JPS63180004A - Combustion method of boiler - Google Patents

Abstract

PURPOSE:To reduce the amount of hydrogen sulfide in combustion gas and prevent the wear of generating tubes without increasing the amount of nitrogen oxides by a method wherein an air fuel is chosen to be low at the upper burner and high at the lower burner. CONSTITUTION:Combustion gas comes out from a three-stage burner group 3, 3', 3'' installed at the bottom of a combustion chamber 1 and passes through a No.1 superheater tube group 4', a fuel economizer 5, and an air preheater 6 and is then discharged from a stack 7. Combustion air is supplied to the burner group 3, 3', 3'' with a forced blower 11, an air duct 12, branch ducts 13, and air-flow limiting dampers 14. An air fuel ratio constituted by the supply amounts of air and fuel is chosen to be 1.25-1.7 at the lowest stage burner 3'' and is reduced towards the most upper stage; therefore, combustion is carried out in the range of 1.0-1.2 for the air fuel ratio as the whole burner group.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in the combustion method of a boiler. Specifically, with the diversification of heavy oil fuels, the present invention provides a method suitable for suppressing the production of hydrogen sulfide during combustion when heavy fuel oil with poor flammability and high sulfur content is used as a fuel. This relates to the combustion method of boilers.

[Conventional technology]

In recent years, with the diversification of heavy oil fuels, boilers equipped with multiple burner groups, for example burner groups of three or more stages, are using heavy fuel oil with poor combustibility and high sulfur content as fuel, and From the viewpoint of suppressing the production of nitrogen oxides, controlling smoke emissions, and saving energy, we adopted a low-oxygen combustion method, that is, a combustion method that lowers the oxygen concentration in the combustion exhaust gas at the combustion equipment outlet, and reduced the air flow to each burner. It is operated by a method in which the air-fuel ratio is distributed evenly (the air-fuel ratio of each burner is kept constant), a method in which the air-fuel ratio is increased from the lower stage to the upper stage (the air-fuel ratio is increased), or a two-stage combustion method.

[Problem that the invention seeks to solve]

However, in the above-mentioned low-oxygen combustion method, the combustion state in the furnace deteriorates and the combustion gas atmosphere changes, and due to this effect, certain parts of the evaporation tube of the furnace (in particular, the evaporation tube near the bottom of the lower burner) There was a problem in that a significant thinning phenomenon that appeared to be caused by corrosion occurred.

Conventionally known measures to prevent corrosion of the evaporator tube include (1) injection of a Mg-based anticorrosive additive, (2) surface treatment by Cr diffusion and penetration treatment, thermal spraying of a corrosion-resistant alloy, etc.

However, in the method (2) above, MgS compounds are generated in an environment containing reducing H and S, which not only causes loss of anticorrosive function, but also may accelerate corrosion depending on the conditions. Due to the method, there is a risk of surface peeling when used at high temperatures for a long period of time.

[Means for solving problems]

The inventors of the present invention endeavored to investigate the cause of the problem in the prior art described above, and found that hydrogen sulfide was generated due to the oxygen-deficient environment (reducing atmosphere) during combustion, and this hydrogen sulfide triggered evaporation. It turned out that the pipes were corroded.

In order to suppress the generation of hydrogen sulfide during the combustion described above, an operating method was attempted in which the air flow distribution ratio used in the conventional method was used to increase the oxygen concentration in the exhaust gas at the furnace outlet and increase the excess air ratio. It was found that this method was also unable to reduce the hydrogen sulfide concentration in the combustion gas, especially near the flame tip of the lower burner.

The inventors of the present invention have conducted intensive studies to suppress the generation of hydrogen sulfide that occurs during combustion by improving combustion, and as a result, the air-fuel ratio to the lower stage was significantly increased, contrary to the conventional method. However, by adopting an operating method that lowers the air-fuel ratio to the upper stage burner, it is possible to significantly suppress the production of hydrogen sulfide during combustion, even with the low-oxygen combustion method as a whole. The present invention was completed based on the discovery that the corrosion of the evaporator tube can be significantly reduced, and the amount of soot and dust in the combustion exhaust gas can also be reduced.1 Furthermore, surprisingly, nitrogen oxides do not particularly increase.

That is, the gist of the present invention is to provide at least three stages of burner groups on the vertical plane of a combustion chamber, to control the amount of fuel supplied to each burner group, and to control the amount of combustion air supplied to each burner or each burner group. In boiler combustion equipment that can be controlled individually,
Heavy oil with a sulfur content of 1% by weight or more, a residual carbon content of 7% by weight or more, and a kinematic viscosity of /θ0 centistokes or more at SO°C is used as fuel, and this is supplied to each burner group. The air-fuel ratio between the air supply amount and the fuel supply amount is 5~/, ? A combustion method for a boiler, characterized in that the air-fuel ratio is decreased from the lowest burner group to the uppermost burner group, and the air-fuel ratio in all burner groups is in the range of 80 −/. , resides in

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

FIG. 1 is a schematic vertical sectional view showing an example of a boiler combustion apparatus used in the method of the present invention.

In the vertical diagram, (1) is a calculation-shaped combustion chamber, whose wall is composed of evaporation tubes (water tubes) (2) that form water-cooled walls, and at the bottom of the combustion chamber (1) there are three stages. Burner group (3), ((to)
, (4). A first superheater tube group (4) is provided downstream of the combustion gas flow path from the combustion chamber (1), and further downstream thereof a first superheater tube group (4). A power economizer (5) and an air preheater (6) are sequentially provided.

Combustion gas passes through these, then through the flue to the chimney (
7) and is emitted into the atmosphere. In order to supply combustion air to the burner groups (3), ((to), (j), a strong pressure ventilation fan αη, an air duct (6), a branch duct (to), and an air flow rate control damper αhi are provided. Further, a fuel pipe (3), a fuel supply branch pipe (9), and a fuel control valve α1 are installed to supply fuel to each burner group.

In the method of the present invention, the sulfur content is 1% by weight as the fuel.
The above, preferably 1 to 7% by weight, the residual a carbon content is 7% by weight or more, preferably 7 to 1% by weight, and the kinematic viscosity at 30°C is io centistokes (C8t) or more,
Preferably, heavy oil having a molecular weight of 100 to 0,000 cSt is used. In particular, the sulfur content is 2 to 6% by weight, the residual carbon content is 10 to 5% by weight, and the kinematic viscosity at SO℃ is 30%.
The effect of the present invention is remarkable when heavy oil having a cst of 0~/o, o o o cst is used.

In this specification, "air-fuel ratio" is calculated as follows. That is, the theoretical air amount (Nm'/Kp-fuel) is calculated by the following formula, assuming that the content of carbon, hydrogen, and sulfur (Kg/Kf-fuel) in the fuel (heavy oil) is C, H, and S, respectively.

Theoretical air volume! ! ;, t9・C+ 24.7・H+, 1
．． ．． 1.7.8 Next, use this to calculate the air-fuel ratio according to the following formula. In the present invention, the air-fuel ratio between the air supply amount and the fuel supply amount in each burner group is as follows: lowermost burner group > middle burner group Group> This is characterized in that combustion is performed under the conditions of the uppermost burner group. More specifically, the air-fuel ratio of the bottom burner group is set to 1. λ5
~/, 7, preferably in the range of 1.3 to 1.6, the air-fuel ratio of the middle burner group is normally /, 0 to /, 2, preferably /,
0! -/, - range, the air-fuel ratio of the top burner group is usually 0.7 to /, 01 preferably 09g -0,9! t
and the air-fuel ratio in all burner groups to be in the range of 1.0 to
The combustion is controlled within the range of 1.2.

In this case, the oxygen concentration in the flue gas at the furnace outlet is O9S −
It is preferable that the S capacity is within the range of .

The difference between the combustion conditions in the method of the present invention and the combustion conditions in the conventional method is that in the conventional method, an incomplete combustion region with an air-fuel ratio of l is formed in the lower burner region for the purpose of suppressing the production of nitrogen oxides, and in the downstream In contrast, in the method of the present invention, a fuel with poor combustibility is used, and the air-fuel ratio in the lowest burner area is set to /, Zj. The point is that combustion conditions are adopted such that a complete combustion region is formed in the range of 1.7 to 1.7, and the entire combustion region forms a complete combustion region.

In the method of the present invention, the air-fuel ratio of the lowest stage burner group is 8-3.
If it is less than that, the combustion condition will deteriorate and the effect of suppressing the generation of hydrogen sulfide during combustion will be small. Note that the method of the present invention is highly effective when using a fuel with poor combustibility as described above, and is less effective when using a fuel with good combustibility.

FIG. 1 is a schematic vertical sectional view showing an example of a combustion chamber portion of a boiler combustion apparatus preferably used in the method of the present invention. The burner shown in the figure is also equipped with a three-stage burner group, and the air flow rate of each burner can be adjusted by air flow control dampers provided above and below the burner. That is, each burner (3)
, ((a), (fuel supply branch pipe (9) to (j), (9'l,
(A predetermined amount of fuel is supplied from 95, and combustion air is supplied from air duct (2) to branch ducts (to).
, -, the air flow rate is distributed vertically by adjusting the opening of the first damper (2), -, and the upper first damper α7), C75, an provided on the inlet side of each burner and the lower first damper λ
The air flow rate of each burner (3), (3'l, (4) is adjusted by adjusting the opening of the damper (to), (to), and po.
The air-fuel ratio is adjusted to a desired range.

FIG. 3 is a schematic longitudinal sectional view showing an example of a combustion chamber portion of a boiler combustion apparatus suitable for use in the method of the present invention.

The one shown in the figure is one in which the combustion air supplied to each burner can be divided into primary air and secondary air, and the flow rates can be adjusted for each.

That is, for a predetermined amount of fuel supplied to each burner (31, (, 3'l, <f), combustion air is supplied to the air duct (2).
The dampers 01), ct'), c2 provided in the primary air flow path of each burner, and the upper dampers provided in the secondary air flow path), (2), (ml The opening degree of each of the lower dampers (23), (2), and (2) is adjusted to adjust the primary air and secondary air to each burner so as to obtain a desired air-fuel ratio.

In particular, the lowest stage burner (35) has a worse combustion condition than the middle stage burner (j) and the upper stage burner (3), and the generation of hydrogen sulfide may increase. It is desirable to adopt an operating method in which the lower damper (2t) of the lowest stage burner (j) is opened almost fully to increase the amount of secondary air and adjust the air-fuel ratio to the desired air-fuel ratio.

Regarding the burner arrangement in the combustion chamber, any of the front combustion type, facing combustion type, and tangential combustion type may be used.
In particular, a tangential combustion type is desirable because it can significantly suppress the production of nitrogen oxides. Figure φ is a schematic cross-sectional view of the burner section of a combustion chamber that has a tangential combustion type burner arrangement. It is blown out and combusted.

Although the case where three stages of burner groups are arranged in the combustion chamber has been specifically described, the present invention is not limited to this, and the present invention is not limited to this, but can also be applied to cases where three stages of burner groups or more burner groups are arranged. It may be. Alternatively, it is also possible to adopt a method in which secondary air is further supplied to the upper part of the burner group in the uppermost stage to perform combustion in the second stage.

〔Example〕

Next, specific embodiments of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Note that the terms used in the examples have the following meanings.

(:) Excess air rate = 2//Ckot-A) A: Oxygen concentration in combustion exhaust gas (4) (1 () Average air amount ('Hrrl/Ko-Fuel) = Theoretical air amount x Excess air rate 010 Total air amount (N-) Average air amount ``Below λ-th air/Above λ-th air'' Himio side of lower stage burner - 1 ~ 3 The air damper configuration shown in Fig. 3 is different from the burner groups in the first stage, and each burner group is Using a boiler combustion apparatus having a tangential combustion type burner arrangement as shown in FIG. 4, combustion was carried out using heavy oil having the properties and combustion conditions shown in Table 1. The results are shown in Table 1.

Comparative Example -/-J In Example 1, the combustion conditions were changed to those shown in Table 1 and combustion was performed. The results are shown in Table 1.

〔Effect of the invention〕

According to the method of the present invention, even when heavy oil with poor combustibility is used as fuel, each burner can be operated in an optimal combustion state, and the generation of hydrogen sulfide during combustion can be significantly reduced. As a result, corrosion of the evaporator tube can be significantly reduced, and the frequency of replacement due to thinning of the evaporator tube can be significantly reduced, which is of great industrial significance. Furthermore, the method of the present invention can also significantly reduce the amount of soot and dust in combustion exhaust gas.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical sectional view showing an example of a boiler combustion apparatus used in the method of the present invention. FIG. 2 is a schematic longitudinal sectional view showing an example of a combustion chamber portion of a preferred boiler combustion apparatus used in the method of the present invention. FIG. 3 is a schematic longitudinal sectional view showing an example of a combustion chamber portion of a boiler combustion apparatus suitable for use in the method of the present invention. Further, Figure 1 is a schematic cross-sectional view of a burner section of a combustion chamber having a tangential combustion type burner arrangement. l: Combustion chamber, 2: L waste pipe, 3,! 1. ? #
: Burner group, No. 1 superheater tube group, Hiro': 7th superheater tube group S: Economizer, 6: Air preheater, R: Chimney, Z: Fuel piping, 12 = Air duct, /6, /6
“: 1st damper, /7, /de, /τ′: Upper co-damper, /11. /
g', /r: Lower No. Co damper, Co/S Co/', 21"
Knee air flow path damper, here, here 2', 2! ': Secondary air flow upper damper, koj, 23'Sko, ? #: Secondary air flow path lower damper. Patent applicant: Mitsubishi Chemical Industries, Ltd. Representative: Patent attorney Haseyo - 1 other person

Claims (4)

[Claims] (1) At least three stages of burner groups are provided on the vertical plane of the combustion chamber, the amount of fuel supplied is controlled for each burner group, and the amount of combustion air supplied is controlled for each burner or each burner group. In the boiler combustion equipment to be obtained, heavy oil having a sulfur content of 1% by weight or more, a residual carbon content of 7% by weight or more, and a kinematic viscosity of 100 centistokes or more at 50°C is used as a fuel. The air-fuel ratio between the air supply amount and the fuel supply amount supplied to the burner group is set to 1.
25 to 1.7, the air-fuel ratio decreases from the lowest burner group to the highest burner group, and combustion is performed with the air-fuel ratio in all burner groups in the range of 1.0 to 1.2. The boiler combustion method. (2) A boiler combustion method according to claim 1, characterized in that each burner in each burner group is arranged in a tangential combustion type in a horizontal section of the combustion chamber. (3) In the boiler combustion method according to claim 1 or 2, the heavy oil has a sulfur content of 2% by weight or more, a residual carbon content of 10% by weight or more, and a kinematic viscosity at 50°C. is 300 centistokes or more. (4) In the boiler combustion method according to any one of claims 1 to 3, the air-fuel ratio of each burner group is set to 1.25 to 1.7 in the lowest burner group, and 1.25 to 1.7 in the middle burner group. 1
．． 0 to 1.2, and 0.7 to 1.0 in the uppermost burner group, and the air-fuel ratio in all burner groups is 1.0 to 1.0.
A method characterized by burning as a range of 2.