Abstract:
This invention describes a new process for hydrotreatment or hydrodesulfurization of petroleum fractions that is thermally coupled to a process for amine treatment that employs a heat pump circuit that is established between a hot source located on the hydrotreatment process and a cold source located on the amine treatment system. The major effect of the process according to the invention is a reduction of CO2 emissions.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to the field of the processes of refining and petrochemistry that employ distillation columns. This field is very vast, and, in a preferred manner, this invention applies to the more limited field of the processes for hydrotreatment or hydrodesulfurization of petroleum fractions. 
         [0002]    This invention does not relate to the reaction or catalytic aspect of said processes but rather to the energy aspect thereof. The operations for physical separation of the components, such as distillation, are very energy-intensive operations. It is necessary to provide the energy that is necessary to bringing the mixture to a boil to separate its components. The efficiency of the separation, in the case of compounds that are similar in nature and are therefore difficult to separate, is generally enhanced by increasing the reflux of the column. 
         [0003]    This increase of the reflux consists in recycling a more or less large part of the effluent that is produced at the top of the column to reinject it into the column in the liquid state. This is reflected by a supplementary energy to be provided at the bottom of the column to reboil this inventory of supplementary product. 
         [0004]    Furthermore, the effluent at the top of the column is to be condensed to be recovered in liquid form. 
         [0005]    This condensation can be done by employing a cooling tower, i.e., an exchanger that uses ambient air as a cooling fluid, which makes it possible for a low energy cost to dissipate excess heat into the atmosphere. The drawback of this type of exchanger is then that the heat is not enhanced. In other cases, this condensation by cooling tower is only partially possible because of the low temperature that is required, since the temperature of the fluid to be condensed cannot be less than that of the ambient air. 
         [0006]    In the field of refining or petrochemistry, there is often recourse to vapor such as a coolant, in particular in the exchangers. In a typical refinery exchanger, generally superheated vapor condenses and yields its heat to the fluid to be heated. This vapor can be obtained from a dedicated heater in which, most often, the combustion of a hydrocarbon, such as natural gas, for example, is carried out. This combustion produces carbon dioxide (CO2), which will contribute to greenhouse gas (GHG) emissions of the site on which the distillation unit is installed. 
         [0007]    In the case where the air is not adequate for cooling the effluent at the top of the column, it is necessary to have recourse to refrigeration by water, if it is used in a sufficient quantity, or by means of cold groups that, with a more or less significant energy expenditure, make it possible to use chilled water. This also gives rise to significant GHG emissions. 
         [0008]    A solution for limiting these GHG emissions is, according to this invention, to install a heat pump circuit between the reboiler of the distillation column and the cooling tower, whose advantages are two-fold:
       On the one hand, to cool the stream in question to temperatures that cannot be reached by a cooling tower system,   On the other hand, to upgrade the heat exchanged at the reboiler of the distillation column by raising its temperature level.       
 
         [0011]    Another field of application of this invention is that of so-called feedstock-effluent exchangers that are often used for preheating the feedstock in various refining processes. 
         [0012]    For the processes that rely on relatively high temperatures, in particular the processes that implement an exothermic reaction, there is often recourse to a feedstock-effluent exchange, with the feedstock being preheated by the hot effluent. However, this feedstock-effluent exchange is limited by the crossover phenomenon: it will not be possible to heat a feedstock beyond the temperature at which the effluent is available. 
         [0013]    The installation of a heat pump in this case makes it possible to overcome this limitation by shifting the temperature levels beyond the crossover temperatures. 
       Examination of the Prior Art 
       [0014]    The primary application of the heat pumps is the heating of either individual or industrial buildings, for example by the supply of heat to a hot water network, or the heating of a greenhouse for cultivating plants. With the principle of the heat pump being the transport of calories between two environments, from a “cold” environment to a “hot” environment, it is possible to operate while supplying cold. Thus, another application of the heat pumps is the air-conditioning of buildings. 
         [0015]    In some cases, the effect that is generally sought by the installation of a heat pump is the energy savings and/or the economic gain relative to another heating method, an oil heater, for example. Actually, the heat pumps are characterized by a coefficient of performance levels that corresponds to the amount of energy that is necessary for the transport of an amount of energy between a hot environment and a cold environment, or vice versa. The smaller the temperature difference between the two environments, the better the performance level will be and the greater the energy savings will be. 
         [0016]    This is the reason for which the heat pumps are advantageously used in heating/air-conditioning applications for which the temperature difference between the desired temperature of the building to be air-conditioned and that of the outside environment that will supply or absorb the calories (groundwater, atmosphere, lithosphere) is generally low, on the order of about 10 degrees Celsius. 
         [0017]    In the case of refining and petrochemistry processes, and in particular for the diesel fuel hydrotreatment-type applications, the situation can be summarized in the following manner: 
         [0018]    It is desired to desulfurize by hydrotreatment an initially hot diesel fuel feedstock, at approximately 130° C., in a process that partly operates at low temperature. Actually, the feedstock is to be cooled to approximately 50° C., but in contrast, large amounts of energy at approximately 130° C. are necessary for the regeneration of the solvent. 
         [0019]    The temperature difference between, on the one hand, the cooled feedstock and, on the other hand, the temperature that is necessary to the regeneration of the solvent, is therefore approximately 80° C. 
         [0020]    In a context of inexpensive energy, this is why this application is not considered advantageous from the standpoint of the performances of a heat pump, because the heat supply by means of a conventional heater by fossil hydrocarbon combustion is the simplest and most economical solution, with the heat of the feedstock to be cooled being dissipated directly into the atmosphere by cooling towers. 
         [0021]    In contrast, in a context of tensions regarding energy, it is possible to prove that a heat pump is a profitable solution despite a fairly low performance coefficient, more particularly also in the case where there is interest in specific greenhouse gas emissions for which the heat pumps offer a good reduction potential. 
         [0022]    This invention describes specifically the installing of a heat pump in this context and shows its energy advantage. 
         [0023]    Actually, such an installation makes it possible both to upgrade a considerable amount of heat (which would be dissipated into the atmosphere according to the prior art), improving the efficiency of the cooling while reducing the required surface area at the cooling tower, and finally to provide the entirety of the heat required for the regeneration of the solvent with an advantageous carbon balance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  shows a diagram of a process for hydrotreatment of a diesel fuel fraction according to the prior art. 
           [0025]      FIG. 2  according to the invention shows the same diagram of the process that is equipped with a heat pump circuit that makes it possible to improve its energy efficiency. 
       
    
    
     SUMMARY DESCRIPTION OF THE INVENTION 
       [0026]    This invention can be defined as an improved process for hydrotreatment of petroleum fractions that integrates a hydrogen/hydrogen sulfide separation by means of an amine treatment unit. 
         [0027]    More specifically, the process according to the invention is a process for hydrotreatment of a petroleum fraction that is thermally coupled to an amine treatment process, making it possible to separate hydrogen from hydrogen sulfide, in which the hydrotreatment process has an exchanger ( 1007 ) that makes it possible to cool the effluent of the hydrotreatment reactor to a temperature of approximately 50° C.; said amine treatment process has a cross-section for regeneration of said amine that employs a distillation column ( 1009 ), equipped with a reboiler ( 1010 ) that operates at a temperature of approximately 130° C. 
         [0028]    The heat exchanger ( 1007 ) plays the role of cold source, and the reboiler ( 1010 ) plays the role of hot source. The ideas of hot source and cold source are taken here in the usual meaning of the order of temperatures. It happens that the terminology is reversed within the context of heat pumps, but this is a simple conventional question. 
         [0029]    The process according to the invention establishes a heat pump circuit between the cold source and the hot source by means of a coolant that circulates between the reboiler ( 1010 ) and the exchanger ( 1007 ) according to the following circuit: 
         [0030]    The coolant ( 208 ) evaporates in the exchanger ( 1007 ) by extracting the calories of the reaction effluent ( 111 ) for producing a vapor ( 209 ) whose temperature and pressure are increased by the compressor ( 1011 ); the high-pressure and high-temperature vapor stream ( 206 ) obtained from the compressor ( 1011 ) is condensed in the reboiler ( 1010 ) from which a pressurized liquid stream ( 207 ) is produced whose temperature is lowered by expansion in the valve ( 1012 ); and the resulting liquid ( 208 ) is then partially vaporized and returns to the exchanger ( 1007 ) in the form of a liquid-vapor mixture. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    To understand the invention, it is necessary to recall the diagram of petroleum fraction hydrotreatment according to the prior art as shown in  FIG. 1 . 
         [0032]    The hydrotreatment diagram, for example of a diesel fuel fraction, is completed by a unit for elimination of acid gases by an amine, a so-called amine unit. 
         [0033]    A feedstock ( 101 ) of diesel fuel to be hydrotreated is available. This feedstock ( 101 ) is obtained from the distillation of a crude oil and is diluted with hydrogen ( 102 ). 
         [0034]    The mixture of feedstock ( 101 ) and hydrogen ( 102 ) is heated in a furnace ( 1001 ). This furnace ( 1001 ) makes it possible to raise the temperature to a level such that after the supply of additional heat of the feedstock-effluent exchanger ( 1002 ), the feedstock is to be at the temperature that is required for the hydrotreatment that is carried out in the reactor ( 1003 ). 
         [0035]    In the reactor ( 1003 ) for hydrotreatment under high pressure (approximately 150 bar) and high temperature (approximately 500° C.), the sulfur is extracted from the feedstock in H2S gaseous form. 
         [0036]    The hot effluent ( 110 ) that is obtained from the hydrotreatment reactor ( 1003 ) is cooled upon contact of the feedstock by passing into a feedstock-effluent exchanger ( 1002 ). 
         [0037]    The cooled effluent ( 111 ) is completed by a supply of wash water ( 103 ) and is cooled again in the cooling tower ( 1004 ). The result is a low-temperature stream ( 109 ) that is separated in a separator flask ( 1005 ) into three streams:
       The primary product ( 105 ), namely the desulfurized diesel fuel,   An aqueous liquid effluent ( 104 ) that consists of acidic wash water, and   A gas effluent ( 106 ) that consists of H 2  and H 2 S. In this gas effluent ( 106 ), there remains a large part of hydrogen that can again be upgraded by recycling, but this requires separating H2 and H 2 S. This H2/H2S separation is done in an absorber ( 1013 ) by a low-amine solution, i.e., sparingly charged with H2S ( 201 ). The result is a purified hydrogen stream ( 107 ) that, after recompression in the compressor ( 1006 ), is completed by a supply of hydrogen ( 108 ) for reaching the amount of hydrogen that is necessary to the hydrotreatment reaction. The ratio by mass of H2/feedstock between the hydrogen and the feedstock to be treated at the reactor ( 1003 ) is preferably between 0.3 and 0.8% by weight.       
 
         [0041]    The stream ( 102 ) is sent to the contact of the feedstock ( 101 ). The liquid effluent ( 202 ) that is obtained from the absorber ( 1013 ) consists of the H2S-charged amine (rich amine). 
         [0042]    The regeneration of amine is carried out at a higher temperature than the absorption. This regeneration requires a feedstock-effluent exchanger ( 1008 ) that makes it possible to heat the rich amine and to cool the low amine. The heated rich amine ( 203 ) is introduced into the regenerator ( 1009 ) in which the heat that is provided at the reboiler ( 1010 ) makes it possible to produce a gas effluent ( 205 ) that consists for the most part of H2S and a liquid effluent ( 204 ) of regenerated amine, i.e., low in H2S (low amine). This hot effluent ( 204 ) is sent to the absorber ( 1013 ) after having been cooled by transferring its calories to the rich amine stream ( 202 ) in the feedstock-effluent exchanger ( 1008 ). 
         [0043]    The description of the diagram according to this invention is based on  FIG. 2  that introduces the circuit, called heat pump circuit below, which makes use of a coolant ( 206 ,  207 ,  208 ,  209 ). 
         [0044]    The heat pump circuit is located between the exchanger ( 1007 ) and the reboiler ( 1010 ) of the distillation column ( 1009 ). The exchanger ( 1007 ) replaces the cooling tower ( 1004 ) according to the diagram of the prior art. 
         [0045]    This coolant ( 209 ) is vapor at the outlet of the exchanger ( 1007 ) up to the inlet of the reboiler ( 1010 ), condenses at the reboiler ( 1010 ), and therefore becomes liquid ( 207 ) up to the inlet of the pressure-reducing valve ( 1012 ). At the outlet of the pressure-reducing valve ( 1012 ) up to the inlet of the exchanger ( 1007 ), the coolant ( 208 ) is in the liquid-vapor state. 
         [0046]    The other modification introduced by the heat pump circuit is the fact that the exchanger ( 1004 ) that is used to cool the effluent of the hydrotreatment reactor, which was a cooling tower according to the prior art, becomes an exchanger ( 1007 ) whose cooling fluid is the coolant of the heat pump circuit in the liquid-vapor state. At the outlet of the exchanger ( 1007 ), the coolant ( 209 ) is entirely vapor. 
         [0047]    The circuit of the heat pump can be described in the following manner: 
         [0048]    The heat is provided to the reboiler ( 1010 ) by the condensation of the coolant ( 206 ) that becomes liquid ( 207 ). The liquid ( 207 ) is expanded in the pressure-reducing valve ( 1012 ) and comes out in the liquid-vapor state ( 208 ). The coolant ( 208 ) evaporates entirely in the exchanger ( 1007 ) by extracting the calories from the reaction effluent ( 111 ) for producing a vapor ( 209 ) whose temperature and pressure will be increased by the compressor ( 1011 ). 
         [0049]    The high-pressure and high-temperature vapor ( 206 ) obtained from the compressor ( 1011 ) condenses in the reboiler ( 1010 ). 
         [0050]    The result is a pressurized liquid stream ( 207 ) whose temperature is lowered by expansion in the valve ( 1012 ). The resulting liquid-vapor mixture ( 208 ) therefore supplies the exchanger ( 1007 ), in which it vaporizes completely. 
         [0051]    Within the framework of this invention, the selection of the coolant can be formulated from the following criteria:
       For purposes of savings, the condensation pressure of the coolant is selected as low as possible, and preferably close to 1 bar (1 bar=10 5  Pascal).   More specifically, the coolant has, on the one hand, a boiling point that is less than or equal to 60° C., and preferably less than 50° C. for a pressure that is less than 5 bar and preferably less than 2 bar, and said coolant has, on the other hand, a condensation temperature that is higher than 120° C. and preferably higher than 130° C., for a pressure that is greater than 1 bar.       
 
         [0054]    The coolant that supplies the heat pump circuit can be selected in a general way in the group that is formed by the refrigeration fluids defined by IUPAC. 
         [0055]    The coolant is preferably selected from the following subgroup: propane, butane, pentane or any mixture of these compounds. 
         [0056]    It can also preferably be selected from the group that is formed by alcohols and diols, having a carbon atom number of between 3 and 10, or any mixture of these compounds. 
       Examples According to the Prior Art and According to the Invention 
     EXAMPLE 1 
       [0057]    This example is in accordance with the state of the art and therefore corresponds to  FIG. 1 . 
         [0058]    The exchanger ( 1004 ) is a cooling tower where an air stream cools the stream obtained from ( 1002 ). 
         [0059]    The heat is provided to the reboiler ( 1010 ) by means of a superheated low-pressure vapor stream ( 206 ′) and from which a condensate stream ( 207 ′) results. 
         [0060]    A stream of 265 t/h of sulfurized diesel fuel is treated. At the inlet of the cooling tower ( 1004 ), the temperature is 128° C., and at the outlet, the latter is 50° C. The dissipation of energy into the cooling tower ( 1004 ) corresponds to 15.85 Gcal/h, or a flow rate of 1,613 t/h of air passing from 25 to 56° C. Gcal/h is the giga abbreviation of 10 9  cal/h. 
         [0061]    The stream of feedstock corresponds to a stream of rich amine ( 202 ) of 56 t/h, or to a feedstock for the reboiler ( 1010 ) of 2.16 Gcal/h. This corresponds to the condensation of 12.4 t/h of low-pressure vapor. 
       EXAMPLE 2 
       [0062]    According to this invention, this example is based on  FIG. 2 . 
         [0063]    The process diagram according to the invention therefore makes identical use of the hydrotreatment part except that the cooling tower ( 1004 ) is replaced by an exchanger ( 1007 ) that uses—as a refrigeration fluid—the coolant ( 208 ) of the heat pump circuit in the liquid-vapor state. The heat pump circuit comprises the compressor ( 1011 ) and the pressure-reducing valve ( 1012 ). 
         [0064]    Relative to the reboiler ( 1010 ), its heating is no longer ensured by the low-pressure vapor condensation, but rather by the condensation of the coolant ( 206 ) that is part of the heat pump loop. 
         [0065]    The heat pump circuit has the following characteristics:
       Coolant: pentane   Pressure and temperature at the outlet of the pressure-reducing valve ( 1012 ): 1.5 bar and 48° C.   Pressure and temperature at the outlet of the compressor ( 1011 ): 12 bar and 184° C.   Power of the compressor: 790 kW (yield 76%)   Power exchanged with the evaporator ( 1007 ): 1,673 kW   Power exchanged with the condenser ( 1010 ): 2,464 kW   Performance coefficient of the heat pump: 3.12       
 
         [0073]    The pentane heat-pump circuit therefore makes it possible to replace the vapor heating of the condenser ( 1010 ) completely and also makes it possible to reduce the consumption of air of the cooling tower ( 1004 ) (replaced by the exchanger ( 1007 )) from 1,613 t/h to 1,198 t/h, or a reduction on the order of 26%. 
         [0074]    The comparison of the energy balance and CO 2  between the hydrotreatment diagram according to this invention ( FIG. 2 ) and the diagram of the prior art ( FIG. 1 ) can be established according to a method that consists in considering the CO 2  emissions linked to the consumption of vapor or electricity. 
         [0075]    The following table provides CO2 emission values that are commonly allowed for specific emissions in Europe (MJ is the abbreviation for megajoules, or 10 6  joules). 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 LP Vapor, 5 bar 
                  86 gCO 2 /MJ 
               
               
                   
                 Electricity 
                 127 gCO 2 /MJ 
               
               
                   
                   
               
             
          
         
       
     
         [0076]    In Example 1 according to the prior art, the emissions are then 18,560 t/year of CO 2  assuming a consumption of 12.4 t/h of vapor for the reboiler ( 1010 ) and 0.1 MW of electricity for the cooling tower ( 1004 ). 
         [0077]    In Example 2 according to the invention, the associated emissions are 2,890 t/year of CO 2 . 
         [0078]    This corresponds to the electrical power consumed over 800 h/year by:
       The compressor ( 1011 ) per 0.79 MW   The exchanger ( 1007 ) per 0.07 MW       
 
         [0081]    The installation of a heat pump circuit between the condenser ( 1010 ) and the cooling tower ( 1004 ) then leads to a reduction on the order of 84% of greenhouse gas emissions in this process. 
         [0082]    Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
         [0083]    In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated. 
         [0084]    The entire disclosures of all applications, patents and publications, cited herein and of corresponding FR application No. 10/04.875, filed Dec. 14, 2010, are incorporated by reference herein. 
         [0085]    The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. 
         [0086]    From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.