Abstract:
The present invention relates to a technology of reducing nitrogen oxide (NOx) which is harmful discharge gas discharged from an internal combustion engine or a combustor, and to an exhaust gas purification system which inputs solid ammonium salt such as ammonium carbamate or ammonium carbonate into a reactor, thermally decomposes and converts the solid ammonium salt into the ammonia by using engine cooling water, exhaust gas, or an electric heater, which are installed in the reactor, and reduces the nitrogen oxide included in the exhaust pipe on a selective catalytic reduction into nitrogen by injecting the ammonia by using a pressure regulator and a dosing valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application Nos. 10-2012-0034670, 10-2012-0145178, and 10-2012-0145181, filed in the Korean Intellectual Property Office on Apr. 3, 2012, Dec. 13, 2012, and Dec. 13, 2012, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to an exhaust gas purification system, and more particularly, to an exhaust gas purification system capable of reducing harmful materials included in exhaust gas of a vehicle by using solid ammonium salt. 
         [0004]    (b) Description of the Related Art 
         [0005]    In general, as a technology of reducing nitrogen oxide discharged from an internal combustion engine, particularly a diesel engine, a method of reducing concentration by exhaust gas recirculation (EGR), and a selective catalytic reduction (SCR) which reduces the nitrogen oxide into nitrogen and oxygen by allowing the nitrogen oxide to react on a catalyst by using a reducing agent such as ammonia, urea, or hydrocarbon are used. 
         [0006]    In a case in which hydrocarbon such as diesel oil is used in the technology of the selective catalytic reduction, there is a merit in that a subsidiary reducing agent supply apparatus is not necessary because fuel of an internal combustion engine or a combustor is used as a reducing agent, however in a case in which oxygen is present in the exhaust gas, there is a drawback in that performance for reducing the nitrogen oxide is low, because the hydrocarbon reacts with the oxygen in advance. 
         [0007]    Considering a technology of the selective catalytic reduction which uses liquid urea, which is another technology of the selective catalytic reduction, when liquid urea, which is made by dissolving urea, which is a material that is present in a solid state at a room temperature, in water, is injected to an exhaust pipe of a vehicle, the liquid urea is converted into ammonia by being thermally decomposed at a temperature equal to or greater than about 150° C., and the ammonia produced as described above reduces the nitrogen oxide into harmless nitrogen with the help of the selective catalytic reduction such as vanadium pentoxide V 2 O 5  or zeolite. The technology of the selective catalytic reduction, which uses the liquid urea, has a merit in that a temperature band of a catalytic reaction is wide, durability is excellent, and high nitrogen oxide purification efficiency of about 60 to 80% may be obtained. 
         [0008]    However, because the technology of the selective catalytic reduction using liquid urea as illustrated in  FIG. 1  uses the liquid urea by mixing with water, there is a drawback in that a storage container in which the liquid urea is stored becomes unnecessarily huge. In addition, the exhaust gas purification system using the liquid urea has a drawback in which subsidiary devices such as a storage container  3  for storing the liquid urea, a pump  5 , an injection module  4 , a mixer  6 , and the like are required. In addition, as the liquid urea remains in the purification system after an engine is stopped, and the remaining liquid urea becomes frozen by an outside environment at a low temperature (equal to or less than −11° C.), an operation of purifying the exhaust gas is not performed, and damage occurs to the entire system. 
         [0009]    In order to complement the aforementioned drawback of the liquid urea, a technology using solid urea (Korean Patent No. 10-0999571) is suggested, but because a thermal decomposition temperature of the solid urea is about 140° C. which is high, there is a drawback in that a large amount of electrical energy or exhaust heat energy is necessary, and when the thermal decomposition temperature is not maintained in the reactor or a pipe, the ammonia is coagulated in the pipe or the like. Further as illustrated in  FIG. 2 , in addition to the ammonia  3 , by-products such as isocyanic acid (HNCO) and cyanuric acid are produced during a process of thermally decomposing the solid urea  2 , and as the by-products are cooled and coagulated in a solid state in a pipe, a valve, and a nozzle, as illustrated in  FIG. 3 , after the engine is stopped, various problems such as damage to a valve, blockage of a nozzle and a pipe, deterioration in purification efficiency and the like occur. 
         [0010]    In addition, in the technology using the solid urea, because a period of time until the ammonia is produced by the thermal decomposition of the solid urea at the time of starting a vehicle is necessary, there is a problem in that the exhaust gas, which is not purified, is discharged to the atmosphere during the period of time until the ammonia is produced. 
         [0011]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention has been made in an effort to provide an exhaust gas purification system in which a problem with a social infrastructure for supplying the liquid urea may be solved by forming solid ammonium salt as a module type for easy mounting instead of using liquid urea and allowing the solid ammonium salt to be used while being replaced at a maintenance place in order to remove nitrogen oxide, and a structure is simple because a separate liquid storage container having a large volume and a liquid injection system are not required. 
         [0013]    In addition, the present invention provides a nitrogen oxide purification system using solid ammonium salt and selective catalytic reduction and a solid ammonium salt reactor used therein, capable of being operated for a period of time that is three and four times longer than that of the related art which uses liquid urea even when a container having the same storage capacity is used, by using the solid ammonium salt of which the content of the ammonia is three to four times greater than that of the liquid urea. 
         [0014]    In addition, the present invention provides a solid ammonium salt reactor which uses an amount of electrical energy smaller than that of the related art which uses solid urea, and does not produce by-products, by using the solid ammonium salt such as ammonium carbamate or ammonium carbonate of which a thermal decomposition temperature is about 60° C. which is low. 
         [0015]    Meanwhile, the present invention provides an exhaust gas purification system, which may prevent a problem that occurs when the ammonia, which is supplied for purifying the exhaust gas, remains in an ammonia supply line, a valve, and a nozzle and is cooled and coagulated in a solid state, and may prevent the exhaust gas from being discharged to the atmosphere in a state of not being purified during a delay time until the ammonia is produced and supplied from the main reactor at the time of starting an engine, by producing and supplying the ammonia at the same time of starting a vehicle. 
         [0016]    An exemplary embodiment of the present invention provides an exhaust gas purification system including: a main reactor configured to produce ammonia from solid ammonium salt; a dosing module connected to the main reactor to adjust a supply of the ammonia produced in the main reactor; and an injection nozzle installed in an exhaust pipe to inject the ammonia supplied from the dosing module to the exhaust pipe. 
         [0017]    In addition, the exhaust gas purification system may further include a gas supply device configured to supply gas to an ammonia supply line connected between the main reactor and the dosing module. 
         [0018]    In addition, the gas supply device may be an air supply device which supplies air to the ammonia supply line. 
         [0019]    In addition, the air supply device may be any one of an air tank, a blower, and an air compressor. 
         [0020]    In addition, the gas supply device may be an exhaust gas supply device which supplies exhaust gas to the ammonia supply line. 
         [0021]    In addition, the exhaust gas supply device may supply the exhaust gas at a rear end side of a diesel particulate filter provided at the exhaust pipe to the ammonia supply line. 
         [0022]    In addition, the exhaust gas supply device may be a blower, or an air compressor. 
         [0023]    In addition, the gas supply device may be an outside air supply device which supplies outside air, which is supplied to a cylinder by a supercharger, to the ammonia line. 
         [0024]    In addition, the outside air supply device may be a blower, or an air compressor. 
         [0025]    In addition, an opening and closing valve may be positioned between the gas supply device and the ammonia supply line. 
         [0026]    In addition, the opening and closing valve may be a two directional (two-way) valve, or a three directional (three-way) valve. 
         [0027]    In addition, a first heating means configured to heat the solid ammonium salt may be provided at the main reactor. 
         [0028]    In addition, the first heating means may use at least one of an electric heater, exhaust gas, and cooling water as a heat source. 
         [0029]    In addition, at least one of an exhaust gas flow path through which exhaust gas flows, and a cooling water flow path through which cooling water flows, may be formed at the main reactor. 
         [0030]    In addition, the exhaust gas flow path may be connected to an exhaust gas inlet pipe into which the exhaust gas flows from the exhaust pipe, and an exhaust gas outlet pipe which allows the flowing exhaust gas to flow out to the exhaust pipe. 
         [0031]    In addition, a blower may be coupled to the exhaust gas outlet pipe. 
         [0032]    In addition, the main reactor may include a housing having an internal space in which the solid ammonium salt is accommodated and having one side which is opened, a cover coupled to the opened one side of the housing; and a sensor unit provided at the cover. 
         [0033]    In addition, the sensor unit may include at least one of a pressure sensor, and a temperature sensor. 
         [0034]    In addition, a third heating means may be provided at the dosing module. 
         [0035]    In addition, the third heating means may use at least one of an electric heater, exhaust gas, and cooling water as a heat source. 
         [0036]    In addition, the dosing module may include at least one of an exhaust gas flow path through which exhaust gas flows and a cooling water flow path through which cooling water flows. 
         [0037]    In addition, the dosing module may include: a valve body; an ammonia flow path formed to penetrate the valve body; a pressure regulator provided at the ammonia flow path to adjust ammonia flow pressure; an adjusting valve provided at the ammonia flow path to adjust a discharge amount of the ammonia; and a temperature sensor provided at the valve body. 
         [0038]    In addition, the exhaust gas purification system may further include an auxiliary reactor having an internal space in which solid ammonium is accommodated, and provided at the ammonia supply line, which connects the main reactor and the dosing module, along a length direction of the ammonia supply line. 
         [0039]    In addition, the main reactor may include a housing having an internal space in which the solid ammonium is accommodated and having an ammonia outlet formed at one side, and the exhaust gas purification system may further include an auxiliary reactor which is installed in a wall of the housing to have a thickness corresponding to the wall of the housing in which the ammonia outlet is formed and has an internal space therein in which solid ammonium is accommodated. 
         [0040]    In addition, the auxiliary reactor may include a fourth heating means which heats the solid ammonium salt. 
         [0041]    In addition, the fourth heating means may be an electric heater. 
         [0042]    In addition, the auxiliary reactor may be heated at the same time of starting an engine, and a heating operation may be stopped at the same time of stopping the engine. 
         [0043]    In addition, the auxiliary reactor may be heated at the same time of starting an engine, and heated before the engine is stopped. 
         [0044]    In addition, the exhaust gas purification system may further include a selective catalytic reduction installed in the exhaust pipe to reduce the nitrogen oxide into nitrogen and water by mixing nitrogen oxide included in exhaust gas with the ammonia injected to the exhaust pipe; and an electronic control unit connected to the main reactor and the dosing module to control production and supply of the ammonia. 
         [0045]    In addition, the main reactor may include a housing of which one side is formed to be opened, a solid ammonium salt cartridge provided in the housing, a cover coupled to the housing so that the opened one side of the housing is sealed, an outlet formed at the other side of the housing and connected to the ammonia dosing module; and a fifth heating means provided at the housing and connected to the electronic control unit. 
         [0046]    In addition, the fifth heating means may use at least one of an electric heater, exhaust gas, and cooling water as a heat source. 
         [0047]    In addition, the exhaust gas purification system may further include a temperature sensor and a pressure sensor installed at the housing and connected to the electronic control unit. 
         [0048]    In addition, the exhaust gas purification system may further include a nitrogen oxide concentration measurement sensor installed at a rear end of the exhaust pipe where the selective catalytic reduction is installed. 
         [0049]    In addition, the exhaust gas purification system may further include an exhaust gas temperature sensor installed at a front end of the exhaust pipe where the selective catalytic reduction is installed, in which a temperature of the dosing module may be adjusted in accordance with the measured temperature. 
         [0050]    In addition, the solid ammonium salt may be ammonium-carbamate (NH 2 COONH 4 ) or ammonium-carbonate ((NH 4 ) 2 CO 3 ). 
         [0051]    In the exhaust gas purification system of the present invention, a solid ammonium salt module may be used and replaced at a maintenance place in accordance with a period of maintenance, and therefore there is a merit in that separate social infrastructure construction is not necessary. 
         [0052]    In addition, because there is no problem that the purification system of the present invention becomes frozen, there is a merit in that the design and the configuration of the system may be simplified. 
         [0053]    In addition, because the solid ammonium salt, which is used in the present invention, has a production amount of the ammonia per the same volume, that is, three to four times more than that of the liquid urea of the related art, there is a merit in that a period of replacing the solid ammonium salt may be lengthened compared to the liquid urea system. 
         [0054]    In addition, because the present invention uses ammonium salt such as ammonium carbamate or ammonium carbonate of which a thermal decomposition temperature is about 60° C., which is low, there is a merit in that a small amount of electrical energy is used in comparison with a case in which the solid urea is used, and a by-product is not produced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0055]      FIG. 1  is a schematic view illustrating a NOx reduction system using liquid urea of the related art. 
           [0056]      FIG. 2  is a reaction system diagram of solid materials which may produce ammonia. 
           [0057]      FIG. 3  is a schematic view illustrating a NOx reduction system using solid urea of the related art. 
           [0058]      FIG. 4  is a schematic view illustrating an exhaust gas purification system according to a first exemplary embodiment of the present invention. 
           [0059]      FIGS. 5A to 5C  are schematic views illustrating various exemplary embodiments of a main reactor disclosed in  FIG. 4 . 
           [0060]      FIGS. 6A to 6C  are schematic views illustrating various exemplary embodiments of a dosing module disclosed in  FIG. 4 . 
           [0061]      FIG. 7  is a flowchart illustrating an operational sequence of the exhaust gas purification system according to the first exemplary embodiment of the present invention. 
           [0062]      FIG. 8  is a schematic view illustrating an exhaust gas purification system according to a second exemplary embodiment of the present invention. 
           [0063]      FIG. 9  is a flowchart illustrating an operational sequence of the exhaust gas purification system according to the second exemplary embodiment of the present invention. 
           [0064]      FIG. 10  is a schematic view illustrating an exhaust gas purification system according to a third exemplary embodiment of the present invention. 
           [0065]      FIG. 11  is a schematic view illustrating an exhaust gas purification system according to a fourth exemplary embodiment of the present invention. 
           [0066]      FIG. 12  is a schematic view illustrating an internal state of an auxiliary reactor in accordance with an operation of a fourth heating means disclosed in  FIG. 11 . 
           [0067]      FIG. 13  is a flowchart illustrating an operational sequence of the exhaust gas purification system according to the fourth exemplary embodiment of the present invention. 
           [0068]      FIG. 14  is a schematic view illustrating an exhaust gas purification system according to a fifth exemplary embodiment of the present invention. 
           [0069]      FIG. 15  is a flowchart illustrating an operational sequence of the exhaust gas purification system according to the fifth exemplary embodiment of the present invention. 
           [0070]      FIG. 16  is a schematic view illustrating an exhaust gas purification system according to a sixth exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0071]      FIG. 4  is a schematic view illustrating an exhaust gas purification system according to a first exemplary embodiment of the present invention.  FIGS. 5A to 5C  are schematic views illustrating various exemplary embodiments of a main reactor  100  disclosed in  FIG. 4 .  FIGS. 6A to 6C  are schematic views illustrating various exemplary embodiments of a dosing module  200  disclosed in  FIG. 4 . 
         [0072]    Referring to  FIGS. 4 to 6C , an exhaust gas purification system according to a first exemplary embodiment of the present invention includes a main reactor  100  which produces ammonia by heating solid ammonium salt S. Referring to  FIGS. 5A to 5C , the main reactor  100  may include a housing  120  having an accommodating portion formed to accommodate the solid ammonium salt S therein, and an ammonia outlet  122 . Here, the housing  120  may have a hermetic structure in a state of accommodating the solid ammonium salt S, or a structure of which one side is opened so that the solid ammonium salt S may be replaced. 
         [0073]    In the main reactor  100 , in a case in which the housing  120  has a structure of which one side is opened, a cover  110  may be coupled to the opened one side of the housing  120 . The cover  110  is detachably coupled to the housing  120 , and a temperature sensor  111  or a pressure sensor  112  may be provided at the cover  110 . 
         [0074]    A first heating means, which heats the solid ammonium salt S accommodated in the housing  120 , may be provided at the housing  120 . The first heating means may be provided in the housing  120  or provided in a wall of the housing  120 . Here, regarding the first heating means, at least one of an electric heater, cooling water and exhaust gas of a vehicle may be used as a heat source. 
         [0075]    First, the first heating means may be one of an electric heater, cooling water or exhaust gas of a vehicle. For example, the solid ammonium salt S accommodated in the housing  120  may be heated by only any one heating means among an electric heater  121 , cooling water or exhaust gas of a vehicle. 
         [0076]    Referring to  FIG. 5A , in a case in which the first heating means is the electric heater  121 , the electric heater  121  is provided in the wall of the housing  120 , and generates heat by electrical energy to heat the solid ammonium salt S accommodated in the housing  120 . 
         [0077]    Referring to  FIG. 5B , in a case in which the first heating means uses the cooling water as a heat source, a cooling water flow path  123 , through which the cooling water may flow, may be formed in the wall of the housing  120 . The cooling water flow path  123  is formed in a coil shape along the wall of the housing  120  and embedded in the wall. Accordingly, the solid ammonium salt S accommodated in the housing  120  may be heated by circulating the cooling water heated while passing through an engine  10 . 
         [0078]    Referring to  FIG. 5C , in a case in which the first heating means uses the exhaust gas as a heat source, an exhaust gas flow path  124 , through which the exhaust gas may flow, may be formed in the wall of the housing  120 . 
         [0079]    The exhaust gas flow path  124  may be connected to an exhaust gas inlet pipe  21  for allowing the exhaust gas to flow from an exhaust pipe  20  to the exhaust gas flow path  124 , and an exhaust gas outlet pipe  22  for allowing the exhaust gas passing through the exhaust gas flow path  124  to flow again to the exhaust pipe  20 . 
         [0080]    Here, a blower  23  may be provided at the exhaust gas outlet pipe  23  so that the circulation of the exhaust gas may be easily performed. Accordingly, the solid ammonium salt S accommodated in the housing  120  may be heated by heat of the circulating exhaust gas in a high temperature. 
         [0081]    In addition to the above description, the first heating means may include two heating means among the electric heater, the cooling water, and the exhaust gas of a vehicle. For example, as illustrated in  FIG. 5B , the accommodated solid ammonium salt S may be heated by the electric heater  121  and the cooling water. 
         [0082]    Referring to  FIG. 5C , the solid ammonium salt S may be heated by the electric heater  121  and the exhaust gas. Here, the solid ammonium salt S may be configured to be heated by the exhaust gas and the cooling water. 
         [0083]    Meanwhile, the first heating means may include the electric heater, the cooling water and the exhaust gas of a vehicle, that is, three heating means. 
         [0084]    Here, the solid ammonium S may be heated by the electric heater, the cooling water and the exhaust gas of a vehicle. 
         [0085]    Referring to  FIG. 4 , the exhaust gas purification system according to the first exemplary embodiment of the present invention includes a dosing module  200  which is provided at an ammonia supply line  400  between the main reactor  100  and an injection nozzle  300 . The dosing module  200  may adjust the ammonia, which flows out of the main reactor  100 , to be supplied to the injection nozzle  300  in static pressure and in a fixed quantity. 
         [0086]    Referring to  FIGS. 6A to 6C , the dosing module  200  may include a valve body  210  having an ammonia flow path  220 . A pressure regulator  230 , which is provided at the ammonia flow path  220  to adjust flow pressure of the ammonia, may be provided at the valve body  210 . In addition, an adjusting valve  240 , which is provided at the ammonia flow path  220  to adjust a discharge amount of the ammonia, may be provided at the valve body  210 . 
         [0087]    In addition, a temperature sensor  260  may be further provided to measure a temperature of the valve body  210 . 
         [0088]    A third heating means for heating the valve body  210  at a temperature equal to or greater than a thermal decomposition temperature of the solid ammonium salt S may be provided at the valve body  210 . Here, the third heating means may be formed together with the valve body  210 . 
         [0089]    Here, the third heating means may use at least one of an electric heater, exhaust gas, and cooling water as a heat source. 
         [0090]    Here, in a case in which the third heating means uses the cooling water or the exhaust gas as a heat source, a cooling water flow path  270  or an exhaust gas flow path  280  may be formed in the valve body  210 . 
         [0091]    The aforementioned dosing module  200  may supply the ammonia flowing out of the main reactor  100  to the injection nozzle  300  in a fixed quantity. In addition, as the valve body  210  is heated at a temperature equal to or greater than a thermal decomposition temperature of the solid ammonium salt S, the ammonia may be prevented from being coagulated in the valve body  210  in a solid state. 
         [0092]    Referring to  FIG. 4 , the exhaust gas purification system according to the first exemplary embodiment of the present invention includes the injection nozzle  300  connected to the dosing module  200 . The injection nozzle  300  is disposed at a front end of a selective catalytic reduction (SCR)  30  in the exhaust pipe  20 , and may inject the ammonia supplied from the dosing module  200  in a direction to the selective catalytic reduction  30 . 
         [0093]    The exhaust gas purification system according to the first exemplary embodiment of the present invention includes gas supply devices  500   a  to  500   c  capable of supplying gas to the ammonia supply line  400 . Here, the supplied gas may be air, exhaust gas, or outside air. 
         [0094]    According to the first exemplary embodiment of the present invention, the gas supply device may be an air supply device  500   a  which supplies air to the ammonia supply line  400 . The air supply device  500   a  may include any one of an air tank, a blower, and an air compressor, and may be connected to the ammonia supply line  400  and an air supply line  600   a.    
         [0095]    Meanwhile, an opening and closing valve  410  may be provided at a connection point where the ammonia supply line  400  and the air supply line  600   a  are connected. 
         [0096]    The opening and closing valve  410  is a configuration to selectively control the flow of the ammonia and the air which are supplied from the ammonia supply line  400  and the air supply line  600   a , and may be a two-directional (two-way) valve or a three-directional (three-way) valve. 
         [0097]    In addition, the opening and closing valve  410  may include one-directional (one-way) valves which are provided at the ammonia supply line  400  at a side of the main reactor  100  and the air supply line  600   a , respectively. Hereinafter, the description will be given based on a configuration, in which the opening and closing valve  410  is the three directional (three-way) valve, for explanatory convenience. 
         [0098]    The exhaust gas purification system according to the first exemplary embodiment of the present invention may include an electronic control unit (not illustrated). The electronic control unit is electrically connected to the main reactor  100 , the dosing module  200 , the opening and closing valve  410 , and a plurality of sensors, and may control production, supply, and flow of the ammonia. 
         [0099]    Here, the sensors are sensors for sensing pressure, temperature and nitrogen oxide (NOx), and may be provided at the main reactor  100 , the dosing module  200 , and the exhaust pipe  20 . 
         [0100]      FIG. 7  is a flowchart illustrating an operational sequence of the exhaust gas purification system according to the first exemplary embodiment of the present invention. 
         [0101]    Hereinafter, a method of operating the exhaust gas purification system according to the first exemplary embodiment of the present invention, which includes the aforementioned configuration, will be described with reference to  FIG. 7 . 
         [0102]    First, when a user starts a vehicle in order to drive the vehicle, the user operates the heating means of the main reactor  100  and the dosing module  200  at the same time of starting the engine. At this time, the heating means, which use the electric heaters  121  and  250  as heat sources, among the heating means, are operated at the same time of starting the engine, and the heating means, which use the exhaust gas or the cooling water as a heat source, are operated with the operation of the heating means, which use the electric heaters  121  and  250  as heat sources, at a predetermined time difference. The reason is that the exhaust gas and the cooling water do not have sufficient thermal energy at the time of starting the engine. In addition, when the exhaust gas or the cooling water has sufficient thermal energy, the heating means, which use the electric heaters  121  and  250  as heat sources, and the heating means, which use the exhaust gas or the cooling water as a heat source, are operated together. In contrast, when the main reactor  100  or the dosing module  200  is excessively heated, the operations of the heating means, which use the electric heaters  121  and  250  as heat sources, are stopped, and only the heating means, which uses the exhaust gas or the cooling water as a heat source, is operated. 
         [0103]    Meanwhile, when the main reactor  100  produces the ammonia by heating the solid ammonium salt S by using the heating means, an internal pressure in the main reactor  100  is increased by the produced ammonia. Further, when the internal pressure in the main reactor  100  reaches a predetermined level, the ammonia flows out of the main reactor  100  and flows into the dosing module  200 . 
         [0104]    The ammonia flowing into the dosing module  200  flows to the injection nozzle  300  in static pressure and in a fixed quantity by the pressure regulator  230  and the adjusting valve  240  which are provided at the valve body  210 , and the ammonia flowing into the injection nozzle  300  is injected to the selective catalytic reduction  30  in the exhaust pipe  20  in static pressure and in a fixed quantity and mixed with the exhaust gas. 
         [0105]    The exhaust gas mixed with the ammonia is purified by removing nitrogen oxide by the selective catalytic reduction  30 , and discharged to the atmosphere. 
         [0106]    Meanwhile, when the user stops the engine, the operation of the heating means of the main reactor  100  is stopped so that the ammonia is not produced. In addition, the opening and closing valve  410  is operated at the same time of stopping the operation of the heating means of the main reactor  100  so that the ammonia supply line  400  at the side of the main reactor  100  is closed and the air supply line  600   a DeletedTextsis opened. 
         [0107]    When the air supply line  600   a  is opened, air is supplied to the dosing module  200  by driving the air supply device  500   a . The air supplied to the dosing module  200  passes through the dosing module  200 , and is discharged to the exhaust pipe  20  through the injection nozzle  300 . At this time, the ammonia remaining in the ammonia supply line  400 , the dosing module  200 , and the injection nozzle  300  is discharged together with the discharge of air. 
         [0108]    Accordingly, the ammonia supply line  400 , the dosing module  200 , and the injection nozzle  300  may be prevented from being clogged by the remaining ammonia which is coagulated in a solid state due to a decrease in temperature. 
         [0109]    In addition, when the discharge of the remaining ammonia by the air supply device  500   a  is completed, the operation of the air supply device  500   a  and the heating operation for the dosing module  200  are stopped. Thereafter, the air supply line  600   a  is closed and the ammonia supply line  400  is opened by driving the opening and closing valve  410 , and as a result the operation of the exhaust gas treatment system according to the first exemplary embodiment of the present invention is ended. 
         [0110]    Meanwhile, an operation end time point of the exhaust gas treatment system according to the first exemplary embodiment of the present invention may be a time point when the operation of the air supply device  500   a  and the heating operation for the dosing module  200  are finished, and in this case, the air supply line  600   a  is closed and the ammonia supply line  400  is opened by driving the opening and closing valve  410  at the same time of starting the engine. 
         [0111]    In addition, the heating operations for the main reactor  100  and the dosing module  200 , which are described above, and the operations of the overall configurations including the pressure regulator  230  and the adjusting valve  240  of the dosing module  200  are flexibly controlled by the electronic control unit. 
         [0112]      FIG. 8  is a schematic view illustrating an exhaust gas purification system according to a second exemplary embodiment of the present invention. 
         [0113]    Referring to  FIG. 8 , an exhaust gas purification system according to a second exemplary embodiment of the present invention includes a main reactor  100  which produces ammonia from solid ammonium salt, a dosing module  200  connected to the main reactor  100  to adjust a supply of the ammonia which is discharged from the main reactor  100 , an injection nozzle  300  connected to the dosing module  200  and disposed in an exhaust pipe  20  to inject the ammonia to the exhaust pipe  20 , and an exhaust gas supply device  500   b  which supplies the exhaust gas to an ammonia supply line  400  between the main reactor  100  and the dosing module  200 . 
         [0114]    In addition, the exhaust gas purification system according to the second exemplary embodiment of the present invention may further include an electronic control unit (not illustrated) electrically connected to the main reactor  100 , the dosing module  200 , the exhaust gas supply device  500   b , and a plurality of sensors to control production, supply, and flow of the ammonia. 
         [0115]    Here, because the main reactor  100 , the dosing module  200 , the injection nozzle  300 , and the electronic control unit are identical or similar to the aforementioned configurations of the first exemplary embodiment, a specific description thereof will be omitted, and hereinafter a description will be given based on configurations different from those of the first exemplary embodiment. 
         [0116]    The exhaust gas supply device  500   b  is one of a blower or an air compressor, and may be provided at an exhaust gas supply line  600   b.    
         [0117]    The exhaust gas supply line  600   b  may have one side connected to the ammonia supply line  400  between the main reactor  100  and the dosing module  200 , and the other side connected to the exhaust pipe  20  at a rear end side of a diesel particulate filter  40  provided at the exhaust pipe  20 . 
         [0118]    Accordingly, the exhaust gas at the rear end side of the diesel particulate filter  40  may be supplied to the ammonia supply line  400  by the exhaust gas supply device  500   b.    
         [0119]    Here, regarding the reason why the exhaust gas at the rear end side of the diesel particulate filter  40  is supplied, a plurality of particulate matters (PM) due to combustion of fuel is included in the exhaust gas at a front end side of the diesel particulate filter  40 . 
         [0120]    Accordingly, there is a concern in that when the exhaust gas at the front end side of the diesel particulate filter  40  is supplied to the ammonia supply line  400 , the dosing module  200  and the injection nozzle  300  including the ammonia supply line  400  are damaged. Therefore, the exhaust gas in which the particulate matters (PM) are removed while passing through the diesel particulate filter  40  is supplied in order to prevent the concern. 
         [0121]      FIG. 9  is a flowchart illustrating an operational sequence of the exhaust gas purification system according to the second exemplary embodiment of the present invention. 
         [0122]    Hereinafter, a method of operating the exhaust gas purification system according to the second exemplary embodiment of the present invention will be described with reference to  FIG. 9 . Here, in the method of operating the exhaust gas purification system according to the second exemplary embodiment of the present invention, because the operations before stopping the engine  10  are identical or similar to the operational method of the aforementioned first exemplary embodiment, a specific description thereof will be omitted. Hereinafter, the operational method after stopping the engine  10  will be specifically described. 
         [0123]    When a user stops the engine  10 , all of the heating means of the main reactor  100  and the dosing module  200  are stopped. Here, the reason why the heating operations for the dosing module  200  and the main reactor  100  are simultaneously stopped in comparison with the first exemplary embodiment is that the dosing module  200  does not need to be heated because the exhaust gas flowing into the dosing module  200  has a high temperature. 
         [0124]    Next, the ammonia supply line  400  at a side of the main reactor  100  is closed and the exhaust gas supply line  600   b  is opened by driving the opening and closing valve  410  at the same time of stopping the operations of the heating means of the main reactor  100  and the dosing module  200 . 
         [0125]    When the exhaust gas supply line  600   b  is opened, the exhaust gas is supplied to the dosing module  200  by driving the exhaust gas supply device  500   b . Further, the exhaust gas supplied to the dosing module  200  passes through the dosing module  200 , and is discharged to the exhaust pipe  20  through the injection nozzle  300 . At this time, the ammonia remaining in the ammonia supply line  400 , the dosing module  200 , and the injection nozzle  300  is discharged together with the discharge of the exhaust gas. Accordingly, the ammonia supply line  400 , the dosing module  200 , and the injection nozzle  300  may be prevented from being clogged by the remaining ammonia which is coagulated in a solid state due to a decrease in temperature. 
         [0126]    In addition, when the discharge of the remaining ammonia is completed by the exhaust gas supply device  500   b , the operation of the exhaust gas supply device  500   b  is stopped. Thereafter, the exhaust gas supply line  600   b  is closed and the ammonia supply line  400  is opened by driving the opening and closing valve  410 , and as a result the operation of the exhaust gas treatment system according to the second exemplary embodiment of the present invention is ended. 
         [0127]    In addition, similarly to the first exemplary embodiment, an operation end time point of the exhaust gas treatment system according to the second exemplary embodiment of the present invention may be a time point when the operation of the exhaust gas supply device  500   b  is finished. This may be controlled by the electronic control unit. 
         [0128]      FIG. 10  is a schematic view illustrating an exhaust gas purification system according to a third exemplary embodiment of the present invention. 
         [0129]    Referring to  FIG. 10 , an exhaust gas purification system according to a third exemplary embodiment of the present invention includes a main reactor  100  which produces ammonia from solid ammonium salt S, a dosing module  200  connected to the main reactor  100  to adjust a supply of the ammonia which is discharged from the main reactor  100 , an injection nozzle  300  connected to the dosing module  200  and disposed in an exhaust pipe  20  to inject the ammonia to the exhaust pipe  20 , and an outside air supply device  500   c  which supplies outside air, which is supplied to a cylinder by a supercharger  700 , to an ammonia supply line  400  between the main reactor  100  and the dosing module  200 . 
         [0130]    In addition, the exhaust gas purification system according to the third exemplary embodiment of the present invention may further include an electronic control unit (not illustrated) electrically connected to the main reactor  100 , the dosing module  200 , the outside air supply device  500   c , and a plurality of sensors to control production, supply, and flow of the ammonia. 
         [0131]    Here, because the main reactor  100 , the dosing module  200 , the injection nozzle  300 , and the electronic control unit are identical or similar to the aforementioned configurations of the first and the second exemplary embodiments, a specific description thereof will be omitted, and hereinafter a description will be given based on configurations different from those of the exemplary embodiments. 
         [0132]    The outside air supply device  500   c  is one of a blower or an air compressor, and may be provided at an outside air supply line  600   c . The outside air supply line  600   c  may have one side connected to the ammonia supply line  400  between the main reactor  100  and the dosing module  200 , and the other side connected to an outside air discharge line  730  provided between the supercharger  700  and the engine  10 . 
         [0133]    Accordingly, the outside air, which flows through the outside air discharge line  730 , may be supplied to the ammonia supply line  400  by the outside air supply device  500   c.    
         [0134]    Meanwhile, in a method of operating the exhaust gas purification system according to the third exemplary embodiment of the present invention, because there is a difference compared to the first exemplary embodiment in that the outside air supply device  500   c  is provided correspondingly to the air supply device  500   a , the operational method of the third exemplary embodiment may be identical or similar to the operational method of the first exemplary embodiment. 
         [0135]      FIG. 11  is a schematic view illustrating an exhaust gas purification system according to a fourth exemplary embodiment of the present invention.  FIG. 12  is a schematic view illustrating an internal state of an auxiliary reactor  800  in accordance with an operation of a fourth heating means  810  disclosed in  FIG. 11 . 
         [0136]    Referring to  FIGS. 11 and 12 , an exhaust gas purification system according to a fourth exemplary embodiment of the present invention includes a main reactor  100  which produces ammonia from solid ammonium salt S, an auxiliary reactor  800  provided at an ammonia supply line  400  connected to the main reactor  100 , a dosing module  200  connected to the auxiliary reactor  400  to adjust a supply of the ammonia which is discharged from the main reactor  100  and the auxiliary reactor, and an injection nozzle  300  connected to the dosing module  200  and disposed in an exhaust pipe  20  to inject the ammonia to the exhaust pipe  20 . 
         [0137]    In addition, the exhaust gas purification system according to the fourth exemplary embodiment of the present invention may further include an electronic control unit (not illustrated) electrically connected to the main reactor  100 , the dosing module  200 , the auxiliary reactor  800 , and a plurality of sensors to control production, supply, and flow of the ammonia. 
         [0138]    Here, because the main reactor  100 , the dosing module  200 , the injection nozzle, and the electronic control unit are identical or similar to the configurations disclosed in the aforementioned exemplary embodiments, a specific description thereof will be omitted, and hereinafter a description will be given based on configurations different from those of the aforementioned exemplary embodiments. 
         [0139]    In addition, the exhaust gas purification system according to the fourth exemplary embodiment of the present invention may include any one of the air supply device  500   a , the exhaust gas supply device  500   b , and the outside air supply device  500   c , which are disclosed in the first exemplary embodiment to the third exemplary embodiment, and are connected to the ammonia supply line  400  between the main reactor  100  and the dosing module  200  in order to discharge the remaining ammonia to the outside after the engine is stopped. 
         [0140]    The auxiliary reactor  800  is a configuration to supply the ammonia to the exhaust pipe at the same time of starting the engine when the engine is started, and may be provided at the ammonia supply line  400  between the main reactor  100  and the dosing module  200  along a length direction of the ammonia supply line  400 . 
         [0141]    The auxiliary reactor  800  may have an internal space in which the solid ammonium salt S is accommodated, and an ammonia inlet and an ammonia outlet provided on the same line as the ammonia supply line  400 . 
         [0142]    In addition, a fourth heating means  810 , which heats the solid ammonium salt S accommodated in the internal space, may be provided. Here, the fourth heating means  810  may be an electric heater in order to rapidly heat the accommodated solid ammonium salt S. 
         [0143]    The aforementioned auxiliary reactor  800  produces the ammonia by rapidly heating the accommodated solid ammonium salt S, and therefore may prevent the exhaust gas from being discharged to the atmosphere in a state of not being purified during a delay time until the ammonia is discharged after being produced in the main reactor  100 . 
         [0144]    In addition, at the time of starting the engine, as the solid ammonium salt S accommodated in the auxiliary reactor  800  produces the ammonia while being heated until the ammonia is discharged after being produced in the main reactor  100 , the solid ammonium salt S accommodated in the auxiliary reactor  800  may be almost exhausted. 
         [0145]    In addition, after the engine is stopped, the remaining ammonia in the ammonia supply line  400  where the auxiliary reactor  800  is provided may be cooled and coagulated in a state of the solid ammonium salt S in an accommodating portion of the auxiliary reactor. That is, the coagulated solid ammonium salt S is converted again into the ammonia at the time of starting the engine, and the exhaustion and the coagulation (production) of the solid ammonium salt S may be repeatedly performed in the accommodating portion of the auxiliary reactor  800  in accordance with whether or not the engine is driven. 
         [0146]      FIG. 13  is a flowchart illustrating an operational sequence of the exhaust gas purification system according to the fourth exemplary embodiment of the present invention. 
         [0147]    Hereinafter, a method of operating the exhaust gas treatment system according to the fourth exemplary embodiment of the present invention will be described with reference to  FIG. 13 . 
         [0148]    First, when a user starts a vehicle in order to drive the vehicle, the user operates the heating means of the main reactor  100 , the dosing module  200 , and the auxiliary reactor  800  at the same time of starting the engine. At this time, the solid ammonium salt S accommodated in the auxiliary reactor  800  is rapidly heated by the fourth heating means  810  and converted into the ammonia, and the produced ammonia is supplied to the exhaust pipe  20  via the dosing module  200  and the injection nozzle  300  at the same time of starting the engine. 
         [0149]    In addition, because an amount of the solid ammonium salt S accommodated in the auxiliary reactor  800  is small, the entire amount of the solid ammonium salt S is exhausted and the ammonia is not produced after a time point when the ammonia is produced and supplied from the main reactor  100  after the engine is started. 
         [0150]    However, the fourth heating means  810  is continuously operated to prevent the auxiliary reactor  800  from being cooled by the outside environment. 
         [0151]    Meanwhile, among the heating means for heating the main reactor  100  and the dosing module  100 , the heating means, which use the electric heater  121  as a heat source, are operated at the same time of starting the engine, and the heating means, which use the exhaust gas or the cooling water as a heat source, are operated with the operation of the heating means, which use the electric heater  121  as a heat source, at a predetermined time difference. 
         [0152]    Thereafter, when the exhaust gas or the cooling water has sufficient thermal energy, the heating means, which uses the electric heater  121  as a heat source, and the heating means, which uses the exhaust gas or the cooling water as a heat source, are simultaneously operated. 
         [0153]    In addition, in an environment where a temperature of the main reactor  100  or the dosing module  200  is excessively increased, or the operation of the heating means, which use the electric heater  121  as a heat source, is not required, the operation of the heating means, which uses the electric heater  121  as a heat source, is stopped, and only the heating means, which uses the exhaust gas or the cooling water as a heat source, is operated. 
         [0154]    Meanwhile, when the main reactor  100  is heated and the ammonia is produced from the solid ammonium salt S, an internal pressure in the main reactor  100  is increased by the produced ammonia. 
         [0155]    Further, when the internal pressure in the main reactor  100  reaches a predetermined level, the ammonia produced in the main reactor  100  flows out of the main reactor  100  and flows into the dosing module  200 . 
         [0156]    The ammonia flowing into the dosing module  200  is supplied to the injection nozzle  300  in static pressure and in a fixed quantity, the ammonia supplied to the injection nozzle  300  is injected to the selective catalytic reduction  30  in the exhaust pipe in static pressure and in a fixed quantity, and the ammonia is mixed with the exhaust gas and discharged to the atmosphere after being purified by removing nitrogen oxide (NOx) by the selective catalytic reduction  30 . 
         [0157]    Meanwhile, when the user stops the engine, the heating operation for the main reactor  100  and the auxiliary reactor  800  is stopped. In addition, the ammonia supply line  400  at sides of the main reactor  100  and the auxiliary reactor  800  is closed and the air supply line  600   a  is opened by driving the opening and closing valve  410  at the same time of stopping the heating operation for the main reactor  100  and the auxiliary reactor  800 . 
         [0158]    When the air supply line  600   a  is opened, air is supplied to the dosing module  200  by driving the air supply device  500 . Further, the air supplied to the dosing module  200  is discharged to the exhaust pipe  300  through the injection nozzle  300 . 
         [0159]    At this time, the ammonia supply line  400 , the dosing module  200 , and the injection nozzle  300  may be prevented from being clogged by the remaining ammonia which is coagulated in a solid state due to a decrease in temperature, by discharging the remaining ammonia together with the discharge of the air. 
         [0160]    In addition, when the discharge of the remaining ammonia is completed by the air supply device  500   a , the operation of the air supply device  500   a  and the heating operation for the dosing module  200  are stopped. Thereafter, the air supply line  600   a  is closed and the ammonia supply line  400  is opened by driving the opening and closing valve  410 , and as a result the operation of the exhaust gas treatment system according to the fourth exemplary embodiment of the present invention is ended. 
         [0161]    Meanwhile, an operation end time point of the exhaust gas treatment system according to the fourth exemplary embodiment of the present invention may be a time point when the heating operations for the air supply device  500   a  and the dosing module  200  are finished so that an amount of the ammonia, which is coagulated in the auxiliary reactor  800 , may be increased, and in this case, the air supply line  500   a  may be closed and the ammonia supply line  400  may be opened by driving the opening and closing valve  410  at the same time of starting the engine. 
         [0162]      FIG. 14  is a schematic view illustrating an exhaust gas purification system according to a fifth exemplary embodiment of the present invention. 
         [0163]    Referring to  FIG. 14 , an exhaust gas purification system according to a fifth exemplary embodiment of the present invention includes a main reactor  100  which produces ammonia from solid ammonium salt, an auxiliary reactor  800  provided at the main reactor  100 , a dosing module  200  connected to the main reactor  100  to adjust a supply of the ammonia which is discharged from the main reactor  100  and the auxiliary reactor  800 , and an injection nozzle  300  connected to the dosing module  200  and disposed in an exhaust pipe  20  to inject the ammonia to the exhaust pipe  20 . 
         [0164]    In addition, the exhaust gas purification system according to the fifth exemplary embodiment of the present invention may further include an electronic control unit (not illustrated) electrically connected to the main reactor  100 , the dosing module  200 , the auxiliary reactor  800 , and a plurality of sensors to control production, supply, and flow of the ammonia. 
         [0165]    Here, because the main reactor  100 , the dosing module  200 , the injection nozzle  300 , and the electronic control unit are identical or similar to the configurations disclosed in the aforementioned exemplary embodiments, a specific description thereof will be omitted, and hereinafter a description will be given based on configurations different from those of the aforementioned exemplary embodiments. 
         [0166]    In addition, the exhaust gas purification system according to the fifth exemplary embodiment of the present invention may include any one of the air supply device  500   a , the exhaust gas supply device  500   b , and the outside air supply device  500   c , which are disclosed in the first exemplary embodiment to the third exemplary embodiment, and are connected to the ammonia supply line  400  between the main reactor  100  and the dosing module  200  in order to discharge the remaining ammonia to the outside after the engine is stopped. 
         [0167]    The auxiliary reactor  800  is a configuration to supply the ammonia to the exhaust pipe  20  at the same time of starting the engine when the engine is started, and may be provided at the main reactor  100 . More specifically, the auxiliary reactor  800  is disposed and installed at the wall to have a thickness corresponding to the wall of the housing in which the ammonia outlet  122  of the main reactor  100  is formed. 
         [0168]    The auxiliary reactor  800  may have an internal space in which the solid ammonium salt S is accommodated, an ammonia inlet is adjacent to an accommodating space of the housing, and an ammonia outlet may be formed to be identical to the outlet  122  formed at the housing  120  of the main reactor  100 . 
         [0169]    In addition, the auxiliary reactor  800  may include a fourth heating means  810  which heats the accommodated solid ammonium salt S. Here, the fourth heating means  810  may be an electric heater in order to rapidly heat the accommodated solid ammonium salt S. 
         [0170]    The aforementioned auxiliary reactor  800  produces the ammonia by rapidly heating the accommodated solid ammonium salt S, and therefore may prevent the exhaust gas from being discharged to the atmosphere in a state of not being purified during a delay time until the ammonia is discharged after being produced in the main reactor  100 . 
         [0171]    In addition, because an amount of the solid ammonium salt S accommodated in the auxiliary reactor  800  is small, the most amount of solid ammonium salt S may be exhausted at a time point when the solid ammonium salt S is heated in the main reactor  100  at the time of starting the engine until the ammonia is produced and discharged and the ammonia is produced. 
         [0172]    In addition, after the engine is stopped, the remaining ammonia in the ammonia supply line  400  where the auxiliary reactor  800  is provided may be cooled and coagulated in a state of the solid ammonium salt in an accommodating portion of the auxiliary reactor  800 . That is, the coagulated solid ammonium salt S is converted again into the ammonia at the time of starting the engine, and the exhaustion and the coagulation of the solid ammonium salt S may be repeatedly performed in the accommodating portion of the auxiliary reactor  800  in accordance with whether or not the engine is driven. 
         [0173]      FIG. 15  is a flowchart illustrating an operational sequence of the exhaust gas purification system according to the fifth exemplary embodiment of the present invention. 
         [0174]    Hereinafter, a method of operating the exhaust gas treatment system according to the fifth exemplary embodiment of the present invention will be described with reference to  FIG. 15 . 
         [0175]    First, when a user starts a vehicle in order to drive the vehicle, the user operates the heating means of the main reactor  100 , the dosing module  200 , and the auxiliary reactor  800  at the same time of starting the engine. At this time, the ammonia is produced by the auxiliary reactor  800  at the same time of starting the engine, and the produced ammonia is supplied to the exhaust pipe  20 . 
         [0176]    Meanwhile, because an amount of the solid ammonium salt S accommodated in the auxiliary reactor  800  is small, the operation of the fourth heating means  810  is stopped after a time point when the ammonia is produced and supplied from the main reactor  100  after the engine is started. The reason is that the auxiliary reactor  800  is in a state of receiving heat by the heating means provided at the main reactor  100  so as not to cause a problem that the auxiliary reactor  800  is cooled by the outside environment. 
         [0177]    Thereafter, the operations from a time point when the engine is stopped to a time point when the operation is finished are identical or similar to the operations of the aforementioned fourth exemplary embodiment of the present invention, and thus hereinafter a specific description will be omitted. 
         [0178]    The exhaust gas purification system according to various exemplary embodiments of the present invention, which is described above, may be used while replacing the solid ammonium salt S at a maintenance place in accordance with a period of maintenance, and therefore there is a merit in that separate social infrastructure construction is not necessary. 
         [0179]    In addition, since the remaining ammonia is discharged through various fluids after the engine is stopped, various problems, which occur when the remaining ammonia is coagulated in a solid state in the ammonia supply line  400 , the dosing module  200 , and the injection nozzle  300 , may be solved. 
         [0180]    In addition, as the ammonia is quickly supplied by the auxiliary reactor  800  at the same time of starting the engine, the exhaust gas, which may be discharged in a state of not being purified during a delay time until the ammonia is produced from the main reactor  100 , is purified, and as a result efficiency of exhaust gas purification may be maximized. 
         [0181]    In addition, as the auxiliary reactor  800  is provided at the ammonia supply line  400  or the main housing  100 , because separate configurations such as a back flow valve is not required, the system may be compactly manufactured, and the system may be easily mounted to a vehicle, which does not have the system. 
         [0182]      FIG. 16  is a schematic view illustrating an exhaust gas purification system according to the sixth exemplary embodiment of the present invention. 
         [0183]    Referring to  FIG. 16 , an exhaust gas purification system according to the sixth exemplary embodiment of the present invention may include a main reactor  100 , a dosing module  200 , an injection nozzle  300 , a selective catalytic reduction  400 , and an electronic control unit  500 . 
         [0184]    Here, because the main reactor  100 , the dosing module  200 , the injection nozzle  300 , and the electronic control unit  500  are identical or similar to the configurations disclosed in the aforementioned exemplary embodiments, a specific description thereof will be omitted, and hereinafter a description will be given based on configurations different from those of the aforementioned exemplary embodiments. 
         [0185]    Here, the selective catalytic reduction  400  is installed in the exhaust pipe  20 , and installed at a rear end of an exhaust pipe  20  where the injection nozzle  300  is installed. The selective catalytic reduction  400  serves to reduce nitrogen oxide included in the exhaust gas into nitrogen and water by mixing the nitrogen oxide with the ammonia which is injected to the exhaust pipe  20 . 
         [0186]    First, the main reactor  100  includes a solid ammonium salt cartridge (not illustrated), which may be replaced, in the housing. Because the solid ammonium salt cartridge may be used while being replaced at a maintenance place in accordance with a period of replacement, there is a merit in that separate social infrastructure construction is not necessary. 
         [0187]    In addition, a fifth heating means may be provided at the housing to adjust a temperature. 
         [0188]    Here, the fifth heating means is identical or similar to the first heating means which heats the main reactor of the first to the fourth exemplary embodiments. 
         [0189]    In addition, the solid ammonium salt or solid ammonium salt cartridge accommodated in the main reactor  100  may be formed of ammonium-carbamate (NH 2 COONH 4 ) or ammonium-carbonate ((NH 4 ) 2 CO 3 ). Because the aforementioned material is thermally decomposed into the ammonia at about 60° C., a temperature for an ammonia production reaction may be maintained to be low, and as a result there is a merit in that a small amount of electrical energy is used, and a by-product, which is produced by decomposition of the solid urea, is not produced in comparison with a case in which the solid urea is used. 
         [0190]    A reaction equation in which the ammonia is produced by the thermal decomposition of the ammonium-carbamate and the ammonium-carbonate is as follows. 
         [0000]      NH 2 COONH 4           2NH 3 +CO 
         [0000]      (NH 4 ) 2 CO 3           2NH 3 +CO 2 +H 2 O 
         [0191]    Further, a representative reaction equation in which NOx is removed on the selective catalytic reduction  400  when the produced ammonia is injected to the exhaust pipe is as follows. 
         [0000]      NO+NO 2 +2NH 3 →2N 2 +3H 2 O
 
         [0192]    In addition, a temperature sensor and a pressure sensor, which are installed at the housing and connected to the electronic control unit  500 , are further included. The fifth heating means may be controlled by the electronic control unit  500  in accordance with the temperature and the pressure measured by the temperature sensor and the pressure sensor. 
         [0193]    In addition, a nitrogen oxide concentration measurement sensor  600 , which is installed at a rear end of the exhaust pipe  20  where the selective catalytic reduction  400  is installed and connected to the electronic control unit  500 , is further included. An injection amount of the ammonia may be adjusted by the ammonia dosing module  200  in accordance with the measured concentration of the nitrogen oxide. 
         [0194]    That is, referring to  FIG. 16 , the concentration of the nitrogen oxide is measured by installing the nitrogen oxide concentration measurement sensor  600  at the exhaust pipe  20  at a rear end of the selective catalytic reduction  400 , and the injection amount of the ammonia is adjusted in proportion to an amount of the nitrogen oxide remaining in the exhaust gas which has passed through the selective catalytic reduction  400 . Accordingly, an amount of the nitrogen oxide in the exhaust gas which is discharged to the atmosphere may be maintained to be equal to or lower than an appropriate level, and the ammonia may be prevented from being excessively injected and discharged to the atmosphere. 
         [0195]    In addition, an exhaust gas temperature sensor  700 , which is installed at a front end of the exhaust pipe  20  where the selective catalytic reduction  400  is installed and connected to the electronic control unit  500 , is further included, and a temperature of the ammonia dosing module  200  may be adjusted in accordance with the measured temperature. 
         [0196]    Because a purification reaction of the nitrogen oxide is reduced when the temperature is lowered before the ammonia injected from the injection nozzle  300  reaches the selective catalytic reduction  400 , the temperature is measured in advance by installing the exhaust gas temperature sensor  700  at the exhaust pipe  20  at a front end of the selective catalytic reduction  400 . By controlling the temperature of the ammonia dosing module  200  through the electronic control unit  500 , the temperatures of the exhaust gas and the ammonia, which flow into the selective catalytic reduction  400 , may be maintained to be equal to or higher than about 180° C. at which the purification reaction of the nitrogen oxide is activated. 
         [0197]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 &lt;Description of symbols&gt; 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 S: Solid ammonium salt 
                   
               
               
                 100: Main reactor 
               
               
                 110: Cover 
                 120: Housing 
               
               
                 121, 250: Electric heater 
                 122: Ammonia outlet 
               
               
                 123, 270: Cooling water flow line 
                 124, 280: Exhaust gas flow line 
               
               
                 200: Dosing module 
               
               
                 230: Pressure regulator 
                 240: Adjusting valve 
               
               
                 300: Injection nozzle