KR20190062994A - Selective catalytic reduction system - Google Patents

Abstract

The present invention relates to a selective catalyst reduction system capable of reducing nitrogen oxides contained in exhaust gas. According to an embodiment of the present invention, the selective catalyst reduction system includes: an exhaust flow path in which exhaust gas moves; a reactor installed on the exhaust flow path and including a catalyst installed therein to reduce nitrogen oxides (NOx) containing exhaust gas; a recirculation flow path branched from the exhaust flow path behind the reactor to join the exhaust flow path in front of the reactor; a heater installed on the recirculation flow path to heat fluids flowing along the recirculation flow path; a heater detouring flow path branched from the recirculation flow path in front of the heater to join the recirculation flow path behind the heater; and a heat exchanger installed on the heater detouring flow path.

Description

{SELECTIVE CATALYTIC REDUCTION SYSTEM}

The present invention relates to a selective catalytic reduction system, and more particularly, to a selective catalytic reduction system used to reduce nitrogen oxides (NOx) contained in exhaust gases.

As industrialization has progressed rapidly, the use of various fossil fuels such as petroleum and coal has increased. As a result, various harmful gases emitted from the combustion process of fossil fuels cause serious air pollution. Typical examples are smog phenomenon and acid rain.

The main cause of air pollution is sulfur oxides (SOx) and nitrogen oxides (NOx) of exhaust gas emitted from engines of vehicles and ships, thermal power plants and factories.

Recently, as the awareness of environmental conservation has increased, regulations on emission of sulfur oxides and nitrogen oxides have been introduced.

In particular, there is a selective catalytic reduction (SCR) system as a typical facility for reducing nitrogen oxides. The selective catalytic reduction system reacts the nitrogen oxides contained in the exhaust gas with the reducing agent while passing the exhaust gas and the reducing agent together in the reactor equipped with the catalyst, thereby reducing the nitrogen and the water vapor.

When this selective catalytic reduction system is used on ships, the emission of NOx from marine diesel engines is controlled by the International Maritime Organization's International Standard for the Prevention of Air Pollution (IMO Tier-III) It is required to use an efficient denitrification system with a low cost and high efficiency.

In general, the catalyst used to reduce the nitrogen oxides contained in the exhaust gas may have an active temperature in the range of 250 degrees Celsius to 500 degrees Celsius. Here, the activation temperature refers to a temperature at which the catalyst can be stably reduced without being poisoned. When the catalyst reacts outside the active temperature range, the efficiency decreases as it is poisoned. Specifically, when the exhaust gas flows having a relatively low temperature of less than 250 ° C, the catalyst poisoning material is generated by the ammonia of sulfur oxides in the exhaust gas (SOx) and a reducing agent (NH ₄₎ response. Catalyst poisoning material may comprise one or more of ammonium sulfate _{(Ammonium sulfate, (NH4) 2} SO 4) and ammonium bisulfite _{(Ammonium bisulfate, NH 4 HSO 4} ). Such a catalyst poisoning material is adsorbed on the catalyst to lower the activity of the catalyst. Therefore, in order to increase the efficiency of the catalyst and minimize the loss due to maintenance, it is required to keep the temperature of the catalyst within the active temperature range.

However, in the case of a low speed diesel engine for ships, it is difficult to completely avoid the poisoning of the catalyst because the emission amount of the exhaust gas changes according to the load change of the diesel engine and the climate environment in which the ship is operating also affects the selective catalytic reduction reaction.

Therefore, when the catalyst is poisoned, the catalyst is heated to remove the poisoning substance. If the catalyst is heated to a temperature higher than the target temperature for removing the poisoning substance, the catalyst may be thermally damaged. For example, when a burner is used as the heating device, the burner continues to operate at the minimum capacity even after the target temperature is reached to maintain the flame according to the characteristics of the burner. Thus, the temperature of the catalyst can be continuously increased beyond the target temperature. Further, even when the heating device malfunctions or fails to accurately calculate the target temperature, the catalyst can be heated to a temperature exceeding the target temperature.

As described above, if the catalyst is heated to a temperature higher than the target temperature necessary for regenerating the catalyst, there is a problem that the catalyst is thermally damaged.

Embodiments of the present invention provide a selective catalytic reduction system capable of regenerating a poisoned catalyst as well as preventing thermal damage of the catalyst during regeneration of the catalyst.

According to an embodiment of the present invention, a selective catalytic reduction (SCR) system for reducing nitrogen oxides contained in an exhaust gas includes an exhaust flow path through which exhaust gas flows, and an exhaust gas flow path provided on the exhaust flow path A recirculation flow path branched from the exhaust flow path in the rear of the reactor and joined to the exhaust flow path in front of the reactor; A heating device bypass flow path branched from the recirculation flow path in front of the heating device and joined to the recirculation flow path behind the heating device; And a heat exchanger installed therein.

The selective catalytic reduction system may further include a blower disposed on the recirculation flow path between a branch point of the exhaust passage and the recirculation passage and a branch point of the recirculation passage and the bypass passage of the heating device.

The selective catalytic reduction system may further include a temperature sensor for measuring the temperature of the exhaust gas flowing into the reactor.

The selective catalytic reduction system may further include a bypass flow path branched from the exhaust flow path and bypassing the reactor and joining to the exhaust flow path again, and a bypass flow path provided on the bypass flow path, And may further include a valve.

In addition, the selective catalytic reduction system may further include a heat recovery flow path connected to the heat exchanger. The heat recovery flow path may be connected to at least one of an economizer or a urea storage tank for storing a urea used as a reducing agent to transfer heat energy.

The selective catalytic reduction system may further include a first exhaust valve disposed on the exhaust passage in front of the reactor, a second exhaust valve disposed on the exhaust passage in the rear of the reactor, A recirculation valve provided on the recirculation flow path between a branch point of the recirculation flow path and a recirculation flow path of the heating device bypass flow path, and a heating device bypass valve provided on the heating device bypass flow path.

In addition, the selective catalytic reduction system described above can be applied to any one of an operation mode for reducing nitrogen oxides contained in the exhaust gas, a regeneration mode for regenerating the catalyst installed in the reactor, and a protection mode for preventing thermal damage of the catalyst installed in the reactor It can be divided into one.

In the operating mode, the first exhaust valve and the second exhaust valve are opened, and the recirculation valve and the heating device bypass valve can be closed. In the regeneration mode, the first exhaust valve and the second exhaust valve and the heating device bypass valve are closed, and the recirculation valve can be opened. In the protected mode, the first exhaust valve and the second exhaust valve and the recirculation valve are closed and the heating device bypass valve can be opened.

According to the embodiment of the present invention, the selective catalytic reduction system not only can regenerate the poisoned catalyst but also can stably prevent the thermal damage of the catalyst during the regeneration of the catalyst.

1 is a block diagram illustrating a selective catalytic reduction system according to an embodiment of the present invention.
FIG. 2 and FIG. 3 are diagrams showing the operational states of the selective catalytic reduction system of FIG. 1. FIG.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

The drawings are schematic and not drawn to scale. The relative dimensions and ratios of the parts in the figures are exaggerated or reduced in size for clarity and convenience in the figures, and any dimensions are merely illustrative and not restrictive. And to the same structure, element or component appearing in more than one drawing, the same reference numerals are used to denote similar features.

The embodiments of the present invention specifically illustrate ideal embodiments of the present invention. As a result, various variations of the illustration are expected. Thus, the embodiment is not limited to any particular form of the depicted area, but includes modifications of the form, for example, by manufacture.

Hereinafter, a selective catalytic reduction (SCR) system 101 according to an embodiment of the present invention will be described with reference to FIGS.

A selective catalytic reduction (SCR) system 101 according to an embodiment of the present invention is used to reduce nitrogen oxides (NOx) contained in the exhaust gas discharged from a power unit. As an example, the power unit can be a two-stroke low-speed or four-stroke medium-speed diesel engine used for shipping.

However, the first embodiment of the present invention is not limited thereto. The power unit may be an internal combustion engine for a plant or an automotive engine. That is, various types of engines known to those skilled in the art can be used as the power unit.

Further, in one embodiment of the present invention, the exhaust gas discharged by the engine has a temperature within a range of 200 degrees Celsius to 500 degrees Celsius, and may be lowered to 150 degrees Celsius or less and less than 200 degrees Celsius in some cases.

1, the selective catalytic reduction system 101 according to an embodiment of the present invention includes an exhaust flow path 610, a reactor 300, a recirculation flow path 680, a heating device 400, A flow path 670, and a heat exchanger 490.

The selective catalytic reduction system 101 according to an embodiment of the present invention includes a blower 450, a temperature sensor 810, a bypass passage 620, a bypass valve 720, a first exhaust valve 711, A second exhaust valve 712, a recirculation valve 780, and a heating device bypass valve 770.

In addition, the selective catalytic reduction system 101 according to an embodiment of the present invention may further include a heat recovery flow path 690.

The exhaust passage 610 moves the exhaust gas containing nitrogen oxides (NOx). The exhaust gas flowing along the exhaust flow path 610 is discharged to the outside through the reactor 300 to be described later. For example, the exhaust flow path 610 may be connected to the exhaust port of the engine to exhaust the exhaust gas discharged from the engine.

The reactor 300 is installed on the exhaust passage 610. That is, the reactor 300 receives the exhaust gas containing nitrogen oxide (NOx) through the exhaust passage 610. The reactor 300 incorporates a catalyst 350 for reducing nitrogen oxides (NOx) contained in the exhaust gas. The catalyst 350 promotes the reaction of the reducing agent with the nitrogen oxides (NOx) contained in the exhaust gas to reduce the nitrogen oxides (NOx) to nitrogen and water vapor.

Also, in one embodiment of the present invention, the catalyst 350 installed in the reactor 300 may be arranged in a multi-layer structure based on the moving direction of the exhaust gas. That is, the catalyst 350 may be provided in the form of a plurality of catalyst modules, and the plurality of catalyst modules may be arranged along the moving direction of the exhaust gas.

Catalyst 350 may be made from a variety of materials known to those skilled in the art, such as zeolite, vanadium, and platinum. In one example, the catalyst 350 may have an active temperature in the range of 200 degrees Celsius to 500 degrees Celsius. Here, the activation temperature refers to a temperature at which the catalyst 350 can be stably reduced without being poisoned. When the catalyst 350 reacts outside the activation temperature range, the catalyst 350 is poisoned and the efficiency is lowered.

For example, occurs the reduction reaction for reducing nitrogen oxide-containing exhaust gas at a relatively low temperature of less than ° C more than 250 ° C, 150, of the exhaust gas sulfur oxides (SOx) and ammonia (NH ₃₎ the reaction Thereby forming a catalyst poisoning substance. Specifically, the poisoning substance that poisons the catalyst 350 may include at least one of ammonium sulfate (NH ₄ ) ₂ SO ₄ and ammonium hydrogen sulfite (NH ₄ HSO ₄ ). Such a catalyst poisoning material is adsorbed on the catalyst to lower the activity of the catalyst 350. Since the catalyst poisonous substance is decomposed at a relatively high temperature, that is, at a temperature within the range of 350 degrees Celsius to 450 degrees Celsius, the catalyst 350 in the reactor 300 can be heated to regenerate the poisoned catalyst 350.

Further, ammonia (NH ₃ ) is used as a reducing agent that directly reacts with the nitrogen oxide in the catalyst 350, which can be supplied in the form of an aqueous solution of urea (CO (NH ₂ ) ₂ ) which is a reducing agent precursor. Since ammonia itself is not easily stored and transported as a pollutant, it is common to use a stable urea aqueous solution. An aqueous solution of urea, CO (NH ₂ ) ₂ ) is hydrolyzed or pyrolyzed to produce ammonia (NH ₃ ) and isocyanic acid (HNCO). And isocyanate (HNCO) decomposes again into ammonia (NH ₃ ) and carbon dioxide (CO ₂ ). That is, it decomposes urea to produce ammonia as a reducing agent that reacts with nitrogen oxides.

For example, the reducing agent may be injected into the exhaust passage 610 in front of the reactor 300 and mixed with the exhaust gas. In the following description, the term front means the upstream direction based on the moving direction of the exhaust gas, and the rear means the downstream direction based on the moving direction of the exhaust gas.

The recirculation flow path 680 branches from the exhaust flow path 610 behind the reactor 300 and joins the exhaust flow path 610 in front of the reactor 300. In one embodiment of the present invention, the recycle flow path 680 may be used in the regeneration of the catalyst 350. Specifically, when the exhaust gas passing through the reactor 300 is recirculated to the front of the reactor 300 through the recirculation passage 680 and the exhaust gas recirculated is heated to heat the catalyst 350 inside the reactor 300, The thermal energy of the exhaust gas heated to heat the catalyst 350 can be minimized after being exhausted through the catalyst 350. That is, the heat energy consumed for heating the catalyst 350 during the regeneration of the catalyst 350 can be minimized.

The heating device 400 is installed on the recirculation passage 680 to raise the temperature of the fluid moving along the recirculation passage 680, that is, the exhaust gas recirculated through the reactor 300. In one embodiment of the present invention, the heating device 400 may be embodied in various forms. In addition, the heating device 400 may be one of an electric heater, an oil burner, or a plasma burner.

The heating device bypass flow path 670 branches from the recirculation flow path 680 in the front of the heating device 400 and joins the recirculation flow path 680 behind the heating device 400. [

The heater bypass flow path 670 can be used when it is not necessary to further raise the temperature of the fluid moving along the recirculation flow path 680, that is, the exhaust gas. That is, when the heating device 400 is in a continuously operating state but it is not necessary to further raise the temperature of the exhaust gas moving along the recirculation passage 680, or rather the temperature of the exhaust gas needs to be lowered, The exhaust gas can be moved by bypassing the heating device 400 through the flow path 670. Thus, even if the heating device 400 is operated, the internal temperature of the reactor 300 can be prevented from rising.

The heat exchanger (490) is installed on the heater bypass flow path (670). The heat exchanger 490 recovers thermal energy of the exhaust gas flowing along the heater bypass flow path 670 and lowers the temperature of the exhaust gas. That is, when it is necessary to lower the temperature of the fluid moving along the recirculation flow path 680, the temperature of the fluid can be lowered by moving to the heating device bypass flow path 670 and passing through the heat exchanger 490.

The heat recovery flow path 690 may connect the heat exchanger 490 with one or more of an economizer 900 or a urea storage tank. That is, the heat recovery flow path 690 transfers the heat energy recovered from the heat exchanger 490 to the economizer 900 and transfers it to a urea storage tank for storing a urea used as a reducing agent to prevent freezing of the urea Can be utilized.

The blower 450 is installed on the recirculation flow path 680 between the branch point of the exhaust flow path 610 and the recirculation flow path 680 and the branch point of the recirculation flow path 680 and the heating device bypass flow path 670. The blower 450 supplies power for moving the exhaust gas passing through the reactor 300 to the recirculation flow path 680. That is, the exhaust gas passing through the reactor 300 by the blower 450 flows along the recirculation flow path 680, flows into the reactor 300 after passing through the heating device 400, or flows into the recycle flow path 680 and the heating It may flow into the reactor 300 after passing through the heat exchanger 490 while moving along the device bypass flow path 6700.

The temperature sensor 810 measures the temperature of the exhaust gas flowing into the reactor 300. The selective catalytic reduction system 101 may further include an additional temperature sensor 820 for measuring the temperature of the exhaust gas through the reactor 300. The temperature sensor 810 and the additional temperature sensor 820 can be used to measure or indirectly estimate the internal temperature of the reactor 300, particularly the temperature of the catalyst 350.

The bypass flow path 620 branches at the exhaust flow path 610, bypasses the reactor 300, and then joins the exhaust flow path 610 again. The bypass flow path 620 bypasses the reactor 300 and discharges the exhaust gas discharged from the engine when the catalyst 350 installed in the reactor 300 is regenerated.

The bypass valve 720 is installed on the bypass flow path 620 to open / close the bypass flow path 620. That is, the bypass valve 720 is closed when the nitrogen oxide contained in the exhaust gas is reduced, and can be opened when the catalyst 350 is regenerated.

The first exhaust valve 711 may be installed on the exhaust passage 610 in front of the reactor 300 and the second exhaust valve 712 may be installed on the exhaust passage 610 in the rear of the reactor 300. The first exhaust valve 711 and the second exhaust valve 712 can open and close the exhaust passage, respectively. The second exhaust valve 712 can prevent the exhaust gas flowing along the bypass flow path 620 from flowing back to the reactor 300 during the regeneration of the catalyst 350. The second exhaust valve may be omitted depending on the case (712).

The recirculation valve 780 can open and close the recirculation passage 680. More specifically, the recirculation valve 780 is connected to the recirculation passage 680 between the recirculation passage 680 and the branch point of the heater bypass passage 670, and the junction point between the recirculation passage 680 and the bypass passage 670 As shown in FIG.

The heating device bypass valve 770 can be installed on the heating device bypass flow path 670 to open and close the heating device bypass flow path 670.

In addition, the selective catalytic reduction system 101 according to an embodiment of the present invention includes an operation mode for reducing the nitrogen oxide contained in the exhaust gas, a regeneration mode for regenerating the catalyst 350 installed in the reactor 300, And a protection mode for preventing thermal damage to the catalyst 350 installed in the catalyst 300.

Hereinafter, the operation principle of the selective catalytic reduction system 101 according to one embodiment of the present invention will be described in detail with reference to FIG. 1 to FIG.

The operating mode can be selected to reduce the nitrogen oxides contained in the exhaust gas. 1, the first exhaust valve 711 and the second exhaust valve 712 are opened and the recirculation valve 780 and the heating device bypass valve 770 and the bypass valve 720 are opened, Is closed. Then, the exhaust gas moves along the exhaust flow path 610 and is exhausted after the nitrogen oxide is reduced through the reactor 300.

The regeneration mode can be selected when the catalyst 350 is poisoned and regenerated. The first exhaust valve 711 and the second exhaust valve 712 and the heater bypass valve 770 are closed and the recirculation valve 780 and the bypass valve 720 are closed as shown in Fig. Is opened. The exhaust gas discharged from the engine is then discharged through the bypass flow path 620 to bypass the reactor 300. And the recycle flow path 680 forms a closed loop including the reactor 300. The blower 450 recirculates the exhaust gas passing through the reactor 300 to the recirculation passage 680 and raises the temperature of the recirculated exhaust gas by the heating device 400 so that the heated exhaust gas is supplied to the catalyst 350 And the catalyst 350 is regenerated. At this time, the temperature at which the poisoning substance is removed and the catalyst 350 can be regenerated is referred to as a target temperature. That is, the heating device 400 raises the temperature of the exhaust gas until the exhaust gas reaches the target temperature.

The protection mode can be selected when it is desired to prevent the catalyst 350 from suffering thermal damage. That is, the protection mode can be selected to prevent the catalyst 350 from being heated to a temperature higher than necessary beyond the target temperature for removing poisoning substances.

For example, when the burner is used as the heating device 400, the burner can be continuously operated at the minimum capacity even after the target temperature is reached to maintain the flame according to the characteristics of the burner. In this case, the temperature of the catalyst 350 may be continuously increased beyond the target temperature. In addition, even when the heating device 400 malfunctions or fails to accurately calculate the target temperature due to a malfunction of the system, the catalyst 350 can be heated to a temperature close to or exceeding a limit temperature at which thermal damage is experienced. In such a situation, the protection mode may be selected to prevent thermal damage to the catalyst 350.

The first exhaust valve 711 and the second exhaust valve 712 and the recirculation valve 780 are closed and the bypass valve 720 and the bypass valve 720 are closed as shown in Fig. Is opened. The exhaust gas discharged from the engine is then discharged through the bypass flow path 620 to bypass the reactor 300. The exhaust gas recirculated along the recirculation flow path 680 can circulate through the heating device bypass flow path 670 while bypassing the heating device 400. Therefore, even if the heating device 400 is operated, the temperature of the catalyst 350 installed in the reactor 300 can be prevented from being continuously increased. The temperature of the exhaust gas flowing along the recirculation flow path 680 and the heater bypass flow path 670 can be lowered through the heat exchanger 490 provided on the heater bypass flow path 670. That is, the temperature of the catalyst 350 can be lowered below the critical temperature when the temperature of the catalyst 350 installed in the reactor 300 is close to or exceeds the limit temperature at which thermal damage is experienced.

Thus, when the temperature of the catalyst 350 is lowered to the proper temperature range for regeneration through the heat exchanger 490, the selective catalytic reduction system 101 can switch from the protection mode to the regeneration mode again. At this time, the internal temperature of the reactor 300 or the temperature of the catalyst 350 can be measured or indirectly estimated through the temperature sensor 810.

The heat energy recovered in the heat exchanger 490 may be transferred to the economizer 900 or the urea storage tank or the like through the heat recovery line 690 and utilized.

The selective catalytic reduction system 101 according to an embodiment of the present invention not only can regenerate the poisoned catalyst 350 but also regenerates the catalyst 350 in the process of regenerating the catalyst 350. [ The damage can be prevented stably.

Further, by utilizing the generated thermal energy for regeneration of the catalyst 350 and utilizing it, it is possible to improve the utilization efficiency of the thermal energy.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. will be.

It is therefore to be understood that the embodiments described above are to be considered in all respects only as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, It is intended that all changes and modifications derived from the equivalent concept be included within the scope of the present invention.

101: Selective Catalytic Reduction System
300: reactor
350: catalyst
400: Heating device
450: Blower
490: Heat exchanger
610:
620: Bypass channel
670: Heater bypass flow
680: Recirculation flow path
690: Heat recovery flow path
711: First exhaust valve
712: Second exhaust valve
720: Bypass valve
770: Heater bypass valve
780: recirculation valve
900: Economizer

Claims (8)

A selective catalytic reduction system for reducing nitrogen oxides contained in an exhaust gas,
An exhaust passage through which the exhaust gas moves;
A reactor provided on the exhaust flow path and provided with a catalyst therein for reducing nitrogen oxides (NOx) contained in the exhaust gas;
A recirculation passage branched from the exhaust passage behind the reactor and joined to the exhaust passage in front of the reactor;
A heating device installed on the recirculation flow path for raising a fluid moving along the recirculation flow path;
A heating device bypass flow branching from the recirculation flow path in front of the heating device and joining the recirculation flow path behind the heating device; And
And a heat exchanger
≪ / RTI > The method according to claim 1,
Further comprising a blower provided on the recirculation passage between a branch point of the exhaust passage and the recirculation passage and a branch point of the recirculation passage and the bypass passage of the heating device. The method according to claim 1,
Further comprising a temperature sensor for measuring the temperature of the exhaust gas flowing into the reactor. The method according to claim 1,
A bypass flow path branched from the exhaust flow path and bypassing the reactor and joining the exhaust flow path again;
A bypass valve provided on the bypass flow passage for opening / closing the bypass flow passage,
Further comprising a catalytic reduction catalyst. The method according to claim 1,
Further comprising a heat recovery flow path connected to the heat exchanger,
Wherein the heat recovery flow path is connected to at least one of an economizer or a urea storage tank for storing a urea used as a reducing agent to transfer heat energy. 6. The method according to any one of claims 1 to 5,
A first exhaust valve provided on the exhaust passage in front of the reactor;
A second exhaust valve disposed on the exhaust passage behind the reactor;
A recirculation valve provided on the recirculation flow path between a branch point of the recirculation flow path and the bypass passage of the heating device and a junction point of the recirculation flow path and the heating device bypass flow path; And
A heating device bypass valve
Further comprising a catalytic reduction catalyst. The method according to claim 6,
An operation mode in which nitrogen oxides contained in the exhaust gas are reduced;
A regeneration mode in which the catalyst installed in the reactor is regenerated; And
A protection mode for preventing thermal damage of the catalyst installed in the reactor
The selective catalytic reduction system comprising: 8. The method of claim 7,
Wherein the first exhaust valve and the second exhaust valve are opened in the operating mode, the recirculation valve and the heating device bypass valve are closed,
In the regeneration mode, the first exhaust valve and the second exhaust valve and the heating device bypass valve are closed, the recirculation valve is opened,
Wherein the first exhaust valve and the second exhaust valve and the recirculation valve are closed and the heating device bypass valve is opened in the protection mode.

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