# Patent

## Title
Method and system for preventing accumulation of solids in a distillation tower

## Abstract

The present disclosure provides a method for preventing accumulation of solids in a distillation tower. The method includes introducing a feed stream into a controlled freeze zone section of a distillation tower; forming solids in the controlled freeze zone section from the feed stream; discontinuously injecting a first freeze-inhibitor solution into the controlled freeze zone section toward a location in the controlled freeze zone section that accumulates the solids; and destabilizing accumulation of the solids from the location with the first freeze-inhibitor solution.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority benefit of U.S. Provisional patent application No. 61/912,978 filed Dec. 6, 2013 entitled METHOD AND SYSTEM FOR PREVENTING ACCUMULATION OF SOLIDS IN A DISTILLATION TOWER, the entirety of which is incorporated by reference herein.
This application is related to but does not claim priority to U.S. Provisional patent application numbers: 61/912,957 filed on Dec. 6, 2013 entitled METHOD AND DEVICE FOR SEPARATING HYDROCARBONS AND CONTAMINANTS WITH A SPRAY ASSEMBLY; 62/044,770 filed on Sep. 2, 2014 entitled METHOD AND DEVICE FOR SEPARATING HYDROCARBONS AND CONTAMINANTS WITH A SPRAY ASSEMBLY; 61/912,959 filed on Dec. 6, 2013 entitled METHOD AND SYSTEM OF MAINTAINING A LIQUID LEVEL IN A DISTILLATION TOWER; 61/912,964 filed on Dec. 6, 2013 entitled METHOD AND DEVICE FOR SEPARATING A FEED STREAM USING RADIATION DETECTORS; 61/912,970 filed on Dec. 6, 2013 entitled METHOD AND SYSTEM OF DEHYDRATING A FEED STREAM PROCESSED IN A DISTILLATION TOWER; 61/912,975 filed on Dec. 6, 2013 entitled METHOD AND SYSTEM FOR SEPARATING A FEED STREAM WITH A FEED STREAM DISTRIBUTION MECHANISM; 61/912,983 filed on Dec. 6, 2013 entitled METHOD OF REMOVING SOLIDS BY MODIFYING A LIQUID LEVEL IN A DISTILLATION TOWER; 61/912,984 filed on Dec. 6, 2013 entitled METHOD AND SYSTEM OF MODIFYING A LIQUID LEVEL DURING START-UP OPERATIONS; 61/912,986 filed on Dec. 6, 2013 entitled METHOD AND DEVICE FOR SEPARATING HYDROCARBONS AND CONTAMINANTS WITH A HEATING MECHANISM TO DESTABILIZE AND/OR PREVENT ADHESION OF SOLIDS; 61/912,987 filed on Dec. 6, 2013 entitled METHOD AND DEVICE FOR SEPARATING HYDROCARBONS AND CONTAMINANTS WITH A SURFACE TREATMENT MECHANISM.


BACKGROUND
Fields of Disclosure
The disclosure relates generally to the field of fluid separation. More specifically, the disclosure relates to the cryogenic separation of contaminants, such as acid gas, from a hydrocarbon.
Description of Related Art
This section is intended to introduce various aspects of the art, which may be associated with the present disclosure. This discussion is intended to provide a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
The production of natural gas hydrocarbons, such as methane and ethane, from a reservoir oftentimes carries with it the incidental production of non-hydrocarbon gases. Such gases include contaminants, such as at least one of carbon dioxide (“CO2”), hydrogen sulfide (“H2S”), carbonyl sulfide, carbon disulfide and various mercaptans. When a feed stream being produced from a reservoir includes these contaminants mixed with hydrocarbons, the stream is oftentimes referred to as “sour gas.”
Many natural gas reservoirs have relatively low percentages of hydrocarbons and relatively high percentages of contaminants. Contaminants may act as a diluent and lower the heat content of hydrocarbons. Some contaminants, like sulfur-bearing compounds, are noxious and may even be lethal. Additionally, in the presence of water some contaminants can become quite corrosive.
It is desirable to remove contaminants from a stream containing hydrocarbons to produce sweet and concentrated hydrocarbons. Specifications for pipeline quality natural gas typically call for a maximum of 2-4% CO2 and 1⁄4grain H2S per 100 scf (4 ppmv) or 5 mg/Nm3 H2S. Specifications for lower temperature processes such as natural gas liquefaction plants or nitrogen rejection units typically require less than 50 ppm CO2.
The separation of contaminants from hydrocarbons is difficult and consequently significant work has been applied to the development of hydrocarbon/contaminant separation methods. These methods can be placed into three general classes: absorption by solvents (physical, chemical and hybrids), adsorption by solids, and distillation.
Separation by distillation of some mixtures can be relatively simple and, as such, is widely used in the natural gas industry. However, distillation of mixtures of natural gas hydrocarbons, primarily methane, and one of the most common contaminants in natural gas, carbon dioxide, can present significant difficulties. Conventional distillation principles and conventional distillation equipment are predicated on the presence of only vapor and liquid phases throughout the distillation tower. The separation of CO2 from methane by distillation involves temperature and pressure conditions that result in solidification of CO2 if a pipeline or better quality hydrocarbon product is desired. The required temperatures are cold temperatures typically referred to as cryogenic temperatures.
Certain cryogenic distillations can overcome the above mentioned difficulties. These cryogenic distillations provide the appropriate mechanism to handle the formation and subsequent melting of solids during the separation of solid-forming contaminants from hydrocarbons. The formation of solid contaminants in equilibrium with vapor-liquid mixtures of hydrocarbons and contaminants at particular conditions of temperature and pressure takes place in a controlled freeze zone section.
Sometimes solids can adhere to an internal (e.g., controlled freeze zone wall) of the controlled freeze zone section rather than falling to the bottom of the controlled freeze zone section.
The accumulation is disadvantageous. The accumulation can interfere with the proper operation of the controlled freeze zone and the effective separation of methane from the contaminants.
A need exists for improved technology, including technology that may prevent accumulation of solids in the controlled freeze zone.
SUMMARY
The present disclosure provides a device and method for separating contaminants from hydrocarbons, among other things.
A method for preventing accumulation of solids in a distillation tower may comprise introducing a feed stream into a controlled freeze zone section of a distillation tower; forming solids in the controlled freeze zone section from the feed stream; discontinuously injecting a first freeze-inhibitor solution into the controlled freeze zone section toward a location in the controlled freeze zone section that accumulates the solids; and destabilizing accumulation of the solids from the location with the first freeze-inhibitor solution.
A method for producing hydrocarbons may comprise introducing a feed stream into a controlled freeze zone section of a distillation tower; forming solids in the controlled freeze zone section from the feed stream; discontinuously injecting a first freeze-inhibitor solution into the controlled freeze zone section toward a location in the controlled freeze zone section that accumulates the solids; destabilizing accumulation of the solids from the location with the first freeze-inhibitor solution; and producing hydrocarbons from the feed stream.
A distillation tower that prevents accumulation of solids in the distillation tower may comprise a stripper section constructed and arranged to separate a feed stream in the distillation tower at a temperature and pressure at which the feed stream forms no solid; and a controlled freeze zone section constructed and arranged to separate the feed stream in the distillation tower at a temperature and pressure at which the feed stream forms solids. The controlled freeze zone section may comprise a first freeze-inhibitor injection mechanism constructed and arranged to inject a first freeze-inhibitor solution in the controlled freeze zone section discontinuously.
The foregoing has broadly outlined the features of the present disclosure in order that the detailed description that follows may be better understood. Additional features will also be described herein.



BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects and advantages of the disclosure will become apparent from the following description, appending claims and the accompanying drawings, which are briefly described below.
FIG. 1 is a schematic diagram of a tower with sections within a single vessel.
FIG. 2 is a schematic diagram of a tower with sections within multiple vessels.
FIG. 3 is a schematic diagram of a tower with sections within a single vessel.
FIG. 4 is a schematic diagram of a tower with sections within multiple vessels.
FIG. 5 is a schematic diagram of a middle controlled freeze zone section and a lower section.
FIG. 6 is a schematic diagram of an upper section.
FIG. 7 is a flowchart of a method within the scope of the present disclosure.



It should be noted that the figures are merely examples and no limitations on the scope of the present disclosure are intended thereby. Further, the figures are generally not drawn to scale, but are drafted for purposes of convenience and clarity in illustrating various aspects of the disclosure.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the features illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications, and any further applications of the principles of the disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. It will be apparent to those skilled in the relevant art that some features that are not relevant to the present disclosure may not be shown in the drawings for the sake of clarity.
As referenced in this application, the terms “stream,” “gas stream,” “vapor stream,” and “liquid stream” refer to different stages of a feed stream as the feed stream is processed in a distillation tower that separates methane, the primary hydrocarbon in natural gas, from contaminants. Although the phrases “gas stream,” “vapor stream,” and “liquid stream,” refer to situations where a gas, vapor, and liquid is mainly present in the stream, respectively, there may be other phases also present within the stream. For example, a gas may also be present in a “liquid stream.” In some instances, the terms “gas stream” and “vapor stream” may be used interchangeably.
The disclosure relates to a system and method that separates a feed stream in a distillation tower. The system and method help prevent the accumulation of solids in a distillation tower by discontinuously injecting a first freeze-inhibitor solution in a middle controlled freeze zone section of the distillation tower. The system and method may also help prevent the accumulation of solids in a distillation tower by injecting a second freeze-inhibitor solution in an upper section of the distillation tower. The first and the second freeze-inhibitor solutions destabilize accumulated solids so that the accumulated solids are dislodged and further accumulation of solids is prevented in the middle controlled freeze zone section and/or the upper section. FIGS. 1-7 of the disclosure display various aspects of the system and method.
The system and method may separate a feed stream having methane and contaminants. The system may comprise a distillation tower 104, 204 (FIGS. 1-2). The distillation tower 104, 204 may separate the contaminants from the methane.
The distillation tower 104, 204 may be separated into three functional sections: a lower section 106, a middle controlled freeze zone section 108 and an upper section 110. The distillation tower 104, 204 may incorporate three functional sections when the upper section 110 is needed and/or desired.
The distillation tower 104, 204 may incorporate only two functional sections when the upper section 110 is not needed and/or desired. When the distillation tower does not include an upper section 110, a portion of vapor leaving the middle controlled freeze zone section 108 may be condensed in a condenser 122 and returned as a liquid stream via a spray assembly 129. Moreover, lines 18 and 20 may be eliminated, elements 124 and 126 may be one and the same, and elements 150 and 128 may be one and the same. The stream in line 14, now taking the vapors leaving the middle controlled freeze section 108, directs these vapors to the condenser 122.
The lower section 106 may also be referred to as a stripper section. The middle controlled freeze zone section 108 may also be referred to as a controlled freeze zone section. The upper section 110 may also be referred to as a rectifier section.
The sections of the distillation tower 104 may be housed within a single vessel (FIGS. 1 and 3). For example, the lower section 106, the middle controlled freeze zone section 108, and the upper section 110 may be housed within a single vessel 164.
The sections of the distillation tower 204 may be housed within a plurality of vessels to form a split-tower configuration (FIGS. 2 and 4). Each of the vessels may be separate from the other vessels. Piping and/or another suitable mechanism may connect one vessel to another vessel. In this instance, the lower section 106, middle controlled freeze zone section 108 and upper section 110 may be housed within two or more vessels. For example, as shown in FIGS. 2 and 4, the upper section 110 may be housed within a single vessel 254 and the lower and middle controlled freeze zone sections 106, 108 may be housed within a single vessel 264. When this is the case, a liquid stream exiting the upper section 110, may exit through a liquid outlet bottom 260. The liquid outlet bottom 260 is at the bottom of the upper section 110. Although not shown, each of the sections may be housed within its own separate vessel, or one or more section may be housed within separate vessels, or the upper and middle controlled freeze zone sections may be housed within a single vessel and the lower section may be housed within a single vessel, etc. When sections of the distillation tower are housed within vessels, the vessels may be side-by-side along a horizontal line and/or above each other along a vertical line.
The split-tower configuration may be beneficial in situations where the height of the distillation tower, motion considerations, and/or transportation issues, such as for remote locations, need to be considered. This split-tower configuration allows for the independent operation of one or more sections. For example, when the upper section is housed within a single vessel and the lower and middle controlled freeze zone sections are housed within a single vessel, independent generation of reflux liquids using a substantially contaminant-free, largely hydrocarbon stream from a packed gas pipeline or an adjacent hydrocarbon line, may occur in the upper section. And the reflux may be used to cool the upper section, establish an appropriate temperature profile in the upper section, and/or build up liquid inventory at the bottom of the upper section to serve as an initial source of spray liquids for the middle controlled freeze zone section. Moreover, the middle controlled freeze zone and lower sections may be independently prepared by chilling the feed stream, feeding it to the optimal location be that in the lower section or in the middle controlled freeze zone section, generating liquids for the lower and the middle controlled freeze zone sections, and disposing the vapors off the middle controlled freeze zone section while they are off specification with too high a contaminant content. Also, liquid from the upper section may be intermittently or continuously sprayed, building up liquid level in the bottom of the middle controlled freeze zone section and bringing the contaminant content in the middle controlled freeze zone section down and near steady state level so that the two vessels may be connected to send the vapor stream from the middle controlled freeze zone section to the upper section, continuously spraying liquid from the bottom of the upper section into the middle controlled freeze zone section and stabilizing operations into steady state conditions. The split tower configuration may utilize a sump of the upper section as a liquid receiver for the pump 128, therefore obviating the need for a liquid receiver 126 in FIGS. 1 and 3.
The system may also include a heat exchanger 100 (FIGS. 1-4). The feed stream 10 may enter the heat exchanger 100 before entering the distillation tower 104, 204. The feed stream 10 may be cooled within the heat exchanger 100. The heat exchanger 100 helps drop the temperature of the feed stream 10 to a level suitable for introduction into the distillation tower 104, 204.
The system may include an expander device 102 (FIGS. 1-4). The feed stream 10 may enter the expander device 102 before entering the distillation tower 104, 204. The feed stream 10 may be expanded in the expander device 102 after exiting the heat exchanger 100. The expander device 102 helps drop the temperature of the feed stream 10 to a level suitable for introduction into the distillation tower 104, 204. The expander device 102 may be any suitable device, such as a valve. If the expander device 102 is a valve, the valve may be any suitable valve that may aid in cooling the feed stream 10 before it enters the distillation tower 104, 204. For example, the valve 102 may comprise a Joule-Thompson (J-T) valve.
The system may include a feed separator 103 (FIGS. 3-4). The feed stream may enter the feed separator before entering the distillation tower 104, 204. The feed separator may separate a feed stream having a mixed liquid and vapor stream into a liquid stream and a vapor stream. Lines 12 may extend from the feed separator to the distillation tower 104, 204. One of the lines 12 may receive the vapor stream from the feed separator. Another one of the lines 12 may receive the liquid stream from the feed separator. Each of the lines 12 may extend to the same and/or different sections (i.e. middle controlled freeze zone, and lower sections) of the distillation tower 104, 204. The expander device 102 may or may not be downstream of the feed separator 103. The expander device 102 may comprise a plurality of expander devices 102 such that each line 12 has an expander device 102.
The system may include a dehydration unit 261 (FIGS. 1-4). The feed stream 10 may enter the dehydration unit 261 before entering the distillation tower 104, 204. The feed stream 10 enters the dehydration unit 261 before entering the heat exchanger 100 and/or the expander device 102. The dehydration unit 261 removes water from the feed stream 10 to prevent water from later presenting a problem in the heat exchanger 100, expander device 102, feed separator 103, or distillation tower 104, 204. The water can present a problem by forming a separate water phase (i.e., ice and/or hydrate) that plugs lines, equipment or negatively affects the distillation process. The dehydration unit 261 dehydrates the feed stream to a dew point sufficiently low to ensure a separate water phase does not form at any point downstream during the rest of the process. The dehydration unit may be any suitable dehydration mechanism, such as a molecular sieve or a glycol dehydration unit.
The system may include a filtering unit (not shown). The feed stream 10 may enter the filtering unit before entering the distillation tower 104, 204. The filtering unit may remove undesirable contaminants from the feed stream before the feed stream enters the distillation tower 104, 204. Depending on what contaminants are to be removed, the filtering unit may be before or after the dehydration unit 261 and/or before or after the heat exchanger 100.
The system may include a line 12 (FIGS. 1-4). The line may also be referred to as an inlet channel 12. The feed stream 10 may be introduced into the distillation tower 104, 204 through the line 12. The line 12 may extend to the lower section 106 or the middle controlled freeze zone section 108 of the distillation tower 104, 204. For example, the line 12 may extend to the lower section 106 such that the feed stream 10 may enter the lower section 106 of the distillation tower 104, 204 (FIGS. 1-4). The line 12 may directly or indirectly extend to the lower section 106 or the middle controlled freeze zone section 108. The line 12 may extend to an outer surface of the distillation tower 104, 204 before entering the distillation tower.
If the system includes the feed separator 103 (FIGS. 3-4), the line 12 may comprise a plurality of lines 12. Each line may be the same line as one of the lines that extends from the feed separator to a specific portion of the distillation tower 104, 204.
The lower section 106 is constructed and arranged to separate the feed stream 10 into an enriched contaminant bottom liquid stream (i.e., liquid stream) and a freezing zone vapor stream (i.e., vapor stream). The lower section 106 separates the feed stream at a temperature and pressure at which no solids form. The liquid stream may comprise a greater quantity of contaminants than of methane. The vapor stream may comprise a greater quantity of methane than of contaminants. In any case, the vapor stream is lighter than the liquid stream. As a result, the vapor stream rises from the lower section 106 and the liquid stream falls to the bottom of the lower section 106.
The lower section 106 may include and/or connect to equipment that separates the feed stream. The equipment may comprise any suitable equipment for separating methane from contaminants, such as one or more packed sections 181, or one or more distillation trays with perforations downcomers and weirs (FIGS. 1-4).
The equipment may include components that apply heat to the stream to form the vapor stream and the liquid stream. For example, the equipment may comprise a first reboiler 112 that applies heat to the stream. The first reboiler 112 may be located outside of the distillation tower 104, 204. The equipment may also comprise a second reboiler 172 that applies heat to the stream. The second reboiler 172 may be located outside of the distillation tower 104, 204. Line 117 may lead from the distillation tower to the second reboiler 172. Line 17 may lead from the second reboiler 172 to the distillation tower. Additional reboilers, set up similarly to the second reboiler described above, may also be used.
The first reboiler 112 may apply heat to the liquid stream that exits the lower section 106 through a liquid outlet 160 of the lower section 106. The liquid stream may travel from the liquid outlet 160 through line 28 to reach the first reboiler 112 (FIGS. 1-4). The amount of heat applied to the liquid stream by the first reboiler 112 can be increased to separate more methane from contaminants. The more heat applied by the reboiler 112 to the stream, the more methane separated from the liquid contaminants, though more contaminants will also be vaporized.
The first reboiler 112 may also apply heat to the stream within the distillation tower 104, 204. Specifically, the heat applied by the first reboiler 112 warms up the lower section 106. This heat travels up the lower section 106 and supplies heat to warm solids entering a melt tray assembly 139 (FIGS. 1-4) of the middle controlled freeze zone section 108 so that the solids form a liquid and/or slurry mix.
The second reboiler 172 applies heat to the stream within the lower section 106. This heat is applied closer to the middle controlled freeze zone section 108 than the heat applied by the first reboiler 112. As a result, the heat applied by the second reboiler 172 reaches the middle controlled freeze zone section 108 faster than the heat applied by the first reboiler 112. The second reboiler 172 also helps with energy integration.
The equipment may include a chimney assembly 135 (FIGS. 1-4). While falling to the bottom of the lower section 106, the liquid stream may encounter one or more of the chimney assemblies 135.
Each chimney assembly 135 includes a chimney tray 131 that collects the liquid stream within the lower section 106. The liquid stream that collects on the chimney tray 131 may be fed to the second reboiler 172. After the liquid stream is heated in the second reboiler 172, the stream may return to the middle controlled freeze zone section 108 to supply heat to the middle controlled freeze zone section 108 and/or the melt tray assembly 139. Unvaporized stream exiting the second reboiler 172 may be fed back to the distillation tower 104, 204 below the chimney tray 131. Vapor stream exiting the second reboiler 172 may be routed under or above the chimney tray 131 when the vapor stream enters the distillation tower 104, 204.
Each chimney 137 has attached to it a chimney cap 133. The chimney 137 serves as a channel that the vapor stream in the lower section 106 traverses. The vapor stream travels through an opening in the chimney tray 131 at the bottom of the chimney 137 to the top of the chimney 137. The opening is closer to the bottom of the lower section 106 than it is to the bottom of the middle controlled freeze zone section 108. The top is closer to the bottom of the middle controlled freeze zone section 108 than it is to the bottom of the lower section 106.
Each chimney assembly 135 includes a chimney cap 133. The chimney cap 133 covers a chimney top opening 138 of the chimney 137. The chimney cap 133 prevents the liquid stream from entering the chimney 137. The vapor stream exits the chimney assembly 135 via the chimney top opening 138.
After falling to the bottom of the lower section 106, the liquid stream exits the distillation tower 104, 204 through the liquid outlet 160. The liquid outlet 160 is within the lower section 106 (FIGS. 1-4). The liquid outlet 160 may be located at the bottom of the lower section 106.
After exiting through the liquid outlet 160, the feed stream may travel via line 28 to the first reboiler 112. The feed stream may be heated by the first reboiler 112 and vapor may then re-enter the lower section 106 through line 30. Unvaporized liquid may continue out of the distillation process via line 24.
The system may include an expander device 114 (FIGS. 1-4). After entering line 24, the heated liquid stream may be expanded in the expander device 114. The expander device 114 may be any suitable device, such as a valve. The valve 114 may be any suitable valve, such as a J-T valve.
The system may include a heat exchanger 116 (FIGS. 1-4). The liquid stream heated by the first reboiler 112 may be cooled or heated by the heat exchanger 116. The heat exchanger 116 may be a direct heat exchanger or an indirect heat exchanger. The heat exchanger 116 may comprise any suitable heat exchanger.
The vapor stream in the lower section 106 rises from the lower section 106 to the middle controlled freeze zone section 108. The middle controlled freeze zone section 108 is constructed and arranged to separate the feed stream 10 introduced into the middle controlled freeze zone section, or into the top of lower section 106, into a solid and a vapor stream. The solid may be comprised more of contaminants than of methane. The vapor stream (i.e., methane-enriched vapor stream) may comprise more methane than contaminants.
The middle controlled freeze zone section 108 includes a lower section 40 and an upper section 39 (FIG. 5). The lower section 40 is below the upper section 39. The lower section 40 directly abuts the upper section 39. The lower section 40 is primarily but not exclusively a heating section of the middle controlled freeze zone section 108. The upper section 39 is primarily but not exclusively a cooling section of the middle controlled freeze zone section 108. The temperature and pressure of the upper section 39 are chosen so that the solid can form in the middle controlled freeze zone section 108.
The middle controlled freeze zone section 108 may comprise a melt tray assembly 139 that is maintained in the middle controlled freeze zone section 108 (FIGS. 1-5). The melt tray assembly 139 is within the lower section 40 of the middle controlled freeze zone section 108. The melt tray assembly 139 is not within the upper section 39 of the middle controlled freeze zone section 108.
The melt tray assembly 139 is constructed and arranged to melt solids formed in the middle controlled freeze zone section 108. When the warm vapor stream rises from the lower section 106 to the middle controlled freeze zone section 108, the vapor stream immediately encounters the melt tray assembly 139 and supplies heat to melt the solids. The melt tray assembly 139 may comprise at least one of a melt tray 118, a bubble cap 132, a liquid 130 and heat mechanism(s) 134.
The melt tray 118 may collect a liquid and/or slurry mix. The melt tray 118 divides at least a portion of the middle controlled freeze zone section 108 from the lower section 106. The melt tray 118 is at the bottom 45 of the middle controlled freeze zone section 108.
One or more bubble caps 132 may act as a channel for the vapor stream rising from the lower section 106 to the middle controlled freeze zone section 108. The bubble cap 132 may provide a path for the vapor stream up the riser 140 and then down and around the riser 140 to the melt tray 118. The riser 140 is covered by a cap 141. The cap 141 prevents the liquid 130 from travelling into the riser and it also helps prevent solids from travelling into the riser 140. The vapor stream's traversal through the bubble cap 132 allows the vapor stream to transfer heat to the liquid 130 within the melt tray assembly 139.
One or more heat mechanisms 134 may further heat up the liquid 130 to facilitate melting of the solids into a liquid and/or slurry mix. The heat mechanism(s) 134 may be located anywhere within the melt tray assembly 139. For example, as shown in FIGS. 1-4, a heat mechanism 134 may be located around bubble caps 132. The heat mechanism 134 may be any suitable mechanism, such as a heat coil. The heat source of the heat mechanism 134 may be any suitable heat source.
The liquid 130 in the melt tray assembly is heated by the vapor stream. The liquid 130 may also be heated by the one or more heat mechanisms 134. The liquid 130 helps melt the solids formed in the middle controlled freeze zone section 108 into a liquid and/or slurry mix. Specifically, the heat transferred by the vapor stream heats up the liquid, thereby enabling the heat to melt the solids. The liquid 130 is at a level sufficient to melt the solids.
The middle controlled freeze zone section 108 may also comprise a spray assembly 129. The spray assembly 129 cools the vapor stream that rises from the lower section 40. The spray assembly 129 sprays liquid, which is cooler than the vapor stream, on the vapor stream to cool the vapor stream. The liquid sprayed from the spray assembly 129 may also be referred to as a spray stream. The spray assembly 129 is within the upper section 39. The spray assembly 129 is not within the lower section 40. The spray assembly 129 is above the melt tray assembly 139. In other words, the melt tray assembly 139 is below the spray assembly 129.
The spray assembly 129 includes one or more spray nozzles 120 (FIGS. 1-4). Each spray nozzle 120 sprays liquid on the vapor stream. The spray assembly 129 may also include a spray pump 128 (FIGS. 1-4) that pumps the liquid. Instead of a spray pump 128, gravity may induce flow in the liquid.
The liquid sprayed by the spray assembly 129 contacts the vapor stream at a temperature and pressure at which solids form. Solids, containing mainly contaminants, form when the sprayed liquid contacts the vapor stream. The solids fall toward the melt tray assembly 139.
The temperature in the middle controlled freeze zone section 108 cools down as the vapor stream travels from the bottom of the middle controlled freeze zone section 108 to the top of the middle controlled freeze zone section 108. The methane in the vapor stream rises from the middle controlled freeze zone section 108 to the upper section 110. Some contaminants may remain in the methane and also rise. The contaminants in the vapor stream tend to condense or solidify with the colder temperatures and fall to the bottom of the middle controlled freeze zone section 108.
The solids form the liquid and/or slurry mix when in the liquid 130. The liquid and/or slurry mix flows from the middle controlled freeze zone section 108 to the lower distillation section 106. The liquid and/or slurry mix flows from the bottom of the middle controlled freeze zone section 108 to the top of the lower section 106 via a line 22 (FIGS. 1-4). The line 22 may be an exterior line. The line 22 may extend from the distillation tower 104, 204. The line 22 may extend from the middle controlled freeze zone section 108. The line may extend to the lower section 106. The line 22 may extend from an outer surface of the distillation tower 104, 204.
The middle controlled freeze zone section 108 may also include a first freeze-inhibitor injection mechanism 270 (FIG. 5). The first freeze-inhibitor injection mechanism 270 is constructed and arranged to inject a first freeze-inhibitor solution in the middle controlled freeze zone section 108. The first freeze-inhibitor injection mechanism 270 may inject the first freeze-inhibitor solution discontinuously 303 (FIG. 7). The first freeze-inhibitor injection mechanism 270 may inject the first freeze-inhibitor solution discontinuously because solids often build-up only on an occasional basis, such as during upset conditions. The first freeze-inhibitor injection mechanism 270 may also inject the first freeze-inhibitor solution continuously. But the continuous injection may lead to undesirable side-effects, such as changing the temperature profile of the system. Continuous injection may also be expensive.
The first freeze-inhibitor injection mechanism 270 introduces and directs the first freeze-inhibitor solution into the middle controlled freeze zone section 108. The first freeze-inhibitor injection mechanism directs the first freeze-inhibitor solution toward a location in the middle controlled freeze zone section 108 where solids are likely to accumulate in the middle controlled freeze zone section 108. For example, the location may be at least one of the spray assembly 129, a controlled freeze zone wall 46 (FIG. 5) of the middle controlled freeze zone section 108, etc. If the location is the controlled freeze zone wall 46, the first freeze-inhibitor injection mechanism 270 may comprise a first freeze-inhibitor injection piping arrangement adjacent to the controlled freeze zone wall 46. The first freeze-inhibitor injection piping arrangement may be coupled to the controlled freeze zone wall 46 or otherwise connected to the controlled freeze zone wall 46. The first freeze-inhibitor injection piping arrangement may be any suitable piping arrangement. Once the first freeze-inhibitor solution contacts the location, solid that has accumulated on the location destabilizes 304 (FIG. 7). The first freeze-inhibitor injection mechanism 270 may have to repeatedly introduce and direct the first freeze-inhibitor solution toward the location to destabilize accumulation of all of the solid that has accumulated at the location.
The first freeze-inhibitor injection mechanism 270 may be located anywhere within the middle controlled freeze zone section 108 where the first freeze-inhibitor mechanism 270 can direct first freeze-inhibitor solution at the location in the middle controlled freeze zone section 108 that is likely to accumulate solids. For example, the first freeze-inhibitor injection mechanism 270 may be within the spray assembly 129 or on the controlled freeze zone wall 46. If the first freeze-inhibitor injection mechanism 270 is within the spray assembly 129, the first freeze-inhibitor injection mechanism 270 may contribute 1 to 5% molar ratios into the middle controlled freeze zone section 108 to that of the stream sprayed from the spray assembly 129 into the middle controlled freeze zone section 108.
The first freeze-inhibitor injection mechanism 270 may be constructed and arranged to independently control at least one of a flow rate of the first freeze-inhibitor solution, a temperature of the first freeze-inhibitor solution, and an angle of the first freeze-inhibitor solution when the first freeze-inhibitor solution is sprayed by the first freeze-inhibitor injection mechanism 270. The flow rate of the first freeze-inhibitor solution may be such that it is dependent on some estimated measure of accumulated solid. The temperature of the first freeze-inhibitor solution may be the same as the temperature of the feed stream sprayed by the spray assembly 129, the portion of the middle controlled freeze zone section 108 sprayed by the first freeze-inhibitor solution or higher than the melting temperature of the solid contaminants in the middle controlled freeze zone section 108. When the temperature of the first freeze-inhibitor solution is higher than the melting temperature of the solid contaminants in the middle controlled freeze zone section 108, the first freeze-inhibitor solution may be able to melt the solid faster than when the temperature of the first freeze-inhibitor solution is that of the feed stream sprayed by the spray assembly 129 or the portion of the middle controlled freeze zone section 108 sprayed by the first freeze-inhibitor solution. The angle of the first freeze-inhibitor solution may be any angle that sprays the first freeze-inhibitor solution at the location.
The first freeze-inhibitor solution may be any CO2 solubilizing solvent that remains unfrozen in the middle controlled freeze zone section 108. For example, the first freeze-inhibitor solution may comprise at least one of light hydrocarbons and light alcohols. The first freeze-inhibitor solution may comprise at least one of ethane, ethanol, methanol, propane, butane, light olefins (e.g., ethylene), light ethers (e.g. dimethyl ether), acetylene, and H2S. Other examples of first freeze-inhibitor solution are also contemplated.
One or more temperature sensors 36 (FIG. 5) may help determine whether the first freeze-inhibitor injection mechanism 270 needs to repeatedly, discontinuously inject the first freeze-inhibitor solution into the middle controlled freeze zone section 108 toward the location. A transmitter and receiver may help each temperature sensor 36 communicate with the first freeze-inhibitor injection mechanism 270. For example, for a given temperature sensor, the signal received by the transmitter may be compared with a value that may be indicative of solids covering the temperature sensor 36. If the signal received by the transmitter exceeds a certain value, it would be possible to send a signal to the first freeze-inhibitor injection mechanism 270 to inject the first freeze-inhibitor solution. For example, a signal may be sent to a pump and/or valve of the first freeze-inhibitor injection mechanism 270 for the pump to turn on and/or the valve to open.
Each temperature sensor 36 may be coupled to the same and/or a different mechanical component. The temperature sensor 36 detects the temperature of the mechanical component. The mechanical component may be the distillation tower 104, 204 and/or included in the distillation tower 104, 204. For example, to detect whether solids have adhered to the controlled freeze zone wall 46 of the middle controlled freeze zone section 108, the mechanical component may be the controlled freeze zone wall 46. If the mechanical component is the controlled freeze zone wall 46, the mechanical component may be an internal surface 31 or an external surface 47 of the controlled freeze zone wall 46 (FIG. 5). The internal surface 31 is the innermost surface of the controlled freeze zone wall 46 and is on an inner surface of the middle controlled freeze zone section 108. The external surface 47 is the outermost surface of the controlled freeze zone wall 46 and is on an outer surface of the middle controlled freeze zone section 108.
Before the distillation tower 104, 204 forms any solid, each temperature sensor 36 detects a baseline temperature of the mechanical component. The baseline temperature is within an expected temperature range. After the distillation tower 104, 204 forms a solid, a temperature sensor 36 may detect an alternative temperature. The temperature sensor 36 may detect the alternative temperature a plurality of times and/or at different intervals in time. The alternative temperature is compared to the expected temperature range to see whether the distillation tower 104, 204 is operating normally. The expected temperature range is a range of temperatures that indicate that the distillation tower 104, 204 is operating normally. Different areas of the distillation tower 104, 204 may have their own expected temperature range that is specific to the nature and purpose of that particular section of the distillation tower 104, 204.
The distillation tower 104, 204 is not operating normally when one or more of a variety of circumstances has occurred. The variety of circumstances may include if solids accumulate on a mechanical component in the middle controlled freeze zone section 108, if the middle controlled freeze zone section 108 is too warm to form solids, if the middle controlled freeze zone section 108 is too cold to melt the solids in the melt tray assembly 139, etc. For example, if the temperature sensor 36 is coupled to the controlled freeze zone external surface 47 within the upper section 39 of the middle controlled freeze zone section 108 then the temperature sensor 36 is expected to detect a fairly cold temperature that is close to the actual temperature of the spray stream within the middle controlled freeze zone section 108. If, in this example, the temperature sensor 36 detects a rise in temperature from that expected of the actual temperature of the feed stream, solids have built-up on the controlled freeze zone wall 46. In other words, if the detected temperature is outside of the expected temperature range by a positive amount then solids have built-up on the controlled freeze zone wall 46. The solids act as an insulator, so solid accumulation is determined when there is an unexpected rise in temperature read by the temperature sensor 36 that is a positive amount outside of the expected temperature range.
Steady state CO2 material balance calculations could be performed around the system to detect the adhesion and/or accumulation of solids in the middle controlled freeze zone section 108. At steady state, the amount of CO2 flowing into the system with the feed stream should substantially equal the sum of i) the amount of CO2 leaving the distillation tower 104, 204 via line 16 and ii) the CO2 leaving the lower section 110 of the distillation tower 104, 204 via the liquid outlet 24. If the amount of CO2 entering the system measurably exceeds the CO2 leaving the system, then CO2 is accumulating in the system, possibly as adhered solid in the middle controlled freeze zone section 108. The amount of CO2 entering the system may be determined by multiplying the feed stream mass flow rate times the CO2 weight percent at the inlet of the distillation tower 104, 204 to obtain a mass CO2 entering/unit time. The amount of CO2 exiting the distillation tower 104, 204 via line 16 and/or liquid outlet 24 may be determined by multiplying the relevant exiting gas (or liquid) mass flow rates times their respective CO2 weight percent, and summing them to obtain a mass CO2 exiting/unit time. The difference of CO2 entering minus CO2 exiting represents the instantaneous rate of CO2 mass accumulation (or loss) in the system at that point in time. By collecting a series of these differences and multiplying them by appropriate time increments, it is possible to sum those products together to determine if there is a net gain (or loss) of CO2 in the system over that period. These measurements may be facilitated by the use of Coriolis flow meters, which measure mass flow rates directly and accurately.
Because what would otherwise appear to indicate an accumulation of CO2 in the middle controlled freeze zone section 108 may be due to increasing liquid levels in the middle controlled freeze zone section 108, corrections may be made for changing levels of fluid that contain CO2 (e.g., melt tray assembly liquid level, reboiler liquid level). Appropriate factors may be considered to convert these liquid level changes to mass changes. The mass changes may then be multiplied by their respective CO2 weight percent. If the total apparent CO2 accumulation as calculated by material balance exceeds the CO2 accumulation as measured by changing liquid levels, then solids may be building in the middle controlled freeze zone section 108 of the distillation tower 104, 204.
The vapor stream that rises in the middle controlled freeze zone section 108 and does not form solids or otherwise fall to the bottom of the middle controlled freeze zone section 108, rises to the upper section 110. The upper section 110 operates at a temperature and pressure and contaminant concentration at which no solid forms. The upper section 110 is constructed and arranged to cool the vapor stream to separate the methane from the contaminants. Reflux in the upper section 110 cools the vapor stream. The reflux is introduced into the upper section 110 via line 18. Line 18 may extend to the upper section 110. Line 18 may extend from an outer surface of the distillation tower 104, 204.
After contacting the reflux in the upper section 110, the feed stream forms a vapor stream and a liquid stream. The vapor stream mainly comprises methane. The liquid stream comprises relatively more contaminants. The vapor stream rises in the upper section 110 and the liquid falls to a bottom of the upper section 110.
To facilitate separation of the methane from the contaminants when the stream contacts the reflux, the upper section 110 may include one or more mass transfer devices 176. Each mass transfer device 176 helps separate the methane from the contaminants. Each mass transfer device 176 may comprise any suitable separation device, such as a tray with perforations, or a section of random or structured packing to facilitate contact of the vapor and liquid phases.
In addition to including one or more mass transfer devices 176, the upper section may also include a second freeze-inhibitor injection mechanism 370 (FIG. 6). The second freeze-inhibitor injection mechanism 370 is constructed and arranged to inject a second freeze-inhibitor solution in the upper section 110. The second freeze-inhibitor injection mechanism 370 may inject the second freeze-inhibitor solution 370 discontinuously. The second freeze-inhibitor injection mechanism 370 may inject the second freeze-inhibitor solution discontinuously because solids often only build-up on an occasional basis, such as during upset conditions. The second freeze-inhibitor injection mechanism 370 may also inject the second freeze-inhibitor solution continuously. But the continuous injection may lead to undesirable side-effects, such as changing the temperature profile of the system. Continuous injection may also be expensive. Generally speaking, the upper section 110 is less likely to need a freeze-inhibitor injection mechanism than the middle controlled freeze zone section 108, because unlike the middle controlled freeze zone section 108 is not constructed and arranged to form solids. However, if solids do form in the upper section, a freeze-inhibitor injection mechanism in the upper section could help prevent the accumulation of solids in the upper section.
The second freeze-inhibitor injection mechanism 370 introduces and directs the second freeze-inhibitor solution into the upper section 110. The second freeze-inhibitor injection mechanism may direct the second freeze-inhibitor solution toward at least one of the one or more mass transfer devices 176 and/or toward the bottom of the upper section 110. If the second-freeze inhibitor injection mechanism 370 directs the second freeze-inhibitor injection solution toward at least one of the one or more mass transfer devices 176, the at least one of the one or more mass transfer devices 176 may help distribute the second freeze-inhibitor injection solution in the upper section to prevent accumulation of solids in the upper section.
The second freeze-inhibitor injection mechanism 370 may be located at any suitable location in the upper section 110. For example, the second freeze-inhibitor injection mechanism 370 may be located at an upper section wall 346 of the upper section 110.
The second freeze-inhibitor injection mechanism 370 may comprise any suitable mechanism. For example, the second freeze-inhibitor injection mechanism 370 may comprise a second freeze-inhibitor injection piping arrangement. The second freeze-inhibitor piping arrangement may be adjacent to the upper section wall 346. The second freeze-inhibitor injection piping arrangement may be coupled to the upper section wall 346 or otherwise connected to the upper section wall 346. The second freeze-inhibitor injection piping arrangement may be any suitable piping arrangement. The second freeze-inhibitor injection mechanism 370 may have to repeatedly introduce and direct the second freeze-inhibitor solution to destabilize accumulation of all of the solid that has accumulated. The second freeze-inhibitor injection mechanism 370 may be the same or a different mechanism from the first freeze-inhibitor injection mechanism 370.
The second freeze-inhibitor injection mechanism 370 may be constructed and arranged to independently control at least one of a flow rate of the second freeze-inhibitor solution, a temperature of the second freeze-inhibitor solution, and an angle of the second freeze-inhibitor solution when the second freeze-inhibitor solution is introduced by the second freeze-inhibitor injection mechanism 370. The flow rate of the second freeze-inhibitor solution may be such that it is dependent on some estimated measure of accumulated solid. The temperature of the second freeze-inhibitor solution may be any suitable temperature that can melt solids. The angle of the second freeze-inhibitor solution may be any angle that sprays the second freeze-inhibitor solution at a desired location, such as at least one of the one or more mass transfer devices 176.
The second freeze-inhibitor solution may be any CO2 solubilizing solvent that remains unfrozen in the upper section 110. For example, the second freeze-inhibitor solution may comprise at least one of light hydrocarbons and light alcohols. The second freeze-inhibitor solution may comprise at least one of ethane, methanol, propane, butane, light olefins (e.g., ethylene), light ethers (e.g. dimethyl ether), acetylene, and H2S. Other examples of second freeze-inhibitor solution are also contemplated. The first and second freeze-inhibitor solutions may comprise the same or different solutions.
Like the first freeze-inhibitor injection mechanism 270, one or more temperature sensors may help determine whether the second freeze-inhibitor injection mechanism 370 needs to repeatedly, discontinuously inject the second freeze-inhibitor solution into the upper section 110. For more information on how the temperature sensor would function, please see the above description of how the temperature sensor functions with the first freeze-inhibitor injection mechanism 270.
After rising, the vapor stream may exit the distillation tower 104, 204 through line 14. The line 14 may emanate from an upper part of the upper section 110. The line 14 may extend from an outer surface of the upper section 110.
From line 14, the vapor stream may enter a condenser 122. The condenser 122 cools the vapor stream to form a cooled stream. The condenser 122 at least partially condenses the stream.
After exiting the condenser 122, the cooled stream may enter a separator 124. The separator 124 separates the vapor stream into liquid and vapor streams. The separator may be any suitable separator that can separate a stream into liquid and vapor streams, such as a reflux drum.
Once separated, the vapor stream may exit the separator 124 as sales product. The sales product may travel through line 16 for subsequent sale to a pipeline and/or condensation to be a liquefied natural gas.
Once separated, the liquid stream may return to the upper section 110 through line 18 as the reflux. The reflux may travel to the upper section 110 via any suitable mechanism, such as a reflux pump 150 (FIGS. 1 and 3) or gravity (FIGS. 2 and 4).
The liquid stream (i.e., freezing zone liquid stream) that falls to the bottom of the upper section 110 collects at the bottom of the upper section 110. The liquid may collect on tray 183 (FIGS. 1 and 3) or at the bottommost portion of the upper section 110 (FIGS. 2 and 4). The collected liquid may exit the distillation tower 104, 204 through line 20 (FIGS. 1 and 3) or outlet 260 (FIGS. 2 and 4). The line 20 may emanate from the upper section 110. The line 20 may emanate from a bottom end of the upper section 110. The line 20 may extend from an outer surface of the upper section 110.
The line 20 and/or outlet 260 connect to a line 41. The line 41 leads to the spray assembly 129 in the middle controlled freeze zone section 108. The line 41 emanates from the holding vessel 126. The line 41 may extend to an outer surface of the middle controlled freeze zone section 108.
The line 20 and/or outlet 260 may directly or indirectly (FIGS. 1-4) connect to the line 41. When the line 20 and/or outlet 260 directly connect to the line 41, the liquid spray may be pumped to the spray nozzle(s) 120 via any suitable mechanism, such as the spray pump 128 or gravity. When the line 20 and/or outlet 260 indirectly connect to the line 41, the lines 20, 41 and/or outlet 260 and line 41 may directly connect to a holding vessel 126 FIGS. 1 and 3). The holding vessel 126 may house at least some of the liquid spray before it is sprayed by the nozzle(s). The liquid spray may be pumped from the holding vessel 126 to the spray nozzle(s) 120 via any suitable mechanism, such as the spray pump 128 (FIGS. 1-4) or gravity. The holding vessel 126 may be needed when there is not a sufficient amount of liquid stream at the bottom of the upper section 110 to feed the spray nozzles 120.
Persons skilled in the technical field will readily recognize that in practical applications of the disclosed methodology, one or more steps may be performed on a computer, typically a suitably programmed digital computer. Further, some portions of the detailed descriptions which follow are presented in terms of procedures, steps, logic blocks, processing and other symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. In the present application, a procedure, step, logic block, process, or the like, is conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, although not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present application, discussions utilizing the terms such as “processing,” “computing,” “calculating,” “detecting,” “determining,” “displaying,” “copying,” “producing,” “storing,” “accumulating,” “adding,” “applying,” “identifying,” “consolidating,” “waiting,” “including,” “executing,” “maintaining,” “updating,” “creating,” “implementing,” “generating,” “transforming,” or the like, may refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.
It is important to note that the steps depicted in FIG. 7 are provided for illustrative purposes only and a particular step may not be required to perform the inventive methodology. The claims, and only the claims, define the inventive system and methodology.
Aspects of the present disclosure may also relate to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable medium. A computer-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, but not limited to, a computer-readable (e.g., machine-readable) medium includes a machine (e.g., a computer) readable storage medium (e.g., read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory devices, etc.), and a machine (e.g., computer) readable transmission medium (electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). The computer-readable medium may be non-transitory. The amounts determined may be displayed in the operator's console.
Furthermore, as will be apparent to one of ordinary skill in the relevant art, the modules, features, attributes, methodologies, and other aspects of the disclosure can be implemented as software, hardware, firmware or any combination of the three. Of course, wherever a component of the present disclosure is implemented as software, the component can be implemented as a standalone program, as part of a larger program, as a plurality of separate programs, as a statically or dynamically linked library, as a kernel loadable module, as a device driver, and/or in every and any other way known now or in the future to those of skill in the art of computer programming. Additionally, the present disclosure is in no way limited to implementation in any specific operating system or environment.
Disclosed aspects may be used in hydrocarbon management activities. As used herein, “hydrocarbon management” or “managing hydrocarbons” includes hydrocarbon extraction, hydrocarbon production, hydrocarbon exploration, identifying potential hydrocarbon resources, identifying well locations, determining well injection and/or extraction rates, identifying reservoir connectivity, acquiring, disposing of and/or abandoning hydrocarbon resources, reviewing prior hydrocarbon management decisions, and any other hydrocarbon-related acts or activities. The term “hydrocarbon management” is also used for the injection or storage of hydrocarbons or CO2, for example the sequestration of CO2, such as reservoir evaluation, development planning, and reservoir management. The disclosed methodologies and techniques may be used to produce hydrocarbons in a feed stream extracted from, for example, a subsurface region. The feed stream extracted may be processed in the distillation tower 104, 204 and separated into hydrocarbons and contaminants. The separated hydrocarbons exit the middle controlled freeze zone section 108 or the upper section 110 of the distillation tower. Some or all of the hydrocarbons that exit are produced, 307 (FIG. 7). Hydrocarbon extraction may be conducted to remove the feed stream from for example, the subsurface region, which may be accomplished by drilling a well using oil well drilling equipment. The equipment and techniques used to drill a well and/or extract the hydrocarbons are well known by those skilled in the relevant art. Other hydrocarbon extraction activities and, more generally, other hydrocarbon management activities, may be performed according to known principles.
As utilized herein, the terms “approximately,” “about,” “substantially,” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numeral ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described are considered to be within the scope of the disclosure.
For the purpose of this disclosure, the term “coupled” means the joining of two members directly or indirectly to one another. Such joining may be stationary or moveable in nature. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another. Such joining may be permanent in nature or may be removable or releasable in nature.
It should be understood that numerous changes, modifications, and alternatives to the preceding disclosure can be made without departing from the scope of the disclosure. The preceding description, therefore, is not meant to limit the scope of the disclosure. Rather, the scope of the disclosure is to be determined only by the appended claims and their equivalents. It is also contemplated that structures and features in the present examples can be altered, rearranged, substituted, deleted, duplicated, combined, or added to each other.
The articles “the”, “a” and “an” are not necessarily limited to mean only one, but rather are inclusive and open ended so as to include, optionally, multiple such elements.

## Claims

1. A method for preventing accumulation of solids in a distillation tower, the method comprising:
introducing a feed stream into a controlled freeze zone section of the distillation tower;
forming the solids in the controlled freeze zone section from the feed stream;
detecting a temperature in the controlled freeze zone section;
comparing the detected temperature to an expected temperature range, wherein the expected temperature range is a range of temperatures at which the controlled freeze zone operates normally;
discontinuously injecting a first freeze-inhibitor solution into the controlled freeze zone section toward a location in the controlled freeze zone section that accumulates the solids, wherein the first freeze-inhibitor solution is injected into the controlled freeze zone section when the detected temperature is outside of the expected temperature range by a positive amount and wherein the temperature of the first freeze-inhibitor solution is controlled independently of the flow rate of the first freeze-inhibitor solution being injected into the controlled freeze zone section; and
destabilizing accumulation of the solids from the location with the first freeze-inhibitor solution.

2. The method of claim 1, wherein the first freeze-inhibitor solution comprises any carbon dioxide solubilizing solvent that remains unfrozen in the controlled freeze zone section.

3. The method of claim 1, wherein the first freeze-inhibitor solution comprises at least one of light hydrocarbons and light alcohols.

4. The method of claim 1, wherein the first freeze-inhibitor solution comprises at least one of ethane, methanol, propane and butane.

5. The method of claim 1, wherein discontinuously injecting the first freeze-inhibitor solution comprises releasing the first freeze-inhibitor solution from the location.

6. The method of claim 1, wherein the location comprises at least one of a spray assembly of the controlled freeze zone section and a first freeze-inhibitor injection piping arrangement adjacent to a controlled freeze zone wall of the controlled freeze zone section.

7. The method of claim 1, further comprising injecting a second freeze-inhibitor solution into an upper section of the distillation tower toward a location in the upper section that accumulates the solids.

8. The method of claim 7, wherein the location in the upper section comprises a second freeze-inhibitor injection piping arrangement adjacent to an upper section wall of the upper section.

9. The distillation tower of claim 7, wherein the second freeze-inhibitor solution comprises at least one of light hydrocarbons and light alcohols.

10. The method of any one of claim 7, wherein the second freeze-inhibitor solution comprises at least one of ethane, methanol, propane and butane.

11. The method of claim 1, further comprising producing hydrocarbons from the feed stream.

12. The method of claim 1, further comprising controlling an angle at which the first freeze-inhibitor solution is injected.

13. The method of claim 1, wherein the controlled freeze zone wall comprises an external surface and wherein the temperature is detected by a temperature sensor coupled to the external surface of the controlled freeze zone wall.

14. A distillation tower that prevents accumulation of solids in the distillation tower, the distillation tower comprising:
a stripper section constructed and arranged to separate a feed stream in the distillation tower at a temperature and pressure at which the feed stream forms no solid;
a controlled freeze zone section constructed and arranged to separate the feed stream in the distillation tower at a temperature and pressure at which the feed stream forms solids;
a temperature sensor configured to detect a temperature in the controlled freeze zone section; and
a first freeze-inhibitor injection mechanism, wherein the first freeze-inhibitor injection mechanism is constructed and arranged to inject a first freeze-inhibitor solution in the controlled freeze zone section discontinuously when the temperature detected by the temperature sensor exceeds a predetermined value amount and wherein the first freeze-inhibitor injection mechanism is constructed and arranged to independently control the temperature and the flow rate of the first freeze-inhibitor solution being injected into the controlled freeze zone section.

15. The distillation tower of claim 14, wherein the first freeze-inhibitor solution comprises any carbon dioxide solubilizing solvent that remains unfrozen in the controlled freeze zone section.

16. The distillation tower of claim 14, wherein the first freeze-inhibitor solution comprises at least one of light hydrocarbons and light alcohols.

17. The distillation tower of claim 14, wherein the first freeze-inhibitor solution comprises at least one of ethane, methanol, propane and butane.

18. The distillation tower of claim 14, further comprising at least one of a spray assembly of the controlled freeze zone section and a first freeze-inhibitor injection piping arrangement adjacent to a controlled freeze zone wall of the controlled freeze zone section.

19. The distillation tower of claim 14, further comprising an upper section constructed and arranged to separate the feed stream in the distillation tower, wherein the upper section comprises a second freeze-inhibitor mechanism constructed and arranged to inject a second freeze-inhibitor solution in the upper section.

20. The distillation tower of claim 19, wherein the second freeze-inhibitor solution comprises at least one of light hydrocarbons and light alcohols.

21. The distillation tower of claim 19, wherein the second freeze-inhibitor solution comprises at least one of ethane, methanol, propane and butane.

22. A method for preventing accumulation of solids in a distillation tower, the method comprising:
providing a distillation tower, wherein the distillation tower comprises:
a stripper section constructed and arranged to separate a feed stream into a bottom liquid stream and a freezing zone vapor stream;
a controlled freeze zone section constructed and arranged to receive the freezing zone vapor stream from the stripper section and to separate the feed stream into solids and a methane-enriched vapor stream, wherein the controlled freeze zone section comprises a melt try assembly and a spray assembly;
a temperature sensor configured to detect a temperature in the controlled freeze zone section; and
a first freeze-inhibitor injection mechanism that is constructed and arranged to inject a first freeze-inhibitor solution in the controlled freeze zone section, wherein the first freeze-inhibitor injection mechanism is coupled to the spray assembly and wherein the first freeze-inhibitor injection mechanism is constructed and arranged to independently control the temperature and the flow rate of the first freeze-inhibitor solution being injected into the controlled freeze zone section;

introducing a feed stream into a controlled freeze zone section of the distillation tower;
separating the feed stream into solids and a methane-enriched vapor stream;
cooling the methane-enriched vapor stream to form a cooled stream;
introducing a liquid spray to the controlled freeze zone section from the spray assembly, wherein the liquid spray comprises at least a portion of the cooled stream;
detecting a temperature in the controlled freeze zone section;
comparing the detected temperature to an expected temperature range, wherein the expected temperature range is a range of temperatures at which the controlled freeze zone operates normally;
discontinuously introducing a first freeze-inhibitor solution into the controlled freeze zone section when the detected temperature is outside of the expected temperature range by a positive amount, wherein the first freeze-inhibitor injection mechanism introduces the first freeze-inhibitor solution to the spray assembly and the first freeze-inhibitor solution is introduced to the controlled freeze zone section as part of the liquid spray from the spray assembly and wherein the temperature of the first freeze-inhibitor solution is controlled independently of the flow rate of the first freeze-inhibitor solution being injected into the controlled freeze zone section; and
destabilizing accumulation of the solids from a location with the first freeze-inhibitor solution.

23. The method of claim 22, wherein the first freeze-inhibitor solution comprises from 1 to 5 mole % of the liquid spray.