CN112082149A - Flue gas recirculation lignite drying method and drying system - Google Patents
Flue gas recirculation lignite drying method and drying system Download PDFInfo
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- CN112082149A CN112082149A CN202010932833.7A CN202010932833A CN112082149A CN 112082149 A CN112082149 A CN 112082149A CN 202010932833 A CN202010932833 A CN 202010932833A CN 112082149 A CN112082149 A CN 112082149A
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C9/00—Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber
- F23C9/003—Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber for pulverulent fuel
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J15/00—Arrangements of devices for treating smoke or fumes
- F23J15/02—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material
- F23J15/022—Arrangements of devices for treating smoke or fumes of purifiers, e.g. for removing noxious material for removing solid particulate material from the gasflow
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23K—FEEDING FUEL TO COMBUSTION APPARATUS
- F23K1/00—Preparation of lump or pulverulent fuel in readiness for delivery to combustion apparatus
- F23K1/04—Heating fuel prior to delivery to combustion apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L15/00—Heating of air supplied for combustion
- F23L15/04—Arrangements of recuperators
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/001—Drying-air generating units, e.g. movable, independent of drying enclosure
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E20/00—Combustion technologies with mitigation potential
- Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery
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- Solid Fuels And Fuel-Associated Substances (AREA)
Abstract
The invention discloses a method and a system for drying lignite by recycling flue gas, wherein the method comprises the following steps: extracting recycled flue gas from the tail of the boiler as a drying agent to carry out first-stage drying on the high-moisture lignite; carrying out coal grinding and pulverizing treatment on the pre-dried lignite in a coal grinding and pulverizing unit, and introducing hot primary air to carry out second-stage drying on the pre-dried lignite; the pulverized lignite which is dried and pulverized is carried by hot primary air and is sent to a burner to be burnt in a hearth of the boiler; and (3) taking the medium-speed coal milling system as a coal milling and pulverizing unit to mill and pulverize the pre-dried lignite. The system comprises: the device comprises a recirculating flue gas unit, an air supply unit, a lignite drying unit and a coal grinding and pulverizing unit. According to the invention, the smoke of the boiler is extracted to pre-dry the lignite so as to reduce the moisture in the coal, so that the residual moisture in the coal meets the range of the drying capacity of the medium-speed pulverizing system, and the high-moisture lignite boiler can select a more stable and reliable medium-speed pulverizing system.
Description
Technical Field
The invention relates to the technical field of power station boiler equipment, in particular to a method and a system for drying lignite through flue gas recirculation.
Background
Lignite is a combustible fossil fuel, and the geological storage of lignite is about 4 trillion t all over the world, and accounts for about 40% of the global coal storage. The lignite resources in China are rich, and according to statistics at the end of the 20 th century, the reserves of lignite are 1300 hundred million t which account for about 13% of the total reserves of coal in China. In the currently proven reserves of brown coal in China, the most of the northeast regions of inner Mongolia accounts for about 75% of the reserves of brown coal in China; the reserve of lignite in southwest areas mainly comprising Yunnan province accounts for about 20 percent of the whole country; lignite in the northeast, east China and south China only accounts for about 5% of the whole country. With the worldwide shortage of energy and the adjustment of energy structures, people pay more and more attention to the development and utilization of low-quality coal such as lignite. The reserves of lignite in China are rich, and natural conditions for developing and utilizing lignite exist. The efficient clean utilization of the lignite can also meet the national policies of energy conservation, consumption reduction and emission reduction.
The unit for burning the lignite has higher requirement on drying output of a pulverizing system. The prior lignite boiler is mainly provided with a medium-speed mill direct-blowing pulverizing system or a fan mill direct-blowing pulverizing system. For medium-low moisture lignite boilers, medium-speed mill direct-fired pulverizing systems are generally adopted, and medium-high moisture lignite boilers and above are generally fan mill direct-fired pulverizing systems.
For the lignite boiler of the powder grinding system with the fan, the drying output is better, but the fan is fast in abrasion, short in maintenance period and poor in stability. The stability of the medium-speed grinding powder making system is good, but the lignite boiler with the medium-speed grinding powder making system generally has the problem of insufficient drying output of a coal mill. The problem of insufficient drying output of the lignite grinding machine of the lignite boiler in the northern area is more obvious in winter, the temperature of gas in the northern area is lower in winter, and the primary air drying capacity is more insufficient after certain heat is consumed by coal thawing.
For the lignite with medium and high moisture, if a more stable medium-speed milling system is selected, higher primary air temperature is needed, and meanwhile, the smoke temperature of a denitration inlet is required to meet the safe operation temperature range of the catalyst. For example, a lignite boiler provided with a medium-speed milling powder system generally needs to increase the primary air temperature to over 380 ℃, even over 400 ℃, and the primary air rate to over 40 percent, even close to 50 percent. If the boiler is designed according to the method, the conventional arrangement scheme needs to improve the temperature of the flue gas entering the denitration, and the denitration needs to adopt a high-temperature catalyst; the design of the preheater also needs to be considered in a key way, the exhaust gas temperature is very high, and the boiler efficiency is low; meanwhile, the coal mill also needs to select a larger model, so that the power consumption is increased; when the moisture of the coal is changed, the adaptation capability of the coal pulverizing system is not strong, and more projects cannot reach the designed primary air temperature; higher primary air rate puts higher requirements on the design of a boiler combustion system.
Disclosure of Invention
Aiming at the problems of insufficient drying output, high exhaust gas temperature and the like of the existing lignite boiler with medium-speed grinding, the invention provides the flue gas recirculation lignite drying method and the drying system, which are used for extracting the tail flue gas of the boiler to pre-dry the lignite so as to reduce the moisture in the coal, so that the residual moisture in the coal meets the range of the drying capacity of the medium-speed grinding powder system, and further, the high-moisture lignite boiler can select a more stable and reliable medium-speed grinding powder system.
To this end, an aspect of the present invention provides a flue gas recirculation lignite drying method, the method comprising:
extracting recycled flue gas from the tail of the boiler as a drying agent to carry out first-stage drying on the high-moisture lignite to obtain pre-dried lignite of which the moisture content meets the moisture adaptation range of a coal grinding and pulverizing unit;
introducing hot primary air to carry out second-stage drying on the pre-dried lignite while carrying out coal grinding and pulverizing treatment on the pre-dried lignite in a coal grinding and pulverizing unit to obtain dried pulverized lignite;
the hot primary air is used for carrying the pulverized lignite which is dried and pulverized into powder, and the pulverized lignite is sent to a combustor to be combusted in a hearth of the boiler;
and the medium-speed coal pulverizing system is used as a coal pulverizing and pulverizing unit to perform coal pulverizing and pulverizing treatment on the pre-dried lignite.
Further, the recirculated flue gas is introduced from an economizer outlet, a low-temperature reheater outlet, a low-temperature superheater outlet or an economizer inlet at the tail of the boiler, and the temperature of the recirculated flue gas is 350-600 ℃; the moisture content of the high-moisture lignite is more than 35 wt%, and the moisture content of the pre-dried lignite is within 35 wt%.
Further, the first section of dried recirculated flue gas is separated to remove carried lignite powder, the separated lignite powder is sent to a coal grinding and pulverizing unit, the separated flue gas returns to a boiler hearth to be mixed with flue gas generated by burning pulverized lignite powder after being dried and pulverized in the boiler hearth, the obtained mixed flue gas passes through each stage of heating surface from an outlet of the boiler hearth to the tail of the boiler, wherein part of the mixed flue gas is taken out from the tail of the boiler as recirculated flue gas to be used as drying agent for the first section of drying, and the other part of the mixed flue gas is used for heating cold primary air and cold secondary air and then is subjected to subsequent environment-friendly treatment.
Further, the hot primary air is hot primary air obtained after the cold primary air is heated or hot primary air obtained after the cold primary air is heated and the cold primary air serving as temperature-adjusting air are mixed and subjected to temperature adjustment, wherein the volume of the temperature-adjusting air is 0-10% of the volume of the cold primary air.
And further, the cold secondary air is heated by the other part of the mixed flue gas and then is fed into the boiler hearth to be mixed with the hot primary air and pulverized lignite which is dried and pulverized to support combustion.
Another aspect of the present invention provides a flue gas recirculation lignite drying system comprising:
the recycling flue gas unit is used for extracting and providing recycling flue gas from the tail part of the boiler and finally returning the recycling flue gas to the hearth;
an air supply unit for supplying at least hot primary air;
the lignite drying unit is used for receiving the recirculated flue gas and carrying out first-stage drying on the high-moisture lignite;
the coal grinding and pulverizing unit is used for receiving the hot primary air and the pre-dried lignite from the lignite drying unit, performing coal grinding and pulverizing treatment on the pre-dried lignite, performing second-stage drying, and providing dried pulverized lignite to a boiler furnace;
wherein, the coal-grinding and powder-making unit is a medium-speed coal-grinding and powder-making system.
Further, the recirculating smoke unit comprises a recirculating smoke exhaust port arranged at the tail part of the boiler, a recirculating smoke pipe and a recirculating fan, the recycling smoke exhaust port is connected with an economizer outlet, a low-temperature reheater outlet, a low-temperature superheater outlet or an economizer inlet, each recycling smoke pipe is divided into three sections, two ends of the first section of recycling smoke pipe are respectively connected with the recycling smoke exhaust port and an inlet of a recycling fan, two ends of the second section of recycling smoke pipe are respectively connected with an outlet of the recycling fan and a lignite drying unit, two ends of the third section of recycling smoke pipe are respectively connected with the lignite drying unit and a boiler furnace, the system comprises a lignite drying unit, at least one recirculation flue gas pipe, at least one recirculation fan, at least one lignite dryer and isolation baffles, wherein the at least one recirculation flue gas pipe and the at least one recirculation fan correspond to the at least one lignite dryer in the lignite drying unit one by one, and the inlet and the outlet of the recirculation fan are provided with the isolation baffles.
Further, the recycling flue gas unit comprises a recycling flue gas outlet, a recycling flue gas pipe and a recycling fan which are arranged at the tail part of the boiler, the recycling flue gas outlet is connected with an economizer outlet, a low-temperature reheater outlet, a low-temperature superheater outlet or an economizer inlet, each recycling flue gas pipe is divided into three sections, two ends of the first section of recycling flue gas pipe are respectively connected with the recycling flue gas outlet and an inlet main pipe of the recycling fan, a plurality of recycling fans are connected in parallel between the inlet main pipe of the recycling fan and the outlet main pipe of the recycling fan through branch pipelines, two ends of the second section of recycling flue gas pipe are respectively connected with an outlet main pipe of the recycling fan and an inlet of a lignite drier in the lignite drying unit, outlets of a plurality of lignite driers in the lignite drying unit are all connected with the outlet main pipe of the lignite drying unit, and two ends of the third section of recycling flue gas pipe are respectively connected with the outlet main pipe of the lignite drying unit and a boiler hearth, the inlet and the outlet of the recirculation fan are provided with isolation baffles, and the inlet and the outlet of the lignite dryer are provided with isolation baffles.
Further, the air supply unit comprises an air preheater, a primary air fan and a secondary air fan, a flue gas inlet of the air preheater is connected with an outlet of the SCR denitration reactor or is connected with an economizer outlet at the tail part of the boiler, a flue gas outlet of the air preheater is connected with the dust removal unit, an air inlet of the air preheater is respectively connected with the primary air fan through a cold primary air pipe and is connected with the secondary air fan through a cold secondary air pipe, an air outlet of the air preheater is respectively connected with the coal milling and pulverizing unit through a hot primary air pipe and is connected with a boiler furnace through a hot secondary air pipe, a temperature adjusting bypass is arranged on a primary air side of the air preheater, and the temperature adjusting bypass is respectively connected with the cold primary air pipe and the hot primary air pipe.
Furthermore, the lignite drying unit is connected with the lignite supply unit through a first coal conveying pipe, the lignite drying unit comprises a plurality of lignite dryers, isolation baffles are arranged at the inlets and the outlets of the lignite dryers, the lignite dryers are contact dryers or non-contact dryers, and when the lignite dryers are contact dryers, air-powder separators are further arranged at the outlets of the lignite dryers;
the pulverized coal pulverizing unit is connected with the lignite drying unit through a second coal conveying pipe, is connected with a burner arranged in a boiler hearth through a pulverized coal pipe, and is connected with an air preheater of the air supply unit through a hot primary air pipe.
According to the lignite drying method and system with the flue gas recirculation provided by the invention, the flue gas at the tail part of the boiler is extracted to pre-dry the high-moisture lignite so as to reduce the moisture in the coal, and the residual moisture in the coal meets the range of the drying capacity of a medium-speed grinding powder system. The lignite after being pre-dried is dried and pulverized by the medium-speed grinding pulverizing system, so that the coal type adaptation range of the medium-speed grinding pulverizing system is improved, the high-moisture lignite boiler can select the more stable and reliable medium-speed grinding pulverizing system, favorable conditions are provided for more stable, more efficient and lower pollution of lignite resources, and the national policies of energy conservation, consumption reduction, cleanness and environmental protection can be better met.
Drawings
Fig. 1 shows a schematic structural diagram of a flue gas recirculation lignite drying system according to an exemplary embodiment of the present invention.
Description of reference numerals:
10-boiler, 11-boiler furnace, 12-boiler tail, 13-burner, 14-SCR denitration reactor; 20-a recirculating smoke exhaust port, 21-a recirculating smoke pipe and 22-a recirculating fan; 30-an air preheater, 31-a primary air fan, 32-a secondary air fan, 33-a cold primary air pipe, 34-a cold secondary air pipe, 35-a temperature-adjusting bypass, 36-a hot primary air pipe and 37-a hot secondary air pipe; 40-a lignite drying unit, 41-a first coal conveying pipe; 50-a coal grinding and pulverizing unit, 51-a pulverized coal pipe and 52-a second coal conveying pipe.
Detailed Description
All of the features disclosed in this specification, or all of the steps in any method or process so disclosed, may be combined in any combination, except combinations of features and/or steps that are mutually exclusive.
Any feature disclosed in this specification may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. That is, unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features.
Aiming at the problem that the existing medium-speed grinding lignite boiler adopts the primary air rate as large as possible and improves the primary air temperature to solve the drying problem of lignite, if the primary air rate exceeds more than 40%, the secondary air rate is low and the combustion organization of the boiler is difficult; under the condition of no primary air temperature improving auxiliary measures, the higher primary air temperature is difficult to coordinate with the stability of a powder making system and the efficiency of a boiler, and the conventional primary air auxiliary heating measures have the problems of high actual investment and operation cost, unobvious effect, low efficiency and the like. The present invention provides a flue gas recirculation lignite drying method and drying system, and is preferably applicable to high moisture lignite having a moisture content of more than 35 wt%, which will be described in detail in the following.
According to an exemplary embodiment of the present invention, the flue gas recirculation lignite drying method actually comprises four flows, namely a recirculation flue gas flow, a lignite flow, an air flow, a boiler flue gas flow.
Specifically, the recirculated flue gas is extracted from the tail of the boiler and used as a drying agent to carry out first-stage drying on the lignite, and the pre-dried lignite with the moisture content meeting the moisture adaptation range of the coal grinding and pulverizing unit is obtained. The method adopts the recycled flue gas as the drying agent to carry out first-stage drying on the high-moisture lignite, the extracted recycled flue gas can be led from the positions including but not limited to an economizer outlet, a low-temperature reheater outlet, a low-temperature superheater outlet or an economizer inlet, etc., the leading-out point of the recycled flue gas is preferably the economizer outlet, the temperature of the recycled flue gas is preferably 350-400 ℃, and the moisture content of the pre-dried lignite obtained after the first-stage drying is within 35 wt%, so that the method is suitable for drying and pulverizing the high-reliability medium-speed pulverized coal pulverizing system, and the medium-speed pulverized coal pulverizing system is suitable for the lignite with the moisture content of more than 35%.
And the pre-dried lignite is subjected to coal grinding and powder preparation treatment, and hot primary air is introduced to perform second-stage drying on the pre-dried lignite to obtain dried and pulverized lignite powder.
After the high-moisture lignite is heated by recirculated flue gas in a lignite dryer (can be in contact drying or non-contact drying), the moisture in the high-moisture lignite is partially evaporated, the moisture of the lignite after the first-stage drying is reduced to a moisture range (within 35%) suitable for medium-speed grinding, the lignite is sent to a medium-speed grinding system to be continuously subjected to coal grinding and powder preparation, meanwhile, hot primary air is used as a drying agent to perform second-stage drying on the lignite after the first-stage drying, and the obtained dried and pulverized lignite is carried by the hot primary air and is sent to combustion equipment arranged in a boiler to be combusted.
According to the invention, the recycled flue gas after the first section of drying is separated to remove carried lignite powder, the separated lignite powder is sent to a coal grinding and pulverizing unit, the separated flue gas is returned to a boiler hearth to be mixed with flue gas generated by burning pulverized lignite powder after being dried and pulverized in the boiler hearth, the obtained mixed flue gas passes through heating surfaces of all stages from an outlet of the boiler hearth to the tail part of the boiler, wherein part of the mixed flue gas is taken as recycled flue gas and is extracted from the tail part of the boiler, and the other part of the mixed flue gas is subjected to denitration, primary air cooling and secondary air cooling by an air preheater and then is subjected to subsequent environmental protection treatment, wherein the environmental protection treatment can comprise environmental protection treatment such as dust removal and desulfurization treatment, and the treated flue gas can be discharged to the atmosphere through a chimney.
Preferably, the hot primary air used in the present invention may be hot primary air obtained by heating cold primary air in the air preheater, or may be hot primary air obtained by mixing and temperature-adjusting hot primary air obtained by heating cold primary air in the air preheater with bypass cold primary air serving as temperature-adjusting air. The proportion of bypass temperature-adjusting air is adjusted according to the operation working condition of the boiler, and the volume of the temperature-adjusting air is preferably 0-10% of the volume of the primary cold air.
In addition, the method of the invention also sends the cold secondary air into the boiler furnace after being heated by the other part of mixed flue gas in the air preheater to be mixed with the hot primary air and the pulverized lignite which is dried and pulverized into powder to support combustion.
The invention adopts a series sectional drying technology to perform sectional drying on the high-moisture lignite, so that the moisture of the lignite finally entering the medium-speed grinding powder-making system is lower than the upper limit of the moisture suitable for the medium-speed grinding, and the high-moisture lignite boiler can select the medium-speed grinding powder-making system with higher reliability. And through selecting reasonable recirculated flue gas volume and flue gas temperature, the boiler has wider application range to lignite moisture, widens the application range of the medium-speed grinding powder system to lignite moisture, enhances the flexibility of the medium-speed grinding powder system to cope with moisture fluctuation of the lignite entering the furnace, breaks through the limitation that the fan grinding powder system must be adopted for high-moisture lignite, effectively avoids the problems of low reliability of the fan grinding powder system due to abrasion of a striking wheel, coking and cracking of a furnace smoke pipe and the like, also avoids the problem that the fan grinding powder system cannot adopt high-efficiency super-parameters due to large thermal deviation in the furnace caused by corner-lacking combustion, breaks through the parameter limitation which can be reached by the lignite unit, improves the parameter grade of the lignite unit, saves more energy and has higher stability.
Fig. 1 shows a schematic structural diagram of a flue gas recirculation lignite drying system according to an exemplary embodiment of the present invention.
As shown in fig. 1, according to an exemplary embodiment of the present invention, the flue gas recirculation lignite drying system includes a recirculation flue gas unit, an air supply unit, a lignite drying unit and a pulverized coal pulverizing unit, wherein the recirculation flue gas unit is drawn out from the tail 12 of the boiler 10 and provides recirculation flue gas, the air supply unit provides at least hot primary air, the lignite drying unit 40 receives the recirculation flue gas and performs a first stage drying on lignite, the pulverized coal pulverizing unit 50 receives the hot primary air and pre-dried lignite from the lignite drying unit 40, performs a second stage drying while performing a pulverized coal pulverizing process on the pre-dried lignite, and provides dried pulverized lignite to the boiler furnace.
Specifically, the recirculated flue gas unit in the present invention has two main arrangements. In the first setting, the recycling flue gas unit comprises a recycling flue gas outlet 20, a recycling flue gas pipe 21 and a recycling fan 22 which are arranged at the tail part of the boiler, the recycling flue gas outlet 20 is connected with an economizer outlet, a low-temperature reheater outlet, a low-temperature superheater outlet or an economizer inlet, each recycling flue gas pipe is divided into three sections, two ends of the recycling flue gas pipe in the first section are respectively connected with the recycling flue gas outlet 20 and an inlet of the recycling fan 22, two ends of the recycling flue gas pipe in the second section are respectively connected with an outlet of the recycling fan 22 and a lignite drying unit 40, two ends of the recycling flue gas pipe in the third section are respectively connected with the lignite drying unit 40 and a boiler furnace, wherein at least one recycling flue gas pipe and at least one recycling fan correspond to at least one lignite dryer in the lignite drying unit, and the inlet and the outlet of the recycling fan are both provided with isolation baffles, can close the separation baffle when corresponding recirculation fan and the reserve shutdown of coal-grinding powder process unit prevent that the flue gas from getting into. In this mode of setting up, recirculation flue gas pipe and recirculation fan one-to-one, the same one-to-one of brown coal desicator and the coal-grinding pulverization unit in recirculation fan and the brown coal drying unit, every coal-grinding pulverization unit corresponds a brown coal desicator.
In the second setting, the recycling smoke unit comprises a recycling smoke outlet 20, a recycling smoke pipe 21 and a recycling fan 22 which are arranged at the tail part 12 of the boiler, the recycling smoke outlet 20 is connected with an economizer outlet, a low-temperature reheater outlet, a low-temperature superheater outlet or an economizer inlet, each recycling smoke pipe is divided into three sections, two ends of the recycling smoke pipe in the first section are respectively connected with the recycling smoke outlet 20 and an inlet main pipe of the recycling fan 22, a plurality of recycling fans 22 are connected in parallel between the inlet main pipe of the recycling fan 22 and an outlet main pipe of the recycling fan 22 through branch pipelines, two ends of the recycling smoke pipe in the second section are respectively connected with an outlet main pipe of the recycling fan 22 and an inlet of a lignite dryer in the lignite drying unit 40, outlets of a plurality of lignite dryers in the lignite drying unit are all connected with an outlet main pipe of the lignite drying unit 40, two ends of a third section of recirculating flue gas pipe are respectively connected with an outlet main pipe of the lignite drying unit 40 and the boiler furnace 11, an inlet and an outlet of the recirculating fan are respectively provided with an isolation baffle, and an inlet and an outlet of the lignite dryer are respectively provided with an isolation baffle. In this setting mode, the mode through setting up female pipe comes parallelly connected a plurality of recirculation fan 22 and a plurality of brown coal desicator that sets up, is convenient for set up isolation barrier from this and comes the independent control.
The method can select the first mode or the second mode according to the unit capacity and the raw coal moisture range, and preferably selects the main pipe form of the second connection mode for the large-capacity unit so as to facilitate the model selection of equipment.
The air supply unit comprises an air preheater 30, a primary air fan 31 and a secondary air fan 32, wherein a flue gas inlet of the air preheater 30 is connected with an outlet of the SCR denitration reactor 14 or is connected with an economizer outlet at the tail part of the boiler (when the SCR denitration reactor is not arranged), an air inlet of the air preheater 30 is respectively connected with the primary air fan 31 through a cold primary air pipe 33 and is connected with the secondary air fan 32 through a cold secondary air pipe 34, and an air outlet of the air preheater 30 is respectively connected with the coal grinding unit 50 through a hot primary air pipe 36 and is connected with the boiler furnace 11 through a hot secondary air pipe 37. The cold primary air becomes hot primary air after exchanging heat with hot flue gas through the air preheater 30, and is conveyed to the coal grinding unit through the primary air pipe 33 to be used as a drying agent for second-stage drying, and the cold secondary air also becomes hot secondary air after exchanging heat with hot flue gas through the air preheater 30, and is conveyed into the boiler 10 through the secondary air pipe 34.
Preferably, a temperature adjusting bypass 35 is arranged on the primary air side of the air preheater 30, and the temperature adjusting bypass 35 is respectively connected with the cold primary air pipe 33 and the hot primary air pipe 37. That is, the outlet of the primary air fan 31 is divided into two paths, one path is connected with the air inlet of the air preheater 30 through the cold primary air pipe 33, and the other path is connected with the hot primary air pipe 36 through the temperature adjusting bypass 35. The cold primary air at the outlet of the primary air fan 31 is divided into two paths, one path is heated by the air preheater 30, the other path is used as temperature-adjusting air to be mixed with the heated hot primary air for temperature adjustment, the proportion of the temperature-adjusting air is adjusted according to the operation condition of the boiler and is generally within 10%, the temperature-adjusting mixed hot primary air is sent to the coal grinding unit for further drying the pre-dried lignite and carrying the dried pulverized lignite to be sent to the hearth 11 of the boiler 1 to be mixed and combusted with the hot secondary air.
The lignite drying unit 40 of the present invention is connected to a lignite feeding unit (not shown) through a first coal conveying pipe 41, so that the lignite is dried in a first stage under the action of the recirculated flue gas after entering the lignite drying unit 40, and then the recirculated flue gas carries the moisture evaporated in the first stage drying and returns to the boiler furnace 11 through the recirculated flue gas pipe and the recirculation nozzle of the boiler after separating the carried lignite powder.
The lignite drying unit comprises a plurality of lignite dryers, the arrangement positions of the lignite dryers can be arranged at any position of a raw lignite conveying route according to units, such as the positions of a coal yard, a coal feeding pipeline of a coal feeder, a first coal conveying pipe and the like, and the number of the lignite dryers is selected according to the arrangement positions. The inlet and the outlet of the lignite dryer are provided with isolation baffles.
Wherein, the brown coal desicator can be contact desicator or non-contact desicator, and when adopting the contact desicator, the export of brown coal desicator is provided with the wind powder separator to the buggy separation that carries in with the flue gas returns, further prefers spiral desicator. When the lignite dryer adopts a contact dryer, the recycled flue gas dries lignite at the first stage and is subjected to gas-solid separation, a small amount of coal dust and volatile matters which can still be carried are circularly sent into a boiler hearth to participate in combustion, no raw coal is lost, and dust removal and environmental protection treatment are not needed.
The pulverized coal pulverizing unit 50 is connected with the lignite drying unit 40 through a second coal conveying pipe 52, is connected with the burner 30 arranged in the boiler furnace 11 through a pulverized coal pipe 51, and is connected with the air preheater of the air supply unit through a hot primary air pipe, so that the pre-dried lignite obtained in the lignite drying unit 40 enters the pulverized coal pulverizing unit 50 and is further dried and pulverized into powder under the action of the hot primary air, and then the pulverized coal of the dried pulverized lignite is carried by the hot primary air and is fed into the burner to be combusted in the boiler furnace. The coal grinding unit is a medium-speed coal grinding system.
The invention can reduce the design smoke temperature of the inlet of the air preheater when the boiler is designed and selected, compared with the conventional lignite boiler provided with a medium-speed grinding powder system, the system provided with the boiler has the advantages that the inlet smoke temperature of the air preheater is lower, the exhaust smoke temperature of the boiler can be reduced by about 10 ℃, and the boiler efficiency is improved. In addition, on the basis of ensuring the drying output of the pulverizing system, the design and the operating temperature of the denitration system can be reduced, a high-temperature catalyst is avoided, and the denitration investment and the operating cost are saved.
The present invention will be further described with reference to the following specific examples.
Taking a 1000MW ultra-supercritical high-moisture lignite-fired boiler as an example, the moisture content of the lignite-fired boiler is 45 wt%, the heat value is 2500kcal/kg, the coal consumption of the boiler is about 790t/h, the coal pulverizing system adopts a medium-speed-mill direct-blowing coal pulverizing system, 8 coal mills are arranged, and 7 coal mills are operated for 1 standby.
If the smoke recycling lignite drying method and the drying system are not adopted, the conventional medium-speed milling powder system cannot adapt to the coal quality of the moisture, and only a fan milling powder system can be adopted. However, the fan is easy to wear, the smoke tube of the high-temperature furnace is easy to coke and crack, the reliability is not high, the large deviation of the wall temperature of the heating surface caused by the large temperature deviation in the furnace caused by corner-lacking combustion cannot be avoided, and the method is not suitable for the unit parameters above the ultra-supercritical state, so the scheme of the invention is an effective choice of the unit.
Wherein, the brown coal desicator arrange the position and can arrange the adjustment according to the unit, if arrange in positions such as coal yard, feeder coal conveying pipeline, coal pulverizer import coal conveying pipe, the quantity of brown coal desicator is along with arranging the position selection, and brown coal desicator can select contact desicator and non-contact desicator. Taking one example as an example, the lignite dryers are arranged at the inlet of the coal mill, each coal mill corresponds to one lignite dryer, and the lignite dryers adopt spiral dryers.
The temperature of the recirculated flue gas is about 350-400 ℃, the recirculated flue gas enters a plurality of recirculation fans through an inlet main pipe of the recirculation fan, then enters an inlet main pipe of the lignite drying unit from an outlet main pipe of the recirculation fan, and is divided into 8 recirculation branch flue gas pipes which are respectively sent into 8 dryers. Wherein, the quantity of recirculation fan sets up 4, and 3 fortune are equipped with one, and the import of each recirculation fan and the entry of each recirculation branch flue gas pipe all set up isolation barrier, close isolation barrier when recirculation fan and the reserve outage of coal pulverizer that correspond prevent that the flue gas from getting into.
The recirculated flue gas enters the lignite dryer and is heated and dried in a countercurrent mode (or in a downstream mode), the flue gas outlet of the lignite dryer is provided with an air-powder separator, and the pulverized coal carried in the flue gas is separated and returned to the pulverized coal outlet of the lignite dryer. The recirculated flue gas carries the moisture evaporated by primary drying to enter the boiler furnace through the recirculated flue gas nozzle of the boiler.
Lignite enters the lignite dryer from the first coal conveying pipe, is mixed with recirculated flue gas in the lignite dryer for first-stage drying, enters the coal mill for further drying and pulverizing after moisture is reduced, hot primary air heated by the air preheater is used as a drying agent of the coal mill and further drying of the lignite is completed in the coal mill, and then the hot primary air carries dried pulverized lignite powder to be fed into a burner to be burned in a boiler hearth.
The invention enables the high-moisture lignite boiler to select a more stable and reliable medium-speed grinding powder system, provides favorable conditions for more stable, more efficient and lower-pollution utilization of lignite resources, and can better meet the national policies of energy conservation, consumption reduction, cleanness and environmental protection.
The invention is not limited to the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification and any novel method or process steps or any novel combination of features disclosed.
Claims (10)
1. A flue gas recirculation lignite drying method, characterized in that the method comprises:
extracting recycled flue gas from the tail of the boiler as a drying agent to carry out first-stage drying on the high-moisture lignite to obtain pre-dried lignite of which the moisture content meets the moisture adaptation range of a coal grinding and pulverizing unit;
introducing hot primary air to carry out second-stage drying on the pre-dried lignite while carrying out coal grinding and pulverizing treatment on the pre-dried lignite in a coal grinding and pulverizing unit to obtain dried pulverized lignite;
the hot primary air is used for carrying the pulverized lignite which is dried and pulverized into powder, and the pulverized lignite is sent to a combustor to be combusted in a hearth of the boiler;
and the medium-speed coal pulverizing system is used as a coal pulverizing and pulverizing unit to perform coal pulverizing and pulverizing treatment on the pre-dried lignite.
2. The method for drying lignite through flue gas recirculation according to claim 1, wherein the recirculated flue gas is introduced from an economizer outlet, a low-temperature reheater outlet, a low-temperature superheater outlet or an economizer inlet at the tail of a boiler, and the temperature of the recirculated flue gas is 350-600 ℃; the moisture content of the high-moisture lignite is more than 35 wt%, and the moisture content of the pre-dried lignite is within 35 wt%.
3. The method for drying lignite through flue gas recirculation according to claim 1, wherein the first section of dried recirculated flue gas is separated to remove carried lignite powder, the separated lignite powder is sent to a coal grinding and pulverizing unit, the separated flue gas is returned to a boiler hearth to be mixed with flue gas generated by burning pulverized lignite powder after being dried and pulverized in the boiler hearth, the obtained mixed flue gas passes through heating surfaces of various stages from an outlet of the boiler hearth to a tail part of a boiler, wherein a part of the mixed flue gas is taken out from the tail part of the boiler as recirculated flue gas to be used as a drying agent for the first section of drying, and the other part of the mixed flue gas is used for heating cold primary air and cold secondary air and then is subjected to subsequent environmental protection treatment.
4. The method for drying lignite through flue gas recirculation according to claim 1, wherein the hot primary air is hot primary air obtained by heating with cold primary air or hot primary air obtained by mixing hot primary air obtained by heating with cold primary air as temperature-adjusting air and adjusting the temperature, wherein the volume of the temperature-adjusting air is 0-10% of the volume of the cold primary air.
5. The method for drying lignite through flue gas recirculation according to claim 3, wherein cold secondary air is heated by the other part of mixed flue gas and then is fed into the boiler furnace to be mixed with hot primary air and pulverized lignite after being dried and pulverized to support combustion.
6. A flue gas recirculation lignite drying system characterized by comprising:
the recycling flue gas unit is used for extracting and providing recycling flue gas from the tail part of the boiler and finally returning the recycling flue gas to the hearth;
an air supply unit for supplying at least hot primary air;
the lignite drying unit is used for receiving the recirculated flue gas and carrying out first-stage drying on the high-moisture lignite;
the coal grinding and pulverizing unit is used for receiving the hot primary air and the pre-dried lignite from the lignite drying unit, performing coal grinding and pulverizing treatment on the pre-dried lignite, performing second-stage drying, and providing dried pulverized lignite to a boiler furnace;
wherein, the coal-grinding and powder-making unit is a medium-speed coal-grinding and powder-making system.
7. The flue gas recycling lignite drying system according to claim 6, wherein the recycling flue gas unit comprises a recycling flue gas outlet and a recycling flue gas pipe and a recycling fan which are arranged at the rear portion of the boiler, the recycling flue gas outlet is connected with an economizer outlet, a low-temperature reheater outlet, a low-temperature superheater outlet or an economizer inlet, each recycling flue gas pipe is divided into three sections, two ends of the first section of the recycling flue gas pipe are respectively connected with the recycling flue gas outlet and an inlet of the recycling fan, two ends of the second section of the recycling flue gas pipe are respectively connected with an outlet of the recycling fan and a lignite drying unit, two ends of the third section of the recycling flue gas pipe are respectively connected with the lignite drying unit and a boiler furnace, wherein at least one recycling flue gas pipe and at least one recycling fan are in one-to-one correspondence with at least one lignite dryer in the lignite drying unit, and the inlet and the outlet of the recirculation fan are provided with isolation baffles.
8. The flue gas recycling lignite drying system according to claim 6, wherein the recycling flue gas unit comprises a recycling flue gas outlet, a recycling flue gas pipe and a recycling fan, the recycling flue gas outlet is connected with an economizer outlet, a low-temperature reheater outlet, a low-temperature superheater outlet or an economizer inlet, each recycling flue gas pipe is divided into three sections, two ends of the first recycling flue gas pipe are respectively connected with the recycling flue gas outlet and an inlet main pipe of the recycling fan, a plurality of recycling fans are connected in parallel between the inlet main pipe of the recycling fan and an outlet main pipe of the recycling fan through branch pipelines, two ends of the second recycling flue gas pipe are respectively connected with an outlet main pipe of the recycling fan and an inlet of a lignite dryer in the lignite drying unit, outlets of a plurality of lignite dryers in the lignite drying unit are all connected with an outlet main pipe of the lignite drying unit, two ends of a third section of recirculating flue gas pipe are respectively connected with an outlet main pipe of the lignite drying unit and a boiler hearth, an inlet and an outlet of the recirculating fan are respectively provided with an isolation baffle, and an inlet and an outlet of the lignite dryer are respectively provided with an isolation baffle.
9. The lignite drying system with flue gas recirculation according to claim 6, wherein the air supply unit comprises an air preheater, a primary air fan and a secondary air fan, a flue gas inlet of the air preheater is connected with an outlet of the SCR denitration reactor or an economizer outlet at the tail of the boiler, a flue gas outlet of the air preheater is connected with a low-temperature economizer or a dedusting unit, an air inlet of the air preheater is connected with the primary air fan through a primary cold air pipe and is connected with the secondary air fan through a secondary cold air pipe, an air outlet of the air preheater is connected with the pulverized coal pulverizing unit through a primary hot air pipe and is connected with a hearth of the boiler through a secondary hot air pipe, a temperature adjusting bypass is arranged at a primary air side of the air preheater, and the temperature adjusting bypass is connected with the primary cold air pipe and the primary hot air pipe.
10. The flue gas recirculation lignite drying system according to claim 6, wherein the lignite drying unit is connected with a lignite supply unit through a first coal conveying pipe, the lignite drying unit comprises a plurality of lignite dryers, an inlet and an outlet of each lignite dryer are provided with isolation baffles, each lignite dryer is a contact dryer or a non-contact dryer, and when the lignite dryer is a contact dryer, an outlet of each lignite dryer is further provided with an air-powder separator;
the pulverized coal pulverizing unit is connected with the lignite drying unit through a second coal conveying pipe, is connected with a burner arranged in a boiler hearth through a pulverized coal pipe, and is connected with an air preheater of the air supply unit through a hot primary air pipe.
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| CN202010932833.7A CN112082149A (en) | 2020-09-08 | 2020-09-08 | Flue gas recirculation lignite drying method and drying system |
| PCT/CN2021/093554 WO2022052500A1 (en) | 2020-09-08 | 2021-05-13 | Lignite drying method and drying system using flue gas recirculation |
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| WO2022052500A1 (en) * | 2020-09-08 | 2022-03-17 | 东方电气集团东方锅炉股份有限公司 | Lignite drying method and drying system using flue gas recirculation |
| CN114659082A (en) * | 2022-03-28 | 2022-06-24 | 西安热工研究院有限公司 | Method and system for increasing low-load denitration inlet smoke temperature by co-combustion of blast furnace gas |
| CN114811575A (en) * | 2022-04-19 | 2022-07-29 | 东方电气集团东方锅炉股份有限公司 | Coal-fired and natural gas dual-purpose boiler system and using method thereof |
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