JPH0625602B2 - Fluidized bed boiler control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling a fluidized bed boiler that uses fluidized fuel such as coal, and more specifically, a method for controlling a fluidized bed boiler that can quickly follow load fluctuations. It is about.

[Prior Art] As is well known, a fluidized bed boiler continuously supplies fuel into a fluid chamber and also supplies air into the fluid chamber through a dispersion plate to burn the fuel and flow the fluid medium. And heat is exchanged by a heat transfer tube arranged in the flow chamber. In this fluidized bed boiler, conventionally, the installation height and the filling amount of the fluidized medium are set so that the heat transfer tube is buried in the fluidized bed.

[Problems to be Solved by the Invention] As described above, in the conventional fluidized bed boiler, the heat transfer tubes are buried in the fluidized bed, and as a characteristic of fluidized bed heat transfer, the overall heat transfer coefficient is lowered even if the air flow velocity is decreased. Since it moves in a non-existing region, even if the fuel supply amount and the air supply amount are reduced to lower the combustion heat of the fuel when the boiler load is reduced, the heat transfer coefficient and the heat transfer area hardly decrease. Therefore, the amount of heat exchange is large, and the temperature of the fluidized bed may suddenly drop, causing immobilization.

Even when the fuel supply amount is increased in response to an increase in boiler load, the solid fuel handled in the fluidized bed boiler has a larger particle size and a lower burning rate than pulverized coal, so the response The sex is bad.

As a countermeasure against this, there is a method in which the fluidized bed is divided into several cells and several cells are treated as a slump state according to the load. However, this method has a problem in that it is very complicated from the viewpoint of control, and it cannot sufficiently cope with frequent load fluctuations.

On the other hand, from the applicant, when the fluidized bed height is changed by changing the fuel supply amount and the air supply amount in response to the fluctuation of the boiler load, the number of heat transfer tubes buried in the fluidized bed is set. A control method has been proposed in which the installation height of the heat transfer tube or the filling amount of the fluidized medium is set so as to be changed (Japanese Patent Application No. 61-199532). In this method, the number of heat transfer tubes buried in the fluidized bed changes when the height of the fluidized bed changes in response to fluctuations in boiler load. For example, when the supply amounts of air and fuel are reduced in response to the decrease in load, the height of the fluidized bed is reduced, and the number of heat transfer tubes buried in the fluidized bed is reduced. On the contrary, when the load increases and the supply amounts of air and fuel are correspondingly increased, the height of the fluidized bed increases, and the number of heat transfer tubes buried in the fluidized bed increases. Therefore, the heat transfer area changes in accordance with the increase / decrease in the boiler load, and the total heat transfer amount transferred from the fluidized bed to the heat transfer tubes is increased / decreased in accordance with the increase / decrease in the load. The fluctuation range of is significantly reduced.

However, the subsequent study confirmed that this method had the following problems. That is, when the amount of air is increased to increase the height of the fluidized bed in response to an increase in load, the amount of NOx is increased due to excess air. On the contrary, when the air amount is reduced to reduce the height of the fluidized bed in response to the decrease in load, SOx is easily generated. (In the case of the desulfurization method using limestone, the desulfurization reaction is mainly However, if the amount of air is small, O ₂ will be insufficient and the desulfurization reaction will not proceed easily. Therefore, even in the boiler of Japanese Patent Application No. 61-199532, the amount of air must be controlled in accordance with the combustion of the solid fuel, and the load responsiveness is deteriorated accordingly.

[Means for Solving the Problem] The method for controlling a fluidized bed boiler according to claim (1) corresponds to the fluctuation of the boiler load, the fuel supply amount is the supply amount F before the load fluctuation.
_When controlling the boiler output by changing from ₀ to the supply amount F ₁ after the load change, first, the fuel supply amount change is made larger than the difference between F ₁ and F _0, and then the above F ₁ and F _0. The fuel supply amount is changed to be smaller than the difference between the fuel supply amount and the fuel supply amount, and then the fuel supply amount is changed to F ₁ .

The control method for a fluidized bed boiler according to claim (2) is the control method according to claim (1), wherein the difference ΔS or Δ between the excess amount S ₁ or T ₂ and the deficiency amount S ₂ or T ₁ of the fuel supply amount. T or S
_1- S ₂ or T ₁ -T ₂ is the amount of solid fuel in the reactor when the fuel supply amount F _{0 is} in the stable state, and the amount of solid fuel in the reactor is stable when the fuel supply amount F _{1 is} in the stable state The difference is almost equal to.

A control method for a fluidized bed boiler according to claim (3), in the control method according to claim (1), an excess amount of fuel supply amount S ₁
Alternatively, T ₂ and the shortage amount S ₂ or T ₁ are made substantially equal.

[Operation] For example, in order to perform control when the boiler load increases according to the method of the present invention, first, fuel is supplied in excess of the supply amount F ₁ corresponding to the changed load. This causes the boiler output to rise rapidly. Next, the fuel is once supplied so that the amount becomes smaller than the above F ₁ . This prevents an excessive increase in boiler output. After that, the fuel supply amount is set to F _1, and the boiler output corresponding to the changed load is maintained.

When the boiler load is lowered likewise is first reduced fuel supply amount to less than F _1, then the feed amount is set to F ₁ after being restored to an amount greater than F _1. As a result, the output can be rapidly reduced in the same manner.

In the embodiment according to claim (2), _{F 0} the supply amount, for example, from _{F 0}
When changing to a larger F ₁ than, than a deficiency of the fuel the amount of excess S _1, that is supplied above the F ₁ fuel in the fuel as shown in Figure 2 is less than the insufficient amount S _2, that F ₁ Also, I am trying to increase by ΔS. The △ S includes a furnace residence solid fuel quantity C ₁ when the boiler is stably operated under the conditions of the supply amount F _1, when stable boiler is operated at a feed rate F ₀ It is equal to the difference between the amount of solid fuel remaining in the furnace C ₀ .

Further, in claim (2), the supply amount when changing from F ₀ to less F ₁ than F _0, the third amount than the above from the fuel shortage T ₁ is excess T ₂ shown in FIG △ Make S larger.

According to the control method of these claims (2), after the fuel supply amount is switched from F ₀ to F ₁ , the fuel burns more stably under the condition of the fuel supply amount of F ₁ earlier. Reach the state.

In the aspect of claim (3), the boiler is operated so that the excess amount S ₁ and the excess amount S ₂ and the shortage amount T ₁ and the excess amount T ₂ are substantially equal to each other.

According to the control method of claims (1) to (3),
It can follow the load fluctuation of the fluidized bed boiler extremely quickly. In addition, nitrogen oxide NOx and sulfur oxide S
The amount of Ox generated is also small.

Embodiments Embodiments will be described below with reference to the drawings.

FIG. 1 is a system diagram of a fluidized bed boiler for explaining a method for controlling a fluidized bed boiler according to an embodiment of the present invention.

Reference numeral 10 is a boiler furnace body, and a dispersion plate 12 is installed at the bottom of the boiler furnace body so as to traverse the inside of the boiler, and an air chamber 14 is partitioned and formed. A forced air blower 17 is connected to the air chamber 14 via a primary air supply pipe 16. Above the dispersion plate 12 is a flow chamber, and a large number of heat transfer tubes 18 are installed. In this embodiment, the heat transfer tubes 18 are installed in multiple stages in the height direction. Reference numeral 20 is a supply pipe of fuel (granular coal in the present embodiment) from a coal supply system, which will be described later, and a plurality of pipes are arranged so as to be uniformly supplied directly above the dispersion plate 12.

A secondary air supply pipe 22 is connected to the freeboard portion above the heat transfer pipe 18. A distribution plate 24 is installed above the secondary air supply pipe 22 so as to cross the inside of the boiler furnace body, and a desulfurization chamber is formed above the distribution plate 24. Reference numeral 26 is a pipe for supplying a desulfurizing agent (limestone in this embodiment) such as limestone or dolomite from the bunker 27, and reference numeral 28
Is a discharge pipe for discharging limestone after the desulfurization reaction.
Further, reference numeral 30 is a waste heat boiler, and a heat transfer tube 32 is arranged therein. A steam drum 34 is connected to the heat transfer pipe 32 via pipes 36 and 38, and a circulation pump 40 is provided in the middle of the pipe 36. The pump 40
The discharge side is connected to one end of the heat transfer tube 18 via a pipe 42, and the other end of the heat transfer tube 18 is connected to the steam drum 34 via a pipe 44. The steam drum 34
A steam extraction pipe 45 is connected to the water supply pump 4 and
It is possible to introduce soft water through 6 and the pipe 47.
Reference numeral 48 is a bag house connected to the waste heat boiler 30, and an induction fan 50 is arranged on the downstream side thereof.

The coal feeding system 52 includes a coal bunker 54, a horizontal rotary valve 56, a weighing conveyor 58, a hammer crusher 60, and a splitter 62, and granular coal is supplied from the supply pipe 20 to the furnace body 10 by, for example, air transfer. .

In this structure, the fluidized medium is filled in the fluidized chamber above the dispersion plate 12, and the granular coal supplied from the supply pipe 20 is burned by the primary air supplied through the air chamber 14 to form the fluidized bed B. To do. After receiving the secondary air supply, the fuel gas enters the desulfurization fluidized bed B ′ and is desulfurized. Then, after exchanging heat with the waste heat boiler 30, the dust is collected in the baghouse 48 and discharged into the atmosphere.

Next, instrumentation will be described with reference to FIG. Incidentally, FIG. 4 is a control block diagram.

A flow rate detector 7 is attached to the primary and secondary air supply pipes 16 and 22.
0 and 72 and flow control valves 74 and 76 are provided, and a furnace O ₂ concentration detection sensor 78 is provided in the furnace body 10. The coal supply pipe 20 is provided with a flow meter 80 and a flow control valve 82, and the water supply pipe 47 is provided with a flow meter 84 and a flow control valve 86. A flow meter 88 and a flow control valve 90 are provided in the steam extraction pipe 45, and the steam drum 3
4 is provided with a pressure gauge 92 and a water level gauge 94.

The signals from the flowmeters 70, 72, 80, 84 and 88 are input to the regulators R _{1 to} R ₅ . Pressure gauge 92 and water level gauge 94
Is input to the regulators R ₆ and R ₇ .

The detection signal of the steam amount, the drum pressure, and the detection signal of the in-furnace O ₂ are input to the controller R ₃ , and the coal supply amount setting signal is adjusted so that the coal amount F ₀ changes to F ₁ corresponding to the boiler load. It is output from R ₃ . At the same time, the detection signal of the steam amount and the drum pressure is input to the coal supply amount calculation circuit 96, a predetermined coal supply amount change curve corresponding to the change of the boiler load is calculated, and added to the coal supply amount setting signal, and the valve Control 82.

The detection signal and the detection signal of the furnace O ₂ of the detection signal and the coal quantity of steam amount and the drum pressure is inputted to the regulator R _1, R _2, control is performed with the valve 74, 76. Further, the steam amount detection signal and the drum level detection signal are input to the controller R ₄ , and the valve 86 is controlled.

In this fluidized bed boiler, coal and air are controlled as follows in response to load fluctuations.

When the load is increased, the amount of coal is increased in a larger amount than the coal supply amount F ₁ corresponding to the target load as shown in FIG. In general, since granular coal has a low burning rate, the amount of heat of fuel increases slowly even if the amount of coal is increased. However, the present invention compensates for this slow increase in the calorific value of combustion by making the increase in coal excessive. Further, thereafter, the coal supply amount is narrowed down below the F ₁ to cancel the influence of the excessive supply, and thereafter, the coal supply amount F ₁ corresponding to the increased load is returned. Further, the amount of air is changed in accordance with the increase in load. By doing so, the boiler output can be rapidly increased and the load increase can be quickly followed. Further, in the case of the present invention, since the air amount can be increased / decreased according to the increase / decrease of the load, the fluctuation of the O ₂ concentration in the furnace is small despite the rapid change of the air amount. Therefore, the NOx generation amount does not increase and the desulfurization reaction becomes stable.

When the load decreases, the coal supply amount is first excessively reduced so as to be smaller than the supply amount F ₁ corresponding to the target load. As a result, the boiler output starts to drop rapidly. Then, the supply amount is set to exceed the supply amount F ₁ so as to compensate for this excessive decrease, and then the supply amount F ₁ is set. By doing so, the boiler output is quickly reduced.

In this fluidized bed boiler, when oversupply during when changing to more F ₁ than F ₀ coal supply amount from F ₀ according to the control method according to claim (2), from the time t ₁ of FIG. 2 of t ₂ Is calculated by the advance / delay calculation FX1 and output.
Then, the supply amount at the time of insufficient supply between the times t ₂ and t ₃ is calculated by the advance / delay calculation FX2 and output. The signal of the difference ΔS between S ₁ and S ₂ is output after a delay of the time calculated by the dead time calculation FX3. FIG. 6 is a graph showing an example of changes over time in the fuel supply amount F output by this control method.

At this time, the values of P and Q of the advance / delay calculations FX1 and FX2 and the dead time can be adjusted according to the difference in coal type and the like. The value of P is a variable that changes the height of the peak, and the value of Q is a variable that changes the length of the skirt of the peak.

By making the difference ΔS between S ₁ and S ₂ equal to the difference between the amount of coal Co present in the bed when balanced with F ₀ and the amount of coal C ₁ present in the bed when balanced with F ₁ , It can be brought to steady state early.

Even when the fuel supply amount is changed from F ₀ to F ₁ smaller than F ₀ as shown in FIG. 3, the insufficient supply amount between t ₁ and t ₂ due to FX1 and FX2 and between t ₂ and t ₃ The excess supply amount is calculated. Then, a signal having a difference ΔS between T ₁ and T ₂ is output after a delay of the time calculated by FX3.

In such a control system, the transfer function is calculated as an arithmetic expression for obtaining a predetermined supply amount curve of the fuel supply amount. The lead / lag calculation and waste time calculation indicated by are performed. For example, P = 10 and Q = 3 for FX1 and P = 7 and Q = 3 for FX2.
FIG. 5 shows an output example of the control signal for the fuel supply amount by the computer in such a case. It can be seen that when the step input signal for increasing the load is input, the supply amount setting signal increases more than the target coal amount, and then decreases from the target value to become the target movement. By making such a movement, it becomes possible to control so that the amount of coal actually burned becomes substantially equal to the input signal of load increase.

In the above embodiment, S ₁ and S ₂ , and T ₁ and T ₂ are different from each other by ΔS and ΔT, respectively, but in the present invention, S ₁ and S ₂ , and T ₁ and T ₂ may be equal to each other. .

In the present invention, when the height of the fluidized bed B is changed in accordance with the fluctuation of the boiler load, the installation height of the heat transfer tubes 18 and the filling amount of the fluidized medium 18 are changed so that the number of buried in the fluidized bed B is changed. May be set. For example, when the boiler load increases, the granular coal supply amount and the primary air supply amount are correspondingly maximized, and all the heat transfer tubes 18 are buried in the fluidized bed B. Further, in the intermediate load state, the granular coal supply amount and the primary air supply amount are reduced accordingly, and the fluidized bed B
Of the heat transfer tube 18 is exposed from the fluidized bed B. Further, when the minimum load condition is reached, the granular coal supply amount and the primary air supply amount are reduced to the minimum amount, and the height of the fluidized bed B further decreases. As a result, the uppermost heat transfer tubes 18 and the middle heat transfer tubes 18 are exposed from the fluidized bed B, and only the lowermost heat transfer tubes 18 are buried in the fluidized bed B.
As described above, when the height of the fluidized bed changes according to the load change of the fluidized bed boiler, the number of the heat transfer tubes 18 buried in the fluidized bed increases or decreases, and the heat transfer area increases or decreases. Therefore, the total amount of heat transferred from the fluidized bed B to the heat transfer tubes 18 increases / decreases in accordance with the increase / decrease in load, which enables more rapid output control and significantly reduces the fluctuation range of the temperature of the fluidized bed B. Become. Further, it is possible to avoid a situation in which a large amount of heat is exchanged even when the boiler load is reduced as in the conventional case and the fluidized bed temperature is rapidly lowered, and it is possible to perform stable boiler operation even in a low load state. Is.

Although granular coal is used as the fuel in the above embodiment, various combustible substances other than coal can be used as the raw material.

[Effects of the Invention] As described above, according to the method for controlling a fluidized bed boiler of claims (1) to (3), it is possible to extremely rapidly follow the load fluctuation of the fluidized bed boiler. Also, the amount of nitrogen oxides and sulfur oxides generated is small.

[Brief description of drawings]

FIG. 1 is a diagram of a fluidized bed boiler for explaining an embodiment of the present invention,
2 and 3 are graphs showing control examples. FIG. 4 is a block diagram of the control system, and FIG. 5 is a graph showing a calculation example of a coal amount control signal by a computer,
FIG. 6 is a graph showing a control example. 12 ... Dispersion plate, 14 ... Air chamber, 16 ... Primary air supply pipe, 18 ... Heat transfer pipe, 20 ... Fuel supply pipe, B ... Fluidized bed.

Claims (3)

[Claims] 1. A fuel supply amount corresponding to a boiler load change from a supply amount F ₀ before a load change to a supply amount F ₁ after a load change.
When the boiler output is controlled by changing to, the fuel supply amount change that is larger than the difference between F ₁ and F ₀ above,
Next, a method of controlling a fluidized bed boiler is characterized in that the fuel supply amount is changed to be smaller than the difference between F ₁ and F _0, and then the fuel supply amount is set to F ₁ . 2. The control method according to claim ₁ , wherein the difference ΔS or ΔT between the excess amount S ₁ or T ₂ and the deficient amount S ₂ or T ₁ of the fuel supply amount, that is, S ₁ -S. ₂ or T ₁ -T
₂ is approximately equal to the difference between the amount of solid fuel in the reactor when the fuel supply amount F _{0 is} in a stable state and the amount of solid fuel in the reactor when the fuel supply amount F _{1 is} in a stable state. A method for controlling a fluidized bed boiler, comprising: 3. The control method according to claim 1, wherein an excess amount S ₁ or T ₂ of the fuel supply amount and an insufficient amount S ₂ of the fuel supply amount.
Alternatively, a method for controlling a fluidized bed boiler is characterized by setting T ₁ to be substantially equal to each other.