US20150203776A1

US20150203776A1 - Method and system for heating a bed of hydrocarbon- containing rocks

Info

Publication number: US20150203776A1
Application number: US14/377,511
Authority: US
Inventors: Harold Vinegar; Scott Nguyen
Original assignee: Genie IP BV
Current assignee: Genie IP BV
Priority date: 2012-02-18
Filing date: 2013-02-18
Publication date: 2015-07-23
Also published as: CN104302870B; WO2013123488A1; CN104302870A; IL233751A0; AU2013221197A1; CA2864863A1

Abstract

Hydrocarbon-containing rocks (e.g, mined oil shale or mined coal or tar sands) are introduced into an excavated enclosure (e.g. a pit or an impoundment) to form. a bed of rocks therein, One or more heaters (e.g. molten salt heaters) are operated to pyrolyze kerogen or bitumen of the rocks. In some embodiments, a hydrocarbon reflux loop is maintained within the enclosure to convectively heat the hydrocarbon-containing rocks by boiling hydrocarbon liquids from a reservoir at the bottom of the enclosure so that vapor passes to the top of the enclosure, condenses, and falls back through the bed. Alternatively or additionally, the rocks may be heated by heaters embedded within wall(s) and/or a floor of the enclosure. Some embodiments relate to techniques for upgrading mined coal to recover both hydrocarbon pyrolysis fluids and upgraded coal (e.g. anthracite coal).

Description

FIELD OF THE INVENTION

Embodiments of the present invention relate to methods and apparatus for heating a bed of kerogen-containing or bitumen-containing rocks, for example, to produce pyrolysis fluids therefrom.

DESCRIPTION OF RELATED ART

Hydrocarbons obtained from subterranean formations are often used as energy resources, as feedstocks, and as consumer products. Concerns over depletion of available hydrocarbon resources and concerns over declining overall quality of produced hydrocarbons have led to development of processes for more efficient recovery, processing and/or use of available hydrocarbon resources. In situ processes may be used to remove hydrocarbon materials from subterranean formations that were previously inaccessible and/or too expensive to extract using available methods. Chemical and/or physical properties of hydrocarbon material in a subterranean formation may need to be changed to allow hydrocarbon material to be more easily removed from the subterranean formation and/or increase the value of the hydrocarbon material. The chemical and physical changes may include in situ reactions that produce removable fluids, composition changes, solubility changes, density changes, phase changes, and/or viscosity changes of the hydrocarbon material in the formation.
Large deposits of heavy hydrocarbons (heavy oil and/or tar) contained in relatively permeable formations (for example in tar sands) are found in North America, South America, Africa, and Asia. Tar can be surface-mined and upgraded to lighter hydrocarbons such as crude oil, naphtha, kerosene, and/or gas oil. Surface milling processes may further separate the bitumen from sand. The separated bitumen may be converted to light hydrocarbons using conventional refinery methods. Mining and upgrading tar sand is usually substantially more expensive than producing lighter hydrocarbons from conventional oil reservoirs.
Retorting processes for oil shale may be generally divided into two major types: aboveground (surface) and underground (in situ). Aboveground retorting of oil shale typically involves mining and construction of metal vessels capable of withstanding high temperatures. The quality of oil produced from such retorting may typically be poor, thereby requiring costly upgrading. Aboveground retorting may also adversely affect environmental and water resources due to mining, transporting, processing, and/or disposing of the retorted material. Many U.S. patents have been issued relating to aboveground retorting of oil shale. Currently available aboveground retorting processes include, for example, direct, indirect, and/or combination heating methods.

SUMMARY OF EMBODIMENTS

Embodiments of the present invention relate to apparatus and methods for heating hydrocarbon-containing matter (e.g. tar sands or kerogen-containing rocks such as pieces of coal or pieces of oil shale) within an enclosure such as a pit or an impoundment or a container. Hydrocarbon-containing rocks 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 kerogen or bitumen thereof into pyrolysis formation fluids comprising 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. Hydrogen may also be separated from the produced gases and used in upgrading of the produced shale or coal oils.
Some embodiments relate to apparatus and methods of heating beds of hydrocarbon-containing rocks (e.g. piece of coal or of oil shale, or tar sand) 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.
Some embodiments relate to apparatus and methods for maximizing an economic and/or an environmental value of the thermally treated hydrocarbon-containing rocks for example, by upgrading coal in a manner now disclosed. Some embodiments relate to apparatus structured for relatively easy removal of thermally treated rocks (e.g. upgraded coal) from the container - for example, in a manner that minimizes the cost of removal or that facilitates re-use of the container.
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 kerogen or bitumen 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 kerogen or bitumen 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. For example, it is possible to sufficiently pyrolyze bituminous coal within the container so as to upgrade the bituminous coal to much more valuable and more environmentally benign anthracite coal.
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, or facilitate the removal of upgraded coal from 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 or coal 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.
In the case of coal, the top seal of the pit or pile is opened after pyrolysis to remove the devolatilized coal. This coal may be more valuable than the initial coal because it has higher carbon content, higher calorific value, ultra lower moisture and volatiles, and lower sulfur. After removing the post-treatment coal, the pit can be refilled with fresh coal for the next pyrolysis. The post-pyrolysis coal may also be steam washed in the pit while still warm to remove ash from the coal and further upgrade the coal to the highest grade metallurgical coal. Circulating steam may achieve both the cooling and washing of the coal.
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.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

FIGS. 1A-1B, 5-12 and 17 illustrate reflux-based systems where repeated boiling of hydrocarbon liquids of a reservoir convectively transfers thermal energy from heater(s) immersed within the liquid reservoir to various locations of the rock bed.

FIGS. 2, and 13-18 relate to systems for pyrolysis of hydrocarbon-containing rocks (e.g. mined oil shale or mined coal or tar sands) arranged in a rock bed in an interior of an excavated enclosure by wall-embedded heaters.

FIGS. 4A-4B relate to methods for re-using an interior of an excavated enclosure. FIGS. 4B and 19-22 relate to techniques for upgrading mined coal within an excavated enclosure.

FIGS. 3 and 23-24 relate to systems where a rock bed of hydrocarbon-containing rocks is heated by horizontal molten salt heaters traversing the rock bed.

DETAILED DESCRIPTION OF EMBODIMENTS

Overview
Embodiments of the present invention relate to apparatus and methods for heating hydrocarbon-containing matter (e.g. tar sands or kerogen-containing rocks such as pieces of coal or pieces of oil shale) within an enclosure such as a pit or an impoundment or a container. Hydrocarbon-containing rocks 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 kerogen or bitumen thereof into pyrolysis formation fluids comprising 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.
Examples of hydrocarbon-containing rocks are kerogen-containing rocks (e.g. mined oil shale or mined coal) and bitumen-containing rocks (e.g. tar sands).
FIGS. 1A-1B, 5-12 and 17 illustrate reflux-based systems where repeated boiling of hydrocarbon liquids of a reservoir convectively transfers thermal energy from heater(s) immersed within the liquid reservoir to various locations of the rock bed. FIGS. 2, and 13-18 relate to systems for pyrolysis of hydrocarbon-containing rocks (e.g. mined oil shale or mined coal or tar sands) arranged in a rock bed in an interior of an excavated enclosure by wall-embedded heaters. FIGS. 4A-4B relate to methods for re-using an interior of an excavated enclosure. FIGS. 4B and 19-22 relate to techniques for upgrading mined coal within an excavated enclosure. FIGS. 3 and 23-24 relate to systems where a rock bed of hydrocarbon-containing rocks is heated by horizontal molten salt heaters traversing the rock bed.
FIGS. 1A-1B is a schematic diagram of a horizontal cross-section of a reflux-based surface pit system for pyrolyzing a bed of hydrocarbon-containing rocks arranged in a rock bed 110—for example, a packed bed of rocks arranged according to any packing (e.g. random packing). In the example of FIGS. 1A-1B, a plurality of heaters 134 arranged substantially at the bottom of the pit heat an interior of the pit so as to heat the hydrocarbon-containing rocks of the rock bed 110. As will be discussed below, for the examples of FIG. 1A-1B, heat convection is a significant mechanism of transferring thermal energy from heaters 134 of rock bed 110.
As illustrated in FIGS. 1A-1C, heaters 134 are immersed within a reservoir 114 of hydrocarbon liquids at the bottom of the pit. Heating of the liquid-phase hydrocarbon fluids of reservoir 114 by immersed heaters 118 drives the hydrocarbon fluids upwards—e.g. by vaporizing the fluids or by reducing a density of hydrocarbon liquids. The upwardly-driven heated hydrocarbon fluids (i) enter vertical chimney 126 via a lower opening 144 thereof; (ii) migrate upwards through vertical chimney 126 to substantially vertically traverse rock bed 110 (see upwardly migrating condensable hydrocarbon vapor (UMCHCV) and (iii) exit vertical chimney via an upper opening 148 thereof.
The heated hydrocarbon fluids may vaporize either before entering chimney 126 or therein. Thus, as illustrated FIGS. 1A-1B, hydrocarbon vapors derived by boiling liquids of reservoir 114 migrate upwards through vertical chimney 126—these upwardly migrating vapors are labeled Upwardly Migrating Condensable Hydrocarbon Vapor (UMCHCV). Because a resistance to fluid flow within the chimneys 126 is significantly lower than within the rock bed 110, the presence of the chimneys 126 may significantly increase a rate at which thermally energy convectively and upwardly migrates to the top of rock bed 110.
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 bitumen or kerogen thereof.
Thus, FIGS. 1A-1B relate to a reflux/reboiling loop whereby hydrocarbon liquids are repeatedly boiled to efficiently and convectively transfer (e.g. over relatively ‘large distances’) thermal energy from immersed heaters to various locations of rock bed 110 including those at relatively ‘high’ elevations. In the example of FIG. 1A-1B, a majority or substantial majority of upward vapor migration occurs within the vertical chimneys where resistance to fluid flow is at least 10 times or at least 100 times or at least 1,000 times an average fluid flow resistance observable within rock bed 110—thus, the presence of the chimneys 126 may significantly increase the efficiency of convection of thermal energy from the immersed heaters to the rock bed 110.
Thus, one advantage of the system of FIGS. 1A-1B is the shorter amount of time required to pyrolyze kerogen or bitumen of the rock bed.
FIG. 2 illustrates one example of a surface pit system for thermally treating a rock bed 110 of hydrocarbon-containing rocks within an interior of an excavated enclosure (e.g. pit or impoundment) that is heated by molten salt heaters. In the specific example of FIG. 2, vertical molten salt heaters 178 (VMSH) are arranged within a tall, thin chamber 184—i.e. a ratio between a height of chamber 184 and at least one horizontal dimension thereof (e.g. a lesser horizontal dimension) may be at least 5 or at least 10. Rocks of rock bed 110 are arranged in the interior of a chamber of an enclosure (e.g. a pit).
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 FIG. 2, a primary mechanism of heating of rock bed 110 is by transfer of thermal energy from the walls of the enclosure (i.e. which are heated by the ‘embedded heaters’) to rock bed 110.
As will be discussed below, one advantage of the apparatus of FIG. 2 is efficiency due to the use of molten salt, an extremely efficient heat-transfer fluid. FIG. 3 is another example of a surface pit system including molten salt heaters—in the example of FIG. 3, the molten salt heaters comprise horizontal conduits that pass through a bed of hydrocarbon-containing rocks. Although not explicitly stated above, is further noted that the immersed 134 of FIGS. 1A-1B may be molten salt heaters.
Reference is made once again to FIG. 2. By relying primarily on wall-embedded heaters rather than heaters located within rock bed 110 (for example, horizontal conduit heaters that traverse rock bed 110), it may be significantly easier to remove post-pyrolysis rocks to re-use the pit to pyrolyze another batch of hydrocarbon-containing rocks. As will be discussed in greater detail below, in some embodiments, these post-pyrolysis rocks may be a valuable and/or environmentally friendly solid hydrocarbon resource.
FIG. 4A is a flowchart of a routine for re-using an enclosure after it has been used to pyrolyze kerogen or bitumen of rocks of a rock-bed. FIG. 4B relates to the specific case where (i) pieces of mined bituminous coal form a rock-bed within an enclosure; and (ii) the bituminous coal is upgraded to anthracite coal within the enclosure—for example, heaters are operated to provide the requisite time-temperature heating history. As will be discussed below, (i) anthracite coal is much more environmentally friendly and potentially more valuable than bituminous coal and (ii) in some embodiments, the techniques FIG. 4B may require subjecting the bituminous coal to a more rigorous time/temperature history than would be required for situations where one is only interested in obtaining hydrocarbon pyrolysis fluids.
For the present disclosure, when the temperature of an object or location is ‘significantly increased,’ this requires an increase of at least 25 degrees Celsius or at least 50 degrees Celsius.
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, FIGS. 1A-1B, 5-12 and 17 illustrate reflux-based systems where repeated boiling of hydrocarbon liquids of a reservoir convectively transfers thermal energy from heater(s) immersed within the liquid reservoir to various locations of the rock bed.
In order to create an anoxic environment within the enclosure (e.g. within the ‘pit’), the pit may be sealed. In the example of FIG. 1A, the pits is sealed from the top by substantially-fluid tight cover 138 (e.g. comprising soil). Furthermore, a presence of clay liner 152 may retain fluids within an interior of the excavated enclosure. A presence of a thermal insulator such as concrete liner 156 may retain thermal energy within an interior of the excavated enclosure. As an alternative to the clay liner 152 and/or concrete liner 156 (i.e. which is illustrated in various figures), it is possible (see, for example, FIG. 10B) to select a location where the underlying source rock has a low permeability to retain fluids within the enclosure interior and/or is a good thermal insulator to retain thermal energy within the enclosure. In yet another example, it is possible to employ a freeze wall and/or wax wall and/or sulfur wall to retain fluids—this may be deployed adjacent to the excavated enclosure or distanced therefrom. For example, a freeze wall or sulfur wall or wax wall structure may enclose a plurality of excavated enclosures.
As illustrated in FIG. 5, rock bed 110 is supported by a grating (e.g. steel grating 120) which is not fluid tight but which has a pore size that is significantly smaller than a characteristic size of the rocks of rock bed 110. The small characteristic pore size of the grating is small (e.g. at most 10 cm prevents rocks of rock bed 110 from falling into and clogging up reservoir 114. Furthermore, in some embodiments a second rock bed of non-pyrolyzable rocks (e.g. a tight gravel filter 122) may also serve this purpose.
As illustrated in FIGS. 5, an upper level 118 of reservoir 114 may be maintained substantially above heaters 134 so that heaters 134 remain immersed within reservoir 114. In some embodiments, the upper level 118 is maintained substantially below an entirety of rock bed 110.
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 FIGS. 6-8, an array of spreader tray(s) 220 are arranged substantially above rock bed 110. Condensation of hydrocarbon vapor above spreader tray causes hydrocarbon liquid (e.g. at or near a boiling point thereof) to accumulate in an ‘upper reservoir’ 214 on the spreader tray(s) 220. Because the upper reservoir 214 is supplied by condensation of hydrocarbon vapor(s) that exits via upper opening 148 of chimney 126, it may be said that upper reservoir 214 is supplied by the lower reservoir 114. Although multiple spreader trays 220 are illustrated in FIGS. 6-7 this is not a limitation and in some embodiments, a single spreader tray 220 (e.g. having multiple voids 224 therein) may be arranged within the enclosure.
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 FIG. 7, the spreader tray assembly (e.g. including the void(s) 224) is useful for horizontally distributing the hydrocarbon liquid (i.e. derived from condensation above rock bed 110) throughout rock bed 110.
In the example of FIG. 8, each void is associated with a lip 228. In order for hydrocarbon liquid of upper reservoir 214 to flow downwardly through a given void, a level of upper reservoir 214 should exceed a height of lip 228 above the spreader tray 220 to which it is attached. The presence of lip 228 around each void 220 helps to temporally smooth a rate at which condensed hydrocarbon liquids flow down through void 220 into bed 104. The presence of lip 228 helps to regulate an amount of hydrocarbon liquid in upper reservoir
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), kerogen or bitumen of hydrocarbon-containing rocks at the very top of rock bed 110 is heated to pyrolysis temperatures before kerogen or bitumen of rocks at lower levels within the top half of rock bed 120. Thus, in some embodiments, and as illustrated in FIGS. 9A-9C, a downwardly moving pyrolysis front may be observed in an upper half of rock bed 110.
As noted above with reference to FIG. 4A, in some embodiments it is desirable to reuse an excavated enclosure (e.g. pit or impoundment). One feature for such re-use is illustrated in FIG. 10A. Substantially vertical chimney 126 may be mounted to support grating 120 in a manner such that the vertical chimney is detachable. In the example of FIG. 10A, chimney 126 may be mounted onto the grating so that a lower distal end of chimney 126 of a cap thereof it mounted into a pipe port. In one example, after mounting of chimney 126, rock bed 110 is formed by introducing hydrocarbon-containing rocks into the excavated enclosure. This may be followed by heating of the rock bed—e.g. to pyrolyze kerogen or bitumen thereof. After pyrolysis, it is possible before removing a majority of rock bed 110 to (i) disengage a distal end of chimney 126 to the mounted ports mounted onto the grating; (ii) pull vertical chimneys 126 out of the excavated enclosure; and (iii) once the chimneys have been removed and there is substantially an absence of heaters and other equipment in an interior of rock bed 110, scoop out rocks of rock bed 110. As is the case with the wall-embedded heater embodiments discussed elsewhere with reference to FIGS. 2 and 13-18, the technique of FIG. 10A may facilitate pit re-use and/or economic exploitation of post-pyrolysis rocks (e.g. upgraded coal) of rock bed 110.
Reference is now made to FIG. 10B. In the example of FIG. 10B, there is no need for a clay liner.
FIG. 11 is schematic illustration of yet another embodiment of the present invention. In the example of FIG. 11, the chimneys are situated substantially at the walls of the excavated enclosure. This is in contract to the example of FIGS. 1A-1B and 5 where the chimneys are surrounded by the rock bed 102.
Illustrated in FIG. 11, but applicable to all reflux-based embodiments is apparatus for regulating a liquid level 118. A fluid level sensor and automatic control valve maintain the level of the boiling oil above the heaters. As pyrolysis occurs, additional coal or shale oil liquid hydrocarbons above this level are produced via the automatic control valve through production pipes.
Outside the pit, the liquid hydrocarbons produced from the pit enter a fractionation tower. There, coal or 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 coal or 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 coal or 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 FIG. 2. The conduits maybe located along the sides and middle of the pit and may extend the length of the pit. Multiple rows of conduits may be added to further enhance the refluxing process. Condensation may initially occur at or near the bottom of the pit and progress upward during the heating process. The heating time of the pit to pyrolysis temperature will be determined approximately by the heat capacity of the packed coal in the pit divided by the total heat input from all the heaters minus any heat losses to the surrounding environment.
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 or coal 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 FIG. 11, a fluid level sensor and automatic control valve maintain the level of the boiling oil above the heaters. As pyrolysis occurs, additional shale oil liquid hydrocarbons above this level are produced via the automatic control valve through production pipes.
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 coal or 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 coal or 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 (FIG. 12). Surface facilities such as processing equipment and heating systems may be shared between multiple pits, thereby reducing the total surface footprint and capital expenditures.
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 FIG. 24) so that the molten salt can self-drain from the pipes and other molten salt equipment into the lower molten salt container which may be placed below grade on the down flow side.

Thermal Conduction Heating of Pit or Pile with Molten Salt Heaters Embedded in Walls

FIGS. 2, and 13-18 relate to systems for pyrolysis of hydrocarbon-containing rocks (e.g. mined oil shale or mined coal or tar sands) arranged in a rock bed in an interior of an excavated enclosure by wall-embedded heaters.
As shown in FIG. 2, a pit is first excavated. The pit may be lined with clay, such as bentonite, to render the 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 with clay is unnecessary. The pit may be constructed below grade level using earth-moving equipment well known in open pit mining operations. A hard insulation layer such as a low density refractory ceramic (firebrick) may then be placed inside the clay barrier to reduce heat losses to the surroundings. The walls of the pit are constructed of a sealed metal structure, and heater pipes are embedded in the walls of the structure. The bottom of the heater walls extend into the layer of clay, creating a seal at their intersection. The pit is then filled with pieces of oil shale, coal, tar sands, or other hydrocarbon-bearing material.
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 FIG. 14, multiple pits may be arranged side by side with each pit sharing common heater walls with its neighboring pits. In this arrangement, heat losses to the surroundings may be minimized.
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.
FIG. 13 shows for example the rise in temperature between two heater walls spaced 16.4 ft (5 m) apart and maintained at a constant temperature of 500° C. The thermal diffusivity of the packed bed is assumed to be 0.004 cm²/sec. The pyrolysis of the hydrocarbon-bearing material is complete in about 3 months when the temperature at the midplane rises to about 325° C. In addition to heat transfer by thermal conduction, natural convection of hot fluids within the packed bed will also be effective and may shorten the heating time and may allow more uniform heating in the packed bed.
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 FIG. 14, an elevated structure supporting a two-axis crane may be installed over the pits. A mechanical claw or scooper connected to the crane fills the pit with hydrocarbon-bearing material transported to the site. Post-pyrolysis, the scooper empties the pit into a container to be transported away from the site. The site may be located near a railroad line or road to facilitate the transportation of material to and from the site of the pit by train or truck. A conveyor belt may also be provided on site for conveying material to and from the pits.
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 FIG. 15. The foundation for the pillar may be surrounded by thermal insulation such as a refractory ceramic and may remain cool while the sounding pit is being heated. A multitude of pillars may be located within the pit, which are sufficient to mechanically support the elevated tracks of the crane.
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 FIG. 16. Looping the piping within the wall naturally creates expansion loops to accommodate thermal expansion.
In some embodiments, horizontal heaters pipes arranged within the walls maintain a substantially constant preselected temperature along a long length as shown in FIG. 16. The heater pipes may also be oriented vertically within the walls as shown in FIG. 2. The advantage of the horizontal heater pipes are the long lengths and hence reduced number of individual heaters and pipe connections. An advantage of the vertical heater pipes is that they may be able to be easily replaced in an event of a failure during the heating process.
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 FIG. 16, the hot molten salt is fed into the heater pipes from a molten salt heat delivery system. The molten salt container and the external piping between them are insulated and heat traced to prevent heat losses and freezing of the molten salt. There is a pump located in the molten salt container that pumps the molten salt to a furnace that heats the molten salt and circulates the molten salt through the heater pipes in the walls. The heating of the furnace may be achieved using processed gas, natural gas, coal, or oil. The heating gas may be gas produced from the process that has been treated to remove undesirable components such as hydrogen sulfide, carbon monoxide and carbon dioxide, and separate valuable natural gas liquids and hydrogen. The hydrogen gas may be utilized in the hydrotreating facility for upgrading the oil produced. The hydrogen sulfide may be treated in a Claus plant to make elemental sulfur and the sulfur may be used to produce fertilizer.
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 FIG. 16, a single molten salt heating system may be shared between multiple pits, thereby reducing the total surface footprint and capital expenditures. Liquid and gas treatment facilities may also be shared by multiple pits.
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/m²or 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 FIG. 17, horizontal pipes heated by circulating molten salt may be located in a lower section of the wall—e.g. immersed in a reservoir of working fluid. The working fluid with a boiling point near the desired operating temperature (350-700° C.) fills the space inside the wall to a level covering the heater pipes. The heater pipes boil the working fluid, and the vapors condense on the walls, thereby imparting the heat of vaporization and heating the wall to a nearly uniform temperature.
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 FIG. 18. Between each heater wall the containers may be arranged in a single or in multiple rows. These rows may be a multitude in both width and height.
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.
Upgrading Coal
The type of coal utilized for this invention is preferably in the range of vitrinite reflectance R_obetween 0.45 and 0.9, most preferably between 0.5 and 0.8. This range of coal types includes sub-bituminous A, high volatile bituminous C, B, and A, and medium volatile bituminous coal. These types of coal have high volatiles and low moisture content. During pyrolysis the hydrocarbon fluids produced comprise light oils with API gravities above 30° API and hydrocarbon gases with maximum C₁-C₄content and minimum CO₂. Low sulfur and low ash coals are preferred.
Production ports may be located at the top of the pit or pile and penetrate through the impermeable seal and insulation. Fluids are produced in the vapor phase through the top port, and the liquids and gases are separated. The API gravity of the produced oil may be 30° API or higher. 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. Hydrogen may also be separated from the produced gases and used in upgrading of the produced oils.
FIG. 4B is a flow chart of a method for upgrading mined coal within an enclosure (e.g. an excavated enclosure). In step S241, pieces of coal are introduced into the enclosure. In step S245, the coal within the pit and/or container is heated over a sufficient amount of time so that: (i) kerogen of the coal is pyrolyzed into hydrocarbon pyrolysis formation fluids which may be recovered from the enclosure (see step S249); and (ii) the coal itself is upgraded to increase the coal vitrinite reflectance and/or to reduce the fraction of volatile matter and/or to increase a fraction of carbon and/or reduce a moisture content and/or to increase a heat content density by weight.
In step S243, the upgraded coal is removed from the enclosure.
In one non-limiting example, (i) the ‘input’ coal introduced in step S241 is primarily bituminous coal (for example, high volatile bituminous coal) and/or sub-bituminous coal and/or primarily coal whose reflectance is less than 1.2 or less than 1.0 or less than 0.8 or less than 0.6 or less than 0.4 and (ii) the upgraded coal has one or more properties of anthracite coal and/or is anthracite coal. Towards this end, in some embodiments, it is possible to heat the coal to achieve specific time-temperature histories.
For example, it is possible to heat this ‘input coal’ over a ‘multi-month’ time period (e.g. for at least 2 months or at least 2.5 months or at least 3 months or at least 3.5 months or at least 4 months or at least 5 months or at least 6 months or at least 7 months), such that the temperature of the heated coal exceeds a MINIMUM_TEMP (e.g. for example, at least 350 degrees C. or at least 375 degrees C. or at least 400 degrees C. or at least 425 degrees C. or at least 450 degrees C. or at least 475 degrees C. or at least 500 degrees C. or at least 550 degrees C. or at least 600 degrees C.) most of the time or substantially all of the time during the ‘multi-week’ or ‘multi-month’ time period.
In some embodiments, a maximum temperature of the bed of coal during the multi-month time period is at most 800 degrees C. or at most 700 degrees C. or at most 600 degrees C.
In some embodiments, the ‘upgraded coal’ removed in step S253 (i) has a reflectance of at least 2.5 or at least 2.75 or at least 3.0 or at least 3.25 or at least 3.5 and/or (ii) comprises (i.e. by total weight or by weight on an ash-free basis) less than 12% or less than 10% or less than 8% or less than 6% volatile matter and/or (iii) has a heat content (i.e. by total weight or by weight on an ash-free basis) that exceeds 33,000 kJ/kg or that exceeds 33,500 kJ/kg or that exceeds 34,000 kJ/kg or that exceeds 34,500 kJ/kg and/or that exceeds 35,000 kJ/kg and/or that exceeds 35,500 kJ/kg and/or (iv) comprises (i.e. by total weight or by weight on an ash-free basis) less than 8% or less than 6% or less than 4% or less than 3% or less than 2.5% sulfur and/or (v) comprises (i.e. by total weight or by weight on an ash-free basis) at least 88% or at least 89% or at least 90% or at least 91% carbon and/or (v) has one or more properties associated with so-called ‘anthracite coal.’
There is no limitation on the features (e.g. physical structure or any other features) of the container and/or pit in which the coal-upgrading routine of FIG. 1 is carried out.
It is noted that the time-temperature history required to achieving specific reflectance property and/or other property related to ‘upgrading coal’ or ‘upgrading a rank of coal’ may at least partially depend upon the type of and/or the properties of the (i) ‘input’ coal and which is subjected to the coal-upgrading process and the (ii) upgraded coal resulting from the process.
The skilled artisan is directed to WO/2003/036035 entitled “IN SITU UPGRADING OF COAL” and U.S. Pat. No. 6,969,123 entitled “Upgrading and mining of coal” both of which are incorporated herein by reference in their entirety. These patent documents describe the upgrading of bitumen coal to anthracite coal in situ. It is now disclosed that similar conditions may be replicated within an enclosure so as to economically exploit the upgraded coal.
As illustrated in FIG. 19, in some embodiments, longer processing times are required when operating at lower temperatures (i.e. as evidenced by the ‘negative’ slopes illustrated in FIG. 19) and/or when upgrading to a ‘higher ranked coal and/or when employing a ‘lower-ranked’ starting material/‘input’ coal.
The example of FIG. 19 illustrates linear curves—this is a simplified example is appreciated that the shape of the curves may differ.
In the example of FIG. 19, the coal rank ‘X2’ exceeds the coal rank ‘X1’ while the coal rank ‘Y2’ exceeds the coal rank ‘Y1.’ FIG. 19 is a hypothetical example, and unless otherwise indicated, is not intended as limiting in any manner. For example, there is no requirement that the ‘curves’ are linear and/or parallel to each other.
FIG. 20A illustrates the time dependencies of various measurable time-dependent properties as a function of time in some embodiments relating to the any coal-upgrading routine disclosed herein. FIG. 20B illustrates that rate at which liquid and gaseous hydrocarbons are from the coal. Both FIGS. 20A-20B relate to hypothetical examples, and unless otherwise indicated, no feature(s) of FIG. 20A and/or FIG. 20B is intended as limiting. Nothing in FIGS. 20A and/or 20B is intended as ‘to-scale’ unless indicated otherwise.
In some embodiments, a bed of rocks is formed from bituminous coal, and a majority of the bed of rocks is maintained (i.e. under anoxic conditions) at a temperature of at least 375 degrees Celsius or of at least 380 degrees Celsius or of at least 385 degrees
Celsius or of at least 390 degrees Celsius for a least 1 week or at least 2 weeks or at least 1 month or at least 2 months or at least 3 months or at least 6 months.
In the example of FIG. 20A, vitrinite reflectance and bulk temperature of the coal, and heater power level is illustrated for one example relating to the upgrading of mined coal under anoxic conditions within an enclosure (e.g. an excavated enclosure). During an earlier period of time (TIME_PERIOD_—1), most kerogen of the coal is pyrolyzed into condensable hydrocarbon pyrolysis fluids (referred to informally as ‘liquids’), while in a latter time period (i.e. TIME_PERIOD_—2), most non-condensable hydrocarbon pyrolysis formation fluids are generated. At a later period in time (TIME_PERIOD_—3), despite the fact that most if not substantially all pyrolysis fluids have been generated from coal kerogen, it is possible to continue to deliver significant power to the coal of the coal bed so as to continue to upgrade the coal. From the point of view of economic pyrolysis fluid recovery, delivery of thermal energy to the coal during TIME_PERIOD_3 may be unnecessary. However, it is now disclosed that this is useful for upgrading mined coal.
Reference is made once again to FIG. 20A. At different times during the coal upgrade process, local coal physical and/or chemical properties may vary at different locations within the container and/or pit. One coal property that may be monitored (e.g. by employing removing coal from then pit and/or container to sample the coal and/or by employing a fiber-optic system to monitor the coal within the pit and/or container) at different times is the vitrinite reflectance. As illustrated in FIG. 20B at times t₀-t₅the temperature in a particular location and/or the bulk-averaged vitrinite reflectance and/or maximum temperature within the pit and/or container may respectively be written as R₀-R₅. In some embodiments when the input coal is so-called high volatile bituminous coal, R₀is at most 1.2 or at most 1.0 or at most 0.8 or at most 0.6 or at most 0.4. In some embodiments, R₂is at most 1.6 or at most 1.4 or at most 1.2. In some embodiments, R₄is at most 2.5 or at most 2.0 or at most 1.8 or at most 1.6. In some embodiments, R₅is at least 2.4 or at least 2.6 or at least 2.8 or at least 3.0 or at least 3.2 or at least 3.4 or at least 3.6 or at least 3.8 or at least 4.0
Pre-Processing of Coal
Pretreatment of the coal may be desirable to produce the best quality post-pyrolysis coal. Pretreatment of the initial coal may include water washing to remove ash and fines. The coal pieces may be pre-sized to select a size range that will easily pack in the pit to achieve a packing with high vertical permeability.
In some embodiments, the coal is pre-processed before heating to reduce the ash content-for example washing the coal (or alternatively mechanical agitation) to reduce the ash content (i.e. as a ‘bulk property’ of coal particles) of the coal. In some embodiments, before the pre-processing the ash content before exceeds 10% or exceeds 15% or exceeds 20%. In some embodiments, the ash content is reduced to no more than 7% or no more than 6% or no more than 5% or no more than 4% or no more than 3%. In some embodiments, the ash content is reduced by at least 20% or at least 30% or at least 40% or at least 50% or at least 60% or at least 70% or at least 80%.
The flotation step of removing inorganic matter could also be done before the bituminous coal is placed in the pit, as well as after. Removing ash may obviate the need to heat the inorganics to high temperatures.
The pre-processing may be carried out in any time or in any location. For example, the pre-processing may be carried out ‘on site’ near the container or pit or off-site.
Post-Processing of Coal After Pyrolysis
After pyrolysis, the top seal of the pit or pile may be opened to remove the devolatilized coal or oil shale. This coal may be more valuable than the initial coal because it has higher carbon content, higher calorific value, ultra lower moisture and volatiles, and lower sulfur and nitrogen. After removing the post-treatment coal or oil shale, the pit can be refilled with fresh coal or oil shale for the next pyrolysis operation. The post-pyrolysis coal or oil shale may also be steam cleaned in the pit while still above 100° C. to achieve both steam stripping and more rapid cooling of the coal or oil shale.
For example, a majority of coal within the pit and/or container may be cooled by at least 150 degrees or at least 200 degrees C. or at least 300 degrees C. within a period of time that does not exceed 1 month or does not exceed 2 weeks or does not exceed 1 week or does not exceed 3 days or does not exceed 2 days or does not exceed 1 day or does not exceed 12 hours or does not exceed 6 hours.
In some embodiments, it is possible to carry out the cooling of the coal by so-called steaming of the coal—i.e. introducing liquid water into the container and/or pit to ‘quickly’ cool the coal to a temperature that is (i) less than 150 degrees C. or less than 125 degrees C. or less than 110 degrees C. and (ii) greater than 80 degrees C. or greater than 90 degrees C. or greater than 95 degrees C. By ‘steaming’ the coal it is possible to simultaneously (i) wash out impurities of the coal (ii) benefit from a ‘quick cooling of the coal’ while (iii) keeping the coal substantially dry.
The coal may be removed from the container and/or pit at a temperature that is about 100 degrees C. or allowed to cool further before removing in step S133.
FIG. 22B relates to a hypothetical example where the water flow rate of liquid water into the pit is dramatically reduced (e.g. by at least 80% or at least 90%) at a time when the coal temperature approached 100 degrees C.
After pyrolysis, the coal may be removed from the pit using buckets that scoop the coal between the columns of heater pipes. The coal may be upgraded during the pyrolysis process because water and volatiles have been removed. The post-pyrolysis coal may have higher carbon content, higher calorific value, lower sulfur, oxygen and nitrogen, higher vitrinite reflectance, and lower ash than the mined coal. Thus this premium coal product may be sold at a higher price than the initial mined coal.
The temperature, time of heating, and pressure of the coal pit may be adjusted to achieve the greatest value added by upgrading the coal to different desirable grades. For example, a high value ultralow volatile anthracite coal may be produced suitable for PCI sintering for metallurgical coking. In general, anthracite coal may be more valuable than lower grades of coal.
A Discussion of FIGS. 23-24
FIG. 23 is a cross section of a horizontal molten salt heating system that traverses a bed of rocks.
As shown in FIG. 24, the hot molten salt is fed from one side of the pit where the molten salt container is located. The molten salt containers and the external piping between them are insulated and heat traced to prevent heat losses and freezing of the molten salt. There is a pump located in the molten salt container that pumps the molten salt to a furnace that heats the molten salt and circulates the molten salt through the heater pipes in the pt. The heating of the furnace may be done using processed gas, natural gas, coal, or oil. The heating gas may be gas produced from the process that has been treated to remove undesirable components such as hydrogen sulfide, carbon monoxide and carbon dioxide, and separate valuable natural gas liquids and hydrogen. The hydrogen gas may be utilized in the hydrotreating facility for upgrading the oil produced. The hydrogen sulfide may be treated in a Claus plant to make elemental sulfur.
A similar molten salt heat delivery system (tank, furnace, pump, and piping manifold) may be placed on the opposite side of the pit to reheat the cold molten salt coming from the pit and recirculate hot molten salt in the opposite direction. Counter-current flow between adjacent heater pipes helps provide uniform heating to the pit. Instead of a second molten salt heat delivery system, the heater piping may be looped inside the pit so that the exterior piping manifold has fewer connections with fewer chances of leaks.
In geographical regions of high average solar intensity, solar radiation may be used to heat the heat transfer fluid using solar collectors such as parabolic troughs, parabolic dishes, or power towers. Parabolic trough solar collectors are preferred as the synthetic oil used to collect the solar heat can also function to transfer the heat to the pit. Furthermore, the operating temperature range of 350-390° C. matches the temperature range required for the pit. To accommodate daily solar intermittency, energy may be stored in high temperature molten salt tanks and sized accordingly.
After pyrolysis is complete, the heaters are de-energized and the oil in the lower section is drained from the pit. Some coal or oil shale liquids may remain in the pores of the matrix and may be evaporated and collected by circulating gases such as methane, CO₂, or nitrogen through the matrix. These gases may be part of a closed-loop heat exchanger involving multiple pits whereby the heated gas is circulated through a pre-pyrolysis coal or oil shale in an adjacent pit, simultaneously cooling down the post-pyrolysis pit and preheating the adjacent pit, thereby increasing the thermal efficiency of the process even further.
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.

Claims

1. A method of heating hydrocarbon-containing rocks comprising:

a. introducing the hydrocarbon-containing rocks into an interior region of an excavated enclosure to form a bed of rocks therein;

b. maintaining a reservoir of hydrocarbon liquids substantially at the bottom of the interior region of the excavated enclosure; and

c. heating the hydrocarbon liquids of the reservoir so as to maintain a hydrocarbon reflux loop within the interior region to convectively heat the hydrocarbon-containing rocks.

2-3. (canceled)

4. The method of claim 1 wherein the interior region is maintained under anoxic conditions during the heating.

5. The method of claim 1 wherein kerogen or bitumen of the rocks are pyrolyzed, the hydrocarbon reflux loop supplying at least a portion of the thermal energy required to pyrolyze kerogen or bitumen of the rocks.

6. The method of claim 1 wherein the reflux loop vertically spans at least a majority of the rock bed and/or of the interior region of the excavated enclosure.

7. The method of claim 1 wherein liquid hydrocarbon vapor of the reflux loop condenses primarily above the rock bed and/or substantially at a top thereof.

8. The method of claim wherein a majority of the hydrocarbon fluid flow of the reflux loop passes via one or more vertical chimneys that substantially vertically traverse the rock bed.

9. The method of claim 8 wherein the vertical chimney passes through an interior of the rock bed.

10. The method of claim 8 wherein wall(s) of the vertical chimney are liquid-tight.

11. The method of claim 8 wherein wall(s) of the vertical chimney are heat conductors to facilitate conductive heat transfer from (i) hydrocarbon fluids migrating within the vertical chimney to (ii) rocks of the bed.

12. The method of claim 1 wherein thermal energy supplied by the reflux loop is sufficient to significantly raise a temperature of at least one location at the top of the rock bed.

13. The method of claim 1 wherein the heater(s) are immersed heaters located within a reservoir of hydrocarbon liquid.

14-19. (canceled)

20. A method of heating hydrocarbon-containing rocks within an excavated enclosure comprising:

a. arranging the hydrocarbon-containing rocks into rock bed within the enclosure so that one or more substantially vertical conduits substantially vertically traverse the rock bed;

b. respectively maintaining lower and upper hydrocarbon liquid reservoirs at upper and lower elevations, the lower elevation being substantially at the bottom of the enclosure and substantially below the rock bed, the upper elevation being above or substantially at the top of the rock bed,

wherein the upper hydrocarbon liquid reservoir is supplied primarily by boiling of hydrocarbon liquids of the lower reservoir so that vapors formed therefrom substantially vertically traverse the rock bed and condense into liquid of the upper reservoir, wherein at least some thermal energy for the pyrolysis is supplied by convective heat transfer from downward movement of hydrocarbon liquid through the rock bed from the upper reservoir to the lower reservoir.

21. The method of claim 20 wherein a floor of the upper reservoir includes a plurality of voids through which hydrocarbon liquids flow downwards into the hydrocarbon bed.

22. The method of claim 20 wherein the voids are distributed over the hydrocarbon bed so as to horizontally substantially evenly distribute downward liquid flow from the upper reservoir into the rock bed.

23-63. (canceled)

64. An coal upgrading method comprising:

a. introducing pieces of coal into an excavated enclosure to form a rock bed therein, a substantial majority of the coal being bituminous coal having vitrinite reflectance of at most 1.8%;

b. heating the coal of the rock bed so that (i) an average temperature of the rock bed is maintained between 250 degrees Celsius and 400 degrees Celsius for at least one week; and (ii) a majority of the bituminous coal is upgraded into anthracite coal having a vitrinite reflectance of at least 2.5%.

65. The method of claim 64 wherein a pressure/temperature history of the coal is regulated so as to maximize a rank of the heated coal.

66. The method of claim 64 wherein a high value ultralow volatile anthracite coal is produced.