CN105069185A - Method for establishing air pre-heater clean factor calculation model by using smoke pressure difference, and application - Google Patents

Abstract

The present invention discloses a method for establishing an air pre-heater clean factor calculation model by using smoke pressure difference, and the method includes: converting an actual measuring pressure difference under conditions of different loads and an excess air coefficient into calculated values under conditions of rated loads, and further establishing the air pre-heater clean factor calculation model. The present invention also discloses an application of the above calculation model to monitoring of fouling conditions of the air pre-heater of a coal-fired boiler SCR denitrification system. According to a formation principle of fouling of the air pre-heater of the SCR denitrification system and a growth form, a fouling monitoring model of the air pre-heater of the denitration boiler is established, wherein the fouling monitoring model integrates data collection, fouling condition monitoring, and diagnosis. The method provided by the present invention can accurately predict fouling conditions of the air pre-heater, meet accuracy requirement of engineering application, guide a soot blower to blow soot timely, eventually achieve demand soot blowing of tail heating surface, improve economy and safety of generator operation, and can provide a technical reference for domestic same-type generators.

Description

A kind of utilize flue gas pressure differential method to set up air preheater cleaning gene computation model method and application

Technical field

The present invention relates to Thermal Automation field, specifically disclose a kind of method utilizing flue gas pressure differential method to set up air preheater cleaning gene computation model.

Background technology

The energy structure of China based on coal causes Air Pollutant Emission total amount to remain high, and regional atmosphere polluting problem becomes clear day by day.Oxides of nitrogen, as major pollutants, has been listed in emphasis the binding indicator.Yangtze River Delta Area belongs to priority control district scope, and according to up-to-date " fossil-fuel power plant atmospheric pollutant emission standard " regulation, Thermal Power Generation Industry coal unit is from July, 2014, and all thermal power generation boilers and gas turbine oxides of nitrogen perform new emission limit: 100mg/m ³.

After boiler installs SCR denitration device additional, Ash Blocking in Air Preheater is serious, and boiler back end ductwork flue gas flow rate increases, economizer wearing and tearing aggravation.Back-end surfaces Slag and accumulating ash, not only can reduce the heating surface thermal efficiency, increases unit coal consumption, and the ash that collapses caused thus, the slag that falls also can produce flameholding and have a strong impact on, and cause unit load down to run, even shut down time serious.

In denitration boiler operatiopn, the slagging scorification of accurate measurements heating surface, dust stratification degree and development trend, and according to the situation of fouling and slagging with run needs, take timely and effectively to blow grey scarfing cinder measure, seem very important.In recent years, artificial intelligence field research is unprecedentedly active, and domestic and international scientific research institutions have all carried out based on the fouling monitoring of intellectual technology and the researchs of intelligent sootblowing such as fuzzy system, neural network and expert systems.Tsing-Hua University develops the on-line monitoring system of Boiler Convection Heating Surface dust stratification state, has been applied to Taiyuan first cogeneration plant No. 11 stoves, achieves the dirty state on_line monitoring of heating surface ash; Southeast China University professor Zhou Keyi etc. has determined the thermal loss computation model that collecting ash causes, and the method for best blowing time period distances is determined according to economy, develop boiler of power plant soot blowing and optimal management system, Yangzhou No.2 Power Plant No. 2 boilers achieve fouling and slagging on-line monitoring and soot blowing and optimal management.Professor Yan Weiping of North China Electric Power University (Baoding) started from 1997 to bear State Power Corporation's emphasis science and technology item, took the lead at home having carried out the research work that coal-fired power station boiler heating surface retrofit monitors theory and practice.It is the boiler soot-blowing real-time monitoring system of core that the people such as professor Sun Baomin of Huabei Electricl Power Univ. (Beijing) develop with neural network, carries out on-line monitoring to boiler heating surface dust stratification, slagging scorification.But up to the present, various collecting ash slagging scorification monitoring technology, does not all have the special example for denitration Supervision of Heating Surface Fouling in Boilers.External fouling and slagging monitoring technology also has no in SCR denitration boiler applications and mentions.

After the contamination of air preheater heating surface, dust stratification, outlet cigarette temperature improves, and flue gas flow area narrows, and cigarette speed increases, and smoke flow resistance increase, therefore can reflect the order of severity of air preheater dust stratification with the change of smoke flow resistance.Large-sized station boiler extensively adopts rotary regenerative air preheater, and due to its structural feature, than being easier to dust stratification, but in actual motion, before and after air preheater dust stratification, inlet outlet pressure differential change is obviously.For rotary regenerative air preheater, its resistance mainly frictional resistance, calculates for general smoke power, can not consider the correction of heat interchange, carry out frictional resistance calculating, that is: by following formula

$\mathrm{\Δ}P=\mathrm{\λ}\frac{l}{d}\·\frac{w^2}{2}\mathrm{\ρ}---\left(1\right)$

In formula: ρ---smoke density, Kg/m ³;

ω---flue gas flow rate, m/s;

Δ P---this section of heating surface pressure drop, Pa;

The length of l---flue, m;

D---equivalent diameter, m;

λ---be coefficient of frictional resistance.

In (1) formula: introduce general resistance coefficient make A be heating surface flue gas actual internal area, obtain following formula:

$\mathrm{\Δ}P=Z\frac{\left(\mathrm{\ω}A\right)}{2A^2}\mathrm{\ρ}---\left(2\right)$

The change of fouling of heating surface degree, flue gas flow and density all has impact to flue gas pressure differential deltap P, and thus pressure reduction can only reflect the size of resistance to flow, and can not represent the change of dust stratification degree.In order to the change of remove smoke flow and density is on the impact of flue gas pressure reduction, formula (2) is converted, derives as shown in the formula statement, the index η that only degree dirty with ash is relevant:

$\mathrm{\η}=\frac{Z}{A}=\frac{2\mathrm{\Δ}P}{{\left(\mathrm{\ω}A\right)}^2\mathrm{\ρ}}---\left(3\right)$

When boiler heating surface dust stratification degree increases the weight of, resistance coefficient Z becomes large, and flue sectional area A diminishes, and dust stratification level index η becomes large; Otherwise dust stratification level index η diminishes.This index eliminates the change of flue gas flow and density to the impact of flue gas differential pressure, and can be similar to and think it is only the function of dust stratification degree, thus it can reflect fouling of heating surface state indirectly.According to document (Fan Congzhen. Principles of Boiler. [M]. Beijing: China Electric Power Publishing House, 1985) method that provides, can following formula be derived:

$\mathrm{\η}=K\frac{\mathrm{\Δ}P}{{\mathrm{Bj}}^2{V}_Y{G}_Y(T+273)}---\left(4\right)$

In formula (4), K is constant; Bj is computing fuel amount; G _y, V _yto be respectively flue gas mass and flue gas volume; T is flue-gas temperature, and Δ P and T can directly be obtained by DCS measuring point real time data.

For the ease of carrying out monitoring to fouling of heating surface degree is unified and compares, cleaning gene CF is adopted to reflect the dust stratification degree of heating surface.

CF＝η ₀/η(5)

Wherein, η ₀for dust stratification index during heating surface perfect condition, when CF equals 1, heating surface is in desirable clean conditions; When CF is less than 1, then heating surface is in grey dirty state, and less pollution is more serious.But due to square being directly proportional of pressure reduction and flow of air preheater, therefore the change of pressure reduction is subject to the impact of flow to a great extent.Directly utilize pressure reduction to calculate the size that cleaning gene can only reflect resistance, and the change of area coefficient can not be embodied.Along with the large-scale popularization in SCR technology at home unit, the serious problem of Ash Blocking in Air Preheater is effectively solved always, and the exploitation of air preheater special soot blowing and optimal system is extremely urgent.

Summary of the invention

Goal of the invention: for solving problems of the prior art, the invention provides a kind of method utilizing flue gas pressure differential method to set up air preheater cleaning gene computation model, this model construction is simple, and desired parameters all obtains by Power Plant DCS direct-detection, improves operation efficiency and cost.

Technical scheme: for realizing above-mentioned technical purpose, the present invention proposes a kind of method utilizing flue gas pressure differential method to set up air preheater cleaning gene computation model, it is characterized in that, comprise the steps:,

Step one: first the actual measurement pressure differential under different load and excess air coefficient is converted the calculated value under rated load, computing formula is as follows:

${\mathrm{\Δp}}_{zs}=\mathrm{\Δ}p{(\frac{{\mathrm{\α}}_0}{\mathrm{\α}}\×\frac{N_0}{N})}^2---\left(1\right)$

Wherein, Δ p _zSrepresentative conversion pressure reduction, unit Pa; Δ p represents actual measurement pressure reduction, unit Pa; α ₀represent flue gas excess air coefficient under standard state; α is the flue gas excess air coefficient of actual measurement; N ₀for specified electric load, unit MW; N is electric load during actual measurement, unit MW;

α calculates according to the following formula:

(O ₂) for surveying the volume fraction of oxygen in flue gas, then actual air primary heater conversion pressure reduction computing formula is:

Step 2: according to formula (3) calculating conversion pressure reduction ideally wherein, described perfect condition be air preheater completely clean time the detected value of each parameter;

Step 3: calculate air preheater cleaning gene, computing formula is:

${\mathrm{CF}}_{ky}=\frac{{\mathrm{\Δp}}_{zs}^{lx}}{{\mathrm{\Δp}}_{zs}^{sj}}---\left(4\right);$

Present invention further proposes the application of said method in the dirty situation of monitoring coal-burning boiler SCR denitration system air preheater ash.

In a particular application, comprise the steps:

First determine the critical cleaning gene of air preheater, computing formula is

Wherein, considering security and the comprehensive basis of economy obtain; CF _minit is former critical cleaning gene; Δ CF _sto CF when considering cold end corrosion and stifled ash _minadjusted value, its value is negative; Δ CF _ecorrespondence and CF during economy principle under the prerequisite of consideration principle of sound accounting _minadjusted value, its value is just;

Then the air preheater cleaning gene comparing calculating and the critical cleaning gene of air preheater determined, when the air preheater cleaning gene calculated is less than the critical cleaning gene of the air preheater determined, ash is blown to heating surface, calculate simultaneously and blow air preheater pressure reduction change before and after ash, that finds that best soot blower period finally realizes back-end surfaces blows ash as required.

In the observation process of reality, preferably take following scheme:

(1) monitor in unit running process, the NH in tail flue gas ₄hSO ₄content, fly ash content, flue-gas temperature, NH ₃concentration, and calculate real-time SO ₂content;

(2) different N H is recorded ₃under escapement ratio, the dirty drag size of ash of air preheater, as recorded the dirty drag size of air preheater ash when 1ppm, 2ppm, 3ppm respectively, to the NH of the back-end surfaces such as air preheater ₄hSO ₄cONCENTRATION DISTRIBUTION is analyzed and researched, and provides areal distribution, for gametic fertility optimal control offers guidance and suggestion, according to NH ₄hSO ₄cONCENTRATION DISTRIBUTION and dust stratification distribution, arrange in soot blower type selecting and soot blower and take specific aim measure;

(3) the knot ash degree of air preheater section is analyzed and researched, formulate and run control measure, reduce dust stratification by modes such as structural adjustment and the method for operation, adjustment soot blower form and soot-blowing modes, regularly water under high pressure purge, improve the heat exchange efficiency of air preheater;

(4) according to the Pyrological data that DCS system obtains, in conjunction with flue gas pressure differential method, set up air preheater pressure reduction Real-Time Monitoring physical model, obtain conversion pressure reduction expression formula.

(5) calculate the cleaning gene characterizing heating surface retrofit degree, cleaning gene is optimized, the calculation flow chart of air preheater cleaning gene under derivation actual condition, as shown in Figure 1;

(6) checking of fouling monitoring model, use root-mean-square error (RMSE) and mean absolute error (MAE) as forecast result of model basis for estimation, verify the accuracy of the dirty degree of ash of this model reflection heating surface, as under BMCR, T-MCR, 80%BMCR, 80%T-MCR tetra-different operating modes, the error between testing model predicted value and actual value;

(7) use this model on-the-spot guidance soot blower to blow ash, calculate and blow air preheater pressure reduction change before and after ash, that finds that best soot blower period finally realizes back-end surfaces blows ash as required.

Beneficial effect: compared with prior art, tool of the present invention has the following advantages:

(1) traditional soot-blowing mode at regular time and quantity usually causes and blows wound or blow ash deficiency, and soot blowing and optimal technology of the present invention is applicable to denitration boiler, can improve security and the economy of unit operation;

(2) the present invention is according to formation basic theory, the growth form of the dirt of SCR denitration system air preheater ash, set up the denitration boiler air preheater fouling monitoring model of the data acquisition of a collection, grey dirty condition monitoring and diagnosis, the present invention can the dirty situation of ash of both Accurate Prediction boiler air preheaters, engineer applied accuracy requirement can be met again, soot blower is instructed to blow ash in time, what finally realize back-end surfaces blows ash as required, improve economy and the security of unit operation, Technical Reference can be provided for domestic unit of the same type;

(3) the present invention can adapt to different capabilities coal-burning boiler, and cleaning gene calculation process is simple, and computing method are easily promoted, and correlation parameter all can obtain from DCS control system, greatly improves operation efficiency, can effectively cut operating costs;

(4) present invention uses flue gas pressure differential method to reflect the dirty degree of air preheater ash, the parameter such as flue gas pressure reduction, temperature, oxygen level, excess air coefficient needed for model calculates all easily obtains, greatly improve arithmetic speed and the simplicity of model, be convenient to the popularization in same type units;

(5) the putting into operation of air preheater fouling monitoring system of the present invention, critical cleaning gene can be tried to achieve fast, and then best soot blower occasion can be judged, achieve and blow ash as required, can reduce and blow grey number of times, reduce steam consumption, thus effectively improve the heat-transfer effect of heated surface at the end of boiler, improve the efficiency of unit, also greatly improve simultaneously and blow grey economy.

Accompanying drawing explanation

Fig. 1 is the calculation flow chart of air preheater cleaning gene under actual condition;

Fig. 2 is that unit puts into operation air preheater seriously stifled ash figure after SCR;

Fig. 3 is the changing trend diagram of the air preheater cleaning gene calculating gained;

Fig. 4 is the pressure reduction comparison diagram that air preheater blows before and after ash;

Fig. 5 is critical cleaning gene determination process flow diagram.

Embodiment

The present invention proposes a kind of method utilizing flue gas pressure differential method to set up air preheater cleaning gene computation model, comprise the steps:

Step one: first the actual measurement pressure differential under different load and excess air coefficient is converted the calculated value under rated load, computing formula is as follows:

${\mathrm{\Δp}}_{zs}=\mathrm{\Δ}p{(\frac{{\mathrm{\α}}_0}{\mathrm{\α}}\×\frac{N_0}{N})}^2---\left(1\right)$

Wherein, Δ p _zSrepresentative conversion pressure reduction, unit Pa; Δ p represents actual measurement pressure reduction, unit Pa; α ₀represent flue gas excess air coefficient under standard state; α is the flue gas excess air coefficient of actual measurement; N ₀for specified electric load, unit MW; N is electric load during actual measurement, unit MW;

α calculates according to the following formula:

(O ₂) for surveying the volume fraction of oxygen in flue gas, then actual air primary heater conversion pressure reduction computing formula is:

Step 2: according to formula (3) calculating conversion pressure reduction ideally wherein, described perfect condition be air preheater completely clean time the detected value of each parameter;

Step 3: calculate air preheater cleaning gene, computing formula is:

${\mathrm{CF}}_{ky}=\frac{{\mathrm{\Δp}}_{zs}^{lx}}{{\mathrm{\Δp}}_{zs}^{sj}}---\left(4\right).$

The air preheater cleaning gene comparing calculating after calculating air preheater cleaning gene and the critical cleaning gene of air preheater determined, when the air preheater cleaning gene calculated is less than the critical cleaning gene of the air preheater determined, ash is blown to heating surface, calculate simultaneously and blow air preheater pressure reduction change before and after ash, that finds that best soot blower period finally realizes back-end surfaces blows ash as required.

Wherein, critical cleaning gene determination process flow diagram, as Fig. 5, is considered unit economy, security requirement and is blown grey maximize revenue principle, and the critical cleaning gene value of different heating surface under different operating mode is also different.Concrete regulation rule is as follows:

(1) unit economy is considered

Dust stratification is followed successively by air preheater, economizer, low temperature superheater on the impact of exhaust gas temperature by the order of severity.When exhaust gas temperature raises remarkable, suitably increase the critical cleaning gene of above-mentioned heating surface.

Dust stratification is followed successively by air preheater, low temperature superheater, economizer on the impact of blower fan power consumption by the order of severity.When blower fan power consumption raises remarkable, suitably increase the critical cleaning gene of above-mentioned heating surface.

(2) unit safety is considered

Burner hearth is the most important part of boiler, when establishing the priority level of the top blast ash that is heated, should list in the highest by the grade of burner hearth.Boiler throw oily combustion-supporting time General Requirements now carry out air preheater and blow ash continuously or close to blowing ash continuously; When dust stratification is heavier for the multiple heating surface of boiler simultaneously, consider that blowing ash order downstream heating surface should have higher priority level.

(3) empirical rule is considered

During load variations, all there is respective change in the flying dust amount of generation and flue gas flow rate, but it is contrary to the impact effect of dust stratification speed.Cry quites, under different load condition, though pollution rate growth rate is distinguished to some extent, the basic law increased is consistent.During underload, ash is dirty to be increased comparatively slowly, suitably reduces the critical cleaning gene of all heating surfaces.

In addition, the present invention also furthers investigate formation mechanism and the control strategy of ammonium hydrogen sulfate, analyzes NH ₄hSO ₄distribution situation under, by controlling the escaping of ammonia rate, temperature, SO ₂oxygenation efficiency, suppresses the growing amount of ammonium hydrogen sulfate from source, effectively can alleviate the low temperature dust stratification of air preheater.Concrete regulate and control method is as follows:

(1) amount of ammonia slip controls:

Above the cold section of layer that warm area between 140 ~ 230 DEG C is positioned at air preheater conventional design and below middle layer, because ammonium hydrogen sulfate is liquid to the Solid State Transformation stage at this warm area, there is extremely strong adsorbability, a large amount of ash content can be caused in air preheater sedimentation, cause air preheater to block and resistance rising, blowing out time serious, will be forced to clear up air preheater.Meanwhile, ammonium hydrogen sulfate or ammonium sulfate itself have stronger corrosivity to metal, can cause catalyst metals bracing frame and the corrosion of cold section of air preheater.In addition, ammonia surplus makes operating cost improve and causes flying dust chemical property to change, flying dust degradation, and recycle value reduces; Can cause new pollution to air again in NH_3 leakage to air, therefore strictly must control NH_3 leakage amount, General Requirements is less than 3 μ L/L.When reactor inlet pipe design is unreasonable, the NH that can induce reaction on device cross section ₃there is deviation in/NOx mol ratio, flow or temperature, thus causes NH ₃leakage and NOx remove not exclusively, affect denitration efficiency.

Sulfur content due to fire coal decides SO in flue gas ₃content, and SO ₃content appreciable impact is formed on ammonium hydrogen sulfate, so for different coals, in SCR, the control of amount of ammonia slip is also different: low-sulfur coal (be 1% containing S amount), amount of ammonia slip < 6 μ L/L; Medium sulphur coal (measuring containing S is 1.5%), amount of ammonia slip < 4 μ L/L; Sulphur coal (measuring containing S is 3%), amount of ammonia slip < 2 μ L/L.Fluid Mechanics Computation (CFD) software optimization can be utilized in the control of amount of ammonia slip to design, SCR denitration device inlet flue gas flow and velocity flow profile are simulated, determine the type of guide vane, quantity and position, make inlet flue gas flow velocity, temperature and even concentration; Simulate the mixing of ammonia, adjustment ammonia-spraying grid (AIG) each spout, makes NH3 mix, finally reduces amount of ammonia slip simultaneously

(2) SO ₂oxygenation efficiency controls

The catalytic component based on vanadium that SCR denitration process uses can to SO in flue gas ₂oxidation produce catalytic action, make it easily be oxidized to SO ₃.SO ₃form sulfuric acid vapor in economizer section, be condensed into acid mist at cold section of air preheater (temperature 177 ~ 232 DEG C), corrosion heating surface.At SCR reactor outlet SO ₃ammonium hydrogen sulfate is generated with the ammonia react of escaping.At SO ₂the control aspect of oxygenation efficiency, for V ₂o ₅class commercial catalyst, the loading of vanadium can not be too high, usually controls can reduce SO about 1% ₂oxidation.In addition, the shape of catalyzer can to SO ₂oxidation has an impact, and Topse company of Denmark develops series of corrugations shape denitrating catalyst, due to its V ₂o ₅component concentration is low, can effectively reduce SO2 oxygenation efficiency.Meanwhile, the wall thickness reducing catalyzer duct also can reduce SO ₂oxygenation efficiency.In addition, adopt and improve catalyst activity component (as WO3) content, also can suppress SO ₂oxidation.

(3) running temperature controls

The temperature of SCR denitration process need between 190 ~ 510 DEG C, but in order to suppress the generation of ammonium hydrogen sulfate usually temperature to be controlled within the scope of 260 ~ 316 DEG C.The dew point of ammonium hydrogen sulfate is by NH ₃, SO ₃and H ₂the dividing potential drop of O determines.

The formation of ammonium hydrogen sulfate is reversible, temperature is elevated to 316 DEG C and ammonium hydrogen sulfate can be made to distil.When the formation about ammonium hydrogen sulfate fouling that Germany and Japan propose the earliest and air preheater run, the mutual relationship of heat accumulating element tube wall temperature obtains the checking of practical operating experiences.Under the condition of high dust, the maximum metal wall temperature that fouling occurs is lower than the acid dew-point temperature of ammonium hydrogen sulfate 4.4 DEG C.But the temperature range that fouling occurs under the condition of low dust concentration extends on the acid dew-point temperature of ammonium hydrogen sulfate, and this feature makes the ammonium hydrogen sulfate of significant proportion be deposited on soot particle, and is taken out of air preheater with soot particle.If there is not this phenomenon, the deposition of ammonium hydrogen sulfate will expand to higher temperature province.In addition, flying dust also has and certain washes away cleaning action.When being less than or equal to 150 DEG C, ammonium hydrogen sulfate is intimate curing, but can remove with slag-blowing equipmemt.

The application of air preheater cleaning gene model in the dirty situation of monitoring coal-burning boiler SCR denitration system air preheater ash of the present invention's foundation is described in detail below by specific embodiment.

First the NH in unit running process in tail flue gas is monitored ₄hSO ₄content, fly ash content, flue-gas temperature, NH ₃concentration, and calculate real-time SO ₂content, and utilize said method to suppress the growing amount of ammonium hydrogen sulfate from source.

Record different N H ₃under escapement ratio, the dirty drag size of ash of air preheater, records the dirty drag size of air preheater ash when 1ppm, 2ppm, 3ppm, respectively to the NH of air preheater back-end surfaces ₄hSO ₄cONCENTRATION DISTRIBUTION is analyzed and researched, and provides areal distribution, for gametic fertility optimal control offers guidance and suggestion, according to NH ₄hSO ₄cONCENTRATION DISTRIBUTION and dust stratification distribution, arrange in soot blower type selecting and soot blower and take specific aim measure.The adhesiveness being in the ammonium hydrogen sulfate of liquid phase region is extremely strong, heat exchange element surface can be adhered to rapidly, and then the flying dust adsorbed in a large amount of flue gas, a large amount of flying dusts is finally caused to be deposited on metal wall or to be stuck in interlayer, air preheater fume side actual internal area is reduced, cause air preheater to block, and then cause air preheater running resistance to increase.According to reality test, if when escape ammonia concentration reaches 1ppm, after air preheater runs 6 months, its resistance adds about 16%; If when escape ammonia concentration reaches 2ppm, after air preheater runs 6 months, its resistance adds about 31%; And when escape oxygen concentration is 3ppm, after air preheater runs 6 months, resistance even adds 53%.As shown in table 1:

The impact that table 1 ammonia is escaped

NH3 escapement ratio	Back-end surfaces change in resistance
		1ppm	↑16.22％
2ppm	↑31.35％
		3ppm	↑53.30％

Can analyze and research to the knot ash degree of air preheater section in period, formulate and run control measure, reduce dust stratification by modes such as structural adjustment and the method for operation, adjustment soot blower form and soot-blowing modes, regularly water under high pressure purge, improve the heat exchange efficiency of air preheater.

According to the Pyrological data that DCS system obtains, in conjunction with flue gas pressure differential method, set up air preheater pressure reduction Real-Time Monitoring physical model, obtain conversion pressure reduction expression formula.Utilize the conventional measuring point founding mathematical models such as the existing temperature of Power Plant DCS, pressure, flow, the variation tendency that monitoring heating surface ash is dirty.For Nanjing power plant 600MW unit rotary regenerative air preheater, Fig. 2 to put into operation air preheater seriously stifled ash figure after SCR for this unit, carries out on-line monitoring, and calculate the real time cleaning factor of air preheater to its dust stratification state.Table 2 lists the major parameter of certain moment air preheater and the item in DCS system thereof.

Table 2 model calculates major parameter

Calculate CF=0.5372 this moment, Fig. 3 is the changing trend diagram that monitoring model calculates the air preheater cleaning gene of gained, the change of air preheater cleaning gene is comparatively frequent as seen from Figure 4, dust stratification is relatively many, because the growth of dust stratification makes cleaning gene slowly decline before blowing ash, after blowing ash, air preheater cleaning gene slowly increases again, so this model more adequately can reflect the development trend that air preheater ash is dirty, realize monitoring the dirty degree of heating surface ash.

Fig. 4 is the pressure reduction comparison diagram that air preheater blows before and after ash, uses cleaning gene to instruct and blows ash, and after blowing ash, air preheater pressure reduction declines clearly.Air preheater pressure reduction is 0.9 to 1.45kPa, and range up to 1.5kPa, air preheater blowing pressure is 1.5MPa, and flow is about 80kg/min.It is respond well that air preheater blows ash, and pressure reduction can remain in normal range substantially.

In order to the accuracy of further verification model, what list in table 3 is true deviation and the model calculation of this boiler air preheater pressure reduction under typical 4 operating modes:

Table 3 air preheater pressure reduction change calculations result

As can be seen from result of calculation, although the model calculation still exists certain error compared with actual value, enough accurate with regard to engineer applied.

Claims (3)

1. utilize flue gas pressure differential method to set up a method for air preheater cleaning gene computation model, it is characterized in that, comprise the steps:

Step one: first the actual measurement pressure differential under different load and excess air coefficient is converted the calculated value under rated load, computing formula is as follows:

${\mathrm{\&Delta;p}}_{zs}=\mathrm{\&Delta;}p{(\frac{{\mathrm{\&alpha;}}_0}{\mathrm{\&alpha;}}\&times;\frac{N_0}{N})}^2---\left(1\right)$

Wherein, Δ p _zsrepresentative conversion pressure reduction, unit Pa; Δ p represents actual measurement pressure reduction, unit Pa; α ₀represent flue gas excess air coefficient under standard state; α is the flue gas excess air coefficient of actual measurement; N ₀for specified electric load, unit MW; N is electric load during actual measurement, unit MW;

α calculates according to the following formula:

for the volume fraction of oxygen in actual measurement flue gas, then actual air primary heater conversion pressure reduction computing formula is:

Step 2: according to formula (3) calculating conversion pressure reduction ideally wherein, described perfect condition be air preheater completely clean time the detected value of each parameter;

Step 3: calculate air preheater cleaning gene, computing formula is:

${\mathrm{CF}}_{ky}=\frac{{\mathrm{\&Delta;p}}_{zs}^{lx}}{{\mathrm{\&Delta;p}}_{zs}^{sj}}---\left(4\right).$

2. the application of method according to claim 1 in the dirty situation of monitoring coal-burning boiler SCR denitration system air preheater ash.

3. application according to claim 2, is characterized in that, comprises the steps:

First the critical cleaning gene of air preheater is determined, then the air preheater cleaning gene calculated according to claim 1 and the critical cleaning gene of air preheater determined is compared, when the air preheater cleaning gene calculated is less than the critical cleaning gene of the air preheater determined, ash is blown to heating surface, calculate simultaneously and blow air preheater pressure reduction change before and after ash, that finds that best soot blower period finally realizes back-end surfaces blows ash as required.