JPH1089619A - Pressurized fluidized bed boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a velocity of desulfurization reaction by a method wherein a fuel nozzle is arranged upward in relation to the horizontal direction. SOLUTION: The height of a fuel outlet is positioned just in the middle between an air dispersion plate 12 and the lowest stage of a heat transfer pipe 15. Particles in a furnace are made to have a sufficiently upward speed and dispersion of fuel is smoothed. The injection direction of a fuel nozzle 51 is arranged upward, for example, by 10 deg. with a horizontal plane. As a result, height at which mixture with combustion air fed from a furnace bottom is effected is situated in a position higher than that of the tip of a nozzle 51. A region of a low CO2 partial pressure is spread upward by an amount equivalent to height higher than that of the tip of the nozzle and a residence time in which a limestone resides in a region of a low CO2 partial pressure is increased. This constitution advances decarboxylation reaction of the limestone, forms fine holes after CO2 goes out, and increases the surface area of the limestone. The partially decarboxylated limestone is moved to a region wherein coal starts combustion reaction and react with SO2 generated by combustion to advance desulfurization reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a pressurized fluidized bed boiler, and more particularly to a fuel nozzle arrangement suitable for promoting a desulfurization reaction in a furnace.

[0002]

2. Description of the Related Art In a pressurized fluidized bed boiler, a fluidized bed is formed in a furnace using limestone as a fluid medium, sulfur oxides (SOx) generated by combustion are absorbed by limestone, and gypsum (CaS
An in-furnace desulfurization method of removing as O ₄ ) is employed. In order to supplement the limestone consumed by the desulfurization reaction and maintain the flow of the fluidized bed, new limestone is mixed into the fuel paste or supplied as a powder into the furnace.

[0003] It is most suitable that coal, which is a fuel, is made into a paste containing water and supplied into a furnace by a high-pressure pump. Although the gas and particles flow violently in the furnace and a sufficient mixing of the particles is realized, the diffusion of the fuel becomes insufficient near the nozzle that supplies the fuel paste into the furnace, and the local combustion reaction proceeds. May cause a temperature rise. If the temperature rises locally, the ash will melt,
Coagulum containing a fluid medium is generated in the furnace, causing flow obstruction. In order to prevent this, it is necessary to disperse and arrange the fuel nozzles. When roughly classified, as shown in FIG. 7, the fuel nozzles are arranged on the floor of the furnace with the ejection direction upward in parallel with the air nozzles. As shown in FIG. 8, there is a method in which a fuel nozzle is arranged on the side of the furnace at right angles to the gas and particle flows in the furnace. In any of the arrangements, the nozzles are arranged evenly on the horizontal surface of the furnace so that the fuel concentration distribution in the plane can be made uniform.

[0004] In the nozzle arrangement shown in FIG.
Immediately above 2, as shown by the fuel nozzle 91 in FIG. 9, since the acceleration in the ascending direction of the particles is not sufficient, the diffusion of the fuel becomes insufficient and the local combustion reaction easily proceeds. In order to prevent local combustion, the fuel nozzle is installed at an intermediate height between the air distribution plate 12 and the lowermost stage of the heat transfer tube 15 (the position of the fuel nozzle 92 in FIG. 9). In this position, acceleration in the upward direction of the particles is achieved, and the fuel can proceed to the combustion reaction in a sufficiently mixed state, thereby preventing a local reaction. Therefore, in the conventional arrangement of the fuel nozzles, the nozzles are arranged at an intermediate height between the lowermost stage of the air distribution plate 12 and the heat transfer tubes 15, and the ejection direction of the nozzles is also horizontal.

[0005]

In the installation of a conventional nozzle, only the arrangement of the furnace in the horizontal plane and the selection of the installation height are important issues. Generally, when the installation height is determined, the nozzle ejection direction is automatically set. Was intended to be horizontally oriented. However, when the fuel paste is ejected in this direction, the low CO ₂ partial pressure region cannot be expanded, and the limestone decarboxylation reaction required for the in-furnace desulfurization reaction which is a feature of the pressurized fluidized bed boiler is promoted. The disadvantage was happening.

[0006] It is an object of the present invention to provide a pressurized fluidized bed boiler in which fuel nozzles are suitably arranged in order to increase the speed of a desulfurization reaction in the pressurized fluidized bed.

[0007]

In a normal-pressure fluidized-bed boiler preceding a pressurized fluidized-bed boiler, the partial pressure of CO ₂ in the furnace is about 0.15 atm at the maximum, and the average temperature of the fluidized bed is 86.
It is lower than the equilibrium partial pressure of CO ₂ (about 0.8 atm as shown in Fig. 6) in the decarboxylation reaction from limestone at around 0 ° C. As a result, the desulfurization reaction activity increases, but the amount of dust scattered on the downstream side increases.

On the other hand, in a pressurized fluidized bed, the total pressure in the furnace is about 9 atm, and the partial pressure of CO ₂ is 1 atm or more.
Therefore, the decomposition equilibrium partial pressure of CO ₂ is higher than that of limestone (CaC
O ₃ ) directly reacts with SO ₂ without decomposition. Accordingly, the amount of dust scattered on the downstream side is small, but the desulfurization performance tends to decrease.

Ca produced by decarboxylation of limestone in nitrogen
O and untreated CaCO ₃ were each brought into contact with a gas containing SO ₂ in a fixed bed, and the time-dependent change of the outlet SO ₂ concentration at that time was measured to determine the absorption rate and amount of SO ₂ and the difference between the two. Were compared. As a result, as shown in FIG. 5, it was found that the absorption amount of SO ₂ was about four times larger than that of CaCO ₃ in CaO, and the absorption rate was faster. The increase in the amount of absorption is due to the development of pores inside the particles of limestone due to the progress of the decarboxylation reaction of limestone, and the diffusion of SO ₂ into the inside of the particles.

Therefore, even in a pressurized fluidized-bed boiler, the number of active sites for the desulfurization reaction can be increased and the desulfurization reaction can be accelerated by accelerating the decarboxylation of limestone and developing pores inside the particles of the medium. . In order to promote the decarboxylation reaction in the pressurized fluidized bed, there are two methods of increasing the ambient temperature and reducing the partial pressure of CO ₂ in the atmosphere. Since there is a limit in increasing the ambient temperature in terms of high-temperature corrosion of the heat transfer tube material in the furnace, it is more effective to lower the partial pressure of CO ₂ . More specifically, it is desirable that the time until mixing of the air and fuel blown at the bottom of the furnace be as long as possible. Limestone in this area is low C
A decarboxylation reaction occurs under a partial pressure of O ₂ , and coal can be encountered in a state in which pores have been developed inside the particles.

If the height of the nozzle is increased to the lower part of the heat transfer tube in order to widen the low CO ₂ partial pressure region, the fuel is injected in a state where the vertical flow of particles is suppressed as shown by 93 in FIG. And may result in local combustion. For this reason, the nozzle is generally installed at an intermediate position between the air distribution plate and the lowermost stage of the heat transfer tube.

[0012] However than the blowing direction of the fuel nozzle as in the prior art and horizontal, for mixing with the air ignited at a position near the height of the fuel nozzle, the region of low partial pressure of CO ₂ is the height of the nozzle Cannot be exceeded. On the other hand, the installation height of the fuel nozzle depends on the air distribution plate 12 and the heat transfer tube 1.
5 When the jetting angle is set upward with respect to the horizontal plane at the middle height of the lower part, the fuel sprayed into the furnace is mixed with the upward particle flow in the center of the furnace as shown in FIG. Combustion can be prevented. At the same time, the region where combustion starts is shifted to a position higher than the height of the nozzle tip, and a region with a low partial pressure of CO ₂ is generated below the region.
Thereby, the region of low CO ₂ partial pressure can be expanded, and the decarboxylation reaction of limestone can be promoted.

Hereinafter, the desulfurization accelerating action by the arrangement of the fuel nozzle according to the present invention will be described with reference to the drawings. FIG. 1 shows an arrangement of a fuel nozzle according to the present invention. Since the height of the fuel outlet is exactly halfway between the air distribution plate 12 and the bottom of the heat transfer tube 15, the particles in the furnace have a sufficient upward velocity, and the fuel is dispersed smoothly. By setting the ejection direction of the fuel nozzle upward with respect to the horizontal plane, the height of mixing with the combustion air supplied from the furnace bottom is higher than the nozzle tip. The low CO ₂ partial pressure region expands upward by this amount, and the limestone stays in the low CO ₂ partial pressure region for a longer residence time. As a result, the decarboxylation reaction of the limestone proceeds, and pores are formed after the CO ₂ escapes, so that the surface area of the limestone increases. The partially decarbonated limestone moves to a region where coal undergoes a combustion reaction, reacts with SO ₂ generated by combustion, and a desulfurization reaction proceeds.

The size of the floor area of a 100 MW class furnace is about 4 m on one side, and the distance from the air distribution plate 12 to the bottom of the heat transfer tube 15 is about 1 m. Air distribution plate 12
When the nozzle is installed at 10 ° upward with respect to the horizontal direction facing the middle of the lowermost stage of the heat transfer tube 15, the flows from both nozzles merge at a height of about 30 cm from the nozzle tip at the center of the furnace. . When comparing the height from the air distribution plate,
When the nozzle was installed horizontally, the height was only 50 cm before the start of combustion. However, when the nozzle was installed 10 ° upward with respect to the horizontal direction, the height was 80 cm before the start of combustion. Can be secured. Therefore, the region of low CO ₂ partial pressure before the start of combustion is expanded 1.6 times by installing the nozzle upward. Assuming that the rising speed of the particles is approximately 1 m / sec, the residence time during this period extends from 0.5 sec to 0.8 sec. Thereby, the progress of the decarboxylation reaction is accelerated, and the desulfurization reaction rate can be increased.

[0015]

Embodiments of the present invention will be described below. [Embodiment 1] The width of the bottom is 7.6 m and the depth is 3.8 m
FIG. 1 shows an example in which the nozzle arrangement according to the present invention is applied to the furnace of FIG.
Shown in Heat transfer tube 1 at a height of 1.0 m from air distribution plate 12
5 are arranged at the bottom. An example is shown in which 16 fuel nozzles 51 are installed at a height of 0.5 m from the air dispersion plate, 8 in total, facing each other. Each nozzle 51 is 10
° Mounted upward.

The fuel ejected from the nozzle 51 crosses about 30 cm above the tip of the nozzle and about 8 cm above the air dispersion plate.
A low CO ₂ partial pressure region of 0 cm is formed.

The fluidized-bed boiler of this embodiment was continuously operated for 380 hours, and a desulfurization rate of 95% or more could be stably maintained during the period.

[Comparative Example] The lowermost stage of the heat transfer tube is arranged at a height of 1.0 m from the air distribution plate of a furnace having a bottom width of 4.0 m and a depth of 3.2 m. In this example, a total of 12 fuel nozzles are provided at three heights of 0.4 m and 0.6 m from the air distribution plate, facing each other in two stages. The upper and lower nozzles are respectively mounted in the horizontal direction.

[Embodiment 2] FIG. 2 shows an example in which a nozzle arrangement according to the present invention is applied to a furnace having a bottom surface width of 4.0 m and a depth of 3.2 m. The lowermost stage of the heat transfer tube 15 is arranged at a height of 1.0 m from the air distribution plate. Fuel nozzle 51
Shows an example in which a total of 12 units are installed in three steps at a height of 0.4 m and 0.6 m from the air distribution plate 12 in two steps. The upper nozzle is mounted 5 ° upward with respect to the horizontal direction, and the lower nozzle is mounted 10 ° upward with respect to the horizontal direction.

The fuel ejected from the lower nozzle 51 crosses about 30 cm above the tip of the nozzle and has a CO ₂ partial pressure of 0.1 cm.
An area of 5 atm or less is formed about 70 cm above the air distribution plate.

When the partial pressure of CO ₂ in the furnace in the height direction was measured, the results shown in FIG. 4 were obtained. Curve 7
1 shows the distribution of CO ₂ partial pressure in the _second embodiment,
2 shows the distribution of the partial pressure of CO ₂ in the comparative example. In the second embodiment, it can be seen that the low CO ₂ partial pressure region extends upward.

Embodiment 3 FIG. 3 shows an example in which a nozzle arrangement according to the present invention is applied to a furnace having a bottom width of 7.6 m and a depth of 3.8 m. The lowermost stage of the heat transfer tube 15 is disposed at a height of 1.0 m from the air distribution plate 12. In this example, a total of 16 fuel nozzles 51 are installed at a height of 0.4 m and 0.6 m from the air distribution plate 12, and four fuel nozzles 51 are arranged in two stages. The upper nozzle is mounted 5 ° upward with respect to the horizontal direction, and the lower nozzle is mounted 10 ° upward with respect to the horizontal direction.

The fuel ejected from the lower nozzle crosses about 30 cm above the nozzle tip and forms a low CO ₂ partial pressure area of about 70 cm above the air dispersion plate.

The fluidized-bed boiler of this embodiment was operated continuously for 210 hours, and a desulfurization rate of 95% or more could be stably maintained during the period.

[0025]

According to the present invention, in a pressurized fluidized bed boiler, limestone is decarbonated by installing a fuel nozzle on the side wall surface of the furnace such that the fuel injection port is directed upward with respect to the horizontal direction. By accelerating, absorption and removal of SO ₂ generated by combustion can be promoted.

[Brief description of the drawings]

FIG. 1 is a diagram showing a nozzle arrangement of a pressurized fluidized-bed boiler according to the present invention.

FIG. 2 is a diagram showing an arrangement of a fuel nozzle according to a second embodiment of the present invention.

FIG. 3 is a diagram showing an arrangement of fuel nozzles according to Embodiment 3 of the present invention.

FIG. 4 is a diagram showing a change in CO ₂ partial pressure in a furnace height direction in each of Embodiment 2 of the present invention and a comparative example.

FIG. 5 is a diagram comparing the desulfurization performance of limestone and the desulfurization performance of decarbonated limestone.

FIG. 6 is a diagram showing the temperature dependence of the equilibrium CO ₂ partial pressure of the limestone decarboxylation reaction.

FIG. 7 is a view showing a fluidized-bed boiler in which a fuel nozzle is arranged on a furnace bottom.

FIG. 8 is a view showing a fluidized-bed boiler in which a fuel nozzle is arranged on a side of a furnace.

FIG. 9 is a view showing a flow state of a lower part of the pressurized fluidized-bed boiler.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Air 2 Fuel paste 11 Pressurized fluidized-bed boiler 12 Air distribution plate 15 Heat transfer tube (lowest stage) 18 Particle flow 21 Paste pump 22 Compressor 51 Fuel nozzle 91, 92, 93 Fuel nozzle

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toru Inada 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Tomohiko Miyamoto 7-1 Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 Inside the Hitachi Research Laboratory, Hitachi, Ltd.

Claims (6)

[Claims] A nozzle for supplying a fuel paste containing pulverized coal and pulverized limestone into a boiler is provided on an inner surface of a side wall of a furnace, and a fluidized bed of fuel is formed by air supplied upward from a hearth. In a pressurized fluidized bed boiler, the nozzle is installed to be inclined upward with respect to the horizontal direction. 2. A plurality of nozzles for supplying a fuel paste containing pulverized coal and pulverized limestone into a boiler are provided on inner walls of a furnace side wall facing each other, and a fluidized bed of fuel is formed by air supplied upward from a furnace floor. In a pressurized fluidized bed boiler to be formed, the nozzle is installed so as to be inclined upward with respect to the horizontal direction. 3. The pressurized fluidized-bed boiler according to claim 1, wherein an inclination angle of the nozzle is 5 to 10 °. 4. A plurality of nozzles for supplying a fuel paste containing pulverized coal and pulverized limestone into a boiler are provided at upper and lower inner surfaces of a furnace side wall facing each other in two stages, and fuel is supplied by air supplied upward from a furnace floor. In the pressurized fluidized bed boiler in which the fluidized bed is formed, the nozzle is installed so as to be inclined upward with respect to the horizontal direction. 5. The pressurized fluidized-bed boiler according to claim 4, wherein the inclination angle of the nozzle is 5 to 10 °. 6. The pressurized fluidized bed boiler according to claim 4, wherein the inclination angle of the upper nozzle is smaller than that of the lower nozzle.