Patent Application
20200156040
This application relates to the field of fluid separation in connection with natural gas processing. The present invention further relates to a gas-to-liquids conversion process wherein gaseous alkanes are converted into higher molecular weight hydrocarbons using an electron beam reactor to form a high-octane transportation fuel. This application relates to the field of producing hydrogen from natural gas.
Much of hydrogen produced is made via steam-methane reforming, a mature production process in which high-temperature steam (700° C.-1,000° C.) is used to produce hydrogen from a methane source, such as natural gas. In steam-methane reforming, methane reacts with steam under 10-25 bar pressure (1 bar=14.5 psi) in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Steam reforming is endothermic in that heat must be supplied to the process for the reaction to proceed.
Hydrocarbon fluids are primarily alkanes, which are molecules consisting only of hydrogen and carbon atoms, with all bonds being single bonds. Alkanes are referred to as “saturated” hydrocarbons as they are saturated with hydrogen. The general formula for saturated hydrocarbons is CnH2n+2 (assuming non-cyclic structures). Saturated hydrocarbons are found as either linear or branched species.
Gas flares are used in the oil and gas industry at petroleum refineries, natural gas processing plants, offshore oil and gas rigs, and at oil and gas production sites. Partly because of the shale gas production boom in the United States, the price of natural gas is suppressed and remains much lower than that of the liquid crude oil. Accordingly, some production companies do not find it economical to transport natural gas to a gathering facility or to a market. Therefore, much natural gas is simply flared.
Several years ago a research team at Texas A&M University conceived of a process for converting natural gas into hydrocarbon liquids using a “direct” conversion method. The process is considered “direct” because it does not require the generation of syngas. The process is essentially three reaction steps and two separation steps to produce hydrocarbon liquids. See Kenneth R. Hall, A New Gas to Liquids (GTL) or Gas to Ethylene (GTE) Technology, Catalysis Today, Vol. 106, pp. 243-46 (Oct. 15, 2005). However, the end result of this process is primarily ethylene and hydrogen, and not a liquid fuel.
To create a product that has greater commercial value, it is desirable to convert the gaseous alkanes into a liquid transportation fuel without need of a synthesis process or a metal catalyst. Further, a need exists for a process of quickly upgrading a naturally-occurring mixture of lower molecular weight fuels available at many production sites into a high-octane transportation fuel without need of large chillers. Further, a need exists for a process for economically upgrading the lower molecular weight hydrocarbons from a gas stream, together into a high-octane liquid gasoline, or into a blend for transportation fuel, at or near a production site.
A process for converting a gas stream comprising primarily light alkanes into a high-octane liquid stream is first provided. The gas stream is preferably a natural gas production stream acquired in connection with oil and gas production operations. The product is hydrogen.
In one aspect, the process includes introducing the natural gas stream to a reactor. The reactor is an electron beam reactor such as a steel flow-type reactor. The reactor is connected hermetically to an accelerator beam window. Preferably, the natural gas stream has first been sweetened by the removal of any CO2 and any sulfuric components before introduction into the reactor.
In order to introduce the natural gas stream, the gas stream may be transported to a natural gas processing facility. The transporting step may comprise moving a natural gas production stream from a wellhead to the reactor by means of a pipeline. Alternatively, natural gas may be moved to the reactor by rail car or by over-the-road tank. Alternatively still, the reactor may be located at a well head or a local gathering facility and connected to a heater treater or other separator so that methane and ethane are flashed off of liquid components and immediately captured.
In one aspect, the process further comprises removing any H2O, from the natural gas production stream. This may be done before transporting the natural gas production stream to the reactor, or upon delivery of the gas stream to the reactor. In any instance, the dehydrated and sweetened natural gas production stream may be fed to the reactor at a rate of, for example, 0.8 gpm/kW.
It is preferred that the gas stream be pressured to at least 15 psi before introduction into the reactor. It is further preferred that the gas stream be heated to at least 100.degree. F. before or upon introduction of the natural gas production stream into the reactor. In one aspect, both the pressuring and the heating are done through the use of one or more blowers.
One aspect includes the production of hydrogen from a process of passing natural gas through a channel of circular shape or rectangular shape under an I-beam radiation in one or multiple positions causing hydrogen to release from the hydrocarbon bonds. The method also includes exposing the natural gas stream to electron beam radiation within the reactor. In one aspect, the gas production stream is moved through an irradiation area within the reactor at a rate of 800 m.sup.3/hour. In any instance, the irradiation generates a substantially liquefied hydrocarbon stream according to:
The method further includes transporting the substantially liquefied hydrocarbon stream into a separator. The separator is preferably a dual scrubber tank operated at 110.degree. F. The separator or scrubber may comprise one or more gas-to-liquid centrifugal separators in series. Alternatively, the separator may comprise a shell-and-tube heat exchanger wherein cooling takes place through heat exchange with chilled water. In this instance, the cooling condenses most remaining gaseous components.
Two fluid streams are released from the separator. These represent a first stream of lighter alkanes, being in the C1 to C5 range, and a second stream primarily of heavier hydrocarbons, representing C6 alkanes and higher. The stream of lighter alkanes is a small stream of mostly non-condensed fluids, and is re-circulated back into the reactor as a gas. At the same time, the heavier alkanes, which are more valuable than the lighter alkanes, are in a liquefied state and are moved off-site for sale. Optionally, fractionation of the heavy carbon components is conducted to separate hydrocarbon species. This may be done, for example, by using a distillation column to generate separate condensate streams. In this process, the liquid condensate is heated to progressively higher temperatures that cause the several components to separate through sequential evaporation. The valuable end products of heptane, hexane and residual octane (and above) are generated. All products are produced as a 100 octane condensate.
In one aspect, the method further comprises monitoring the hydrogen (H2) content in the non-condensed fluids (or gases) released from the separator. When the hydrogen content reaches 10% by volume in the non-condensed fluids, the non-condensed fluids are sent to a pressure swing absorption unit (or other separator) for removal of the hydrogen gases. In this instance, re-circulating non-condensed fluids from the substantially liquefied hydrocarbon stream back into the reactor comprises returning the gases after separation of the hydrogen content in the pressure swing absorption unit.
In another aspect, natural gas passes under electron-beam radiation causing hydrogen to release from the hydrocarbon bonds. The free hydrogen then can pass through a condenser and can be separated from larger alkanes. The free hydrogen can be separated using, e.g., a pressure swing adsorption or micro channels. Remaining compounds can be recycled. The free hydrogen can be compressed and stored. The recycled gaseous alkanes can be mixed with fresh natural gas and passed under the Electron-beam to produce more hydrogen.
In another aspect, a process of recovering hydrogen from the conversation of a gas stream that is primarily a mixture of light alkanes into a high-octane liquid stream, comprises transporting the gas stream to a reactor at a gas processing facility; introducing the gas stream into a reactor whereupon components of the gas stream are exposed to electron beam radiation within the reactor to increase the molecular weight of hydrocarbons in the gas stream, thereby producing an upgraded radiolysis fluid stream and recovering a first portion of hydrogen; transporting the radiolysis fluid stream into a separator, thereby producing a first gaseous stream comprising primarily light alkanes and hydrogen, and a second liquid stream comprising primarily heavy alkanes; re-circulating the first stream back into an inlet of the reactor for additional irradiation and upgrading; and transporting the second liquid stream as condensate to a distillation column; and fractionating the condensate into to recover hydrogen.
So that the present inventions can be better understood, certain drawings, charts, graphs and/or flow charts are appended hereto. It is to be noted, however, that the drawings illustrate only selected embodiments of the inventions and are therefore not to be considered limiting of scope, for the inventions may admit to other equally effective embodiments and applications.
As used herein, the term “fluid” refers to gases, liquids, and combinations of gases and liquids.
As used herein, the term “gas” refers to a fluid that is in its vapor phase at 1 atm and 15 C to 20 C.
As used herein, the term “oil” refers to a hydrocarbon fluid containing primarily a mixture of condensable hydrocarbons.
The inventions are described herein in connection with certain specific embodiments. However, to the extent that the following detailed description is specific to a particular embodiment or a particular use, such is intended to be illustrative only and is not to be construed as limiting the scope of the inventions. In certain embodiments, large amounts of hydrogen more very easily and cost effectively.
Natural gas is frequently produced from subsurface reservoirs. The primary component of natural gas is the group of light alkanes consisting of methane (C1) and ethane (C2). These are known as saturated acyclic hydrocarbons. Fractions of propane (C3), butane (C4) and pentane (C5) are also found in raw natural gas streams, although these fractions are more commonly liquefied at ambient conditions.
In one embodiment, hydrogen can be prepared from a process of passing natural gas through a channel of circular shape or rectangular shape under an I-beam radiation in one or multiple positions causing hydrogen to release from the hydrocarbon bonds. Free hydrogen is separated from the compound of the first pass and is re-injected through to cause more separation of the hydrogen element. This hydrogen can get separated and using either pressure swing adsorption or micro channels and the compound can be recycled again. The compound can be moved through multi I-Beam rays as hydrogen is separated from the gas. In one aspect the recycled gas is mixed with fresh natural gas and is passed under the I-beam to produce more hydrogen. The mixture of natural gas and recycled gases can be passed through multi channels to produce hydrogen. Hydrogen is filter between each channel to reduce the effects of hydrogen blanketing.
It is desirable to upgrade the otherwise non-condensable components into a higher molecular weight hydrocarbon form for use as a high-octane fuel or for use as a fuel blend. Accordingly, processes are offered herein for converting the gaseous alkanes from a natural gas stream into a 100 octane condensate. Each process involves the continuous exposure of a natural gas source to electron beam radiation to generate heavy hydrocarbon fluids as liquid radiolytic products, and the re-circulation of remaining light alkanes. The processes also involve the removal of hydrogen gas from the light alkanes before re-circulation.
In one embodiment, natural gas passes under electron-beam radiation causing hydrogen to release from the hydrocarbon bonds. The free hydrogen then can pass through a condenser and can be separated from larger alkanes. The free hydrogen can be separated using, e.g., a pressure swing adsorption or micro channels. Remaining compounds can be recycled. The free hydrogen can be compressed and stored. The recycled gaseous alkanes can be mixed with fresh natural gas and passed under the Electron-beam to produce more hydrogen.
In the system 100, a natural gas source is first shown schematically at “NG.” The natural gas NG is preferably associated with oil and gas production operations. In one preferred embodiment, the natural gas NG is a gas production stream located at a production facility or an FPSO. In this instance, the gas NG has been separated from production liquids such as through gravity separation. At many production facilities, a certain amount of natural gas is used on-site as fuel gas, with the remaining gas stream being flared. Thus, in one aspect herein, the natural gas NG represents a gas stream that would otherwise have been flared.
In one embodiment, natural gas can heated to up to 500 F and passed through a circular or rectangular channel under an I-beam ray to release the hydrogen from the natural gas flow. Natural gas and the recycled gases are heated up to 700 F and are passed through a rectangular or circular channel under an I-beam ray to release hydrogen and capture from the natural gas and recycled gas mixture. Alternatively, Natural gas is heated to up to 500 F and is passed through a circular or a rectangular channel under multiple I-beam rays to release the hydrogen gas from the natural gas and collect the hydrogen gas. In one example, the recycled gas is heated to 750 F and is passed through a circular or a rectangular channel under an I-beam ray to release more hydrogen. In one embodiment, the mixture of hydrogen and recycled gases are heated to up to 750 F and are passed through a circular or rectangular channel under multiple stages of I-beam rays and the hydrogen gas is collected from each stages or only the final stage. In one aspect Natural gas is heated to up to 500 F and is passed through an I-beam and using a circular or rectangular reactor containing certain metallic catalyst to encourage further release of the hydrogen gas.
In one embodiment, natural gas and recycled gases are heated to up to 800 F and are passed through a circular or rectangular reactors under I-beam ray containing a certain metallic catalyst to release higher amounts of hydrogen.
In one embodiment, natural gas and recycled gases are heated to up to 800 F and are passed through circular or rectangular reactors containing certain metallic catalysts under multiple I-beam rays at different stages while the hydrogen gas is continuously removed.
In one embodiment, natural gas and natural gas is heated up to 500 F and pressurized up to 1000 Psig and is passed through a circular or rectangular high pressure channel under an I-beam to release the hydrogen gas.
In one embodiment, natural gas and and recycled gases are heated up to 800 F and are pressurized up to 1000 psig and are passed through high pressure circular or rectangular channels under I-Beam ray to release the hydrogen gas.
In one embodiment, natural gas and is heated up to 500 F and pressurized up to 1000 psig pressure and is passed through a circular and rectangular channel and is passed through a circular or rectangular channel under multiple I-beam rays to produce higher levels of hydrogen.
In one embodiment, natural gas and gas and recycled gases are heated to up to 800 F and pressurized to up to 1000 psig and are passed through circular or rectangular channel under multiple I-beam rays to produce higher levels of hydrogen.
In one embodiment, natural gas and is heated up to 500 F and pressurized up to 1000 Psig and is passed through a circular or rectangular channel containing certain active metallic catalyst under multiple I-beam rays to increase the release of hydrogen gas.
In one embodiment, natural gas and the recycled gases are heated to up to 800 F and pressurized to up to 1000 Psig and are passed through a circular or rectangular channel containing a metallic catalyst under multiple I-beam rays to release the hydrogen gas from the mixture.
It is understood that the present inventions are not limited to the nature of the source for the natural gas NG. Other sources of light alkanes besides conventional oil and gas production operations may be utilized as the natural gas source NG. These may include gas produced from so-called tight shale formations such as the Barnett Shale or the Eagle Ford shale. These may also include gas obtained from coalbed methane recovery, biomass conversion operations, permafrost melt outgassing and landfill outgassing.
In any of these events, the natural gas source NG is delivered to the facility 100 by means of a transport line 101. The transport line 101 may be a pipeline; alternatively, the line 101 may be an offloading line from a truck, a rail car or a storage tank. In one aspect of operation, 28,000 ft3/hour of natural gas is passed through line 101, or 672,000 ft3/day.
It is observed that in connection with the production or recovery of hydrocarbon gases, natural gas is not always produced in a “clean” form, that is, a gas stream made up almost entirely of methane and ethane (C1-C2); rather, gas production streams will typically include other lighter alkane components such as propane, butane and pentane (C3-C5). In addition, a gas production stream will frequently include non-hydrocarbon elements such as hydrogen, nitrogen, carbon dioxide and hydrogen sulfide, causing the gas to be “sour.” Thus, in one embodiment, the facility 100 includes a gas processing system, shown schematically at 110.
The gas processing system 110 may also be used for the removal of water (H2O). This may be done before transporting the natural gas NG to the facility 100, or upon delivery of the light alkanes NG to a locus of the facility 100. Water may be removed through a gravity separator or through cryogenic dehydration. Cryogenic dehydration generally comprises cooling the wet natural gas through Joule-Thomson expansion. Cooling is applied until the components to be removed precipitate by condensation or formation of hydrates.
Water separation may also be accomplished by chemically mixing methanol, glycol or a paraffin solvent into a raw gas stream to cause the water to break out of solution. This is referred to as dehydration by absorption. The water and glycol are then captured through a bottom aqueous stream. Water separation may alternatively be carried out through an adsorptive process using an adsorbent suitable for retaining water. Examples include molecular sieves and silica gels.
The gas processing system 110 may also be used for the removal of carbon dioxide (CO2) and sulfuric components from the natural gas source NG. Sulfuric compounds may include, for example, hydrogen sulfide (H2S) carbonyl sulfide and mercaptans. Processes are known for removing such non-hydrocarbon components from a gas production stream. Such processes are referred to as “sweetening.”
Carbon dioxide and sulfur compounds may be removed through any of physical absorption processes, chemical absorption processes, physical-chemical absorption processes, liquid oxidation processes, adsorption processes and membrane processes. Membrane processes used for natural gas separation can be simultaneously performed for removal of carbon dioxide and hydrogen sulfide. Any of these processes are well-known to those of ordinary skill in the art of natural gas processing.
Generally, chemical absorption processes comprise the use of a gas scrubber wherein the sour natural gas components are reversibly bound to a solvent such as an amine by chemical or physical absorption. The scrubber may simply be a series of mixing tanks. Chemical absorption processes generally comprise an alkanolamine scrubbing wherein aqueous solutions of monoethanolamine, di-ethanolamine, di-isopropylamine, di-glycolamine or methyldiethanolamine are used as absorbents. After mixing, the solvent undergoes a regeneration step where the sour natural gas components are desorbed unchanged. The solvent is then recycled to a first scrubber.
In physical absorption processes, carbon dioxide and hydrogen sulfide are generally physically dissolved in a solvent. The solvent may be, for example, N-methylpyrrolidone (or Purisol®), methanol (or (Rectisol®), Propylene Carbonate (Fluor Solvent™), a mixture of poly(ethylene glycol dimethyl ether), poly(ethylene glycol methyl isopropyl ether), DEPG (Selexol™ or Coastal AGR®) and propylene carbonate. Physical-chemical absorption processes generally comprise using a combination of solvents in physical absorption and chemical absorption processes.
In instances where the carbon dioxide component is particularly high, the sour gas may first be taken through a Joule-Thompson valve for flash cooling, and then carried into a cryogenic distillation tower or bulk fractionation unit for the removal of CO2. Where the H2S component is unusually high, the sour gas stream may be flowed across an adsorbent bed. Adsorbent beds operate on the principle that different molecules can have different affinities for adsorption. This provides a mechanism for the adsorbent to discriminate between different gases. The adsorbent is preferably chosen from activated charcoal, iron oxide, zinc oxide and zeolitic molecular sieves.
A typical natural gas stream may also comprise nitrogen. In this instance, the gas processing system may further comprise a purification stage wherein nitrogen (N2) is removed from the natural gas NG. This is particularly applicable where the nitrogen concentration is great than about 2% by volume. Nitrogen is typically removed via membrane separation. In one aspect of the system 100, nitrogen is removed at the back end using membrane separator 170.
It is observed that sweetening processes are required in order to bring a natural gas stream into pipeline specification. Pipeline spec. generally requires the following levels:
Of course, true pipeline spec. gas is not required for the present GTL conversion process as the presence of so-called heavy hydrocarbons (C6+) is actually desirable. C6 through C10 alkanes, alkenes and isomeric cycloalkanes are the top components of gasoline, naphtha and jet fuel as well as specialized industrial solvent mixtures.
After gas processing 110 is conducted, the dehydrated and/or sweetened gas is carried out through gas line 102. Line 102 delivers natural gas through an optional flow meter 103, and then to an electron beam reactor 130. At this point, the alkane gas composition may enter the reactor 130 as, for example, 95% CH4 and 5% C2H6. The natural gas production stream may be fed to the reactor 130 at a rate of, for example, 0.8 gpm/kW. The reactor 130 is an electron beam reactor such as a steel flow-type reactor connected hermetically to an accelerator beam window. This may be referred to as a “pipe and E-beam window” design.
It is preferred that the gas stream be pressured to at least 15 psi before introduction into the reactor 130. It is further preferred that the gas stream be heated to at least 100.degree. F. before or upon introduction of the natural gas stream into the reactor 130. In one aspect, both the pressuring and the heating are done through the use of one or more blowers 120.
In the illustrative facility 100, a pair of blowers 120 is shown. Each blower 120 represents a mechanism for delivering natural gas 110 under slight pressure to the reactor 130. Line 102 splits into separate lines 105 for delivery of natural gas 110 to the blowers 120. Each line 105 includes a gate valve 108 for controlling the flow of natural gas 110 into the respective blowers 120. The blowers 120 may have a 500 scf/minute or greater air handling capacity.
The blowers 120 deliver warmed and compressed gas through lines 121. A gate valve 128 is provided along each line 121 to selectively control gas flow. Warmed and compressed gas then enters the reactor 130 where the gas stream is exposed to electron beam radiation. The gas flow rate in the irradiation zone may vary over the range 500 to 1,000 m.sup.3/hour. Preferably, the gas production stream is moved through an irradiation area within the reactor at a rate of about 800 m3/hour.
In one aspect, the flow rate is calculated as:
The electron beam may be generated by 1 MeV at 400 kW. The rate of energy consumption may be 0.5 to 2.0 kW/m.sup.3 (absorbed dose rate). In one aspect, the e-beam power requirements are:
P=0.5 kWh/m3*900 Nm3/h=450 kW/h
The reactor may use, for example, an Avrora-9B UEVK cascade accelerator as a source of electron radiation. The accelerator generates an electron energy of 500 keV, a beam current to 80 mA, and a beam power to 40 kW. The following table demonstrates excitation requirements for low molecular weight hydrocarbon products:
The irradiation process generates a substantially liquefied hydrocarbon stream according to:
In this process, liquid radiolytic products are accumulated in a mixture of CnH2n+2 and CmH2m+2, as follows:
The light alkalies absorb more energy of ionizing radiation, allowing the growth of alkyl radicals as “radiolysis products.”
The absorbed does (D) may be calculated according to one embodiment as:
where: .epsilon.=efficiency P=power M=flow rate
The dose rate may be calculated as:
In another embodiment, the folio wing design parameters may be used:
The required retention time in the e-beam reactor may be calculated according to:
where: D1=total absorbed dose; and D2=absorbed dose efficiency.
Recirculation is calculated as
Treatment capacity is calculated as
For a reactor operating at 20 kW, 33,600 ft.sup.3/day of natural gas may be processed. For a reactor operating at 400 kW, 672,000 ft.sup.3/day of natural gas may be processed.
It is noted that 6,000 ft.sup.3/day equates to 1 barrel. 672 mcf/day equates to 112 bbl. At a 94% conversion rate, this equates to 105 bbl/day.
Returning to
The separator 140 may comprise or one or more gas-to-liquid centrifugal separators in series. Alternatively, the separator 140 may comprise a shell-and-tube (or jacketed tube) heat exchanger wherein cooling takes place through heat exchange with water (+16.degree. C.) and/or boiling propane (−42.degree. C.). In this instance, the cooling condenses most remaining gaseous components so that liquid alkanes are condensed.
In the processing facility 100, line 131 delivers the radiolysis products into the top of a heat exchanger 142. In the illustrative heat exchanger 142, chilled water is used for cooling the radiolysis products as a shell-and-tube heat exchanger. The water is chilled in a cooling tower 180 and then distributed to the exchanger 142 through line 181. Ball valve 188 controls the flow of water from the cooling tower 180 along line 181. The chilled water is optionally divided into two or more lines 185 for delivery to respective pumps 186. A second ball valve 189 resides along re-merged lines 185 to control the flow of chilled water into the heat exchanger 142. After circulating through the heat exchanger 142, the water is returned to the cooling tower 180 via return line 182. Ball valves 188 and 189 and check valve 189′ control the return of water to the cooling tower 180 along line 182.
During cooling of the radiolysis products, liquid alkanes gravitationally fall from the heat exchanger 142 and into a lower condensation basin 144. The liquid alkanes represent higher hydrocarbon components such as heptanes, hexanes and octanes. These radiolysis products are released into line 141 for export from the facility 100. At the same time, lighter alkanes and entrained gases such as nitrogen or hydrogen will rise back up into a distillation column 146. These gaseous components optionally exit the column 146 overhead through line 149.
It is observed here that during fluid separation, the separator 140 is carefully monitored and controlled. Temperature control “TC” is shown at the top of the heat exchanger 142 while temperature indicator “TI” is shown at the top of the distillation column 146. Pressure “P” and temperature “T” gauges are provided along the condensation basin 144.
In lieu of using a tube-and-shell type heat exchanger 142 with a chilling tower wherein liquids fall out, the separator may alternatively be a fractionator which fractionates the heavy hydrocarbons, or condensate, in the liquefied stream in the distillation column. In this step, the liquid condensate is heated to specific temperatures that cause the several components to separate through sequential evaporation. It is observed that the boiling points and densities of the respective alkanes increase with an increase in the number of carbon atoms. The boiling points are lower for branched isomers than for slightly branched or linear ones. Components of the condensate are separated into separate products using a vertical fractional distillation system where components are separated into “fractions” based on their boiling properties.
Regardless of the type of separator 140, it can be seen from
The lighter alkanes, being in the C1 to C5 range, flow through line 149 and are recirculated back into the reactor 130. A liquid sample port 143 is provided below a fluid level for the condensation basin 144 for testing the condensate. The products of radiolysis may be analyzed using a Q-Mass Perkin-Elmer chromatograph--mass spectrometer wherein helium is a carrier gas. Similarly, a gas sample port 147 is provided at the top of the condensation basin 144 or near a bottom of the distillation column 146 for sampling gases.
Referring to line 149, gaseous components representing a small stream of the lighter, non-condensed alkanes NG are re-circulated back into the reactor 130. The gaseous components are optionally heated at heater 145, and are then delivered to a separator 170 for the removal of hydrogen. In the arrangement of
Generally, membrane separator use the following process steps: (i) absorption of an impurity from the gas phase into a membrane matrix, (ii) diffusion through the membrane, and (iii) desorption out of the membrane and into the gas phase. Membranes generally are polymer membranes preferably chosen from asymmetric cellulose acetate or triacetate, composite layers of silicone/polysulfone, composite layers of polyetherimide, and composite layers of silicone/polycarbonate.
In one embodiment, the membrane separator is a PRISM separator. The following table (Table 1) demonstrates operating conditions for a membrane separator, in one aspect:
The following table (Table 2) demonstrates hydrogen and hydrocarbon gas output specifications for the membrane separator, in one aspect:
TABLE-US-00005 TABLE 2 H2 Rich Stream H2 Purity (mol %) 98.2 H2 Removal (scfm) 1,800 Flow Rate (scfm) 1,833 Pressure 18 Temperature (F.) 140 Product Stream H2 Content (mol %) 29.7 Flow Rate (scfm) 1,866 Pressure (pisa) 130 Temperature (F.) 143
Hydrogen is removed from the membrane separator 170 through release line 172. The hydrogen gas is taken through a compressor 175, and then delivered under pressure to a hydrogen storage tank 190. Line 177 indicates a pressurized hydrogen line that feeds into the tank 190. Pressure “P” and temperature “T” gauges are provided for monitoring conditions within the tank 190. When the tank 190 is deemed full, hydrogen may be sent off-site for sale or re-use in another commercial context.
In one aspect, the gases escaping from the lower condensate basin 144 are monitored for hydrogen (H2) content. Hydrogen (H2) content may be monitored by using an H2 sensor proximate a discharge line (147 or 149) from the reactor 140. When the hydrogen content reaches 10% by volume in the non-condensed gases, the gases are then sent to the membrane separator 170. Alternatively, the gases in line 149 may be sent to a pressure swing absorption (“PSA”) unit (not shown) for removal of the hydrogen gases. In this instance, re-circulating non-condensed gases in line 149 back into the reactor 130 comprises returning the non-condensed gases after separation of the hydrogen content in the pressure swing absorption unit.
In PSA processes, a gaseous mixture is carried under pressure for a period of time over a first bed of a solid sorbent that is selective, or relatively selective, for one or more components, usually regarded as a contaminant, that is to be removed from the gaseous mixture. The components that are selectively adsorbed are referred to as the heavy component, while the weakly adsorbed components that pass through the bed are referred to as the light components.
Thus, the molecular species that do not selectively fill the micropores or open volume of the adsorbent are usually the “light” components.
Adsorbents for PSA systems are usually very porous materials chosen because of their large surface area. Typical adsorbents are activated carbons, silica gels, aluminas and zeolites. In some cases, a polymeric material can be used as the adsorbent material. Though the gas adsorbed on the interior surfaces of microporous materials may consist of a layer of only one, or at most a few molecules thick, surface areas of several hundred square meters per gram enable the adsorption of a significant portion of the adsorbent's weight in gas.
Different molecules can have different affinities for adsorption into the pore structure or open volume of the adsorbent. This provides one mechanism for the adsorbent to discriminate between different gases. In addition to their affinity for different gases, zeolites and some types of activated carbons, called carbon molecular sieves, may utilize their molecular sieve characteristics to exclude or slow the diffusion of some gas molecules into their structure. This provides a mechanism for selective adsorption based on the size of the molecules and usually restricts the ability of the larger molecules to be adsorbed. Either of these mechanisms can be employed to selectively fill the micropore structure of an adsorbent with one or more species from a multi-component gas mixture.
In the present case, hydrogen molecules are considered to be the contaminant. The pressure swing absorption unit, or “PSA,” is preferably operated to remove hydrogen at 100 psi, and is maintained at 120.degree. F. (or higher) to ensure that no condensation occurs in the vessels.
Whether using a membrane separator or a PSA unit, excess hydrogen can be captured and re-purposed. For example, H2 may be used in fuel cell vehicles. See
http://www.consumerenergycenter.org/transportation/fuelcell/index.html
Referring again to the separator 170, conditions within the separator 170 are monitored. Temperature control “TC” and pressure control “PC” systems are associated with the separator 170. In one aspect, a gas line 122 is teed off of the blowers 120 to inject heated gas, under modest pressure, into the separator 170.
Hydrocarbon gases are released from the separator 170 through return line 171. Gate valve 178 provides selective control of gases along return line 171. In addition, a flow meter 173 and a check valve 179 are provided along return line 171. Low carbon gases are delivered back to gas lines 105 where they are ultimately returned to the reactor 130 for radiolytic treatment.
As noted, the heavier alkanes, or condensate, which are more valuable than the lighter alkanes, are in a liquefied state and are released through line 141. In one aspect, the liquid components are moved on to a separate distillation column (not shown) where the heavy hydrocarbons undergo fractionation. In this process, the liquid condensate is heated to progressively higher temperatures that cause the several components to separate through sequential evaporation. Components of the condensate are separated into separate carbon products using a vertical fractional distillation system where components are separated into “fractions” based on their boiling properties. The valuable end products of heptane, hexane and octane (and above) are generated, with each product exiting the column at a different vertical location. All products are produced as a 100 octane condensate.
Those of ordinary skill in the art will understand that there are other types of fractionation besides distillation/condensation. These include fractionation by molecular filtration, preferably by means of semi-permeable and selective membrane, fractionation by adsorption, preferably by means of molecular sieve, fractionation by absorption, in particular by means of absorbing oil, fractionation by cryogenic expansion, in particular by means of expansion turbine, and fractionation by compression, preferably by means of gas compressor. Any of these may be employed in the present inventions.
The condensate in line 141 may optionally be filtered.
As can be seen, a process for converting natural gas into hydrocarbon liquids through electron radiation, liquid condensation, and distillation is provided. While it will be apparent that the inventions herein described are well calculated to achieve the benefits and advantages set forth above, it will be appreciated that the inventions are susceptible to modification, variation and change without departing from the spirit thereof.
This application is a continuation-in-part of application Ser. No. 16/254,330, filed Jan. 22, 2019, which is a continuation of application Ser. No. 14/921,817, filed Oct. 23, 2015, which claims the benefit of U.S. Ser. No. 62/067,623 filed Oct. 23, 2014. That application is entitled “Gas-To-Liquids Conversion Process Using Electron Beam Irradiation,” and is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62067623 | Oct 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16254330 | Jan 2019 | US |
| Child | 16751795 | US | |
| Parent | 14921817 | Oct 2015 | US |
| Child | 16254330 | US |
