CN109519960A - A kind of coal-powder boiler combustion control method monitored on-line based on oxygen content and unburned carbon in flue dust - Google Patents
A kind of coal-powder boiler combustion control method monitored on-line based on oxygen content and unburned carbon in flue dust Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N3/00—Regulating air supply or draught
- F23N3/002—Regulating air supply or draught using electronic means
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N5/00—Systems for controlling combustion
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
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- F23N2223/00—Signal processing; Details thereof
- F23N2223/10—Correlation
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
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Abstract
The present invention relates to a kind of regulation methods of big coal fired boilers quasi-optimalization burning, it is characterized in that heat loss is divided into the adjustable amount of operation and the amount of cannot be adjusted, more reasonably define the optimization aim that can regulate and control and reach, pass through the measurement of oxygen content and temperature easy to accomplish, and the on-line monitoring of unburned carbon in flue dust, it can realize the judgement to combustion conditions, and burning is adjusted and organized accordingly, make boiler in coal, when load variations, it is rapidly reached and maintains quasi-optimal operating status, method is easy, it is easy, this method works for the energy-saving and emission-reduction of big coal fired boilers, and the flexibility of raising fired power generating unit adaptation load fluctuation is of great significance.
Description
Technical field
The present invention relates to big coal fired boilers combustion control methods, are based on oxygen content and unburned carbon in flue dust more particularly to one kind
The coal-powder boiler combustion control method of on-line monitoring.
Background technique
Big coal fired boilers are that thermal power generation is used to provide the key equipment of thermal energy, the main purpose of combustion control in the process
It is to make coal dust full combustion and keep heat loss minimum, improves the utilization rate of coal to reach energy-efficient purpose；In addition, protecting
While demonstrate,proving coal dust full combustion, combustion-supporting air capacity is reduced as far as by regulation, nitrogen oxides can be effectively reduced
(NOx) discharge, is of great significance for environmental protection.
Especially energy field a large amount of clean energy resourcies pour in recent years, it is desirable that thermal power generation will frequently quickly significantly
Load adjustment, to adapt to the natural quality of clean energy resource.Therefore, in the case where load frequently changes, how by having in time
Effect ground firing optimization, makes boiler be in optimum condition always, is directly related to the Important Project project of " energy-saving and emission-reduction ".
It publishes in Southeast China University Fan Congzhen chief editor's Principles of Boiler teaching material, sentences in Beijing hydraulic and electric engineering publishing house in May, 1986
Determine the index of boiler optimum operating condition --- the expression formula of the thermal efficiency is defined as:
=100- (q2+q3+q4+q5+q6) (counter balancing method expression formula) (2)
Since counter balancing method is more targeted for various heat losses, so in engineering generally in this way.Burning
Optimization will solve the problems, such as to be exactly to pass through firing optimization boiler thermal efficiency is made to consistently achieve maximum value under different operating conditions, it may be assumed that
Wherein:
Qr: per kilogram fuel brings the heat (input heat) of boiler into, can approximation take combustion applied lower calorific value
kJ/kg；
Q1: per kilogram fuel boiler efficiently uses heat, can pass through inlet and outlet enthalpy, steam flow and the combustion of boiler working substance
Coal amount calculates, kJ/kg；
q1==(Q1/Qr) × 100: boiler effective use heat accounts for the percentage of input heat；
q2=(Q2/Qr) × 100: boiler exhaust heat loss accounts for the percentage of input heat, Q2It discharges fume for per kilogram fuel hot
It loses (kJ/kg), can be calculated according to theoretical air requirement, combustion product and its specific heat, Coal-fired capacity, exhaust gas temperature and excess air coefficient
Out；
q3=(Q3/Qr) × 100: heat loss that boiler chemical is imperfect combustion accounts for the percentage of input heat, Q3For per kilogram
Heat loss that chemistry of fuel is imperfect combustion (kJ/kg) need to be calculated according to fuel gas content in the flue gas of measurement and Coal-fired capacity；
q4=(Q4/Qr) × 100: boiler Mechanical adsorption accounts for the percentage of input heat, Q4For per kilogram
Heat loss that mechanical fuel is imperfect combustion (kJ/kg) need to contain according to solid combustible in the combustion product (flue gas, lime-ash) of measurement
It measures (flying dust, ash content carbon) and coal ash content calculates；
q5=(Q5/Qr) × 100: boiler radiation loss account for input heat percentage, with boiler structure, heat preservation situation and
Coal-fired capacity is related；
q6=(Q6/Qr) × 100: the other heat loss of boiler account for the percentage of input heat, the physics heat waste taken away such as lime-ash
Lose etc..
If carrying out burning optimization to boiler in real time by the index it can be seen from the forming of Efficiency Calculation formula above
Regulation, just must weight to as-fired coal, using gas and solid combustible content in base calorific value, as-fired coal ingredient, flue gas
Accurate, reliable, the continuous on-line monitoring of equal progress, and to accomplish this point, it is the thing for being difficult to accomplish in engineering.It is logical
It often, is all the boiler heat balance test for spending a large amount of human and material resources to implement limited times for different load, common coal, for
Different load and coal measure all relevant parameters and calculate various heat losses value, so that it is determined that corresponding opposite optimal combustion
Operating condition and its relevant parameter, the reference method of operation and control parameter as actual motion.Obviously, this method is difficult to cover institute
There is the operating condition of live complexity, burning optimization regulation also rests in scope only by rule of thumb more casual.
Summary of the invention
In view of the problems of the existing technology, creativeness proposes a kind of based on flue gas oxygen content and unburned carbon in flue dust the present invention
The coal-powder boiler burning quasi-optimal operating condition Judging index and quasi-optimalization of on-line monitoring regulate and control method, and it is adjustable that heat loss is divided into operation
Whole amount and the amount of cannot be adjusted, more reasonably define the optimization aim that can regulate and control and reach, pass through oxygen content easy to accomplish
The on-line monitoring of measurement and unburned carbon in flue dust with temperature, can realize the judgement to combustion conditions, and adjustment and group accordingly
Burning is knitted, makes boiler in coal, load variations, be rapidly reached and maintains quasi-optimal operating status.
A kind of technical solution taken to realize the present invention: coal-powder boiler monitored on-line based on oxygen content and unburned carbon in flue dust
Combustion control method, below the various heat losses that are just related to from formula (2) start with, derive technical solution of the present invention.
1) simplification to various heat losses in thermal efficiency expression formula:
Firstly, various heat losses are divided into the loss of online adjustable heat and online cannot be adjusted heat loss and merging is similar
Heat loss makes simplification to the judgement of boiler optimum operating condition, obtains following result:
q5、q6Or Q5、Q6Heat loss accounting very little and cannot by firing optimization be improved significantly, belong to online
It cannot be adjusted heat loss, cast out as burning quasi-optimal operating condition Judging index and do not considered；
q3、q4Or Q3、Q4The reason of heat loss is incomplete combustion loss, is occurred is identical, i.e., anoxic, temperature are inadequate
And the tail-off time is insufficient, therefore, if q4Loss is optimal state, q3Should generally also it reach；And gaseous combustible object is opposite
Solid combustible more easy to burn out, also therefore very little can use q to loss accounting4It loses while representing q3Loss, is not present in it
In quasi-optimal combustion conditions Judging index, difficulty brought by online flue gas analysis is avoided；
q2Or Q2Heat loss can be divided into two parts in fact, and a part is the Theoretical combustion determined by combustion reaction equation
The heat that product is taken away with flue gas, calculating is related to the ingredient of combustion product, more complicated, is the inevitable outcome of combustion reaction,
It is nonadjustable；Another part is the heat taken away with flue gas due to having fed excessive air, is that burning needs to adjust
The part of reduction, i.e. one of the target of burning optimization, are defined as " adjustable heat loss due to exhaust gas ", useIt indicates, i.e., every public affairs
Jin fuel exhaust gas heat loss's disalignment is adjustable and the part that is used, unit kJ/kg；In addition, the leakage of exhaust gas heat loss's disalignment
Wind-heat loss is also not belonging to adjustable part of burning, and does not also account for herein；
After making above-mentioned simplification, formula (3) becomes following form:
2) solving makes the smallest optimization problem of the sum of " adjustable heat loss due to exhaust gas " and " Mechanical adsorption ", and
Take into account the influence of " the unburned heat loss of chemistry ":
According to boiler theory, in the whole range of real-time, tunable, air of this two heat loss all with infeed boiler auxiliary combustion
Measure it is related, the air capacity usually use " excess air coefficient " α indicate, is defined as:
α=V/V0 (5)
Wherein:
V: the practical air capacity for feeding boiler of per kilogram fuel, Nm3/kg；
V0: per kilogram fuel theoretical air requirement, Nm3/ kg can be converted according to as-fired coal, composition of air by combustion reaction equation
It obtains,
Promote coal-fired completely burned as far as possible to provide enough oxygen, answers V > V0, it may be assumed that α > 1, α are existed by oxygen amount meter
The volume content O of oxygen in the flue gas that line measures2(%) is calculate by the following formula to obtain:
Then (4) formula is write as:
According to optimum theory, which can be obtained by solving following equation, to obtain the minimum heat loss of acquirement
Best excess air coefficient α2,4:
Therefore the target of combustion control, which can be attributed to, seeksQ4The derivative of (α), and (7) formula is kept to set up:
According to the definition of " adjustable heat loss due to exhaust gas ", calculation formula is indicated are as follows:
Wherein:
The average level pressure specific heat per unit volume of air, kJ/Nm3DEG C, can be found by the physical parameter of air；
t2: exhaust gas temperature, DEG C；
t1: air enters temperature when furnace, is environment temperature；
It enables:Then
(8) formula has following form:
When coal, exhaust gas temperature, one timing of environment temperature, design value can use to simplify the calculation, A may be regarded as constant, by (9)
It is theoretical air requirement in the systemic heat of furnace that formula, which can be seen that its physical significance,It is incremented by Q- α coordinate diagram for one
Straight line 1, it may be assumed that " adjustable heat loss due to exhaust gas "It is proportional between excess air coefficient α, then have:
Mechanical adsorption Q4It can indicate are as follows:
Wherein:
afh、alz: the share of flying dust, the total ash quantity of clinker Zhan, afh+alz=1；
Ay: fire coal applies base ash content, the timing of coal quality one its be definite value；
Cfh、Clz: flying dust, boiler slag carbon content, CfhIt is related with α, it can be by unburned carbon in flue dust on-Line Monitor Device the real time measure；
In above formula, to remove the trouble for monitoring ash content carbon on-line from, approximatively by phosphorus content flying marking in lime-ash
Amount is to substitute, i.e. Cfh=Clz, because large capacity coal dust boiler ash sediment share very little, will not bring very big error；
By (12) formula, unburned carbon in flue dust CfhIt is the function of α, i.e. Q4It is also the function of α, but Relationship Comparison is complicated, even if together
One boiler its relationship in different types of coal, different load can also have a greater change, and cannot be expressed with a simple formula,
But its changing rule we can qualitatively be stated from following discussion；
According to Theory of Combustion, when excess air coefficient is smaller, since the oxygen as one of burning condition connects with fuel
Having a sudden inspiration can be reduced, and keep uncombusted particle more, thus Q4It is larger；With the increase of α, Q4It is gradually reduced and will be maintained at lesser
In range；And when α is sufficiently large, and another condition that burning will be destroyed, i.e., in more excess air since temperature is lower,
Burning can be postponed, and uncombusted particle can also increase, and make Q4It can increase again with the increase of α；Therefore, Q4It is bent with the changing rule of α
Line 2 must be recessed, a Dan Gu, small curvature curve, which will change with boiler load, the variation for using coal etc., but its
Shape or changing rule will not change, and by (12) formula, the derivative of the curve is expressed as:
Because(α) is a straight line, thenAlso the curve 3 for one with recessed, Dan Gu, small curvature feature；
Bring (11), (13) formula into (7) formula, then the condition for obtaining burning quasi-optimal operating condition is:
OrDefinition:
EktIt is defined as new big coal fired boilers " quasi-optimal operating condition index of discrimination ", when:
When, meet (7) formula, then boiler combustion is in quasi-optimal operating condition；
Due to cfhUncertain with the relationship of α, reality will substitute into limited real-time monitoring value when calculating, and (16) formula can be approximate
Ground is expressed as:
DefinitionFor " average quasi-optimal operating condition index of discrimination ", whenWhen, boiler combustion is in " approximate quasi-optimal
Operating condition "；
(16) or in (19) formula, when load and the timing of coal one, denominator B is a fixed number for being greater than 0, can also approximation take design
Value calculates, by adjusting air output, i.e. change α when operation, and to CfhOn-line monitoring.Take α, CfhMonitor value substitutes into (19) formula and calculates
?According toThe degree of deviation 1 judges the superiority and inferiority of combustion position；
IfThen search direction is the direction for reducing α；IfThen search direction is to make the increased direction α,
Optimization algorithm optimizing can be selected, set up (18) formula, then boiler is in quasi-optimal combustion conditions at this time, i.e., in 1 curve 3 of attached drawing
Situation represented by 4 points, α at this time2,4For " best excess air coefficient ", particularly, whenWhen, it may be assumed thatIt says
Bright Q4Reaching minimum, situation represented by 5 points, Combustion Operation of Boilers have been approached quasi-optimal operating condition in 1 curve 2 of attached drawing, this
The important symbol that can only differentiate with unburned carbon in flue dust on-line monitoring result when being combustion control.
In view of combustion with meagre oxygen is beneficial to reduce nitrogen oxides (NOx) generation, can make denitration cost reduction, should control
EktIn a small range variation (being determined after should specifically doing technical economic analysis) greater than 1.
It is the big coal fired boilers monitored on-line based on flue gas oxygen content and unburned carbon in flue dust that the present invention derives above
Quasi-optimal combustion conditions discriminant criterion and control method.Although this method cannot definitely illustrate energy-efficient particular number,
Quasi-optimal combustion conditions are kept inherently to illustrate that boiler always works in state the most energy-efficient, effect is inevitable in cost core
It is embodied in calculation.
The present invention " a kind of coal-powder boiler combustion control method monitored on-line based on oxygen content and unburned carbon in flue dust " is brought
Beneficial effect be:
1. a kind of coal-powder boiler combustion control method monitored on-line based on oxygen content and unburned carbon in flue dust, is not limited to energy
Balance quantitatively more reasonably defines the optimization aim that can regulate and control and reach；The guidance of thermal efficiency method is evaded simultaneously
A series of operating parameters such as real-time monitoring Coal-fired capacity, steam flow, heat output of fuel, smoke components are needed when combustion control
And the difficulty of all various heat losses is calculated, only pass through the measurement of flue gas oxygen content and temperature easy to accomplish in current engineering
And the on-line monitoring of unburned carbon in flue dust can realize the judgement to combustion conditions, and adjust and organize burning accordingly, make boiler
In coal, load variations, it is rapidly reached and maintains quasi-optimal operating status, method is easy, easy；
2. a kind of coal-powder boiler combustion control method monitored on-line based on oxygen content and unburned carbon in flue dust, for large-scale coal dust
The energy-saving and emission-reduction of furnace and the flexibility for improving fired power generating unit adaptation load fluctuation are of great significance.
Detailed description of the invention
Fig. 1 is a kind of relevant boiler of coal-powder boiler combustion control method monitored on-line based on oxygen content and unburned carbon in flue dust
The qualitative representation of functional relation between heat loss Q and excess air coefficient α；
In figure: 1. " adjustable heat loss due to exhaust gas "Curve, 2. mechanical unburned heat loss Q4Curve, 3.Curve,
4.Heat loss minimum point, 5.Q4Heat loss minimum point.
Specific embodiment
Below in conjunction with attached drawing 1 and specific embodiment, invention is further described in detail, specific reality described herein
Example is applied only to explain the present invention, is not intended to limit the present invention.
For using design coal as the coal-powder boiler under table mountain bituminous coal, any load (other coals can also be used,
Such as " multifuel combustion ", but coal-fired ingredient is relatively stable in a period of time), flue gas oxygen content on-line monitoring uses Shanghai precision instrument
" the GD36-800 Oxygen Measuring Instrument " of finite instrument company production, unburned carbon in flue dust on-line monitoring use Jilin northeast
" the BAC-A type calcination formula flying dust carbon determination system " of the Katyuan electricity Yuan Science and Technology Ltd. production, temperature measure the thermoelectricity that can choose any one kind of them
Even, cold air and exhaust gas temperature can survey to obtain, and the present embodiment sets air temperature t1=25 DEG C, exhaust gas temperature t2=140
DEG C, average level pressure specific heat per unit volume is checked in by air propertykJ/Nm3.℃。
The coal application based component see the table below:
It asks: EktBoiler combustion quasi-optimal operating condition and best excess air coefficient α when=12,4(shown in 4 points of attached drawing)
Solution: guaranteeing a certain load of boiler and uses that coal is relatively stable, and flame central position, fineness of pulverized coal are adjusted to most
Good value, oxygen at furnace exit, exhaust gas temperature, environment temperature, boiler flyash carbon content on-Line Monitor Device are working properly, and adjusting is sent
Air quantity mechanism is sensitive.
1, the denominator B in (19) formula is solved
Theoretical air requirement V can be calculated by coal-fired ingredient according to boiler theory0=6.1Nm3/ kg, by V0、Ay、t1
And t2It brings (17) formula into, obtains:
2, boiler combustion approximate construction optimum operating condition under current working is determined
1) judge boiler current combustion situation
Measure current flue gas oxygen content O2It substitutes into formula (6) and calculates to obtain excess air coefficient α(0)For initial point；Measurement is current to fly
Grey phosphorus content Cfh(α(0)).If Δ α > 0 (sufficiently small empirical value), precision L > 0, adjustment wind pushing mechanism makes α(1)=α(0)+ Δ α,
Measure Cfh(α(1)).By Δ α, Cfh=Cfh(α(0)), Δ Cfh=Cfh(α(1))-Cfh(α(0)) substitute into (19) formula calculateIf:
2) with α(i)For starting point, if step-length h=- Δ α (or h=h, i ≠ 0).Adjustment wind pushing mechanism makes α(i+1)=α(i)+ h,
Measure Cfh(α(i+1)).By Δ α=α(i+1)-α(i), Cfh=Cfh(α(i)), Δ Cfh=Cfh(α(i+1)-Cfh(α(i)), i=0,1,2,
3 ..., which successively substitute into (19) formula, calculatesWhen:
3) with α(i)For starting point, if step-length h=Δ α (or h=h, i ≠ 0).Adjustment wind pushing mechanism makes α(i+1)=α(i)+ h,
Measure Cfh(α(i+1)).By Δ α=α(i+1)-α(i), Cfh=Cfh(α(j)), Δ Cfh=Cfh(α(i+1))-Cfh(α(i)), i=0,1,2,
3 ..., which successively substitute into (19) formula, calculatesWhen:
It solvesFor " quasi- best excess air coefficient " (referring to attached drawing), at this timeThat is:
Boiler combustion at this time is in approximate " standard " optimum operating condition.
3, when operating status changes (such as load, coal ...), EktBy ≠ 1, above step is repeated, determines and keeps new
Approximate " standard " optimum operating condition of boiler combustion.
By above embodiments, the optimal combustion of coal-powder boiler based on flue gas oxygen content and unburned carbon in flue dust on-line monitoring is realized
Burn the judgement and regulation of operating condition.
The above is only the preferred embodiment of the present invention, it is noted that for the ordinary skill of the art
For personnel, various improvements and modifications may be made without departing from the principle of the present invention, these improvements and modifications
It should be considered as protection scope of the present invention.
Claims (1)
1. a kind of coal-powder boiler combustion control method monitored on-line based on oxygen content and unburned carbon in flue dust, it is comprised the step of:
1) the classical thermal efficiency method for determining boiler optimum operating condition
The thermal efficiency is defined as:
Since counter balancing method is more targeted for various heat losses, burning optimization will solve the problems, such as to be exactly to pass through firing optimization
Boiler thermal efficiency is set to consistently achieve maximum value under different operating conditions, it may be assumed that
Wherein:
Qr: per kilogram fuel brings the heat (input heat) of boiler into, can approximation take combustion applied lower calorific valuekJ/
kg；
Q1: per kilogram fuel boiler efficiently uses heat, can pass through inlet and outlet enthalpy, steam flow and the Coal-fired capacity of boiler working substance
It calculates, kJ/kg；
q1=(Q1/Qr) × 100: boiler effective use heat accounts for the percentage of input heat；
q2=(Q2/Qr) × 100: boiler exhaust heat loss accounts for the percentage of input heat, Q2For per kilogram fuel heat loss due to exhaust gas
(kJ/kg), it is calculated according to theoretical air requirement, combustion product and its specific heat, Coal-fired capacity, exhaust gas temperature and excess air coefficient；
q3=(Q3/Qr) × 100: heat loss that boiler chemical is imperfect combustion accounts for the percentage of input heat, Q3For per kilogram fuel
Chemical imperfect combustion heat loss (kJ/kg) need to calculate according to fuel gas content in the flue gas of measurement and Coal-fired capacity；
q4=(Q4/Qr) × 100: boiler Mechanical adsorption accounts for the percentage of input heat, Q4For per kilogram fuel
Mechanical adsorption (kJ/kg) need to be calculated according to solid combustible content in the combustion product flue gas of measurement, lime-ash
Flying dust, ash content carbon and coal ash content；
q5=(Q5/Qr) × 100: boiler radiation loss accounts for the percentage of input heat, with boiler structure, heat preservation situation and fire coal
Amount is related；
q6=(Q6/Qr) × 100: the other heat loss of boiler account for the percentage of input heat, the physics heat loss taken away such as lime-ash；
Feature of present invention is simplified to above-mentioned classical thermal efficiency method, to export, " one kind is based on oxygen content and flying marking
Measure the coal-powder boiler combustion control method of on-line monitoring "
2) simplification to various heat losses in thermal efficiency expression formula:
Firstly, various heat losses are divided into the loss of online adjustable heat and online cannot be adjusted heat loss and the similar heat waste of merging
It loses, simplification is made to the judgement of boiler optimum operating condition, obtains following result:
q5、q6Or Q5、Q6Heat loss accounting very little and cannot by firing optimization be improved significantly, belong to online non-adjustable
Whole heat loss is cast out as burning quasi-optimal operating condition Judging index and is not considered；
q3、q4Or Q3、Q4The reason of heat loss is incomplete combustion loss, is occurred is identical, i.e., anoxic, temperature are inadequate and fire
The time is insufficient to the greatest extent, therefore, if q4Loss is optimal state, q3Should generally also it reach；And gaseous combustible object can with respect to solid
Combustion things more easy to burn out, also therefore very little can use q to loss accounting4It loses while representing q3Loss, makes it be not present in quasi-optimal
In combustion conditions Judging index, difficulty brought by online flue gas analysis is avoided；
q2Or Q2Heat loss can be divided into two parts in fact, and a part is the Theoretical combustion product determined by combustion reaction equation
The heat taken away with flue gas, calculating is related to the ingredient of combustion product, more complicated, is the inevitable outcome of combustion reaction, is not
It is adjustable；Another part is the heat taken away with flue gas due to having fed excessive air, is that burning is needed to adjust and reduced
Part, i.e. one of the target of burning optimization is defined as " adjustable heat loss due to exhaust gas ", usesIt indicates, i.e., per kilogram fires
Expect the part that exhaust gas heat loss's disalignment is adjustable and is used, unit kJ/kg；In addition, the heat of leaking out of exhaust gas heat loss's disalignment
Loss is also not belonging to adjustable part of burning, and does not also account for herein；
After making above-mentioned simplification, formula (3) becomes following form:
3) solving makes the smallest optimization problem of the sum of " adjustable heat loss due to exhaust gas " and " Mechanical adsorption ", and takes into account
The influence of " the unburned heat loss of chemistry ":
According to boiler theory, in the whole range of real-time, tunable, this two heat loss all have with the air capacity for feeding boiler auxiliary combustion
It closes, which usually uses " excess air coefficient " α to indicate, is defined as:
α=V/V0 (5)
Wherein:
V: the practical air capacity for feeding boiler of per kilogram fuel, Nm3/kg；
V0: per kilogram fuel theoretical air requirement, Nm3/ kg can be converted according to as-fired coal, composition of air by combustion reaction equation
It arrives,
Promote coal-fired completely burned as far as possible to provide enough oxygen, answers V > V0, it may be assumed that α > 1, α pass through oxygen amount meter on-line measurement
To flue gas in oxygen volume content O2(%) is calculate by the following formula to obtain:
Then (4) formula is write as:
According to optimum theory, which can be obtained by solving following equation, to obtain the minimum heat loss of acquirement most
Good excess air coefficient α2,4:
Therefore the target of combustion control, which can be attributed to, seeksQ4The derivative of (α), and (7) formula is kept to set up: according to
The definition of " adjustable heat loss due to exhaust gas ", calculation formula indicate are as follows:
Wherein:
The average level pressure specific heat per unit volume of air, kJ/Nm3DEG C, can be found by the physical parameter of air；
t2: exhaust gas temperature, DEG C；
t1: air enters temperature when furnace, is environment temperature；
It enables:Then
(8) formula has following form:
When coal, exhaust gas temperature, one timing of environment temperature, design value can use to simplify the calculation, A may be regarded as constant, can by (9) formula
To find out, physical significance is theoretical air requirement in the systemic heat of furnace,It is an incremental straight line in Q- α coordinate diagram
(1), it may be assumed that " adjustable heat loss due to exhaust gas "It is proportional between excess air coefficient α, then have:
Mechanical adsorption Q4It can indicate are as follows:
Wherein:
afh、alz: the share of flying dust, the total ash quantity of clinker Zhan, afh+alz=1；
Ay: fire coal applies base ash content, the timing of coal quality one its be definite value；
Cfh、Clz: flying dust, boiler slag carbon content, CfhIt is related with α, it can be by unburned carbon in flue dust on-Line Monitor Device the real time measure；
In above formula, for remove from on-line monitoring ash content carbon trouble, approximatively by phosphorus content in lime-ash with unburned carbon in flue dust come
Substitution, i.e. Cfh=Clz, because large capacity coal dust boiler ash sediment share very little, will not bring very big error；
By (12) formula, unburned carbon in flue dust CfhIt is the function of α, i.e. Q4It is also the function of α, but Relationship Comparison is complicated, even if same
Boiler its relationship in different types of coal, different load can also have a greater change, and cannot be expressed with a simple formula, but its
Changing rule we can qualitatively be stated from following discussion；
According to Theory of Combustion, when excess air coefficient is smaller, due to the oxygen and fuel contact machine as one of burning condition
It can reduce, keep uncombusted particle more, thus Q4It is larger；With the increase of α, Q4It is gradually reduced and will be maintained at lesser range
It is interior；And when α is sufficiently large, and another condition that burning will be destroyed, i.e., in more excess air since temperature is lower, burning
It can postpone, uncombusted particle can also increase, and make Q4It can increase again with the increase of α；Therefore, Q4With the variation rule curve of α
It (2), must be recessed, a Dan Gu, small curvature curve, which will change with boiler load, the variation for using coal etc., but its
Shape or changing rule will not change, and by (12) formula, the derivative of the curve is expressed as:
BecauseFor a straight line, thenAlso the curve (3) for one with recessed, Dan Gu, small curvature feature；
Bring (11), (13) formula into (7) formula, then the condition for obtaining burning quasi-optimal operating condition is:
Or
Definition:
EktIt is defined as new big coal fired boilers " quasi-optimal operating condition index of discrimination ", when:
When, meet (7) formula, then boiler combustion is in quasi-optimal operating condition；
Due to CfhUncertain with the relationship of α, reality will substitute into limited real-time monitoring value when calculating, and (16) formula can approximate earth's surface
It is shown as:
DefinitionFor " average quasi-optimal operating condition index of discrimination ", whenWhen, boiler combustion is in " quasi-optimal operating condition "；
(16) or in (19) formula, when load and the timing of coal one, denominator B is a fixed number for being greater than 0, can also approximation take design value meter
It calculates, by adjusting air output, i.e. change α when operation, and to CfhOn-line monitoring.Take α, CfhMonitor value substitutes into (19) formula and calculates
According toThe degree of deviation 1 judges the superiority and inferiority of combustion position；
IfThen search direction is the direction for reducing α；IfThen search direction is to make the increased direction α, optional
With optimization algorithm optimizing, set up (18) formula, then boiler is in quasi-optimal combustion conditions at this time, i.e., 4 point institute table in curve (3)
The situation shown, α at this time2,4For " best excess air coefficient ", particularly, whenWhen, it may be assumed thatIllustrate Q4It reaches
To minimum, situation represented by 5 points, Combustion Operation of Boilers have been approached quasi-optimal operating condition in curve (2), this is also combustion control
When only with the important symbol that can differentiate of unburned carbon in flue dust on-line monitoring result.
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