KR20230082733A - SCR system equipped with soot blower that prevents dust in the exhaust gas generated during the cement manufacturing process from adhering to the SCR catalyst - Google Patents

Abstract

The present invention relates to an SCR system to which a soot blower is applied to suppress dust in exhaust gas generated during the cement manufacturing process from adhering to an SCR catalyst, and specifically, dust in exhaust gas generated during the cement manufacturing process This SCR catalyst is prevented from sticking by adhesion or deposition, thereby preventing catalyst wear and damage, catalyst surface and cell clogging, and increasing the differential pressure of the catalyst. It relates to a method for reducing nitrogen oxides (NOx) based on a selective catalytic reduction method in which a soot blower is applied for maintenance.

Description

SCR system equipped with soot blower that prevents dust in the exhaust gas generated during the cement manufacturing process from adhering to the SCR catalyst }

The present invention relates to an SCR system to which a soot blower is applied to suppress dust in exhaust gas generated during the cement manufacturing process from adhering to an SCR catalyst, and specifically, dust in exhaust gas generated during the cement manufacturing process This SCR catalyst is prevented from sticking by adhesion or deposition, thereby preventing catalyst wear and damage, catalyst surface and cell clogging, and increasing the differential pressure of the catalyst. It relates to a method for reducing nitrogen oxides (NOx) based on a selective catalytic reduction method in which a soot blower is applied for maintenance.

The cement industry is an industry that builds the foundation of a nation along with the steel and petrochemical industries, and consumes a large amount of resources and energy. In terms of environment, there are many negative aspects such as generation of dust, CO ₂ and nitrogen oxides (NOx). has come to the fore In addition, interest in recycling industrial by-products into 'cement raw materials' or 'fuel' is increasing.

Since high-temperature monochlorination firing is essential for maintaining and improving the production process and quality, the cement industry inevitably has process conditions in which NOx is generated, and harmful substances including carbon monoxide and dust are emitted. are being added.

Currently, Selective Non- Catalytic Reduction (SNCR) is operated as a method to reduce nitrogen oxides in the domestic cement production process, but the removal efficiency is 40 to 70% in the reaction temperature range of 850 to 1030 ℃. It is difficult to meet the recent standards that are being strengthened.

Among the denitrification technologies for removing nitrogen oxides in the cement manufacturing process, representative processes are the SNCR process and the Selective Catalytic Reduction (SCR) process.

Selective non-catalytic reduction (SNCR) is a method of decomposing NOx by directly injecting a reducing agent into high-temperature exhaust gas without using a catalyst.

SNCR has a low initial installation cost compared to other NOx reduction technologies and is easy to apply to existing facilities, so it does not require a separate installation space, so it has excellent applicability but low efficiency. In the reaction temperature range of 850 ~ 1030 ℃, NOx reduction efficiency shows 40 ~ 70% of denitrification efficiency, but in the temperature range above the reaction temperature range, NOx generation increases due to the oxidation reaction of the supplied reducing agent (urea hydrogen, ammonia water), In the low temperature range, the reducing agent does not react efficiently and ammonia slip occurs.

Reducing agents used in SNCR include ammonia or ammonia water, urea or urea water, ammonium carbamate, pyridine, ammonium acetate, cyanuric acid, ammonium carbonate, etc. In terms of production, urea water is used in most SNCR processes.

When using ammonia water as a reducing agent in a thermal power plant or industrial incinerator, it is advantageous to use urea water because ammonia itself is a toxic substance, and various regulations are severe in addition to the problem of having a harmful effect on the human body.

In the case of ammonia, it has excellent selectivity for NO compared to other types of reducing agents and is mainly used in the SCR process. It must be stored in a heavy-walled storage tank or built on a protective ground, and in the event of a leakage accident, it is difficult to quickly respond to it due to difficulty in accessing the accident site, so there is a risk of expanding large-scale accidents. In addition, a large amount of NH ₃ is required to cover SCR facilities of current power generation and incineration facilities.

Currently, in thermal power plants or industrial incinerator denitrification (SCR) facilities, denitrification facilities that apply urea water as a reducing agent are increasing in consideration of stable operation and environmental aspects.

Selective Catalytic Reduction (SCR) is a technology that uses ammonia as a reducing agent to convert NOx, one of air pollutants, into harmless N ₂ and H ₂ O. It shows high denitrification efficiency and has several advantages such as easy operation and maintenance As a result, it is the most representative technology for reducing NOx among the technologies developed so far, and it has already been commercialized worldwide and is in operation in various plants. It is widely used in Japan to remove more than 90% of NOx from boilers using fossil fuels, and is used in gas turbines and internal combustion engines in the United States. The principle of this method is to directly inject ammonia, and after injecting ammonia gas diluted with air or steam into the exhaust gas, supply it to the catalyst layer to reduce NOx, and the reduction reaction proceeds as follows. this reaction Since most of NOx is NO, reaction formula (1) becomes the main reaction.

4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (1)

SCR is a process in which NH ₃ in ammonia or urea water selectively reacts with NOx on a catalyst to convert it into N ₂ , and is used to remove NOx emitted from gas turbines, diesel engines, and thermal power plants. The NOx reduction efficiency by SCR can be up to 90% or more, and it also contributes to the removal of VOCs, dioxins/furans and mercury.

In the case of ammonia, it has excellent selectivity for NO compared to other types of reducing agents and is mainly used in the SCR process. It must be stored in a heavy-walled storage tank or built on a protective ground, and in the event of a leakage accident, it is difficult to quickly respond to it due to difficulty in accessing the accident site, so there is a risk of expanding large-scale accidents. In addition, a large amount of NH ₃ is required to cover SCR facilities of current power generation and incineration facilities.

The domestic cement industry has been installing and operating SNCR facilities since 2004 to reduce nitrogen oxides, and overseas, SCR facilities are being installed and operated in various industrial processes to improve NOx efficiency. SCR technology is widely used in thermal power plants, incineration plants and other industries.

In the cement industry, for the first time in the world, SCR equipment was applied at the Solnhofen cement plant in Germany. At the Solnhofen Cement Plant in Germany, using the pilot plant research results, SCR facilities were installed in the front of the dust collection facility (High Dust) in 2000, and catalysts were installed in three places of the 6-stage reactor. SCR inlet NOx concentration of 1,050 mg/Nm ³ and outlet 200 mg/Nm ³ were achieved, and SCR facilities are being built and operated in the cement manufacturing process.

There are three major types of SCR applied to overseas cement manufacturing processes, which are classified into 1) High Dust SCR, 2) Tail End SCR, and 3) Semi-Dust SCR.

As mentioned above, the domestic cement industry is installing and operating SNCR facilities to reduce nitrogen oxides, but as the efficiency is influenced by the state of the cement manufacturing process, there are limits to meeting the currently strengthening emission standards. Accordingly, the cement manufacturing process requires the application of SCR technology, which is attracting attention due to the recently tightened NOx emission regulations worldwide.

In addition, if the existing SNCR efficiency is about 40 to 70%, when linked with SCR, the nitrogen oxide reduction efficiency is more than 90%, so in addition to the utilization of the SNCR system, the SCR system suitable for the domestic cement manufacturing process is essential. What needs to be done is the reality.

As a system for reducing nitrogen oxides (NOx) generated in the cement manufacturing process, the SCR (selective catalytic reduction) system is the most suitable, but due to the high dust concentration load of the kiln, the catalyst is clogged by dust and the electric precipitator (electric precipitation, EP) or bag filter (BF), the SCR system cannot be installed. It is possible to install an SCR system at the downstream of EP or BF with a relatively low dust load, that is, in a process with a low dust concentration load. This has a problem in that it cannot play a role in improving air quality from an environmental point of view.

The present invention is to recognize and solve the above problems, to reduce the risk of abrasion and damage to the SCR catalyst even under high air volume exhaust gas conditions containing dust, to extend the life of the catalyst, and to prevent dust from depositing on the catalyst. The purpose is to prevent a decrease in activity.

A first aspect of the present invention is a nitrogen oxide reduction system having an SCR reactor that performs a selective catalytic reduction (SCR) on ammonia gas and dust containing NOx generated during the cement manufacturing process, (1) exhaust gas (2) While suppressing the adhesion or deposition of dust on the fixed catalyst layer, (2) supplying oxygen gas as a reactant as far as possible by intermittently injected compressed air, and at the same time intermittent forward and/or reverse disturbance to each fixed catalyst layer Provided is a nitrogen oxide reduction system designed to increase the overall nitrogen oxide removal efficiency of an SCR reactor by mixing reaction gases in a direction that removes or weakens a longitudinal reaction gas gradient within the system.

A second aspect of the present invention is a method for removing nitrogen oxides (NOx) in exhaust gas generated during the cement manufacturing process in the nitrogen oxide reduction system of the first aspect, through a soot blower, It prevents dust in the exhaust gas from sticking to the SCR catalyst due to adhesion or deposition, preventing catalyst abrasion and damage, and catalyst surface and cell clogging, thereby preventing the catalyst from increasing differential pressure and preventing catalyst activity from deteriorating. Provided is a nitrogen oxide (NOx) removal method characterized by continuously maintaining the activity of the catalyst.

Hereinafter, the present invention will be described.

In order to apply the SCR process to the cement manufacturing process, it is necessary to secure countermeasures against catalyst masking and poisoning problems caused by dust in exhaust gas flowing into the SCR catalyst layer.

Adhesion often occurs when limestone with high Na ₂ O and K ₂ O components is used in cement manufacturing.

In addition, as a method of reducing the inflow of dust into the SCR catalyst layer, there is a method of installing a cyclone dust collector or an electrostatic bag filter, but the dust collection efficiency is low because the size of dust is as small as 20 to 30 μm.

Meanwhile, as a method of removing solid particles attached to the SCR catalyst, a method of washing a solid catalyst layer such as honeycomb using technologies such as high-pressure gas injection and a sonic horn is utilized. However, since the risk of catalyst damage increases when impact is continuously repeated for particle removal, the present invention provides a fundamental solution to suppressing the attachment or deposition of dust in the exhaust gas generated during the cement manufacturing process to the fixed catalyst layer. It was meant to be.

That is, the nitrogen oxide reduction system of the present invention having an SCR reactor that performs a selective catalytic reduction (SCR) on ammonia gas and dust containing NOx generated during the cement manufacturing process continuously flows through a fixed catalyst layer. For the exhaust gas flow, compressed air is injected intermittently through soot blowers installed before and/or after the fixed catalyst layer to provide forward and/or reverse disturbance, so that dust in the exhaust gas adheres to or deposits on the fixed catalyst layer. It is characterized by obstruction. In addition, in the nitrogen oxide reduction system of the present invention, the soot blower intermittently injects compressed air at the front and/or the rear of each fixed catalyst layer, to the NOx-containing exhaust gas flow mixed with ammonia gas as a reducing agent, While supplying oxygen gas as far as possible, the overall nitrogen oxide removal efficiency of the SCR reactor is improved by mixing the reaction gas in a direction that removes or weakens the longitudinal reaction gas gradient in each fixed catalyst layer through intermittent forward and/or reverse agitation. It is characterized by elevation.

4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (1)

[soot blower]

As described above, the soot blower in the present invention is applied for the purpose of reducing nitrogen oxides generated in the cement manufacturing process, and is different from the soot blower applied to the SCR system of a gas turbine or thermal power plant. Gas turbines and thermal power plants produce dust of up to 10 g/Nm ³ , but the cement manufacturing process generates dust of up to 120 g/Nm ³ , making it difficult to reduce nitrogen oxides with a simple SCR system due to excessive dust. there is.

In the SCR system for reducing nitrogen oxides generated in the cement manufacturing process, the present invention has soot blowers for compressed air injection installed at the bottom and top of the SCR catalyst to prevent dust from adhering to and depositing on the SCR catalyst to prevent a rise in the differential pressure of the catalyst and wear of the catalyst. This can prolong the life of the catalyst.

The nitrogen oxide reduction system of the present invention, equipped with an SCR reactor that performs selective catalytic reduction (SCR) on dust, NOx-containing exhaust gas and ammonia gas generated during the cement manufacturing process, is Reduces the risk of abrasion and damage of the SCR catalyst due to dust even under high air volume exhaust gas conditions containing dust, extends the life of the catalyst, and reduces the activity of the catalyst as dust is deposited on the catalyst To prevent this, a soot blower that sprays compressed air is applied. A soot blower is a type of SCR catalytic dust (air) flushing device.

That is, in order to reduce the risk of abrasion and damage of the catalyst when reducing nitrogen oxides under high dust conditions, extend the lifespan, and prevent dust from depositing on the catalyst and reducing the activity of the catalyst, according to the present invention, a soot blower (soot blower) blower) is applied, a soot blower is installed before and/or after the solid catalyst layer to supply high-pressure air. Through this, more efficient nitrogen oxide reduction is possible.

In the SCR system according to one embodiment of the present invention, in the SCR reactor, two or more fixed catalyst layers are vertically spaced apart from the exhaust gas flow generated during the cement manufacturing process, and a plurality of catalyst layers are sprayed with compressed air at regular intervals. Two soot blowers are arranged in a vertical direction. Since the shape of the catalyst module (FIG. 6) is implemented as an air flow, it is impossible to shake off the dust inside the catalyst when spraying horizontally.

In addition, in the SCR system according to one embodiment of the present invention, the catalyst layers are stacked vertically spaced apart in multiple stages,

If the SCR system is up flow, the exhaust gas flow flows from the vertical bottom to the top of the catalyst layer, and the soot blower is (1) in the same direction as the exhaust gas flow at the bottom of each catalyst layer or (2) in the same direction as the exhaust gas flow at the bottom of each catalyst layer and at the top of each catalyst layer In the direction opposite to the exhaust gas flow, compressed air is injected;

If the SCR system is down flow, the exhaust gas flow flows from the vertical top to the bottom of the catalyst layer. It may be to inject compressed air in a direction opposite to the exhaust gas flow.

The soot blower may be continuously and repeatedly operated at the same time as the cement manufacturing process starts.

The higher the pressure of the compressed air injected from the soot blower, the better, and may be, for example, 5 to 9 kg _f /cm ² .

The soot blower injects compressed air for 10 to 30 seconds at intervals of 1 to 3 minutes for each catalyst layer arranged in multiple stages, and changes the time and/or differential pressure of the compressed air from the first catalyst layer to the last layer in the direction of exhaust gas flow. According to this, automatic valves installed in each line may be sequentially injected under program control.

For example, compressed air is injected in the same direction as the exhaust gas flow at the bottom of the first catalyst layer, compressed air is sprayed in the opposite direction to the exhaust gas flow at the top of the first catalyst layer, and then compressed in the same direction as the exhaust gas flow at the bottom of the second catalyst layer. Air is sprayed, and compressed air is sprayed on the top of the second catalyst layer in a direction opposite to the exhaust gas flow.

For example, compressed air is simultaneously injected in the same direction as the exhaust gas flow at the bottom of each catalyst layer, and then compressed air is simultaneously injected in the opposite direction to the exhaust gas flow at the top of each catalyst layer.

For example, compressed air is sequentially injected in the same direction as the exhaust gas flow at the lower end of each catalyst layer, and then compressed air is sequentially injected in the opposite direction to the exhaust gas flow at the top of each catalyst layer.

The soot blower for injecting compressed air in the same direction as the exhaust gas flow and the soot blower for injecting compressed air in the opposite direction to the exhaust gas flow may operate in conjunction with each other or independently.

Hereinafter, the configuration of the present invention for achieving the object as described above will be described in more detail with reference to the accompanying drawings.

1 is an SCR reactor in which a soot blower is installed at the bottom of each SCR catalyst (left side view) and at the top of each SCR catalyst (right side view) so that the flow of injecting compressed air is in the same direction as the exhaust gas flow according to one embodiment of the present invention. As a cross-sectional view showing, it is configured to minimize dust in the catalyst layer by spraying air at a pressure of 5 to 9 kg _f / cm ² in the same direction as the exhaust gas flow so that the minimized dust can pass through the next catalyst layer.

Figure 2 is a cross-sectional view showing the flow of compressed air by applying soot blowers to the lower and upper ends of the SCR catalyst layer according to one embodiment of the present invention. As a result, the soot blower at the top of the catalyst layer injects air at a pressure of 5 ~ 9 kg _f / cm ² in the opposite direction to the exhaust gas flow to minimize dust at the bottom of each catalyst layer, and the minimized dust passes from the top of each catalyst layer to the next catalyst layer. configured so that it can be In the case of the right side of FIG. 2, the relationship between the flow of exhaust gas and the flow of compressed air is the same.

3 is an SCR system design diagram in which the exhaust gas flow is up flow and a soot blower is applied at the bottom of the SCR catalyst layer in the cement manufacturing process. In some cases, exhaust gas from which dust has been partially removed is introduced into the SCR catalyst layer through a cyclone.

4 is an SCR system design diagram in which the exhaust gas flow is up flow in the cement manufacturing process and soot blowers are applied to the bottom and top of the SCR catalyst layer. In some cases, exhaust gas from which dust has been partially removed is introduced into the SCR catalyst layer through a cyclone.

5 is a design diagram of an SCR system in which the exhaust gas flow is down flow in a cement manufacturing process and soot blowers are applied to the top and bottom of the SCR catalyst layer. In some cases, exhaust gas from which dust has been partially removed is introduced into the SCR catalyst layer through a cyclone.

3 to 5 show the SCR system applied to the cement manufacturing process. The volume of the SCR catalyst is designed in consideration of the amount of exhaust gas and dust in the cement manufacturing plant, the catalyst is stacked in multiple stages, and the soot blower is installed at the bottom of the catalyst layer. (Fig. 3) or the upper and lower ends (Figs. 4 and 5) in the same direction as the exhaust gas flow and in the opposite direction to the exhaust gas flow. The soot blower injects compressed air for a certain period of time at regular time intervals for each catalyst stacked in multiple stages, and injects compressed air from the first catalyst layer to the last catalyst layer in the exhaust gas direction. The above process is continuously repeated as soon as the cement manufacturing process starts. The pressure of the compressed air is 5~9 kg _f /cm ² .

Anyone with ordinary knowledge in the art pertaining to the design of the present invention can make various modifications, and such changes will fall within the scope of the claims.

[SCR catalyst]

Metals used for metal oxide catalysts include V, Fe, W, Cu, Mo, Mn, Ce, Ni, Sn, and the like in order of frequency of use. Also, the reactivity between metals or their compounds and nitrogen oxides is Pt, MeO ₂ , CuO, Fe ₂ O ₃ , Cr ₂ O ₃ , Co ₂ O 3 , MoO ₃ , NiO, _{WO 3 ,} Ag ₂ O, ZrO ₂ , Al Reactivity decreases in the order of ₂ O ₃ , SiO ₂ , and PhO. Metal oxide catalysts use a mixture of two or more metals or compounds that are highly reactive with nitrogen oxides. Examples of frequently used catalysts include V ₂ O ₅ -Al ₂ O ₃ catalyst, V ₂ O ₅ -SiO ₂ -TiO ₂ catalyst, Pt catalyst, WO ₃ -TiO ₂ catalyst, Fe ₂ O ₃ -TiO ₂ catalyst, CuO-TiO ₂ catalyst, and CuO-Al ₂ O ₃ catalyst. Catalysts mainly used in SCR are V2O ₅ catalysts, and among them, V ₂ O ₅ -Al ₂ O ₃ catalysts and V ₂ O ₅ -TiO ₂ catalysts are most often used.

NH ₃ -SCR is a technology that can remove more than 90% of NOx emitted from stationary sources, and is the best available control technology (BACT) among NOx control technologies to date in terms of price competitiveness and stability of catalytic activity. is in commercialization.

Catalysts used in NH ₃ -SCR can be largely classified into noble metal catalysts, metal oxides, and zeolites in which Cu or Fe is ion-exchanged. An NH ₃ -SCR catalyst containing a noble metal element as an active component shows excellent NOx removal efficiency at a low temperature of 250 °C or less. Among the zeolite catalysts, the most representative types used for NH ₃ -SCR include Cu-ZSM5 and Fe-ZSM5 catalysts in which Cu or Fe is ion-exchanged. Cu-ZSM5 exhibits excellent activity at 200-300 °C, and Fe-ZSM5 exhibits relatively good activity at high temperatures of 500 °C or higher. However, zeolite catalysts have problems such as deterioration of activity due to moisture, deterioration of activity due to SO ₂ , and deterioration of activity due to hydrocarbons present in exhaust gas. The metal oxide catalyst used in NH ₃ -SCR includes manganese oxides, cerium oxides, tungsten oxides, and vanadium oxides as active components, TiO ₂ and Al ₂ O as supports. There are catalysts prepared by being supported on ₃ , etc. A catalyst using manganese oxide and cerium oxide shows superior catalytic activity at a low temperature of 250 ° C or less than a VOx/TiO ₂ catalyst using vanadium oxide as an active component, and this is called a low-temperature SCR catalyst (LTC). It is known that these catalysts have a very large deactivation effect by SO ₂ compared to their excellent activity at low temperatures, and that the catalytic activity of catalysts containing manganese oxide as an active component is greatly reduced by moisture contained in exhaust gas. On the other hand, the VOx/TiO ₂ catalyst in which vanadium oxide is added as an active component to TiO ₂ as a support exhibits excellent NOx removal efficiency at a temperature of 250-400 ° C, and is different from other catalysts in terms of activity reduction due to moisture and durability against SO ₂ It shows very good performance compared to catalysts. For this reason, VOx/TiO ₂ -based catalysts are widely used for commercial purposes.

The SCR process can obtain a removal efficiency of more than 90% in the temperature range of 300 ~ 450 ℃ when using the Pt-V ₂ O ₅ /TiO ₂ catalyst. However, the cost of the catalyst is high and the reduction unit of nitrogen oxide is relatively high due to the deactivation problem according to the reaction conditions.

SCR catalysts are classified into plate-type catalysts, corrugate-type catalysts, and monolith extrusion catalysts according to their shape and manufacturing method (FIG. 6).

In the plate-type catalyst, after coating a catalytically active material on a metal mesh support, a plate-shaped catalyst cartridge with a bent surface is manufactured, and each cartridge is fitted to form a catalyst block. Exhaust gas flows through the gap between the plate catalysts, so the reaction area per unit volume is low, but the thermal and mechanical durability of the catalyst is excellent and the pressure loss due to the catalyst is low, so it is mainly used in coal-fired power plants with a lot of particulate matter in the exhaust gas. there is.

Corrugate-type catalysts are prepared by preparing a corrugated carrier made of ceramic or glass fibers and then coating the carrier with a slurry containing a catalytically active material. It has the advantages of a short catalyst production period, light weight, and a large reaction area per unit volume, but has low mechanical strength and durability, making it difficult to apply it as a pollutant emission source with a large amount of fly-ash in exhaust gas.

Monolith extruded catalyst is an integral structure, and the inside and outside of the catalyst are made of the same material, so the composition is the same in any part, and the opening of the catalyst can be manufactured in various geometric shapes. It shows the highest reaction area per unit volume among the three catalyst shapes, and has the advantage of easy catalyst regeneration, but the catalyst production period is long, and its durability is intermediate between plate and corrugate catalysts.

In general, the catalyst used in SCR is a honeycomb type and is more economical because of its large geometric surface area. The basic raw material for maintaining the shape of the catalyst is titanium dioxide (TiO ₂ ), and vanadium pentoxide (V ₂ O ₅ ) and tungsten trioxide (WO ₃ ) are added.

The volume of the SCR catalyst can be designed considering the amount of exhaust gas and dust during the cement manufacturing process.

[reducing agent]

SCR decomposes NOx into harmless N ₂ and H ₂ O through a reducing agent. Reducing agents used in the SCR reaction can be classified into HC-SCR using hydrocarbon, H ₂ -SCR using hydrogen, and NH ₃ -SCR using ammonia.

Ammonia (NH ₃ ) is a reducing agent mainly used in the currently commercialized catalytic reduction process (SCR) because its selectivity for NO is superior to other types of reducing agents (hydrocarbons and carbon monoxide). However, NH ₃ has disadvantages in that it is highly toxic, corrodes various equipment, and requires high costs for storage and transportation.

The injection concentration of NH ₃ used in the SCR reaction is controlled according to the concentration of NOx contained in the exhaust gas, and most of NH ₃ is used as a reducing agent in the SCR reaction when an appropriate temperature is maintained as the SCR reaction proceeds.

In the SCR system of the present invention, there is no mutual interference between the reducing agent supply and the soot blower.

In order to supply the reducing agent to the SCR system, the ammonia injection nozzle may be located in front of the first catalyst layer in the direction of exhaust gas flow.

For example, the ammonia injection system adjusts the pump flow rate while looking at the NOx reduction efficiency, with a minimum of 2 to 5 meters before the catalyst layer, a maximum of 5 to 10 meters, and one or more nozzles single or combined, with an injection flow rate of more than 1 liter per hour.

In addition, in the case of the reducing agent for reducing nitrogen oxides in the SCR system of the present invention, (1) nitrogen oxides are reduced by urea water supplied from the SNCR at the front end, and then nitrogen oxides are reduced by SCR by slip and (2) ammonia water in the SCR system By reducing nitrogen oxides through injection, dual supply of reducing agent is also possible.

Meanwhile, when a vaporizer for forming ammonia by urea decomposition reaction is installed outside the SCR reactor, the ammonia formed in the vaporizer may be supplied to the SCR reactor through an ammonia injection grid (AIG). AIG (Ammonia injection grid) can mix the ammonia formed in the carburetor with NOx-containing flue gas and supply it to the SCR reactor.

[SCR system operating conditions]

An NOx removal post-treatment system in which an SCR catalyst is currently used is performed by a reaction to remove NOx on a catalyst using NH ₃ and urea as a reducing agent.

4NH ₃ + 4NO + O ₂ →4N ₂ + 6H ₂ O (1,224 kJ/mol) (One)

As shown in Reaction Formula (1), the SCR reaction proceeds very quickly on a catalyst in an oxygen atmosphere in the range of 200-400 °C. At this time, the stoichiometric ratio of NH ₃ and NO can be said to be 1.0 because NOx is present in more than 95% of NOx in general exhaust gas. In the NH ₃ -SCR reaction, NH ₃ , which should be used as a reducing agent, reacts with oxygen on the catalyst to undergo a direct oxidation reaction, generating NOx such as NO, NO ₂ and N ₂ O, which negatively affects the catalyst activity. Therefore, in consideration of this point, the present invention can adjust the operating conditions of the soot blower in various ways according to the change in the air volume of the exhaust gas generated in the cement manufacturing process and introduced into the SCR system.

[Catalyst inactivation]

When the SCR system is applied to the cement manufacturing process, the catalyst deactivation problem must be considered. SO ₃ in flue gas reacts with NH ₃ to form ammonium sulfate (NH ₄ HSO ₃ ), which causes catalyst deactivation and is deposited on the heat exchanger at the rear of the SCR facility, leading to corrosion. In order to suppress the deactivation of the catalyst by the sulfur component, the oxidation rate of SO ₂ to SO ₃ should be suppressed and the reaction for the adsorption of SO ₂ on the catalyst surface should be controlled. The deactivation of these SCR catalysts must be controlled in consideration of optimal process combination design technology and economic feasibility.

SO ₂ contained in exhaust gas from the cement industry is as low as 10 to 20 mg/N㎥, but if the SO ₂ concentration increases due to input of high-sulfur fuel, etc., fouling that blocks the pores of the SCR filter may occur. there is.

In particular, the reduction in catalyst efficiency due to fouling can cause serious problems in downtime and increase in operating costs, as there is no alternative other than filter replacement.

As illustrated in FIGS. 3 and 4, the SCR system to which the soot blower is applied according to the present invention has a hopper installed at the bottom of the SCR reactor so that dust and reaction products of SO ₃ are not attached to the catalyst layer through the soot blower. It can be collected by designing the process so that it does not leak and falls out of the flue-gas stream.

[Method of removing nitrogen oxides (NOx) in flue gas generated during the cement manufacturing process]

The method for removing nitrogen oxides (NOx) according to the present invention prevents the phenomenon in which dust in the exhaust gas generated during the cement manufacturing process is adhered to or deposited on the SCR catalyst through a soot blower to prevent the catalyst from being fixed. It is possible to continuously maintain the activity of the catalyst by preventing an increase in differential pressure of the catalyst and preventing a decrease in the activity of the catalyst due to abrasion and damage and clogging of the surface and cells of the catalyst.

Therefore, even under globally tightened NOx emission regulations, the cement manufacturing process enables industrial by-products to be used as cement raw materials or fuel.

In addition, in the method for removing nitrogen oxides (NOx) according to the present invention, exhaust gas generated during the cement manufacturing process may be treated to reduce nitrogen oxides by a selective non-catalytic reduction method, and then nitrogen oxides reduced by a selective catalytic reduction method.

Due to the nature of the cement manufacturing process, excessive dust accumulates on the SCR catalyst layer, causing a decrease in catalyst activity and the risk of catalyst wear or damage due to ^dust . The nitrogen oxide reduction system of the present invention, which reduces nitrogen oxides by passing the exhaust gas of high air volume contained in a soot blower applied SCR facility, minimizes the concentration of nitrogen oxides while minimizing the problems caused by the above-mentioned excessive dust. and play a major role in improving the air quality environment.

1 shows an SCR reactor in which a soot blower is installed at the bottom of each SCR catalyst (left side view) and at the top of each SCR catalyst (right side view) so that the flow of compressed air is in the same direction as the exhaust gas flow according to the direction of the exhaust gas flow it is a cross section
2 shows a flow of spraying compressed air by applying a soot blower to the bottom and top of the SCR catalyst of the present invention, so that the flow of spraying compressed air is in the same direction as the exhaust gas flow according to the direction of the exhaust gas flow, so that each SCR catalyst Bottom, on top of each SCR catalyst in the direction opposite to the flue-gas flow (left view) and on top of each SCR catalyst in the same direction as the flue-gas flow, below each SCR catalyst in the opposite direction of the flue-gas flow (right view) A cross-sectional view showing an SCR reactor with a blower installed.
3 is an SCR system design diagram in which the exhaust gas flow is up flow and a soot blower is applied at the bottom of the SCR catalyst layer in the cement manufacturing process.
4 is an SCR system design diagram in which the exhaust gas flow is up flow in the cement manufacturing process and soot blowers are applied to the bottom and top of the SCR catalyst layer, and are a left view, a front view, and a right view of the design.
5 is a design diagram of an SCR system in which the exhaust gas flow is down flow in a cement manufacturing process and soot blowers are applied to the bottom and top of the SCR catalyst layer.
6 illustrates plate-type catalysts, corrugate-type catalysts, and monolith extrusion catalysts.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are only intended to clearly illustrate the technical features of the present invention, but do not limit the protection scope of the present invention.

[Example 1]

Referring to FIG. 3, which is a cross-sectional view showing the flow of compressed air by applying a soot blower to the bottom of the SCR catalyst layer, dust is removed from the bottom of the catalyst by spraying air at a pressure of 5 to 9 kg _f / cm ² in the same direction as the exhaust gas flow. is minimized so that the minimized dust can pass through the catalyst of the next layer. This reduces the risk of abrasion and damage of the SCR catalyst by dust generated in the cement manufacturing process, extends the life of the catalyst, and prevents dust from depositing on the catalyst to reduce the activity of the catalyst. Nitrogen oxide reduction is possible.

[Example 2]

Referring to FIG. 2, which is a cross-sectional view showing the flow of compressed air by applying soot blowers to the lower and upper ends of the SCR catalyst layer, the soot blower at the lower or upper portion of the catalyst layer flows in the same direction as the exhaust gas flow, and the soot blower at the upper or lower portion of the catalyst layer It is configured to minimize dust at the bottom or top of the catalyst layer by spraying air at a pressure of 5 to 9 kg _f / cm ² in the opposite direction to the exhaust gas flow, and to allow the minimized dust to pass from the top or bottom of the catalyst layer to the next catalyst layer. As in Example 1, when the soot blower was applied only to the bottom of the catalyst layer, a large amount of dust was deposited on the top of each catalyst layer, which caused the differential pressure of the SCR catalyst to increase, reducing the denitration efficiency. As a way to solve this problem, a soot blower was applied to both the upper and lower portions of the catalyst layer as described above. This reduces the risk of abrasion and damage of the SCR catalyst by dust generated in the cement manufacturing process, extends the life of the catalyst, and prevents dust from depositing on the catalyst to reduce the activity of the catalyst. Nitrogen oxide reduction is possible. The soot blower injects compressed air for 10 to 30 seconds at intervals of 1 to 3 minutes for each catalyst stacked in multiple stages, and injects compressed air from the first catalyst layer to the last catalyst layer in the exhaust gas direction. The above process is continuously repeated as soon as the cement manufacturing process starts. The pressure of the compressed air is 5~9 kg _f /cm ² .

1: SCR reactor
2: Catalyst
3: soot blower

Claims (15)

A nitrogen oxide reduction system equipped with an SCR reactor that performs selective catalytic reduction (SCR) on ammonia gas and exhaust gas containing NOx and dust generated during the cement manufacturing process,
For the exhaust gas flow continuously flowing through the fixed catalyst layer, compressed air is intermittently injected through a soot blower installed at the front and / or the rear of the fixed catalyst layer to provide forward and / or reverse disturbance,
(1) while suppressing the attachment or deposition of dust in the exhaust gas to the fixed catalyst layer,
(2) Oxygen gas, which is a reactant, is supplied as far as possible by intermittently injected compressed air, and reacts in the direction of removing or weakening the longitudinal reaction gas gradient in each fixed catalyst layer through intermittent forward and/or reverse disturbance. A nitrogen oxide reduction system characterized by being designed to increase the overall nitrogen oxide removal efficiency of the SCR reactor by mixing the gas. The method of claim 1, even if the exhaust gas with a high air volume of 450,000 Nm ³ /hr or more containing 120 g/Nm ³ or more of dust generated in the cement manufacturing process passes through the SCR reactor, it is intermittently compressed through a soot blower. A nitrogen oxide reduction system characterized in that it is designed to suppress wear of the SCR catalyst by dust by injecting air forward and/or backward into the exhaust gas flow. The method of claim 1, wherein in the SCR reactor, two or more fixed catalyst layers are vertically spaced apart from the exhaust gas flow generated during the cement manufacturing process,
A nitrogen oxide reduction system characterized by the vertical arrangement of a plurality of soot blowers spraying compressed air at regular intervals from the catalyst layer. The method of claim 1, wherein the catalyst layer is stacked vertically spaced apart in multiple stages, and the exhaust gas flow flows from the vertical bottom to the top of the catalyst layer,
The soot blower blows compressed air (1) in the same direction as the exhaust gas flow at the bottom of each catalyst layer or (2) in the same direction as the exhaust gas flow at the bottom of each catalyst layer and in the opposite direction to the exhaust gas flow at the top of each catalyst layer;
The soot blower blows compressed air in (1) the same direction as the exhaust gas flow at the top of each catalyst layer or (2) the same direction as the exhaust gas flow at the top of each catalyst layer and the opposite direction to the exhaust gas flow at the bottom of each catalyst layer. reduction system. The method of claim 1, wherein the soot blower injects compressed air for 10 seconds to 30 seconds at intervals of 1 minute to 3 minutes for each catalyst layer spaced apart in multiple stages, and blows compressed air from the first catalyst layer to the last layer in the direction of exhaust gas flow. Nitrogen oxide reduction system characterized by sequentially spraying with program control through automatic valves installed in each line according to time and/or differential pressure changes. The system for reducing nitrogen oxides according to claim 1, wherein the pressure of the compressed air injected from the soot blower is 5 to 9 kg _f /cm ² . The system for reducing nitrogen oxides according to claim 1, wherein the soot blower is continuously and repeatedly operated at the same time as the cement manufacturing process starts. The nitrogen oxide reduction system according to claim 1, wherein the ammonia injection nozzle is located in front of the initial catalyst layer in the direction of exhaust gas flow. The method of claim 1, wherein the ammonia injection nozzle is disposed at a position 2 to 10 meters apart from the front end of the first catalyst layer in the direction of exhaust gas flow, and the injection flow rate of each nozzle is 1 liter or more per hour, corresponding to the NOx reduction efficiency. ) Nitrogen oxide reduction system characterized by controlling the flow rate. The method of claim 1, wherein (1) nitrogen oxide is reduced by urea water supplied from the SNCR at the front end and then nitrogen oxide is reduced by SCR by ammonia slip and (2) nitrogen oxide is reduced by spraying ammonia water in the SCR system. Nitrogen oxide reduction system characterized by dual supply. The nitrogen oxide reduction system according to any one of claims 1 to 10, wherein the fixed bed catalyst is a plate type, corrugate type or monolith extruded type. The method of any one of claims 1 to 10, wherein the nitrogen oxide reduction system equipped with an SCR reactor and a soot blower is installed before or after a cyclone, electric precipitation or bag filter. Featured Nitrogen Oxide Reduction System. A method for removing nitrogen oxides (NOx) in exhaust gas generated during the cement manufacturing process in the nitrogen oxide reduction system according to any one of claims 1 to 10,
The soot blower prevents dust in the exhaust gas generated during the cement manufacturing process from being adhered to or deposited on the SCR catalyst to prevent wear and damage to the catalyst and clogging of the catalyst surface and cells. A nitrogen oxide (NOx) removal method characterized by continuously maintaining the activity of the catalyst by preventing an increase in the differential pressure of the catalyst and preventing a decrease in the activity of the catalyst. The method of claim 13, wherein the cement manufacturing process uses industrial by-products as cement raw materials or fuel. 14. The method for removing nitrogen oxides (NOx) according to claim 13, wherein exhaust gas generated during the cement manufacturing process is subjected to nitrogen oxide reduction treatment by a selective non-catalytic reduction method and then nitrogen oxide reduction treatment by a selective catalytic reduction method.

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