COAL-AIR SYNCHRONOUS DYNAMIC COORDINATED CONTROL METHOD FOR COAL-FIRED UNIT

Abstract

A coal-air synchronous dynamic coordinated control method for a coal-fired unit is provided, comprising: determining functional relationship between unit loads and designed coal feed rates and functional relationship between unit loads and flue gas operation wet-basis oxygen contents, respectively; obtaining a theoretical wet flue gas volume and a combustion-supporting dry air volume per unit mass of burning coal, and calculating an actual combustion-supporting dry air volume per unit mass of burning coal; calculating an actual low calorific value of feed coal; calculating a combustion-supporting dry air volume and an outlet wet flue gas volume; according to the target value of load instruction at a future time point, calculating a coal feed rate variation and a combustion-supporting dry air volume variation; obtaining an operation wet-basis oxygen content variation; and obtaining target values of the coal feed rate and the operation wet-basis oxygen content to be adjusted.

Claims

1. A coal-air synchronous dynamic coordinated control method for a coal-fired unit, comprising the following: S1: in a steady-state operation mode of the coal-fired unit, acquiring configured coal feed rates and configured flue gas operation wet-basis oxygen contents under different loads, and then determining a corresponding functional relationship between unit loads L and the configured coal feed rates W.sub.coal,b, and a corresponding functional relationship between the unit loads L and the configured flue gas operation wet-basis oxygen contents O.sub.2,b; S2: using a regression analysis method, obtaining a regression function of a theoretical wet flue gas volume W.sub.flue,th,wet per unit mass of burning coal and a theoretical combustion-supporting dry air volume W.sub.air,th,dry per unit mass of burning coal based on a low calorific value by fitting, judging accuracy of the regression function, and calculating an actual combustion-supporting dry air volume W.sub.air,act,dry per unit mass of burning coal, and according to air temperature, relative humidity and atmospheric pressure, calculating air saturated vapor pressure P.sub.H.sub.2.sub.O and a water vapor proportion φ per unit volume of dry air, and then calculating an actual combustion-supporting wet air volume W.sub.air,act,wet per unit mass of burning coal and a wet flue gas volume W.sub.flue,act,wet actually produced per unit mass of burning coal; S3: calculating predicted values W.sub.air,h of a required combustion-supporting dry air volume and predicted values W.sub.flue,h of a produced wet flue gas volume for the total burning coal per hour under different loads, and by comparing the predicted values W.sub.air,h and design values W.sub.air,b of the required combustion-supporting dry air volume, and the predicted values W.sub.flue,h and design values W.sub.flue,b of the produced wet flue gas volume for the total burning coal per hour under different loads, verifying whether relative deviations δ are within an acceptable range; S4: acquiring current load L.sub.τ and actual coal feed rate W.sub.coal,act of the coal-fired unit, calculating a configured coal feed rate W.sub.coal,b,τ under the current unit load L.sub.τ through the corresponding functional relationship between the unit loads L and the configured coal feed rates W.sub.coal,b and calculating an actual low calorific value Q.sub.net,act of feed coal; S5: according to the actual coal feed rate W.sub.coal,act, actual operation wet-basis oxygen content O.sub.2,act and the actual low calorific value Q.sub.net,act of feed coal, calculating a combustion-supporting dry air volume BW.sub.air,act,dry and a combustion-supporting wet air volume BW.sub.air,act,wet entering a boiler in real time, and the wet flue gas volume BW.sub.flue,act,wet at an outlet of a boiler economizer; S6: according to a load instruction curve of the coal-fired unit, determining a target value of a load instruction at a future time point Δτ, and calculating a unit load change rate E.sub.L within the time Δτ, calculating a coal feed rate W.sub.coal,τ+Δτ at the future time point Δτ, and calculating a coal feed rate variation ΔW.sub.coal within the time Δτ, and then calculating a combustion-supporting dry air volume variation ΔBW.sub.air,act,dry and a combustion-supporting wet air volume variation ΔBW.sub.air,act,wet within the time Δτ; S7: calculating an operation wet-basis oxygen content variation ΔO.sub.2,1 caused by a change of the combustion-supporting dry air volume, and according to the corresponding functional relationship between the unit loads L and the configured flue gas operation wet-basis oxygen contents O.sub.2,b, obtaining a flue gas operation wet-basis oxygen content O.sub.2,b,τ at the future time point Δτ, and calculating a set wet-basis oxygen content variation ΔO.sub.2,2 within the time Δτ, and then obtaining an operation wet-basis oxygen content variation ΔO.sub.2 within the time Δτ; and S8: on the basis of a coal feed rate instruction and an operation wet-basis oxygen content instruction of an original DCS sequence control logic of the unit, respectively superimposing the coal feed rate variation ΔW.sub.coal and the operation wet-basis oxygen content variation ΔO.sub.2 simultaneously in advance to obtain a target value W.sub.coal,new of the coal feed rate to be adjusted and a target value O.sub.2,new of the operation wet-basis oxygen content to be adjusted.

2. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the corresponding functional relationship between the unit loads L and the configured coal feed rates W.sub.coal,b, and the corresponding functional relationship between the unit loads L and the configured flue gas operation wet-basis oxygen contents O.sub.2,b are respectively:
W.sub.coal,b=f(L.sub.τQ.sub.net,b),
O.sub.2,b=g(L), where, L is unit load, in MW, W.sub.coal,b is configured coal feed rate, in t/h, Q.sub.net,b is configured low calorific value of coal, in MJ/kg, O.sub.2,b, is configured flue gas operation wet-basis oxygen content, in %.

3. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the theoretical wet flue gas volume W.sub.flue,th,wet per unit mass of burning coal and the theoretical combustion-supporting dry air volume W.sub.air,th,dry per unit mass of burning coal are obtained by fitting elemental analysis data and industrial analysis data of multiple existing sets of coal samples from utility boilers.

4. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 3, wherein the industrial analysis data comprises received base ashes, received base water and low calorific values, and the elemental analysis data comprises contents of carbon, hydrogen, oxygen, nitrogen, and sulfur.

5. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the theoretical wet flue gas volume per unit mass of burning coal W.sub.flue,th,wet, the theoretical combustion-supporting dry air volume per unit mass of burning coal W.sub.air,th,dry, the air saturated vapor pressure P.sub.H.sub.2.sub.O, water vapor proportion per unit volume of dry air φ, the actual combustion-supporting wet air volume W.sub.air,act,wet per unit mass of burning coal, the wet flue gas volume W.sub.flue,act,wet actually produced per unit mass of burning coal, and the actual combustion-supporting dry air volume W.sub.air,act,dry per unit mass of burning coal are respectively: $W_{\mathrm{flue},\mathrm{th},\mathrm{wet}}=a_1\times Q_{net}+{\beta }_1,$ $W_{\mathrm{air},\mathrm{th},\mathrm{dry}}=a_2\times Q_{net}+{\beta }_2,$ $P_{H_{2}O}=611.7927+42.7809\times T_{air}+1.6883\times T_{air}^2+0.012079\times T_{air}^3+0.00061637\times T_{\mathrm{air}}^4,$ $\phi =0.3866\times \left(\varphi \times P_{air}/100\right)/\left(P_{atm}-\varphi \times P_{air}/100\right),$ $W_{\mathrm{air},\mathrm{act},\mathrm{dry}}=W_{\mathrm{flue},\mathrm{th},\mathrm{wet}}\times \frac{O_2}{21-O_2\times \left(1+\phi \right)}+W_{\mathrm{air},\mathrm{th},\mathrm{dry}}\times \frac{21-O_2}{21-O_2\times \left(1+\phi \right)},$ $W_{\mathrm{air},\mathrm{act},\mathrm{wet}}=W_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times \left(1+\phi \right),$ $W_{\mathrm{flue},\mathrm{act},\mathrm{wet}}=W_{\mathrm{flue},\mathrm{th},\mathrm{wet}}\times \frac{21}{21-O_2\times \left(1+\phi \right)}+W_{\mathrm{air},\mathrm{th},\mathrm{dry}}\times \frac{21}{21-O_2\times \left(1+\phi \right)},$ where, W.sub.flue,th,wet is theoretical wet flue gas volume per unit mass of burning coal, in m.sup.3/kg, W.sub.air,th,dry is theoretical combustion-supporting dry air volume per unit mass of burning coal, in m.sup.3/kg, Q.sub.net is low calorific value of coal, in MJ/kg, α.sub.1, α.sub.2, β.sub.1, β.sub.2 are all constants, P.sub.H.sub.2.sub.O is air saturated vapor pressure, in Pa, T.sub.air is air temperature, in ° C., φ is air relative humidity, in %, P.sub.atm is atmospheric pressure, in Pa, W.sub.air,act,dry is actual combustion-supporting dry air volume per unit mass of burning coal, in m.sup.3/kg, W.sub.air,th,dry is theoretical combustion-supporting dry air volume per unit mass of burning coal, in m.sup.3/kg, W.sub.flue,th,wet is theoretical wet flue gas volume per unit mass of burning coal, in m.sup.3/kg, W.sub.flue,act,wet is actually produced wet flue gas volume per unit mass of burning coal, in m.sup.3/kg, O.sub.2 is flue gas operation wet-basis oxygen content, in %, φ is water vapor volume proportion per unit volume of dry air.

6. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the accuracy of the regression function is judged by the variances, and the variances are greater than 0.9.

7. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the predicted value W.sub.air,h of the required combustion-supporting dry air volume and the predicted value W.sub.flue,h of the produced flue gas volume under a configured operation wet-basis oxygen content for the total burning coal per hour are respectively:
W.sub.air,h=W.sub.air,act,dry×W.sub.coal,b×(1−γ)×1000,
W.sub.flue,h=W.sub.flue,act,wet×W.sub.coal,b×(1−γ)×1000 where, W.sub.air,h is predicted value of the required combustion-supporting dry air volume for the total burning coal per hour, in m.sup.3/h, W.sub.flue,h is predicted value of the produced wet flue gas volume for the total burning coal per hour, in m.sup.3/h, W.sub.air,act,dry is actual combustion-supporting dry air volume per unit mass of burning coal, in m.sup.3/kg, W.sub.flue,th,wet is theoretical wet flue gas volume per unit mass of burning coal, in m.sup.3/kg, W.sub.coal,b is configured coal feed rate, in t/h, γ is incomplete combustion heat loss ratio of feed coal.

8. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the acceptable range of the relative deviations δ is −5%˜+5%, and the relative deviations δ comprises a relative deviation δ.sub.1 between the predicted values W.sub.air,h and design values W.sub.air,b of the required combustion-supporting dry air volume for the total burning coal per hour, and a relative deviation δ.sub.2 between the predicted values W.sub.flue,h and design values W.sub.flue,b of the produced wet flue gas volume for the total burning coal per hour, and the relative deviation δ.sub.1 and the relative deviation δ.sub.2 are respectively: ${\delta }_1=\frac{W_{\mathrm{air},h}-W_{\mathrm{air},b}}{W_{\mathrm{air},b}}\times 100\%,$ ${\delta }_2=\frac{W_{\mathrm{flue},h}-W_{\mathrm{flue},b}}{W_{\mathrm{flue},b}}\times 100\%,$ where, W.sub.air,h is predicted value of the required combustion-supporting dry air volume for the total burning coal per hour, in m.sup.3/h, W.sub.flue,h is predicted value of the produced wet flue gas volume for the total burning coal per hour, in m.sup.3/h, W.sub.air,b is design value of the required combustion-supporting dry air volume for the total burning coal per hour, in m.sup.3/h, W.sub.flue,b is design value of the produced wet flue gas volume for the total burning coal per hour, in m.sup.3/h.

9. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the actual low calorific value Q.sub.net,act of feed coal is: $Q_{\mathrm{net},\mathrm{act}}=\frac{W_{\mathrm{coal},b,r}\times Q_{\mathrm{net},b}}{W_{\mathrm{coal},\mathrm{act}}},$ where, Q.sub.net,act is actual low calorific value of feed coal, in MJ/kg, Q.sub.net,b is configured low calorific value of feed coal, in MJ/kg, W.sub.coal,act is actual coal feed rate under the current unit load L.sub.τ, in t/h, W.sub.coal,b,i is configured coal feed rate under the current unit load L.sub.τ, in t/h.

10. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the current unit load L.sub.τ, the actual coal feed rate W.sub.coal,act, the actual operation wet-basis oxygen content O.sub.2,act, and the actual low calorific value Q.sub.net,act of feed coal are all obtained through a DCS system of the unit.

11. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, under the actual coal feed rate, the combustion-supporting dry air volume BW.sub.air,act,dry, the combustion-supporting wet air volume BW.sub.air,act,wet, and the wet flue gas volume BW.sub.flue,act,wet at outlet are respectively: $B{W}_{\mathrm{air},\mathrm{act},\mathrm{dry}}=\left(W_{\mathrm{flue},\mathrm{th},\mathrm{wet}}\times \frac{O_{2,\mathrm{act}}}{21-O_{2,\mathrm{act}}\times \left(1+\phi \right)}+W_{\mathrm{air},\mathrm{th},\mathrm{dry}}\times \frac{21-O_{2,\mathrm{act}}}{21-O_{2,\mathrm{act}}\times \left(1+\phi \right)}\right)\times W_{\mathrm{coal},\mathrm{act}}\times 1000,$ ${\mathrm{BW}}_{air,\mathrm{act},\mathrm{wet}}=B{W}_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times \left(1+\phi \right),$ ${\mathrm{BW}}_{\mathrm{flue},\mathrm{act},\mathrm{wet}}=\left(W_{\mathrm{flue},\mathrm{th},\mathrm{wet}}\times \frac{21}{21-O_{2,\mathrm{act}}\times \left(1+\phi \right)}+W_{\mathrm{air},\mathrm{th},\mathrm{dry}}\times \frac{21\times \phi }{21-O_{2,\mathrm{act}}\times \left(1+\phi \right)}\right)\times W_{\mathrm{coal},\mathrm{act}}\times 1000,$ where, BW.sub.air,act,dry is combustion-supporting dry air volume, in m.sup.3/h, BW.sub.air,act,wet is combustion-supporting wet air volume, in m.sup.3/h, O.sub.2,act is actual operation wet-basis oxygen content, in %, W.sub.air,th,dry is theoretical combustion-supporting dry air volume per unit mass of burning coal, in m.sup.3/kg, W.sub.flue,th,wet is theoretical wet flue gas volume per unit mass of burning coal, in m.sup.3/kg, BW.sub.flue,act,wet is wet flue gas volume at outlet, in m.sup.3/h, W.sub.coal,act is actual coal feed rate under the current unit load L.sub.τ, in t/h, φ is water vapor volume proportion per unit volume of dry air.

12. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the load instruction curve is set in advance by a power grid dispatch center.

13. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the unit load change rate E.sub.L within the time Δτ, the coal feed rate W.sub.coal,τ+Δτ at the future time point Δτ, the coal feed rate variation ΔW.sub.coal within the time Δτ, and the combustion-supporting dry air volume variation ΔBW.sub.air,act,dry and the combustion-supporting wet air volume variation ΔBW.sub.air,act,wet within the time Δτ are respectively: $E_L=\frac{L_{\tau +\Delta \tau }-L_{\tau }}{L_{\tau }}\times 100,$ $W_{\mathrm{coal},\tau +\Delta \tau }=W_{\mathrm{coal},\mathrm{act}}\times \left(1+\frac{E_L}{100}\right),$ $\Delta W_{\mathrm{coal}}=W_{\mathrm{coal},\tau +\Delta \tau }-W_{\mathrm{coal},\mathrm{act}},$ $\Delta {\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{dry}}=W_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times \Delta W_{\mathrm{coal}}\times 1000,$ $\Delta {\mathrm{BW}}_{air,\mathrm{act},\mathrm{wet}}=\Delta {\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times \left(1+\phi \right),$ where, E.sub.L is unit load change rate within the time Δτ, in %, L.sub.τ is current unit load, in MW, L.sub.τ+Δτ is unit load after the time Δτ, in MW, W.sub.coal,τ+Δτ is coal feed rate at the future time point Δτ, in t/h, W.sub.coal,act is current actual coal feed rate under the current unit load L.sub.τ, in t/h, ΔW.sub.coal is coal feed rate variation within the time Δτ, in t/h, ΔBW.sub.air,act,dry is combustion-supporting dry air volume variation within the time Δτ, in m.sup.3/h, ΔBW.sub.air,act,wet is combustion-supporting wet air volume variation within the time Δτ, in m.sup.3/h, W.sub.air,act,dry is actual combustion-supporting dry air volume per unit mass of coal, in m.sup.3/kg, φ is water vapor volume proportion per unit volume of dry air.

14. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the operation wet-basis oxygen content variation ΔO.sub.2,1 caused by the change of the combustion-supporting dry air volume, the set wet-basis oxygen content variation ΔO.sub.2,2 within the time Δτ, and the operation wet-basis oxygen content variation ΔO.sub.2 within the time Δτ are respectively: $\Delta O_{2,1}=\frac{\Delta B{W}_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times 21}{B{W}_{\mathrm{flue},\mathrm{act},\mathrm{wet}}+\Delta {\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{wet}}}$ $\Delta O_{2,2}=O_{2b\tau }-O_{2,\mathrm{act}},$ $\Delta O_2=\Delta O_{2,1}+\Delta O_{2,2},$ where, ΔO.sub.2,1 is operation wet-basis oxygen content variation caused by the change of the combustion-supporting dry air volume, in %, ΔBW.sub.air,act,dry is combustion-supporting dry air volume variation within the time Δτ, in m.sup.3/h, ΔBW.sub.air,act,wet is combustion-supporting wet air volume variation within the time Δτ, in m.sup.3/h, BW.sub.flue,act,wet is wet flue gas volume at outlet, in m.sup.3/h, ΔO.sub.2,2 is set wet-basis oxygen content variation within the time Δτ, in %, O.sub.2,bτ is flue gas operation wet-basis oxygen content at the future time point Δτ, in %, O.sub.2,act is actual operation wet-basis oxygen content, in %, ΔO.sub.2 is operation wet-basis oxygen content variation within the time Δτ, in %.

15. The coal-air synchronous dynamic coordinated control method for the coal-fired unit according to claim 1, wherein the target value W.sub.coal,new of the coal feed rate to be adjusted and the target value O.sub.2,new of the operation wet-basis oxygen content to be adjusted are respectively:
W.sub.coal,new=W.sub.coal,act+ΔW.sub.coal,
O.sub.2,new=O.sub.2,act+ΔO.sub.2, where, W.sub.coal,new is target value of the coal feed rate to be adjusted, in t/h, W.sub.coal,act is actual coal feed rate under the current unit load L.sub.τ, in t/h, ΔW.sub.coal is coal feed rate variation within the time Δτ, in t/h, O.sub.2,new is target value of the operation wet-basis oxygen content to be adjusted, in %, O.sub.2,act is actual operation wet-basis oxygen content, in %, ΔO.sub.2 is operation wet-basis oxygen content variation within the time Δτ, in %.

Description

BRIEF DESCRIPTION

[0022] Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein:

[0023] FIG. 1 is a logic block diagram of a traditional series air-coal sequence coordinated control; and

[0024] FIG. 2 is a logic block diagram of a coal-air synchronous dynamic coordinated control in an embodiment.

DETAILED DESCRIPTION

[0025] The technical solutions of the present disclosure are explained clearly and completely below in conjunction with the accompanying drawings, and apparently, the described embodiments are merely a part of the embodiments of the present disclosure, not all the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by one of ordinary skill in the art without creative work fall within the protective scope of the present disclosure.

[0026] As shown in FIG. 2, a coal-air synchronous dynamic coordinated control method for a coal-fired unit can calculate the combustion-supporting dry air volume and the wet flue gas volume online in real time, obtain the target value of the coal feed rate to be adjusted and the target value of the operation wet-basis oxygen content to be adjusted according to the instruction change of the unit load, and simultaneously set the adjustments of the coal feed rate and the operation wet-basis oxygen content in the same proportion. It comprises the following steps in sequence:

[0027] S1: in a steady-state operation mode of the unit, acquiring designed coal feed rates and designed flue gas operation wet-basis oxygen contents under different loads, and then determining: a polyline function of the designed coal feed rates W.sub.coal,b with the unit load L as an independent variable, and a polyline function of the designed flue gas operation wet-basis oxygen contents O.sub.2,b, with the unit load L as an independent variable:

W.sub.coal,b=f(L,Q.sub.net,b),

O.sub.2,b=g(L),

where,
L is unit load, in MW,
W.sub.coal,b is designed coal feed rate, in t/h,
Q.sub.net,b is designed low calorific value of coal, in MJ/kg,
O.sub.2,b, is designed flue gas operation wet-basis oxygen content, in %.

[0028] S2: using the regression analysis method, obtaining a regression function of a theoretical wet flue gas volume W.sub.flue,th,wet per unit mass of burning coal and a theoretical combustion-supporting dry air volume W.sub.air,th,dry per unit mass of burning coal based on the low calorific value by fitting the elemental analysis data and industrial analysis data of multiple existing sets of coal samples from utility boilers, judging the accuracy of the regression function by variance, if the variance is greater than 0.9, it indicates that the accuracy of the fitting is high, and then calculating an actual combustion-supporting dry air volume W.sub.air,act per unit mass of burning coal, and according to air temperature, relative humidity and atmospheric pressure measured in real-time, calculating the air saturated vapor pressure P.sub.H.sub.2.sub.O and a water vapor volume proportion φ per unit volume of dry air, and then calculating an actual combustion-supporting wet air volume W.sub.air,act,wet per unit mass of burning coal and an actually produced wet flue gas volume W.sub.flue,act,wet per unit mass of burning coal:

[00001]$W_{\mathrm{flue},\mathrm{th}}={\alpha }_1\times Q_{\mathrm{net}}+{\beta }_1,$$W_{\mathrm{air},\mathrm{th}}={\alpha }_2\times Q_{\mathrm{net}}+{\beta }_2,$$W_{\mathrm{air},\mathrm{act},\mathrm{dry}}=W_{\mathrm{flue},\mathrm{th},\mathrm{wet}}\times \frac{O_2}{21-O_2\times \left(1-\phi \right)}+W_{\mathrm{air},\mathrm{th},\mathrm{dry}}\times \frac{O_2}{21-O_2\times \left(1+\phi \right)},$$P_{H_{2}O}=611.7927+42.7809\times T_{\mathrm{air}}+1.6883\times T_{\mathrm{air}}^2+0.012079\times T_{\mathrm{air}}^3+0.00061637\times T_{\mathrm{air}}^4,$$\phi =0.3866\times \left(\varphi \times P_{\mathrm{air}}/100\right)\left(P_{\mathrm{atm}}-\varphi \times P_{\mathrm{air}}/100\right),$$W_{\mathrm{air},\mathrm{act},\mathrm{wet}}=W_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times \left(1+\phi \right),$$W_{\mathrm{flue},\mathrm{act},\mathrm{wet}}=W_{\mathrm{flue},\mathrm{th},\mathrm{wet}}\times \frac{21}{21-O_2\times \left(1+\phi \right)}+W_{\mathrm{air},\mathrm{th},\mathrm{dry}}\times \frac{21\times \phi }{21-O_2\times \left(1+\phi \right)},$

where,
W.sub.flue,th,wet is theoretical wet flue gas volume per unit mass of burning coal, in m.sup.3/kg,
W.sub.air,th,dry is theoretical combustion-supporting dry air volume per unit mass of burning coal, in m.sup.3/kg,
W.sub.air,act,dry is actual combustion-supporting dry air volume per unit mass of burning coal, in m.sup.3/kg,
W.sub.flue,act,wet is wet flue gas volume produced by the wet basis of per unit mass of burning coal, in m.sup.3/kg,
Q.sub.net is low calorific value of coal, in MJ/kg,
O.sub.2 is flue gas operation wet-basis oxygen content, in %,
α.sub.1, α.sub.2, β.sub.1, β.sub.2 are all constants, and are 0.2467, 0.2496, 0.718, 0.3125, respectively,
P.sub.H.sub.2.sub.O, is air saturated vapor pressure, in Pa,
T.sub.air is air temperature, in ° C.,
Φ is air relative humidity, in %,
P.sub.atm is atmospheric pressure, in Pa,
φ is water vapor volume proportion per unit volume of dry air.

[0029] S3: according to the results of industrial analysis (received base ashes, received base water, low calorific values) and elemental analysis (carbon, hydrogen, oxygen, nitrogen, sulfur), obtaining design values of the required combustion-supporting dry air volume W.sub.air,b and design values of the produced wet flue gas volume W.sub.flue,b for the total burning coal per hour under different loads;

[0030] calculating predicted values of the required combustion-supporting dry air volume W.sub.air,h and predicted values of the produced wet flue gas volume W.sub.flue,h for the total burning coal per hour under the designed wet-basis oxygen contents of different loads:

W.sub.air,h=W.sub.air,act,dry×W.sub.coal,b×(1−γ)×1000,

W.sub.flue,h=W.sub.flue,act,wet×W.sub.coal,b×(1−γ)×1000,

where,
W.sub.air,h is predicted value of the required combustion-supporting dry air volume for the total burning coal per hour, in m.sup.3/h,
W.sub.flue,h is predicted value of the produced wet flue gas volume for the total burning coal per hour, in m.sup.3/h,
W.sub.air,act,dry is actual combustion-supporting dry air volume per unit mass of burning coal, in m.sup.3/kg,
W.sub.flue,act,wet is predicted value of the theoretical wet flue gas volume per unit mass of burning coal, in m.sup.3/kg,
W.sub.coal,b is designed coal feed rate, in t/h,
γ is incomplete combustion heat loss ratio of feed coal, and its value is 0.42%.

[0031] Calculating the relative deviation δ.sub.1 between the predicted values W.sub.air,h and design values W.sub.air,b of the required combustion-supporting dry air volume for the total burning coal per hour under different loads, and the relative deviation δ.sub.2 between the predicted values W.sub.flue,h and design values W.sub.flue,b of the produced wet flue gas volume for the total burning coal per hour under different loads, if the relative deviations δ.sub.1 and δ.sub.2 are both within −5%˜+5%, the fitting deviations are within the acceptable range:

[00002]${\delta }_1=\frac{W_{\mathrm{air},h}-W_{\mathrm{air},b}}{W_{\mathrm{air},b}}\times 100\%,$${\delta }_2=\frac{W_{\mathrm{flue},h}-W_{\mathrm{flue},b}}{W_{\mathrm{flue},b}}\times 100\%,$

where,
W.sub.air,h is predicted value of the required combustion-supporting dry air volume for the total burning coal per hour, in m.sup.3/h,
W.sub.flue,h is predicted value of the produced wet flue gas volume for the total burning coal per hour, in m.sup.3/h,
W.sub.air,b is design value of the required combustion-supporting dry air volume for the total burning coal per hour, in m.sup.3/h,
W.sub.flue,b is Design Value of the Produced Wet Flue Gas Volume for the Total Burning Coal Per Hour, in m.sup.3/h.

[0032] S4: acquiring the current load L.sub.i and the actual coal feed rate W.sub.coal,act displayed by the DCS system of the unit, calculating a designed coal feed rate W.sub.coal,b,τ under the current unit load L.sub.τ through the corresponding functional relationship between the unit loads L and the designed coal feed rates W.sub.coal,b, and calculating an actual low calorific value Q.sub.net,act of feed coal;

[00003]$Q_{\mathrm{net},\mathrm{act}}=\frac{W_{\mathrm{coal},b,\tau }\times Q_{\mathrm{net},b}}{W_{\mathrm{coal},\mathrm{act}}},$

where,
Q.sub.net,act is actual low calorific value of feed coal, in MJ/kg,
Q.sub.net,b is designed low calorific value of feed coal, in MJ/kg,
W.sub.coal,act is actual coal feed rate under the current unit load L.sub.τ, in t/h,
W.sub.coal,b,τ is designed coal feed rate under the current unit load L.sub.τ, in t/h.

[0033] S5: according to the actual coal feed rate W.sub.coal,act, the actual operation wet-basis oxygen content O.sub.2,act and the actual low calorific value of feed coal Q.sub.net,act displayed by the DCS system of the unit, calculating a combustion-supporting dry air volume BW air,act,dry and a combustion-supporting wet air volume BW.sub.air,act,wet entering the boiler, and the wet flue gas volume BW.sub.flue,act,wet at the outlet of a boiler economizer under the actual unit load L.sub.τ:

[00004]${\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{dry}}=\left(W_{\mathrm{flue},\mathrm{th},\mathrm{wet}}\times \frac{O_{2,\mathrm{act}}}{21-O_{2,\mathrm{act}}\times \left(1+\phi \right)}+W_{\mathrm{air},\mathrm{th},\mathrm{dry}}\times \frac{21-O_{2,\mathrm{act}}}{21-O_{2,\mathrm{act}}\times \left(1+\phi \right)}\right)\times W_{\mathrm{coal},\mathrm{act}}\times 1000,$${\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{wet}}={\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times \left(1+\phi \right),$${\mathrm{BW}}_{\mathrm{flue},\mathrm{act},\mathrm{wet}}=\left(W_{\mathrm{flue},\mathrm{th},\mathrm{wet}}\times \frac{21}{21-O_{2,\mathrm{act}}\times \left(1+\phi \right)}+W_{\mathrm{air},\mathrm{th},\mathrm{dry}}\times \frac{21\times \phi }{21-O_{2,\mathrm{act}}\times \left(1+\phi \right)}\right)\times W_{\mathrm{coal},\mathrm{act}}\times 1000,$

where,
BW.sub.air,act,dry is combustion-supporting dry air volume, in m.sup.3/h,
BW.sub.air,act,wet is combustion-supporting wet air volume, in m.sup.3/h,
BW.sub.flue,act,wet is outlet wet flue gas volume, in m.sup.3/h,
W.sub.air,th,dry is theoretical combustion-supporting dry air volume per unit mass of burning coal, in m.sup.3/kg,
W.sub.flue,th,wet is theoretical wet flue gas volume per unit mass of burning coal, in m.sup.3/kg,
O.sub.2,act is actual flue gas operation wet-basis oxygen content, in %,
φ is water vapor volume proportion per unit volume of dry air,
W.sub.coal,act is actual coal feed rate under the current unit load L.sub.τ, in t/h,

[0034] S6: according to a load instruction curve of the unit set in advance by the power grid dispatch center, determining the target value of a load instruction at a future time point Δτ, and calculating a unit load change rate E.sub.L within the time Δτ, calculating the coal feed rate W.sub.coal,τ+Δτ at the future time point Δτ and calculating a coal feed rate variation ΔW.sub.coal within the time Δτ, and then calculating a combustion-supporting dry air volume variation ΔBW.sub.air,act and a combustion-supporting wet air volume variation ΔBW.sub.air,act,wet within the time Δτ:

[00005]$E_L=\frac{L_{\tau +\Delta \tau }-L_{\tau }}{L_{\tau }}\times 100,$$W_{\mathrm{coal},\tau +\Delta \tau }=W_{\mathrm{coal},\mathrm{act}}\times \left(1+\frac{E_L}{100}\right),$$\Delta W_{\mathrm{coal}}=W_{\mathrm{coal},\tau +\Delta \tau }-W_{\mathrm{coal},\mathrm{act}},$$\Delta {\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{dry}}=W_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times \Delta W_{\mathrm{coal}}\times 1000,$$\Delta {\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{wet}}=\Delta {\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times \left(1+\phi \right),$

where,
E.sub.L is unit load change rate within the time Δτ, in %,
L.sub.τ is current unit load, in MW,
L.sub.τ+Δτ is unit load after the time Δτ, in MW,
W.sub.coal,τ+Δτ is coal feed rate at the future time point Δτ, in t/h,
W.sub.coal,act is actual coal feed rate under the current unit load L.sub.τ, in t/h,
ΔW.sub.coal is coal feed rate variation within the time Δτ, in t/h,
ΔBW.sub.air,act,dry is combustion-supporting dry air volume variation within the time Δτ, in m.sup.3/h,
ΔBW.sub.air,act,wet is combustion-supporting wet air volume variation within the time Δτ, in m.sup.3/h,
W.sub.air,act,dry is actual combustion-supporting dry air volume per unit mass of coal, in m.sup.3/kg,
φ is water vapor volume proportion per unit volume of dry air.

[0035] S7: according to the combustion-supporting dry air volume variation ΔBW.sub.air,act,dry converting an operation wet-basis oxygen content variation ΔO.sub.2,1 caused by the change of the combustion-supporting dry air volume, and according to the corresponding functional relationship between the unit loads L and the designed flue gas operation wet-basis oxygen contents O.sub.2,b, obtaining the flue gas operation wet-basis oxygen content O.sub.2,b,τ at the future time point Δτ, and calculating a set wet-basis oxygen content variation ΔO.sub.2,2 within the time Δτ, and then calculating an operation wet-basis oxygen content variation ΔO.sub.2 within the time Δτ;

[00006]$\Delta O_{2,1}=\frac{\Delta {\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{dry}}\times 21}{{\mathrm{BW}}_{\mathrm{flue},\mathrm{act},\mathrm{wet}}+\Delta {\mathrm{BW}}_{\mathrm{air},\mathrm{act},\mathrm{wet}}},$$\Delta O_{2,2}=O_{2,b,\tau }-O_{2,\mathrm{act}},$$\Delta O_2=\Delta O_{2,1}+\Delta O_{2,2},$

where,
ΔO.sub.2,1 is operation wet-basis oxygen content variation caused by the change of the combustion-supporting dry air volume, in %, ΔBW.sub.air,act,dry is combustion-supporting dry air volume variation within the time Δτ, in m.sup.3/h, ΔBW.sub.air,act,wet is combustion-supporting wet air volume variation within the time Δτ, in m.sup.3/h,
BW.sub.flue,act is outlet wet flue gas volume, in m.sup.3/h,
ΔO.sub.2,2 is set wet-basis oxygen content variation within the time Δτ, in %,
O.sub.2,b,τ is flue gas operation wet-basis oxygen content at the future time point Δτ, in %,
O.sub.2,act is actual operation wet-basis oxygen content, in %,
ΔO.sub.2 is operation wet-basis oxygen content variation within the time Δτ, in %.

[0036] S8: on the basis of the coal feed rate instruction and the operation wet-basis oxygen content instruction of the original DCS sequence control logic of the unit, respectively superimposing the coal feed rate variation ΔW.sub.coal and the operation wet-basis oxygen content variation ΔO.sub.2 simultaneously in advance to obtain a target value W.sub.coal,new of the coal feed rate to be adjusted and a target value O.sub.2,new of the operation wet-basis oxygen content to be adjusted:

W.sub.coal,new=W.sub.coal,act+ΔW.sub.coal,

O.sub.2,new=O.sub.2,act+ΔO.sub.2,

where,
W.sub.coal,new is target value of the coal feed rate to be adjusted, in t/h,
W.sub.coal,act is actual coal feed rate under the current unit load L.sub.τ, in t/h,
ΔW.sub.coal is coal feed rate variation within the time Δτ, in t/h,
O.sub.2,new is target value of the operation wet-basis oxygen content to be adjusted, in %, O.sub.2,act is actual operation wet-basis oxygen content, in %,
ΔO.sub.2 is operation wet-basis oxygen content variation within the time Δτ, in %.

[0037] Specific embodiments are given below for detailed explanation:

[0038] A unit of 350 MW was selected, and the calculation of the target value of the coal feed rate to be adjusted and the target value of the wet-basis oxygen content to be adjusted within 30 seconds when the current unit load was 300 MW, comprised the following steps:

[0039] S1: In a steady-state operation mode of the unit, the designed coal feed rates and flue gas operation wet-basis oxygen contents under the loads of 367.5 MW, 350 MW, 367.5 MW, 175 MW, and 87.5 MW were acquired, and the designed low calorific value of coal Q.sub.net,b was 21.652 MJ/kg, as shown in Table 1. Then the specific functional relationship between the unit loads L and the designed coal feed rates W.sub.coal,b was:

W.sub.coal,bk×L+b,

where,
L is unit load, in MW;
W.sub.coal,b is designed coal feed rate, in t/h;
k and b are both constants, and are 0.3545 and 9.7697, respectively,

TABLE-US-00001 TABLE 1 Coal feed rates and flue gas operation wet- basis oxygen contents under different loads Items Units Numeral values Load rate % 105 100 75 50 25 Unit load L MW 367.5 350 267.5 175 87.5 Designed flue gas % 3.6 3.6 3.6 4.5 6.8 operation wet-basis oxygen content O.sub.2, b Designed coal feed t/h 139.23 135.38 103.39 72.36 40.75 rate W.sub.coal, b

[0040] S2: It was known that the wet-basis oxygen content O.sub.2,b was 3.6%, the designed low calorific value of coal feed Q.sub.net,b was 21.652 MJ/kg, then it can be calculated that W.sub.flue,th,wet=6.059548 m.sup.3/kg and W.sub.air,th,dry=5.716839 m.sup.3/kg, and by fitting the elemental analysis data and industrial analysis data of more than 500 sets of coal samples from utility boilers, the variances of the theoretical wet flue gas volume W.sub.flue,th,wet per unit mass of burning coal and the theoretical combustion-supporting dry air volume W.sub.air,th,dry per unit mass of burning coal were respectively 0.9763 and 0.9858, both of which were greater than 0.9, therefore the accuracy of the fitting was high, and the actual combustion-supporting dry air volume per unit mass of burning coal were calculated to be W.sub.air,act,wet=6.97741 m.sup.3/kg. The designed air temperature was 20° C., the relative humidity was 55%, the atmospheric pressure was 101000 Pa, and the water vapor proportion in unit volume of dry air was calculated to be φ=0.00499.

[0041] S3: When the unit load was 367.5 MW, according to the results of industrial analysis and elemental analysis, the design value W.sub.air,b of the required combustion-supporting dry air volume for the total burning coal per hour under the unit load of 367.5 MW was 952746 m.sup.3/h, and the design value W.sub.flue,b of the produced wet flue gas volume was 1030231 m.sup.3/h; it was known that the designed coal feed rate W.sub.coal,b was 139.23 t/h, then the predicted value of the required combustion-supporting dry air volume for the total burning coal per hour was W.sub.air,h=6.97741×139.23×(1-0.42%)×1000=967385 m.sup.3/h, and the predicted value of the produced wet flue gas volume for the total burning coal per hour was W.sub.flue,h=7.3552×139.23×(1-0.42%)×1000=1019768 m.sup.3/h; the relative deviation of the combustion-supporting dry air volume was

[00007]${\delta }_1=\frac{\left(967385-952746\right)}{952746}\times 100\%=1.54\%,$

and the relative deviation of the produced wet flue gas volume was

[00008]${\delta }_2=\frac{\left(1019768-1030231\right)}{91030231}\times 100\%=-1.02\%.$

[0042] The calculation process under other loads was the same as that under the load of 367.5 MW, and will not be repeated here. The specific calculation results are shown in Table 2.

[0043] According to the calculation results in Table 2, it can be seen that the relative deviations between the predicted values W.sub.air,h and design values W.sub.air,b of the required combustion-supporting dry air volume for the total burning coal per hour under different loads were 1.54%˜2.61%, the relative deviations between the predicted values W.sub.flue,h and design values W.sub.flue,b of the produced wet flue gas volume were −0.1.02%˜+0.63%, and the relative deviations were all between −5% and 5%, so it can be judged that the fitting deviation was within the acceptable range.

TABLE-US-00002 TABLE 2 Predicted values and design values of the required combustion-supporting dry air volume and the produced wet flue gas volume for the total burning coal per hour Items Units Numeral values Unit load L MW 367.5 350 267.5 175 87.5 Design value of the required m.sup.3/h 952746 926373 707502 524053 341609 combustion-supporting dry air volume for the total burning coal per hour W.sub.air, b Predicted value of the required m.sup.3/h 967385 940635 718365 531706 350539 combustion-supporting dry air volume for the total burning coal per hour W.sub.air, h Relative deviation δ.sub.1 % 1.54 1.54 1.54 1.46 2.61 Design value of the produced m.sup.3/h 1030231 1001769 765077 564154 363923 flue gas volume for the total burning coal per hour W.sub.flue, b Predicted value of the produced m.sup.3/h 1019768 991569 757264 559082 366224 flue gas volume for the total burning coal per hour W.sub.flue, h Relative deviation δ.sub.2 % −1.02 −1.02 −1.02 −0.90 0.63

[0044] S4: When the current unit load L.sub.τ was 300 MW, the actual coal feed rate W.sub.coal,act displayed by the DCS system of the unit was 121.5 t/h, and through the corresponding functional relationship between the unit loads L and the designed coal feed rates W.sub.coal,b, the designed coal feed rate under the current unit load of 300 MW was calculated to be W.sub.coal,b,τ=0.3545×300+9.769=116.12 t/h, then the actual low calorific value of feed coal was calculated to be

[00009]$Q_{\mathrm{net},\mathrm{act}}=\frac{116.12\times 21.652}{121.5}=20.693\mathrm{MJ}/\mathrm{Kg}.$

[0045] S5: When the current unit load L.sub.τ was 300 MW, the actual operation wet-basis oxygen content O.sub.2,act was 3.2%, then the combustion-supporting dry air volume entering the boiler can be calculated to be:

[00010]$B{W}_{air,a\mathrm{ct},\mathrm{dry}}=\left(\left(0.2496\times 20.693+0.3125\right)\times \frac{21-3.2}{21-3.2\times \left(1+0.00499\right)}+\left(0.2467\times 20.693+0.718\right)\times \frac{3.2}{21-3.2\times \left(1+0.00499\right)}\right)\times 121.5\times 1000=793414m^3/h,$

[0046] the wet flue gas volume at the outlet of the boiler economizer was calculated to be:

[00011]$B{W}_{\mathrm{flue},\mathrm{act},\mathrm{wet}}=\left(\left(0.2467\times 20.693+0.718\right)\times \frac{21}{21-3.2\times \left(1+0.00499\right)}+\left(0.2496\times 20.693+0.3125\right)\times \frac{21\times 0.00499}{21-3.2\times \left(1+0.00499\right)}\right)\times 121.5\times 1000=839350m^3/h.$

[0047] S6: The current time was 13:15:00, the current unit load displayed by the DCS system of the unit L.sub.τ was 300 MW, and according to the load instruction curve of the unit set in advance by the power grid dispatch center, the unit load L.sub.τ+Δτ after 30 seconds was 303.85 MW or 295.765 MW,

[0048] therefore, the unit load change rate within 30 seconds was calculated to be

[00012]$E_L=\frac{303.85-300}{300}\times 100=1.283\%\mathrm{or}$$E_L=\frac{295.765-300}{300}\times 100=-1.412\%,$

[0049] the coal feed rate after 30 seconds was calculated to be

[00013]$W_{\mathrm{coal},\tau +\Delta \tau }=121.5\times \left(1+\frac{1.283}{100}\right)=123.059t/h\mathrm{or}$$W_{\mathrm{coal},\tau +\Delta \tau }=121.5\times \left(1+\frac{-1.412}{100}\right)=119.784t/h,$

[0050] and the coal feed rate variation within 30 seconds was calculated to be ΔW.sub.coal=123.059−121.5=1.559 t/h or ΔW.sub.coal=119.784-121.5=−1.716 t/h,

[0051] then the combustion-supporting dry air volume variation within 30 seconds was calculated to be

[00014]$\Delta B{W}_{air,a\mathrm{ct},\mathrm{dry}}=\left(\left(0.2496\times 20.693+0.3125\right)\times \frac{21-3.2}{21-3.2\times \left(1+0.00499\right)}+\left(0.2467\times 20.693+0.718\right)\times \frac{3.2}{21-3.2\times \left(1+0.00499\right)}\right)\times 1.559\times 1000=10180m^3/h\mathrm{or}\Delta {\mathrm{BW}}_{air,a\mathrm{ct},\mathrm{dry}}=\left(\left(0.2496\times 20.693+0.3125\right)\times \frac{21-3.2}{21-3.2\times \left(1+0.00499\right)}+\left(0.2467\times 20.693+0.718\right)\times \frac{3.2}{21-3.2\times \left(1+0.00499\right)}\right)\times \left(-1.716\right)\times 1000=-11205m^3/h.$

[0052] S7: According to the combustion-supporting dry air volume variation ΔBW.sub.air,act,dry, air,act,dry, the operation wet-basis oxygen content variation caused by the change of the combustion-supporting dry air volume was converted to be

[00015]$\Delta O_{2,1}=\frac{10180\times 21}{839350+10180\times \left(1+0.00499\right)}=0.252\%\mathrm{or}$$\Delta O_{2,1}=\frac{-11205\times 21}{834350-11205\times \left(1+0.00499\right)}=-0.286\%,$

[0053] according to the corresponding functional relationship between the unit loads L and the designed flue gas operation wet-basis oxygen contents O.sub.2,b, the design value O.sub.2,b,τ of the flue gas operation wet-basis oxygen content after 30 seconds was 3.6%, and the set wet-basis oxygen content variation within 30 seconds was calculated to be ΔO.sub.2,2=3.6−3.2=0.40%, then the operation wet-basis oxygen content variation within 30 seconds was calculated to be ΔO.sub.2=0.252+0.40=0.652% or ΔO.sub.2=−0.286+0.40=0.114%.

[0054] S8: On the basis of the coal feed rate instruction and the operation wet-basis oxygen content instruction of the original sequence control logic of the unit, the coal feed rate variation and the operation wet-basis oxygen content variation were respectively superimposed simultaneously in advance to obtain the target value of the coal feed rate to be adjusted:

W.sub.coal,new=121.5+1.559=123.059 t/h or W.sub.coal,new=121.5−1.716=119.784 t/h

[0055] and the target value of the operation wet-basis oxygen content to be adjusted:

O.sub.2,new=3.2+0.652=3.852% or O.sub.2,new=3.2+0.114=3.314%.

[0056] According to the obtained the target value W.sub.coal,new=119.784 t/h of the coal feed rate to be adjusted and the target value O.sub.2,new=3.314% of the operation wet-basis oxygen content to be adjusted, the adjustments of the coal feed rate and the operation wet-basis oxygen content were simultaneously set in the same proportion.

[0057] Although the present invention has been disclosed in the form of embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0058] For the sake of clarity, it is to be understood that the use of ‘a’ or ‘an’ throughout this application does not exclude a plurality, and ‘comprising’ does not exclude other steps or elements.