33m, this illustrates the increase along with after-flame air flow rate proportioning, stove combustion central area moves up gradually, as a>0.87, stove combustion central area with the reduction of a on move, as a<0.87, stove combustion central area is substantially fixing, moves on no longer with the minimizing of a.As burner region a>1, sufficient oxygen is had around coal dust, be beneficial to and carry out chemistry combustion reaction completely, but the combustion process of coke is slower, coal dust needs at the certain distance ability after-flame of stove chamber inner movement after burner outlet ejection, therefore during a=1.05, stove combustion central temperature appears near 31m, near namely above the 3rd row's burner.As burner region a<1, part coal dust carries out incomplete chemical combustion reaction at burner region, and along with the increase of furnace height, distance burnout degree region is nearer, and oxygen is more sufficient, is more beneficial to the Thorough combustion of coal dust.As a<0.87, whole burner region severe depletion of oxygen, most of coal dust carries out imperfect combustion, carries out Thorough combustion after can only entering burnout degree region.

After after-flame stratification of wind, there is again a peak value in temperature, this is because flue gas is through after-flame stratification of wind, burnout degree temperature is lower, the disturbance that high-temperature flue gas is subject to cold air causes the flue-gas temperature in this region to reduce, although after-flame air quantity supplements the air capacity of coke burning, causes flue-gas temperature to rise, but coke burns, the value that causes temperature to rise is weaker than the value that cold wind causes flue-gas temperature to decline, and therefore there will be at after-flame stratification of wind (i.e. y=35.4m) phenomenon that temperature declines.Flue gas is after after-flame stratification of wind, owing to obtaining sufficient oxygen, unburnt coke is burnt away, flue-gas temperature is gone up to a certain extent, until when combustion heat release amount is less than heating surface caloric receptivity, flue-gas temperature starts slow decline, and therefore behind burnout degree district, flue gas there will be the phenomenon of temperature recovery.

In addition along with after-flame air quantity accounts for the increase of total secondary air flow ratio, the mean temperature entirety in stove on each height cross section is on a declining curve.This is because along with the increase of after-flame air quantity ratio, burner region oxygen supply concentration reduces gradually, and pulverized coal particle imperfect combustion degree increases gradually, and combustion heat release amount reduces gradually, and the heat of generation is less than water-cooling wall caloric receptivity, therefore causes cigarette temperature to decline.Flue gas is through burnout degree, and burnout degree momentum is larger, and the degree that flue-gas temperature declines is more obvious.

When burnout degree accounts for total secondary air flow more than 30%, furnace flame occurs that layering is on-the-spot, namely on furnace height direction, forms Liang Ge combustion high temperature district, thus causes flue gas temperature of hearth outlet can increase with the increase of after-flame air quantity.

Fig. 7 is different operating mode lower hearth outlet flue gas mean temperature figure, as seen from the figure, operating mode 1-4 cigarette temperature is respectively 1089 DEG C, 1100 DEG C, 1113 DEG C and 1119 DEG C, along with the increase of after-flame amount, the average cigarette temperature of furnace outlet increases gradually, but compared with the former design conditions of BMCR, amplitude of variation remains within 20 DEG C.

Drawing by analyzing, changing after-flame air quantity comparatively large on the impact of in-furnace temperature field distribution, less on furnace outlet gas temperature impact.Along with the increase of after-flame air quantity, stove combustion central temperature region starts upwards to shift, and gradually near front-back wall, in heating surface and stove, highest temperature region distance shortens, heating surface is absorbed heat reduce, the simultaneously heating surface metal possibility that easily produces coking, be burned, has an impact to the economy of boiler and security.

In step S104, those of ordinary skill in the art, after reading this patent, can adopt various method to carry out air distribution to described boiler.Such as, computer software is adopted directly to set, or by setting etc. the operation of boiler.

As one of them embodiment, when in described boiler, thermo parameters method meets pre-set level, after-flame air quantity accounts for the ratio of total secondary air flow is a number range, in this number range, choose the proportional numerical value that after-flame air quantity accounts for total secondary air flow, described boiler is carried out to the air distribution of Secondary Air.

The number range obtained according to numerical simulation carries out the air distribution of Secondary Air, can improve the accuracy of air distribution.The result of numerical simulation is used by engineering practice, avoids the series of problems that artificial air distribution causes.

As one of them embodiment, described described boiler is carried out to the step of the air distribution of Secondary Air after, comprise the following steps:

In the running of described boiler, when the proportional numerical value that after-flame air quantity accounts for total secondary air flow is greater than the maximum of described number range or is less than the minimum of a value of described number range, then send alarm signal.

The number range that numerical simulation obtains, also can be used for monitoring the running status of boiler, if the ratio that after-flame air quantity accounts for total secondary air flow breaches described number range, illustrates that problem has likely appearred in boiler operatiopn.

Compared with general technology, the Mathematical Modeling that the Secondary Air air distribution method establishment of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention is corresponding with each physical and chemical processes that coal dust firing is formed, adopt the method for numerical simulation to obtain after-flame air quantity when thermo parameters method in described boiler meets pre-set level and account for the ratio of total secondary air flow, and the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler.The present invention is consuming time short in numerical simulation, assesses the cost low, and the regulation and control at implementation procedure Zhong Buxu power plant scene coordinate, and analog result has good visuality.Overcome the degree of accuracy that artificial air distribution produces not high, easily can cause the problem of stove combustion instability, improve the efficiency of combustion of boiler, can greatly reduce the pollutant produced in combustion process simultaneously.

Referring to Fig. 8, is the structural representation of the Secondary Air blowing system of the swirl flow combustion pulverized-coal fired boiler that liquidates before and after the present invention.

Liquidate before and after the present invention the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler, comprises configuration model module 801, Mathematical Models module 802, analog module 803 and air distribution module 804;

Described configuration model module 801, for the design parameter of the swirl flow combustion pulverized-coal fired boiler that liquidates according to front and back, according to the structure in turbulent burner, furnace hopper region, burner region, burner upper area and pendant superheater region, set up the gridding structural model of described boiler;

Described Mathematical Models module 802, for according to described gridding structural model, set up the Mathematical Modeling of gas-phase turbulent flow process, gas-solid two flow process, radiant heat transfer process, Volatile process, coke combustion and the NO_x formation process that coal dust firing is formed;

Described analog module 803, for simulating process of coal combustion according to the described Mathematical Modeling set up, obtaining after-flame air quantity when thermo parameters method in described boiler meets pre-set level and accounting for the ratio of total secondary air flow;

Described air distribution module 804, for when described boiler operatiopn, the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler.

As one of them embodiment, described design parameter comprises that furnace width, furnace height, ceiling flex point absolute altitude, horizontal flue are dark, the spacing of the number of turbulent burner, adjacent turbulent burner, the boundary condition of burner hearth entrance and the boundary condition of furnace outlet.

The complete network structure chart of boiler can be set up like this, and the accuracy of modeling can be ensured according to setting parameter modeling.

As one of them embodiment, when in described boiler, thermo parameters method meets pre-set level, after-flame air quantity accounts for the ratio of total secondary air flow is a number range, described air distribution module is used in this number range, choose the proportional numerical value that after-flame air quantity accounts for total secondary air flow, described boiler is carried out to the air distribution of Secondary Air.

The number range obtained according to numerical simulation carries out the air distribution of Secondary Air, can improve the accuracy of air distribution.The result of numerical simulation is used by engineering practice, avoids the series of problems that artificial air distribution causes.

As one of them embodiment, also comprise alarm module, described alarm module is used in the running of described boiler, when the proportional numerical value that after-flame air quantity accounts for total secondary air flow is greater than the maximum of described number range or is less than the minimum of a value of described number range, sends alarm signal.

The number range that numerical simulation obtains, also can be used for monitoring the running status of boiler, if the ratio that after-flame air quantity accounts for total secondary air flow breaches described number range, illustrates that problem has likely appearred in boiler operatiopn.

Compared with general technology, the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention sets up the Mathematical Modeling corresponding with each physical and chemical processes that coal dust firing is formed, adopt the method for numerical simulation to obtain after-flame air quantity when thermo parameters method in described boiler meets pre-set level and account for the ratio of total secondary air flow, and the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler.The present invention is consuming time short in numerical simulation, assesses the cost low, and the regulation and control at implementation procedure Zhong Buxu power plant scene coordinate, and analog result has good visuality.Overcome the degree of accuracy that artificial air distribution produces not high, easily can cause the problem of stove combustion instability, improve the efficiency of combustion of boiler, can greatly reduce the pollutant produced in combustion process simultaneously.

The above embodiment only have expressed several embodiment of the present invention, and it describes comparatively concrete and detailed, but therefore can not be interpreted as the restriction to the scope of the claims of the present invention.It should be pointed out that for the person of ordinary skill of the art, without departing from the inventive concept of the premise, can also make some distortion and improvement, these all belong to protection scope of the present invention.Therefore, the protection domain of patent of the present invention should be as the criterion with claims.

Claims (8)

1. front and back liquidate a Secondary Air air distribution method for swirl flow combustion pulverized-coal fired boiler, it is characterized in that, comprise the following steps:

Liquidate according to front and back the design parameter of swirl flow combustion pulverized-coal fired boiler, according to the structure in turbulent burner, furnace hopper region, burner region, burner upper area and pendant superheater region, sets up the gridding structural model of described boiler;

According to described gridding structural model, set up the Mathematical Modeling of gas-phase turbulent flow process, gas-solid two flow process, radiant heat transfer process, Volatile process, coke combustion and the NO_x formation process that coal dust firing is formed;

Described Mathematical Modeling according to setting up is simulated process of coal combustion, obtains after-flame air quantity when thermo parameters method in described boiler meets pre-set level and accounts for the ratio of total secondary air flow;

When described boiler operatiopn, the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler; Wherein, when in described boiler, thermo parameters method meets pre-set level, after-flame air quantity accounts for the ratio of total secondary air flow is a number range, chooses the proportional numerical value that after-flame air quantity accounts for total secondary air flow, described boiler is carried out to the air distribution of Secondary Air in this number range.

2. front and back according to claim 1 liquidate the Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler, it is characterized in that, in the step of the described gridding structural model setting up described boiler, described design parameter comprises that furnace width, furnace height, ceiling flex point absolute altitude, horizontal flue are dark, the spacing of the number of turbulent burner, adjacent turbulent burner, the boundary condition of burner hearth entrance and the boundary condition of furnace outlet.

3. front and back according to claim 1 liquidate the Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler, it is characterized in that, described set up the step of the Mathematical Modeling of gas-phase turbulent flow process, gas-solid two flow process, radiant heat transfer process, Volatile process, coke combustion and the NO_x formation process that coal dust firing is formed after, comprise and adopt hot test to the step verified of described Mathematical Modeling set up:

Hot test is carried out to described boiler, obtains hot test result;

Adopt described Mathematical Modeling to carry out thermal simulation to described boiler, obtain thermal simulation result;

Described thermal simulation result and described hot test result are compared, verifies whether described Mathematical Modeling meets default capabilities.

4. front and back according to claim 3 liquidate the Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler, it is characterized in that, if the gap between described thermal simulation result and described hot test result is less than or equal to preset difference value, then judge that described Mathematical Modeling meets default capabilities.

5. front and back according to claim 1 liquidate the Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler, it is characterized in that, described described boiler is carried out to the step of the air distribution of Secondary Air after, comprise the following steps:

In the running of described boiler, when the proportional numerical value that after-flame air quantity accounts for total secondary air flow is greater than the maximum of described number range or is less than the minimum of a value of described number range, then send alarm signal.

6. front and back liquidate a Secondary Air blowing system for swirl flow combustion pulverized-coal fired boiler, it is characterized in that, comprise configuration model module, Mathematical Models module, analog module and air distribution module;

Described configuration model module, for the design parameter of the swirl flow combustion pulverized-coal fired boiler that liquidates according to front and back, according to the structure in turbulent burner, furnace hopper region, burner region, burner upper area and pendant superheater region, set up the gridding structural model of described boiler;

Described Mathematical Models module, for according to described gridding structural model, set up the Mathematical Modeling of gas-phase turbulent flow process, gas-solid two flow process, radiant heat transfer process, Volatile process, coke combustion and the NO_x formation process that coal dust firing is formed;

Described analog module, for simulating process of coal combustion according to the described Mathematical Modeling set up, obtaining after-flame air quantity when thermo parameters method in described boiler meets pre-set level and accounting for the ratio of total secondary air flow;

Described air distribution module, for when described boiler operatiopn, the ratio accounting for total secondary air flow according to described after-flame air quantity carries out the air distribution of Secondary Air to described boiler; Wherein, when in described boiler, thermo parameters method meets pre-set level, after-flame air quantity accounts for the ratio of total secondary air flow is a number range, described air distribution module is used in this number range, choose the proportional numerical value that after-flame air quantity accounts for total secondary air flow, described boiler is carried out to the air distribution of Secondary Air.

7. front and back according to claim 6 liquidate the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler, it is characterized in that, described design parameter comprises that furnace width, furnace height, ceiling flex point absolute altitude, horizontal flue are dark, the spacing of the number of turbulent burner, adjacent turbulent burner, the boundary condition of burner hearth entrance and the boundary condition of furnace outlet.

8. front and back according to claim 6 liquidate the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler, it is characterized in that, also comprise alarm module, described alarm module is used in the running of described boiler, when the proportional numerical value that after-flame air quantity accounts for total secondary air flow is greater than the maximum of described number range or is less than the minimum of a value of described number range, send alarm signal.