NOx emission reduction system and method

A method and system to reduce NOx emissions from an engine connected to a fuel tank and an exhaust line, the apparatus including, a reformer to reform the fuel into hydrogen (H2); a fuel cell stack to convert the hydrogen into electricity; a reduction unit disposed on the exhaust line to convert the NOx into N2; a first bypass line to provide a fluid communication between the first fuel tank and the fuel reformer; a second bypass line to provide a fluid communication between the fuel reformer and the fuel cell stack; a first reformate line to provide a fluid communication between the second bypass line and the exhaust line. The hydrogen is mixed with the NOx in the exhaust line, and then the reduction unit uses the hydrogen to convert the NOx into nitrogen (N2).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2010-0002695, filed in the Korean Intellectual Property Office on Jan. 12, 2010, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

An exemplary embodiment of the present disclosure relates to a vehicular NOx emission reduction system and method, which operate using hydrogen from a fuel cell.

2. Description of the Related Art

NOx, which refers to NO2and NO, is a common atmospheric pollutant. NOx is generated naturally by microorganism, but is also generated during the combustion of fossil fuels. NOx combines with water vapor to form nitrous acid or nitric acid, which are precipitated as acid rain. Also, nitrous acid and nitric acid photochemically react with hydrocarbons in the air, to form aldehydes, acrolein, and Peroxy Acetyl Nitrate (PAN), which are secondary pollutants. In addition, NOxforms nitrous oxide (N2O), which is a green house gas that also reacts with other pollutants, to form photochemical smog, thereby causing much damage to urban environments.

When the fuel is combusted at high temperature, such as during heavy acceleration in a vehicle, atmospheric nitrogen is subject to an oxidation reaction. This generates a large amount of NOx, especially in diesel engines. NO2is a red-brown poisonous gas having a pungent odor, and is considered a main cause of several respiratory diseases.

In addition to NOx, diesel engines also produce particulate matter (PM). Specifically, there is an inverse proportion relation between the relative amounts of NOxand PM produced by diesel engines (when the NOxis reduced, the PM amount is increased, and vice versa). In other words, when a diesel engine operates at a high temperature and a high ignition point, such that a high rate of combustion is achieved, the amount of PM is reduced, but the amount of NOxis increased. For this reason, it is difficult to simultaneously reduce the PM and the NOx, in an internal combustion engine. Further, exhaust treatment devices are needed, in order to satisfy proposed Euro-V or Euro-VI regulations.

Recently, NOxemission standards have been tightened, resulting in research into methods of catalytically treating NOxwith N2. For example, currently proposed NOx reduction methods include NOxStorage and Reduction (NSR), HC-SCR, Urea-SCR, etc. The NSR method associates a diesel fuel cracking catalyst (DFC) with a lean NOxtrap (LNT). The DFC method converts the diesel fuel into H2, CO, etc., to reduce the formation of NOxduring combustion, and the remaining NOxis discharged through a peroxygen atmosphere, to further reduce NOxemissions. As a result, NOxemissions can be reduced by up to 90%, under the condition of a 7% O2atmosphere. As compared to the Urea-SCR method, the NSR method can be more readily applied to smaller diesel engines and is less complex. However, the NSR method is more costly, in that the LNT includes a large amount of precious metal catalysts.

The Urea-SCR method uses urea as a reduction agent and has a higher NOx removal rate than other systems. However, when the injection control and the system design are not optimized, NH3slip and salts are generated, which may generate white PM in the discharge gas. In addition, in order to prevent the lifespan of the catalyst from being rapidly shortened, due to reaction with sulfur oxides, and to prevent the corrosion of the apparatus due to ammonium, the Urea-SCR method uses an expensive corrosion resistant materials, which reduces price competitiveness. Further, since the Urea-SCR catalyst (a V-based catalyst) is classified as a hazardous material, the movement thereof between nations is restricted. Therefore, there is a demand for the development of an alternate technology.

U.S. Pat. No. 7,163,668 B2, teaches a method of reducing NOxemissions, using a hydrogen selective catalytic reduction (H-SCR) unit. In particular, an Ag/Alumina catalyst with low De-NOxactivity is used in conjunction with a reducing agent composed of a mixture of hydrogen and diesel fuel, it has been reported that the activity of the catalyst is rapidly increased, even at low temperatures, such that the activate temperature zone is expanded. Therefore, a new possibility of the diesel De-NOx technology has been emerging.

In the above-mentioned PatentFIG. 1shows a process that reforms (POX+WGS) diesel fuel in a partial oxidation unit10a, and a WGS catalyst10cmixes H2and CO generated thereby with an exhaust stream14containing NON. The resultant passes through an H-SCR catalyst layer to perform a De-NOxreaction. In particular, in order to increase the yield of H2, H2O is supplied from the outside, before the WGS reaction is performed, using air for the reforming.

In addition,FIG. 2shows a method that reforms hydrogen using oxygen in an exhaust stream for the reforming reaction, without supplying air from the outside, as inFIG. 1. However, despite the possibility, more studies are still demanded to practically use the NO reduction apparatus.

SUMMARY

The present disclosure provides a method and an apparatus using by-products of a fuel cell, in order to reduce NOxemissions from a vehicle having a diesel engine.

In addition, the present disclosure provides a method and an apparatus using an anode off gas (AOG) of a fuel cell, in order to reduce NOxemissions.

Further, the present disclosure provides a control unit that controls the use of by-products of a fuel cell, according to whether a vehicle is operated.

Moreover, the present disclosure provides a control unit that controls the ratio of a reformate gas and an AOG that is distributed to an NOxreduction apparatus.

An exemplary embodiment of the present disclosure provides a method for reducing NOxemissions from an engine that includes a main fuel line, through which fuel is delivered from a fuel tank, and an exhaust line that discharges the exhaust, the method including: reforming fuel supplied from the fuel tank in a fuel reformer, to generate a reformate gas; delivering the generated reformate gas to the exhaust line and a fuel cell stack; and transferring the exhaust and the reformate gas to a reduction unit, to reduce NOxto N2.

An exemplary embodiment of the present disclosure provides a method for reducing NOxfrom exhaust discharged from an engine that includes a main fuel line through which fuel is delivered from a fuel tank, and an exhaust line that discharges the exhaust, the method including: reforming a fuel supplied from a separate fuel tank in a fuel reformer, to generate reformate gas; delivering the generated reformate gas to the exhaust line and a fuel cell stack; and transferring the exhaust and the reformate gas to a reduction unit to reduce NOxusing hydrogen of the reformate gas.

The method for reducing NOx may further include oxidizing and developing the reformate gas in the stack and delivering anode off gas (AOG) from the stack to the exhaust line. The reducing the NOxuses hydrogen included in the AOG the hydrogen of the reformate gas for reducing the NOx.

An exemplary embodiment of the present disclosure provides an NOxemission reduction system to reduce emissions from exhaust discharged from an engine that includes a main fuel line through which fuel is delivered from a fuel tank, and an exhaust line that discharges the exhaust, the apparatus including: a fuel reformer, a stack, a reduction unit, and a reformate gas control value.

According to various embodiments, the fuel reformer reforms the fuel supplied from the fuel tank, to generate a reformate gas. The fuel cell stack oxidizes the reformate gas to produce electricity, and discharges an anode off gas (AOG). The reduction unit reduces NOxdischarged through the exhaust line, using hydrogen as a reducing agent. The reformate gas control valve is connected to the stack to control the distribution of the reformate gas to the exhaust line and the fuel cell stack.

According to various embodiments of the present disclosure, provided is an NOxemission reduction system to reduce NOxemission from exhaust discharged from an engine that includes a main fuel line through which fuel is delivered from a fuel tank, and an exhaust line that discharges the exhaust, the apparatus including: another fuel tank, a fuel reformer, a fuel cell stack, a reduction unit, and a reformate gas control value.

According to various embodiments, the other fuel tank supplies another fuel to the fuel reformer, which reforms the fuel into a reformate gas. The reformate gas is supplied to the fuel cell stack, to generate electricity. The stack discharges an anode off gas (AOG). The reduction unit reduces NOxdischarged through the exhaust line, using hydrogen as a reducing agent. The reformate gas control valve is connected to the stack to selectively distribute the reformate gas to the exhaust line and the fuel cell stack.

According to various embodiments, the fuel reformer may include a water/gas shift reactor.

An exemplary embodiment of the present disclosure includes a heat source and an anode off gas control valve. The heat source heats the fuel reformer, using the AOG. The anode off gas control value controls the supply the AOG to the heat source.

According to various embodiments, the anode off gas control valve may be further connected to the exhaust line and may control the distribution of the AOG to the heat source unit and the exhaust line.

According to various embodiments, the fuel tank may supply diesel fuel.

According to various embodiments, the reduction unit may reduce NOxthrough a preferential selective catalytic reduction reaction using hydrogen. In addition, the reduction unit may use an Ag/Alumina catalyst.

According to various embodiments, the system may include a controller that controls the reformate gas control valve, such that the reformate gas is not delivered to the exhaust line when the engine is off and the fuel reformer and the stack are operated.

An exemplary embodiment of the present disclosure may include a controller that controls the anode off gas control valve and the reformate gas control valve, respectively, so that the AOG and the reformate gas are not delivered to the exhaust line, when the engine is off and the fuel reformer and the stack are operated.

According to various embodiments, the controller controls the anode off gas control valve and the reformate gas control value, respectively, so that the anode off gas and the reformate gas are delivered by an amount in inverse proportion to used power when the engine, the fuel reformer, and the stack are in an operation state and power generated from the stack is used through an external circuit.

Further, an exemplary embodiment of the present disclosure can control the amount of hydrogen supplied to the reduction unit, according to the driving state of the vehicle and the power demands applied to the fuel cell stack.

An exemplary embodiment of the present disclosure blocks the hydrogen introduction from the fuel cell stack, when the vehicle is not driven, thereby making it possible to reduce the waste of fuel introduced into the fuel cell.

DETAILED DESCRIPTION

As those skilled in the art would realize, the described exemplary embodiments may be modified in various ways, without departing from the spirit or scope of the present disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. In addition, when an element is referred to as being “on” another element, it can be directly on the other element or may be indirectly on the other element, with one or more intervening elements interposed therebetween. Also, when an element is referred to as being “connected to” another element; it can be directly connected to the other element, or may be indirectly connected to the other element, with one or more intervening elements interposed therebetween.

FIG. 1illustrates an NOxemission reduction system300, according to an exemplary embodiment of the present disclosure. Referring toFIG. 1, the system300includes a driving unit, a fuel cell system100, and a reduction unit130. The reduction unit130may be a hydrogen selective catalytic reduction (H-SCR) unit. The driving unit102includes a fuel tank210, a fuel line M1, an engine220, and an exhaust line M2. The driving unit may be incorporated into a vehicle. The fuel cell system100includes a fuel reformer110and a fuel cell stack120. The system300further includes: reformate lines R1and R2that respectively connect the reformer and the stack120to the exhaust line M1; a bypass line B1that connects the fuel tank210to the reformer110; and bypass lines B2and B3that independently connect the reformer110and the stack120. Herein, such connections may be referred to as fluid communications.

The fuel tank210stores a fuel to operate the engine220. The fuel is supplied to the engine220through the fuel line M1. The fuel is also supplied to the fuel reformer110, through the bypass line B1. The fuel is generally diesel fuel, and the engine220is generally a diesel engine, but the present disclosure is not limited thereto, as other fuels and engine types may also be used. The engine220combusts the fuel, and exhaust from the engine220is discharged through the exhaust line M2.

The fuel reformer110reforms the fuel supplied from the fuel tank210, to generate a reformate gas. Generally, in the fuel reformer110the fuel undergoes a water gas shift (WGS) reaction and/or a preferential carbon monoxide oxidation (PROX) reaction, or the like. The fuel reformer110may also include a desulfurizer to remove a sulfur component from the fuel. The WGS reaction produces hydrogen and a carbon monoxide byproduct. The PROX reaction reduces the concentration of the carbon monoxide, such that the reformate gas is composed of primarily hydrogen gas (H2). Herein, the reformate gas may be referred to simply as hydrogen (H2).

The reformate gas is supplied to anodes of the stack120, via the bypass line B2, where it is oxidized to generate electricity. The electricity can be supplied to various devices, such as components of a vehicle including the engine220. In particular, the reformate gas supplied to the stack120is oxidized into water, while electrons are collected by the anodes of the stack120.

The stack120may produce an anode off gas (AOG) which may include water vapor and H2that was not oxidized in the stack120. Herein the AOG may be referred to as hydrogen (H2). The AOG may be supplied to the exhaust line M2, via the reformate line R2, where it is mixed with the exhaust. The resultant mixture (mixed exhaust stream) is then delivered to the reduction unit230, via the exhaust line M2. The AOG may also be returned to the reformer110, via the bypass line B3, where it is used to operate a heat source (not shown), such as a burner, included in the reformer110. The heat source may be used to heat the reformer110to a preset operating temperature. The AOG may also be mixed with natural gas, propane, etc, prior to being supplied to the heat source.

The reduction unit230removes NOxfrom the mixed exhaust stream. In particular, the reduction unit230includes a catalyst that facilitates a reduction reaction between the NOxand the hydrogen of the mixed exhaust stream. In other words, the hydrogen from the reformate gas and/or the AOG is used as a reducing agent, to reduce the NOxthrough a preferential catalytic reduction reaction. The catalyst may be an Ag/alumina catalyst, to expand an active temperature zone of the preferential catalytic reduction reaction.

FIG. 2illustrates a NOxemission reduction system400, according to another exemplary embodiment of the present disclosure. As shown inFIG. 2, the system400is similar to the system300, so only the differences will be described in detail. In particular, the system includes reformate lines R3and R4, in place of the reformate lines R1and R2. In addition, the system includes an anode off gas control valve130disposed on the bypass line B3, and a reformate gas control valve140disposed on the bypass line B2. The reformate line R2extends between the valve140and the exhaust line M2. The reformate line R4extends between the valve130and the exhaust line M2.

The fuel is transferred from the fuel tank210to the reformer110and the engine220, via lines B1and M1, respectively. The fuel reformer110reforms the fuel into a reformate gas, as described above.

The reformate gas control valve140is disposed on the bypass line B2, between the fuel reformer110and the stack120, and is also connected to the reformate line R3. The reformate gas control valve140selectively controls the amount of the reformate gas that is delivered from the fuel reformer110, to the stack120and to the exhaust line M2. The reformate gas control valve140may be a proportionate valve, so as to adjust the relative amounts of the reformate gas that is delivered to the stack120and the exhaust line M2. The reformate gas control valve140may include a pump (not shown) or a blower (not shown), etc., in order to reinforce the delivering force. The reformate gas control valve140may include a check valve, etc., in order to prevent backflow.

The anode off gas control valve130is disposed on the bypass line B3, and receives the AOG discharged from the stack120. The reformate line R4provides a fluid communication between the anode off gas control valve130and the exhaust line M2. The anode off gas control valve130controls the distribution amount, ratio, and period of the AOG gas to the reformer110and the exhaust line M2, and may be similar to the reformate gas control valve140.

The heat source (not shown) of the fuel reformer110is used to control the temperature thereof. In order to prevent improper ignition (backfire) of the AOG, due to the temperature of the heat source, the AOG may be supplied in pulses. The anode off gas control valve130may be used to create such pulses.

As described above, the reduction unit230receives the reformate gas/AOG and the exhaust, via the exhaust line M2. The reduction unit chemically reduces the NOxincluded in the exhaust into N2, using hydrogen as a reducing agent.

FIG. 3illustrates an NOxemission reduction system500, according to an aspect of the present disclosure. As shown inFIG. 3, the reduction system500is similar to the reduction system400, so only differences therebetween will be described in detail. Unlike the reduction system400, the reduction system500further includes another fuel tank215to supply fuel to the reformer110.

As a result, the fuel reformer110may receive fuel from either of the fuel tanks210,215. The fuel included in the fuel tank215may be a fuel such as natural gas, propane, city gas, or the like, which may be more readily processed by the reformer110into a reformate gas, as compared to diesel fuel or gasoline. Thus, quality and/or production efficiency of the reformer110may be increased.

FIG. 4illustrates an NOxemission reduction system600, according to an aspect of the present disclosure. The reduction system600is similar to the reduction system400, so only differences therebetween will be described in detail. As shown inFIG. 3, the reduction system includes a controller300that controls the operation of the valves130and140. In particular, the controller may vary the amount of hydrogen that is applied to the exhaust line, in accordance with the amount of NOxproduced by the engine220.

When the reduction system600is employed in a vehicle, such as in a recreational vehicle, tractor trailer, or the like, the fuel cell stack120may be used to provide electrical power to the vehicle, when the engine220is not operated. In such a case, the controller300controls the reformate gas control valve140and the anode off gas control valve130, such that hydrogen is not supplied to the exhaust line M2.

In addition, when the engine220and the fuel cell stack120are simultaneously operated, the controller may vary the amount of hydrogen that is applied to the exhaust line M2, in accordance with the amount of NOxproduced by the engine220and/or the amount of load applied to the fuel cell stack120. In other words, when there is a high demand for electricity, and a low load on the engine220, the amount of the reformate gas and/or AOG that is supplied to the exhaust line M2may be reduced. In addition, when there is a low load applied to the fuel cell stack120and a high load applied to the engine120, the amount of the reformate gas and/or the AOG supplied to the exhaust line M2may be increased.