JPH05172325A - Method of reducing nox in batch type burning furnace and device to reduce nox - Google Patents

Abstract

PURPOSE:To present a method and device that can be adopted regardless of the burning temperature and reduce NOx effectively by supplying fuel on the upstream side in the direction of the combustion exhaust gas flow from the heat exchanger when the temperature in the furnace or the combustion exhaust gas temperature is higher than a set value and supply air on the downstream side in the direction of the combustion exhaust gas flow from the spot where the fuel is supplied. CONSTITUTION:When the temperature in the furnace or the combustion exhaust gas temperature is higher than a set value, fuel that gives a reducing reaction to NOx in the combustion exhaust gas is supplied to the combustion exhaust gas that flows through an exhaust gas channel 7 on the upstream side in the direction of the combustion exhaust gas flow from a heat exchanger 12, and the air to burn the fuel that is left unburned is supplied to the downstream side in the direction of the combustion exhaust gas flow from the fuel supplying spot. Here a temperature sensor 13 that detects the temperature in the furnace or the combustion gas temperature, fuel supply means 15, 17, and air supply means 19 are provided, and fuel is supplied when the temperature detected by the temperature sensor 13 is higher than a set value. With this arrangement the method and device in the title can be adopted regardless of the calcining temperature and NOx can be reduced effectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is provided with a burner for heating the inside of a furnace and an exhaust gas passage for discharging combustion exhaust gas of the burner from the inside of the furnace. NOx in a batch type firing furnace in which a heat exchanger for preheating the combustion air by exchanging heat with the combustion exhaust gas is installed in the exhaust gas passage.
The present invention relates to a reduction method and a NOx reduction device.

[0002]

2. Description of the Related Art In such a batch type firing furnace, the temperature inside the furnace is gradually raised by a burner, for example, from room temperature to reach a predetermined firing temperature, and the firing temperature is maintained for a predetermined time. Like gradually lowering it,
By subjecting the material to be fired in the furnace to a predetermined firing treatment, the temperature of the fired material is changed so that the temperature changes with time. As a method for reducing NOx in such a batch-type firing furnace, conventionally, in general, by making the amount of air supplied to the fuel supplied to the burner extremely small, slow combustion is caused to lower the combustion temperature, and N
A method of reducing Ox, that is, a method of reducing NOx by improving combustion of a burner has been adopted.

[0003]

However, for example, in a batch type firing furnace used for firing ceramics or the like, since the firing temperature is as high as 1700 to 1800 ° C., slow combustion in the burner as described above is performed. The NOx reduction method of raising the combustion temperature to lower the combustion temperature cannot be adopted because the furnace temperature cannot be raised to a predetermined firing temperature. Therefore, in such a batch type firing furnace, NOx reduction measures cannot be taken. It wasn't done. The present invention has been made in view of the above circumstances, and an object of the present invention is that it can be adopted regardless of the firing temperature, and N can be effectively used.
An object of the present invention is to provide a NOx reduction method and a NOx reduction device in a batch type firing furnace that can reduce Ox.

[0004]

A method for reducing NOx in a batch-type firing furnace, which is a first characteristic configuration of the present invention, is a method of flowing a gas through the exhaust gas passage when the temperature in the furnace or the combustion exhaust gas temperature is equal to or higher than a set value. The fuel for reducing NOx in the combustion exhaust gas is supplied to the combustion exhaust gas on the upstream side of the heat exchanger in the combustion exhaust gas flow direction, and to the combustion exhaust gas flow direction lower side than the fuel supply point. The air for burning the unburned portion of the fuel is supplied.

The NOx reduction device in the batch type firing furnace, which is the second characteristic configuration of the present invention, is provided with temperature detecting means for detecting the temperature inside the furnace or the temperature of the combustion exhaust gas, and the exhaust gas passage is connected to the heat exchanger from the heat exchanger. The fuel supply means for supplying the fuel for reducing NOx in the combustion exhaust gas to the upstream side in the combustion exhaust gas flow direction, and the unburned portion of the fuel to the downstream side in the combustion exhaust gas flow direction from the fuel supply means. Air supply means for supplying air to be burned is provided, and the fuel supply means is configured to supply fuel when the temperature detected by the temperature detection means is equal to or higher than a set value.

In the NOx reduction device for a batch type firing furnace, which is the third characteristic configuration of the present invention, the heat exchanger includes a front stage part and a rear stage part located lower than the front stage part in the combustion exhaust gas flow direction. The fuel supply means is provided on the upstream side in the combustion exhaust gas flow direction with respect to the front-stage portion, and the air supply means is provided between the front-stage portion and the rear-stage portion.

[0007]

According to the first characteristic configuration of the present invention, when the furnace temperature or the combustion exhaust gas temperature becomes equal to or higher than the set temperature and the NOx content rate in the combustion exhaust gas of the burner becomes high,
At a place where the temperature of the combustion exhaust gas on the upstream side in the combustion exhaust gas flow direction is higher than that of the heat exchanger, a fuel for reducing NOx is supplied to the combustion exhaust gas flowing through the exhaust gas passage to generate an oxygen-deficient region, and NOx is reduced by effectively reacting the reducing fuel and NOx in the combustion exhaust gas. or,
Exhaust heat of the combustion exhaust gas is recovered by exchanging heat between the combustion exhaust gas and the combustion air with a heat exchanger on the lower side in the combustion exhaust gas flow direction than the fuel supply point. Further, air is supplied at a place where the temperature of the combustion exhaust gas on the lower side in the combustion exhaust gas flow direction is lower than that of the fuel supply point to lower the unburned content of the reducing fuel and lower the combustion temperature to generate NOx. The reducing fuel is burned to prevent the reducing fuel from being discharged in an unburned state.

According to the second characteristic constitution, when the temperature detected by the temperature detecting means becomes equal to or higher than the set value and the content ratio of NOx in the combustion exhaust gas of the burner becomes high, the combustion is carried out more than the heat exchanger. By the fuel supply means provided on the higher side of the exhaust gas flow direction in the combustion exhaust gas temperature is higher, the fuel for reducing NOx is supplied to the combustion exhaust gas flowing through the exhaust gas passage to generate an oxygen deficient region, and NOx is reduced by effectively reacting the reducing fuel and NOx in the combustion exhaust gas. Further, the heat exchange between the combustion exhaust gas and the combustion air is performed by a heat exchanger provided on the lower side of the fuel supply means in the combustion exhaust gas flow direction, and excess heat of the combustion exhaust gas is recovered. or,
Air is supplied by the air supply means provided at the place where the temperature of the combustion exhaust gas is lower on the lower side of the combustion exhaust gas flow direction than the fuel supply means, and the unburned portion of the reducing fuel is reduced in combustion temperature. Combustion in a state that suppresses the generation of NOx,
Prevent the reducing fuel from being discharged in an unburned state.

According to the third characteristic structure, the temperature of the combustion exhaust gas is lowered by exchanging heat between the combustion exhaust gas and the combustion air at the front stage of the heat exchanger, and By supplying air by the air supply means, the unburned portion of the reducing fuel supplied by the fuel supply means is burned in a state where the combustion temperature is lowered and NOx generation is suppressed. Further, the heat generated by burning the reducing fuel is exchanged with the combustion air at the rear stage of the heat exchanger to be recovered. Therefore, according to this characteristic configuration, in comparison with a configuration in which a single heat exchanger is provided and the air supply means is provided on the upstream side in the combustion exhaust gas flow direction with respect to the heat exchanger, the heat exchanger is provided at the front stage of the heat exchanger. Can effectively lower the temperature of combustion exhaust gas,
Since the unburned portion of the reducing fuel can be burned at a lower combustion temperature, the generation of NOx can be suppressed more effectively. Further, in the case where a single heat exchanger is provided and the air supply means is provided on the lower side in the combustion exhaust gas flow direction than the heat exchanger, the heat generated by burning the reducing fuel cannot be recovered. Since the heat generated by burning the reducing fuel in the latter part of the heat exchanger can be exchanged with the combustion air and recovered, the combustion air can be effectively preheated.

[0010]

According to the first characteristic configuration, as in the conventional case,
The burner is slowly burned to lower the combustion temperature and N
Since it is not a method of reducing Ox, it can be used regardless of the firing temperature, and NOx in the combustion exhaust gas can be effectively reduced.

According to the second characteristic configuration, it is possible to obtain the NOx reduction device in the batch type firing furnace suitable for realizing the NOx reduction method in the batch type firing furnace described in the first characteristic configuration.

According to the third characteristic configuration, it is possible to obtain the NOx reduction device in the batch type firing furnace suitable for realizing the NOx reduction method in the batch type firing furnace described in the first characteristic configuration. Moreover, although reducing fuel is separately supplied for NOx reduction, the combustion air can be preheated by the heat of burning the reducing fuel to increase the combustion temperature and reduce the fuel supply amount to the burner. Therefore, it is possible to offset the increased fuel amount due to the supply for NOx reduction by the reduced amount, and it is possible to suppress the increase in the fuel supply amount as a whole as much as possible.

[0013]

EXAMPLE Next, according to an example of the present invention, a ceramic 170 was used.
An example applied to a batch type firing furnace for firing at a high temperature of about 0 to 1800 ° C. will be described based on FIGS. 1 to 4.

In the figure, reference numeral 1 is a furnace body, and a door 3 is opened in a furnace 2 inside the furnace body 1, and a carriage 4 on which a material S to be fired is placed is put in the furnace.

A gas burner 5 for heating the inside of the furnace 2 is provided on each of the left and right sides of the furnace body 1. An exhaust gas passage 7 is connected to the rear side of the furnace body 1. Then, as shown in FIG. 4, inside the carriage 4, an exhaust gas passage 4a inside the carriage that communicates with the exhaust gas passage 7 in a state where the carriage 4 is placed in a furnace is provided, and an upper stand of the carriage 4 is provided inside the carriage. A plurality of exhaust gas inlets 4b communicating with the exhaust gas passage 4a are formed. Therefore, the combustion exhaust gas of the gas burner 5 in the furnace 2 is exhausted by the exhaust fan 6 into the exhaust gas inlet 4b, the exhaust gas passage 4a in the carriage, and
The gas is discharged to the outside of the furnace through the exhaust gas passage 7.

In the figure, 8 is a fuel gas supply path for the gas burner 5, 9 is an electromagnetic flow rate adjusting valve interposed in the fuel gas supply path 8, and the fuel for the gas burner 5 is adjusted by adjusting the opening. The amount of gas supply is adjusted. Further, 10 is a combustion air supply passage for supplying combustion air to the gas burner 5 by the blower fan 11.

Reference numeral 12 is a heat exchanger for preheating the combustion air by exchanging heat between the combustion air flowing through the combustion air supply passage 10 and the combustion exhaust gas flowing through the exhaust gas passage 7. The front stage portion 12A and the rear stage portion 12B located below the front stage portion 12A in the combustion exhaust gas flow direction. That is, the combustion temperature of the gas burner 5 is raised by preheating the combustion air supplied to the gas burner 5.

In the figure, 13 is a temperature sensor for detecting the temperature in the furnace 2. C is a temperature sensor 1 for adjusting the combustion amount of the gas burner 5 so that the temperature of the furnace 2 becomes a set value.
Flow rate adjusting valve 9 so that the detected temperature of 3 becomes the set value.
It is a control device that adjusts the amount of fuel gas supplied to the gas burner 5 by adjusting the opening degree of and the amount of combustion air supplied to the gas burner 5 by adjusting the rotation speed of the blower fan 11.

In FIG. 3, reference numeral 14 denotes a wheel portion of the carriage 4 in the furnace 2
It is a sand seal that isolates you from being exposed to the atmosphere of
The wheel portion of the carriage 4 is prevented from being damaged by being exposed to the high temperature atmosphere in the furnace 2 or the combustion exhaust gas.

In the batch-type firing furnace constructed as described above, after the carriage 4 on which the article S to be fired is placed is placed in the furnace, the controller C gradually raises the temperature in the furnace from room temperature to 1700. Up to about 1800 ° C., hold the firing temperature for a predetermined time, and then gradually lower it, that is, control so that the temperature changes with the passage of a preset time, The object S to be fired is subjected to a predetermined firing process.

Next, a NOx reducing device for reducing NOx in the combustion exhaust gas of the gas burner 5 in the batch type firing furnace configured as described above will be described.

In the exhaust gas passage 7, the exhaust gas passage 7 is located on the upstream side of the front end portion 12A of the heat exchanger 12 in the combustion exhaust gas flow direction.
The reducing fuel supply passage 16 on each of the left and right sides near the inlet of the
A plurality of fuel ejection nozzles 15 for ejecting the fuel gas flowing therethrough upward into the exhaust gas passage 7 are arranged side by side at predetermined intervals in the lateral direction. Reference numeral 17 denotes an electromagnetic flow rate adjusting valve interposed in the reducing fuel supply passage 16, and by adjusting the opening thereof, a state in which the fuel gas is ejected from the fuel ejection nozzle 15 and a state in which the fuel gas is not ejected, and an ejection state In, the amount of fuel gas to be ejected is adjusted. Therefore, the fuel injection nozzle 15 and the electromagnetic flow rate adjusting valve 17 constitute fuel supply means for supplying the reducing exhaust gas that reduces NOx in the exhaust gas to the exhaust gas flowing through the exhaust gas passage 7. There is.

Further, the fuel injection nozzle 1 in the exhaust gas passage 7
A blower fan 20 that passes through an air supply passage 18 is provided on the lower side in the combustion exhaust gas flow direction than the installation position of 5 and on each of the left and right sides between the front stage 12A and the rear stage 12B of the heat exchanger 12. A plurality of air jet nozzles 19 for jetting the air from the above into the exhaust gas passage 7 upward are arranged side by side at a predetermined interval in the lateral direction. Therefore, the air ejection nozzle 19 functions as an air supply unit that supplies the air for burning the unburned portion of the reducing fuel gas supplied by the fuel ejection nozzle 15.

When the temperature detected by the temperature sensor 13 exceeds the set value, the control device C switches the flow rate adjusting valve 17 from the closed state to the open state, adjusts its opening degree, and ejects from the fuel ejection nozzle 15. The amount of the reducing fuel gas is controlled to be a predetermined amount, the blower fan 20 is switched from a stopped state to an operating state, and the rotation speed of the blower fan 20 is adjusted so that the amount of air ejected from the air ejection nozzle 19 is reduced. It is controlled so that it becomes a predetermined amount.

Next, the NOx reducing action of the NOx reducing device constructed as described above will be explained.

The temperature of the combustion exhaust gas flowing in the exhaust gas passage 7 can be estimated by the temperature detected by the temperature sensor 13 for detecting the temperature of the furnace 2. For example, when the temperature detected by the temperature sensor 13 is 1200 to 1600 ° C., the temperature of the combustion exhaust gas near the inlet of the exhaust gas passage 7 where the fuel injection nozzle 15 is provided is approximately 1200 to 1600 ° C. because it is substantially equal to the temperature in the furnace 2. The temperature of the combustion exhaust gas in the vicinity where the air jet nozzle 19 is provided is heat-exchanged with the combustion air flowing through the combustion air supply passage 10 by the front stage portion 12A of the heat exchanger 12. The temperature drops considerably to about 700 to 1000 ° C.

Then, when the temperature detected by the temperature sensor 13 reaches the set value set between 1200 and 1600 ° C., the control device C switches the electromagnetic flow rate adjusting valve 17 to the open state, and the opening degree thereof. Is controlled based on the opening degree information of the flow rate adjusting valve 9 so that the amount of reducing fuel gas ejected from the fuel ejecting nozzle 15 is adjusted to a predetermined amount with respect to the amount of fuel gas supplied to the gas burner 5, At the same time, the blower fan 20 is switched to the operating state, and its rotation speed is controlled based on the opening degree information of the electromagnetic flow rate adjusting valve 17, so that the amount of air ejected from the air ejection nozzle 19 becomes
The amount of the reducing fuel gas ejected from the fuel ejection nozzle 15 is adjusted to be equal to or larger than the theoretical air amount.

That is, the fuel injection nozzle 15 supplies the reducing fuel gas to the combustion exhaust gas flowing through the exhaust gas passage 7 to generate an oxygen-deficient region, and the fuel gas and NOx in the combustion exhaust gas. By reacting NOx, NOx becomes N ₂ and is reduced, and the fuel gas that has contributed to the reaction becomes CO. Further, the air ejection nozzle 1 is provided on the lower side in the combustion exhaust gas flow direction than the reducing fuel gas supply point.
By supplying air at 9, the unburned portion of the reducing fuel gas containing CO is burned. Since the temperature of the combustion exhaust gas in the vicinity of the air ejection nozzle 19 is considerably lowered as described above (about 700 to 1000 ° C.), even if the unburned part of the reducing fuel gas is burned, NOx Generation can be suppressed, and moreover, by supplying air from a plurality of air ejection nozzles 19 which are dispersed in the lateral direction, the unburned components of the reducing gas fuel are combusted in stages, so the combustion temperature is further lowered. Therefore, the generation of NOx can be further suppressed.

Further, the heat generated by burning the unburned portion of the NOx reducing gas fuel is exchanged with the combustion air flowing through the combustion air supply passage 10 by the rear stage portion 12B of the heat exchanger 12. Recovered by exchanging heat.

When the supply amount of the reducing fuel gas is about 5% of the supply fuel gas amount to the gas burner 5, NOx in the combustion exhaust gas can be reduced by about 15%. Further, the more the supply amount of the reducing fuel gas increases, the more effective the NOx reduction becomes,
NOx in the combustion exhaust gas is supplied by supplying the reducing fuel gas to the gas burner 5 in an amount of about 20% of the supplied fuel gas.
Can be reduced by about 50%.

[Other Embodiments] Next, other embodiments will be listed.

In the above embodiments, the case where the present invention is applied to a firing furnace having a high firing temperature such as firing a ceramic is illustrated, but the present invention can be applied regardless of the firing temperature.

As the fuel for NOx reduction, it is preferable to use the fuel gas exemplified in the above embodiment because it is well mixed with the combustion exhaust gas, but in addition to the fuel gas, kerosene or heavy oil. Liquid fuels such as, or solid fuels such as coal can also be used.

In the above-mentioned embodiment, the heat exchanger 12 is constituted by the front-stage part 12A and the rear-stage part 12B located on the lower side of the front-stage part 12A in the combustion exhaust gas flow direction. Alternatively, the heat exchanger 12 may be configured as a single unit, and the air supply means 19 may be provided on the upstream side in the combustion exhaust gas flow direction or on the downstream side in the combustion exhaust gas flow direction with respect to the heat exchanger 12.

In the above embodiment, when the temperature detected by the temperature sensor 13 reaches the set value, the blower fan 20 is switched to the operating state and air is ejected from the air ejection nozzle 19. However, instead of this, the blower fan 20 is always operated at a constant rotation speed,
The air ejection nozzle 19 may be configured to constantly eject a fixed amount of air.

In the above embodiment, the controller C
The case where the electromagnetic flow rate adjusting valve 17 is controlled at the time when the detected temperature of the temperature sensor 13 reaches the set value has been exemplified, but instead of this, when the detected temperature of the temperature sensor 13 reaches the set value, Manual solenoid valve 17
May be switched to the open state, and the opening thereof may be adjusted so that the amount of reducing fuel gas ejected from the fuel ejection nozzle 15 is a predetermined amount with respect to the amount of fuel gas supplied to the gas burner 5. ..

In the above-described embodiment, the case where the injection of the reducing fuel gas from the fuel injection nozzle 15 is controlled based on the detection information of the temperature sensor 13 that detects the temperature of the furnace 2 has been described as an example. In addition to the temperature sensor 13, a temperature sensor for separately detecting the temperature of the combustion exhaust gas near the inlet of the exhaust gas passage 7 is provided, and the reducing fuel gas from the fuel injection nozzle 15 is based on the detection information of this temperature sensor. The control device C may be configured to control the ejection of

It should be noted that although reference numerals are given in the claims for convenience of comparison with the drawings, the present invention is not limited to the configuration of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a plan view of a batch type firing furnace to which the present invention is applied.

FIG. 2 is a side view of a batch type firing furnace to which the present invention is applied.

FIG. 3 is a front sectional view of a batch type firing furnace to which the present invention is applied.

FIG. 4 is a side sectional view of a batch type firing furnace to which the present invention is applied.

[Explanation of symbols]

 5 Burner 7 Exhaust Gas Path 12 Heat Exchanger 12A Front Stage 12B Rear Stage 13 Temperature Detection Means 15, 17 Fuel Supply Means 19 Air Supply Means

Claims (3)

[Claims] 1. A burner (5) for heating the inside of a furnace and an exhaust gas passage (7) for discharging combustion exhaust gas of the burner (5) from the inside of the furnace are provided, and combustion air for the burner (5) is provided. A batch type in which a heat exchanger (12) for preheating the combustion air by exchanging heat with the combustion exhaust gas flowing through the exhaust gas passage (7) is interposed in the exhaust gas passage (7). A method for reducing NOx in a firing furnace, wherein the combustion exhaust gas flowing through the exhaust gas passage (7) is burned more than the heat exchanger (12) when the furnace temperature or the combustion exhaust gas temperature is equal to or higher than a preset value. On the good side in the exhaust gas flow direction,
A fuel for reducing NOx in the combustion exhaust gas is supplied, and the fuel is supplied at a position lower than the fuel supply point in the combustion exhaust gas flow direction.
A method for reducing NOx in a batch type firing furnace for supplying air for burning unburned components of the fuel. 2. A burner (5) for heating the inside of the furnace and an exhaust gas passage (7) for discharging combustion exhaust gas of the burner (5) from the inside of the furnace are provided, and combustion air for the burner (5) is provided. A batch type in which a heat exchanger (12) for preheating the combustion air by exchanging heat with the combustion exhaust gas flowing through the exhaust gas passage (7) is interposed in the exhaust gas passage (7). A NOx reduction device in a firing furnace, comprising temperature detection means (13) for detecting the temperature in the furnace or the temperature of combustion exhaust gas, and the exhaust gas passage (7) is connected to the exhaust gas passage rather than the heat exchanger (12). Fuel supply means (15), (17) for supplying the fuel for reducing NOx in the combustion exhaust gas to the upstream side in the flow direction, and the combustion exhaust gas flow direction than the fuel supply means (15), (17) The unburned portion of the fuel is burned on the lower side. That air air supply means (19) is provided for supplying the fuel supply means (15),
(17) A NOx reduction device in a batch type firing furnace configured to supply fuel when the temperature detected by the temperature detecting means (13) is equal to or higher than a set value. 3. The heat exchanger (12) comprises a front part (12).
A) and a rear stage (12B) located on the lower side of the front stage (12A) in the combustion exhaust gas flow direction, and the fuel supply means (15) and (17) include the front stage (12).
The batch according to claim 2, which is provided on the upstream side of A) in the combustion exhaust gas flow direction, and wherein the air supply means (19) is provided between the front stage portion (12A) and the rear stage portion (12B). NOx reduction device in a firing furnace.