JPH0372882B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method of operating a fluidized bed boiler when the load is reduced, and more specifically, a plurality of air/fuel systems are individually provided in the fluidized bed, and a plurality of air/fuel systems are provided individually in the fluidized bed. The present invention relates to an operating method for stopping a cell to be stopped among the plurality of cells in response to a reduction in the load of a boiler among layer regions (hereinafter referred to as cells) that are substantially divided into layers.

In a fluidized bed boiler where the fluidized bed is divided into multiple cells and each cell has multiple supply air and fuel systems, when the boiler load is reduced, the fluidized bed temperature also decreases as the load decreases. I will do it. In such a boiler, an appropriate temperature range exists for the fluidized bed temperature in order to maintain stable combustion. Therefore, if the load is lowered while each cell is left in operation, the bed temperature will drop below the lower limit of the appropriate temperature range, making the boiler unusable. Therefore, it is conceivable that by stopping one of the plurality of supply air/fuel systems, one cell in the fluidized bed transitions from the fluidized bed state to the fixed bed state and stops the cell. In this case, in other cells to which air and fuel are being supplied, in order to maintain the flow state, the amount of air and fuel supplied to the stopped cell is incremented to supply air and fuel corresponding to the boiler load. , the layer temperature of this cell increases and falls within the proper temperature range. Thereafter, by continuing to appropriately control the supply air and fuel flow rates of the remaining cells other than the stopped cells, it becomes possible to further reduce the boiler load. However, in reality, when such a cell is to be stopped, the following problems occur, and thus it has not been possible to stop the cell. In other words, when the air flow rate is stopped, the unburned matter in the cell burns in a lack of oxygen,
Since the heat is not radiated, the temperature becomes high, and the ash melts and condenses, obstructing the flow and adhering to the heat exchanger tubes, causing damage to the boiler. Furthermore, if the cell is suddenly stopped, the amount of heat transfer decreases, and as a result, the steam pressure and steam temperature from the steam pipe suddenly decrease. In other words, the quality of the steam deteriorates.

The purpose of the present invention is to solve the above-mentioned technical problems,
When shutting down the cell when the boiler load is reduced, the ash in the cell is prevented from melting and condensing, and the quality of the steam flowing out from the steam pipe, that is, the steam pressure and temperature, can be maintained constant. An object of the present invention is to provide a method of operating a certain fluidized bed boiler when the load is reduced.

The present invention reduces the amount of fuel and air in a cell that is a fluidized bed region divided into a plurality of regions according to a decrease in load in a cell that is to be stopped, and a plurality of thermometers are provided in the cell that is to be stopped. to detect the temperature,
The value of the air flow rate is determined so that the supply of fuel to the cell to be stopped is stopped, the combustion of unburned fuel is completed, and the movement of layer material from other flowing cells is small. Based on the state of dispersion of the temperature detected by each thermometer, air is continued to be supplied to the cell to be stopped at the flow rate of the above value, and after the combustion of the unburned material is completed, the steam pressure and Determine the rate of change in decreasing time so that the temperature remains constant,
This is a method of operating a fluidized bed boiler when the load is reduced, which is characterized by gradually reducing the amount of air at the determined reduction time change rate.

In addition, the present invention reduces the fuel and air in the cell that is a fluidized bed area divided into a plurality of cells according to the decrease in load in the cell that is to be stopped, and attaches a plurality of thermometers to the cell that is desired to be stopped. A fuel cell is installed to detect the temperature, and the fuel supply to the cell to be stopped is stopped so that the combustion of unburned fuel is completed and the movement of bed material from other flowing cells is reduced. The value of the air flow rate is determined based on the state of dispersion of the temperature detected by each thermometer, and air is continued to be supplied to the cell to be stopped at the flow rate of the above value, and after the combustion of unburned material is completed. , determine the decreasing time change rate so that the steam pressure and steam temperature are constant, and gradually decrease the air at the determined decreasing time change rate, and in the middle of gradually decreasing the air, the layer temperature This method of operating a fluidized bed boiler during load reduction is characterized by increasing the air reduction time change rate when the temperature of the ash in the cell rises to near the melting temperature.

FIG. 1 is an overall system diagram of an embodiment of the present invention. The fluidized bed boiler 1 has a fluidized bed 2. The fluidized bed 2 consists of a bed material such as limestone, silica sand, etc. In this fluidized bed 2, cells 4 and 5 having two air/fuel systems are formed. In addition, as shown in the second figure, there is a partition wall 3 having a fluidized bed at least in the upper part.
It may be divided into a plurality of cells by.

Primary combustion air from an air supply means (not shown) is regulated by an air flow rate adjustment means 50 and supplied to the cell 4 from below the cell 4 through the passage 6. In addition, the cell 4 has a fuel supply means (not shown).
Fuel, such as lime, is supplied from above or below the cell 4 through a flow path 8 while being regulated by a fuel flow rate regulating means 7. As for the other cell 5, air flow rate adjustment means 9 and fuel flow rate adjustment means 11 are provided similarly to the cell 4, and each of the adjustment means 9, 1
Air and fuel conditioned by the flow path 10
and are supplied to the cell 5 via the flow path 12, respectively.

When air and fuel are supplied to the fluidized bed 2 in this manner, the fuel is combusted within the fluidized bed 2, and the combustion exhaust gas is discharged to the outside through the flow path 13.
The combustion energy of the fluidized bed 2 is absorbed by a fluid, such as steam, passing through the heat transfer tube 14, and the heated steam passes through a flow path 15 and is supplied to a driving source such as a turbine. The temperature of the steam passing through the flow path 15 is detected by a temperature detector 30, and a detection signal is sent to a control circuit 32. A steam temperature setting signal 31 is input to the control circuit 32, and when the steam temperature is higher than the set value, the valve 33 is opened to supply water to an injection means 34 such as a sprayer. This injection means 34 injects water into the flow path 15 to cool the steam temperature. The flow rate of water injected from the injection means 34 is controlled by the control circuit 32 via the valve 33, so that the steam temperature can always be maintained at a constant value.

Further, the pressure and flow rate of the steam flowing through the flow path 15 are detected by a pressure detector 16 and a flow rate detector 17. Signals from the detectors 16 and 17 are input to a calculator 18. This calculator 18 calculates air and fuel flow rates in normal mode to enable optimal operation. That is, this calculator 18 calculates the supply air flow rate and fuel flow rate corresponding to the signal from the steam flow rate detector 17 as the boiler load, and also calculates the air flow rate and fuel flow rate in response to fluctuations in the signal from the steam pressure detector 16. Correctly calculate and. In the normal mode, the result calculated by the calculator 18 is sent to the air flow rate control means 50 via the line 19, the stop calculator 20 of the cell 4, and the line 21, and is sent via the line 22. A fuel flow rate command signal is sent to the flow rate adjustment means 7. The flow rate adjusting means 50 adjusts the air flow rate based on the air flow command signal and supplies the air to the cell 4 . The flow rate adjusting means 7 adjusts the fuel flow rate based on the fuel flow rate command signal and supplies the fuel to the cells 4 .
Further, a signal from the computing unit 18 is sent via a line 23 to a stopping computing unit 24 of the cell 5, and an air flow rate command signal is further sent to the flow rate adjusting means 9 via a line 25. Further, a fuel flow rate command signal is sent to the flow rate adjusting means 11 via the line 26.
The flow rate adjustment means 9 and the flow rate adjustment means 11 adjust a predetermined flow rate of air/fuel based on the above-mentioned signals and supply the air/fuel to the cell 5. In addition, cell stop arithmetic unit 2
0 and 24, in the above-mentioned normal mode, the signals of the same level as the signal from the arithmetic unit 18 are sent to the lines 21, 22,
Send on 25th and 26th.

The cell 4 is provided with a plurality of temperature detectors 27, and layer temperature detection signals from the temperature detectors 27 are sent to the stop calculation unit 20 of the cell 4. In addition, cell 5 also has a plurality of temperature detectors 28 like cell 4.
is provided, and the layer temperature detection signal is sent to the stop arithmetic unit 24 of the cell 5. When the stop calculation unit 20 of the cell 4 determines the start of cell stop based on the steam flow rate detection signal, the steam pressure detection signal, and the layer temperature detection signal of the cell 4, the calculation unit 1 in the normal mode
8, and sends a new supply air flow rate command signal and a new supply fuel flow rate command signal to the flow rate adjustment means 50 and the flow rate adjustment means 7 as the calculation outputs of the stop calculation unit 20, respectively, and the sent signals A predetermined flow rate of air/fuel is supplied to the cell 4 based on the following. Although the case where cell 4 is stopped has been described here, the case where cell 5 is stopped is also the same as cell 4.

FIG. 3 is a graph showing the relationship between boiler load and bed temperature. When the load on the boiler is reduced while the two cells 4 and 5 are in operation, the bed temperature decreases from the upper limit T1 of the appropriate temperature range to the lower limit T2 as indicated by reference numeral 11. If the bed temperature becomes lower than the lower limit value T2, the boiler cannot be operated properly as described above. Therefore, when the bed temperature reaches the lower limit value T2, the cell 4 is stopped by the cell stop method according to the present invention. The temperature is raised again to the upper limit T1.
In this way, it is possible to further reduce the boiler load by putting only the cell 5 into operation, as indicated by reference numeral l2. In a fluidized bed boiler having a plurality of cells, a desired boiler load can be achieved by sequentially stopping the cells in this manner.

FIG. 4 is a flowchart of an operating method when the boiler load is reduced according to the present invention. Assume that the boiler load is reduced from 100% to 50% as shown in Figure 3. Note that fluidized bed 2 is used to simplify the explanation.
is divided into two equal parts, that is, cell 4 and cell 5 are equal. First, line 19,2
0 are sent to the air flow regulating means 50, 9 and the fuel flow regulating means 7, 11 to throttle the fuel and air supplied to the cells 4, 5. The air flow rate supplied to the cell 4 narrowed in this way is a predetermined value.
When it becomes less than V1, cell stop operation is started at step n1. Note that this constant value V1 is determined by the lower limit of the layer temperature.
This is the air flow rate when T2 is reached. The order of cells to be stopped is determined in advance, and in this embodiment, cell 4 is stopped first. In step n2, the air and fuel flow rates of the cell 5 are supplied based on the calculation output from the calculator 18, and in the other cell 4, the air flow rate and the fuel flow rate are respectively adjusted by the flow rate adjustment means 50 and 7. This narrowed air flow rate is V2 (<
It is determined whether or not V1) has been reached. Here, the air flow rate V2 is when the flow state of cell 4 is not intense,
In other words, this is the flow rate at which the movement of layer material from other flowing cells 5 is reduced. As an indicator, it is 1 to 5 times, preferably 1.5 to 2.5 times, the air flow rate equivalent to the flow start speed, and in a flow state, the bed temperature indicated by the plurality of detectors 27 shows almost the same value, and the bed material is the same. Although the air moves, they exhibit separate movements at this air flow rate.In other words, there are variations in the temperature detected by the plurality of thermometers 27 installed in the cell 4 whose operation is to be stopped, and the detected temperature varies. Based on the state of variation, the value of the air flow rate to be supplied to the cell 4 to be stopped is determined, and this value is set as V2. At step n2, it is determined whether the air flow rate is V2 or not. If it is equal to or higher than V2, the process moves to step n3, where the fuel and air flow rates are further reduced, and when the air flow rate reaches V2, the process moves to step n5. If the air flow rate is less than V2 at step n2, the process moves to step n4, where the fuel supply is stopped and the air flow rate is increased to V2.The process returns to step n2 again, and when the air flow rate reaches V2, the process moves to step n5.

In step n5, the supplied fuel flow rate is gradually decreased while maintaining the air flow rate at V2.
Completely stops at n6. In steps n5 and n6, the fuel supply is stopped and air is continued to be supplied to completely burn the fuel in the cell 4. Let this combustion time be W. In other words, the combustion time W is determined by changing the cell 4 from a state of heavy flow to a state of low flow so that fuel does not enter from the cell 5, stopping the fuel supply to the cell 4, and supplying air to the cell 4. This is the time required to completely burn out all unburned matter. Although this combustion time W depends on the type of coal used as fuel, it is approximately 2 to 5 minutes. By providing the fuel time W in this way, it is possible to prevent the unburned content in the cell 4 from being incompletely combusted and reaching a high temperature.
Therefore, melting and condensation of ash are eliminated and
NOX is suppressed.

Even before such combustion time W elapses, it is determined in step n6a whether the O ₂ concentration or NOX concentration of the exhaust gas is equal to or higher than a certain value α, and if it is equal to or higher than α, it is determined that the unburned matter has been burned out. as step n8
Move to. Here, α is, for example, the pollution control concentration. If it is less than α, the process moves to step n7, where it is determined whether or not the time W has ended, and if the time W has elapsed, the process moves to step n8.

In step n8, the supply air is gradually narrowed down. In this way, at the same time as the unburned content in cell 4 is burned out, the air is gradually narrowed down.
NOX generation is suppressed. Referring to Figure 5,
When the air flow rate is gradually decreased after the combustion time W has elapsed, as shown by the solid line l3 in FIG. 5, the cell 4 gradually transitions from the fluidized bed state to the fixed bed state. Therefore, a sudden drop in the amount of heat transferred to the heat transfer tubes 14 can be avoided, and the steam pressure and steam temperature can be maintained at approximately constant values as shown by the solid line l4 in FIG. 5 2 and the solid line l5 in FIG. 5 3. It becomes possible to do so. If the air flow rate is suddenly stopped as shown by the broken line l3a in FIG. 5, the broken line l4a in FIG. 52 and the broken line l4a in FIG.
As shown by l5a, the steam pressure and steam temperature suddenly decrease and fluctuate. In other words, the quality of the steam deteriorates.

At step n8, the air flow rate is gradually reduced.
It is determined whether step n9 is zero or not. If it is zero, the process moves to step n12, the supply air is completely stopped, and the operation of the cell 4 is stopped and completed in step n13.

If the air flow rate is not zero in step n9, the process moves to step n10, where it is determined whether the layer temperature of the cell 4 is equal to or higher than T3. Here, T3 is a temperature close to the melting temperature of clinker, for example 950°.

When the layer temperature of the cell 4 is T3 or higher, the process moves from step n10 to step n11, and the air flow rate is rapidly reduced. The operation in step n11 prevents the cell 4 from burning and extinguishes the fire.
Therefore, clinker generation is prevented. When the layer temperature of the cell 4 is less than T3, the process returns to step n8, and the air flow rate is gradually reduced at a normal slow speed.

At step n11, the air flow rate is rapidly reduced, and when the air flow rate becomes completely zero, step n12
Then, the process moves to step n13, and the cell 4 is completely stopped.

As described above, according to the present invention, it is possible to completely burn out the unburned matter in the cell by appropriately adjusting the air flow rate to the cell to be stopped and the combustion time of the unburned matter. This prevents the bed temperature from rising due to the combustion of unburned matter in the stop cell, thereby preventing the ash within the cell from melting and condensing. Furthermore, by reducing the supply air flow rate as smoothly as possible and stopping the operation after the combustion time of the unburned matter has been completed, the cell to be stopped will slowly transition from the fluidized bed state to the fixed bed state, A sudden drop in the amount of heat transferred to the internal heat exchanger tubes is avoided, and therefore fluctuations in the pressure and temperature of the steam generated by the boiler can be reduced. In other words, deterioration of steam quality is prevented.

In other words, in the present invention, in response to a reduction in boiler load, among cells which are layer regions divided into a plurality of parts,
This method involves stopping the fuel supply to that one cell, then decreasing and stopping the supply of air. In this way, after the fuel is stopped, supply air is supplied at a constant flow rate in order to complete the combustion of the unburned fuel in the cell, and the value of this constant flow rate is determined by the number of Determined based on the state of temperature dispersion detected by the thermometer, this value is the value at which there is less migration of bed material from other flowing cells, and the combustion of unburned material is reduced. After completion, the rate of change in decreasing time is determined so that the steam pressure and steam temperature are constant, and the amount of supplied air is decreased.

Moreover, in the present invention, when reducing the flow rate of supplied air, a problem peculiar to a fluidized bed is that when the air flow rate decreases and the air flow velocity becomes small, the fluidized bed state shifts to the fixed bed state, and this transition is sudden. If this occurs, there is a risk that fluctuations in steam pressure and temperature generated by the boiler will become large, and to prevent this, the flow rate of the supply air is reduced so that the transition occurs slowly.

Further, according to the present invention, when the layer temperature rises to near the melting temperature of the ash in the cell while the air is being gradually reduced, the air reduction time change rate is increased, thereby causing the ash to melt and melt. Condensation disappears.

[Brief explanation of drawings]

FIG. 1 is an overall system diagram of an embodiment of the present invention, FIG. 2 is a simplified sectional view of another embodiment of the fluid boiler 1, and FIG. 3 is a graph showing the relationship between boiler load and bed temperature. FIG. 4 is a flowchart showing an operating method when the boiler load is reduced according to the present invention, and FIG. 5 is a response waveform diagram when the boiler load is changed. 1... Fluidized bed boiler, 2... Fluidized bed, 4, 5...
...Cell, 9,50...Air flow rate adjustment means, 7,1
DESCRIPTION OF SYMBOLS 1... Fuel flow rate adjustment means, 16... Steam pressure detector, 17... Steam flow rate detector, 20, 24... Cell stop calculator, 27, 28... Temperature detector, 3
0...Steam temperature detector.

Claims (1)

[Claims] 1. Among the cells that are divided into a plurality of fluidized bed regions, the fuel and air in the cell to be stopped is decreased in accordance with the decrease in load, and the cell to be stopped is set at a plurality of temperatures. A meter is installed to detect the temperature, and the fuel supply to the cell to be stopped is stopped to complete the combustion of the unburned fuel and to reduce the movement of bed material from other flowing cells. The value of the air flow rate is determined based on the state of dispersion of the temperature detected by each thermometer, and air is continued to be supplied to the cell to be stopped at the flow rate of the above value, and the unburned matter is combusted. Load reduction of a fluidized bed boiler characterized by determining a reduction time change rate and gradually reducing air at the determined reduction time change rate so that the steam pressure and steam temperature are constant after completion. How to drive at the time. 2. Among the cells that are divided into multiple fluidized bed regions, reduce the fuel and air in the cell you want to stop in accordance with the decrease in load, and set multiple thermometers in the cell you want to stop to check the temperature. Detect and stop the fuel supply to the cell to be stopped to complete the combustion of the unburned fuel and adjust the air flow rate so that the movement of bed material from other flowing cells is reduced. The value is determined based on the state of dispersion in the temperature detected by each thermometer, and air is continued to be supplied to the cell to be stopped at the flow rate of the above value, and after the combustion of unburned material is completed, the steam pressure is In order to keep the steam temperature constant, the rate of change in decreasing time is determined, and the air is gradually decreased at the determined rate of decreasing time. A method of operating a fluidized bed boiler during load reduction, characterized by increasing the rate of change in air reduction time when the temperature rises to near the melting temperature of the fluidized bed boiler.