JPS60207809A - Method of operating fluidized-bed burner - Google Patents

Abstract

PURPOSE:To make it possible to correctly detect the fluidization starting period of a medium by detecting an abrupt rise of the rising ratio of the temperature within the layer when starting cells which are in standstill, in a method of controlling the operation and stop of each cell of the fluidized-bed burner having a plurality of cells. CONSTITUTION:Air chambers 3a and 3b are partitioned and formed at the lower part of a porous plate 2 of a main body 1 of a fluidized-bed boiler, and cells 7a and 7b are formed at the upper parts of the air chambers 3a and 3b through a diaphragm 6. In this case, when the cell 7a is started while the cell 7a is in operation, the opening degree of a damper 10 is gradually increased through a timer 9. That is, the opening degree of the damper 10 is stepwisely increased every unit time, and a temperature detector 11 detects the change in the layer temperature within the unit time and supplies a result of the detection to a control box 8. The control box 8 calculates the rising ratio of the temperature within the layer per unit time from the result of the detection, and estimates the fluidization starting time of the cell 7a from the time point where the temperature in the unit time abruptly increases.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluidized bed combustion apparatus, and more particularly to an apparatus in which a fluidized bed section is formed into a plurality of sections, and which can smoothly operate and stop each section.

Fluidized bed combustion equipment can burn well even relatively flame-retardant materials (
Because it can be incinerated), its fields of use are expanding. One of these combustion devices is a fluidized bed boiler that recovers the heat generated by combustion as hot water, steam, etc.; A boiler has been developed in which the boiler load can be widened by operating and stopping each cell, and the fluidized bed can be easily started. In this type of boiler, it is necessary to accurately detect the operating state of each cell, especially when restarting a cell that has been shut down, when fluidization starts. That is, in the conventional operating method, the density of the fluidized medium in the layer above the cell (section) during which the operation is stopped gradually increases because it is not supplied with fluidizing gas. Therefore, if an attempt is made to restart the cell, fluidization will not occur unless the pressure of the fluidizing gas is made higher than that of the operating cell. Also, the concentration inside the layer becomes low.

In such a state, if more air than the fluidization start air amount is injected when starting the cell, the layer temperature of the cell that is already in operation will be raised to 1, for example.
This causes the temperature to drop by 50°C or more, causing fluctuations in steam conditions. In addition, the amount of air supplied to other operating cells becomes excessive, and a large amount of nitrogen oxides (NOx) is generated under high partial pressure. Conversely, if the air supply amount is less than the fluidization starting air amount, there is a problem that the startup time becomes longer. Therefore, there has been a demand for a method for accurately detecting the timing of cell flow initiation, but none of these methods has been able to satisfy that demand.

First, there is a method of determining a general formula for calculating the amount of air required to start fluidizing the activated cell using a semi-empirical formula, and estimating the time to start fluidizing from the amount of supplied air based on this formula. However, the timing at which fluidization starts varies depending on various factors such as the properties of the fluidized medium, its particle size, particle size distribution, whether or not fuel is injected into the media layer, the cell temperature during stoppage, and the presence or absence of heat exchanger tubes in the cell. . Therefore, estimation of the fluidization start point using the general formula (") is inevitably extremely inaccurate, and at least this method alone cannot be put to practical use.

Next, visual inspection may be considered, but visibility is difficult within the bed and in the empty tower due to some of the media being scattered due to operating cells, combustion gas, etc., and the surface of the fluidized bed is originally as clear as the surface of water. Therefore, accurate detection is still difficult.

In addition, special consideration must be given to the furnace structure in order to form the viewing section, which poses safety and economic problems, especially in practical plants.

This invention was constructed in view of the above-mentioned problems,
It is an object of the present invention to provide an operating method capable of accurately detecting the timing at which fluidization of a fluidizing medium in each cell begins.

In short, this invention focuses on the fact that the rate of temperature rise in the layer rapidly increases at the time fluidization starts in the activated cell, and detects the timing at which fluidization of the medium starts by detecting this temperature change. This is a method in which the content is

Next, prior to a detailed explanation of the present invention, the relationship between the fluidization start time and the change in the rate of increase in temperature in the bed will be discussed, including experimental results by the inventors.

In FIG. 1, a plurality of air chambers 3a, 3b, and 3c are defined in the lower part of the perforated plate 2 of the boiler body 1, and by supplying and shutting off air to each air chamber, the medium in the upper part can be removed. cause fluidization or cessation. Note that in the illustrated example, partition walls are not formed within the medium layer;
The partition wall may be formed at all or part of the height of the stationary layer. Hereinafter, the medium arrangement portion above each air chamber will be referred to as a cell, regardless of the presence or absence of a partition wall. In the case of FIG. 1, fluidizing air is supplied to the air chambers 3a and 3b, and the medium in the cells 4a and 4b above them is fluidized to form a fluidized bed. On the other hand, the cell 4c is about to start up, and the amount of air supplied to the air chamber 3c is gradually increasing. As the amount of air supply increases, fluidizing air gradually penetrates into the stationary bed, and the fluidizing air gradually burns the heated material in the bed, or if the supplied air is preheated, the heat causes the bed to cool down. The temperature begins to rise. When the air supply amount is further increased and fluidization of the medium starts, the layer temperature rapidly increases because the medium is rapidly mixed with a high temperature medium from a cell such as the adjacent chamber 4b which is in operation.

In the above case, if a certain amount of fuel has been charged into the stationary bed, the combustion state of the fuel will suddenly improve as fluidization begins, and the bed temperature will rise more rapidly.

FIG. 2 shows a case where a hot air stove is used to start up the cell. In this case, air heated by the hot blast furnace 5 is supplied as fluidized air when starting the cell, and this hot air is supplied when starting the cell 4c. When the supply of hot air is gradually increased, this heated gas penetrates into the stationary layer and the temperature of that layer increases;
Well, it's relatively lenient. However, when fluidization begins, the particles in this stationary layer rapidly mix with the high temperature medium particles in the upper part of the adjacent chamber, and the temperature of the layer rises rapidly. In this case, the inventors also experimentally confirmed the above-mentioned problem, and were able to confirm that in any cell startup method, the temperature inside the cell (temperature) rose rapidly as the cell began to fluidize.

FIG. 3 shows an embodiment of the invention. In the figure, air chambers 3a and 3b are formed in the lower part of the perforated plate 2 of the fluidized bed boiler main body l, and air chambers 3a and 7b are formed in the upper part through the partition wall 6.
is formed.

Here, this embodiment will be described assuming that self-service b is in operation and self-service a is about to be started. Although each sensor and control section are shown only on the cell a side, they can be attached to other cells as well. Reference numeral 8 denotes a control box for storing memory and issuing command signals, and when starting the self-a, the opening degree of the damper 1o is gradually increased via a timer 9. That is, the damper opening degree is increased stepwise for each unit time, and changes in layer temperature within this unit time are detected by the temperature detector 11 and manually inputted to the control box 8. Based on this detection result, the control box 8 calculates the rate of increase in the temperature in the layer per unit time, and estimates the time when the fluidization of the self-a starts when the temperature in the unit time suddenly increases.

In addition to directly arranging the detector within the bed, the temperature can also be detected by arranging the detector in close contact with the outside of the wall surface of the fluidized bed, thereby extending the life of the detector. In the case of a wall with a membrane structure (j), it is best to place it in the center of the fin where it will not be affected by the water pipe.

FIG. 4 shows an example of this detection state. For activated cells, unit time 1. to increase the air supply amount step by step. In the case shown, the unit time circle is 10 seconds,
Let the air increase amount per unit time be 2ooNm'/h.

In the first stage, the temperature rise is relatively small and the rate of rise is almost constant. However, after a predetermined period of time (approximately 120 seconds in the illustrated example), the humidity i suddenly increases, and it is assumed that fluidization has started. In the case shown, unit time (1,)
(10 seconds in the illustrated example), the temperature rise (Te) is approximately 8
℃, and the start of fluidization is confirmed. It was experimentally confirmed that fluidization started when the temperature increased by 5°C or more.

At this point, the adjustment of the opening degree of the damper IO is temporarily stopped and the fluid state is maintained. However, since the air supply amount at this point is the minimum flow rate that maintains the fluid state, channeling and bubbling are likely to occur, so the air supply amount is appropriately controlled from now on. Although the case where the air supply is increased in stages has been described above, the present invention is not limited to this, and the air supply amount may be increased continuously by, for example, increasing the damper opening degree continuously. However, it can be said that it is easier to detect the temperature increase rate per unit time with a stepwise increase.

In the above case, it is preferable to detect the differential pressure within the cell, supplementarily detect the fluidization start time based on this, and use the dirt as a correction value to perform more precise control. In FIG. 3, numeral 12 is a differential pressure detector that detects the differential pressure between the waste inlet and outlet, and this differential pressure is also manually input to the control box 8 as a signal. FIG. 5 shows the relationship between this differential pressure ΔP and the flow rate of air supplied into the layer. By increasing the flow rate of the fluidizing air supplied into the bed, the differential pressure △P increases and fluidization starts at the differential pressure PI, and as fluidization begins, the differential pressure slightly decreases to P, and the flow rate is increased thereafter. It is also known that the differential pressure is almost constant. The fluidization start time can be estimated by detecting the state in which the fluidization start speed (Umfρ decreases from Um, 4) at this differential pressure P1. Since the state of pressure fluctuation is unknown, it is difficult to detect the start of fluidization.

The results detected as described above are input as correction values for the fluidization start estimation based on the change in layer temperature described above. However, the relationship between ΔP and the air velocity varies greatly depending on the properties of the media particles, and there are cases where the change from Pl to P is unclear, so it is important to note that only changes in the differential pressure between p and -p are enough to determine the flow. The estimation of the start of 1'i cannot be performed very accurately. Note that UT in Fig. 5 is the terminal velocity of free fall of one medium particle, and if the flow velocity is increased beyond this, all the medium will be scattered to the empty column, resulting in a fluidized bed t.
It disappears. Therefore, the fluidized bed has an air flow rate of U m f,
to UT. Reference numeral 13 in FIG. 3 is a flow rate detector that detects the flow rate of the fluidizing gas, and by detecting the flow rate, the control box 8 calculates the air flow velocity. In the above case, an inert gas containing 1J of combustion exhaust gas should be supplied to the cell whose operation is stopped.
It may also be possible to prevent the ash from melting and solidifying due to burning. Reference numeral 14 in the figure represents an exhaust gas supply conduit for this purpose.

By carrying out this invention, the fluidization start timing of each cell can be accurately detected, and the cells can be operated and stopped freely without changing the steam conditions. Furthermore, when a small amount of fuel is previously supplied to the top of or into the non-fluidized bed, it is possible to facilitate the initiation of combustion in that bed.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of a fluidized bed boiler showing the operating status of each cell, FIG. 4
The figure is a diagram showing the relationship between bed temperature, fluidized air amount, and time.
FIG. 5 is a diagram showing the relationship between differential pressure ΔP and air flow velocity. 1... Fluidized bed boiler main body 7a, 7b... Cell 8... Control box 11... Humidity detector 12... Differential pressure detection Device 13...Flow rate detector

Claims (1)

[Claims] 1. In a method for controlling the operation and stop of each cell of a fluidized bed combustion apparatus having a plurality of cells, when starting a cell that is not in operation, supplying fluidizing gas to the cell A fluidized bed combustion device characterized in that the amount of air is controlled to increase gradually, the temperature change in the cell is detected in a unit time, and the amount of air at the time when the temperature in the unit time sharply increases is regarded as the amount of air at which fluidization starts. How to drive. 2. The fluidized bed combustion apparatus according to claim 1, wherein the unit time is about 10 seconds, and the time point when the temperature rise in this unit time is about 5° C. or more is regarded as the fluidization start time. how to drive. 3. A method for operating a fluidized bed combustion apparatus according to claim 1 or 2, characterized in that an inert gas is supplied to the cells that are not in operation. 4. Claims 1 to 3 are characterized in that the differential pressure between the fluidizing gas inlet and outlet of the fluidized bed is detected, and the variation in the differential pressure is controlled as a correction value for the control. A method of operating a fluidized bed combustion apparatus according to any one of the above.