CN110657421B

CN110657421B - Low-NOx mixed combustion system and mixed combustion method

Info

Publication number: CN110657421B
Application number: CN201910926714.8A
Authority: CN
Inventors: 王志强; 郑少伟; 程星星; 许焕焕; 傅加鹏
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2019-09-27
Filing date: 2019-09-27
Publication date: 2020-08-04
Anticipated expiration: 2039-09-27
Also published as: CN110657421A

Abstract

The invention discloses a low NOx mixed combustion system and a mixed combustion method, wherein the mixed combustion system comprises: the inlet of the pyrolysis reactor is connected with a coal source and is used for pyrolyzing coal to prepare semicoke and pyrolysis gas; an inlet of the pyrolysis semicoke bin is connected with a solid outlet of the pyrolysis reactor, and a heat exchanger is arranged in the pyrolysis semicoke bin and used for cooling the pyrolyzed semicoke; the inlet of the coal mill is respectively connected with the outlet of the pyrolysis semicoke bin and the semicoke source; the boiler is sequentially provided with a burnout zone, a NOx reduction zone, a main combustion zone and a preheating ignition zone from top to bottom, and a first combustor, a second combustor and a third combustor are sequentially arranged on the side walls of the NOx reduction zone, the main combustion zone and the preheating ignition zone; inlets of the first combustor and the second combustor are connected with a pyrolysis gas outlet of the pyrolysis reactor; and the inlet of the third combustor is connected with the outlet of the coal mill through a gas path.

Description

Low-NOx mixed combustion system and mixed combustion method

Technical Field

The invention relates to the technical field of efficient low-nitrogen combustion of semicoke and gasified residual carbon, in particular to a low-NOx co-combustion system and a low-NOx co-combustion method for a power station boiler, which utilize high-volatile coal to support combustion of semicoke and gasified residual carbon.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

China is a large energy consumption and production country, coal is a main energy resource in China, and China has a large number of coal varieties, and anthracite coal with the deepest coalification degree to lignite coal with the lowest coalification degree are stored, wherein the storage amount of low-rank coal accounts for about half of the total amount. The direct combustion or gasification efficiency of low-rank coal is low, and the pollutant and carbon emission amount is large. The pyrolysis technology is used for carrying out quality-divided conversion and gradient utilization on the low-rank coal, and the method is an important mode for high-efficiency clean utilization of the low-rank coal. Pyrolysis gas and tar generated by coal pyrolysis in the pyrolysis process are used as high-grade raw materials, a large amount of semicoke and gasification residual carbon generated after pyrolysis are combusted and generated, the semicoke and the gasification residual carbon are effectively utilized, and clean and efficient gradient utilization of low-rank coal is realized. However, the pyrolysis by-product semi-coke and gasified residual carbon belong to ultra-low volatile carbon-based fuel, and the problems of difficult ignition and stable combustion, low burnout rate, high nitrogen oxide emission and the like are difficult to overcome by adopting the traditional combustion technology. The realization of clean and efficient combustion utilization of the fuel becomes a key technical bottleneck for restricting the graded conversion of low-rank coal.

The blending combustion of the high volatile coal and the semicoke (gasification residual carbon) is an effective method for generating electricity by utilizing the combustion of the semicoke (gasification residual carbon). That is, a certain proportion of semicoke (gasified residual carbon) is co-burned in a large power station pulverized coal boiler to replace power coal. At present, the industrial test of blending burning semicoke of a power station boiler is carried out in China, but the blending burning semicoke is not high in proportion and is only about 30%, and the efficiency of the boiler after blending burning is also reduced.

The method is mainly characterized in that coal types with different characteristics are mixed and then are sent into a furnace for combustion, the phenomenon of oxygen contention exists due to the difference of coal quality, high-volatile coal types can be combusted in advance, and low-volatile coal types are combusted in an oxygen deficiency state, so that ignition and stable combustion of the low-volatile coal types are inhibited, and the burnout rate of mixed fuel is reduced. The inventors have found that the ignition property can be improved by increasing the oxygen concentration, the combustion becomes stable, the burn-out rate is improved, and the amount of NOx produced increases as the oxygen concentration is increased. Improving combustion characteristics and reducing NOx emissions are contradictory by increasing oxygen concentration. Therefore, the proportion of blending semicoke of the power station boiler is improved, and the emission of NOx is reduced, so that the key for realizing the clean combustion of the ultra-low volatile carbon-based fuel is realized.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention aims to provide a low-NOx mixed combustion system and a mixed combustion method. The method can realize the high-efficiency combustion of the semicoke or the gasified residual carbon, and can reduce the emission of NOx at the same time.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a low NOx co-combustion system, comprising:

the inlet of the pyrolysis reactor is connected with a coal source and is used for pyrolyzing coal to prepare semicoke and pyrolysis gas;

an inlet of the pyrolysis semicoke bin is connected with a solid outlet of the pyrolysis reactor, and a heat exchanger is arranged in the pyrolysis semicoke bin and used for cooling the pyrolyzed semicoke;

the inlet of the coal mill is respectively connected with the outlet of the pyrolysis semicoke bin and the semicoke source;

the boiler is sequentially provided with a burnout zone, a NOx reduction zone, a main combustion zone and a preheating ignition zone from top to bottom, and a first combustor, a second combustor and a third combustor are sequentially arranged on the side walls of the NOx reduction zone, the main combustion zone and the preheating ignition zone;

inlets of the first combustor and the second combustor are connected with a pyrolysis gas outlet of the pyrolysis reactor;

and the inlet of the third combustor is connected with the outlet of the coal mill through a gas path.

And the semi-coke powder ground in the coal mill enters a third combustor for combustion under the carrying action of wind.

In some embodiments, the top of the boiler is connected to the pyrolysis reactor by a pipe. The high-temperature flue gas in the boiler is introduced into the pyrolysis reactor through the pipeline for pyrolyzing the coal in the pyrolysis reactor, so that the energy consumption required by coal pyrolysis can be saved.

Further, the device also comprises a first dryer and a second dryer which are respectively connected with the pyrolysis reactor and the coal mill.

The first dryer and the second dryer are used for drying the coal and the semicoke respectively, and subsequent combustion reaction is facilitated after drying.

Furthermore, the flue gas outlet of the pyrolysis reactor is respectively connected with the first dryer and the second dryer.

The flue gas that cools down after carrying out the pyrolysis to the coal gets into first desicator and second desicator respectively in, carries out the drying to coal and semicoke, can effectively improve the waste heat utilization ratio of flue gas.

And further, a semi-coke bin is connected between the second dryer and the coal mill, and an outlet of the semi-coke bin is connected with the coal mill. The semicoke bin is used for temporarily storing the dried semicoke so as to facilitate quantitative supply.

In some embodiments, the outlet end of the boiler is provided with an air preheater, and the outlet end of the air preheater is connected with the primary air inlet of the coal mill.

The air preheated by the air preheater enters the coal mill, and the milled semicoke powder is carried to the boiler for combustion, and the air temperature is higher, so that the stable operation of the boiler is favorably maintained.

A low NOx co-combustion method comprises the following steps:

pyrolyzing coal to obtain pyrolysis coal gas and high-temperature semicoke, cooling the high-temperature semicoke, mixing the high-temperature semicoke with the existing semicoke, grinding the high-temperature semicoke into powder, enabling semicoke powder to enter a preheating ignition area of a boiler under the preheating and carrying effects of primary air, mixing the semicoke powder with secondary air, preheating, igniting, preheating and igniting;

and the pyrolysis coal gas enters an NOx reduction zone and a main combustion zone of the boiler respectively to be combusted, so that a strong reducing atmosphere is formed, and NOx generated by semicoke combustion is reduced.

In some embodiments, the pyrolysis temperature of the coal is 400-.

In some embodiments, the present char comprises 40% to 60% by weight of the total char after mixing.

In some embodiments, the primary air is at a temperature of 380-.

In some embodiments, the pyrolysis gas introduced into the NOx reduction zone comprises 17% to 25% by volume of the pyrolysis gas introduced into the primary combustion zone.

In some embodiments, the excess air factor in the pre-heat ignition zone is between 0.85 and 0.95.

The beneficial technical effects of the invention are as follows:

the utility model discloses a power station boiler system utilizes high temperature flue gas to carry out pyrolysis to bituminous coal, produces pyrolysis coal gas mixture and high temperature semicoke, sends into the furnace after mixing the high temperature semicoke that the pyrolysis generated and former semicoke and burns, has overcome different coal types because the difference of coal quality, strives for oxygen when the mixed combustion, and the burning is unstable, and the burnout rate is low problem.

According to the power station boiler system, the preheating ignition area is formed at the bottom of the hearth, the semicoke is preheated and ignited in the preheating ignition area, and because the semicoke has a rich pore structure, a large amount of oxygen enters the inside of semicoke particles through pores in the preheating ignition area, so that the oxygen can be fully contacted with the semicoke in advance, and meanwhile, a small amount of volatile matters contained in the semicoke are preheated, separated and combusted, so that ignition of the semicoke is facilitated, and meanwhile, NOx smoke with a certain concentration is generated.

The utility model discloses a power station boiler system utilizes the coal gas mixture that the pyrolysis bituminous coal produced to spout into the burning-supporting semicoke of semicoke main combustion area, has formed rich fuel burning in the main combustion area, reduces the formation of NOx, and the temperature reaches the highest simultaneously, and the semicoke is violently burnt, and high temperature and violent burning make a large amount of fixed carbon in the semicoke react, and nitrogen element releases thereupon, has realized the ignition of semicoke, has steadily burnt and has burnt completely. Meanwhile, the coal gas mixture is sprayed into the NOx reduction region to form a strong reducing atmosphere combustion region, the reduction strength is increased, more nitrogen elements are reduced, and the generation and emission of NOx are greatly reduced.

The system utilizes the high-temperature flue gas as a heat source of the pyrolysis reactor and the dryer to carry out high-efficiency pyrolysis and drying on the bituminous coal, thereby realizing high-efficiency utilization of flue gas waste heat, obviously reducing pyrolysis energy consumption and saving the treatment cost of the bituminous coal.

The system utilizes the heat exchanger to cool the high-temperature semicoke, and high-temperature steam generated by cooling water flowing through the heat exchanger is sent to the boiler to be continuously heated and then is used for driving the steam turbine to generate power. The utilization of the waste heat of the high-temperature semicoke is realized.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is a schematic structural diagram of a low NOx mixed combustion system according to an embodiment of the invention.

The device comprises a bituminous coal conveying device 1, a semicoke conveying device 2, a semicoke conveying device 3, a first dryer 4, a second dryer 5, a pyrolysis reactor 6, a pyrolysis semicoke bin 7, a heat exchanger 8, a semicoke bin 9, a pyrolysis semicoke coke feeder 10, a coke feeder 11, a coal mill 12, a boiler 13, an air preheater 14, an over-fire air nozzle 15, a first combustor 16, a second combustor 17, a third combustor 18, an over-fire area 19, a NOx reduction area 20, a main combustion area 21, a preheating ignition area 22 and a fan.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As shown in fig. 1, the low NOx co-firing system comprises a bituminous coal conveyor 1, a semicoke conveyor 2, a first dryer 3, a second dryer 4, a pyrolysis reactor 5, a pyrolysis semicoke bin 6, a heat exchanger 7, a semicoke bin 8, a pyrolysis semicoke coke feeder 9, a coke feeder 10, a coal mill 11, a boiler body 12, an air preheater 13, an over-fire air nozzle 14, a first burner 15, a second burner 16, a third burner 17 and a fan 22;

the bituminous coal conveying device 1 and the semicoke conveying device 2 are respectively connected with the first dryer 3 and the second dryer 4;

the first dryer 3 and the second dryer comprise a drying chamber and a flue gas chamber, the drying chamber comprises a material inlet and a dried material outlet, and the flue gas chamber comprises a high-temperature flue gas inlet and a cooling flue gas outlet;

the first dryer 3 is connected with the pyrolysis reactor 5, the pyrolysis reactor 5 comprises a material inlet, a heat supply flue gas inlet, a cooling flue gas outlet, a coal gas mixture outlet and a pyrolysis semicoke outlet, the pyrolysis reactor 5 is suitable for pyrolyzing bituminous coal in the pyrolysis reactor to obtain a coal gas mixture and pyrolysis semicoke, the coal gas mixture obtained by pyrolysis is sent to a semicoke main combustion area and a NOx reduction area of a boiler, and the generated high-temperature semicoke is sent to a pyrolysis semicoke bin 6 for cooling;

a heat exchanger 7 is arranged in the pyrolysis semi-coke bin 6, and a semi-coke inlet of the pyrolysis semi-coke bin 6 is connected with a pyrolysis semi-coke outlet of the pyrolysis reactor;

the heat exchanger 7 comprises a cooling water inlet at the upper end and a high-temperature steam outlet at the lower end, and the generated high-temperature steam is sent into a hearth to be heated for driving a steam turbine to generate electricity;

the high-temperature semicoke is subjected to heat exchange through a heat exchanger 7 and cooled to be low-temperature semicoke, and is mixed with semicoke in an original semicoke bin 8 and then enters a semicoke coal mill 11 for mixing and grinding;

the second dryer is connected with the semicoke storage bin 8;

the pyrolysis semicoke bin 6 and the semicoke storage bin 8 are respectively connected with a high-temperature semicoke feeder 9 and a semicoke feeder 10 and conveyed to a semicoke coal mill 11 to be ground into semicoke powder;

the ground semi-coke powder is preheated under the drive of primary air and enters the boiler 12 for combustion and power generation;

a semicoke preheating ignition area 21, a semicoke main combustion area 20, a NOx reduction area 19 and a burnout area 18 are arranged in a hearth in the boiler 12, an air preheater 13 is installed in a flue at the tail part of the boiler, primary air output by the air preheater 13 carries semicoke powder through a pipeline and is sent into the semicoke preheating ignition area 21 of the boiler, the primary air design temperature reaches 400 ℃, a high-temperature flue gas extraction opening is formed in a horizontal flue of the boiler 12, and the extracted high-temperature flue gas is connected with a heat supply flue gas inlet of the pyrolysis reactor 5 and used as a heat source.

The method for low NOx co-combustion of the power station boiler by using the high-volatile coal to support combustion of the semicoke comprises the following steps:

the bituminous coal and the semicoke are dried by the first dryer 3 and the second dryer 4 to obtain dry bituminous coal and dry semicoke, the smoke flowing through the smoke chamber in the second dryer 4 is discharged after being cooled, the dried bituminous coal is conveyed to the pyrolysis reactor 5 by the conveying device to be pyrolyzed, the pyrolysis temperature is 450 ℃, and high-temperature semicoke and mixed coal gas are generated. The high-temperature semicoke enters a pyrolysis semicoke bin 6 to exchange heat with a heat exchanger 7 and be cooled to obtain low-temperature semicoke, the heat exchanger transfers the heat of the high-temperature semicoke to cooling water, the cooling water is heated to obtain high-temperature water vapor, the high-temperature water vapor is sent to a boiler to heat and drive a steam turbine to generate electricity, and mixed gas generated by pyrolysis is sprayed into a semicoke gas combustion area and an NOx reduction area of a hearth in a grading manner.

The low-temperature semicoke cooled by heat exchange of the pyrolysis semicoke bin 6 and the original semicoke are mixed and sent to a coal mill 11, the mass percentage of the original semicoke in the total mixed semicoke is 50%, the ground semicoke powder is preheated by primary air (the temperature is 380-. Pyrolysis gas generated by pyrolyzing bituminous coal is sprayed into the main combustion area 20 of the semicoke to support combustion of the semicoke, rich fuel combustion is formed in the main combustion area, generation of NOx is reduced, meanwhile, the temperature reaches the highest, the semicoke is combusted violently, a large amount of fixed carbon in the semicoke is reacted by high-temperature and violent combustion, nitrogen elements are released along with the reaction, and ignition, stable combustion and burnout of the semicoke are realized. Meanwhile, the coal gas mixture is sprayed into the NOx reduction region, the pyrolysis coal gas introduced into the NOx reduction region accounts for 20% of the volume of the pyrolysis coal gas introduced into the main combustion region, a strong reducing atmosphere combustion region is formed, the reducing strength is increased, more nitrogen elements are reduced, and the generation and emission of NOx are greatly reduced.

The high-temperature flue gas extracted by the horizontal flue of the boiler is connected with a heating pipe of the pyrolysis reactor 5, the heating pipe provides a heat source for the pyrolysis reactor 5 through the introduced high-temperature flue gas, bituminous coal is pyrolyzed in the pyrolysis reactor, and the generated coal gas mixture is discharged through a pipeline at the top of the pyrolysis reactor 5. The cooling flue gas is connected with the flue gas inlet of the flue gas chambers of the first dryer 3 and the second dryer 4, and the heat exchange and cooling are further carried out in the dryers, so that the flue gas waste heat is fully utilized, the energy consumption of drying and pyrolysis is obviously reduced, and the treatment cost of raw coal is saved.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low NOx co-combustion system, characterized by: the method comprises the following steps:

2. The low NOx co-combustion system according to claim 1, wherein: the top of the boiler is connected with the pyrolysis reactor through a pipeline;

3. The low NOx co-combustion system according to claim 2, wherein: a flue gas outlet of the pyrolysis reactor is respectively connected with a first dryer and a second dryer;

furthermore, a semi-coke bin is connected between the second dryer and the coal mill, and an outlet of the semi-coke bin is connected with the coal mill.

4. The low NOx co-combustion system according to claim 1, wherein: and an outlet end of the boiler is provided with an air preheater, and the outlet end of the air preheater is connected with a primary air inlet of the coal mill.

5. A low NOx co-combustion method is characterized in that: the method comprises the following steps:

6. The low NOx co-combustion method according to claim 5, characterized in that: the pyrolysis temperature of the coal is 400-600 ℃.

7. The low NOx co-combustion method according to claim 5, characterized in that: the mass percentage of the existing semicoke in the mixed total semicoke is 40-60%.

8. The low NOx co-combustion method according to claim 5, characterized in that: the temperature of the primary air is 380-420 ℃.

9. The low NOx co-combustion method according to claim 5, characterized in that: the pyrolysis gas introduced into the NOx reduction zone accounts for 17-25% of the volume of the pyrolysis gas in the main combustion zone.

10. The low NOx co-combustion method according to claim 5, characterized in that: the excess air factor in the pre-heating ignition area is 0.85-0.95.