JPS6347961B2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> This invention relates to the structure of a fluidized bed boiler.

<Prior art and its problems> In a conventional natural circulation fluidized bed boiler, an evaporation tube is placed within the fluidized bed, the generated steam is sent to a drum, and the steam is then taken out from the drum and transferred into the fluidized bed. A structure was adopted in which the heat was sent to the superheater tube located at the location. However, in a boiler, there is a need for a means to cope with load fluctuations, and in addition, there are various problems associated with burning fuel in a fluidized bed.

The former type of load fluctuations are responded to by controlling the fuel supply, which is no different from conventional boilers, but in fluidized bed boilers, the amount of fluidized medium is large and the amount of heat it holds is also large, and it is difficult to start up. Another problem with increased load is that it takes time to raise the temperature of the medium. The so-called time constant of the device is large. In other words, the response to change has become slow. For this purpose, the evaporator tubes are arranged diagonally in the bed or placed in the fluidized bed with the heat exchanger tube panel surface vertical, and the layer level (layer thickness) is changed to change the surface area of the heat exchanger tubes in contact with the medium. We are responding accordingly. This is because the heat transfer by the fluidized medium can provide four times the amount of heat transfer compared to the heat transfer to the furnace wall tube in a normal furnace. This is because the fluidized medium, which is high in temperature and has a large specific heat, directly collides with the surface of the heat transfer tube and transfers heat. However, on the other hand, the thickness of the heat transfer tube at the boundary between the surface of the fluidized bed and the space is particularly large, causing problems such as water leakage from the heat transfer tube and shutdown of the boiler.

In other words, the main issues to be solved are as follows.

(1) Countermeasures against rapid wear of heat transfer tubes (2) Problems when starting up the fluidized bed (a) Problems in dealing with the large time constant of the fluidized bed (This also deals with load fluctuations.) ( b) Damage to superheater tubes due to delay in steam feeding at startup <Objective of the invention> The present invention is to propose a compact fluidized bed boiler structure that facilitates steam generation and its control and causes less damage to heat transfer tubes. With the goal.

<Summary of the Means> In short, the present invention provides a water wall pipe that surrounds the combustion gas space above the fluidized bed and allows boiler water to circulate naturally.
A drum with a water section and a steam section is provided to receive the steam generated in the water wall tube, and the fluidized bed has a horizontal tube section and a bent tube section where boiler water flows through forced circulation and exchanges heat with the fluidized medium in the bed. The fluidized bed boiler is characterized in that a plurality of evaporation tube panels are positioned therein, and a circulation pipe line is provided for supplying the steam/water mixed fluid that has passed through the evaporation tube panels to the drum.

<Embodiment> The structure of an apparatus according to an embodiment of the present invention will be described below with reference to the drawings. A gas space 2 and a fluidized bed are provided below the gas space 2 in a chamber partitioned into a rectangular cross section by a finned tube wall 3 that is insulated from the outside by a heat insulating material 3a. The tubes of the finned tube wall 3 are steam generating tubes, and these rise from a header 4 located below the fluidized bed 1 and are connected to a drum 5 which receives a steam/water mixed fluid and supplies steam thereto. The header 4 receives fluid supply from the drum 5 via a downcomer pipe 6.

Tube 1 located in the fluidized bed and through which heat is transferred from the fluidized medium
0 (evaporation tube panel) is connected to the header 11 that receives the supply of boiler water. Boiler water is supplied to this header 11 from a pump 8 for forced circulation. This tube 10 (hereinafter the tube of the evaporation tube panel will be simply referred to as tube 10) is formed into a panel shape, consisting of a horizontal tube section and a bent tube section, and extends horizontally so as to be entirely immersed in the fluidized bed. The horizontal extension of the pipe 10 and the use of a forced circulation pump are related to all of the problems (1), (2) (a) and (b) mentioned above.

In other words, in the past, the load was controlled by placing the bed diagonally to the horizontal, but by extending it horizontally, the depth (thickness) of the fluidized bed can be reduced. (a) The amount of fluidized medium can be reduced. It is easy to start up (because the amount of fluidized medium is small, the temperature of the medium can be raised in a short amount of time for the same amount of fuel), and it is easy to respond to load fluctuations.

(b) Since it is immersed, the uppermost tube of the evaporator panel can be located far from the layer surface and is less likely to be damaged. (The area near the bed surface is in a boiling state, and the wear of the tubes due to media particle splash is more severe the closer to the bed surface.) Also, since combustion occurs in the fluidized bed, when using sulfur-containing fuel, SO ₂ As the concentration of gas increases and the layer is at a high temperature (above 700°C), the tube will also be damaged by oxidation.

(c) Since the superheater tube is also immersed in the horizontally arranged layer, (b)
As with the above, there is little damage to the tube.

(d) Since a forced circulation pump is used, the amount of boiler water supplied to the pipe 10 serving as the evaporation pipe can be easily changed, and the response to the boiler load is easy.

This effect is achieved.

Downcomer pipe 7 leads from drum 5 to pump 8 .
The pump 8 supplies fluid to the inlet header 11a, and the generated steam/water mixed fluid is returned to the drum 5 from the outlet header 11b through a riser pipe 9 serving as a circulation conduit.

Next, let us consider steam generation by employing two systems: the natural circulation (water wall tube) system and the forced circulation system that uses the forced circulation pump 8 to supply canned water to the evaporation tube 10 as described above.

The fluidized bed boiler according to the present invention uses a fluidized bed to generate steam, and usually uses fine coal particles as fuel.

Fluidized beds have the characteristic of being able to burn fuels that are difficult to burn or have low calories, but on the other hand, the amount of media that forms the fluidized bed is large, and it takes time to heat up, which is a characteristic of fluidized beds. It has the drawbacks of poor response and large time constant. For this reason, in order to respond to the load, as in the present invention, the fluidized bed is divided into a plurality of sections by partition walls 12, and the number of operating sections is changed to respond.
However, even in compartments where combustion air has been shut off, a small amount of air is usually supplied in preparation for restart. Therefore, it is not possible to rapidly cut off the heat supply to the steam pipe and increase the supply using the "open combustion" of fine coal and the heat retained in the fluidized medium, and it is not possible to expect a good response like in the case of combustion of liquid fuel.

On the other hand, natural circulation of boiler water in a multi-bent heat exchanger tube panel results in large boiler water flow resistance at the bends, and it is also difficult to remove the accumulation of steam bubbles. In addition, in naturally circulating boiler water, the pressure difference based on the difference in specific gravity between the boiler water column in the downcomer pipe and the air-water mixed water column in the evaporator pipe is the power for water circulation, and even if the load increases, the inlet of the evaporator pipe in the layer It is not possible to expect a rapid increase in the flow rate of boiler water in the evaporation tube because the pressure in the evaporator tube hardly changes.

Further, even when the circulation force of boiler water including the water tube wall is increased, the amount of boiler water flowing through the evaporation tube does not increase rapidly due to the bending resistance of the multiple bends.

On the other hand, when forced circulation is used in an intrabed heat exchanger tube, the heat transfer of boiler water in the fluidized bed is carried out by the high temperature fluidized medium flowing and directly contacting the tube surface, which allows the heat transfer by the combustion gas in the empty tower to be more efficient. It has a thermal coefficient of approximately four times as much, and is characterized by the ability to freely control the amount of boiler water supplied by controlling the pump, rapidly increasing the amount of evaporation, and rapidly increasing the amount of heat transfer.
Further, in this case, the steam bubbles are not retained on the upper surface of the evaporator tube, but are transported together with the boiler water to the boiler drum.

In other words, even if both the water wall tube and the evaporator tube are forced circulation, unlike the relationship between heavy oil combustion and the furnace in a normal boiler, the response of the main heat imparting section is significantly slower than that of heavy oil combustion, and the time constant is large. There is only a fluidized bed section, and there are difficulties in designing the load-responsive circulation of boiler water.

That is, it is preferable in terms of design and boiler control that only the heat exchanger tubes in the fluidized bed undergo forced circulation, and the other parts use natural circulation, which does not require any special equipment for circulation.

That is, in order to improve load response, the present invention provides two systems, natural circulation and forced circulation, in one boiler.

The fluidized bed 1 is divided into a plurality of sections by partition walls indicated by the reference numeral 12. Each compartment includes a fuel supply device (not shown) and a duct 71, a pressure air chamber 70,
An air supply device consisting of a perforated plate 72 is provided. These fuel and air supply devices are equipped with flow rate control valves (not shown), and the output of the boiler can be easily controlled by controlling the flow rate using these valves and by controlling the number of sections in which the divided fluidized bed is operated. .

In the illustrated embodiment, another fluidized bed 41 is provided alongside the fluidized bed 1 (first fluidized bed).
This fluidized bed 41 is smaller than the first fluidized bed 1 and is located below the rectangular gas space 42 . The gas space 42 shares the boundary wall (cooling wall) 33 of the gas space 2 as a cooling wall. The other boundary wall, designated by reference numeral 43, is formed by a plurality of evaporator tubes that are supplied with fluid from the header 44 via the downcomer pipe 6 and send the generated steam to the drum 5.

Headers 47 (see FIG. 2) are located outside the boundary wall, and superheated steam pipes 46 connecting the headers 47 extend horizontally into the fluidized bed 41 and are immersed therein. When using this fluidized bed combustion apparatus, first the first fluidized bed 1 is started, and when superheated steam is required, the fluidized bed 41 is started. Like the first fluidized bed, the fluidized bed 41 is divided into a plurality of sections to facilitate control of steam temperature, and receives fuel supply for each section for combustion.

At the top of the boundary wall 43, a flue 5 is connected from the gas space 42.
Spaced tube portion 43a (as shown in FIG. 1, this is a structure in which a part of the tube is bent and extended every other tube to form a gas passage in the tube wall) so that combustion gas can be sent to the spaced tube portion 43a. ) will be established. The lower part 51 of the flue is formed in the shape of a hopper, and the lower part 51 is shaped like a hopper.
is located in the flue. The battle 52 is deflected by 180° before the combustion gas flows from the gas space 42 to the flue 50, and the fine particles accompanying the combustion gas are separated here and stored in a hopper-like part in the lower part 51 of the flue. and is placed in the position shown so that it can be removed from the device. The gas flowing through the flue 50 first passes through two superheater sections 55 and 56 (this superheater section 5
5 and 56 are connected in series to the superheater tube 46. ), then passes through the economizer 57 and is discharged outside the device.

The combustion gases from the gas space 2 flow across the gas space 42 through spaced tubes 33a forming gas passages in the upper part of the fluid-cooled boundary wall 33.

As a further modification of the above embodiment, a fluidized bed combustion apparatus can be constructed in which another fluidized bed is provided in addition to the one described above, and the steam in the reheater tube is heated by the heat transfer medium of the bed.

<Effects of the Invention> By implementing this invention, the following effects can be obtained.

(a) Forced circulation means and natural circulation means are installed in one boiler to reduce the load fluctuations of the boiler during rated operation.Forced circulation is achieved by installing an evaporation tube in the bed of a fluidized bed boiler that receives boiler water supply, which has a slow response. The pump should have good responsiveness.

(b) A horizontally extending evaporator tube panel is installed in the fluidized bed,
Retention of air bubbles is prevented by forced can water circulation, thereby reducing the thickness of the fluidized bed, and (a) reducing the amount of medium heated by combustion and improving responsiveness.

(b) Due to the thin layer thickness, the power of the fan that supplies the fluidizing air can be saved.

(c) By being horizontally extended and immersed in the layer, it can prevent the wear and corrosion of the tube that occurs when it is located close to the layer surface, and is effective in preventing damage to the tube.

(d) The evaporator tube panel and the superheater tube panel are located in separate fluidized beds, and upon startup, the fluidized bed in which the superheater tube panel is located is not activated to prevent damage to the superheater tube.

(e) The tubes of the tube groups in the evaporator tube panel and superheater tube panel are extended horizontally to reduce the layer thickness, and the height of the boiler is shortened to make the equipment more compact.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a fluidized bed combustion apparatus according to the present invention, FIG. 2 is a side view of the fluidized bed combustion apparatus as seen from the left side of FIG. 1, and FIG.
FIG. 2 is a rear view of the fluidized bed combustion apparatus as seen from the rear side of the figure. 1... Fluidized bed (first fluidized bed), 2... Gas space,
3...Tube wall with fins, 3a...Insulating material, 4...
Header, 5... Drum, 6... Descending pipe, 7... Descending pipe, 70... Pressure air chamber, 71... Duct, 7
2... Perforated plate, 8... Pump, 9... Rising pipe, 1
0...Pipe (evaporation tube panel), 11...Header, 1
1a...Inlet header, 11b...Outlet header, 1
2... Partition wall, 33... Boundary wall, 33a... Spaced tube part, 41... Fluidized bed (other fluidized bed),
42... Gas space, 43... Boundary wall, 43a...
Space tube section, 47... Header, 50...
...Flue, 51...Lower part of the flue, 52...Bassful, 55, 56...Superheater section, 57...Economizer.

Claims (1)

[Claims] 1. A water wall tube is provided that surrounds the combustion gas space above the fluidized bed and allows boiler water to circulate naturally. A drum is provided that has a water section and a steam section that receive the steam generated in this water wall tube. A plurality of evaporator tube panels each consisting of a horizontal tube section and a bent tube section through which the fluid flows in forced circulation to exchange heat with the bed fluidized medium are positioned, and the steam/water mixed fluid that has passed through the evaporator tube panels is supplied to the drum. A fluidized bed boiler characterized by having a circulation pipe.