Abstract:
This invention relates to methods and apparatus for the energy efficient separation of ethane and propane from any hydrocarbon feed, i.e., from natural gas, natural gas liquids, liquid natural gas, or from gases from refinery or petroleum plants.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to methods and apparatus for separating hydrocarbons more economically. More particularly, the methods and apparatus of the present invention are concerned with a method and apparatus for the energy efficient separation of ethane and propane from any hydrocarbon feed, i.e., from natural gas, natural gas liquids, liquid natural gas, or from gases from refinery or petroleum plants. 
       BACKGROUND OF THE INVENTION 
       [0002]    Natural gas is a combustible mixture of hydrocarbons. While natural gas primarily contains methane, the lightest hydrocarbon, it also contains varying amounts of heavier hydrocarbons. These heavier hydrocarbons include ethane (C 2 H 6 ), propane (C 3 H 8 ), n-butane (n-C 4 H 10 ), isobutane (i-C 4 H 10 ), pentanes (C 5 H 12 ), and higher molecular weight hydrocarbons. When processed and purified, these heavier hydrocarbons are known as natural gas liquids (“NGL”) and the pentanes and higher molecular weight hydrocarbons are known as natural gasoline. 
         [0003]    In addition to methane and heavier hydrocarbons, natural gas includes other impurities such as carbon dioxide (CO 2 ), nitrogen (N 2 ), hydrogen sulfide (H 2 S), oxygen (O 2 ), and other rare gases such as argon, helium, nitrogen, and xenon. These impurities and heavier hydrocarbons must be separated from methane to produce pipeline quality methane. The heavier hydrocarbons are further separated into NGL components ethane, propane, butane, and natural gasoline. 
         [0004]    Processes for separating hydrocarbons are well known in the art. While there are a great number of configurations for the various process used to separate hydrocarbons, the typical configuration for the processing of natural gas hydrocarbons comprises: 1) acid gas removal, 2) dehydration, 3) mercury removal, 4) nitrogen removal, 5) NGL separation, 6) NGL fractionation. Processes to remove contaminates from the hydrocarbon components include well known methods including absorption, adsorption, and cryogenic condensation. NGL separation is typically accomplished by either absorption using a lean oil absorption process or by cryogenic expansion of the hydrocarbons followed by distillation in a demethanizing column. The process involving a lean oil absorption can separate a mixture of methane and ethane from heavier hydrocarbons, while the cryogenic expansion-distillation process can separate methane from heavier hydrocarbons. The NGL fractionation processes employ distillation columns to separate the various NGL components. A deethanizer column is used to separate ethane from propane and the less volatile components and a depropanizer column is used to separate propane from the butane and natural gasoline components. 
         [0005]    Separation of hydrocarbons using distillation systems requires the input of energy to generate the vapor needed by the process. However, many prior art systems have not been very energy efficient. The energy added to the process typically is removed later in the process as waste heat. To increase the efficiency of distillation systems, some prior art devices have used mechanical compression to elevate the temperature of the vapor so that the heat of vaporization can be recovered. However, as far as the inventors are aware, these improvements in distillation systems have not been applied to take advantage of recoverable energy in the light ends section of the NGL fractionation process. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to a systems and processes for the separation of ethane, propane, and heavier hydrocarbons from a hydrocarbon containing feed. In the methods and apparatus of the present invention, a hydrocarbon feed is processed in a distillation tower, e.g., a deethanizer column or a depropanizer column, to separate lighter hydrocarbons from heavier NGL. 
         [0007]    In the present invention, a hydrocarbon feed is introduced to a distillation column at one or more feed trays. Overhead products are recovered from the column and heavier NGL are collected from the bottom of the column. To improve the economics of the operation, the condensing temperature of the overhead products are increased by compression such that the temperature of the overhead product is greater then the boiling point of the bottom product. This provides the driving force necessary to transfer heat from the overhead product to the bottom product and reduce the amount of external heat necessary for the process. Further, the distillation column in the present invention is operated at lower temperature and pressures then conventional distillation columns used for the separation of hydrocarbons. These improvements reduce the overall energy consumption of the system by at least twenty-percent. 
         [0008]    One embodiment of the invention recovers heat from the overhead product of the deethanizer using a refrigerant. The refrigerant is compressed to increase the temperature of the refrigerant to supply the driving force necessary to transfer heat to the bottom of the deethanizer column. 
         [0009]    Another embodiment of the invention recovers heat from the overhead product of the depropanizer. The overhead product of the depropanizer is compressed to lower the operating pressure of the depropanizer and increase the temperature of the depropanizer product and supplies the driving force necessary to transfer heat the deethanizer column and/or the depropanizer column. 
         [0010]    Another embodiment of the invention recovers heat from both the overhead product of both the deethanizer column and the depropanizer column. A refrigerant is used to recover heat from the deethanizer. The refrigerant is compressed to increase the temperature of the refrigerant to supply the driving force necessary to transfer heat to the deethanizer column. The overhead product of the depropanizer is compressed to increase the temperature of the depropanizer product and supplies the driving force necessary to transfer heat the deethanizer column and/or the depropanizer column. 
         [0011]    In accordance with one aspect of the invention, there is provided process for the distillation of hydrocarbons for a hydrocarbon-containing feed, comprising the steps of: (1) introducing the hydrocarbon containing feed to a first distillation column; (2) withdrawing a first overhead product comprising ethane and substantially free from heavier hydrocarbons from the top of the first distillation column; (3) withdrawing a first bottoms product comprising propane and heavier hydrocarbons and substantially free from ethane from the bottom of the first distillation column; (4) feeding the first bottoms product from the bottom of the first distillation column into a second distillation column; (5) withdrawing a second overhead product comprising propane and substantially free from heavier hydrocarbons from the top of the second distillation column; (6) withdrawing a second bottoms product comprising heavier hydrocarbons from the bottom of the second distillation column; (7) using a refrigerant to recover heat from the first overhead product; (8) compressing the refrigerant to generate a first recompression heat; (8) and using at least some of the recompression heat produced as a heat source. 
         [0012]    Wherein the process described above further comprises the step of using at least some of the first recompression heat as a heat source for the first distillation column. The hydrocarbon containing feed further comprises a mixture of ethane and heavier hydrocarbons, a mixture of ethane, propane, and heavier hydrocarbons, or a mixture of ethane and propane. Wherein the heavier hydrocarbon mixture further comprises a mixture of n-butane, methylpropane, and natural gasoline 
         [0013]    Wherein the process described above further comprises compressing the refrigerant to a pressure of about 450 psia to about 550 psia. The first distillation column is operated at a pressure of about 245 psia to about 295 psia. The first distillation column is operated with a bottom temperature of about 100 degrees Fahrenheit to about 180 degrees Fahrenheit and a top temperature of about −30 degrees Fahrenheit to about 60 degrees Fahrenheit. The second distillation column is operated at a pressure of about 140 psia to about 245 psia, with a bottom temperature of about 180 degrees Fahrenheit to about 260 degrees Fahrenheit and a top temperature of about 70 degrees Fahrenheit to about 120 degrees Fahrenheit. 
         [0014]    Wherein the process described above further comprises the step of compressing the second overhead produce to generate a second recompression heat and using at least some of the second recompression heat thereby produced is used as a heat source for the second distillation column. Wherein at least some of the second recompression heat thereby produced is used as a heat source for the first distillation column or for the first distillation column. Wherein the second overhead product is compressed to a pressure of about 435 psia to about 525 psia. 
         [0015]    In accordance with another aspect of the invention, there is provided process for the distillation of hydrocarbons for a hydrocarbon-containing feed, comprising the steps of: (1) introducing the hydrocarbon containing feed to a first distillation column; (2) withdrawing an first overhead product comprising ethane and substantially free from heavier hydrocarbons from the top of the first distillation column; (3) withdrawing a first bottoms product comprising propane and heavier hydrocarbons and substantially free from ethane from the bottom of the first distillation column; (4) feeding the first bottoms product from the bottom of the first distillation column into a second distillation column; (5) withdrawing a second overhead product comprising propane and substantially free from heavier hydrocarbons from the top of the second distillation column; (6) withdrawing a second bottoms product comprising heavier hydrocarbons from the bottom of the second distillation column; (7) compressing the second overhead product to generate a first recompression heat; (8) and using at least some of the first recompression heat produced as a heat source. 
         [0016]    Wherein the process described above further comprises the step of using at least some of the first recompression heat as a heat source for the first distillation column or the second distillation column. The hydrocarbon containing feed further comprises a mixture of ethane and heavier hydrocarbons, a mixture of ethane, propane and heavier, or a mixture of ethane and propane. Wherein the heavier hydrocarbons further comprises a mixture of a mixture of n-butane, methylpropane, and natural gasoline, 
         [0017]    Wherein the process described above further comprises operating the first distillation column at a pressure of about 245 psia to about 495 psia, with a bottom temperature of about 100 degrees Fahrenheit to about 260 degrees Fahrenheit and a top temperature of about −30 degrees Fahrenheit to about 110 degrees Fahrenheit. Wherein the second distillation column is operated at a pressure of about 150 psia to about 295 psia. Wherein the second overhead product is compressed to a pressure of about 435 psia to about 525 psia. Wherein the second distillation column is operated with a bottom temperature of about 180 degrees Fahrenheit to about 260 degrees Fahrenheit and a top temperature of about 70 degrees Fahrenheit to about 120 degrees Fahrenheit. 
         [0018]    Wherein the process described above further comprises the step of using a refrigerant to recover heat from the first overhead product, the refrigerant is compressed to generate a second recompression heat and at least some of the second recompression heat thereby produced is used as a heat source for the first distillation column. Wherein the refrigerant is compressed to a pressure of about 450 psia to about 550 psia. 
         [0019]    In accordance with another aspect of the invention, there is provided an apparatus for the distillation of a hydrocarbon-containing feed, comprising: (1) a first distillation column having a least one stage; (2) a second distillation column having at least one stage; (3) a means for introducing a hydrocarbon containing feed into the first distillation column at one or more stages; (4) a means for withdrawing a first overhead product from the first distillation column; (5) a means for providing heat to the second distillation column; (6) a means for removing heat from the first overhead product using a refrigerant; (7) a means for compressing the refrigerant to generate a first recompression heat; (8) a means for using some of the first recompression heat as a heat source; (9) a means for withdrawing a first bottoms product from the first distillation column and introducing the first bottoms product into the second distillation column; (11) a means for withdrawing a second bottoms product from the second distillation column; (12) a means for withdrawing a second overhead product from the second distillation column; (13) and a means for providing heat to the second distillation column. 
         [0020]    Wherein the apparatus described above further comprises a means for compressing the second overhead product and using some of the recompression heat of the second overhead product to heat the second distillation column or the first distillation column. Wherein at least one stage of the first distillation column comprises one or more sieve trays, valve trays, conventional or high efficiency trays, any conventional or high capacity trays, bubble cap trays, and structured or random packing. Wherein at least one stage of the second distillation column comprises one or more sieve trays, valve trays, conventional or high efficiency trays, any conventional or high capacity trays, bubble cap trays, and structured or random packing. 
         [0021]    Wherein the means for compressing a second overhead product comprises one or more centrifugal compressors or reciprocating compressors. 
         [0022]    Wherein the means for using some of the recompression heat of the second overhead product to heat the first distillation column comprises a shell and tube heat exchanger or a plate type heat exchanger. 
         [0023]    Wherein the means for using some of the recompression heat of the second overhead product to heat the first distillation column comprises a shell and tube heat exchanger, or a plate type heat exchanger. 
         [0024]    In accordance with another aspect of the invention, there is provided an apparatus for the distillation of a hydrocarbon-containing feed, comprising: (1) a first distillation column having a least one stage; (2) a second distillation column having at least one stage; (3) a means for introducing a hydrocarbon containing feed into the first distillation column at one or more stages; (4) a means for withdrawing a first overhead product from the first distillation column; (5) a means for removing heat from the first overhead product; (6) a means for withdrawing a first bottoms product from the first distillation column and introducing the first bottoms product into the second distillation column; (7) a means for providing heat to the second distillation column; (8) a means for withdrawing a second bottoms product from the second distillation column; (9) a means for withdrawing a second overhead product from the second distillation column; (10) a means for compressing the second overhead product to generate a first recompression heat; (11) a means for using some of the first recompression heat as a heat source; (12) and a means for providing heat to the second distillation column. 
         [0025]    Wherein the apparatus described above further comprises a means for using some of the first recompression heat to heat the second distillation column or the first distillation column. Wherein at least one stage of the first distillation column comprises one or more sieve trays. 
         [0026]    Wherein the means for compressing a second overhead product comprises one or more centrifugal compressors or reciprocating compressors 
         [0027]    Wherein the means for using some of the recompression heat of the second overhead product to heat the first distillation column comprises a shell and tube heat exchanger or a plate type heat exchanger. 
         [0028]    Wherein the means for using some of the recompression heat of the second overhead product to heat the second distillation column comprises a shell and tube heat exchanger or a plate type heat exchanger. 
         [0029]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
           [0031]      FIG. 1  is a process flow diagram of the improvement of the current invention to recover heat from the deethanizer, upgrading the heat by compressing, and using that heat to reduce fuel requirements. 
           [0032]      FIG. 2  is a is a process flow diagram of the improvement of the current invention to recover heat from the depropanizer, upgrading the heat by compressing, and using the heat to reduce fuel requirements. 
           [0033]      FIG. 3  is a process flow diagram of the improvement of the current invention to recover heat from the deethanizer and the depropanizer, upgrading the heat by compressing, and using the heat to reduce fuel requirements. 
           [0034]      FIG. 4  is a process flow diagram of the improvement of the current invention to recover heat from the depropanizer operating at higher temperatures, upgrading the heat by compressing, and using the heat to reduce fuel requirements. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    As used herein, “a” or “an” means one or more than one. 
         [0036]    The methods and apparatus of the present invention will now be illustrated with reference to  FIGS. 1 through 3 . It should be understood, that these are merely illustrative and not exhaustive examples of the scope of the present invention and that variations which are understood by those having ordinary skill in the art are within the scope of the present invention. 
         [0037]    Looking first at the system illustrated in  FIG. 1 , a hydrocarbon feed typically comprising ethane, propane, and heavier hydrocarbons is introduced to deethanizer  161  through feed line  101  at tray  161   d . Deethanizer  161  is preferably operated at a pressure of about 270 psia, although other operating pressures may be used, has chimney trays  161   a ,  161   b  and  161   c , and feed trays  161   d ,  161   e , and  161   f.    
         [0038]    Lighter hydrocarbons, primarily ethane, are withdrawn from the top of deethanizer  161  via first overhead product line  112  typically at temperature of approximately 14 degrees Fahrenheit. Heat is recovered from the first overhead product by deethanizer condenser  171 . Any condenser that can provide the necessary heat transfer duty requirement can be utilized as deethanizer condenser  171 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. After condensing, the first overhead product is split into two streams based on a typical reflux to distillate ratio (external reflux ratio) of about 0.8 to 0.9. The first portion is directed to line  102  as ethane product. The second portion is directed to line  115  and reintroduced into deethanizer column  161  at tray  161   f  as reflux to provide liquid traffic down the deethanizer column. 
         [0039]    Heavier hydrocarbons are withdrawn from chimney tray  161   a  via line  114  and directed to deethanizer reboiler  172 . Any reboiler that can provide the necessary heat transfer duty requirement can be utilized as deethanizer reboiler  172 . Types of reboilers include kettle type reboilers, thermosyphon reboilers, fired heater reboilers, forced circulation reboilers, and stab-in reboilers. Heavier hydrocarbons, primarily propane and heavier hydrocarbons, are withdrawn from the bottom of deethanizer  161  via first bottoms product line  113  typically at a temperature of about 140 degrees Fahrenheit. Line  113  is connected to balance line  117  of deethanizer reboiler  172 . Balance line  1 . 17  is used to maintain the same liquid level in deethanizer  161  and deethanizer reboiler  172 . After absorbing heat in deethanizer reboiler  172 , vapor from deethanizer reboiler  172  is directed to deethanizer  161  at chimney tray  161   a  via line  116 . A first bottoms product is extracted via balance line  117  and is directed to depropanizer  162  through line  121 . 
         [0040]    Refrigerant is used to condense the first overhead product in deethanizer condenser  171 . Any refrigerant having good thermodynamic properties such as a boiling point below the target temperature, a high heat of vaporization, a moderate density in liquid form, and relatively high gas density is preferred. In this embodiment, a propane refrigerant is used. The refrigerant is compressed in compressor  191  to a pressure of 500 psia. Any compressor capable of compressing the refrigerant to the necessary pressures can be utilized as compressor  191 . This includes axial compressors, centrifugal compressors, diaphragm compressors, multistage compressors, reciprocating compressors, and rotary compressors. The refrigerant is directed to deethanizer side reboiler  173 . Any heat exchanger that can provide the necessary heat transfer duty requirement can be utilized as deethanizer side reboiler  173 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. A side stream is drawn from chimney tray  161   c  and directed to deethanizer side reboiler  173  via line  118 . The side stream is partially vaporized using the heat recovered from the deethanizer overhead product and the mixed phase stream is reintroduced to deethanizer  161  at chimney tray  161   b . The refrigerant is then directed to heat exchanger  174  where it is cooled. Any heat exchanger that can provide the necessary heat transfer duty requirement can be utilized as heat exchanger  174 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. Finally, the refrigerant is directed to ethane condenser  171  and recovers the latent heat of condensation from the first overheat product. 
         [0041]    The first overhead product is introduced into depropanizer  162  at feed tray  162   d . Depropanizer  162  is typically operated at a pressure of about 190 psia, and has chimney trays  162   a ,  162   b , and  162   c  and feed trays  162   d ,  162   e , and  162   f . Lighter hydrocarbons, primarily propane, are withdrawn from the top of depropanizer  162  via second overhead product line  122  at temperature of approximately 99 degrees Fahrenheit. The second overhead product is condensed with second overhead condenser  181  and split into two streams based on a reflux to distillate ratio (external reflux ratio) of about 1.55 to 1.75. Any condenser that can provide the necessary heat transfer duty requirement can be utilized as second overhead condenser  181 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. The first portion is directed to line  103  as propane product. The second portion is directed to line  125  and reintroduced into depropanizer  162  at tray  162   f  as reflux to provide liquid traffic down the depropanizer column. 
         [0042]    A side stream is withdrawn from chimney tray  162   a  via line  124  and directed to depropanizer reboiler  182 . Any reboiler that can provide the necessary heat transfer duty requirement can be utilized as depropanizer reboiler  182 . Types of reboilers include kettle type reboilers, thermosyphon reboilers, fired heater reboilers, forced circulation reboilers, and stab-in reboilers. Heavier hydrocarbons, such as gasoline, are withdrawn from the bottom of depropanizer  162  via second bottoms product line  123  typically at a temperature of about 220 degrees Fahrenheit. Line  123  is connected to balance line  127  of depropanizer reboiler  182 . Balance line  127  is used to maintain the same liquid level in depropanizer  162  and depropanizer reboiler  182 . After absorbing heat in depropanizer reboiler  182 , vapor from depropanizer reboiler  182  is directed to depropanizer  162  at chimney tray  162   a  via line  116 . A second bottoms product is extracted via balance line  127  and is directed to line  104  as natural gasoline product. 
         [0043]    The system described in  FIG. 1  is intended to reduce the external fuel requirements of the system, in some cases, by approximately forty-percent or more. Taking into account the mechanical energy required to compress the refrigerant the overall reduction in energy consumption is typically approximately twenty-one percent. 
         [0044]    Turning now to  FIG. 2 , a similar reduction in energy required for the NGL separation process is achieved by compressing the overhead vapor of the depropanizer and transferring heat from the depropanizer overhead vapor to the depropanizer and/or the deethanizer. 
         [0045]    Looking first at the ethane separation step, a hydrocarbon feed typically comprising ethane, propane, and heavier hydrocarbons is introduced to deethanizer  261  through feed line  201  at tray  261   d . Deethanizer  261  is typically operated at a pressure of about 270 psia, and has chimney trays  261   a ,  261   b , and  261   c  and feed trays  261   d ,  261   e , and  261   f.    
         [0046]    Lighter hydrocarbons, primarily ethane, are withdrawn from the top of deethanizer  261  via first overhead product line  212  typically at a temperature of approximately 14 degrees Fahrenheit. Heat is recovered from the first overhead product by deethanizer condenser  271 . Any condenser that can provide the necessary heat transfer duty requirement can be utilized as deethanizer condenser  271 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. After condensing, the first overhead product is split into two streams based on a typical reflux to distillate ratio (external reflux ratio) of about 0.8 to 0.9. The first portion is directed to line  202  as ethane product. The second portion is directed to line  215  and reintroduced into deethanizer  261  at tray  261   f  as reflux to provide liquid traffic down the deethanizer column. 
         [0047]    A side stream withdrawn from chimney tray  261   a  via line  214  and directed to deethanizer reboiler  272 . Any reboiler that can provide the necessary heat transfer duty requirement can be utilized as deethanizer reboiler  272 . Types of reboilers include kettle type reboilers, thermosyphon reboilers, fired heater reboilers, forced circulation reboilers, and stab-in reboilers. Heavier hydrocarbons, primarily propane and heavier hydrocarbons, are withdrawn from the bottom of deethanizer  261  via first bottoms product line  213  typically at a temperature of about 140 degrees Fahrenheit. Line  213  is connected to balance line  217  of deethanizer reboiler  272 . Balance line  217  is used to maintain the same liquid level in deethanizer  261  and deethanizer reboiler  272 . After absorbing heat in deethanizer reboiler  272 , vapor from deethanizer reboiler  272  is directed to deethanizer  261  at chimney tray  261   a  via line  216 . A first bottoms product is extracted via balance line  217  and is directed to depropanizer  262 . 
         [0048]    The first bottoms product is introduced to depropanizer  262  through feed line  221  at tray  261   c . Depropanizer  262  is typically operated at a pressure of about 190 psia, and has chimney trays  262   a ,  262   b , and  262   c  and feed trays  262   d ,  262   e , and  262   f.    
         [0049]    Lighter hydrocarbons, primarily propane, are withdrawn from the top of depropanizer  262  via second overhead product line  222  at temperature of approximately 99 degrees Fahrenheit. Heat is recovered from the first overhead product by compressing the second overhead product with second overhead compressor  291  to approximately 500 psia. Any compressor capable of compressing the refrigerant to the necessary pressures can be utilized second overhead compressor  291 . This includes axial compressors, centrifugal compressors, diaphragm compressors, multistage compressors, reciprocating compressors, and rotary compressors. After recovering the heat, which will be described later, the second overhead product is condensed with second overhead condenser  281  and split into two streams based on a reflux to distillate ratio (external reflux ratio) of about 1.55 to 1.75. The first portion is directed to line  203  as propane product. The second portion is directed to line  225  and reintroduced into depropanizer  262  at tray  262   e  as reflux to provide liquid traffic down the depropanizer column. 
         [0050]    After compressing, the second overhead product is split with a portion directed to depropanizer side reboiler  283  via line  231  and a portion directed to deethanizer reboiler  272  via line  232 . A liquid side stream is taken from depropanizer  262  at chimney tray  262   c  via line  228  and directed to depropanizer side reboiler  283 . A portion of the heat recovered from the second overhead product is transferred to the side stream from depropanizer  262  in depropanizer side reboiler  283 . Any heat exchanger that can provide the necessary heat transfer duty requirement can be utilized for side reboiler  283 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. A portion of the side stream is vaporized and the mixed stream is returned to depropanizer  262  at chimney tray  262   b  thus transferring heat from the second overhead product to depropanizer  262 . 
         [0051]    Similarly, a portion of the heat recovered from the second overhead product is transferred to deethanizer reboiler  272 . The heat transferred to deethanizer reboiler  272  vaporizes a portion of the first bottoms product. The vapor is returned to deethanizer  261 , thus transferring heat from depropanizer  262  to deethanizer  261 . 
         [0052]    After transferring a portion of the heat recovered from the second overhead product, lines  231  and  232  are combined into line  233  which is directed to deethanizer side reboiler  273 . Any heat exchanger that can provide the necessary heat transfer duty requirement can be utilized as deethanizer side reboiler  273 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. A liquid side stream is taken from deethanizer  261  at chimney tray  261   c  via line  218  and a portion of the liquid side stream is vaporized by transferring a portion of the heat recovered from the second overhead product to the liquid side stream and the mixed vapor/liquid stream is returned to deethanizer  261  at chimney tray  261   b , thus transferring heat from the second overhead product to deethanizer  261 . Finally, the second overhead product stream is condensed in depropanizer reflux condenser  281 . 
         [0053]    A side stream withdrawn from chimney tray  262   a  via line  224  and directed to deethanizer reboiler  282 . Any reboiler that can provide the necessary heat transfer duty requirement can be utilized as deethanizer reboiler  282 . Types of reboilers include kettle type reboilers, thermosyphon reboilers, fired heater reboilers, forced circulation reboilers, and stab-in reboilers. Heavier hydrocarbons, primarily propane and heavier hydrocarbons, are withdrawn from the bottom of depropanizer  262  via second bottoms product line  223  typically at a temperature of about 220 degrees Fahrenheit. Line  223  is connected to balance line  227  of depropanizer reboiler  282 . Balance line  227  is used to maintain the same liquid level in depropanizer  262  and depropanizer reboiler  282 . After absorbing heat in depropanizer reboiler  282 , vapor from depropanizer reboiler  282  is directed to depropanizer  262  at chimney tray  262   a  via line  226 . A second bottoms product is extracted via balance line  227  and is directed to product line  204 . 
         [0054]    This system described by  FIG. 2  is intended to reduce the external fuel requirements of the system, in some cases, by approximately forty percent or more. Taking into account the mechanical energy required to compress the refrigerant the overall reduction in energy is typically approximately twenty percent. 
         [0055]    Turning now to  FIG. 3 , a similar reduction in energy required for the NGL separation process is achieved by compressing the overhead vapor of the depropanizer and transferring heat of the overhead vapor to the depropanizer and the deethanizer and by compressing the overhead vapor of the deethanizer and transferring the heat of the overhead vapor to the bottom of the deethanizer. 
         [0056]    A hydrocarbon feed typically comprising ethane, propane, and heavier hydrocarbons is introduced to deethanizer  361  through feed line  301  at tray  361   d . Deethanizer  361  is typically operated at a pressure of about 270 psia and has chimney trays  361   a ,  361   b , and  361   c  and feed trays  361   d ,  361   e , and  361   f.    
         [0057]    Lighter hydrocarbons, primarily ethane, are withdrawn from the top of deethanizer  361  via first overhead product line  312  typically at temperature of approximately 14 degrees Fahrenheit. Heat is recovered from the first overhead product by deethanizer condenser  371 . Any condenser that can provide the necessary heat transfer duty requirement can be utilized as deethanizer condenser  371 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. After condensing, the first overhead product is split into two streams based on a typical reflux to distillate ratio (external reflux ratio) of about 0.8 to 0.9. The first portion is directed to line  302  as ethane product. The second portion is directed to line  315  and reintroduced into deethanizer column  361  at tray  361   f  as reflux to provide liquid traffic down the deethanizer column. 
         [0058]    A side stream is withdrawn from chimney tray  361   a  via line  314  and directed to deethanizer reboiler  372 . Any reboiler that can provide the necessary heat transfer duty requirement can be utilized as deethanizer reboiler  372 . Types of reboilers include kettle type reboilers, thermosyphon reboilers, fired heater reboilers, forced circulation reboilers, and stab-in reboilers. Heavier hydrocarbons, primarily propane and heavier hydrocarbons, are withdrawn from the bottom of deethanizer  361  via first bottoms product line  313  typically at a temperature of about 140 degrees Fahrenheit. Line  313  is connected to balance line  317  of deethanizer reboiler  372 . Balance line  317  is used to maintain the same liquid level in deethanizer  361  and deethanizer reboiler  372 . After absorbing heat in deethanizer reboiler  372 , vapor from deethanizer reboiler  372  is directed to deethanizer  361  at chimney tray  361   a  via line  316 . A first bottoms product is extracted via balance line  317  and is directed to depropanizer  362  through line  321 . 
         [0059]    Refrigerant is used to condense the first overhead product in ethane condenser  371 . Any refrigerant having good thermodynamic properties such as a boiling point below the target temperature, a high heat of vaporization, a moderate density in liquid form, and relatively high gas density is preferred. In this embodiment, a propylene refrigerant is used. The refrigerant is compressed in second overhead product compressor  391  to a pressure of 500 psia. Any compressor capable of compressing the refrigerant to the necessary pressures can be utilized as second overhead product compressor  391 . This includes axial compressors, centrifugal compressors, diaphragm compressors, multistage compressors, reciprocating compressors, and rotary compressors. The refrigerant is directed to deethanizer side reboiler  373 . Any heat exchanger that can provide the necessary heat transfer duty requirement can be utilized as deethanizer side reboiler  373 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. A side stream is drawn from chimney tray  361   c  vial line  318  and directed to deethanizer side reboiler  373  and is partially vaporized using the heat recovered from the deethanizer overhead product. The mixed phase stream is reintroduced to deethanizer  361  at chimney tray  361   b . The refrigerant is then directed to heat exchanger  374  where it is cooled. Any heat exchanger that can provide the necessary heat transfer duty requirement can be utilized as heat exchanger  374 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate- and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. Finally, the refrigerant is directed to ethane condenser  371  and recovers the latent heat of condensation from the first overheat product. Any condenser that can provide the necessary heat transfer duty requirement can be utilized as ethane condenser  371 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. 
         [0060]    The first bottoms product is introduced to depropanizer  362  through feed line  321  at tray  361   d . Depropanizer  362  is typically operated at a pressure of about 190 psia, has chimney trays  362   a ,  362   b , and  362   c  and feed trays  362   d ,  362   e , and  362   f.    
         [0061]    Lighter hydrocarbons, primarily propane, are withdrawn from the top of depropanizer  362  via second overhead product line  322  at temperature of approximately 99 degrees Fahrenheit. Heat is recovered from the first overhead product by compressing the second overhead product with second overhead compressor  391  to approximately 500 psia. After recovering the heat, which will be described later, the second overhead product is condensed with depropanizer reflux condenser  384  and split into two streams based on a typical reflux to distillate ratio (external reflux ratio) of about 1.55 to 1.75. The first portion is directed to line  302  as propane product. The second portion is directed to line  325  and reintroduced into depropanizer  362  at tray  362   f  as reflux to provide liquid traffic down the depropanizer column. 
         [0062]    After compressing, the second overhead product is split with a portion directed to depropanizer side reboiler  383  via line  331  and a portion directed to deethanizer reboiler  372  via line  332 . A liquid side stream is taken from depropanizer  362  at chimney tray  362   c  via line  328  and directed to depropanizer side reboiler  383 . A portion of the heat recovered from the second overhead product is transferred to side stream in depropanizer side reboiler  383 . Any heat exchanger that can provide the necessary heat transfer duty requirement can be utilized as depropanizer side reboiler  383 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. A portion of the side stream is vaporized and the mixed stream is returned to depropanizer  362  at chimney tray  362   b , thus transferring heat from the second overhead product to the bottom of depropanizer  362 . 
         [0063]    Similarly, a portion of the heat recovered from the second overhead product is transferred to deethanizer reboiler  372 . The heat transferred to deethanizer reboiler  372  vaporizes a portion of the first bottoms product. The vapor is returned to deethanizer  361  via line  316  and reintroduced into deethanizer  361  at chimney tray  361   a , thus transferring heat from depropanizer  362  to deethanizer  361 . 
         [0064]    After transferring a portion of the heat recovered from the second overhead product, lines  331  and  332  are combined into line  333  which is directed to depropanizer reflux condenser  384  where it is condensed. Any condenser that can provide the necessary heat transfer duty requirement can be utilized depropanizer reflux condenser  384 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. 
         [0065]    A side stream withdrawn from chimney tray  362   a  via line  324  and directed to deethanizer reboiler  382 . Any reboiler that can provide the necessary heat transfer duty requirement can be utilized as deethanizer reboiler  382 . Types of reboilers include kettle type reboilers, thermosyphon reboilers, fired heater reboilers, forced circulation reboilers, and stab-in reboilers. Heavier hydrocarbons, primarily propane and heavier hydrocarbons, are withdrawn from the bottom of depropanizer  362  via second bottoms product line  323  typically at a temperature of about 220 degrees Fahrenheit. Line  323  is connected to balance line  327  of depropanizer reboiler  382 . Balance line  327  is used to maintain the same liquid level in depropanizer  362  and depropanizer reboiler  382 . After absorbing heat in depropanizer reboiler  382 , vapor from depropanizer reboiler  382  is directed to depropanizer  362  at chimney tray  362   a  via line  326 . A second bottoms product is extracted via balance line  327  and is directed to product line  304 . 
         [0066]    Turning now to  FIG. 4 , a retrofitting an existing unit can result in similar reduction in energy required for the NGL separation process. This is achieved by compressing the overhead vapor of the depropanizer and transferring heat from the depropanizer overhead vapor to the deethanizer. 
         [0067]    Looking first at the ethane separation step, a hydrocarbon feed typically comprising ethane, propane, and heavier hydrocarbons is introduced to deethanizer  461  through feed line  401  at tray  461   d . Deethanizer  461  is typically operated at a pressure of about 265 psia to about 495 psia, and has chimney trays  261   a ,  261   b , and  261   c  and feed trays  261   d ,  261   e , and  261   f.    
         [0068]    Lighter hydrocarbons, primarily ethane, are withdrawn from the top of deethanizer  461  via first overhead product line  412  typically at a temperature of approximately −10 degrees Fahrenheit to about 110 degrees Fahrenheit. Heat is recovered from the first overhead product by deethanizer condenser  471 . Any condenser that can provide the necessary heat transfer duty requirement can be utilized as deethanizer condenser  471 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. After condensing, the first overhead product is split into two streams based on a typical reflux to distillate ratio (external reflux ratio) of about 0.8 to 0.9. The first portion is directed to line  402  as ethane product. The second portion is directed to line  415  and reintroduced into deethanizer  461  at tray  461   f  as reflux to provide liquid traffic down the deethanizer column. 
         [0069]    A side stream withdrawn from chimney tray  461   a  via line  414  and directed to deethanizer reboiler  472 . Any reboiler that can provide the necessary heat transfer duty requirement can be utilized as deethanizer reboiler  472 . Types of reboilers include kettle type reboilers, thermosyphon reboilers, fired heater reboilers, forced circulation reboilers, and stab-in reboilers. Heavier hydrocarbons, primarily propane and heavier hydrocarbons, are withdrawn from the bottom of deethanizer  461  via first bottoms product line  413  typically at a temperature of about 120 degrees Fahrenheit to about 260 degrees Fahrenheit. Line  313  is connected to balance line  417  of deethanizer reboiler  472 . Balance line  417  is used to maintain the same liquid level in deethanizer  461  and deethanizer reboiler  472 . After absorbing heat in deethanizer reboiler  472 , vapor from deethanizer reboiler  472  is directed to deethanizer  461  at chimney tray  461   a  via line  416 . A first bottoms product is extracted via balance line  417  and is directed to depropanizer  462 . 
         [0070]    The first bottoms product is introduced to depropanizer  462  through feed line  421  at tray  461   e . Depropanizer  262  is typically operated at a pressure of about 190 psia, and has chimney trays  462   a ,  462   b , and  462   c  and feed trays  462   d ,  462   e , and  462   f.    
         [0071]    Lighter hydrocarbons, primarily propane, are withdrawn from the top of depropanizer  462  via second overhead product line  422  at temperature of approximately 99 degrees Fahrenheit. Heat is recovered from the first overhead product by compressing the second overhead product with second overhead compressor  491  to approximately 500 psia. Any compressor capable of compressing the refrigerant to the necessary pressures can be utilized second overhead compressor  491 . This includes axial compressors, centrifugal compressors, diaphragm compressors, multistage compressors, reciprocating compressors, and rotary compressors. After recovering the heat, which will be described later, the second overhead product is condensed with second overhead condenser  481  and split into two streams based on a reflux to distillate ratio (external reflux ratio) of about 1.55 to 1.75. The first portion is directed to line  403  as propane product. The second portion is directed to line  225  and reintroduced into depropanizer  462  at tray  462   e  as reflux to provide liquid traffic down the depropanizer column. 
         [0072]    After compressing, the second overhead product directed to deethanizer side reboiler  473  via line  423 . A liquid side stream is taken from deethanizer  461  at chimney tray  461   c  via line  418  and directed to deethanizer side reboiler  473 . A portion of the heat recovered from the second overhead product is transferred to the side stream from deethanizer  461  in deethanizer side reboiler  473 . Any heat exchanger that can provide the necessary heat transfer duty requirement can be utilized for side reboiler  473 . This includes shell and tube heat exchangers, double pipe and multitube section heat exchangers, plate type exchangers, plate-and-frame heat exchangers, brazed-plate-and frame heat exchangers, bayonet-tube heat exchangers, spiral-tube heat exchangers, falling-film heat exchangers, cryogenic-service spiral-tube heat exchangers, and air-cooled heat exchangers. Finally, the second overhead product stream is condensed in depropanizer reflux condenser  481 . 
         [0073]    A side stream withdrawn from chimney tray  462   a  via line  424  and directed to deethanizer reboiler  482 . Any reboiler that can provide the necessary heat transfer duty requirement can be utilized as deethanizer reboiler  482 . Types of reboilers include kettle type reboilers, thermosyphon reboilers, fired heater reboilers, forced circulation reboilers, and stab-in reboilers. Heavier hydrocarbons, primarily propane and heavier hydrocarbons, are withdrawn from the bottom of depropanizer  462  via second bottoms product line  423  typically at a temperature of about 220 degrees Fahrenheit. Line  423  is connected to balance line  427  of depropanizer reboiler  482 . Balance line  427  is used to maintain the same liquid level in depropanizer  462  and depropanizer reboiler  482 . After absorbing heat in depropanizer reboiler  482 , vapor from depropanizer reboiler  482  is directed to depropanizer  462  at chimney tray  462   a  via line  426 . A second bottoms product is extracted via balance line  427  and is directed to product line  404 . 
         [0074]    This system described by  FIG. 4  is intended to reduce the external fuel requirements of the system, in some cases, by approximately forty percent or more. Taking into account the mechanical energy required to compress the refrigerant the overall reduction in energy is typically approximately fifteen percent. 
         [0075]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.