JP4420155B2 - 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. 9-159132 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, the combustion exhaust gas generated by burning garbage in the combustion furnace is cooled to 450 to 650 ° C. by the heated water 20 from the economizer 16 in the waste heat boiler 12 and removed by the filter 13. . Part or all of the combustion exhaust gas that has exited the filter 13 is supplied to the heating furnace 14, and is heated in the heating furnace 14 by reheating using the auxiliary fuel 21, and the steam superheater 15 is further removed from the waste heat boiler 12. Overheated to about 500 ° C. with saturated steam 22 from. Further, the exhaust gas from the combustion exhaust gas is recovered by the economizer 16 and the air afterheater 17. Thereafter, the combustion exhaust gas is exhausted from the chimney 19 through the induction fan 18.
[0004]
[Problems to be solved by the invention]
When combustible materials are treated in such a combustion method, the dust concentration after being removed by a filter becomes a problem. If the dust concentration cannot be controlled below a certain value, corrosion of the boiler tube due to salt or the like in the dust becomes a problem in the boiler disposed downstream for heat recovery. Further, if the amount of unburned flue gas generated in the combustion furnace is small, waste heat cannot be effectively recovered in the subsequent heating furnace.
[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]
A first means for solving the above problems is a fluidized bed furnace or a grate furnace, a partial oxidation furnace with a combustion reaction, the furnace temperature is 500 to 800 ° C., and the air ratio is 0.15 to 0. .9 to incompletely burn or partially oxidize the waste to generate a combustible gas having an oxygen equivalent concentration of -30 to -2% at the outlet of the partial oxidation furnace, and in the partial oxidation furnace of the combustible gas The temperature of the combustible gas is controlled to 500 to 800 ° C. by controlling the residence time of the gas, and then the combustible gas is introduced into the ceramic filter to remove the dust concentration to 0.1 g / Nm ³ or less and adhere to the ceramic filter. The ash to be removed is removed with a dust removal gas having an oxygen concentration of 5% or less, and the combustible gas removed from the dust is burned at a high temperature in a combustion furnace downstream of the ceramic filter, and burned in a boiler at the rear stage of the combustion furnace. To 350-540 ° C, 50- A heat recovery method from waste, characterized in that heat recovery is performed using 100 ata steam.
[0007]
Here, the “oxygen equivalent concentration” is defined as the difference between the oxygen concentration in the atmosphere and the oxygen concentration considered to be consumed by the gas that may be oxidized. For example, when oxygen (O ₂ ) is 2%, carbon monoxide (CO) is 4%, hydrogen (H ₂ ) is 2%, and methane (CH ₄ ) is 1%, carbon monoxide (CO) is 4% Consumes 2% oxygen (O ₂ ) to oxidize to carbon dioxide (CO ₂ ), and similarly 2% hydrogen (H ₂ ) consumes 1% oxygen (O ₂ ) and methane ( 1% of CH ₄ ) consumes 2% of oxygen (O ₂ ). Therefore, the “oxygen equivalent concentration” in this case is 2- (2 + 1 + 2) = − 3%. This number is an index indicating the degree of combustion of the partially oxidized gas in the atmosphere and the degree of air ratio in the previous combustion. In other words, the smaller this value, the higher the potential as a combustible gas.
[0008]
In the partial oxidation furnace, partial oxidation of the waste is performed, and a combustible gas having a relatively low temperature of 500 to 800 ° C. is sent to the dust removing device inlet. Here, the reason why the temperature at the inlet of the dust removing device is set in the above range is that if it is less than 500 ° C, there is a possibility of explosion due to re-ignition in a downstream pipe or a combustion furnace. This is because the material melts and adheres to the walls and filters in the dust removing device. The air ratio is adjusted so that the “oxygen equivalent concentration” at the furnace outlet at this time becomes −30 to −2% . The reason is that if the “oxygen equivalent concentration” is less than −30% , problems such as tar adhesion as a strong reducing gas occur, and if it exceeds −2% , combustion that can sufficiently reduce dioxin is formed in the combustion furnace. This is because it disappears.
[0009]
In the case of the present invention, by making the “oxygen equivalent concentration” and the dust removal temperature within this set range, the melt adhesion of the salt which is a problem in the high temperature dust remover in the oxygen atmosphere is eliminated. In other words, by controlling to the above-mentioned setting “oxygen equivalent concentration”, the ash that is removed by the dust removing device becomes solid particles that are covered with unburned carbon or unburned hydrocarbon around a salt mainly composed of NaCl or KCl, In addition, by controlling the dust removal temperature within the above set range, the unburned matter covering the salt remains in its state without causing liquefaction or gasification reaction, so the dust collector in the dust remover and the salt are in direct contact with each other. And no adhesion of salt to the dust collector. In addition, since it is in this temperature zone, dust can be removed without excessive cooling through equipment such as a temperature-decreasing tower, and the dust concentration in the dust remover is 0.1 g / Nm ³ or less. Therefore, a high temperature field that decomposes dioxins in a combustion furnace can be realized by combustion of combustible gas. At this time, the dust removing device can be appropriately selected from a bag filter, a ceramic filter, a high-temperature electrostatic precipitator, an inertial precipitator, a high-performance cyclone, a centrifugal precipitator and the like depending on the temperature of the combustible gas and the ash component. Is possible.
[0010]
In the case of the method of the present invention, dust is removed so that the dust concentration is 0.1 g / Nm ³ or less with a dust removing device, so that salt-containing dust is reduced and corrosion of boiler tubes installed downstream of the combustion furnace is prevented. It can be drastically reduced.
[0011]
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.
[0012]
By using a filter-type dust collector as the dust remover and removing the deposits on the filter body of the dust collector with a gas with an oxygen concentration of 2% or less, dust can be removed efficiently, and harmful gas Emissions are further suppressed. Here, the oxygen concentration is set to 2% or less in order to suppress the oxidation of the combustible gas by oxygen and reduce the risk of unnecessary explosion and combustion. This gas having an oxygen concentration of 2% or less can be obtained by using nitrogen, water vapor, exhaust gas recirculation gas, or using a pressure swing adsorption method or a membrane separation method.
[0013]
The dust-removed ash is blown off by blowing in the dust-removing gas that is removed when the differential pressure across the dust collector reaches a set value. A general dust remover blows the gas for dusting out at regular intervals. However, in the method of the present invention, it is necessary to prevent the precoat layer pre-coated on the surface of the dust collector from being dropped, so that dust collection is not performed. It is necessary to control the pressure drop of the duster. That is, even if the pressure drop is caused by the dust removal gas, the predetermined differential pressure for maintaining the precoat layer is determined, and control is performed so that the dust removal operation is started only when the pressure exceeds that value. The pressure of the dust removal gas is preferably 1 to 3 kg / cm ² .
[0014]
The second means for solving the above problem is to blow a gas containing oxygen into the ash from which dust has been removed, and to reduce the unburned content contained in the ash to a certain concentration or less by a combustion reaction of the ash and the gas. , A waste treatment method characterized by holding the gas in a range of 400 to 750 ° C. for a certain period of time and returning the gas generated by the combustion reaction to the partial oxidation furnace. The dust-removed ash is combusted by being brought into contact with a gas containing oxygen, and the state is maintained for a certain period of time, so that the unburned matter is reduced to a certain concentration or less while fixing the salt contained in the ash as it is. The unburned component is a compound composed mainly of carbon and hydrogen. By this combustion reaction, the unburned content is reduced to approximately 6 wt% or less, although it varies depending on the needs of each waste incineration plant. At this time, the temperature of the ash is controlled so as to be within a range of 400 to 750 ° C. When the temperature is lower than this temperature range, the combustion reaction does not easily proceed, and when the temperature is higher than the upper limit, the salt in the ash dissolves and the salt cannot be fixed. Therefore, the combustion reaction needs to proceed within the temperature range.
[0015]
Since the gas generated by the combustion reaction contains unburned components, the gas is returned to the partial oxidation furnace in order to effectively use the energy.
[0016]
A third means for solving the above problems, the furnace temperature to 500 to 800 ° C., by controlling the air ratio from 0.15 to 0.9 by incomplete combustion or partial oxidation of waste oxygen at the outlet Fluidized bed furnace that generates a combustible gas having a reduced concentration of −30 to −2%, controls the residence time of the combustible gas in the furnace, and controls the temperature of the combustible gas to 500 to 800 ° C. or a partial oxidation reactor is a grate furnace, a ceramic filter for dust removal the concentration of dust of the combustible gas is placed downstream thereof to 0.1 g / Nm ³ or less, the combustible that is disposed downstream is dust A combustion furnace for burning gas, a boiler for recovering heat from the burned gas disposed at the rear stage of the combustion furnace using steam of 350 to 540 ° C. and 50 to 100 ata, and ash removed from the dust by the ceramic filter as oxygen High temperature treatment with gas containing A processor of waste; and a ash treatment apparatus.
[0017]
In the partial oxidation furnace, the waste is partially oxidized, and a combustible gas of 500 to 800 ° C. is generated at the dust removing device inlet. The partial oxidation air ratio is adjusted so that the “oxygen equivalent concentration” at the furnace outlet at this time becomes −30 to −2% . Thereby, combustible gas with low oxygen concentration and few dangers, such as an explosion, is produced | generated. Further, the combustible gas is dedusted without excessive cooling by equipment such as a temperature reducing 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 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. In addition, by setting the “oxygen equivalent concentration” to a value within a certain range, fluctuations in the potential of the generated combustible gas are reduced and stable operation becomes possible.
[0018]
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.
[0019]
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.
[0020]
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. Things are thrown into the furnace, ignited and partially oxidized to produce combustible gas. Connected to the partial oxidation furnace 1 are a dust removing device 2 for removing dust from the combustible gas, a combustion furnace 3 for burning the combustible gas, a boiler 4 for recovering heat of the burned gas, and a device 5 for treating the dust ash. Yes.
[0021]
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. Further, the air ratio is controlled so that the “oxygen equivalent concentration” of the gas generated by partial oxidation is −30 to −2% . The air ratio at this time is about 0.15 to 0.5. 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 500 to 800 ° C. The reason for this temperature range is that there is a possibility of reignition or explosion in the downstream at 500 ° C. or lower, and there is a problem that salt in the dust melts and adheres to the dust removing device at 800 ° C. or higher. .
[0022]
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.
[0023]
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. Moreover, 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 tens of minutes to several hours, and a removal time of about 0.02 seconds to several seconds. Is desirable.
[0024]
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.
[0025]
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 500 ° C. or higher and 50 at or higher is installed at the subsequent stage of the combustion furnace 3, so that 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 more 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).
[0026]
【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.
[0027]
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 800 ° C. in the fluidized bed furnace 1, waste municipal waste is supplied to the fluidized bed furnace 1, and the air ratio is 0.2. A combustible gas was generated by partial oxidation by operating between ˜0.5. The combustible gas was supplied to the dust removing device 2 at about 650 ° 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. For exhaustion, gas and nitrogen gas with recirculation of the exhaust gas and reduced oxygen concentration to 2% or less are used, with a discharge pressure of 1 to 3 kg / cm ² , a discharge interval of 1 to 2 hours, and a discharge time of 0.1. The range was from second to 0.3 second. 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. The dust-removed ash is brought into contact with air, the unburned content is lowered from 8% to 0.1% or less and transferred to the next process of landfill disposal, and the air becomes a product gas containing several thousand ppm of CO. It was returned to. The dust-removed ash was kept at about 700 ° C. for 1 hour, and during this time, the combustion reaction with unburned matter and air was maintained. Experiments were conducted using pure oxygen gas instead of air, and similar results were obtained.
[0028]
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 450 to 650 ° C., and dust was removed by 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 in the range of 3 to 7 kg / cm ² , the removal interval of 10 seconds to 20 minutes, and the removal time of 0.05 seconds 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 danger 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, it was possible to recover heat using steam at 540 ° C. and 100 ata in the boiler 3 </ b> A in the combustion furnace 3 and the subsequent boiler 4. 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.
[0029]
【The invention's effect】
As described above, in the present invention, since the partially oxidized gas is removed 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 efficient. At the same time, heat can be recovered efficiently by installing a high-temperature and high-pressure boiler. In addition, by setting the “oxygen equivalent concentration” and the dust concentration of dust removal within a certain range, there is no need to worry about corrosion of boiler tubes and the like, and stable operation can be performed. Furthermore, emission of harmful gases such as dioxin and furan can be suppressed.
[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 (2)

In a fluidized bed furnace or a grate type furnace with partial combustion with combustion reaction, the waste temperature is incomplete by controlling the furnace temperature to 500-800 ° C and the air ratio to 0.15-0.9. Combustion or partial oxidation produces a combustible gas having an oxygen equivalent concentration of -30 to -2% at the partial oxidation furnace outlet, and controls the residence time of the combustible gas in the partial oxidation furnace. After controlling the temperature to 500 to 800 ° C., the combustible gas is introduced into the ceramic filter to remove the dust concentration to 0.1 g / Nm ³ or less, and the ash adhering to the ceramic filter is used for dust removal with an oxygen concentration of 5% or less. The combustible gas, which has been dusted off and removed by dust, is burned at a high temperature in a combustion furnace downstream of the ceramic filter, and steam at 350 to 540 ° C. and 50 to 100 ata from the gas burned in the boiler at the rear stage of the combustion furnace. Heat recovery using A method for recovering heat from waste. The in-furnace temperature is controlled to 500 to 800 ° C., the air ratio is controlled to 0.15 to 0.9 to incompletely burn or partially oxidize the waste , and the oxygen equivalent concentration at the outlet is −30 to −2 %. generates a combustible gas, the partial oxidation furnace is a fluidized bed furnace or grate furnace discharges by controlling the temperature of the combustible gas to 500 to 800 ° C. the residence by controlling the time in the furnace of the combustible gas A ceramic filter installed downstream thereof to remove dust concentration of the combustible gas to 0.1 g / Nm ³ or less, a combustion furnace installed downstream thereof and combusting the combusted gas removed from the dust, and the combustion furnace A boiler that recovers heat from the burned gas disposed in the rear stage using steam at 350 to 540 ° C. and 50 to 100 ata, and an ash that recovers the ash removed from the dust by the ceramic filter and treats it with oxygen-containing gas at a high temperature Having a processing device A heat recovery device from waste.

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