JPH06265105A - Fine powder solid fuel combustion device - Google Patents

Abstract

PURPOSE:To provide a stable combustion down to a low load in a boiler furnace for directly transporting fine powder coal from a mill to a main burner and igniting it there. CONSTITUTION:A part of fine powder coal mixture gas fed from a mill 08 to a main burner 02 is branched and a rich and a lean mixture gas are separated by a cyclone separator 102 and then the rich mixture gas is merged again to the left mixture gas not being branched. The lean mixture gas is taken out of an upper part of the cyclone separator 102 and supplied to an upper burner 06. An adjusting valve 105 placed at a downstream side of the branching point is adjusted to change a ratio of splitting, thereby a concentration of fuel supplied to the main burner 02 can be freely adjusted to a value which is suitable for combustion, so that it is possible to perform a stable combustion down to the low load state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion apparatus that uses fine powder solid fuel in a furnace such as a boiler or a chemical industrial furnace.

[0002]

2. Description of the Related Art FIG. 5 is an overall system diagram showing an example of a conventional fine powder solid fuel combustion apparatus. In this figure, (01)
Is the furnace body, (02) is the main burner body, (03) is the main burner fuel nozzle, (04) is the main burner air nozzle, and (0
5) is an overfiring air (hereinafter referred to as OFA) nozzle, (06) is an upper burner (hereinafter referred to as UB) fuel nozzle, (07) is an additional air (hereinafter referred to as AA) nozzle, and (08) is coal crushing. Machine, (09)
Is solid fuel, (10) is carrier air, (11) is a ventilator, (12) is pulverized solid fuel mixture, (13) is UB fuel mixture, (14) is combustion air, and (15) is Fine powder solid fuel mixture transport pipe, (16) UB fuel mixture transport pipe,
(17) is an air duct for combustion, (18) is OFA, (1
9) is an OFA duct, (20) is AA, (21) is AA
Duct, (22) inside the furnace, (23) main burner flame,
(24) shows the main burner combustion exhaust gas, (25) shows the UB combustion flame, and (26) shows the combustion exhaust gas.

The solid fuel (09) sent to the coal crusher (08) is pulverized and mixed with the carrier air (10) sent at the same time, and pulverized solid fuel mixture (12) is mixed.
And is fed into the main burner body (02) and the UB fuel nozzle (06) through the fine powder solid fuel transport pipe (15).

A main burner fuel nozzle (03) and a main burner air nozzle (04) are incorporated in the main burner body (02), and a fine powder solid fuel mixture (( 12) is the main burner fuel nozzle (03)
Is injected into the furnace (22). On the other hand, combustion air (1
4) is a combustion air duct (1
7), sent for main burner body (02), O
The main burner air nozzle (04) and OFA nozzle (05) are divided into FA (18) and AA (20), respectively.
And is injected into the furnace (22) from the AA nozzle (07).

From the main burner fuel nozzle (03) into the furnace (2
The pulverized solid fuel mixture (12) injected into 2) is ignited by an ignition source (not shown), and the main burner flame (2
3) is formed to continue combustion. Main burner flame (23)
In the vicinity of the ignition point burns by reacting with oxygen supplied by the transfer air (10) and a part of the combustion air (14) blown from around the main burner fuel nozzle (03), and in the subsequent combustion zone. Main burner air nozzle (04)
Combustion is continued by the oxygen in the combustion air (14) blown from.

In the conventional boiler, nitrogen oxides (hereinafter referred to as N
In order to suppress the generation of O _x ), the transfer air (10) blown from the main burner fuel nozzle (03) and the combustion blown around the main burner fuel nozzle (03) and from the main burner air nozzle (04). The sum of the working air (14) and the working air (14) is less than or equal to the stoichiometric amount of the fine solid fuel injected from the main burner fuel nozzle (03).
5) The following atmosphere (22) in the furnace is in a reducing atmosphere. The NO _x generated by the combustion of the fine powder solid fuel blown from the main burner fuel nozzle (03) is reduced because the combustion region is in the reducing atmosphere. Therefore, the NO _x concentration in the main burner combustion exhaust gas (24) decreases immediately before the OFA (18) charging section, and instead, intermediate products such as HCN · NH ₃ are generated. Because of the reducing atmosphere, considerable combustible components remain in the main burner combustion exhaust gas (24).

Next, in order to burn combustible components in the main burner flue gas (24), O gas is discharged from the OFA nozzle (05).
FA (18) is blown into the furnace (22). OFA
The injection amount of (18) is the combustion air (14) and the transfer air (10) injected from the main burner main body (02) with respect to the amount of the fine solid fuel injected from the main burner fuel nozzle (03). And OFA (18) are 1.0 by air ratio
It should be ~ 1.05. Thus, OFA (18)
When promoting combustion of the main burner flue gas (24) by charging, the air ratio after charging OFA (18) is 1.0 to 1.
The low value of 05 is set to prevent the intermediate product in the main burner combustion exhaust gas (24) from being converted into NO _{x due} to the oxidation reaction caused by the addition of OFA (18).

A UB fuel nozzle (06) is mounted above (in the downstream of) the OFA (18) charging part. Then, the UB fuel mixture (13) sent from the pulverized solid fuel transport pipe (15) through the UB fuel mixture transport pipe (16) branched from the UB fuel nozzle (06) into the furnace ( 22). UB fuel mixture (13)
Is a shunt of the pulverized solid fuel mixture (12), and the weight ratio of the carrier air (10) to the pulverized solid fuel (AIR
/ COAL) and the particle size distribution of the pulverized solid fuel can be regarded as almost the same as that of the pulverized solid fuel mixture (12). By the injection of the UB fuel mixture (13), a reducing atmosphere is formed after the UB fuel mixture (13) injection part, and O
The NO _x increased by the FA (18) injection is reduced and converted to N ₂ .

A single stage or multiple stages (two stages in the illustrated example) of AA nozzles (07) are provided above the UB fuel nozzles (06) (in the downstream). The sum of the amount of OFA (18) and the amount of transfer air (10) in the UB fuel mixture (13) is the amount of residual combustible components in the main burner combustion exhaust gas (24) and U
It is less than or equal to the stoichiometric ratio of the sum of the fine powder solid fuel in the B fuel mixture (13), and AA from the UB fuel mixture (13) injection part
(20) In the furnace (22) region up to the injection part, the air ratio is usually set to 0.75 to 1.0 to suppress the increase of NO _x due to the injection of the UB fuel mixture (13). However, AA (2
0) Since the reducing atmosphere is up to the blow-in portion, combustible components remain in the main burner combustion exhaust gas (24). The AA (20) is blown in order to complete the combustion of this combustible component and form a clean combustion exhaust gas (26).

[0010]

Main burner flame (23)
Ignition stability of the air-fuel ratio (AIR / COA) of the carrier air (10) of the fine solid fuel mixture (12) blown from the main burner fuel nozzle (03) into the furnace (22) and the fine solid fuel (AIR / COA
L) is greatly affected. FIG. 6 is a diagram showing the relationship between the ignition distance of the fine solid fuel flame and AIR / COAL. This is the result of an experiment conducted by the inventors of the present invention using a test furnace, but it is generally accepted data at present. It can be seen from Fig. 6 that the ignition distance of the fine solid fuel flame shows a tendency to increase as AIR / COAL increases. A large ignition distance means that the ignition stability of the flame is poor.

According to FIG. 6, the smaller the fixed carbon / volatile matter ratio (fuel ratio) of the fine powdered solid fuel, the smaller the required ignition distance for stabilizing the ignition of the flame is AIR / COAL. But in coal crushing, coal crusher (08)
Moisture brought in with coal into the coal crusher (0
It is necessary to crush the coal in 8) and dry it so that the pulverized coal can be conveyed by air. When the amount of crushed coal is large, a large amount of air for transportation (10) is required. Therefore, AIR / COAL cannot be adjusted freely.

FIG. 7 shows the amount of crushed coal (or combustion load) of a commonly used coal crusher (08) and AIR / COAL.
It shows the relationship with. This figure shows that AIR / COAL tends to increase as the amount of pulverized coal decreases. This is because the fine powder solid fuel mixture (12) contains fine powder solid fuel in the transport pipe (15). This is because it is indispensable to maintain the minimum required flow rate in order to convey the material without sedimentation and deposition. Therefore, the carrier air (10) cannot be throttled below a certain flow rate, which makes stable combustion at low loads difficult.
In such a system in which the fine powdered solid fuel is directly sent from the coal pulverizer (08) to the main burner fuel nozzle (03) for combustion, the AIR / COAL adjustment cannot be freely performed in the past.
Therefore, stable combustion in a wide load range was difficult.

On the other hand, the UB fuel mixture (13) introduced to form the reducing atmosphere necessary for NO _x suppression completes combustion by the AA (20) introduced in the downstream, but the AA (20 ) Because the charging part is near the furnace outlet,
U in the oxidizing atmosphere formed by the introduction of AA (20)
The residence time of the B fuel mixture (13) is short, and the temperature of the surrounding combustion exhaust gas (26) is low. Therefore, the pulverized solid fuel in the UB fuel mixture (13) needs to be miniaturized as much as possible in order to shorten the combustion completion time. Conventionally, the pulverized solid fuel fed to the main burner fuel nozzle (03) is Since the same particle size was sent in, there was a drawback that a large amount of unburned material was generated.

[0014]

In order to solve the above-mentioned conventional problems, the present invention directly conveys finely divided solid fuel pulverized by a pulverizer to a main burner fuel nozzle and blows it into a furnace for combustion. In the apparatus, the mixture transport pipe for forming a rich mixture that branches from the fine powder solid fuel mixture transport pipe from the outlet of the crusher to the main burner fuel nozzle, and the inlet to the mixture transport pipe for forming a rich mixture The connected powder outlet is provided in the cyclone-type separator that joins downstream of the branch point of the fine powder solid fuel mixture transport pipe, and in the fine powder solid fuel mixture transport pipe between the branch point and the merge point. And a mixed mood flow control valve, and an exhaust pipe for connecting the gas outlet of the separator to a UB fuel nozzle provided downstream of the main burner fuel nozzle. It is intended to propose a device.

[0015]

In the present invention, a part of the fine powder solid fuel pulverized by the pulverizer and conveyed by air is branched and guided to the cyclone type separator, and separated into the concentrated and light fine powder solid fuel mixture. Then, the dense pulverized solid fuel mixture is taken out from the powder outlet of the separator, rejoined to the remaining pulverized solid fuel mixture which has not branched, and burned by the main burner. By adjusting the mixed flow control valve provided between the branch point and the confluence point, the fuel concentration of the dense fine powder solid fuel mixture is adjusted. Further, the fine pulverized solid fuel mixture separated by the separator is taken out from the gas outlet of the separator and burned by the upper burner.

In this way, the concentration of the fuel supplied to the main burner can be freely adjusted to a value suitable for combustion, so that stable combustion can be achieved up to a low load. Further, since the particle diameter of the fuel supplied to the upper burner becomes small, the generation of NO _x can be suppressed without increasing the unburned content.

[0017]

[First Embodiment] FIG. 1 is an overall system diagram showing a first embodiment of the present invention, FIG. 2 is a system diagram showing the same main part, and FIG. 3 is a longitudinal sectional view showing the same main part. In these figures, the same parts as those of the conventional one described with reference to FIG. 5 are designated by the same reference numerals to avoid redundancy, and detailed description thereof is omitted.

As reference numerals newly shown in FIGS. 1 to 3, (101) is a mixture transport pipe for forming a rich mixture, (102) is a cyclone type separator, and (103) is a main mixture transport conduit. ，
(104) is exhaust pipe, (105) is mixed mood flow control valve, (106)
Shows a mixture of dense fine solid fuel, (107) shows a mixture of fine fine solid fuel, (108) shows a low AIR / COAL mixture, and (109) shows an exhaust merging pipe.

In this embodiment, a coal crusher (08)
From the pulverized solid fuel mixture transport pipe (15) at the outlet, a single or a plurality of concentrated mixture-forming mixture transport pipes (101) are branched and connected to the inlets of the cyclone separator (102). Then, the pulverized solid fuel mixture transport pipe (1) after branching the mixture transport pipe (101) for forming a rich mixture
A rich mixed flow control valve (105) is installed in 5). The powder outlet at the bottom of the cyclone separator (102) is connected by a pipe to the downstream of the dense mixed mood flow control valve (105) installation part of the fine powder solid fuel mixture transport pipe (15), and the gas outlet at the top is ， Exhaust pipe (104) through exhaust pipe (109)
After being piped, the pipe is further branched to each UB fuel nozzle (06).

The pulverized solid fuel mixture (12) pulverized by the coal pulverizer (08) and pneumatically transported to the pulverized solid fuel mixture transport pipe (15) is used as a mixed flow control valve (105).
Is divided into a predetermined ratio by one side, and one side is connected to the cyclone type separator (102) from the mixture transfer pipe (101) for forming a rich mixture.
The other mixture is sent to the rich mixture main pipe (103) as it is through the mixed mood flow control valve (105).

The fine powder solid fuel mixture (12) sent to the cyclone type separator (102) is separated into a dense fine powder solid fuel mixture (106) and a light fine powder solid fuel mixture (107). The dense pulverized solid fuel mixture (106) is sent from the powder outlet at the bottom of the cyclone separator (102) to the concentrated mixture transportation main pipe (103), and the pulverized solid fuel mixture (12) is sent separately. Mix with low air / coal mixture (108)
To form. The AIR / COAL value of the low AIR / COAL mixture (108) can be adjusted by the mixed mood flow control valve (105). Low
The AIR / COAL mixture (108) is sent from the rich mixture transportation main pipe (103) to each main burner fuel nozzle (03), and the inside of the furnace (2
It is blown into 2) and used for combustion.

On the other hand, the light fine solid fuel mixture (107) separated from the dense fine solid fuel mixture (106) in the cyclone type separator (102) is exhausted from the upper gas outlet to the exhaust pipe (104).
It is sent to the exhaust merging pipe (109) through the UB fuel nozzle, and is blown from the UB fuel nozzle (06) into the furnace (22) for combustion. The fine solid fuel in the light fine solid fuel mixture (107) is about 10% or less of the whole, and the particle size is also extremely fine.

FIG. 8 shows an example of the particle size distribution of the pulverized solid fuel pulverized by the coal pulverizer (10), and FIG. 9 shows carbon particles when the oxygen concentration in the combustion field is 3% and the combustion temperature is 1300 ° C. FIG. 3 is a diagram showing the relationship between the diameter of the and the time required for the carbon particles to burn and disappear. It can be seen from FIG. 8 that the particle size of the fine solid fuel in the light fine solid fuel mixture (107) is 10 μm or less. Further, from FIG. 9, it can be estimated that the time required to complete the combustion of the pulverized solid fuel is extremely short.

[0024]

[Second Embodiment] FIG. 4 is an overall system diagram showing a second embodiment of the present invention. In this figure as well, the same parts as those described above are designated by the same reference numerals and detailed description thereof is omitted.

The difference of this embodiment from the first embodiment is that U
The B fuel nozzle (06) is provided below the main burner body (02), and the exhaust pipe (104) of the cyclone type separator (102) is provided.
Connecting the UB fuel mixture transport pipe (16) that was communicated with
That is, the fine pulverized solid fuel mixture (107) was put into the furnace (22) for combustion. In this case, UB
“UB” of the fuel nozzle (06) is an abbreviation for underburner.

The second embodiment is advantageous when flame-retardant coal having a high fuel ratio and low volatility, such as anthracite, is used as a fuel. When the UB fuel nozzle (06) is close to the furnace outlet as in the first embodiment, in the case of flame-retardant coal, there is a possibility that the coal is discharged from the furnace without completing the combustion. In this case, after passing through the high temperature region for a long residence time and then discharged from the furnace, combustion is easy to complete.

OFA (18) and AA in this embodiment
(20) sets the distribution according to the flammability of the fuel used. That is, OFA in the case of extremely flame-retardant coal
(18) Increase the input amount, and conversely, increase the AA (20) input amount in the case of coal with a low degree of flame retardancy.

[0028]

According to the present invention, in a system in which a pulverized solid fuel is directly fed from a coal pulverizer to a main burner fuel nozzle for combustion, the fuel concentration of the pulverized solid fuel mixture can be freely set to a value suitable for combustion. Since it can be adjusted, stable combustion can be achieved even with a low load that has never been seen before.

Further, since the particle size of the fine powdered solid fuel in the UB fuel mixture used for forming the reducing atmosphere necessary for suppressing NO _x becomes extremely small, the unburned content does not increase and NO
_x can be reduced.

[Brief description of drawings]

FIG. 1 is an overall system diagram showing a first embodiment of the present invention.

FIG. 2 is a system diagram showing a main part of the first embodiment.

FIG. 3 is a longitudinal sectional view showing a main part of the first embodiment.

FIG. 4 is an overall system diagram showing a second embodiment of the present invention.

FIG. 5 is an overall system diagram showing an example of a conventional fine solid fuel combustion device.

[Fig. 6] Fig. 6 shows the ignition distance and AIR / CO of the fine solid fuel flame.
It is a figure which shows the relationship with AL.

[Fig. 7] Fig. 7 shows the crushed coal amount (or combustion load) and AIR /
It is a figure which shows the relationship with COAL.

FIG. 8 is a diagram showing an example of a particle size distribution of a pulverized solid fuel pulverized by a coal pulverizer.

FIG. 9 is a diagram showing the relationship between the diameter of carbon particles and the time required for the carbon particles to burn and disappear.

[Explanation of symbols]

 (01) Furnace body (02) Main burner body (03) Main burner fuel nozzle (04) Main burner air nozzle (05) OFA nozzle (06) UB fuel nozzle (07) AA nozzle (08) Coal crusher (09) Solid fuel (10) Carrier air (11) Fan (12) Fine solid fuel mixture (13) UB fuel mixture (14) Combustion air (15) Fine solid fuel mixture transport pipe (16) UB fuel mixture Air transport pipe (17) Combustion air duct (18) OFA (19) OFA duct (20) AA (21) AA duct (22) Inside furnace (23) Main burner flame (24) Main burner combustion exhaust gas (25) UB Combustion flame (26) Combustion exhaust gas (101) Air-fuel mixture transportation pipe for forming rich air-fuel mixture (102) Cyclone type separator (103) Rich air-fuel mixture main pipe (104) Exhaust pipe (105) Mixed mood Regulating valve (106) dark pulverized solid fuel mixture (107) pale pulverized solid fuel mixture (108) Low AIR / COAL mixture (109) exhaust merging pipe

Claims (1)

[Claims] 1. A device in which a fine solid fuel pulverized by a pulverizer is directly conveyed to a main burner fuel nozzle by air and blown into a furnace to burn the fine solid fuel from an outlet of the pulverizer to the main burner fuel nozzle. A mixture mixture forming pipe for forming a rich mixture mixture branched from the fuel mixture conveying pipe, and an inlet connected to the mixture mixture forming mixture mixture forming pipe and a powder outlet for the branch point of the fine solid fuel mixture conveying pipe. A cyclone separator that joins downstream of the fuel cell, a mixed mood flow control valve provided in the fine powder solid fuel mixture transport pipe between the branch point and the merge point, and a flow downstream of the main burner fuel nozzle. A fine powder solid fuel combustion apparatus, comprising: an upper burner fuel nozzle that is provided; and an exhaust pipe that connects the gas outlet of the separator.