CN103968415B - Flue gas recirculation Combustion System of Boiler Burning Fine and operating mode changing method thereof - Google Patents

Abstract

Flue gas recirculation Combustion System of Boiler Burning Fine and operating mode changing method thereof, belong to pulverized-coal fired boiler oxygen-enriched combusting and regulate and control method, solves pulverized-coal fired boiler from air burning to the adjustment difficult problem oxygen-enriched combusting operating mode handoff procedure.Combustion System of Boiler Burning Fine of the present invention, comprises feeder, burner, boiler, denitrator, air preheater, ash handling equipment, desulfurizer and air-introduced machine; Operating mode changing method of the present invention, comprises and arranges that checkout equipment, recycle valve and intake valve control, control pressure fan rate of discharge and control note oxygen amount step; The present invention is from the coherent detection point combustion system, obtain the running parameter of operating mode handoff procedure, circulating ratio is determined, with oxygen at furnace exit determination primary and secondary air note oxygen flow with flue gas recycled amount, make amount of circulating gas, air mass flow, the fluctuation of oxygen injection rate in handoff procedure in the reasonable scope, realize the switching from air burning to oxygen-enriched combusting operating mode safely and steadly, and maintain the CO in flue gas ₂concentration.

Description

Flue gas recirculation Combustion System of Boiler Burning Fine and operating mode changing method thereof

Technical field

The invention belongs to pulverized-coal fired boiler oxygen-enriched combusting to regulate and control method, be specifically related to a kind of flue gas recirculation Combustion System of Boiler Burning Fine and operating mode changing method thereof, be applicable to coal-burning boiler by air burning to the control in oxygen-enriched combusting operating mode handoff procedure.

Background technology

Carbon dioxide is the main cause causing global warning and extreme climate to take place frequently.The resources supplIes of " rich coal, weak breath, oil starvation " determines Chinese energy resource structure and is still using coal as main energy sources within the long duration from now on.2011, Chinese CO ₂discharge capacity 8241Mt, occupies first place in the world, and accounts for 24.6% of world's total release.In view of energy resource structure and the carbon emission reduction task of China, be badly in need of finding a kind of clean coal combustion technology reducing carbon emission.According to the United Nations's inter-governmental climate change committee (IPCC) report, carbon capture and Plugging Technology Applied (CCS) feasibility by force, effectively significantly can reduce greenhouse gas emission; According to another the prediction of international energy office (IEA), the electric power of the year two thousand fifty 90% will come from novel oxygen-enriched combusting power plant.

Collecting carbonic anhydride technology mainly contains three kinds of modes: catch after seizure, oxygen-enriched combustion technology and burning before burning.Before burning, trapping technique is mainly integral gasification combined circulation technology (IGCC); After burning, carbon trapping technique mainly contains amine method-MEA, cooling ammonia process etc.; Oxygen-enriched combustion technology is by O ₂with with CO ₂for the flue gas recycled of Main Ingredients and Appearance burns with certain proportion feeding burner hearth and fuel mix, because entering containing the nitrogen in traditional combustion mode in furnace atmosphere, the CO in flue gas ₂concentration can enrichment gradually, and after after burning, a flue gas part enters burner hearth and oxygen mix by flue gas in the mode of recirculation, for transfer the fuel with as burnt wind, another part enters CO after dedusting, condensation, drying ₂compression device, can realize Pollutant in Coal Burning Boiler and CO ₂near-zero release.Therefore, oxygen-enriched combustion technology has larger technical advantage and commercial viability, and its counter investment cost is low, can be used for the transformation of existing boiler, can apply again in new power plant construction.

Current Chinese scholars has carried out more detailed sunykatuib analysis to the Technological Economy of oxygen-enriched combustion system, but has no report based on the application study of oxygen-enriched combusting control system.The Ade of Korea S etc. adopt the predictive control algorithm of nonlinear model to set about from carbonated drink side and fume side, establish the Dynamic Mechanism Mathematical Modeling of oxygen-enriched combustion boiler, and done step disturbance simulation for oxygen quality flow, coal consumption amount, main steam mass flow etc., obtain the change curve (ComputersandChemicalEngineering of some state parameters under oxygen-enriched combusting condition, 2011,35:25 – 40.); The M.Pottmann of the U.S. has carried out the dynamic analog research of Rich Oxygen Combustion, has carried out discussing (EnergyProcedia, 2011,4:951 – 957.) to the design concept of simulation process and criterion, control strategy and optimization; Hispanic I.Guedea etc. have studied the control strategy of fluidized bed smoke cyclic process, by regulating the rotating speed controlled circulation flue gas flow of pressure fan, guarantee hearth combustion is stablized, set up feedback control strategy with this understanding, and carried out simulation and experimental study, its flue gas recirculation control strategy experimental study to oxygen-enriched combusting provides guidance (EnergyProcedia, 2011,4:972 – 979).

Because oxygen enrichment coal-burning boiler have employed brand-new technological process, the steady switching realized from air burning to oxygen-enriched combusting operating mode is a technical barrier.Above-mentioned research is in laboratory stage mostly, and actual air/oxygen-enriched combusting switchover operation condition depends on the rate of change of flue gas recycling rate and the coordination of air mass flow.

Summary of the invention

The invention provides a kind of flue gas recirculation Combustion System of Boiler Burning Fine, its operating mode changing method is provided simultaneously, solve pulverized-coal fired boiler from air burning to the adjustment difficult problem oxygen-enriched combusting operating mode handoff procedure, realize the mutual switching of air and oxygen-enriched combusting operating mode with making system stability, and maintain the CO in flue gas ₂concentration.

A kind of flue gas recirculation Combustion System of Boiler Burning Fine provided by the present invention, comprises the feeder, burner, boiler, denitrator, air preheater, ash handling equipment, desulfurizer and the air-introduced machine that connect successively, it is characterized in that:

Described air-introduced machine connects exhaust smoke valve entrance and recycle valve entrance respectively by pipeline, exhaust smoke valve outlet chimney, intake valve entrance is communicated with air, intake valve outlet is connected air blower inlet with recycle valve outlet by pipeline, pressure fan outlet connects air preheater air intake by pipeline simultaneously, First air stop valve entrance and the outlet of Secondary Air stop valve, the outlet of First air stop valve connects primary air fan entrance, primary air fan outlet connects feeder outlet and burner inlet by primary air duct, first oxygen filling container connects described primary air duct by the first note oxygen valve, air preheater air outlet slit and Secondary Air stop valve entrance connecting secondary air pipe line, Secondary Air pipeline connects burner Secondary Air entrance, and the second oxygen filling container connects described Secondary Air pipeline by the second note oxygen valve.

Air and flue gas recycled enter from intake valve and recycle valve respectively, two-way is divided into: a route air preheater heating is as Secondary Air after pressure fan, another road is through the outlet of Secondary Air stop valve and the mixing of First air stop valve entrance, through primary air fan and feeder, boiler combustion is sent into by burner after being mixed by coal dust, flue gas, through denitrator, air preheater, ash handling equipment, desulfurizer, is entered chimney through air-introduced machine by flue gas.

The operating mode changing method of described flue gas recirculation Combustion System of Boiler Burning Fine, comprises and arranges checkout equipment step, recycle valve and intake valve rate-determining steps, controls pressure fan rate of discharge step and control note oxygen amount step, it is characterized in that:

(1) checkout equipment step is arranged:

In air-introduced machine outlet, recycle valve outlet, pressure fan outlet, measuring point is set respectively, measures pressure, temperature and flow;

Measuring point is set in the outlet of the first note oxygen valve outlet port, the second note oxygen valve outlet port and boiler furnace back-end ductwork, measures oxygen amount;

(2) recycle valve and intake valve rate-determining steps, comprises following sub-step:

(2.1). calculate the standard volume flow of set measuring point

$V_i^n=\frac{P_i^n}{1.01\×{10}^5}\×\frac{273.15}{T_i^n+273.15}\×Q_i^n,$

In formula, be respectively the pressure of measuring point, temperature, flow, obtained by field measurement; I=1,2,3; I=1 is air-introduced machine outlet, and i=2 is recycle valve outlet, and i=3 is pressure fan outlet; N controls number of times for switching;

(2.2). calculate the circulating ratio η of flue gas after switching for n-th time ⁿwith circulating ratio rate of change Δ η ⁿ:

Calculate the circulating ratio η of flue gas after switching for n-th time ⁿ:

When switching to oxygen-enriched combusting from air, open recycle valve gradually, close intake valve gradually, in handoff procedure, control the circulating ratio rate of change Δ η of flue gas ⁿ: 0< Δ η ⁿ<0.8%/min, wherein,

${\mathrm{\&Delta;\&eta;}}^n=\frac{|{\mathrm{\&eta;}}^n-{\mathrm{\&eta;}}^{n-1}|}{{\mathrm{\&eta;}}^n}\&times;100\%,$

Circulating ratio η after having switched ⁿcontrol 0.6 ~ 0.8;

(3) pressure fan rate of discharge step is controlled:

Calculate pressure fan rate of discharge rate of change

${\mathrm{\&Delta;\&delta;}}_3^n=\frac{V_3^n-V_3^{n-1}}{V_3^n},$

In formula, it is the standard volume flow of pressure fan outlet after switching for n-th time; it is the standard volume flow of pressure fan outlet after switching for (n-1)th time;

In handoff procedure, be mixed into air blower inlet gas by circulating flue gas and air, make pressure fan rate of discharge rate of change until handoff procedure completes;

(4) note oxygen amount step is controlled:

Calculate and switch rear hearth outlet oxygen amount rate of change for n-th time

$A_0^n=\underset{j1=1}{\overset{m/2}{\&Sigma;}}{U}^u\left(j1\right)-\underset{j2=m/2+1}{\overset{m}{\&Sigma;}}{U}^n\left(j2\right),$

In formula, m is the total sampling number of oxygen amount in furnace outlet flue gas, is even number; U ⁿ(j1), U ⁿ(j2) be switch first, post-sampling oxygen amount in rear hearth exiting flue gas for n-th time, obtained by field measurement; J1, j2 are respectively first, post-sampling number of times;

According to the oxygen determination value after oxygen at furnace exit rate of change and primary and secondary air note oxygen, regulate the required oxygen flow injected: oxygen at furnace exit rate of change the oxygen content control of First air oxygen is 18% ~ 21%, and after Secondary Air note oxygen, oxygen content control is 35% ~ 40%.

The present invention can ensure unit safety, stably realize the mutual switching of air and oxygen-enriched combusting operating mode, and maintains the CO in flue gas ₂concentration, the burning realizing flue gas recirculation Combustion System of Boiler Burning Fine switches control.

At pulverized coal firing boiler by air burning in oxygen-enriched combusting handoff procedure, often open recycle valve, close intake valve once, be called and once switch; The present invention, from the measuring point be arranged in combustion system, obtains the Parameters variation data from air to oxygen-enriched combusting handoff procedure, mainly through the adjustment of recycle valve and air inlet valve, controls flue gas recycled amount, obtains the circulating ratio of flue gas recycled; By theoretical and experimental study, the flue gas recycling rate and rate of change, pressure fan rate of discharge rate of change and oxygen at furnace exit rate of change that switch operating mode are controlled in the scope of setting, if circulating ratio η ⁿlower than 0.6, carbon dioxide in flue gas concentration enrichment amount can reduce, and circulating ratio is higher than 0.8, and the inleakage of system increases, and is also unfavorable for the enrichment of carbon dioxide; The rate of change of circulating ratio is too large, and in handoff procedure, burner hearth parameter fluctuation becomes large, causes unstable combustion.By great many of experiments, the disturbance of pressure fan rate of discharge need control at 5%/min as the change of best, too high air flow rate makes air preheater heat exchange inharmonious with note oxygen amount; Meanwhile, the rate of change of oxygen at furnace exit in handoff procedure too high or too low, note oxygen amount is accelerated or the minimizing of oxygen injection rate, fuel combustion all can be made incomplete; First air oxygen content control is 18% ~ 21%, and can meet entrained coal dust can fully catch fire; By Secondary Air oxygen content control 35% ~ 40%, burning of coal dust can be kept.

Accompanying drawing explanation

Fig. 1. the embodiment schematic diagram of flue gas recirculation Combustion System of Boiler Burning Fine of the present invention;

Fig. 2. flue gas recirculation coal powder boiler combustion changing method schematic flow sheet of the present invention.

Detailed description of the invention

Below in conjunction with drawings and Examples, the present invention is further described.

An embodiment of flue gas recirculation Combustion System of Boiler Burning Fine of the present invention, as shown in Figure 1, comprises the feeder GM, burner RSQ, boiler GL, denitrator TX, air preheater KY, ash handling equipment CH, desulfurizer TL and the air-introduced machine YF that connect successively;

Described air-introduced machine YF connects exhaust smoke valve H1 entrance and recycle valve H3 entrance respectively by pipeline, exhaust smoke valve H1 outlet chimney YC, intake valve H2 entrance is communicated with air KQ, intake valve H2 exports and is connected pressure fan SF entrance with recycle valve H3 outlet by pipeline, pressure fan SF outlet connects air preheater KY air intake by pipeline simultaneously, First air stop valve H5 entrance and Secondary Air stop valve H4 export, First air stop valve H5 exports and connects primary air fan FG entrance, primary air fan FG exports and connects feeder GM outlet and burner RSQ entrance by primary air duct, first oxygen filling container ZY1 connects described primary air duct by the first note oxygen valve H7, air preheater KY air outlet slit and Secondary Air stop valve H4 entrance connecting secondary air pipe line, Secondary Air pipeline connects burner RSQ Secondary Air entrance, and the second oxygen filling container ZY2 connects described Secondary Air pipeline by the second note oxygen valve H6.

The embodiment one of operating mode changing method, as shown in Figure 2, comprises and arranges checkout equipment step, recycle valve and intake valve rate-determining steps, controls pressure fan rate of discharge step and control note oxygen amount step:

(1) checkout equipment step is arranged:

Air-introduced machine YF export 1., recycle valve H3 export 2., pressure fan SF outlet 3. measuring point is set respectively, measure pressure, temperature and flow;

First note oxygen valve H7 export 5., second note oxygen valve H6 export 4. with boiler GL burner hearth back-end ductwork outlet 6. measuring point is set, measure oxygen amount;

(2) recycle valve and intake valve rate-determining steps, comprises following sub-step:

(2.1). calculate the standard volume flow of set measuring point

$V_i^{60}=\frac{P_i^{60}}{1.01\&times;{10}^5}\&times;\frac{273.15}{T_i^{60}+273.15}\&times;Q_i^{60},$

In formula, be respectively the pressure of measuring point, temperature, flow, obtained by field measurement; I=1,2,3; I=1 is air-introduced machine outlet, and i=2 is recycle valve outlet, and i=3 is pressure fan outlet;

(2.2). calculate the circulating ratio η of flue gas after switching for the 60th time ⁶⁰with circulating ratio rate of change Δ η ⁶⁰:

Calculate the circulating ratio η of flue gas after switching for the 60th time ⁶⁰:

When switching to oxygen-enriched combusting from air, open recycle valve gradually, close intake valve gradually, in handoff procedure, control the circulating ratio rate of change Δ η of flue gas ⁶⁰: Δ η ⁶⁰=0.5%/min, the circulating ratio η after having switched ⁶⁰be 0.72;

(3) pressure fan rate of discharge step is controlled:

Calculate pressure fan rate of discharge rate of change

${\mathrm{\&Delta;\&delta;}}_3^{59}=\frac{V_3^{60}-V_3^{59}}{V_3^{60}},$

In formula, it is the standard volume flow of pressure fan outlet after switching for the 60th time; it is the standard volume flow of pressure fan outlet after switching for the 59th time;

In handoff procedure, be mixed into air blower inlet gas by circulating flue gas and air, make pressure fan rate of discharge rate of change until handoff procedure completes;

(4) note oxygen amount step is controlled:

Calculate and switch rear hearth outlet oxygen amount rate of change for the 60th time

$A_0^{60}=\underset{j1=1}{\overset{m/2}{\&Sigma;}}{U}^{60}\left(j1\right)-\underset{j2=m/2+1}{\overset{m}{\&Sigma;}}{U}^{60}\left(j2\right),$

In formula, m is the total sampling number of oxygen amount in furnace outlet flue gas, is even number, m=7200; U ⁶⁰(j1), U ⁶⁰(j2) be switch first, post-sampling oxygen amount in rear hearth exiting flue gas for the 60th time, obtained by field measurement; J1, j2 are respectively first, post-sampling number of times, j1=3600, j2=3600;

According to the oxygen determination value after oxygen at furnace exit rate of change and primary and secondary air note oxygen, regulate the required oxygen flow injected: oxygen at furnace exit rate of change the oxygen content control of First air oxygen after 20.5% Secondary Air note oxygen oxygen content control 38%.

The embodiment two of operating mode changing method, as shown in Figure 2, comprises and arranges checkout equipment step, recycle valve and intake valve rate-determining steps, controls pressure fan rate of discharge step and control note oxygen amount step:

(1) checkout equipment step is arranged:

Air-introduced machine YF export 1., recycle valve H3 export 2., pressure fan SF outlet 3. measuring point is set respectively, measure pressure, temperature and flow;

First note oxygen valve H7 export 5., second note oxygen valve H6 export 4. with boiler GL burner hearth back-end ductwork outlet 6. measuring point is set, measure oxygen amount;

(2) recycle valve and intake valve rate-determining steps, comprises following sub-step:

(2.1). calculate the standard volume flow of set measuring point

$V_i^{25}=\frac{P_i^{25}}{1.01\&times;{10}^5}\&times;\frac{273.15}{T_i^{25}+273.15}\&times;Q_i^{25},$

In formula, be respectively the pressure of measuring point, temperature, flow, obtained by field measurement; I=1,2,3; I=1 is air-introduced machine outlet, and i=2 is recycle valve outlet, and i=3 is pressure fan outlet; Switching control number of times is 25;

(2.2). calculate the circulating ratio η of flue gas after switching for the 25th time ²⁵with circulating ratio rate of change Δ η ²⁵:

Calculate the circulating ratio η of flue gas after switching for the 25th time ²⁵:

When switching to oxygen-enriched combusting from air, open recycle valve gradually, close intake valve gradually, in handoff procedure, control the circulating ratio rate of change Δ η of flue gas ²⁵: Δ η ²⁵=0.1%/min, the circulating ratio η after having switched ²⁵be 0.5;

(3) pressure fan rate of discharge step is controlled:

Calculate pressure fan rate of discharge rate of change

${\mathrm{\&Delta;\&delta;}}_3^{25}=\frac{V_3^{25}-V_3^{24}}{V_3^{25}},$

In formula, it is the standard volume flow of pressure fan outlet after switching for the 25th time; it is the standard volume flow of pressure fan outlet after switching for the 24th time;

In handoff procedure, be mixed into air blower inlet gas by circulating flue gas and air, make pressure fan rate of discharge rate of change until handoff procedure completes;

(4) note oxygen amount step is controlled:

Calculate and switch rear hearth outlet oxygen amount rate of change for the 25th time

$A_0^{25}=\underset{j1=1}{\overset{m/2}{\&Sigma;}}{U}^{25}\left(j1\right)\underset{j2=m/2+1}{\overset{m}{\&Sigma;}}{U}^{25}\left(j2\right),$

In formula, m is the total sampling number of oxygen amount in furnace outlet flue gas, is even number, m=3000; U ²⁵(j1), U ²⁵(j2) be switch first, post-sampling oxygen amount in rear hearth exiting flue gas for the 25th time, obtained by field measurement; J1, j2 are respectively first, post-sampling number of times, j1=1500, j2=1500;

According to the oxygen determination value after oxygen at furnace exit rate of change and primary and secondary air note oxygen, regulate the required oxygen flow injected: oxygen at furnace exit rate of change the oxygen amount of First air oxygen is 17%, and after Secondary Air note oxygen, oxygen amount is 32%.

The embodiment three of operating mode changing method, as shown in Figure 2, comprises and arranges checkout equipment step, recycle valve and intake valve rate-determining steps, controls pressure fan rate of discharge step and control note oxygen amount step:

(1) checkout equipment step is arranged:

Air-introduced machine YF export 1., recycle valve H3 export 2., pressure fan SF outlet 3. measuring point is set respectively, measure pressure, temperature and flow;

First note oxygen valve H7 export 5., second note oxygen valve H6 export 4. with boiler GL burner hearth back-end ductwork outlet 6. measuring point is set, measure oxygen amount;

(2) recycle valve and intake valve rate-determining steps, comprises following sub-step:

(2.1). calculate the standard volume flow of set measuring point

$V_i^{80}=\frac{P_i^{80}}{1.01\&times;{10}^5}\&times;\frac{273.15}{T_i^{80}+273.15}\&times;Q_i^{80},$

In formula, be respectively the pressure of measuring point, temperature, flow, obtained by field measurement; I=1,2,3; I=1 is air-introduced machine outlet, and i=2 is recycle valve outlet, and i=3 is pressure fan outlet; Switching control number of times is 80;

(2.2). calculate the circulating ratio η of flue gas after switching for the 80th time ²⁵with circulating ratio rate of change Δ η ⁸⁰:

Calculate the circulating ratio η of flue gas after switching for the 80th time ⁸⁰:

When switching to oxygen-enriched combusting from air, open recycle valve gradually, close intake valve gradually, in handoff procedure, control the circulating ratio rate of change Δ η of flue gas ⁸⁰: Δ η ⁸⁰=0.05%/min, the circulating ratio η after having switched ⁸⁰be 0.82;

(3) pressure fan rate of discharge step is controlled:

Calculate pressure fan rate of discharge rate of change

${\mathrm{\&Delta;\&delta;}}_3^{80}=\frac{V_3^{80}-V_3^{79}}{V_3^{80}},$

In formula, it is the standard volume flow of pressure fan outlet after switching for the 80th time; it is the standard volume flow of pressure fan outlet after switching for the 79th time;

In handoff procedure, be mixed into air blower inlet gas by circulating flue gas and air, make pressure fan rate of discharge rate of change until handoff procedure completes;

(4) note oxygen amount step is controlled:

Calculate and switch rear hearth outlet oxygen amount rate of change for the 80th time

$A_0^{80}=\underset{j1=1}{\overset{m/2}{\&Sigma;}}{U}^{80}\left(j1\right)-\underset{j2=m/2+1}{\overset{m}{\&Sigma;}}{U}^{80}\left(j2\right),$

In formula, m is the total sampling number of oxygen amount in furnace outlet flue gas, is even number, m=9000; U ⁸⁰(j1), U ⁸⁰(j2) be switch first, post-sampling oxygen amount in rear hearth exiting flue gas for the 80th time, obtained by field measurement; J1, j2 are respectively first, post-sampling number of times, j1=4500, j2=4500;

According to the oxygen determination value after oxygen at furnace exit rate of change and primary and secondary air note oxygen, regulate the required oxygen flow injected: oxygen at furnace exit rate of change the oxygen amount of First air oxygen is 21.1%, and after Secondary Air note oxygen, oxygen amount is 40%.

Claims (2)

1. a flue gas recirculation Combustion System of Boiler Burning Fine, comprise the feeder (GM), burner (RSQ), boiler (GL), denitrator (TX), air preheater (KY), ash handling equipment (CH), desulfurizer (TL) and the air-introduced machine (YF) that connect successively, it is characterized in that:

Described air-introduced machine (YF) connects exhaust smoke valve (H1) entrance and recycle valve (H3) entrance respectively by pipeline, exhaust smoke valve (H1) outlet chimney (YC), intake valve (H2) entrance is communicated with air (KQ), intake valve (H2) outlet is connected pressure fan (SF) entrance with recycle valve (H3) outlet by pipeline, pressure fan (SF) outlet connects air preheater (KY) air intake by pipeline simultaneously, First air stop valve (H5) entrance and Secondary Air stop valve (H4) outlet, First air stop valve (H5) outlet connects primary air fan (FG) entrance, primary air fan (FG) outlet connects feeder (GM) outlet and burner (RSQ) entrance by primary air duct, first oxygen filling container (ZY1) connects described primary air duct by the first note oxygen valve (H7), air preheater (KY) air outlet slit and Secondary Air stop valve (H4) entrance connecting secondary air pipe line, Secondary Air pipeline connects burner (RSQ) Secondary Air entrance, and the second oxygen filling container (ZY2) connects described Secondary Air pipeline by the second note oxygen valve (H6).

2. the operating mode changing method of flue gas recirculation Combustion System of Boiler Burning Fine described in claim 1, comprises and arranges checkout equipment step, recycle valve and intake valve rate-determining steps, controls pressure fan rate of discharge step and control note oxygen amount step, it is characterized in that:

(1) checkout equipment step is arranged:

In air-introduced machine (YF) outlet, recycle valve (H3) outlet, pressure fan (SF) outlet, measuring point is set respectively, measures pressure, temperature and flow;

Measuring point is set in the first note oxygen valve (H7) outlet, the second note oxygen valve (H6) outlet and the outlet of boiler (GL) burner hearth back-end ductwork, measures oxygen amount;

(2) recycle valve and intake valve rate-determining steps, comprises following sub-step:

(2.1). calculate the standard volume flow of set measuring point

$V_i^n=\frac{P_i^n}{1.01\&times;{10}^5}\&times;\frac{273.15}{T_i^n+273.15}\&times;Q_i^n,$

In formula, be respectively the pressure of measuring point, temperature, flow, obtained by field measurement; I=1,2,3; I=1 is air-introduced machine outlet, and i=2 is recycle valve outlet, and i=3 is pressure fan outlet; N controls number of times for switching;

(2.2). calculate the circulating ratio η of flue gas after switching for n-th time ⁿwith circulating ratio rate of change Δ η ⁿ:

Calculate the circulating ratio η of flue gas after switching for n-th time ⁿ:

When switching to oxygen-enriched combusting from air, open recycle valve gradually, close intake valve gradually, in handoff procedure, control the circulating ratio rate of change Δ η of flue gas ⁿ: 0< Δ η ⁿ<0.8%/min, wherein,

${\mathrm{\&Delta;\&eta;}}^n=\frac{\left|{\mathrm{\&eta;}}^n-{\mathrm{\&eta;}}^{n-1}\right|}{{\mathrm{\&eta;}}^n}\&times;100\%,$

Circulating ratio η after having switched ⁿcontrol 0.6 ~ 0.8;

(3) pressure fan rate of discharge step is controlled:

Calculate pressure fan rate of discharge rate of change

${\mathrm{\&Delta;\&delta;}}_3^n=\frac{V_3^n-V_3^{n-1}}{V_3^n},$

In formula, it is the standard volume flow of pressure fan outlet after switching for n-th time; it is the standard volume flow of pressure fan outlet after switching for (n-1)th time;

In handoff procedure, be mixed into air blower inlet gas by circulating flue gas and air, make pressure fan rate of discharge rate of change until handoff procedure completes;

(4) note oxygen amount step is controlled:

Calculate and switch rear hearth outlet oxygen amount rate of change for n-th time

$A_0^n=\underset{j1=1}{\overset{m/2}{\&Sigma;}}{U}^n\left(j1\right)-\underset{j2=m/2+1}{\overset{m}{\&Sigma;}}{U}^n\left(j2\right),$

In formula, m is the total sampling number of oxygen amount in furnace outlet flue gas, is even number; U ⁿ(j1), U ⁿ(j2) be switch first, post-sampling oxygen amount in rear hearth exiting flue gas for n-th time, obtained by field measurement; J1, j2 are respectively first, post-sampling number of times;

According to the oxygen determination value after oxygen at furnace exit rate of change and primary and secondary air note oxygen, regulate the required oxygen flow injected: oxygen at furnace exit rate of change the oxygen content control of First air oxygen is 18% ~ 21%, and after Secondary Air note oxygen, oxygen content control is 35% ~ 40%.