JPS6115322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion control device for a moving bed municipal waste incinerator having boiler equipment for utilizing residual heat.

Conventionally, in order to maintain a constant pressure in the waste heat boiler drum of an incinerator, excess steam is discharged to an atmospheric condenser to control the pressure in the drum. By the way, in the current incinerator boiler, the can water capacity is extremely large, and the generation of steam bubbles in the can water due to fluctuations in can pressure.
The height of the liquid level in the air-water drum due to condensation, the so-called swell swelling, appears significantly, and it is therefore difficult to precisely suppress liquid level fluctuations through water supply control. For this reason, in order to control the pressure of the tank by releasing excess steam, it is common to increase the sensitivity of the regulator during operation, and changes in the amount of heat absorption appear as they are or are magnified as changes in the amount of evaporation, and the fluctuation width and fluctuation cycle are The number becomes significantly larger. It is difficult to control this fluctuating amount of steam by controlling the amount of waste supplied or the amount of combustion air due to the heterogeneity and responsiveness of the waste. Furthermore, in order to stably supply steam to the outside, the above-mentioned fluctuations must be excluded, resulting in a significant decrease in utilization efficiency. On the other hand, the waste heat boiler of an incinerator usually has a margin of about 6 kg/cm ² between the turbine end normal pressure and the boiler's maximum pressure, and even if this pressure difference cannot be utilized in its entirety,
By utilizing the function as a steam accumulator due to the large can water capacity and steel material capacity, it is possible to smooth out not only short period fluctuations in the steam flow rate but also somewhat long period changes in absorbed heat amount. In order to achieve this smoothing, it is necessary to improve the water supply control described above and to take into account the allowable range for liquid level fluctuations in the design, but these can be done using conventional techniques.

On the other hand, from the standpoint of stable combustion control of waste,
Stabilizing boiler evaporation and stabilizing waste incineration are closely related and can be achieved simultaneously. However, as described above, when attempting to control fluctuations in the amount of evaporation to a constant value by incineration control, controllability is extremely poor, and as a result, it is impossible to achieve sufficient stable combustion of waste. By the way, as already mentioned, the boiler pressure when setting a constant load is
It has excellent fluctuation characteristics, and by selecting this as a control variable for stable garbage combustion control, it is possible to achieve stable garbage combustion without difficulty.

In addition to the above, NOx for garbage incinerators
Regulation is also an issue. Conventionally, no combustion control system has considered NOx suppression;
The method of operating an incinerator is to increase the combustion ventilation temperature,
It is conceivable to cause internal ignition in the drying stage to promote drying and carbonization gasification at the same time, and at the same time to reduce the oxygen concentration in the gas combustion zone in the furnace by restricting ventilation in the combustion stage and after-combustion stage. Furnace cooling by overfire air is extremely effective, either by using recirculated exhaust gas or by water spray.
NOx suppression is possible.

Furthermore, the furnace temperature in the incinerator can be changed in accordance with the calorie value of the waste, but conventionally the furnace temperature has been controlled using in-furnace cooling air. However, when in-furnace cooling air is used, it is not easy to stir and mix the in-furnace cooling air and combustion gas, and it is difficult to detect a uniform temperature. Because of the acceleration of combustion and the opposite response, satisfactory results could not be obtained. Therefore, it is desirable to control the furnace temperature not by using fresh air but by using recirculated gas or water spray.

As a means of suppressing NOx, NH ₃ denitrification methods and the like have been proposed. This method has problems such as high NH ₃ consumption cost, NH ₄ Cl deposition and corrosion on the boiler heat transfer surface, and white smoke generation from the chimney. Therefore, the above-mentioned NOx suppression cannot be achieved by controlling the operation method. As the first step, it is desirable to use NH ₃ denitrification as an auxiliary method.

In view of the above, the present invention provides a novel combustion control device for a municipal waste incinerator.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the combustion control device, which is composed of an evaporation stabilization control circuit, a NOx suppression control circuit, a furnace temperature control circuit, a boiler load correction circuit, a charging speed control circuit, and the like. The evaporation stabilization control circuit includes a boiler pressure regulator 2 to which the drum pressure signal a of the boiler 1 is input, an air advance regulator 3 to which the output of the boiler pressure regulator is input, an air-fuel ratio setting device 4, and an automatic/manual switching setting device 5, an adder 6 to which the outputs of the air advance controller 3 and the air-fuel ratio setting device 4 are added, an air flow rate controller 7 to which the output of the adder is input; An air flow control valve 8 controlled by the air flow controller, and an input flow controller 9 into which the output of the automatic/manual switching setting device 5 is input.
, a grate drive signal generator 10 controlled by the input amount controller, and the like. The ventilation amount control valve 8 is connected to the ventilation pipe 1 from the ventilation blower 11.
2 to control the amount of ventilation under the grate to the drying grate 13, combustion grate 14, and post-combustion grate 15. The grate drive signal generator 10 outputs drive signals to the grate drive devices 16, 17, and 18.

The NOx suppression control circuit includes a sampling device 19 that extracts a portion of the exhaust gas, a NOx concentration detection device 20 and an O ₂ concentration detection device 21 to which a portion of the exhaust gas is supplied, and a NO ₂ concentration O ₂ converter 22. , an oxygen concentration setting device 23, an averaging device 24, an oxygen concentration controller 25, a manual bias setting device 26, an output of the manual bias setting device, and the air-fuel ratio setting device 4.
and an adder 27 which adds the output of the adder 27 and inputs the result to the adder 6.

The furnace temperature control circuit includes a nonlinear circuit 28 to which the furnace temperature signal b is input, a furnace temperature controller 29 to which the output of the nonlinear circuit is input, and an exhaust gas recirculation circuit controlled by the furnace temperature controller. It is composed of a quantity control valve 30 and the like. This exhaust gas recirculation amount control valve controls the amount of exhaust gas recirculated from the exhaust gas recirculation device 31 via the recirculation blower 32.

33 is a boiler load correction circuit, and the boiler load 3 is adjusted by a signal from the boiler load correction circuit.
4 is controlled.

The feeding speed control circuit is composed of an automatic/manual switching setting device 35 to which the garbage feeding amount signal c is input, the above-mentioned feeding amount controller 9 to which the output of the automatic/manual switching setting device is input, etc. .

In Fig. 1, d is an airflow rate signal, 36 is a garbage input hopper, 37 is a rotary kiln, and 38 is a rotary kiln.
3 represents a dust collector, and 39 represents a standard level of dust.

The operation and effect of the combustion control device having the above configuration will be explained for each of the above circuits.

The evaporation stability control circuit operates by detecting the boiler drum pressure and correcting the deviation from the set pressure in order to control the waste feeding speed and ventilation amount according to the set evaporation amount based on the required steam amount or required incineration amount. do. Note that the allowable range of pressure fluctuation is set to be large enough to absorb and alleviate the difference in heat balance.

The boiler pressure regulator 2 to which the drum pressure signal a is input sets the amount of increase in waste feed to be corrected when the pressure decreases and the increase in the amount of air proportional to this, and vice versa when the pressure increases. , operates to set the amount of reduction in waste feed to be corrected and the amount of air reduction proportional to this. For this purpose, the output of the controller 2 is led to the air advance controller 3, and the output of the controller 2 is changed so that temporary large pressure fluctuations can be dealt with only by manipulating the air. It operates to set the amount of air proportional to the rate of change so that when the pressure increases, the air amount decreases, and when the pressure decreases, the amount of air increases. Further, the output signal of the regulator 2 is outputted as a setting value of the garbage input amount regulator 9, and after passing through the air-fuel ratio setting device 4, is added to the output of the regulator 3 by an adder 6, This becomes the required value of the ventilation amount in this evaporation amount stabilization control circuit, and is led to the ventilation amount controller 7.

Due to the operation of the evaporation stabilization control circuit described above, in a waste incineration boiler that has a large can water capacity and a large heat penetration compared to the evaporation amount, there may be some excess or deficiency of boiler steam due to uneven combustion of waste. The pressure on the drum is smoothed by self-evaporation or condensation of vapor bubbles resulting from allowing fluctuations in the drum pressure, thereby reducing the burden on control operations and significantly improving controllability. Furthermore, the above-mentioned advance control of the amount of air relative to the amount of evaporation increases control responsiveness and improves controllability by controlling the combustion of dried waste on the grate.
As a result, stable combustion of garbage can be carried out without difficulty.

The NOx suppression control circuit sets an appropriate exhaust gas oxygen concentration for the garbage currently being twisted based on the average NOx concentration over a certain period of time in the past, and controls the amount of airflow under the grate by manipulating the amount of ventilation under the grate. Controls the oxygen concentration in exhaust gas to suppress and maintain NOx generation at low levels. As shown in Figure 2, NOx is
By performing low-oxygen combustion, the level can be suppressed to a sufficiently low level. Taking advantage of this, in the NOx suppression control circuit, a part of the exhaust gas is guided from the sampling device 19 to the NOx concentration detection device 20 and the O ₂ concentration detection device 21, and the detection results are sent to the NOx concentration O ₂ converter. 22 and the NOx concentration converted into O ₂ is input to an oxygen concentration setting device 23 . This oxygen concentration setting device 23 is a nonlinear circuit for calculating the appropriate oxygen concentration O ₂ to be newly set for the average value x of the NOx concentration within a certain time TN according to the following formula, as shown in FIG. and a bias circuit that can be set manually by the operator while observing the generation of NOx.

O ^* ₂ = ₂ + α (NO ^* _x - x) + ' ₂ However, NO ^* _x : Tolerable limit value of NOx concentration α: α = 0 (NO ^* _x > x) α = Normal number (NO ^* _x ≦ x ) ₂ : Constant ' ₂ : Bias amount of oxygen concentration that can be set artificially by the operator As a result, the oxygen concentration setting device 23 outputs a new appropriate exhaust gas oxygen concentration to the oxygen concentration controller 25 at fixed time intervals TN. Output and retained as target value. This oxygen concentration controller 25 is connected to the averaging device 2.
While measuring the oxygen concentration signal that changes smoothly and smoothed by After passing through the setter 26, it is added to the airflow requirement value of the drum pressure control circuit.

The operation of the NOx suppression control circuit described above does not directly deal with dynamic fluctuations in NOx concentration.
A new appropriate exhaust gas oxygen concentration is set based on the average NOx concentration over a certain period of time in the past, and the oxygen concentration is maintained at a predetermined value through slow control, reducing the burden on control operations and reducing the burden on the boiler pressure control system. There is also less interference. Furthermore, since it includes a bias setting circuit that can be set based on operator observation, unnecessarily low oxygen combustion can be avoided in the case of waste that generates a small amount of NOx.

In the above-described furnace temperature control circuit, an allowable furnace temperature range is set to prevent incompletely burned ash from melting and damage to the furnace, and the furnace temperature is maintained within this range. As such a circuit, a circuit that recirculates exhaust gas into the furnace or performs water spraying is considered in order to suppress the rise in furnace temperature due to the above-mentioned low-oxygen combustion. In FIG. 1, exhaust gas recirculation is used, and the furnace temperature signal b passes through a nonlinear circuit 28 and enters a furnace temperature controller 29. The nonlinear circuit 28 has a polygonal characteristic shown in FIG. Therefore, the controller 29 sends a certain amount of exhaust gas into the furnace when the furnace temperature is within the permissible range, increases this amount when it exceeds the upper limit, and decreases this amount when it falls below the lower limit, thereby controlling the furnace temperature. It operates to maintain the temperature within the permissible range.

A reliable cooling effect can be obtained by the exhaust gas recirculation or water spray described above, and furthermore, these operations do not affect the oxygen concentration in the exhaust gas, so the NOx
Interference with the suppression control circuit can be eliminated.
Furthermore, by providing a permissible range for fluctuations in furnace temperature, interference with the boiler pressure control circuit can be reduced.

The boiler load correction circuit 33 roughly evaluates the quality of the garbage currently being burned from the average amount of garbage input over a certain period of time in the past, and determines an appropriate amount so that the average amount of garbage input does not deviate greatly from the specified input amount. Set boiler load. For this purpose, the amount of garbage input into the garbage input hopper 36 and the input time are checked every fixed period of time TB, and the average amount of garbage input during that period is calculated. The deviation between the average waste input amount and the specified input amount can be further reduced by correcting the boiler load. Therefore, the boiler load correction circuit 33 decreases the boiler load 34 if the average garbage input amount (incineration amount) of the past fixed time TB is larger than the specified value, and conversely increases the output if it is smaller than the specified value. Output and retain this.

In the boiler load correction circuit described above, the waste input speed is not always tightly controlled to a specified value by the cut-out speed of the drying grate 13, but the boiler load corresponding to the average waste quality is corrected at regular intervals. By controlling the input speed indirectly, dynamic interference between the input amount control and other control circuits can be avoided, and as a result, NOx suppression control, boiler pressure control, etc. It is possible to achieve both.

The charging speed control circuit measures and controls the charging speed with respect to the requested value of the amount of waste to be charged from the boiler pressure control circuit. As a measurement value of this feeding speed,
The average input speed during the specified number of times (1 to 2 times) of garbage input into the hopper 36 by the crane is maintained as an output at any time. The feeding speed controller 9 measures this average feeding speed and performs proportional control based on the deviation between this value and the required value of the feeding speed.
The controller 9 outputs a continuous amount such as current, and this output is input to the grate drive signal generator 10. This transmitter 10 integrates a continuous signal, outputs a grate drive signal when the integrated value becomes constant, and is simultaneously reset to start a new integration. This grate drive signal is transmitted to the grate drive device 1.
6, 17, 18, and each time this signal is received, said grate drive 16, 17, 18 performs one reciprocating motion.

A flowchart of the above-described control in the control device of FIG. 1 described above is as shown in FIG. 5. In FIG. 5, when incineration amount control is implemented, furnace temperature control and stable garbage combustion control are required. Also, depending on the boiler pressure control when setting the load, priority is given to the garbage feeding operation, and the ventilation amount is additionally controlled. Evaporation amount stabilization control and NOx suppression control are required as separate items at a lower level than incineration amount control.

As described above, the present invention corrects the pressure by combustion control while allowing some fluctuations in the boiler pressure, provides a tolerance for fluctuations in the furnace temperature, and controls the furnace temperature through exhaust gas recirculation, water spraying, etc. In addition to setting and controlling the exhaust gas oxygen concentration that matches the waste quality, the average waste input amount is controlled by modifying the boiler load at regular intervals, thereby stabilizing the amount of boiler evaporation and reducing NOx.
It is possible to simultaneously perform suppression control, furnace temperature control, and waste input amount control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figure 2 is a diagram showing the NOx concentration versus exhaust gas oxygen concentration, Figure 3 is a diagram showing the characteristics of the oxygen concentration setting device, Figure 4 is a diagram showing the characteristics of the nonlinear circuit, and Figure 5 is the diagram shown in Figure 1. This is a flowchart of the control of the device. 1: Boiler, 33: Boiler load correction circuit.

Claims (1)

[Claims] 1. In the combustion control system of a municipal waste incinerator equipped with a waste gas boiler, there is an evaporation stabilization control circuit that controls the waste feed rate and ventilation amount to keep the pressure of the boiler drum constant, and a ventilation control circuit that controls the amount of ventilation based on the NOx concentration over a certain period of time. A NOx suppression control circuit that controls the oxygen concentration of exhaust gas by correcting the amount of oxygen, a furnace temperature control circuit that sets the upper and lower limits of the furnace temperature and controls the furnace temperature through exhaust gas circulation or water spray, and a NOx control circuit that controls the amount of heat that can be recovered depending on the amount of waste. 1. A combustion control device for a municipal waste incinerator, characterized by comprising a boiler load correction circuit that sets a boiler load accordingly.