JPH062810A - Fluidized bed combustion device and its operating method - Google Patents

Abstract

PURPOSE:To prevent friction and reduction in wall thickness of a heat transfer pipe without increasing nitrogen oxide contained in discharged gas by a method wherein a ratio between an amount of combustion air supplied to a fluidized bed location having a lower surface temperature of the heat transfer pipe and a fluidized bed location having a higher surface temperature of the heat transfer pipe and an amount of coal is independently controlled, respectively. CONSTITUTION:A ratio (a) between an amount of air and an amount of coal supplied to a lower part of a group 3 of heat transfer pipes of which surface temperatures are about 500 deg.C or less is increased as a fuel ratio of the supplied coal is decreased. In turn, a ratio (b) between the air volume and the amount of coal supplied to the lower part of a group 4 of heat transfer pipes of which surface temperatures are about 500 deg.C or more is decreased as the ratio (a) is increased and then a ratio (c) between an entire amount of air and an amount of coal is operationally controlled in such a manner as it always keeps a substantial constant value so as to enable a low NOx combustion to be attained even if the fuel ratio of the applied coal is varied. With such an arrangement as above, a ratio between the coal and the combustion air supplied into the fluidized bed is kept constant without being varied by the fuel ratio of the coal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluidized bed combustion apparatus in which a heat exchanger is installed in a fluidized bed and a method of operating the same, and particularly to reduce wear and thinning of a heat transfer tube embedded in the fluidized bed due to a fluidized medium. And a method of operating the same.

[0002]

2. Description of the Related Art Generally, in a fluidized bed combustor such as a fluidized bed boiler, lime, silica sand, coal ash or the like is used as a fluid medium, and combustion air is jetted from a wind box provided at the bottom of the fluidized bed. While fluidizing and heating by a suitable method, solid fuel such as coal is put into the fluidized bed from the upper part (upper filling method) or the lower part (lower filling method), mixed with the fluid medium and burned, and then the fluidized bed It is configured to cause heat exchange with a heat transfer tube installed therein. As described above, in the fluidized bed combustion device, the heat exchange between the fluidized bed and the heat transfer tubes is performed in the form of heat absorption by contact, so that the heat transfer characteristics are excellent, and even if the heat transfer area is small, a predetermined heat absorption effect can be obtained. There is a feature that can be obtained. Further, the temperature in the fluidized bed is 700 to 900 ° C., which is lower than that in a general boiler furnace, so that the generation of thermal NOx (nitrogen oxide) is small and Ca
When O or MgO is used as the fluid medium, S
The feature is that the generation of Ox (sulfur oxide) can be suppressed. Note that, as typical representative publicly known examples, for example, JP-A-58-19611 and JP-A-63-201209.
The gazette etc. are mentioned.

[0003]

As described above, the heat transfer tube installed in the fluidized bed of the conventional fluidized bed combustion apparatus has a problem that the fluidized medium is easily worn and thinned.
Wear reduction of the heat transfer tube in the fluidized bed in the fluidized bed combustion device is a phenomenon in which the fluid medium collides with the surface of the heat transfer tube and wears the heat transfer tube, and the nature of the oxide film formed on the surface of the heat transfer tube is the heat transfer tube. Has a great effect on the wear of. That is, in a heat transfer tube with a high surface temperature, a thick oxide film is formed, and even if the fluidized medium collides with the heat transfer tube and the oxide film on the surface peels off, the oxide film is immediately regenerated. The meat loss of is negligible. On the other hand, the surface temperature is almost 50
In a heat transfer tube having a temperature of 0 ° C. or less, an oxide film that plays a protective role against wear of a fluid medium is insufficiently formed, and the oxide film is thin. Therefore, once the oxide film is peeled off due to the collision of the fluid medium, the surface of the heat transfer tube is easily exposed. In particular, when coal having a low fuel ratio (fixed carbon / volatile matter) and a low fuel ratio is burned in a fluidized bed, the proportion of combustion in the fluidized bed is large due to the large amount of volatile matter. The oxygen concentration in the fluidized bed is lower than in the case of burning coal with a specific ratio. Therefore, in a heat transfer tube with a low surface temperature, when the oxide film peeled off due to the collision of the fluid medium is not regenerated, the fluid medium directly collides with the heat transfer tube and burns coal with a high fuel ratio. Compared with, the thickness of the heat transfer tube is increased. For example, when the coal having a fuel ratio of about 1.0 is subjected to fluidized bed combustion, the wear loss of the heat transfer tube is 5 compared to the case of coal having a fuel ratio of about 2.0.
It will increase by 10 times. The relationship between the fuel ratio of coal and the amount of wear loss of heat transfer tubes is shown in FIG. As a method for avoiding the problem of thinning the heat transfer tube, when burning coal with a low fuel ratio, increase the ratio of the amount of air supplied to the fluidized bed to the amount of coal to make it oxygen rich. Although a method of suppressing the decrease in oxygen concentration in the fluidized bed can be considered by this method, in this case, there is a problem that nitrogen oxide (NOx) in the exhaust gas increases.

The object of the present invention is to solve the above-mentioned problems of the prior art and to increase the amount of nitrogen oxides in the exhaust gas.
A fluidized bed combustor suitable for preventing wear and thinning of a heat transfer tube installed in a fluidized bed of a fluidized bed combustor and an operating method thereof.

[0005]

In order to achieve the above object of the present invention, in a heat transfer tube provided in a fluidized bed of a fluidized bed combustion apparatus of the present invention, for example, a low temperature heat transfer tube having a surface temperature of about 500 ° C. or less. Coal that can independently control the amount of combustion air supplied to the site where the is installed and the amount of combustion air supplied to the site where the high temperature heat transfer tube having a surface temperature of approximately 500 ° C. or more is installed And a combustion air supply means, and the ratio of the combustion air supply amount to the coal supply amount to the portion where the heat transfer tube having a surface temperature of approximately 500 ° C. or less is installed is determined by the fuel ratio of coal (fixed carbon / fixed carbon / The amount of volatile matter is inversely proportional to the ratio, and the ratio of the total amount of combustion air supplied to the fluidized bed and the amount of coal supplied is controlled to be almost constant to achieve low NOx combustion. is there.

[0006]

[Function] A high-temperature heat transfer tube surface having a surface temperature of approximately 500 ° C. or more has a thick oxide film that protects against wear of the fluid medium, and therefore burns coal with a low fuel ratio. Even when it is used, the thinning effect due to wear is small. On the other hand, when a low fuel ratio coal is supplied to a low temperature heat transfer tube with a surface temperature of approximately 500 ° C or less, the combustion ratio in the fluidized bed increases because the volatile content is large, so the film on the surface of the heat transfer tube is increased. Is less than the oxygen concentration required for regeneration.
Therefore, the ratio of the air supply amount and the coal supply amount to each fluidized bed is increased or decreased by changing the fuel ratio of the coal used for fluidized bed combustion (as the fuel ratio decreases, the air supply amount / air supply amount /
By increasing the ratio of the coal supply amount), it is possible to eliminate the oxygen deficiency on the surface of the heat transfer tube. As a result, the regeneration of the oxide film on the surface of the heat transfer tube is promoted, and it is possible to prevent wear thinning due to collision of the fluid medium with the surface of the heat transfer tube. On the other hand, the ratio of the air supply amount / coal supply amount to the fluidized bed provided with the heat transfer tube having the surface temperature of about 500 ° C. or higher is decreased in the opposite manner to the above, and the air supply amount and the coal in the entire fluidized bed combustion device are reduced. By controlling the supply amount ratio to be a predetermined ratio for achieving low NOx combustion, an increase in nitrogen oxides in the exhaust gas can be suppressed.

[0007]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG. 1 is a sectional view showing an example of the structure of the fluidized bed portion of the fluidized bed combustion apparatus of the present invention. In FIG. 1, the fluidized bed 2 is provided with a heat transfer tube group 3 having a surface temperature of about 500 ° C. or lower and a heat transfer tube group 4 having a surface temperature of about 500 ° C. or higher. The combustion air 9 is provided below the heat transfer tube group 2 whose surface temperature is about 500 ° C. or below and below the heat transfer tube group 3 whose surface temperature is about 500 ° C. or above. The second air chamber 7 is branched and supplied to the second air chamber 7, and the amount of air supplied to each air chamber is controlled by the flow rate control valve 10. The combustion air 9 supplied to each air chamber is supplied to the fluidized bed 2 filled with the fluidized medium through the perforated plate 5. On the other hand, the coal 11 is the coal supply pipe 8
Is supplied into the fluidized bed 2 and burned while being mixed and stirred with the fluidized medium, and the generated heat is recovered in the heat transfer tube groups 3 and 4 in the fluidized bed 2 arranged in the fluidized bed 2 to generate steam or steam. Recovered as warm water. FIG. 2 is an explanatory diagram of the operating method of the embodiment shown in FIG. That is, the ratio a of the amount of air supplied to the lower portion of the heat transfer tube group 3 having a surface temperature of about 500 ° C. or lower and the amount of coal are increased as the fuel ratio of the supplied coal decreases. On the other hand, the ratio b of the amount of air supplied to the lower part of the heat transfer tube group 4 whose surface temperature is about 500 ° C. or higher and the amount of coal b
Is decreased as the value of a increases, and the ratio c of the total amount of air to the amount of coal is always maintained at a substantially constant value so that low NOx combustion can be achieved even if the fuel ratio of the coal used changes. Control. As a result, the ratio of the coal supplied to the fluidized bed 2 to the combustion air is kept constant without changing depending on the fuel ratio of the coal. That is, it is possible to prevent wear loss of the heat transfer tube without increasing nitrogen oxides.
FIG. 3 shows a heat transfer tube group 3 having a surface temperature of about 500 ° C. or less.
And a heat transfer tube group 4 having a surface temperature of about 500 ° C. or higher is installed in different fluidized bed combustion furnaces.
The method of supplying combustion air into the fluidized bed combustion furnace and the method of operation are almost the same as those in the embodiment shown in FIG.

[0008]

According to the present invention, even if various kinds of coal having different fuel ratios are used, the oxygen deficiency of the heat transfer tube group having a low surface temperature arranged in the fluidized bed of the fluidized bed combustion apparatus can be prevented. Since this can be eliminated and the oxide film can be regenerated, it is possible to effectively prevent wear thinning due to collision of the fluidized medium with the surface of the heat transfer tube. On the other hand, since the ratio of the total combustion air amount to the coal amount is a predetermined combustion ratio, low NOx combustion can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a cross-sectional structure of a fluidized bed portion of a fluidized bed combustion apparatus exemplified in an embodiment of the present invention.

FIG. 2 is an explanatory view showing an operating method of the fluidized bed combustion apparatus of FIG.

FIG. 3 is a schematic view showing a sectional structure of a fluidized bed portion of a fluidized bed combustion apparatus showing another embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the wear loss of the heat transfer tube and the time in fluidized bed combustion of low fuel ratio coal and high fuel ratio coal for a heat transfer tube having a surface temperature of 500 ° C. or less.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fluidized bed furnace main body 2 ... Fluidized bed 3 ... Heat transfer tube group whose surface temperature is about 500 ° C. or lower 4 ... Heat transfer tube group whose surface temperature is about 500 ° C. or higher 5 ... Perforated plate 6 ... First air chamber 7 ... Second air chamber 8 ... Coal supply pipe 9 ... Combustion air 10 ... Flow control valve 11 ... Coal

Claims (3)

[Claims] 1. A fluidized bed combustor in which a heat transfer tube is arranged in a fluidized bed to perform fluidized bed combustion for heat exchange, and the amount of combustion air and the amount of coal to be supplied to a fluidized bed portion where the surface temperature of the heat transfer tube is low. And a ratio of the amount of combustion air and the amount of coal supplied to the fluidized bed where the surface temperature of the heat transfer tube is high are independently provided for supplying coal and combustion air. Fluidized bed combustion equipment. 2. The fluidized bed combustion apparatus according to claim 1, wherein the heat transfer tubes having a low surface temperature are about 500 ° C. or lower, and the heat transfer tubes having a high surface temperature are about 500 ° C. or more. 3. A method for operating a fluidized bed combustion apparatus in which a heat transfer tube is arranged in a fluidized bed to perform heat exchange by fluidized bed combustion, and the ratio of the total amount of combustion air supplied to the fluidized bed to the amount of coal is The ratio of the amount of combustion air supplied to the fluidized bed where the heat transfer tube having a surface temperature of approximately 500 ° C. or less is provided without change and the amount of coal is the ratio of the volatile content of the coal used to the fixed carbon, That is, a method for operating a fluidized bed combustion apparatus, which is characterized in that the fluidized bed combustion is performed while increasing and decreasing in inverse proportion to the fuel ratio of coal.