Patent Application
20130168295
Oil shale is a sedimentary rock with significant amounts of kerogen, which is a mixture of organic material, rather than a specific chemical, from which liquid hydrocarbons can be extracted. It is the geological precursor to petroleum. Worldwide, the oil shale resource base is conservatively estimated to be 2.6 trillion bbl. About 2 trillion bbl is located within the United States. About 1.5 trillion bbl of oil shale resources (>10 gal/ton) is found in the Green River formation of Colorado (Piceance Creek basin), Utah (Uinta basin) and Wyoming (Green River and Washakie basins).
Oil sands (sometimes referred to as tar sands) are a type of petroleum deposit containing naturally occurring mixtures of sand, clay, water, and a dense and extremely viscous form of petroleum technically referred to as bitumen. Oil sands are found in large amounts in many countries throughout the world, but are found in extremely large quantities in Canada and Venezuela, each of which has oil sand reserves approximately equal to the world's total reserves of conventional crude oil. As a result of the development of Canadian oil sands reserves, 44% of Canadian oil production in 2007 was from oil sands.
In previous attempts at recovery hydrocarbons, and more specifically producing commercial grade oil, from oil shale, conventional subsurface and strip mining methods are combined with high-temperature processing, also called retorting, to extract petroleum-like distillates. The retorting methods can be classified into indirect retorting and direct retorting. Not only is a plentiful water supply required, but certain processing methods have associated groundwater contamination issues. The available technologies suffer from requiring appreciable amounts of water and further suffer from low thermal efficiency and low recovery rates.
Oil shale can be produced through traditional mining methods, including underground mining or surface mining. The mined ore is crushed and retorted. Surface retorting processes are divided into three main types: indirect retorting, direct retorting, and a combination of the two. In indirect retorting, pyrolysis is driven by the transfer of sensible heat from a heat carrier to the oil shale. In direct retorting, shale gas is partially recycled into the bottom of the process vessel where it moves upward, countercurrently to the crushed shale. Combustion of shale gas with air heats the shale to retorting temperatures due to direct countercurrent contact between the hot gas and the oil shale. A third type of retorting is a combination of the indirect and direct retorting processes.
In indirect processes, shale retorts can be grouped into three categories:
The so-called “Tosco II” process belongs to the indirect process. In this process, retorting is accomplished in a pyrolysis drum, also known as a rotary kiln, where externally heated ceramic balls, 15 millimeters in diameter, are mixed with preheated shale that has been crushed to a size of less than 12 millimeters. The balls are separated from the hot, spent shale on a trommel and re-circulated through a ball heater. The products are drawn off to a collection system for the removal of dust and recovery of liquids and gases. The advantages of this process are that it utilizes all the shale that is mined, has good heat transfer in the solid-to-solid system, and achieves yield of 90%. The disadvantages are that the process is complex and requires appreciable quantities of water to condense the liquid products and to prevent dusting of the finely-divided spent shale.
One direct, retorting process uses a vertical, refractory-lined vessel through which crushed shale moves downward by gravity, counter currently to the retorting gases. Recycled gases enter the bottom of the retort and are heated by the hot, spent shale as they pass upward through the vessel. Air and some additional recycle gases are injected into the retort through a distributor system located above the heat recovery zone, mixing with the rising hot recycled gases. Combustion of the gases and of some residual carbon heats the shale immediately above the combustion zone to retorting temperature. Oil vapors and gases are cooled by the incoming shale, and the oil leaves the top of the retort as a mist. The advantage of this process is that there is no cooling water requirements. Disadvantages include a severe heat loss in spent sand, small unit throughput and poor scale-up economics, and expensive construction and replication of retorting equipment. Oil yield is also not high due to the fact that air (with oxygen) introduced into the retort for combustion is in excess, and the excess oxygen burns out some shale oil produced, or mainly due to the fact that part of the shale oil produced is pyrolyzed by the hot combusted gas.
The use of a so-called Alberta Taciuk Processor (ATP) is a combination of indirect retorting and direct retorting. The ATP was originally designed to extract bitumen from oil sands but has found application in oil shale processing. Presently, this retorting technology is used in Australia to process oil shale deposits found in Central Queenland. In the ATP process, a kiln retort combines direct and indirect heat transfer through recirculation of gas and of hot solids. Some of the processed shale is mixed with the fresh feed to provide the energy, through solid-to-solid heat transfer, for combustion and retorting. With ATP technology, about 20% of the energy from raw shale is sufficient to support the process energy requirements. The advantages of the process are that it increases oil and gas yields, improves thermal efficiency, reduces process water use and minimizes the residual coke on the spent shale. The disadvantages of the process include that, with its multi-stage strategy, the ATP processor does not achieve anywhere near maximum capacity and, even more detrimentally, it has problems handling the fines generated by the process.
Oil Sands production process includes surface mining and in-situ based on the depth of reservoir. Surface mining process currently uses hot water extraction process with caustic soda (NaOH) addition. The in-situ processes have steam assisted gravity drainage (SAGD), vapor extraction process (VAPEX), Toe to heel air injection (THAI), Cyclic steam stimulation (CSS), etc. Production of commercial grade oil from oil sands of hot water extraction process typically has the separate steps of mining, crushing, extraction, separation, dilution and upgrading. The production of commercial grade oil from oil sands typically result in the generation of tailing ponds, particularly along the Athabasca River in northern Canada, which have been estimated to contain 187 billion gallons of sludge that includes phenols, arsenic, mercury, polycyclic aromatic hydrocarbons and naphthenic acids. The size and scale of these tail ponds are immense. To date these ponds cover at least 80 square miles of boreal forest and wetlands.
The method of the present invention is adaptable for use in both the oil sands and oil shale processing industries and does not have many of the disadvantages inherent in prior art processes.
Reference is made to the drawing in which
The present invention attempts to overcome the problems known in the prior art of surface retorting. According to the present process the retort is a horizontal, slightly declined cylindrical retorting. In this invention, the shale solids with residual carbon are combusted in a calciner, and approximately 30-50% of solids from the calciner can be recycled back to retort to provide the energy. The solid-solid contacts enhance heat transfer and improve the thermal efficiency. Furthermore, combustion and retorting occur in different units and cyclones are used to separate the large particle materials from mixtures, which controls fines better than prior art processes. Without the need of large amount of water in the process, the process offers better water management. Furthermore, recovered waste heat from flue gas is used to preheat the raw shale.
In the present process the type of cracking employed is both catalytic cracking and thermal cracking. Catalytic cracking uses a solid acid catalyst, such as aluminum oxide and silicon dioxide, in conjunction with moderately-high temperatures to aid in the process of breaking down large hydrocarbon molecules into smaller ones. In thermal cracking, elevated temperatures and pressures are used to break the long chain alkanes down into shorter chain alkanes and alkenes.
In general a long chain alkane which is cracked without access to air or additional hydrogen will produce a shorter chain alkane plus an alkene, thus preserving the hydrogen to carbon ratio found in the original chain. For example:
C22H46→C11H24 (an alkane)+C1H22 (an alkene)
The cracking reactions produce some carbonaceous material (e.g. coke) that deposits on the catalyst and very quickly reduces the catalyst reactivity. It is a feature of the present invention that the catalyst is regenerated by burning off the deposited coke in a downstream calciner to be reactive again and recycle back to the retort. The combustion of the coke is exothermic, thus it produces a large amount of heat, which can be recovered to be used in the preheater.
The present invention is advantageous over prior art oil shale and oil sands upgrading processes for reasons including the following: (1) The entire process is a dry process, having no tailings problem.; (2) by using an effective catalyst in the retort stage, it combines the prior art extraction step and upgrading step together; and (3) recycling the catalyst improves the economics of the process. (4) The residue carbon in spent shale/sand can be burned in a calciner and resulted tailings present no contamination to the environment.
With reference now to
Once suitably sized, the material is subject to drying and preheating in step 3. Many commercial material dryers can be used in the present process. For example, a rotary dryer, which is a large, rotating cylindrical tube, that slopes slightly so that the discharge end is lower than the material feed end in order to convey the material through the dryer under gravity, can be advantageously used. In this step both oil shale and oil shale is is preheated to 80-120° C. Oil sands, which carry more interpore moisture than oil shale, will in addition be dried to a moisture content of less than about 5%. Oil shale moisture will vary from site to site, and typically will be in the range of 3%-5%, and generally additional drying is necessary. Any dust generated in the drying/preheating step 3 can be collected in optional dust collector 4.
The preheated material can be conveyed, such as by being trucked or a mechanical conveyed, to the retort step in which, it should be noted, not water is required. The preferred apparatus to be used in the retort process 5 is a rotary retort furnace, which is a cylindrical vessel which is rotated slowly about its axis. The material to be processed is fed into the upper end of the cylinder. As the retort rotates, material gradually moves down towards the lower end, and may undergo a certain amount of stifling and mixing. Hot gases pass along the retort in the direction of the material flow.
In the rotary retort the material is subject to cracking.
The catalyst is inserted in dry form with the material into the rotary furnace. Preferably the catalyst will be present in the furnace in the amount of about 15-45wt % of the feed, with the actual amount dependent on ore quality of the oil sands or oil shale being processed in the furnace. In view of the quantity of catalyst being used, according to the present process the catalyst is regenerated and recycled back to the process after regeneration. With the catalyst being recycled according to the present invention, much less new catalyst has to be added to the furnace during a continuous process to keep catalyst levels within the furnace at the preferred limits.
The catalyst serves to semi-crack the oil sands or oil shale during the retort step by breaking down long hydrocarbon chains to shorter chains.
The preferred catalysts are zeolite catalysts, which provide high yields and selectivity for higher-boiling hydrocarbon fuel. After a catalytic cracking process, almost all of the long chain alkanes and alkenes have been converted to lower chain/molecular weight material of the short chain, lowering the boiling point of hydrocarbon at least 150° C. Zeolite catalysts involve chain scission, isomerisation, hydrogen transfer and saturation. By utilizing a catalyst in the retort process, the yield is improved and the reaction temperature can be lowered about 100-150° C. The catalytic pyrolysis produces less viscous and more upgraded products for later refining.
Zeloites can be natural or synthetic crystalline aluminosilicates, which have a large number of uniform openings or cavities on the surface area, relatively smaller and uniform holes connected each other inside. For hydrated form, a typical formula is as follows:
xM2/nO:Al2O3:ySiO2:zH2O
where, x, y, z represents the moles of metal cation, silica oxide and water; M represents at least one transition metal cation, which can be nickel, cobalt, tungsten or molybdenum or the combination of two. For example, nickel together with tungsten has been found extremely effective on wide stock and has a large range of applications.
The acidic supportive matrix can be alumina, silica alumina or alumina-alumina phosphate-silica, etc. Noble metals like platinum may also be used.
The catalysts typically have the appearance of fine powers, with a bulk density of 0.80 to 0.96 g/cc and having a particle size distribution ranging from 10 to 150 micron and an average particle size is from 60 to 100 micron. The catalytic sites in the zeolite are strong acids (equivalent to 90% sulfuric acid) and can provide most of the catalytic activity.
The products from the dry retort process 5 of the present invention are gas, which contains the desired hydrocarbons extracted from the oil sands and oil shale, and solids having residue carbon. To realize the desired products the gas has to be cooled and condensed. The preferred method of achieving this is to use a multi-stage condenser, although a fractioning column may also be utilized.
The hot gas is directed to a multi stage condenser system 6 having water coolers in which the gas temperature is gradually cooled to allow the gas to condense and return to a liquid state and thereby achieve the desired hydrocarbon products. As the gas is cooled, the first hydrocarbon phase is the heaviest American Petroleum Institute gravity, approximately 25 API. As the gases continue through the condenser cooling elements, the petroleum crude oil liquid becomes lighter, since volatilization levels decreases along with temperature.
The solid residual material from the retort are directed to calciner step 7 to regenerate the catalyst by burning off deposited coke on the catalytic material. On preferred type of calciner is an updraft vessel where the entrained dried, material enters in the lower portion of the calciner entrained in combustion air. The calciner is maintained at a temperature sufficient to volatilize the carbon components on the catalyst, preferably between about 350° C.-550° C., depending upon the composition of the solid residual material, and most preferably between about 350° C.-450° C. Material too heavy to be entrained, which is approximately 450° C., will fall out in line 8 and will be sent to disposal can go to heat recovery step 14, which can be an indirect heat exchanger and, after the heat values have been recovered, to disposal. The gas stream exiting from calcining step 7 is sent to gas-solids separation step 9. The solids from the gas-solids separation step 9 will be comprised of finer catalyst and coarser spent shale/oil sands. Therefore, the solids can be screened to separate the recovered catalyst from the spent shale/oil sands. All the recovered catalyst can be recycled back to retort step 5 via conduit 11. The recovered spent shale/oil sands, which will still have significant heat value in the form of unburnt carbon, can be split into two streams, 12, which is recycled spent oil shale/sand, and 13, which is spent oil shale/sands. Stream 12 can be recycled to the retort to be used as fuel. Stream 13, which is approximately 900° C. as it comes out of gas-solids separator 9, can go to heat recovery step 14, and, after the heat values have been recovered, for reclamation. The amount of spent shale/sands that will be recycled to the retort step will typically vary from 30-65%, depending on factors such as the amount of catalyst used in the retort and the desired temperature in the retort.
The flue gas, which is approximately 900° C., recovered from gas-solid separation step 9 will typically be recovered the heat step 14 and then go to cooling tower at step 15, in which there is a water spray to control the fines problem that has plagued other processes. The gas is thereafter directed to a bag house where the recovered fines are sent for reclamation as spent shale or sands and the cleaned gas is sent to atmosphere. The heat recovered from the flue gas step 14 has one or more uses:
(a) a first recovered heat can be sent to other areas of the process, as depicted it goes to drying/ preheating step 3 but it can also be sent to other steps.
(b) a second recovered heat, alternatively or in addition, will be used for power generation step 19; such as a turbine, to generate power that can be used in the plant as a whole.
(c) a third recovered heat if available can go to an in-situ process to generate hot steam used in underground mining of oil shale and oil sands.
As addition, the heat can also be recovered from the spent shale coming from calciner step 8 and step 13.
There can be other modifications of the process of the present invention. For instance, a hot gas/solids separator can be used in line 18 to remove some of the fines from the gas in conduit 18 prior to the gas being used in the heat recovery step.
Thus, with the present process no large amount of cooling water needed, only a small amount to handle fines, thus the process is environmentally friendly, and provides for easier reclamation utilizing the spent scale after production. In addition, there is better control of fines during production and there are no fines are in the product, which makes the process reliable and sustainable.
