JP3799846B2 - Method and apparatus for recovering heat from waste - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for recovering heat from waste.
[0002]
[Prior art]
Japanese Laid-Open Patent Publication No. 7-35322 proposes a method in which municipal waste or industrial waste (hereinafter referred to as “waste”) is partially oxidized, gasified, and burned. An outline of the structure of a typical example is shown in FIG. 6 of the accompanying drawings.
[0003]
In FIG. 6, waste is gasified in a partial combustion fluidized bed furnace 51 in a reducing atmosphere with a fluidized bed temperature of 450 to 650 ° C. and an air ratio of about 0.15 to 0.5. The dust is introduced into the secondary combustion furnace 53 through a dust collector 52 such as the above. The produced gas is mixed with secondary air in the secondary combustion furnace 53 and completely burned at a high temperature of 800 to 1000 ° C. At this time, desalting agent is supplied to suppress generation of HCl gas, and heat recovery is performed. A dust recovery line 54 is installed below the dust collector 52. Part of the desalting agent and all or part of the dust are cooled by the cooler 55 and then returned to the partial oxidation fluidized bed furnace. It is supposed to be.
[0004]
[Problems to be solved by the invention]
In such a combustion method, when the waste is burned after being partially oxidized, a desalting agent must be used in the secondary combustion furnace. Therefore, the dust concentration becomes high, which is disadvantageous in terms of dust removal. If the dust concentration in the secondary combustion furnace is not controlled below a certain value, the corrosion of the boiler tube due to the salt in the dust becomes a problem in the boiler arranged in the subsequent stage for heat recovery.
[0005]
The present invention has been made to solve such problems, and a method and apparatus for recovering heat from waste that can be partially oxidized and efficiently recovered without causing the above problems. The issue is to provide.
[0006]
[Means for Solving the Problems]
The first means to solve the above problem is to reduce the waste in a partial oxidation furnace with a combustion reaction by controlling the furnace temperature to 400 to 800 ° C. and the air ratio to 0.15 to 0.9. incomplete combustion, or by partial oxidation to produce a combustible gas in an atmosphere, the combustible gas is introduced into the ceramic filter at 250 to 450 ° C. and dedusted dust concentration 0.1 g / Nm ³ or less, dust has been the A method for recovering heat from waste, characterized in that natural gas is burned at a high temperature in a combustion furnace, and heat is recovered from the gas burned in the combustion furnace or in a boiler disposed downstream of the combustion furnace. It is.
[0007]
In the partial oxidation furnace, partial oxidation of waste is performed, and a combustible gas having a relatively low temperature of 250 to 450 ° C. is sent to the inlet of the dust removing device. Here, the reason why the temperature at the dust removing device inlet is set in the above range is that there is a problem such as tar adhesion below 250 ° C, and there is a possibility of dioxins formation and clogging due to salt above 450 ° C. Because there is. In this case the air ratio in the partial oxidation furnace to adjust the air ratio to be 0.15 to 0.9. The reason is that if the air ratio is less than 0.15 , problems such as tar adhesion occur as a strong reducing gas, and if it is above 0.9 , oxidation of the combustible gas is promoted before being introduced into the secondary combustion furnace. Because. This keeps the oxygen concentration at the furnace outlet low and reduces the risk of explosion due to combustible components and oxygen. Since the temperature at the inlet of the dust removing device is relatively low in this way, dust can be removed without excessive cooling through equipment such as a temperature reducing tower. In the dust remover, the combustible gas is burned in the combustion furnace after the dust concentration is set to 0.1 g / Nm ³ or less, and the temperature can be efficiently increased. The dust removal device at this time may use a bag filter, a ceramic filter, a high-temperature electric dust collector, an inertial dust collector, a high-performance cyclone, a centrifugal dust collector, or the like depending on the temperature of the combustible gas. In the above boiler disposed in the combustion furnace or downstream of the combustion furnace, heat can be efficiently recovered from the combustion gas, and a high-temperature and high-pressure boiler becomes possible.
[0008]
In the case of the method of the present invention, the dust concentration is removed so that the dust concentration is 0.1 g / Nm ³ or less by the dust removing device, so that the amount of salt in the dust is reduced, and there is a possibility of corrosion of the boiler tube or the like in the subsequent stage. Decrease drastically.
[0009]
Furthermore, harmful gas emissions can be suppressed. Since the combustible gas after being partially oxidized in the partial oxidation furnace is mixed with an oxidant in the combustion furnace and burned at a high temperature, discharge of unburned components such as CO is almost completely suppressed. In addition, since the combustible gas is dedusted and then burned at a high temperature, the concentration of the aromatic organic compound resulting from soot is lowered, and as a result, the concentration of dioxins that are incomplete combustion products is also reduced.
[0010]
The second means for solving the above-mentioned problem is a waste processing method in which the deposit on the ceramic filter is periodically removed with a gas having an oxygen concentration of 5% or less in the first means . Thereby, dust can be efficiently removed and emission of harmful gas is further suppressed. Here, the oxygen concentration is set to 5% or less in order to suppress the oxidation of the combustible gas with oxygen and reduce the risk of unnecessary explosion and combustion. This gas having an oxygen concentration of 5% or less can be obtained by exhaust gas recirculation, pressure swing adsorption or membrane separation.
[0011]
A third means for solving the above-mentioned problem is a waste processing method in which, in the first means, deposits on the ceramic filter are periodically removed with nitrogen gas. By using nitrogen to remove deposits, the combustible gas does not oxidize in the dust collector. In addition, unnecessary explosions and combustion caused by this means are eliminated.
[0012]
A fourth means for solving the above problem is a waste treatment method according to any one of the first to third means described above, wherein an ignition source is disposed in a combustion furnace and combustible gas is continuously burned. Combustible gas is fed into the combustion furnace to burn after being dust, by placing the ignition source here, danger of explosion by mixing again combustible gas and air and misfire can be avoided.
[0014]
The fifth means for solving the above-mentioned problem is that the in- furnace temperature is controlled to 400 to 800 ° C. and the air ratio is controlled to 0.15 to 0.9 to generate inflammable gas by incompletely burning or partially oxidizing the waste. A partial oxidation furnace, a ceramic filter that is installed downstream and removes the dust concentration in the combustible gas at 250 to 450 ° C. to 0.1 g / Nm ³ or less , and a combustion furnace installed downstream An apparatus for recovering heat from waste, comprising a boiler disposed in the combustion furnace or downstream of the combustion furnace.
[0015]
A sixth means for solving the above problem is the waste processing apparatus according to the fifth means, wherein an ignition source is disposed in the combustion furnace.
[0016]
In the partial oxidation furnace, the waste is partially oxidized, and a combustible gas having a relatively low temperature of 250 to 450 ° C. is generated at the dust removing device inlet. In this case the air ratio in the partial oxidation furnace to adjust the air ratio so that the 0-from 15 to 0.9. Thereby, combustible gas with low oxygen concentration and few dangers, such as an explosion, is produced | generated. Moreover, since this combustible gas is comparatively low temperature, dust is removed without excessive cooling by facilities, such as a temperature reduction tower. After the dust concentration is reduced to 0.1 g / Nm ³ or less in the downstream dust removal system connected by a duct from the furnace outlet of the partial oxidation furnace, the combustible gas is burned in the downstream combustion furnace and efficiently heated. Is done. The dust removal device at this time may use a bag filter, a ceramic filter, a high-temperature electric dust collector, an inertial dust collector, a high-performance cyclone, a centrifugal dust collector, or the like depending on the temperature of the combustible gas. In the above boiler disposed in the combustion furnace or downstream of the combustion furnace, heat can be efficiently recovered from the combustion gas, and a high-temperature and high-pressure boiler becomes possible. In the case of this apparatus, since dust is removed so that the dust concentration is 0.1 g / Nm ³ or less, the amount of salt in the dust is reduced, and the corrosion of the downstream boiler tube and the like is extremely reduced.
[0017]
Furthermore, harmful gas emissions can be suppressed. Since the combustible gas after being partially oxidized in the partial oxidation furnace is mixed with an oxidant in the combustion furnace and burned at a high temperature, discharge of unburned components such as CO is almost completely suppressed. In addition, since the combustible gas is dedusted and then burned at a high temperature, the concentration of the aromatic organic compound resulting from soot is lowered, and as a result, the concentration of dioxins that are incomplete combustion products is also reduced.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3 of the accompanying drawings.
[0019]
FIG. 1 is a diagram showing a schematic configuration of an embodiment of the present invention. In the figure, reference numeral 1 denotes a partial oxidation furnace, and the partial oxidation furnace 1 is supplied with air for oxidation or air-based gas whose oxygen concentration is controlled by steam or exhaust gas. Waste is thrown into the furnace and ignited and partially oxidized to generate combustible gas. The partial oxidation furnace 1 is sequentially connected with a dust removing device 2 for removing dust from the combustible gas, a combustion furnace 3 for burning the combustible gas, and a boiler 4 for recovering the heat of the burned gas.
[0020]
In the partial oxidation furnace 1, the temperature in the furnace may be such that the waste can self-combust and can be partially oxidized, and is preferably 400 to 800 ° C. The air ratio in the partial oxidation is controlled, the air ratio at this time is Ru is approximately about 0.15 to 0.9. Thereafter, the temperature of the combustible gas is controlled by the residence time in the partial oxidation furnace 1, and the combustible gas is sent to the dust removing device 2 at 250 to 450 ° C. The reason for setting this temperature range is that deposits such as tar are problematic at 250 ° C. or lower, and there are problems of dioxins formation and eye clogging due to salts such as NaCl and KCl above 450 ° C.
[0021]
Next, the combustible gas is brought to the dust removing device 2, and the dust removing device 2 removes dust to a concentration of 0.1 g / Nm ³ or less. If dust is removed to this concentration, the amount of salt in the dust is reduced, so that corrosion of the boiler tube and the like in the subsequent stage is reduced. FIG. 2 shows the relationship between the dust concentration after dust removal and the service life of the wake boiler tube. From this figure, it can be seen that if the dust concentration after dust removal is 0.1 g / Nm ³ or less, the corrosion of the downstream boiler tube can be suppressed to a practical level.
[0022]
Although it is desirable to use a candle-type ceramic filter as shown in FIG. 3 for the dust removing device 2, it is also possible to use a filter cloth or a honeycomb-shaped ceramic filter having an opening of 10 mm or less. It is desirable to perform the removal with a gas having an oxygen concentration of 5% or less, or nitrogen in order to suppress oxidation of the combustible gas and reduce the risk of unnecessary explosion and combustion. Considering the effect of peeling off the deposits, the conditions for the removal method are a gas pressure of 1 kg / cm ² or more, a removal interval of several seconds to several tens of minutes, and a removal time of about 0.02 seconds to several tens of seconds. It is desirable.
[0023]
The combustible gas is removed by the dust removing device 2 and then introduced into the combustion furnace 3 where the temperature rises to about 1000 ° C. Since complete combustion is performed here, discharge of unburned gas and the like is almost completely suppressed. In addition, since the dust is previously removed from the combustible gas, the concentration of the aromatic organic compound resulting from soot is lowered, and as a result, the concentration of the dioxin substance that is an incomplete combustion product is also reduced.
[0024]
In the present embodiment, as a preferable example, a boiler, for example, a water pipe of a high-temperature and high-pressure boiler 4 having a temperature of 300 ° C. or higher and 20 at or higher is installed at the subsequent stage of the combustion furnace 3, and heat can be efficiently recovered from the combustion gas. . High temperature air can be recovered as required. Since dust removal is performed in advance, corrosion of the boiler tube due to dust can be suppressed. When recovering heat from a high temperature field with an exhaust gas temperature of 600 ° C. or higher where the corrosion effect of hydrogen chloride gas increases, a boiler tube made of a ceramic material having corrosion resistance may be used to extend the life of the boiler tube. . The exhaust gas after heat recovery is discharged from the chimney through a downstream exhaust gas treatment facility (not shown).
[0025]
【Example】
An embodiment of the present invention will be described with reference to FIG. In this embodiment, a fluidized bed furnace 1 is employed as the partial oxidation furnace of the apparatus shown in FIG. Others are the same as the apparatus of FIG. 1, and in FIG. 4, the same code | symbol is attached | subjected to FIG. 1 and a common part.
[0026]
In the apparatus shown in FIG. 4, the fluidized air temperature is set to 20 to 650 ° C. and the sand layer temperature is set to 400 to 600 ° C. in the fluidized bed furnace 1, and municipal waste as waste is supplied to the fluidized bed furnace 1 at 1 t / h. Was partially oxidized by operating between 0.2 and 0.8 to produce a combustible gas. The combustible gas was supplied to the dust removing device 2 at 250 to 450 ° C., and dust was removed by a candle type ceramic filter. The material of the candle type ceramic filter is SiO ₂ , Al ₂ O ₃ , SiC, cordierite, a composite of the above materials, or a ceramic fiber type of an inorganic material similar thereto, or a porous body type. Nitrogen gas was used for the drop-off, and the drop-off pressure was 4 kg / cm ² , the drop-off interval was 5 to 50 minutes, and the drop-off time was in the range of 0.1 to 20 seconds. Accordingly, those dust concentration before flowing into the filtration apparatus 2 was 5 to 20 g / Nm ³ is dust to 0.1 g / Nm ³ or less. The removed dust and the like were detoxified in a melting furnace and an incinerator after collection. The combustible gas after such dust removal was burned in the combustion furnace 3 and the temperature was raised to 900 to 1000 ° C. At this time, it was possible to recover heat by using steam at 350 to 540 ° C. and 50 to 100 at the subsequent boiler 4. Although stainless steel, Inconel and other alloy steels were used as boiler tubes, no significant corrosion was observed, and depending on the material, corrosion resistance that could be used for multiple years was confirmed. Moreover, when high temperature air was also collected, it was found that high temperature air at 350 to 700 ° C. could be collected.
[0027]
Moreover, the applicability in the grate furnace shown in FIG. 5 was also confirmed. The apparatus shown in FIG. 5 employs a grate furnace 1 as a partial oxidation furnace. Others are the same as FIG. 1 apparatus. In this grate furnace 1, the oxidizing air temperature is set to 20 to 250 ° C., the grate upper temperature is set to 500 to 800 ° C., and municipal waste as waste is supplied into the furnace, and the air ratio is 0.3 to 0.9. Partial oxidation was performed by operating in between. The combustible gas was supplied to the dust removing device 2 at 250 to 450 ° C., and dust was removed using a candle type ceramic filter and a honeycomb type ceramic filter. The material of the ceramic filter is SiO ₂ , Al ₂ O ₃ , SiC, cordierite, a composite of the above materials, or a ceramic fiber type of an inorganic material similar thereto, or a porous body type. Nitrogen gas was used for the removal, and the removal pressure was 3 kg / cm ² , the removal interval was 10 to 20 minutes, and the removal time was in the range of 0.05 to 15 seconds. Thus, what is dust concentration before entering the dust collector 2 was 1 to 5 g / Nm ³ is dust to 0.1 g / Nm ³ or less. The removed dust and the like were detoxified in a melting furnace and an incinerator after collection. The combustible gas after dust removal was burned in the combustion furnace 3 and the temperature was raised to 900 to 1100 ° C. In the combustion furnace 3, a combustible gas was continuously burned with a constant ignition source using a pilot burner (not shown) to avoid dangers such as explosion. This burner uses natural gas or kerosene as a fuel, and a burner having an output of several tens of thousands kcal / h to several hundred thousand kcal / h is disposed. At this time, heat recovery could be performed using steam at 540 ° C. and 100 ata in the boiler 4 at the subsequent stage. Although stainless steel, Inconel and other alloy steels were used as boiler tubes, no significant corrosion was observed, confirming stable operation for over a year.
[0028]
【The invention's effect】
As described above, in the present invention, since the partially oxidized gas is dedusted at a relatively low temperature and then burned in a combustion furnace, a high temperature is obtained, so that the treatment of gasified waste is efficiently performed. At the same time, it can efficiently recover heat by installing a high-temperature and high-pressure boiler. Moreover, emission of harmful gases such as dioxin and furan can be suppressed. Furthermore, the entire plant can be simplified and the required installation area can be reduced as compared with the prior art.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing the relationship between the dust concentration and the useful life of a boiler tube.
3 is a schematic view of a candle-type ceramic filter that can be used in the dust removing device of FIG. 1; FIG.
FIG. 4 is a schematic configuration diagram of an apparatus according to an embodiment of the present invention.
FIG. 5 is a schematic configuration diagram of an apparatus showing a modification of the apparatus of FIG. 4;
FIG. 6 is a schematic configuration diagram of a conventional waste treatment apparatus.
[Explanation of symbols]
1 Partial oxidation furnace 2 Dust removal equipment 3 Combustion chamber 4 Boiler

Claims (6)

Combustible waste by incomplete combustion or partial oxidation in a reducing atmosphere by controlling the furnace temperature to 400-800 ° C and the air ratio to 0.15-0.9 in a partial oxidation furnace with combustion reaction A gas is generated, the combustible gas is introduced into a ceramic filter at 250 to 450 ° C., dust is removed to a concentration of 0.1 g / Nm ³ or less , and the combusted gas removed is burned at a high temperature in a combustion furnace, A method for recovering heat from waste, comprising recovering heat from a gas combusted in a boiler disposed in the combustion furnace or downstream of the combustion furnace. The method for recovering heat from waste according to claim 1, wherein deposits on the ceramic filter are periodically removed with a gas having an oxygen concentration of 5% or less. The method for recovering heat from waste according to claim 1, wherein deposits on the ceramic filter are periodically removed with nitrogen gas. The method for recovering heat from waste according to any one of claims 1 to 3, wherein an ignition source is provided in the combustion furnace, and the combustible gas is continuously burned. A partial oxidation furnace that generates a combustible gas by incompletely burning or partially oxidizing waste by controlling the furnace temperature to 400 to 800 ° C. and the air ratio to 0.15 to 0.9, and installed downstream thereof. A ceramic filter that removes dust in the combustible gas at a temperature of 250 to 450 ° C. to a concentration of 0.1 g / Nm ³ or less , a combustion furnace installed downstream thereof, and in the combustion furnace or downstream of the combustion furnace An apparatus for recovering heat from waste, comprising a boiler disposed. The apparatus for recovering heat from waste according to claim 5 , wherein the combustion furnace is provided with an ignition source.

Images