Abstract:
Disclosed herein is a method and apparatus for recovering hydrogen in the process of desulfurizing petroleum hydrocarbon, in which hydrogen is recovered from the fuel fraction obtained by hydrodesulfurization, and the recovered hydrogen is reused, so that the existing hydrodesulfurization equipment for producing ultralow-sulfur diesel fuel can be utilized to the utmost and simultaneously the effluence of hydrogen from fuel fraction can be minimized, thereby reducing production costs.

Description:
RELATED APPLICATIONS 
       [0001]    This is a §371 of International Application No. PCT/KR2009/004437, with an international filing date of Aug. 10, 2009 (WO 2010/018954, published Feb. 18, 2010), which is based on Korean Patent Application No. 10-2008-0079800 filed Aug. 14, 2009. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a method of recovering hydrogen used in the desulfurization process of petroleum hydrocarbon and an apparatus for producing ultralow-sulfur diesel fuel using the method. More particularly, the present disclosure relates to a method and apparatus for recovering hydrogen in a process of desulfurizing petroleum hydrocarbon, in which hydrogen is recovered from the fuel fraction obtained by hydrodesulfurization, and the recovered hydrogen is reused, so that the existing hydrodesulfurization equipment for producing ultralow-sulfur diesel fuel can be utilized to the utmost and simultaneously the effluence of hydrogen from a fuel fraction can be minimized, thereby reducing production costs. 
       BACKGROUND 
       [0003]    When petroleum containing a large amount of sulfur is fractionated by atmospheric distillation, various petroleum products, such as gasoline, lamp oil (kerosene), light oil (diesel oil), lube oil, heavy oil and the like, are obtained. All of these petroleum products contain sulfur compounds, and, particularly, contain a larger amount of sulfur compounds as they approximate heavy oil. Gasoline containing a large amount of sulfur does not have good inflammability. Further, Lamp oil, light oil and heavy oil containing a large amount of sulfur produce sulfur dioxide gas in the combustion gas to cause air pollution. 
         [0004]    As methods of desulfurizing such petroleum products, conventionally, a method of washing petroleum products with a sulfuric acid aqueous solution or a sodium hydroxide aqueous solution, a method of bringing petroleum products into contact with acidic white clay to adsorb sulfur, and the like have been used. However, these methods are problematic in that sulfur is insufficiently removed, and loss from refining is increased. Recently, a hydrodesulfurization method has been widely used. In this hydrodesulfurization method, mercaptans, chained sulfur compounds and cyclic sulfur compounds, which are sulfur compounds existing in petroleum fractions, are reacted with hydrogen using catalysis at high temperature and pressure to decompose sulfur compound molecules, thus separating these sulfur compounds into hydrogen carbide and hydrogen sulfide. This hydrodesulfurization method has exhibited excellent sulfur removal effects to such a degree that the content of sulfur in the petroleum product is decreased to 0.1 wt %. 
         [0005]    Recently, worldwide, as the regulation of sulfur content in fuel has become strict, the necessity for ultralow-sulfur diesel fuel which contains in amount of 10 ppm or less has been emphasized. Therefore, in order to produce ultralow-sulfur diesel fuel, new desulfurization technologies based on adsorption, solvent extraction or the like have been developed. However, these new desulfurization technologies are problematic in that operation costs are increased by the excessive consumption of hydrogen, and in that large-scale investment, such as the reconstruction of the existing desulfurization equipment, the introduction of new process equipment, or the like, are required. 
         [0006]    Therefore, currently, most oil refining companies are producing ultralow-sulfur diesel fuel containing sulfur in a concentration of 10 ppm or less by controlling process variables, such as desulfurizing catalyst temperature, pressure, reaction rate and the like, while directly using the existing desulfurization equipment. 
         [0007]    However, as shown in  FIG. 1 , the conventional hydrodesulfurization process for producing ultralow-sulfur diesel fuel is performed by the steps of: separating the hydrocarbon fraction having passed through a desulfurizer  12  into a fuel fraction, which is a tower-bottom fraction, and a mixed gas of hydrogen and hydrogen sulfide using a high-pressure separator  13 ; passing the mixed gas through a hydrogen sulfide absorbing tower to remove hydrogen sulfide therefrom, compressing the mixed gas using a compressor  17  and then recirculating the compressed mixed gas; and transferring the fuel fraction to a stripper  18  to remove hydrogen sulfide (H 2 S). However, since this conventional hydrodesulfurization process is conducted under the conditions of a high pressure of 50 kg/cm 2  or more, low LHSV (amount of diesel fuel treated per 1 m 3  of catalyst) and high hydrogen partial pressure, and a high-pressure separator provided at the rear end of a hydrodesulfurizer is also operated under the condition of high pressure, there is a problem in that the solubility of hydrogen increases, so that a large amount of hydrogen dissolves in the tower-bottom fraction of the high-pressure separator and is then discharged, and the discharged hydrogen is directly used as fuel gas, thereby deteriorating the grade of quality of the hydrogen. That is, this conventional hydrodesulfurization process is problematic in that expensive hydrogen is discharged and then mixed with cheap fuel gas and then used, thus increasing the total production cost. 
       SUMMARY 
       [0008]    Accordingly, the present disclosure provides a method and apparatus for recovering hydrogen in the process of desulfurizing petroleum hydrocarbon, which can utilize the existing hydrodesulfurization equipment for producing ultralow-sulfur diesel fuel to the utmost and simultaneously can minimize the effluence of hydrogen from the fuel fraction obtained by a hydrodesulfurization process. 
         [0009]    The present disclosure shows a method and apparatus for recovering hydrogen dissolved in petroleum hydrocarbon fraction by sequentially passing the petroleum hydrocarbon fraction discharged from the rear end of a high-pressure separator installed in a desulfurizer through a low-pressure separator, a low-temperature separator and a hydrogen sulfide absorbing tower to separate hydrogen from the hydrocarbon fraction and then recirculating the separated hydrogen. 
         [0010]    Therefore, the present disclosure provides a method and apparatus for recovering hydrogen in the process of desulfurizing petroleum hydrocarbon, which can reduce production costs by minimizing the effluence of hydrogen from the fuel fraction obtained by a hydrodesulfurization process. 
         [0011]    Further, the present disclosure provides a method and apparatus for recovering hydrogen in the process of desulfurizing petroleum hydrocarbon, which can reduce production costs by directly utilizing the existing hydrodesulfurization equipment and simultaneously minimizing the effluence of hydrogen used in a desulfurization process. 
         [0012]    According to the present disclosure, a low-pressure separator, a low-temperature separator, a hydrogen sulfide absorbing tower and a hydrogen recovery pipe are sequentially disposed at the rear end of a high-pressure separator in the hydrodesulfurization process, and the hydrogen discharged from the hydrogen sulfide absorbing tower is recovered, so that the hydrogen included in the petroleum hydrocarbon fraction obtained by a hydrodesulfurization process can be separated, recovered and then reused, with the result that the production costs caused by the mixing of expensive hydrogen and inexpensive petroleum hydrocarbon fraction can be minimized, and ultralow-sulfur diesel fuel can be produced at low cost, thereby strengthening the competitiveness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic view showing a conventional hydrodesulfurization process; and 
           [0014]      FIG. 2  is a schematic view showing a process of recovering hydrogen using a hydrodesulfurization process according to the present disclosure. 
       
    
    
     DESCRIPTION OF THE ELEMENTS IN THE DRAWINGS 
       [0000]    
       
           1 . petroleum hydrocarbon 
           2 ,  4 . recirculated hydrogen 
           3 . replenished hydrogen 
           11 . heating furnace 
           12 . desulfurizer 
           13 . high-pressure separator 
           14 . low-pressure separator 
           15 . low-temperature separator 
           16 . hydrogen sulfide absorbing tower 
           17 . compressor 
           18 . stripper 
           19 . compressor for replenishing hydrogen 
       
     
       DETAILED DESCRIPTION 
       [0027]    An embodiment of the present disclosure provides a method of recovering hydrogen in a process of desulfurizing petroleum hydrocarbon, including: removing sulfur from a mixture of petroleum hydrocarbon and hydrogen using a desulfurizer; separating the mixture into a petroleum hydrocarbon fraction and a hydrogen mixture using a high-pressure separator; passing the petroleum hydrocarbon fraction through a low-pressure separator to separate it into ultralow-sulfur petroleum hydrocarbon and a mixture of hydrogen and hydrogen sulfide; passing the mixture of hydrogen and hydrogen sulfide through a low-temperature separator to separate a light oil fraction in the mixture; passing the remaining mixture of hydrogen and hydrogen sulfide, from which the light oil fraction was separated, through a hydrogen sulfide absorbing tower to obtain hydrogen; and recirculating the hydrogen obtained by the hydrogen sulfide absorbing tower. 
         [0028]    Another embodiment of the present disclosure provides an apparatus for recovering hydrogen in a process of desulfurizing petroleum hydrocarbon, including: a desulfurizer removing sulfur from a mixture of petroleum hydrocarbon and hydrogen; a high-pressure separator separating the mixture into a petroleum hydrocarbon fraction and a hydrogen mixture; a low-pressure separator through which the petroleum hydrocarbon fraction is passed to separate it into ultralow-sulfur petroleum hydrocarbon and a mixture of hydrogen and hydrogen sulfide; a low-temperature separator through which is passed the mixture of hydrogen and hydrogen sulfide to separate a light oil fraction in the mixture; a hydrogen sulfide absorbing tower through which the remaining mixture of hydrogen and hydrogen sulfide is passed, from which the light oil fraction was separated, to obtain hydrogen; and an apparatus recirculating the hydrogen obtained by the hydrogen sulfide absorbing tower. 
         [0029]    Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. 
         [0030]    As shown in  FIG. 2 , the method of removing hydrogen according to the present disclosure is a novel method of separating and recovering hydrogen included in a petroleum hydrocarbon fraction having undergone a hydrodesulfurization process by sequentially disposing a low-pressure separator  14 , a low-temperature separator  15 , a hydrogen sulfide absorbing tower  16  and a hydrogen recovery pipe at the rear end of a high-pressure separator  13  in a hydrodesulfurization process for producing ultralow-sulfur diesel fuel. 
         [0031]    The method of recovering hydrogen in the hydrodesulfurization process according to the present disclosure, shown in  FIG. 2 , is described as follows. 
         [0032]    In  FIG. 2 , petroleum hydrocarbon  1 , which is the major raw material for the desulfurization process, may be lamp oil, light oil or diesel oil having a boiling point of 180˜450° C., and has a sulfur content of about 2,000˜15,000 ppm. Petroleum hydrogen  1  is mixed with hydrogen and then passes through a heating furnace  11  to be previously heated to a temperature of 280˜360° C., which is a temperature necessary for desulfurization. In this case, in order to heat the mixture of petroleum hydrocarbon and hydrogen, one or more heat exchangers may be additionally provided. 
         [0033]    The heated mixture of petroleum hydrocarbon and hydrogen is supplied to a desulfurizer  12 . The desulfurizer  12  is charged with NiMo and/or CoMo catalyst which is used for deep desulfurization, and the pressure in the desulfurizer  12  is 40˜80 kg f /cm 2 . The content of sulfur in the petroleum hydrocarbon having passed through the desulfurizer  12  is very low. That is, this petroleum hydrocarbon has a sulfur content of 10 ppm or less, except for hydrogen sulfide (H 2 S). 
         [0034]    The mixture of hydrogen and petroleum hydrocarbon, the sulfur content of which is greatly reduced by the desulfurizer  12 , passes through a high-pressure separator  13  to be separated into a mixed gas of hydrogen and hydrogen sulfide and petroleum hydrocarbon fraction containing hydrogen. The high-pressure separator  13  is operated under the conditions of a temperature of 200˜260° C. and a pressure of 35˜75 kg f /cm 2 . The mixed gas of hydrogen and hydrogen sulfide, separated through the top of the high-pressure separator  13 , passes through a hydrogen sulfide absorbing tower charged with amine to remove hydrogen sulfide from the mixture by adsorption, and is then compressed by a compressor  17  and then recirculated. Meanwhile, since the high-pressure separator  13  is operated under the condition of high pressure, the solubility of hydrogen increases, so that the ultralow-sulfur petroleum hydrocarbon, which corresponds to the fraction placed at the bottom of the high-pressure separator  13 , includes a large amount of hydrogen, and this ultralow-sulfur petroleum hydrocarbon containing a large amount of hydrogen is discharged through the bottom of the high-pressure separator  13 . 
         [0035]    Therefore, in the present disclosure, in order to recover hydrogen from the hydrogen-containing petroleum hydrocarbon discharged from the bottom of the high-pressure separator  13 , the hydrogen-containing petroleum hydrocarbon fraction is passed through a low-pressure separator  14 . The low-pressure separator  14  serves to separate hydrogen by creating a low-pressure atmosphere such that the hydrogen dissolved in petroleum hydrocarbon as a result of the high-pressure condition of the high-pressure separator  13  disposed at the front end of this low-pressure separator  14  is vaporized into the form of a gas. The optimal operation of the low-pressure separator  14  for separating a maximum of hydrogen may be conducted under the conditions of a temperature of 200˜260° C. and a pressure of 25˜35 kg f /cm 2 . 
         [0036]    The mixed gas of hydrogen and hydrogen sulfide separated from the low-pressure separator  14  passes through a low-temperature separator  15 . The gas mixture separated from the top of the low-pressure separator  14  includes a very small amount of petroleum hydrocarbon in addition to hydrogen and hydrogen sulfide. When this gas mixture passes through the low-temperature separator  15 , petroleum hydrocarbon having a relatively high due point is condensed in the form of liquid to separate this petroleum hydrocarbon from the gas mixture. Therefore, the mixed gas of hydrogen and hydrogen sulfide is discharged from the top of the low-temperature separator  15 , and the petroleum hydrocarbon fraction is discharged from the bottom thereof. The optimal operation of the low-temperature separator  15  may be conducted under the conditions of a temperature of 38˜50° C. and a pressure of 25˜35 kg f /cm 2 . 
         [0037]    The mixed gas of hydrogen and hydrogen sulfide discharged from the top of the low-temperature separator  15  is introduced into a hydrogen sulfide absorbing tower  16  charged with an amine. When hydrogen containing hydrogen sulfide is reused in a desulfurization process, the hydrogen sulfide causes the corrosion of apparatuses such as a compressor and the like and hinders the hydrodesulfurization reaction from taking place in the desulfurization process. Therefore, the hydrogen sulfide absorbing tower  16  serves to recover and reuse only the pure hydrogen by allowing the adsorbent to adsorb hydrogen sulfide. Examples of the adsorbent may include, but are not limited to, an amine, ammonia, sodium hydroxide, calcium hydroxide and the like, preferably, amine. 
         [0038]    The hydrogen  2  recovered by the hydrogen sulfide absorbing tower  16  is transferred to the inlet pipe of a compressor  17  for replenishing hydrogen, and is then further mixed with the recirculated hydrogen  4  recirculated from the top of the high-pressure separator  13  with combining replenished hydrogen  3 , and is then recirculated together with the petroleum hydrocarbon  1 . 
         [0039]    Hereinafter, the present disclosure will be described in more detail with reference to the following Example. However, the scope of the present disclosure is not limited thereto. 
       Example 1 
       [0040]    As shown in  FIG. 2 , the yearly hydrogen consumption and cost for using hydrogen occurring when ultralow-sulfur diesel fuel is produced using the method and apparatus for recovering hydrogen by sequentially disposing a low-pressure separator, a low-temperature separator, a hydrogen sulfide absorbing tower and a hydrogen recovery pipe at the rear end of a high-pressure separator in the hydrodesulfurization process according to the present disclosure were compared with those occurring when ultralow-sulfur diesel fuel is produced using conventional technology. The results thereof are given in Table 1 below: 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Comparative 
                   
                   
               
               
                   
                 Example 
                 Example 
               
               
                   
                 (prior art) 
                 1* 
                 Decrement 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Yearly hydrogen 
                 43,618 
                 41,340 
                 2,278 Reduction 
               
               
                 consumption, nm3/h 
               
               
                 Cost for using hydrogen, 
                 839 
                 795 
                   44 Reduction 
               
               
                 billion won/year 
               
               
                   
               
               
                 *Results of process operation of SK energy No. 6MDU, hydrogen 229 won/nm 3, 350 days/year 
               
             
          
         
       
     
         [0041]    As given in Table 1 above, when ultralow-sulfur diesel fuel was produced using the method and apparatus for recovering hydrogen by sequentially disposing a low-pressure separator, a low-temperature separator, a hydrogen sulfide absorbing tower and a hydrogen recovery pipe at the rear end of a high-pressure separator  13  in the hydrodesulfurization process according to the present disclosure, the cost of expensive hydrogen, occupying 50% or more of the production cost in the process of producing ultralow-sulfur diesel fuel, was greatly reduced to 5% or more. 
         [0042]    The foregoing examples and embodiments are provided merely for the purposes of illustration and explanation and are in no way to be construed as limiting. While reference to various embodiments are shown, the words used herein are words of description and illustration, rather than words of limitation. Further, although reference to particular means, materials, and embodiments are shown, there is no limitation to the particulars disclosed herein. Rather, the embodiments extend to all functionally equivalent structures, methods, and uses, such as are within the scope of the appended claims.