Thermal decomposition method

Abstract

To provide a thermal decomposition method that improves thermal efficiency of a carbonization furnace by burning a combustible gas in a carbonization furnace.SOLUTION: A thermal decomposition method comprises: a carbonization step of carbonizing organic waste in a carbonization furnace 3; an oxygen supply step that supplies oxygen to the carbonization furnace 3; and an oxidation step that oxidizes a combustible gas generated from the organic waste in the carbonization furnace 3, wherein the oxygen supply step comprises a supply control step that controls an amount of supplied oxygen to be less than an equivalent amount for oxidizing the combustible gas.SELECTED DRAWING: Figure 1

Description

Technical Field

[0004] , , , , ,

[0003]

[0001] The present invention relates to a thermal decomposition method.

Background Art

[0002] Patent Document 1 describes a method (thermal decomposition method) for producing valuable substances (carbides) from organic waste and its system. This system includes a carbonization device that produces carbides and pyrolysis gas (flammable gas) from organic waste such as sludge by indirect heating supplied from the outer casing side, and a secondary combustion chamber that burns the pyrolysis gas generated by carbonization to produce combustion exhaust gas and supplies the combustion exhaust gas to the carbonization furnace. In this system, the combustion exhaust gas obtained by burning the pyrolysis gas in the secondary combustion chamber is supplied to the carbonization furnace, and the heat quantity of the pyrolysis gas is utilized as the heat quantity for the carbonization process.

[0003] Patent Document 2 describes a sludge heat treatment method and a sludge heat treatment device for obtaining a sludge treatment product (carbide) with an odor intensity suppressed to a certain value or less from sludge containing a large amount of odor substances. The sludge heat treatment device used in this sludge heat treatment method includes a heating furnace for heating sludge, a sludge loading section for loading sludge into the heating furnace, a sludge unloading section for unloading the sludge treatment product unloaded from the heating furnace outside the sludge heat treatment device, a thermometer for measuring the temperature inside the heating furnace, a hot blast furnace for supplying hot air to the heating furnace, an oxygen supply control section for controlling the amount of oxygen supplied to the heating furnace, an oxygen supply section for supplying oxygen to the heating furnace, and an oxygen concentration meter for measuring the oxygen concentration inside the heating furnace. The heating furnace is an externally heated furnace and has a kiln that is substantially cylindrical and conveys sludge in the axial direction while heating it in a state where it does not contact the outside air, and a jacket provided to surround the kiln.

[0004] In the sludge heat treatment method described in Patent Document 2, the oxygen concentration inside the kiln is adjusted to suppress the odor intensity of the treated sludge to below a certain value and to keep the content of organic compounds in the treated sludge above a certain value. An oxygen concentration meter measures the current oxygen concentration inside the kiln and outputs the measured value to the oxygen supply control unit. The oxygen supply control unit is given a predetermined oxygen concentration setting value to be maintained inside the kiln, and this setting value is determined according to the target values ​​of odor intensity and organic compound content of the treated sludge obtained after heat treatment. Based on the current oxygen concentration inside the kiln and the above oxygen concentration setting value, the oxygen supply control unit determines the amount of oxygen to be supplied by the oxygen supply unit. Next, the oxygen supply control unit outputs an oxygen supply signal containing the above oxygen amount information to the oxygen supply unit. Based on the oxygen supply signal output from the oxygen supply control unit, the oxygen supply unit supplies oxygen inside the kiln. The oxygen supplied inside the kiln oxidizes and decomposes the odor substances contained in the sludge, suppressing the odor intensity of the treated sludge to below a certain value. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2003-095629 [Patent Document 2] Japanese Patent Publication No. 2010-125392 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The method and system for producing valuable materials from organic waste described in Patent Document 1 requires large-scale equipment, such as combustion of pyrolysis gas (combustible gas) in a secondary combustion furnace and equipment to supply the combustion exhaust gas of the pyrolysis gas to a carbonization furnace, and heat loss of combustion exhaust gas due to these facilities is unavoidable. In addition, the need to transport the combustible pyrolysis gas to the secondary combustion furnace makes the equipment for safety measures complex. The sludge heating treatment method and sludge heating treatment apparatus described in Patent Document 2 incorporates measures to oxidize and decompose odorous substances contained in the sludge in the furnace, but the post-treatment of combustible gases generated during carbonization is not considered.

[0007] This invention has been made in view of the above circumstances, and its purpose is to provide a pyrolysis method that improves the thermal efficiency of a carbonization furnace by burning a combustible gas in the carbonization furnace. [Means for solving the problem]

[0008] The characteristic configuration of the pyrolysis method according to the present invention for achieving the above objective includes a carbonization step of carbonizing organic waste in a carbonization furnace, an oxygen supply step of supplying oxygen to the carbonization furnace, and an oxidation step of oxidizing the combustible gas generated from the organic waste in the carbonization furnace, wherein the oxygen supply step includes a supply control step of controlling the amount of oxygen supplied so that it is less than the equivalent amount required to oxidize the combustible gas. Furthermore, in the supply control step, oxygen is supplied based on the total amount of combustible gas generated per unit mass from the organic waste, the amount of organic waste supplied to the carbonization furnace per unit time, and the carbonization temperature of the organic waste, which have been previously obtained for each of several different temperatures. It's at a single point.

[0009] When carbonizing organic waste in a carbonization furnace to obtain charred material, if the amount of oxygen supplied to the carbonization furnace increases relative to the charred material, the oxidation (combustion) of the charred material will proceed more easily. Therefore, according to the above configuration, in order to suppress the oxidation of the charred material and oxidize (combust) only the combustible gas generated from the organic waste, less than the equivalent amount of oxygen needed to oxidize the combustible gas is supplied to the carbonization furnace. The supplied oxygen usually combines with the gaseous combustible gas at a faster rate than with the solid charred material. Therefore, by supplying less than the equivalent amount of oxygen needed to oxidize the combustible gas to the carbonization furnace, the oxidation of the charred material can be suppressed while only the combustible gas can be oxidized within the carbonization furnace.

[0010] Furthermore, with the above configuration, since the combustible gas is oxidized within the carbonization furnace, the heat generated by this oxidation is used for carbonization within the furnace without any loss such as heat being released to the outside. This improves thermal efficiency. In other words, by oxidizing the combustible gas within the carbonization furnace and utilizing it as a heat source for the carbonization furnace, energy savings can be achieved.

[0011] Furthermore, with the above configuration, the amount of flammable gas contained in the exhaust gas discharged from the carbonization furnace is significantly reduced, resulting in exhaust gases with a low risk of ignition. This improves the safety of the carbonization system and allows for the simplification of the carbonization system.

[0012] Further characteristic configuration of the thermal decomposition method according to the present invention That is, The supply control step includes a feedback control step that controls the amount of supplied oxygen so that the oxygen concentration is less than 1.0 volume%. Furthermore, a further characteristic feature of the pyrolysis method according to the present invention is that it further includes an oxygen concentration measurement step for measuring the oxygen concentration of the internal atmosphere of the carbonization furnace. .

[0013] With the above configuration, the oxygen concentration in the internal atmosphere of the carbonization furnace can be controlled to less than 1.0 volume%, thereby suppressing the oxidation of the carbides while oxidizing only the combustible gases within the carbonization furnace.

[0014] Further characteristic features of the pyrolysis method according to the present invention include a carbonization step of carbonizing organic waste in a carbonization furnace, an oxygen supply step of supplying oxygen to the carbonization furnace, and an oxidation step of oxidizing the combustible gas generated from the organic waste in the carbonization furnace. ,of The oxygen supply step includes a feedback control step that controls the amount of oxygen supplied so that the oxygen concentration is less than 1.0 volume%. Furthermore, a further characteristic feature of the pyrolysis method according to the present invention is that it includes an oxygen concentration measurement step for measuring the oxygen concentration of the internal atmosphere of the carbonization furnace. .

[0015] According to the above configuration, the oxygen concentration in the internal atmosphere of the carbonization furnace is controlled to less than 1.0% by volume, so that only the combustible gas can be oxidized in the carbonization furnace while suppressing the oxidation of the carbide. In addition, the combustible gas is oxidized in the carbonization furnace, and the oxidation heat is used as the heat source of the carbonization furnace, achieving energy saving. Further, since the content of the combustible gas contained in the exhaust gas exhausted from the carbonization furnace is significantly reduced, the exhaust gas has a low risk of ignition, the safety of the carbonization system is improved, and the carbonization system can be simplified.

[0016] The characteristic configuration of the pyrolysis method according to the present invention for achieving the above object lies in that the oxygen supplied in the oxygen supply step is supplied as an oxygen-containing gas with an oxygen concentration of less than 5%.

[0017] When oxygen is supplied into the carbonization furnace at a high concentration, the time until the supplied oxygen diffuses into the furnace atmosphere, mixes with the combustible gas, and is used for oxidation becomes longer. As a result, a locally high-oxygen-concentration atmosphere (region) will occur in the space inside the carbonization furnace. When the carbide enters the atmosphere with a high oxygen concentration, the carbide will be oxidized. However, according to the above configuration, by supplying an oxygen-containing gas with a low concentration of less than 5% oxygen into the carbonization furnace, it is possible to prevent a locally high-oxygen-concentration atmosphere from occurring in the carbonization furnace and suppress the oxidation of the carbide. Thereby, only the combustible gas can be oxidized in the carbonization furnace.

Brief Description of the Drawings

[0020] [Figure 1] Flow diagram of the carbonization system [Figure 2] Explanation diagram of the carbonization furnace, supply mechanism, and oxygen supply device [Figure 3] Control flow of oxygen supply amount [Figure 4] Explanation diagram of the carbonization furnace, supply mechanism, and another oxygen supply device

Embodiments for Carrying Out the Invention

[0021] Based on the drawings, a pyrolysis method according to an embodiment of the present invention will be described. Hereinafter, a carbonization system that converts organic waste such as sludge, like sewage sludge, into a fuel resource with good handling properties by pyrolyzing and carbonizing it will be exemplified and described.

[0022] 〔Overall Configuration of Carbonization System〕 FIG. 1 shows a flow diagram of a carbonization system A.

[0023] The carbonization system A includes, as facilities for carbonizing sludge, a carbonization furnace 3 (an example of a carbonization step) for carbonizing sludge and a supply mechanism F for supplying sludge to the carbonization furnace 3, and is operated and controlled by a control unit C which is a central control mechanism equipped with a CPU and a storage device (not shown). In the carbonization furnace 3, the sludge is carbonized to obtain carbide, and at the same time, exhaust gas containing a tar component, char, and combustible gas (dry distillation gas, for example, gases such as methane, hydrogen, and carbon monoxide) that condenses due to temperature reduction is generated. The sludge of the present embodiment is dried in a predetermined moisture content in advance in an upstream process (not shown), and after being granulated into, for example, several millimeters of granules, it is supplied to the supply mechanism F.

[0024] As post-treatment facilities for the carbide of sludge, the carbonization system A includes a cooler 91 for cooling the carbide discharged from the carbonization furnace 3 and a stock tank 93 for storing the cooled carbide in preparation for shipment.

[0025] Carbonization system A includes an oxygen supply device 5 (an example of an oxygen supply step) that supplies oxygen to the carbonization furnace 3 as a treatment facility for the exhaust gas of the carbonization furnace 3, and a gas pipe 7 that draws exhaust gas from the carbonization furnace 3. Furthermore, along the gas pipe 7, extending downstream from the carbonization furnace 3, there is a thermometer T for measuring the temperature of the exhaust gas, a gas property measuring device 6 for measuring gas properties such as the oxygen concentration in the exhaust gas, a flow meter FL for measuring the flow rate of the exhaust gas, a secondary combustion furnace 94, a purification device 95 for removing odorous gases and soot, and an exhaust device 96 such as a fan. The exhaust gas containing combustible gas generated in the carbonization furnace 3 is oxidized (combusted) in the carbonization furnace 3 by oxygen supplied from the oxygen supply device 5 (an example of an oxidation step), and after being combusted in the secondary combustion furnace 94, it is purified in the purification device 95 and released to the outside (atmosphere). The gas property measuring device 6 measures the oxygen concentration in the exhaust gas upstream of the secondary combustion furnace 94 (an example of an oxygen concentration measurement step) and sends the measurement results to the control unit C, etc. The control unit C controls the operation of the carbonization system A based on the measurement results of the gas property measuring device 6 so that the carbides do not oxidize in the carbonization furnace 3.

[0026] [Explanation of each part] [Feeding mechanism] The supply mechanism F includes a hopper 1 for temporarily storing sludge to be supplied to the carbonization furnace 3, a feeder 2 for supplying sludge from the hopper 1 to the carbonization furnace 3, and a purge mechanism 4 for supplying an inert gas such as nitrogen to the feeder 2.

[0027] Hopper 1 is a storage container made of metal or the like that temporarily stores sludge, which is transported and supplied from the upstream side by a conveyor or the like, before supplying it to the carbonization furnace 3. A feeder 2 is connected to the bottom of hopper 1. Sludge is supplied from hopper 1 on the upstream side to feeder 2 on the downstream side by free fall from hopper 1.

[0028] The feeder 2 is a feeding device that cuts sludge from the hopper 1 at a constant speed (constant feeding speed) and supplies it to the downstream carbonization furnace 3. The feeder 2 has a rotary valve 20, which is a quantitative cutting device such as a rotary valve, and a slide valve 21, which is a gate valve that can shut off the space on the hopper 1 side and the space on the rotary valve 20 side. The rotary valve 20 and slide valve 21 are made of metal or the like. When supplying sludge from the feeder 2 to the carbonization furnace 3, the slide valve 21 is opened to connect the space on the hopper 1 side and the space on the rotary valve 20 side, and the rotary valve 20 is operated. When stopping the supply of sludge from the feeder 2 to the carbonization furnace 3, the slide valve 21 is closed to shut off the space on the hopper 1 side and the space on the rotary valve 20 side, and the rotary valve 20 is stopped.

[0029] The purge mechanism 4 is a device that supplies inert gas such as nitrogen to the supply unit 2 at a predetermined supply rate, equipped with a gas cylinder that serves as a source of inert gas, a flow control device such as a valve (not shown), and other components. The supply unit 2 is prevented from backflowing exhaust gas from the carbonization furnace 3 by the inert gas supplied from the purge mechanism 4, and is thus protected from contamination by condensation of tar components and other substances contained in the exhaust gas.

[0030] [Carbonization furnace] As shown in Figures 1 and 2, the carbonization furnace 3 is a plug-flow type heating furnace that performs pyrolysis treatment by continuously heating, carbonizing, and discharging sludge supplied in a fixed quantity from the supply mechanism F. The carbonization furnace 3 heats the sludge to, for example, 250 degrees Celsius to 600 degrees Celsius. As shown in Figure 2, the carbonization furnace 3 is an externally heated rotary kiln equipped with an inner cylinder 30, which is a metal rotating container for containing and heating the sludge; an outer cylinder 31, which is a metal container for containing the inner cylinder 30; a hot air generator 35, which supplies hot air as a heat transfer medium to heat the inner cylinder 30 into the space between the inner cylinder 30 and the outer cylinder 31; and an inlet side mechanism 33 and an outlet side mechanism 34, which have a drive mechanism (not shown) for rotating the inner cylinder 30, a receiving mechanism for receiving the sludge supply, and a discharge mechanism for discharging the carbonized material. An oxygen supply device 5 is connected to the carbonization furnace 3, and the oxygen supply device 5 supplies a gas containing a low concentration of oxygen (an example of an oxygen-containing gas, hereinafter referred to as low-oxygen gas) into the inner cylinder 30.

[0031] The outer cylinder 31 is a containment container that houses the inner cylinder 30 in its internal space, and is a heating container for heating the outer circumference of the inner cylinder 30 by bringing hot air into contact with it. The outer cylinder 31 has a hot air inlet pipe 31a provided on the outer circumference on the downstream side of the outer cylinder 31, which introduces hot air (for example, 600 degrees Celsius) from the hot air generator 35 into its internal space, and a hot air outlet pipe 31b provided on the outer circumference on the upstream side, which exhausts the hot air from its internal space. The hot air introduced into the internal space of the outer cylinder 31 exchanges heat with the inner cylinder 30 and is then exhausted from the hot air outlet pipe 31b.

[0032] The inner cylinder 30 is a cylindrical, metal heating container. With sludge contained inside the inner cylinder 30, it heats the sludge by rotating around its axis as the center of rotation, while agitating the sludge inside, through heat transfer from outside the cylinder. The inner cylinder 30 is rotationally driven by a motor (not shown) or the like.

[0033] The sludge supplied to the carbonization furnace 3 is supplied to the inner cylinder 30 via the inlet mechanism 33. The sludge supplied to the inner cylinder 30 is carbonized by heat transfer from the inner cylinder 30, and is subsequently pushed downstream by sludge supplied from the upstream side (so-called plug flow), reaching the outlet mechanism 34. The carbonized material that reaches the outlet mechanism 34 is discharged from the carbonization furnace 3 and transferred to the cooler 91.

[0034] When the sludge supplied to the inner cylinder 30 is carbonized, exhaust gas containing combustible gases such as carbonization gas and components that condense at low temperatures, such as tar components, is generated. In the carbonization furnace 3, low-oxygen gas is supplied into the inner cylinder 30 from the oxygen supply device 5 to suppress the oxidation (combustion) of the carbonized material, while the combustible gases generated during carbonization are oxidized (combusted) within the inner cylinder 30. The thermal energy generated by the oxidation of these combustible gases is used as heat to carbonize the sludge within the inner cylinder 30, contributing to energy conservation. The gas supplied to the inner cylinder 30 and the exhaust gas generated in the inner cylinder 30 (including the gas generated by the oxidation of combustible gases) are released to the outside (atmosphere) via the outlet mechanism 34, gas pipe 7, and exhaust device 96. Due to oxidation within the inner cylinder 30, the concentration of combustible gases in the exhaust gas flowing out from the outlet mechanism 34 is sufficiently reduced to prevent ignition, thus improving safety. Furthermore, the prevention of oxidation of carbides in the oxygen supply device 5 and the inner cylinder 30, as well as the oxidation of flammable gases, will be described later along with the explanation of the oxygen supply device 5.

[0035] [Oxygen supply device] As described above, the oxygen supply device 5 is a device that supplies low-concentration oxygen to the inner cylinder 30 of the carbonization furnace 3. As shown in Figure 2, the oxygen supply device 5 has a supply unit body 50 which is a source of low-oxygen gas with a lower oxygen concentration than air, an oxygen nozzle 57 which is installed inside the inner cylinder 30 and supplies the low-oxygen gas supplied from the supply unit body 50 into the inner cylinder 30, and a low-oxygen gas supply pipe 53 which supplies the low-oxygen gas from the supply unit body 50 to the oxygen nozzle 57. In order to avoid carbonization of the carbonized material, the oxygen supply device 5 supplies less than an equivalent amount of oxygen to the inner cylinder 30 by supplying low-oxygen gas to oxidize the combustible gas generated during the carbonization of sludge inside the inner cylinder 30.

[0036] Since the carbonization furnace 3 performs a plug-flow type carbonization process, the amount of combustible gas (mass or molar amount) generated in the inner cylinder 30 per unit time is proportional to the amount of sludge (mass) supplied to the inner cylinder 30 per unit time. Therefore, in this embodiment, the total amount of combustible gas that generates carbonized material per unit mass is acquired in advance for several different temperatures (several carbonization temperatures) and stored as characteristic information (e.g., characteristic curves and calibration curves) in the memory device of the control unit C. The control unit C, described later, supplies low-oxygen gas to the oxygen supply device 5 so that the amount of oxygen (mass or molar amount) supplied per unit time by the low-oxygen gas is less than the equivalent amount (e.g., 99% of the equivalent amount) required to oxidize the combustible gas generated during the carbonization of sludge in the inner cylinder 30, based on this characteristic information, the amount of sludge supplied to the inner cylinder 30 per unit time, and the carbonization temperature of the sludge (e.g., the temperature of the hot air supplied from the hot air generator 35 or the temperature of the exhaust gas measured by the thermometer T).

[0037] The supply unit body 50 includes a nitrogen gas supply source 51 such as a nitrogen cylinder, and an oxygen gas supply source 52 that supplies oxygen-containing gas (oxygen gas or air, hereinafter simply referred to as high-oxygen gas) such as an oxygen cylinder or air compressor. The low-oxygen gas supply pipe 53 is connected to the nitrogen gas supply source 51 on its upstream side and to the oxygen nozzle 57 on its downstream side. The low-oxygen gas supply pipe 53 is equipped with a nitrogen amount control valve 55 that adjusts the flow rate of nitrogen gas supplied from the nitrogen gas supply source 51. One end of the oxygen gas supply pipe 54 is connected to the oxygen gas supply source 52, and the other end of the oxygen gas supply pipe 54 is connected between the nitrogen amount control valve 55 and the oxygen nozzle 57 in the low-oxygen gas supply pipe 53. The oxygen gas supply pipe 54 is equipped with an oxygen amount control valve 56 that adjusts the flow rate of high-oxygen gas supplied from the oxygen gas supply source 52. The nitrogen amount control valve 55 and the oxygen amount control valve 56 are automatic valves equipped with a drive mechanism such as an actuator.

[0038] The supply unit 50 adjusts the opening of the nitrogen amount control valve 55 and the oxygen amount control valve 56 based on the command from the control unit C to prepare low-oxygen gas with a predetermined oxygen concentration and flow rate, and supplies the low-oxygen gas to the oxygen nozzle 57. The flow rate of the low-oxygen gas is the total flow rate of nitrogen gas and high-oxygen gas. The oxygen concentration of the low-oxygen gas is the ratio of the oxygen gas flow rate in the high-oxygen gas to the total flow rate. The oxygen concentration of the low-oxygen gas should be between 1.0 volume% and less than 5.0 volume%.

[0039] The oxygen nozzle 57 is, for example, a linear, tubular member that supplies low-oxygen gas to the internal atmosphere of the inner cylinder 30. The oxygen nozzle 57 is positioned inside the inner cylinder 30 along the axial direction of the inner cylinder 30, with the side connected to the low-oxygen gas supply pipe 53 supported by the inlet mechanism 33. The oxygen nozzle 57 is positioned on the upper side inside the inner cylinder 30, spaced apart from the inner wall of the inner cylinder 30 and the sludge and carbonized particle layer inside the inner cylinder 30.

[0040] The oxygen nozzle 57 is sealed at its terminal end, and four (or more) openings 58 are formed on the side of the oxygen nozzle 57 tube to allow low-oxygen gas to flow into the inner cylinder 30. The openings 58 are located from the center of the carbonization furnace 3 downstream, where the furnace gas temperature exceeds 300 degrees Celsius. When the temperature of combustible gas exceeds 300 degrees Celsius, it reacts with oxygen instantaneously. By providing multiple openings 58 along the axial direction of the inner cylinder 30 from the center of the carbonization furnace 3 downstream, low-oxygen gas is supplied into the inner cylinder 30 to promote the oxidation of the combustible gas, while the oxygen supplied into the inner cylinder 30 is instantly consumed and does not remain, thus suppressing the oxidation of the carbonized material. Furthermore, it is possible to prevent the carbonization furnace 3 from being maintained in an explosive gas atmosphere where combustible gas and oxygen gas are mixed. In addition, each of the openings 58 is formed facing upward. By forming the opening 58 facing upwards, it is possible to prevent low-oxygen gas from being blown onto the char, thereby suppressing the oxidation of the char, while allowing only the combustible gas to be oxidized inside the carbonization furnace.

[0041] [Control Unit] As shown in Figure 1, the control unit C is the central control mechanism for the carbonization system A, and in this embodiment, it includes an oxygen supply control mechanism that controls the operation of the oxygen supply device 5. The control unit C controls the operation of the carbonization system A according to operation instructions from the user or others, based on operation plans, operational values, characteristic information, and input devices (not shown) that are stored in advance in a memory device.

[0042] [Control at the start of carbonization] As shown in Figure 2, when the control unit C starts carbonizing sludge in the carbonization furnace 3, it starts the operation of the exhaust device 96 (see Figure 1) (exhausting exhaust gas from the carbonization furnace 3), the heating of the carbonization furnace 3, the supply of inert gas by the purge mechanism 4, and the supply of nitrogen gas only from the oxygen supply device 5, and then opens the slide valve 21 and starts supply by the rotary valve 20. The start timing of the operation of the exhaust device 96 (exhausting exhaust gas from the carbonization furnace 3), the heating of the carbonization furnace 3, and the supply of inert gas by the purge mechanism 4 should be simultaneous or in this order.

[0043] In this embodiment, the control unit C starts supplying inert gas by the purge mechanism 4 and nitrogen gas only by the oxygen supply device 5, and then starts supplying by the rotary valve 20. After a predetermined time has elapsed (for example, 5 minutes), the control unit C performs delay control to open the slide valve 21. This delay control reduces the oxygen concentration inside the inner cylinder 30 in advance, suppressing the oxidation of carbonized material. Furthermore, it allows the residual moisture inside the rotary valve 20 to be sufficiently dried before the sludge is supplied to the rotary valve 20, preventing the growth of deposits after the start of supply.

[0044] [Control during carbonization] When carbonization begins to progress in the carbonization furnace 3 (for example, when the exhaust gas temperature exceeds 300 degrees Celsius), the control unit C starts supplying low-oxygen gas (oxygen) from the oxygen supply device 5.

[0045] In this embodiment, the control unit C determines the target flow rate (hereinafter referred to as the specified value) of the oxygen flow rate valve 56 so that the mass flow rate (molar amount) of oxygen supplied per unit time by the low-oxygen gas is 99% of the equivalent amount needed to oxidize the combustible gas generated during the carbonization of sludge in the inner cylinder 30, based on characteristic information, the amount of sludge supplied to the inner cylinder 30 per unit time, and the temperature of the exhaust gas measured by the thermometer T. Furthermore, it determines a corrected value by applying a predetermined correction to the specified value, sets the oxygen flow rate valve 56 to the corrected value, and controls the oxygen supply amount (an example of the amount of oxygen supplied) by supplying low-oxygen gas to the oxygen supply device 5 (an example of a supply control step). This control flow will be described later.

[0046] As shown in Figure 1, during carbonization in the carbonization furnace 3, the control unit C controls the internal pressure of the carbonization furnace 3 to a gentle negative pressure (slight negative pressure) of approximately -150 Pa or more and -50 Pa or less by adjusting the output of the exhaust device 96, etc. By controlling the internal pressure of the carbonization furnace 3 to such a slight negative pressure, the induction of uncontrolled air (oxygen) into the carbonization furnace 3 can be avoided.

[0047] The control unit C controls the operation of the exhaust system 96, the heating of the carbonization furnace 3, the supply of inert gas by the purge mechanism 4, the supply of low-oxygen gas (oxygen) by the oxygen supply device 5, and the supply of sludge by the supply mechanism F to remain constant in principle during the carbonization of sludge in the carbonization furnace 3. However, if the oxygen concentration in the exhaust gas measured by the gas property measuring device 6 exceeds a predetermined concentration (for example, 1 volume%), the control unit C controls the amount of oxygen supplied from the oxygen supply device 5 to prevent the oxygen concentration in the exhaust gas from exceeding that predetermined concentration. In this embodiment, the oxygen concentration in the exhaust gas is equal to the oxygen concentration in the furnace atmosphere of the carbonization furnace 3. The control flow of the oxygen supply amount executed by the control unit C will be described later.

[0048] [Control at the end of carbonization] As shown in Figures 1 and 2, when the carbonization of sludge in the carbonization furnace 3 is terminated or stopped by the user's instructions, the control unit C first closes the slide valve 21 and stops the supply of sludge from the supply mechanism F to the carbonization furnace 3. Even after closing the slide valve 21, the control unit C continues to supply inert gas by the purge mechanism 4 for a predetermined time, and then terminates the supply of inert gas by the purge mechanism 4 and low-oxygen gas by the oxygen supply device 5.

[0049] By continuing to supply inert gas by the purge mechanism 4 even after closing the slide valve 21, residual moisture inside the rotary valve 20 after the completion of carbonization can be thoroughly dried. This prevents the growth of deposits when carbonization is restarted.

[0050] Even after closing the slide valve 21 and stopping the supply of sludge from the supply mechanism F to the carbonization furnace 3, the supply of low-oxygen gas (oxygen) by the oxygen supply device 5 is continued, which burns the combustible gas generated from the carbonized material remaining in the carbonization furnace 3 and prevents the combustible gas from being released to the outside (atmosphere).

[0051] The concept of "predetermined time" after closing the slide valve 21 includes cases where it is a fixed time predetermined (for example, 10 minutes), a time when the internal gas temperature of the carbonization furnace 3 fluctuates until it drops below a predetermined temperature, or a time obtained by multiplying the average residence time of the carbonization furnace 3 or the time required to discharge the entire amount from the carbonization furnace 3 by a predetermined coefficient. For example, this predetermined time can be set to twice the time required to discharge the entire amount from the carbonization furnace 3.

[0052] In this embodiment, when the control unit C stops (ends) the carbonization of sludge in the carbonization furnace 3, it first closes the slide valve 21. Even after closing the slide valve 21, the control unit C continues the operation of the rotary valve 20, the supply of inert gas by the purge mechanism 4, the operation of the carbonization furnace 3, and the supply of low-oxygen gas by the oxygen supply device 5. After the sludge inside the carbonization furnace 3 has been sufficiently carbonized and most of the carbonized material has been transferred to the cooler 91 (see Figure 1), the control unit C stops heating the carbonization furnace 3 and stops the supply of low-oxygen gas by the oxygen supply device 5, and starts supplying only nitrogen gas. Subsequently, when the internal gas temperature of the carbonization furnace 3 falls below a predetermined temperature (for example, below 300 degrees Celsius), the control unit C stops (ends) the operation of the rotary valve 20, the supply of inert gas by the purge mechanism 4, the supply of nitrogen gas by the oxygen supply device 5, and the operation of the exhaust device 96. By maintaining the operation of the rotary valve 20 until the supply of inert gas by the purge mechanism 4 is stopped, it is possible to prevent condensable components from condensing and adhering to a part of the rotary valve 20.

[0053] [Explanation of the oxygen supply control flow] Figure 3 shows the control flow of the oxygen supply amount executed by the control unit C. In the following, refer to Figure 3 for the control flow and Figure 2 for other details. This control is executed during carbonization and at the end of carbonization by closing the slide valve 21, and continues until a predetermined time has elapsed and the supply of low-oxygen gas by the oxygen supply device 5 is stopped.

[0054] When carbonization begins in the carbonization furnace 3, the control unit C determines a specified value X based on characteristic information, the amount of sludge supplied to the inner cylinder 30 per unit time, and the temperature of the exhaust gas measured by the thermometer T (#1), and then determines a corrected value Y by subtracting a correction coefficient Z from the specified value X (#2). In this embodiment, the initial value of the correction coefficient Z is zero, but a predetermined value is set as needed in step #9, which will be described later.

[0055] Once the control unit C determines the correction value Y (#2), it sets the target flow rate of the oxygen amount control valve 56 to the correction value Y (#3) and measures the oxygen concentration of the exhaust gas with the gas physical property measuring device 6 (#4). If the oxygen concentration of the exhaust gas is less than a predetermined concentration (less than 1.0 volume%) in this embodiment (#5, Yes), the control unit C determines whether the oxygen concentration of the exhaust gas is above a lower limit (for example, any value between 0.1 and 0.3 volume%) (#6). If the oxygen concentration of the exhaust gas is above the lower limit (#6, Yes), it maintains the target flow rate of the oxygen amount control valve 56 (#7) and determines whether carbonization has been completed (#8).

[0056] In this embodiment, as described later, when the internal gas temperature of the carbonization furnace 3 falls below a predetermined temperature (for example, below 300 degrees Celsius), it is determined that carbonization is complete (#8, Yes), and the oxygen quantity control valve 56 is closed. When the internal gas temperature of the carbonization furnace 3 rises above a predetermined temperature (for example, above 300 degrees Celsius), it is determined that carbonization is in progress (#8, No), and the process returns to step #4, where the measurement of oxygen concentration by the gas property measuring device 6 continues (#4), and the process is repeated.

[0057] The oxygen concentration of the exhaust gas is measured by the gas property measuring device 6 (#4). If the oxygen concentration of the exhaust gas is not below a predetermined concentration (#5, No), the correction coefficient Z is updated by adding a predetermined amount ΔZ (positive value) (#9, Example of a feedback control step), and the process returns to step #2. The oxygen concentration of the exhaust gas is measured by the gas property measuring device 6 (#4). If the oxygen concentration of the exhaust gas is not above the lower limit (#6, No), the correction coefficient Z is updated by adding a predetermined amount ΔZ (negative value) (#9, Example of a feedback control step), and the process returns to step #2. The predetermined amount ΔZ can be, for example, a fixed flow rate value, a value corresponding to one increment of the oxygen amount control valve 56, or a predetermined amount corresponding to the specified value X (for example, 1 / 100th of the specified value X). In step #2, the correction value Y is determined based on the specified value X and the updated correction coefficient Z (#2), and this process is repeated. Alternatively, step #6 may be omitted, and if the oxygen concentration in the exhaust gas is below a predetermined concentration (#5, Yes), the target flow rate of the oxygen control valve 56 may be maintained (#7).

[0058] As described above, a pyrolysis method is provided that improves the thermal efficiency of a carbonization furnace by burning a combustible gas inside the carbonization furnace.

[0059] [Another embodiment] (1) In the above embodiment, the case in which the carbonization furnace 3 is a rotary kiln was described as an example, but the carbonization furnace 3 can be any device capable of heating the sludge to the extent that it is carbonized. For example, the carbonization furnace 3 may be a heating device that heats the sludge from the inside of the container by equipping the container with an electric heating device or a screw or stirring paddle heated by a heat transfer medium in the container that holds the sludge, or a fluidized bed heating device that holds the sludge in layers in a tank-shaped container and heats the layers by blowing hot air from below. In these cases, an oxygen nozzle 57 is placed inside the container that holds the sludge.

[0060] (2) In the above embodiment, the feeder 2 had a slide valve 21, but the slide valve 21 can be omitted.

[0061] (3) In the above embodiment, an example was given in which low-oxygen gas is supplied into the inner cylinder 30 by a single oxygen nozzle 57 having a plurality of openings 58. However, the oxygen nozzle 57 is not limited to one, and low-oxygen gas may be supplied into the inner cylinder 30 by a plurality of oxygen nozzles 57. Also, the oxygen nozzle 57 is not limited to having a plurality of openings 58, but may have only a single opening 58.

[0062] (4) In the above embodiment, nitrogen was given as an example of an inert gas. However, instead of nitrogen, other gases that do not produce oxidation reactions, such as argon or carbon dioxide, or low-oxygen concentration gases with a very low risk of oxidation reactions may be used as the inert gas (for example, exhaust gas after secondary combustion in the secondary combustion furnace 94, or exhaust gas from other industrial facilities such as incinerators or power plants).

[0063] (5) In the above embodiment, the carbonization system A was described as comprising an oxygen supply device 5 that supplies oxygen to the carbonization furnace 3 and a supply mechanism F that supplies sludge to the carbonization furnace 3, as exhaust gas treatment equipment for the carbonization furnace 3. The carbonization system A is not limited to this case, and in addition to the oxygen supply device 5, or in place of the oxygen supply device 5, a second supply mechanism S may be provided as another oxygen supply device to supply another type of waste (for example, food waste; hereinafter simply referred to as food waste) that has a higher oxygen content than organic waste to the carbonization furnace 3.

[0064] Figure 4 shows a case where a second supply mechanism S is provided instead of the oxygen supply device 5. The second supply mechanism S can have a similar configuration to supply mechanism F, for example, and is supplied with food waste that has been dried to a predetermined moisture content in a separate upstream process (not shown) and then crushed, cut, or granulated into granules of several millimeters, for example. The second supply mechanism S supplies food waste to the carbonization furnace 3 in addition to the sludge supplied by supply mechanism F. This food waste is carbonized in the carbonization furnace 3 and also acts as an oxidizing agent for oxidizing the exhaust gas containing combustible gases. The control unit C controls the amount of waste supplied from the second supply mechanism S (another example of the amount of oxygen supplied) (another example of the supply control step) so that the amount of oxygen supplied to the carbonization furnace 3 by the waste is less than the equivalent amount needed to oxidize the combustible gases generated during the carbonization of sludge in the inner cylinder 30. As a result, the carbonization system A recycles the food waste as carbonized material along with the sludge and utilizes the oxygen contained in the food waste to oxidize the exhaust gas.

[0065] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise. Moreover, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention. [Industrial applicability]

[0066] This invention can be applied to a thermal decomposition method. [Explanation of Symbols]

[0067] 3: Carbonization furnace 5: Oxygen supply device 6: Gas property measurement device 30: Inner cylinder 31: Outer cylinder A: Carbonization system C: Control section F: Feeding mechanism S:Second supply mechanism

Claims

1. The carbonization step involves carbonizing organic waste in a carbonization furnace, An oxygen supply step of supplying oxygen to the carbonization furnace, The carbonization step includes oxidizing the combustible gas generated from the organic waste in the carbonization furnace, The oxygen supply step includes a supply control step that controls the amount of oxygen supplied so that it is less than the equivalent amount needed to oxidize the flammable gas. A pyrolysis method in which, in the supply control step, oxygen is supplied based on the total amount of combustible gas generated from the organic waste per unit mass, which has been previously obtained for each of several different temperatures, the amount of the organic waste supplied to the carbonization furnace per unit time, and the carbonization temperature of the organic waste.

2. The pyrolysis method according to claim 1, wherein the supply control step includes a feedback control step that controls the amount of supplied oxygen so that the oxygen concentration is less than 1.0 volume%.

3. The carbonization step involves carbonizing organic waste in a carbonization furnace, An oxygen supply step of supplying oxygen to the carbonization furnace, The carbonization step includes oxidizing the combustible gas generated from the organic waste in the carbonization furnace, The pyrolysis method includes a feedback control step that controls the amount of oxygen supplied so that the oxygen concentration is less than 1.0 volume percent.

4. The pyrolysis method according to claim 2 or 3, further comprising an oxygen concentration measurement step of measuring the oxygen concentration of the internal atmosphere of the carbonization furnace.

5. The pyrolysis method according to any one of claims 1 to 3, wherein the oxygen supplied in the oxygen supply step is supplied as an oxygen-containing gas with an oxygen concentration of less than 5.0 volume%.

Images