JPH1122903A - Fluid bed boiler control method and apparatus - Google Patents

Abstract

(57) [Problem] To provide a fluidized bed boiler in which an evaporator and a superheater are housed in different fluidized bed beds and provided with a desuperheater on the superheater side, have a large operating margin within the operating range of bed temperature. The present invention provides a coal supply ratio control method and a control device capable of good output control. SOLUTION: A boiler output is controlled based on a total amount of heat supplied to a first fluidized-bed bed and a second fluidized-bed bed, and a temperature difference between an inlet and an outlet of a desuperheater or a water injection flow rate of the desuperheater. The degree of superheat of the steam is controlled by adjusting the ratio of distributing the total heat supply to each fluidized bed so as to reduce the deviation. Further, it is preferable that the coal feed ratio be distributed so that the bed temperature difference between the first bed and the second bed is reduced as long as the difference between the inlet and outlet temperature of the desuperheater or the difference between the flow rates of the injected water is within a predetermined range. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling a fluidized-bed boiler used in thermal power generation, and more particularly to a method for controlling a superheater having an evaporator in a first bed layer and a superheater in a second bed layer. Control method and apparatus for controlling the distribution of heat supply to each bed in a two-bed fluidized bed boiler having a water cooler in the middle and adjusting the amount of water injected to keep the steam temperature at the boiler outlet constant About.

[0002]

2. Description of the Related Art Fluid bed boilers used for thermal power generation are:
A fluid medium such as limestone is placed on a dispersion plate made of a perforated plate, and an airflow having an appropriate flow rate range is supplied from below to make the fluid medium a stable boiling state to form a fluidized bed. This is a boiler that burns efficiently by continuously supplying coarsely pulverized coal with some limestone. A heat exchanger through which water or steam passes is inserted into the fluidized bed of the boiler, and a heat exchanger is also provided in an empty tower through which the combustion gas flows, to utilize heat. The fluidized bed boiler is capable of suspending and burning even coal with a large particle size, and has a large heat transfer coefficient between the bed and the heat transfer surface due to fluidization of the bed medium. Thus, there is an advantage that a large amount of heat can be input, and simultaneous desulfurization in a furnace can be performed when limestone or the like is used as a fluid medium.

[0003] Some fluidized-bed boilers have a multi-stage fluidized bed so that the installation area is effectively used.
The fluidized-bed boiler to which the present invention is applied, for example, as shown schematically in FIG. 5, is provided with an upper and lower two-stage fluidized bed in a main combustion furnace, and an evaporator EVAP is installed in the fluidized bed of the upper bed. Then, the superheater SH is stored in the lower bed layer. In detail, the economizer ECO and the evaporator EVAP are housed in the water-cooled wall and the fluidized bed of the reburning furnace, and the water-cooled pipe is installed in the furnace wall of the main combustion furnace. Charcoal E
A CO and a superheater 1SH are provided, and the generated heat is effectively collected as a whole to constitute a highly efficient boiler.
The reheater RH reheats the steam from the high pressure turbine.
Are also stored in the sky tower or lower bed.

FIG. 6 is a flow sheet showing a process in which feed water generates steam having a predetermined pressure and temperature by a fluidized-bed boiler. The steam drum is connected to a number of water tubes embedded in the water cooling walls of the main combustion furnace and the reburning furnace, the evaporator of the upper bed, and the evaporator of the reburning furnace bed. The water in the steam drum is naturally circulated through an evaporator or the like and heated to evaporate in the steam drum. The water level of the steam drum is kept constant by controlling the flow rate of water supplied from the water supply pump in the figure. The feedwater is heated by a economizer ECO provided in the empty tower, and then poured into a steam drum. After the steam generated by the steam drum is separated into steam and water, it is superheated by the superheater 1SH in the empty tower and the superheaters 2SH and FSH in the lower bed to become superheated steam. A desuperheater is provided between the superheater 2SH and the superheater FSH, and the branched feedwater is injected into superheated steam to reach a predetermined steam temperature before sending the steam to the high-pressure turbine.

[0005] Combustion of coal at a low temperature in a fluidized bed generates a large amount of sulfur oxides, and burning at a high temperature generates a large amount of nitrogen oxides. Therefore, a severe limit range is set for the combustion temperature in order to prevent air pollution and preserve the environment. Generally, it is operated between about 760-860 ° C. Therefore, when the area of the fluidized bed is constant, the load fluctuation range is limited between the lower limit temperature and the upper limit temperature, and it is not possible to widely cope with a load change request. On the other hand, a fluidized-bed boiler has a feature that almost no heat is transmitted when it is not in a fluidized state.

For this reason, a fluidized bed boiler used for thermal power generation divides a number of supply nozzles for supplying fluidizing air from below the fluidized bed into a plurality of groups called cells, and starts and stops each cell. Thereby, the area of the flowing portion is changed. When there is an output request that exceeds the range of loads that can be handled by changing the coal combustion temperature from the lower limit temperature to the upper limit temperature with the same fluidized bed area, the number of fluidized operating cells is increased or decreased. The upper and lower fluidized beds are, for example, an S cell used for starting ignition of the fluidized bed, an A cell adjacent thereto, and a B cell, a C cell, a D cell, and an E cell adjacent to the fluidized fluidized bed in order. Has been split.

[0007] As a result, the relationship between the output and the bed temperature, that is, the static characteristics within the operable range of the fluidized-bed boiler, shows a saw-shaped characteristic as shown in the upper part of FIG. FIG.
Represents an example of typical static characteristics of a two-stage fluidized-bed boiler using a load as a horizontal axis, a bed temperature as a vertical axis, and a combination of operating cells as parameters. Since the upper and lower two-stage beds have different areas and the like, there is a difference in cell size, and it is not possible to make the static characteristics with respect to the amount of coal supplied and the load equal. In the drawing, the thick solid line represents the static characteristic curve of the upper bed, and the thick dotted line represents the static characteristic curve of the lower bed. It goes without saying that if the operating environment such as the type of coal or the flow state changes, these static characteristics change, and the position and inclination of the curve slightly change. The curve shown in the lower part of FIG. 7 shows the amount of water injection required to obtain the necessary degree of superheat under the conditions, as a ratio to the steam flow rate.

Since the fluidized-bed boiler has a saw-shaped characteristic as described above, if cell switching is performed during continuous operation, a large disturbance occurs, and stable control becomes difficult. Therefore, during normal continuous operation, it is preferable that the output can be controlled by adjusting the coal supply amount, that is, by adjusting the bed temperature without changing the cell configuration. Therefore, for example, 100%, 75%, 50%, 4
Aiming at operation near a fixed point having a predetermined load factor between the maximum load and the minimum load, such as 0% load, stable control is performed at a temperature within the permissible range of the bed temperature and a sufficient margin up to the limit temperature. The cell area and the combination are determined so that they can be performed. Further, the power generation amount of the power plant, that is, the demand for the load, usually targets the operation near the fixed point having the above-mentioned predetermined load factor.

In the drawing, a curve SE drawn on the rightmost side shows a relationship between the boiler output and the bed temperature when all the cells from the S cell to the E cell are operated. The heat transfer in the fluidized bed is very good, so that the flowing working cells show the same bed temperature. As the coal supply increases from the minimum combustion temperature, the combustion temperature increases, the output increases, and the amount of steam generated increases. As the amount of steam generated increases, the output of the superheater must increase to maintain the same degree of superheat. Thus, by adjusting the combustion temperature in the upper and lower fluidized beds, while maintaining the steam pressure in the steam drum and the steam temperature at the boiler outlet at predetermined values, the amount of generated steam is an amount corresponding to the consumption in the power generation turbine. Is controlled so that

Although the operation is possible up to the maximum limit temperature, the temperatures at the U100 point of the upper fluidized bed and the L100 point of the lower fluidized bed, which are pre-optimized operating conditions at the rated value, are set at the maximum limit temperature in consideration of the operation margin. It is designed to be slightly lower. If there is an output deviation, it can be solved by adjusting the coal temperature along the characteristic curve to adjust the bed temperature. If the degree of superheat of the steam has a deviation from the target value, the amount of water injected into the desuperheater provided between the superheaters connected in series is eliminated.

A curve SD drawn to the left of the curve SE is a characteristic curve when the E cell is stopped from the above cell combination and the D cell is operated from the S cell. For example, U75 and L75 on this line , It is possible to deal with a load of 75% of the rating. Curve S- drawn on the left
C is a characteristic curve when operating from the S cell to the C cell, and the operating points U50 and L50 at a 50% load factor are plotted on this curve.
And the operating point U40 at the operation minimum load of 40% load factor
And L40 exist. The curve SB drawn on the left is a case where the S cell, the A cell, and the B cell are operated. However, since the output for the minimum load is insufficient, the operation is not normally performed in this cell configuration.

As described above, in a two-bed fluidized-bed boiler used for thermal power generation, the optimal operating conditions corresponding to the load factor differ for each stage. These operating conditions vary depending on environmental conditions such as the type of coal, and must be determined in advance by simulation or actual measurement. Therefore, in the prior art, the number of operating cells and the combustion temperature determined according to the static characteristics of the boiler obtained in advance are determined for each of the upper stage having the evaporator and the lower stage having the superheater in accordance with the load state in which stable operation is required. In order to achieve this, control is performed to change the ratio of the amount of coal fed to both the upper and lower stages so that the predetermined amount of coal is fed.At the same time, the final steam superheat degree is adjusted by controlling the injection of water into the desuperheater. It was normal to do.

That is, the distribution of coal in the upper and lower stages is set according to a predetermined function, and when a deviation from the plan occurs, the temperature difference at the inlet / outlet of the desuperheater, which is closely related to the amount of injected water, is determined by a predetermined value. The method of correcting the coal supply distribution ratio so that If the steam superheat is strictly controlled by the amount of water injected into the desuperheater, the distribution of the coal supply to the upper and lower fluidized beds may deviate from the value regulated by the bed temperature operation. The bed temperature of the fluidized bed has the characteristic that it increases when the amount of coal fed into the bed is increased, but if the amount of injected water is strictly adjusted based on the static characteristics of the upper and lower stages, either It is easy for such a fluidized bed to have to operate tightly near the combustion temperature control limit.

Therefore, in order to respond satisfactorily to the increase / decrease of the boiler master, that is, the boiler load command, so that both the upper and lower coal supply amounts do not meet the above-mentioned restrictions, the upper and lower layer temperatures must meet the boundary of the layer temperature operation range. You have to have enough room for it. Further, since the upper and lower layer temperatures are operated in the same direction with respect to the same disturbance, it is preferable that the upper and lower layer temperatures maintain values close to each other. As described above, if the bed temperatures in the upper and lower stages are kept close to each other, it is possible to respond to the boiler load increase / decrease command sufficiently widely, and the operation characteristics of the plant will be improved. Therefore, while the main purpose of the upper and lower coal supply ratio control is to maintain an appropriate degree of superheat, it is preferable that the secondary purpose is to approximate the upper and lower layer temperatures. Conventionally, there has been no technical idea to simultaneously maintain the superheat degree of steam and approximate the bed temperature by controlling the upper and lower coal feed ratios.

[0015]

Accordingly, an object of the present invention is to provide a fluidized-bed boiler in which an evaporator and a superheater are housed in different fluidized-bed beds, in which the bed temperature falls within an operating range. An object of the present invention is to provide a coal feed rate control method and a control device that have a large operating margin and enable good output control.

[0016]

In order to solve the above-mentioned problems, a method for controlling a fluidized-bed boiler according to the present invention has a structure in which an evaporator and a superheater are housed in different fluidized-bed beds and a desuperheater is provided on the superheater side. For a fluidized-bed boiler, the boiler output is controlled based on the total amount of heat supplied to the first fluidized-bed bed and the second fluidized-bed bed, and the temperature difference at the inlet and the outlet of the desuperheater is reduced or reduced. The superheat degree of the steam is controlled by adjusting a ratio of distributing the total amount of supplied heat to each fluidized bed so as to reduce the deviation of the flow rate of the water injected into the heater.

Further, as long as the temperature difference between the inlet and the outlet of the desuperheater or the deviation of the flow rate of the water injected into the desuperheater is within a predetermined range, the coal feeding is performed so that the layer temperature difference between the first and second beds is reduced. It is preferable to distribute the quantity ratio. In addition,
The supply heat amount and the distribution ratio can be adjusted based on the static characteristics in which the relationship between the load request amount and the supply heat amount for each bed is determined for each coal type.

Further, the fluidized-bed boiler control device of the present invention includes an evaporator in the first bed layer and a superheater in the second bed layer. Means for setting the boiler load as a boiler master signal for a two-stage fluidized bed boiler in which the steam temperature at the boiler outlet is kept constant by adjusting the boiler master signal, and the heat quantity supplied to the first and second beds. Means for distributing and setting as setting, evaporator supply heat quantity adjusting means for issuing a first bed coal supply quantity supply command based on a deviation signal of heat quantity supplied to the first bed, and deviation signal of heat quantity supplied to the second bed And a superheated section calorie supply calorie control means for transmitting a second bed coal supply quantity supply command based on the
The supply calorie distribution setting means performs a dead zone process or a gap gain process on a deviation signal of a desuperheater injection flow rate or a desuperheater inlet / outlet temperature difference, and a difference between a bed temperature of the first bed and a bed temperature of the second bed. , And outputs a supply heat amount distribution command for the first bed and the second bed corresponding to the sum of the signals. In addition, it is preferable to adjust the supplied heat amount and the distribution ratio based on the static characteristics in which the relationship between the required load amount and the supplied heat amount for each bed is determined for each type of coal.

Further, the second fluidized bed boiler control device of the present invention provides a dead zone calculation or a gap calculation for a difference between a set value of a superheater water injection flow rate or a set value of a temperature changer inlet / outlet temperature determined from boiler static characteristics and an actually measured value. Means for performing a gain operation; means for performing a function operation on a signal representing a difference between the upper and lower layer temperature signals;
A means for adding the deviation signals subjected to these two arithmetic processings to obtain a combined deviation, a means for performing an adjusting operation on the combined deviation signal, and a correction of the supply heat amount setting in the upper and lower stages by using the adjusted output. It is characterized by comprising means for performing.

In the fluidized bed boiler control method and control apparatus of the present invention, the superheater injection flow rate has a predetermined appropriate value, but the optimum value has a range, so that the control target value is not necessarily 1
The point does not need to be set, and it is conceived that there is no operational problem as long as the point is within a certain area. If this water injection flow allowable range is called tolerance, the upper and lower coal supply ratio should be selected so that the upper and lower bed temperatures are as close as possible to each other, provided that the water injection amount falls within this tolerance. Thus, the controllable range of the steam amount and the steam temperature is expanded to obtain a good control result.

According to the fluidized bed boiler control method of the present invention, the boiler output is controlled based on the total amount of heat supplied to the first fluidized bed and the second fluidized bed, and the inlet and outlet of the desuperheater are controlled. The superheat degree of steam is controlled by adjusting the ratio of the total supply heat amount to each fluidized bed so as to reduce the temperature difference deviation of steam, so that the superheat degree of steam is reduced after regulating the overall steam generation amount. Control is performed by allocating the coal supply using the temperature decrease in the warmer as an index.

According to this control method, as long as the condition that the control by the desuperheater is kept within the above-mentioned tolerance is satisfied, the operation is performed so that the bed temperature of the upper and lower fluidized bed is more approximated therein. As a result, the bed temperature approaches the average value of the optimum values of the fluidized beds determined from the design values, and the margin to the temperature regulation value increases. Therefore, as compared with the conventional case where a predetermined coal supply amount is supplied for each fluidized bed, the evaporation amount and the bed temperature are controlled, and the steam superheat degree is strictly controlled by the cooling water injection flow rate. This has the effect of increasing the control width of the fluidized bed and improving the ability to suppress disturbance. It is needless to say that the same effect can be obtained by using the deviation from the design value of the flow rate of the water cooler instead of the temperature difference between the inlet and outlet of the cooler.

Further, the coal supply ratio is distributed so that the bed temperature difference between the first bed and the second bed is reduced as long as the temperature difference between the inlet and the outlet of the desuperheater or the water flow difference is within a predetermined range. When the temperature difference between the inlet and outlet temperature of the desuperheater and the deviation of the injection flow rate are large and the steam superheat greatly deviates from the desired value, the steam temperature is controlled more directly and the response of the desuperheater with good responsiveness is improved. When the difference in inlet and outlet temperatures and the amount of injected water are within the above-mentioned tolerances, while performing the function sufficiently, control is performed to make the bed temperature uniform, thereby expanding the stable controllable range that can be controlled without changing the cell configuration. Can be.

The operation variable that can be actually operated to control the bed temperature is the amount of coal supplied, but the amount of steam and the steam temperature are affected by the bed temperature, and the amount of steam from the supply of coal until the bed temperature changes. The delay is large. Therefore, it is necessary to perform a predictive operation at the stage of determining the above control variables, and control is performed by taking in the static characteristics of the boiler. However, the boiler static characteristics vary depending on the conditions, and the variation greatly depends on the type of coal. Therefore, the static characteristics representing the relationship between the load demand and the amount of heat supplied per bed for each type of coal are examined in advance, and the type of coal is determined. It is preferable that the supply heat amount and the distribution ratio be adjusted based on the static characteristics corresponding to the change.

The upper and lower stage ratio control in the fluidized bed boiler control method of the present invention is a control for maintaining the upper and lower stage heat amounts in an appropriate balance based on static characteristics. Therefore, in an unsteady state such as when the bed temperature is changed by a load change command or the like, the control may instead become a disturbance factor. Therefore, when the rate of change of the layer temperature difference between the first bed and the second bed is equal to or greater than a predetermined value, it is preferable to stop the control operation based on the layer temperature difference.

Further, in the fluidized-bed boiler control device of the present invention, the supply heat amount distribution setting means includes a dead zone process or a gap for the deviation signal obtained by comparing the flow rate of the cooling water inlet or the temperature difference between the inlet and outlet of the cooling heater with a reference value. A signal obtained by performing the gain processing and a signal based on the difference between the bed temperatures of the first and second beds are input, and the boiler master signal is distributed to the first and second beds in accordance with the sum of the signals. , And outputs a supply heat amount distribution command.

Therefore, the distribution of heat supply to the first bed and the second bed is determined by determining the difference between the flow rate of the injected water and the deviation of the flow rate of the injected water between the first bed and the second bed when the deviation of the injected flow rate of the desuperheater is larger than a predetermined dead zone width. The distribution of the coal supply is adjusted so that the bed temperature differences are all small, but when the water injection flow rate deviation is smaller than the dead zone width, the supplied heat amount is distributed so that the bed temperature differences become small. For this reason, when the flow rate of the injected water is within the predetermined range and there is little problem in the process, the layer temperature difference between the upper and lower layers is eliminated, and the margin to the upper limit temperature or the lower limit temperature is increased, and as a result, the compensation width for disturbance is reduced. Becomes larger.

If the amount of supplied heat and the distribution ratio are adjusted based on the static characteristics obtained from the relationship between the required load and the amount of supplied heat for each bed for each type of coal, the type and blend of coal changes. In this case, control based on a correct correlation can be achieved.

Further, in the fluidized bed boiler control apparatus according to the second embodiment of the present invention, a dead zone calculation or a gap gain calculation is performed for the deviation of the superheater water injection flow rate or the temperature difference between the inlet and outlet of the desuperheater, and the difference between the upper and lower bed temperature signals is calculated. Is subjected to a function operation, and the deviation signals obtained by performing these two operation processes are added to obtain a combined deviation, and an adjustment operation is performed on the combined deviation signal. Make sure to modify the settings distribution. Therefore, while the superheater injection flow rate deviation or the like is small, the deviation output becomes zero or minute, and the control deviation input corrects the upper and lower supply heat amount setting distribution in a direction to equalize the upper and lower layer temperatures. Furthermore, due to this correction operation, the superheater water injection flow rate fluctuates, and the signal after processing such as dead zone calculation and the deviation signal of the upper and lower layer temperatures become equal and cancel out, and the equilibrium state is reached at the point where the combination deviation becomes zero. Become.

Thus, it is possible to make the bed temperatures of the upper and lower stages as close as possible while securing an appropriate flow rate of the superheater. As a result, the boiler load adjustment range is secured as much as possible without impairing the control situation of steam temperature control.
This makes it possible to achieve a desired operating condition for the fluidized-bed boiler. It goes without saying that the control method and the apparatus of the present invention can be applied to the case where the evaporator and the superheater are housed in either fluidized bed.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a fluidized-bed boiler control method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the fluidized-bed boiler to which the present invention is applied, a main combustion furnace is installed separately in an upper stage and a lower stage, an evaporator is arranged in the upper fluidized bed, and a superheater and a reheater are arranged in the lower fluidized bed. Is arranged. Therefore, the boiler heat input command from the boiler master is distributed to the upper and lower stages of the main combustion furnace. Is determined by the ratio of the lower coal supply to the total coal supply. FIG. 1 is a block diagram showing the relationship between the amount of coal supplied to the upper and lower stages, the boiler output, and the degree of superheat. The total amount of coal added to the upper and lower levels determines the boiler output,
The value obtained by dividing the lower coal supply by the total coal supply determines the degree of superheat.

Here, the ratio of the lower coal supply to the total coal supply is referred to as the upper / lower ratio. Since the combustion efficiency actually differs depending on the bed temperature, the amount of heat supplied is used in consideration of the combustion efficiency instead of the amount of coal supplied. The upper / lower ratio governs the degree of superheat of steam, that is, the steam temperature, and is determined from static characteristics corresponding to each load. The static characteristics refer to the relationship between the fluidized bed temperature and the steam pressure / temperature determined according to the amount of supplied coal and the amount of supplied heat, and vary depending on the combustion conditions in the boiler, and the difference greatly depends on the type of coal. The upper / lower ratio control is a control for distributing the boiler heat input demand to the upper and lower stages based on the static characteristics.

Although the boiler input demand for the required load, that is, the requirement of the total heat supply is constant irrespective of the type of coal, the static characteristics of the boiler vary for each boiler load and cell configuration and for each type of coal. Since the lower ratio changes each time the load, cell configuration, and coal type change, the upper / lower ratio control is performed by a circuit that takes these factors into consideration. Conventionally, the degree of superheat has been adjusted by the amount of water injected into the desuperheater inserted between the superheaters. When the balance of the amount of heat supplied to the fluidized bed changes, the degree of superheat changes, and the flow rate of water injection changes with the control of the desuperheater. Therefore, the supply heat amount balance may be monitored using the water injection flow rate as an index to adjust the upper and lower tier ratio. However, this method requires a correction in consideration of the size of the load, and has a disadvantage that a flowmeter error in a low flow rate region is large.

FIG. 2 is a flow sheet showing a main control circuit of the fluidized bed boiler in this embodiment. The parts added to the conventional control flow shown in FIG. 6 are represented by bold lines to facilitate understanding. The upper / lower ratio control used in the present embodiment takes in the temperature difference deviation between the inlet and the outlet of the desuperheater and the difference between the upper and lower layer temperatures and processes them, and according to the information, the command generated in the conventional coal feed control device It is a metamorphosis. According to the control method of the present invention, when the output is controlled by the total heat supply amount of the upper and lower stages, and the superheat degree is controlled by the ratio of the upper and lower stages, the layer temperatures of the upper and lower stages are made as close as possible. The deviation of the degree of superheat is eliminated by adjusting the flow rate of the cooling water injection. However, measures are required to maintain the flow rate of water injection or the temperature difference between the inlet and outlet of the desuperheater caused by water injection within a certain appropriate management zone.

FIG. 3 shows the static characteristics of the fluidized-bed boiler and the amount of water injection required to obtain the required degree of superheat.
It is the drawing in which the operation state when operating with a load was filled in.
The water flow rate of the cooler or the temperature difference between the inlet and the outlet can allow a slight deviation as shown by the oblique line with respect to the curve A showing the static characteristics. An operation that approximates the lower layer temperature L75 can be performed.

FIG. 4 is a block diagram showing an upper / lower ratio control circuit in the fluidized-bed boiler control apparatus of this embodiment. The total boiler heat input demand is created through the first function converter FG1 which receives the boiler input demand BID and converts it into heat. Next, the heat input demand is passed through a second function converter FG2 in which the lower-stage static characteristics are stored, and a base signal of the lower master heat input demand is created. The multiplier MLT multiplies the lower master heat input demand signal by the upper / lower ratio set by the upper / lower ratio control circuit to obtain a lower master heat input demand signal. The upper master heat input demand signal is supplied to the first subtractor S
UB1 is calculated by subtracting the lower master heat input demand from the total boiler heat input demand. Where the second function converter F
G2 is for calculating the lower supply heat quantity based on the static characteristics in consideration of the cell configuration with respect to the load. Since the static characteristics vary depending on the type of coal, a plurality of function converters prepared for each type of coal are switched and used. .

The upper / lower ratio control circuit receives the boiler master base signal, obtains the temperature reduction width set value by the third function converter FG3, and compares the value with the temperature reduction width measured by the second subtractor SUB2. Then, a temperature decrease width deviation signal is obtained. The temperature reduction width can be obtained as a difference between the steam temperature at the outlet of the second superheater 2SH and the steam temperature at the inlet of the final superheater FSH. The temperature reduction width in the desuperheater is an index representing the balance of the upper and lower stage calorific values. Since the appropriate set value of the temperature reduction width according to the operating conditions is determined as the boiler static characteristic in relation to the heat distribution in the upper and lower stages, the third function converter FG3 is used as the second function converter FG.
As in the case of No. 2, a plurality of comparison tables prepared for each coal type are stored, and are switched and used according to the situation.

The temperature reduction width deviation signal is input to a dead band circuit GAP whose gain is small when the input is near zero and whose gain becomes large when the input is increased to a certain level, for example, 5%. Sent to The difference signal between the upper and lower layer temperatures is fetched, subjected to appropriate processing by the fourth function converter FG4, and sent to the adder ADD. The adder ADD adds the above-mentioned temperature decrease width deviation signal and the layer temperature difference signal to each other to control the upper / lower ratio control controller P.
I is input. The upper / lower ratio control controller PI performs a proportional integration operation on the combination deviation input and inputs the output to the multiplier MLT to transform the lower master heat input demand signal.

According to the fluidized bed boiler control apparatus of this embodiment, the bed temperature of each stage is controlled by feeding back the difference between the bed temperature of the upper and lower stages and the temperature difference between the inlet and the outlet of the cooler to the upper / lower ratio control circuit. And the upper and lower layer temperatures tend to be the same.
In addition, since the dead zone calculation is performed for the temperature difference in the desuperheater, when the temperature difference deviation is within the dead zone, the temperature difference deviation between the inlet and the outlet of the desuperheater is not adjusted, and the layer temperatures in the upper and lower stages are accordingly increased. A force to strongly equalize works. For this reason, uniformization of the layer temperature is achieved more easily.

Since the balance of the upper and lower stages of heat quantity appears in the spray flow rate when the steam has a predetermined degree of superheat, the upper and lower stages of the coal supply ratio control is performed using this as an index instead of the temperature difference between the inlet and outlet of the desuperheater. It is also possible to do. However,
In the case where the spray flow rate is to be controlled, it is necessary to take a countermeasure such that a circuit for correcting the flow rate based on the relative value evaluation with respect to the load is required, and the flow rate is low in measurement accuracy particularly in a low flow rate region. Although the case where only one temperature reducer is provided has been described above for simplification of description, the same operation and effect can be expected when a plurality of temperature reducers are provided. When a plurality of machines are used, a temperature difference or the like may be used by averaging values measured for each machine.

Although the fluidized bed is divided into a plurality of cells, the bed temperature may be calculated using an average value. In the bed temperature balance control, it is preferable not to perform abrupt correction even after the load is set, and it is desired to gradually adjust and correct the upper and lower tier ratios. Therefore, when the difference between the upper and lower layer temperatures is large, it is preferable to limit the temperature deviation width and use gain adjustment together.

In addition, when the load changes, the upper / lower ratio control may cause a disturbance. Therefore, the change rate of the bed temperature may be monitored and the upper / lower ratio control may be operated only when the bed temperature is stable. Although the case where the switching is performed on the circuit in order to cope with the static characteristics that change for each coal type has been described, the switching may be performed using a storage device, or the static characteristics table may be directly rewritten. Static characteristics can be measured during operation and automatically rewritten.

[0043]

As described in detail above, according to the present invention, by controlling the upper and lower layer temperatures to be close to each other, the load change adjustment range of the boiler can be adjusted without impairing the controllability of the steam temperature. It can be made as large as possible, contributing to stable operation of the plant and improvement of operation performance.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the concept of upper / lower ratio control in a fluidized bed boiler control method of the present invention.

FIG. 2 is a flow sheet showing a main control circuit of the fluidized bed boiler in the present embodiment.

FIG. 3 is a drawing showing an operation state according to the present embodiment on a graph of static characteristics.

FIG. 4 is a block diagram illustrating an upper / lower ratio control circuit in the fluidized bed boiler control device of the present embodiment.

FIG. 5 is a drawing showing a fluidized-bed boiler to which the present invention is applied.

FIG. 6 is a flow sheet of a conventional fluidized-bed boiler control method.

FIG. 7 is a drawing showing static characteristics in an operable range of a fluidized-bed boiler.

[Explanation of symbols]

 ADD adder FG function converter GAP dead-zone calculator MLT multiplier PI controller SUB subtracter

 ──────────────────────────────────────────────────続 き Continued on the front page (71) Applicant 591195031 Development Electric Co., Ltd. 4-5-2 Kudankita, Chiyoda-ku, Tokyo (72) Inventor Yoshimasa Tsunoda 6-15-1, Ginza, Chuo-ku, Tokyo Power supply development (72) Inventor Toshimasa Jindai 6-15-1, Ginza, Chuo-ku, Tokyo Power Supply Development Co., Ltd. (72) Koji Sasatsu 6-15-1, Ginza, Chuo-ku, Tokyo Power Supply Development Co., Ltd. (72) Inventor Toshiro Ito 2-11-1, Minamisuna, Koto-ku, Tokyo Kawasaki Heavy Industries, Ltd.Tokyo Design Office (72) Inventor Toru Kasai 6-19-20 Tsukiji, Chuo-ku, Tokyo Soken (72) Inventor Soyasu Kitamura 4-5-2, Kudankita, Chiyoda-ku, Tokyo Development Electric Co., Ltd. (72) Katsumi Fujita 4-chome, Kudankita, Chiyoda-ku, Tokyo Ban No. 5 open power generation care within Co., Ltd.

Claims (9)

[Claims] 1. A fluidized-bed boiler containing an evaporator in a first bed layer, a superheater in a second bed layer, and a desuperheater on the superheater side. The boiler output is controlled based on the total amount of heat supplied to the two beds, and the ratio of the total amount of heat supplied to the second bed is adjusted so as to reduce the temperature difference between the inlet and the outlet of the desuperheater. A fluidized-bed boiler control method, comprising controlling the degree of superheat of steam. 2. The coal supply ratio is distributed so that the bed temperature difference between the first bed and the second bed is reduced as long as the temperature difference between the inlet and the outlet of the desuperheater is within a predetermined range. 2. The method for controlling a fluidized-bed boiler according to claim 1, wherein: 3. The method according to claim 1, wherein the supply heat amount and the distribution ratio are adjusted based on a static characteristic obtained from a relationship between a load requirement amount and a supply heat amount for each bed for each coal type. Fluid bed boiler control method. 4. The method according to claim 1, wherein the control operation based on the layer temperature difference is stopped when the rate of change of the layer temperature of the first bed or the second bed is equal to or more than a predetermined value. A method for controlling a fluidized-bed boiler according to any one of the first to third aspects. 5. The method of controlling a fluidized-bed boiler according to claim 1, wherein a difference in flow rate of water injected into the desuperheater is used instead of a temperature difference between an inlet and an outlet of the desuperheater. Fluidized bed boiler control method. 6. A steam temperature at a boiler outlet by housing an evaporator in a first bed layer and a superheater in a second bed layer, and adjusting a water injection flow rate of a desuperheater provided on the superheater side. Means for setting a boiler load as a boiler master signal, means for distributing and setting a boiler master signal as a heat supply setting for the first and second beds, and to the first bed. Evaporating section supply calorie supply means for transmitting a first bed coal supply amount supply command based on the deviation signal of the supply heat amount of the second bed, and supplying a second bed coal supply amount supply command based on the deviation signal of the supply heat amount to the second bed. And a supply heat amount control means for transmitting the superheat portion heat amount, and the supply heat amount distribution setting means includes a dead zone process or a gap gay for a deviation signal of a desuperheater injection flow rate or a desuperheater inlet / outlet temperature difference signal. A signal obtained by performing the processing and a signal based on the difference between the bed temperatures of the first bed and the second bed are input, and a supply heat quantity distribution command for the first bed and the second bed corresponding to the sum thereof is output. A fluidized-bed boiler control device. 7. The fluidized bed according to claim 5, wherein the supply heat amount and the distribution ratio are adjusted based on static characteristics obtained by determining a relationship between a load requirement amount and a supply heat amount for each bed for each type of coal. Boiler control device. 8. The apparatus further comprises means for detecting a rate of change in the bed temperature of the first bed and the second bed and switching a signal based on the bed temperature difference to a predetermined value when the rate of change is larger than a predetermined value. The fluidized-bed boiler control device according to claim 5 or 6. 9. A steam temperature at a boiler outlet by adjusting an injection flow rate of an evaporator in a first bed layer and a superheater in a second bed layer, and adjusting a water injection flow rate of a desuperheater provided on the superheater side. Control device for a two-bed fluidized-bed boiler that keeps the temperature constant and the difference between the set value of the superheater water injection flow rate or the set value of the temperature difference between the inlet and outlet of the desuperheater determined from the boiler static characteristics and the measured value On the other hand, means for performing a dead zone calculation or gap gain calculation, means for performing a function calculation on the signal of the difference between the upper and lower layer temperature signals, and a deviation signal obtained by adding the deviation signals having been subjected to these two computations to form a combined deviation signal A fluidized-bed boiler, comprising: means for performing an adjusting operation on the combined deviation signal; and means for correcting the distribution of the set amount of heat supply in the upper and lower stages using the adjusted output. Control device.