JP4108624B2 - Combustion control method and waste treatment apparatus - Google Patents

Description

  The present invention relates to a combustion control method and a waste treatment apparatus suitable for burning waste and the like, and more particularly to supply control of combustion air.

  In addition to direct incineration using a stoker-type incinerator or fluidized bed incinerator, waste combustion treatment methods include pyrolysis gas generated by pyrolyzing waste at high temperature in the combustion furnace, There is known a gasification and melting system in which a combustible component contained in a thermal decomposition residue is charged into this combustion furnace to burn and melt.

  As an example of this gasification and melting system, pyrolysis gas generated by pyrolyzing waste and some pyrolysis residue are introduced into a high-temperature furnace, and combustion air is supplied in two stages while swirling. Thus, a two-stage combustion method for burning and melting is employed. That is, the amount of air supplied to the first stage combustion chamber is adjusted to be less than the stoichiometric ratio of the combustion object, while the amount of air supplied to the second stage combustion chamber is oxygen in the combustion exhaust gas. The concentration is adjusted so as to be within the set range, and the generation of CO and NOx is suppressed by correcting the amount of air based on the combustion temperature in the first stage combustion chamber (Patent Document 1). reference.).

JP 2002-162015 A

  However, in the combustion treatment of waste, the amount of oxygen necessary for combustion may vary depending on the qualitative and quantitative variation of the combustible material in the combustion object. For this reason, if the combustion air is supplied excessively, the amount of NOx in the exhaust gas increases, and if it is insufficient, CO is generated. In particular, since NOx has a strict regulation value for the emission amount, the above-described air supply control method may cause the NOx emission amount to exceed the regulation value even if CO emissions are suppressed.

  This invention makes it a subject to suppress discharge | emission of NOx and CO below to an appropriate value.

In order to solve the above problems, the present invention measures the oxygen concentration of exhaust gas discharged from a combustion furnace that burns waste and the like in the exhaust gas flow path on the downstream side of the combustion furnace, and this measured oxygen concentration is measured. In a combustion control method for controlling increase / decrease in the amount of combustion air supplied to a combustion furnace so as to be held at either a set value or a set range, the NOx concentration of the exhaust gas is measured in the exhaust gas flow path, and this measured NOx When the concentration exceeds a predetermined upper limit value, the increase in the supply amount of combustion air is stopped, and when the concentration is lower than the lower limit value, the decrease in the supply amount of combustion air is stopped.

  As described above, the combustion air supply control is performed according to the oxygen concentration, and as a new control means, when the detected value of the NOx concentration exceeds the upper limit value, the increase in the air supply amount is stopped, preferably decreased. When the value falls below the lower limit value, NOx emission and CO emission can be suppressed by adding control to stop, preferably increase, the decrease in the air supply amount.

A waste treatment apparatus for realizing a combustion control method according to the present invention includes a pyrolysis reactor that pyrolyzes waste, and combustion that burns pyrolysis gas generated from the pyrolysis reactor and a part of the pyrolysis residue. A melting furnace, an oxygen concentration measuring means for measuring the oxygen concentration of exhaust gas discharged from the combustion melting furnace, and the oxygen concentration of the exhaust gas measured by the oxygen concentration measuring means is held at either a set value or a set range. in waste disposal and control means for increasing or decreasing control the supply amount of combustion air supplied to the combustion melting furnace to the NOx concentration measurement means for measuring the NOx concentration in the exhaust gas is provided, the control means, NOx concentration When the NOx concentration measured by the measuring means exceeds a predetermined upper limit value, the increase in the supply amount of combustion air is stopped, and when the NOx concentration falls below the lower limit value, the supply amount of combustion air is decreased. The realized by stopping.

  According to the present invention, NOx and CO emissions can be suppressed to below appropriate values.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an overall configuration diagram of an embodiment in which the present invention is applied to a waste plant. As shown in the figure, when the waste carried by the truck 1 is put into the garbage pit 2, it is conveyed to the garbage crusher 4 by the crane 3, crushed to a predetermined size, and supplied to the conveyor 5. . The waste transported by the transport machine 5 is put into a pyrolysis drum 6, where pyrolyzed gas and pyrolysis residue of the pyrolyzed waste are separated by a discharge device 7, and the pyrolyzed gas is gas line 8. Then, it is led to the combustion melting furnace 9. On the other hand, the pyrolysis residue is supplied to the combustion melting furnace 9 through the conveying line 12 after being cooled, separated and refined through the cooling drum 10 and the pyrolysis solid matter separation equipment 11. The combustion melting furnace 9 includes a burner (not shown) at the top, a first air nozzle 13 provided on the furnace wall below the burner, and second and second nozzles sequentially provided downward from the first air nozzle 13. 3 air nozzles (14 in total). The second and third air nozzles 14 are supplied with air fed from the inside of the garbage pit 2 through the air supply line 15 by the forced blower 16 and are ejected from here into the combustion melting furnace 9. Yes. A slag discharge port 17 for discharging molten slag at the bottom of the combustion melting furnace 9 is provided to open toward the water surface of the water tank 18. The molten slag supplied into the water tank 18 is supplied to the slag yard 19.

  The high-temperature combustion exhaust gas discharged from the combustion melting furnace 9 is sequentially recovered by a high-temperature air heater 20 and a waste heat boiler 21, and then cooled by a temperature-reduction tower 22 to remove a dust filter 23 and a desalting bag. Dust removal and desalting are performed by the filter 24 and discharged from the chimney 26 through the induction blower 25 to the atmosphere. Here, a part of the combustion exhaust gas discharged from the induction fan 25 is led to the exhaust gas circulation fan 27 and used for cooling the outer wall of the combustion melting furnace 9 and the like. The desalted residue recovered by the desalting bag filter 24 is recovered by the desalted residue recovering device 28, treated with heavy metal, ash-solidified and discharged out of the system. The high-temperature air recovered and heated by the high-temperature air heater is partly used for the heating air for the pyrolysis drum 6 via the heating furnace 28 for starting, while the remaining air is It is cooled by the heated air cooler 29 and returned to the high temperature air heater 20 via the heated air blower 30 again. In addition, the water vapor | steam produced | generated from the heat | fever collect | recovered by the waste heat boiler 21 is utilized for an electric power generation by the steam turbine or the generator 31. FIG.

  The combustion air supply control system includes a flow rate control valve 32 disposed on the discharge side of the forced air blower 16 in the air supply line 15, a control device 33 for controlling the flow rate control valve 32, an oxygen analyzer 34, And a NOx concentration analyzer 35. The oxygen analyzer 34 samples the dusted combustion exhaust gas discharged from the dust removal bag filter 23 and measures the oxygen concentration in the exhaust gas. The measured value of the oxygen concentration is input to the control device 33, and the difference from the set value or set range of the oxygen concentration is obtained. This difference is input to the control means made up of PID or the like in the control device 33, and an air amount for reducing the difference is calculated. The NOx concentration analyzer 35 measures the NOx concentration in the exhaust gas by sampling the cleaned exhaust gas discharged from the desalting bag filter 24 from the downstream side of the induction blower 25. The measured value of the NOx concentration is input to the control device 33, and, as will be described later, when the concentration falls outside a preset concentration range, a certain restriction is imposed on the air amount control based on the oxygen concentration described above.

  Next, the operation of the combustion air supply control system in the waste plant configured as described above will be described in detail. In the combustion melting furnace, the combustion in the primary combustion region from the burner to the first air nozzle 13 is performed with insufficient air less than the stoichiometric ratio supplied from the first air nozzle 13, and thereby the fuel NOx is reduced. Occurrence is reduced. The temperature in the primary combustion zone is adjusted to a high temperature of 1000 to 1200 ° C., for example. On the other hand, the combustion in the secondary combustion zone from the first air nozzle to the second and third air nozzles 14 is performed with the air supplied from the second and third air nozzles 14, and this air supply amount is The amount is controlled by subtracting the amount of air supplied in the primary combustion zone from the amount obtained by adding a certain amount of excess air to the stoichiometric ratio required for complete combustion of pyrolysis gas and pyrolysis residue.

  Control of the amount of air supplied to the secondary combustion zone is basically adjusted so as to maintain the oxygen concentration of the combustion exhaust gas at either a set value or a set range. The oxygen concentration of the combustion exhaust gas is determined by guiding the exhaust gas that has passed through the dust filter 23 and removed to dust to the oxygen analyzer 34. When the oxygen concentration value SP is higher than the measurement value PV, the control device 33 compares the measurement value PV of the oxygen concentration measured by the oxygen analyzer 34 with the oxygen concentration value SP that is a preset reference value. The amount of air supplied to the secondary combustion zone is increased, and a command value for reducing the difference between the two is output to the flow control valve 32 to complete combustion. Further, when the measured value PV is higher than the oxygen concentration value SP, a command value for reducing the supply amount of air is output to the flow control valve 32 to suppress generation of NOx.

  However, if the amount of waste input changes or the composition of the combustible material related to the heat generated by the pyrolysis gas changes, the required amount of air changes, and the amount of air is adjusted based on the oxygen concentration. In some cases, the generation of NOx and CO may not be suppressed below the appropriate value. That is, when the air supply amount becomes excessive, NOx is generated, and when supply is insufficient, CO is generated.

  Therefore, in the present embodiment, in order to suppress NOx and CO emissions, the NOx concentration of exhaust gas is measured, and when the measured value exceeds a predetermined upper limit value, the increase in the air supply amount is stopped. Preferably, it is decreased, and when it falls below the lower limit value, the decrease in the air supply amount is stopped, preferably increased, so that the air amount control according to the oxygen concentration is limited. Thereby, while suppressing the increase in NOx discharge | emission amount when a NOx measured value exceeds an upper limit, generation | occurrence | production of CO when it falls below a lower limit can be suppressed.

  FIG. 2 is a model diagram showing how the air supply amount is controlled in the NOx measurement value. In the figure, the solid line represents the change in the air supply amount based on the NOx measurement value, and the dotted line represents the change prohibited due to the restriction on the supply amount control based on the oxygen concentration. First, when the NOx measurement value falls within the range of the lower limit value or more and the upper limit value or less, as described above, the air supply amount PID control based on the oxygen concentration is performed, and the air is maintained so as to keep the set value or the like. The amount is increased or decreased automatically.

  On the other hand, when the NOx measurement value exceeds the upper limit value, the increase in the air supply amount is stopped, and either the decrease or the maintenance operation is performed. That is, when the oxygen concentration value SP is higher than the measured value PV, the air supply amount is basically controlled to be increased. However, the restriction of control based on the NOx measured value is added, so that the increase of the air supply amount is increased. It is prohibited, and an operation for reducing the air supply amount by D control (differential operation) (an operation for suppressing the increase) is permitted. Further, when the measured value PV is higher than the oxygen concentration value SP, the air supply amount is basically controlled to be reduced. However, the control by the NOx measurement value permits the reduction of the air supply amount, and the D control is used. Operations that increase the air supply amount (operations that try to suppress the decrease) are prohibited.

  On the other hand, when the NOx measurement value is below the lower limit value, the decrease in the air supply amount is stopped, and either increase or maintenance is performed. That is, when the oxygen concentration value SP is higher than the measured value PV, an increase in the air supply amount is permitted, and an operation for decreasing the air amount by the D control is prohibited. On the other hand, when the measured value PV is higher than the oxygen concentration value SP, a decrease in the air supply amount is prohibited, and an operation for increasing the air supply amount by D control is permitted.

  Here, if the measured NOx value exceeds the upper limit value, the output value of the air supply amount is set to the high limit value, and if the high limit value is set to decrease along with the decrease of the output value, the limit is activated and the output works. The increase in value can be stopped. On the other hand, when the measured NOx value is lower than the lower limit value, the decrease in the output value can be stopped by setting the output value as the low limit value.

  Further, it is preferable to provide an off-delay timer at the upper and lower limits of the NOx measurement value so that, for example, when the NOx value deviates from a state exceeding the upper limit value, the timing for releasing the control restriction is delayed for a predetermined time. That is, in order to prevent the limit and release from being repeated each time the measured NOx value fluctuates near the upper limit, a timer is provided so that the limit is released when a predetermined time is continued. During automatic calibration of the NOx concentration analyzer 35, control based on the NOx concentration is not provided, and control according to the oxygen concentration is continued.

  In this way, when the output value of the air supply amount is processed, an output signal of the valve opening degree corresponding to the air supply amount is transmitted from the control device 33 to the flow rate adjustment valve 32, and the second and second A suitable amount of air is supplied to the secondary combustion zone via the three air nozzles 14.

  Next, the effect of the control described above will be described with reference to FIG. FIG. 3A is an example according to the prior art, and FIG. 3B is an example according to the present embodiment. In each case, the horizontal axis represents time, and the vertical axis represents NOx concentration, oxygen concentration, and combustion air amount from the top according to each solid line. Note that the NOx concentration and the oxygen concentration indicate values measured by the NOx concentration analyzer 35 and the oxygen analyzer 34, respectively, and the combustion air amount corresponds to the air supply amount.

  As is clear from FIG. 3 (a), the NOx concentration increased slightly after increasing the amount of combustion air as the oxygen concentration decreased, resulting in exceeding the regulation value (for example, 100 ppm). Yes. That is, it is considered that waste was oxidized in the secondary combustion zone due to excessive supply of air and a large amount of NOx was generated. On the other hand, FIG. 3 (b) increases the combustion air amount as the oxygen concentration decreases, and when the NOx concentration exceeds the upper limit (for example, 85 ppm), the increase in the combustion air amount is stopped and the supply amount is increased. Therefore, the NOx concentration can be kept below the regulation value. Further, even when the NOx concentration is lower than the lower limit value (for example, 75 ppm), the reduction of the combustion air amount is stopped, so that CO generation can be prevented.

  As described above, according to this embodiment, the oxygen concentration and NOx concentration in the dusted combustion exhaust gas are measured, and the air supply according to the NOx concentration is compared with the conventional control of the air supply amount according to the oxygen concentration. By limiting the amount by controlling the amount, the NOx concentration is always below a regulation value (for example, 100 ppm), and CO generation can be prevented.

1 is an overall configuration diagram of a waste plant according to an embodiment of the present invention. In embodiment of this invention, it is a model figure which shows the mode of control of the air supply amount in a NOx measured value. It is a diagram explaining the effect of air supply amount control in the NOx measurement value by the embodiment of the present invention.

Explanation of symbols

6 Pyrolysis drum 9 Combustion and melting furnace 14 Second and third air nozzles 23 Bag filter for dust removal 24 Bag filter for desalting 32 Flow control valve 33 Controller 34 Oxygen analyzer 35 NOx concentration analyzer

Claims (2)

Measure the oxygen concentration of the exhaust gas discharged from the combustion furnace that burns waste, etc., in the exhaust gas flow path on the downstream side of the combustion furnace, and hold the measured oxygen concentration at either the set value or the set range In the combustion control method for increasing and decreasing the supply amount of combustion air supplied to the combustion furnace as described above,
When the NOx concentration of the exhaust gas is measured in the exhaust gas flow path, and the measured NOx concentration exceeds a predetermined upper limit value, the increase in the supply amount of the combustion air is stopped and the lower limit value is exceeded Stops the decrease in the supply amount of the combustion air. A pyrolysis reactor for pyrolyzing waste, a combustion melting furnace for burning a pyrolysis gas generated from the pyrolysis reactor and a part of the pyrolysis residue, and oxygen in exhaust gas discharged from the combustion melting furnace Oxygen concentration measuring means for measuring the concentration, and supply amount of combustion air supplied to the combustion melting furnace so that the oxygen concentration of the exhaust gas measured by the oxygen concentration measuring means is maintained at either a set value or a set range in waste disposal and control means for increasing or decreasing control,
NOx concentration measuring means for measuring the NOx concentration of the exhaust gas is provided, and the control means supplies the combustion air supply amount when the NOx concentration measured by the NOx concentration measuring means exceeds a predetermined upper limit value. Is stopped, and when it falls below the lower limit, the decrease in the supply amount of the combustion air is stopped.

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