WO2021174979A1

WO2021174979A1 - Multi-coal-type adaptive combustion system and method suitable for w flame boiler

Info

Publication number: WO2021174979A1
Application number: PCT/CN2020/140971
Authority: WO
Inventors: 房凡; 严万军; 张伟; 陈煜�; 张朋飞; 马翔; 吴庆龙; 白鹏; 严响林; 周虹光
Original assignee: 西安热工研究院有限公司; 西安西热锅炉环保工程有限公司
Priority date: 2020-03-03
Filing date: 2020-12-29
Publication date: 2021-09-10
Also published as: CN111189042A

Abstract

Disclosed are a multi-coal-type adaptive combustion system and method suitable for a W flame boiler. The system comprises a downward-injection secondary air nozzle (3), downward-inclination secondary air nozzles (4) and burn-out air nozzles (5) which are respectively in communication with a secondary air bellows of a W flame boiler (1); the downward-injection secondary air nozzle (3) is vertically arranged on an arch of the W flame boiler (1) and is positioned behind a side of a main pulverized coal nozzle (7) of a burner (6); the downward-inclination secondary air nozzles (4) are obliquely arranged at the lower part of front and rear walls of a lower furnace of the W flame boiler (1); and the burn-out air nozzles (5) are horizontally arranged at the upper part of throats of front and rear walls of an upper furnace of the W flame boiler (1), and can swing up and down.

Description

A multi-coal adaptive combustion system and method suitable for W flame boiler

Technical field

The invention belongs to the technical field of energy saving and emission reduction of coal-fired thermal power units, and relates to a combustion technology of a W flame boiler, in particular to a multi-coal adaptive combustion system and method suitable for a W flame boiler.

Background technique

The W-flame boiler is the main type of furnace that burns low-volatile coal in my country. Due to the use of low-volatile coal, W-flame boilers are usually designed with a small furnace volume and high furnace center temperature, which makes the NOx concentration produced by combustion much higher than other furnace boilers, and the boiler combustion efficiency is relatively low.

With the continuous convenience of transportation and the opening up of overseas coal markets, power plants in regions that previously relied on W flame boilers can purchase lower-priced bituminous coal. Therefore, the increasingly severe coal market situation puts forward new requirements for W-flame boilers, that is, the scope of adaptation of coal types is required to control the fuel cost of power plants.

Summary of the invention

The purpose of the present invention is to provide a multi-coal adaptive combustion system and method suitable for W-flame boilers, broaden the coal-type adaptability of W-flame boilers, effectively control NOx produced by combustion, improve boiler combustion efficiency, and prevent boiler furnace coking, At the same time, it has the ability to burn bituminous coal in a wide proportion.

A multi-coal adaptive combustion system suitable for W-flame boilers, including downward secondary air nozzles, downward-inclined secondary air nozzles and over-fired air nozzles respectively connected with the secondary air boxes of the W-flame boiler;

The downward secondary air nozzles are vertically arranged on the arch of the W-flame boiler, behind the main pulverized coal nozzle side of the burner; the downwardly inclined secondary air nozzles are arranged obliquely at the lower part of the front and rear walls of the lower furnace of the W-flame boiler; the exhaust air nozzles It is horizontally arranged on the upper part of the throat of the front and rear walls of the furnace of the W flame boiler.

Preferably, there are several downward secondary air nozzles, downwardly inclined secondary air nozzles and over-fired air nozzles, which are evenly distributed along the width of the furnace at their respective positions.

Further, the burner includes a thick-lean separator and a main pulverized coal nozzle and exhaust gas nozzle connected after the thick-lean separator, the exhaust gas nozzle being arranged in one of the several downstream secondary air nozzles.

Preferably, the angle between the downwardly inclined secondary air nozzle and the front and rear walls of the lower furnace of the W flame boiler is 45° to 75°.

Preferably, the over-combustion air nozzle adopts a structure that swings up and down.

A multi-coal adaptive combustion method suitable for W flame boilers, based on the combustion system described in any one of the above;

The secondary air is fed into the whole furnace at multiple points and grades through the downward secondary air nozzle, the downwardly inclined secondary air nozzle and the burn-out air nozzle, so that the pulverized coal is in a low-oxygen combustion state and inhibits the entire combustion of the pulverized coal The formation of NOx in the process; at the same time, wind walls are formed at different positions of the furnace to prevent the water wall from coking.

Preferably, the down-shot secondary air injected into the furnace at high speed through the down-shot secondary air nozzles injects high-temperature flue gas in the furnace to form a large high-temperature flue gas recirculation zone that can pass under the furnace arch and reach the root of the pulverized coal airflow. The initial ignition of the pulverized coal airflow can adapt to the ignition requirements of different coal types;

At the same time, the down-shot secondary air through the down-shot secondary air nozzle is sent vertically downwards into the furnace, forming an angle with the main pulverized coal airflow of the main pulverized coal nozzle of the W flame boiler burner, and slowing down the diffusion of the secondary air to the pulverized coal airflow. Time, strengthen the reducing atmosphere in the early stage of pulverized coal ignition, and effectively suppress the formation of NOx in the early stage of combustion.

Preferably, the downwardly inclined secondary air is sent to the furnace through the downwardly inclined secondary air nozzles at the lower part of the lower furnace, and the secondary air is obliquely sent downwards into the furnace, and the downward secondary air is used to further inject the fired pulverized coal air flow downward to increase the pulverized coal air flow. The depth of the down shot is used to expand the upper space of the cold ash hopper in the furnace of the W flame boiler;

The downwardly inclined secondary air is fed into the furnace at a high speed and inclined downwards, so that it has sufficient incident rigidity to form an effective air classification in the lower furnace, and at the same time supports the flame to prevent the cold ash hopper from being directly washed away.

Preferably, the speeds of the downward secondary air and the downwardly inclined secondary air are higher than 40 m/s.

Preferably, the over-fired air is sent into the furnace through a swingable over-fired air nozzle to form a full furnace air classification, which is used to adjust the temperature of the main steam and reheat steam of the boiler to meet the needs of heat exchange after the combustion of different coal types.

The invention provides a multi-coal adaptive combustion system and method suitable for W-flame boilers. By rationally arranging secondary air and other means, the coal-type adaptability of W-flame boilers can be broadened, NOx produced by combustion can be effectively controlled, and boiler combustion can be improved. Efficiency, prevent the boiler furnace from coking, and have the ability to burn bituminous coal in a wide proportion; it is suitable for reforming or newly built W flame boilers that need to burn different volatile coal types. Used on W flame boiler, the effect is excellent, mature and reliable, and the transformation investment and risk are small.

Description of the drawings

Fig. 1 is a schematic diagram of the principle of the combustion method in the example of the present invention.

Fig. 2 is a schematic diagram of the structure of the combustion system in the example of the present invention.

Fig. 3 is a top view of the furnace arch of the W-flame boiler burner described in the example of the present invention.

In the figure, W flame boiler 1, furnace arch 2, downward secondary air nozzle 3, downwardly inclined secondary air nozzle 4, over-fired air nozzle 5, burner 6, main pulverized coal nozzle 7, exhaust gas nozzle 8, down Shooting secondary air ①, downward dipping secondary air ②, burn-out air ③.

Detailed ways

In order to further explain the technical solutions and functions adopted by the present invention, the specific structure, implementation, features and functions of the present invention are proposed below in conjunction with FIG. 1, FIG. 2 and FIG. 3. The detailed description is as follows.

The present invention is a multi-coal adaptive combustion system suitable for W flame boilers. The downward secondary air is separately arranged behind the main pulverized coal nozzle side of the burner on the furnace arch to inject high-temperature flue gas to form a direct flow to the root of the pulverized coal. The high-temperature flue gas recirculation zone strengthens the initial ignition of the pulverized coal air flow; at the same time, the downwardly inclined secondary air arranged at the lower part of the front and rear walls of the lower furnace is matched with the downward secondary air, and the pulverized coal air flow is multi-staged to increase the pulverized coal flow. The depth of airflow downwards expands the space utilization rate of the lower furnace, which facilitates the burning of pulverized coal and reduces the local high temperature zone; finally, the over-fired air that can swing up and down is arranged at the upper part of the throat of the front and rear walls of the upper furnace, and the secondary air is downwards. Cooperating with the down-dipping secondary air, a multi-point and graded air supply method for the whole furnace is constructed to make the pulverized coal in a low-oxygen combustion state and reduce the generation of NOx. The adopted system and process are mature and reliable, which reduces the production of NOx during the combustion process while ensuring the combustion efficiency of the W flame boiler. At the same time, it realizes the safe, clean and efficient use of a variety of coal types in the W flame boiler, and expands the W flame boiler coal. Kind of adaptability.

Among them, the downward secondary air is arranged behind the main pulverized coal nozzle side of the burner on the W-flame boiler arch, and the downward secondary air sends the secondary air vertically downward into the furnace through the downward secondary air nozzle through the downward secondary air nozzle. , The pulverized coal air flow that is on fire is directed downward, increasing the downward depth of the pulverized coal air flow. The downwardly inclined secondary air is arranged at the lower part of the front and rear walls of the lower furnace of the W flame boiler, and the downwardly inclined secondary air is sent to the furnace obliquely downward through the downwardly inclined secondary air nozzle at the lower part of the lower furnace, and further injects the pulverized coal on fire. The downward airflow increases the depth of the pulverized coal airflow and expands the upper space of the cold ash hopper in the furnace of the W flame boiler.

The down-shot secondary air on the arch is injected into the furnace at a high speed, and the high-temperature flue gas in the furnace is injected to form a large high-temperature flue gas recirculation zone that can pass under the furnace arch and reach the root of the pulverized coal airflow, which strengthens the initial ignition of the pulverized coal airflow and adapts Fire requirements of different coal types. The down-shooting secondary air on the arch is sent vertically downwards into the furnace, at a certain angle with the main pulverized coal air flow of the burner, which slows down the time for the secondary air to diffuse to the pulverized coal air flow, strengthens the reducing atmosphere in the early stage of pulverized coal ignition, and effectively suppresses it The formation of NOx at the beginning of combustion.

On the upper part of the throat of the front and rear walls of the furnace of the W flame boiler, an over-fired air is set up. The over-fired air is taken from the secondary air. Down-shot secondary air, down-dip secondary air and over-fired air form a multi-point and graded secondary air feed in the whole furnace. The air classification of the whole furnace makes the pulverized coal in a low-oxygen combustion state and suppresses the pulverized coal. The formation of NOx during the entire combustion process. At the same time, a protective wind wall is formed at different positions in the furnace to prevent the water wall from coking.

The burn-out air nozzle can swing up and down to adjust the temperature of the main steam and reheat steam of the boiler to meet the heat exchange requirements of different coal types after combustion.

The present invention is a multi-coal adaptive combustion method suitable for W flame boiler. Its principle is shown in Figure 1. Its core idea mainly includes the following three aspects:

(1) Constructing a multi-stage jetting pulverized coal air distribution method in the lower furnace to increase the effective residence time of the pulverized coal in the furnace, expand the space utilization of the furnace, strengthen the evaporation and heat absorption of the water wall, reduce the local high temperature zone, and reduce the furnace Export smoke temperature.

The specific measures are: 1) Arrange the downward secondary air behind the back fire side of the main pulverized coal nozzle of the burner on the arch. It is sent down into the furnace, and the fired pulverized coal airflow is directed downward by the ejection effect of the high-speed secondary air on the arch, which increases the depth of the pulverized coal airflow downwards, expands the space utilization rate of the lower furnace, and increases the effectiveness of the pulverized coal in the furnace. The residence time facilitates the exhaustion of the pulverized coal and reduces the temperature of the flue gas at the outlet of the furnace. 2) Arrange the downwardly inclined secondary air at the lower part of the front and rear walls of the lower furnace, and the downwardly inclined secondary air is sent into the furnace obliquely through the downwardly inclined secondary air nozzle at the lower part of the lower furnace, and further injects the pulverized coal on fire down. , Increase the depth of the down shot of the pulverized coal airflow, and expand the use of the upper space of the cold ash hopper in the furnace of the W flame boiler.

(2) Inject high-temperature flue gas to form a large-scale high-temperature flue gas recirculation zone that can pass under the furnace arch and reach the root of the pulverized coal airflow, strengthen the initial ignition of the pulverized coal airflow, and adapt to the switching of different coal types.

The specific measure is to use the downstream secondary air arranged behind the main pulverized coal nozzle of the burner to inject it into the furnace at a high speed, and the high-temperature flue gas at the throat of the ejected furnace returns to the root of the pulverized coal airflow, thereby directly igniting the pulverized coal airflow. Promote the rapid ignition of pulverized coal.

(3) Constructing a multi-point, graded air supply method for the whole furnace, so that the pulverized coal is always in a low-oxygen combustion state, avoiding the formation of a high-temperature and high-oxygen overlap zone, and reducing the generation of NOx during the combustion process. At the same time, a protective wind wall is formed at different positions in the furnace to prevent the water wall from coking.

The specific measures are as follows: 1) The secondary air is injected vertically downwards into the furnace, and it is at a certain angle with the main pulverized coal air flow of the burner, which slows down the time for the secondary air to diffuse to the pulverized coal air flow and strengthens the reducibility of the pulverized coal at the initial stage of ignition. Atmosphere, effectively suppress the formation of NOx in the initial stage of combustion; 2) The lower furnace chamber is tilted down and the secondary air also uses nozzles to send the secondary air into the furnace chamber at a high speed and inclined downwards, so that it has sufficient incident rigidity to form an effective air classification in the lower furnace chamber. At the same time, the flame is supported to prevent the cold ash hopper from being directly washed away; 3) An over-combustion air is set on the upper part of the throat of the front and rear walls of the upper furnace. At the same time, the burn-out air nozzle can swing up and down, which can be used to adjust the temperature of the main steam and reheat steam of the boiler to meet the needs of heat exchange after the combustion of different coal types.

In specific use, as shown in Figure 2, a multi-coal adaptive combustion system suitable for W-flame boilers of the present invention includes a downward secondary air nozzle 3 and downwardly inclined secondary air provided on the W-flame boiler 1. Nozzle 4 and burn-out wind nozzle 5. Correspondingly, the downstream secondary air ①, the downwardly inclined secondary air ② and the over-fired air ③ are all from the boiler secondary air.

The W-flame boiler burner 6 generally adopts a pulverized coal concentration separation method, and the pulverized coal gas flow is divided into a dense phase pulverized coal gas flow and a light phase pulverized coal gas flow after the concentration separation. The dense-phase pulverized coal airflow, that is, the main pulverized coal airflow, is sent into the furnace through the main pulverized coal nozzle 7 of the burner, and the light-phase pulverized coal airflow is sent into the furnace through the exhaust gas nozzle 8.

As shown in Figure 3, the downward secondary air nozzle 3 is arranged behind the main pulverized coal nozzle 7 of the burner 6 on the furnace arch 2, at the backfire side of the furnace, and the downward secondary air ① passes through the downward secondary air nozzle. 3 Spray vertically downwards into the furnace. As shown in Figure 2, the downwardly inclined secondary air nozzle 4 is arranged at the lower part of the front and rear walls of the lower furnace of the W flame boiler 1, and the downwardly inclined secondary air ② is sprayed into the furnace through the downwardly inclined secondary air nozzle 4 obliquely downward. The over-fired air nozzle 5 is arranged on the upper part of the throat of the front and back walls of the upper furnace of the W flame boiler 1. The over-fired air ③ is injected into the furnace through the over-fired air nozzle 5. The over-fired air nozzle 5 is in a form that can swing up and down, which can be used to adjust the boiler. The steam temperature of main steam and reheat steam can meet the demand of heat exchange after the combustion of different coals.

Downward secondary air ① can inject high-temperature flue gas backflow, as shown in Figure 1, forming a large-scale high-temperature flue gas recirculation zone that can pass under the furnace arch and reach the root of the pulverized coal airflow, as shown in the high-temperature recirculation flue gas location in the middle of Figure 1. It shows that the initial ignition of the enhanced pulverized coal airflow is used to meet the requirements of different coal types.

Downwardly inclined secondary air ② is injected downwardly into the furnace at a high speed, as shown in Fig. 1, which can compress the middle temperature and even low temperature flue gas recirculation area in the upper part of the cold ash hopper in the W flame boiler furnace, and expand the use of the upper space of the cold ash hopper.

Overfire air ③ is injected into the upper furnace, as shown in Figure 1, to control the excess air coefficient of the lower furnace combustion of the W-flame boiler, and form oxygen-deficient combustion in the lower furnace.

Downward secondary air ① and downward secondary air ② generally have a speed higher than 40m/s. After being injected into the furnace, the pulverized coal flow can be directed downward in multiple stages, effectively increasing the downward depth of the pulverized coal flow, which is not only beneficial to the coal The combustion of the powder also improves the space utilization rate of the lower furnace, avoids the formation of a high temperature and high oxygen recombination zone, and suppresses the generation of NOx during the combustion process while ensuring the combustion efficiency of the boiler.

Downshot secondary air ① is sent vertically downwards into the furnace, arranged at an angle to the pulverized coal airflow, slows down the time for the secondary air to diffuse into the pulverized coal combustion area, strengthens the reducing atmosphere at the early stage of pulverized coal ignition, and effectively suppresses NOx at the initial stage of combustion The generation. Down-shot secondary air①, down-dip secondary air② and out-of-combustion air ③ form a multi-point secondary air feeding mode in the whole furnace, so that the pulverized coal is in a low-oxygen combustion state and reduces the generation of NOx; The different positions of the furnace form a wind wall to prevent the water wall from coking.

In summary, the present invention is a multi-coal adaptive combustion system and method suitable for W-flame boilers, using the reasonable arrangement and air distribution of the secondary air to solve the problem of high NOx generated by the combustion of W-flame boilers, poor combustion economy, The characteristics of the limited adaptability of coal types are as follows:

(1) Combining the characteristics of the double-arch furnace structure of the W-flame boiler, the present invention reasonably sets the secondary air feed mode, increases the depth of the pulverized coal airflow, increases the space utilization rate of the furnace, prevents local high temperatures, and reduces the furnace outlet Smoke temperature.

(2) The present invention prolongs the stroke of the pulverized coal particles in the furnace, increases the effective residence time of the pulverized coal particles in the furnace, and facilitates the burn-out effect of the pulverized coal particles under the condition of air staged combustion, while ensuring that the pulverized coal particles are in the furnace. The reduction distance in the furnace can effectively control the formation of NOx during the combustion process.

(3) The present invention uses the special structure of the upper and lower furnaces of the W-flame boiler to arrange secondary air nozzles in different areas of the flame stroke (furnace arch, lower furnace front and rear walls, upper furnace front and rear walls) to gradually fill in combustion air, Multi-point air classification is formed to reduce the generation of NOx during the combustion of pulverized coal in the whole furnace.

(4) The present invention adopts various methods such as strengthening the initial ignition of pulverized coal, increasing the utilization rate of furnace space, multi-point grading air distribution to realize intensity controllable combustion and other means, and realizes the requirement of burning coal with different volatile content in W flame boiler. Combining with the optimization of the furnace combustion zone, the W flame boiler can also burn bituminous coal in a wide proportion.

Claims

A multi-coal adaptive combustion system suitable for a W flame boiler, which is characterized in that it comprises downward secondary air nozzles (3) and downwardly inclined secondary air respectively connected with the secondary air boxes of the W flame boiler (1) Nozzle (4) and over-fired air nozzle (5);

The downward secondary air nozzle (3) is vertically arranged on the arch of the W flame boiler (1), behind the main pulverized coal nozzle (7) side of the burner (6); the downwardly inclined secondary air nozzle (4) is arranged obliquely In the lower part of the front and rear walls of the lower furnace of the W flame boiler (1); the over-burning air nozzle (5) is horizontally arranged on the upper part of the front and rear wall throats of the upper furnace of the W flame boiler (1).
A multi-coal adaptive combustion system suitable for W flame boilers according to claim 1, characterized in that the downward secondary air nozzle (3), the downwardly inclined secondary air nozzle (4) and the over-fired air nozzle (5) There are a number of them, which are evenly distributed along the width of the furnace at their respective positions.
A multi-coal adaptive combustion system suitable for W flame boilers according to claim 2, wherein the burner (6) comprises a thick-lean separator and a main pulverized coal nozzle connected behind the thick-lean separator (7) and exhaust gas nozzle (8), exhaust gas nozzle (8) is arranged in one of several downward secondary air nozzles (3).
The multi-coal adaptive combustion system suitable for W flame boilers according to claim 1, characterized in that the angle between the downwardly inclined secondary air nozzle (4) and the front and rear walls of the lower furnace of the W flame boiler (1) It is 45° to 75°.
The multi-coal adaptive combustion system suitable for W flame boilers according to claim 1, characterized in that the burn-out air nozzle (5) adopts a structure that swings up and down.
A multi-coal adaptive combustion method suitable for W flame boilers, characterized in that it is based on the combustion system according to any one of claims 1-5;

The secondary air passes through the downward secondary air nozzle (3), the downwardly inclined secondary air nozzle (4) and the burn-out air nozzle (5) to form multiple points and graded feeds in the entire furnace, so that the pulverized coal is in an oxygen-deficient condition. The combustion state suppresses the generation of NOx during the entire combustion process of pulverized coal, thereby reducing the generation of NOx; at the same time, a wind wall is formed at different positions of the furnace to prevent the water wall from coking.
A multi-coal adaptive combustion method suitable for W flame boilers according to claim 6, characterized in that the secondary air jetted down through the downward secondary air nozzle (3) is injected into the furnace at a high speed, and the furnace is ejected. The internal high-temperature flue gas forms a large high-temperature flue gas recirculation zone that can pass under the furnace arch and reach the root of the pulverized coal airflow, which strengthens the initial ignition of the pulverized coal airflow and adapts to the ignition requirements of different coal types;

At the same time, the secondary air shot down through the down shot secondary air nozzle (3) is sent vertically downwards into the furnace, forming an angle with the main pulverized coal air flow of the main pulverized coal nozzle (7) of the W flame boiler burner (6) to slow down The time that the secondary air diffuses into the pulverized coal airflow strengthens the reducing atmosphere in the early stage of pulverized coal ignition and effectively suppresses the generation of NOx in the early stage of combustion.
A multi-coal adaptive combustion method suitable for W flame boilers according to claim 6, characterized in that the downwardly inclined secondary air passes through the downwardly inclined secondary air nozzle (4) to incline the secondary air towards the lower part of the lower furnace It is sent down into the furnace, and the secondary air is matched with the downstream secondary air to further direct the fired pulverized coal air flow downward, increase the depth of the pulverized coal air flow downward, and expand the upper space of the cold ash hopper in the furnace of the W flame boiler;

The downwardly inclined secondary air is fed into the furnace at a high speed and inclined downwards, so that it has sufficient incident rigidity to form an effective air classification in the lower furnace, and at the same time supports the flame to prevent the cold ash hopper from being directly washed away.
The multi-coal adaptive combustion method suitable for W flame boilers according to claim 6, characterized in that the speeds of the downward secondary air and the downward secondary air are higher than 40m/s.
The multi-coal adaptive combustion method suitable for W flame boilers according to claim 6, characterized in that the over-fired air is sent into the furnace through the up-and-down swinging over-fired air nozzle (5) to form the air in the whole furnace. Classification is used to adjust the temperature of the main steam and reheat steam of the boiler to meet the needs of heat exchange after the combustion of different coals.