Abstract:
Processes to separate a light hydrocarbon stream comprising ethylene, ethane, and C3+ hydrocarbons into an ethylene stream, an ethane stream, and a C3+ hydrocarbon stream, including: feeding the light hydrocarbon stream to a deethanizer; separating the light hydrocarbons in the deethanizer to form a C3+ hydrocarbon bottoms stream and a C2-rich overhead stream comprising ethylene and ethane; separating the C2-rich stream in a C2-rectifier to form a first ethylene stream and an ethane-rich bottoms stream; and separating the ethane-rich bottoms stream in a C2-splitter to form a second ethylene stream and an ethane stream.

Description:
FIELD 
       [0001]    The embodiments relate generally to the water quenching of pyrolysis furnace effluent, and more particularly to partially water quenching the effluent upstream from the water quench tower inlet. 
       BACKGROUND 
       [0002]    Low molecular weight hydrocarbons and olefins can be produced in a pyrolysis furnace which provides heat sufficient to break chemical bonds in higher molecular weight hydrocarbons. The hydrocarbon feedstock to be cracked in a pyrolysis furnace usually consists of hydrocarbon gases such as ethane, propane, butane, or hydrocarbon liquids such as naphtha, kerosene, gas oil, or other available hydrocarbon feedstock. Hydrocarbon products produced when cracking gas feeds can include olefins such as ethylene and propylene, coke, and gasoline range hydrocarbons (C5+). Hydrocarbon products produced when cracking liquid feeds and heavier feedstocks can also include light and mid-range hydrocarbons, as well as coke and other heavy oils. To help control the cracking process, steam is typically used to dilute the feedstock hydrocarbon in the pyrolysis furnace; the amount of steam used can be characterized by the ratio of steam to total hydrocarbon fed to the pyrolysis furnace, hereinafter referred to as the steam to hydrocarbon weight ratio. After the cracking reaction, the resulting pyrolysis furnace effluent is typically cooled through indirect heat exchange to produce high pressure steam, and can also undergo a second indirect heat exchange to produce medium or low pressure steam, or other methods of heat recovery. 
         [0003]    Typical downstream processing for cracked ethane/propane feed includes a water quench tower to cool the cracked gases and to condense and separate the dilution steam and gasoline from the lighter hydrocarbons. Typical downstream processing for cracked naphtha or other liquid hydrocarbon feedstock can also include a fractionator to separate the heavy and mid-range hydrocarbons from the steam, gasoline, and light-end hydrocarbons, upstream from the water quench tower. The water quench towers are also used as a source of low level heat to supply hot water for process heating. 
         [0004]    One example of the downstream processing of effluent from a hydrocarbon cracker includes a steam diluted cracker effluent immediately cooled to a temperature below 650° C. (1200° F.), sufficient to stop the cracking reaction, through direct heat exchange with water, steam, or oil introduced through a primary ejector. One or more indirect heat exchangers are then used to recover heat and to produce high, medium, or low pressure steam prior to feeding the effluent to a fractionation tower or a quench tower. A secondary ejector is also disclosed, which can be used to cool the process stream to the desired fractionation tower or quench tower inlet temperature downstream of the indirect heat exchangers. 
         [0005]    Another second example of the downstream processing of effluent from a hydrocarbon cracker includes a steam diluted cracker effluent cooled by direct and indirect heat exchange upstream of a fractionation tower. The overhead vapor product from the fractionation tower is then fed directly to a water quench tower to separate gasoline range hydrocarbons from ethylene and propylene. 
         [0006]    Due to the conventional design of the water quench process, existing water quench towers are capacity-limited. A need exists to increase the capacity of new or existing water quench towers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The detailed description will be better understood in conjunction with the accompanying drawings as follows: 
           [0008]      FIG. 1  depicts a simplified schematic illustration of a process for water quenching a pyrolysis furnace effluent according to one embodiment. 
           [0009]      FIG. 2  depicts a simplified schematic illustration of a process for fractionating and water quenching a pyrolysis furnace effluent according to one embodiment. 
       
    
    
       [0010]    The embodiments are detailed below with reference to the listed Figures. 
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0011]    Before explaining the embodiments in detail, it is to be understood that the embodiments are not limited to the particular embodiments and that they can be practiced or carried out in various ways. 
         [0012]    The embodiments relate to designs of the water quench operation, providing the benefits of increased capacity for existing water quench towers or decreased design diameter for new water quench towers, with a corresponding benefit of decreasing the required capital investment, and improves the versatility of the water quench process such that a wider variety of feedstock hydrocarbons can be fed to the pyrolysis furnace. A one or more catalytic converters can be used instead of one or more pyrolysis furnaces. 
         [0013]    The embodiments relate to processes for water quenching a pyrolysis furnace effluent. The pyrolysis furnace effluent can be a stream of mixed hydrocarbon vapors and steam. The pyrolysis furnace effluent can be partially quenched in one or more stages using at least a first quench water stream to form a mixed vapor-liquid stream. The mixed phase stream can then be fed to a water quench tower to separate the vapor and liquid. The vapor can be further quenched with a second quench water stream supplied by one or more lines at various locations in the quench tower to form an overhead water-lean vapor product stream enriched in light hydrocarbons. Quenching can result in condensing a portion of the hydrocarbons and at least a portion of the steam, and the condensate can be collected in an oil-water separator. The liquid hydrocarbon and water can be recovered from the oil-water separator, and a portion of the recovered water (with or without some oil) can be cooled and recycled to the first and second quench water streams. 
         [0014]    The recovered water recycled to the first and second quench water streams can be cooled by one or more heat exchangers, in series or in parallel flow configurations. 
         [0015]    The partially quenched hydrocarbon stream can be fed to a liquid collection zone of the water quench tower at a location below the lowest vapor-liquid contact surface to facilitate efficient quench tower operation. 
         [0016]    The pyrolysis furnace effluent can have a steam to hydrocarbon feed weight ratio known in the art, in one embodiment between about 0.2 and about 1.0, or in another embodiment between 0.2 and 0.7. The pyrolysis furnace effluent can be effluent from a gas cracker used for the production of olefins, and in one embodiment can have a steam to hydrocarbon weight ratio from about 0.2 to about 0.4. The pyrolysis furnace effluent from a gas cracker can be cooled in the partial quench from a temperature greater than 175° C., for example about 250° C., to a temperature between about 65° C. and 115° C. In another embodiment, the pyrolysis furnace effluent from a gas cracker can be cooled in the partial quench to a temperature between about 80° C. and 100° C. 
         [0017]    The water quench tower can operate at a pressure of between about 0.1 MPa and about 0.5 MPa. In another embodiment, the water quench tower can be operated at a pressure of between about 0.15 MPa and about 0.4 MPa. 
         [0018]    The pyrolysis furnace effluent can comprise a cracked liquid hydrocarbon, such as cracked naphtha, having steam to hydrocarbon weight ratios between about 0.4 and about 0.6 in one embodiment, or cracked kerosene, having steam to hydrocarbon weight ratios between about 0.5 and about 0.7 in another embodiment. In another embodiment of the invention, the pyrolysis furnace effluent can be fractionated upstream of the partial water quenching. The pyrolysis furnace effluent can be fed to a fractionation tower, where the effluent can be quenched and fractionated with a first quench oil stream (and gasoline reflux) to form the steam and hydrocarbon vapor stream for the partial water quenching described above. Liquid hydrocarbons can be collected from the fractionation tower. A first portion of the collected liquid hydrocarbons can be recovered as a product. A second portion of the collected liquid hydrocarbons can be cooled and recycled for use in the first quench oil stream. The pyrolysis furnace effluent can be partially quenched using a second hydrocarbon quench stream prior to the fractionation tower. In one embodiment, the pyrolysis furnace effluent can be partially quenched with oil at a temperature from about 350° C. to about 850° C., or from about 350° C. to about 550° C., to a temperature from about 170° C. to about 400° C. or from about 200° C. to about 300° C. In another embodiment, the pyrolysis furnace effluent can be partially quenched with oil to a temperature between about 235° C. to about 265° C. The second portion of the collected liquid hydrocarbon can be cooled and recycled to form the first and second quench oil streams. In one embodiment, the cooling of the collected liquid hydrocarbon can include indirect heat exchange. The process can include refluxing the fractionation tower with hydrocarbon recovered from the oil-water separator. 
         [0019]    Embodiments relate to apparatus for water quenching a pyrolysis furnace effluent of gas and oil vapor. The apparatus can include means for partially quenching the pyrolysis furnace effluent with a first quench water stream in one or more stages to produce a mixed vapor-liquid stream; means for feeding the mixed vapor-liquid stream to a water quench tower to separate the vapor and liquid; means for further quenching the separated vapor with a second quench water stream in the quench tower to form an overhead vapor product comprising light hydrocarbons; means for collecting water and liquid hydrocarbons from the quench tower in an oil-water separator; means for separately recovering oil and water from the oil-water separator; means for cooling a portion of the recovered water; and, means for recycling the cooled water to the first and second water streams. 
         [0020]    Embodiments relate to apparatus for water quenching a pyrolysis furnace effluent. The apparatus includes one or more water quench fittings in a feed line to a water quench tower for partially quenching a hydrocarbon stream comprising gas and oil vapor with a first quench water stream to form a mixed vapor-liquid stream in the feed line; where the hydrocarbon stream can be a furnace effluent or a partially cooled furnace effluent, for example. The water quench tower can include a vapor-liquid contacting zone in between a bottoms liquid collection zone and an overhead vapor outlet. One or more lines are provided for supplying a second quench water stream to the vapor-liquid contacting zone in the quench tower to form an overhead water-lean vapor product enriched in light hydrocarbons and a liquid bottoms product comprising heavier hydrocarbons and water. Another line can be provided to transfer the liquid bottoms product from the quench tower to an oil-water separator. Another line can be provided to recover oil from the oil-water separator. A further line can be provided to recover water from the oil-water separator. The apparatus can include one or more heat exchangers to cool a portion of the recovered water, and lines to recycle the cooled water to the first and second water streams. 
         [0021]    The apparatus can include a pyrolysis furnace for supplying the hydrocarbon stream to the water quench fitting. The water quench tower can have an inlet for receiving the mixed vapor-liquid stream from the feed line below a lowermost vapor-liquid contact medium. In an embodiment, the apparatus includes an upstream fractionation unit having a fractionation tower for receiving effluent from the pyrolysis furnace and a first quench oil supply stream to the fractionation tower for quenching vapor to form the hydrocarbon stream to the water quench fitting. The fractionation tower can include a liquid hydrocarbons collection zone and a line can be provided for recovering a first portion of the collected liquid hydrocarbons from the collection zone. A heat exchanger can be provided for cooling a second portion of the collected liquid hydrocarbons from the collection zone, and a line can be included to recycle at least part of the cooled portion from the heat exchanger to the first quench oil stream. An oil quench fitting can be disposed in a feed line to the fractionation tower for partially quenching the effluent with a second quench oil stream. The second quench oil stream can include part of the cooled portion from the oil heat exchanger. The apparatus can include a line for refluxing the fractionation tower with oil from the oil-water separator 
         [0022]    With reference to the figures,  FIG. 1  depicts a simplified schematic illustration of a process for water quenching a pyrolysis furnace effluent according to one embodiment. The processes can have process equipment such as a water quench tower  10 , oil-water separator  12 , one or more heat exchangers  14   a ,  14   b , and other well known process equipment not shown such as valves, control valves, filters, strainers, cyclones, pumps and the like. Water quench tower  10  contains vapor-liquid contacting elements or devices such as trays, mesh, fixed packing, random packing, liquid spray nozzles, or the like, which allow for contact of a vapor and a liquid in a countercurrent flow. Heat exchangers  14   a  and  14   b  can be fin-fan exchangers, shell and tube exchangers, plate exchangers, or other indirect heat exchangers well known in the art. Heat exchangers  14   a  and  14   b  can be operated in parallel or series configuration, and can include as many parallel or series multiple- or single-service heat exchangers as are economical for individual plant operations and depending on the services available. 
         [0023]    Supply line  16  and quench water line  18  transmit pyrolysis furnace effluent and quench water, respectively, to water quench fitting  20 . Water quench fitting  20  can be an injection nozzle, a rotating nozzle, a mixing tee, a static mixer, or other equipment sufficient to adequately mix and transfer heat and mass between vapor and liquid stream to achieve thermal equilibrium at the inlet to the quench tower  10 . Line  22  transmits the resulting mixture from the water quench fitting  20  to water quench tower  10 . One or more lines such as lines  24  and/or  26  supply cooled water to water quench tower  10  and to quench water line  18 . Overhead vapor product line  28  transmits the vapor product from water quench tower  10  and line  30  transmits the liquid product from water quench tower  10  to oil-water separator  12 . Lines  32  and  34  allow recovery of hydrocarbons and water from the oil-water separator  12 , respectively. Water is recovered from oil-water separator  12  in line  36 , which can supply the water to heat exchangers  14   a  and  14   b  to cool the fluid passing to lines  24  and  26 . Line  34   a  can be used to recover water from the system, where line  34   a  recovers a portion of the water from line  36 . Lines  36 ,  24  and/or  26  supply cool water to water quench tower  10  and to quench water line  18 ; although three supply lines are illustrated, any number of supply lines can be used to effectuate water quench fitting  20  and quench tower  10  operation. 
         [0024]    The apparatus as described above can be used in processes for water quenching a pyrolysis furnace effluent. A conventional pyrolysis furnace (not shown) is used to crack a hydrocarbon feed, diluted with steam, to form smaller hydrocarbon molecules according to cracking methods well known to the skilled artisan. The cracked hydrocarbon feed can be partially cooled in one or more indirect heat exchangers (not shown) as is well known in the art, forming pyrolysis furnace effluent in line  16 . 
         [0025]    Pyrolysis effluent in line  16  can be partially quenched by mixing with a first quench water stream via line  18  in water quench fitting  20  to form a partially quenched stream in line  22 . For example, the pyrolysis furnace effluent can be from an ethane/propane gas cracker at a temperature ranging between about 175° C. and about 370° C. The pyrolysis furnace effluent can be cooled to a temperature between about 70° C. and about 115° C. by direct heat exchange with quench water stream  18  in water quench fitting  20 . The cooled product from water quench fitting  20 , which can be a vapor-liquid mixture, can be fed to water quench tower  10  through line  22 . In one embodiment, pyrolysis furnace effluent  16  can be cooled to a temperature between 80° C. and 100° C. by direct heat exchange with quench water via line  18  in water quench fitting  20 . The quench water in line  18  can conveniently originate from oil-water separator  12  or an external source. 
         [0026]    Partially quenched vapor-liquid stream in line  22  can be fed to a lower end of water quench tower  10  where the vapor travels upward through water quench tower  10 , and the liquid collects at the bottom of water quench tower  10 . As the vapor flows up water quench tower  10 , it is contacted by water supplied to water quench tower  10  via lines  24 ,  26 , further cooling the vapor to an exit temperature of between about 15° C. and about 50° C. in the vapor product stream  28 . In another embodiment, the exit temperature of the vapor product stream  28  can be from about 30° C. to about 40° C. The absolute pressure of vapor product stream  28  can be between about 0.1 MPa and about 0.5 MPa. In another embodiment, the absolute pressure of vapor product stream  28  can be between about 0.15 MPa and about 0.4 MPa. 
         [0027]    A fraction of the heavier hydrocarbons and steam present in pyrolysis furnace effluent  16  condenses during the partial quenching. Steam and additional heavy hydrocarbons condense in water quench tower  10  as they are contacted and cooled by the water supplied to water quench tower  10  via lines  24 ,  26 . The condensate collects in the bottom of water quench tower  10  and is transferred to oil-water separator  12  through condensate transfer line  30 . The temperature of the condensed hydrocarbons and water exiting the bottom of water quench tower  10  in stream  30  can be between about 60° C. and about 110° C. In another embodiment, the temperature of the bottoms liquid from water quench tower  10  can be from about 80° C. to about 90° C. 
         [0028]    Oil-water separator  12  gravity separates the condensate into hydrocarbon and water phases. The hydrocarbons can be recovered via line  32 ; the aqueous phase can be recovered via line  34  and if desired used as a process heating source in the conventional manner; and quench water can be recycled via line  36 . Any heavy hydrocarbons or sediment that collects in separator  12  can be recovered via line  38 . 
         [0029]    Quench water in line  36  can be cooled in one or more heat exchangers  14   a ,  14   b , and supplied to the water quench tower  10  and water quench fitting  20  through lines  18 ,  24 , and  26 , as needed to control the operation of the process. The quench water in line  36  can be cooled in heat exchangers  14   a ,  14   b  to a temperature of between about 15° C. and about 70° C. for supply in lines  18  and  24 . In another embodiment, the quench water line  36  can be cooled to a temperature of between about 30° C. and about 40° C. If desired, one or more quench water lines  26  can supply quench water to line  18  or from another source to water quench tower  10 , where the water in line  26  can be at a temperature intermediate of quench water line  24  and the quench water from the oil-water separator  12 . Although illustrated as two separate pieces of equipment, oil-water separator  12  can be integrated into the bottom section of the quench tower  10 . The quench water in lines  36 ,  18  may contain some oil, dissolved gases, other chemicals due to solubility, incomplete separation, etc., or any desired process additives. 
         [0030]      FIG. 2  depicts a simplified schematic illustration of a process for fractionating and water quenching a pyrolysis furnace effluent according to one embodiment. Pyrolysis furnace effluent is supplied to fractionation tower  110  by line  112 . Line  112  and line  114 , if used, can supply line  116  feeding to fractionation tower  110 . Liquid bottoms product from fractionation tower  110  is transmitted in line  118  for supply to lines  120  and  122 . Line  120  can recover the heavy oil product and line  122  can supply oil to one or more heat exchangers  124   a  and  124   b , operated in series or in parallel, and then to fractionation tower  110  via lines  126 ,  128 , and  130 . Lines  126  and  128  can optionally supply oil to line  114 , if desired. 
         [0031]    Fractionation tower  110  can have one or more side draws  132 , and one or more circulating loops can provide cooling and reflux to the fractionation tower, such as through heat exchanger  134  and line  136 . Overhead vapor product line  138  transmits vapor from fractionation tower  110  to a water quench system which in the embodiment of  FIG. 2  includes water quench tower  210 , oil-water separator  212 , and one or more heat exchangers  214   a ,  214   b . Water quench tower  210  contains vapor-liquid contacting elements or devices such as trays, mesh, fixed packing, random packing, liquid spray nozzles, or the like, which allow for contact of a vapor and a liquid in a countercurrent flow. Heat exchangers  214   a  and  214   b  can be fin-fan exchangers, shell and tube exchangers, plate exchangers, or other indirect heat exchangers well known in the art. Heat exchangers  214   a  and  214   b  can be operated in parallel or series configuration, and can include as many heat exchange units as are economical for specific plant operations. 
         [0032]    Supply line  138  transmits hydrocarbons and steam, quench water line  218  transmits quench water, and the two streams are mixed in water quench fitting  220 . Water quench fitting  220  can be an injection nozzle, a rotating nozzle, a mixing tee, a static mixer, or other well known equipment sufficient to adequately mix a vapor and a liquid stream upstream of the inlet to reduce the vapor traffic in the inlet water quench tower  210 . Line  222  transmits the effluent from the water quench fitting  220  to quench tower  210 . Lines  224  and  226  supply cooled water to water quench tower  210  and to quench water line  218 . Overhead vapor product line  228  transmits vapor from water quench tower  210 . Line  230  transmits the bottoms liquid to oil-water separator  212 . Lines  232  and  234  allow recovery of hydrocarbons and water, respectively, from oil-water separator  212 . Quench water is recovered from oil-water separator in line  236 , which can supply the water to heat exchangers  214   a  and  214   b  to cool the fluid passing to lines  224  and  226 . 
         [0033]    The embodiment exampled in  FIG. 2  can be operated to fractionate and water quench a liquid pyrolysis furnace effluent. For example, a pyrolysis furnace effluent  112 , such as cracked naphtha, gas oil, or cracked kerosene, diluted with steam, and generally containing light, mid-range, and heavy hydrocarbons, exits the furnace and any indirect heat exchangers (not shown) and can be fed to fractionation tower  110  at a temperature of between about 350° C. and about 900° C., or between about 350° C. and about 550° C. Pyrolysis furnace effluent  112  can be oil quenched to a temperature between about 200° C. and about 300° C. by direct heat exchange with oil from line  114 . The oil quenched effluent can be fed to fractionation tower  110  via line  116 . In another embodiment, the pyrolysis furnace effluent  112  can be oil quenched to a temperature between about 235° C. and 300° C. 
         [0034]    The fractionation tower  110  can condense and separate the heavier hydrocarbons from the light and mid-range hydrocarbons and any steam used to dilute the hydrocarbon in the pyrolysis furnace. The heavy hydrocarbons collected at the bottom of fractionation tower  110  can be used as quench oil or reflux for the fractionation tower  110 . Fractionation tower  110  can be operated such that dilution steam in effluent  112  does not condense or collect in fractionation tower  110 , i.e. above the boiling point of water. As the vapors flow up fractionation tower  110 , they are contacted with liquid oil, further cooling the vapors to an exit temperature between about 90° C. and 300° C. in line  138 . In an embodiment, the exit temperature of the vapor in line  138  can be between about 90° and 250° C., or between about 90° C. and 150° C. 
         [0035]    The temperature of the condensed hydrocarbons exiting the bottom of fractionation tower  110  in line  118  can be between about 150° C. and about 300° C. The condensed hydrocarbons in line  118  are recovered in line  120 . A portion of the condensed hydrocarbons can be supplied to line  122 . Oil in line  122  can be cooled in one or more heat exchangers  124   a ,  124   b , operating in series or in parallel, to a temperature between about 90° C. and about 300° C. in lines  126 ,  128 , and  130 . If desired, lines  126 ,  128  can supply oil to line  114  or can supply additional cool oil to the fractionation tower  110 , where oil line  126  can be at a temperature intermediate that of line  128  and the bottoms from fractionation tower  110 . The pyrolysis furnace effluent can be processed to produce overhead vapor product line  138  exiting the fractionation tower  110 . 
         [0036]    Overhead vapor product line  138 , exiting the fractionation tower  110  at a temperature between about 90° C. and about 300° C., can be water quenched. Vapor from line  138  can be cooled to a temperature between about 70° C. and about 250° C. by direct heat exchange with quench water via line  218  in water quench fitting  220 . The partially quenched stream in line  222  can be supplied to water quench tower  210 . In another embodiment, vapor in line  138  can be cooled to a temperature between about 80° C. and about 100° C. by direct heat exchange with quench water from line  218  in water quench fitting  220 . 
         [0037]    The partially quenched vapor-liquid stream in line  222  can be fed to a lower end of water quench tower  210  where the vapor travels up and the liquid collects at the bottom. As the vapor flows up, the vapor is contacted by water from one or more cool water supply lines  224 ,  226 , further cooling the vapors to an exit temperature of between about 15° C. and about 50° C. in line  228 . In another embodiment, the exit temperature of the vapor can be from about 30° C. to about 40° C. The absolute pressure of water quench tower  210  at line  228  can be between about 0.1 MPa and about 0.5 MPa. In another embodiment, the absolute pressure at line  228  can be between about 0.15 MPa and about 0.4 MPa. 
         [0038]    A fraction of the heavier hydrocarbons and steam present in pyrolysis furnace effluent  216  condenses during the partial quench. Steam and additional heavy hydrocarbons condense in water quench tower  210  as they are contacted and cooled by the water supplied to water quench tower  210  through lines  224 ,  226 . The condensate collects in the bottom of water quench tower  210  and is transferred to oil-water separator  212  through condensate transfer line  230 . The temperature of the bottoms liquid from quench tower  210  in stream  230  can be between about 60° C. and about 110° C. In another embodiment, the temperature of the bottoms liquid can be from about 80° C. to about 90° C. 
         [0039]    Oil-water separator  212  separates the condensate into hydrocarbon and water phases. The hydrocarbons can be recovered in line  232 . The aqueous phase can be recovered via line  234  and if desired used as a process heating source in the conventional manner. Quench water can be recycled via line  236 . Quench water stream  236  can be cooled in one or more heat exchangers  214   a ,  214   b , and supplied to the water quench tower  210  and water quench fitting  220  through lines  218 ,  224 , and  226 , as needed to control the operation of the process. The quench water stream  236  recovered from the oil-water separator  212  can be cooled in heat exchangers  214   a ,  214   b  to a temperature of between about 10° C. and about 70° C. for use as cool water supply in streams  218  and  224 . In another embodiment, the quench water stream  236  can be cooled to a temperature of between about 30° C. to about 40° C. One or more quench water streams  226  can supply quench water stream  218  or can supply additional quench water to water quench tower  210 , where water stream  226  can be at a temperature intermediate of quench water stream  224  and the temperature of the quench water in the oil-water separator  212 . The condensed hydrocarbons are recovered from oil-water separator  212  via gasoline stream  232 . A portion of the gasoline recovered in stream  232  can, if desired, be used to reflux the top of fractionation tower  110  via line  237 ; the remainder of the gasoline can be recovered via gasoline stream  238 . 
         [0040]    The energy balance surrounding the water quench tower and auxiliary equipment remains the same with or without a partial quench step included in the process. As a result, there are many benefits to using the partial quench step in the process. A primary benefit can be in the sizing requirements for the water quench tower. By use of a partial water quench upstream of the water quench tower, the capacity of an existing quench tower can be increased substantially. The design diameter for a new water quench tower can be significantly decreased. The capacity increase or design diameter decrease can be achieved by using a partial water quenching step to decrease the net vapor traffic at the bottom of the water quench tower. Use of a water quench fitting can reduce fouling by removing most of the coke or solids from the vapor before the vapor is contacted with liquid on the contacting surfaces in the water quench tower. 
         [0041]    For the prior art process without a partial water quenching step, the design diameter of a water quench tower is generally controlled by the amount of steam required during the furnace de-coking process. With a partial water quench upstream of the water quench tower as in the present invention, steam flow rates during the de-coking process are no longer the controlling factor in the design process because the partial quench upstream of the water quench tower can condense this extra steam, thereby decreasing the net vapor traffic in the water quench tower, and decreasing the required diameter during the de-coking process. 
         [0042]    The use of a partial water quenching step can also improve the versatility of the overall process. For processes currently limited to a particular feedstock hydrocarbon due to additional vapor traffic requirements when other feedstock hydrocarbons are used, the use of a partial water quenching step can decrease the vapor traffic reaching the water quench tower, thereby allowing use of a broader range of feedstock hydrocarbons, improving the versatility of the process. 
         [0043]    The benefits outlined above will become more apparent in the examples given below. 
         [0044]    Table 1 gives a comparison of simulation results for a water quench process similar to that as illustrated in  FIG. 1 . A comparison of simulation results are given for processes with and without water quenching in a water quench fitting  20  upstream of the water quench tower  10 , where the pyrolysis furnace effluent  16  is from an ethane/propane cracker, having a steam to hydrocarbon feed ratio of 0.3 based on weight. An additional comparison is given for the same pyrolysis furnace effluent  16  having an additional 20 metric tons per hour of de-coking steam. For each comparison, the water quench tower  10  has an equivalent number of stages, such that a comparison of design diameter decrease or capacity increase based upon tower volume can be made. The overhead vapor product in line  28  is approximately equivalent for each comparison, indicating that side-by-side comparison of the simulation results can be performed without misleading results. The limiting design factors are liquid flooding and net vapor traffic at the bottom of water quench tower  10 . 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Water quench for E/P cracker effluent. 
               
             
          
           
               
                   
                   
                 Quench tower 
                 Resulting Quench 
               
               
                   
                 Stream or Unit 
                 pressure (kg/sq cm) 
                 tower diameter (m) 
               
             
          
           
               
                   
                 16 
                 18 
                 24 
                 28 
                 10 
                 10 
               
               
                   
                   
               
             
          
           
               
                 Comp. 1 
                 Flow rate 
                 169 
                 0 
                 870 
                 136 
                   
                   
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 250 
                 N/A 
                 38 
                 39 
                 1.41 
                 3.97 
               
               
                   
                 (° C.) 
               
               
                 Comp. 2 
                 Flow rate 
                 189 
                 0 
                 1173 
                 135 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 250 
                 N/A 
                 38 
                 38.4 
                 1.41 
                 4.3 
               
               
                   
                 (° C.) 
               
               
                 EX. 1 
                 Flow rate 
                 169 
                 200 
                 660 
                 136 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 250 
                 38 
                 38 
                 41.3 
                 1.41 
                 3.7 
               
               
                   
                 (° C.) 
               
               
                 Ex. 2 
                 Flow rate 
                 189 
                 504 
                 660 
                 136 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 250 
                 38 
                 38 
                 40.8 
                 1.41 
                 3.7 
               
               
                   
                 (° C.) 
               
               
                 Ex. 3 
                 Flow rate 
                 169 
                 600 
                 300 
                 132 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 250 
                 38 
                 38 
                 40.2 
                 3.41 
                 2.6 
               
               
                   
                 (° C.) 
               
               
                   
               
             
          
         
       
     
         [0045]    Comparative examples 1 and 2 provide the design basis for water quench tower  10  without using the partial water quench  18  upstream of the water quench tower  10 . Comparative example 1 illustrates conditions for design of a water quench tower  10  under normal operating conditions, and Comparative Example 2 illustrates design for operations during de-coking, with an additional 20 tonnes per hour of steam added to the pyrolysis furnace effluent  16 . As can be seen in Table 1, the design diameter of the resulting water quench tower  10  should be based upon de-coking, 4.3 m. By comparison, Example 1, normal operating conditions with a partial quench stream  18 , and Example 2, de-coking conditions with a partial quench stream  18 , illustrate the decrease in design diameter that can be achieved by utilizing partial quench water stream  18 . The total combined amount of quench water used in quench water streams  18 ,  24 , and  26  remains constant for the same rate of pyrolysis furnace effluent  16 , illustrative of the equivalence of the energy balance, as mentioned earlier. The resulting design diameter decreases to 3.7 m, and the design diameter is no longer limited by de-coking, when a water quench fitting  20  is added to the process. The simulation results indicate a 14% decrease in design diameter, or, an existing tower can process an additional 35% more cracked gas when retrofitted to perform a partial quench, based on diameter. 
         [0046]    Example 3 in Table 1 illustrates an additional benefit that can be realized by operating the water quench tower  10  at a slightly elevated pressure. By increasing the pressure in the water quench tower  10  from 0.14 MPa to 0.34 MPa, the design diameter can be decreased further, to 2.6 m. This correlates to nearly a 30% further decrease in tower diameter, or, an existing tower can handle twice the capacity of a tower operating at lower pressure, based on design diameter results. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Water quench of a fractionator overhead product stream where the 
               
               
                 fractionator processed naphtha cracker effluent. 
               
             
          
           
               
                   
                   
                 Resulting 
               
               
                   
                   
                 Quench 
               
               
                   
                   
                 tower 
               
               
                   
                   
                 diameter 
               
               
                   
                 Stream or Unit 
                 (m) 
               
             
          
           
               
                   
                 138 
                 218 
                 224 
                 226 
                 228 
                 210 
               
               
                   
                   
               
             
          
           
               
                 Comp. 3 
                 Flow rate 
                 263.6 
                 0 
                 722.7 
                 600 
                 135.4 
                   
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 118.1 
                 N/A 
                 38 
                 60 
                 39.9 
                 4.5 
               
               
                   
                 (° C.) 
               
               
                 Comp. 4 
                 Flow rate 
                 283.6 
                 0 
                 730 
                 1080 
                 135.2 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 112.7 
                 N/A 
                 38 
                 60 
                 39.4 
                 4.8 
               
               
                   
                 (° C.) 
               
               
                 Ex. 4 
                 Flow rate 
                 263.6 
                 600 
                 730 
                 0 
                 135.5 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 117 
                 60 
                 38 
                   
                 40.4 
                 3.8 
               
               
                   
                 (° C.) 
               
               
                 Ex. 5 
                 Flow rate 
                 283.6 
                 1060 
                 730 
                 0 
                 135.5 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 113.9 
                 60 
                 38 
                   
                 40.3 
                 3.8 
               
               
                   
                 (° C.) 
               
               
                   
               
             
          
         
       
     
         [0047]    Table 2 gives a similar comparison of simulation results for a pyrolysis furnace effluent of cracked naphtha, with a steam to hydrocarbon ratio of 0.5 based on weight, where the pyrolysis furnace effluent is fractionated upstream of the water quench tower, similar to the process of  FIG. 2 . Comparative examples 3 and 4 give simulation results for the water quench tower  210 , processing the overhead product  138  from a fractionation tower  110 . Comparative example 3 is for normal operating conditions, and comparative example 4 is for de-coking conditions where an additional 20 tonnes/hour steam are employed. Design of a water quench tower  210  without use of a partial water quench fitting  220  is again limited based on de-coking, having a design diameter of 4.8 m. By comparison, Examples 4 and 5 illustrate that with the addition of a partial water quench fitting  220 , the design diameter of water quench tower  210  is no longer limited based on de-coking, and the design diameter decreases to 3.8 m with use of water quench fitting  220 . The simulation results indicate a potential design diameter decrease of 21%, or, the capacity of an existing water quench tower  210  can be increased by as much as 59% when retrofitted with water quenching fitting  220 . 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Water quench of fractionator overheads where the fractionator processes a 
               
               
                 kerosene cracker effluent. 
               
             
          
           
               
                   
                   
                 Resulting Quench 
               
               
                   
                   
                 tower diameter 
               
               
                   
                 Stream or Unit 
                 (m) 
               
             
          
           
               
                   
                 138 
                 218 
                 224 
                 228 
                 210 
               
               
                   
                   
               
             
          
           
               
                 Comp. 5 
                 Flow rate 
                 324 
                 0 
                 1550 
                 140.8 
                   
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 95 
                 N/A 
                 38 
                 38.1 
                 4.95 
               
               
                   
                 (° C.) 
               
               
                 Comp. 6 
                 Flow rate 
                 344 
                 0 
                 1815 
                 142 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 95.9 
                 N/A 
                 38 
                 40.2 
                 5.19 
               
               
                   
                 (° C.) 
               
               
                 Ex. 6 
                 Flow rate 
                 324 
                 770 
                 790 
                 143.2 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 97.5 
                 38 
                 38 
                 41.1 
                 3.98 
               
               
                   
                 (° C.) 
               
               
                 Ex. 7 
                 Flow rate 
                 344 
                 1025 
                 790 
                 144.4 
               
               
                   
                 (tonnes/h) 
               
               
                   
                 Temperature 
                 97.6 
                 38 
                 38 
                 39.7 
                 3.95 
               
               
                   
                 (° C.) 
               
               
                   
               
             
          
         
       
     
         [0048]    Table 3 again illustrates simulation results for a process similar to that of  FIG. 2 , except that the pyrolysis furnace effluent  112  is a cracked heavy hydrocarbon, such as kerosene, with a steam to hydrocarbon feed ratio of 0.6. The results again show a significant decrease in the design diameter of water quench tower  210 , and again show that de-coking is no longer limiting on design diameter when a water quench fitting  220  is added to the process. The results for cracked kerosene indicate a decrease in design diameter of 23%, or, the capacity of an existing water quench tower  210  can be increased by approximately 70% when retrofitted with a water quench fitting  220 . 
         [0049]    As is illustrated in the above examples, addition of a partial water quench fitting upstream of the water quench tower can provide the benefits of additional capacity or a smaller design diameter. The additional capacity can improve the versatility of existing columns and can potentially allow the use of a wider range of feedstock hydrocarbons for pyrolysis furnace operation. The smaller design diameter can decrease capital costs associated with new construction. Column design limits based upon de-coking are also alleviated by use of a partial water quench upstream of the water quench tower. Additionally, use of a water quench fitting can reduce fouling by removing most of the coke or solids from the vapor before the vapor is contacted with liquid on the contacting surfaces in the water quench tower. 
         [0050]    The embodiments herein can use a catalytic converter instead of a pyrolysis furnace. 
         [0051]    While these embodiments have been described with emphasis on the embodiments, it should be understood that within the scope of the appended claims, the embodiments might be practiced other than as specifically described herein.