Operating method of rotary surface melting furnace

Abstract

This invention provides an operating method for a rotary surface melting furnace that can suppress the reduction in processing efficiency by suppressing the scattering of the material being processed. [Solution] A method for operating a rotary surface melting furnace, wherein a furnace chamber is partitioned by a furnace ceiling formed by an inner cylinder and a furnace bottom formed by an outer cylinder, and a material to be processed supplied from a storage section formed between the outer circumferential surface of the inner cylinder and the inner circumferential surface of the outer cylinder is melted by combustion of a central burner installed in the center of the furnace ceiling or a plurality of peripheral burners arranged around the central burner, and molten slag is discharged by dripping from a slag outlet formed in the center of the furnace bottom, wherein the operation of the central burner is controlled based on an indicator showing the scattering state of the material to be processed supplied to the furnace chamber.

Description

Technical Field

[0001] The present invention relates to an operation method of a rotary surface melting furnace.

Background Art

[0002] A rotary surface melting furnace is configured to melt a workpiece supplied from a storage portion formed between the outer peripheral surface of the inner cylinder and the inner peripheral surface of the outer cylinder in a furnace chamber partitioned by a furnace ceiling formed by the inner cylinder and a furnace bottom formed by the outer cylinder, by combustion of a plurality of burners installed on the furnace ceiling, and to drip and discharge molten slag from a slag discharge port formed at the center of the furnace bottom.

[0003] Patent Document 1 discloses a rotary surface melting furnace that can accurately detect the clogging state of the slag discharge port and efficiently prevent the clogging state of the slag discharge port when the workpiece has a high melting point or the melt flowability of the melt is poor.

[0004] The rotary surface melting furnace includes a heating burner provided at the center of the furnace ceiling, a plurality of burners around the heating burner, a slag discharge port heating means for heating the melt around the slag discharge port, a slag discharge port clogging state detecting means for detecting the clogging state of the slag discharge port, and a first control means for heating the slag discharge port by the slag discharge port heating means when it is detected by the slag discharge port clogging state detecting means that the slag discharge port is in a clogged state.

[0005] The heating burner provided at the center of the furnace ceiling is a special burner installed so as to be able to move in and out toward the slag discharge port in order to heat the slag discharge port when the slag discharge port is in a clogged state, and normally, the melting process is performed by a plurality of burners provided around the heating burner.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] In the rotary surface melting furnace described above, the bottom ash and fly ash generated in the incinerator are fed into the furnace chamber as the material to be processed. They accumulate in a mortar-like shape in the furnace chamber, centered around the outlet, and are maintained at a high temperature of approximately 1300°C by multiple peripheral burners (referred to as "combustors" in Patent Document 1) positioned around the furnace ceiling, and are melted from the surface.

[0008] The exhaust gas generated in the furnace chamber flows down into a flue connected to the slag outlet, where it is purified by exhaust gas treatment equipment such as an air preheater, cooling tower, dust collector, and acid gas purification device before being discharged through the chimney.

[0009] Fly ash accompanying the exhaust gas is discharged from the system by a dust discharge device installed at the bottom of the air preheater, cooling tower, and dust collector.

[0010] However, if fine particles such as fine ash contained in the material to be processed are stirred up in the furnace by the flow of combustion gas from the surrounding burners, they may flow out into the flue from the outlet without being melted. This could result in a large amount of fine particles, which should have been melted, flowing into the flue and accumulating at the bottom of the air preheater, cooling tower, and dust collector.

[0011] In such cases, it was necessary to stop the operation of the melting furnace and remove the accumulated fine ash, which resulted in a significant decrease in the processing efficiency of the rotary surface melting furnace.

[0012] The object of the present invention is to provide a method for operating a rotary surface melting furnace that can suppress a decrease in processing efficiency by suppressing the scattering of the material to be processed. [Means for solving the problem]

[0013] To achieve the above objectives, the first characteristic configuration of the rotary surface melting furnace operation method according to the present invention is a rotary surface melting furnace operation method wherein a material to be processed supplied from a storage section formed between the outer peripheral surface of the inner cylinder and the inner peripheral surface of the outer cylinder is melted by combustion of a central burner installed in the center of the furnace ceiling or a plurality of peripheral burners arranged around the central burner, and molten slag is discharged by dripping from a slag outlet formed in the center of the furnace bottom, wherein the operation of the central burner is controlled based on an indicator showing the scattering state of the material to be processed supplied to the furnace chamber.

[0014] The material to be processed, supplied to the furnace chamber, melts from the surface due to the combustion heat from the central burner or multiple peripheral burners and flows out from the slag outlet. At this time, the central part of the furnace chamber is mainly heated by the central burner, and the surface of the unmelted material supplied to the furnace chamber from the storage area is heated by the peripheral burners. When the flow of combustion air and combustion exhaust gas supplied to the peripheral burners acts on the surface of the material to be processed supplied to the furnace chamber, fine particles of the material may be stirred up and scattered into the flue from the slag outlet without being melted. Therefore, by controlling the operation of the central burner based on an indicator showing the scattering state of the material to be processed, and adjusting the balance with the peripheral burners, it becomes possible to perform a stable melting process while suppressing the scattering of fine particles.

[0015] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the indicator includes at least one of the following: a change in the amount or composition of dust accumulated in the air preheater provided in the flue communicating with the sludge outlet; a change in the amount or composition of fly ash collected by the dust collector; a change in the in-furnace camera image taken of the furnace chamber; or a change in the composition of the material to be processed stored in the storage section.

[0016] As the amount of fine particles dispersed increases, the amount of dust accumulated in the air preheater in the flue increases, or the proportion of easily dispersed fine particles (processed material) in the dust increases, the amount of fly ash collected by the dust collector increases, or the proportion of easily dispersed fine particles (processed material) in the collected fly ash increases. Therefore, all of these can be suitably used as indicators of the dispersion state of the processed material. Furthermore, since the dispersion state of fine particles can be grasped based on images taken by an in-furnace camera capable of photographing the inside of the furnace, in-furnace camera images can be suitably used as an indicator of the dispersion state of the processed material. In addition, dispersion also increases when the proportion of easily dispersed fine particles in the processed material stored in the storage section increases, so changes in the composition of the processed material stored in the storage section can be suitably used as an indicator of the dispersion state of the processed material. The first two indicators allow for real-time assessment of the state, while the latter can be suitably used as an indicator that allows for prediction in advance of an increase in the dispersion of fine particles.

[0017] The third characteristic configuration is that, in addition to the first or second characteristic configuration described above, the central burner is ignited when it is determined, based on the indicator, that it is necessary to suppress the scattering of the material to be processed supplied to the furnace chamber.

[0018] If it is determined based on the indicators that it is necessary to suppress the scattering of the material being processed, the central burner can be ignited to suppress the amount of combustion by the surrounding burners without causing temperature fluctuations in the furnace chamber, thereby suppressing the scattering of fine particles contained in the material being processed.

[0019] The fourth characteristic configuration is that, in addition to the first or second characteristic configuration described above, if it is determined that it is necessary to suppress the scattering of the material to be processed supplied to the furnace chamber based on the indicator after the start of operation of the central burner, the output of the central burner is increased.

[0020] When the central burner is operating during normal operation or when the scattering state deteriorates after the start of the operation of the central burner, by increasing the output of the central burner, melting can be promoted before the object to be processed scatters, and the scattering of fine particles contained in the object to be processed can be effectively suppressed by further suppressing the combustion amount by the peripheral burners.

Advantages of the Invention

[0021] As described above, according to the present invention, even in a situation where the object to be processed is likely to fly up in the furnace, it has become possible to provide an operation method for a rotary surface melting furnace that can surely melt the object to be processed while suppressing the flying up.

Brief Description of the Drawings

[0022] [Figure 1] Explanatory drawing of a melting treatment facility equipped with a rotary surface melting furnace according to the present invention [Figure 2] Explanatory drawing showing a partial cross-section of the melting furnace [Figure 3] Explanatory drawing of the melting furnace in plan view [Figure 4] Cross-sectional view of the furnace chamber showing the state where the object to be processed has scattered [Figure 5] Cross-sectional view of the furnace chamber showing the state where the center burner is ignited

Embodiments for Carrying Out the Invention

[0023] Hereinafter, embodiments of an operation method for a rotary surface melting furnace according to the present invention will be described. In FIG. 1, a melting treatment facility 100 is shown. The melting treatment facility 100 includes a rotary surface melting furnace 1 (hereinafter simply referred to as "melting furnace 1"), air preheaters 2A, 2B, 2C provided in a flue through which combustion gas generated in the melting furnace 1 flows down, a desuperheating tower 3, dust collectors 4A, 4B, a neutral substance recovery device 5, an exhaust gas treatment facility such as a catalytic reaction tower 6, etc. The exhaust gas purified by the exhaust gas treatment device is exhausted from a chimney 8 through an induced draft fan 7.

[0024] In the melting furnace 1, materials to be processed, such as bottom ash, fly ash, or sewage sludge generated in the waste incinerator, are fed into the furnace chamber 1A, which is maintained at a temperature of approximately 1300°C by the combustion heat from combustion air containing fuel gas LNG and oxygen gas supplied to multiple burners 10 located on the furnace ceiling. The slag produced from the melted materials is then dripped from the outlet 1B at the bottom of the furnace into the cooling water tank 20 and recovered as granulated slag.

[0025] The combustion gas generated in furnace chamber 1A flows down from the slag outlet 1B to the secondary combustion chamber 1C, where it is subjected to secondary combustion by the air supplied to the secondary combustion chamber 1C. It then flows down to the air preheaters 2A, 2B, and 2C, where it is cooled to approximately 800°C through heat exchange with the combustion air supplied to the burner.

[0026] Subsequently, the exhaust gas is cooled by water injection in the cooling tower 3, and then mixed with filter cloth protectant and activated carbon injected from the upstream flue of the dust collector 4A. The activated carbon, which has adsorbed mercury and other substances contained in the exhaust gas, is captured in the dust collector 4A along with the filter cloth protectant. Acidic gas components such as hydrogen chloride contained in the exhaust gas are neutralized by a neutralizing agent and activated carbon injected from the upstream flue of the dust collector 4B, and the neutralizing agent and activated carbon are captured in the dust collector 4B. After passing through the dust collector 4B, the exhaust gas is led to the catalytic reaction tower 6 after passing through the neutralized product recovery device 5, where nitrogen oxides and dioxins are decomposed, and then exhausted from the chimney 8.

[0027] Figure 2 shows the specific structure of the melting furnace 1. The melting furnace 1 consists of a furnace body and a secondary combustion chamber 1C. The melting furnace 1 is configured such that the material to be processed, supplied from a storage section 17 formed between the outer circumferential surface of the inner cylinder 11 and the inner circumferential surface of the outer cylinder 12, is melted by the combustion heat of a central burner 10C installed in the center of the furnace ceiling 13 or a plurality of peripheral burners 10S arranged around the central burner 10C, and the molten slag is discharged by dripping from a slag outlet 1B formed in the center of the furnace bottom 14.

[0028] As shown in Figure 3, the furnace ceiling 13, which is circular in plan view, has a central burner 10C installed in the center, and six peripheral burners 10S installed radially outward at a predetermined distance from the center, at equal intervals in the circumferential direction. As shown in Figure 1, fuel gas and preheating air (which may be oxygen-enriched air or oxygen gas) are supplied to the central burner 10C and the peripheral burners 10S, respectively.

[0029] The melting furnace 1 is equipped with a control unit 30, which is a computer on which a melting control program is installed (see Figure 1). Based on values ​​input from sensors that measure the temperature of the furnace chamber 1A, the amount of slag produced, the components of the exhaust gas, etc., the control unit 30 controls the rotational speed of the outer cylinder 12 by the drive mechanism 19 and the combustion control of the central burner 10C and peripheral burners 10S so that the furnace can be operated at an appropriate temperature and an appropriate amount of slag produced.

[0030] As shown in Figure 4, the material to be processed 18 stored in the storage section 17 is supplied into the furnace chamber 1A by cutting blades installed at the lower end of the inner cylinder 11 due to the relative rotation of the outer cylinder 12, which is rotationally driven by the drive mechanism 19 (see Figure 2), and the fixed inner cylinder 11, and accumulates in a mortar-like shape around the outlet 1B. Due to the combustion heat from the central burner 10C and / or the surrounding burners 10S, molten slag flows down from the surface of the material to be processed 18 towards the outlet 1B in a high-temperature environment of approximately 1300°C and drips into the cooling water tank 20 below.

[0031] In an environment where the material to be processed, shortly after being cut into the furnace chamber 1A by the cutting blades, is subjected to wind pressure from a large amount of gas supplied to the surrounding burner 10S and the combustion flame, if the material to be processed contains a large amount of lightweight fine particles, such as fly ash components generated in the incinerator, then, as shown in Figure 4, the fine particles are lifted up by the wind pressure and flow down into the flue from the outlet 1B without melting.

[0032] The fly ash components that gasify during melting are cooled to about 800°C as they pass through the air preheaters 2A, 2B, and 2C, and some of them accumulate at the bottom. These are then cut out by the cutting device 22 of the dust removal device 21 located at the bottom and discharged outside the system.

[0033] When fine ash, which is stirred up in the furnace chamber 1A and flows down into the flue from the outlet 1B without melting, accumulates in the dust removal device 21, it becomes necessary to stop the operation of the melting furnace and remove the accumulated fine ash, which leads to a decrease in the amount of material to be melted.

[0034] Therefore, as shown in Figure 5, in the melting furnace operation method according to the present invention, the control unit 30 is configured to control the operation of the central burner 10C based on an index indicating the scattering state of the material to be processed 18 supplied to the furnace chamber 1A.

[0035] When using the peripheral burner 10S, the melting efficiency can be increased by directly heating the workpiece 18 that has just been cut into the furnace chamber 1A. Therefore, in normal operation, taking fuel efficiency into consideration, the central burner 10C is stopped once the furnace chamber 1A reaches a certain temperature, and only the peripheral burner 10S is operated.

[0036] However, as described above, when gas flows such as combustion air supplied to the surrounding burner 10S act on the surface of the material to be processed 18 supplied to the furnace chamber 1A, fine particles of the material to be processed 18 may be blown up and scattered into the flue from the outlet 1B without being melted.

[0037] Therefore, the control unit 30 controls the operation of the central burner 10C based on an indicator showing the scattering state of the workpiece 18, and adjusts the balance with the surrounding burners 10S to control the process in a way that suppresses the scattering of fine particles while performing a stable melting process.

[0038] As indicators, at least one or a combination of the following can be used: changes in the amount or composition of dust accumulated in the air preheaters 2A, 2B, and 2C provided in the flue connected to the sludge outlet 1B; changes in the amount or composition of fly ash collected by the dust collectors 4A and 4B; changes in the in-furnace camera image taken of the furnace chamber 1A; or changes in the composition of the material to be processed 18 stored in the storage section 17.

[0039] An increase in the amount of fine particles dispersed leads to an increase in the amount of dust accumulated in the air preheater in the flue, or an increase in the proportion of the treated material composed of easily dispersed fine particles in the dust, an increase in the amount of fly ash collected by the dust collector, or an increase in the proportion of the treated material composed of easily dispersed fine particles in the collected fly ash. Therefore, all of these can be suitably used as indicators of the dispersion state of the treated material.

[0040] Specifically, dust transported by the first conveyor mechanism 23 (see Figure 1) that transfers dust extracted from air preheaters 2A, 2B, and 2C, and dust transported by the second conveyor mechanism 24 (see Figure 1) that transfers dust extracted from dust collectors 4A and 4B, can be sampled, and their composition can be measured using an X-ray fluorescence analyzer (XRF). For example, if the material to be processed is incinerator ash or incinerator fly ash, components such as SiO2, CaO, Al2O3, and Fe2O3 can be detected as fine particles that are easily dispersed, and it can be determined that fine particles are being dispersed when the ratio of these components increases. For example, an index can be defined that can evaluate the degree of dispersion based on the weight ratio of fine particles that cause dispersion to the weight of dust, and the weight ratio of the components determined by X-ray fluorescence analysis (XRF) during furnace operation can be input to the control unit 30 as an index.

[0041] When using the amount of dust generation as an indicator, the weight of dust per unit time can be used as the indicator, and a threshold value indicating the dispersion state can be set for that value. In this case, it is preferable to take into account the amount of slag generated per unit time. For example, the correlation between the amount of slag generated and the weight of dust can be investigated in advance when there is no dispersion of fine particles, and when the correlation is met during operation, the indicator can be set to a standard value (e.g., "1"), and if the correlation is exceeded, the value of the indicator can be increased (e.g., greater than "1"). If the correlation is not met, the value of the indicator can be decreased (e.g., less than "1").

[0042] When using the amount of fly ash collected by a dust collector as an indicator, a threshold value indicating the dispersion state can be set based on the content of fine particles such as SiO2, CaO, Al2O3, and Fe2O3 contained in the weight of fly ash per unit time.

[0043] Alternatively, a camera may be installed on the furnace ceiling 13 to photograph the molten state inside the furnace, and the scattering state of fine particles may be detected by image processing of the images captured by the camera. By comparing this with a predetermined set of scattering amounts in multiple stages, an index indicating the degree of scattering may be input to the control unit 30.

[0044] Furthermore, it is also possible to configure the system to detect the composition of the material to be processed stored in the storage section 17 and to input the degree of increase in the composition of fine particles that are easily dispersed as an indicator to the control unit 30. For example, the material to be processed may be sampled from the material transport mechanism 25 (see Figure 1) that transports the material to be processed 18 into the storage section 17, and the weight ratio of fine particles that are easily dispersed may be determined based on the results of X-ray fluorescence analysis (XRF) and input to the control unit 30 as an indicator. In this case, however, there is a time lag between when the material is put into the storage section 17 and when it is actually cut out into the furnace chamber 1A, so the control unit 30 needs to take this time lag into consideration and perform the necessary control.

[0045] Regardless of which indicator is used, if there are differences in the degree of dispersion between indicators, objective control becomes difficult, so it is preferable to normalize each indicator in advance.

[0046] When the control unit 30 determines, based on an indicator, that it is necessary to suppress the scattering of the material to be processed 18 supplied to the furnace chamber 1A, it ignites the central burner 10C to suppress the amount of combustion by the surrounding burners without causing temperature fluctuations in the furnace chamber. By reducing the air pressure from the air supplied to the surrounding burners 10S and the combustion flame, it suppresses the scattering of fine particles from the surface of the material to be processed 18.

[0047] If the control unit 30 determines, based on an indicator, that the scattering of the material to be processed 18 supplied to the furnace chamber 1A has deteriorated after the start of operation of the central burner 10C, it increases the output of the central burner 10C. By increasing the output of the central burner, melting is promoted before the material to be processed scatters, and the scattering of fine particles contained in the material to be processed 18 can be effectively suppressed by further suppressing the amount of combustion by the surrounding burners 10S.

[0048] If the control unit 30 determines, based on an indicator, that the scattering condition has been suppressed after the start of operation of the central burner 10C, it extinguishes the central burner 10C. By extinguishing the central burner 10C, the energy efficiency for melting can be improved. For example, it becomes possible to restore the combustion state of the surrounding burners 10S, whose combustion had been suppressed.

[0049] Regardless of the index value, it is preferable for the control unit 30 to operate by setting the fuel supply amount and air supply amount to the central burner 10C to a predetermined value that is greater than the fuel supply amount and air supply amount to each peripheral burner 10S.

[0050] When the fuel and air supply amounts to the central burner 10C are set to predetermined values ​​greater than the fuel and air supply amounts to the surrounding burners 10S, the reduction in the fuel and air supply amounts to the surrounding burners 10S reduces the influence of combustion gases blown from the surrounding burners 10S onto the unmelted workpiece 18 supplied to the furnace chamber 1A, thereby suppressing scattering. At the same time, the heat supplied from the central burner 10C maintains a predetermined furnace chamber temperature, thereby suppressing scattering of the workpiece while maintaining a stable melting state.

[0051] Furthermore, by reducing the amount of air supplied to the peripheral burner 10S while keeping the amount of fuel supplied to the central burner 10C and the amount of fuel supplied to the peripheral burner 10S unchanged, and increasing the amount of air supplied to the central burner 10C by the same amount, it is possible to maintain a stable melting state while suppressing the scattering of the material being processed.

[0052] Furthermore, by operating the central burner 10C at all times, regardless of whether or not the material being processed is scattered, it is possible to avoid the scattering of the material that would occur if only the peripheral burners 10S were operated. If scattering of the material occurs even when the central burner 10C is operating, the amount of fuel supplied to the central burner 10C should be increased.

[0053] The embodiments described above are merely examples of the present invention, and the specific configuration of each part can be modified and designed as appropriate within the scope that the effects of the present invention are achieved. [Explanation of symbols]

[0054] 1: Surface melting furnace 1A: Furnace room 1B: Slag mouth 10C: Central burner 10S: Peripheral burner 11: Inner cylinder 12: Outer cylinder 13: Hearth ceiling 14: Hearth bottom 17: Storage section 18: Items to be processed 100: Melting treatment equipment

Claims

1. A method for operating a rotary surface melting furnace, wherein a furnace chamber is partitioned by a furnace ceiling formed by an inner cylinder and a furnace bottom formed by an outer cylinder, and the material to be processed, supplied from a storage section formed between the outer circumferential surface of the inner cylinder and the inner circumferential surface of the outer cylinder, is melted by combustion of a central burner installed in the center of the furnace ceiling or a plurality of peripheral burners arranged around the central burner, and the molten slag is discharged by dripping from a slag outlet formed in the center of the furnace bottom, A method for operating a rotary surface melting furnace, which controls the operation of the central burner based on an indicator showing the scattering state of the material to be processed supplied to the furnace chamber.

2. The method for operating a rotary surface melting furnace according to claim 1, wherein the indicator includes at least one of the following: a change in the amount or composition of dust accumulated in an air preheater provided in a flue communicating with the slag outlet; a change in the amount or composition of fly ash collected by a dust collector; a change in the image of the furnace chamber taken by an in-furnace camera; or a change in the composition of the material to be processed stored in the storage section.

3. A method for operating a rotary surface melting furnace according to claim 1 or 2, wherein, based on the indicators, it is determined that it is necessary to suppress the scattering of the material to be processed supplied to the furnace chamber, and the central burner is ignited.

4. A method for operating a rotary surface melting furnace according to claim 1 or 2, wherein, after the start of operation of the central burner, it is determined that it is necessary to suppress the scattering of the material to be processed supplied to the furnace chamber based on the indicator, the output of the central burner is increased.

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