Patent Publication Number: US-2021172676-A1

Title: Preparing hydrocarbon streams for storage

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. Ser. No. 14/974,602, filed on Dec. 18, 2015, and entitled “PREPARING HYDROCARBON STREAMS FOR STORAGE,” which claims priority to U.S. Provisional Application Ser. No. 62/156,664, filed on May 4, 2015, and entitled “PROCESSING AND STORING A FEEDSTREAM AT ATMOSPHERIC PRESSURE.” The content of these applications is incorporated by reference in its entirety herein. 
    
    
     BACKGROUND 
     Liquefying hydrocarbon gas can facilitate transport and storage of hydrocarbons and related material. Generally, the processes greatly reduce the volume of gas. The resulting liquid is well-suited to transit long distance through pipelines and related infrastructure. For pipeline transportation, it may be most economical to transport hydrocarbon liquid at ambient temperature and high pressure because it is easier to address requirements for wall thickness of the pipe without the need to insulate the entire length of the pipeline. For storage, it may be better for hydrocarbon liquid to be at or near atmospheric pressure to economically resolve the insulation and wall thickness requirements. 
     SUMMARY 
     The subject matter of this disclosure relates generally to hydrocarbon processing. The embodiments may form a fluid circuit that incorporates components to prepare an incoming liquid ethane stream for storage. These components can include a distilling unit embodied as a plurality of vessels to separate the incoming liquid ethane stream into a liquid for storage. The fluid circuit can also include a demethanizer column that is in position downstream of the vessels. 
     Some embodiments configure the vessels to permit a position for the demethanizer column in the back or “tail” end of the fluid circuit. The vessels can reduce the amount of flash gas processed by the demethanizer column. In turn, compression requirements are lower in order maintain pressure of the flash gas and boil-off gas that the embodiments combine together for processing at the demethanizer column. This boil-off gas can originate from storage of the final, liquid ethane product. In this way, horsepower requirements for the embodiments will compare favorably to other processes that may utilize, for example, one or more demethanizer columns at the “front” end of the fluid circuit. 
     Some embodiments may be configured to process a propane stream. This stream can also transit a pipeline to a processing facility that is adjacent to embodiments of the processing system. Temperatures may be warmer for propane, thus reducing refrigeration requirements and, possibly eliminating a refrigeration circuit alltogether. In one implementation, the components may use a deethanizer in lieu of the demethanizer column. The lighter hydrocarbons would be methane. Propane can be stored at ambient temperature and pressure of 208 psig. 
     The embodiments can also be configured to recover other hydrocarbons from the incoming ethane stream. These other hydrocarbons are particularly useful as fuel gas and/or as raw materials for use in various petrochemical applications. In this way, the embodiments may avoid unnecessary loss of products from the feed stream, effectively adding value and/or optimizing profitability of the liquefaction process. 
     The embodiments may find use in many different types of processing facilities. These facilities may be found onshore and/or offshore. In one application, the embodiments can incorporate into and/or as part of processing facilities that reside on land, typically on (or near) shore. These processing facilities can process the feedstock from production facilitates found both onshore and offshore. Offshore production facilitates use pipelines to transport feedstock extracted from gas fields and/or gas-laden oil-rich fields, often from deep sea wells, to the processing facilitates. For liquefying processes, the processing facility can turn the feedstock to liquid using suitably configured refrigeration equipment or “trains.” In other applications, the embodiments can incorporate into production facilities on board a ship (or like floating vessel). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made briefly to the accompanying drawings, in which: 
         FIG. 1  depicts a schematic diagram of an exemplary embodiment of a processing system with a fluid circuit that is useful to prepare incoming hydrocarbon feedstock for storage; 
         FIG. 2  depicts an example of the fluid circuit for use in the processing system of  FIG. 1 ; 
         FIG. 3  depicts an example of a mixing unit for use in the fluid circuit of  FIG. 2 ; 
         FIG. 4  depicts a flow diagram of an exemplary embodiment of a process to prepare incoming hydrocarbon feedstock for storage; 
         FIG. 5  depicts a flow diagram of an example of the process of  FIG. 4 ; and 
         FIG. 6  depicts a flow diagram of an example of the process of  FIGS. 4 and 5 . 
     
    
    
     Where applicable like reference characters designate identical or corresponding components and units throughout the several views, which are not to scale unless otherwise indicated. The embodiments disclosed herein may include elements that appear in one or more of the several views or in combinations of the several views. Moreover, methods are exemplary only and may be modified by, for example, reordering, adding, removing, and/or altering the individual stages. 
     DETAILED DESCRIPTION 
     The discussion below contemplates embodiments that are useful to process liquid hydrocarbons for storage. The embodiments herein feature improvements that can reduce the overall size and, in turn, the overall investment necessary for commercial processing of ethane and other hydrocarbon streams. Large operations that process quantities of liquid ethane in excess of 120,000 barrels per day may benefit in particular because the embodiments can use components that are substantially smaller than similar components, even when such similar components are “split” to more easily fabricate and ship to the installation site or facility. Other embodiments are contemplated with the scope of the disclosed subject matter. 
       FIG. 1  illustrates a schematic diagram of an exemplary embodiment of a processing system  100  (also “system  100 ”) for use to process hydrocarbon streams. The system  100  can receive a feedstock  102  from a source  104 . The feedstock  102  can comprise liquid with a composition that is predominantly ethane, although the system  100  may be useful for other compositions as well. In one implementation, incoming feedstock  102  may comprise ethane liquid with a first concentration of methane of approximately 3% or less. The system  100  can have a fluid circuit  106  to process incoming feedstock  102  to form one or more products (e.g., a first product  108  and a second product  110 ). The products  108 ,  110  can exit the system  100  to a storage facility  112 , a pipeline  114 , and/or other collateral process equipment. In operation, the fluid circuit  106  is configured so that the first product  108  meet specifications for storage, e.g., at the storage facility  112 . These specifications may require a second concentration of methane that is lower than the first concentration of incoming feedstock  102 . In one example, the second concentration of methane in the first product  108  for may be approximately 1% or less. 
     The fluid circuit  106  can circulate fluids (e.g., gases and liquids). For clarity, these fluids are identified and discussed in connection with operations of the embodiments herein as a process stream  116 . At a high level, the embodiments may include a pre-cooling unit  118 , a distilling unit  120 , a mixing unit  122 , and a demethanizer unit  124 . In one implementation, the fluid circuit  106  can receive a return stream  126  that may originate from the storage facility  112 , although this disclosure is not limited only to that configuration. The fluid circuit  106  can also be configured to separately couple the separator unit  120  and the demethanizer unit  124 , as shown by the phantom line enumerated by the numeral  128 . This configuration mixes outlet products from each of the units  120 ,  124  together to form the first product  108 . As also shown in  FIG. 1 , the fluid circuit  106  may couple with certain collateral equipment, namely, a refrigeration unit  130  that couples with the fluid circuit  106 . Examples of the refrigeration unit  130  may circulate a refrigerant  132  to coolers and/or like devices that condition temperature of the process stream  116  at one or more of the units  118 ,  120 ,  122 ,  124 . 
     Broadly, use of the distilling unit  120  permits the demethanizer unit  124  to be located at the end of the fluid circuit  106 . This position reduces the volume of incoming feedstock  102  that the demethanizer unit  124  processes during operation of the system  100 . Some embodiments only require the demethanizer unit  124  to process approximately 20% of incoming feedstock  102 , with the distilling unit  120  (and or other units in the fluid circuit  106 ) configured to process approximately 80% of incoming feedstock  102 . In such embodiments, the demethanizer unit  124  receives and processes predominantly “flashed” gas (also, “vapor”) that results from one or more of the other units  118 ,  120 ,  122 . This feature is useful to reduce costs of the system  100  because the size of the demethanizer unit  124  is much smaller when at the “tail” end of the system  100  than in other positions further upstream in the fluid circuit  106 . In one implementation, the demethanizer unit  124  has a diameter that is nine (9) feet or less. 
       FIG. 2  illustrates an example of components to implement the processing system  100  to achieve the second concentration of methane in the first product  108 . The refrigeration unit  130  can be configured to disperse the refrigerant  132  as a first refrigerant  134  and a second refrigerant  136 . The refrigerants  134 ,  136  can facilitate thermal transfer at coolers disposed throughout the fluid circuit  106 . In turn, the coolers can be configured to implement cooling in stages (also, “cooling stages”) to reduce temperature of the process stream  116 . Compositions for the refrigerants  134 ,  136  can include propylene and ethylene, respectively; however, other compositions may also pose as workable solutions to affect thermal transfer in the coolers. In the pre-cooling unit  118 , the first refrigerant  134  can circulate across one or more coolers (e.g., a first cooler  138 , a second cooler  140 , and a third cooler  142 ). The second refrigerant  136  can regulate temperature at coolers at each of the separation unit  120  and the demethanizer unit  124 . For the present implementation, the units  120 ,  124  can be configured to include one or more coolers (e.g., a fourth cooler  144 , a fifth cooler  146 , and a sixth cooler  148 , a seventh cooler  150 ). 
     At the distilling unit  120 , the fluid circuit  106  may include a separator  152  to form vapor, liquid, and mixed phase products. The separator  152  can generally be configured as a plurality of vessels (e.g., a first vessel  154 , a second vessel  156 , and a third vessel  158 ). The fluid circuit  106  may also include a fourth vessel  160  that couples with a demethanizer column  162  at the demethanizer unit  124 . For operation, the components  160 ,  162  may benefit from use of one or more peripheral components (e.g., a first peripheral component  164  and a second peripheral component  166 ). Examples of these peripheral components  164 ,  166  can include pumps, boilers, heaters, and like devices that can facilitate operation of the vessel  160  and/or the demethanizer  162 . In one implementation, the second peripheral component  166  may embody a boiler that couples with both the fourth vessel  160  and with the refrigeration unit  130  to condition temperature of the first refrigerant  134 . 
     The fluid circuit  106  may couple the vessels  156 ,  158  with a flash drum  168  or like vessel. The flash drum  168  can couple with the storage facility  112  to provide the first product  108  for storage. The fluid circuit  106  may also include one or more throttling devices (e.g., a first throttling device  170 , a second throttling device  172 , and a third throttling device  174 ). Examples of the throttling  170 ,  172 ,  174  can include valves (e.g., Joule-Thompson valves) and/or devices that are similarly situated to throttle the flow of a fluid stream. These devices may be interposed between components in the fluid circuit  106  as necessary to achieve certain changes in fluid parameters (e.g., temperature, pressure, etc.). As noted below, the device may provide an expansion stage and a cooling stage, where applicable, to reduce pressure and/or temperature of the process stream  116 . 
       FIG. 3  illustrates an example of a mixing unit  200  for use in the processing system  100  of  FIGS. 1 and 2 . This example can couple with the storage facility  112 , the separation unit  120 , and the demethanizer unit  162 . In one implementation, the mixing unit  200  may include a heat exchanger  202  that couples with a compression system  204 . Examples of the heat exchanger  202  can include cross-flow devices of varying designs (e.g., spiral flow, counter-current flow, distributed flow, etc.), although other devices and designs that can effectively transfer thermal energy may also be desirable. The compression system  204  can have one or more compressors (e.g., a first compressor  206  and a second compressor  208 ) and one or more coolers (e.g., a first cooler  210  and a second cooler  212 ). 
     Referring back to  FIG. 2 , the fluid circuit  106  can direct the process stream  116  through the various components to generate the products  108 ,  110 . The pre-cooling unit  118  can sub-cool the incoming feedstock  102  from a first temperature to a second temperature that is less than the first temperature. Incoming feedstock  102  may enter the device (at  176 ) at ambient temperature that prevails at the system  100  and/or surrounding facility. The coolers  138 ,  140 ,  142  can effectively reduce temperature of incoming feedstock  102  by at least about 120° F., with one example being configured to condition the process stream  116  to exit the cooling stages (at  178 ) at approximately −40° F. The fourth cooler  144  may provide a cooling stage to further reduce temperature of the liquefied ethane stream. This cooling stage can reduce temperature of the liquefied ethane stream by at least approximately 10° F., with one example of the fourth cooler  144  being configured so that the liquefied ethane stream exits this cooling stage (at  180 ) at approximately −50° F. 
     The fluid circuit  106  can direct the liquefied ethane stream to the first throttling device  170 . In one implementation, this device can be configured to reduce pressure of the liquefied ethane stream  116  from a first pressure to a second pressure that is less than the first pressure. The first pressure may correspond with the super critical pressure for incoming feedstock  102 . For liquid ethane, this super critical pressure may be approximately 800 psig or greater. The expansion stage can reduce pressure by at least approximately 700 psig. In one example, the first expansion unit  170  being configured so that the liquefied ethane stream exits this expansion stage (at  182 ) at approximately 100 psig. Expansion across the first throttling unit  170  may also provide a cooling stage to further lower the temperature of the process stream  108 , e.g., to approximately −58° F. 
     The fluid circuit  106  can process the liquefied ethane stream at the reduced pressure and reduced temperature to obtain the first product  108 . In use, the first product  108  will meet the methane concentration and other specifications for storage. Examples of these processes can form a top product and a bottom product at each of the vessels  154 ,  156 ,  158 . The top product can be in vapor form. The bottom product can be in liquid form and/or mixed-phase form (e.g., a combination of liquid and vapor), often depending on temperature and/or pressure of the resulting fluid. In one implementation, the fluid circuit  106  can be configured to direct a mixed-phase bottom product from the first vessel  154  to the second vessel  156 . The second throttling unit  172  can provide an expansion stage (and a cooling stage) to reduce pressure and temperature and produce a mixed-phase product between the vessels  154 ,  156 . For example, the mixed-phase product can exit the expansion/cooling stage (at  184 ) at approximately 8 psig and approximately −120° F. prior to entry into the second vessel  156 . 
     The fluid circuit  106  can be configured to combine the vapor top products from the vessels  154 ,  156  upstream of the fifth cooler  146 . In use, the fifth cooler  146  can provide a cooling stage so that the combined mixed phase product exits the cooling stage (at  186 ) at approximately −138° F. prior to entry into the third vessel  156 . The fluid circuit  106  can also combine the bottom product from the vessels  156 ,  158 , either in liquid form and/or mixed-phase form, as the process stream  116 . The sixth cooler  148  can provide a cooling stage so that the combined mixed phase bottom product exits the cooling stage (at  188 ) at approximately −132° F. and approximately 2 psig. 
     The fluid circuit  106  can direct the combined liquid bottom product to the flash drum  168  at a reduced temperature and pressure. The flash drum  168  can form a liquid product and a vapor product. The fluid circuit  106  can direct the liquid product to the storage facility  112  or elsewhere as desired. 
     As best shown in  FIG. 3 , the fluid circuit  106  can direct the vapor product from the flash drum  168  through the heat exchanger  202 . Downstream of the heat exchanger  202 , the fluid circuit  106  can combine the vapor product from the flash drum  168  with incoming return stream  126 , often the boil-off vapor that forms at the storage facility  112 . The compressors  206 ,  208  and the coolers  210 ,  212  can condition temperature and pressure of the combined vapor stream upstream of the heat exchanger  202 . The conditioned vapor flows onto the demethanizer column  162  via the heat exchanger  202 . 
     Referring back to  FIG. 2 , processes at the demethanizer column  162  can form a top product and a bottom product, typically in vapor phase and liquid (or mixed) phase, respectively. In one implementation, the bottom product exits the demethanizer column  162  to the third throttling device  174 . The third throttling device  174  can provide an expansion stage to reduce pressure (and temperature) of this bottom product between the second vessel  156  and the demethanizer column  162 . For example, the bottom product can enter the expansion stage (at  190 ) at approximately 470 psig and approximately 57° F. and exit the expansion stage (at  194 ) at approximately 8 psig and approximately −114° F. prior to entry into the second vessel  156 . 
     The fluid circuit  106  can be configured to recycle the top product from the demethanizer column  162 . The seventh cooler  150  may operate as an overhead condenser for the demethanizer column  162 . This overhead condenser can provide a cooling stage so that the top product exits the cooling stage (at  196 ) at approximately X° F. The cooled top product enters the fourth vessel  160 , operating here as a reflux drum. In turn, the fourth vessel  160  can form a top product and a bottom product. The pump  164  can pump the liquid bottom product from the fourth vessel  160  back to the demethanizer column  162 . The top product can be predominantly methane vapor that exits the system  100  as the second product  110  via the heat exchanger  202  ( FIG. 3 ). 
       FIGS. 4, 5, and 6  depict flow diagrams of an exemplary embodiment of a process  300  to prepare incoming liquid ethane (and, generally, feedstock  102 ) for storage. In  FIG. 4 , the process  300  can include, at stage  302 , distilling an incoming feedstock at a plurality of vessels to form a vapor and a liquid for storage. The process  300  can also include, at stage  304 , directing the vapor to a demethanizer column and, at stage  306 , circulating liquid from the demethanizer back to the plurality of vessels. As shown in  FIG. 5 , the process  300  can also include, at stage  308 , cooling the incoming feedstock upstream of the plurality of vessels and, at stage  310 , throttling flow of the incoming feedstock upstream of the plurality of vessels. 
     Referring also to  FIG. 6 , stage  302  in the process  300  can incorporate various stages to distill the incoming feedstock, as desired. In one implementation, these stages may include, at stage  312 , forming a first top product and a first bottom product from the incoming feedstock in a first vessel. The stages may also include, at stage  314 , directing the first bottom product and the liquid from the demethanizer column to a second vessel and, at stage  316 , separating the first bottom product into a second top product and a second bottom product in the second vessel. The stages may further include, at stage  318 , mixing the first top product with the second top product upstream of a third vessel, at stage  320 , cooling the first top product and the second top product upstream of the third vessel, and, at stage  322 , forming a third bottom product from the first top product and the second top product in the third vessel. 
     As used herein, an element or function recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the embodiments is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.