KR20060062430A - Heat recovery steam generator system including nox removal catalyst arranged in multi-stage pattern - Google Patents

Abstract

The present invention is a technology that utilizes a plurality of spaces merely serving as a maintenance in the heat recovery boiler as the installation space of the catalyst layer for removing nitrogen oxides in the exhaust gas, the temperature band of the exhaust gas passing through the maintenance space It characterized in that the multi-stage arrangement in a separable manner for the flue gas denitrification catalyst layer having an activity in. Accordingly, not only can the space efficiency inside the boiler be improved, but also the flexibility of the process can be achieved, thereby optimizing the heat recovery. In particular, since the exhaust gas treatment in the low temperature zone by the multi-stage arrangement of the catalyst layer is possible, problems such as suppression of generation of catalyst poison forming material, prolongation of catalyst life, and suppression of corrosion of the device can be solved at once.

Nitrogen oxide, denitrification catalyst, maintenance and repair space, heat recovery boiler, low temperature treatment

Description

Heat Recovery Steam Generator System Including NOx Removal Catalyst Arranged in Multi-stage Pattern}

1 shows a schematic process of a combined cycle power plant including a typical heat recovery boiler system.

2 is a schematic illustration of a series of devices arranged in the duct of a typical heat recovery boiler.

3 is a diagram illustrating a schematic process of a combined cycle power plant including a heat recovery boiler system according to one embodiment of the present invention.

FIG. 4 shows an embodiment in which the catalyst bed is introduced in a separable manner into the maintenance space of the heat recovery boiler system.

5 is a front and side view of one embodiment of a honeycomb catalyst bed module configured to be introduced in a separable manner into a maintenance space of a heat recovery boiler system, in accordance with the present invention.

* Description of the symbols for the main parts of the drawings *

1: duct inlet 2: high pressure superheater

3: high pressure evaporator 4: autoclave                 

5: low pressure evaporator 6: low pressure

7: High pressure drum 8: Low pressure drum

9: cast stone 10: heat recovery boiler

11: natural gas tank 12: generator

13: gas turbine 14: minor smoke

15: Ammonia or Urea Injection Glyde

16: Water tank / deaerator 17: Maintenance and repair space

18: duct outlet 21, 23: flue gas denitration catalyst layer

22, 24: space for catalyst bed 31: wheels

32: rail 33: vertical stage of the catalyst bed module

34: catalyst bed module

The present invention relates to a system in which a catalyst layer is mounted in multiple stages in a maintenance space in a boiler to effectively remove nitrogen oxides contained in exhaust gas discharged from a conventional heat recovery boiler having a small installation space for mounting a denitration catalyst. More specifically, the present invention provides the nitrogen oxide removal activity corresponding to the temperature of the maintenance space formed in the existing array boiler system where the space for installing the denitration catalyst as a single layer in the high temperature region is narrow or there is no space other than the high temperature region. A flue gas denitrification catalyst layer having a zone is dispersed and installed in multiple stages in a separable manner over two or more areas of the maintenance space, and thus, relates to a heat recovery boiler system capable of effectively removing nitrogen oxides in exhaust gas.

In general, nitrogen oxides are generated from stationary sources such as industrial boilers, gas turbines, thermal power plants, waste incineration plants, marine engines, and petrochemical plants. Techniques for removing such nitrogen oxides can be classified into three types. First, there is a fuel denitrification method in which fossil fuel is treated to remove nitrogen compounds contained therein in order to prevent generation of nitrogen oxide in advance. Second, since the combustion method is different depending on the fuel used, there is a method of improving the combustion conditions through excess air injection, staged combustion, and the like. Finally, there is a post-treatment method for removing the generated nitrogen oxides by exhaust gas treatment.

In the case of a fuel denitrification method, only about 16% of all nitrogen compounds are reported to be removed even if hydrogen is reacted for a long time under high temperature reaction conditions to remove nitrogen compounds contained in the fuel. In addition, in the case of improving combustion conditions, it is known that it is virtually impossible to achieve an efficiency of at least 30 to 40% due to the inverse correlation between nitrogen oxide emission conditions and thermal efficiency.

Therefore, since the nitrogen oxide removal technology by the post-treatment method is excellent in terms of nitrogen oxide removal efficiency, it is applied to the actual commercialization process.

The post-treatment method is generally classified into a wet method and a dry method, and the wet method has an advantage of removing nitrogen oxide and sulfur oxide at the same time, and has been applied to a process in which a small amount of nitrogen oxide is generated. However, in order to apply the above method, since the solubility of NO in water is not good, it must be oxidized to NO ₂ before absorbing NO in an aqueous solution, which is not preferable in terms of economical process, and in the process of oxidizing NO to NO ₂ . The problem arises of having to reprocess NO ₃ and N ₂ O ₄ produced as by-products.

Due to the above problems, the dry method has been actively studied among the post-treatment techniques. Drying process ammonia at high temperature (above 850 ℃) without using catalyst. Nitrogen selectively by injection only And nitrogen oxides using selective non-catalytic reduction (SNCR) and catalysts that reduce to water. And Selective Catalytic Reduction (SCR) for reducing to water. The former has the advantage that 50% or more of nitrogen oxides can be removed at a relatively low cost, but the unreacted ammonia released forms ammonium salts, etc., thereby plugging or eroding the device at the rear of the reactor. There is a difficulty in operation because it may cause a phenomenon and the operating temperature band is narrow. Therefore, in order to remove nitrogen oxides generated from the fixed source, selective catalytic reduction method has been in the spotlight in terms of economic and technical aspects.

In the selective catalytic reduction method, the catalyst is reduced nitrogen oxides such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) to nitrogen and water using ammonia as the reducing agent as in Schemes 1 to 4 below. However, since the exhaust gas contains oxygen, nitrogen oxides are actually removed according to the reaction schemes 3 and 4.

6NO + 4NH ₃ → 5N ₂ + 6H ₂ O

6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O

2NO ₂ + 4NH ₃ + O ₂ → 3N ₂ + 6H ₂ O

However, in the above process, ammonia to be used as a reducing agent may react with oxygen to generate nitrogen and nitrogen oxides as shown in Schemes 5 to 8.

4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O

4NH ₃ + 4O ₂ → 2N ₂ O + 6H ₂ O

4NH ₃ + 5O ₂ → 4NO + 6H ₂ O

4NH ₃ + 7O ₂ → 4NO ₂ + 6H ₂ O

In general, the oxidation reaction of ammonia occurs actively as the reaction temperature rises to a high temperature, it occurs competitively with the reduction reaction of nitrogen oxides, the conversion rate of nitrogen oxides changes with temperature. In the absence of water, the reaction according to Scheme 6 hardly occurs. In particular, the reactions of Schemes 7 and 8 should be suppressed because they produce nitrogen oxides, and the rate of the reaction increases as the reaction temperature increases.

Prior literatures relating to techniques for specifically implementing the removal of nitrogen oxides in the exhaust gas according to the selective catalytic reduction method described above are as follows.

US Patent No. 5,132,103 discloses a method for removing unreacted ammonia, carbon monoxide, hydrocarbons, etc. after nitrogen oxide removal by injecting ammonia used as a reducing agent to the front of a gas turbine and continuously installing a denitration catalyst and an oxidation catalyst inside the boiler. Is starting.

U.S. Pat.No. 6,074,619 discloses that the size of the ammonia drop and the size of the ammonia drop after the injection of ammonia in order to reduce the size of the ammonia droplets injected with the reducing agent in order to enhance the nitrogen oxide removal efficiency and to suppress the unreacted ammonia emissions. A method of controlling the optimum distance between ammonia injection location and denitrification catalyst is disclosed.                         

U. S. Patent No. 5,320, 428 discloses a method for enhancing efficiency by varying the catalyst coated mixer or catalyst arrangement to increase the contact of the exhaust gas with the catalyst to remove nitrogen oxides.

U.S. Patent No. 5,988,115 discloses a method for maximizing denitrification efficiency by obtaining a uniform distribution of the reducing agent reaching the catalyst stage by adjusting the arrangement and injection angle of the nozzle of the reducing agent injection grid for efficiently injecting the reducing agent used in the selective reduction reaction. Disclosed is a method for installing an injection grid for the same.

U.S. Patent No. 5,681,536 discloses an ammonia infusion grid capable of uniformly mixing anhydrous ammonia and air used as a reducing agent, and by supplying ammonia anhydrous and air to a double pipe configured separately, This is to maximize the area so that there is no excessive or insufficient area of ammonia supply.

US Patent No. 5,139,757 discloses a method for inducing a stepwise reaction by dividing a catalytic reaction stage for removing nitrogen oxides into three parts and rotating them at regular time intervals. Specifically, ammonia is adsorbed onto the catalyst as a first step and rotated to pass a flue gas containing nitrogen oxide as a second step to induce a nitrogen oxide removal reaction by a selective reduction reaction, and as a final step, nitrogen oxide. Unreacted ammonia is removed by passing air which is not included.

Meanwhile, the combined cycle power plant generates electricity by combining two types of heat cycles to improve thermal efficiency as shown in FIG. 1. That is, for example, the fuel provided from the fuel supply means such as the natural gas tank 11 is combusted, and the power generator 12 is primarily operated by the gas turbine 13 cycle to generate power, and secondly from the gas turbine. After recovering a portion of the large amount of heat remaining in the exhaust gas of 500 ° C. or more discharged into the atmosphere through the secondary stone 14, the steam turbine is generated by using the recovered heat to turn the steam turbine.

The heat recovery boiler 10 for producing steam for operating the steam turbine uses a high temperature exhaust gas at the rear end of the gas turbine, and the high temperature exhaust gas is a high pressure superheater (2), a high pressure evaporator (3), a high pressure burner (high) in the duct. Pressure economizer: 4) followed by low pressure evaporator (5) and low pressure carburettor (6), which are discharged through the main stack (9), in the process of producing steam to operate steam turbines and hot water. To prepare. As can be seen from FIG. 1, a plurality of maintenance and repair spaces 17 are provided for each device in the heat recovery boiler so as to properly cope with various equipment failures. In addition, a high pressure drum 7 and a low pressure drum 8 are provided on the upper side of the boiler, and water required for steam generation from the water supply tank / deaerator 16 is provided.

Typically, the heat recovery boiler is intended to maximize the heat exchange rate, the inside of which is a high pressure superheater (2), a high pressure evaporator (3), a high pressure mill (4), as shown in FIG. A space for maintenance and repair is secured in the space between the low pressure evaporator 5 and the low pressure economizer 6 and has a structure filled with a group of heat exchange tubes except for this space. Therefore, when the initial design does not consider the installation of the catalyst for removing nitrogen oxides, it is inevitable to remove the heat exchange tube group in order to install the denitration catalyst of a single layer separately, and the loss due to the reduction in construction cost and thermal efficiency is enormous.

Meanwhile, in order to remove nitrogen oxides in the exhaust gas, a denitrification catalyst layer having a separate high temperature activity is formed in a high temperature region (for example, near a high pressure evaporator) in a heat recovery boiler. For example, Korean Patent No. 309959 It is disclosed in the call. However, moisture and sulfur oxides are generally present in the flue-gases, which produce salts on the catalyst, thereby lowering the activity of the catalyst. The reaction which is the main cause of poisoning of the catalyst is made according to the following reaction formulas 9 to 12.

2NH ₃ + H ₂ O + 2NO ₂ → NH ₄ NO ₃ + NH ₄ NO ₂

2SO ₂ + O ₂ → 2SO ₃

NH ₃ + SO ₃ + H ₂ O → NH ₄ HSO ₄

SO ₃ + H ₂ O → H ₂ SO ₄

In the case of Scheme 9, nitrogen dioxide and ammonia react to form nitrate (ammonium nitrate), and it is known that such nitrate does not decompose and form catalyst poisoning at 150 ° C or higher. However, since the injection of ammonia in the actual process is sprayed at a temperature of 150 ° C. or higher, poisoning of the catalyst is eventually caused by the sulfur trioxide produced by Scheme 10 forming sulfates according to Scheme 11 without remaining on the catalyst surface. In addition, sulfuric acid is generated by Reaction Scheme 12 to provide a cause of corrosion of the catalyst layer and the rear equipment.

In this regard, currently commercially available flue gas denitrification processes are high energy consuming processes that are mostly constructed depending on the high temperature activity of the catalyst. Therefore, when the denitrification process is additionally applied to the existing heat recovery boiler without the denitrification catalyst, heat exchanger tube groups such as superheater and evaporator are already installed in the temperature band around 350 ° C, which is the catalytic activity temperature of the high temperature catalyst. Therefore, in order to install the catalyst, the already installed heat exchanger tube group should be removed and the catalyst should be installed in the space. Therefore, the increase in construction cost and decrease in heat exchange rate are inevitable, and the operation at high temperature not only accelerates the thermal fatigue of the catalyst layer and shortens the life, but also the catalyst such as ammonium sulfate because the oxidation reaction of sulfur dioxide increases as described above. The problem is that the poison is formed.

 As described above, the prior art in which the flue gas denitrification catalyst layer is arranged in a single layer form in a separate high temperature region has a problem due to the high temperature operation as described above. Therefore, it is preferable to use a catalyst having excellent nitrogen oxide removal efficiency at low temperature so as to suppress the formation of sulfate and sulfuric acid caused during high temperature operation. In this regard, the recent development of a catalyst having a low temperature active zone or a catalyst having a wide range of active zones covering both high and low temperatures suggests the possibility of solving problems in high temperature operation.                         

However, even in the above case, if a separate catalyst bed mounting space is provided in the design of the heat recovery boiler, the space utilization of the heat recovery boiler does not meet the tendency of the facility and the arrangement of other devices in the heat recovery boiler. Proper balance with the recovery function can lead to problems in process flexibility. In addition, in the existing system that does not provide a separate catalyst mounting space in the heat recovery boiler, the process for removing nitrogen oxide in the exhaust gas cannot be performed unless the heat exchange tube group is significantly removed as described above.

As such, the above mentioned prior arts refer mostly to the installation of an injection grid for uniform distribution of ammonia (or urea) introduced into the reductant or to the selective catalytic reduction reactor in a separate space of the boiler using a high temperature catalyst. In most cases, only the denitrification catalyst is installed and used as a single layer, and in particular, no attempt is made to utilize the maintenance space more usefully.

In order to solve the above-mentioned problems, the inventors have continually studied the high temperature active band catalysts conventionally used in the region corresponding to at least two or more maintenance spaces present in a conventional heat recovery boiler system. Process equipment during initial design by eliminating the catalyst mounting space that is conventionally provided as a separate single layer by allowing a multistage arrangement with a band catalyst or a multistage arrangement of a catalyst having a wide range of active zones in the at least two holding and spaces. It has been found that it can confer simplicity and flexibility. In particular, according to the above configuration, it is possible to achieve an excellent flue gas denitrification effect without additional changes to the boiler system that is not previously provided with a separate catalyst layer mounting space.

Accordingly, an object of the present invention is to provide a heat recovery boiler system in which a flue gas denitrification catalyst layer is formed without special structural changes in a conventional heat recovery boiler system having no separate catalyst mounting space.

It is another object of the present invention to provide a heat recovery boiler system that utilizes a region that serves only as a maintenance and maintenance space as a mounting space of a flue gas denitration catalyst layer.

Still another object of the present invention is to provide a heat recovery boiler system which can provide a simplicity and flexibility of a process by omitting a space of a flue gas denitrification catalyst layer conventionally mounted in a single layer in a high temperature zone.

The heat recovery boiler system of the present invention for achieving the above object,

Steam from the water provided by the water supply means by heat exchange between the exhaust gas and the heat exchange tube group as the exhaust gas introduced through the boiler duct sequentially contacts the high pressure steam generator and the low pressure steam generator having the heat exchange tube group. In the heat recovery boiler to generate,

A maintenance space is formed between each of the constituent members in the high pressure steam generator and the low pressure steam generator located in the boiler duct, and a reducing agent for removing nitrogen oxide contained in the exhaust gas by a selective catalytic reduction method. Means for injecting into the boiler duct are provided, and the catalyst layer having the flue gas denitrification performance corresponding to the temperature of the exhaust gas passing through the maintenance space is separated in two or more areas in the maintenance space. It is characterized by.

According to an exemplary embodiment of the present invention, the low pressure steam generating unit includes a low pressure evaporator connected to the liquid water supply means and a low pressure evaporator connected to the low pressure economizer as a constituent member, and the low pressure drum installed outside the boiler duct is the low pressure. It is connected to the evaporator. In addition, the high-pressure steam generating unit as a component member, the high-pressure carburettor connected to the liquid water supply means, the high-pressure evaporator connected to the high-pressure economizer, the high-pressure drum connected to the high-pressure evaporator and installed outside the boiler duct and the high-pressure superheat connected to the high-pressure drum Contains groups.

The present invention may be achieved in the following with reference to the accompanying drawings, but the present invention is not limited to the drawings.

In the present invention, the expression "high temperature band" and "low temperature band" does not mean a particularly limited range, but for convenience, typically means a temperature band of about 250 to 450 ° C and about 150 to 250 ° C, respectively.

As described above, in the conventional heat recovery boiler system structure, the space for maintenance and repair is replaced with the space for the catalyst layer for the flue gas denitrification without providing a space for the installation of the single-layer flue gas denitration catalyst. It is utilized, but considering the temperature drop caused by the flow of exhaust gas in the boiler (ie, the heat recovery), the catalyst layer is arranged in multiple stages in a separable manner.

Inside the heat recovery boiler is generally the highest temperature (ie the temperature at which the flue gas enters the heat recovery boiler from the gas turbine) is about 400-600 ° C. (typically about 500 ° C.) and after the heat recovery The temperature of the finally discharged gas is about 80-120 ° C. (typically about 100 ° C.), with a wide temperature distribution throughout the heat recovery boiler. As described above, the combined cycle power plant uses steam exhaust gas of high temperature to install water vapor in multiple stages for energy efficiency and maintenance.

3 is a diagram illustrating a schematic process of a combined cycle power plant including a heat recovery boiler system according to one embodiment of the present invention.

According to the drawing, as described with reference to FIG. 1, the hot exhaust gas flowing into the heat recovery boiler through the duct inlet 1 first passes through the high pressure steam generating unit. That is, while passing through the high-pressure superheater (2) and the high-pressure evaporator (3) generates a high pressure steam pressure by heat exchange between the heat exchange tube group and the exhaust gas is transferred to the high pressure drum (7), the high pressure steam of the high pressure drum It can be used to operate the steam turbine. At this time, the temperature of the exhaust gas is lowered as the high pressure superheater and the high pressure evaporator pass. However, since the temperature of the exhaust gas is still relatively high (typically about 300 to 400 ° C), high temperature energy can be used. Therefore, the exhaust gas passes through the low pressure steam generator 7 and passes through the low pressure steam generating unit.

In the low pressure steam generating section, the flue gas passing through the high pressure steam generating section generates a medium pressure steam pressure while passing through the low pressure evaporator (5), and the generated steam is used for operation of the steam turbine through the low pressure drum (8) or in the power plant. Used for warm drainage. At this time, the temperature of the exhaust gas is lowered as it passes through the low pressure evaporator to reach the low temperature region. However, since such a low temperature region also contains a degree of heat that can be utilized as a heat energy source, the relatively low temperature flue gas is discharged through the main stone 9 after passing through the low pressure coke 6. The heat energy recovered through the low pressure coke may be used for warm water drainage in a power plant.

As described above, the exhaust gas transferred from the steam turbine 13 into the boiler duct 1 exhibits various temperature distributions until it is discharged through the main stones 9. Therefore, when using a commercially available catalyst for the removal of nitrogen oxides in the flue gas having a wide temperature distribution, it is mainly active at a high temperature of about 350 ℃ or more part of the heat exchange tube group to be treated in the active zone of the high temperature catalyst The catalyst layer must be fitted after removing. In this regard, even if the above-mentioned high temperature catalyst is installed in the maintenance space in the heat recovery boiler, the area corresponding to the high temperature zone is limited, so that sufficient flue gas denitrification effect cannot be obtained.

However, with the recent development of catalysts having flue gas denitrification activity in the low temperature zone, in one embodiment of the present invention, a high temperature zone catalyst is installed in a maintenance space corresponding to the high temperature zone, while maintaining and repairing the low temperature zone. The low temperature zone catalyst is installed in the space. Therefore, in the said specific example, a catalyst layer is provided in multiple stages over several maintenance space.                     

In addition to low temperature zone catalysts, catalysts have recently been developed that exhibit flue gas denitrification activity over a wide band including high and low temperatures. According to another embodiment of the present invention, a catalyst layer having activity over a wide band is installed in multiple stages over two or more maintenance spaces. In the above embodiment, even in the case of a broadband catalyst, in order to achieve the flue gas denitrification effect required for the whole process, the installation space of the catalyst layer is narrow with only a single maintenance space.

In FIG. 3, the maintenance space in which the catalyst layer can be installed is preferably a space 21 between the high pressure evaporator and the high pressure carburettor, a space 22 between the high pressure carburettor and the low pressure evaporator, and a low pressure evaporator and a low pressure economizer. Space 23 between the low pressure coke and the duct outlet 18. However, in the above embodiments, the space between the high-pressure superheater and the high-pressure evaporator typically corresponds to a temperature range exceeding 450 ° C., so that the flue gas denitrification efficiency may be lowered beyond the active range of the catalyst currently available. However, since the deterioration of the catalyst layer and the generation of catalyst poisons can be caused, the catalyst layer is not installed in the space.

FIG. 4 shows an embodiment in which the catalyst bed is introduced in a separable manner into the maintenance space of the heat recovery boiler system. The figure shows an embodiment in which the internal high pressure mill 4 and the low pressure evaporator 5 are integrally formed according to the heat recovery boiler. In this case, therefore, the maintenance space between the autoclave and the low evaporator will not be utilized for the catalyst bed mounting. At this time, in the maintenance and repair space between the high-pressure evaporator (3) and the high-pressure carburettor (4) due to the internal arrangement of the boiler, the catalyst layer 21 having the flue gas denitrification performance over the high-temperature band or the broadband because the exhaust gas generally corresponds to the high-temperature band. ), And the high temperature zone catalyst layer is composed of two stages considering the internal structure of the heat recovery boiler applied. In addition, in the maintenance space between the low-pressure evaporator 5 and the low-pressure coking machine 6 corresponding to the low-temperature zone, the catalyst layer 23 having the activity over the low-temperature zone or the broadband is mounted, but constituted in one stage. In the embodiment shown in FIG. 4, the high-temperature zone catalyst layer is configured in two stages and the low-temperature zone catalyst layer is configured in one stage, but the present invention is not limited thereto.

According to the present invention, the catalyst usable in the high temperature zone in the boiler is not particularly limited, but the temperature of 250 to 450 ° C., the space velocity of 35,000 hr ⁻¹ , the oxygen concentration of 1 to 15%, and the initial stage of nitrogen oxide of 1,000 ppm or less It is preferable to use a catalyst having a nitrogen oxide removal efficiency of 50% or more under concentration conditions and maintaining durability at high temperatures. Such high temperature catalysts are disclosed in Korean Patent Nos. 314758, 439005, and the like, which are incorporated by reference in the present invention. On the other hand, the catalyst usable in the low temperature zone is also not particularly limited, but nitrogen oxides under conditions of a temperature of 150 to 250 ° C., a space velocity of 20,000 hr ⁻¹ , an oxygen concentration of 1 to 15%, and an initial nitrogen oxide concentration of 1,000 ppm or less It is preferable to use a catalyst having a removal efficiency of 50% or more. Such low temperature catalysts are disclosed in US Pat. No. 6,641,790, Korean Patent No. 382051, and the like, which are incorporated by reference in the present invention.

On the other hand, it is not particularly limited as a catalyst having activity over a band covering both high and low temperature zones in the heat recovery boiler, but the temperature of 150 to 450 ℃, the space velocity of 15,000hr ^-1 , oxygen of 1 to 15% It is preferable to use a catalyst that has a nitrogen oxide removal efficiency of 70% or more under a concentration and an initial concentration of nitrogen oxide of 1,000 ppm or less, and which can maintain durability even in a high temperature region. Examples of such broadband catalysts are disclosed in Korean Patent Application No. 2003-67200, which is incorporated herein by reference.

In addition, the drawing shows a process in which the introduced flue gas is processed through a honeycomb-type catalyst layer, and ammonia or urea as a reducing agent is introduced through the injection grid 15 as shown in FIG. 3. The construction of such an injection grid is already known in the art. Particularly, the catalyst layer may be formed by coating or impregnating a catalyst component on a structure selected from the group consisting of a metal plate, a metal fiber, a ceramic filter, and a honeycomb, or by molding (extruding) the catalyst component into a honeycomb form. Techniques for producing such catalyst-containing structures are well known in the art.

On the other hand, in the flue gas NOx removal reaction in the exhaust gas according to the present invention, the space velocity (gas hourly space velocity; GHSV) is between about 1000~60,000 hr ^-1, preferably from about 5,000~15,000hr ^-1. In addition, the molar ratio of the reducing agent (NH ₃ ) to the nitrogen oxide (NOx) is about 0.6 to 1.2, preferably about 0.8 to 1.2. In this regard, the characteristics of the exhaust gas (for example, the concentration of nitrogen oxides), the reaction conditions, the performance of the catalyst, and the like will be considered comprehensively in determining the number of stages and the arrangement of the catalyst layer mounted in the above-mentioned maintenance space. .

5 is a front and side view of one embodiment of a honeycomb catalyst bed module configured to be introduced in a separable manner into a maintenance space of a heat recovery boiler system, in accordance with the present invention.

As shown in the drawings, in the present invention, the catalyst layer mounted in the maintenance space in the heat recovery boiler is preferably configured in the form of a detachable module 34, for the following reasons:

In the present invention, the maintenance space in which the catalyst layer is mounted should secure a space for maintenance and repair when various problems occur in the heat recovery boiler. In this case, therefore, the catalyst layer must be easily removed and then remounted after the maintenance and repair work is completed. That is, the denitrification catalyst is normally installed, when the problem occurs in the heat recovery boiler, the catalyst layer is removed, maintenance and repair are performed, and then the denitrification catalyst is again mounted. To this end, the figure shows the modular catalyst layer as a preferred embodiment. That is, the rail is installed in the heat recovery boiler and the wheels 31 are installed in the catalyst layer module to facilitate the removal and installation of the catalyst layer. In particular, each catalyst layer module in the figure is composed of four vertical stages 33, each end is provided with a rail 32, each module is provided with wheels. Accordingly, the catalyst layer module 34 can be easily attached and detached.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.                     

Example 1

In order to confirm whether the nitrogen oxide removal method of the present invention is applicable to the actual process, the catalyst bed module is arranged in multiple stages as shown in FIGS. 3 and 4 in the maintenance space of the 75 MW combined cycle power plant heat recovery boiler. After nitrogen oxide removal performance was measured.

The test was conducted 15 times and was performed under conditions that reached a steady state after a certain time after starting. The conditions such as the exhaust gas flow rate, the temperature of the exhaust gas in the installed catalyst stage, and the space velocity (exhaust gas flow rate / installation catalyst volume) of the installed catalyst stage are shown in Table 1 below. In addition, the test results are shown in Table 2 below.                     

As a result, as shown in Table 2, the total nitrogen oxide removal efficiency was 78% or more on average, and it was confirmed that the emission of unreacted ammonia was maintained at 4 ppm or less. Therefore, it was confirmed that the nitrogen oxide removal method by the multistage installation of the catalyst in the heat recovery boiler of the present invention is efficient.

As described above, the present invention can not only increase the efficiency of the space but also provide flexibility to the process by mounting the flue gas denitration catalyst layer in multiple stages in a space utilized as a maintenance and repair space in a conventional heat recovery boiler. Optimization of sequence recovery can be achieved. In particular, the exhaust gas treatment in the low temperature zone by the multi-stage arrangement of the catalyst layer enables the formation of catalyst poison forming materials (eg, ammonium sulfate and / or ammonium nitrate), prolongs catalyst life, inhibits corrosion of the device, and the like. We can solve problem in one step.

Simple modifications and variations of the present invention can be readily used by those skilled in the art, and all such variations or modifications can be considered to be included within the scope of the present invention.

Claims (8)

Steam from the water provided by the water supply means by heat exchange between the exhaust gas and the heat exchange tube group as the exhaust gas introduced through the boiler duct sequentially contacts the high pressure steam generator and the low pressure steam generator having the heat exchange tube group. In the heat recovery boiler to generate, A maintenance and repair space is formed between the members constituting the high pressure steam generator and the low pressure steam generator located in the boiler duct, and the reducing agent for removing nitrogen oxide contained in the exhaust gas by a selective catalytic reduction method is used. Means for injecting into the duct is provided, and the catalyst layer having a flue gas denitrification performance corresponding to the temperature of the exhaust gas passing through the maintenance space is installed in multiple stages in a separable manner over two or more areas of the maintenance space. A heat recovery boiler system characterized by the above-mentioned. According to claim 1, wherein the low pressure steam generating unit comprises a low pressure evaporator connected to the liquid water supply means and a low pressure evaporator connected to the low pressure economizer as a constituent member, the low pressure drum installed outside the boiler duct is connected to the low pressure evaporator There is; And a high pressure steam generator connected to a liquid water supply means, a high pressure evaporator connected to the high pressure economizer, a high pressure drum connected to the high pressure evaporator and installed outside the boiler duct, and a high pressure superheater connected to the high pressure drum. An array recovery boiler system comprising: The low temperature catalyst layer and the high temperature catalyst layer are arranged in multiple stages as catalyst layers, wherein the low temperature catalyst layer has a temperature of 150 to 250 ° C., a space velocity of 20,000 hr ⁻¹ , an oxygen concentration of 1 to 15%, and nitrogen of 1,000 ppm or less. The nitrogen oxide removal efficiency is 50% or more under the initial concentration condition of the oxide, and the high temperature catalyst layer has a temperature of 250 to 450 ° C., a space velocity of 35,000 hr ⁻¹ , an oxygen concentration of 1 to 15%, and an initial nitrogen oxide concentration of 1,000 ppm or less. A heat recovery boiler system, characterized in that the nitrogen oxide removal efficiency is more than 50% under the conditions. The catalyst layer according to claim 1, wherein the catalyst layer has a nitrogen oxide removal efficiency of 70% or more under a temperature of 150 to 450 ° C., a space velocity of 15,000 hr ⁻¹ , an oxygen concentration of 1 to 15%, and an initial nitrogen oxide concentration of 1,000 ppm or less. An array recovery boiler system, characterized in that the multi-stage arrangement. The heat recovery boiler system according to claim 1, wherein the selective catalytic reduction reaction in the boiler is performed under a space velocity of 1000 to 60,000 hr ⁻¹ and a molar ratio of reducing agent to nitrogen oxides of 0.6 to 1.2. The method of claim 1, wherein the catalyst layer is characterized in that the catalyst component is coated or impregnated in a structure selected from the group consisting of a metal plate, a metal fiber, a ceramic filter, and a honeycomb, or a catalyst component formed into a honeycomb structure. Heat recovery boiler system. 2. The heat recovery boiler system of claim 1, wherein said catalyst bed is modularized to facilitate separation and mounting. 3. The maintenance and repair of claim 2, wherein the catalyst layer is disposed between the high-pressure evaporator and the high-pressure carburettor, between the high-pressure evaporator and the low-pressure evaporator, between the low-pressure evaporator and the low-pressure evaporator, and between the low-pressure economizer and the outlet of the boiler duct. A heat recovery boiler system, characterized in that it is mounted in multiple stages in a separable manner over two or more areas of the space.

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