JP3305175B2 - Sand bed combustion rate adjustment method for fluidized bed furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to combustion control in a sand bed of a fluidized-bed furnace, and more particularly to a method of adjusting a burning rate of a sand bed in a fluidized-bed furnace.

[0002]

2. Description of the Related Art Conventionally, a fluidized bed furnace, which is most frequently used as an incinerator for sludge generated in a sewage treatment plant, forms a sand layer by accumulating sand at a furnace bottom, and a space above the sand layer is freeboarded. The sand layer and the free board form a combustion zone in the furnace. The sand layer flows by high-temperature high-pressure air supplied from below to become a fluidized bed, and instantaneously dries and incinerates waste put in the furnace in the sand. At this time, since the sand has a very large heat capacity and a high heat transfer coefficient, it supplies heat to the sludge as waste at a high speed for drying and ignition. On the other hand, the combustion heat generated by the combustion of the waste keeps the sand at a high temperature and enables continuous instantaneous combustion. After the waste is burned instantaneously, the ash becomes fly ash and scatters into the gas, and is collected by a dust collector. Taken out of The incineration residue is separated from the sand by a screen and taken out, and the separated sand is circulated into the furnace from the top of the furnace.

[0003]

In the conventional construction described above, each of the combustion zones of the fluidized bed and the freeboard has an appropriate combustion rate defined by the furnace structure, the amount of fluidized sand, and the sludge properties. (The amount of combustion components burned in each combustion zone and the total amount of combustion components of the combustion material charged into the furnace)
When operating the furnace, it is necessary to maintain the respective combustion rates of the fluidized bed and the freeboard at appropriate values. In the fluidized bed, it is necessary to maintain a heat balance between heat of absorption such as drying and heat of combustion.

For this purpose, the amount of heat supplied together with high-pressure air from below the sand layer is adjusted to control the temperature of the fluidized bed,
The combustion rate is controlled by adjusting the amount of sludge introduced into the furnace and the amount of secondary combustion air supplied to the freeboard.

[0005] However, the properties of the sludge, which is a combustion product (moisture,
Since the heat generation amount is not constant, the heat balance in the fluidized bed is lost, and when the combustible component gasified in the fluidized bed and burned in the freeboard increases, the combustion rate in the freeboard increases. Therefore, there has been a problem that the freeboard temperature rises and the high-temperature exhaust gas has a thermal adverse effect on the exhaust gas treatment equipment at the latter stage of the furnace.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a method for adjusting a burning rate of a sand bed in a fluidized-bed furnace capable of controlling a burning rate in a fluidized bed to an arbitrary value.

[0007]

In order to solve the above-mentioned problems, a method for adjusting the burning rate of a sand layer of a fluidized-bed furnace according to the present invention has a sand layer at the bottom of the furnace and supplies the sand from below the sand layer by a fluidized air supply system. The high-pressure fluidized air causes the sand in the sand layer to flow to form a fluidized bed, and the burned material introduced into the furnace is dried and burned in the fluidized bed, and the sand discharged from the sand discharge port together with the incineration residue is circulated through the sand. In a fluidized bed furnace that is circulated into the furnace through the system, the temperature in the fluidized bed is measured as the sand bed temperature, and the temperature in the freeboard formed in the furnace space above the fluidized bed is measured as the freeboard temperature. When the measured temperature difference obtained by subtracting the sand layer temperature from the temperature becomes larger than the set value, the amount of fluidized sand flowing in the fluidized bed is increased by adding fluidized sand from the outside to the sand circulation system. It is obtained by the.

Further, when the measured temperature difference becomes larger than a set value, the amount of flowing air supplied to the sand layer from the flowing air supply system is reduced to make the fluidized state of the fluidized bed slow. .

[0009] Further, an amount of air commensurate with the decrease in the amount of flowing air is supplied to the freeboard as air for secondary combustion. In addition, adjustment of the amount of fluidized sand and determination of the amount of fluidized The amount and the air distribution ratio of the secondary combustion air amount are appropriately adjusted.

[0010] With the above configuration, when the burning rate of the sand layer decreases due to a change in the properties of the burned material and the unburned components flowing into the freeboard from the fluidized bed increase, the amount of combustion heat generated on the freeboard by the on-bed combustion increases. The measured temperature difference tends to increase as a result. Therefore, by using the measured temperature difference as an index indicating the combustion rate, automatic control based on objective numerical values becomes possible without depending on the subjectivity of the operator.

For this reason, when the measured temperature difference becomes larger than the set value, it is determined that the sand layer combustion rate has fallen below the set value, and the amount of flowing sand is increased. This increase in the amount of fluidized sand results in an increase in the heat capacity and the amount of heat conduction in the fluidized bed, resulting in an increase in the sand layer combustion rate.

When the measured temperature difference becomes larger than a set value, the flow rate of the fluidized bed is reduced by reducing the amount of flowing air. This slowing down of the fluidized state results in an increase in the residence time of the combustion material in the fluidized bed, resulting in an increase in the sand layer combustion rate.

Further, when the measured temperature difference becomes larger than the set value, an amount of air corresponding to the decrease in the amount of flowing air is supplied to the freeboard as secondary combustion air. The supply of the secondary combustion air secures the amount of oxygen necessary for combustion in the freeboard, and the low-temperature secondary combustion air is mixed into the freeboard atmosphere gas, thereby lowering the freeboard temperature. It is possible to prevent adverse effects on the downstream exhaust gas treatment facility.

Further, an increase in the amount of fluidized sand acts as an increase in the load on the fluidized air, and also acts as a factor in slowing down the fluidized state of the fluidized bed. Repeated reduction of the amount leads to excessive slowing of the fluidized state, resulting in a loss of heat balance in the fluidized bed. For this reason, the operation state is determined based on the operation index (PV: process value) such as the current value of the flowing sand amount, the current value of the flowing air amount, the current value of the furnace temperature, etc., and the flow is appropriately adjusted according to the operation state. The balance of heat in the fluidized bed is maintained by appropriately adjusting the amount of sand and the distribution ratio of air between the amount of flowing air and the amount of air for secondary combustion.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a fluidized bed furnace 1 has a sand layer 2 formed by storing sand at a bottom portion, a top portion communicating with a flue 3, and a sand inlet 4 for charging sand at an upper portion. And a combustion material inlet 5 for charging a dewatered cake to be incinerated.

The fluidized bed furnace 1 has a sand discharge port 6 and a diffuser 7 on the lower side, and a fluidized air supply system 8 is connected to the diffuser 7. The flowing air supply system 8 has a hot blast stove 9 communicating with the diffuser 7, and the hot blast stove 9 has a burner for burning fuel supplied by a fuel pump 10. The air passage 11 constituting the flowing air supply system 8 has a front end connected to the hot stove 9, a base end communicating with the discharge port of the flow blower 12, and utilizing waste heat of exhaust gas from the flue 3 on the way. Air preheater 1
3 is interposed. The air passage 11 branches off upstream of the air preheater 13, the branch passage 14 communicates with the free board 15 of the fluidized bed furnace 1, and a first air volume regulator 16 a is provided on the suction side of the fluid blower 12. , The second on the fork 14
An air volume controller 17a is provided. Further, a first air flow meter 16b is provided at a position downstream of the branch point of the air passage 11;
The branch passage 11 is provided with a second airflow meter 17b.

A sand circulation system 18 is connected to the sand discharge port 6. The sand circulation system 18 has a conveyance path 19 constituted by a bucket conveyor, a screw conveyor, or the like. 20, a vibrating sieve 21 and a sand hopper 22 for separating combustion residues from the discharged sand are provided. Further, a sand replenishment system 18a communicates with the sand inlet 4.

The fluidized bed furnace 1 has a first thermometer 23 for measuring the sand layer temperature of the sand layer (fluidized bed) 2 and a free board temperature of the free board 15 for measuring various physical quantities serving as operation indexes. A second thermometer 24 for measuring and a sand amount measuring means (for example, a device for measuring the thickness of the sand layer 2 by an ultrasonic wave or a load) for measuring the sand amount in the sand layer 2 are provided. The control device 26 for controlling the operation of the fluidized-bed furnace 1 includes a first thermometer 23, a second thermometer 24, and various controls such as a first air volume regulator 16a and a second air volume regulator 17a in the fluidized air supply system 8. Element and first air flow meter 16b and second air flow meter 17b
And other control elements such as a bucket conveyor, a screw conveyor and a rotary valve 21 in the sand circulation system 18, and a signal line of the sand amount measuring means 25.

In the above configuration, the control device 26
Judgment is performed based on the values of various operation indices indicating the operation state of the furnace, such as the current value of the amount of flowing sand, the current value of the amount of flowing air, and the current value of the temperature in the furnace, and the control described below is performed.

At the time of the incineration operation, the air blown by the fluid blower 12 is supplied to the hot blast stove 9 through the air preheater 13, and the high-temperature, high-pressure flowing air accompanied by the combustion heat generated in the hot blast stove 9 is passed through the diffuser 7 to form 2 and the sand of the sand layer 2 is fluidized to form a fluidized bed. In this state, the dewatered cake as a combustion product is charged into the furnace from the combustion material input port 5, and the input combustion product is dried and burned in the fluidized bed, and the sand discharge port 6
The sand is discharged together with the incineration residue, and the discharged sand is circulated into the furnace through a sand circulation system 18. In the sand circulation system 18, the combustion residue is classified from the sand by the vibrating sieve 21, the sand is stored in the sand hopper 22, the sand is replenished, and the sand is returned to the sand inlet 4 through the transport path 19.

When the burning rate of the sand layer decreases due to a change in the properties of the combustion material (water content of the dewatered cake, calorific value) or the like, and the unburned components flowing into the free board 15 from the sand layer (fluidized bed) 2 increase, The amount of heat of combustion generated in the freeboard 15 by the on-layer combustion increases, and the temperature of the freeboard 15 increases. Therefore, the temperature in the sand layer (fluidized bed) 2 is measured as the sand layer temperature by the first thermometer 23, and the temperature in the freeboard 15 is measured as the freeboard temperature by the second thermometer 24. Is used as an index indicating the combustion rate. By using this physical quantity as a driving index, automatic control based on objective numerical values becomes possible without relying on the subjectivity of the operator.

When the measured temperature difference obtained by subtracting the sand layer temperature from the freeboard temperature becomes larger than a set value, the control device 26 replenishes the sand replenishment system 18a with the fluidized sand to the sand circulation system 18 so that the sand layer is replenished. (Fluidized bed) The amount of fluidized sand flowing in the fluidized bed 2 is increased. Since the sand has a high heat transfer coefficient and a large heat capacity, an increase in the amount of flowing sand results in an increase in the heat capacity and the amount of heat conduction in the sand layer 2, resulting in an increase in the sand layer combustion rate.

When the measured temperature difference becomes larger than the set value, the controller 26 adjusts the first air volume controller 16a and the second air volume controller 17a to flow from the air passage 11 to the hot air passage 9. Reduce the amount of flowing air to reduce the amount of flowing air,
The flow state of the sand layer (fluidized bed) 2 is made slow. This slowing down of the fluidized state results in an increase in the residence time of the combustion material in the fluidized bed, resulting in an increase in the sand layer combustion rate.

At this time, an amount of air corresponding to the reduced amount of the flowing air is supplied to the free board 15 through the branch passage 14 as the air for secondary combustion. The supply of the secondary combustion air secures the amount of oxygen necessary for combustion in the freeboard 15 and ensures that low-temperature secondary combustion air that does not pass through the air preheater 13 is mixed into the atmosphere gas of the freeboard 15. As a result, the freeboard temperature is reduced, and adverse effects on the subsequent exhaust gas treatment facility can be prevented.

The increase in the amount of fluidized sand acts as an increase in the load on the fluidized air, and also acts as a factor in slowing down the fluidized state of the fluidized bed. If the amount is repeatedly reduced, the fluidized state may be excessively slowed, which may result in a loss of heat balance in the fluidized bed. For this reason, the control device 26
The operating state is determined on the basis of an operation index (PV: process value) such as the current value of the flowing sand amount, the current value of the flowing air amount, the current value of the furnace temperature, and the like. The heat balance in the sand layer (fluidized bed) 2 is maintained by appropriately performing the adjustment and the adjustment of the air distribution ratio between the amount of the flowing air and the amount of the secondary combustion air.

[0026]

As described above, according to the present invention, by using the measured temperature difference between the freeboard and the sand layer as an index indicating the combustion rate, an objective numerical value can be obtained without depending on the subjectivity of the worker. The automatic control based on the above becomes possible. Since an increase in the amount of fluidized sand results in an increase in heat capacity and an amount of heat conduction in the fluidized bed, it can be used as a control factor for increasing the sand layer combustion rate. Slowing of the fluidized state increases the residence time of the combustion products in the fluidized bed, and thus can be used as a control factor for increasing the sand layer burning rate. By mixing the low-temperature secondary combustion air, it is possible to lower the freeboard temperature and prevent adverse effects on the subsequent exhaust gas treatment facility. The heat balance in the fluidized bed can be maintained by appropriately adjusting the amount of fluidized sand and adjusting the distribution ratio of air between the amount of flowing air and the amount of secondary combustion air in accordance with the operation state. .

[Brief description of the drawings]

FIG. 1 is a schematic view of a fluidized bed furnace showing an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fluidized bed furnace 2 sand layer 6 sand discharge port 7 wind box 8 flowing air supply system 9 hot blast stove 11 blower path 12 fluid blower 15 free board 16a first air volume controller 17a second air volume controller 18 sand circulation system 18a sand replenishment system 19 Conveying path 23 First thermometer 24 Second thermometer 26 Control device

Claims (4)

(57) [Claims] 1. A furnace having a sand layer at the bottom thereof, wherein a high-pressure flowing air supplied from below the sand layer by a flowing air supply system causes the sand in the sand layer to flow to form a fluidized bed. In a fluidized-bed furnace in which sand is dried and burned in a fluidized bed and discharged together with incineration residues from the sand discharge port into the furnace through a sand circulation system, the temperature in the fluidized bed is measured as the sand bed temperature, Measure the temperature of the freeboard formed in the furnace space above the freeboard as the freeboard temperature.If the measured temperature difference, which is obtained by subtracting the sand layer temperature from the freeboard temperature, becomes larger than the set value, the sand circulation system A method for adjusting a burning rate of a sand layer in a fluidized bed furnace, wherein the amount of flowing sand flowing in the fluidized bed is increased by adding the flowing sand. 2. The method according to claim 1, wherein when the measured temperature difference becomes larger than a set value, the amount of flowing air supplied to the sand layer from the flowing air supply system is reduced to make the fluidized state of the fluidized bed slower. Item 3. The method for adjusting a burning rate of a sand layer of a fluidized bed furnace according to Item 1. 3. The method for adjusting a sand layer combustion rate of a fluidized bed furnace according to claim 2, wherein an amount of air corresponding to the amount of decrease in the amount of flowing air is supplied to the freeboard as air for secondary combustion. 4. A method for adjusting the amount of fluidized sand by judging based on values of various operation indices indicating the operating state of the furnace, such as the current value of the fluidized sand amount, the current value of the fluidized air amount, and the current value of the furnace temperature. 4. The method for adjusting a sand layer combustion rate of a fluidized bed furnace according to claim 3, wherein the air distribution ratio between the amount of flowing air and the amount of air for secondary combustion is adjusted appropriately.