JP2006051433A - Method of reducing dioxin and bromine type dioxin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a relatively simple method of reducing dioxins and bromine type dioxins effectively. <P>SOLUTION: The method for the reduction of dioxins comprises controlling production of dioxins by cooling exhaust gas rapidly and removing dioxin-containing flying ash in the exhaust gas with a dust collector 7. Production of dioxins is controlled by keeping the temperature of the exhaust gas at the inlet of the collector 7 at 160-180°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for reducing dioxins in which production of dioxins and bromine-based dioxins is suppressed by a relatively simple method.

  Conventionally, various methods for reducing highly toxic organochlorine compounds (such as dioxins) generated from waste incinerators, electric furnaces (melting furnaces), boilers using waste fuel, and the like have been proposed.

  It is known that organochlorine compounds such as dioxins are discharged from waste incinerators and the like. The Dioxin Countermeasures Special Measures Law defines PCDDs (polychlorodibenzo-para-dioxins), PCDFs (polychlorodibenzofurans), and coplanar PCBs as dioxins. Here, PCDDs and PCDFs are collectively referred to as chlorinated dioxins PCDD / Fs, and so far, dioxins generally refer to chlorinated dioxins PCDD / Fs. In addition to dioxins, brominated dioxins are known.

  Dioxins are generally dibenzo-para-dioxins or dibenzofurans in which part or all of the hydrogen in the structural formula is replaced by chlorine alone. On the other hand, brominated dioxins in which part or all of hydrogen in the structural formula of dibenzo-para-dioxin or dibenzofuran is replaced with bromine are brominated dioxins and a part or all of the hydrogen. Brominated dioxins including those substituted with bromine and chlorine (that is, compounds having both bromine and chlorine) are referred to.

  In order to reduce the dioxins emitted from waste incinerators, etc., it is first necessary to measure the dioxins contained in the exhaust gas. This is done in accordance with “Dioxin Standard Measurement Manual for Waste Disposal” and “JIS K 0311” by the Environmental Maintenance Division.

  In this method, the exhaust gas in the exhaust gas duct is sucked into the exhaust gas sampling device by a vacuum suction fan as sampling exhaust gas, and after passing the exhaust gas through the water in the container bottle, the exhaust gas is passed through the adsorbent in the adsorbent holder, and further diethylene glycol in the container bottle And so on. After adsorbing the dioxins to the adsorbent through the sampling exhaust gas to the exhaust gas sampling device for a predetermined time or a predetermined amount, the adsorbent holder is removed and moved to a separate measuring device to extract the dioxins from the adsorbent and the container bottle The dioxins collected inside are extracted and analyzed, the dioxins are identified and quantified, and the concentration of dioxins is measured from the amount of exhaust gas sampled by a gas meter. Furthermore, based on the measured concentration, the total amount of dioxins in the exhaust gas discharged from the exhaust gas duct at the predetermined time is estimated. The exhaust gas measurement method is positioned as an “official method” for measuring dioxins in Japan, and standards for exhaust gas sampling methods, sample pretreatment methods, and analysis methods are established. Further, as a method for measuring dioxins other than the above official method, the GfA method (measuring method by GfA, Germany), the glass water cooling method and the like are known.

Further, Patent Document 1 introduces a sampling tube to an adsorbent while heating so that the exhaust gas temperature is maintained above the dew point temperature of water, and continuously adsorbs dioxins with the adsorbent for a long time. A method is disclosed in which the average concentration of dioxins during the adsorbed time is measured by taking out the adsorbent, extracting dioxins adsorbed on the adsorbent, analyzing and measuring the dioxins.
JP 2002-39923 A

  Patent Document 1 discloses a method for measuring the average concentration of dioxins in exhaust gas over a long period of time, but does not disclose any method for reducing dioxins in exhaust gas.

  Moreover, even if the amount of dioxins produced can be measured to some extent accurately by the dioxins measurement method as described above, there are very many types of dioxins produced by the combustion of waste, The production of dioxins is intricately intertwined with factors such as combustion temperature, unburned carbon content (factors closely related to the combustion state), chlorine concentration, gas cooling unit and dust collector operating temperature. Dioxins generation and decomposition behavior due to fluctuations in each factor, and generation of dioxins greatly vary depending on the relationship with related substances, so it is effective to grasp all these complex generation behaviors in the actual machine and effectively generate dioxins. It is difficult to reduce it.

  As a conventionally known method for reducing dioxins, it is considered effective to rapidly cool high-temperature exhaust gas from a waste incinerator or the like. Accordingly, high-temperature exhaust gas is supplied to a dust collector. Rapid cooling to about 200 ° C. or less is performed in front. In general, a system that adsorbs dioxins and heavy metals by blowing activated carbon at the inlet of the dust collector and removes fly ash containing dioxins and the like with a dust collector is common.

  In the above, the temperature of the exhaust gas at the inlet of the dust collector is set to about 200 ° C. or less. The use limit temperature of the bag filter provided in the dust collector 7 is about 200 ° C. When the temperature exceeds this temperature, the bag filter is heated. This is because of damage. On the other hand, a denitration device may be provided downstream of the dust collector. The catalyst provided in the denitration apparatus shows a peak of denitration effect at, for example, around 380 ° C. However, considering the suppression of secondary generation of dioxins, the exhaust gas cooled to 200 ° C or less as described above is re-approxated to around 230-250 ° C. It is heated and introduced into the denitration equipment. For suppressing the production of dioxins, it is advantageous to make the exhaust gas temperature as low as possible. However, as described above, it is necessary to reheat the cooled exhaust gas for denitration. In order to minimize energy loss as much as possible, the exhaust gas temperature at the inlet of the dust collector is generally set to 200 ° C. as high as possible.

  On the other hand, the Special Measures Law for Countermeasures against Dioxins clearly states “promotion of research and research on brominated dioxins by the government”. Therefore, the necessity for measurement and reduction of brominated dioxins will increase in the future. Conceivable.

  Brominated dioxins are dibenzo-para-dioxin or dibenzofuran in which a part or all of the hydrogen in the structural formula is replaced only by bromine (brominated dioxins), and part or all of the hydrogen is bromine. These brominated dioxins are only known to have the property of being easily photodegraded compared to chlorinated dioxins, including the mechanism of their formation, etc. The form of is not elucidated.

  The brominated dioxins can be measured by the same sampling method as the measurement of the chlorinated dioxins, but since brominated dioxins are easily photodegraded, measurement in a state in which photolysis is prevented is necessary. For this reason, there is a problem that the measurement is technically troublesome and requires time and labor. Incidentally, as a method for measuring brominated dioxins, “provisional investigation method of polypromodibenzo-para-dioxin and polypromodibenzofuran” was announced by the Ministry of the Environment in October 2002.

  Even if bromine-based dioxins can be measured by carrying out the troublesome measurement operation as described above, the mechanism and form of bromine-based dioxins are not clarified. At present, no method has been established that can effectively reduce the number of species.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for reducing dioxins and brominated dioxins capable of effectively reducing dioxins and brominated dioxins. Is.

  The present invention is a method for reducing dioxins, wherein the generation of dioxins is suppressed by quenching the exhaust gas and fly ash containing dioxins in the exhaust gas is removed by a dust collector, wherein the dust collection It is a method for reducing dioxins, characterized in that the exhaust gas temperature at the inlet of the apparatus is maintained at 160 to 180 ° C.

  In the above means, it is preferable to control the exhaust gas temperature at the inlet of the dust collector to 170 ° C.

  The present invention maintains the exhaust gas temperature at the inlet of the dust collector at 160 ° C. to 180 ° C., preferably 170 ° C. based on the correlation obtained by measuring the chlorinated dioxin concentration and bromine dioxin concentration in the fly ash. This is a method for reducing brominated dioxins characterized by simultaneously reducing brominated dioxins using chlorinated dioxins as an index.

  According to the dioxin reduction method of the present invention, the generation of dioxins can be effectively reduced by maintaining the exhaust gas temperature at the inlet of the dust collector at 160 ° C. to 180 ° C. Further, the exhaust gas at the inlet of the dust collector By controlling the temperature to 170 ° C., the production of dioxins can be more reliably reduced.

  Moreover, according to the method for reducing brominated dioxins of the present invention, the exhaust gas at the inlet of the dust collector is based on the correlation obtained by measuring the chlorinated dioxins concentration in the fly ash and the brominated dioxins concentration. By maintaining the temperature at 160 ° C. to 180 ° C., preferably 170 ° C., brominated dioxins can be reduced simultaneously with chlorinated dioxins using chlorinated dioxins as an index.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a conceptual diagram showing an example of an apparatus for carrying out the dioxins and bromine dioxins reduction method of the present invention. First, the case of reducing dioxins (chlorinated dioxins PCDD / Fs) will be described. .

In FIG. 1, 1 is a waste fluidized bed incinerator having a fluidized bed 2 for incinerating waste, a secondary combustion chamber 3 (rear combustion process), and a boiler 1a. The exhaust gas discharged from the waste fluidized bed incinerator 1 is introduced into the gas cooling chamber 5 through the economizer 4 that heats the water supplied to the boiler 1a, and is rapidly cooled by the cooling water sprayed from the spray device 6, Activated carbon for adsorbing dioxins in the exhaust gas and Ca (OH) ₂ for absorbing hydrogen chloride in the exhaust gas are added and guided to the dust collector 7, and the activated carbon and the like are contained by the bag filter 8. Fly ash is removed. At this time, dioxins in the exhaust gas are captured by the fly ash by blowing the activated carbon, and in this example, about 99.4% of the total discharge amount of dioxins is contained in the fly ash in the example of the apparatus of FIG. Is removed. Therefore, the concentration of dioxins in fly ash was used as an index indicating the emission of dioxins. Here, the numerical values appended to the ash and fly ash indicate the ratio when the total amount of dioxins discharged from the incineration facility is 100%.

  The exhaust gas from which fly ash has been removed by the bag filter 8 is reheated to a temperature (for example, 230 to 250 ° C.) suitable for removing NOx and dioxins by the reheater 9, and then the denitration apparatus 10 loaded with the catalyst. In this way, denitration is performed, and finally the exhaust gas is discharged from the chimney 11 to the atmosphere.

  The production / dechlorination / decomposition behavior of dioxins in a waste incineration process such as the waste fluidized bed incinerator of FIG. 1 is based on the types and components of waste, reaction conditions (temperature, time, atmosphere, etc.) and catalyst. Influenced by differences in fly ash components. For this reason, dioxins discharged from the incineration process are characterized by containing many types of isomers. This suggests that there are various reaction fields with different temperatures, residence times, atmospheres, etc. during the incineration process, and that characteristic dioxin formation / dechlorination / decomposition reactions occur at each site. . Therefore, in order to reduce dioxins discharged from incineration facilities, it is necessary to understand not only the production and decomposition mechanism from a microscopic viewpoint, but also the generation behavior of dioxins with a view to the entire incineration process flow.

  Until now, laboratory-scale experiments have been conducted under conditions of reaction temperatures of about 250 to 500 ° C. in order to grasp the generation / dechlorination / decomposition behavior of dioxins. However, sufficient knowledge has not been obtained about the generation and decomposition behavior of dioxins in a temperature range of 200 ° C. or less existing after the dust collector. Therefore, in the waste fluidized bed incinerator 1, in order to search for a dioxin generation factor in a low temperature region after the dust collector 7 when the exhaust gas is rapidly cooled and introduced into the dust collector 7, the dust collector 7. The relationship between the exhaust gas temperature at the inlet and the production of dioxins was investigated.

  At present, a bag filter 8 having a limit temperature of 200 ° C. or lower is generally employed in a dust collector 7 for performing exhaust gas treatment in an apparatus such as the waste fluidized bed incinerator 1 of FIG. 1 (at 200 ° C. or higher). The bag filter 8 is damaged by heat). For this reason, the exhaust gas is quenched in the gas cooling chamber 5 so that the exhaust gas temperature at the inlet of the dust collector 7 is 200 ° C. or lower and the temperature is adjusted to 200 ° C. or lower. Is used to adsorb and remove dioxins and heavy metals, and to remove the fly ash with the dust collector 7.

  In a report that examined the possibility of removing dioxins by the adsorption action of unburned carbon contained in incineration exhaust gas, dioxins were analyzed even at low temperatures of about 150 ° C, based on a comparison of dioxin concentration and homolog balance before and after the bag filter. It has been pointed out that there is a possibility of generating. Moreover, in the test which heated PVC with copper oxide at the temperature of 200 degreeC, it was reported that a lot of dioxins produced | generated around one week after a heating.

  Thus, even in a low temperature range of 150 to 200 ° C., it is suggested that the dust containing unburned carbon, a chlorine source, and a metal compound may generate dioxins by being heated for a long time. However, there is no report example which investigated the production | generation of dioxins in detail in the low temperature range of 150-200 degreeC as mentioned above.

  Therefore, an experimental study was conducted on the production of dioxins (chlorinated dioxins PCDD / Fs) under the low temperature conditions.

As shown in FIG. 2, model fly ash in which SiO ₂ is mixed with CuCl ₂ .2H ₂ O (0.5%), Cu (OH) ₂ (2%) and soot (0.2%) as a carbon source ( (Hereinafter referred to as MFA), a sample of 0.2% soot as a carbon source supported on molten fly ash generated when municipal waste incineration fly ash (and furnace bottom ash) is melted (hereinafter: fly ash + soot) Furthermore, 250 mg of each sample of 0.2% terephthalic acid supported on molten fly ash as a carbon source (hereinafter “fly ash + terephthalic acid”) was sealed with air on a Pyrex (registered trademark) ampoule 21. PCDD / Fs produced after heating for 1 day to 1 week at a temperature of 150 to 200 ° C. in an electric furnace was measured. At the same time, polychlorobenzenes PCBZs, which are one of the organic chlorine compounds generated in the waste incineration process, were measured.

Ampoule 21 had an inner diameter of about 10 mm, a length (cylindrical portion) of about 100 mm, and a volume of about 7.85 cm ³ . The carbon source enclosed in the ampoule is about 0.5 mg (0.042 mmol with the total amount of “carbon C = 12”), so the amount of oxygen gas required for complete oxidation of this is estimated to be about 0.042 mmol. be able to. Since the amount of oxygen in the air contained in an ampoule having a volume of about 7.85 cm ³ is estimated to be about 0.07 mmol, it can be determined that sufficient oxygen for the reaction was secured in the ampoule.

  Lists of low temperature heating test results of model fly ash MFA, fly ash + soot, fly ash + terephthalic acid are shown in [Table 1], [Table 2], and [Table 3], respectively.

  These include PCDD / Fs generation when heated at 300 ° C. for 30 minutes based on 300 to 370 ° C., which is an optimum generation temperature range in which PCDD / Fs is generated from unburned carbon, and a heating time of 30 to 60 minutes. Concentrations are also listed. In addition, when the sample is heated at 300 ° C. for 30 minutes, the PCDD / Fs generation amount is considered to be a level close to the maximum. Therefore, this value is referred to as the “generation potential” of the experimental sample for convenience. I will decide.

  When MFA was heated at a low temperature of 200 ° C. or lower, as shown in FIG. 3, the PCDD / Fs generation amount tended to increase as the temperature increased. At this time, the amount of PCDDs and PCDFs produced and the rate of increase were small until the temperature was around 180 ° C., but after about 180 ° C., PCDDs showed an increasing tendency, and PCDFs showed a rapid increasing tendency. Moreover, as shown in [Table 1], the PCDDs and PCDFs production potentials of MFA are 900 ng / g and 4600 ng / g, respectively, while the production ratios when heated at 200 ° C. for 1 week (168 hours) are respectively. About 10% and about 6%. However, as shown in FIGS. 4A and 4B, the PCDD / Fs generation amount showed an increasing tendency even after one week. Under a temperature condition of around 200 ° C., the PCDD / Fs concentration tends to increase even after one week, and it can be predicted that the final PCDD / Fs yield will increase by heating for a longer time.

  As shown in [Table 2] and FIG. 5, the amount of dioxins produced when fly ash + soot was heated at a low temperature of 200 ° C. or lower showed a tendency to increase with increasing temperature as in the case of heating MFA. . At this time, the amount of PCDDs produced and the rate of increase are small until the temperature is around 180 ° C., but the amount of PCDDs produced tends to increase after about 180 ° C., and the amount of PCDFs produced and the rate of increase are Although it was small up to about 170 ° C., it increased after about 170 ° C., and increased more rapidly when it exceeded 180 ° C.

  The concentrations of PCDDs and PCDFs when fly ash (raw ash) with a very low dioxin concentration was heated at 200 ° C. for 1 week were 3.4 ng / g and 2.0 ng / g, respectively, as shown in [Table 2]. . On the other hand, the concentration of PCDDs and PCDFs when flying ash + soot is heated at 200 ° C. for 1 week is 220 ng / g and 630 ng / g, respectively, and compared with the yield when heating only raw ash under the same conditions, 60 And 300 times. Therefore, it can be said that the generation of PCDD / Fs from carbon or the like contained in the raw ash did not greatly affect the test results. The generation potentials of fly ash + soot PCDDs and PCDFs shown in [Table 2] are 470 ng / g and 4100 ng / g, respectively, whereas the generation ratios of both after heating at 200 ° C. for 1 week are about 47% and about 15%. Therefore, fly ash + soot tended to be higher than MFA as the production ratio in the low temperature range with respect to the PCDD / Fs production potential.

  When fly ash + terephthalic acid was heated at a temperature of 200 ° C. or lower, the yield of PCDDs tended to increase with temperature, as shown in [Table 3] and FIG. At this time, the amount of PCDFs produced was small and there was almost no change in the amount produced even when the temperature was increased. However, the amount of PCDDs produced was small until the temperature was around 170 ° C, but it was produced after about 170 ° C. The amount showed a sharp increasing trend. On the other hand, the PCDFs concentration when changing the heating temperature in the range of 150 to 200 ° C. in [Table 3] is 0.53 to 3.9 ng / g, which is not much different from the concentration when only the raw ash is heated. . Therefore, it is considered that the PCDFs generation is not caused by terephthalic acid but rather by a small amount of unburned carbon contained in the fly ash. The phenomenon in which PCDDs are selectively generated from precursors has also been obtained by experiments using, for example, chlorophenols (PCPs). Both PCPs and terephthalic acid are monocyclic compounds in which a functional group is substituted on one benzene ring. Therefore, the generation of dioxins starting from such monocyclic compounds is presumed to be mainly PCDDs generation by condensation.

  By the way, from the above series of tests, when comparing the production ratio of PCDDs and PCDFs with respect to the production potential (production amount at 300 ° C.), the former showed a high tendency. This indicates that PCDDs are more easily generated than PCDFs in a low temperature range of 200 ° C. or lower.

  Furthermore, when the monocyclic compound is present in the reaction field, PCDDs are selectively generated ([Table 3], FIG. 6), and this effect may increase the abundance ratio of PCDDs. When PCDD / Fs contained in the ash of the bag filter 8 actually obtained from the municipal waste incineration facility or in the exhaust gas after the bag filter 8 is analyzed, the PCDDs concentration is often higher than the PCDFs. This phenomenon is caused by the fact that “in the low temperature range of 200 ° C. or lower, PCDDs are more easily generated than in PCDFs” and “the bag filter 8 in this temperature range or in the pipe after the bag filter 8 in the temperature range. This can be explained for two reasons: “It is considered that the generation of PCDDs is continued for a long time in the dust.”

  From the results shown in FIGS. 3, 5, and 6, as a characteristic phenomenon in the test in which various samples are heated, the reaction temperature is about 160 ° C. to 180 ° C., particularly PCDD / Fs at the boundary of 170 ° C. The production amount (or production rate) of sucrose increases rapidly. A similar trend can be said for PCBZs, and therefore also for coplanar PCBs that are structurally closer to PCDDs and PCDFs than PCBZs.

  Therefore, as an operating temperature of the bag filter 8 of the dust collector 7 for suppressing dioxins (including coplanar PCB), it is one guideline to first set in the range of about 160 ° C to 180 ° C. From the viewpoint of suppressing the production of dioxins, it can be said that a temperature lower than 160 ° C. is advantageous, but since the risk of corrosion of pipes and the like increases, it is reasonable to set the lower limit of the temperature range to about 160 ° C. . However, selecting a higher temperature because it is necessary to reheat the exhaust gas to around 230 to 250 ° C., which is a temperature necessary for the catalyst of the denitration apparatus 10, and in both FIG. 3, FIG. 5, and FIG. Considering the temperature condition that does not cause a rapid increase, it has been found most preferable to set the temperature of the exhaust gas at the inlet of the dust collector 7 to 170 ° C.

  Here, in order to stably control the temperature at the inlet of the dust collector 7, it is premised that the operating states of the secondary combustion chamber 3 and the gas cooling chamber 5 on the upstream side of the dust collector 7 are stabilized. As described above, since the operation state on the upstream side of the dust collector 7 is stabilized and the temperature at the inlet of the dust collector 7 is accurately controlled to, for example, 170 ° C., the generation of PCDD / Fs can be effectively suppressed. It has been found that it is very important to improve the temperature control level as an order of reduction measures.

  For this purpose, in FIG. 1, a thermometer 22 is installed at the inlet of the dust collector 7, and the water spray amount of the spray device 6 is adjusted by the controller 23 based on the detected temperature of the thermometer 22. Therefore, the temperature at the inlet of the dust collector 7 can be always accurately maintained at 170 ° C., for example.

  According to the apparatus of FIG. 1, the exhaust gas temperature at the inlet of the dust collector 7 is measured by the thermometer 22, and the controller 23 is maintained so that the detected temperature of the thermometer 22 is always accurately maintained at 170 ° C., for example. The water spray amount of the spray device 6 is adjusted according to a command from Thereby, the exhaust gas temperature at the inlet of the dust collector 7 is controlled so as to be always accurately maintained at 170 ° C.

  Next, an analysis test of the dioxins (chlorinated dioxins PCDD / Fs) concentration and bromine-based dioxins concentration was performed using actual fly ash (removed fly ash of the dust collector 7). As described above, since brominated dioxins are easily photodegraded, the analysis of dioxins was carried out using a method for preventing photodegradation. For this reason, the measurement of brominated dioxins requires time and effort compared to the analysis of chlorinated dioxins (PCDD / Fs).

  Then, the analytical values of the chlorinated dioxins concentration and bromine dioxin concentration obtained above were compared as shown in FIGS. 7 (A), (B), (C), and (D). FIG. 7A shows a case where M1CDFs (a kind of chlorinated dioxins) and M1BDFs (a kind of brominated dioxins) are compared, and FIG. 7B shows an O8CDF (a kind of chlorinated dioxins) and M1BH7CDFs. FIG. 7C shows a case where O8CDD (a kind of chlorinated dioxins) and M1BH7CDD (a kind of bromine-type dioxins) are compared. 7 (D) shows the case where O8CDD (a kind of chlorinated dioxins) and D2BH6CDDs (a kind of brominated dioxins) are compared.

  From the comparison results of the chlorinated dioxins concentration and brominated dioxins concentration in FIGS. 7 (A), (B), (C), and (D), the production of chlorinated dioxins and brominated dioxins is approximately proportional. The knowledge that it has a correlation was obtained.

  In addition, the confirmation test for confirming the precision of the test which analyzed the said chlorinated dioxin density | concentration and bromine-type dioxin density | concentration was implemented. That is, repeated analysis was performed using the same actual fly ash, and the results are shown in [Table 4].

  As apparent from [Table 4], each measurement value of the analysis results repeatedly performed is stable with little error, and thus the chlorinated dioxin concentration and bromine dioxin concentration were measured with high accuracy. Therefore, the comparison results of the chlorinated dioxins concentration and the brominated dioxins concentration shown in FIGS. 7A, 7B, 7C, and 7D were reliable.

  From the comparison of the chlorinated dioxins concentration and brominated dioxins concentration in Fig. 7 (A), (B), (C), (D), the production of chlorinated dioxins and brominated dioxins has a substantially proportional relationship. As described above, brominated dioxins using chlorinated dioxins, which are relatively easy to measure, as an index, without having to measure brominated dioxins that require time and labor as described above. The production amount of can be predicted.

  Furthermore, as shown in FIG. 3, the amount of PCDD / Fs generated increases with the temperature of the exhaust gas, and the amount of PCDD / Fs generated and the rate of increase are small until the temperature is around 180 ° C, but about 180 ° C. As shown in FIGS. 7A, 7B, 7C, and 7D, chlorinated dioxins are obtained. And the production of brominated dioxins is obtained, the exhaust gas temperature at the inlet of the dust collector 7 is controlled to 160 ° C. to 180 ° C., preferably 170 ° C. to reduce the PCDD / Fs. It was found that brominated dioxins could be reduced simultaneously.

  Here, the case where the exhaust gas temperature at the inlet of the dust collector 7 is controlled to 160 ° C. to 180 ° C., preferably 170 ° C., to reduce the brominated dioxins simultaneously with the chlorinated dioxins has been described. Since it was possible to obtain the correlation between the formation of chlorinated dioxins and brominated dioxins from FIGS. 7A, 7B, 7C, and 7D, other conventionally known dioxins were obtained. In the method for reducing the number of bromines, the production of brominated dioxins can be simultaneously reduced by using chlorinated dioxins as an index.

  As described above, from the results shown in FIGS. 3, 5, and 6 in the test in which the fly ash sample was heated in a low temperature range of 200 ° C. or less, dust collection was required to reduce the production of dioxins (including coplanar PCB). Since it has become a standard to keep the exhaust gas temperature at the inlet of the apparatus 7 in the range of about 160 ° C. to 180 ° C., by controlling the exhaust gas temperature at the inlet of the dust collector 7 in the range of 160 ° C. to 180 ° C. , Production of dioxins (including coplana PCB) can be effectively reduced.

  Further, in FIG. 3, FIG. 5, and FIG. 6, the temperature at which neither PCDDs nor PCDFs cause a sudden increase is selected, and the exhaust gas is exhausted to around 230 to 250 ° C., which is the temperature required for the catalyst in the denitration apparatus 10. Since a higher temperature is selected in order to reduce the heating temperature range when reheating the gas, it was found that the temperature of the exhaust gas at the inlet of the dust collector 7 is most preferably 170 ° C. By controlling the exhaust gas temperature at the inlet of the dust collector 7 to 170 ° C., the production of dioxins (chlorinated dioxins PCDD / Fs) can be effectively reduced, and at the same time, the exhaust gas is regenerated for the denitration device 10. Energy loss required for heating can be suppressed as much as possible.

  Furthermore, from the comparison results of FIGS. 7 (A), (B), (C), and (D), there is a correlation that the production of chlorinated dioxins and brominated dioxins in fly ash has a substantially proportional relationship. Therefore, it was possible to estimate the production of brominated dioxins using the chlorinated dioxin concentration as an index without measuring the brominated dioxins concentration, which takes time and effort.

  Furthermore, as described above, there is a correlation between the generation of chlorinated dioxins and brominated dioxins, and the amount of PCDD / Fs generated and the rate of increase are small until the temperature is around 180 ° C. as shown in FIG. Since the relationship between the exhaust gas temperature and the generation of PCDD / Fs showing a rapid increase tendency after about 180 ° C. was obtained, the exhaust gas temperature at the inlet of the dust collector 7 was set to 160 ° C. to 180 ° C., preferably 170 ° C. By controlling to reduce the production of chlorinated dioxins, the production of brominated dioxins can be effectively reduced at the same time.

  The method for reducing dioxins and bromine-based dioxins of the present invention is not limited to the embodiment described above, and various modifications can be made without departing from the scope of the present invention. is there.

It is a conceptual diagram which shows an example of the apparatus which implements the reduction method of dioxins and brominated dioxins of this invention. It is explanatory drawing of the ampule for a test which sealed the sample. It is a diagram which shows the relationship between the amount of PCDD / Fs production | generation in the case of model fly ash MFA, and reaction temperature. (A) is a diagram showing the relationship between the amount of PCDDs produced and the reaction time, and (B) is a diagram showing the relationship between the amount of PCDFs produced and the reaction time. It is a diagram which shows the relationship between the amount of PCDD / Fs production | generation in the case of fly ash + soot, and reaction temperature. It is a diagram which shows the relationship between the amount of PCDD / Fs production | generation in the case of fly ash + terephthalic acid, and reaction temperature. (A), (B), (C), (D) are graphs showing comparison of analytical values of chlorinated dioxins and brominated dioxins.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Waste fluidized bed incinerator 5 Gas cooling room 6 Spray apparatus 7 Dust collector 22 Thermometer 23 Controller

Claims (3)

  A method for reducing dioxins, wherein the generation of dioxins is suppressed by quenching the exhaust gas and fly ash containing dioxins in the exhaust gas is removed by the dust collector, wherein the exhaust gas at the inlet of the dust collector A method for reducing dioxins, characterized in that the temperature is maintained at 160 ° C to 180 ° C.   The method for reducing dioxins according to claim 1, wherein the exhaust gas temperature at the inlet of the dust collector is controlled to 170 ° C.   The chlorinated dioxins by maintaining the exhaust gas temperature at the dust collector inlet according to claim 1 or 2 based on the correlation obtained by measuring the concentration of chlorinated dioxins and bromine dioxins in fly ash A method for reducing brominated dioxins, characterized in that brominated dioxins are simultaneously reduced using as an index.

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