Patent Publication Number: US-11034889-B2

Title: Method and system for improving spatial efficiency of a furnace system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/400,500, filed on Jan. 6, 2017. U.S. patent application Ser. No. 15/400,500 is a continuation of U.S. patent application Ser. No. 14/964,235, filed on Dec. 9, 2015 (now U.S. Pat. No. 9,567,528). U.S. patent application Ser. No. 14/964,235 is a continuation of U.S. patent application Ser. No. 13/789,039, filed on Mar. 7, 2013 (now U.S. Pat. No. 9,239,190). U.S. patent application Ser. No. 13/789,039 claims priority to, and incorporates by reference for any purpose the entire disclosure of, U.S. Provisional Patent Application No. 61/680,363, filed Aug. 7, 2012. U.S. patent application Ser. No. 15/400,500, U.S. patent application Ser. No. 14/964,235, U.S. patent application Ser. No. 13/789,039, and U.S. Provisional Patent Application No. 61/680,363 are incorporated herein by reference. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates generally to an apparatus for refining operations, and more particularly, but not by way of limitation, to furnace systems having vertically-oriented radiant sections. 
     History of the Related Art 
     Delayed coking refers to a refining process that includes heating a residual oil feed, made up of heavy, long-chain hydrocarbon molecules, to a cracking temperature in a furnace system. Typically, furnace systems used in the delayed coking process include a plurality of tubes arranged in a multiple-pass configuration. Often times, a furnace system includes at least one convection section and at least one radiant section. The residual oil feed is pre-heated in the at least one convection section prior to being conveyed to the at least one radiant section where the residual oil feed is heated to the cracking temperature. In some cases, design considerations dictate that the furnace system include multiple convection sections and multiple radiant sections. Such an arrangement requires an area of sufficient size in which to place the furnace system. 
     In some cases, space constraints limit the number of radiant sections that can be placed in a side-by-side arrangement in a given area. This results in the furnace system being constructed with less than an ideal number of radiant sections. Thus, it would be beneficial to design the furnace system to allow placement of multiple radiant sections or convection sections in a smaller area. 
     U.S. Pat. No. 5,878,699, assigned to The M.W. Kellogg Company, discloses a twin-cell process furnace utilizing a pair of radiant cells. The pair of radiant cells are arranged in close proximity to each other in a generally side-by-side orientation. An overhead convection section is placed above, and centered between the pair of radiant cells. Combustion gas is drawn into the convection section via induced and forced-draft fans. The twin-cell process furnace requires a smaller area and allows increased flexibility in heating multiple services and easier radiant tube replacement. 
     SUMMARY 
     The present invention relates to an apparatus for refining operations. In one aspect, the present invention relates to a furnace system. The furnace system includes at least one lower radiant section having a first firebox disposed therein and at least one upper radiant section disposed above the at least one lower radiant section. The at least one upper radiant section has a second firebox disposed therein. The furnace system further includes at least one convection section disposed above the at least one upper radiant section and an exhaust corridor defined by the first firebox, the second firebox, and the at least one convection section. Arrangement of the at least one upper radiant section above the at least one lower radiant section reduces an area required for construction of the furnace system. 
     In another aspect, the present invention relates to a method for reducing an area required for construction of a furnace system. The method includes providing at least one lower radiant section and providing at least one upper radiant section. The method further includes arranging the at least one upper radiant section above the at least one lower radiant section and providing a convection section disposed above the at least one upper radiant section. Arrangement of the at least one upper radiant section above the at least one lower radiant section reduces the area required for construction of the furnace system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the method and system of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a schematic diagram of a refining system according to an exemplary embodiment; 
         FIG. 2  is a schematic diagram of a prior-art furnace system; 
         FIG. 3  is a cross-sectional view of a radiant section of a furnace system according to an exemplary embodiment; 
         FIG. 4  is a schematic diagram of a furnace system according to an exemplary embodiment; 
         FIG. 5  is a schematic diagram of a furnace system according to an exemplary embodiment; and 
         FIG. 6  is a flow diagram of a process for constructing a furnace system according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention will now be described more fully with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
       FIG. 1  is a schematic diagram of a refining system according to an exemplary embodiment. A refining system  100  includes an atmospheric-distillation unit  102 , a vacuum-distillation unit  104 , and a delayed-coking unit  106 . In a typical embodiment, the atmospheric-distillation unit  102  receives a crude oil feedstock  120 . Water and other contaminants are typically removed from the crude oil feedstock  120  before the crude oil feedstock  120  enters the atmospheric distillation unit  102 . The crude oil feedstock  120  is heated under atmospheric pressure to a temperature range of, for example, between approximately 650° F. and approximately 700° F. Lightweight materials  122  that boil below approximately 650° F.-700° F. are captured and processed elsewhere to produce, for example, fuel gas, naptha, gasoline, jet fuel, and diesel fuel. Heavier materials  123  that boil above approximately 650° F.-700° F. (sometimes referred to as “atmospheric residuum”) are removed from a bottom of the atmospheric-distillation unit  102  and are conveyed to the vacuum-distillation unit  104 . 
     Still referring to  FIG. 1 , the heavier materials  123  enter the vacuum-distillation unit  104  and are heated at very low pressure to a temperature range of, for example, between approximately 700° F. and approximately 800° F. Light components  125  that boil below approximately 700° F.-800° F. are captured and processed elsewhere to produce, for example, gasoline and asphalt. A residual oil feed  126  that boils above approximately 700° F.-800° F. (sometimes referred to as “vacuum residuum”) is removed from a bottom of the vacuum-distillation unit  104  and is conveyed to the delayed-coking unit  106 . 
     Still referring to  FIG. 1 , according to exemplary embodiments, the delayed-coking unit  106  includes a furnace  108  and a coke drum  110 . The residual oil feed  126  is preheated and fed to the furnace  108  where the residual oil feed  126  is heated to a temperature range of, for example, between approximately 900° F. and approximately 940° F. After heating, the residual oil feed  126  is fed into the coke drum  110 . The residual oil feed  126  is maintained at a pressure range of, for example, between approximately 25 psi and approximately 75 psi for a specified cycle time until the residual oil feed  126  separates into, for example, hydrocarbon vapors and solid coke  128 . In a typical embodiment, the specified cycle time is approximately 10 hours to approximately 24 hours. Separation of the residual oil feed  126  is known as “cracking.” The solid coke  128  accumulates starting at a bottom region  130  of the coke drum  110 . 
     Still referring to  FIG. 1 , according to exemplary embodiments, after the solid coke  128  reaches a predetermined level in the coke drum  110 , the solid coke  128  is removed from the coke drum  110  through, for example, mechanical or hydraulic methods. Removal of the solid coke  128  from the coke drum  110  is known as, for example, “cutting,” “coke cutting,” or “decoking.” Flow of the residual oil feed  126  is diverted away from the coke drum  110  to at least one second coke drum  112 . The coke drum  110  is then steamed to strip out remaining uncracked hydrocarbons. After the coke drum  110  is cooled by, for example, water injection, the solid coke  128  is removed via, for example, mechanical or hydraulic methods. The solid coke  128  falls through the bottom region  130  of the coke drum  110  and is recovered in a coke pit  114 . The solid coke  128  is then shipped from the refinery to supply the coke market. In various embodiments, flow of the residual oil feed  126  may be diverted to the at least one second coke drum  112  during decoking of the coke drum  110  thereby maintaining continuous operation of the refining system  100 . 
       FIG. 2  is a schematic diagram of a prior-art furnace system. A prior-art furnace system  200  typically includes a plurality of convection sections  202  and a plurality of radiant sections  204 . The arrangement depicted in  FIG. 2  shows, for example, two convection sections  202  oriented generally above four radiant sections  204 . The plurality of radiant sections  204  are typically oriented in a side-by-side arrangement with respect to each other. During operation, the residual oil feed  126  (shown in  FIG. 1 ) enters one of the plurality of convection sections  202  through a convection inlet  206 . Flue gas, generated by the plurality of radiant sections  204 , rises through the plurality of convection sections  202  and pre-heats the residual oil feed  126 . The residual oil feed  126  exits the plurality of convection sections  202  via a convection outlet  208  and is conveyed to one of the plurality of radiant sections  204 . The preheated residual oil feed  126  enters the plurality of radiant sections  204  via a radiant inlet  210  and is heated to the cracking temperature. Once heated, the residual oil feed  126  leaves the plurality of radiant sections  204  via a radiant outlet  212  and is conveyed to the coke drum  110  (shown in  FIG. 1 ). 
       FIG. 3  is a cross-sectional view of a radiant section according to an exemplary embodiment. A radiant section  300  includes a burner unit  302 . By way of example, the radiant section  300  shown in  FIG. 2  includes a pair of oppositely disposed burner units  302 . A firebox  304  is defined between the pair of oppositely disposed burner units  302 . A process coil  306  is disposed within the firebox  304 . In a typical embodiment, the process coil  306  contains the residual oil feed  126  (shown in  FIG. 1 ). During operation of the radiant section  300 , combustion byproducts and exhaust gases, referred to as “flue gases,” accumulate in the firebox  304 . In a typical embodiment, the flue gasses are exhausted through an upper opening  308  of the firebox. 
       FIG. 4  is a schematic diagram of a furnace system according to an exemplary embodiment. A furnace system  400  includes at least one convection section  402 , at least one lower radiant section  404 , and at least one upper radiant section  406 . By way of example, the furnace system  400  depicted in  FIG. 4  illustrates, for example, two convection sections  402 , two lower radiant sections  404 , and two upper radiant sections  406 ; however, any number of convection sections  402 , any number of lower radiant sections  404 , and any number of upper radiant sections  406  may be utilized depending on design requirements. In a typical embodiment, the at least one upper radiant section  406  is mounted above the at least one lower radiant section  404 . Arrangement of the at least one upper radiant section  406  above the at least one lower radiant section  404  allows the furnace system  400  to be constructed in a smaller area in comparison to prior art side-by-side arrangements as shown in  FIG. 2 . In an exemplary embodiment, the furnace system  400  shown in  FIG. 4  places four radiant sections ( 404 ,  406 ) in an area that would ordinarily be required for a furnace system having two radiant sections ( 404 ,  406 ). 
     Still referring to  FIG. 4 , a first firebox  422  associated with the at least one lower radiant section  404  is fluidly coupled, and thermally exposed, to a second firebox  424  associated with the at least one upper radiant section  406 . In a typical embodiment, the at least one convection section  402  is fluidly coupled, and thermally exposed, to the second firebox  424 . During operation, the at least one lower radiant section  404  and the at least one upper radiant section  406  produce exhaust gasses and combustion byproducts known as “flue gases.” In a typical embodiment, flue gases that have accumulated in the first firebox  422  and the second firebox  424  rise through the at least one convection section  402 . The flue gases provide convective heat transfer to the at least one convection section  402 . The first firebox  422 , the second firebox  424 , and the at least one convection section  402  together define an exhaust corridor  426  for exhaustion of the flue gases. A stack  408  is mounted above, and fluidly coupled to, the at least one convection section  402 . Flue gases accumulating in the exhaust corridor  426  are exhausted through the stack  408 . 
     Still referring to  FIG. 4 , the at least one convection section  402  includes a convection inlet  410  and a convection outlet  412 . In similar fashion, the at least one lower radiant section  404  includes a first radiant inlet  414  and a first radiant outlet  416 . The at least one upper radiant section  406  includes a second radiant inlet  418  and a second radiant outlet  420 . In a typical embodiment, the convection inlet  410  receives the residual oil feed  126  (shown in  FIG. 1 ). The convection outlet  412  is fluidly coupled to the first radiant inlet  414  and the second radiant inlet  418 . In a typical embodiment, the first radiant outlet  416  and the second radiant outlet  420  are fluidly coupled to the coke drum  110  (shown in  FIG. 1 ). In various alternative embodiments, the convection outlet  412  is fluidly coupled to the first radiant inlet  414  and a second convection outlet (not explicitly shown) is coupled to the second radiant inlet  418 . 
     Still referring to  FIG. 4 , during operation, the residual oil feed  126  (shown in  FIG. 1 ) enters the at least one convection section  402  via the convection inlet  410 . The residual oil feed  126  is pre-heated in the at least one convection section  402  by convective heat transfer. Next, the residual oil feed  126  leaves the at least one convection section  402  via the convection outlet  412  and is conveyed to one of the at least one lower radiant section  404  or the at least one upper radiant section  406 . The residual oil feed  126  enters the at least one lower radiant section  404  via the first radiant inlet  414 . The residual oil feed  126  enters the at least one upper radiant section  406  via the second radiant inlet  418 . 
     In the at least one lower radiant section  404  and the at least one upper radiant section  406 , the residual oil feed  126  is heated to a cracking temperature in the range of, for example, between approximately 900° F. and approximately 940° F. After heating, the residual oil feed  126  leaves the at least one lower radiant section  404  via the first radiant outlet  416 . The residual oil feed  126  leaves the at least one upper radiant section  406  via the second radiant outlet  420 . Upon leaving the at least one lower radiant section  404  or the at least one upper radiant section  406 , the residual oil feed  126  is conveyed to the coke drum  110  (shown in  FIG. 1 ). In a typical embodiment, the at least one lower radiant section  404  and the at least one upper radiant section  406  are fluidly connected in parallel to the at least one convection section  402 . However, in various alternative embodiments, the at least one lower radiant section  404  and the at least one upper radiant section  406  may be connected in series to the at least one convection section  402 . 
     Still referring to  FIG. 4 , during operation, the at least one lower radiant section  404  and the at least one upper radiant section  406  are independently controlled. In a typical embodiment, a temperature of the residual oil feed  126  at the first radiant outlet  416  is substantially equal to a temperature of the residual oil feed  126  at the second radiant outlet  420 . In a typical embodiment, flue gas discharged from the lower radiant section  404  will soften a flux profile of a process coil associated with the upper radiant section  406 . As used herein, the term “flux profile” refers to heat input per surface area of process coil. Softening the flux profile of the upper radiant section  406  tends to increase a run length of the upper radiant section  406 . That is, improved flux profile tends to increase an amount of time between required cleanings of the upper radiant section  406  due to accumulated coke. 
     Advantages of the furnace system  400  will be apparent to those skilled in the art. First, as previously discussed, arrangement of the at least one upper radiant section  406  above the at least one lower radiant section  404  allows the furnace system  400  to be constructed in a substantially smaller area. This is particularly advantageous in situations having critical space constraints. Second, the furnace system  400  reduces a capital investment commonly associated with many prior furnace systems. The furnace system  400  reduces a quantity of material associated with, for example, the stack  408  and as well as other associated exhaust corridors. 
       FIG. 5  is a schematic diagram of a furnace system according to an exemplary embodiment. A furnace system  500  includes a plurality of convection sections  502  and a plurality of radiant sections  504 . In a typical embodiment, the furnace system  500  is similar in construction to the furnace system  400  discussed above with respect to  FIG. 4 ; however, the furnace system  500  includes, for example, eight radiant sections  504  and four convection sections  502 . Thus, the embodiment shown in  FIG. 5  demonstrates that a furnace system  500 , having eight radiant sections  504  may be constructed on an area ordinarily required for a four-pass furnace system. 
       FIG. 6  is a flow diagram of a process for constructing a furnace system according to an exemplary embodiment. A process  600  starts at step  602 . At step  604 , at least one lower radiant section is provided. At step  606 , at least one upper radiant section is provided. At step  608 , the at least one upper radiant section is arranged above the at least one lower radiant section. At step  610 , at least one convection section is provided and disposed above the at least one upper radiant section. Arrangement of the at least one upper radiant section above the at least one lower radiant section substantially reduces an area required for the furnace system. The process  600  ends at step  612 . 
     Although various embodiments of the method and system of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth herein. For example, although the embodiments shown and described herein relate by way of example to furnace systems utilized in delayed coking operations, one skilled in the art will recognize that the embodiments shown and described herein could also be applied to other furnace systems utilized in refining operations such as, for example a crude heater, a vacuum heater, a visc breaker heater, or any other appropriate device for heating fluid in a refining operation. Further, the furnace systems shown and described herein could, in various embodiments, include any number of convection sections, upper radiant sections, and lower radiant sections. The embodiments shown and described herein are exemplary only.