JP2010065932A - Device and method for controlling combustion in secondary combustion furnace for pyrolysis gas - Google Patents

Abstract

[PROBLEMS] To stably burn pyrolysis gas in a secondary combustion furnace of a gasification melting furnace and suppress CO and NOx concentration in exhaust gas without generating incomplete combustion or an abnormal local high temperature region. It is an object of the present invention to provide a combustion control apparatus and method for a secondary combustion furnace of a waste gasification and melting furnace that can be used.
SOLUTION: Waste is pyrolyzed in a gasification melting furnace 1 to combust gasified pyrolysis gas, and secondary combustion provided with a lower air blowing port 31, an intermediate air blowing port 32, and an upper air blowing port 33 through which air is blown. In the combustion control device 40 of the furnace 30, the combustion control device 40 includes temperature measuring means 41, 42, and 43 that measure the temperature in the furnace near the air outlets of each stage, and the air outlets of each stage measured by the temperature measuring means. Blowing air amount control means 31A, 32A, and 33A for controlling the amount of air blown from the blowing ports of each stage based on the furnace temperature distribution shape derived from the nearby furnace temperature are provided.
[Selection] Figure 1

Description

  TECHNICAL FIELD The present invention relates to a combustion control apparatus and a combustion control method for thermally decomposing waste in a gasification melting furnace and combusting gasified pyrolysis gas in a secondary combustion furnace, and particularly to reducing harmful components in exhaust gas. It relates to the control of combustion air.

  As a waste disposal method such as municipal waste and industrial waste, there is a gasification melting treatment method in which waste is pyrolyzed to generate pyrolysis gas, and the pyrolysis residue is melted into slag. There are several types of melting furnaces for performing this type of treatment, and one of them is a coke bed type waste gasification melting furnace. For example, a waste gasification and melting furnace shown in Patent Document 1 is a gasification and melting furnace that thermally decomposes and gasifies waste, melts the pyrolysis residue, and partially burns the generated pyrolysis gas, A secondary combustion furnace for secondary combustion of the pyrolysis gas that has been burned and discharged from the gasification melting furnace.

  In the waste gasification and melting furnace of Patent Document 1, a high temperature combustion zone is formed by depositing and burning coke at the bottom of the furnace, and the pyrolysis residue is melted. Above, waste is thrown in to form a waste accumulation layer, and the waste is thermally decomposed by the high temperature gas rising from the high temperature combustion zone below. An extended large space (free board) is provided above the waste accumulation layer, and partial combustion of pyrolysis gas generated by pyrolysis of waste is performed here.

  The partially burned pyrolysis gas is introduced into a secondary combustion furnace connected to a melting furnace, and is completely burned in the secondary combustion furnace. The combustion gas is sent to a boiler, a gas turbine, etc., and heat is recovered.

In the secondary combustion furnace described in Patent Document 1, as combustion air for gradually burning the pyrolysis gas, and for cooling to prevent the furnace from becoming excessively hot due to the combustion gas, Blowers for blowing air are provided in three stages in the vertical direction. In the combustion of the pyrolysis gas in this secondary combustion furnace, the temperature of the combustion gas is 850 ° C. or higher, which can decompose tar content and dioxins contained in the gas, and dust is fused to the furnace wall. In order to prevent the life of the furnace body from being shortened due to thermal damage of the body, it is for combustion to be blown from the air outlets of each stage so that the temperature becomes 1000 ° C. or lower, that is, the temperature of the combustion gas is in the range of 850 ° C. This is done by adjusting the amount of air and cooling air.
JP 2003-074819 A

  In a secondary combustion furnace that uses thermal energy by burning pyrolysis gas generated in a waste gasification and melting furnace, it is important to suppress the concentrations of CO and NOx that are harmful components in the exhaust gas. CO is generated by incomplete combustion of the pyrolysis gas, and thermal NOx is generated by locally generating a high temperature region in the combustion of the pyrolysis gas.

  When the pyrolysis gas is burned by the secondary combustion furnace described in Patent Document 1, the pyrolysis gas is introduced from the gasification melting furnace to the lower part of the secondary combustion furnace, and the pyrolysis gas rises while the lower, middle, and upper stages. Are combusted by the combustion air blown from the respective air outlets, and further cooled so that the temperature of the combustion gas falls within an appropriate range. In Patent Document 1, the amount of combustion air blown is suppressed at the first (lower) blower port, and the amount of combustion air blown is sequentially increased at the subsequent blower ports (middle and upper rows). Further, the combustion gas temperature is adjusted by adjusting the amount of combustion air blown in each stage. However, the waste is a mixture of various kinds of waste, and the properties of the waste supplied in the process of gasifying and melting the waste greatly fluctuate. The calorific value fluctuates due to the gas component fluctuation of the generated gas. For this reason, it may be difficult to stably perform pyrolysis gas combustion in the secondary combustion furnace. As a result, CO may be generated due to incomplete combustion of the pyrolysis gas, or local combustion may occur in the combustion of the pyrolysis gas. When the high temperature region is generated, thermal NOx is generated and the concentration of CO and NOx, which are harmful components in the exhaust gas, increases. In addition, the load on the processing apparatus that renders the exhaust gas harmless increases, which may hinder the operation of the apparatus.

  As described above, in Patent Document 1, in an operation in which the temperature in the secondary combustion furnace is set to a predetermined temperature range, the temperature is set to the lower limit temperature (850 ° C.) or more in order to decompose tar and dioxins. In order to prevent the adhesion of dust to the furnace wall and to prevent the lifetime in the furnace from being shortened, by setting the temperature to the upper limit temperature (1000 ° C.) or less, each purpose can be satisfied, but stable combustion of pyrolysis gas, There are cases where it is not sufficient in terms of suppressing the generation of CO and NOx.

  The present invention has been made to solve the above-described problems. In the secondary combustion furnace of the gasification and melting furnace, the pyrolysis gas is stably burned, and incomplete combustion and abnormal local high-temperature regions are caused. It is an object of the present invention to provide a combustion control device and method for a secondary combustion furnace of a waste gasification melting furnace that can suppress the CO and NOx concentration in exhaust gas without being generated.

  The present invention is a combustion control of a secondary combustion furnace provided with a lower blower port, a middle blower port, and an upper blower port that burn pyrolyzed gas obtained by pyrolyzing waste in a gasification melting furnace and blowing air. The present invention relates to an apparatus and a combustion control method.

  The present invention relates to a combustion control device, in which the combustion control device measures the temperature in the furnace near the air outlet of each stage, and the temperature in the furnace near the air outlet of each stage measured by the temperature measuring means. And a blown air amount control means for controlling the amount of air blown from the blower opening of each stage based on the temperature distribution shape in the furnace derived from the above.

  Further, the present invention relates to a combustion control method, measuring the temperature in the furnace near the air outlet of each stage, and based on the temperature distribution shape in the furnace derived from the temperature in the furnace near the air outlet of each stage, It is characterized by controlling the amount of air blown from the air outlet of each stage.

  In the present invention, the temperature in the vicinity of the lower air outlet, the middle air outlet, and the upper air outlet is measured to obtain the temperature distribution in the furnace, and as a result, the air ratio distribution is obtained. The amount of air at each air outlet is controlled so that this air ratio distribution has a predetermined shape.

  More specifically, in the present invention, the temperature distribution shape in the furnace is the temperature distribution shape in the furnace where the temperature rises in the order of the vicinity of the lower air outlet, the vicinity of the middle air outlet, and the vicinity of the upper air outlet, or the temperature drops. If the temperature distribution shape is in the furnace, the temperature near the lower air vent and the temperature near the middle air vent are the same, and the temperature near the upper air vent is higher than the temperature near the lower air vent and the temperature near the middle air vent. The blowing air amount control means controls the amount of air blown from the blowing ports of each stage so that the temperature distribution shape in the furnace is low or the temperature distribution shape in the furnace in the vicinity of the middle blowing port is the highest.

  According to the present invention, the temperature distribution shape in the secondary combustion furnace is measured, the shape is determined, and the air blown from the air outlets of each stage so as to obtain a preferable temperature distribution, that is, a preferable air ratio distribution described later. Since the amount is controlled, the combustion in the secondary combustion furnace can be appropriately controlled, and the generation of CO and NOx can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. This explanation describes the configuration of the waste gasification and melting furnace and the secondary combustion furnace, the operation method of the gasification and melting furnace, the air ratio distribution and temperature distribution in the secondary combustion furnace, and the amount of air supplied from the air outlets of each stage. The flow chart to be controlled will be described in order.

<Configuration of waste gasification melting furnace>
FIG. 1 is a diagram showing a schematic configuration of a waste gasification melting furnace to which the present invention is applied. This waste gasification and melting furnace is a gasification and melting furnace 1 that thermally decomposes and gasifies waste and partially burns the pyrolysis gas, and the pyrolysis gas discharged from the gasification and melting furnace 1 is secondary. This is a facility equipped with a secondary combustion furnace 30 for burning.

  In the present embodiment, the gasification melting furnace 1 is a coke bed type, and is provided with an inlet 2 for introducing waste, auxiliary materials, and the like at the upper part of the furnace, An exhaust port 3 for combustible gas generated by thermal decomposition of waste is provided on the upper side. An outlet 4 for discharging the molten slag is provided at the bottom of the furnace.

  The gasification melting furnace 1 is divided into three regions including a lower shaft portion 1c, a middle shaft portion 1b, and a free board portion 1a in terms of function. Each of these areas has the following functions. The lower shaft portion 1c burns the deposited coke to form a high-temperature combustion zone, burns the pyrolysis residue of the waste and melts ash, and the middle shaft portion 1b fluidizes the input waste. However, the area to be dried and pyrolyzed, the free board portion 1a is an area to partially burn the generated pyrolysis gas. In the figure, 50 indicates a waste accumulation layer. Charges such as waste to be introduced into the furnace are supplied from the respective supply devices, are weighed by a predetermined amount, and are introduced from the waste inlet 2. 21 is a waste supply device that supplies waste such as municipal waste, 22 is a coke supply device that is used as an auxiliary fuel, and 23 is a limestone supply device that is used as a component adjusting material for the generated slag.

  The gasification melting furnace 1 is provided with tuyere for blowing an oxygen-containing gas into each of the above regions. The lower shaft portion 1c is provided with a main tuyere 5 that burns the deposited coke to form a high-temperature combustion zone, burns the pyrolysis residue and blows in oxygen-enriched air for melting, and the middle shaft portion 1b is provided with a sub tuyere 6 that blows air for gently flowing the waste that has been thrown in, and partially burning and thermally decomposing the waste, and the free board 1a is thermally decomposed. A three-stage tuyere 7 for blowing air for partially burning the pyrolysis gas generated in this way and maintaining the inside of the furnace at a predetermined temperature is provided. The oxygen enriched air pipe connected to the main tuyere 5, the air pipe connected to the sub tuyere 6, and the air pipe connected to the three-stage tuyere 7 are respectively connected to a flow control device 8 and a flow control. A device 9 and a flow rate adjusting device 10 are provided.

  A duct for introducing the pyrolysis gas discharged from the discharge port 3 of the gasification melting furnace 1 is connected to the lower part of the secondary combustion furnace 30 connected to the gasification melting furnace 1. In the process of rising in the secondary combustion furnace 30, secondary combustion air is supplied and burned, and heat is recovered by the boiler 35 or a gas turbine or the like. The secondary combustion furnace 30 is provided with an air blowing port for blowing secondary combustion air in three stages along the gas flow direction, and a lower air blowing port 31, a middle air blowing port 32, and an upper air blowing port 33 are installed from below. Yes. Secondary air flow rate adjusting devices 31A, 32A, and 33A are installed in the air blowing ports 31, 32, and 33, respectively, so that the air flow rate can be individually adjusted. In addition, thermometers 41, 42, 43 are provided at heights corresponding to the lower air blowing port 31, the middle air blowing port 32, and the upper air blowing port 33, respectively, and the height corresponding to each air blowing port in the secondary combustion furnace 30. The temperature inside the furnace is measured.

  Reference numeral 40 denotes a secondary combustion air control device. The secondary combustion air control device 40 allows the lower air blowing port 31, the middle air blowing port 32, and the upper air blowing port 33 to be controlled based on the measured values of the thermometers 41, 42, and 43 near the respective air blowing ports of the secondary combustion furnace 30. The flow rate of air blown into the secondary combustion furnace from each is controlled.

<Operation method of gasification melting furnace and secondary combustion furnace>
The gasification melting furnace 1 and the secondary combustion furnace 30 configured as described above are operated in the following manner.

  First, a predetermined amount of waste, coke, and limestone are charged from the inlet 2 of the gasification melting furnace 1 and oxygen-enriched air or air is supplied from the main tuyere 5, the sub tuyere 6, and the three-stage tuyere 7, respectively. Is blown. Coke and limestone are deposited on the bottom of the furnace of the lower shaft portion 1c, where hot air of oxygen-enriched air is blown from the main tuyere 5, and the coke burns to form a high-temperature combustion zone, resulting in pyrolysis residues of waste Is burned and ash is melted. The molten slag in which the pyrolysis residue is melted is discharged from the tap 4. In addition, the thrown-in waste stays while flowing in the middle shaft portion 1b above the high-temperature combustion zone to form a waste accumulation layer 50, and the hot gas rising from the lower shaft portion 1c and the sub tuyere 6 It is dried by air blown from and then pyrolyzed. The pyrolysis gas generated by pyrolysis is partially burned by the air blown from the three-stage tuyere 7 of the free board portion 1a. The partially decomposed pyrolysis gas is sent from the discharge port 3 to the secondary combustion furnace 30. In the secondary combustion furnace 30, combustion air is blown from the air blowing ports 31, 32, and 33 of each stage, the pyrolysis gas burns in stages, and eventually complete combustion. The combustion gas is sent to the boiler 35 and heat is recovered.

<Method for controlling the amount of blown air for combustion in the secondary combustion furnace>
Next, a method for controlling the amount of combustion air blown from each stage of the secondary combustion furnace will be described in relation to the air ratio distribution of the secondary combustion furnace.

  In the gasification melting furnace 1, oxygen and air are supplied from the main tuyere 5, the sub tuyere 6, and the three-stage tuyere 7 in order to partially oxidize and thermally decompose the waste.

  In the secondary combustion furnace 30, secondary combustion air is supplied in order to burn the pyrolysis gas introduced from the gasification melting furnace 1, and the combustion gas temperature after the pyrolysis gas burns is set to a temperature suitable for heat recovery. In order to cool to a low temperature and to rapidly cool to a temperature below the NOx generation temperature range so as to suppress the generation of NOx, cooling air is supplied. In the secondary combustion furnace 30, along the flow direction (from the lower part to the upper part) of the pyrolysis gas introduced from the gasification melting furnace 1, heights such as the lower air blowing port 31, the middle air blowing port 32, and the upper air blowing port 33 are provided. Air blowing ports are provided in three stages in the direction, and air is supplied as secondary combustion air in the upstream region of the flow of pyrolysis gas and as cooling air in the downstream region.

  The amount of air supplied to the gasification melting furnace 1 and the secondary combustion furnace 30 will be described using the “air ratio” as follows. Here, the air ratio is the ratio of the actual supply air amount to the theoretical air amount necessary for completely combusting the combustible component of the waste, and the air ratio = 1 is the theoretical air amount. In order to consider the amount of air supplied to each stage blowing port of the secondary combustion furnace 30 from the viewpoint of the air ratio, for example, the blowing amount of the lower stage blowing port 31 is supplied to the upstream side, that is, the gasification melting furnace 1. For example, the total of the air amount and the air amount supplied to the lower air blowing port 31 is expressed as an air ratio of 1.0.

  In the gasification melting furnace 1, in order to partially oxidize and thermally decompose waste, air and oxygen are supplied with an air ratio of less than 1 (for example, 0.8).

  In the secondary combustion furnace 30, when the air ratio is represented by the total accumulated amount of the air amount supplied to the gasification melting furnace 1 and the air amount supplied to each stage air outlet of the secondary combustion furnace 30, the pyrolysis gas is expressed. In the area to be combusted, the air blown is used as combustion air, and the air ratio has reached less than 1 to 1. In the area in which the air ratio has reached 1, the combustion of the pyrolysis gas is finished, and downstream from that place. In the region on the side, the blown air is used as cooling air for cooling the combustion gas generated by the combustion of the pyrolysis gas, and the air ratio is larger than 1 in that region.

  The region where the air ratio is less than 1 is a region in which less air than the theoretical value is supplied to the combustion of the pyrolysis gas, and the pyrolysis gas is gradually burned. Form in region. In this region, the local high temperature region does not occur. Next, the region where the air ratio reaches 1 is a region where the accumulated air amount reaches the theoretical air amount, and combustion of the pyrolysis gas has been completed, and this region is a preferred location (middle stage) of the secondary combustion furnace 30. (Between the air blowing port 32 or the lower air blowing port 31 and the middle air blowing port 32). The region where the air ratio is 1 or more is a region where the accumulated air amount becomes larger than the theoretical air amount, and the blown air is used to cool the combustion gas to a preferable temperature. This region is formed in a region from the middle blower port 32 to the upper blower port 33 and further to the outlet of the secondary combustion furnace 30.

<Air ratio distribution and temperature distribution in the secondary combustion furnace>
The amount of air blown from the air outlets of each stage is controlled so that the air ratio distribution in the secondary combustion furnace becomes a preferable air ratio distribution, but it is difficult to directly detect the air ratio distribution. Then, it demonstrates that the air ratio distribution in a secondary combustion furnace can be grasped | ascertained by measuring the temperature distribution in a secondary combustion furnace.

  In the region where the pyrolysis gas of the secondary combustion furnace 30 is combusted, the combustion of the pyrolysis gas proceeds from the region where the air ratio is less than 1 toward the region where the air ratio is 1, and the furnace temperature increases accordingly, and the air ratio is 1 This means that the maximum temperature is reached in the region where the combustion gas is cooled, and in the region where the combustion gas is cooled, the amount of cooling air increases as the air ratio becomes larger than 1. The combustion gas is cooled and the furnace temperature decreases. .

  An example of the temperature distribution is shown in FIG. 2 in order to explain the relationship between the temperature distribution in the secondary combustion furnace 30 and the air ratio distribution.

  In FIG. 2, the horizontal axis indicates the position of the pyrolysis gas in the flow direction (from the lower part to the upper part), and also indicates the positions of the lower, middle, and upper air blowing ports. The vertical axis represents temperature. In the case of FIG. 2, the furnace temperature is the highest between the lower air outlet and the middle air outlet, indicating that the air ratio has reached 1. From here, the air ratio is less than 1 at the upstream position in the flow direction of the pyrolysis gas, and the temperature rises in the flow direction from the vicinity of the lower air blowing port, and the air ratio is increased. At the position downstream of the position in the flow direction of the pyrolysis gas from the position where the temperature in the furnace reaches the maximum, the temperature in the furnace decreases and the air ratio becomes larger than 1, indicating that it is used as cooling air. Thus, by measuring the temperature distribution in the secondary combustion furnace, the air ratio distribution in the secondary combustion furnace can be grasped.

  Furthermore, an example of changing the temperature distribution by changing the air ratio distribution will be given. For example, the maximum temperature position moves to the upstream side or the downstream side of the gas flow depending on which blower port position the blown air amount is adjusted to reach the air ratio 1. In addition, to a region where the total secondary combustion air amount, which is the sum of the amount of air blown from all the air outlets of the secondary combustion furnace, is constant, acting as combustion air (region where the air ratio is 1 or less) The shape of the temperature distribution can be changed by changing the ratio of the amount of air blown and the amount of air blown to the region acting as cooling air (the region where the air ratio is greater than 1). For example, if the air is blown from the upper air outlet and the middle air outlet and the lower air outlet, the combustion air and the cooling air are blown to the lower air outlet and the middle air outlet. Combustion is performed relatively abruptly in the upstream region of the furnace, the furnace temperature becomes high, and a relatively large amount of cooling air is blown after the combustion is completed. Indicates.

Preferable air ratio distribution, preferable temperature distribution Varying the amount of air blown from the air outlet of each stage, examining the temperature distribution in the secondary combustion furnace and the state of NOx generation in the exhaust gas at the secondary combustion furnace outlet, Preferred air ratio distribution in the secondary combustion furnace that can completely burn the pyrolysis gas in the combustion furnace and suppress the generation of NOx, and preferred temperature distribution in the secondary combustion furnace that can be associated with the air ratio distribution Asked.

  In actual gasification and melting furnaces and secondary combustion furnaces, when the total amount of secondary combustion air in the secondary combustion furnace is constant and air is mainly blown from the lower air blower, and from the upper air blower For the case of mainly blowing, the temperature in the vicinity of the air blowing ports in the lower, middle and upper stages and the NOx concentration in the exhaust gas at the outlet of the secondary combustion furnace are measured, and the results are shown in FIGS. . 3 and 4, the horizontal axis indicates the measurement time, the vertical axis indicates the furnace temperature and the NOx concentration, the solid line indicates the temperature near the lower air vent, the broken line indicates the temperature near the middle air vent, and the dotted line indicates the upper air vent. The temperature in the vicinity is shown.

  In the case of mainly air blowing from the lower air blowing port, as shown in FIG. 3, the maximum temperature in the secondary combustion furnace is measured in the vicinity of the lower air blowing port and is about 1000 ° C., and the minimum temperature is near the upper air blowing port. It is measured at about 800 ° C. Moreover, it is about 1000 degreeC, about 900 degreeC, and about 800 degreeC in order of a lower stage blower opening, a middle stage blower opening, and an upper stage blower opening, and it is temperature-falling along a gas flow. The NOx concentration in the exhaust gas at the outlet of the secondary combustion furnace is 80 to 100 ppm, which is a relatively high concentration. It is inferred that the pyrolysis gas is burned at an air ratio of 1 near the lower air blowing port where the maximum temperature is measured. From the above situation, after the pyrolysis gas is introduced into the secondary combustion furnace, the pyrolysis gas is rapidly burned in a section near the lower air blower port to generate a local high temperature region, resulting in the generation of thermal NOx and NOx concentration Indicates that it is higher.

  On the other hand, in the case of mainly air blowing from the upper air blowing port, as shown in FIG. 4, the maximum temperature in the secondary combustion furnace is about 1000 ° C. measured near the lower air blowing port or near the middle air blowing port, The minimum temperature is about 900 ° C. measured near the upper air outlet. Further, the temperatures in the vicinity of the lower air outlet and the vicinity of the middle air outlet are substantially the same, and the temperature drops between the vicinity of the middle air outlet and the vicinity of the upper air outlet. The NOx concentration in the exhaust gas at the outlet of the secondary combustion furnace is 60 to 80 ppm, which is a low concentration.

  The temperature in the vicinity of the lower air vent and the vicinity of the middle air vent is almost the same, and the temperature is measured between the middle air vent and the upper air vent. After the gas is introduced, the pyrolysis gas is burned in the region from the inlet to the vicinity of the middle air outlet, and the air ratio is 1 near the middle air outlet. Since the ratio is less than 1 and the atmosphere is reducing, the generated NOx is reduced, and the combustion gas after complete combustion is rapidly cooled in the vicinity of the upper air blowing port, and in a short time to below the temperature range where thermal NOx is generated. Since it was cooled, the NOx concentration in the exhaust gas at the outlet of the secondary combustion furnace is as low as 60 to 80 ppm.

  From these results, the following became clear.

  The preferred air ratio distribution in the secondary combustion furnace that can completely burn the pyrolysis gas in the secondary combustion furnace and suppress the generation of NOx is as follows: a) The air ratio is less than 1 to 1 in the secondary combustion furnace. And b) after that, cooling air is blown so that the total amount of blown air becomes a predetermined air ratio, so that the combustion gas is cooled quickly. By doing so, ie, a), the pyrolysis gas is rapidly burned to generate a local high temperature region, and as a result, it is possible to prevent thermal NOx from being generated and increase the NOx concentration in the exhaust gas, In order to provide a region where the ratio is less than 1 and a reducing atmosphere, the generated NOx is reduced, and further, the temperature range below the temperature range where the combustion gas after complete combustion is rapidly cooled by the cooling air and the thermal NOx is generated by b) Since it cools in a short time until the NOx concentration in the exhaust gas can be suppressed.

  What is necessary is just to blow air from the blower opening of each step so that it may become such an air ratio distribution. According to such a blowing method, the pyrolysis gas is completely combusted, so that the generation of CO due to incomplete combustion is prevented, the generation of a local high temperature region is prevented, and the temperature is short below the temperature range where thermal NOx is generated. Since it cools in time, it can suppress the generation of NOx, can expand the high temperature region above 850 ° C, and also increases the residence time in the high temperature region for pyrolyzing the generated dioxins, thus suppressing the generation of dioxins it can.

  In order to grasp the air ratio distribution in the secondary combustion furnace, that is, the area where the air ratio is less than 1, the area where the air ratio is 1 and the area where the air ratio is 1 or more in the secondary combustion furnace To determine the air ratio distribution that is difficult to determine directly. The determination is made by replacing with a temperature distribution that is easy to determine.

  In order to obtain a preferable air ratio distribution, the temperature distribution in the secondary combustion furnace associated with the air ratio distribution is obtained by measuring the temperature in the vicinity of the air outlets of each stage, Controls the amount of air supplied from the stage air outlet.

<Flow diagram for controlling the amount of air supplied from the air outlets of each stage>
In the combustion control of the pyrolysis gas in the secondary combustion furnace according to the present invention, the combustion air amount is controlled in the following steps as seen in FIG.
(1) Temperature distribution determination First, the temperature in the furnace near the blow ports 31, 32, 33 in the lower, middle, and upper stages in the secondary combustion furnace 30 is measured to obtain the temperature distribution. Determine whether it is appropriate or inappropriate.

  There are four types of temperature distribution shapes, as shown in FIG. It is determined which type of the following shapes A to D the temperature distribution shape obtained by the temperature measurement corresponds to, and the air flow rate at the air outlets of each stage is controlled.

Shape A: The temperature near the lower air vent and the middle air vent is almost the same, and the temperature near the upper air vent is low. Shape B: The temperature near the middle air vent is the highest, near the lower air vent and the upper air vent. Temperature is low Shape C: The temperature near the lower air vent is the lowest, and the temperature rises in the order near the middle air vent and near the upper air vent. Shape D: The temperature near the lower air vent is the highest, and the middle air vent The temperature decreases in the order of the vicinity and the vicinity of the upper air outlet. Preferred temperature distribution shapes are shape A and shape B. Because the temperature near the lower air vent and the middle air vent are almost the same, or the temperature near the middle air vent is the highest, and the temperature drops between the middle air vent and the upper air vent The air ratio distribution gradually increases from less than 1 to 1, indicating that the air ratio is 1 near the middle air outlet and the air ratio is 1 or more near the upper air outlet. After the pyrolysis gas is introduced into the secondary combustion furnace, the pyrolysis gas is combusted in the region from the inlet to the vicinity of the middle air outlet, and the combustion gas is appropriately cooled by the cooling air downstream after the combustion is completed. ing.

  In the shape C, the temperature increases sequentially toward the downstream side of the gas flow, and the temperature does not decrease. This indicates that in the secondary combustion furnace, the pyrolysis gas does not completely burn in the secondary combustion furnace without exceeding the air ratio 1, but causes incomplete combustion. All the air supplied to the secondary combustion furnace acts as combustion air and is insufficient for complete combustion.

  In the shape D, the temperature in the vicinity of the lower air blowing port is the highest, and the temperature gradually decreases toward the downstream side of the gas flow. Near the lower air blowing port or upstream thereof, the air ratio exceeds 1, and all air supplied to the secondary combustion furnace acts as cooling air.

  It is determined whether the temperature distribution shape obtained by the measurement is appropriate or inappropriate, and if it is inappropriate, the amount of air blown from the air outlet is adjusted.

    ・ If the temperature distribution shape is shape A or shape B, go to the next step to determine the minimum temperature.

    When the temperature distribution shape is the shape C, the air blowing amount from the lower air blowing port 31 is increased so as to be the shape A or the shape B. By increasing the combustion air, the air ratio as a whole becomes 1 or more, and the pyrolysis gas is completely burned in the secondary combustion furnace 30 so that the air blown from the upper air blowing port 33 acts as cooling air.

    When the temperature distribution shape is the shape D, the amount of air blown from the lower air blowing port 31 is decreased so as to be the shape A or the shape B. By reducing the amount of air blown from the lower air blowing port 31, the region where the air ratio is 1 is set between the lower air blowing port 31 and the middle air blowing port 32 or in the vicinity of the middle air blowing port 32.

-After performing such an operation to improve, determine whether the temperature distribution shape is appropriate or inappropriate.
(2) Minimum temperature determination Next, it is determined whether the minimum temperature of the temperature distribution is a predetermined value or more.

    ・ If the minimum temperature is above the specified value, go to the next step for determining the maximum temperature.

    ・ If the minimum temperature is lower than the specified value, there will be a problem because the amount of heat stored in the combustion gas is small and the amount of heat to be recovered is insufficient. Therefore, it is determined which air outlet near which the position indicating the lowest temperature is located, and the air outlet that increases or decreases the air blowing volume is selected and controlled.

    When the position showing the minimum temperature is near the lower air blowing port 31, the air blowing amount from the lower air blowing port 31 is increased to promote combustion of the pyrolysis gas and raise the temperature.

When the position indicating the lowest temperature is near the upper air blowing port 33, the air blowing amount from the upper air blowing port 33 is decreased to suppress the cooling of the combustion gas and increase the temperature.
(3) Maximum temperature determination Next, it is determined whether the maximum temperature in the temperature distribution is equal to or lower than a predetermined value.

    ・ If the maximum temperature is below the specified value, go to the next step to determine the temperature difference between the lower and middle stages.

・ If the maximum temperature is higher than the specified value, a problem arises because combustion of the combustion gas produces a local high temperature region and NOx is generated. Therefore, the temperature of the air is reduced to a predetermined value by increasing the amount of air blown from the middle air blowing port 32 and increasing the amount of air for cooling the combustion gas. As a result, the total amount of blown air increases and as a result the minimum temperature level decreases, so the minimum temperature is judged again and control is performed.
(4) Lower-middle temperature difference determination Since the minimum temperature and the maximum temperature are within the predetermined temperature range by the control so far, the temperature difference between the temperature near the lower air blow port 31 and the temperature near the middle air blow port 32 is further small. Control is performed as follows.

    If the temperature difference between the temperature near the lower air outlet 31 and the temperature near the middle air outlet 32 is equal to or less than a predetermined value (for example, 100 ° C.), the control is terminated.

    ・ If the temperature difference between the temperature near the lower air outlet 31 and the temperature near the middle air outlet 32 is larger than a predetermined value, the amount of air blown from the lower air outlet 31 is increased and the same amount as the increase is increased to the middle It decreases from the amount of air blown from the blower port 32. Since the air blown from the lower air blowing port 31 acts as combustion air, by increasing this, the combustion of the pyrolysis gas is promoted, the temperature near the lower air blowing port 31 rises, and the temperature near the middle air blowing port 32 Get closer to.

  By executing the controls (1) to (4) above, it is possible to always realize the optimum temperature distribution, and as a result, it is possible to realize the combustion control in the secondary combustion furnace 30 with the optimum air ratio distribution.

  FIG. 7 shows the temperature in the vicinity of the air blowing port of each stage of the secondary combustion furnace and the NOx concentration in the exhaust gas at the outlet of the secondary combustion furnace when this control method is applied. The horizontal axis indicates the measurement time, the vertical axis indicates the furnace temperature and NOx concentration, the solid line indicates the temperature near the lower air outlet, the broken line indicates the temperature near the middle air outlet, and the dotted line indicates the temperature near the upper air outlet. As shown in FIG. 7, the maximum temperature in the secondary combustion furnace is about 1000 ° C. measured in the vicinity of the lower air outlet or the middle air outlet, and the minimum temperature is about 900 ° C. measured in the vicinity of the upper air outlet. The difference between the maximum temperature and the minimum temperature is about 100 ° C. Further, the temperature in the vicinity of the lower air outlet and the vicinity of the middle air outlet are substantially the same.

  From the result of such temperature distribution, it is preferable that the air ratio is gradually increased from less than 1 to 1 in the region from the vicinity of the lower air inlet to the vicinity of the intermediate air outlet in the secondary combustion furnace, and then becomes a predetermined air ratio. It is recognized that the air ratio distribution is obtained. As a result, the NOx concentration in the exhaust gas at the outlet of the secondary combustion furnace is 40 to 80 ppm and the average is 58 ppm, and the generation of NOx is suppressed. Thus, it can be confirmed that the combustion of the secondary combustion furnace can be appropriately controlled by controlling the amount of air blown from the blower opening of each stage of the secondary combustion furnace, and the generation of NOx is suppressed.

It is a schematic block diagram of the gasification melting furnace of one Embodiment of this invention. It is a figure explaining the shape of the temperature distribution of a secondary combustion furnace. It is a figure which shows the time change of the secondary combustion furnace temperature and NOx density | concentration at the time of making the ventilation from a lower stage ventilation port into a main body. It is a figure which shows the time change of a secondary combustion furnace temperature and NOx density | concentration at the time of making mainly the ventilation from an upper stage ventilation port. It is a flowchart of the combustion air control by this invention. It is a figure which shows the temperature distribution shape in a secondary combustion furnace. It is a figure which shows the time change of the secondary combustion furnace temperature and NOx density | concentration in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gasification melting furnace 30 Secondary combustion furnace 31 Lower air blower 31A Air quantity control means (flow control apparatus)
32 Middle air blower 32A Air volume control means (flow rate adjusting device)
33 Upper vent 33A Air volume control means (flow rate adjusting device)
40 Control device 41, 42, 43 Temperature measuring means (thermometer)

Claims (4)

In a combustion control device for a secondary combustion furnace having a lower blower port, a middle blower port, and an upper blower port that burn pyrolyzed gas obtained by pyrolyzing waste in a gasification melting furnace and blowing air,
The combustion control device is based on temperature measuring means for measuring the temperature in the furnace near the air outlet of each stage and the temperature distribution shape in the furnace derived from the temperature in the furnace near the air outlet of each stage measured by the temperature measuring means. A combustion control device for a secondary combustion furnace, comprising: a blown air amount control means for controlling the amount of air blown from the blower opening of each stage.   When the temperature distribution shape in the furnace is the temperature distribution shape in the furnace where the temperature rises in the order of the vicinity of the lower air outlet, the vicinity of the middle air outlet, and the vicinity of the upper air outlet, or the temperature distribution shape in the furnace where the temperature drops The temperature distribution in the furnace is similar to the temperature in the vicinity of the lower air vent and the middle air vent, and the temperature in the upper air vent is lower than the temperature in the vicinity of the lower air vent and the temperature in the middle air vent. The secondary combustion according to claim 1, wherein the blown air amount control means controls the amount of air blown from the blower ports of each stage so that the temperature distribution in the furnace is the highest in the vicinity of the blower port. Furnace combustion control device. In the combustion control method of the secondary combustion furnace provided with the lower stage air inlet, the middle stage air outlet, and the upper stage air inlet that burns the pyrolyzed gas obtained by thermally decomposing waste in the gasification melting furnace and blowing air,
Measure the temperature in the furnace near the air outlet of each stage,
Combustion control method for a secondary combustion furnace, characterized in that the amount of air blown from the air outlet of each stage is controlled based on the measured temperature distribution shape in the furnace derived from the temperature in the furnace near the air outlet of each stage. .   When the temperature distribution shape in the furnace is the temperature distribution shape in the furnace where the temperature rises in the order of the vicinity of the lower air outlet, the vicinity of the middle air outlet, and the vicinity of the upper air outlet, or the temperature distribution shape in the furnace where the temperature drops The temperature distribution in the furnace is similar to the temperature in the vicinity of the lower air vent and the middle air vent, and the temperature in the upper air vent is lower than the temperature in the vicinity of the lower air vent and the temperature in the middle air vent. 4. The combustion control method for a secondary combustion furnace according to claim 3, wherein the amount of air blown from the air outlets of each stage is controlled so that the temperature distribution shape in the furnace is the highest in the vicinity of the air outlets.

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