JPH0125964B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of operating a swirling fluidized bed combustion furnace for incinerating waste with a low calorific value.

[Prior art]

In a swirling fluidized bed combustion furnace, municipal waste, industrial waste, coal, peat, oil-containing sand, etc., which have a relatively high calorific value and a low calorific value that can be incinerated without the constant addition of auxiliary fuel, are burned. In this case, the amount of fluidized medium used is usually adjusted so that the amount of fluidized medium in the furnace remains constant. This method was effective in maintaining the retained heat of the fluidized bed almost constant, as well as the flow rate and pressure of the fluidizing air supplied into the fluidized bed, and achieving stable combustion. However, on the other hand, there was a tendency to operate using a larger amount of fluid medium than necessary. This is because the larger the amount of fluidized media held in the furnace, the smaller the influence of changes in the input amount of materials to be combusted, moisture content, composition, etc., and the ratio of calorific value in the fluidized bed to the total calorific value. The temperature of the fluidized bed required for combustion (usually 500 to 600°C or higher) can be maintained even when incinerating low-calorific materials with a small calorific value, and the air for the fluidized bed supplied to the fluidized bed increases. This is because the influence of fluctuations in flow rate, pressure, or temperature is reduced. That is, because priority was given to stable combustion, it was usual to operate the reactor at the maximum amount of fluid medium held in the reactor to accommodate the maximum fluctuation range of the amount of combustible material, etc., and the minimum lower calorific value.

Such normal combustion conditions also have some disadvantages. In other words, as the amount of the fluidized medium increases, the layer of the fluidized bed also becomes higher, so the amount and pressure of fluidizing air to be supplied into the fluidized bed that fluidizes the fluidized medium also increases. When using blower rotational speed control, suction vane control, damper control, etc. to adjust the supply amount of This wasteful power cost could amount to 10 to 20% of the total operating cost and could not be ignored.

Furthermore, since the proportion of the calorific value in the fluidized bed to the total calorific value is high, the temperature of the fluidized bed becomes higher than necessary, which is undesirable. In other words, if the temperature of the fluidized bed becomes too high, part of the fluidized medium and incineration residue will melt and become clinker, causing poor fluidization, deposits on the furnace walls, etc., or harmful metals being vaporized into the exhaust gas. In some cases, harmful effects such as damage to the furnace walls, hearth, etc. may occur. In addition, especially for those equipped with equipment for heat recovery by installing a heat transfer surface in the fluidized bed, excessive heat may be applied or the heat transfer surface may be exposed to high temperatures, resulting in shortened lifespan and performance. There was a problem with the surface. In order to solve these problems, the temperature of the fluidized bed is kept below a certain level (800-900°C) by controlling the amount of combustibles input and by injecting water or blowing air. In this case, there are disadvantages such as a decrease in throughput, an increase in consumption of the fluidizing medium, installation of large air supply equipment, and increase in operating costs.

[Purpose of the invention]

In order to eliminate such drawbacks, the present invention aims to increase the fluidized bed temperature by changing the amount of fluidized medium held in a swirling fluidized bed combustion furnace that has a throat section above the fluidized bed based on the temperature of the fluidized bed. The purpose is to provide a method for maintaining the temperature within a certain range.

[Detailed description of the invention]

The present invention provides a swirling fluidized bed combustion furnace having a throat section above the fluidized bed, in which the temperature of the fluidized bed is
If the temperature is below 680°C and there is sufficient air blowing equipment to the fluidized bed, control is performed to increase the amount of fluidized medium held in the combustion furnace, and when the temperature of the fluidized bed is above 700°C, the height of the fluidized bed layer is increased. This method of operating a fluidized bed combustion furnace is characterized in that the amount of fluidized medium held in the combustion furnace is controlled to be reduced if there is a margin.

The present inventors have conducted various studies in order to solve the problems of the conventional method described above. It has been found that the temperature of the fluidized bed can be maintained appropriately by this method.

Next, the present invention will be explained based on FIGS. 1 to 3.

FIG. 1 is a schematic cross-sectional view of a swirling flow type fluidized bed combustion furnace of the present invention, in which reference numeral 1 is an incinerator, 2 is an air supply device, 3 is an air chamber provided at the bottom of the incinerator, and 4 is a furnace. Floor (air chamber ceiling), 5 is a fluidized bed, 6 is a dust supply device, 7 is a discharge chute, 8 is a distributor, 9 is a fluidized medium supply device, 10 is a non-combustible material discharge device, 11 is a secondary air supply device , 12 is an exhaust gas discharge device, 13 is a deflector portion, 14 is a throat portion, 15 is a freeboard portion, 16 is a water supply device, and 17 is a water sprinkler device.

In the incinerator 1 shown in FIG. 1, the materials to be incinerated are supplied into a fluidized bed 5 from a dust supply device 6, and the fluidized bed 5 is filled with combustion air supplied from an air supply device 2 through an air chamber 3 and a hearth 4. It is fluidized by.
Due to the shape of the deflector 13 (the shape of the right furnace wall) and the velocity distribution of the blowing air from the air chamber, which is smaller on the left side and larger on the right side, the fluidized medium is given a swirling flow in the direction of the arrow shown in the figure. It is being For this reason, the supplied combustion material is combusted (primary combustion) while being swept away by the movement of the fluidized bed while diffusing within the fluidized bed, and some volatile matter, CO gas, other pyrolysis gases, fine powder, etc. rise. Secondary combustion occurs in the throat section 14 and freeboard section 15 above the fluidized bed as a result of the gas flow. During this time, a part of the fluid medium is extracted from the discharge chute 7 together with non-combustible materials contained in garbage, etc., and is separated into fluid media (sand) and non-combustible materials by a distributor, and the separated incineration media are A predetermined amount of the fluid is supplied to the combustion furnace via the fluidized medium supply device 9, while incombustibles are taken out of the system through the incombustibles discharge device 10. A fluidized medium supply device is usually provided with a fluidized medium storage tank.

Volatile matter, pyrolysis gas such as CO gas, or combustible fine powder from the fluidized bed is removed from residual oxygen in the combustion air or secondary air supplied from the secondary air supply device 11 in the throat section 14 and freeboard section 15. The generated exhaust gas is sent to the water sprinkler device 1.
After being partially cooled by the water introduced from 7, it is led to an exhaust gas treatment device (not shown) via an exhaust gas discharge device.

FIG. 2 shows the analysis results of gas in each part of the furnace. In Figure 2, a, b, c, d, e, f,
Each symbol of g is a, b, c, d, shown in Figure 1.
The graphs correspond to the symbols e, f, and g, and show the results of sampling and analyzing the gas at the positions of the symbols in FIG. 1. In addition, FIG. 2 shows the measurement of oxygen concentration at each part when secondary air is not supplied.

As can be seen from this figure, in the combustion furnace, the proportion of primary combustion is large in the fluidized bed sections a to c, but it can be seen that secondary combustion also occurs in the throat section and freeboard section. Combustion can thus be divided into primary combustion and secondary combustion. Naturally, the ratio of primary combustion to the total combustion increases as the height of the fluidized bed increases, that is, as the residence time of gas in the fluidized bed increases. In other words, even under similar operating conditions, the amount of heat generated in the fluidized bed increases as the amount of fluidized medium held in the furnace increases. The heat balance in the fluidized bed section is explained as follows.

Heat input q ₁ : Primary combustion heat (heat generated due to combustion in the fluidized bed) Heat input or heat output q ₂ : Heat input/output from the freeboard section/throat section (radiant heat or fluidized medium flows through the freeboard section or throat section) q ₃ : Heat required to change the temperature of the fluidized bed (heat due to the heat capacity of the furnace wall, fluidized medium, etc.) Heat output q ₄ : Sensible heat required to raise the temperature (blow air, supplied fuel, furnace Heat required to raise the temperature of the fluidized medium, etc. input from outside to the fluidized bed temperature) q ₅ : Latent heat required to raise the temperature (latent heat of vaporization of moisture, etc. contained in the supplied fuel, etc.) q ₆ : Entrained heat (heat required to raise the temperature of the fluidized bed) q ₇ : Heat radiation (heat escaping from the walls, floor, etc. that make up the fluidized bed) (heat accompanying the gas exiting from the fluidized bed, incombustibles extracted into the exhaust chute, fluidized media, etc.) This assumes operation, but differs slightly at startup, shutdown, auxiliary combustion, etc. When q ₁ increases by increasing the fluidized bed height by increasing the amount of fluidized medium held in the furnace, the fluidized bed temperature increases accordingly and q ₄ , q ₆ , and q ₇ increase, and q ₂ increases in the case of heat output and decreases in the case of heat input, and the balance changes so that heat is output at q ₃ . That is, depending on the heat balance, the larger the height of the fluidized bed, the higher the fluidized bed temperature. Part 3 outlines the changes in fluidized bed temperature, height, and air chamber pressure when the amount of fluidized medium in the furnace is changed in actual operation.
As shown in the figure.

In FIG. 3, the vertical axis shows the temperature of the fluidized bed or the height of the fluidized bed in the furnace and the pressure of the air chamber, and the horizontal axis shows time.

As can be seen from Figure 3, when the fluidized medium in the furnace begins to be withdrawn, the temperature of the fluidized bed decreases in proportion to the amount withdrawn, and naturally the height of the fluidized bed and the pressure in the air chamber also decrease. As the addition begins, the height of the fluidized bed and the pressure in the air chamber increase,
Further, when the addition of the fluid medium is finished, the temperature of the fluid gradually increases. Since the fluidized medium is added gradually in order to cause a sudden change in the temperature of the fluidized bed, the temperature is kept almost constant during the addition operation.

Next, the present invention will be explained in more detail based on the two-layer swirling flow type fluidized bed incinerator for municipal waste shown in FIG.

In FIG. 4, reference numeral 21 is a two-layer swirling flow fluidized bed incinerator, 22 is a forced air blower, 23 is an air preheating section, 24 is an air chamber for a moving bed, 25 is an air chamber for a fluidized bed, 26 is a fluidized bed, 27 is the freeboard section, 28
The discharge chute 29 is a non-combustible material removal conveyor, 30
3 is a vibrating sieve, 31 is a sand circulation elevator, 32 is a manual switching device, 33 is a sand storage tank, 34 is a manual switching valve, 3
5 is a garbage input hopper, 36 is a dust supply device, 37 is a secondary air blower, 38 is a cooling water tank, 39 is an injection water pressure pump, 40 is a furnace top cooling water spray nozzle,
41 is a gas cooling chamber, 42 is a hot water generator, 43 is a heat exchanger tube, 44 is a gas cooling water spray nozzle, 45 is an electrostatic precipitator, 46 is a furnace pressure control valve, 4
7 is an induced blower, 48 is a chimney, 49 is a non-combustible material storage tank, 50 is a fly ash storage tank, A is an ammeter, F is a flow meter,
M is a motor, P is a pressure gauge, and T is a thermometer.

In FIG. 4, primary air for both fluidization and combustion is sucked and pressurized by a forced air blower 22, and then preheated by exhaust gas in an air preheating section 23. Moving layer air chamber 2
4 and the fluidized bed air chamber 25, the air is introduced into the lower part of the fluidized bed through a hole provided in the ceiling thereof. A fluidized medium, such as sand, is fluidized by this air to form a fluidized bed 26, and a fluidized bed is formed in the central part. Forms a fluidized bed with swirling motion in the direction. The municipal waste put into the waste input hopper is fed from the top of the furnace onto the moving bed section by the dust supply device, and the municipal waste that falls into the moving bed section is covered by a fluidized medium that swirls from the fluidized bed section so as to cover it. It spreads as it buries itself and is accompanied by
The CO, volatile matter, and combustible particulates that are decomposed and burned in the fluidized bed are completely burned in the throat section and freeboard section 27, and the non-combustibles with small particle size are transferred to the furnace. It is emitted along with the gas rising inside. In addition, from the side wall of the freeboard part,
In many cases, pressurized secondary air for combustion is blown in by the secondary air blower 37 to reduce the load on the forced air blower 22, thereby reducing power and improving the heat balance in the fluidized bed. The combustion exhaust gas is transferred to the cooling water tank 38.
After being partially cooled by water sprayed from the top cooling water spray nozzle 40 by the water injection pressure pump 39, the water is led to the gas cooling chamber and heated to the hot water generator 4.
After heating the water flowing through the heat transfer tube 43 of No. 2, it is cooled by water sprayed from the gas cooling water spray nozzle 44, and then guided to the air preheating section 23, where it is heated to a heating furnace through heat exchange. After the combustion air sent is heated, it is discharged from the chimney 48 via an electrostatic precipitator 45, a furnace pressure control valve 46, and an induced blower 47. During this time, the gas cooling chamber 4
1. The fly ash separated from the exhaust gas by the air preheating section 23, the electrostatic precipitator 45, etc. is sent to the fly ash storage tank 50.

Large-diameter noncombustibles are blown by the fluidized medium to a discharge chute at the end of the hearth (ceiling of the air chamber), and are taken out of the furnace together with a portion of the fluidized medium by the noncombustibles removal conveyor 29 and passed through a vibrating sieve. At 30, the fluid is classified and discharged from the fluid medium. This is usually taken out in a fixed amount at fixed intervals. The fluidized medium separated by the vibrating sieve is lifted up by the sand circulation elevator 31 and thrown into the furnace again to form a fluidized medium circulation system.

A temperature detection end is inserted into the fluidized bed section 26. The temperature is for example 550~650℃ especially 600℃
If the temperature is so low that there is a concern about maintaining the following combustion, manually operate the switching valve 34 to take out the fluid medium from the sand storage tank 33 and transfer it to the sand circulation elevator 31 mentioned above. and add it to the furnace.
At this time, the height of the fluidized bed and the pressure in the air chamber gradually increase, so while monitoring the flow meter of the forced air blower so as not to change the air volume of the forced air blower, increase the rotation speed and increase the rotation speed if the motor rotation speed is controlled. For vane control, the vane is raised, and for damper control, the opening is increased to increase the wind pressure. vice versa
If the temperature of the fluidized bed part 26 is high, about 700°C to 850°C, the manual switching device 32 located between the sand circulation elevator 31 and the inlet part to the furnace is manually switched to change the flow of the fluidized medium to sand. It is extracted to the storage tank 33. In this case, it goes without saying that the blower should be operated in the opposite direction to that when adding the fluidized medium to the incinerator so as not to change the air volume of the blower. When removing the fluidized medium, the inside of the furnace is at a high temperature, so if the fluidized medium is removed at that temperature, the equipment will be damaged. Therefore, the discharge chute and the non-combustible material removal conveyor are cooled down to 50-300°C or at least 400°C using a water-cooled casing or the like. Due to its cooling capacity, the speed at which the fluidized medium is removed from the furnace is kept low, so it takes time to remove the fluidized medium, and in the example shown in Figure 3, it takes time to remove the fluidized medium.
It takes approximately 1 hour to withdraw the fluidized medium resulting in a fluidized bed temperature drop of 150°C. During this period, the height of the fluidized bed decreased by approximately 13%.

Conversely, when a fluidized medium is added, the temperature of the fluidized bed is temporarily lowered due to the sensible heat removed by the added fluidized medium. Therefore, when the purpose is to raise the temperature, it is necessary to add it little by little while observing the fluidized bed temperature. In the example shown in Figure 3, the fluidized bed temperature had already fallen to about 600℃, so the addition was continued gradually to prevent the fluidized bed temperature from dropping any further, increasing the height of the fluidized bed by about 15%. It took about 3 hours, but the final temperature of the fluidized bed was about 200℃.
The temperature rose to nearly 800℃.

As explained above, raising and lowering the temperature of the fluidized bed by adjusting the amount of fluidized medium held in the furnace has a great effect, but since it cannot be replaced with a simple response reaction, various methods are required to automatically perform this operation. Requires a circuit that includes information-based judgment. Therefore,
Rather, if the fluidized bed temperature is low and the height of the fluidized bed can still be raised, an alarm or display of "addition of fluidized medium" will be displayed on the control panel, etc., and the fluidized bed temperature will be high.
If the height of the fluidized bed can still be lowered, a practical method is to issue an alarm or display that says "fluidized medium has been removed" and manually adjust the amount of fluidized medium while monitoring the temperature of the fluidized bed. It is. Of course, in the case of an operation panel with a built-in microcomputer, it is also possible to perform automatic control by making judgments as explained in connection with FIG. 3. In addition, when withdrawing or adding a fluidized medium, after withdrawing or adding a predetermined amount, check the fluidized bed temperature after a pause period of withdrawal or addition according to the change in the amount of fluidized medium. It is safe to perform extraction or addition while determining whether to continue extraction or addition operations. In addition,
This pause time is longer for addition than for withdrawal. The amount to be extracted or added at one time is preferably about 20°C to 100°C depending on the temperature change, and about 1.5% to 15% depending on the height of the fluidized bed. The resting time is preferably about 5 to 50 minutes for extraction and 10 to 100 minutes for addition.

The rate of withdrawal or addition must also be kept below a certain value as described above. In the extraction operation, it is safer and requires less operation if the amount of extraction during normal circulation of the fluid medium is continued.

Further, in the case of manual operation, it is desirable to issue an alarm or display when appropriate operating conditions for the extraction or addition operation are reached to ensure that the operator executes the extraction or addition operation.

Next, we will discuss how the height of the fluidized bed is measured.

Visual confirmation from a manhole etc. when the operation is stopped or actual measurement by lowering a weight are reliable methods, but they have the disadvantage that they cannot be performed during operation.

The pressure in the air chamber (indicated by 3 in FIG. 1 and 24 or 25 in FIG. 4) is commonly used as a means for measuring during operation. In other words, "air chamber pressure" is equal to "furnace pressure + pressure loss passing through the fluidized bed + blowout pressure loss from the air chamber",
The air chamber pressure or furnace pressure can be easily measured, and the blowout pressure loss from the air chamber can also be easily calculated from the blowout air volume, pressure, temperature, etc., and the pressure loss passing through the fluidized bed is calculated by calculating the apparent weight per unit area of the fluidized bed and the fluidized bed pressure loss. Since it is approximately equal to the product of the layer heights, it can be easily determined using the following formula.

[Fluidized bed height] = [Air chamber pressure] - [Furnace pressure] - [
Blowout pressure loss from the air chamber] / [apparent weight per unit volume of the fluidized bed] By the way, the maximum point of the fluidized bed bed height is usually determined by the amount of air flowing into the fluidized bed from the facility's forced feeder, etc., depending on the furnace structure. It depends on the capacity of the blowing equipment. This is because the maximum operating power of the air blowing equipment is determined based on economic efficiency, and the capacity of other equipment such as the incinerator and sand storage tank is set accordingly. Therefore, there is no need to particularly check the height of the fluidized bed during operation.

In a device that attempts to control wind pressure by controlling the rotation speed of the feeder drive section, it is only necessary to know where the rotation speed is within the variable range, and in the case of suction vane control or damper control, the opening degree can also be determined. It is sufficient to know where in the variable range the position is.

The meaning of “the height of the fluidized bed can still be lowered” often comes from the structural limitations of the furnace. That is, it depends on the various detection ends provided in the fluidized bed section, the dust supply device of the example shown in FIG. 1, the position of the deflector, etc. Therefore, the air chamber pressure and forced air blower wind pressure control position at the height of the fluidized bed can be confirmed and checked using those values. Therefore, although it may be somewhat indirect to use such information in place of information regarding the height of the fluidized bed, it is practically acceptable.

The amount of fluidized media tends to increase gradually in municipal waste incinerators, etc. because there are things that can become fluidized media, such as sand and debris that are mixed in with the combustion materials, and in industrial waste, including paper sludge incinerators. In some cases, such as in a material incinerator, the fluidized medium gradually decreases as it is consumed, but the amount of change is not that large. Therefore, if you measure the approximate amount when the operation is stopped, the amount consumed or the amount of combustibles brought in per unit time and unit volume, the amount to be extracted can be easily determined based on the capacity of the non-combustibles removal conveyor shown in Figure 4. Since the addition amount can be easily determined from the addition rate and addition time, the approximate amount of fluidized medium held in the furnace can be estimated. If such management is used in combination, safer operations can be achieved.

〔Effect of the invention〕

The present invention is capable of reducing operating costs in a fluidized bed combustion furnace by changing the height of the fluidized bed in response to changes in the composition and moisture content of the material to be combusted.
As a result of being able to operate at an appropriate fluidized bed temperature, damage to the incinerator due to an increase in fluidized bed temperature can be reduced and the life of the fluidized medium can be extended.

[Brief explanation of drawings]

Figure 1 is a cross-sectional schematic diagram of a swirling fluidized bed combustion furnace, Figure 2 is a chart showing the analysis results of gas in each part of the furnace shown in Figure 1, and Figure 3 is a diagram showing the extraction and addition of fluidized media. a chart showing the changes in the temperature of the fluidized bed, the height of the fluidized bed and the air chamber pressure during the operation;
FIG. 4 shows a cross-sectional schematic diagram of a two-layer swirling flow fluidized bed incinerator. 1... Combustion furnace, 2... Air supply device, 3... Air chamber, 4... Hearth, 5... Fluidized bed, 6... Dust supply device, 8... Distributor, 9... Fluidized medium feeding device,
DESCRIPTION OF SYMBOLS 10... Incombustible discharge device, 13... Deflector part, 14... Throat part, 21... Two-layer swirl flow type fluidized bed incinerator, 22... Forced blower, 23...
Air preheating section, 24...Air chamber for moving layer, 25...
Air chamber for fluidized bed, 26... Fluidized bed, 30... Vibrating sieve, 31... Sand circulation elevator, 32... Manual switching device, 33... Sand storage tank, 34... Manual switching valve,
35... Garbage input hopper, 36... Dust supply device,
37...Secondary air blower, 41...Gas cooling room,
45...Electrostatic precipitator, 48...Chimney.

Claims (1)

[Claims] 1. In a swirling fluidized bed combustion furnace having a throat section above the fluidized bed, if the temperature of the fluidized bed is 680°C or less and there is sufficient air blowing equipment to the fluidized bed, The amount of fluidized medium held in the combustion furnace is controlled to increase, and when the temperature of the fluidized bed is 700°C or higher and there is sufficient height of the fluidized bed layer, the amount of fluidized medium held in the combustion furnace is controlled to be decreased. A method of operating a swirling fluidized bed combustion furnace having a throat section above the fluidized bed. 2. A patent claim that stabilizes combustion in a combustion furnace by changing the amount of fluidized medium held in the combustion furnace by a predetermined constant amount, and then stopping the change in the amount held for a certain period of time according to the amount of change. A method for operating a swirling fluidized bed combustion furnace having a throat section above the fluidized bed according to scope 1. 3. A throat section in the upper part of the fluidized bed according to claim 1, which detects the margin of the air blowing equipment to the fluidized bed or the margin of the fluidized bed bed height by the position within the adjustment range of the air pressure adjustment mechanism for blowing into the fluidized bed. A method of operating a swirling fluidized bed combustion furnace having: 4. In the upper part of the fluidized bed according to claim 1, which detects the margin of the air blowing equipment to the fluidized bed or the margin of the height of the fluidized bed layer based on the pressure of the air chamber for blowing air into the fluidized bed. A method of operating a swirling fluidized bed combustion furnace having a throat section.