TWI412400B - Removal device of trace and harmful substances in exhaust gas and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a long-term stable and highly reliable removal apparatus of trace harmful substances in exhaust gas, and its operation method. <P>SOLUTION: The removal apparatus of trace harmful substances in exhaust gas is disposed with; a denitration device equipped with a denitration catalyst layer having a function of removing nitrogen oxide in exhaust gas in order from the upstream side to oxidize metallic mercury, in an exhaust gas flow channel discharged from a combustion facility; an air preheater for heat-exchanging air for combustion of the combustion facility to exhaust gas; a dust removal device having a bag filter containing oxidation catalysts for metallic mercury; and a desulfurization device for removing sulfur oxide in exhaust gas. The bag filter may be disposed in front of the desulfurization device. <P>COPYRIGHT: (C)2006,JPO&amp;NCIPI

Description

Removal device for trace harmful substances in exhaust gas and operation method thereof

The invention relates to a trace harmful substance contained in a combustion exhaust gas of petroleum or coal, in particular, a metal mercury compound removing device and a running method thereof, which are also stable after long-term use, and can effectively remove trace amounts of exhaust gas of metal mercury compound A device for removing harmful substances and a method for operating the same.

Using the exhaust gas from a combustion equipment like the boiler petroleum or coal etc., in addition to photochemical smog or acid rain reasons of substance of nitrogen oxides (NO _X) or sulfur oxide (SO _X) other than the metal containing trace amounts of toxic substances Heavy metal compounds such as mercury. As an effective method for removal of NO _X by the Department of ammonia (NH ₃₎ or the like as a reducing agent selective catalytic reduction of the exhaust gas denitration method, in thermal power plants as the center, it is widely used. For the catalyst, mainly using vanadium (V), molybdenum (Mo) or tungsten (W) as the active ingredient, titanium oxide (TiO ₂ ) as the carrier, especially vanadium as the active ingredient, not only high activity In addition, the deterioration of the impurities contained in the exhaust gas is small, and it can be used from a lower temperature, etc., and is now the mainstream of the denitration catalyst (JP-A-50-128681, etc.). Further, in general, the catalyst component is formed into a honeycomb or plate-like structure, and various manufacturing methods for the invention are invented.

On the other hand, with respect to the exhaust gas from the combustion equipment for removing SO _x, because limestone paste, wet desulfurization apparatus for absorbing and removing the SO _x in the exhaust gas, the desulfurizing efficiency can be achieved, so that desulfurization mainstream. A semi-dry desulfurization apparatus using lime or magnesium hydroxide ((Mg)OH ₂ ) as an absorbent is proposed. The desulfurization method using the semi-dry desulfurization device described above directly sprays an absorbent such as limestone into the exhaust gas in the exhaust gas flow path on the upstream side of the dust removing device, and sprays the exhaust gas flow path or the dust removing device for a predetermined time. The method of removing SO _{X in} the exhaust gas. Although this method is not suitable for high-efficiency desulfurization, it has the economic advantage of low equipment cost.

On the other hand, in recent years, there has been an increase in the action of reducing the discharge of metallic mercury compounds present in petroleum or coal combustion exhaust gas. Once the metal mercury compound is discharged into the atmosphere, the food chain also has a great impact on the human body. A trace amount of harmful substances such as metal mercury brought in by petroleum or coal, and the gasification component is moved to the exhaust gas by combustion. It is generally considered that the metal mercury is discharged in the combustion range near 1500 ° C in gaseous metal mercury, but it is confirmed that the exhaust gas flow path is in a relatively low temperature range (300 to 450 ° C range), and the metal mercury is coexisting hydrogen chloride (HCl) as follows. (1) Partial oxidation to mercuric chloride (HgCl ₂ ). Further, it is known that the reaction is in a temperature range of about 300 ° C to 450 ° C and is promoted by a denitrification catalyst. Further, it is known that the reaction is carried out at a temperature of 300 ° C or lower, substantially completely toward the right, and the metal mercury is oxidized to mercury chloride.

_{Hg + HCl + 1 / 2O 2} = HgCl 2 + H 2 O (1)

It is known that mercury chloride (HgCl ₂ ) produced by the above reaction formula (1) has a lower vapor pressure than metal mercury, and is desorbed and removed by a dust removing device disposed on the downstream side of the exhaust gas flow path, and is easy to be water. The absorption is absorbed by the absorption liquid such as limestone paste of the wet desulfurization device, or absorbed by the spray absorbent of the semi-dry desulfurization device.

However, most of the unoxidized metal mercury is discharged directly from the chimney in a gaseous form (metal mercury vapor).

Therefore, as a technique for reducing the discharge amount of metal mercury, it is proposed to spray the activated carbon in the exhaust gas flow path on the upstream side of the dust removing device disposed in the low temperature range, and effectively remove the metal mercury by the adsorption effect or the catalytic effect of the activated carbon. The method (conventional technique 1), or the invention described in Japanese Laid-Open Patent Publication No. 2003-53142, wherein the heat exchange in the exhaust gas flow path of the denitration catalyst, the air preheater, the dust removing device, and the heat exchanger is sequentially disposed from the upstream side. a low temperature region (below 300 ° C) on the downstream side of the device, a solid oxidation catalyst layer is provided to oxidize the metal mercury, and then a wet desulfurization device is used to absorb and remove the absorption liquid (conventional technique 2), and further, the exhaust gas is contained. A filter cloth for a harmful substance is a method of using a filter bag for treating an exhaust gas which retains a metal mercury adsorbent (Japanese Laid-Open Patent Publication No. Hei 10-66814; conventional technique 5).

Patent Document 1: JP-A-2003-53142 Patent Document 2: Japanese Patent Publication No. Hei 10-66814

Invention disclosure

The above conventional techniques (1 to 3) have problems as described below.

That is, when the conventional technology 1 is applied to a combustion apparatus of a large-scale power generation facility, since the amount of process gas is increased, the amount of activated carbon used is extremely large, and continuous use of activated carbon is not economical and practical. In addition, a large amount of activated carbon is mixed into the dust captured by the dust removing device, so that dust treatment becomes difficult.

Further, although the conventional technique 2 focuses on the catalyst reaction of the above formula (1) at a low temperature, it is more efficient, but a new oxidation catalyst layer must be added to the exhaust gas treatment device already provided. Therefore, it is necessary to have a space for the arrangement of the oxidizing catalyst layer, which is not only disadvantageous in terms of cost, but if a new oxidizing catalyst layer is provided, it will greatly increase the ventilation resistance in the exhaust gas flow path. The induction fan must be placed in the exhaust gas flow path. Further, the presence of a large amount of the exhaust gas SO _x, as shown in Figure 3, significant deterioration of the catalyst by oxidation at low temperature, while the lack of long-term stability of the point.

In addition, the conventional technique 3 maintains the metal mercury adsorbent on the filter cloth, but when adsorbing the metal mercury, since the adsorption capacity of the adsorbent decreases with the use time and the adsorption amount is saturated, it is necessary to exchange the adsorbent in a short time, not only It is uneconomical, and the disposal cost of the filter cloth which adsorbs a large amount of metal mercury compounds becomes enormous.

An object of the present invention is to provide a device for removing trace harmful substances in exhaust gas having high reliability and long-term stability, and a method for operating the same, which overcomes the problems of the above-mentioned conventional techniques.

The invention described in claim 1 is an exhaust gas flow path discharged from a combustion apparatus for burning petroleum or coal, and an air preheater for exchanging heat between combustion air of the combustion equipment and the exhaust gas is sequentially disposed from the upstream side (6). And a device for removing trace harmful substances in the exhaust gas of the dust removing device (7) of the filter bag equipped with the filter cloth for carrying the metal oxide oxidizing catalyst.

The metal mercury component contained in the exhaust gas discharged from the combustion equipment (4) such as a boiler fueled by petroleum or coal is a combustion process of the above-mentioned fuel at a high temperature of about 1500 ° C, and the metal mercury compound present in the fuel is decomposed. Metallic mercury. The metal mercury in the above-mentioned exhaust gas varies depending on the fuel property, but is almost present as metal mercury vapor. When the metal mercury vapor discharged from the combustion equipment (4) such as a boiler is subjected to the exhaust gas purification treatment in the exhaust gas flow path, the temperature of the exhaust gas is lowered, and as the temperature is lowered, as shown in the above formula (1), the exhaust gas coexists in the exhaust gas. The hydrogen chloride (HCl) is partially oxidized to form mercury chloride (HgCl ₂ ).

This reaction is based on the thermodynamic equilibrium. The lower the temperature, the easier it is to proceed to the right side of the above reaction formula (1), and the residence time of the metal mercury vapor in the environment of 60 to 400 ° C is greatly affected. In addition, it is understood that the reaction is carried out at a temperature of 300 to 400 ° C, and is promoted by a denitration catalyst of a denitration device (5) constituting one of the exhaust gas treatment devices used, especially when the concentration of HCl in the exhaust gas is high. Promoted. Therefore, the metal mercury compound which is oxidized by the denitration catalyst and converted into HgCl ₂ or the like is adsorbed on one of the exhaust gas treatment devices disposed on the downstream side of the denitration device (5) in the exhaust gas flow path due to the characteristic. The surface of the dust in the dust removing device (7) and the adsorbent which is easily adsorbed to the lime paste or the like in the desulfurization device (8a, 8b).

Therefore, the exhaust gas treatment system for removing the oxidized metal mercury compound obtained by the machine on the downstream side of the denitration device (5) by the denitration catalyst in the denitration device (5) oxidizes the metal mercury, and removes the metal mercury compound in the exhaust gas. Effective means.

However, even if there is no denitration device (5) using the denitration catalyst in the equipment, it is also an effective means to provide only the filter bag carrying the catalyst to the exhaust gas flow path of the combustion device.

In the invention according to the first aspect of the invention, the oxidation function of the metal mercury is imparted to the filter bag itself, and the metal mercury is oxidized on the filter bag to be converted into a compound of mercury chloride, which is easily adsorbed to the dust, and The cloth is made of non-woven fabric, so the gas flow is disordered. It is not as simple as the normal solid oxidation catalyst (laminar flow). Even with low concentration of HCl and metallic mercury, high-efficiency metal mercury can be expected because of the high contact efficiency between HCl and metal mercury. Oxidation reaction.

Therefore, in the invention described in claim 1, the dust removing device (7) having the filter bag for carrying the metal oxide oxidizing catalyst is heat-exchanged by the air preheater (6), and is inefficiently contacted with a lower temperature. The exhaust gas is a structure suitable for oxidizing a low concentration of metallic mercury.

In the dust removing device (7) having the filter bag carrying the oxidation catalyst as disclosed in the first aspect of the invention, the denitration device (5) is provided on the upstream side, even if the denitration device (5) When the amount of leakage of NH ₃ is more markedly deteriorated over the years, the dust deposit layer formed on the surface of the filter bag filter cloth promotes the precipitation of fine pore blocking substances such as acidic ammonium sulfate which is precipitated at a low temperature because the filter cloth is contained. Since the oxidation of the metal mercury is deteriorated, it can be used for a long time (the dust accumulation layer formed on the surface of the filter bag filter cloth, and the acidic ammonium sulfate is precipitated because the ammonium sulfate does not reach the filter cloth to which the oxidation catalyst is attached, so The filter cloth pores are not blocked by ammonium sulfate).

In addition, in the conventional technique 3, the metal mercury adsorbed by the filter cloth is in the original metal state, and although the adsorption time of the filter cloth is decreased when the use time of the filter cloth is increased, the present invention described in the first aspect of the patent application is filtered. The oxidation catalyst contained in the bag converts the metal mercury into mercury chloride or the like, and since the mercury chloride or the like is easily separated from the filter cloth, the filter cloth is not clogged.

According to the invention of claim 1 of the invention, the trace amount of harmful substances contained in the exhaust gas discharged from the combustion device (4) for burning petroleum or coal can be stably settled for a long time, and oxidatively decomposed and efficiently removed. .

The invention of claim 2 is an exhaust gas flow path on the upstream side of the air preheater (6), and is equipped with a denitration catalyst layer having a function of removing nitrogen oxides in the exhaust gas and oxidizing metal mercury. The apparatus (5) is provided with a spray absorbent paste (absorption liquid such as limestone paste) on the exhaust gas flow path on the downstream side of the dust removing device (7), and a wet desulfurization device (8a) for removing sulfur oxides in the exhaust gas. The device for removing trace harmful substances in the exhaust gas of the first application of the patent scope is as follows.

The invention of claim 3 is applied to the exhaust gas flow path on the flow side before the air preheater (6), and is equipped with a denitration catalyst layer having a function of removing nitrogen oxides in the exhaust gas and oxidizing metal mercury. The device (5) is disposed in the exhaust gas flow path between the air preheater (6) and the dust removing device (7), and is provided with a spray absorbent paste (using slaked lime or magnesium hydroxide) in the exhaust gas passage to remove the exhaust gas. The semi-dry desulfurization device (8b) of the sulfur oxide is a device for removing trace harmful substances in the exhaust gas according to claim 1 of the patent application.

Further, the apparatus for removing a trace amount of harmful substances according to item 3 of the above patent application may further provide a wet type desulfurization apparatus (8a) on the downstream side of the semi-dry type desulfurization apparatus (8b).

However, in the United States, etc., most of the two types of coal are now used. These are EB coal (Eastern Bituminous) and PRB (Powder River Basin) coal. In particular, the PRB coal system has a large amount of reserves, which is also cheap, so it is expected that the amount of use will increase in the future. The above two coal systems have the following characteristics.

Since EB coal contains a high concentration of sulfur and chlorine, it is also characterized by a high concentration of SO _X and HCl in the combustion exhaust gas of the coal. In addition, PRB coal contains a very low concentration of chlorine, but because of its high ash concentration, it tends to adhere to the boiler wall.

Therefore, the exhaust gas treatment technology produced by the above two types of coal combustion is also carried out as generally the following steps.

EB coal: exhaust gas → denitrification → heat exchange → dust removal → wet desulfurization (high efficiency desulfurization) → chimney (a) PRB coal: exhaust gas → denitrification → heat exchange → semi-dry desulfurization (simple desulfurization) → Dust removal→chimney (b)

Further, in the above step (b), on the downstream side of the dust removing step, a wet desulfurization step may be further incorporated. The step (a) corresponds to the invention described in claim 2 of the present invention, and the step (b) corresponds to the invention described in claim 3 of the invention.

Regarding the above-mentioned removal of the metal mercury in the boiler exhaust gas, since the high concentration of HCl exists in the exhaust gas in the above step (a), it is relatively easy to use the oxidation catalyst contained in the denitration catalyst in the denitration step. The mercury chloride is recovered, but in the above step (b), since the concentration of HCl in the exhaust gas is low, the oxidation reaction of the denitration catalyst by the denitration step is difficult to occur. In particular, in the above step (b), how to effectively remove the technically most important thing in the metal mercury system.

The invention described in the second and third aspects of the application of the present invention removes metallic mercury in the exhaust gas as follows.

The metal mercury is converted into mercuric chloride by the oxidation, and the mercuric chloride is adsorbed to the dust particles, but in the above step (a) of the second paragraph of the corresponding patent application, as described above, the concentration of HCl in the exhaust gas is relatively high. Since the temperature conditions are also the same, the rightward reaction of the above (1) is promoted in the denitration device (5), and more oxidation products of the metal mercury are obtained as compared with the above step (b). Therefore, the unreacted metal mercury is oxidized by the filter bag carrying the oxidation catalyst of the metal mercury, and a part is removed by the filter bag, and further, the metal mercury flowing from the downstream side of the exhaust gas flow path of the filter bag is made. The oxidation product is removed by a method of absorbing the absorption liquid in the wet desulfurization apparatus (8a).

That is, since the above step (a) can treat the exhaust gas passing through the wet desulfurization device (8a), the denitration device (5) and the dust removal device (7), the high concentration of HCl in the exhaust gas can be effectively utilized. Mercuric chloride is oxidized and no HCl is consumed in the wet desulfurization unit (8a).

In addition, in the above step (b) of the third paragraph of the patent application, since the concentration of HCl in the exhaust gas is relatively low, although the oxidation of the metal mercury occurs in the denitration device (5) as in the step (a), In the filter bag of the dust removing device (7) in the low temperature range, the mercury component such as mercury chloride is oxidized by the oxidation catalyst to oxidize the metal mercury, and is recovered and removed from the dust removing device (7).

In the above step (b), the air preheater (6) disposed in the exhaust gas flow path on the downstream side of the denitration device (5) cools the exhaust gas to a filter bag having a lower reaction temperature than the denitration device (5) Since the reaction catalyst of the above reaction formula (1) is easily carried out in the right direction, the oxidation reaction of the metal mercury can be carried out, and the metal mercury can be effectively oxidized even at a low concentration of HCl.

That is, even if the concentration of HCl in the exhaust gas in the above step (b) is low, on the filter bag of the dust removing device (7), the metal mercury is oxidized by oxygen other than chlorine on the filter medium (Hg + 1/2 O ₂ = HgO). ), in the denitration catalyst layer of the denitration device (5), even if it is not converted into sufficient mercury chloride (HgCl ₂ ), it can be efficiently converted in the low temperature range to carry the filter bag of the oxidation catalyst. Mercuric chloride (HgO + 2HCl = HgCl ₂ + H ₂ O).

The oxidation product of the metal mercury such as mercury chloride recovered in the above steps (a) and (b) is transferred to a water layer for purification treatment.

Further, in the step (b), in the semi-dry desulfurization stage, the paste-like absorbent is sprayed on the exhaust gas, dried, and then recovered by the dust removing device (7), but since the absorbent must be removed together with the dust, " The order of semi-dry desulfurization → dust removal cannot be changed. In the above step (b), even in the semi-dry desulfurization stage, the metal mercury in the denitration device (5) on the upstream side is oxidized to a mercury component such as mercuric chloride, and a certain amount can be removed, but the removal is not charged. Share. Moreover, in the semi-dry desulfurization stage, HCl in a certain degree of exhaust gas (having an effect of promoting oxidation due to the oxidation catalyst of metal mercury) is also removed. Therefore, the filter bag provided in the dust removal stage provided in the low temperature range suitable for the balance is loaded with the oxidation catalyst, and the metal hydroxide is adsorbed and the mercury chloride is adsorbed on the filter cloth to capture the dust. Further, since the non-woven fabric is used as the filter cloth, the gas flow is not a single-layer laminar flow of a normal solid oxidation catalyst. When the exhaust gas passes through the filter cloth, the contact of the low concentration of HCl and the metal mercury in the exhaust gas is caused by the disorder of the air flow. The efficiency is high, and high-efficiency oxidation reaction of metal mercury occurs.

In the present invention, as shown in the side view of the filter bag of FIG. 2(a) and the enlarged view of the surface thereof, as shown in FIG. 2(b), the metal mercury in the exhaust gas is protruded from the surface of the filter cloth of the filter bag 1. The oxidation catalyst contained in 1a is oxidized to be converted into mercuric chloride, and the obtained metallic mercury compound 2 such as particulate mercuric chloride is captured together with the dust adsorbed inside the filter cloth, and then shaken off from the filter cloth. In the meantime, it is ensured that sufficient time (residence time) is adsorbed to the dust, and it is extremely effective for the metal mercury compound 2 for removing the oxidation product.

Therefore, even if it is necessary to provide the above-mentioned (b) step of the semi-dry desulfurization device (8b) upstream of the filter bag, the oxidizing catalyst carried by the filter bag can effectively remove mercury chloride.

In this way, in the above step (a) or the above step (b) in the present invention, the metal mercury can be effectively oxidized, and the obtained mercuric chloride can be recovered with high removal rate.

Conventionally, since the oxidized metal mercury becomes mercury oxide or the like, it is necessary to recover and remove the mercury oxide in the dust by the desulfurization apparatus. Therefore, in the subsequent step of oxidizing the metal mercury, a desulfurization stage must be provided, but in the present invention, for example, Even if it is necessary to use a semi-dry desulfurization device (8b) (the recovery rate of mercury chloride of the metal mercury oxide is considerably lower than that of the wet desulfurization (8a)), the coal-fueled exhaust gas treatment device, A filter bag for carrying a metal mercury oxidizing catalyst can be disposed in the exhaust gas flow path on the downstream side of the semi-dry desulfurization device (8b) to remove the metal mercury component from the exhaust gas at a high removal rate.

Thus, in the invention of claim 2 (the invention formed by the above step (a)), the denitration device (5) on the upstream side and the oxide portion of the metal mercury generated in the filter bag are filtered. The bag is adsorbed and removed, and then absorbed and removed by the absorption liquid in the wet desulfurization set (8a).

Further, in the invention of the third application of the patent application (the invention formed by the above step (b)), the denitration device (5) on the upstream side mainly oxidizes mercury chloride or the like after oxidizing the metal mercury by oxygen. One of the products is quantitatively removed by a semi-dry desulfurization device (8b), and further, the filter bag containing the oxidation catalyst is disposed in a low temperature range, and simultaneously oxidized metal mercury and adsorbed oxidation products are captured on the filter cloth to capture dust. Efficient removal of metallic mercury.

In the patent scope of the invention, Paragraph 4, based on the above-described denitration catalyst of the denitration catalyst layer of two or more kinds selected from titanium oxide (TiO _2), silicon oxide (SiO _2), alumina (Al ₂ O ₃ ) the compound as the first component, and two or more metals selected from the group consisting of molybdenum (Mo), vanadium (V), and tungsten (W) or an oxide thereof as the second component, as in the first aspect of the patent application A device for removing trace harmful substances in exhaust gas according to any one of the items 3.

According to the invention of claim 4, the denitration catalyst of the denitration catalyst layer has two or more compounds selected from the group consisting of TiO ₂ , SiO ₂ and Al ₂ O ₃ as the first component, and two kinds thereof. The above metal selected from Mo, V and W or its oxide is used as the second component, but the first component has a function as a carrier of a catalyst, and the second component has a denitration reaction and oxidation of metal mercury. However, it is considered that the above-mentioned effects of the first component and the second component are not single, and the first component and the second component are combined to function as the two.

According to the invention of claim 4, Hg is converted into HgCl ₂ or HgO ₂ by a denitration catalyst from HCl or oxygen contained in the exhaust gas. Further, the obtained HgCl ₂ or the like is adsorbed on the surface of the dust in the dust removing device, and is easily absorbed by the absorbent such as lime paste in the desulfurization device.

However, the denitration catalyst layer for the denitration device (5) having the function of oxidizing metal mercury provided by the exhaust gas treatment of the combustion equipment (4) of the boiler or the like is divided into a plurality of denitration catalysts to achieve the target denitration rate. The denitration catalyst layer is generally provided with a plurality of sections in the gas flow direction, and supplies a corresponding amount of NH _{3 of} the required denitration performance to perform denitration of the exhaust gas. NH ₃ in the exhaust gas supplied to the suction line of the denitration catalyst on the surface of the active points, the NO _X in the exhaust gas to react with decomposed into harmless nitrogen (N _2). Since the NH ₃ adheres to the denitration catalyst active point and the metal mercury (Hg) is inhibited from adhering to the denitration catalyst active point, the oxidation reaction rate of the metal mercury is lowered.

That is, in the denitration device (5), although a majority of the denitration catalyst layer is provided in the gas flow direction, because of the comparison of the denitration catalyst layer on the upstream side, there is a high concentration in the exhaust gas. The supplied NH ₃ is not effective for the oxidation reaction of Hg, and the consumption of NH ₃ due to the denitration reaction is close to the range of the denitration catalyst layer on the downstream side, and finally Hg is effectively oxidized. Further, since the reaction rate of the oxidation reaction of Hg is further lowered when the concentration of HCl in the exhaust gas is low, the denitration catalyst layer on the upstream side having a high NH ₃ concentration in the denitration catalyst layer hardly has an expectation of Hg. The idea of the oxidation reaction is preferred.

Therefore, in order to obtain the desired denitration performance, it is often impossible to obtain sufficient oxidation of Hg with the required amount of denitration catalyst. Further, since a large amount of catalytic toxic alkali, alkaline earth metal, arsenic (As) compound, and phosphorus (P) compound exist in the combustion exhaust gas of petroleum or coal, the denitration catalyst deteriorates during long-term use, but at this time The above-mentioned toxic components adsorbed on the surface of the catalyst greatly reduce the NH ₃ adsorption amount of the denitrification catalyst, and the high concentration of NH _{3 is} also supplied to the denitration catalyst layer on the downstream side, and the Hg oxidation rate is further significantly reduce. When the concentration of HCl in the exhaust gas is thin, the degree of decrease in the oxidation rate of Hg is more pronounced.

On the other hand, in order to use the denitration catalyst as described above, the metal mercury (Hg) is oxidized in the presence of low temperature and HCl to produce HgCl ₂ . Since the concentration of the oxidized Hg is extremely low, the usual solid denitration catalyst is used. At the time, there must be means to increase the contact efficiency of low concentration HCl and low concentration metal mercury. Further, the sulfur oxide (SO _X ) present in the exhaust gas reacts with the NH ₃ leaked from the denitrification catalyst on the upstream side to produce acidic ammonium sulfate (NH ₄ HSO ₄ ) because the oxidation ability of the denitration catalyst is remarkable. It is reduced, so there must be a means to suppress the precipitation of such acidic ammonium sulfate.

In addition, since the exhaust gas of the combustion equipment for burning petroleum or coal contains a relatively high concentration of dust, even if the solid denitration catalyst layer is disposed in the exhaust gas flow path after dust removal, it must be kept at a certain interval (interval between the catalysts; (Pitch)), the majority of the denitration catalyst layer is provided, but when the distance between adjacent catalyst layers is increased, the speed at which the metal hydroxide of the trace component is diffused and adsorbed on the catalyst surface is reduced. Therefore, it is required to have a denitration catalyst layer designed to reduce the spacing between the catalyst layers as much as possible, but at this time, the gas flow path in the catalyst layer is blocked or the pressure loss which cannot be ignored is increased due to dust, which will damage the power generation equipment. Power generation efficiency. Further, the concentration of HCl required for the oxidation reaction of the metal mercury is also lowered depending on the type of the fuel to be used. In this case, the contact efficiency between the low-concentration HCl and the low-concentration metal mercury must be improved.

The invention described in the fifth aspect of the invention of the present invention is invented in view of the circumstances.

The invention described in claim 5 is in the denitration device described above, and the denitration catalyst layer of the denitration catalyst layer on the downstream side is compared in the majority of the denitration catalyst layer disposed in the gas flow direction. The concentration of the second component of the medium is reduced stepwise compared to the concentration of the second component of the denitrification catalyst of the denitration catalyst layer on the upstream side, as in any one of claims 1 to 4 of the patent application scope. A device for removing trace harmful substances from exhaust gas.

In order to maintain the required denitration performance, in the exhaust gas denitration device, a majority of the denitration catalyst layer 3 is usually disposed in the gas flow direction as shown in FIG. 5 (the denitration catalyst layer 3a, 3b, ... of FIG. 5). According to the invention described in claim 5, the denitration catalyst layer (for example, the denitration catalyst layer 3a) on the upstream side of the denitration catalyst layer in the majority of the gas flow direction is disposed in the gas flow direction. The second component of the concentration-dispersing denitration catalyst is characterized. At this time, the denitration catalyst layer on the upstream side of the second component is supported at a high concentration to efficiently denitrify the nitrogen oxides, and as a result, the NH ₃ supplied in the exhaust gas is Comparing the denitration catalyst layer in the upstream section consumes almost all of it. Therefore, in comparison with the denitration catalyst layer on the downstream side (for example, the denitration catalyst layer 3b), the metal mercury in the exhaust gas can be efficiently oxidized. At this time, the denitration performance of the denitration catalyst of each catalyst layer is planned, and the denitration rate of the entire denitration catalyst layer 3 can be obtained.

In addition, a large amount of sulfur oxides (SO _X ) are present in the exhaust gas of the combustion exhaust gas of petroleum or coal, and although the oxidation of SO ₂ must be suppressed, the oxidation activity of the denitration catalyst layer on the downstream side is compared. Since the carrying amount of the two components is low, the SO ₂ oxidation rate as a whole of the denitration catalyst can be suppressed.

This is because the SO ₂ oxidation system is expressed by the following chemical formula (2), and the equilibrium relationship of the SO ₃ concentration in the exhaust gas is compared with the second component of the above-mentioned denitration catalyst, and the denitration catalyst layer on the upstream side is compared. When the SO ₂ oxidation reaction is carried out, the SO ₃ concentration in the denitration catalyst layer on the downstream side is increased, and the oxidation reaction of SO ₂ is less likely to occur due to chemical equilibrium, and the direction of SO ₂ oxidation of the entire catalyst is suppressed.

SO ₂ +1/2O ₂ → SO ₃ (2)

According to the invention described in claim 5, in the denitration catalyst layer disposed in the majority of the gas flow direction, the denitration catalyst layer in the majority of the denitration catalyst layer in the gas flow direction is compared with the denitration touch on the upstream side The medium layer is a second component having oxidative activity dispersed at a relatively high concentration, and the denitration of the exhaust gas is efficiently performed in the presence of ammonia, and the lower concentration in the denitration catalyst layer on the downstream side is compared. The second component dispersedly supported is a denitration catalyst layer which inhibits the oxidation reaction from the downstream side of the upstream side, and can efficiently oxidize metallic mercury in the exhaust gas. Further, since the carrier concentration of the second component having the oxidation activity of the denitration catalyst layer on the downstream side is lower as described above, the SO ₂ oxidation rate as the denitration catalyst can be suppressed, and the pressure can be lowered. The concentration of SO ₃ in the exhaust gas.

According to the invention of the sixth aspect of the invention, the oxidation catalyst of the metal mercury in the filter bag of the dust removing device (7) is a metal of titanium (Ti), molybdenum (Mo) and vanadium (V) or an oxide thereof. The apparatus for removing trace harmful substances in the exhaust gas as described in any one of the first to fifth aspects of the patent application.

The denitration catalyst layer of the above-mentioned denitration device (5) is equipped with a denitration catalyst containing an oxidation catalyst in a temperature range (300 to 400 ° C) which is usually set, even if the conversion of the metal mercury into mercury chloride is caused. When the temperature is high, especially when the concentration of HCl in the exhaust gas is low, it is difficult to oxidize the metal mercury.

Therefore, in the exhaust gas in the low temperature range after the heat exchange of the air preheater (6) constituting the machine of the exhaust gas purifying device, a filter bag carrying the oxidation catalyst is provided, and in the state in which the exhaust gas temperature is lowered, the exhaust gas can be oxidized. Metallic mercury.

According to the invention of the sixth aspect of the invention, the oxidation catalyst for metal mercury used in the filter bag of the dust removing device (7) is formed of a metal of Ti, Mo and V or an oxide thereof, and among them, The metal or metal oxide which is substantially the same as the above-mentioned denitration catalyst component can also be directly used as an oxidation catalyst for metal mercury.

According to the invention of the sixth aspect of the invention, the mercury oxide remaining in the exhaust gas is oxidized by the oxidation catalyst in the filter bag of the dust removing device (7), and the obtained mercury oxide such as mercury chloride can be captured by the filter bag.

According to the invention described in claim 7, the filter bag of the dust removing device (7) carries the amount of the oxidation catalyst of the metal mercury used in the filter cloth, and the denitration touch used by the denitration device (5) oxidation catalyst in an amount of above medium, which is used in an amount of 100 to 500g / m ² the application of an exhaust gas removing apparatus patentable scope according to any one of items 1 to item 6 trace amounts of toxic substances.

According to the invention described in claim 7, the concentration of the oxidation catalyst in the filter bag of the dust removing device (7) disposed on the downstream side of the denitration catalyst layer of the denitration device (5) may be higher than The concentration of the second component of the same component of the denitration catalyst layer of the denitration device (5) is caused by the oxidation of SO ₂ to SO ₃ due to the temperature range of the oxidation catalyst in the filter bag. Hard to happen.

The filter bag carrying the oxidation catalyst is a cross-sectional structure as shown in FIG. 2, and the gap between the fiber material of the filter bag 1 and the catalyst held by the fiber is a structure capable of removing exhaust gas, and the structure becomes a promoting substance. The structure of the move. As described above, the metal mercury in the exhaust gas is extremely small. In particular, when the concentration of HCl in the exhaust gas is low, it is necessary to increase the contact efficiency between the two to effectively carry out the reaction between the metal mercury and the HCl on the oxidation catalyst in the filter bag. However, since the non-woven fabric as described above disturbs the gas flow and increases the moving speed of the substance, it is suitable to improve the contact efficiency between the metal mercury and HCl. Further, in the filter bag 1, since the pressure loss is suppressed, the filter cloth passing speed of 1 m/min or less is usually designed to be in the filter bag 1, and the time during which the metal mercury and the HCl are sufficiently contacted can be obtained.

The filter cloth used in the filter bag 1 containing the oxidation catalyst function described above is not particularly problematic as long as it can be applied to the material of the combustion exhaust gas of petroleum or coal, and as the material, for example, polyimide or polyamide can be used. Polyphenylene sulfide, polytetrafluoroethylene or glass fiber. The amount of the oxidizing catalyst used in the filter cloth is preferably from 100 to 500 g/m ^{2 in the} area of the filter cloth, and preferably from 200 to 400 g/m ² . This is because, as shown in Fig. 4, when the amount of the oxidation catalyst used is too small, a sufficient catalyst effect cannot be obtained, and when the pressure loss of the system is excessive or the filter cloth after the exhaust gas treatment is regenerated, the charge cannot be charged. Shake off the dust.

According to the invention described in claim 7, the concentration of the oxidation catalyst of the filter bag carrying the oxidation catalyst is higher than the oxidation-active second component of the denitration catalyst layer of the denitration device (5). The concentration of the denitration catalyst layer can suppress SO ₂ in the oxidizing exhaust gas to form SO ₃ . On the other hand, because the oxidation catalyst is on the filter bag, compared with the denitration catalyst layer of the denitration device (5), it is in the low temperature range because the oxidation reaction from SO ₂ to SO _{3 is} difficult to occur, and there is no oxidation of SO _{2 .} the danger to SO _3, a sufficient amount of the oxidation catalyst, even containing a trace amount of metal mercury, also oxidized.

Further, in the filter bag of the dust removing device (7), the amount of the oxidation catalyst for carrying the metal mercury used in the filter cloth is 100 to 500 g/m ² , and a sufficient catalyst effect can be obtained, and in addition, in the filter bag. The pressure loss when the exhaust gas passes does not become large, and the oxidation of the metal mercury can be performed without impairing the effect of shaking off the dust.

According to the invention described in claim 8, the operating temperature of the denitration device (5) is from 250 ° C to 450 ° C, and the operating temperature of the filter bag containing the metal mercury oxidizing catalyst of the dust removing device is from 120 ° C to 250 ° C. The method for operating a device for removing trace harmful substances in exhaust gas as described in any one of claims 1 to 7.

According to the invention described in claim 8, the denitration catalyst can be activated at a temperature of from 250 ° C to 450 ° C to promote the denitration reaction, and the metal oxide can be oxidized at an active temperature of 120 ° C to 250 ° C.

In the temperature range (300 to 400 ° C) where the denitrification catalyst is usually set, the denitration catalyst supporting the oxidation catalyst is equipped, even if the mercury is converted into mercury chloride, the temperature is high, especially the concentration of HCl in the exhaust gas is low. It is difficult to oxidize metallic mercury.

Therefore, in the exhaust gas in the low temperature range after the heat exchange of the air preheater (6) constituting the machine of the exhaust gas purifying device, a filter bag carrying the oxidation catalyst is provided, and in the state in which the exhaust gas temperature is lowered, the exhaust gas can be oxidized. Metallic mercury.

According to the invention described in the eighth aspect of the invention, in the temperature range in which the denitration catalyst is active and the temperature at which the oxidation catalyst is active, the exhaust gas can be denitrated and oxidized to metal mercury.

Further, in the honeycomb shape other than the plate shape of the denitration catalyst used in the present invention, the same effect can be obtained, and the shape thereof is not limited.

The best form for implementing the invention

The following describes the embodiments of the present invention.

The following embodiment of the present invention performs boiler exhaust gas treatment in accordance with the flow charts shown in Figs. 1(a) and 1(b).

In the flow chart shown in Fig. 1(a), the exhaust gas passage discharged from the boiler 4 for burning petroleum or coal removes nitrogen oxides in the exhaust gas from the upstream side in the presence of ammonia, and is configured to have oxidation. Denitration device 5 for denitration catalyst layer of metal mercury function, and air preheater 6 for exchanging heat between combustion air and exhaust gas of combustion equipment, and dust removal device for filter bag having oxidation catalyst containing metal mercury 7. A desulfurization device 8 for removing sulfur oxides in the exhaust gas with an absorbent such as limestone paste, and a chimney 9 for discharging the purified exhaust gas to the atmosphere.

Further, in the flow chart shown in FIG. 1(b), the nitrogen oxides in the exhaust gas are removed from the upstream side in the presence of ammonia, and the denitration catalyst layer having the function of oxidizing metal mercury is disposed. The device 5, and an air preheater 6 for exchanging heat between the combustion air of the combustion equipment and the exhaust gas, and a semi-dry desulfurization device 8b for directly removing the SO _X in the exhaust gas by directly spraying an absorbent such as limestone into the exhaust gas, and A dust removing device 7 having a filter bag containing a metal-containing mercury oxidation catalyst, and a chimney 9 for discharging the purified exhaust gas in the atmosphere.

Example [Example 1]

The oxidation catalyst for metal mercury held in the filter bag is based on 85 kg of titanium oxide powder (TiO ₂ content: 90 wt% or more, SO ₄ content: 3 wt% or less), and 10.7 kg of ammonium molybdate ((NH ₄ ) is added). _6. Mo ₇ O _{2 4} .4H ₂ O), 9.9 kg of ammonium metavanadate (NH ₄ VO ₃ ) and 12.8 kg of oxalic acid, adjust the water, mix, granulate, dry and calcine in sequence. The powder is pulverized into a moderate particle diameter to obtain a catalyst raw material powder. Water is added thereto to obtain a catalyst paste. The Tefair filter cloth was immersed in the catalyst paste, and after carrying the catalyst component, it was dried at 150 ° C to obtain a filter bag carrying the metal mercury oxidation catalyst. The catalyst carrier of the filter bag was 350 g/m ² .

Further, 70 kg of titanium oxide powder (TiO ₂ content: 90 wt% or more, SO ₄ content: 3 wt% or less), aluminum compound powder (Al ₂ O ₃ ), and 70 kg of cerium sol (SiO ₂ ) were used as the denitrification catalyst. The first component, adding 7kg of molybdenum trioxide (MoO ₃ ) and 1.6kg of ammonium metavanadate (NH ₄ VO ₃ ) as the second component, after adding alumina/silicate fiber, will adjust the water mixture. The catalyst paste obtained by the smelting is applied to a metal porous metal plate, and is pressed into a predetermined shape to obtain a plate-shaped denitration catalyst. This plate-shaped denitration catalyst was calcined at 500 °C.

For the coal-fired boiler test equipment, a catalyst layer containing the above-mentioned denitration catalyst is disposed, and on the downstream side, an air preheater for exhaust gas desuperheating and a filter bag for carrying the oxidation catalyst are sequentially disposed. Further, a wet desulfurization device (limestone-gypsum method) is disposed downstream.

[Embodiment 2]

In the same manner as in Example 1, a filter bag carrying a metal mercury oxide catalyst was prepared, and further, 70 kg of titanium oxide powder (TiO ₂ content: 90 wt% or more, SO _x content: 3 wt% or less), and 0.9 kg of aluminum compound powder were used. (Al ₂ O ₃ ) as the first component of the denitrification catalyst, adding 7 kg of molybdenum trioxide (MoO ₃ ) and 1.6 kg of ammonium metavanadate (NH ₄ VO ₃ ) as the second component, adding alumina After the bismuth silicate fiber, the catalyst paste obtained by kneading the water is applied to a metal porous metal plate, and press-processed into a predetermined shape to obtain a plate-shaped denitration catalyst. This plate-shaped denitration catalyst was calcined at 500 °C.

For the coal-fired boiler test equipment, a catalyst layer containing the above-mentioned denitration catalyst is disposed, and on the downstream side, an air preheater and a filter bag carrying the oxidation catalyst are sequentially disposed. Further, a wet desulfurization device (limestone-gypsum method) is disposed on the further downstream side.

[Example 3]

In the same manner as in Example 1, a filter bag carrying a metal mercury oxide catalyst was prepared, and further, 70 kg of titanium oxide powder (TiO ₂ content: 90 wt% or more, SO ₄ content: 3 wt% or less), and 0.9 kg of aluminum compound powder were used. (Al ₂ O ₃ ) as the first component of the denitration catalyst, adding 20 kg of ammonium metatungstate (NH ₄ ) ₆ [H ₂ W _{1 2} O _{4 0} ], 1.6 kg of ammonium metavanadate (NH) ₄ VO ₃ ) As a second component, after adding alumina/silicate fiber, the catalyst paste obtained by kneading the water is applied to a metal porous metal plate, and processed into a predetermined shape to obtain a plate shape. Denitrification catalyst. This plate-shaped denitration catalyst was calcined at 500 °C.

For the coal-fired boiler test equipment, a catalyst layer containing the above-mentioned denitration catalyst is disposed, and on the downstream side, an air preheater and a filter bag carrying the oxidation catalyst are sequentially disposed. Further, a wet desulfurization device (limestone-gypsum method) is disposed on the further downstream side.

[Example 4]

A filter bag carrying a denitration catalyst and an oxidation catalyst was prepared in the same manner as in Example 1, except that the catalyst carrier carrying the oxidation catalyst was 76 g/m ² . The configuration of the test equipment is the same as in the first embodiment.

[Example 5]

70 kg of titanium oxide powder (TiO ₂ content: 90 wt% or more, SO ₄ content: 3 wt% or less) was used as the first component of the denitration catalyst, and 7 kg of molybdenum trioxide (MoO ₃ ) and 3.2 kg of vanadium oxide were added. Ammonium acid (NH ₄ VO ₃ ) and 0.9 kg of aluminum compound (Al ₂ O ₃ ) are used as the second component. After adding alumina/silicate fiber and 14Kg of cerium sol (SiO ₂ ), the water is mixed. The catalyst paste obtained by the smelting is applied to a metal porous metal plate, and is pressed into a predetermined shape to obtain a plate-shaped denitration catalyst. This plate-shaped denitration catalyst was calcined at 500 °C.

The denitration catalyst adjusted in the first embodiment was placed on the denitration catalyst layer adjusted on the upstream side by using the catalyst in the downstream denitration catalyst layer, and the denitration device was set as the denitration device. Test device. Further, the filter carried at this time is the same as that of the first embodiment.

[Embodiment 6]

Using the filter bag for carrying the denitrification catalyst and the oxidation catalyst used in Example 1, the denitration catalyst and the air preheater were sequentially disposed in the same test equipment, and the semi-dry type was further provided in the downstream portion. After the desulfurization device, a filter bag carrying the catalyst is disposed.

[Embodiment 7]

The denitration catalyst layer used in Example 1 was not provided, and after the air preheater was desuperheated, a filter bag carrying the catalyst was placed, and a wet desulfurization device was disposed at a downstream portion thereof.

[Comparative Example 1]

The experiment was carried out in the same manner as in the test apparatus of Example 1, except that the content of the vanadium component of the high oxidation activity was reduced, and the same oxidation catalyst as that of the oxidation catalyst held in the filter bag of Example 1 was used.

That is, the oxidation catalyst for the metal mercury held in the filter bag is based on 85 kg of titanium oxide powder (TiO ₂ content: 90 wt% or more, SO ₄ content: 3 wt% or less), and 10.1 kg of ammonium molybdate (( NH ₄ ) ₆ .Mo ₇ O _{2 4} .4H ₂ O), 2.0 kg of ammonium metavanadate (NH ₄ VO ₃ ) and 2.6 kg of oxalic acid, adjust the water, mix, granulate, dry and calcine The obtained powder was pulverized into a moderate particle diameter to obtain a catalyst raw material powder. Water is added thereto to obtain a catalyst paste. The Tefair filter cloth was immersed in the catalyst paste, and after carrying the catalyst component, it was dried at 150 ° C to obtain a filter bag carrying the metal mercury oxidation catalyst. The catalyst carrier of the filter bag was 350 g/m ² .

[Comparative Example 2]

The denitration catalyst layer of Example 1 was placed, and a normal filter bag having no oxidation catalyst function was further provided, and a wet desulfurization apparatus was disposed in the downstream portion. The configuration of the test equipment is the same as in the first embodiment.

In addition, the so-called filter bag which does not have an oxidation catalyst function as used herein refers to a test glass fiber as a filter cloth material, and is backwashed in a pulsed manner by a flow rate in the range of 0.8 to 1.3 m/min. Type.

With the compositions of the above Examples 1 to 7 and Comparative Examples 1 and 2, the above-mentioned test equipment of the entire exhaust gas purification system was compared under the conditions shown in Table 1, and the Hg removal performance was compared. The results obtained are summarized in Table 2. As shown in Table 2, it is understood that when the system is constructed by the catalyst of the present invention, the overall Hg removal performance is excellent.

Industrial use

The present invention is used as a removal device for a trace amount of harmful substances contained in the combustion exhaust gas of petroleum or coal, in particular, a metal mercury compound removal device and an operation method thereof, and can be utilized for boiler exhaust gas treatment and the like.

4. . . Combustion equipment

5. . . Denitration device

6. . . Air preheater

7. . . Dust removal device

8a, 8b. . . Desulfurization device

9. . . chimney

Fig. 1 is a flow chart showing an exhaust gas treatment system of an embodiment of the present invention.

Fig. 2 is a view showing the configuration of a main part of a filter bag carrying an oxidation catalyst.

[Fig. 3] shows the change in the function of the denitrification catalyst in the coexistence of SOx at a low temperature.

[Fig. 4] shows the correlation between the amount of denitrification catalyst and the catalyst function

Fig. 5 is a view showing an arrangement structure of a catalyst layer in a denitration device.

4. . . Combustion equipment

5. . . Denitration equipment

6. . . Air preheater

7. . . In addition to the device

8a, 8b. . . Desulfurization device

9. . . chimney

Claims (8)

A device for removing trace harmful substances in exhaust gas, characterized in that, in an exhaust gas passage discharged from a combustion equipment for burning petroleum or coal, an air pre-cooling is performed from the upstream side to heat exchange between combustion air of the combustion equipment and the exhaust gas. The heat exchanger has a dust removing device of a filter bag equipped with a filter cloth for carrying a metal oxide oxidizing catalyst. For example, the apparatus for removing trace harmful substances in the exhaust gas according to the first aspect of the patent application, wherein the exhaust gas passage on the flow side before the air preheater is equipped with a denitration touch having the function of removing nitrogen oxides in the exhaust gas and oxidizing metal mercury In the denitration device of the medium layer, a wet absorbent desulfurization device for removing sulfur oxides in the exhaust gas is disposed in the exhaust gas passage on the downstream side of the dust removing device, and a spray absorbent paste (using an absorbent such as limestone paste). For example, the apparatus for removing trace harmful substances in the exhaust gas according to the first aspect of the patent application, wherein the exhaust gas passage on the flow side before the air preheater is equipped with a denitration touch having the function of removing nitrogen oxides in the exhaust gas and oxidizing metal mercury The denitration device of the medium layer is disposed in the exhaust gas passage between the air preheater and the dust removing device, and is provided with a spray absorbent paste (using slaked lime or magnesium hydroxide, etc.) in the exhaust gas passage to remove half of the sulfur oxides in the exhaust gas. Dry desulfurization unit. The apparatus for removing trace harmful substances in the exhaust gas according to any one of the first to third aspects of the patent application, wherein the denitration catalyst layer of the denitration catalyst layer is selected from the group consisting of titanium oxide (TiO ₂ ) , silicon oxide (SiO _2), alumina (Al ₂ O ₃₎ of the compound as a first component, two or more kinds selected from molybdenum (Mo), vanadium (V) and tungsten (W) of metal or oxide thereof As the second ingredient. The apparatus for removing trace harmful substances in exhaust gas according to any one of the first to third aspects of the patent application, wherein in the denitration device, a plurality of denitration catalyst layers disposed in a gas flow direction are used Comparing the concentration of the second component of the denitration catalyst of the denitration catalyst layer on the downstream side, the concentration of the second component of the denitration catalyst of the denitration catalyst layer on the upstream side is more gradually reduced. The apparatus for removing trace harmful substances in exhaust gas according to any one of claims 1 to 3, wherein the oxidation catalyst of the metal mercury in the filter bag of the dust removing device is made of titanium (Ti) and molybdenum ( Mo) and a metal of vanadium (V) or an oxide thereof. The apparatus for removing trace harmful substances in exhaust gas according to any one of the items 1 to 3, wherein the filter bag of the dust removing device carries the amount of the oxidation catalyst of the metal mercury used in the filter cloth. It is more than the amount of the oxidation catalyst in the denitration catalyst used in the denitration apparatus, and the usage amount is 100 to 500 g/m ² . The operation method of the apparatus for removing trace harmful substances in the exhaust gas according to any one of the items 1 to 3, wherein the operation temperature of the denitration device is 250 ° C to 450 ° C, and the dust removing device contains metal mercury The operating temperature of the filter bag of the oxidation catalyst is from 120 ° C to 250 ° C.