Abstract:
A method for reducing nitrogen oxide with a catalyst and a system thereof comprises the following steps: (A) a step of guiding exhaust, selectively guiding the exhaust containing the nitrogen oxide into an oxygen removing reaction room based on the oxygen content of the exhaust. (If both the oxygen content and the temperature of the exhaust are in a required range, it is not necessary to use the oxygen removing reaction room); (B) a step of introducing the oxygen remover, introducing the oxygen remover into the oxygen removing reaction room from the storage vessel based on the consistency of oxygen in the exhaust. (If both the oxygen content and the temperature of the exhaust are in a required range, it is not necessary to introduce the oxygen remover); (C) a step of oxygen removing reaction, the oxygen remover generating an oxygen removing reaction in the reaction room to cause a function of oxygen removal; (d) a step of catalytic reaction, converting the oxygen removed exhaust a catalyst. (A proper reduction agent can be injected as required); and a step of discharging, discharging the catalyzed exhaust.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method for removing nitrogen oxide with catalyst and a system thereof.  
           [0003]    2. Description of Related Art  
           [0004]    Due to the development of industries, the electricity consumption is unceasingly increasing and various power plant equipment and combustion systems are continuously established in accordance with the human demand. However, the exhaust generated from burning results in the problem of environment protection. The major source of nitrogen oxide (NOx) is a product originated from a burning process while the coal and the petroleum, which are used in our daily life, are made. The secondary source of nitrogen oxide (NOx) is from the discharged end gas during the nitric acid being used or made in a factory. The side effects of Nox to the human body are briefly listed hereinafter:  
           [0005]    A. In case of Nox existing in the atmosphere in company with HC (hydrocarbon), it may produce a kind of poisonous chemical smoke after being exposed under ultraviolet rays.  
           [0006]    B. If the human body exposes in an environment with excessive consistency of NOx, the NOx will infiltrate the cells of lungs via the respiratory system to hinder the oxygen being delivered to all parts in the body such that the health of the body is threatened directly.  
           [0007]    C. The NOx restrains the growths of vegetables and plants and the complete organism&#39;s habit may be affected seriously.  
           [0008]    D. The acid rain resulting from the NOx can cause dead aquatics and plants, eroded buildings and hair failings.  
           [0009]    Currently, countries all over the world have started to seriously control the NOx.  
           [0010]    The typical conventional ways for de-nitrification are: the selected catalytic reduction (SCR), the selected non-catalytic reduction (SNCR) and wet de-nitrification technique, wherein, the way of SCR is more popular and important.  
           [0011]    Nevertheless, it is undesirable that there are still following defects residing in the method of SCR:  
           [0012]    A. The catalyst used is extremely expensive.  
           [0013]    B. The equipment used has a huge size: the catalyst bed is considerably large.  
           [0014]    C. The initial set up cost is excessively high: The reducing agent needed by the SCR is ammonia and it is necessary to increase a lot of extra equipment for is storing, treating and delivering the ammonia such that it incurs many expenses and the initial set up cost becomes increased greatly. Therefore, the set up cost of the SCR is higher than that of the exhaust generating equipment such as the diesel engine, the boiler or the like in many application fields.  
           [0015]    D. It will cause the problem of the second air pollution: If ammonia is treated improperly to occur leakage, it can cause the problem of the second air pollution.  
           [0016]    E. The operation cost is excessively high: A great deal of ammonia has to be used while in operation so that a considerably high operation cost is needed.  
           [0017]    A comparison table underneath lists various techniques of de-nitrification:  
                                                                                   Possible           Controlled       Removing   Space       Status of skill   secondary       technique   Expense   rate   needed   Principle   development   pollution   Remark                   Improvement   Low   15-30   No   NOx is restrained by   At the stage   No   No       of burning               way of decreasing the   of practically                       consistency of oxygen   used.                       in the burning zone,                       shortening the                       stagnation time in the                       high temperature zone                       and reducing the                       burning temperature       Low NOx   Low   30-60   No   NOx is restrained by   Commercial-   No   Limited       burner               way of decreasing   ized       removal rate                       the consistency of                       oxygen in the                       burning zone,                       shortening the                       stagnation time in                       the high temperature                       zone and reducing                       the burning                       temperature       Selected   Medium   30-60   Smaller   NH 3  is injected in the   Commercial-   Ammonia   Not suitable for       non-           than   high temperature   ized   leakage   fuel with high       catalytic           SCR   zone under the           sulfur       reduction               condition of no       (SNCR)               catalyst, NOx is                       reduced and                       removed within an                       optimal range of                       reaction temperature                       870-1000° C.       Selected   High   80-90   Reactor   NH 3  is used as the   Commercial-   The   Not suitable for       catalytic           and   reducing agent, NOx   ized   catalyst is   fuel with high       reduction           storage   on the catalyst is       aged and   sulfur       (SCR)           trough   removed by way of       discarded                   are   the selected       and                   installed   reduction, and the       ammonia                       optimal reaction       is leaked                       temperature is in a       (small                       range of 280-400° C.       amount)       Electronic   High   &gt;80   Power   NOx is oxidized by   A leading   The   Used with dry       light beam           utility   way of electronic   test is in a   discard   FGD                   and   light raying and   state of                   reaction   neutralizes with NH 3     being                   room   to form solid   developed                       substances for being                       recovered       Wet de-   High   &gt;80   A reactor   Lye, oxidizer and   A leading   Waste   A de-       ntrification           and   reducing agent are   test is in a   water and   sulfurizing and                   agent   utilized to remove   state of   solid   de-nitrifying                   adding   NOx by way of   being   discard   system can be                   equipment   absorption-oxidation,   developed       developed                       oxidation-absorption                       or oxidation-                       absorption-reduction                  
 
           [0018]    It can be learned from the above comparison table that various conventional ways for removing nitrogen oxide have their own advantages and disadvantages. Hence, it is believed that any one of the preceding conventional ways is imperfect.  
         SUMMARY OF THE INVENTION  
         [0019]    A method for reducing nitrogen oxide with a catalyst and a system thereof according to the present invention comprises the following steps: (A) a step of guiding exhaust, selectively guiding the exhaust containing the nitrogen oxide into an oxygen removing reaction room based on the oxygen content of the exhaust. (If both the oxygen content and the temperature of the exhaust are in a required range, it is not necessary to use the oxygen removing reaction room); (B) a step of introducing the oxygen remover, introducing the oxygen remover into the oxygen removing reaction room from the storage trough based on the consistency of oxygen in the exhaust. (If both the oxygen content and the temperature of the exhaust are in a required range, it is not necessary to introduce the oxygen remover); (C) a step of oxygen removing reaction, the oxygen remover generating an oxygen removing reaction in the reaction room to cause a function of oxygen removal; (d) a step of catalytic reaction, converting the oxygen-removed exhaust with a catalyst and a proper reduction agent can be injected as required; and (E) a step of discharging, the catalyzed exhaust being discharged to the open air. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The present invention can be more fully understood by reference to the following detailed description and an accompanying drawing, in which:  
         [0021]    [0021]FIG. 1 is a system diagram for removing nitrogen oxide with catalyst according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Referring to FIG. 1, basically, a method for removing nitrogen oxide according to the present invention comprises a step of guiding exhaust A, a step of introducing oxygen remover B, a step of removing oxygen C, a step of catalyst reaction D and a step of exhaust discharging E.  
         [0023]    Wherein, the step of guiding exhaust A is to guide the originally discharged exhaust into an oxygen removing reaction room  1  with a pipeline for further oxygen removing reaction to an extent that the oxygen content of the exhaust can be treated with the catalyst. Therefore, if the oxygen content of the exhaust is within a preset range, such as 0-5%, the step A can be neglected.  
         [0024]    The step of introducing oxygen remover B is to supply the oxygen removable substance in a storage vessel 2 by way of a pipeline. The oxygen removable substance is not limited as the organic complex such as gasoline, diesel fuel, heavy oil, kerosene, stain removing oil, gas, natural gas, coal, hydrogen, methanol, ethanol, propanol, butanol, methane, ethane, propane, or benzene or bio-oil, or the acutely reactive metal such as sodium or magnesium, or the oxygen remover such as powder (nitride). In order to be supplied with a proper amount of the oxygen removable substance, a deliver pump/wind mill 21 can be used and the deliver pump can be detectably controlled with a calculated delivered amount. It is noted that the step B can be omitted in case of the oxygen content being in a preset range such as 0-5%.  
         [0025]    The step of removing oxygen C is to operate an ignition device such as igniting an ignition rod and to produce an oxygen removing reaction for the preceding oxide such that the nitrogen oxide residue can be reduced to an extent of the oxygen content of the exhaust being treated with the catalyst. Thus, the output exhaust after the oxygen removing reaction can be detected the oxygen content thereof with an oxygen detection apparatus  11  and the temperature thereof with a temperature detection apparatus  12  such that the pumped amount of the oxygen remover and the temperature of the exhaust can be adjusted in accordance with the detected values. Besides, in order to detect the consistency of the nitrogen oxide, a nitrogen oxide detection apparatus  13 ,  14  can be added in front of and in back of the oxygen detection apparatus  11  and the temperature detection apparatus  12 .  
         [0026]    The step of catalyst reaction D is to treat the oxygen removed exhaust by way of a catalyst apparatus  3  after the oxygen removing reaction. The catalyst used in the reaction is oxidation-reduction catalyst such as palladium or the like and the loader for the catalyst can be made of metal, ceramics and etc. with a flat shape or a honeycomb arrangement. Further, a reducing agent vessel  31  is provided to communicate with the catalyst apparatus  3  for supplying the reducing agent by way of a controllable pump.  
         [0027]    The step of discharging E is to discharge the catalyzed exhaust via a funnel such that the nitrogen oxide in the exhaust can be reduced to an extent of being less contaminated.  
         [0028]    In order to prove the method disclosed in the present invention being practicable, following two embodiments will be explained in detail to verify the practicability thereof.  
         [0029]    Embodiment 1:  
         [0030]    Simulated experimental example:  
         [0031]    Equipment: Reaction test apparatus in the laboratory  
         [0032]    Catalyst: PM oxidation-reduction catalyst is adopted.  
         [0033]    Speed in the catalyst space: 12,000 L/H  
         [0034]    Temperature controlled in the reaction tester: 350° C.  
         [0035]    Simulated gas for nitrogen oxide (NOx): Nitrogen monoxide (NO)  
         [0036]    Oxide remover and simulated reducing agent gas: Propylene (C 3 H 8 )  
         [0037]    The gaseous nitrogen monoxide (NO) with consistency of 1100 ppm is injected into the reaction test apparatus together with the propylene (C 3 H 8 ) with consistency of 900 ppm and the consistency of oxygen (O 2 ) in the nitrogen monoxide (NO) is removed to an extent of 0.5% original consistency.  
         [0038]    Test result:  
         [0039]    Range of reaction temperature is 100-610° C.  
         [0040]    When the ration of the gaseous nitrogen monoxide (NO) to propylene (C 3 H 8 ) (NO/HC ration) is less than 20, the conversion efficiency of the nitrogen monoxide is 80%.  
         [0041]    When the ration of propylene(C 3 H 8 ) to oxygen (O 2 ) is less than 1.4, the conversion efficiency of the nitrogen monoxide (NO) is 95%.  
         [0042]    Embodiment 2:  
         [0043]    A. The exhaust source containing nitrogen oxide (NOx):  
         [0044]    Data rationed running power of the diesel engine unit: 100 KW (Kilowatts)  
         [0045]    I) Flow rate of dry base exhaust: 10 Nm 3 /min (cubic meter/minute, at a state of 0° C. and 1 atmosphere without vapor).  
         [0046]    II) The oxygen content (O 2 ) of the exhaust: 10%.  
         [0047]    III) The nitrogen oxide (NOx): 501 ppmdv (dry volume ratio in per one millionth)  
         [0048]    B. The oxygen remover (fuel):  
         [0049]    Diesel fuel (thermal value about 8,800 kcal/liter).  
         [0050]    C. The catalyst:  
         [0051]    Precious metal catalyst (Palladium or other special elements).  
         [0052]    Loader for the catalyst: Metal honeycomb loader with 100 cell/in 2  (number of holes in an area of square inches).  
         [0053]    D. Technique for controlling the oxygen content of the exhaust:  
         [0054]    The oxygen content of the exhaust generating from ordinary combustion is about 3-15% and the selected oxygen remover is injected into the reaction room for removing the oxygen or into the exhaust system to consume the oxygen in the exhaust.  
         [0055]     The amount of required diesel fuel in the embodiment 2 can be figured out as the following:  
         [0056]    1) The mole&#39;s number per minute of oxygen in the exhaust:  
         [0057]    10 Nm 3 /min*10%*1000 liter/m 3 ÷22.4 liter/mole @0° C. 1 atm=44.6 mole/min  
         [0058]    2) Reaction formula for oxygen removal:  
         [0059]    Suppose the mean molecular formula of the diesel fuel is C 8 H 18 , the required mole number of oxygen per mole of the diesel fuel during the reaction of oxygen removal is shown in the following reaction formula:  
         1C 8 H 18 +12.5O 2 →8CO 2 +9H 2 O  
         [0060]    3) The required flow rate of the oxygen remover: The consistency of oxygen (02) in the exhaust is reduced to 6% from 10% and the flow rate of the required injected diesel fuel is:  
         [0061]    The flow rate of the diesel fuel calculated in embodiment 2: The oxygen has to be reduced to 26.8 mole/min from 44.6 mole/min and it is necessary to consume 17.8 mole/min oxygen.  
         [0062]    The chemical reaction formula is:  
         1.4C 8 H 18 +17.8O 2 →11.2CO 2 +12.6H 2 O  
         [0063]    ∵ The molecular weight of C 8 H 18  is: (12*8)+(1*18)=114  
         [0064]    ∵ Once the consumed oxygen is 17.8 mole/min, the required C 8 H 18  is  
         [0065]    =&gt;114 g/mole*1.4 mole/min=159.6 g/min  
         [0066]    =&gt;159.6 g/min*60 min/hr=9576 g/hr=9.6 kg/hr  
         [0067]    E. The relation between the oxygen content of the exhaust and the de-nitrified efficiency:  
         [0068]    The experimental result shows the oxygen content of the exhaust is inversely proportional to the de-nitrified efficiency of the exhaust after catalyst reaction, that is, the less the oxygen is contained in the exhaust, the lower the consistency of nitrogen oxide (NOx) is provided in the exhaust after catalyst reaction. On the contrarily, the more the oxygen is contained in the exhaust, the worse the de-nitrified efficiency is.  
         [0069]    F. Calculation and measurement for the oxygen content of the exhaust and the oxygen remover:  
         [0070]    i) The oxygen content of the exhaust can be measured at both the front end and the rear end of the catalyst bed for calculating the amount of the oxygen remover needed.  
         [0071]    ii) When the ingredients in the exhaust and the flow rate of the exhaust are fixed, the oxygen content of the exhaust can be assumed to be unchanged after being measured such that the required fixed oxygen remover can be figured out.  
         [0072]    iii) When the ingredients in the exhaust is fixed and the flow rate of the exhaust is changed, the oxygen content thereof can be detected after being measured and the quantity of the required injected oxygen remover can be figured out by way of the variation of the flow rate.  
         [0073]    iv) When the ingredients in the exhaust and the flow rate of the exhaust are changed with respect to the state of the oxygen removing reaction, it is necessary to measure the oxygen content by way of oxygen detecting device and the measured signal is sent to a calculation control system such that the required injected oxygen remover can be figured out.  
         [0074]     The oxygen detecting device is placed at the front end of the catalyst bed to perform the measurement.  
         [0075]    G. The choice of the catalyst:  
         [0076]    An oxidation-reduction catalyst is used.  
         [0077]    H. The choice of the loader for the catalyst:  
         [0078]    i) The honeycomb metal loader;  
         [0079]    ii) The honeycomb ceramic loader;  
         [0080]    iii) The foamed ceramic loader;  
         [0081]    iv) The plate loader.  
         [0082]     100 cell/in 2  (the number of holes in an area per square inch) honeycomb metal loader is adopted.  
         [0083]    I. The reaction temperature and the reaction efficiency of the de-nitrified catalyst:  
         [0084]    A range of the reaction temperature of the de-nitrified catalyst is 100-610° C. and the higher the temperature is, the better the de-nitrified efficiency is in the range.  
         [0085]     The operation temperature of the present embodiment is 475° C.  
         [0086]    J. The initial cost and the operation cost are lowered:  
         [0087]    It is about 70-80% the initial and the operation cost used in the selective catalyst reduction  
         [0088]    It is appreciated that the present invention has offered an effective method with lower cost to reduce, and even more, to remove the nitrogen oxide in the discharged exhaust. Accordingly, the present invention has a remarkable contribution for both of the industries and the environment protection.  
         [0089]    While the invention has been described with reference to preferred embodiments thereof, it is to be understood that modifications or variations may be easily made without departing from the spirit of this invention, which is defined by the appended claims.