JP2014024052A - Fly ash circulation type exhaust gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fly ash circulation type exhaust gas treatment method capable of stably reducing the concentration of acid gas of a bag filter outlet up to a low level in the blowing-in equivalent ratio of a little sodium-based chemical, by further effectively using an unreacted portion unreacted with the acid gas, by almost completely converting the sodium-based chemical such as sodium bicarbonate introduced into an exhaust gas flue into sodium carbonate, in the exhaust gas treatment method for removing the acid gas such as hydrogen chloride and sulfur oxide included in exhaust gas.SOLUTION: The fly ash circulation type exhaust gas treatment method returns a part of this bag filter fly ash to the exhaust gas flue 1 on the bag filter inlet side, by taking out the fly ash (smoke dust in the exhaust gas + the sodium-based chemical and a reacted product material of the acid gas + an unreacted sodium-based chemical) collected by a bag filter 2 from a bottom part 11 of the bag filter. A circulation amount of the bag filter fly ash is set to 3 times - 14 times expressed by the fly ash circulation magnification ratio.

Description

  The present invention removes acidic gases such as hydrogen chloride and sulfur oxide contained in exhaust gas discharged from waste treatment facilities such as waste incinerators and gasification and melting furnaces, and exhaust gas released into the atmosphere. The present invention relates to a fly ash circulation type exhaust gas treatment method for detoxification.

  In recent years, there has been a strong demand for countermeasures against global warming, and in the construction plan for waste incinerators and other waste treatment facilities, we will promote the development of facilities that take into account the prevention of global warming. There is a strong demand for improving the total power generation capacity through energy recovery, effective utilization, and high efficiency of power generation.

  Most of the general waste such as municipal waste and industrial waste discharged from various factories are processed in waste incinerators, gasification melting furnaces, industrial waste incinerators, etc., which are generated in the process. The exhaust gas contains soot dust, hydrogen chloride (HCl), sulfur oxide (SOx), nitrogen oxide, heavy metals, and the like, and appropriate treatment is performed for the removal thereof.

  In particular, in the local governments that have stricter exhaust gas treatment standards, in order to satisfy these standards, wet smoke cleaners have been conventionally used, and for example, both HCl and SOx are operated and managed at 5 ppm or less. In addition, dioxins and mercury contained in the exhaust gas are removed as necessary.

  This wet smoke cleaning device has good acid gas removal performance, but the temperature is reduced to the water saturation temperature, so the outlet gas is used to prevent subsequent devices such as catalytic denitration devices, chimney corrosion prevention and white smoke generation. It is necessary to increase the temperature by installing a heat exchanger in the line.

  For example, if the temperature is raised using steam, the amount of power generated by the steam turbine decreases, so it cannot be said that the apparatus is preferable in terms of energy recovery. In addition, the actual situation is that it is an exhaust gas treatment apparatus that requires dedicated wastewater treatment and the like, and the construction cost of the facility is high, and there is also a problem in downsizing.

  Slaked lime (calcium hydroxide) and baking soda (sodium bicarbonate) are used as neutralizers for dry exhaust gas treatment that can remove acid gases such as hydrogen chloride and sulfur oxides. It is known that the reactivity with gas is high.

  For example, in the following Non-Patent Document 1, by using a sodium-based chemical such as sodium bicarbonate, at a temperature range of 170 to 210 ° C., the equivalent ratio is 1.2, and HCl and SOx are high by 98% and 90%, respectively. It has been reported that the removal rate and the HCl and SOx concentrations at the bag filter outlet were 10 ppm or less at an equivalent ratio of 1.3.

  This is because, under high temperature, for example, in an atmosphere of 140 ° C. or higher, baking soda is thermally decomposed according to the following formula and converted to porous and highly reactive sodium carbonate, so that the acid gas removal efficiency is greatly improved. Is.

2NaHCO ₃ → Na ₂ CO ₃ + CO ₂ + H ₂ O
In addition, it has been reported that the amount of collected ash can be reduced by about 25% compared to the slaked lime method.

  Non-Patent Document 2 described below reports that it takes tens of seconds to several minutes in a temperature atmosphere of 100 to 200 ° C. to decompose sodium bicarbonate almost completely.

  Moreover, in the following patent document 1, by using sodium-based chemicals such as sodium bicarbonate as an acid gas removing agent in the exhaust gas, by efficiently removing the acid gas in the exhaust gas to a low concentration without reducing the temperature of the exhaust gas, An exhaust gas treatment method and exhaust gas treatment equipment capable of avoiding poisoning of a denitration catalyst installed on the downstream side are disclosed. This is a technology that leads to further energy recovery.

Similarly, the following Patent Document 2 discloses the acidity of a catalyst having vanadium pentoxide (V ₂ O ₅ ) as an active component by efficiently removing sulfur oxide (SO ₂ ) in exhaust gas to an extremely low concentration. Disclosed is an exhaust gas treatment method capable of avoiding poisoning due to ammonium sulfate and prolonging the continuous use period of the catalyst. By contacting the exhaust gas containing SO ₂ with sodium bicarbonate and / or sodium carbonate powder The exhaust gas treatment method is described in which the exhaust gas having an SO ₂ concentration of 5 ppm or less is passed through a catalyst containing V ₂ O ₅ as an active component.

  Further, in Patent Documents 3 and 4 below, a chemical is supplied to detours provided on the upstream side and the downstream side of the bag filter, and the high temperature exhaust gas at the bag filter outlet is used as a carrier gas. An exhaust gas treatment method and an exhaust gas treatment facility for securing a residence time and making a chemical porous are disclosed. These patent documents also describe that the drug is crushed immediately before the drug is introduced.

JP 2004-000866 A JP 2004-082103 A JP 2002-136840 A JP 2002-028439 A

"Acid gas removal technology using a new dry exhaust gas treatment system" Takuma Co., Ltd., Masaaki Kurata et al. `` Kinetic of Sodium Bicarbonate Decomposition '' Wang Hu, J.M.Timur Dogu, Gulsen Dogu, AICHE Journal Sept. 1986 Vol.32, No.9

  As mentioned above, dry-type exhaust gas treatment equipment using baking soda is expected to be one of the energy-saving high-performance dry-type exhaust gas treatments that replaces wet smoke cleaning equipment, but sodium bicarbonate is a chemical compared to conventional slaked lime. The price is 3 to 4 times higher, the chemical usage is further reduced, and the acid gas removal performance is stably maintained at 5 ppm for both HCl and SOx, which is the same level as that of the wet smoke cleaning device. Further improvement in performance that can secure removal performance is a major issue.

  In addition, fly ash collected by a bag filter in dry exhaust gas treatment using conventional baking soda contains dust in the exhaust gas, reaction products of chemicals and acid gases, unreacted chemicals, and filter aids. However, according to the conventional methods described in Patent Documents 1 to 4 and Non-Patent Document 1, in any case, unreacted chemicals in fly ash containing undecomposed baking soda are not efficiently used and used. There has been a problem that the removal efficiency of acid gas with respect to the amount of drug is limited, and the amount of sodium bicarbonate used cannot be reduced.

  For example, in Patent Documents 3 and 4, as a means for solving this problem, in a line for crushing baking soda and supplying it to the flue, it is retained in advance at 140 ° C. or more for 1 to 3 seconds to decompose and porous the baking soda. However, it can be said that the thermal decomposition time of baking soda is too short to reach the level at which the intended purpose can be achieved.

  That is, according to Non-Patent Document 2, it is reported that it takes tens of seconds to several minutes in a temperature atmosphere of 100 to 200 ° C. to decompose baking soda almost completely. In the described method, the pyrolysis time of sodium bicarbonate at a high temperature is short, the conversion reaction into porous sodium carbonate is insufficient, and a large improvement in the performance of removing acidic gas remains a problem. This is because in the demonstration test separately conducted by the present inventors, sodium bicarbonate was blown into the flue gas flue at the bag filter inlet and a residence time of 2 to 3 seconds was secured at 180 ° C. or higher, and there was no residence time. It can also be seen from the results of comparing the acid gas removal performance in this case that almost no performance difference was confirmed.

  In other words, the reaction between baking soda chemicals and acid gas is dominated by the cake layer formed on the filter cloth surface of the bag filter. To increase the acid gas removal efficiency, more cake layers are formed. It is more effective to do.

  The object of the present invention is to solve the above-mentioned problems of the prior art, and to convert sodium-based chemicals consisting of sodium bicarbonate introduced into the flue gas flue almost completely into porous sodium carbonate having extremely high reactivity, and to be acidic. The concentration of acidic gases such as hydrogen chloride and sulfur oxides at the bag filter outlet is reduced by using the unreacted portion of the sodium-based chemicals that could not react with the gas more efficiently and using very little sodium-based chemicals. The present invention is to provide a fly ash circulation type exhaust gas treatment method that can stably lower the gas to a low level and can drastically improve the acid gas removal efficiency.

  As a result of intensive studies in view of the above points, the present inventors have converted sodium-based drugs made of sodium bicarbonate and the like introduced into the flue into porous carbonate and highly reactive sodium carbonate, and, moreover, In order to more efficiently use the unreacted portion of the sodium-based chemical that did not react with the acid gas, fly ash collected by the bag filter (reaction product of dust + sodium-based chemical and acid gas in the exhaust gas) + Unreacted drug) is taken out from the bottom of the bag filter, and a part of this bag filter fly ash is returned to the flue gas flue on the bag filter inlet side to circulate the unreacted drug. And found that the concentration of acidic gases such as hydrogen chloride and sulfur oxides at the bag filter outlet can be dramatically and stably reduced with the amount of used, and the present invention was completed. Which has led to that.

  In order to achieve the above object, the invention of the fly ash circulation type exhaust gas treatment method according to claim 1 uses a sodium-based chemical as a chemical for removing acid gas contained in the exhaust gas, and uses the sodium-based chemical in the flue gas flue on the bag filter inlet side. A dry exhaust gas treatment method in which a sodium chemical is introduced, a salt is formed by a reaction between an acid gas in the exhaust gas and the sodium chemical, and fly ash containing the salt is collected and removed by a bag filter. The fly ash collected by the filter (dust in exhaust gas + reaction product of sodium chemical and acid gas + unreacted sodium chemical) is taken out from the bottom of the bug filter, and a part of this bug filter fly ash is It is characterized by returning to the flue gas flue on the filter inlet side.

  Here, as a means for returning a part of the bag filter fly ash to the exhaust gas flue on the bag filter inlet side, a part of the desalted / desulfurized exhaust gas discharged from the bag filter may be used as a carrier gas. Air or other gas may be used as the carrier gas. Moreover, you may use mechanical means, such as a conveyor, and you may combine this and a carrier gas system.

  The invention of claim 2 is the fly ash circulation type exhaust gas treatment method of claim 1, wherein the fly ash circulating amount of bag filter fly ash returned to the flue gas flue on the bag filter inlet side is represented by the following formula: It is characterized by being 3 to 14 times in terms of circulation magnification.

Fly ash circulation ratio = (circulated fly ash cut-off amount + fly ash emission amount) / fly ash emission amount The invention of claim 3 is the fly ash circulation type exhaust gas treatment method according to claim 1 or 2. The sodium-based chemical is sodium bicarbonate (NaHCO ₃ ), porous sodium carbonate (Na ₂ CO ₃ ) previously produced by thermally decomposing sodium bicarbonate, or sodium sesquicarbonate.

  Invention of Claim 4 is a fly ash circulation type exhaust gas processing method as described in any one of Claims 1-3, Comprising: A filter aid with a sodium-type chemical | medical agent in the exhaust gas flue of the bag filter entrance side It is characterized by introducing.

  The invention of claim 5 is the fly ash circulation type exhaust gas treatment method according to claim 4, wherein the filter aid is activated carbon, and in addition to supplying sodium-based chemicals to the exhaust gas flue on the bag filter inlet side. In addition, activated carbon powder is blown, and part of the bag filter fly ash is returned to the flue gas flue on the bag filter inlet side, so that removal of acid gas and dioxins and mercury are simultaneously advanced. .

  The invention of the fly ash circulation type exhaust gas treatment method of claim 1 uses a sodium-based chemical as a chemical for removing acid gas contained in the exhaust gas, and injects the sodium-based chemical into the exhaust gas flue on the bag filter inlet side, Is a dry exhaust gas treatment method in which a salt is formed by a reaction between an acid gas and a sodium-based chemical, and fly ash containing the salt is collected and removed by a bag filter, and the fly ash ( Take out the dust in the exhaust gas + reaction product of sodium chemical and acid gas + unreacted sodium chemical) from the bottom of the bag filter, and return a part of this bag filter fly ash to the exhaust flue on the bag filter inlet side According to the invention of claim 1, the sodium-based agent made of sodium bicarbonate or the like introduced into the flue is converted into porous and highly reactive sodium carbonate. Unreacted sodium-based chemicals that could not react with the acid gas can be used more efficiently, and at a very small sodium-based chemical blowing equivalent ratio, such as hydrogen chloride and sulfur oxides at the bag filter outlet The concentration of the acid gas can be stably lowered to a low level, and the acid gas removal efficiency can be drastically improved.

  In addition, according to the invention of claim 1, compared to the dry exhaust gas treatment using conventional baking soda, both the amount of sodium bicarbonate used and the chemical cost can be reduced by about 20%, and the fly ash disposal amount is For example, compared to dry exhaust gas treatment using slaked lime, there is a reduction effect of about 30% or more, and it is possible to contribute to prolonging the life of a tight final disposal site.

Furthermore, according to the invention of claim 1, since it is possible to achieve the acidic gas removal performance of harmful gases similar to the conventional wet smoke cleaning device, it can contribute to the prevention of global warming from the improvement of power generation efficiency and CO ₂ reduction effect. It is advantageous in that an economical and compact high-performance dry exhaust gas treatment device can be provided.

  The invention of claim 2 is the fly ash circulation type exhaust gas treatment method of claim 1, wherein the fly ash circulating amount of bag filter fly ash returned to the flue gas flue on the bag filter inlet side is represented by the following formula: Expressed by the circulation magnification, it is 3 to 14 times.

Fly ash circulation ratio = (Circulated fly ash cutout amount + discharge amount outside fly ash system) / Exhaust fly ash system discharge amount According to the invention of claim 2, the fly ash circulation ratio is 3 times or more, preferably 3-14. By controlling it twice, sodium-based chemicals such as sodium bicarbonate introduced into the flue are almost completely converted to porous and highly reactive sodium carbonate, and sodium-based chemicals that could not react completely with acid gas. Unreacted components can be used more efficiently, and the concentration of acidic gases such as hydrogen chloride and sulfur oxides at the bag filter outlet can be stably reduced to a low level with an extremely small sodium chemical blowing equivalent ratio. And the acid gas removal efficiency can be dramatically improved.

In the fly ash circulation type exhaust gas treatment method according to the first or second aspect of the present invention, the sodium-based chemical is sodium bicarbonate (NaHCO ₃ ), porous sodium carbonate (Na ₃ ) previously produced by thermally decomposing sodium bicarbonate. ₂ CO ₃ ) or sodium sesquicarbonate is preferable.

  Invention of Claim 4 is a fly ash circulation type exhaust gas processing method as described in any one of Claims 1-3, Comprising: A filter aid with a sodium-type chemical | medical agent in the exhaust gas flue of the bag filter entrance side According to the invention of claim 4, the addition of the filter aid generally reduces the pressure loss of the fly ash cake layer deposited on the filter cloth surface of the bag filter and the flying by the pulse. There is an effect that the ash cake layer is more effectively removed.

  The invention of claim 5 is the fly ash circulation type exhaust gas treatment method according to claim 4, wherein the filter aid is activated carbon, and in addition to supplying sodium-based chemicals to the exhaust gas flue on the bag filter inlet side. In addition, activated carbon powder is blown and part of the bag filter fly ash is returned to the flue gas flue on the bag filter inlet side, so that removal of acid gas and dioxins and mercury can proceed simultaneously. Therefore, according to the invention of claim 5, when activated carbon powder is blown in addition to the supply of sodium-based chemicals such as baking soda, dioxins and mercury are simultaneously removed due to the circulation effect of fly ash, and there is little activated carbon. Since it is removed to a very low concentration by the input amount, there is an effect that it is possible to easily comply with strict exhaust gas treatment standards without adding a special removal device.

It is a flow sheet which shows the specific example of the apparatus which enforces the fly ash circulation type exhaust gas processing method of this invention. In the Example of the fly ash circulation type exhaust gas processing method of this invention, it is a graph which shows the relationship between desalination performance and an equivalence ratio. In the Example of the fly ash circulation type exhaust gas processing method of this invention, it is a graph which shows the relationship between desulfurization performance and an equivalence ratio. It is a graph which shows the time-dependent change of the hydrogen chloride density | concentration and sulfur dioxide density | concentration in the entrance / exit of a bag filter in the Example of the fly ash circulation type exhaust gas processing method of this invention. It is a flow sheet which shows another specific example of the apparatus which enforces the fly ash circulation type exhaust gas processing method of the present invention.

  Next, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

  FIG. 1 is a flow sheet showing a specific example of an apparatus for carrying out a fly ash circulation type exhaust gas treatment method according to the present invention.

  Referring to the figure, the fly ash circulation type exhaust gas treatment method according to the present invention is, for example, hydrogen chloride, sulfur contained in exhaust gas discharged from waste treatment facilities such as a garbage incinerator, gasification melting furnace and industrial waste incinerator. An exhaust gas treatment method for removing acidic gas such as oxides and detoxifying exhaust gas released into the atmosphere, and using sodium-based chemicals such as baking soda as a chemical for removing acidic gas contained in exhaust gas The sodium-based chemical is introduced into the flue gas flue (1) on the bag filter inlet side, a salt is formed by the reaction between the acidic gas and the sodium-based chemical in the exhaust gas, and the fly ash containing the salt is removed from the bag filter (2 This is a so-called dry exhaust gas treatment method that collects and removes by the above method.

  And the fly ash circulation type exhaust gas treatment method according to the present invention uses fly ash (dust in the exhaust gas + reaction product of sodium-based chemical and acid gas + unreacted sodium-based chemical) collected by the bag filter (2). The bag filter (2) is taken out from the bottom and a part of the bag filter (BF) fly ash is returned to the exhaust gas flue (1) on the bag filter inlet side.

  In the embodiment shown in FIG. 1, the exhaust gas after desalting and desulfurization was used as a carrier gas for the circulation of fly ash.

  Here, the circulation amount of the bag filter fly ash returned to the flue gas flue (1) on the bag filter (2) inlet side is represented by the fly ash circulation magnification represented by the following formula and is 3 to 14 times. preferable.

Fly ash circulation ratio = (circulated fly ash cutout + fly ash system discharge) / fly ash system discharge A fly ash circulation exhaust gas treatment method according to the present invention also includes an exhaust flue on the bag filter inlet side. It is preferable to add a filter aid together with the sodium-based drug.

  Hereinafter, the fly ash circulation type exhaust gas treatment method according to the present invention will be described in detail.

  In FIG. 1, flue (1) of exhaust gas containing soot discharged from a waste treatment facility such as a waste incinerator or a gasification melting furnace and acid gases such as hydrogen chloride and sulfur oxide is a bag filter (2 )It is connected to the. The flue gas flue (1) on the bag filter inlet side is connected with a chemical / filter aid introduction pipe (3) for introducing a sodium-based chemical and a filter aid. The proximal end of the introduction pipe (3) is connected to a sodium-based chemical heating burner (4), and the intermediate part of the introduction pipe (3) is provided with a filter aid supply device (5) and a chemical downstream thereof. A supply device (6) is provided, and a drug / filter aid supply fan (7) is interposed downstream of the drug supply device (6).

In the exhaust gas treatment method according to the present invention, for example, sodium bicarbonate (NaHCO ₃ ) or porous sodium carbonate (Na ₂ CO ₃ ) previously produced by thermally decomposing sodium bicarbonate is used as an agent for removing acidic gas contained in the exhaust gas. Furthermore, sodium-based drugs such as sodium sesquicarbonate are used.

When the acid gas removal agent is, for example, baking soda (NaHCO ₃ ), the particle size of the fly ash is not limited, but baking soda is preferable in terms of removal performance. In the case where the circulation method is not adopted conventionally, there is a method of using an anti-caking agent when the pulverized diameter of the baking soda is 10 μm or less. In either case, circulation of fly ash can be employed.

  The filter aid may be used for general exhaust gas treatment, and examples thereof include particles having a high porosity such as diatomaceous earth and zeolite, perlite, Tesisorb, and Shirasu balloon. When high efficiency removal of mercury and dioxins is required, a filter aid containing activated carbon is used.

  Then, the sodium chemical agent and the filter aid are blown into the exhaust gas flow in the exhaust gas flue (1) on the bag filter inlet side by the operation of the supply fan (7).

Thus, when the sodium-based chemical and the above-mentioned filter aid are blown into the exhaust gas flue (1), thermal decomposition of the sodium-based chemical occurs in the bag filter (2), and at the same time the acidic gas (HCl, React with SOx). Here, when the sodium-based agent is, for example, sodium bicarbonate (NaHCO ₃ ), the reaction formula (2) of HCl and SO _{2 based on} the decomposition formula (1) of sodium bicarbonate and the produced sodium carbonate (Na ₂ CO ₃ ) And (3) is as follows.

Undecomposed baking soda and acid gas react directly, but the reactivity is low, so basically, the baking soda is thermally decomposed, and the porous and highly reactive sodium carbonate (Na ₂ CO ₃ ) produced It is reasonable to think that the main reaction is with acid gas.

2NaHCO ₃ → Na ₂ CO ₃ + H ₂ O + CO ₂ (1)
Na ₂ CO ₃ + 2HCl → 2NaCl + H ₂ O + CO ₂ (2)
Na ₂ CO ₃ + SO ₂ + 1 / 2O ₂ → Na ₂ SO ₄ + CO ₂ (3)
The decomposition of these baking sodas and the reaction with acid gas is mainly carried out on the filter cloth (cake layer) in the bag filter (2), and the fly ash that is periodically washed off is collected. Fly ash collected by the bag filter (2) contains dust in the exhaust gas, a reaction product of a sodium-based chemical and an acidic gas, an unreacted chemical, and a filter aid.

  Subsequently, the bag filter (hereinafter also referred to as BF) fly ash is taken out from the bottom of the bag filter (2) by the discharge conveyor (11), and further, the bag filter fly ash is sorted by the sorting conveyor (12). It introduce | transduces into a bag filter fly ash storage tank (14) from a flow pipe (13), and the remainder is discharged | emitted out of a system from a bag filter fly ash discharge pipe (15).

  The exhaust port (8) having been subjected to demineralization / desulfurization treatment is connected to the exhaust port at the upper part of the bag filter (2), and an intermediate portion of the exhaust gas discharge duct (8) having been subjected to demineralization / desulfurization treatment and the bag filter (2) Between the exhaust gas flue (1) on the exhaust gas introduction side, an exhaust gas circulation duct (9) after desalting and desulfurization treatment is provided, and a fly ash circulation fan (10) is interposed in the middle of the circulation duct (9). It has been.

  A circulation fly ash supply conveyor (16) is provided at the bottom of the bag filter fly ash storage tank (14). Bag filter fly ash is supplied into the circulation duct (9) on the downstream side of the fly ash circulation fan (10) of the exhaust gas circulation duct (9) subjected to the desalting / desulfurization treatment. As a result, a part of the desulfurized and desulfurized exhaust gas discharged from the bag filter (2) exhaust port is used as a carrier gas, and the bag filter (BF) fly ash is exhaust gas flue (1) on the bag filter (2) inlet side. ).

  As described above, the bag filter (BF) fly ash contains soot in exhaust gas, a reaction product of a sodium-based chemical and an acidic gas, an unreacted chemical, and a filter aid. According to the circulation type exhaust gas treatment method, sodium-based chemicals made of baking soda introduced into the exhaust gas flue (1) are converted into sodium carbonate almost completely porous and highly reactive. The unreacted content of the hydrogen gas can be used more efficiently, and an acidic gas such as hydrogen chloride (HCl) and sulfur oxide (SOx) at the outlet of the bag filter (2) can be obtained with a very low baking soda equivalent ratio. The concentration can be stably lowered to a low level, and the acid gas removal efficiency can be dramatically improved.

  Moreover, in the fly ash circulation type exhaust gas treatment method according to the present invention, the circulation amount of the bag filter fly ash returned to the exhaust gas flue (1) on the bag filter (2) inlet side is represented by the fly ash circulation magnification represented by the following formula. 3 times to 14 times is preferable.

Fly ash circulation ratio = (circulated fly ash cutout + fly ash system discharge) / fly ash system discharge: Thus, the circulation rate of bag filter fly ash is 3 to 14 in terms of fly ash circulation ratio. If it is double, as shown in the examples described later, sodium bicarbonate introduced into the flue gas flue (1) is converted into sodium carbonate, which is almost completely porous and highly reactive, and the acidity of the sodium-based drug Unreacted components with gas can be used more efficiently, and the concentration of acidic gases such as hydrogen chloride and sulfur oxides at the bag filter (2) outlet can be stably reduced with an extremely small equivalent ratio. The level can be lowered to, for example, 5 ppm or less, and the acid gas removal efficiency can be dramatically improved.

  Here, in the method of the present invention using a part of the bag filter (2) outlet exhaust gas, that is, desalted / desulfurized exhaust gas, as the carrier gas for circulating fly ash, BF fly ash discharged from the bag filter (2) The switching between the fly ash storage tank (14) side and the external discharge pipe (15) side is switched by the ratio of the number of pulses of the bag filter (2) or the ratio of the elapsed time, and in the fly ash storage tank (14). It is preferable to adjust the amount of fly ash circulation by adjusting the extraction of the bag filter fly ash so that the level of the bag filter fly ash becomes constant. Moreover, it is preferable that the circulation fly ash supply conveyor (16) controls the rotation speed by an inverter so that the weight of the fly ash storage tank (14) becomes constant.

  In this method, for example, when the ratio of the fly ash storage tank (14) side to the extra-system discharge pipe (15) side is set to 6: 1, the fly ash circulation magnification calculated by the above formula becomes 7 times. .

  In addition, before the bag filter (2), a sodium-based chemical reaction tower (not shown) that forms a salt by reacting an acidic gas such as hydrogen chloride or sulfur oxide contained in the exhaust gas with a sodium-based chemical or a temperature reduction When installing a tower (not shown), the BF fly ash removed by the bag filter (2) is returned to the flue gas flue (1) in front of the sodium-based chemical reaction tower. Circulation may be performed.

  Further, in the embodiment of FIG. 1, a part of the demineralized / desulfurized exhaust gas exhaust duct (8) connected to the exhaust port on the upper part of the bag filter (2) is a part of the exhaust gas. Is used to return bag filter (BF) fly ash as carrier gas to the flue gas flue (1) on the bag filter (2) inlet side. After being sent to the other equipment (17) and subjected to the necessary purification treatment, it is discharged from the existing chimney to the atmosphere by the operation of the induction fan (18).

  FIG. 5 is a flow sheet showing another specific example of an apparatus for carrying out the fly ash circulation type exhaust gas treatment method of the present invention, showing a specific example using air as a carrier gas for the circulation of fly ash. It is.

  As shown in the figure, fly ash does not show solidification, aggregation, wetness, etc., so there is no problem even if air is used for fly ash circulation. Depending on the method, a method such as heating the air may be employed.

  When air or other gas is used as the carrier gas for fly ash circulation, or when fly ash is circulated by a mechanical method, desalination / desulfurization treatment connected to the exhaust port at the top of the bag filter (2) has been completed. The desulfurized and desulfurized exhaust gas discharged from the exhaust gas exhaust duct (8) is all sent to other facilities (17) such as a denitration facility, and after necessary purification treatment is performed, an induction fan (18 ) Is released from the existing chimney to the atmosphere.

  Next, examples of the present invention will be described together with comparative examples, but the present invention is not limited to these examples.

Example 1
The method of the present invention was carried out by the apparatus for carrying out the fly ash circulation type exhaust gas treatment method of the present invention shown in FIG.

By removing acidic gases such as hydrogen chloride (HCl) and sulfur oxide (SOx) contained in the exhaust gas at a flow rate of 2500 m ³ N / h discharged from the boiler outlet of the incinerator and a temperature of about 190 ° C. In order to detoxify the exhaust gas discharged into the exhaust gas, sodium bicarbonate (NaHCO ₃ ) (sodium-based chemical) is used as a chemical for removing acid gas contained in the exhaust gas, and the flue gas flue at the bag filter (BF) inlet side (1) Sodium bicarbonate was added to the mixture, salt was formed by the reaction between the acidic gas in the exhaust gas and sodium bicarbonate, and fly ash containing the salt was collected by a bag filter (BF) (2).

Here, sodium bicarbonate (NaHCO ₃ ) (trade name: Briskarb Premium 20, Brunner Mond) having an average particle size of 17 μm was used as the agent for removing acid gas.

  Moreover, the filter aid was put into the exhaust gas flue (1) on the bag filter (BF) inlet side together with the sodium-based chemical. Here, diatomaceous earth or the like (trade name Bag Ace S, manufactured by Hitachi Zosen) or a diatomaceous earth + activated carbon-based agent (trade name Bag Ace E, manufactured by Hitachi Zosen) was used as a filter aid.

When sodium chemical agent made of baking soda (NaHCO ₃ ) and the above-mentioned filter aid are blown into the flue gas flue (1), pyrolysis of sodium bicarbonate (1) and in the exhaust gas mainly on the filter cloth in the bag filter Reactions (2) and (3) with the acidic gas (HCl, SOx) occur simultaneously. The decomposition and reaction equations are as follows.

2NaHCO ₃ → Na ₂ CO ₃ + H ₂ O + CO ₂ (1)
Na ₂ CO ₃ + 2HCl → 2NaCl + H ₂ O + CO ₂ (2)
Na ₂ CO ₃ + SO ₂ + 1 / 2O ₂ → Na ₂ SO ₄ + CO ₂ (3)
Fly ash collected by the bag filter (2) is periodically removed, and the fly ash contains dust in the gas, reaction product of baking soda and acid gas, unreacted chemicals, and filter aid. It was.

  Next, the bag filter (BF) fly ash is taken out from the bottom of the bag filter (2) by the discharge conveyor (11), and further the bag filter fly ash is sorted by the sorting conveyor (12). 13) was introduced into the fly ash storage tank (14), and the remainder was discharged out of the system through the discharge pipe (15).

  The exhaust port (8) having been subjected to demineralization / desulfurization treatment is connected to the exhaust port at the upper part of the bag filter (2), and an intermediate portion of the exhaust gas discharge duct (8) having been subjected to demineralization / desulfurization treatment and the bag filter (2) Between the exhaust gas flue (1) on the exhaust gas introduction side, an exhaust gas circulation duct (9) after desalting and desulfurization treatment is provided, and a fly ash circulation fan (10) is interposed in the middle of the circulation duct (9). It has been.

  A circulation fly ash supply conveyor (16) is provided at the bottom of the bag filter fly ash storage tank (14). Bag filter fly ash was supplied into the circulation duct (9) on the downstream side of the fly ash circulation fan (10) of the exhaust gas circulation duct (9) subjected to the desalting / desulfurization treatment. As a result, a part of the desulfurized and desulfurized exhaust gas discharged from the bag filter (2) exhaust port is used as a carrier gas, and the bag filter (BF) fly ash is exhaust gas flue (1) on the bag filter (2) inlet side. ).

FIG. 2 shows the circulation amount of the bag filter fly ash returned to the flue gas flue (1) on the bag filter (2) inlet side, expressed by the fly ash circulation magnification represented by the following formula, and is 1 time (fly ash circulation). None) A graph showing the relationship between the demineralization performance and the equivalent ratio when changed to 3 times, 7 times, and 14 times is shown, and FIG. 3 is also a graph showing the relationship between the desulfurization performance and the equivalent ratio. In addition, when a fly ash circulation magnification is 1 time (no fly ash circulation), it will be a comparative example.

Fly ash circulation ratio = (circulated fly ash cutout + fly ash system discharge) / fly ash system discharge Here, the equivalence ratio is the amount by which hydrogen chloride (HCl) and sulfur oxide (SOx) react. It is the ratio of the amount of the drug actually supplied to the total amount of the sodium-based drug.

  Regarding the fly ash discharged from the bag filter (2), switching between the fly ash storage tank (14) side and the external discharge pipe (15) side is switched according to the ratio of the pulse frequency of the bag filter (2), The amount of fly ash circulation was adjusted by adjusting the cut out of the bag filter fly ash so that the level of the bag filter fly ash in the fly ash storage tank (14) was constant. Specifically, the pulse interval of the bag filter (2) was set to 20 minutes, and was distributed between the fly ash storage tank (14) side and the external discharge pipe (15) side (external discharge side) according to the number of pulses. In addition, the circulation fly ash supply conveyor (16) was controlled by the inverter so that the weight of the fly ash storage tank (14) was constant.

  As can be seen from the results of FIG. 2 and FIG. 3, when the fly ash circulation ratio was 3 times, the desalting / desulfurization rate was slightly improved as compared with the condition without circulation. In addition, when the fly ash circulation ratio was 7 times or more, a great improvement effect was seen particularly in the desulfurization performance. However, when the fly ash circulation rate is 14 times, the desalination / desulfurization rate is not so greatly improved compared to when the fly ash circulation rate is 7 times. The ash circulation magnification is preferably 3 to 14 times.

Example 2
As sodium-based chemicals, baking soda having an average particle size of 13 μm is used, the fly ash circulation magnification is 7 times, and the other conditions are the same as in Example 1, and the fly ash circulation type exhaust gas treatment method of the present invention is used. Desalination / desulfurization performance was measured.

  FIG. 4 shows a graph showing changes over time in the hydrogen chloride (HCl) concentration and the sulfur oxide (SOx) concentration at the inlet / outlet of the bag filter (2) at a fly ash circulation ratio of seven.

  As can be seen from the results in the figure, when the equivalence ratio is 1.05, the HCl concentration and SOx concentration at the outlet of the bag filter (2) are stable at 2 ppm or less, and the removal rates are extremely high, 99% and 95%, respectively. High removal performance was obtained. In the aforementioned Non-Patent Document 1, when the equivalence ratio is 1.2, the removal rates of HCl and SOx are 98% and 90%, respectively, and when the equivalence ratio is 1.3, both the outlet concentrations of HCl and SOx are both Compared with what was 10 ppm or less, it has confirmed that the performance improved dramatically.

  When the bag filter fly ash is circulated by the method of the present invention, undecomposed at the entrance of the bag filter (2) is returned together with the bag filter fly ash in addition to the newly supplied sodium-based chemical (bicarbonate). Of sodium bicarbonate, which is pyrolyzed on the filter cloth in the bag filter and converted to porous and highly reactive sodium carbonate, and sodium carbonate that could not react with acid gas is also circulated. Therefore, it is considered that both the HCL and SOx outlet concentrations are stable at 2 ppm or less at a low equivalent ratio even when the inlet concentration varies greatly in the short term.

  The present inventors almost completely converted the sodium-based drug consisting of sodium bicarbonate introduced into the flue into porous and highly reactive sodium carbonate, and yet the sodium-based drug that could not react with the acid gas had not yet been converted. Fly ash collected by a bag filter (soot dust in exhaust gas + reaction product of sodium chemical and acid gas + unreacted chemical (including undecomposed baking soda)) + filtration Auxiliary agent) is taken out from the bottom of the bag filter, and a part of the bag filter fly ash is returned to the flue gas flue on the bag filter inlet side to circulate unreacted chemicals. It was found that the concentration of acidic gases such as hydrogen chloride and sulfur oxide at the bag filter outlet can be dramatically and stably reduced.

  FIGS. 2 to 4 show an example of the acid gas removal performance. However, when the fly ash is circulated, the removal performance is dramatically improved compared to the case where the fly ash is not circulated. In particular, very high removal performance has been confirmed even when the blowing equivalent ratio of baking soda is low at around 1 equivalent. This is due to the circulation of fly ash, which is due to the porous carbon dioxide in which most of the undecomposed baking soda is highly reactive. The effect of being converted to soda is large, and is due to new knowledge and inventions.

  In other words, bag filters are used in the exhaust gas treatment using baking soda, but the introduced baking soda accumulates on the filter cloth of the bag filter, and the reaction between pyrolysis and acid gas proceeds. It is a system in which dust is periodically removed every time. However, as described above, baking soda is almost completely pyrolyzed and converted to highly reactive sodium carbonate, which depends on the temperature conditions and the particle size of the drug, but it takes several tens of seconds to several minutes. It can be said that some baking soda is highly likely to be removed by the bag filter without thermal decomposition. In particular, since baking soda is continuously blown, it can be said that baking soda blown immediately before the bag filter is wiped out has a short thermal decomposition time. Therefore, the circulation of fly ash solves this problem.

  In various tests based on this circulation effect, by controlling the circulation rate of bag filter fly ash at 3 times or more, preferably 3 to 14 times, the acid gas removal efficiency is drastically reduced at an extremely low equivalent ratio. The present inventors have found that it can be improved and have completed the present invention.

  In addition, according to the present invention, compared to the conventional dry exhaust gas treatment using baking soda, both the amount of sodium bicarbonate used and the chemical cost can be reduced by about 20%, and the amount of fly ash disposal is, for example, slaked lime. Compared to the dry exhaust gas treatment used, there is a reduction effect of about 30% or more, which can contribute to the extension of the life of the final disposal site.

Furthermore, according to the present invention, the acid gas removal performance of harmful gases wet Araikemuri device comparable, for example HCl, and SOx both 5ppm or less, so can be achieved, the increase and CO ₂ reduction of power generation efficiency, global warming The present invention can provide an economical and compact high-performance dry-type exhaust gas treatment apparatus, and the effect of the present invention is great.

Example 3
In the fly ash circulation type exhaust gas treatment according to the present invention, sodium bicarbonate as a sodium chemical is used, and dioxins and mercury are removed by mixing activated carbon with a filter aid and supplying it to the bag filter. It was confirmed. The fly ash circulation magnification was 7 times, and other test conditions were the same as in Example 1. Table 1 below shows the removal performance of dioxins.

As can be seen from the results in Table 1, the dioxin (DXN) removal rate is 81 to 83 in the case where activated carbon is not added and the fly ash is not circulated (Experiment No. 1) and is circulated (Experiment No. 2). When the bag filter inlet dioxin concentration is high, for example, in the case of inlet DXN1.58 (ng-TEQ / m ³ N), the outlet concentration is 0.26 (ng-TEQ / m ^3). N), exceeding the strict national standards of 0.1 (ng-TEQ / m ³ N).

On the other hand, when activated carbon was blown in 30 (mg / m ³ N) and fly ash was circulated (Experiment No. 3), the DXN outlet concentration was reduced to 0.0028 (ng-TEQ / m ³ N). The removal rate of 99.6% is achieved with high efficiency. DXN may be re-synthesized when the operating temperature of bag filters, etc. is high, but this effect is small at 190 ° C, which is the test condition. Even with a small amount of activated carbon, high removal performance is maintained.

Next, the removal performance of mercury is shown in Table 2 below.

  As can be seen from the results in Table 2 above, in the case where activated carbon was not added, the mercury removal rate was 52.5 with no circulation of fly ash (Experiment No. 1) and with circulation (Experiment No. 2), respectively. %, 65.9-68.2%, the performance improved by about 15% when circulating. Adsorbents close to activated carbon components such as unburned carbon exist in the fly ash, and the effect of circulation was confirmed.

On the other hand, when activated carbon 30 (mg / m ³ N) was added and circulated (Experiment No. 3), the mercury removal rate improved to 94.5%. Recently, mercury has been seen as a problem in waste incinerators, and this removal is required. However, even with a small amount of activated carbon input, high removal performance was achieved even at high temperatures. It can be judged as a circulation effect.

  As can be seen from the results in Table 1 and Table 2 above, when activated carbon powder is blown in addition to the supply of baking soda, the removal of dioxins and mercury proceeds simultaneously due to the circulation effect of fly ash, and the amount of activated carbon input is small. Therefore, it is possible to easily comply with strict exhaust gas treatment standards without adding a special removal device.

Example 4
In the fly ash circulation type exhaust gas treatment method according to the present invention, in order to confirm the influence of pressure loss in the bag filter when sodium bicarbonate (NaHCO ₃ ) which is a sodium-based chemical is used and the fly ash is circulated, The test was conducted.

  As in the case of Example 1 above, baking soda is introduced into the flue gas flue (1) on the bag filter (BF) inlet side, a salt is formed by the reaction of the acidic gas and baking soda in the exhaust gas, and the salt is contained. Fly ash was collected by a bag filter (BF) (2). Moreover, the filter aid which consists of diatomaceous earth etc. with the sodium bicarbonate was injected | thrown-in to the exhaust gas flue (1) of the bag filter (BF) entrance side. The fly ash collected by the bug filter (2) was periodically removed. The bag filter fly ash circulation amount returned to the exhaust gas flue (1) on the bag filter (2) inlet side is represented by the fly ash circulation magnification represented by the above formula, and is 1 time (no fly ash circulation), 3 The test was carried out by changing the magnification by 7 times, 7 times, and 14 times.

Table 3 below shows fly ash circulation magnification, exhaust gas amount (wetness) [m ³ N / h], bag filter temperature [° C.], bag filter inlet HCl concentration (oxygen 12% conversion) [ppm], bag filter inlet SOx Concentration (oxygen 12% conversion) [ppm], fly ash removal interval [min], and pressure loss (ΔP _{BF (t)} ) (average value) [Pa] at the bag filter are collectively shown.

As can be seen from the results in Table 3 above, the pressure loss increases as the fly ash circulation magnification increases, but the relationship is not directly proportional to the circulation magnification. The pressure loss between the bag filter inlet and outlet is approximately expressed by the resistance coefficient (ζ) of the filter cloth and the resistance coefficient (α) of the cake layer (powder accumulation layer), and is calculated by the following equation (1). [Furubayashi, Nagai; Estimation of dioxin removal performance by activated carbon, from Chemical Engineering Papers, 30, 54-64 (2004)].

Here, ΔP _{BF (t)} is the pressure loss [kPa] of BF at the gas passage time t, ζ is the resistance coefficient of the filter cloth [(min / m) ^1.32 / s], and α is the cake layer ( (Powder accumulation layer) resistance coefficient [(m ² / kg) · (min / m) ^1.32 / s], m _{D (t, i)} is the powder of the i-th filter cloth row at the gas passing time t The body deposition amount [kg / m ² ], μ _G is the gas viscosity [Pa · s], and u _{F (t, i)} is the filtration rate [m / min] of the i-th filter cloth row at the gas passing time t. , N represents the number of filter cloth rows [-], respectively.

The u _F value, m _D value, and ΔP _BF value at the gas passing time t are calculated as follows, as shown in the above paper. That is, the calculation was performed by repeatedly calculating the above formula (1) and the following formula (2), formula (3), and formula (4) from i = 1 to N.

Here, said Formula (1) is based on the relationship that (DELTA) _PBF value of each filter cloth row | line | column is all equal. Equation (2) below shows the relationship between the average filtration rate and the u _F value in each filter cloth row. Using these equations were first calculated u _F value in a flow-through gas time t.

Then, the following equation (3), between the passage gas hourly t~t + Δt is regarded as a u _F value constant, calculates the powder deposition amount of increase in the filter cloth column during this period, further the following equation The m _D value was calculated from (4).

Thus using the u _F value and m _D value obtained to determine the resistance coefficient of the resistance coefficient ζ and the cake layer of the filter cloth to match the pressure drop characteristics of the Verification (powder deposition layer) alpha.

Here, _{u F} (average), the average filtration rate [m / _{min], A BF} represents a total filtration area of the fabric braze installed in the bag filter ^{[m 2].}

Table 4 below shows the fly ash circulation magnification, the resistance coefficient (ζ) of the filter cloth calculated using the above formula, and the resistance coefficient (α) of the cake layer (powder deposition layer).

As can be seen from the results of Table 4 above, the resistance coefficient (ζ) of the filter cloth is an eigenvalue and was constant at 1.6 × 10 ⁷ regardless of the circulation magnification, but the cake layer (powder deposition layer) The resistance coefficient (α) of the ash decreased as the fly ash circulation magnification increased from 1 (Experiment No. 1) to 14 (Experiment No. 4).

  From this, it is considered that secondary flocculation of fly ash occurs by repeating the fly ash circulation, and is apparently deposited on the filter cloth in a state where the particle diameter is increased.

1: exhaust gas flue 2: bag filter 3: drug / filter aid introduction pipe 4: sodium-based drug heating burner 5: filter aid supply device 6: drug supply device 7: drug / filter aid supply fan 8: desalting Desulfurized exhaust gas exhaust duct 9: Desalted and desulfurized exhaust gas circulation duct 10: Fly ash circulation fan 11: Fly ash discharge conveyor 12: Sorting conveyor 13: Bag filter fly ash flow pipe 14: Bag filter fly ash storage tank 15: Bag filter fly ash discharge pipe 16: Circulating fly ash supply conveyor

Claims (5)

A sodium-based chemical is used as a chemical for removing acid gas contained in the exhaust gas, and the sodium-based chemical is introduced into the exhaust gas flue on the bag filter inlet side to form a salt by the reaction between the acidic gas in the exhaust gas and the sodium-based chemical. , A dry exhaust gas treatment method for collecting and removing fly ash containing the salt with a bag filter,
Remove fly ash (dust in exhaust gas + reaction product of sodium chemical and acid gas + unreacted sodium chemical) collected from the bag filter from the bottom of the bug filter, A fly ash circulation type exhaust gas treatment method characterized by returning to the flue gas flue at the bag filter inlet side. The amount of circulation of bag filter fly ash returned to the flue gas flue on the bag filter inlet side is represented by the fly ash circulation magnification represented by the following formula, and is 3 to 14 times. Ash circulation type exhaust gas treatment method.
Fly ash circulation rate = (circulated fly ash cutout + fly ash system discharge) / fly ash system discharge The sodium-based agent is sodium bicarbonate (NaHCO ₃ ), porous sodium carbonate (Na ₂ CO ₃ ) previously produced by thermally decomposing sodium bicarbonate, or sodium sesquicarbonate, wherein: The fly ash circulation type exhaust gas treatment method described in 1.   The fly ash circulation type exhaust gas treatment method according to any one of claims 1 to 3, wherein a filter aid is introduced together with a sodium-based chemical into the flue gas flue on the bag filter inlet side.   The filter aid is activated carbon. In addition to supplying sodium-based chemicals to the flue gas flue on the bag filter inlet side, activated carbon powder is blown into the flue gas flue on the bag filter inlet side. 5. The fly ash circulation type exhaust gas treatment method according to claim 4, wherein the removal of acid gas and the removal of dioxins and mercury are simultaneously advanced by returning to step (5).

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