Well-site methane pyrolysis unit and method for pyrolysis of well-site methane as an alternative to flaring

Abstract

A methane pyrolysis reactor and method comprising the steps of passing a natural gas stream (11) through a porous permeable plate (3) to form natural gas bubbles, bubbling the natural gas stream through a molten metal column (2) supported by the porous permeable plate (3) to react the methane to obtain hydrogen and carbon dioxide, and separating a hydrogen gas stream (12) and carbon slag, wherein the size of the pores in the porous permeable plate (3) is such that the capillary pressure required for the molten metal to enter the pores exceeds the bottom pressure of the molten metal column (2).

Description

[Technical Field]

[0001] The present disclosure relates to an apparatus for the thermal decomposition of methane to produce hydrogen. Embodiments disclosed herein relate specifically to a well site methane pyrolysis apparatus and well site methane pyrolysis as an alternative to flaring. [Background technology]

[0002] Currently, well site methane, especially in remote locations, is disposed of inexpensively through flaring. However, flaring produces CO2. While simply releasing methane into the atmosphere is even cheaper than flaring, methane is estimated to have a Greenhouse Warming Potential (GWP) that is 28 to 36 times worse than carbon dioxide. Therefore, direct methane release is not a suitable alternative.

[0003] Carbon dioxide (CO2) is the most important long-lived greenhouse gas in the Earth's atmosphere. The accelerating increase in atmospheric carbon dioxide concentrations, primarily due to anthropogenic emissions from fossil fuel use and deforestation, is leading to global warming, and the need to reduce carbon dioxide emissions has become a major global concern.

[0004] Typical hydrogen production is also primarily based on steam reforming of natural gas, a technology that produces significant amounts of carbon dioxide as a by-product and therefore contributes to carbon dioxide emissions. Alternative hydrogen production technologies that do not involve direct CO2 emissions are under investigation. One method for reforming fossil hydrocarbons to produce hydrogen while avoiding the formation of CO2 is direct thermal or thermocatalytic decomposition, also known as cracking or pyrolysis. The thermal decomposition of methane-based natural gas is a promising approach in this field. Furthermore, unburned natural gas may contain H2S or other harmful gases, which are also decomposed by pyrolysis.

[0005] The simplified reaction equation below: CH4 → C + 2H2 The methane pyrolysis reaction described by is endothermic, with a standard reaction enthalpy of 74.8 kJ / mol.

[0006] High temperatures and long residence times favoring equilibrium compositions reduce the probability of producing intermediates such as ethane, ethylene, and acetylene because such hydrocarbons are unstable at high temperatures. Recent pyrolysis device designs are primarily based on fluidized beds for the application of catalysts, i.e., metals (e.g., Ni, Fe, Cu, Co), which increase reaction rates and allow for lower reaction temperatures by reducing activation energy. Nevertheless, all catalysts suffer from deactivation due to carbon deposition on active sites or even mechanical attrition of the catalyst. In addition to catalyst deactivation, the formation of solid carbon during the cracking reaction can lead to reactor clogging. An approach for continuous hydrocarbon cracking that circumvents these limitations is to utilize liquid metals (such as molten pure tin, indium, gallium, or lead, or alloys of these with nickel, platinum, or palladium, which can increase their catalytic activity) as heat transfer fluids in pyrolysis bubble column reactors. A simple mechanistic model for hydrocarbon bubbles is that they continuously renew their interface, which functions as a microreactor, releasing solid carbon particles floating on the surface of the liquid metal and gaseous hydrogen bubbling from the top of the liquid metal column. In this way, the aforementioned drawback of clogging of catalytic reactors can be avoided. The floating carbon particle slug can be vacuum-removed from the surface of the molten metal as an example of carbon particle removal. Furthermore, the liquid metal and / or the generated carbon can function as potential catalysts to accelerate the reaction.

[0007] The application of this technology presents challenges, including 1) maintaining the molten metal in the reactor chamber at temperatures often greater than 1000°C by preventing excessive heat loss from the vessel, 2) continuing to heat the metal inductively or with a hydrogen flame to replace heat lost to the endothermic methane pyrolysis reaction and heat leaks, and 3) removing and disposing of the resulting carbon slag, which make methane pyrolysis difficult to apply to wellsite methane, especially in remote locations. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an improved pyrolysis apparatus that has higher efficiency and is smaller than current technology systems would be beneficial and welcome in the art.

[0009] In one aspect, the subject matter disclosed herein is directed to a much smaller methane bubble size, which allows for a shorter molten metal column to be utilized, thereby enabling a more compact design, resulting in faster reaction rates and more complete conversion of methane to hydrogen. The porous permeable plates used to support the molten metal column and to introduce natural gas into the bottom of the molten metal column allow the gas to flow easily upward into the column, while preventing the molten metal and most of its heat from flowing downward, thereby reducing heat loss from the molten metal and the energy required to keep it at a high temperature. [Brief explanation of the drawings]

[0010] A complete understanding of the disclosed embodiments of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. [Figure 1] FIG. 1 is a schematic cross-sectional view of a pyrolysis apparatus according to a first embodiment. [Figure 2]FIG. 2 is a schematic cross-sectional view of a pyrolysis apparatus according to a second embodiment. [Figure 3] FIG. 3 is a schematic cross-sectional view of a pyrolysis apparatus according to a third embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view of a portion of a pyrolysis apparatus according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] According to one aspect, the present subject matter is directed to a pyrolysis apparatus in which natural gas (wellsite methane) flows from below through a molten metal column where it is cracked into hydrogen and carbon. The molten metal is supported by a porous, permeable ceramic frit. The pore size of the ceramic frit allows the natural gas to flow upward through it, forming bubbles as it contacts the molten metal column, but at the same time, the pores are small enough to prevent the molten metal from flowing downward through it. An insulating layer of ceramic microspheres is positioned below the permeable ceramic frit. Finally, another porous, permeable ceramic frit is positioned below the insulating layer of ceramic microspheres to filter out suspended particles in the raw natural gas.

[0012] Reference will now be made in detail to the embodiments of the present disclosure, one or more examples of which are illustrated in the figures. Each example is provided by way of explanation of the disclosure, not as a limitation of the disclosure. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. References throughout this specification to "an embodiment" or "one embodiment" or "some embodiments" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the disclosed subject matter. Thus, the appearances of the phrases "in one embodiment" or "in one embodiment" or "in some embodiments" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0013] When presenting elements of various embodiments, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the element. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0014] Referring now to the drawings, Figure 1 shows a schematic diagram of an exemplary pyrolysis apparatus according to one embodiment of the present disclosure. In particular, the exemplary embodiment shown in Figure 1 shows a pyrolysis apparatus 1 in which a molten metal column 2 is supported from below by a porous permeable plate 3, specifically a porous permeable ceramic top frit 3.

[0015] According to one embodiment, the temperature of the molten metal column 2 is in the range of 1000-1100°C.

[0016] The size of the pores in the ceramic top frit 3 is such that, when considering capillary pressure, the pores are too small for the molten metal to even enter, let alone flow through, the ceramic top frit 3. Capillary pressure is equal to twice the product of the interfacial tension of the molten metal (with respect to natural gas) and the cosine of the contact angle (between the molten metal and the ceramic) divided by the pore diameter. All liquid metals have high surface tensions in a vacuum and correspondingly high interfacial tensions with any gas. Therefore, very high pressures are required to deform the liquid metal surface into micrometer-sized pores. Such high inlet pressures are likely to far exceed the column weight pressure at the bottom of any column of liquid metal of any reasonable height. Therefore, the liquid metal is prevented from penetrating the pores.

[0017] That is, the capillary pressure required for the molten metal to enter the pores of the ceramic top frit 3 exceeds the bottom pressure of the molten metal column 2 (which is given by its density times the gravitational acceleration times the height of the column), thus preventing the molten metal from entering the pores.

[0018] However, methane can be pumped upwards through the frit to the bottom of the molten metal over a large area of ​​the ceramic top frit 3 in the form of small micrometer-sized bubbles instead of the millimeter-sized bubbles reported in the literature.

[0019] The smaller the pores in the ceramic top frit 3, the higher the molten metal 2 column can be without the molten metal entering the pores. Smaller pores also create smaller methane bubbles that heat up faster. If the bubbles heat up more quickly, a shorter molten metal column can be used, which allows for a more compact design. However, there is a practical limit and trade-off to the minimum pore size, as smaller pores mean a larger pressure drop for the methane across the ceramic top frit 3, reducing gas flow.

[0020] In an exemplary embodiment, a 10 μm pore size (as Coor's P-10-C) can support a molten metal column 2 70 inches in height, which is likely much taller than a column according to the present disclosure would be in practice.

[0021] According to the embodiment of FIG. 1, to reduce downward heat loss, a ceramic top frit 3 rests on an insulating layer 4 of high-temperature hollow ceramic microspheres. This hollowness results in low mass density, low thermal conductivity, a closed surface, and low heat capacity. The spherical shape ensures isotropic properties and a low surface-to-volume ratio. Exemplary ceramic microsphere materials can be aluminosilicate or amorphous aluminum phosphate or borosilicate glass. The microbubbles should have the lowest possible thermal conductivity. In an exemplary embodiment, the ceramic microspheres are K1 (65 microns) and S15 (55 microns), both produced by 3M, and have a thermal conductivity approximately twice that of still air. Within each 3M series, thermal conductivity increases with decreasing microbubble size, so larger sized microbubbles are preferred.

[0022] Finally, this layer 4 of hollow ceramic microspheres sits on top of a second porous permeable plate 5, specifically a porous permeable ceramic lower frit 5, which filters out particulates in the raw natural gas being pumped upwardly through it. The pores of the ceramic lower frit 5 may be much larger than the pores of the ceramic upper frit 3, as it is used only as a coarse particulate filter.

[0023] The molten metal column is contained laterally by a vessel 6 made of a high-temperature solid metal, preferably steel, with a melting point of 1370°C. A dewar bin is arranged around the steel vessel to avoid heat loss. The dewar bin walls 7 are made of a highly insulating material, preferably FRCI manufactured by Orbital Ceramics of Forrest Machining Inc., which is similar to the thermal tiles used to protect spacecraft as they re-enter Earth's atmosphere.

[0024] Heat loss from the top of the dewar bottle is significantly reduced by limiting the height of the molten metal column of hot liquid to less than one-third of the total height of the dewar bottle. According to the exemplary embodiment of Figure 1, a headspace 8 is shown above the molten metal column 2.

[0025] A carbon slag layer 9 forms on top of the molten metal column 2 because the density of carbon is much lower than the density of the liquid metal. A vacuum line 10 is present to occasionally suck the carbon slag from the top of the molten metal column 2.

[0026] According to the embodiment of FIG. 1, the pyrolysis device 1 operates as follows: A natural gas stream 11 enters the pyrolysis device 1 from the bottom and first passes through a ceramic lower frit 5, which removes fine particles from the natural gas stream by filtration. The natural gas stream then passes through an insulating layer of ceramic microspheres 4 and a porous, permeable ceramic upper frit 3, where it breaks down into small, micrometer-sized bubbles with diameters of less than a tenth of a millimeter. The micrometer-sized bubbles pass through the molten metal column 2 and are heated almost instantly to the ambient fluid temperature. Despite the low thermal conductivity of any gas, these micrometer-sized bubbles allow for near-instantaneous transfer of heat and immediate temperature equilibration all the way to the bubble center. As a result, the pyrolysis reaction rate increases accordingly. Solid carbon and gaseous hydrogen formed as products of the pyrolysis reaction are released to the top of the liquid metal column, and small carbon soot particles form a layer 9 that floats on top of the liquid metal surface due to density differences.

[0027] The methane pyrolysis reaction is an endothermic reaction, so heat must be supplied to the molten metal column to maintain the correct temperature. Some of the H2 produced is converted to H2 by the following reaction (ΔH0 = -486 kJ / mol): 2H2+O2→2H2O It can be combusted according to the formula (I) to provide heat to the molten metal column. Being a highly exothermic reaction, combustion of 15% of the produced H2 can provide enough heat to continue the decarburization reaction.

[0028] A hydrogen gas stream 12 exits the top of the pyrolyzer 1. The hydrogen thus produced can be used to power an internal combustion engine or a fuel cell to generate electricity.

[0029] The carbon soot is removed from the top of the molten metal column 2 and can be sold to the tire or other industries.

[0030] In some embodiments, solar energy may be used to generate electricity to heat the molten metal, or to directly or assist in heating the molten metal using sufficiently advanced solar concentrators.

[0031] Continuing with reference to Figure 1, a further embodiment of a pyrolysis apparatus according to the present disclosure is shown in Figure 2. Like reference numerals represent the same or corresponding parts, elements, or components already illustrated in Figure 1 and described above, and will not be described again here. In this embodiment, a flame nozzle 13 may be disposed around the molten metal column 2 to provide heat to the molten metal column 2.

[0032] Continuing with reference to Figures 1 and 2, a further embodiment of a pyrolysis apparatus is shown in Figure 3. The same reference numerals represent the same or corresponding parts, elements, or components as already illustrated in Figures 1 and 2 and described above, and will not be described again here. In particular, according to this embodiment, a coil 14 for induction heating of the molten metal may be used.

[0033] In yet another embodiment, and with particular reference to FIG. 4 , to maintain a small pore size for small bubble formation while not excessively increasing the pressure drop when pumping methane through the ceramic top frit 3, the ceramic top frit 3 is divided into a thin veneer of the finest pore size frit 15 on top of a thicker section of larger pore size frit 16. According to one embodiment, the veneer of the finest pore size frit 15 can be P-½-AC (0.5 micron pores) from Coors. Thus, with regard to the top frit, if the ceramic top frit 3 is made from a single material, the pore sizes can range from ½ micron if the ceramic top frit 3 is divided into a veneer of the finest pore size frit 15 on top of a larger pore size frit 16 (up to 10 microns).

[0034] In yet another embodiment, not shown, the bottom frit can be cup-shaped and extend around the periphery instead of simply being a flat, horizontal disk at the bottom of the column, to further increase the surface area in contact with the molten metal column 2.

[0035] While the present invention has been described in terms of various specific embodiments, it will be apparent to those skilled in the art that many modifications, changes, and omissions are possible without departing from the spirit and scope of the claims. Additionally, unless otherwise specified herein, the order or sequence of any process or method steps may be varied or rearranged according to alternative embodiments.

Claims

1. 1. A methane pyrolysis reactor comprising: a vessel (6); a porous permeable plate (3) disposed in the lower part of the vessel (6); at least one natural gas inlet (11) disposed below the porous permeable plate (3); and at least one hydrogen product outlet (12) disposed in the upper part of the reactor, wherein the porous permeable plate (3) is adapted to allow a natural gas stream to pass therethrough and to support a molten metal column (2) between the porous permeable plate (3) and a headspace (8) at the upper part of the vessel (6), the pores of the porous permeable plate (3) being sized such that the capillary pressure required for molten metal to enter the pores exceeds the pressure at the bottom of the molten metal column (2); and a thermal insulation layer (4) below the porous permeable plate (3) adapted to allow the natural gas stream to pass therethrough.

2. 2. The methane pyrolysis reactor of claim 1, further comprising a suction line (10) at the top of the molten metal column (2).

3. 2. The methane pyrolysis reactor of claim 1, further comprising a second porous permeable plate (5) below the insulating layer (4) adapted to filter out particulates from the natural gas stream and to allow the natural gas stream to pass through.

4. 2. The methane pyrolysis reactor of claim 1, further comprising a dewar bin (7) disposed around the container (6).

5. 2. The methane pyrolysis reactor of claim 1, further comprising a flame nozzle (13) disposed around the vessel (6) and the molten metal column (2).

6. 2. The methane pyrolysis reactor of claim 1, further comprising an induction heating coil (14) disposed around the vessel (6) and the molten metal column (2).

7. 2. The methane pyrolysis reactor of claim 1, wherein the porous permeable plate (3) is divided into a thin veneer of finer pore size plate (15) overlying a thicker section of larger pore size plate (16).

8. 1. A process for methane pyrolysis comprising: - passing a natural gas stream (11) through a thermal insulation layer (4) located below a porous permeable plate (3) and then passing said natural gas stream (11) through said porous permeable plate (3) to form natural gas bubbles; - bubbling said natural gas stream through a molten metal column (2) supported by said porous permeable plate (3) in order to react methane to obtain hydrogen and carbon; - separating the hydrogen gas stream (12) and the carbon slag, The method wherein the size of the pores in the porous permeable plate (3) is such that the capillary pressure required for the molten metal to enter the pores exceeds the pressure at the base of the molten metal column (2).

9. 9. The method of claim 8, wherein the step of separating the carbon slag comprises sucking the carbon slag from a carbon slag layer (9) above the molten metal column (2).

10. 10. The method of claim 8 or 9, further comprising filtering the natural gas stream (11) upstream of the porous permeable plate (3).

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