JPH07198111A - Combustor inside temperature control method for circulating fluidized bed boiler - Google Patents

Abstract

PURPOSE:To prevent an exhaust gas from deteriorating by keeping a temperature in a combustor at a specified temperature regardless of the degree of a load. CONSTITUTION:A cyclone dust separator 25 is connected to a combustor 21 which has a dense bed 29 on the bottom and a water screen 22 on the internal surface, and a separated circulating bed material 30 is fed to the combustor 21 for a circulating fluidized bed boiler. For such a circulating fluidized bed boiler, the internal surface of the water screen of the combustor 21 is covered by a refractory material, and the circulating bed material 30 which is separated by the cyclone dust separator 25 is constituted to be fed in the combustor 21 by an external heat-exchanger 27, and the heat-obsorption amount in the external heat-exchanger 27 is made larger when a boiler load is large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control system in a combustor in a circulating fluidized bed boiler.

[0002]

2. Description of the Related Art Generally, as a boiler capable of efficiently burning fuel while satisfying exhaust gas emission standards,
A circulating fluidized bed boiler is known in which a fluidized bed formed of relatively large particles such as gravel, that is, a recirculation bed of fine particles such as sand, ash and limestone is formed on a dense bed.

The structure will be described. As shown in FIG. 3, a combustor 1 and a cyclone 2 are connected by a connecting duct 3. Inside the combustor 1, there is a dense bed 4 and a circulating bed material as a recirculation layer. 5 is formed, fuel F and combustion air a are supplied into the combustor 1, is burned at about 800 ° C., and almost all of the circulating bed material 5 entrained in the combustion gas G is treated by the cyclone 2. The separated circulating bed material 5 is supplied into the combustor 1 through the recycle pipe 6.

On the other hand, FIG. 4 shows that the circulating bed material 5 separated from the cyclone 2 is supplied to the external heat exchanger 7 to absorb heat and then supplied to the combustor 1. In such a circulating fluidized bed boiler, the combustor 1
As shown in FIG. 5, the inner wall surface is a water cooling wall 8 because it absorbs heat,
A heat insulating material 9 is arranged so as to surround the water cooling wall 8. In addition, 10 is a gas duct and 11 is a loop seal.

[0005]

However, the conventional circulating fluidized bed boiler as described above has a problem. That is, when the change width of the boiler load is required to be wide from low load to high load, or when the combustion characteristics of the fuel used change greatly, the water cooling wall 8 of the combustor 1 acts as a heat absorption surface. It will absorb heat energy.

Therefore, when the boiler load is extremely low or when a fuel having a low calorific value is used, the heat absorption in the combustor 1 becomes excessive and the combustion temperature decreases as shown by the broken line in FIG. There was a problem that it could not be continued or the desulfurization reaction expected in the combustor 1 could not be maintained. In FIG. 6, broken line A shows the characteristics of the circulating fluidized bed boiler shown in FIG. 4 and broken line B shows the characteristics of the circulating fluidized bed boiler shown in FIG.

[0007]

SUMMARY OF THE INVENTION A temperature control method in a combustor in a circulating fluidized bed boiler according to the present invention is a combustor having a dense bed at a lower portion and a water cooling wall on an inner surface thereof, and connected to the combustor, In a circulating fluidized bed boiler comprising a cyclone for separating the circulating bed material and supplying the circulating bed material separated by the cyclone to the combustor, an area of at least 50% or more of the inner wall surface of the water cooling wall of the combustor. With a refractory material, the circulating bed material separated by the cyclone is configured to be supplied into the combustor via an external heat exchanger, and when the boiler load is large, the heat absorption amount in the external heat exchanger is increased. It is configured to be large.

[0008]

[Operation] In the temperature control method inside the combustor in the circulating fluidized bed boiler of the present invention, there is substantially no endothermic action by the water cooling wall, and therefore the temperature inside the compass can be maintained only by the endothermic control by the external heat exchanger. As a result, combustion can be maintained under a wide range of operating conditions, and the desulfurization reaction expected can be maintained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a temperature control system in a combustor in a circulating fluidized bed boiler according to the present invention will be described below with reference to FIGS. Reference numeral 21 denotes a combustor, which covers the inner surface of the water cooling wall 22 with a refractory material 23 and the outer surface of a heat insulating material 24 as shown in the sectional view of FIG.
The water cooling wall 22 is surrounded by and sandwiched on both sides with a heat insulating material. The combustor 21 and the cyclone 25 are connected by a connecting duct 26.

The area covered with the refractory material 23 is the water cooling wall 2.
2 must be at least 50% or more, 50
% To 80% is preferable, but the effect of the present invention can be obtained by covering the entire surface. In addition, refractory material 2
The thickness of 1 is the range in which the temperature in the combustor 21 can be controlled by the present invention, and the design conditions are different for each. An external heat exchanger 27 is provided with a tube 28 and configured to have a large heat absorption amount. A dense bed 29 and a circulating bed material 30 are formed in the combustor 21, and are configured to supply the fuel F and the combustion air a for combustion. In addition, 31 is a gas duct and 32 is a recycling pipe.

In such a structure, the internal temperature of the combustor 21 is a predetermined temperature, specifically about 80 even when the boiler load is low or the fuel having a low calorific value is used.
It is set so that it can be maintained at about 0 ° C. Then, the inside of the combustor 21 tends to reach a high temperature when the load is high or when a fuel having a high calorific value is used. However, at this time, the heat absorption amount in the external heat exchanger 27 is increased from the circulation bed material 30 separated by the cyclone 25.

In these controls, the temperature inside the combustor 21 is detected, and the signal is used to control the opening of a valve provided at the bottom of the external heat exchanger 27 to control the flow rate of the low temperature circulating bed material 30. To do. That is, the circulation bed material 30 which has absorbed heat in the external heat exchanger 27 is supplied from the recycle pipe 32 into the combustor 21, and the temperature inside the furnace is lowered.

FIG. 6 shows the relationship between the boiler load and the combustion temperature in the combustor. The action of the circulating bed material 30 causes the temperature inside the combustor 21 to be about 800 ° C. as indicated by the solid line C.
The temperature can be maintained at the predetermined temperature. A curve A shows the characteristics of the boiler shown in FIG. 4, and a curve B shows the characteristics of the boiler shown in FIG. In the case of the boiler having the structure shown in FIG. 3, the curve B, and FIG. 5, since the heat absorption depends only on the water cooling wall 8 in the combustor 5, the heat absorption cannot be adjusted in the operation below the rated point of the boiler. However, there is a drawback that a temperature drop occurs due to excessive heat absorption under a low load.

In the boiler shown in FIG. 4, the combustion temperature of the combustor 1 is maintained at an appropriate value in the adjustment range of the external heat exchanger 7, but the heat absorption on the heat transfer surface in the furnace shown in FIG. There was a drawback that a temperature drop occurred below a certain boiler load. When the temperature inside the combustor burns at a temperature below a certain level, the unburned content in the exhaust gas increases, or the concentration of sulfur oxides in the exhaust gas rises and exceeds the regulation value. It is necessary to maintain the proper value, but the conventional temperature control system in the combustor of the boiler could not be operated satisfactorily for the above reason.

[0015]

As is apparent from the above description, according to the temperature control system in the combustor in the circulating fluidized bed boiler according to the present invention, the water cooling wall is covered with the refractory material to eliminate the endothermic action in the combustor, and the external By controlling the amount of heat absorbed by the heat exchanger and adjusting the amount of heat in the circulating bed material, the temperature inside the combustor is maintained at a specified temperature, so not only stable combustion can be obtained continuously, but also the expected desulfurization reaction. Can be maintained.

Moreover, since the water-cooled wall can be used as a strength member, the wall thickness can be made thinner and the overall structure can be made lighter than in the case where the combustor is simply composed of a refractory material and a heat insulating material. There is.

[Brief description of drawings]

FIG. 1 is a schematic side view of a circulating fluidized bed boiler according to the present invention.

2 is a cross-sectional view of the combustor of FIG.

FIG. 3 is a schematic side view of a conventional circulating fluidized bed boiler.

FIG. 4 is a schematic side view of another conventional circulating fluidized bed boiler.

5 is a cross-sectional view of the combustor of the boiler of FIGS. 3 and 4. FIG.

FIG. 6 is a temperature characteristic diagram in the combustor.

[Explanation of symbols]

1,21 Combustor 2,25 Cyclone 3,26 Cyclone 4,29 Dens bed 5,30 Circulating bed material 6,32 Recycling pipe 7,27 External heat exchanger 8,22 Water cooling wall 9,24 Insulation material 10,31 Gas duct 11 Loop seal 23 Refractory material 28 Tube

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tamotsu Takebayashi 3-1-1 Tamama, Tamano-shi, Okayama Mitsui Engineering & Shipbuilding Co., Ltd. Tamano Works

Claims (1)

[Claims] 1. A circulating bed material comprising a combustor having a dense bed at a lower portion and having a water cooling wall on an inner surface thereof, and a cyclone connected to the combustor and separating a circulating bed material, the circulating bed material being separated by the cyclone. In a circulating fluidized bed boiler adapted to supply to the combustor, at least 50% or more of the inner wall surface of the water cooling wall of the combustor is covered with a refractory material, and the circulating bed material separated by the cyclone is heated by external heat. Controlling the temperature inside the combustor in a circulating fluidized bed boiler, characterized in that the heat is absorbed in the external heat exchanger when the boiler load is large, by supplying the heat to the inside of the combustor via the exchanger. method.