JPS59191806A - Denitrating combustion of pulverized coal and burner thereof - Google Patents

Abstract

PURPOSE:To reduce the production of unburnt content in ash and NOX in exhaust gas without increasing the size of a device, by a method wherein fuel, indicating a fuel ratio equivalent to or less than that of pulverized coal, is injected under atmosphere containing recycling combustion exhaust gas. CONSTITUTION:More fine pulverized coal 4, which is auxiliary fuel and fed through an auxiliary fuel feed pipe 5 by means of recycling combustion exhaust gas, is injected through an auxiliary injection nozzle 7 in a lower furnace 17 at a speed higher than that of pulverized coal conveyed by the air after passing through an auxiliary fuel pipe 6. As a result of the auxiliary fuel after injection being heated by means of ambient main combustion flame and the radiant heat of a furnace, it produces a volatile component, but the volatile component is present under atmosphere of recycling combustion gas being low in an O2 partial pressure, whereby combustion lag occurs and the volatile component is burnt as production and disappearance of a carbon hydride series radial is repeated. This enables reduction in production of an unburnt content in ash and NOX in exhaust gas without increasing the size of a device.

Description

Detailed Description of the Invention ° The present invention relates to a pulverized coal denitrification combustion method, and in particular to a combustion method and burner for a coal-fired boiler device suitable for reducing nitrogen oxides (hereinafter referred to as NOx) in exhaust gas. It is related to.

Since NO is considered to be one of the causative substances of photochemical oxidants and acid rain, there is a demand for the development of a combustion method that effectively suppresses its generation. As combustion methods for such purposes, (1) exhaust gas recirculation method, (2) two-stage combustion method, and (3) reduction combustion method (denitrification combustion method) are known. The exhaust gas recirculation method works by mixing exhaust gas! This is a method of reducing fiNO by using air with a reduced partial pressure as a combustion gas and performing slow combustion. In the two-stage combustion method, burners are generally arranged in multiple stages, and the first stage burner performs the first combustion at a low air ratio, which is advantageous for reducing NOx, and then the unburned matter produced by the combustion is sent to the wake of the burner. Reburning occurs in the presence of a device consisting of an after-aero system. In addition, the reduction combustion method is carried out using the same equipment as the two-stage combustion method, but in this method, a combustion region with a large excess of fuel is formed on the downstream side of the multi-stage burner, and the reduction radicals generated in the region are NO, which is generated in the upstream burner section, is reduced to N2, while unburned components are completely combusted in the presence of air supplied from the after-air system, as in the case of the two-stage combustion method described above. It is. These combustion methods are excellent when burning fluid fuels such as LNG and heavy oil, but when applied to pulverized coal that has a large nitrogen compound content and a relatively large fuel ratio, There are various drawbacks as described below. 1st
The disadvantage of this method is that it uses slow combustion conditions, which increases the amount of unburned matter in the ash and unavoidably causes unburned losses. Second
The disadvantage of this method is that it is inevitable to increase the size of the furnace due to the adoption of slow combustion conditions and the provision of a complete combustion zone due to after air. Still, the third
The disadvantage of this is that, especially when high fuel ratio coal is combusted, the unburned content also increases with the increase in NO emissions.

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art;
The object of the present invention is to provide a pulverized coal combustion method that can reduce unburned content in ash and NO□ in exhaust gas without requiring an enlarged device.

In order to achieve the above object, the present invention provides a method for injecting air-borne pulverized coal into a furnace from a fuel nozzle of a burner to inject the pulverized coal from at least a part of the fuel nozzle to the furnace. The present invention is characterized in that a fuel exhibiting a fuel ratio equal to or lower than that of the pulverized coal is injected in an atmosphere containing recirculated combustion exhaust gas so as to penetrate the combustion zone of the pulverized coal and reach its downstream side.

With the above configuration, the air-borne pulverized coal is injected at high speed from a part (hereinafter referred to as the sub-outlet) of the fuel outlet (hereinafter referred to as the main outlet) (hereinafter referred to as the main outlet). The pulverized coal combustion flame (hereinafter referred to as the main combustion flame) and the radiant heat of the furnace heat the pulverized coal combustion flame (hereinafter referred to as the main combustion flame) and generate volatile components. Because it is in the atmosphere of combustion exhaust gas, combustion is delayed, and as the flow velocity decreases on the downstream side of the main combustion flame, it does not react with the residual 02 in the exhaust gas until it becomes possible to mix with the exhaust gas of the combustion flame. However, it burns while repeatedly generating and extinguishing hydrocarbon radicals (HC) (see below (
1) and (2), etc.). At that time, NO and hydrocarbon radicals in the main combustion flame exhaust gas are defined as (2) and (2) below.
Since the reaction of equation 3) is repeated, so-called in-furnace denitrification combustion does not proceed for each burner, and a reduction in NO emissions can be achieved satisfactorily.

■・C+02→・uc 1K −−−−−=−−−−−
−−−−−−−−−<1>. HC+NO-+. NH+
P ・・・・・・・・・・・・・・・・・・・・・(
2). NH+ No -') N2+ P...
・・・・・・・・・・・・・・・・・・・・・(3) (In each of the above formulas, H-C is a volatile hydrocarbon component, P is COl・O
H, I (representing a product such as 20) In the present invention, it is desirable that the formation of the main combustion flame be as good as possible, so that the combustion of the air-borne pulverized coal is suitably achieved, and the unburned Loss can be prevented. In addition, the auxiliary fuel should be a fuel that exhibits a fuel ratio equal to or lower than that of air-borne pulverized coal, but this is done in order to advantageously achieve the production of volatile components necessary for NO reduction and to avoid increasing unburned losses. It's for a reason.

Examples of such auxiliary fuels include pulverized coal having a fuel ratio equal to or lower than that of air-borne pulverized coal, gaseous fuels such as LNG, and liquid fuels such as heavy fuels.

The pulverized coal used as the auxiliary fuel is preferably finer than the air-borne pulverized coal. By doing so, the surface area of the pulverized coal increases, and the generation of volatile components becomes even better. The amount of recirculated flue gas used is generally preferably 2 to 15% (by volume) of the total amount of flue gas.

The present invention is widely applicable to conventional pulverized coal burners for furnaces. Conventional burners generally have a structure in which a main air outlet, a secondary air outlet, a tertiary air outlet, etc. are sequentially arranged from the center toward the outer periphery. This can be easily reversed by providing one or more sub-outlets in one part of the above-mentioned main outlet to eject the auxiliary fuel in an atmosphere of recirculated combustion exhaust gas. Usually, a plurality of auxiliary nozzles are arranged around the center point of the main nozzle in the form of isolated islands along the rotational direction. Alternatively, it is preferable to provide it in a divided manner.

The shapes of the main ejection port and the sub-ejection port are generally circular, but may also be square, rectangular, or annular.

In addition, if a fireproof material is provided around the outer periphery of the outer cylinder that forms the secondary air passage leading to the secondary air outlet, the root of the main combustion flame will be maintained at a high temperature due to its radiant heat effect, making combustion even more effective. Since this can be achieved satisfactorily, it is preferable in terms of preventing unburned losses. The thickness of the refractory material body is preferably 1/12 or more of the inner diameter of the throat.

Hereinafter, the present invention will be explained in more detail with reference to embodiments shown in the drawings.

The burner shown in FIGS. 1 and 2 includes a circular main ejection port 3 having two isolated island-shaped circular sub-ejection lowers at target positions near the outer periphery, which are sequentially provided from the center toward the outer periphery. It is mainly composed of a secondary air outlet 10 and a tertiary air outlet 13.

In the burner configured as described above, the air-carried pulverized coal 1 is sent through the main fuel pipe (passage) z and then injected into the furnace 17 from the main fuel outlet 3, and is separately injected into the furnace 17 through the secondary air injection port 10 and the tertiary air injection port 10. It is combusted in contact with secondary air and tertiary air, respectively, which are injected from the outlet 13. The above-mentioned secondary and tertiary air is supplied to an FDP (forced blower), and then passes through a branch pipe and an air volume adjustment device (all of which are not shown) to the wind box wall 15 and the cone-shaped throat ( The secondary air is introduced into a wind box 14 surrounded by a heat transfer wall (heat transfer wall) 16, and the secondary air is adjusted in air volume and given a swirling force by a secondary register 8, and then further developed into a swirling flow in a secondary swirling chamber 9. On the other hand, the tertiary air is subjected to air volume adjustment and swirling force by the tertiary register 11, and then becomes a further developed swirling flow in the tertiary swirling chamber 12, and then flows from the secondary air outlet 10 and the tertiary air outlet 13 to the furnace. It is injected into 17.

Because of the stirring action caused by the swirling flow of secondary air and tertiary air, the pulverized coal injected from the main jetting port 3 is efficiently combusted with a short flame, so it is no.

The production of fuel will increase, but the unburned loss will decrease.

On the other hand, finer pulverized coal 4, which is an example of an auxiliary fuel, is conveyed through the auxiliary fuel supply pipe 5 by the recirculated combustion exhaust gas, which is generally heated at 200 to 380°C, and then passes through the 1 auxiliary fuel pipe 6 before being ejected from the auxiliary jet. The lower air is injected into the furnace 17 at a higher speed than the fineness of the air. The auxiliary fuel after the injection is heated by the surrounding main combustion flame and the radiant heat of the furnace and generates volatile components, but since these volatile components are in the atmosphere of recirculated combustion exhaust gas with low 02+ pressure, combustion is delayed. , it reacts with the remaining 02 in the exhaust gas only when it becomes possible to mix with the exhaust gas of the main combustion flame as the flow velocity decreases on the downstream side of the main combustion flame, and hydrocarbon radicals are repeatedly generated and extinguished. However, it will burn. The hydrocarbon-based diradicals generated above react with NO in the main combustion flame exhaust gas according to equations (2) and (3) described above, thereby successfully achieving a reduction in NOa.

Furthermore, since the auxiliary fuel used is pulverized coal that is finer than air-borne pulverized coal, its combustibility is excellent, and the amount of unburned fuel is also small.

According to this embodiment, low NO combustion is possible without increasing unburned loss for each burner, so the apparatus can be made into a shed.

Next, FIG. 3 shows a burner according to another embodiment of the present invention, in which instead of the island-like sub-nozzle shown in FIG. The structure is the same except that two sub-spout 7A are provided, and the main spout 3A is also divided into two.

According to this embodiment, since a divided main combustion flame is formed based on the three divided main ejection ports, contact between NO and hydrocarbon radicals is even better. In addition to the effects of the embodiment shown in , low NO processing is further improved.

4 to 6 show a burner according to another embodiment of the present invention, in which a main jet nozzle 3 forming a circular shape as shown in FIG.
In place of A and auxiliary ejection lower A, a main ejection port 3B and an auxiliary ejection lower B forming an annular shape are provided, and an outer cylindrical body that forms a secondary air passage leading to the secondary air ejection port 10 has a resistant structure. The structure is similar to that shown in FIG. 3 except that the human body 19 is provided. In addition, in the same figure, 18 is an auxiliary combustion oil gun provided in the center of the burner, 21 is a passage for recirculating combustion exhaust gas 20 provided outside the auxiliary combustion oil gun 18, and the tip on the furnace side is a passage. Lid body 24 and sub-spout lower BK
A communicating opening 23 is provided. Also, of the main fuel passage 2 that guides the air conveyed pulverized coal 1, a sub-ejection lower B
A shielding plate 22 having a plurality of small holes 25 as shown in FIG. 7 is provided on the upstream side of the opening in a portion corresponding to the opening.

In the burner configured as described above, most of the air-carried pulverized coal 1 sent through the main fuel passage 2 is injected into the furnace from the main jet port 3B, and is split and combusted in the same manner as in the embodiment shown in FIG. Ru.

On the other hand, one part of the pulverized coal is stored in the through hole and the shielding plate 2 shown in FIG.
The leakage flow IC passes through the small hole 25 of No. 2 and becomes a leakage flow IC, which is mixed with the recirculated exhaust gas 20 passing through the opening 23 and then injected into the furnace from the sub-injection lower B as an auxiliary fuel. It will show the same action and effect as.

According to this embodiment, in addition to the effects of the previously described embodiments, since the refractory material body 19 is provided on the outer periphery of the outer cylindrical body forming the secondary air passage, the root of the main combustion flame reaches a high temperature due to its radiation effect. combustion stability can be achieved.

Although typical embodiments of the present invention have been described above, the present invention is of course not limited to these, and there may be various other modifications and applications within the spirit of the present invention. Needless to say. For example, the present invention may be implemented in combination with two-stage combustion, which is an example of a known denitrification combustion method, and thereby an even more excellent reduction in NO can be achieved.

As described above, according to the present invention, high-rate combustion of air-borne pulverized coal can be achieved by penetrating the combustion zone of air-borne pulverized coal and injecting auxiliary fuel with a low fuel ratio into the atmosphere of recirculated combustion exhaust gas. At the same time, a reducing atmosphere is formed on the downstream side of the combustion zone to improve the reduction of fcNO generated by the combustion,
As a result, low NO combustion can be performed without any unburned loss during combustion, and the entire combustion apparatus can be downsized.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a pulverized coal burner according to an embodiment of the present invention, FIG. 2 is a partial main view in the A direction of FIG. 1, and FIG. 3 is a pulverized coal burner according to another embodiment of the present invention. 4 is a partial perspective view of the pulverized coal burner according to another embodiment of the present invention, which corresponds to the direction A in FIG. 1, and FIG. 5 is a partial cross-sectional view in the direction of arrows taken along line B-B in FIG. 4, FIG. 6 is a cross-sectional view in the direction of arrows along line C-C in FIG. 4, and FIG. FIG. 5 is a perspective explanatory view of a shielding plate provided at the sub-spout part of the burner shown in FIG. 4; 1... Air conveyed pulverized coal, 2... Main fuel pipe (passage),
3.3A, 3B...Main injection port, 4-...Auxiliary fuel, 7.
7A, 7B... Sub-air outlet, 10... Secondary air outlet, 13... Tertiary air outlet, 16... Throat, 1
7...Furnace, 19...Refractory material body, 20...Recirculation combustion exhaust gas, 21...Recirculation combustion exhaust gas passage, 22.
... Shielding plate, 23 ... Opening, 24 ... Lid, 2
5...Small hole, IC...leakage flow. Agent: Patent Attorney Takeshi Kawakita Continued from page 1 0 Inventor: Narato Nakashita 6-9 Takaracho, Kure City, Babcock Hitachi Co., Ltd. Kure Factory

Claims (3)

[Claims] (1) In a method in which air-borne pulverized coal is injected into a furnace from a fuel nozzle of a burner to perform combustion, the combustion area of the pulverized coal is penetrated from at least a part of the fuel nozzle to the downstream side. A pulverized coal denitrification combustion method characterized by injecting a fuel exhibiting a fuel ratio equal to or lower than that of the pulverized coal in an atmosphere containing recirculated combustion exhaust gas so as to reach the above pulverized coal. (2) In a pulverized coal burner equipped with an air conveying pulverized coal outlet, a secondary air outlet, a tertiary air outlet, etc. sequentially from the center toward the outer periphery, at least one part of the air conveying pulverized coal outlet A pulverized coal denitration burner characterized in that one or more sub-injection ports are provided for injecting fuel having a fuel ratio equal to or lower than that of the pulverized coal in an atmosphere containing recirculated combustion exhaust gas. (3) The pulverized coal denitrification burner according to claim 2, characterized in that a refractory material body is provided on the outer periphery of the outer cylindrical body that forms the secondary air passage leading to the secondary air outlet.