JPH02254216A - Pressure controller for furnace and flue duct of boiler - Google Patents

Abstract

PURPOSE:To prevent pressure from being sharply dropped immediately after the occurrence of an FCB and the like by a method wherein a preset value signal inappropriate to each of the operation terminals of a forced draft fan, a furnace inlet damper and an induced draft fan is held for a fixed period of time during which control is continuously effected depending on only the effect of a feedback PI control signal. CONSTITUTION:Changing-over devices 101, 102 and 103 are additionally provided on the outlet side of a function generator 84 that sets an air duct pressure preset value for an air duct pressure control loop, on the outlet side of a PI controller 82 that produces a signal of instructing the opening degree of a furnace inlet damper for an air flow rate control loop, and on the outlet side of a function generator 92 that produces an induced draft fan operation terminal preset value signal for a furnace pressure control loop. respectively. An inputted signal is outputted, as it is, as an output signal Y before a first cut back (FCB) and the like occur and, when the FCB and the like occur, the inputted signal is held for a fixed period of time and the changing rate of the output signal Y is controlled until the output signal Y and the inputted signal X coincide with each other. Thus, a furnace pressure can be prevented from being sharply dropped.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a furnace/flue duct pressure control device for a balanced draft boiler, and in particular to a FCB (first cut back)
The present invention relates to a boiler furnace/flue duct pressure control device suitable for reducing the phenomenon in which the boiler furnace pressure suddenly decreases.

[Prior Art] Fig. 5 shows an overview of a pressure control system for a balanced draft boiler.

As shown in FIG. 5, the control method for a balanced draft boiler is to control the pressure in the air duct 2 to a specified value by the pushing force of the forced draft fan 1, and to control the amount of air supplied to the furnace 4. 4 is controlled by adjusting the opening degree of a damper 3 installed at the inlet of the furnace 4, and an induced draft fan 8 flows out from the furnace 4 to the chimney side via the combustion gas duct 6 and the denitrification device and desulfurization device 7 installed on the gas duct. The pressure in the furnace 4 is controlled by adjusting the amount of combustion gas. In Figure 5, 5
1 is an air duct pressure transmitter, 52 is an air duct pressure control circuit, 53 is an air flow meter, 54 is an air flow transmitter, 55
56 is a furnace pressure transmitter, and 57 is a furnace pressure control circuit.

The configuration of these control systems is shown in FIG.

That is, the pressure in the air duct 2 is taken into the control device as a signal from the air duct pressure transmitter 51, and the deviation from the air duct pressure set value signal generated from the fuel flow rate request signal 83 via the function generator 84 is calculated using a subtractor. 85, passed through the PIIJ'4B unit 86, and then added by an adder 87 to the forced draft fan operating end set value signal created from the air flow rate request signal 80 via the function generator 93 and rate of change limiter; A forced draft fan operating end command signal (meaning a signal given to the operating end of a damper, vane, etc. attached to the forced draft fan) is generated, and by adjusting the function of the forced draft fan 1, the pressure in the air duct 2 is increased. controlled.

The air flow rate of the air duct 2 is taken into the control device as a signal from the air flow rate transmitter 54, the deviation from the air flow Y request signal 80 is taken by the subtractor 81, and the air flow rate is sent to the PI controller 82 to generate the furnace artificial damper command. It becomes a signal, and by adjusting the opening degree of the furnace artificial damper 3, the air duct 2
The flow rate of air sent into the furnace 4 is controlled to a specified value.

The pressure of the furnace 2 is taken into the control device as a signal from the furnace pressure transmitter 56, the deviation from the furnace pressure set value 88 is taken by the subtractor 89, and after passing through the PI controller 90, the forced draft fan operation described above is performed. The induced draft fan operating end setting value signal determined by the function generator 92 from the end command signal is added by the adder 91 to generate the induced draft fan operating end command signal (a signal given to the operating end of the damper, vane, etc. attached to the induced draft fan). ) is created, and by adjusting the function of the induced draft fan 8, the combustion gas duct 6 and desulfurization equipment 7 are connected from the furnace 4.
The amount of combustion gas flowing out to the chimney side changes, and the pressure of the furnace 4 is controlled.

In cases where the amount of heat supplied to the inside of the furnace 4 decreases extremely rapidly in a short period of time, such as during FCB or load shedding (hereinafter referred to as FCB, etc.), the temperature of the combustion gas inside the furnace 4 also rapidly decreases. As a result, the pressure drops rapidly.

According to the conventional control circuit configuration shown in FIG.
At certain times, the fuel demand signal 83 and the air flow rate demand signal 80 also drop sharply in synchronization with the load command, which instantly drops sharply.

Therefore, as can be seen from the fact that the function generator 84 is generally a monotonically increasing function and the direction of the +- (plus/minus) signs of the subtractors 81 and 85, immediately after the occurrence of FCB, etc. , the furnace artificial damper 3 and the forced draft fan 1 both move in the throttling direction, which has a negative effect in the sense of suppressing the amount of air forced in from upstream in response to the above-mentioned sudden decrease in furnace pressure. In other words, it acted to promote a decrease in furnace pressure.

[Problem to be solved by the invention]

As mentioned above, immediately after the occurrence of FCB, etc., the furnace 4 should be
This is in the sense of dealing with extremely transient situations that differ from the balance under normal operating conditions with respect to the operation of forced draft fan 1, furnace artificial damper 3, and induced draft fan 8, which are important positions in pressure control III. This is not taken into account, and despite such transient conditions, the control loop is superimposed with a set value determined by the balance of the normal operating situation as a preceding signal, which can lead to sudden changes in the control loop. There was a problem in that the operation could promote a significant pressure drop, leading to the risk of destruction of the outer wall due to the external pressure of the furnace and its trailing flue.

The purpose of the present invention is to hold the inappropriate set value signals for the three operating terminals for a certain period of time in the above transient situation, and during that time, to continue control by relying only on the operation of the feedback PI control signal, immediately after the occurrence of FCB etc. The purpose is to prevent a sudden pressure drop.

[Means to solve the problem]

The above purpose is to provide a boiler furnace that supplies and burns fuel;
A forced draft fan that supplies combustion air to the boiler furnace through an air duct, and an induced draft fan that discharges combustion gas from the boiler furnace through the gas duct, and an output of a combustion air flow rate request signal generator. An air flow control device that controls a damper installed in the air duct based on the deviation signal between the signal and the signal from the air flow transmitter in the air duct, and an air duct pressure set value transmission that is transmitted based on the fuel request signal to the boiler. An air duct pressure control device that controls the opening of the pusher or its damper based on the signal from the device, the signal from the air duct pressure transmitter, and the signal from the pusher drafter operating end set value signal generator, and the boiler furnace. The induced draft fan is operated based on the signal from the internal pressure signal generator, the signal from the boiler furnace internal setting pressure signal generator, and the signal from the induced draft fan operating end signal generator that sends a signal based on the forced draft fan operating end command signal. In a boiler furnace/flue duct pressure control device equipped with a furnace pressure control device that controls the damper opening degree, when an FCB or the like that suddenly changes the boiler load occurs, the output signal before the occurrence is held for a predetermined period of time, and then the output signal is A switching device is provided in the air flow rate control device, the air duct pressure setting value transmitting device, the induced draft fan operating end signal generating device, and each output signal circuit, for switching to an output signal commensurate with the human input signal while limiting the rate of change of the input signal. This problem is solved by a boiler furnace/flue duct pressure control device featuring the following characteristics.

〔Example] FIG. 1 shows an embodiment of a control circuit according to the present invention.

The interaction of the components is similar to that described in the prior art section of FIG. A device 2102 is installed at the outlet of the PI controller 82 of the flow rate temperature loop, and a function generator 9 of the furnace pressure control loop is connected to the function generator 9 of the furnace pressure control loop.
The difference is that a device 103 is added to the outlet of No. 2.

Added device 101. ．． The operation of 102.103 is the second
As shown in the figure, the signal of human power The rate of change of the output signal Y is controlled until a failure (or a slight deviation) occurs. After that, signal Y again
The same value as the value of the signal X is output.

The above circuit addition device eliminates the problem of F
The negative effects of the forced draft fan 1 and the furnace rodan bar 3 on the sudden drop in furnace pressure immediately after the occurrence of CB etc. are eliminated by the following two effects. First, the function generator 84 is a setting (target) signal for pressure control of the air duct 2.
Immediately after the occurrence of FCB, etc., the exit signal of (determined in advance). After stabilization, the rate of change is limited and the signal generated by the conventional circuit is restored.

FIG. 3 shows an example of a specific circuit for realizing the operation shown in FIG. 2. 15o and 151 are changeover switches;
2 is a memory circuit, 153 is a rate of change limiter, 154 is a subtracter, 155 is an absolute value calculator, 156 is an H/L monitor, 15
7 and 158 are switching signals for changeover switches 150 and 151.

Next, the behavior of the air flow rate request signal 80, which is the flow rate setting (item 1) signal of the air duct 2, is limited by a circuit device similar to that described above.

The above-mentioned two operations eliminate the above-mentioned negative effects, reduce the sudden drop in pressure in the furnace 4 immediately after occurrence of FCB, etc., and can also be expected to smoothly shift control to a new balance point.

On the other hand, with regard to the induced draft fan 8, adding only part numbers 101 and 102 will not allow the furnace 4 to
In order to prevent the pressure from decreasing, the forced draft fan operating end command signal, which is the output signal of the adder 87, is in an increasing direction.Since the function of the function generator 92 is generally in the form of a monotonous increase, the output signal of the function generator 92 is in an increasing direction.

Therefore, as it is, an increasing signal will be superimposed on the induced draft fan control end command signal by the adder 91 immediately after the occurrence of FCB, etc., which will promote the amount of combustion gas flowing out from the furnace 4. In its meaning, it has a negative effect. Therefore, in the present invention, as shown in FIG.
By adding the circuit device 103 having the same function as 02, the above-mentioned negative effects are eliminated.

AUTO/) (In the case of a circuit configuration that has an AND selector station circuit, instead of installing part number 102 in Figure 1, the station switch, which is normally in the AUTO state, is automatically switched to the HAND side at the same time as an FCB occurs. It is conceivable to have a configuration that provides functionality.

As a result, the command signal to the furnace artificial damper 3 immediately after the occurrence of FCB etc. is held in the same way as described in the present invention.

After an F'CB or the like occurs, the operator may gradually return to control over the balanced state of the system by manual operation while monitoring the system state.

[Effects of the Invention] According to the present invention, it is possible to eliminate the influence of the operation of the harmful advance control set value signal in the air duct pressure control n, air flow rate control, and furnace pressure control loop on the furnace pressure drop immediately after the occurrence of FCB, etc. Therefore, a sudden drop in the furnace pressure can be prevented.

[Brief explanation of drawings]

Fig. 1 is an embodiment of the boiler furnace/flue duct pressure control system according to the present invention, and Fig. 2 is used in the present invention to hold the output signal value for a certain period of time after occurrence of FCB, etc., and then limit the rate of change. FIG. 3 is a specific circuit configuration diagram of the switching device, FIG. 4 is a boiler furnace/flue duct pressure control system diagram of the conventional technology, and FIG. 5 is a balanced ventilation type It is a block diagram of the smoke duct related device of a boiler. 1... Forced draft fan, 2... Air duct, 3... Furnace artificial damper, 4... Boiler furnace, 6... Gas duct, 8... Induced draft fan, 51... Air duct Pressure transmitter, 54...Air flow rate transmitter, 56...Firepower pressure transmitter, 80...Air flow rate request signal, 83...Fuel request signal, 84...Air duct pressure set value function generation 88...Furnace pressure set value, 92...Induced draft fan operating end set value function generator, 93...Forced draft fan operating end set value function generator, 101.102.103...Switching Device. Applicant Babcock Hitachi Co., Ltd. Agent Patent Attorney Takeshi Kawakita

Claims (1)

[Claims] A boiler furnace that supplies and burns fuel, a forced draft fan that supplies combustion air to the boiler furnace through an air duct, and an induced draft fan that discharges combustion gas from the boiler furnace through a gas duct, and an air flow rate control device that controls a damper provided in the air duct based on a deviation signal between the output signal of the combustion air flow rate request signal generator and the signal from the air flow rate transmitter in the air duct, and a fuel request to the boiler. Based on the signal from the air duct pressure set value transmitter, which is transmitted based on the signal, the signal from the air duct pressure transmitter, and the signal from the push draft fan operating end set value signal generator, the opening degree of the pusher or its damper is determined. The air duct pressure control device to be controlled, the signal from the boiler furnace internal pressure signal generator, the signal from the boiler furnace internal setting pressure signal generator, and the induced draft fan operating end signal that transmits the signal based on the forced draft fan operating end command signal. Occurs when FCB, etc. that suddenly changes the boiler load occurs in a boiler furnace/flue duct pressure control device equipped with an induced draft fan or a furnace pressure control device that controls the damper opening based on the signal from the generator. A switching device that holds the previous output signal for a predetermined time and then switches to an output signal that matches the input signal while limiting the rate of change of the output signal.
A boiler furnace/flue duct pressure control device, characterized in that the air flow rate control device, the air duct pressure set value transmitting device, the induced draft operating end signal generating device, and each output signal circuit are provided.