Abstract:
A method and system to reduce NO x  emissions from an engine connected to a fuel tank and an exhaust line, the apparatus including, a reformer to reform the fuel into hydrogen (H 2 ); a fuel cell stack to convert the hydrogen into electricity; a reduction unit disposed on the exhaust line to convert the NO x  into N 2 ; 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 NO x  in the exhaust line, and then the reduction unit uses the hydrogen to convert the NO x  into nitrogen (N 2 ).

Description:
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 
     1. Field 
     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 
     NO x , which refers to NO 2  and 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, NO x  forms nitrous oxide (N 2 O), 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 NO x , especially in diesel engines. NO 2  is a red-brown poisonous gas having a pungent odor, and is considered a main cause of several respiratory diseases. 
     In addition to NO x , diesel engines also produce particulate matter (PM). Specifically, there is an inverse proportion relation between the relative amounts of NO x  and PM produced by diesel engines (when the NO x  is 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 NO x  is increased. For this reason, it is difficult to simultaneously reduce the PM and the NO x , in an internal combustion engine. Further, exhaust treatment devices are needed, in order to satisfy proposed Euro-V or Euro-VI regulations. 
     Recently, NO x  emission standards have been tightened, resulting in research into methods of catalytically treating NO x  with N 2 . For example, currently proposed NOx reduction methods include NO x  Storage and Reduction (NSR), HC-SCR, Urea-SCR, etc. The NSR method associates a diesel fuel cracking catalyst (DFC) with a lean NO x  trap (LNT). The DFC method converts the diesel fuel into H 2 , CO, etc., to reduce the formation of NO x  during combustion, and the remaining NO x  is discharged through a peroxygen atmosphere, to further reduce NO x  emissions. As a result, NO x  emissions can be reduced by up to 90%, under the condition of a 7% O 2  atmosphere. 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, NH 3  slip 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 NO x  emissions, using a hydrogen selective catalytic reduction (H-SCR) unit. In particular, an Ag/Alumina catalyst with low De-NO x  activity 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 Patent  FIG. 1  shows a process that reforms (POX+WGS) diesel fuel in a partial oxidation unit  10   a , and a WGS catalyst  10   c  mixes H 2  and CO generated thereby with an exhaust stream  14  containing NO N . The resultant passes through an H-SCR catalyst layer to perform a De-NO x  reaction. In particular, in order to increase the yield of H 2 , H 2 O is supplied from the outside, before the WGS reaction is performed, using air for the reforming. 
     In addition,  FIG. 2  shows a method that reforms hydrogen using oxygen in an exhaust stream for the reforming reaction, without supplying air from the outside, as in  FIG. 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 NO x  emissions 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 NO x  emissions. 
     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 NO x  reduction apparatus. 
     An exemplary embodiment of the present disclosure provides a method for reducing NO x  emissions 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 NO x  to N 2 . 
     An exemplary embodiment of the present disclosure provides a method for reducing NO x  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 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 NO x  using 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 NO x  uses hydrogen included in the AOG the hydrogen of the reformate gas for reducing the NO x . 
     An exemplary embodiment of the present disclosure provides an NO x  emission 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 NO x  discharged 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 NO x  emission reduction system to reduce NO x  emission 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 NO x  discharged 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 NO x  through 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. 
     Additional aspects and/or advantages of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the present disclosure will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings, of which: 
         FIG. 1  is a block diagram showing an NO x  emission reduction system to reduce NO x  exhaust emissions from a diesel engine, using a fuel cell stack, according to an exemplary embodiment of the present disclosure. 
         FIG. 2  is a block diagram showing an exemplary embodiment of an NO x  emission reduction system to reducing NO x  emissions from a diesel engine using a fuel cell stack, according to an exemplary embodiment of the present disclosure. 
         FIG. 3  is a block diagram of an NO x  emission reduction system that includes separate fuel tank, according to an exemplary embodiment of the present disclosure. 
         FIG. 4  is a block diagram schematically showing a connection state of a controller, according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The exemplary embodiments are described below, in order to explain the aspects of the present disclosure, by referring to the figures. 
     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. 1  illustrates an NO x  emission reduction system  300 , according to an exemplary embodiment of the present disclosure. Referring to  FIG. 1 , the system  300  includes a driving unit, a fuel cell system  100 , and a reduction unit  130 . The reduction unit  130  may be a hydrogen selective catalytic reduction (H-SCR) unit. The driving unit  102  includes a fuel tank  210 , a fuel line M 1 , an engine  220 , and an exhaust line M 2 . The driving unit may be incorporated into a vehicle. The fuel cell system  100  includes a fuel reformer  110  and a fuel cell stack  120 . The system  300  further includes: reformate lines R 1  and R 2  that respectively connect the reformer and the stack  120  to the exhaust line M 1 ; a bypass line B 1  that connects the fuel tank  210  to the reformer  110 ; and bypass lines B 2  and B 3  that independently connect the reformer  110  and the stack  120 . Herein, such connections may be referred to as fluid communications. 
     The fuel tank  210  stores a fuel to operate the engine  220 . The fuel is supplied to the engine  220  through the fuel line M 1 . The fuel is also supplied to the fuel reformer  110 , through the bypass line B 1 . The fuel is generally diesel fuel, and the engine  220  is generally a diesel engine, but the present disclosure is not limited thereto, as other fuels and engine types may also be used. The engine  220  combusts the fuel, and exhaust from the engine  220  is discharged through the exhaust line M 2 . 
     The fuel reformer  110  reforms the fuel supplied from the fuel tank  210 , to generate a reformate gas. Generally, in the fuel reformer  110  the fuel undergoes a water gas shift (WGS) reaction and/or a preferential carbon monoxide oxidation (PROX) reaction, or the like. The fuel reformer  110  may 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 (H 2 ). Herein, the reformate gas may be referred to simply as hydrogen (H 2 ). 
     The reformate gas is supplied to anodes of the stack  120 , via the bypass line B 2 , where it is oxidized to generate electricity. The electricity can be supplied to various devices, such as components of a vehicle including the engine  220 . In particular, the reformate gas supplied to the stack  120  is oxidized into water, while electrons are collected by the anodes of the stack  120 . 
     The stack  120  may produce an anode off gas (AOG) which may include water vapor and H 2  that was not oxidized in the stack  120 . Herein the AOG may be referred to as hydrogen (H 2 ). The AOG may be supplied to the exhaust line M 2 , via the reformate line R 2 , where it is mixed with the exhaust. The resultant mixture (mixed exhaust stream) is then delivered to the reduction unit  230 , via the exhaust line M 2 . The AOG may also be returned to the reformer  110 , via the bypass line B 3 , where it is used to operate a heat source (not shown), such as a burner, included in the reformer  110 . The heat source may be used to heat the reformer  110  to 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 unit  230  removes NO x  from the mixed exhaust stream. In particular, the reduction unit  230  includes a catalyst that facilitates a reduction reaction between the NO x  and 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 NO x  through 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. 2  illustrates a NO x  emission reduction system  400 , according to another exemplary embodiment of the present disclosure. As shown in  FIG. 2 , the system  400  is similar to the system  300 , so only the differences will be described in detail. In particular, the system includes reformate lines R 3  and R 4 , in place of the reformate lines R 1  and R 2 . In addition, the system includes an anode off gas control valve  130  disposed on the bypass line B 3 , and a reformate gas control valve  140  disposed on the bypass line B 2 . The reformate line R 2  extends between the valve  140  and the exhaust line M 2 . The reformate line R 4  extends between the valve  130  and the exhaust line M 2 . 
     The fuel is transferred from the fuel tank  210  to the reformer  110  and the engine  220 , via lines B 1  and M 1 , respectively. The fuel reformer  110  reforms the fuel into a reformate gas, as described above. 
     The reformate gas control valve  140  is disposed on the bypass line B 2 , between the fuel reformer  110  and the stack  120 , and is also connected to the reformate line R 3 . The reformate gas control valve  140  selectively controls the amount of the reformate gas that is delivered from the fuel reformer  110 , to the stack  120  and to the exhaust line M 2 . The reformate gas control valve  140  may be a proportionate valve, so as to adjust the relative amounts of the reformate gas that is delivered to the stack  120  and the exhaust line M 2 . The reformate gas control valve  140  may include a pump (not shown) or a blower (not shown), etc., in order to reinforce the delivering force. The reformate gas control valve  140  may include a check valve, etc., in order to prevent backflow. 
     The anode off gas control valve  130  is disposed on the bypass line B 3 , and receives the AOG discharged from the stack  120 . The reformate line R 4  provides a fluid communication between the anode off gas control valve  130  and the exhaust line M 2 . The anode off gas control valve  130  controls the distribution amount, ratio, and period of the AOG gas to the reformer  110  and the exhaust line M 2 , and may be similar to the reformate gas control valve  140 . 
     The heat source (not shown) of the fuel reformer  110  is 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 valve  130  may be used to create such pulses. 
     As described above, the reduction unit  230  receives the reformate gas/AOG and the exhaust, via the exhaust line M 2 . The reduction unit chemically reduces the NO x  included in the exhaust into N 2 , using hydrogen as a reducing agent. 
       FIG. 3  illustrates an NO x  emission reduction system  500 , according to an aspect of the present disclosure. As shown in  FIG. 3 , the reduction system  500  is similar to the reduction system  400 , so only differences therebetween will be described in detail. Unlike the reduction system  400 , the reduction system  500  further includes another fuel tank  215  to supply fuel to the reformer  110 . 
     As a result, the fuel reformer  110  may receive fuel from either of the fuel tanks  210 ,  215 . The fuel included in the fuel tank  215  may be a fuel such as natural gas, propane, city gas, or the like, which may be more readily processed by the reformer  110  into a reformate gas, as compared to diesel fuel or gasoline. Thus, quality and/or production efficiency of the reformer  110  may be increased. 
       FIG. 4  illustrates an NO x  emission reduction system  600 , according to an aspect of the present disclosure. The reduction system  600  is similar to the reduction system  400 , so only differences therebetween will be described in detail. As shown in  FIG. 3 , the reduction system includes a controller  300  that controls the operation of the valves  130  and  140 . In particular, the controller may vary the amount of hydrogen that is applied to the exhaust line, in accordance with the amount of NO x  produced by the engine  220 . 
     When the reduction system  600  is employed in a vehicle, such as in a recreational vehicle, tractor trailer, or the like, the fuel cell stack  120  may be used to provide electrical power to the vehicle, when the engine  220  is not operated. In such a case, the controller  300  controls the reformate gas control valve  140  and the anode off gas control valve  130 , such that hydrogen is not supplied to the exhaust line M 2 . 
     In addition, when the engine  220  and the fuel cell stack  120  are simultaneously operated, the controller may vary the amount of hydrogen that is applied to the exhaust line M 2 , in accordance with the amount of NO x  produced by the engine  220  and/or the amount of load applied to the fuel cell stack  120 . In other words, when there is a high demand for electricity, and a low load on the engine  220 , the amount of the reformate gas and/or AOG that is supplied to the exhaust line M 2  may be reduced. In addition, when there is a low load applied to the fuel cell stack  120  and a high load applied to the engine  120 , the amount of the reformate gas and/or the AOG supplied to the exhaust line M 2  may be increased. 
     Although a few exemplary embodiments of the present disclosure have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these exemplary embodiments, without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.