CN103077305B - Large coal-fired boiler flue gas flow flexible measurement method - Google Patents

Abstract

A kind of large coal-fired boiler flue gas flow flexible measurement method, described method measures induced draft fan inlet flue gas pressure <i>p</iGreatT.Gr eaT.GT on the left of large coal-fired boiler in real time _li(kPa), left side induced draft fan exiting flue gas pressure <i>p</iGreatT.Gr eaT.GT _lo(kPa), local atmospheric pressure p _act(kPa), left side induced draft fan entrance flue gas temperature <i>t</iGreatT.Gr eaT.GT _l(DEG C), right side induced draft fan inlet flue gas pressure <i>p</iGreatT.Gr eaT.GT _ri(kPa), right side induced draft fan exiting flue gas pressure <i>p</iGreatT.Gr eaT.GT _ro(kPa), right side induced draft fan entrance flue gas temperature <i>t</iGreatT.Gr eaT.GT _r(DEG C), and calculate induced draft fan exiting flue gas flow <i>q</iGreatT.Gr eaT.GT according to the flow-pressure characteristic of induced draft fan _g.Compare with traditional fire coal boiler fume flow-measuring method, the present invention has that reliability is high, accuracy of measurement good, rapid dynamic response speed, implementation cost are low, safeguard the advantages such as simple.

Description

Large coal-fired boiler flue gas flow flexible measurement method

Technical field

The present invention relates to a kind of method for measuring large coal-fired boiler flue gas flow, belonging to boiler technology field.

Background technology

Fuel generates flue gas and release heat with the oxygen generation chemical reaction in air in boiler, Measurement accuracy flue gas flow contributes to implementing more efficiently monitor and forecast to combustion process and relevant device thereof, optimize the dynamically accurate proportioning in wind, the full combustion process of coal, improve the burning efficiency of boiler.

In addition in order to effectively control the discharge capacity of atmosphere pollution, current fuel-burning power plant large-sized boiler generally installs sweetener, and starts progressively to install denitration device additional.In desulfurization and denitrification process, except needing SO in real-time Measurement accuracy flue gas ₂, NO _xconcentration outside, also need to measure flue gas flow, to control the input amount of desulfurizing agent and denitrfying agent, reduce costs under the prerequisite ensureing desulphurization and denitration effect, prevent from causing secondary pollution.After application wet desulphurization equipment the most general is arranged on boiler induced-draft fan outlet, flue gas flow refers to induced draft fan exiting flue gas flow; Apply SCR(SCR technology the most general) denitration device is arranged on boiler economizer exit, and flue gas flow refers to economizer exit flue gas flow.There is certain difference in two place's flue gas flows, mainly causes because boiler air preheater leaks out.

At present, the measurement of flue gas flow is faced with many difficulties.First, large-sized boiler smoke flow channels cross section is rectangle and very thick, is furnished with the equipment such as various heating surfaces in flue, is difficult to find the position that is applicable to installing flow measurement device and front and back straight length can not meet the demands; Secondly, carry a large amount of fly ash granules in flue gas, can cause serious wearing and tearing during flow at high speed to conventional measurement devices, flying dust also can be deposited in the pressure pipeline of measurement mechanism and result in blockage simultaneously, and measurement mechanism is difficult to ensure serviceable life; Again, also SO is included in flue gas ₂, NO _xdeng gas, temperature is reduced to these gases to a certain degree can generate corrosive liquids with the water vapour generation chemical reaction in flue gas, corrosion measuring device also coheres flue dust, causes measurement mechanism accuracy to reduce or damages, and particularly there is this phenomenon when to leak out in flue and more easily occurs; Finally, because flue gas flow measurement mechanism is non-standard restriction device, its coefficient of flow needs on-site proving, demarcate environment very severe, the installation and removal of standard measuring equipment is all more difficult, causes demarcation costly, and can only carry out cold conditions demarcation, calibration accuracy is difficult to ensure.Therefore, be necessary to explore a kind of new flue gas flow measuring method, to improve reliability and the accuracy of flue gas flow measurement, and reduce measurement cost.

Summary of the invention

The object of the invention is to the drawback for prior art, the large coal-fired boiler flue gas flow flexible measurement method that a kind of Measurement reliability is high, accuracy good, implementation cost is low is provided.

Problem of the present invention realizes with following technical proposals:

A kind of large coal-fired boiler flue gas flow flexible measurement method, described method measures induced draft fan exiting flue gas pressure on the left of large coal-fired boiler in real time p _lo(kPa), left side induced draft fan inlet flue gas pressure p _li(kPa), local atmospheric pressure p _act(kPa), left side induced draft fan entrance flue gas temperature t _l(DEG C), right side induced draft fan exiting flue gas pressure p _ro(kPa), right side induced draft fan inlet flue gas pressure p _ri(kPa), right side induced draft fan entrance flue gas temperature t _r(DEG C), and utilize following formulae discovery induced draft fan exiting flue gas flow q _g(Nm ³/ s):

， ， ，

Wherein, k _gfor coefficient of flow, obtain by demarcating; m _lfor flue gas flow variable (Nm on the left of standardization ³/ s); m _rfor flue gas flow variable (Nm on the right side of standardization ³/ s).

Above-mentioned large coal-fired boiler flue gas flow flexible measurement method, described method measures Oxygen Amount in Flue Gas after left side air primary heater in real time o _lo(%), Oxygen Amount in Flue Gas before left side air primary heater o _li(%), Oxygen Amount in Flue Gas after right hand side air primary heater o _ro(%), Oxygen Amount in Flue Gas before right hand side air primary heater o _ri, and utilize following formula to calculate economizer exit flue gas flow (%) q _m(Nm ³/ s):

。

Above-mentioned large coal-fired boiler flue gas flow flexible measurement method, the scaling method of described coefficient of flow is:

Under boiler rated load, boiler coal feeding amount, air output, furnace pressure is kept to stablize, Oxygen Amount in Flue Gas after Oxygen Amount in Flue Gas, left and right sides air preheater before record boiler left and right sides induced draft fan exiting flue gas pressure, left and right sides induced draft fan inlet flue gas pressure, left and right sides induced draft fan entrance flue gas temperature, local atmospheric pressure, boiler air-supply volume, left and right sides air preheater

Coefficient of flow k _gadopt following formulae discovery:

，

，

，

，

，

，

Wherein: q _g0for induced draft fan exiting flue gas flow (Nm under declared working condition ³/ s); m _l0for flue gas flow variable (Nm on the left of standardization under declared working condition ³/ s); m _r0for flue gas flow variable (Nm on the right side of standardization under declared working condition ³/ s); p _lo0for left side induced draft fan exiting flue gas pressure (kPa) under declared working condition; p _li0for left side induced draft fan inlet flue gas pressure (kPa) under declared working condition; t _l0for left side induced draft fan entrance flue gas temperature (DEG C) under declared working condition; p _ro0for right side induced draft fan exiting flue gas pressure (kPa) under declared working condition; p _ri0for right side induced draft fan inlet flue gas pressure (kPa) under declared working condition; t _r0for right side induced draft fan entrance flue gas temperature (DEG C) under declared working condition; q _m0for economizer exit flue gas flow (Nm under declared working condition ³/ s); o _li0for Oxygen Amount in Flue Gas (%) before left side air preheater under declared working condition; o _ri0for Oxygen Amount in Flue Gas (%) before right side air preheater under declared working condition; o _lo0for Oxygen Amount in Flue Gas (%) after left side air preheater under declared working condition; o _ro0for Oxygen Amount in Flue Gas (%) after right side air preheater under declared working condition; q _s0for boiler economizer exit amount of theoretical flue gas (Nm under declared working condition ³/ s); q _a0for boiler air-supply volume (Nm under declared working condition ³/ s), get primary air flow, secondary air flow sum; η _a0for boiler furnace under rated loan condition and pulverized coal preparation system air leak rate of air curtain (%), data during desirable boiler thermal output experiment or boiler design value; Q _arfor coal net calorific value as received basis (MJ/kg); M _arfor coal receives base moisture content (%).

The present invention, according to the flow-pressure characteristic of induced draft fan, utilizes induced draft fan to export and inlet flue gas pressure, flue-gas temperature calculating induced draft fan exiting flue gas flow; Utilize before and after air preheater after the correction of oxygen amount increase air-heater leakage on this basis, calculating economizer exit flue gas flow; Its coefficient of flow is by the computational analysis on-line proving of air output and chemistry of fuel composition.

Compare with traditional fire coal boiler fume flow-measuring method, the present invention has the following advantages:

(1) reliability is high.Flexible measurement method avoids installs apparatus for measuring air quantity in rugged environment, and measuring process by the impact of flying dust entrained in flue gas, not by the impact of corrosive gas in flue gas, does not have very high reliability.

(2) accuracy of measurement is good, rapid dynamic response speed.After demarcating, within the scope of boiler full load, the relative error of hard measurement flue gas flow can be controlled in ± 2% within, this accuracy for flue gas flow is measured is enough.In addition, the response that induced draft fan entrance, top hole pressure change flue gas flow is very sensitive, measures rapid dynamic response speed.

(3) implementation cost is low, maintenance is simple.Hard measurement does not need to increase extra measurement mechanism, and calibration process does not need install in flue and dismantle extra flow calibrating device yet, and save equipment and human resources, implementation cost is cheap.Meanwhile, computation process realizes in unit DCS, safeguards very convenient.

Accompanying drawing explanation

Below in conjunction with accompanying drawing, the invention will be further described.

Fig. 1 is that flue gas flow calculates configuration logic.

Symbol inventory used is in figure or in literary composition: ADD is additional calculation module; SUB is subtraction module; MUL is multiplication computing module; DIV is division calculation module; SQU is extraction of square root computing module;

q _gfor induced draft fan exiting flue gas flow (Nm ³/ s); k _gfor coefficient of flow (dimensionless); m _lfor flue gas flow variable (Nm on the left of standardization ³/ s); m _rfor flue gas flow variable (Nm on the right side of standardization ³/ s); q _mfor economizer exit flue gas flow (Nm ³/ s); o _lifor Oxygen Amount in Flue Gas (%) before left side air primary heater; o _lofor Oxygen Amount in Flue Gas (%) after left side air primary heater; o _rifor Oxygen Amount in Flue Gas (%) before right hand side air primary heater; o _rofor Oxygen Amount in Flue Gas (%) after right hand side air primary heater; p _lofor left side induced draft fan exiting flue gas pressure (kPa); p _lifor left side induced draft fan inlet flue gas pressure (kPa); p _actfor local atmospheric pressure (kPa); t _lfor left side induced draft fan entrance flue gas temperature (DEG C); p _rofor right side induced draft fan exiting flue gas pressure (kPa); p _rifor right side induced draft fan inlet flue gas pressure (kPa); t _rfor right side induced draft fan entrance flue gas temperature (DEG C); q _g0for induced draft fan exiting flue gas flow (Nm under declared working condition ³/ s); m _l0for flue gas flow variable (Nm on the left of standardization under declared working condition ³/ s); m _r0for flue gas flow variable (Nm on the right side of standardization under declared working condition ³/ s); p _lo0for left side induced draft fan exiting flue gas pressure (kPa) under declared working condition; t _l0for left side induced draft fan entrance flue gas temperature (DEG C) under declared working condition; p _li0for left side induced draft fan inlet flue gas pressure (kPa) under declared working condition; p _ro0for right side induced draft fan exiting flue gas pressure (kPa) under declared working condition; p _ri0for right side induced draft fan inlet flue gas pressure (kPa) under declared working condition; t _r0for right side induced draft fan entrance flue gas temperature (DEG C) under declared working condition; q _m0for economizer exit flue gas flow (Nm under declared working condition ³/ s); o _li0for Oxygen Amount in Flue Gas (%) before left side air preheater under declared working condition; o _ri0for Oxygen Amount in Flue Gas (%) before right side air preheater under declared working condition; o _lo0for Oxygen Amount in Flue Gas (%) after left side air preheater under declared working condition; o _ro0for Oxygen Amount in Flue Gas (%) after right side air preheater under declared working condition; q _s0for boiler economizer exit amount of theoretical flue gas (Nm under declared working condition ³/ s); q _a0for boiler air-supply volume (Nm under declared working condition ³/ s), get primary air flow, secondary air flow sum; η _a0for boiler furnace under rated loan condition and pulverized coal preparation system air leak rate of air curtain (%), data during desirable boiler thermal output experiment or boiler design value; Q _arfor coal net calorific value as received basis (MJ/kg); M _arfor coal receives base moisture content (%).

Embodiment

The present invention carries out according to the following steps:

(1) flue gas flow calculates

Induced draft fan exiting flue gas flow rate calculation formula is:

（1）

Wherein: q _gfor induced draft fan exiting flue gas flow (Nm ³/ s); k _gfor coefficient of flow (dimensionless); m _lfor flue gas flow variable (Nm on the left of standardization ³/ s); m _rfor flue gas flow variable (Nm on the right side of standardization ³/ s).

Economizer exit flue gas flow computing formula is:

（2）

Wherein: q _mfor economizer exit flue gas flow (Nm ³/ s); o _lifor Oxygen Amount in Flue Gas (%) before left side air primary heater; o _lofor Oxygen Amount in Flue Gas (%) after left side air primary heater; o _rifor Oxygen Amount in Flue Gas (%) before right hand side air primary heater; o _rofor Oxygen Amount in Flue Gas (%) after right hand side air primary heater.

(2) standardization flue gas flow variable calculates

On the left of standardization, flue gas flow variable computing formula is:

（3）

Wherein: p _lofor left side induced draft fan exiting flue gas pressure (kPa); p _lifor left side induced draft fan inlet flue gas pressure (kPa); p _actfor local atmospheric pressure (kPa); t _lfor left side induced draft fan entrance flue gas temperature (DEG C).

On the right side of standardization, flue gas flow variable computing formula is:

（4）

Wherein: p _rofor right side induced draft fan exiting flue gas pressure (kPa); p _rifor right side induced draft fan inlet flue gas pressure (kPa); t _rfor right side induced draft fan entrance flue gas temperature (DEG C).

(3) coefficient of flow is demarcated

Coefficient of flow is obtained by calibration experiment.Before calibration experiment, technical analysis is carried out to boiler fired coal, determine coal net calorific value as received basis, moisture content, ash.Keep ature of coal to stablize, under boiler rated load, carry out calibration experiment.Boiler coal feeding amount, air output, furnace pressure is kept to stablize during experiment, Oxygen Amount in Flue Gas after Oxygen Amount in Flue Gas, left and right sides air preheater before record boiler left and right sides induced draft fan inlet flue gas pressure, left and right sides induced draft fan exiting flue gas pressure, left and right sides induced draft fan exit gas temperature, local atmospheric pressure, boiler air-supply volume, left and right sides air preheater.

Coefficient of flow adopts following formulae discovery:

（5）

Wherein: q _g0for induced draft fan exiting flue gas flow (Nm under declared working condition ³/ s); m _l0for flue gas flow variable (Nm on the left of standardization under declared working condition ³/ s); m _r0for flue gas flow variable (Nm on the right side of standardization under declared working condition ³/ s).

Under declared working condition, on the left of standardization, flue gas flow variable computing formula is:

（6）

Wherein: p _lo0for left side induced draft fan exiting flue gas pressure (kPa) under declared working condition; p _li0for left side induced draft fan inlet flue gas pressure (kPa) under declared working condition; t _l0for left side induced draft fan entrance flue gas temperature (DEG C) under declared working condition.

Under declared working condition, on the right side of standardization, flue gas flow variable computing formula is:

（7）

Wherein: p _ro0for right side induced draft fan exiting flue gas pressure (kPa) under declared working condition; p _ri0for right side induced draft fan inlet flue gas pressure (kPa) under declared working condition; t _r0for right side induced draft fan entrance flue gas temperature (DEG C) under declared working condition.

Under declared working condition, boiler induced-draft fan exiting flue gas flow adopts following formulae discovery:

（8）

Wherein: q _m0for economizer exit flue gas flow (Nm under declared working condition ³/ s); o _li0for Oxygen Amount in Flue Gas (%) before left side air preheater under declared working condition; o _ri0for Oxygen Amount in Flue Gas (%) before right side air preheater under declared working condition; o _lo0for Oxygen Amount in Flue Gas (%) after left side air preheater under declared working condition; o _ro0for Oxygen Amount in Flue Gas (%) after right side air preheater under declared working condition.

Under declared working condition, boiler economizer exit flue gas flow adopts following formulae discovery:

（9）

Wherein: q _s0for boiler economizer exit amount of theoretical flue gas (Nm under declared working condition ³/ s); q _a0for boiler air-supply volume (Nm under declared working condition ³/ s), get primary air flow, secondary air flow sum; η _a0for boiler furnace under rated loan condition and pulverized coal preparation system air leak rate of air curtain (%), data during desirable boiler thermal output experiment or boiler design value.

Under declared working condition, boiler amount of theoretical flue gas adopts following formulae discovery:

（10）

Wherein: Q _arfor coal net calorific value as received basis (MJ/kg); M _arfor coal receives base moisture content (%).

Implementation step of the present invention

(1) Preparatory work of experiment

Implement flue gas flow hard measurement to need to confirm that the following signal of boiler is normal: Oxygen Amount in Flue Gas after Oxygen Amount in Flue Gas, left and right sides air preheater before left and right sides induced draft fan exiting flue gas pressure, left and right sides induced draft fan inlet flue gas pressure, left and right sides induced draft fan entrance flue gas temperature, left and right sides air preheater.Because the zirconia O2 analyzer error of onsite application is comparatively large, need before experiment to adopt oxygen content to be that 5% calibrating gas is demarcated it.

Before experiment, technical analysis is carried out to boiler as-fired coal matter, obtain coal net calorific value as received basis, moisture content, ash data.Measure local atmospheric pressure.

Confirm burner hearth and the pulverized coal preparation system air leak rate of air curtain of measuring and calculating during thermal performance experiment, or search the design load of burner hearth and pulverized coal preparation system air leak rate of air curtain.

(2) calibration experiment

Ensureing, under the condition that ature of coal is stable, boiler coal feeding amount, primary air flow, secondary air flow to be dropped into Non-follow control, primary air pressure, secondary wind pressure drop into and automatically control, and furnace pressure controls to drop into automatically, stop blowing ash.Keep boiler coal feeding amount, primary air flow, secondary air flow to stablize, start experiment.The change of experimental session furnace pressure is less than ± 50Pa; On the right side of air preheater front left Oxygen Amount in Flue Gas mean variation be less than ± 0.2%.After these parameter stabilities, record following data: Oxygen Amount in Flue Gas after Oxygen Amount in Flue Gas, left and right sides air preheater before left and right sides induced draft fan exiting flue gas pressure, left and right sides induced draft fan inlet flue gas pressure, left and right sides induced draft fan entrance flue gas temperature, left and right sides air preheater.

(3) coefficient of flow calculates

According to calibration experiment record data, formula 5-formula 10 is utilized to calculate flue gas flow coefficient.

(4) on-the-spot configuration

In unit scattered control system (DCS), realize formula 1 ~ formula 4 in the mode of configuration, as shown in Figure 1.In accompanying drawing 1, the meaning of each configuration symbol: ADD is additional calculation module; SUB is subtraction module; MUL is multiplication computing module; DIV is division calculation module; SQU is extraction of square root computing module.The coefficient of flow that calibration experiment is obtained k _gset, hard measurement logic can put into operation.

Claims (1)

1. a large coal-fired boiler flue gas flow flexible measurement method, is characterized in that, described method measures induced draft fan exiting flue gas pressure p on the left of large coal-fired boiler in real time _lo, unit is KPa, left side induced draft fan inlet flue gas pressure p _li, unit is KPa, local atmospheric pressure p _act, unit is KPa, left side induced draft fan entrance flue gas temperature t _l, unit is DEG C, right side induced draft fan exiting flue gas pressure p _ro, unit is KPa, right side induced draft fan inlet flue gas pressure p _ri, unit is KPa, right side induced draft fan entrance flue gas temperature t _r, unit is DEG C, and utilizes following formulae discovery induced draft fan exiting flue gas flow q _g, unit is Nm ³/ s:

$q_g=K_g(M_L+M_R),M_L=\sqrt{\frac{(p_{Lo}-p_{Li})(p_{Li}-p_{act})}{t_L+273.15}},M_R=\sqrt{\frac{(p_{Ro}-p_{Ri})(p_{Ri}-p_{act})}{t_R+273.15}},$

Wherein, K _gfor coefficient of flow, obtain by demarcating; M _lfor flue gas flow variable on the left of standardization, unit is Nm ³/ s; M _rfor flue gas flow variable on the right side of standardization, unit is Nm ³/ s;

Described method measures Oxygen Amount in Flue Gas O before left side air primary heater in real time _li, unit is Oxygen Amount in Flue Gas O after %, left side air primary heater _lo, unit is Oxygen Amount in Flue Gas O before %, right hand side air primary heater _ri, unit is Oxygen Amount in Flue Gas O after %, right hand side air primary heater _ro, unit is %, and utilizes following formula to calculate economizer exit flue gas flow q _m, unit is Nm ³/ s:

$q_m=K_g(M_L\frac{20.67-O_{Lo}}{20.67-O_{Li}}+M_R\frac{20.67-O_{Ro}}{20.67-O_{Ri}});$

Described coefficient of flow is demarcated according to the following steps:

Calibration experiment is carried out under boiler rated load, boiler coal feeding amount, air output, furnace pressure is kept to stablize during experiment, Oxygen Amount in Flue Gas after Oxygen Amount in Flue Gas, left and right sides air preheater before record boiler left and right sides induced draft fan inlet flue gas pressure, left and right sides induced draft fan exiting flue gas pressure, left and right sides induced draft fan exit gas temperature, local atmospheric pressure, boiler air-supply volume, left and right sides air preheater;

Flow coefficient k _gcomputing formula be:

$K_g=\frac{q_{g0}}{(M_{L0}+M_{R0})}$

$M_{L0}=\sqrt{\frac{(p_{Lo0}-p_{Li0})(p_{Li0}+p_{act})}{t_{L0}+273.15}},$

$M_{R0}=\sqrt{\frac{(p_{Ro0}-p_{Ri0})(p_{Ri0}+p_{act})}{t_{R0}+273.15}},$

$q_{g0}=q_{m0}\frac{20.67-0.5(O_{Li0}+O_{Ri0})}{20.67-0.5(O_{Lo0}+O_{Ro0})},$

$q_{m0}=q_{s0}+\frac{100q_{a0}(O_{Li0}+O_{Ri0})}{(100-{\mathrm{\&eta;}}_{a0})(41.34-O_{Li0}-O_{Ri0})},$

$q_{s0}=\frac{100q_{a0}}{100-{\mathrm{\&eta;}}_{a0}}\&lsqb;1+\frac{0.0012(41.34-O_{Li0}-O_{Ri0})}{Q_{ar}}{M}_{ar}\&rsqb;,$

Wherein: q _g0for induced draft fan exiting flue gas flow under declared working condition, unit is Nm ³/ s; M _l0for flue gas flow variable on the left of standardization under declared working condition, unit is Nm ³/ s; M _r0for flue gas flow variable on the right side of standardization under declared working condition, unit is Nm ³/ s; p _lo0for induced draft fan exiting flue gas pressure in left side under declared working condition, unit is KPa; p _li0for induced draft fan inlet flue gas pressure in left side under declared working condition, unit is KPa; t _l0for left side induced draft fan entrance flue gas temperature under declared working condition, unit is DEG C; p _ro0for induced draft fan exiting flue gas pressure in right side under declared working condition, unit is KPa; p _ri0for induced draft fan inlet flue gas pressure in right side under declared working condition, unit is KPa; t _r0for right side induced draft fan entrance flue gas temperature under declared working condition, unit is DEG C; q _m0for economizer exit flue gas flow under declared working condition, unit is Nm ³/ s; O _li0for Oxygen Amount in Flue Gas before left side air preheater under declared working condition, unit is %; O _ri0for Oxygen Amount in Flue Gas before right side air preheater under declared working condition, unit is %; O _lo0for Oxygen Amount in Flue Gas after left side air preheater under declared working condition, unit is %; O _ro0for Oxygen Amount in Flue Gas after right side air preheater under declared working condition, unit is %; q _s0for boiler economizer exit amount of theoretical flue gas under declared working condition, unit is Nm ³/ s; q _a0for boiler air-supply volume under declared working condition, unit is Nm ³/ s, gets primary air flow, secondary air flow sum; η _a0for boiler furnace under rated loan condition and pulverized coal preparation system air leak rate of air curtain, unit is %, data during desirable boiler thermal output experiment or boiler design value; Q _arfor coal net calorific value as received basis, unit is MJ/Kg; M _arfor coal receives base moisture content, unit is %.