CN103148507A - 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 which is formed by the pulverized coal combustion; according to the established mathematical model, simulating the process of the pulverized coal combustion, and obtaining a proportion of an air volume with complete combustion in a total secondary air volume when the gas concentration distribution inside the boiler meets a preset index; and when the boiler is in operation, according to the proportion of the air volume with the complete combustion in the total secondary air volume, executing air distribution of the secondary air for the boiler. 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 the liquidate Secondary Air air distribution method and system of swirl flow combustion pulverized-coal fired boiler

Technical field

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

Background technology

The energy resource structure of China within the long term still take coal as main.Because a large amount of fire coals are used to generating, the NO that discharges _X(nitrogen oxide) accounts for the significant proportion of national total displacement, and environment has been caused serious destruction.Therefore, the NO in boiler combustion process _XDischarge capacity is answered reduce.For a long time by exhaustive exploitation, coal reserve begins to manifest deficiency due to coal in China, and pressure appears in coal supply.Therefore, reducing NO _XHow discharging time allows the burning of fuel-efficient, and boiler combustion efficiency is improved, and is also the major issue that power plant is concerned about.

In thermal power generation, the boiler operatiopn quality is closely connected with the Furnace Aerodynamic Field situation.Furnace Aerodynamic Field can guarantee that not only boiler safety moves reliably, has guaranteed again the economy of power plant preferably.Burner is the key equipment that affects 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 generally is applied to Process In A Tangential Firing, is applicable to Pump for Medium and Small Power Generating Set; The swirl flow combustion boiler and turbulent burner generally is applied to liquidate is applied to large-scale unit.Compare with DC burner, the aspects such as the steady combustion of turbulent burner is good, combustion economization is high, cigarette temperature deviation 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 with air-flow strongly due to coal dust, and the temperature rise that fluid field in furnace is too fast and local excessive oxygen make 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 that changes the Secondary Air partition _XDischarging and improving efficiency of combustion is a kind of important means.At present to 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 that sometimes the stove internal combustion is unstable, cause burner outlet to be burned, or local heating's face coking, also can cause boiler extinguishment when serious, the security and the economy that reduce power plant reduce; In addition, present way can't configure rational Secondary Air to boiler, thereby has affected the efficiency of combustion of boiler; And the mode of artificial air distribution can cause a large amount of pollutant of generation in combustion process, and environment is caused very large destruction.

Summary of the invention

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

A kind of the liquidate Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler of front and back comprises the following steps:

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

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

According to the described Mathematical Modeling of setting up, process of coal combustion is simulated, when obtaining the satisfied default index of the interior gas concentration distribution of described boiler, the after-flame air quantity accounts for the ratio of total secondary air flow;

When described boiler operatiopn, the ratio that accounts for total secondary air flow according to described after-flame air quantity is carried out the air distribution of Secondary Air to described boiler.

Compare with general technology, the Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention is set up the Mathematical Modeling corresponding with formed each physical and chemical processes of coal dust firing, adopt the method for numerical simulation to obtain distribute after-flame air quantity when satisfying default index of gas concentration in described boiler and account for the ratio of total secondary air flow, and described boiler is carried out the air distribution of Secondary Air according to the ratio that described after-flame air quantity accounts for total secondary air flow.The present invention is consuming time short in numerical simulation, assesses the cost low, do not need the regulation and control at power plant scene to coordinate in implementation procedure, and analog result has good visuality.Overcome the degree of accuracy that artificial air distribution produces not high, easily can cause the unsettled problem of stove internal combustion, improved the efficiency of combustion of boiler, can greatly reduce the pollutant that produces in combustion process simultaneously.

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

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

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

Described analog module is used for according to the described Mathematical Modeling of setting up, process of coal combustion being simulated, and when obtaining the satisfied default index of the interior gas concentration distribution of described boiler, the after-flame air quantity accounts for the ratio of total secondary air flow;

Described air distribution module is used for when described boiler operatiopn, and the ratio that accounts for total secondary air flow according to described after-flame air quantity is carried out the air distribution of Secondary Air to described boiler.

Compare with general technology, the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention is set up the Mathematical Modeling corresponding with formed each physical and chemical processes of coal dust firing, adopt the method for numerical simulation to obtain distribute after-flame air quantity when satisfying default index of gas concentration in described boiler and account for the ratio of total secondary air flow, and described boiler is carried out the air distribution of Secondary Air according to the ratio that described after-flame air quantity accounts for total secondary air flow.The present invention is consuming time short in numerical simulation, assesses the cost low, do not need the regulation and control at power plant scene to coordinate in implementation procedure, and analog result has good visuality.Overcome the degree of accuracy that artificial air distribution produces not high, easily can cause the unsettled problem of stove internal combustion, improved the efficiency of combustion of boiler, can greatly reduce the pollutant that produces in combustion process simultaneously.

Description of drawings

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 the boiler structure front view;

Fig. 3 is the boiler structure front view;

Fig. 4 is the turbulent burner structural representation;

Fig. 5 is the grid zoning schematic diagram of boiler;

Fig. 6 is high each cross section of stove O2 CONCENTRATION DISTRIBUTION schematic diagram under different operating modes;

Fig. 7 is high each cross section of stove NOx CONCENTRATION DISTRIBUTION schematic diagram under different operating modes;

Fig. 8 is different operating mode lower hearths outlets NOx mean concentration schematic diagram;

Fig. 9 is high each cross section of stove CO CONCENTRATION DISTRIBUTION schematic diagram under different operating modes;

Figure 10 is different operating mode lower hearths outlets CO mean concentration schematic diagram;

Figure 11 is different operating mode lower hearth outlet CO and NOx mean concentration tendency chart;

Figure 12 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.

The specific embodiment

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

See also Fig. 1, be 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 Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler comprises the following steps:

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

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

S103 simulates process of coal combustion according to the described Mathematical Modeling of setting up, and when obtaining the satisfied default index of the interior gas concentration distribution of described boiler, the after-flame air quantity accounts for the ratio of total secondary air flow;

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

Take DG2060/26.15-II2 type boiler as example, according to the actual operating data of power plant, set up the Mathematical Modeling of whole burner hearth.On the basis that guarantees 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 the cold conditions simulation in full burner hearth zone, draw the adjustable extent of inside and outside secondary wind swirl intensity; Under the prerequisite of safe operation of the boiler, namely improved boiler combustion efficiency, guarantee again NO _XDischarge capacity is in critical field.

As one of them embodiment, in the step of the described gridding structural model of setting up described boiler, described design parameter comprises that furnace width, furnace height, ceiling flex point absolute altitude, horizontal flue are dark, the number of turbulent burner, the spacing of 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 guaranteed according to the setting parameter modeling.

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

Take Shanwei, the Guangdong Province DG2060/26.15-II2 of power plant type boiler as example, this power plant is equiped with 2 660MW coal-burning steam turbine generator groups.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 to see Table 1.

Table 1 boiler main is wanted 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 has been arranged steam, pendant superheater and high temperature superheater; Horizontal flue is comprised of water-cooling wall extension and rear Yan Jing extension, internal placement high temperature reheater; After rear vertical shaft, the wall top is provided with enclosure wall superheater; 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 main want operational factor to see respectively Fig. 2, Fig. 3 and table 2.

Table 2 boiler main is wanted operational factor

Title	Unit	The BMCR operating mode
			The furnace outlet excess air coefficient	-	1.14
Primary air flow	Kg/s	137
			Secondary air flow (not containing after-flame wind)	Kg/s	385.6
The after-flame air quantity	Kg/s	111.2
			Primary air ratio	%	21.62

Secondary air ratio	%	78.38
			Air temperature of burner	℃	77
Burner Secondary Air temperature	℃	335
			Wind wind speed of burner	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 eddy flow wind wind speed	m/s	30.8

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

This model is Opposite Firing Boiler, comprises the turbulent burner of whole burner hearth and 36 same structures, and front-back wall is arranged respectively 3 layers, and every layer has the spacing of 6 burners and adjacent burner identical.

Whole model meshes adds up to 2,270,000 left and right, design feature according to model, adopt the method for independent grid division, burner hearth is divided into 5 zones, be respectively: turbulent burner, furnace hopper zone, burner region, burner upper area and pendant superheater zone.In the process of dividing, model all adopts structured grid, turbulent burner and hearth combustor zone 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 that the mesh quality of two two faces and mesh shape from differing greatly and causing error.

Because the turbulent burner structure is comparatively complicated, during grid division with centre wind, a wind, inside and outside secondary air channel is divided separately.It is less that the furnace hopper zone reaches the coal dust firing impact to flowing of fluid field in furnace, so 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, so burner region adopts the thin grid configuration in close centre, two ends.The grid zoning schematic diagram of boiler is seen Fig. 5.The setting of model coordinate direction can be found out, the X-axis positive direction is along the burner hearth front wall to rear wall direction, the Y-axis positive direction is along the furnace height direction, the Z axis positive direction is along the left wall of burner hearth to right wall direction, because all numerical simulations of the present invention are all to carry out on same foundation, so all coordinate directions of the present invention are all unified.

The entrance of burner hearth mainly is divided into three parts: turbulent burner, side after-flame wind, after-flame wind, the entry condition of each several part is obtained by actual operating data.Each porch turbulence intensity is stronger, so turbulence intensity is set as 10%.The line size of each entrance represents with the water conservancy equivalent diameter, and the hydraulic equivalent diameter computing formula is:

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

In following formula: D _HBe the water conservancy equivalent diameter; A is the wetted perimeter area; S is the wetted perimeter diameter; The burner inlet boundary condition sees Table 3.

Outlet and wall boundary condition: in actual motion, furnace outlet is under state for little negative pressure, and therefore in simulation, furnace outlet adopts the pressure export type, and outlet pressure is set as-200pa.Furnace heating surface is set to without the static wall of slippage, and owing to carrying out the cold conditions simulation, main result is velocity field in stove, and is uncorrelated with wall surface temperature, so wall surface temperature adopts default setting, namely 77 ℃.

Table 3 burner inlet boundary condition

In step S102, 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.Relate to wherein that two of gas-phase turbulent flows, gas-solid flow, pulverized coal particle heating, coal dust Volatile, volatile matter and coke burning, the interior radiant heat transfer of stove and NO _xGeneration and the process such as reduction, this chapter has set up the required Mathematical Modeling of each process for the subject study object, model is as follows.

(1) governing equation

The numerical simulation coal dust firing is the steady-flow process of a three-dimensional, 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:

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

Momentum conservation equation:

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

Energy conservation equation:

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

State equation:

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

In above-mentioned formula: S _m, S _f, S _RRepresent the source phase;

Average speed for reference axis x, y, three directions of z; U' is the fluctuation velocity of reference axis x, y, three directions of z;

Be mean temperature; g _iBe i direction gravitational acceleration component; The coefficient of kinetic viscosity of μ for being caused by molecular thermalmotion; ρ is density; P is pressure.

(2) vapor phase stream movable model

Simulation use both sides' journey turbulence model can be used for the comparatively complicated Fluid Flow in A of simulation, and simulate effect is better during gas-phase turbulent flow, and on limited computer resource basis, amount of calculation is less, and is therefore comparatively general in application.

Both sides' journey turbulence model is divided into by the fluid-flow mode difference: standard k-ε model, RNG k-ε model and realizable k-ε model.Standard k-ε model is fit to be applied to the general of fluid and flows, and RNG k-ε model is fit to be applied to that rotating machinery produces flows, realizable k-ε model be fit to be applied to the flow field problem such as the rotating jet, backflow of fluid,

Object of the present invention comprises flowing of turbulent burner and opposite-flushing type boiler furnace gas thereof, in Fluid Flow in A, the phenomenons such as rotating jet and backflow can appear, therefore turbulence model is selected the realizablek-ε model with swirling modification, considered the impact of swirl flow, can flow by the simulate eddy flow.

$\frac{\∂\left(\mathrm{\ρk}\right)}{\∂t}+\frac{\∂\left(\mathrm{\ρk}{u}_i\right)}{\∂x_i}=\frac{\∂}{\∂x_j}\left[(\mathrm{\μ}+\frac{{\mathrm{\μ}}_t}{{\mathrm{\σ}}_k})\frac{\∂k}{\∂x_j}\right]+G_k-\mathrm{\ρ\ϵ}$

$\frac{\&PartialD;\left(\mathrm{\&rho;\&epsiv;}\right)}{\&PartialD;t}+\frac{\&PartialD;\left(\mathrm{\&rho;\&epsiv;}{u}_i\right)}{\&PartialD;x_i}=\frac{\&PartialD;}{\&PartialD;x_j}(\mathrm{\&mu;}+\frac{{\mathrm{\&mu;}}_t}{{\mathrm{\&sigma;}}_{\mathrm{\&epsiv;}}})+\mathrm{\&rho;}{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA00002988511700052.png,HDA00002988511700071.png"\; state="\{\{state\}\}">C</figure-callout>}}_1\mathrm{S\&epsiv;}-\mathrm{\&rho;}{C}_2\frac{{\mathrm{\&epsiv;}}^2}{k+\sqrt{\mathrm{v\&epsiv;}}}$

${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA00002988511700052.png,HDA00002988511700071.png"\; state="\{\{state\}\}">C</figure-callout>}}_1=\max [0.43,\frac{\mathrm{\&eta;}}{\mathrm{\&eta;}+5}]$

η＝Sk/ε

In above-mentioned formula: k is the turbulent flow energy; ε is dissipative shock wave; μ _tBe coefficient of eddy viscosity; σ _kAnd σ _εIt is respectively the turbulent prandtl number of turbulent flow energy and dissipative shock wave thereof; G _kThe turbulent flow that expression causes due to average velocity gradient can produce item; C ₂Be constant; S is the mean strain rate; V is the 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 the gas-solid phase flow model.In process of coal combustion, fluid turbulent needs to consider on the randomness impact of pulverized coal particle, so the orbiting motion of pulverized coal particle adopts Stochastic Separated Flow Model.The equation of motion of pulverized coal particle is as follows:

$\frac{d{u}_p}{\mathrm{dt}}=F_D(u-u_p)+\frac{g_x({\mathrm{\&rho;}}_p-\mathrm{\&rho;})}{{\mathrm{\&rho;}}_p}+F_x$

In following formula: F _D(u-u _p) be the suffered tractive force of particle unit mass; U is gaseous substance speed; ρ _pBe grain density; ρ is gaseous substance density; F _xSummation for suffered other power of particle.

(4) radiation model

Furnace heat transfer mainly contains radiant heat transfer and heat convection, and because temperature in stove is higher, heat convection only accounts for the very little part of total heat exchange amount, can ignore, so furnace heat transfer can be seen the radiant heat transfer process as.For coal dust firing, this model has adopted P-1 radiation model.

Radiant heat flux:

$q_r=-\frac{1}{3(a+{\mathrm{\&sigma;}}_s)-C{\mathrm{\&sigma;}}_s}\&dtri;G$

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

Introduce parameter Γ:

$\mathrm{\&Gamma;}=\frac{1}{3(a+{\mathrm{\&sigma;}}_s)-C{\mathrm{\&sigma;}}_s}$

The 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 following formula: σ is this Boltzmann's constant;

Merge two formulas, obtain following formula:

-▽q _r＝aG-4aσT ⁴

General-▽ q _rBring energy equation into, thereby obtain due to the caused calorie source of radiation.

(5) Volatile model

The coal dust decomposes is the process of a complexity, and the thermal decomposition product temperature influence is larger, 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:

$\frac{\mathrm{dV}}{\mathrm{dt}}=\frac{d{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HDA00002988511700052.png,HDA00002988511700071.png"\; state="\{\{state\}\}">V</figure-callout>}}_1+d{V}_2}{\mathrm{dt}}(a_1{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HDA00002988511700052.png,HDA00002988511700071.png"\; state="\{\{state\}\}">K</figure-callout>}}_1+a_2{K}_2)$

$\frac{\mathrm{dC}}{\mathrm{dt}}=-({\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HDA00002988511700052.png,HDA00002988511700071.png"\; state="\{\{state\}\}">K</figure-callout>}}_1+K_2)C$

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

When temperature was low, first formula played a major role, and when temperature was higher, second formula played a major role.

(6) coke combustion model

Coke is the remainder that fugitive constituent is separated out rear coal dust, coal dust is in temperature during less than 1000 ℃, burning velocity depends mainly on the chemical reaction kinetics factor, after temperature is greater than 1400 ℃, burning depends mainly on the diffusion velocity of O2, therefore power/diffusing surface rate process model is adopted in the burning of this paper coke, 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 ₀δ _p

In formula: k _sBe kinetic constant; k _dBe the volume diffusion constant; A _cBe pre-exponential factor; E _cBe activation energy; φ is the chemical equivalent factor; Sh is the particle mass tranfer coefficient; D ₀Be diffusion coefficient; δ _pBe particle diameter.

(7) NOx generation model

In the 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 exert an influence substantially to temperature field in furnace, velocity field and each material concentration field computation result substantially, therefore the present invention adopts the method for post processing to the simulation of NOx, namely first whole burner hearth is carried out thermal simulation, utilize the fluid field in furnace that calculates after restraining to carry out generation-reduction reaction of NOx.Studies show that, utilize NOx result and the actual conditions that this method obtains to meet better, therefore proved the reasonability that adopts the NOx generation model.The present invention has ignored Quick-type NOx, adopts the Desoete mechanism model, thinks that fugitive constituent N first is converted into intermediate product NH3 and HCN, and then further reaction generates NOx, and char N is directly reacted generation NOx.

As one of them embodiment, after the described step of setting up Mathematical Modeling, comprise the step that adopts hot test that the described Mathematical Modeling of setting up is verified:

Described boiler is carried out hot test, obtain the hot test result;

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

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

The Mathematical Modeling of setting up is verified, can be guaranteed the accuracy of model before numerical simulation.Only have in the situation that has satisfied default capabilities, just carry out numerical simulation, avoided 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, judge that described Mathematical Modeling satisfies default capabilities.

Judge that by preset difference value Mathematical Modeling satisfies default capabilities, make deterministic process that the standard that quantizes arranged, improved efficient.

In step S103, on BMCR design conditions bases, account for the ratio of total secondary air flow by changing the after-flame air quantity, the aerodynamic field of breeze airflow in regulating stove, make fuel be in " oxygen-enriched combusting " or " fuel-rich combustion " stage, by the mutation analysis to stove internal combustion situation, and the generation of NOx and emission behaviour, in the research stove, the impact on the stove internal combustion of velocity field, temperature field, provide foundation for realizing the low NOx drainage technological transformation.

The present invention is carrying out following transformation on the basis of former design conditions: on furnace outlet excess air coefficient, total secondary air flow, secondary wind swirl intensity constant basis, reduce respectively the inside and outside Secondary Air air quantity of burner, the air quantity that reduces on average is increased to the air quantity of after-flame wind, and the ratio that makes the after-flame air quantity account for total secondary air flow changes.Set three operating modes, detail parameters sees Table 4.

Each duty parameter of table 4

Change after-flame wind air flow rate proportioning to O in stove ₂The impact of CONCENTRATION DISTRIBUTION: Fig. 6 is the high direction different cross section of stove O under different operating modes ₂Concentration profile.Along with the increase of after-flame air quantity, furnace height direction O ₂CONCENTRATION DISTRIBUTION trend is substantially constant.At furnace height direction y＜32.7m with lower area, O ₂Concentration reduces gradually with the increase of y value, is down to minimumly at 32m place near zone, and this is because coal dust firing need to consume a large amount of O ₂, O ₂Consumption is far longer than O ₂Supply; In 32.7m＜y＜35.4m zone, O ₂Concentration increases gradually with the increase of y value, rises to the highlyest at y=35.4m place near zone, and this is that a large amount of air sprays in stove because this zone is after-flame wind zone, and the coal dust firing oxygen demand is less than oxygen-supplying amount.At y〉35.4m zone, along with the increase O of y value ₂, O ₂Concentration descends gradually.

In 20＜y＜55 zones, O ₂4 peak values have appearred in concentration value, and this is because peak cross section is the burner outlet central cross-section, and the air in burner region and after-flame wind district is all to be provided by burner, and these section oxygen-supplying amounts are greater than oxygen demand, so oxygen concentration is higher.

The impact of change after-flame wind air flow rate proportioning on NOx CONCENTRATION DISTRIBUTION in stove: Fig. 7 is the high different cross section NOx of stove concentration profile under different operating modes, as seen from the figure, under each operating mode, basically identical along each cross section NOx mean concentration distribution trend of furnace height direction.Being mainly manifested in the hearth combustor zone is the main generation district of NOx, zone (being the y=22m near zone) NOx concentration is higher between ground floor burner and the second layer, then reduce gradually along the high direction NOx concentration of stove, this is the impact due to the reducing atmosphere field, and the NOx that a part generates is reduced.

Can analyze and draw, O ₂Basically identical with NOx CONCENTRATION DISTRIBUTION trend, main manifestations is along with O ₂The reduction of concentration, NOx concentration also decreases.Explanation is along with O ₂The reduction of concentration, Deoxidation Atmosphere in Furnace strengthens, and makes NOx concentration reduce.But on the burner outlet central cross-section, O ₂Concentration is just opposite with NOx concentration trend, is mainly because burner is the entrance of furnace air, air in large supply in the growing amount of NOx.

In burner region, along with stove internal combustion stability strengthens gradually, O ₂Consumption increase, O ₂Concentration reduces gradually, and reducing atmosphere strengthens, and the NOx amount of being reduced that causes generating increases, and each is the overall downward trend of NOx mean concentration appearance in cross section highly, and regional NOx mean concentration is minimum in the y=32m left and right.In after-flame wind zone, due to replenishing of after-flame wind, unburnt coke burns away and generates NOx, and reduction field that should the zone is destroyed, oxidized in the NOx part that burner region is reduced, regenerate NOx, cause after-flame wind zone to increase with furnace height, the average growing amount of NOx increases to a certain extent, substantially peak value occurs near the y=37m zone.As y〉during 37m, along with O ₂The reduction of concentration, the reducing power of uncombusted coke improves relatively, so the NOx growing amount reduces gradually.

Along with the increase of after-flame air quantity, NOx generation situation changes greatly in stove, is in particular in: along with the increase of after-flame air quantity, the NOx mean concentration in stove inner height direction each cross section reduces.Along with the after-flame air quantity increases, the burner region excess air coefficient reduces to 0.78 by 1.05, this zone is changed fuel-rich combustion into by oxygen-enriched combusting, aggravate the imperfect combustion degree of this zone pulverized coal particle, extended the distance of coal dust after-flame, so coal dust can reduce relatively at the NOx that burner region generates.Because the burner region reducing atmosphere increases gradually, the NOx amount that is reduced increases gradually, causes each section of burner region NOx mean concentration, and is the highest when a=0.1, minimum when a=0.78 simultaneously.Although along with the increase of after-flame wind ratio, the NOx that is reduced oxidized degree again increases, under low a operating mode, total NOx growing amount is less, therefore at y〉each section of 32.7m NOx mean concentration, the highest when a=0.1, minimum when a=0.78.

Fig. 8 is the mean concentration curve of different operating mode lower hearth outlet NOx, and along with the increase of after-flame air quantity, furnace outlet cross section NOx concentration reduces gradually, but slippage reduces gradually, is respectively 562ppm, 356ppm, 312ppm and 293ppm.Explanation changes the after-flame air quantity and can reduce gradually NOx discharging impact in certain after-flame air quantity proportion.

Changing after-flame wind air flow rate proportioning is high each cross section of stove CO CONCENTRATION DISTRIBUTION under different operating modes on the impact of CO discharge capacity: Fig. 9.Under different operating modes, basically identical along furnace height direction CO CONCENTRATION DISTRIBUTION trend, but different operating mode after-flame of lower time stratification of wind has larger difference with lower area CO concentration.Along with the increase of after-flame air quantity, the burner region excess air coefficient reduces, and coal dust firing can not get sufficient O ₂, making the insufficient degree aggravation of coal dust firing, burner region CO growing amount increases, along with a large amount of after-flame wind are injected burner hearth, for coal dust firing provides sufficient O ₂, in the time of the coke burning, CO is rapid and O also ₂React, CO concentration reduces rapidly.

Figure 10 is different operating mode lower hearths outlet CO mean concentration figure, and furnace outlet CO concentration illustrates the coal dust uncombusted greater than 0, has heat loss due to unburned gas in stove.Along with the increase of after-flame air quantity, furnace outlet CO mean concentration is respectively: 163ppm, 350ppm, 673ppm, 981ppm, and the concentration increment increases gradually, and the increase along with the after-flame air quantity is described, and stove internal combustion chemistry not exclusively heat loss increases gradually.

The result of the test of boiler performance test shows, when improving the after-flame air quantity and accounting for total secondary air flow ratio, boiler thermal output can corresponding reduction.Along with the after-flame air quantity increases, the CO discharge capacity is increase tendency, and boiler efficiency is reduction trend.

The impact of change after-flame wind air flow rate proportioning on the stove internal combustion: change after-flame wind air flow rate proportioning to temperature field, O ₂The impact of CONCENTRATION DISTRIBUTION, NOx CONCENTRATION DISTRIBUTION and CO CONCENTRATION DISTRIBUTION.The quality of boiler operatiopn is relevant with the aerodynamic characteristics factor in stove.Cigarette temperature, temperature case and medium atmosphere near water-cooling wall in burner hearth are all closely related with Aerodynamic Characteristics.If the cigarette temperature is too high near heating surface, as easy as rolling off a logly cause local heating's face coking; If the burner region excess air coefficient is too low, this zone reducing atmosphere concentration is higher, and ash fusion point reduces, and has increased the possibility of coking, as high-melting-point Fe ₂O ₃Be reduced to low melting point FeO by CO, cause the coking of stove internal heating surface.Therefore normally in service at boiler will avoid occurring generating in excess Temperature and stove near heating surface the situation of too much reducing atmosphere as far as possible.

Energy-conservation and to reduce discharging is one of important indicator of boiler operatiopn, in the situation that the normal operation of boiler, how when improving boiler thermal output, reduce the NOx concentration of emission, economy and the feature of environmental protection of power plant there is greatly impact.The present invention analyzes and draws secondary air flow to the impact of stove Combustion Characteristics and the reasonable adjustable extent of secondary air flow by relation and the impact thereof between NOx CONCENTRATION DISTRIBUTION, CO CONCENTRATION DISTRIBUTION and temperature field distribution three in stove.

Figure 11 is different operating mode lower hearth outlet CO and NOx mean concentration tendency chart, can find out the increase along with the after-flame air quantity, and furnace outlet CO concentration increases gradually, and NOx concentration reduces gradually, and both trend is opposite.Explanation is along with the increase of boiler heat loss due to unburned gas, and the NOx discharge capacity reduces gradually.

Greater than 0.23 the time, the NOx discharge capacity surpasses design load when after-flame air quantity ratio, but at 0.3 o'clock, and burner in the stove zone reducing atmosphere increases, and peak reaches 47781ppm, has increased heating surface coking possibility.

The after-flame air quantity was over 0.3 o'clock, in stove, lamination has appearred in temperature, move on stove internal combustion central temperature and reduced the time of staying of coal dust firing in stove, cause not exclusively heat loss increase of chemistry, the furnace flame central temperature appears at the water-cooling wall near zone, very easily causes the water wall high temperature corrosion accident.

Normally in service at boiler, the unsuitable too high and burner region reducing atmosphere concentration of heating surface near zone temperature should be not too much, and the ratio that the after-flame air quantity accounts for secondary air flow should remain between 0.23-0.3.In this scope, furnace outlet NOx discharge capacity can not surpass design load, and the CO discharge capacity has also reduced coking and the high temperature corrosion possibility of heating surface simultaneously lower than 360ppm.

In step S104, those of ordinary skills can adopt the whole bag of tricks to carry out air distribution to described boiler after reading this patent.For example, adopt computer software directly to set, perhaps by the operation of boiler being set etc.

As one of them embodiment, the gas concentration ratio that after-flame air quantity when satisfying default index accounts for total secondary air flow that distributes is a number range in described boiler, choose the proportional numerical value that the after-flame air quantity accounts for total secondary air flow in this number range, described boiler is carried out the air distribution of Secondary Air.

The number range that obtains according to numerical simulation is carried out the air distribution of Secondary Air, can improve the accuracy of air distribution.Make the result of numerical simulation be used by engineering practice, the series of problems of having avoided artificial air distribution to cause.

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

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

The number range that numerical simulation obtains also can be used for the running status of boiler is monitored, and has broken through described number range if the after-flame air quantity accounts for the ratio of total secondary air flow, illustrates that problem might appear in boiler operatiopn.

Compare with general technology, the Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention is set up the Mathematical Modeling corresponding with formed each physical and chemical processes of coal dust firing, adopt the method for numerical simulation to obtain distribute after-flame air quantity when satisfying default index of gas concentration in described boiler and account for the ratio of total secondary air flow, and described boiler is carried out the air distribution of Secondary Air according to the ratio that described after-flame air quantity accounts for total secondary air flow.The present invention is consuming time short in numerical simulation, assesses the cost low, do not need the regulation and control at power plant scene to coordinate in implementation procedure, and analog result has good visuality.Overcome the degree of accuracy that artificial air distribution produces not high, easily can cause the unsettled problem of stove internal combustion, improved the efficiency of combustion of boiler, can greatly reduce the pollutant that produces in combustion process simultaneously.

See also Figure 12, be 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 Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler comprises configuration model module 201, Mathematical Models module 202, analog module 203 and air distribution module 204;

Described configuration model module 201, design parameter for the swirl flow combustion pulverized-coal fired boiler that liquidates according to front and back, according to the structure in turbulent burner, furnace hopper zone, burner region, burner upper area and pendant superheater zone, set up the gridding structural model of described boiler;

Described Mathematical Models module 202, be used for according to described gridding structural model, set up the Mathematical Modeling of the formed gas-phase turbulent flow process of coal dust firing, two flow process of gas-solid, radiant heat transfer process, Volatile process, coke combustion and nitrogen oxide generative process;

Described analog module 203 is used for according to the described Mathematical Modeling of setting up, process of coal combustion being simulated, and when obtaining the satisfied default index of the interior gas concentration distribution of described boiler, the after-flame air quantity accounts for the ratio of total secondary air flow;

Described air distribution module 204 is used for when described boiler operatiopn, and the ratio that accounts for total secondary air flow according to described after-flame air quantity is carried 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 number of turbulent burner, the spacing of 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 guaranteed according to the setting parameter modeling.

As one of them embodiment, the gas concentration ratio that after-flame air quantity when satisfying default index accounts for total secondary air flow that distributes is a number range in described boiler, described air distribution module is used for choosing the proportional numerical value that the after-flame air quantity accounts for total secondary air flow in this number range, described boiler is carried out the air distribution of Secondary Air.

The number range that obtains according to numerical simulation is carried out the air distribution of Secondary Air, can improve the accuracy of air distribution.Make the result of numerical simulation be used by engineering practice, the series of problems of having avoided artificial air distribution to cause.

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

The number range that numerical simulation obtains also can be used for the running status of boiler is monitored, and has broken through described number range if the after-flame air quantity accounts for the ratio of total secondary air flow, illustrates that problem might appear in boiler operatiopn.

Compare with general technology, the Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler of liquidating before and after the present invention is set up the Mathematical Modeling corresponding with formed each physical and chemical processes of coal dust firing, adopt the method for numerical simulation to obtain distribute after-flame air quantity when satisfying default index of gas concentration in described boiler and account for the ratio of total secondary air flow, and described boiler is carried out the air distribution of Secondary Air according to the ratio that described after-flame air quantity accounts for total secondary air flow.The present invention is consuming time short in numerical simulation, assesses the cost low, do not need the regulation and control at power plant scene to coordinate in implementation procedure, and analog result has good visuality.Overcome the degree of accuracy that artificial air distribution produces not high, easily can cause the unsettled problem of stove internal combustion, improved the efficiency of combustion of boiler, can greatly reduce the pollutant that produces in combustion process simultaneously.

The above embodiment has only expressed several embodiment of the present invention, and it describes comparatively concrete and detailed, but can not therefore be interpreted as the restriction to the scope of the claims of the present invention.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 (10)

1. the front and back Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler that liquidates, is characterized in that, comprises the following steps:

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

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

According to the described Mathematical Modeling of setting up, process of coal combustion is simulated, when obtaining the satisfied default index of the interior gas concentration distribution of described boiler, the after-flame air quantity accounts for the ratio of total secondary air flow;

When described boiler operatiopn, the ratio that accounts for total secondary air flow according to described after-flame air quantity is carried out the air distribution of Secondary Air to described boiler.

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

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

Described boiler is carried out hot test, obtain the hot test result;

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

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

4. the front and back according to claim 3 Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler that liquidates, 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, judge that described Mathematical Modeling satisfies default capabilities.

5. the front and back according to claim 1 Secondary Air air distribution method of swirl flow combustion pulverized-coal fired boiler that liquidates, it is characterized in that, the gas concentration ratio that after-flame air quantity when satisfying default index accounts for total secondary air flow that distributes is a number range in described boiler, choose the proportional numerical value that the after-flame air quantity accounts for total secondary air flow in this number range, described boiler is carried out the air distribution of Secondary Air.

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

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

7. the front and back Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler that liquidates, is characterized in that, comprises configuration model module, Mathematical Models module, analog module and air distribution module;

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

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

Described analog module is used for according to the described Mathematical Modeling of setting up, process of coal combustion being simulated, and when obtaining the satisfied default index of the interior gas concentration distribution of described boiler, the after-flame air quantity accounts for the ratio of total secondary air flow;

Described air distribution module is used for when described boiler operatiopn, and the ratio that accounts for total secondary air flow according to described after-flame air quantity is carried out the air distribution of Secondary Air to described boiler.

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

9. the front and back according to claim 7 Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler that liquidates, it is characterized in that, the gas concentration ratio that after-flame air quantity when satisfying default index accounts for total secondary air flow that distributes is a number range in described boiler, described air distribution module is used for choosing the proportional numerical value that the after-flame air quantity accounts for total secondary air flow in this number range, described boiler is carried out the air distribution of Secondary Air.

10. the front and back according to claim 9 Secondary Air blowing system of swirl flow combustion pulverized-coal fired boiler that liquidates, it is characterized in that, also comprise alarm module, described alarm module is used for the running at described boiler, the proportional numerical value that accounts for total secondary air flow when the after-flame air quantity sends alarm signal during greater than the maximum of described number range or less than the minimum of a value of described number range.

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