Methods and systems for separating compounds

Methods and systems for separating a desublimatable compound from hydrocarbons is disclosed. A feed fluid stream, consisting of a hydrocarbon and a desublimatable compound, is passed into an upper chamber of a vessel. The feed fluid stream is cooled in the upper chamber, thereby desublimating a portion of the desublimatable compound out of the feed liquid stream to form a product gas stream and a desublimatable compound snow which is collected in the lower chamber of the vessel. A lower portion of the desublimatable compound snow is melted to form a liquid desublimatable compound stream such that an upper portion of the solid desublimatable compound snow remains as an insulative barrier between the upper chamber and the liquid desublimatable compound stream. The liquid desublimatable compound stream is removed at a rate that matches a production rate of the solid desublimatable compound snow, thereby maintaining the insulative barrier.

TECHNICAL FIELD

The methods and processes described herein relate generally to fluid separations.

BACKGROUND

Separation of fluid components is often energy intensive or complex. Separating components can be done, but the higher the purity required, the more unit operations are typically required. Alternatives to traditional fluid separation techniques are required.

SUMMARY

In a first aspect, the disclosure provides a method for continuously separating a desublimatable compound from hydrocarbons. A vessel with an upper chamber and a lower chamber is provided. A feed fluid stream is passed into the upper chamber. The feed fluid stream consists of a hydrocarbon and a desublimatable compound. The feed fluid stream is cooled in the upper chamber, thereby desublimating a portion of the desublimatable compound out of the feed liquid stream to form a solid desublimatable compound snow and a product gas stream. The solid desublimatable compound snow is collected in the lower chamber. A lower portion of the solid desublimatable compound snow is melted to form a liquid desublimatable compound stream such that an upper portion of the solid desublimatable compound snow remains as an insulative barrier between the upper chamber and the liquid desublimatable compound stream. The liquid desublimatable compound stream is removed at a rate that matches a production rate of the solid desublimatable compound snow, thereby maintaining the insulative barrier. The product gas stream is removed from the upper chamber.

In a second aspect, the disclosure provides a method for continuously separating components. A vessel with an upper chamber and a lower chamber is provided. A feed fluid stream is passed into the upper chamber. The feed fluid stream consists of methane and carbon dioxide. A cold liquid stream is flashed into the upper chamber, thereby reducing the temperature of the upper chamber. The cold liquid stream consists of methane. The carbon dioxide is desublimated out of the feed fluid stream to form a solid carbon dioxide snow and a product gas stream. The solid carbon dioxide snow is collected in the lower chamber. A lower portion of the solid carbon dioxide snow is melted to form a liquid carbon dioxide stream such that an upper portion of the solid carbon dioxide snow remains as an insulative barrier between the upper chamber and the liquid carbon dioxide stream. The liquid carbon dioxide stream is removed at a rate that matches a production rate of the solid carbon dioxide snow, thereby maintaining the insulative barrier. The product gas stream is removed from the upper chamber.

In a third aspect, the disclosure provides a system for continuously separating components. A vessel consists of an upper chamber and a lower chamber. The upper chamber consists of a feed gas inlet, a cooling source, and a product gas outlet. The lower chamber consists of a product liquid outlet and a heat source. The feed fluid inlet is configured to pass a feed gas stream through the feed gas inlet into the upper chamber. The feed fluid stream consists of a hydrocarbon and a desublimatable compound. The cooling source cools the feed gas stream, thereby desublimating a portion of the desublimatable compound out of the feed gas stream to form a solid desublimatable snow and a product gas stream. The solid desublimatable compound snow falls into the lower chamber. A heat source melts a lower portion of the solid desublimatable compound snow in the lower chamber to form a liquid desublimatable compound stream such that an upper portion of the solid desublimatable compound snow remains as an insulative barrier between the upper chamber and the liquid desublimatable compound stream. The product liquid outlet is configured to remove the liquid desublimatable compound stream at a rate that matches a production rate of the solid desublimatable compound snow, thereby maintaining the insulative barrier. The product gas outlet is configured to remove the product gas stream from the upper chamber.

Further aspects and embodiments are provided in the foregoing drawings, detailed description and claims.

DETAILED DESCRIPTION

Definitions

As used herein, “C1” refers to methane, “C2” refers to ethane, “C3” refers to propane, and “C3+” hydrocarbons refers to hydrocarbons with three or more carbon atoms.

As used herein, “natural gas” refers to a gas containing primarily methane, and that may have other ingredients, such as ethane, propane, butane, water, and carbon dioxide.

As used herein, “desublimate” refers to a compound undergoing a phase change from gas directly to solid. “Desublimatable” means that at the pressure and temperature conditions in a vessel, the compound is able to desublimate. In a preferred embodiment, “desublimatable compounds” include carbon dioxide, sulfur oxides, nitrogen oxides, carbon monoxide, and combinations thereof.

Separations of components is often complicated by the presence of components that are miscible or have similar boiling points. For example, propane has some solubility in water and heptane has a boiling point nearly identical to water. Streams of hydrocarbons contaminated with carbon dioxide and water add to the overall complications. The present invention discloses methods and systems for separating desublimatable compounds, such as carbon dioxide, from hydrocarbons, such as natural gas. In one embodiment of the present invention, a feed liquid or gas stream containing a hydrocarbon and a desublimatable compound is passed into an upper chamber of a vessel. In the instance that the feed stream is a liquid, passing the feed stream into the upper chamber flashes the stream to a gas. A second stream, primarily composed of the hydrocarbon, is flashed into the vessel. The flashing of one or both streams cools the upper chamber such that the desublimatable compound is cooled and desublimates directly to a solid snow. This solid snow collects in a lower chamber of the vessel where it is melted. The melting, by heating element or reinjection of a heated liquid desublimatable compound stream, occurs in a bottom portion of the lower chamber. The snow is melted at a rate that an upper portion of the solid snow remains as a solid, providing an insulative barrier between the upper chamber and the resultant liquid. The liquid is removed at a rate to maintain the insulative barrier, as well. The gas formed in the upper chamber is also removed from the vessel. By this process, a compound, such as carbon dioxide, can be removed from hydrocarbons, such as natural gas, in a single vessel. This eliminates any solids handling issues. Further, as the compound snow descends and is melted from solid to liquid, any hydrocarbons trapped in void spaces of the snow are expelled as the void spaces collapse, driving the hydrocarbons out of the resultant liquid and up into the upper chamber, increasing separation purity.

Now referring toFIG.1,FIG.1is a flow diagram showing a method for separating compounds that may be used in one embodiment of the present invention. A vessel100consists of an upper chamber10and a lower chamber12. An inductive heater14is installed in a lower portion of the lower chamber12. The upper chamber is kept at a pressure of 6 bar. A feed fluid stream30is a natural gas stream and contains at least 20 wt % carbon dioxide. The feed fluid stream30is at a pressure of at least 25 bar and a temperature less than −55° C. A cold liquid stream38, a natural gas stream with no more than 3 wt % carbon dioxide, is at a pressure of 50 bar and a temperature less than −102° C. In other words, the cold liquid stream38meets standards for pipeline transportation of natural gas. The feed fluid stream30is passed into the upper chamber10where any liquid present in the feed fluid stream30is flashed to a vapor. Simultaneously, the cold liquid stream38is flashed into the upper chamber10, resulting in further vapor. The vaporization requires heat which is absorbed from the vapor and results in the carbon dioxide desublimating to form a solid carbon dioxide snow31in the upper chamber10. This solid carbon dioxide snow31falls from the upper chamber10into a top portion33of the lower chamber12.

The inductive heater14warms a lower portion35of the lower chamber12. This melts the solid carbon dioxide snow located in the lower portion35, forming a liquid carbon dioxide stream34. The heat is kept low enough to only melt the lower portion35while leaving the solid carbon dioxide snow settled in the upper portion33as an insulative barrier between the upper chamber10and the liquid carbon dioxide stream. The term “insulative” means first that the heat does not propagate back into the upper chamber10and second that the vapor of the upper chamber10is physically separated from the liquid carbon dioxide stream34, preventing vaporization of the liquid back into the vapor. The liquid carbon dioxide stream34is removed at a rate that matches the production rate of the solid carbon dioxide snow31, maintaining the insulative barrier in upper portion33.

The vapor that did not desublimate leaves the upper chamber10as product gas stream32. A portion of the product gas stream36is passed through a refrigeration loop16where the product gas stream is pressurized and cooled to produce the cold liquid stream38. The balance of the product gas stream40is a product stream that can be further processed to remove the remaining carbon dioxide or can be used as a natural gas stream without further processing.

In this embodiment, if the surface area around the lower portion35is sufficient, the use of an inductive heater14may not be necessary. Simply removing any insulation from the lower portion of the lower chamber12may be able to provide sufficient heat from ambient air to melt the solid carbon dioxide snow.

Now referring toFIG.2,FIG.2is a flow diagram showing a method for separating compounds that may be used in one embodiment of the present invention. A vessel200consists of an upper chamber10and a lower chamber12. The upper chamber contains an indirect-contact heat exchanger15equipped with vibrators. A feed gas stream30, consisting of a desublimatable compound and hydrocarbons, is passed into the upper chamber10. The desublimatable compound desublimates onto the heat exchanger15, which is vibrated to cause the solids to flake off as a solid desublimatable compound snow31which falls from the upper chamber10into a top portion33of the lower chamber12.

A warm liquid stream42, consisting of the desublimatable compound, is pumped into a lower portion35of the lower section12, melting the solid desublimatable compound snow located in the lower portion35, forming a liquid desublimatable compound stream34. The temperature and flow rate of the warm liquid stream42is kept low enough to only melt the lower portion35while leaving the solid desublimatable compound snow settled in the upper portion33as an insulative barrier between the upper chamber10and the liquid desublimatable compound stream. The term “insulative” means first that the heat does not propagate back into the upper chamber10and second that the vapor of the upper chamber10is physically separated from the liquid desublimatable compound stream34, preventing vaporization of the liquid back into the vapor. The liquid desublimatable compound stream34is removed at a rate that matches the production rate of the solid desublimatable compound snow31, maintaining the insulative barrier in upper portion33.

The vapor that did not desublimate leaves the upper chamber10as product gas stream32. A portion of the product gas stream36is passed through a refrigeration loop16where the product gas stream is pressurized and cooled to produce the cold liquid stream38. The balance of the product gas stream40is a product stream.

Now referring toFIG.3,FIG.3is a flow diagram showing a method for separating compounds that may be used in one embodiment of the present invention. A vessel300consists of an upper chamber10and a lower chamber12. An auger18is installed in the lower chamber12. A feed fluid stream30, consisting of a desublimatable compound and hydrocarbons, is passed into the upper chamber10where any liquid present in the feed fluid stream30is flashed to a vapor. Simultaneously, a cold liquid stream38is flashed into the upper chamber10, resulting in further vapor. The vaporization requires heat which is absorbed from the vapor and results in the desublimatable compound desublimating to form a solid desublimatable compound snow31in the upper chamber10. This solid desublimatable compound snow31falls from the upper chamber10into a top portion33of the lower chamber12.

A warm liquid stream42, consisting of the desublimatable compound, is pumped into a lower portion35of the lower section12, melting the solid desublimatable compound snow located in the lower portion35, forming a liquid desublimatable compound stream34. The temperature and flow rate of the warm liquid stream42is kept low enough to only melt the lower portion35while leaving the solid desublimatable compound snow settled in the upper portion33as an insulative barrier between the upper chamber10and the liquid desublimatable compound stream. The term “insulative” means first that the heat does not propagate back into the upper chamber10and second that the vapor of the upper chamber10is physically separated from the liquid desublimatable compound stream34, preventing vaporization of the liquid back into the vapor. The liquid desublimatable compound stream34is removed at a rate that matches the production rate of the solid desublimatable compound snow31, maintaining the insulative barrier in upper portion33. The solid desublimatable compound is conveyed from the upper portion33to the lower portion35by the auger18.

The vapor that did not desublimate leaves the upper chamber10as product gas stream32. A portion of the product gas stream36is passed through a refrigeration loop16where the product gas stream is pressurized and cooled to produce the cold liquid stream38.

Now referring toFIG.4,FIG.4is an isometric cutaway view of a system for separating compounds that may be used in one embodiment of the present invention. The vessel400consists of an upper chamber10and a lower chamber12. The upper chamber has a feed gas inlet, a cooling source, and a product gas outlet. The lower chamber has a product liquid outlet and a heat source14.

The feed fluid inlet is configured to pass a feed gas stream through the feed gas inlet into the upper chamber. The feed fluid stream consists of a hydrocarbon and a desublimatable compound. The cooling source cools the feed fluid stream. In this embodiment, the cooling source is a cold liquid stream that is flashed into the upper chamber10. The vaporization requires heat which is absorbed from the feed fluid stream and results in the desublimatable compound desublimating to form a solid desublimatable compound snow in the upper chamber10, as well as a product gas stream. The solid desublimatable compound snow falls into the lower chamber12, forming an insulative barrier33.

In this embodiment, the heat source14is a set of heating coils wrapped around a lower portion35of the lower chamber12. The heat source14melts a lower portion of the solid desublimatable compound snow in the lower chamber to form a liquid desublimatable compound stream in a manner that an upper portion of the solid desublimatable compound snow remains as an insulative barrier between the upper chamber and the liquid desublimatable compound stream. The product liquid outlet is configured to remove the liquid desublimatable compound stream at a rate that matches a production rate of the solid desublimatable compound snow, thereby maintaining the insulative barrier. The product gas outlet is configured to remove the product gas stream from the upper chamber.

In some embodiments, the solid may bridge as it collects as insulative barrier33. Heating the walls is not always necessary, but in some embodiments, heating will prevent bridging and lead to a proper insulative barrier33.

In some embodiments, the desublimatable compound is selected from the group consisting of carbon dioxide, sulfur oxides, nitrogen oxides, carbon monoxide, and combinations thereof. In some embodiments, the hydrocarbon is selected from the group consisting of methane, ethane, propane, and combinations thereof.