CN114907034B

CN114907034B - Cement firing system and method capable of realizing rapid switching operation of air combustion and local oxy-fuel combustion

Info

Publication number: CN114907034B
Application number: CN202210774527.4A
Authority: CN
Inventors: 陈昌华; 代中元; 林敏燕; 武晓萍; 万夫伟
Original assignee: Tianjin Cement Industry Design and Research Institute Co Ltd; China National Building Material Group Co Ltd CNBM
Current assignee: Tianjin Cement Industry Design and Research Institute Co Ltd; China National Building Material Group Co Ltd CNBM
Priority date: 2022-07-01
Filing date: 2022-07-01
Publication date: 2023-04-14
Anticipated expiration: 2042-07-01
Also published as: CN114907034A

Abstract

The invention discloses a cement burning system and a method capable of realizing rapid switching operation of air combustion and local total oxygen combustion, which consists of a cement burning main system and a total oxygen combustion subsystem, wherein a tertiary air pipe of the main system is additionally provided with a tertiary air branch pipe connected to a self-enrichment furnace of the subsystem, a flue gas communicating pipeline is additionally arranged between the outlet of a main high-temperature fan of the main system and the outlet of a sub high-temperature fan of the subsystem, an air communicating pipeline is additionally arranged on a low-temperature circulating flue gas supply pipeline at the inlet of a low-temperature circulating fan of the subsystem, and valves are respectively arranged on the tertiary air branch pipe, the flue gas communicating pipeline and the air communicating pipeline. When cement burning is carried out, the two systems are adopted to run in parallel to carry out air combustion and local oxy-fuel combustion, or the two systems are adjusted to carry out air combustion and local oxy-fuel combustion fast switching operation according to requirements, so that the problems of continuity and stability of the running of the cement burning system when the oxy-fuel combustion subsystem is in an ignition stage or needs to pause the output of carbon dioxide-rich flue gas under abnormal working conditions are solved.

Description

Cement firing system and method capable of realizing rapid switching operation of air combustion and local oxy-fuel combustion

Technical Field

The invention relates to the technical field of cement burning, in particular to a cement burning system and a cement burning method capable of realizing quick switching operation of air combustion and local oxy-fuel combustion.

Background

Fossil energy is taken as the most main energy source in the world, and huge CO is brought by the consumption process of the fossil energy ₂ Emissions become an important source of emissions for the greenhouse effect. The current situation of rich coal, lean oil and little gas in China determines that the proportion of coal in the structure of primary energy in China is difficult to change in a short term. In recent years, the total carbon emission amount in China exceeds the United states, the carbon dioxide emission state becomes the largest carbon dioxide emission state in the world, and the carbon emission reduction situation is very severe.

The total oxygen combustion is based on the existing industrial kiln system, high-purity oxygen is used to replace combustion air, and simultaneously, the total oxygen combustion adoptsThe medium flow and the heat transfer characteristic of the hearth are adjusted by the circulation of the flue gas, and CO with the volume concentration of up to 80 percent can be obtained ₂ Flue gas, thereby capturing and purifying CO at low cost ₂ The permanent sealing or resource utilization of the CO can be realized, and the large-scale industrial CO is realized ₂ Enrichment and emission reduction. The existing analysis shows that compared with other carbon capture modes, the oxy-fuel combustion technology has the advantages of investment cost, operation cost and CO ₂ The method has the advantages of emission reduction cost, large scale, compatibility with the prior art and the like.

The existing oxy-fuel combustor is mainly used for float glass kiln, glass fiber kiln, steel rolling heating furnace, forging furnace, heat treatment furnace and the like, and the fuel is mainly natural gas. The coal-fired oxy-fuel combustor is less applied in industry, chinese patent publication No. CN101825278A proposes an oxygen-enriched combustor, and US patent No. US20110126780A1 proposes an oxy-fuel combustion boiler pulverized coal combustor, and the two patents are mainly directed at oxy-fuel combustion of a coal-fired power generation boiler. As for the cement industry kiln, because the production arrangement and the reaction conditions of the cement industry kiln are greatly different from those of glass, thermal power kilns and the like, and special designs of a cooler, a system air and the like are required, the actual case of operating a pure oxygen combustion technology does not exist in the cement industry at present.

A large amount of carbon dioxide is generated in the cement production process, and according to statistics, 0.6-0.7 t of carbon dioxide is discharged when 1t of cement is produced.

Carbon dioxide in the cement kiln waste gas mainly comes from the following two aspects:

1. carbon dioxide generated in fuel combustion flue gas accounts for about 40%;

2. the carbon dioxide produced by decomposition of the carbonate in the feedstock comprises about 60%.

The carbon capture and sequestration technology is the most feasible new technology for reducing carbon dioxide emission in the cement industry at present, wherein the oxy-fuel combustion technology has a better development prospect in the carbon capture and sequestration technology.

Oxy-fuel combustion refers to the combustion of fuel by using industrial oxygen instead of air, so that the fuel can be combusted more completely, and compared with air combustion, oxy-fuel combustion has the following advantages:

1) Compared with the air combustion, the oxy-fuel combustion process has the advantages that about 79% of nitrogen in the air does not participate in the combustion any more, so that the flame temperature can be increased;

2) The content of nitrogen in the flue gas is low, the combustion product is a triatomic product, the heat transfer effect of a triatomic substance is higher than that of a diatomic substance, and the heating efficiency is improved;

3) The nitrogen does not participate in smoke discharge any more, so that the smoke quantity can be greatly reduced, and the heat loss of the smoke discharge is reduced.

At present, the oxy-fuel combustion technology is widely applied to float glass and glass fiber kilns, the application of the oxy-fuel combustion technology in the cement industry is still in the research and development stage, and the oxy-fuel combustion technology is mainly adopted in a decomposing furnace and a rotary kiln in the cement industry.

In the oxy-fuel combustion process of the cement kiln with high oxygen concentration, oxygen and circulating flue gas are required to be introduced into the kiln to replace air as combustion gas, but how to inject the oxygen and the circulating flue gas into the cement kiln is a key technical difficulty. In a conventional oxy-fuel combustion system, oxygen and circulating flue gas are generally mixed, and the mixed gas is transported through a pipeline and injected into a cement kiln. However, in the high oxygen concentration oxy-fuel combustion system, if the air supply mode that oxygen and circulating flue gas are mixed first and the mixed gas is transported through a pipeline and then injected into a cement kiln is still adopted, a serious safety problem exists. Because in the flue gas circulation system, even if the bag-type dust remover is arranged to remove dust from the circulating flue gas, a small amount of carbon-containing particles with small particle sizes are still carried in the flue gas, if high-concentration industrial oxygen (with the volume fraction of about 80-95%) and the circulating flue gas are directly mixed and transported according to a conventional method, the small amount of carbon-containing particles carried in the circulating flue gas are easy to catch fire and burn after encountering pure oxygen, once the mixed gas burns in a pipeline, a serious safety accident is caused, the equipment body is endangered, and meanwhile, the safety of operating personnel is threatened. Chinese patent publication No. CN105650628A proposes an oxygen-enriched combustion device of a circulating fluidized bed and an oxygen-enriched combustion air supply method thereof, wherein oxygen and circulating flue gas are not mixed before entering a furnace body, are respectively conveyed in respective pipelines, and are supplied with air at a plurality of positions of different heights of the furnace body, thereby solving the safety problem in the oxygen conveying and mixing process. However, the air supply mode of the patent only aims at the circulating fluidized bed, and is not applicable to the oxy-fuel combustion of the cement kiln.

In addition, because the fuel combustion and the raw material decomposition process in the cement decomposing furnace are coupled, the combustion temperature in the hearth of the decomposing furnace is relatively low, generally 900-1100 ℃, if the medium-low temperature circulating flue gas (generally below 400 ℃) out of the burning system directly enters the decomposing furnace, the temperature of the combustion area in the decomposing furnace is difficult to maintain above the ignition temperature of the pulverized coal, and the flame in the decomposing furnace is unstable and even flameout. Therefore, it is necessary to raise the temperature of the oxygen and the circulating flue gas before introducing them into the cement decomposing furnace. Under the condition of oxygen enrichment and carbon enrichment, as the theoretical combustion temperature of the fuel is greatly improved, the safety and pollutant emission of a combustion device also face great challenges, and the main problems are as follows: 1) The problems of deflagration, unstable combustion and furnace wall ablation are easy to occur in the combustion device; 2) NO is easy to cause in the combustion process when the flame temperature rises in the oxygen-rich state _X The emission is increased, and the flue gas denitration load of a subsequent waste gas treatment system is increased.

For megaton cement production line, discharging CO in smoke every year ₂ Can reach 60-70 ten thousand tons. Due to CO ₂ Relatively small consumption market, and CO in flue gas in cement production process ₂ The production of the full capture is too large, resulting in exceeding market demand. Therefore, the development of the carbon capture technology of the partial total oxygen combustion flue gas of the cement kiln, which has reliable technology and low operation cost and does not influence the existing production operation working condition, is a more practical and feasible method for carbon emission reduction in the cement industry. However, the following problems still exist:

1) When the total oxygen combustion carbon enrichment system is in an ignition stage, the air combustion working condition is used for ignition and temperature rise so as to reduce the consumption of industrial oxygen; or when the carbon dioxide-rich flue gas output needs to be suspended under an abnormal working condition, the problem that the running state is rapidly switched from the local oxy-fuel combustion state to the air combustion state is faced;

2) The pipeline safety problem is caused by the ignition and combustion of residual carbon particles in the flue gas and industrial oxygen in a mixed conveying mode of medium and low temperature circulating flue gas and industrial oxygen;

3) The processes of raw material decomposition heat absorption and combustion heat release are coupled, and medium-low temperature circulating flue gas is directly introduced into a decomposing furnace, so that the problems that fuel is difficult to ignite, flame is unstable, and flameout is easy to occur in the combustion process are caused;

4) The middle-low temperature circulating flue gas is directly introduced into the decomposing furnace, and the raw materials of the decomposing furnace are difficult to lift by wind due to small working condition air quantity, so that the problem of material collapse is caused.

Disclosure of Invention

The invention provides a cement burning system and a method capable of realizing quick switching operation of air burning and local oxy-fuel burning for solving the problems in the prior art. The tertiary air pipe of the main system is additionally provided with a tertiary air branch pipe connected to the self-enrichment furnace of the subsystem, a flue gas communicating pipeline is additionally arranged between the outlet of a main high-temperature fan of the main system and the outlet of a sub high-temperature fan of the subsystem, an air communicating pipeline is additionally arranged on a low-temperature circulating flue gas supply pipeline at the inlet of a low-temperature circulating fan of the subsystem, and valves are respectively arranged on the tertiary air branch pipe, the flue gas communicating pipeline and the air communicating pipeline for switching and adjusting, so that the rapid switching operation of air combustion and local total oxygen combustion is realized. Meanwhile, in a preheating and predecomposition link of the firing kiln tail, a main system and a subsystem are operated in parallel; in the rotary kiln, the calcined raw materials generated by the main system and the subsystem are simultaneously fed into the kiln to produce cement clinker; mutual interference between the main system and the subsystems, such as mutual wind channeling, pressure fluctuation interference and the like, is reduced.

The invention is realized in this way, a cement calcination system capable of realizing rapid switching operation of air combustion and local oxy-fuel combustion, which consists of a main cement calcination system and an oxy-fuel combustion subsystem, wherein a main high-temperature fan, a main dust collector, a main exhaust fan and a chimney are sequentially arranged on an outlet air pipe at the top of a main preheater unit of the main cement calcination system;

the total oxygen combustion subsystem consists of a sub-preheater unit, a self-enrichment furnace, a flue gas preheating unit, a Venturi throat, a sub-high-temperature fan, a cooler, a sub-dust collector, a medium-temperature circulating fan, a medium-temperature circulating flue gas supply pipeline, a low-temperature circulating fan, a low-temperature circulating flue gas supply pipeline, a fuel supply pipeline and an industrial oxygen supply pipeline; a feeding pipe of a penultimate sub cyclone cylinder of the sub-preheater unit is connected with a raw material feeding pipe of the self-enrichment furnace, a feeding pipe of a last-stage sub cyclone cylinder of the sub-preheater unit is connected with a kiln tail smoke chamber of a main cement calcination system, and an outlet air pipe at the top of the sub-preheater unit is sequentially provided with a sub-high temperature fan, a cooler and a sub-dust collector; the medium-temperature circulating fan is arranged on a medium-temperature circulating flue gas supply pipeline, one end of the medium-temperature circulating flue gas supply pipeline is connected with a pipeline between the sub high-temperature fan and the cooler, and the other end of the medium-temperature circulating flue gas supply pipeline is connected with the flue gas preheating unit; the low-temperature circulating fan is arranged on a low-temperature circulating flue gas supply pipeline, one end of the low-temperature circulating flue gas supply pipeline is connected with a pipeline of a gas outlet of the sub dust collector, and the other end of the low-temperature circulating flue gas supply pipeline is connected with a fuel supply pipeline;

the flue gas preheating unit is used for preheating low-temperature circulating flue gas and medium-temperature circulating flue gas to above 900 ℃ through fuel; the bottom flue gas outlet of the flue gas preheating unit is connected with the bottom inlet of the venturi throat, the top outlet of the venturi throat is connected with the bottom of the cylinder of the self-enrichment furnace, and the top outlet of the self-enrichment furnace is connected with the inlet of the last-stage cyclone cylinder;

the fuel supply pipeline is respectively connected with the flue gas preheating unit and a coal injection pipe at the upper part of the venturi throat pipe, and the industrial oxygen supply pipeline is respectively connected with the flue gas preheating unit and an oxygen pipe at the lower part of the venturi throat pipe;

the cement calcination main system is characterized in that a tertiary air pipe is additionally arranged in a tertiary air pipe of the cement calcination main system, a tertiary air branch pipe is connected to an inlet at the bottom of a venturi throat, a flue gas communicating pipeline is additionally arranged between an outlet of a main high-temperature fan and an outlet of a sub high-temperature fan, a low-temperature circulating flue gas supply pipeline at an inlet of a low-temperature circulating fan is additionally provided with an air communicating pipeline, a tertiary air communicating valve is arranged on the tertiary air pipe, a flue gas communicating valve is arranged on the flue gas communicating pipeline, and an air communicating valve is arranged on the air communicating pipeline; and a coal feeding air valve entering the preheating furnace is arranged on a fuel supply pipeline at the inlet of the flue gas preheating unit, and a cooler valve is arranged on a pipeline at the inlet of the cooler.

Preferably, the flue gas preheating unit comprises a burner and a preheating furnace, the burner is mounted at the top of the preheating furnace, the head of the burner extends into the preheating furnace, the burner comprises an oil pipe, an inner primary air pipe, a coal pipe and an outer primary air pipe which are coaxially sleeved from inside to outside in sequence, and a central oil gun channel, an inner primary air channel, a coal powder channel and an outer primary air channel are sequentially formed in the burner from inside to outside; the tail parts of the inner primary air pipe and the outer primary air pipe are both connected with an industrial oxygen supply pipeline, and the tail part of the coal pipe is connected with a fuel supply pipeline;

the head ports of the oil pipe, the coal pipe and the outer primary air pipe are aligned to form the head of the burner; a distance H0 is reserved between the head of the inner primary air pipe and the head of the combustor, so that an air-coal premixing channel is formed at the head of the combustor by the inner primary air channel and the coal powder channel; an air-coal premixing adjusting ring which can move back and forth along the axial direction of the burner is arranged between the inner primary air channel and the pulverized coal channel, so that the length of the air-coal premixing channel can be adjusted between 0 and H0;

the preheating furnace consists of a spiral-flow chamber, a reducing section and a hearth from top to bottom, wherein the spiral-flow chamber is of a volute structure, so that flue gas entering from an inlet of the spiral-flow chamber enters in a volute tangential spiral flow;

and a fuel-rich zone positioned in the center of the hearth, an oxygen-rich zone positioned outside the fuel-rich zone and a carbon-rich zone positioned between the oxygen-rich zone and the furnace wall are formed in the preheating furnace.

Further preferably, the air-coal premixing adjusting ring is arranged on the inner side wall of the inner primary air pipe.

Further preferably, the inlet of the inner primary air channel and the outlet of the outer primary air channel are provided with a swirler.

Further preferably, a refractory material layer is arranged outside the outer primary air channel.

Further preferably, flow controllers are respectively arranged on the industrial oxygen supply pipelines connected with the oxygen pipes at the lower parts of the inner primary air pipe, the outer primary air pipe and the venturi throat.

Further preferably, a burner mounting hole is formed in the center of a top cover of the swirling flow chamber, and the head of the burner extends into the swirling flow chamber through the burner mounting hole.

Further preferably, the inner diameter of the reducing section is gradually increased from top to bottom.

Preferably, a medium-temperature circulating air valve is arranged on a medium-temperature circulating flue gas supply pipeline at an inlet of the medium-temperature circulating fan, and a low-temperature circulating air valve is arranged on a low-temperature circulating flue gas supply pipeline at an inlet of the low-temperature circulating fan.

Preferably, the venturi throat is divided into a lower contraction section, a throat area high-speed section and an upper expansion section from bottom to top, the lower contraction section is inserted into the oxygen pipe, the oxygen pipe is inserted into the venturi throat in a downward inclination manner to be close to the axial center of the venturi throat, and an included angle between the oxygen pipe and the horizontal direction is 30-60 degrees, so that the industrial oxygen and the circulating flue gas are uniformly mixed; the coal injection pipe is inserted into the upper expansion section and is inserted to be close to the inner wall of the upper expansion section, so that circulating flue gas and coal powder are mixed at a vortex low-pressure area formed outside the upper expansion section; the number of the oxygen pipes and the number of the coal injection pipes are respectively 2-4, and the oxygen pipes and the coal injection pipes are symmetrically arranged along the circumference.

Preferably, the raw material feeding pipe is arranged at the bottom of the column of the self-enriching furnace.

A cement burning method capable of realizing air combustion and local oxy-fuel combustion fast switching operation is characterized in that a cement burning main system and an oxy-fuel combustion sub-system are adopted to operate in parallel to carry out air combustion and local oxy-fuel combustion when cement burning is carried out, or the air combustion and the local oxy-fuel combustion are carried out by adjusting between the cement burning main system and the oxy-fuel combustion sub-system according to requirements;

the cement calcination main system and the oxy-fuel combustion sub-system are connected in parallel without crossing in a preheating predecomposition link; in the clinker calcination link, two raw materials decomposed by a cement calcination main system and a total oxygen combustion subsystem enter a rotary kiln together for calcination to prepare cement clinker;

the method comprises the following specific steps of switching from a partial oxy-fuel combustion state to an air combustion state:

s1, sequentially opening a tertiary air communicating valve, a smoke communicating valve and an air communicating valve;

s2, stopping conveying the industrial oxygen, and closing a coal feeding air valve of the preheating furnace;

s3, stopping the sub-dust collectors, the sub-exhaust fans, the medium-temperature circulating fan, the medium-temperature circulating air valve, the cooler and the cooler inlet valve in sequence;

s4, adjusting the air pulling quantity of a main exhaust fan and the coal feeding quantity of the self-enrichment furnace, introducing the flue gas out of the total oxygen combustion subsystem into a main dust collector of a cement calcination main system, and enabling the temperature of the flue gas out of the self-enrichment furnace to reach 850-900 ℃;

the specific steps for switching from the air combustion state to the partial oxy-fuel combustion state are as follows:

s1, sequentially starting a cooler, a cooler inlet valve, a medium-temperature circulating air valve, a medium-temperature circulating fan, a sub exhaust fan and a sub dust collector;

s2, opening a coal feeding air valve of the preheating furnace for conveying industrial oxygen;

s3, sequentially closing an air communicating valve, a smoke communicating valve and a tertiary air communicating valve;

s4, adjusting the air drawing quantity of the medium-temperature circulating fan, the coal feeding quantity of the self-enrichment furnace and the preheating furnace and the industrial oxygen flow, so that the temperature of the flue gas discharged from the preheating furnace is up to over 900 ℃, and the temperature of the flue gas discharged from the self-enrichment furnace is up to 850-1000 ℃.

Preferably, when the partial oxy-fuel combustion is carried out, raw meal is fed into a sub-preheater unit in an oxy-fuel combustion subsystem, is preheated by the sub-preheater unit and then is fed into a self-enrichment furnace for pre-decomposition, and then enters a rotary kiln for calcination; the smoke from the enrichment furnace is subjected to heat exchange through a sub-preheater unit under the air draft of a sub-high-temperature fan, and part of the smoke is returned to the preheating furnace as medium-temperature circulating smoke; cooling and collecting dust for the rest flue gas, and using a part of the cooled and collected flue gas as low-temperature circulating flue gas;

the method is characterized in that the pre-decomposed raw material in the self-enrichment furnace is decomposed by adopting a mode of twice total oxygen combustion carbon enrichment, and the method comprises the following specific steps:

the method comprises the following steps: taking low-temperature circulating flue gas from a pipeline of a gas outlet of the sub-dust collector, wherein the low-temperature circulating flue gas carries pulverized coal to enter a pulverized coal channel of the combustor; the industrial oxygen is divided into two parts which respectively enter an inner primary air channel and an outer primary air channel of the burner, the industrial oxygen of the inner primary air channel enters in a swirling mode, the industrial oxygen in the outer primary air channel is ejected out in a swirling mode, the supply amount of the industrial oxygen meets the oxygen amount required by the combustion of the pulverized coal in the preheating furnace, and the pulverized coal is stably combusted in the preheating furnace after being ejected out;

taking medium-temperature circulating flue gas from a pipeline between a sub high-temperature fan and a cooler, introducing the medium-temperature circulating flue gas into a cyclone chamber of a preheating furnace in a tangential cyclone manner, and making the medium-temperature circulating flue gas move downwards along the wall under the centrifugal force of the cyclone chamber at the top; the pulverized coal and the industrial oxygen are sprayed out from the burner and then are ignited and combusted in the preheating furnace, so that a fuel-rich area positioned in the center of the hearth, an oxygen-rich area positioned outside the fuel-rich area and a carbon-rich area positioned between the oxygen-rich area and the furnace wall are formed in the space in the preheating furnace; the combustion heat of the pulverized coal raises the temperature of the middle-low temperature circulating flue gas to over 900 ℃;

step two: the high-temperature circulating flue gas with the temperature of more than 900 ℃ of the flue gas outlet preheating unit reversely moves upwards;

step three: the high-temperature circulating flue gas enters a Venturi throat, and industrial oxygen is sprayed into the inlet of the Venturi throat to increase the oxygen concentration of a central area to be more than 30%; spraying pulverized coal at the outlet of the venturi throat, wherein the outlet gas forms jet flow, and a vortex low-pressure area is formed on the outer side of the upper part of the venturi throat under the action of the jet flow;

step four: the coal powder enters the self-enrichment furnace along with the circulating flue gas to burn and release heat, raw materials are fed into a raw material feeding pipe of the self-enrichment furnace, so that the raw materials are decomposed in the self-enrichment furnace, and CO is released ₂ Self-enriched furnace flue gas dry basis CO ₂ The concentration is more than 80 percent, and the temperature is 850-1000 ℃.

Further preferably, the fineness of the coal dust is controlled to be 80um, and the screen residue is lower than 20%; the oxygen concentration of the industrial oxygen is not lower than 80%; the temperature of the low-temperature circulating flue gas is lower than 150 ℃, and CO is ₂ Concentration higher than 60%, O ₂ The concentration is lower than 10%; the temperature of the medium-temperature circulating flue gas is lower than 400 ℃, and CO is ₂ Concentration higher than 60%, O ₂ The concentration is less than 10%.

Preferably, according to the combustion characteristics of the pulverized coal, the length of the air-coal premixing channel is adjusted by adjusting the air-coal premixing adjusting ring, and/or the ignition and flame stability of the pulverized coal are enhanced by adjusting the amount of industrial oxygen entering the inner primary air channel and the outer primary air channel, so that the pulverized coal is stably combusted in the preheating furnace after being sprayed.

Preferably, in the third step, the average wind speed of the section of the throat area high-speed section of the venturi throat pipe is 25-50 m/s, the average wind speed of the section of the outlet of the upper expansion section is 5-15 m/s, and the wind speed of the throat area high-speed section is more than 2 times of the wind speed of the outlet of the upper expansion section.

The invention has the advantages and positive effects that:

1. the cement burning system can be adjusted between the main cement burning system and the oxy-fuel combustion subsystem according to requirements to perform air combustion and local oxy-fuel combustion fast switching operation, so that the problems of continuity and stability of operation of the cement burning system when the oxy-fuel combustion subsystem is in an ignition stage or needs to suspend carbon dioxide-rich flue gas output under abnormal working conditions are solved; in the preheating and predecomposition link of the firing kiln tail, a main system and a subsystem are adopted to run in parallel, and in the clinker calcining link, calcined raw materials generated by the main system and the subsystem are simultaneously fed into a rotary kiln to produce cement clinker, so that the mutual interference between the main system and the subsystem is reduced; when local oxy-fuel combustion is carried out, the oxy-fuel combustion subsystem adopts graded circulating air, medium-temperature circulating air (150-400 ℃) is taken from a position between the sub high-temperature fan and the cooler and directly enters the preheating furnace, and low-temperature circulating air (lower than 150 ℃) is taken from a position behind the sub dust collector and is used as pulverized coal conveying air, so that the heat recovery is promoted, the energy consumption is reduced, and the carbon enrichment is realized while the safety of pulverized coal conveying is ensured.

2. In the total oxygen combustion subsystem, the raw material is pre-decomposed into a primary combustion area and a secondary combustion area which are operated in series, raw material is not fed into the primary combustion area where a combustor and a preheating furnace are arranged, pulverized coal is conveyed through low-temperature circulating flue gas, industrial oxygen is divided into two parts to supply air to the inner side and the outer side of a pulverized coal channel, and medium-temperature circulating is carried outThe annular flue gas supplies air from the cyclone chamber of the preheating furnace to the wall, so that the coal powder flame in the preheating furnace is stable, the furnace wall of the preheating furnace is not ablated, and the low NO is realized _X Discharging and fully burning off the coal dust, and heating the middle-low temperature circulating flue gas to above 900 ℃ in a preheating furnace; in the secondary combustion zone where the Venturi throat and the self-enriching furnace are positioned, the secondary combustion zone is subjected to material operation, high-temperature circulating flue gas is introduced into the bottom of the secondary combustion zone, industrial oxygen and coal powder are sprayed in the secondary combustion zone to decompose raw materials, and jet flow is formed through the arranged Venturi throat to support the materials, so that the problem of high-temperature furnace wall skinning caused by raw material collapse and local deflagration of the coal powder is solved, NO (NO) generated by combustion of the coal powder is inhibited _X Releasing to make the flue gas temperature of the self-enrichment furnace be 850-1000 ℃, and dry-based CO ₂ The concentration is more than 80 percent, and the full decomposition of the raw material is realized.

3. According to the combustor provided by the invention, the industrial oxygen is not contacted with the coal powder and the circulating flue gas in the conveying process, and the coal conveying air for conveying the coal powder adopts the low-temperature circulating flue gas at the temperature of less than 150 ℃, so that the spontaneous combustion of unburned carbon particles in the circulating flue gas is avoided, and the safety problem of spontaneous combustion caused by the mixed conveying of the industrial oxygen and the coal powder in an oxy-fuel combustion subsystem is solved.

4. According to the burner provided by the invention, the air-coal premixing adjusting ring capable of moving back and forth along the axial direction of the burner is additionally arranged between the inner primary air channel and the pulverized coal channel, so that the length of the air-coal premixing channel can be flexibly adjusted, whether industrial oxygen and pulverized coal are premixed in the burner or not can be adjusted according to the combustion characteristics of the pulverized coal, the problems of unstable flame and even flameout are avoided, and the ignition and flame stability of coal are enhanced; or the problem that the head of the burner is burnt out when the flame is tempered to the premixing area due to the excessively high flame burning speed is avoided, the deflagration and the tempering of the pulverized coal are prevented, and the ignition and the flame stability of the pulverized coal are enhanced on the premise of no tempering.

5. The burner provided by the invention can adjust the amount of industrial oxygen entering the inner primary air channel and the outer primary air channel according to the combustion characteristics of the pulverized coal, thereby preventing the deflagration and the tempering of the pulverized coal and strengthening the ignition and flame stability of the pulverized coal; and the outer primary air is high-speed rotational flow air, so that the flame stability is further enhanced.

6. According to the preheating furnace provided by the invention, the medium-temperature circulating flue gas (150-400 ℃) enters from the cyclone chamber at the top of the preheating furnace and flows downwards in the cyclone chamber in a wall-attached rotating manner, and because the medium-temperature circulating flue gas is relatively low in temperature and low in oxygen content, a low-temperature protective gas film is formed in front of the furnace wall and the flame, the refractory material on the wall surface of the preheating furnace is effectively protected, and the flame is prevented from being ablated.

7. According to the venturi throat, the pulverized coal is located in the upper expansion area of the venturi throat, the industrial oxygen is introduced into the lower contraction area of the venturi throat, and the industrial oxygen and the circulating flue gas are uniformly mixed through the venturi throat and then are contacted with the pulverized coal, so that the pulverized coal deflagration caused by high local oxygen concentration in the self-enrichment furnace is prevented, and the wall surface of the self-enrichment furnace is prevented from being skinned; the gas at the outlet of the venturi throat forms jet flow, so that a vortex low-pressure area is formed at the outer side of the upper expansion section under the action of the jet flow, the circulating flue gas and the pulverized coal are back-mixed in the area, the oxygen concentration of the circulating flue gas at the outer side is relatively low, and NO (nitric oxide) generated by pulverized coal combustion is inhibited _X And (4) releasing.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a process flow diagram of a cement burning system capable of realizing rapid switching operation of air combustion and partial oxy-fuel combustion provided by an embodiment of the invention;

FIG. 2 is a schematic structural diagram of a flue gas preheating unit provided in the embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a preheating furnace according to an embodiment of the present invention;

FIG. 4 is a schematic view of a cyclone chamber according to an embodiment of the present invention;

FIG. 5 is a first schematic structural diagram of a burner provided in an embodiment of the present invention;

FIG. 6 isbase:Sub>A schematic structural view of the section A-A of FIG. 5;

FIG. 7 is a schematic structural diagram II of a burner according to an embodiment of the present invention;

FIG. 8 is a schematic structural view of the section B-B of FIG. 7;

FIG. 9 is a schematic structural view of a venturi throat provided in accordance with an embodiment of the present invention;

FIG. 10 is a top view of a venturi throat provided by embodiments of the present invention.

Wherein: g 1-industrial oxygen; g 2-medium temperature circulating flue gas; g 3-low temperature circulating flue gas; f-pulverized coal; a-a fuel rich zone; b-an oxygen-rich zone; a C-carbon rich region; h-length of the air-coal premixing area; m-raw meal; k-cement clinker;

1-cement calcination primary system; 101-a first stage main cyclone; 102-a second stage main cyclone; 103-third stage main cyclone; 104-a fourth stage main cyclone; 105-fifth stage main cyclone; 106-main decomposing furnace; 107-kiln tail smoke chamber; 108-a rotary kiln; 109-a cooling machine; 110-a kiln head burner; 111-tertiary air pipe; 112-a primary high temperature fan; 113-a primary dust collector; 114-a primary exhaust fan; 115-a chimney;

2-a oxy-fuel combustion subsystem;

201-first stage sub-cyclone; 202-second stage sub-cyclone; 203-third stage sub-cyclones; 204-fourth stage cyclone; 205-fifth stage sub-cyclone;

206-self-enriching furnace; 2061, raw material feeding pipe;

207-venturi throat; 2071-lower narrowing section; 2072-throat area high speed section; 2073-an upper dilating segment; 2074-oxygen hose; 2075-coal injection pipe;

208-preheating furnace; 2081-a swirl chamber; 2082-a variable diameter section; 2083-hearth; 20811-swirl chamber inlet; 20812-cyclone chamber top cap; 20813-burner mounting holes;

209-a burner; 2091-central oil gun passage; 2092-inner primary air cyclone; 2093-inner primary air passage; 2094-pulverized coal passage; 2095-outer primary air passage; 2096-outer primary air cyclone; 2097-air-coal premixing passage; 2098-air-coal premixing adjusting ring; 2099-layer of refractory material;

210-a high temperature blower; 211-medium temperature circulating fan; 212-medium temperature circulating air valve; 213-a cooler; 214-a sub-dust collector; 215-sub-blowers; 216-low temperature circulating fan; 217-low temperature circulating air valve; 218-a pulverized coal bunker; 219-inner primary air flow controller; 220-outer primary air flow controller; 221-secondary air flow controller; 222-tertiary air branch pipe; 223-tertiary air communicating valve; 224-an air communication valve; 225-flue gas communication pipe; 226-flue gas communication valve; 227-cooler valve; 228-enter preheating furnace coal feeding air valve;

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Examples

Referring to fig. 1 to 10, the present embodiment provides a cement burning system capable of realizing fast switching operation between air burning and partial oxy-fuel combustion, which comprises a main cement burning system 1 and an oxy-fuel combustion subsystem 2, wherein two to seven stages of preheaters can be used as preheater units of the two systems, and the present embodiment is described by taking a five-stage preheater as an example.

The main system 1 for cement calcination comprises a main preheater unit, a main decomposing furnace 106, a kiln tail smoke chamber 107, a rotary kiln 108, a cooler 109, a kiln head burner 110, a tertiary air pipe 111, a main high-temperature fan 112, a main dust collector 113, a main exhaust fan 114 and a chimney 115, wherein the main preheater unit is a five-stage cyclone preheater. Raw materials entering the cement calcining main system 1 are fed into an air pipe at the outlet of the secondary main cyclone 102 through a pipeline to perform gas-solid heat exchange, and enter the primary main cyclone 101 under the drive of airflow; after gas-solid separation is performed in the first-stage main cyclone 101, the material is fed into an outlet air pipe of the third-stage main cyclone 103 from a feeding pipe of the first-stage main cyclone 101. In the above manner, the second stage main cyclone 102, the third stage main cyclone 103 and the fourth stage main cyclone 104 are entered in sequence. The raw material gas-solid separated by the fourth-stage main cyclone 104 enters the main decomposing furnace 106, the decomposition of the raw material (the decomposition of calcium carbonate in the raw material into calcium oxide) is completed in the main decomposing furnace 106, the decomposed raw material enters the fifth-stage main cyclone 105 along with the airflow, and the raw material is fed into the kiln tail smoke chamber 107 after the gas-solid separation.

The total oxygen combustion subsystem 2 is composed of a sub-preheater unit, a self-enrichment furnace 206, a flue gas preheating unit, a Venturi throat 207, a sub-high-temperature fan 210, a cooler 213, a sub-dust collector 214, a medium-temperature circulating fan 211, a medium-temperature circulating flue gas supply pipeline, a low-temperature circulating fan 216, a low-temperature circulating flue gas supply pipeline, a fuel supply pipeline and an industrial oxygen supply pipeline, wherein the sub-preheater unit is also a five-stage cyclone preheater. The discharge pipe of the fourth stage cyclone 204 of the sub-preheater unit is connected with the raw material feeding pipe 2061 of the self-enrichment furnace 206, the top outlet of the self-enrichment furnace 206 is connected with the inlet of the fifth stage cyclone 205, and the discharge pipe of the fifth stage cyclone 205 of the sub-preheater unit is connected with the kiln tail smoke chamber 107 of the main cement calcination system 1. Raw materials entering the total oxygen combustion subsystem 2 are fed into an air pipe at the outlet of the secondary cyclone 202 through a pipeline to perform gas-solid heat exchange, and enter the primary cyclone 201 under the drive of airflow; after gas-solid separation in the first stage cyclone 201, the material is fed into the outlet air pipe of the third stage cyclone 203 from the feeding pipe of the first stage cyclone 201. In the above manner, the second stage sub-cyclone 202, the third stage sub-cyclone 203 and the fourth stage sub-cyclone 204 are entered in sequence. The raw material after gas-solid separation by the fourth stage cyclone 204 enters the self-enrichment furnace 206, the decomposition of the raw material is completed in the self-enrichment furnace 206, the decomposed raw material enters the fifth stage cyclone 205 along with the airflow, and the raw material is fed into the kiln tail smoke chamber 107 after gas-solid separation.

The raw materials of the cement calcination main system 1 and the raw materials of the oxy-fuel combustion subsystem 2 enter a kiln tail smoke chamber 107 together, the raw materials are calcined into cement clinker in a rotary kiln 108, and the high-temperature clinker is discharged out of the cement calcination system after being cooled by a cooling machine 109.

The sub high-temperature fan 210, the cooler 213, the sub dust collector 214 and the sub exhaust fan 215 are sequentially arranged on an outlet air pipe at the top of the sub preheater unit; the medium temperature circulating fan 211 is arranged on a medium temperature circulating flue gas supply pipeline, one end of the medium temperature circulating flue gas supply pipeline is connected with a pipeline between the sub high temperature fan 210 and the cooler 213, the other end of the medium temperature circulating flue gas supply pipeline is connected with a flue gas preheating unit, and a medium temperature circulating air valve 212 is arranged on the medium temperature circulating flue gas supply pipeline at the inlet of the medium temperature circulating fan 211; the low-temperature circulating fan 216 is arranged on a low-temperature circulating flue gas supply pipeline, one end of the low-temperature circulating flue gas supply pipeline is connected with a pipeline of a gas outlet of the sub dust collector 214, the other end of the low-temperature circulating flue gas supply pipeline is connected with a fuel supply pipeline, and a low-temperature circulating air valve 217 is arranged on the low-temperature circulating flue gas supply pipeline at the inlet of the low-temperature circulating fan 216; the bottom flue gas outlet of the flue gas preheating unit is connected with the bottom inlet of the venturi throat 207, and the top outlet of the venturi throat 207 is connected with the bottom of the cylinder of the self-enrichment furnace 206; the fuel supply pipeline is respectively connected with the flue gas preheating unit and the coal injection pipe 2075 at the upper part of the venturi throat 207, and the industrial oxygen supply pipeline is respectively connected with the flue gas preheating unit and the oxygen pipe 2074 at the lower part of the venturi throat 207.

The tertiary air pipe 111 of the cement calcination main system 1 is additionally provided with a tertiary air branch pipe 222 which is connected to the inlet at the bottom of the venturi throat 207 and can introduce the tertiary air of the main system into the self-enrichment furnace 206 of the subsystem, a flue gas communicating pipeline 225 is additionally arranged between the outlet of the main high-temperature fan 112 and the outlet 210 of the sub high-temperature fan and can introduce the flue gas of the subsystem into the main dust collector 113 of the main system, and a low-temperature circulating flue gas supply pipeline at the inlet of the low-temperature circulating fan 216 is additionally provided with an air communicating pipeline for supplying coal air under the air combustion state; the tertiary air branch pipe 222 is provided with a tertiary air communicating valve 223, the flue gas communicating pipeline 225 is provided with a flue gas communicating valve 226, the air communicating pipeline is provided with an air communicating valve 224, a fuel supply pipeline at the inlet of the flue gas preheating unit is provided with a coal feeding air valve 228 of the preheating furnace, and a pipeline at the inlet of the cooler 213 is provided with a cooler valve 227 for switching and adjusting.

The temperature of the low-temperature circulating flue gas g3 is lower than 150 ℃, and the main component of the low-temperature circulating flue gas is CO ₂ ，CO ₂ Concentration (volume fraction) higher than 60%, O ₂ The concentration is lower than 10%; the temperature of the medium-temperature circulating flue gas g2 is lower than 400 ℃, and the main component of the medium-temperature circulating flue gas is CO ₂ ，CO ₂ Concentration higher than 60%, O ₂ The concentration is less than 10%. The fuel used is pulverized coal F, and the fineness is controlled to 80um and the screen residue is lower than 20 percent. The oxidant used for combustion is industrial oxygen g1, and the concentration of the industrial oxygen g1 is not less than 80%.

Referring to fig. 2, the flue gas preheating unit is used for preheating low-temperature circulating flue gas g3 and medium-temperature circulating flue gas g2 to above 900 ℃ by using fuel; the flue gas preheating unit comprises a burner 209 and a preheating furnace 208, the burner 209 is installed at the top of the preheating furnace 208, the head of the burner 209 extends into the preheating furnace 208, and the preheating furnace 208 is used for heating medium-temperature circulating flue gas g2 and low-temperature circulating flue gas g 3.

The burner 209 is a cylindrical structure, see fig. 5, and comprises an oil pipe, an inner primary air pipe, a coal pipe and an outer primary air pipe which are coaxially sleeved from inside to outside in sequence, wherein four channels are formed inside, and a central oil gun channel 2091, an inner primary air channel 2093, a coal powder channel 2094 and an outer primary air channel 2095 are respectively arranged from inside to outside. The head ports of the oil pipe, the coal pipe and the outer primary air pipe are aligned to form the head of the burner 209; a distance H0 is reserved between the head of the inner primary air pipe and the head of the combustor 209, so that the inner primary air channel 2093 and the coal powder channel 2094 form an air-coal premixing channel 2097 at the head of the combustor 209; an air-coal premixing adjusting ring 2098 which can move back and forth along the axial direction of the burner 209 is arranged between the inner primary air channel 2093 and the coal powder channel 2094, so that the length of the air-coal premixing channel 2097 can be adjusted between 0 and H0. The air-coal premixing adjusting ring 2098 of this embodiment is disposed on the inner wall of the inner primary air duct.

Referring to fig. 3 and 4, the preheating furnace 208 is composed of a cyclone chamber 2081, a reducer section 2082 and a hearth 2083 from top to bottom. The swirl chamber 2081 is of a volute structure, so that the flue gas entering from the inlet 20811 of the swirl chamber enters in a volute tangential swirl manner. A burner mounting hole 20813 is arranged in the center of the swirl chamber top cover 20812, the burner 209 is mounted at the top of the preheating furnace 208 through the burner mounting hole 20813, and the head of the burner 209 extends into the swirl chamber 2081. A refractory material layer 2099 is arranged outside the outer primary air channel 2095 of the burner 209 and used for heat insulation, so that the flame radiation in the preheating furnace 208 is prevented from transferring heat to the burner 209, the internal temperature of the burner 209 is overhigh, and the industrial oxygen g1 is oxidized on wall steel in the conveying process in the burner 209. The circumference of the cross section of the swirling chamber 2081 is smaller than that of the hearth 2083, and the inner diameter of the reducer 2082 is gradually increased from top to bottom, so that the circulating flue gas swirling flow operation is accelerated to fully cover the circumferential direction of the furnace wall.

Referring to fig. 1, 9 and 10, the bottom outlet of the furnace 2083 is connected with the bottom of the venturi throat 207 through a pipe, and the top of the venturi throat 207 is connected with the bottom of the column of the self-enriching furnace 206; the raw material feeding pipe 2061 is provided at the bottom of the column of the self-enriching furnace 206. The venturi throat 207 is divided into a lower contraction section 2071, a throat area high-speed section 2072 and an upper expansion section 2073 from bottom to top, the lower contraction section 2071 is inserted into the oxygen pipe 2074, the oxygen pipe 2074 is inserted into the axial center of the venturi throat 207 in a downward inclination manner, an included angle between the oxygen pipe 2074 and the horizontal direction is 30-60 degrees, so that the industrial oxygen g1 and the circulating flue gas are uniformly mixed, and the insertion depth of the embodiment is 300-1000 mm; the upper expansion section 2073 is inserted into the coal injection pipe 2075, and the coal injection pipe 2075 is horizontally inserted to be close to the inner wall of the upper expansion section 2073, so that the circulating flue gas and the coal powder are mixed at a vortex low-pressure region formed at the outer side of the upper expansion section 2073, and the insertion depth of the embodiment is 100-500 mm; the number of the oxygen pipes 2074 and the number of the coal injection pipes 2075 are 2 to 4 respectively, and the oxygen pipes and the coal injection pipes are symmetrically arranged along the circumference. In this embodiment, the oxygen pipes 2074 and the coal injection pipes 2075 are all provided with 2 branches, and 4 branches are uniformly distributed in the circumferential direction.

In the total oxygen combustion subsystem 2, the fuel supply pipeline is divided into two paths and is respectively connected with a coal pipe and a coal injection pipe 2075 at the upper part of the venturi throat 207; the low-temperature circulating flue gas supply pipeline is connected with a fuel supply pipeline; the medium-temperature circulating flue gas supply pipeline is connected with an inlet of the cyclone chamber 2081; the industrial oxygen g1 supply pipeline is divided into three paths and is respectively connected with the outer primary air pipe, the inner primary air pipe and the oxygen pipe 2074 at the lower part of the venturi throat 207, and the industrial oxygen g1 supply pipeline connected with the outer primary air pipe, the inner primary air pipe and the oxygen pipe 2074 at the lower part of the venturi throat 207 is respectively provided with a flow controller. Pulverized coal F is introduced into the fuel supply pipeline, industrial oxygen g1 is introduced into the industrial oxygen g1 supply pipeline, low-temperature circulating flue gas g3 is introduced into the low-temperature circulating flue gas supply pipeline, and medium-temperature circulating flue gas g2 is introduced into the medium-temperature circulating flue gas supply pipeline.

Since the position of the air-coal premixing adjusting ring 2098 can move back and forth along the axial direction of the burner 209, the length of the air-coal premixing passage 2097 can be adjusted before 0H 0. The distance between the head of the air-coal premixing adjusting ring 2098 and the head of the burner 209 is H, when H is greater than 0, the inner primary air (i.e., the industrial oxygen g 1) in the inner primary air passage 2093 and the coal-feeding air (i.e., the low-temperature circulating flue gas g 3) in the pulverized coal passage 2094 are premixed into one stream in the air-coal premixing passage 2097 (i.e., a premixing area), and the stream is ejected out of the burner 209 after passing through the air-coal premixing passage 2097. The larger the length of the air-coal premixing passage 2097 is, the stronger the premixing degree is, and the more uniform the contact of the pulverized coal F and the industrial oxygen g1 is.

Referring to fig. 5 and 6, when the fuel is a fire-retardant coal (such as anthracite), if there is no air-coal premixing passage 2097, the pulverized coal and the industrial oxygen g1 are ejected from the two passages of the burner 209 independently, and the air supply of the coal is the low temperature circulating flue gas g3, which may cause insufficient oxygen supply during the combustion of the pulverized coal, and cause the problems of unstable flame and even flameout. By adjusting the air-coal premixing adjusting ring 2098 additionally arranged between the inner primary air passage 2093 and the coal dust passage 2094, the industrial oxygen g1 and the coal dust F are premixed in the combustor 209, so that the coal dust F can be in contact with the industrial oxygen g1 in advance before being ejected, and the ignition and flame stability of coal can be enhanced. The inner primary air is rotational flow when entering the air-coal premixing passage 2097, the coal powder passage 2094 is direct flow, and the inner primary air collides with coal conveying air under the effect of rotational flow centrifugal force in the air-coal premixing passage 2097, so that the premixing effect of the industrial oxygen g1 and the coal powder F is improved.

For medium-flammability coal, the length H of the premixing area can be flexibly adjusted by the air-coal premixing adjusting ring 2098, so as to enhance the ignition and flame stability of the coal without tempering.

Referring to fig. 7 and 8, for combustible coal, if the industrial oxygen g1 and the pulverized coal F are premixed in advance in the burner 209, there is a problem that the flame burns at a too high speed, and the flame is tempered to the premixing zone, thereby burning out the head of the burner 209. At this time, the tempering problem can be solved by adjusting the position of the air-coal premixing adjusting ring 2098, that is, the air-coal premixing adjusting ring 2098 is inserted to a depth to the outlet of the burner 209, so that the premixing area disappears, the outlet of the burner 209 has four channels, the industrial oxygen g1 and the coal powder F are not premixed in the burner 209 and are sprayed out from the respective channels, because the coal powder F and the industrial oxygen g1 are isolated from each other before being sprayed out, the flame can not be tempered to the channel of the burner 209, the state is a non-premixing mode combustion, the burner is suitable for easily ignited coal quality, and the head of the burner 209 can be prevented from being burnt out.

In addition, the industrial oxygen flow of the inner primary air passage 2093 can be adjusted by the inner primary air flow controller 219, when the coal is inflammable, the industrial oxygen flow of the inner primary air passage 2093 is reduced, the industrial oxygen g1 premixed with the pulverized coal is reduced, the oxygen concentration in the inner primary air outlet is reduced, and the pulverized coal is prevented from deflagration and backfire. When the coal is difficult to burn, the flow of the industrial oxygen g1 of the inner primary air channel 2093 is increased, and the flame stability of pulverized coal ignition is enhanced.

A can realize the air combustion and burn the cement of fast switch over operation of the partial oxy-fuel combustion, the said cement burns the method and adopts cement to calcine the main system 1 and burn the sub-system 2 and run in parallel to carry on the air combustion and burn the partial oxy-fuel combustion, or regulate in order to burn the main system 1 and burn the fast switch over operation of the partial oxy-fuel combustion between the two systems of sub-system 2 in cement calcine according to the needs;

the cement calcination main system 1 and the oxy-fuel combustion subsystem 2 are connected in parallel and have no cross in the preheating predecomposition link; in the clinker calcining step, the two raw materials decomposed by the cement calcining main system 1 and the oxy-fuel combustion subsystem 2 enter the rotary kiln 108 together for calcining to prepare the cement clinker.

s1, sequentially opening a tertiary air communicating valve 223, a smoke communicating valve 226 and an air communicating valve 224;

s2, stopping conveying the industrial oxygen g1, and closing a coal feeding air valve 228 of the preheating furnace;

s3, sequentially stopping the sub dust collector 214, stopping the sub exhaust fan 215, closing the low-temperature circulating air valve 217, stopping the medium-temperature circulating fan 211, closing the medium-temperature circulating air valve 212, stopping the cooler 213 and closing the cooler inlet valve 227;

s4, adjusting the air pulling quantity of the main exhaust fan 114 and the coal feeding quantity of the coal fed into the self-enrichment furnace 206, introducing the flue gas out of the oxy-fuel combustion subsystem into a main dust collector 113 of the main cement calcination system 1, and enabling the temperature of the flue gas out of the enrichment furnace 206 to reach 850-900 ℃;

the specific steps of the oxy-fuel combustion subsystem 2 for rapidly switching from the air combustion state to the oxy-fuel combustion state are as follows:

s1, sequentially starting a cooler 213, a cooler inlet valve 227, a medium-temperature circulating air valve 212, a medium-temperature circulating fan 211, a low-temperature circulating air valve 217, a sub-exhaust fan 215 and a sub-dust collector 214;

s2, starting industrial oxygen g1, and starting a coal feeding air valve 228 of the preheating furnace;

s3, closing the air communicating valve 224, the smoke communicating valve 226 and the tertiary air communicating valve 223 in sequence;

s4, adjusting the air drawing quantity of the medium-temperature circulating fan 211, the coal feeding quantity of the self-enrichment furnace 206 and the preheating furnace 208 and the flow of the industrial oxygen g1, so that the temperature of the flue gas out of the preheating furnace 208 is above 900 ℃, and the temperature of the flue gas out of the enrichment furnace 206 is 850-1000 ℃.

When partial oxy-fuel combustion is carried out, raw meal is fed into a sub-preheater unit in the oxy-fuel combustion subsystem 2, is preheated by the sub-preheater unit and then is fed into a self-enrichment furnace 206 for pre-decomposition, and then enters a rotary kiln 108 for calcination; the flue gas from the enrichment furnace 206 is subjected to heat exchange through the sub-preheater unit under the air suction of the sub-high temperature fan 210, part of the flue gas out of the sub-preheater unit is returned to the preheating furnace 208 as medium-temperature circulating flue gas g2, the rest of the flue gas is cooled by the cooler 213, dust is collected by the sub-dust collector 214, part of the flue gas is used as low-temperature circulating flue gas g3, and the rest of the flue gas rich in carbon dioxide is discharged out of the cement burning system through the sub-exhaust fan 215.

The oxy-fuel combustion subsystem 2 adopts a mode of two-time oxy-fuel combustion in series to carry out pulverized coal combustion and raw material decomposition, and comprises the following specific steps:

the method comprises the following steps: taking low-temperature circulating flue gas g3 from a pipeline at a gas outlet of the sub dust collector 214, wherein the low-temperature circulating flue gas g3 carries coal dust F to enter a coal dust channel 2094 of the combustor 209; the industrial oxygen g1 is divided into two parts and respectively enters an inner primary air channel 2093 and an outer primary air channel 2095 of the combustor 209, the industrial oxygen g1 of the inner primary air channel 2093 enters in a swirling mode, the industrial oxygen g1 in the outer primary air channel 2095 is ejected out in a swirling mode, the supply amount of the industrial oxygen g1 meets the oxygen amount required by combustion of the coal dust in the preheating furnace 208, and the coal dust is stably combusted in the preheating furnace 208 after being ejected out.

Step two: taking the medium-temperature circulating flue gas g2 from a pipeline between the sub high-temperature fan 210 and the cooler 213, introducing the medium-temperature circulating flue gas g2 into a cyclone chamber 2081 of the preheating furnace 208 in a tangential cyclone manner, and making the medium-temperature circulating flue gas move downwards along the wall under the centrifugal force of the top cyclone chamber 2081; the pulverized coal and the industrial oxygen g1 are sprayed out from the burner 209 and then ignited and combusted in the preheating furnace 208, so that a fuel-rich area A positioned in the center of the hearth 2083, an oxygen-rich area B positioned outside the fuel-rich area and a carbon-rich area C positioned between the oxygen-rich area and the furnace wall are formed in the space in the preheating furnace 208; the combustion heat of the pulverized coal raises the temperature of the middle-low temperature circulating flue gas to over 900 ℃.

Step three: the high-temperature circulating flue gas which is discharged from the preheating furnace 208 and has the temperature of over 900 ℃ moves upwards in a reverse direction.

Step four: the high-temperature circulating flue gas enters the Venturi throat 207, and industrial oxygen g1 is sprayed into a lower contraction section 2071 at the inlet of the Venturi throat 207, so that the oxygen concentration in the central area is increased to more than 30%; coal dust is injected into the upper expansion section 2073 at the outlet of the venturi throat 207, and the outlet gas forms a jet flow, so that a vortex low-pressure region is formed outside the upper expansion section 2073 under the action of the jet flow.

Step five: the coal powder enters the self-enriching furnace 206 along with the circulating flue gas to burn and release heat, raw materials are fed into a raw material feeding pipe 2061 at the bottom of the column of the self-enriching furnace 206, so that the raw materials are decomposed in the self-enriching furnace 206, and CO is released ₂ Self-enriched furnace 206 flue gas dry basis CO ₂ The concentration is more than 80 percent, and the temperature is 850-1000 ℃.

In the whole cement burning process, cement raw materials are divided into 2 parts, the 1 st part is fed into a main preheater unit of a main cement burning system 1, enters a main decomposing furnace 106 for decomposition after being preheated, and then enters a rotary kiln 108 for burning; the 2 nd part is fed into a sub-preheater unit of the oxy-fuel combustion subsystem 2, is preheated and then fed into a self-enrichment furnace 206 for decomposition, and then enters a rotary kiln 108 for calcination. The coal powder is divided into 3 parts, the 1 st part is fed into a rotary kiln 108 through a kiln head burner 110 and is used for calcining cement clinker; part 2 is fed to the main decomposition furnace 106 for raw meal decomposition; the 3 rd part is divided into 2 groups, one group is fed into the smoke preheating unit of the total oxygen combustion subsystem 2 and is used for circulating smoke to heat; the other group is fed to the self-enrichment furnace 206 of the oxy-fuel combustion subsystem 2 for raw meal decomposition.

In the oxy-fuel combustion subsystem 2, a central oil gun passage 2091 in the center of the burner 209 is used to ignite the preheat furnace 208. The two

primary air passages

2093 and 2095 feed industrial oxygen g1 in an amount to meet the amount of oxygen required for combustion of the pulverized coal in the preheater 208. An inner primary air cyclone 2092 is arranged at the inlet of the inner primary air passage 2093, so that the industrial oxygen g1 entering the inlet of the inner primary air passage 2093 flows downwards in a rotating manner under the action of the inner primary air cyclone 2092; the outer primary air passage 2095 is located outside the pulverized coal passage 2094, and an outer primary air cyclone 2096 is arranged at an outlet of the outer primary air passage 2095, so that the industrial oxygen g1 in the outer primary air passage 2095 is ejected in a high-speed rotational flow mode under the action of the outer primary air cyclone 2096, and the stability of flames in the preheating furnace 208 can be enhanced.

Air is taken from an outlet pipeline of the sub high-temperature fan 210, and medium-temperature circulating flue gas g2 at the temperature of 150-400 ℃ enters from an inlet 20811 of the cyclone chamber and flows downwards along the wall surface in a rotating manner. Because the industrial oxygen g1 is used as an oxidant, the oxygen content is greatly improved relative to air, the corresponding flame temperature is relatively high, the high-temperature area can reach more than 1300 ℃, and when the flame contacts the side wall of the preheating furnace 208, the burning loss of the refractory material on the furnace wall surface is easily caused. The medium-temperature circulating flue gas g2 enters the preheating furnace 208 in a swirling manner, so that a low-temperature protective gas film is formed between the furnace wall and the flame due to relatively low temperature and low oxygen content, and the refractory materials on the wall surface of the preheating furnace 208 are effectively protected from being ablated by the flame.

Taking air from the sub-dust collector 214, taking low-temperature circulating flue gas g3 below 150 ℃ as air for conveying pulverized coal, and taking low-temperature circulating flue gas CO ₂ The concentration is not lower than 60%, and the coal powder is fed into a coal powder channel 2094 of the burner 209 through the low-temperature circulating flue gas g 3; the industrial oxygen g1 is divided into two parts and enters the combustor 209, wherein one part of the industrial oxygen enters the inner primary air channel 2093 of the combustor 209 in a rotational flow manner, the flow of the industrial oxygen is controlled by the inner primary air flow controller 219, the other part of the industrial oxygen enters the outer primary air channel 2095 of the combustor 209, the flow of the industrial oxygen is controlled by the outer primary air flow controller 220, the supply amount of the industrial oxygen g1 meets the oxygen amount required by the combustion of the pulverized coal in the preheating furnace 208, and the combustion of the pulverized coal in the preheating furnace 208 is stable after the pulverized coal is sprayed out; the medium-temperature circulating flue gas g2 tangentially enters from a cyclone chamber inlet 20811 of the preheating furnace 208 in a cyclone manner and moves downwards along the wall under the centrifugal force of a top cyclone chamber 2081; the space in the preheating furnace 208 forms rich combustion in the center of a hearth 2083The furnace comprises a material area A, an oxygen-rich area B positioned outside a fuel-rich area, and a carbon-rich area C positioned between the oxygen-rich area and a furnace wall; the pulverized coal F and industrial oxygen g1 (the oxygen concentration is not lower than 80%) are sprayed out from the burner 209 and then ignited and combusted in the preheating furnace 208, for one-time combustion, the combustion heat of the pulverized coal is regulated and controlled to enable the flue gas out of the preheating furnace 208 to flow out from the bottom of the preheating furnace 208, the temperature is over 900 ℃, and CO in the flue gas is above 900 DEG ₂ The concentration is more than 60 percent. The advantages of the air supply mode are as follows: 1) The coal powder F and the industrial oxygen g1 are not mixed in the conveying process, and the coal powder is conveyed by adopting low-temperature circulating flue gas g3, so that the safety problem of spontaneous combustion caused by the mixed conveying of the industrial oxygen g1 and the coal powder F of the oxy-fuel combustion subsystem 2 is solved; 2) The medium-temperature circulating flue gas g2 directly enters the preheating furnace 208 and moves downwards along the wall, so that the function of protecting a gas film is achieved before the pulverized coal combustion flame and the wall surface, and the wall surface can be prevented from being burnt by the high-temperature flame.

The air supply mode of the flue gas preheating unit provided by the invention is as follows: the low-temperature circulating flue gas g3 is used as coal conveying air for conveying coal powder; supplying air to the medium-temperature circulating flue gas g2 from a cyclone chamber 2081 of the preheating furnace 208 in an adherence manner; two industrial oxygen g1 are used as inner primary air supply at the inner side of the coal powder passage 2094, whether the coal powder is premixed with the coal powder in advance is determined according to the combustion characteristics of the coal powder, and the industrial oxygen is ejected out of the coal powder passage 2094 in a high-speed rotational flow mode to be used as outer primary air. So that three zones, namely a fuel-rich zone A, can be established in the space of the preheating furnace 208 and positioned in the center of the hearth 2083; the oxygen-enriched area B is positioned outside the fuel-enriched area; and the carbon-rich area C is positioned between the fuel-rich area and the furnace wall. The advantages of the zone combustion method are as follows: 1. the peroxide coefficient in the fuel-rich area is less than 1, and the fuel-rich area is a reducing atmosphere and can inhibit the generation of NOx; 2. the carbon-rich region is mainly CO ₂ And the gas temperature is relatively low, so that the furnace wall surface can be protected, and flame can be prevented from burning the furnace wall.

The high temperature circulating flue gas from the preheating furnace 208 passes through the pipeline and then moves vertically upwards, enters the Venturi throat 207, industrial oxygen g1 is sprayed into a lower contraction section 2071 at the inlet of the Venturi throat 207 to increase the oxygen concentration of a central area to more than 30 percent, the average wind speed of the cross section of a high-speed section 2072 in the throat area is 25-50 m/s, the average wind speed of the cross section of an outlet of an upper expansion section 2073 is 5-15 m/s, and the wind speed of the high-speed section 2072 in the throat area is the wind speed of the outlet of the upper expansion section 2073The wind speed is more than 2 times. The high temperature circulating flue gas continues to move upwards, the gas at the outlet of the venturi throat 207 forms jet flow, the coal powder is sprayed into the upper expansion section 2073 through the coal spraying pipe 2075, a vortex low-pressure area is formed outside the upper expansion section 2073 under the action of the jet flow, the circulating flue gas and the coal powder are back mixed in the area, the oxygen concentration of the circulating flue gas at the outer side is relatively low, and NO is inhibited from being burnt by the coal powder _X And (4) releasing.

The pulverized coal injected from the coal injection pipe 2075 moves upward along with the circulating flue gas and is combusted in the self-enrichment furnace 206 as secondary combustion. Raw material is fed from the bottom of the column of the self-enriching furnace 206, and a raw material feeding pipe 2061 is positioned above the height of the coal injection pipe 2075. The full decomposition of raw meal is realized in the self-enrichment furnace 206, and CO is released ₂ The temperature of the flue gas from the enrichment furnace 206 is 850-1000 ℃, and the dry-based CO of the flue gas from the enrichment furnace 206 ₂ The concentration is more than 80%.

The flue gas from the enrichment furnace 206 is subjected to heat exchange through a sub-preheater unit under the air draft of a sub-high temperature fan 210, and part of the flue gas is returned to the preheating furnace 208 as medium-temperature circulating flue gas g 2; after the remaining flue gas is cooled and dust-collected by the cooler 213, a part of the remaining flue gas is used as low-temperature circulating flue gas g3, and the remaining flue gas is rich in carbon dioxide and is discharged out of the cement burning system.

In summary, the cement burning system of the invention can be adjusted between the main cement burning system 1 and the oxy-fuel combustion subsystem 2 as required to perform air combustion and local oxy-fuel combustion fast switching operation, thus solving the problems of continuity and stability of the operation of the cement burning system when the oxy-fuel combustion subsystem 2 is in an ignition stage or under abnormal working conditions and the output of carbon dioxide-rich flue gas needs to be suspended; in the preheating and predecomposition link of the firing kiln tail, a main system and a subsystem are operated in parallel; in the rotary kiln, the calcined raw materials generated by the main system and the subsystem are simultaneously fed into the kiln to produce cement clinker; mutual interference between the main system and the subsystems, such as mutual wind channeling, pressure fluctuation interference and the like, is reduced. Secondly, when partial oxy-fuel combustion is carried out, in the oxy-fuel combustion subsystem 2, raw materials are decomposed and divided into a primary combustion area and a secondary combustion area which are connected in series for operation, pulverized coal is conveyed through low-temperature circulating flue gas, raw materials are not fed into the primary combustion area, and industrial oxygen g1 is divided into two parts and is communicated with the pulverized coalAir is supplied from the inner side and the outer side of the flue 2094, the medium-temperature circulating flue gas g2 is sent into the preheating furnace 208 from the inlet 20811 of the cyclone chamber of the preheating furnace, and the medium-temperature circulating flue gas and the low-temperature circulating flue gas are heated to more than 900 ℃ in the preheating furnace, so that the coal powder flame in the preheating furnace 208 is stable, the furnace wall of the preheating furnace is not ablated, and the low NO is realized _X The problems of difficult fuel ignition, unstable flame and easy flameout in the combustion process when the medium-low temperature circulating flue gas is directly introduced into the decomposing furnace can be solved, and the safety problem of spontaneous combustion caused by mixed transportation is avoided; the secondary combustion zone carries out material mixing operation, high-temperature circulating flue gas is introduced into the secondary combustion zone, industrial oxygen and coal powder are injected into the secondary combustion zone to decompose raw materials, and the material is supported by the jet flow of the Venturi throat 207, so that the problem of furnace wall high-temperature skinning caused by raw material collapse and local deflagration of the coal powder is solved, NO (nitric oxide) generated by coal powder combustion is inhibited _X Releasing; the temperature of the flue gas from the enrichment furnace 206 is 850-1000 ℃, and the dry basis CO is ₂ The concentration is more than 80 percent, and the full decomposition of the raw material is realized. And thirdly, when local oxy-fuel combustion is carried out, circulating air is taken in a grading manner by the oxy-fuel combustion subsystem 2, medium-temperature circulating air (150-400 ℃) is taken from a position between the sub high-temperature fan and the cooler 213 and directly enters the preheating furnace, and low-temperature circulating air (lower than 150 ℃) is taken from a position behind the sub dust collector and used as pulverized coal conveying air, so that the heat recovery is improved and the energy consumption is reduced while the safety of pulverized coal conveying is ensured.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A cement calcination system capable of realizing rapid switching operation of air combustion and local oxy-fuel combustion is characterized by comprising a cement calcination main system and an oxy-fuel combustion sub-system, wherein a main high-temperature fan, a main dust collector, a main exhaust fan and a chimney are sequentially arranged on an outlet air pipe at the top of a main preheater unit of the cement calcination main system;

the total oxygen combustion subsystem consists of a sub-preheater unit, a self-enrichment furnace, a flue gas preheating unit, a Venturi throat, a sub-high-temperature fan, a cooler, a sub-dust collector, an intermediate-temperature circulating fan, an intermediate-temperature circulating flue gas supply pipeline, a low-temperature circulating fan, a low-temperature circulating flue gas supply pipeline, a fuel supply pipeline and an industrial oxygen supply pipeline; a feeding pipe of a penultimate sub-cyclone of the sub-preheater unit is connected with a raw material feeding pipe of the self-enrichment furnace, a feeding pipe of a last-stage sub-cyclone of the sub-preheater unit is connected with a kiln tail smoke chamber of the main cement calcination system, and an outlet air pipe at the top of the sub-preheater unit is sequentially provided with the sub-high temperature fan, the cooler and the sub-dust collector; the medium-temperature circulating fan is arranged on a medium-temperature circulating flue gas supply pipeline, one end of the medium-temperature circulating flue gas supply pipeline is connected with a pipeline between the sub high-temperature fan and the cooler, and the other end of the medium-temperature circulating flue gas supply pipeline is connected with the flue gas preheating unit; the low-temperature circulating fan is arranged on a low-temperature circulating flue gas supply pipeline, one end of the low-temperature circulating flue gas supply pipeline is connected with a pipeline of a gas outlet of the sub dust collector, and the other end of the low-temperature circulating flue gas supply pipeline is connected with a fuel supply pipeline;

the flue gas preheating unit is used for preheating low-temperature circulating flue gas and medium-temperature circulating flue gas to over 900 ℃ through fuel; the bottom flue gas outlet of the flue gas preheating unit is connected with the bottom inlet of the venturi throat, the top outlet of the venturi throat is connected with the bottom of the cylinder of the self-enrichment furnace, and the top outlet of the self-enrichment furnace is connected with the inlet of the last-stage cyclone cylinder;

the fuel supply pipeline is respectively connected with the flue gas preheating unit and a coal injection pipe at the upper part of the Venturi throat, and the industrial oxygen supply pipeline is respectively connected with the flue gas preheating unit and an oxygen pipe at the lower part of the Venturi throat;

the flue gas preheating unit comprises a burner and a preheating furnace, the burner is arranged at the top of the preheating furnace, the head of the burner extends into the preheating furnace, the burner comprises an oil pipe, an inner primary air pipe, a coal pipe and an outer primary air pipe which are coaxially sleeved from inside to outside in sequence, and a central oil gun channel, an inner primary air channel, a coal powder channel and an outer primary air channel are formed in the burner from inside to outside in sequence; the tail parts of the inner primary air pipe and the outer primary air pipe are both connected with an industrial oxygen supply pipeline, and the tail part of the coal pipe is connected with a fuel supply pipeline;

the preheating furnace consists of a spiral-flow chamber, a reducing section and a hearth from top to bottom, wherein the spiral-flow chamber is of a volute structure, so that flue gas entering from an inlet of the spiral-flow chamber enters in a volute type tangential spiral-flow manner;

forming a fuel-rich area positioned in the center of the hearth, an oxygen-rich area positioned outside the fuel-rich area and a carbon-rich area positioned between the oxygen-rich area and the furnace wall in the preheating furnace;

the cement calcination main system is characterized in that a tertiary air pipe of the cement calcination main system is additionally provided with a tertiary air branch pipe which is connected to an inlet at the bottom of a Venturi throat, a flue gas communication pipeline is additionally arranged between an outlet of a main high-temperature fan and an outlet of a sub high-temperature fan, a low-temperature circulating flue gas supply pipeline at an inlet of a low-temperature circulating fan is additionally provided with an air communication pipeline, a tertiary air communication valve is arranged on the tertiary air branch pipe, a flue gas communication valve is arranged on the flue gas communication pipeline, and an air communication valve is arranged on the air communication pipeline; and a coal feeding air valve entering the preheating furnace is arranged on a fuel supply pipeline at the inlet of the flue gas preheating unit, and a cooler valve is arranged on a pipeline at the inlet of the cooler.

2. The system for cement combustion with rapid switching operation between air combustion and partial oxy-fuel combustion as claimed in claim 1, wherein the adjusting ring for air-coal premixing is disposed on the inner wall of the inner primary air pipe.

3. The cement burning system capable of realizing the rapid switching operation between the air burning and the partial oxy-fuel combustion as claimed in claim 1, wherein the inlet of the inner primary air channel and the outlet of the outer primary air channel are provided with swirlers; and a refractory material layer is arranged outside the outer primary air channel.

4. The cement burning system capable of realizing the rapid switching operation of the air burning and the partial oxy-fuel combustion as claimed in claim 1, wherein flow controllers are respectively arranged on industrial oxygen supply pipelines connected with oxygen pipes at the lower parts of the inner primary air pipe, the outer primary air pipe and the venturi throat.

5. The cement burning system capable of realizing the rapid switching operation between the air burning and the partial oxy-fuel combustion as claimed in claim 1, wherein a burner mounting hole is arranged at the center of a top cover of the cyclone chamber, and the head of the burner extends into the cyclone chamber through the burner mounting hole; the inner diameter of the reducing section is gradually increased from top to bottom.

6. The cement burning system capable of realizing the rapid switching operation between the air burning and the partial oxy-fuel combustion as claimed in claim 1, wherein a medium temperature circulating air valve is arranged on the medium temperature circulating flue gas supply pipeline at the inlet of the medium temperature circulating fan, and a low temperature circulating air valve is arranged on the low temperature circulating flue gas supply pipeline at the inlet of the low temperature circulating fan.

7. The cement burning system capable of realizing the rapid switching operation between the air burning and the partial oxy-fuel combustion as claimed in claim 1, wherein the venturi throat is divided into a lower contraction section, a throat area high-speed section and an upper expansion section from bottom to top, the lower contraction section is inserted into the oxygen pipe, the oxygen pipe is inserted into the venturi throat in a downward inclination manner to be close to the axial center of the venturi throat, and an included angle between the oxygen pipe and the horizontal direction is 30-60 degrees, so that the industrial oxygen and the circulating flue gas are uniformly mixed; the coal injection pipe is inserted into the upper expansion section and is inserted to be close to the inner wall of the upper expansion section, so that circulating flue gas and coal powder are mixed at a vortex low-pressure area formed outside the upper expansion section; the number of the oxygen pipes and the number of the coal injection pipes are respectively 2-4, and the oxygen pipes and the coal injection pipes are symmetrically arranged along the circumference.

8. The system for cement burning capable of achieving the rapid switching operation between air burning and partial oxy-fuel combustion as claimed in claim 1, wherein the raw material feeding pipe is disposed at the bottom of the column of the self-enriching furnace.

9. A cement burning method capable of realizing rapid switching operation between air burning and partial oxy-fuel combustion based on the cement burning system as claimed in any one of claims 1 to 8, wherein the cement burning method is characterized in that the air burning and the partial oxy-fuel combustion are performed by using a main cement burning system and an oxy-fuel combustion subsystem which are operated in parallel or adjusted between the main cement burning system and the oxy-fuel combustion subsystem as required to perform rapid switching operation between air burning and partial oxy-fuel combustion;

s4, adjusting the air pulling quantity of a main exhaust fan and the coal feeding quantity of a self-enrichment furnace, introducing the flue gas out of the oxy-fuel combustion subsystem into a main dust collector of a cement calcination main system, and enabling the temperature of the flue gas out of the self-enrichment furnace to be 850-900 ℃;

s3, closing an air communicating valve, a smoke communicating valve and a tertiary air communicating valve in sequence;

s4, adjusting the air drawing amount of the medium-temperature circulating fan, the coal feeding amount of the self-enrichment furnace and the preheating furnace and the industrial oxygen flow, so that the temperature of the flue gas discharged from the preheating furnace is over 900 ℃, and the temperature of the flue gas discharged from the enrichment furnace is 850-1000 ℃.

10. The method for cement burning capable of realizing rapid switching operation between air burning and partial oxy-fuel combustion as claimed in claim 9, wherein when the partial oxy-fuel combustion is performed, raw meal is fed into the sub-preheater unit in the oxy-fuel combustion subsystem, is preheated by the sub-preheater unit, is fed into the self-enrichment furnace for pre-decomposition, and then is calcined in the rotary kiln; the smoke from the enrichment furnace is subjected to heat exchange through a sub-preheater unit under the air draft of a sub-high-temperature fan, and part of the smoke is returned to the preheating furnace as medium-temperature circulating smoke; cooling and collecting dust for the rest flue gas, and using a part of the cooled and collected flue gas as low-temperature circulating flue gas;

the method comprises the following steps: taking low-temperature circulating flue gas from a pipeline at a gas outlet of the sub dust collector, wherein the low-temperature circulating flue gas carries pulverized coal to enter a pulverized coal channel of a combustor; the industrial oxygen is divided into two parts which respectively enter an inner primary air channel and an outer primary air channel of the burner, the industrial oxygen of the inner primary air channel enters in a swirling mode, the industrial oxygen in the outer primary air channel is ejected out in a swirling mode, the supply amount of the industrial oxygen meets the oxygen amount required by the combustion of the pulverized coal in the preheating furnace, and the pulverized coal is stably combusted in the preheating furnace after being ejected out;

taking the medium-temperature circulating flue gas from a pipeline between the sub high-temperature fan and the cooler, tangentially and rotationally introducing the medium-temperature circulating flue gas into a cyclone chamber of the preheating furnace, and making the medium-temperature circulating flue gas move downwards along the wall under the centrifugal force of the cyclone chamber at the top; the pulverized coal and the industrial oxygen are sprayed out from the burner and then are ignited and combusted in the preheating furnace, so that a fuel-rich area positioned in the center of the hearth, an oxygen-rich area positioned outside the fuel-rich area and a carbon-rich area positioned between the oxygen-rich area and the furnace wall are formed in the space in the preheating furnace; the combustion heat of the pulverized coal raises the temperature of the middle-low temperature circulating flue gas to over 900 ℃;

step two: the high-temperature circulating flue gas with the temperature of over 900 ℃ of the flue gas outlet preheating unit reversely moves upwards;

step three: the high-temperature circulating flue gas enters a Venturi throat, and industrial oxygen is sprayed into the inlet of the Venturi throat to increase the oxygen concentration of the central area to be more than 30%; spraying coal powder into the outlet of the venturi throat, wherein the outlet gas forms jet flow, and a vortex low-pressure area is formed on the outer side of the upper part of the venturi throat under the action of the jet flow;

step four: the coal powder enters the self-enrichment furnace along with the circulating flue gas to burn and release heat, raw materials are fed into a raw material feeding pipe of the self-enrichment furnace, so that the raw materials are decomposed in the self-enrichment furnace, and CO is released ₂ Self-enriched furnace flue gas dry basis CO ₂ The concentration is more than 80 percent, and the temperature is 850 to 1000 ℃.

11. The cement burning method capable of realizing the rapid switching operation between the air burning and the partial oxy-fuel combustion as claimed in claim 9 or 10, characterized in that the fineness of the pulverized coal is controlled to 80um screen residue lower than 20%; the oxygen concentration of the industrial oxygen is not lower than 80%; the temperature of the low-temperature circulating flue gas is lower than 150 ℃, and CO is ₂ Concentration higher than 60%, O ₂ The concentration is lower than 10%; the temperature of the medium-temperature circulating flue gas is lower than 400 ℃, and CO is ₂ Concentration higher than 60%, O ₂ The concentration is less than 10%.

12. The cement combustion method capable of realizing rapid switching operation of air combustion and partial oxy-fuel combustion according to claim 10, characterized in that according to the combustion characteristics of the pulverized coal, the length of the air-coal premixing passage is adjusted by adjusting the air-coal premixing adjusting ring, and/or the ignition and flame stability of the pulverized coal are enhanced by adjusting the amount of industrial oxygen entering the inner primary air passage and the outer primary air passage, so that the pulverized coal is stably combusted in the preheating furnace after being sprayed.

13. The method for burning the cement capable of realizing the fast switching operation between the air burning and the local oxy-fuel combustion as claimed in claim 10, wherein in the third step, the average wind speed of the cross section of the throat high-speed section of the venturi throat is 25 to 50m/s, the average wind speed of the outlet cross section of the upper expansion section is 5 to 15m/s, and the wind speed of the throat high-speed section is more than 2 times of the outlet wind speed of the upper expansion section.