JP2560897B2 - Fluidized bed boiler - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fluidized bed boiler that performs fluidized combustion of coal or the like.

[Prior Art] As is well known, a fluidized bed boiler continuously supplies fuel into a fluid chamber and also supplies air into the fluid chamber through a dispersion plate to burn the fuel and flow the fluid medium. And heat is exchanged by a heat transfer tube arranged in the flow chamber. In this fluidized bed boiler, conventionally, the installation height and the filling amount of the fluidized medium are set so that the heat transfer tube is buried in the fluidized bed.

In the conventional fluidized bed boiler, the heat transfer tubes are buried in the fluidized bed, and the characteristic of fluidized bed heat transfer is that the overall heat transfer coefficient does not decrease even when the air velocity decreases, so the boiler load has decreased. In this case, even if the fuel supply amount and the air supply amount are reduced to lower the combustion of the fuel, the heat transfer coefficient and the heat transfer area hardly decrease. Therefore, a large amount of heat is exchanged, the temperature of the fluidized bed is rapidly lowered, and operation may be stopped.

As a countermeasure against this, Japanese Patent Laid-Open No. 63-153301 discloses that the fluidized bed height is changed by changing the fuel supply amount and the air supply amount (superficial velocity), or by further supplying and discharging the fluidized medium. It is described that the number of heat transfer tubes buried in the bed is controlled to maintain the fluidized bed temperature constant.

[Problems to be Solved by the Invention] However, even in the method of controlling a fluidized bed boiler disclosed in Japanese Patent Laid-Open No. 63-153301, the heat transfer coefficient does not decrease unless the heat transfer tubes are actually sufficiently exposed outside the fluidized bed. The output cannot be adjusted unless the superficial velocity is reduced to such an extent that the uppermost heat transfer tube is exposed outside the fluidized bed. For this reason, the output cannot be controlled in the high load region, and it is difficult to keep the fluidized bed temperature constant.

Further, in the method of controlling a fluidized bed boiler of Japanese Patent Laid-Open No. 63-155301, the difference in heat transfer coefficient between the state where the heat transfer tube is outside the fluidized bed and the state where it is inside the fluidized bed is utilized. When the static height of the fluidized bed is high, such as 500 mm or more, the expansion bed height becomes 750 to 1000 mm, so, for example, when the vertical pitch of the heat transfer tubes is around 100 mm, the superficial velocity is changed. In some cases, a plurality of heat transfer tubes in a certain number of stages may be exposed to the outside of the fluidized bed at one time, or conversely, a plurality of heat transfer tubes may enter the fluidized bed at once. In such cases,
Since a slight change in the superficial velocity causes a large change in the output, there is a problem that the output cannot be adjusted accurately and the fluidized bed temperature cannot be made constant when the control is performed.

[Means for Solving the Problems] A fluidized bed boiler of the present invention continuously supplies fuel into a fluid chamber and also supplies air into the fluid chamber through a dispersion plate to burn the fuel and flow the fluid medium. The heat transfer tubes arranged in the flow chamber are used to perform heat exchange, the air supplied to the flow chamber is increased or decreased to increase or decrease the superficial velocity in the flow chamber, and the fuel supply amount is increased. In a fluidized bed boiler in which the boiler load is controlled by increasing or decreasing, the stationary bed height in the fluidized chamber is 400 mm or less, and the fluidized bed height during fluidization is twice the stationary bed height. The heat transfer tubes are arranged in a space just above the upper surface of the fluidized bed and in which particles scattered from the fluidized bed are present at a height of 3 times or less of the height of the stationary bed, From the top of the fluidized bed during fluidization by increasing or decreasing the velocity It is characterized in that the load of the boiler to increase or decrease the frequency of contact between the scattered particles and the heat transfer tube and configured to increase or decrease between.

[Operation] In the fluidized bed boiler, when fluidizing air is supplied into the fluidized chamber, the fluidized medium is fluidized and the bed expands to increase the bed height to form a fluidized bed. In this fluidized bed, the particles are violently flowing, but when the bubbles blow out from the fluidized bed or the bubbles burst on the surface (upper surface) of the fluidized bed, the particles come out of the fluidized bed. Jump out. Then, in the upper space portion continuing to the upper surface of the fluidized bed, a region in which a considerable amount of the protruding particles exists is formed.

The existence probability of particles in the upper space region continuing to the upper surface of the fluidized bed is smaller than that in the fluidized bed, and becomes smaller as it goes up, but the external heat transfer coefficient due to contact of the particles with the heat transfer tube is Larger than when not touching.

In this area, the particles jump out upward and then descend along the peripheral walls of the tube from the top of the heat transfer tube when it descends, reducing the film resistance formed around the tube and reducing the coefficient of heat transfer outside the tube. Also has the effect of increasing the. Therefore, for the heat transfer tubes installed up to three times the height of the stationary bed in the upper space continuing to the upper surface of the fluidized bed, the heat transfer coefficient of 50% or more of the heat transfer tubes embedded in the fluidized bed itself can be obtained. To be

The higher the superficial velocity, the higher the probability of particles existing at the same position. That is, the heat transfer coefficient outside the pipe also increases. On the contrary, when the superficial velocity becomes small, the external heat transfer coefficient becomes small.

The present invention utilizes this relationship to control the load (heat transfer load) by increasing or decreasing the superficial velocity.

In the fluidized bed boiler of the present invention, when the superficial velocity is changed (as long as the value of the superficial velocity is within the operating range of the fluidized bed boiler), the height of the fluidized bed changes and the superficial velocity changes. As the abundance of particles in the space above the fluidized bed changes, the load changes continuously and gradually over a wide range from u _mf (minimum fluidization velocity) to the virtually upper superficial velocity. . Therefore, the load can be adjusted even in the high load region. In addition, the load can be adjusted with high accuracy.

In the fluidized bed boiler of the present invention, the fluidized bed has a static bed height (height when not fluidized, height above the gas outlet of the gas distribution plate) of 400 mm or less, particularly 300 mm or less Is preferred. In this shallow bed fluidized bed, even if the superficial velocity changes, the height of the fluidized bed (bed height during fluidization) does not change so much, so even if the superficial velocity changes, all the heat transfer tubes scatter from the fluidized bed. This is because the particles are present in the space above the fluidized bed in which they are present.

In the present invention, the height of the fluidized bed during fluidization is set to be not more than twice the height of the stationary bed, preferably not more than 1.5 times. By setting it in this range, it is possible to suppress local large bubble ejection from the fluidized bed. In order to achieve this range, it is preferable to use, as the dispersion plate, one in which the gas ejection direction is the side (lateral) direction.

Thus, in the present invention, the height of the stationary layer in the fluidized chamber is 400 m.
A shallow bed fluidized bed of m or less, a fluidized bed height at the time of fluidization is not more than twice the height of the stationary bed, and the above is present in a space immediately above the upper surface of the fluidized bed where particles scattered from the fluidized bed are present. The heat transfer tubes are arranged in multiple stages at a height not more than 3 times the height of the stationary layer, and the superficial velocity is increased or decreased to contact the particles scattered in the space from the upper surface of the fluidized bed with the heat transfer tubes. Since the frequency is increased / decreased to increase / decrease the boiler load, the static bed height of the fluidized bed is set low to limit the fluidized height of the fluidized bed at the time of fluidization. Since the arrangement position in the space is specified, it is possible to prevent the heat transfer tube from being directly buried in or in contact with the flowing fluidized bed itself, and to the extent possible, particles that have scattered from the upper surface of the fluidized bed are contained in the heat transfer tube. It is a shallow fluidized bed with reliable contact and a low static bed height, which limits fluidization height. Since the range is set to a large range, the particles scattered from the upper surface of the fluidized bed can be made to exist in a considerable amount in the space immediately above the upper surface of the fluidized bed. Therefore, by disposing a heat transfer tube at a specified position in the space, the superficial velocity is increased / decreased, and the contact frequency between the particles scattered in the space and the heat transfer tube is increased / decreased. It is possible to gradually and continuously change the heat transfer index over a wide range of superficial velocity as shown in, and particularly in a practical range of superficial velocity,
The average heat transfer index of a plurality of stages of heat transfer tubes can be made to be approximately linearly proportional to the superficial velocity. Therefore, the load can be adjusted accurately even in the high load region, and the stable combustion can be continued by maintaining the temperature of the fluidized bed constant.

Embodiments Embodiments will be described below with reference to the drawings.

FIG. 1 is a vertical sectional view of a fluidized bed boiler according to an embodiment of the present invention.

Reference numeral 10 is a boiler furnace body, a dispersion plate 12 is installed at the bottom of the inside of the boiler so as to traverse the inside of the boiler, and an air chamber
14 are sectioned. A supply pipe 16 for primary air is connected to the air chamber 14. Above the dispersion plate 12 is a flow chamber, and a large number of heat transfer tubes 18 are installed. In this embodiment, the heat transfer tubes 18 are installed so as to have three stages in the height direction, and are also installed in a staggered arrangement in the vertical direction. Reference numeral 20 denotes a fuel (in the present embodiment, granular coal) supply pipe, and a plurality of supply pipes are arranged immediately above the dispersion plate 12 so as to be uniformly supplied.

A secondary air supply pipe is provided in the freeboard section above the heat transfer pipe 18.
22 is connected. A distribution plate 24 is installed above the secondary air supply pipe 22 so as to traverse the inside of the boiler furnace body, and a desulfurization chamber is formed above it. Reference numeral 26 is a pipe for supplying a desulfurizing agent (limestone in this embodiment) such as limestone or dolomite, and reference numeral 28 is a discharge pipe for discharging the limestone after the desulfurization reaction. Reference numeral 30 is an exhaust gas outlet provided at the top of the boiler furnace body.

A fluid medium storage tank 32 is connected to the furnace body 10 via a supply pipe 36 having a supply valve 34. Further, a pipe 38 for extracting the fluidized medium is connected, and an extraction valve 40 is installed. Further, a differential pressure gauge 42 for detecting the differential pressure between the freeboard section and the air chamber 14, a thermometer 44 for measuring the temperature of the fluidized bed F, and a pressure detector 46 in the air chamber 14 are installed.

The heat transfer tube 18 is installed in the space region G above the fluidized bed F and above the fluidized bed F where particles scattered from the fluidized bed F are present.

In this structure, the fluidized medium is filled in the fluidized chamber above the dispersion plate 12, and the granular coal supplied from the supply pipe 20 is burned by the primary air supplied through the air chamber 14 to form the fluidized bed F. To do.

The combustion gas that has passed through the fluidized bed F enters the desulfurization fluidized bed D through the dispersion plate 24 after receiving the supply of the secondary air, becomes the exhaust gas after the sulfur content is removed, and is discharged from the outlet 30. .

Then, when the coal supply amount and the primary air supply amount are increased / decreased in response to the fluctuation of the boiler load, the height of the fluidized bed F is increased / decreased and the amount of particles scattered from the fluidized bed F is also increased / decreased.
The amount of particles in the upper space region G of the fluidized bed F increases and decreases, and the total amount of heat transferred to the heat transfer tubes 18 also increases and decreases.

FIG. 2 (b) is a model diagram showing bubbles in the fluidized bed F. As shown in the figure, the bubbles generated at the bottom in the fluidized bed F move upward while associating and gradually growing, It bursts on the upper surface FS of the fluidized bed F. Along with this, the particles are scattered from the upper surface FS of the fluidized bed F to the space region G above it. Since the particles scattered in the space region G come into contact with the heat transfer tube 18, efficient heat transfer is performed.

FIG. 2 (a) is a distribution chart of the existence ratio (void ratio) of particles from the fluidized bed F to the upper space region G of the fluidized bed F. As shown in FIG. 2 (a), the porosity is almost constant in the fluidized bed F, but the porosity increases sharply in the upper space region G, and the porosity increases toward the upper side (the number of particles decreases). Become). As the superficial velocity increases, the voidage in the fluidized bed F increases, and the voidage in the upper space region G decreases (the amount of scattered particles increases). Therefore, by increasing or decreasing the superficial velocity, the contact frequency between the particles and the heat transfer tubes 18 can be increased or decreased, and the load on the fluidized bed boiler can be increased or decreased.

FIG. 3 is a graph showing the results of measuring the relationship between the heat transfer coefficient and the superficial velocity under the conditions described below.

The hard axis Z in FIG. 3 is a dimensionless heat transfer index of the heat transfer coefficient defined by the following equation.

h _x : Outer heat transfer coefficient of height X heat transfer tube h _max : Outer heat transfer coefficient of heat transfer tube buried in fluidized bed h _∞ : Outer heat transfer coefficient of heat transfer tube where no particles come into contact with each other. It is a square one.

The height of the dispersion plate 12 from the air ejection holes 50 of the distributor to the center of each heat transfer tube 18 is as follows.

Height to lower heat transfer tube X ₁ : 400 mm Height to middle heat transfer tube X ₂ : 510 mm Height to upper heat transfer tube X ₃ : 620 mm Other conditions are as follows.

Outer diameter of heat transfer tube 18: 50 mm Fluidization medium: u _mf (minimum fluidization speed) of silica sand of 0.174 m / sec Static bed height L _c : 200 mm Fluidized bed height: 300 mm (u−u _mf = 2 m / sec When the difference between the superficial velocity u and u _mf is 1 m / sec, the amount of coal supplied: 80
kg / h Same as above Primary air amount: 750 Nm ³ / h In this embodiment, when u-u _mf = 2, the load is 100%, and when u-u _mf = 0.7, the load is 40%. .

From FIG. 3, it is recognized that the heat transfer index Z changes gently over a wide range of the superficial velocity u. In particular, u-
In the practical operating range where u _mf is 0.5 to 2, the average Z value is almost linearly proportional to the superficial velocity. Therefore, in this range, the load of the fluidized bed boiler can be continuously and easily adjusted with extremely high accuracy. Further, even when the heat transfer amount load is reduced, that is, when the superficial velocity and the coal supply amount are reduced to reduce the boiler load, the heat transfer amount is reduced at almost the same rate according to the reduction rate of the superficial velocity, so the flow rate is reduced. The temperature of the bed F can be maintained substantially constant, stable combustion of coal can be performed in the fluidized bed F, and stable operation of the boiler can be performed.

FIG. 4 shows the heat transfer index Z when the installation heights X ₁ , X ₂ , X ₃ and L _c of the heat transfer tubes in the fluidized bed boiler shown in JP-A-63-153301 are set as follows. It is the measured data showing the relationship with the superficial velocity.

X ₁ : 400mm X ₂ : 510mm X ₃ : 620mm L _c : 370mm (Note that in this Japanese Patent Laid-Open No. 63-153301, the number of heat transfer tubes buried in the fluidized bed is changed according to the load change.) as FIG. 4, in JP-a-63-153301, the u-u _mf
Z value rises rapidly in the range of 0.2 to 0.8, and u- _umf is 1
In the range of ˜2, the Z value hardly changes. Therefore, according to Japanese Patent Laid-Open No. 63-153301, it is difficult to control the load accurately and easily, and it is difficult to control the load particularly in the high load range. In other words, in the range where the Z value in the high load area hardly changes, the heat transfer coefficient hardly changes even if the load is lowered, as in the conventional fluidized bed boiler in which the heat transfer tube is buried in the fluidized bed, and therefore the fluidized bed temperature is I will go down.

[Effects] As described above, in the fluidized bed boiler of the present invention, the heat transfer tube is arranged in the space portion immediately above the fluidized bed, in which the particles scattered from the fluidized bed exist, as the configuration described in the claims. Therefore, the change in heat transfer coefficient due to contact of particles can be made approximately proportional to the change in superficial velocity.
The output of the fluidized bed boiler can be controlled accurately and easily by accurately following a large load change. Moreover, this load control is performed by adjusting the superficial velocity and is extremely quick.

Further, in the fluidized bed boiler of the present invention, even if the load is adjusted, the temperature of the fluidized bed can be maintained constant and stable combustion can be continued.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a fluidized bed boiler for explaining an embodiment of the present invention, and FIG. 2 is a graph and a sectional view showing a state inside the fluidized bed. FIG. 3 is a graph showing the experimental results of the apparatus of the embodiment. FIG. 4 is a graph showing the experimental results of the conventional device. 12 ... Dispersion plate, 14 ... Air chamber, 16 ... Primary air supply pipe, 18 ... Heat transfer pipe, 20 ... Fuel supply pipe, F ... Fluidized bed, D ... Desulfurization fluidized bed, G ... The spatial area above the fluidized bed.

Claims (1)

(57) [Claims] 1. A fuel is continuously supplied into a fluid chamber, and air is supplied into the fluid chamber through a dispersion plate to burn the fuel and to flow a fluid medium. The heat load is controlled by a heat pipe, the air supplied to the flow chamber is increased or decreased, the superficial velocity in the flow chamber is increased or decreased, and the supply amount of the fuel is increased or decreased to control the boiler load. In the fluidized bed boiler
The fluidized bed is a shallow bed fluidized bed with a height of 400 mm or less in the fluidized chamber, the fluidized bed height during fluidization is not more than twice the height of the fluidized bed, and the fluidized bed is immediately above the upper surface of the fluidized bed. The heat transfer tubes are arranged in multiple stages in the space where the particles scattered from are located at a height not more than 3 times the height of the stationary bed, and the superficial velocity is increased or decreased to scatter from the upper surface of the fluidized bed into the space. A fluidized bed boiler characterized in that the load of the boiler is increased / decreased by increasing / decreasing the frequency of contact between the particles and the heat transfer tube.