Patent Application
20150101814
Embodiments of the present invention relate to methods and apparatus for heating a bed of rocks to produce pyrolysis fluids (for example, alkylthiophene-rich hydrocarbon pyrolysis fluids) therefrom.
The world's supply of conventional sweet, light crude oil is declining, and discoveries and access to new resources for this premium oil are becoming more challenging. To supplement this decline and to meet the rising global demand, oils of increasing sulfur content are being produced and brought to market. Sources of sulfur-rich oil may be found in Canada, Venezuela, the United States (California), Mexico and the Middle East.
Although sulfur-rich oils, such as Maya crude, contribute significantly to the world's oil reserves, the economic and environmental costs of refining heavy oils can be significant. Many sulfur-rich hydrocarbons are sourced from a subset of Type II kerogen known to be sulfur-rich, called Type II-s or IIs. A schematic representation of one type of organic matter in Type IIs kerogen is illustrated below:
Originating from a marine-depositional environment, Type II-s kerogen is rich in sulfur-bearing organic compounds, and during thermal maturation produces oil and bitumen with high sulfur content. For example, the oil produced in some Iraqi oil fields have sulfur content of ˜4%.
Sulfur-rich oils include both conventional oils as well as unconventional oils. As conventional oil becomes less available (e.g. due to the increased cost of producing conventional oil from remote locations) and/or unable to meet world demand, it can be replaced with production of unconventional oils. Unconventional oils may be derived from a number of sources, including but not limited to oil sands, oil shale, coal, biomass, and bitumen deposits.
Presently, however, sulfur-rich oils are expensive to develop and bring to market for a variety of reasons. Sulfur rich oils must be treated with costly hydrogen gas during the refining process to lower the sulfur content of the oil, a process called hydrodesulfurization. Hydrotreating includes the effort to hydrodesulfurize and hydrodenitrify. Furthermore, sulfur rich oils are typically hydrotreated in sturdy but costly vessels due to the high pressures and temperatures required. When the sulfur-rich oils include significant quantities of metals, their presence of them may poison the catalysts, thereby requiring larger quantities of expensive catalyst.
Embodiments of the present invention relate to apparatus, methods and compositions associated with oil production from sulfur-rich Type IIs kerogen. One example of a Type IIs kerogen is kerogen of the Ghareb formation of Jordan.
Embodiments of the present invention relate to apparatus and methods for pyrolyzing sulfur-rich type IIs kerogen within an enclosure such as a pit or an impoundment or a container. Hydrocarbon-containing rocks (i.e. pieces of oil shale including sulfur-rich type IIs kerogen) are introduced into the enclosure to form a bed (e.g. a packed-bed) of rock therein. Oxygen may be evacuated (e.g. under vacuum or by means of an inert sweep gas) to create a substantially oxygen-free environment within the enclosure. In different embodiments, the enclosure may be a pit, or an impoundment or a container. The enclosure may be entirely below ground level, partially below and partially above, or entirely above ground level.
Operation of heaters in thermal communication with the hydrocarbon-containing rocks may sufficiently heat the rocks to convert the sulfur-rich type IIs kerogen thereof into pyrolysis formation fluids comprising sulfur-rich hydrocarbon pyrolysis fluids. The formation fluids may be recovered via production conduits, or via a liquid outlet located at or near the bottom of the enclosure and/or via a vapor outlet located near the top of the enclosure, or in any other manner.
After they exit the pit, the NGL (natural gas liquids) such as propane and butane may be separated from the methane and ethane gases because of the high economic value of NGL.
Some embodiments relate to apparatus and methods of heating beds of hydrocarbon-containing rocks (e.g. pieces of oil shale comprising type IIs kerogen) in a manner that has an improved efficiency and/or minimizes capital costs and/or accelerates the heating so as to allow for expedited recovery of the hydrocarbon pyrolysis fluids. Towards this end, it is now disclosed techniques whereby thermal energy is transferred to the hydrocarbon-containing rocks from molten salt heaters and/or from immersed heaters and/or in a system where convection is the dominant heat transfer mechanism.
In some embodiments related to heat convection and efficient heat transfer, thermal energy is transferred to the hydrocarbon-containing rocks primarily by liquid-immersed heaters deployed at or near the bottom of the container. In particular, the heaters may be immersed in a reservoir of hydrocarbon liquids (e.g. having a boiling point between 300 and 400 degrees) located at or near a bottom of the container. The direct thermal coupling between the heaters and the liquid in direct contact with the heaters significantly (e.g. by one or more orders of magnitude) increases an efficiency of heat transfer from the heaters to heat the hydrocarbon liquid of the immersing reservoir.
The hot hydrocarbon fluid (i.e. liquid or vapors boiled therefrom) of the reservoir upwardly migrates to locations above or near the top of the bed—for example, via one or more vertical conduits that vertically traverse the rock bed. The presence of the vertical conduits helps to maximize the fraction of thermal energy from the heaters that migrates directly to the top of the bed of particles.
The upward migration of hydrocarbon fluid (e.g. via the vertical conduit(s)) convectively transfers thermal energy supplied by the immersed heaters to these locations above or near the top of the bed. When this hydrocarbon fluid subsequently falls downwards through the rock bed, this thermal energy supplied by the immersed heater is convectively transferred to an interior of the rock bed.
In some embodiments, the walls of the vertical conduit(s) are substantially fluid-tight and/or thermally insulated so that most, or substantially an entirety, of the thermal energy of the reservoir-originating hydrocarbon fluids remains within the vertical conduit(s) during the upward migration of the hydrocarbon fluids. Because a relatively small fraction of thermal energy transferred to the bed during upward migration of the hot hydrocarbon fluids, it may be said that the primary heat transfer mechanism of thermal energy from the heaters to the bed of particle is downward heat convection. One advantage of relying specifically on heat convection is that it is assisted by gravity and may be much more efficient.
Some embodiments of the present invention provide two efficiency-related features: (i) transfer of thermal energy to hydrocarbon liquids from the immersed heaters; and (ii) gravity-assisted downward heat convection to the bed of particles.
Some embodiments of the present invention relate to convective re-boiling loops. In these embodiment, thermal energy from the immersed heaters boils liquids of the reservoir into condensable hydrocarbon vapor—for example, the liquid may enter the vapor phase before entering the vertical conduit or within the vertical conduit. Because of the relatively low density of hot hydrocarbon vapors, gravity drives upwards migration of the hydrocarbon vapors. The hydrocarbon vapor may condense (i) above and/or (ii) within the rock bed—e.g. in an upper half thereof or as the vapor moves downwards in the bed. In the later case, condensation of hydrocarbon vapors within the rock transfers phase-change enthalpy to the hydrocarbon rocks, further increasing a thermal efficiency of the heating process.
As an alternate to a re-boiling loop where buoyancy drives upwards migration of the heated gas-phase hydrocarbon fluids from the reservoir, it is possible to employ a gas lift or other pumping system to drive upward migration of liquid-phase hydrocarbon fluids from the reservoir from the bottom of the container to locations above or near the top of the rock bed. In these embodiments, hydrocarbon liquids are sent through the vertical conduits and then fall back through the bed. In both re-boiling embodiments (i.e. where vapor migrates upwards through the vertical conduits) as well as liquid embodiments (i.e. where hydrocarbon liquid or a multi-phase flow primarily comprising liquids flow upwards through the conduit), the bed of rocks may be heated such that type IIs kerogen of upper locations of the particle beds is pyrolyzed before that of lower locations of the particle bed. Thus, in some embodiments, a downwardly-moving pyrolysis front may be observed.
Although not a requirement, in one preferred embodiment, the immersed heaters are molten salt heaters. Molten salt heaters may be preferred because of their high thermal efficiency and uniform temperatures.
Furthermore, it is noted that molten salt may be employed as a heat transfer fluid in heaters that are not necessarily immersed heaters. For example, as discussed below, molten salt heaters may be deployed substantially at a wall of the enclosure or within a wall thereof.
In some embodiments, the enclosure may be sealed after the type IIs kerogen is pyrolyzed and hydrocarbon pyrolysis fluids are recovered. Alternatively, the post-pyrolysis rocks may be recovered from the container and the container may be reused.
In some embodiments, the apparatus for pyrolyzing hydrocarbon-containing rocks may substantially lack horizontally-oriented heaters that are deployed in locations significantly above the floor of the enclosure. For example, advection heaters embedded within or outside the walls or within a floor of the enclosure may be used to heat the hydrocarbon-containing rocks to pyrolysis temperatures.
In some embodiments, horizontal heaters that can maintain a constant preselected temperature along a long length are utilized. The heaters may be electrical heaters such as Curie heaters or SECT heaters. The heaters may be pipes heated by a heat transfer media such as molten salts, heated oils, and heated gases such as CO2, nitrogen, or steam or combustion air.
Heated molten salts may be circulated through the pipes to boil the oil in the lower section to pyrolyze the oil shale comprising type IIs kerogen in the pit. The advantages of the molten salt heating are the extremely high energy efficiency and the high heat transfer efficiency of molten salt. Only small diameter piping is required and uniform temperatures are achieved over long lengths. Hence the length of the surface pit may be very long, for example at least 30 meters or at least 100 meters or at least 200 meters or at least 500 meters longer. The piping may also be looped inside the pit so that the exterior piping manifold has fewer connections with fewer chances of leaks.
The pit may be constructed below grade level using earth-moving equipment. The pit may be lined with clay, such as bentonite, to render the walls and bottom substantially impermeable to liquids and vapors. It may be desirable to choose a location where the surface geology is a naturally-occurring clay so that lining the pit is unnecessary.
To assist in the understanding of the invention and for purposes of illustrative discussion, some embodiments are herein described, by way of example only, with reference to the accompanying drawings and images. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced. Dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale. The drawings are not to be considered as blueprint specifications.
Embodiments of the present invention relate to compositions (e.g. oils) containing one or more types of heterocyclic compounds including (i) sulfur heterocyclic compounds such as the single-ring alkylthiophenes, or the multi-ringed alkylbenzothiophenes or alkyldibenzothiophenes and (ii) nitrogen heterocyclic compounds such as the single-ringed alkylpyridines or alkylpyrroles, or the multi-ringed alkylquinolines, alkylisoquinolines, alkylacridines, and alkylindoles, and alkylcarbazoles.
The term ‘alkylthiophenes’ includes thiophene C4H4S as well as alkylated thiophenes. ‘Alkylated thiophenes’ are thiophenes where an alykl group is bonded to one or more locations on the thiophene ring. Thiophene C4H4S is an ‘alkylthiophene’ but is not an ‘alkylated thiophene.’ Examples of alkylated thiophenes include but are not limited to methyl thiophenes, di-methyl thiophenes, ethyl thiophenes, ethyl methyl-thiophenes, propyl thiophenes, etc. Analogous definitions (i.e. analogous to ‘alkylthiophenes’) apply to the multi-ring sulfur heterocyclic compounds (i.e. alkylbenzothiophenes and alkyldibenzothiophenes) to the single-ring nitrogen heterocyclic compounds (i.e. alkylpyridines and alkylpyrroles) and to the multi-ring nitrogen heterocyclic compounds (i.e. alkylquinolines, alkylisoquinolines alkylacridines, and alkylindoles and alkylcarbazoles).
By way of example, methyl thiophenes are a ‘C1 alkylthiophene’ because the total number of carbon atoms of alkyl groups bonded to a member of the thiophene ring is exactly 1. Both di-methyl thiophenes and ethyl thiophenes are ‘C2 alkylthiophenes’ because the total number of carbon atoms of bonded-alkyl group(s) bounded to a member of thiophene ring is exactly 2. C3 alkylthiophenes are molecules where the total number of carbon atoms of bonded-alkyl group(s) bounded to a member of thiophene ring is exactly 3—thus, C3 alkylthiophenes include tri-methyl thiophenes, methyl ethyl thiophenes and propyl thiophenes. Analogous definitions (i.e. analogous to ‘alkylthiophenes’) apply to the multi-ring sulfur heterocyclic compounds (i.e. alkylbenzothiophenes and alkyldibenzothiophenes) to the single-ring nitrogen heterocyclic compounds (i.e. alkylpyridines and alkylpyrroles) and to the multi-ring nitrogen heterocyclic compounds (i.e. alkylquinolines, alkylisoquinolines alkylacridines, and alkylindoles and alkylcarbazoles).
For a positive integer N, the terms ‘CN alkylthiophenes’ and ‘CN thiophenes’ are used synonymously and refer to alkylthiophenes (which also happen to be ‘alkylated thiophenes’) where the total number of carbon atoms of bonded-alkyl group(s) bounded to a member of thiophene ring is exactly N. Analogous definitions (i.e. analogous to ‘alkylthiophenes’) apply to the multi-ring sulfur heterocyclic compounds (i.e. alkylbenzothiophenes and alkyldibenzothiophenes) to the single-ring nitrogen heterocyclic compounds (i.e. alkylpyridines and alkylpyrroles) and to the multi-ring nitrogen heterocyclic compounds (i.e. alkylquinolines, alkylisoquinolines alkylacridines, and alkylindoles and alkylcarbazoles).
For a positive integer N, the terms ‘CN+ alkylthiophenes’ and ‘CN+ thiophenes’ are used synonymously and refer to alkylthiophenes (which also happen to be ‘alkylated thiophenes’) where the total number of carbon atoms of bonded-alkyl group(s) bounded to a member of thiophene ring is greater than or equal to N. Analogous definitions (i.e. analogous to ‘alkylthiophenes’) apply to the multi-ring sulfur heterocyclic compounds (i.e. alkylbenzothiophenes and alkyldibenzothiophenes) to the single-ring nitrogen heterocyclic compounds (i.e. alkylpyridines and alkylpyrroles) and to the multi-ring nitrogen heterocyclic compounds (i.e. alkylquinolines, alkylisoquinolines alkylacridines, and alkylindoles and alkylcarbazoles).
For positive integers N, M (M>N), the terms ‘CN-CM alkylthiophenes’ and ‘CN+ thiophenes’ are used synonymously and refer to alkylthiophenes (which also happen to be ‘alkylated thiophenes’) where the total number of carbon atoms of bonded-alkyl group(s) bounded to a member of thiophene ring is either (i) exactly N; or (ii) exactly M or (iii) greater than N and less than M. Analogous definitions (i.e. analogous to ‘alkylthiophenes’) apply to the multi-ring sulfur heterocyclic compounds (i.e. alkylbenzothiophenes and alkyldibenzothiophenes) to the single-ring nitrogen heterocyclic compounds (i.e. alkylpyridines and alkylpyrroles) and to the multi-ring nitrogen heterocyclic compounds (i.e. alkylquinolines, alkylisoquinolines, alkylacridines, and alkylindoles and alkylcarbazoles).
When determining concentration of alkylthiophenes (or, by analogy, alkylbenzothiophenes or alkyldibenzothiophenes or alkylpyridines and alkylpyrroles or alkylquinolines, or alkylisoquinolines or alkylacridines or alkylindoles or alkylcarbazoles), the location to which alkyl group(s) are attached is immaterial.
For the present invention, an ‘alkylthiophene-rich oil’ is an oil where a majority (or a substantial majority) of the sulfur compounds are alkylthiophenes and/or an oil that is at least 10% or at least 20% by volume alkylthiophene. For the present invention, an ‘alkylpyridine and/or alkylpyrrole rich oil’ is an oil where a majority (or a substantial majority) of the nitrogen compounds are alkylpyridines or alkylpyrroles and/or an oil that is at least 10% or at least by volume either alkylpyridines or alkylpyrroles.
For the present disclosure, a ‘sulfur-rich feedstock’ or a ‘sulfur-rich pyrolysis liquid’ is at least 3% wt/wt or at least 4% wt/wt sulfur.
For the present disclosure, sulfur-rich type IIs kerogen is at least 6% wt/wt or at least 7% wt/wt or at least 8% wt/wt sulfur. For the present disclosure, ‘low temperature pyrolysis’ is pyrolysis that occurs at temperatures of at most 290 degrees Celsius over a period of at least 3 months or at least 6 months or at least 1 year. In some embodiments, ‘low temperature pyrolysis’ occurs between 270 degrees Celsius and 290 degrees Celsius over this period of at least 3 months or at least 6 months or at least 1 year. In some embodiments, ‘low temperature pyrolysis’ occurs between 280 degrees Celsius and 290 degrees Celsius over this period of at least 3 months or at least 6 months or at least 1 year. In this temperature range, pyrolysis proceeds quickly enough to be feasible, while favoring formation of easier-to-hydrotreat species.
Overview
Embodiments of the present invention relate to apparatus and methods for sulfur-rich type IIs kerogen (e.g. pieces of oil shale—e.g. mined oil shale)) within an enclosure such as a pit or an impoundment or a container. Hydrocarbon-containing rocks comprising sulfur-rich type IIs kerogen are introduced into the enclosure to form a bed (e.g. a packed-bed) of rock therein. Oxygen may be evacuated (e.g. under vacuum or by means of an inert sweep gas) to create a substantially oxygen-free environment within the enclosure. In different embodiments, the enclosure may be a pit, or an impoundment or a container. The enclosure may be entirely below ground level, partially below and partially above, or entirely above ground level.
Operation of heaters in thermal communication with the hydrocarbon-containing rocks may sufficiently heat the rocks to convert type IIs kerogen thereof into pyrolysis formation fluids comprising hydrocarbon pyrolysis fluids. The formation fluids (e.g. sulfur rich, e.g. rich in alkylthiophenes) may be recovered via production conduits, or via a liquid outlet located at or near the bottom of the enclosure and/or via a vapor outlet located near the top of the enclosure, or in any other manner.
As illustrated in
The heated hydrocarbon fluids may vaporize either before entering chimney 126 or therein. Thus, as illustrated
Upon exiting vertical chimney 126, the hydrocarbon vapors may condense back into the liquid phase upon contacting a surface whose temperature is below its boiling point at that pressure. As condensed hydrocarbon liquids fall back downwards through the rock bed 110 (i.e. labeled Downwardly Migrating Hydrocarbon Liquids (DMHCL)), they convectively heat the rocks of rock-bed 110—for example, sufficiently to pyrolyze type IIs kerogen thereof.
Thus,
Thus, one advantage of the system of
At least one wall of the excavated enclosure containing rock bed 110 is heated by the vertical molten salt heaters 178. In the example of
Reference is made once again to
For the present disclosure, an ‘excavated enclosure’ refers to artificially dug pit or a natural pit (i.e. modified in some manner) or to a pile of soil/earth formed or modified by excavation—e.g. to form an impoundment at least partly above-ground. For the present disclosure, a ‘substantial majority’ refers to at least 75%.
For the present disclosure, when a fluid (e.g. molten salt or any other fluid) is ‘hot’ a temperature thereof is at least 200 degrees Celsius or at least 300 degrees Celsius.
Reflux Based Systems
For the present disclosure, a ‘hydrocarbon reflux loop’ describes the (i) boiling of hydrocarbon liquid into condensable hydrocarbon vapors; (ii) the upward migration of the hydrocarbon vapors; (iii) the condensation of the hydrocarbon carbon vapors back into liquid at a higher location than where the liquid was boiled (e.g. above the rock bed or substantially at a top of the rock bed); and (iv) gravity-driven downward migration (i.e. ‘falling’) of the hot hydrocarbon liquids back down through the rock bed to convectively transfer thermal energy from the hydrocarbon liquids to the rocks of the rock bed. It is requirement of the ‘reflux loop’ for the condensed hydrocarbon liquids to be subsequently re-boiled back into hydrocarbon vapors to repeat the upward migration, condensation, and downward migration to convectively transfer thermal energy to the rocks.
As noted above,
In order to create an anoxic environment within the enclosure (e.g. within the ‘pit’), the pit may be sealed. In the example of
As illustrated in
As illustrated in
As noted above, once condensable hydrocarbon vapors exit from a top of chimney 126 via upper opening 148, they may condense at locations at or above a top of rock bed 110 but within the sealed excavated enclosure, e.g. due to the lower temperatures at the top of the enclosure. In some embodiments, in order to horizontally distribute the liquid-phase condensed hydrocarbon fluids to various locations within the rock bed 110, it may be useful to provide a liquid distribution system above rock bed 110 so as to distribute the condensate over a variety of horizontal locations of rock bed 110.
In the examples of
Hydrocarbon liquid falls through one or more voids 224 within or between spreader tray(s) and then falls through the rock bed 110. As illustrated in
In the example of
One salient feature provided by embodiments of the present invention is the downward heat convention in an upper half of rock bed 110 that is driven by heaters (e.g. immersed heaters) below rock bed 110. Thus, despite the fact that a majority or substantial majority of thermal energy delivered to rock bed 110 comes from heaters below rock bed 110, it is possible to generate downward convection (i.e. by means of the vertical chimneys 126) in an upper half of rock bed 110.
In some embodiments, as a result of the downward heat convection (e.g. driven by thermal energy supplied by heaters 134 immersed within lower hydrocarbon liquid reservoir 114), type IIs kerogen of hydrocarbon-containing rocks at the very top of rock bed 110 is heated to pyrolysis temperatures before type IIs kerogen of rocks at lower levels within the top half of rock bed 120. Thus, in some embodiments, and as illustrated in
As noted above with reference to
Reference is now made to
Illustrated in
Outside the pit, the liquid hydrocarbons produced from the pit enter a fractionation tower. There, shale oil with a preselected boiling point cut is removed and drained into the bottom of the pit just above the boiling hydrocarbon liquid. This circulation from the fractionation tower constantly refreshes the boiling hydrocarbons at the bottom of the pit and maintains the composition of the boiling hydrocarbons at the desired boiling point range.
For the present disclosure, when a rock bed is situated within an enclosure, an ‘external heater’ is a heater located outside of the chamber/region where the rock bed is situated. This is in contrast to heaters within the rock bed—for example, conduits which traverse the rock bed.
During heating, a 118 level of reservoir covers the heater pipes. The spacing between pipes is calculated to provide continuous boiling of the oil. Typical heater spacing may be, for example, 5 ft, 10 ft or greater. The heat transfer from the heater pipes immersed in oil may be 1000 watts/ft, 5000 watts/ft, 10,000 watts/ft or higher. The optimal spacing may be determined by numerical simulations or by scale model experimentation in the lab.
Heating of the oil shale to pyrolysis temperatures is achieved via a refluxing process where boiling hydrocarbon vapors condense on the colder sections of the pit and impart the heat of vaporization. Liquid hydrocarbons return to the oil bath through the oil shale matrix by gravity and capillary forces. The refluxing process may be enhanced by adding slotted conduits to provide preferential pathways for vapor flow to reach the colder section, as shown in
The hydrocarbon liquid of reservoir 114 that may be used for starting the heating may be a diesel oil with a boiling point above 300° C. The heater pipes should be heated to a temperature where the heater pipe skin temperature is higher than the boiling point of the oil but not above 375° C. where coking of the diesel oil may occur. An optimum temperature may be in the range 300-375° C., 325-370° C., or 340-360° C. When operating at the higher temperature ranges, the heater pipes may be coated with coke inhibitors such as silicates to prevent scale from forming.
As the pyrolysis proceeds, the condensed hydrocarbon pyrolysis liquids will mix with the diesel oil in the bottom of the pit. The boiling point distribution will gradually change to that of the shale oil. If the boiling point distribution gets too elevated in temperature, it may be desirable to circulate additional diesel cut into the bottom section to maintain the boiling point in the above mentioned ranges.
As shown in
Outside the pit, the liquid hydrocarbons produced from the pit enter a fractionation tower. There shale oil with a preselected boiling point cut is removed and drained into the bottom of the pit just above the boiling hydrocarbon liquid. This circulation from the fractionation tower constantly refreshes the boiling hydrocarbons at the bottom of the pit and maintains the composition of the boiling hydrocarbons at the desired boiling point range.
The pressure in the pit may be maintained at atmospheric pressure or at an elevated pressure (e.g. 1 to 3 atm.). The higher the pressure during pyrolysis, the higher quality the oil and gas produced. The pressure that can be maintained may be determined by the depth of the pit and the amount of soil added above the seal. Higher pressures improve the oil qualities but increase the possibility of gaseous leakage from the pit.
Maintaining pressure with non-condensable gases may also be used to control the height of the refluxing process and thereby controlling the volume of oil shale being heated at a given time. This minimizes the initial amount of diesel required for the refluxing process. As pyrolysis occurs at the lower sections of the pit, the pressure is lowered and the shale oil that is generated adds to the refluxing supply and establishes an incrementally higher reflux point in the pit.
The boiling point distribution of the refluxing oil may also be varied by adjusting the pressure in the pit to achieve different heating temperatures if desired. The boiling temperature can be increased by elevating the pressure. The optimum pressure may be in the range of 1-3 atm. For instance, hexadecane has a boiling point of ˜300° C. at 1 atm. At 2 atm., the boiling point increases to ˜350° C. By operating the pit at elevated pressures and temperatures, at the end of pyrolysis, hydrocarbon liquids remaining in the pit may be flashed to vapor by lowering the pressure of the pit.
In some embodiments, production pipes may be located in the pit or pile. Liquids are produced from the production pipe at the bottom and gases produced from the production pipe at the top of the pit or pile.
The top of the seal may be covered with a thermally insulating layer of refractory ceramic or clay or combinations of the two to limit heat losses to the environment. Additional pits may be constructed adjacent to existing pits (
The pipes may be constructed with Grayloc fittings so that they can be easily removed. The pipes are sloped at an angle between 0.1-2° (see
As shown in
A layer of insulation may be placed on top of the pit to reduce heat losses. The pit is then covered with an impermeable layer, which is sealed at the top of the wall to prevent the escape of-fluids or vapors. This layer may be clay, stainless steel lining, silicone rubber, or other impermeable material. The insulation at the top of the pit may be located above or below the impermeable layer. If the layer of insulation is located below the impermeable sheet it is preferred that it be comprised of closed cell insulation to prevent liquids accumulating in the insulation. It is preferred that this layer of insulation and the impermeable seal be made of a flexible material such that it can be rolled in place following the filling of the pit and unrolled upon completion of the pyrolysis process.
As shown in
The spacing between parallel heater walls is calculated to provide thermal conduction heating of the hydrocarbon material in a time period of about a few months. Typical heater wall spacing may be, for example, 10 ft, 20 ft, 30 ft or greater spacing. The heater walls may be oriented along the long axis of the pit or the short axis of the pit.
The array of pits may be very long, for example 100 ft, 300 ft, 1000 ft, 3000 ft or longer. The width of the pit may by 50 ft, 100 ft, 200 ft, 300 ft or wider. The depth of the pit may be 10 ft, 30 ft, 50 ft, 100 ft or deeper. As shown in
For pits with widths that are substantially long, for example 100 ft or longer, pillars to support the elevated tracks for the two-axis crane may be located within the pit as shown in
Heater pipes are embedded in the heater walls and radiantly heat the walls to a nearly uniform temperature. The heater walls may be constructed of a metal frame with metal sheeting covering the frame. The sheeting may be welded along the joints to seal the wall from entrance of any produced vapors. The metal frame is designed and sized to handle the load from the material in the pit without substantial deformation. The width of the wall is sufficiently large to accommodate the outer diameter of the heater pipes, though sufficiently small to maintain a large solid angle from the heater pipe to the wall, thereby increasing the effectiveness of the radiant heat transfer. The surfaces of the pipe and the surfaces of the wall may also be roughened and blackened to increase emissivity of the surfaces and hence the radiant heat transfer. The interior of the walls surrounding the heater pipes may act effectively as a black body and maintain a substantial constant wall temperature.
Low molecular weight gases with good thermal conductivity such as hydrogen or helium may be added to the inner space of the wall to further enhance heat transfer from the heater pipes to the heater walls.
The space within the heater walls may also be filled with solid granular material with high thermal conductivity, such as copper, aluminum or iron balls, to enhance heat transfer from the heater pipes to the heater walls.
Within the metal frame of the heater wall is a structure to support the heater pipes. The steel support frame may be lubricated with graphite or other high temperature lubricant to prevent sticking during the initial thermal expansion of the heater pipes. The heater piping may be looped along the long axis of the wall and may have multiple passes within the walls before existing as shown in
In some embodiments, horizontal heaters pipes arranged within the walls maintain a substantially constant preselected temperature along a long length as shown in
The heaters may be pipes heated by a heat transfer fluids such as molten salts, heated oils (such as Therminol VP-1 (Solutia) or DowTherm A (Dow Chemical), which are eutectic mixtures of biphenyl (C12H10) and diphenyl oxide (C12H10O) with operating temperatures up to 400° C.)), and heated gases such as CO2, nitrogen, supersaturated steam or combustion air. The heaters may also be electrical heaters such as Curie heaters or SECT heaters.
Molten salts are the preferred heat transfer fluids according to some embodiments. Molten salts have high heat capacity, low viscosity, and may be operated to high temperatures, for example, 450° C., 550° C., 600° C., 700° C., or higher depending on the specific molten salt. This allows for high heat transfer from the circulating molten salt to the heater walls using reasonable pipe diameters and flow rates. Pipe diameters may be, for example, 3″, 5″ or higher. Flow rates may be for example, 1 kg/s, 5, kg/s, 15 kg/s or higher. The other heat transfer fluids (e.g. oils or gases) may be used for preheating the pipes above the melting point of the molten salt used in this invention.
The molten salt may comprise nitrate or nitrite salts such as HiTec salt, HiTec XL, Solar Salt, etc. The molten salt may also comprise carbonates, chlorides, or fluoride salts. The molten salts may be a single, binary, ternary, quaternary or other mixture of compounds. The molten salt may be chosen to have a maximum use temperature of 375° C. or higher.
As shown in
Counter-current flow between adjacent heater pipes in the same wall helps provide uniform heating to the pit. The heater piping may be looped inside the pit so that the exterior piping manifold has fewer connections with fewer chances of leaks
Molten salt heat delivery systems can achieve very high thermal efficiencies, for example, 80-90%, if the furnaces are multipass and the incoming gases are preheated by the exhaust gases. The longer the length of the heater piping in the pit compared to the insulated section outside the pit, the more thermally efficient the molten salt heaters become. If the length of the heater in the pit is, for example, ten times the length of the insulated section outside the pit, the overall thermal efficiency may approach the furnace efficiency.
Gases for the molten salt furnaces may also be preheated by passing the gases through piping in previously pyrolyzed pits that have not cooled yet.
As shown in
The pipes from a non-heated pit may be preheated using a heat transfer fluid from one of the adjacent piles or pits. Alternatively, a gas combustor can be used to blow hot combustion gases through the pipes for preheating. Electrical heating of the pipes using Joule heating, skin effect heating, or induction heating, can also be used.
The heat injection rate from the wall into the pit may be 500 W/m2, 1000 W/m2 or higher. The heat injection from a single heater pipe may be 500 W/ft, 1000 W/ft or higher, depending on the temperature of the heat transfer fluid and the diameter and spacing of the heater pipes. The temperature of the heat transfer fluid in the heater pipes may be in the range 400-700° C. or 500-600° C., or preferably about 550° C. The optimal spacing between heater pipes may be determined by numerical simulations using a computer program such as STARS (CMG, Calgary) or by pilot experimentation. The spacing of the heater pipes may be, for example, 5 ft, 10 ft, or greater. The thickness of the wall may be, for example, 0.5 ft, 1.0 ft, 1.5 ft or greater.
The heater walls may also be heated by using boiling, reflux and condensation as the heating method. As shown in
The working fluid for the desired operating temperature range of 350-700° C. may be fluids such as synthetic oils, molten salts, or molten metal. This invention preferably utilizes synthetic oils such as Therminol VP-1 (Solutia) or DowTherm A (Dow Chemical) as the working fluid. These oils have a boiling points approaching 400° C. when pressurized up to 150 psi. When operating at the higher temperature ranges, the inner side of the walls may be coated with coke inhibitors such as silicates to prevent scale from forming.
The gas pressure in the pit may be maintained at atmospheric pressure or slightly elevated pressures (e.g. 1 bar gauge). The higher the gas pressure during pyrolysis, the higher quality of the oil and gas produced. The gas pressure that can be maintained in the pit may be determined by the quality of the seal of the impermeable cover. Higher gas pressures in the pit improve the oil qualities but increase the possibility of gaseous leakage and odors from the pit. Alternatively, a slight vacuum may be applied through the gas production piping to collect the vapors. This reduces the chances for leakage of odors from the pit but may result in a somewhat lower quality of oil product.
In a second embodiment, the hydrocarbon-bearing material is not directly filled into the pit but rather it is transported to the facility in specially designed reusable shipping containers by rail or truck. The containers may have sizes of 8×9.5×48 ft or larger. The containers are lowered into the pit and arranged into a rectangular array between the walls as shown in
An insulating blanket may be rolled over the top of the containers after a row of heaters is placed in the pit. This row may then be heated by the two adjacent heater walls, bringing the material in the containers to pyrolysis temperatures. Thermally conductive material may be placed between adjacent containers to enhance heat transfer between the containers. The liquids and gases are produced through a port on the top of the containers and treated at an onsite location. As successive rows of containers are loaded into the pit, heating of the new row commences. After a row is fully pyrolyzed in ˜3-4 months, the containers are allowed to cool. The containers with post-pyrolysis material are then removed from the pit and transported out of the facility.
The containers used in the pits may be constructed from a high strength alloy with good high temperature corrosion resistance such as 347H stainless steel. The corners of the containers are rounded to reduce stress concentrations during the multiple thermal cycling of the containers.
In order to minimize costs, the containers used for heating in the pits may also be different than the shipping containers. In this case the post-pyrolysis material may be transferred from the heating containers to the shipping containers. The shipping containers may then be of standard steel construction.
In the description and claims of the present application, each of the verbs, “comprise” “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb.
All references cited herein are incorporated by reference in their entirety. Citation of a reference does not constitute an admission that the reference is prior art.
The articles “a” and “an” are used herein to refer to one or to more than one. (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.
The term “including” is used herein to mean, and is used interchangeably with, the phrase “including but not limited” to.
The term “or” is used herein to mean, and is used interchangeably with, the term “and/or,” unless context clearly indicates otherwise.
The term “such as” is used herein to mean, and is used interchangeably, with the phrase “such as but not limited to”.
The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will occur to persons skilled in the art.
| Number | Date | Country | |
|---|---|---|---|
| 61868523 | Aug 2013 | US |
