Patent Grant
9150794
The present invention relates to a method of improving a heavy hydrocarbon, such as bitumen, to a lighter more fluid product and, more specifically, to a final hydrocarbon product that is refinery-ready and meets pipeline transport criteria without the addition of diluent. A solid asphaltene by-product is created for easy handling and further processing. The invention is targeted to enhance Canadian bitumen, but has general application in improving any heavy hydrocarbon.
Refining sweet crude resources require less capital input and have a much lower cost of processing than heavy sour crudes. However, the global availability of light, sweet crude to supply to refineries for the production of transportation fuels is on the decline making the processing of heavy sour crude an increasingly important option to meet the world's demand for hydrocarbon-based fuels.
Most (if not all) commercial upgraders for processing heavy crude have been built to convert heavy viscous hydrocarbons into crude products that range from light sweet to medium sour blends. Heavy oil upgraders basically achieve this by high intensity conversion processes which either release up to 20% by weight of the feedstock as a coke byproduct and another 5% as off-gas product, or require hydro-processing such as hydrocracking and hydro-treating to maximize the conversion of the heavy components in the feedstock to lighter, lower sulfur liquid products and gas.
Processes have been disclosed to convert and/or condition Oil Sands bitumen into pipeline transportable and refinery acceptable crude. Of note, thermal cracking, catalytic cracking, solvent deasphalting and combinations of all three (for example, visbreaking and solvent deasphalting) have been proposed to convert bitumen to improve its characteristics for transport and use as a refinery feedstock.
Thermal Cracking
Visbreaking or viscosity breaking, a form of thermal cracking, is a well known petroleum refining process in which heavy and/or reduced crudes are pyrolyzed, or cracked, under comparatively mild conditions to provide products that have lower viscosities and pour points, thus reducing required amounts of less-viscous and increasingly costly to obtain blending hydrocarbons known as diluent to improve fluidity of the crude, and make the crude meet minimum transport pipeline specifications (minimum API gravity of 19).
There are two basic visbreaking configurations, the coil-only visbreaker and the coil-and-soak visbreaker. Both require heaters to heat the crude, with the coil-only style employing cracking only in the heater tubes. Coil-only visbreakers operate at about 900° F. at the heater outlet with a residence time of about 1 minute. Gas oil is recycled to quench the reaction. In the coil-and-soak visbreaker, a vessel is used at the outlet of a furnace to provide additional residence time for cracking of the crude. The crude sits and continues to crack/react as the temperature slowly reduces. The coil-and-soak visbreaker runs at heater outlet temperatures of 800° F. The soaker drum temperature reduces down to 700° F. at the outlet with aggregate residence times of over 1 hour.
Examples of such visbreaking methods are described in Beuther et al., “Thermal Visbreaking of Heavy Residues”, The Oil and Gas Journal. 57:46, Nov. 9, 1959, pp. 151-157; Rhoe et al., “Visbreaking: A Flexible Process”, Hydrocarbon Processing, January 1979, pp. 131-136; and U.S. Pat. No. 4,233,138. The yield structure is approximately same for either configuration: 1-3% light ends, 5% (wt) naphtha and 15% (vt) gas oil. The remainder remains as heavy oil or bitumen. The products are separated in a distillation column for further processing or blending.
A concern with standard visbreaking schemes is that for Canadian Bitumen, the operating temperatures are above the limit (around 700° F.-720° F.) where significant coking impacts operability (Golden and Bartletta, Designing Vacuum Units (for Canadian heavy crudes), Petroleum Technology Quarterly, Q2, 2006, pp. 105). In addition, heat is added over a short period of time in the heater, so local heat fluxes are not uniform and can peak well above coking initiation limits; and the heat is not maintained consistently allowing for condensation reactions to occur. Attempting to apply conventional visbreaking to Canadian Bitumen is limited due to the propensity for coking and inability of these systems to manage this issue.
In the first part of U.S. Pat. No. 6,972,085 and in patent application US2008/0093259 an attempt is made to address the desire for a constant and sustained application of heat to the crude over an extended period of time. Essentially, the heater and the holding vessel are merged into one vessel to create a continuous heated bath for the crude. Multiple heating levels are applied to the crude at various times. This is an improvement over standard visbreaking but does not eliminate hot spots within the processed crude, permitting coking due to temperature peaks above optimal levels for cracking.
Combination of Thermal/Catalytic Cracking and Solvent Deasphalting
In U.S. Pat. No. 4,454,023 a process for the treatment of heavy viscous hydrocarbon oil is disclosed, the process comprising the steps of: visbreaking the oil; fractionating the visbroken oil; solvent deasphalting the non-distilled portion of the visbroken oil in a two-stage deasphalting process to produce separate asphaltene, resin, and deasphalted oil fractions; mixing the deasphalted oil (“DAO”) with the visbroken distillates; and recycling and combining resins from the deasphalting step with the feedstock initially delivered to the visbreaker. The U.S. '023 patent provides a means for upgrading lighter hydrocarbons (API gravity>15) than Canadian Bitumen but is burdened by the misapplication of the thermal cracking technology that will over-crack and coke the hydrocarbon stream, and by the complexity and cost of a two-stage solvent deasphalting system to separate the resin fraction from the deasphalted oil. In addition, the need to recycle part of the resin stream increases the operating costs and complexity of operation.
In U.S. Pat. No. 4,191,636, heavy oil is continuously converted into asphaltenes and metal-free oil by hydrotreating the heavy oil to crack asphaltenes selectively and remove heavy metals such as nickel and vanadium simultaneously. The liquid products are separated into a light fraction of an asphaltene-free and metal-free oil and a heavy fraction of an asphaltene- and heavy metal-containing oil. The light fraction is recovered as a product and the heavy fraction is recycled to the hydrotreating step. Catalytic conversion of Canadian heavy bitumen (API gravity<10) using this '636 process is a high-intensity process that tends to have reliability issues with rapid catalyst deactivation impacting selectivity and yield.
In U.S. Pat. No. 4,428,824, a solvent deasphalting unit is installed upstream of a visbreaking unit to remove the asphaltenes from the visbreaking operation. In this configuration, the visbreaking unit can now operate at higher temperatures to convert the heavier molecules to lighter hydrocarbon molecules without fouling, since the asphaltenes are removed from the product stream entirely. However, the yield of the bitumen is greatly reduced (by 10-15%) since the early removal of the asphaltenes in the process prevents thermal conversion of this portion of the crude into a refinable product.
As in U.S. Pat. No. 4,428,824, U.S. Pat. No. 6,274,032, disclosed a process for treating a hydrocarbon feed source comprising a fractionator to separate the primary crude components, followed by a Solvent Deasphalting (SDA) unit to work on the heavier crude asphaltene rich component, and a mild thermal cracker for the non-asphaltene stream. The asphaltene rich stream is processed in a gasification unit to generate syngas for hydrogen requirements. Placing an SDA unit upstream of a thermal cracker reduces the overall yield of the bitumen as refinery feed, since the asphaltene portion of the crude, comprising up to 15% of Canadian bitumen, is removed from consideration for inclusion in some format as crude. This loss in product yield is not compensated for by the increased cracking in the visbreaker.
In U.S. Pat. No. 4,686,028 a process for the treatment of whole crude oil is disclosed, the process comprising the steps of deasphalting a high boiling range hydrocarbon in a two-stage deasphalting process to produce separate asphaltene, resin, and deasphalted oil fractions, followed by upgrading only the resin fraction by hydrogenation or visbreaking. The U.S. Pat. No. 4,686,028 invention applies visbreaking to a favourable portion of the whole crude stream to minimize coke generation. However, PAT '028 is limited by missing a large part of the crude that could benefit from optimal conversion and thus a large portion of the crude does not end up as pipeline product without the need of transport diluent.
In U.S. Pat. No. 5,601,697 a process is disclosed for the treatment of topped crude oil, the process comprising the steps of vacuum distilling the topped crude oil, deasphalting the bottoms product from the distillation, catalytic cracking of the deasphalting oil, mixing distillable catalytic cracking fractions (atmospheric equivalent boiling temperature of less than about 1100 degrees F.) to produce products comprising transportation fuels, light gases, and slurry oil. U.S. Pat. No. '697 is burdened by the complexity, cost, and technical viability of vacuum distilling a topped heavy crude to about 850° F. and catalytic cracking the deasphalted oil to produce transportation fuels.
In U.S. Pat. No. 6,533,925, a process is described involving the integration of a solvent deasphalting process with a gasification process and an improved process for separating a resin phase from a solvent solution comprising a solvent, deasphalted oil (DAO) and resin. A resin extractor with the solvent elevated in temperature above that of the first asphaltene extractor is included in the '925 invention. The asphaltene stream is treated but removed prior to any thermal conversion eliminating the possibility of obtaining a value uplift into useable refinery feedstock. The impact is a reduction in the potential overall yield of the crude stream.
In U.S. Patent application 2007/0125686, a process is disclosed where a heavy hydrocarbon stream is first separated into various fractions via distillation with the heavy component sent to a mild thermal cracker (visbreaker). The remaining heavy liquid from the mild thermal cracker is solvent deasphalted in an open art SDA unit. The asphaltenes separated from the SDA are used as feed to a gasifier. The deasphalted oil is blended with the condensed mild thermal cracker vapour to form a blended product. As stated with Pat'023 above, visbreaking faces the challenges of early coke generation. Specifically, the '686 patent application explains that the intent of this mild thermal cracker is to crack the non-asphaltene material exclusively, which is also not practical with Canadian bitumen. In addition, additional energy is required in the distillation steps with most of the separated components being recombined for pipeline transport.
Treatment of SDA Generated Asphaltene-Rich Stream
In U.S. Pat. No. 4,421,639 a solvent deasphalting process uses a 2nd asphalt extractor to concentrate asphaltene material (and recovery of more deasphalted oil). The concentrated asphalt stream is sent through a heater to get to 425° F. at 18 psia and uses a flash drum and stream stripper to separate solvent (in this case propane) from the asphalt stream. Asphalt product, in liquid form, is pumped to storage. This arrangement only works if the asphalt rich stream is liquid at these conditions. It is burdened by plugging if any appreciably solid asphaltenes are present as in asphaltene-rich streams like bitumen.
In U.S. Pat. No. 3,847,751, the concentrated asphaltene product from the SDA unit is mixed with solvent to transport as a liquid solution to a spray dryer. The spray nozzle design and pressure drop dictates the size of liquid droplets that are formed. The smaller the light hydrocarbon (solvent) droplet, the faster it will flash completely to vapour. The smaller the heavy hydrocarbon (asphaltene) particle the more surface area available for heat transfer to cool the heavy droplets down with the goal of producing a dry, non-sticky solid particle. Additional cold gas is added to the bottom of the spray dryer to enhance cooling by additional convective heat transfer as well as increasing the droplet residence time by slowing its descent rate (via upward cooling gas flow) in order to reduce the size of the vessel (which tend to be extremely large). This arrangement is not required if the asphaltene particles that have settled out in the extractor are in a solid form in the solvent at the process operating temperature.
In U.S. Pat. No. 4,278,529, a process for separating a solvent from a bituminous material by pressure reduction without carry-over of bituminous material is illustrated. The fluid-like phase comprising bituminous material and solvent is reduced in pressure by passage through a pressure reduction valve and introduced into a steam stripper. The pressure reduction vaporizes part of the solvent and also disperses a mist of fine bituminous particles in the solvent. The concern with this approach is that the remaining asphaltene remains wet and sticky and has not enough solvent left to keep the heavy bituminous phase (with many solids) flowable.
In U.S. Pat. No. 4,572,781 a solvent deasphalting process for separating substantially dry asphaltenes of high softening point from heavy hydrocarbon material using a centrifugal decanter to separate a liquid phase from a highly concentrated slurry of solid asphaltenes is described. This process attempts to handle a rich asphaltene stream that has solid particles but is a highly costly process since the separation of the solids is done through a solid/liquid separation with additional solvent needed to make the material flow to the decanter. Invariably, the separated solid material is still relatively wet and needs another drying step to recover the solvent as a vapour. The solvent vapour needs to be condensed for re-use, another high energy step.
In U.S. Pat. No. 7,597,794, a dispersion solvent is introduced into the asphalt phase after separation by solvent extraction and the asphalt phase undergoes rapid phase change in a gas-solid separator and is dispersed into solid particles while the solvent vaporizes, resulting in low temperature separation of asphalt and solvent with adjustable size of the asphalt particles. The challenge with flash/spray driers using liquid solvent as the transport media is the propensity for the asphaltenes generated in this integrated process to remain wetted before, during and after the flash drying phase. In addition, with this integrated process, the asphaltene continues to liquefy at elevated temperatures. A wetted asphaltene sticks to all surfaces and fouls and plugs the equipment readily. The reduced reliability from using this approach makes this operation costly for heavy crudes with high asphaltenic content.
In U.S. Pat. No. 7,964,090 a method for upgrading heavy asphaltenic crudes using SDA and gasification is shared. Of interest in this patent, a stream to a gasifier is generated by mixing a hydrocarbon comprising one or more asphaltenes and one or more non-asphaltenes with a solvent, wherein a ratio of the solvent to the hydrocarbon is about 2:1 to about 10:1. The asphaltene rich stream is transferred out of the SDA to a gasifier as a liquid stream. The large quantities of solvent used in transport are consumed in the gasifier, downgraded in value to a fuel gas equivalent. Since the asphaltenes tend to be liquid, using a solvent to transport the material in the quantities stated is feasible. For a solid asphaltene, this method would require 10-20 times more solvent to transport and this quantity of expensive solvent would be consumed and its value reduced.
It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of illustration. As will be realized, the invention is capable for other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.
Essentially, an improved process for producing a pipeline-ready crude and refinery feedstock from heavy crude oils, such as Canadian Oil Sands bitumen, is described, with said process consisting of: (1) optimal asphaltene conversion with minimum coke and offgas make, in a full bitumen stream, within a reactor to produce a thermally affected asphaltene-rich fraction, a minimum non-condensable vapour stream and an increased refinery-feed liquid stream; (2) deasphalting said thermally affected asphaltene-rich fraction into a refinery-feed liquid stream and a concentrated asphaltene stream; (3) Selectively hydrotreating specific hydrocarbon components as required for pipeline specification and, finally blending of all the liquid streams to produce a refinery feed; and (4) inertial separation of the concentrated solid asphaltene stream for conversion in a gasifier, power or asphalt plant.
The bitumen is thermally treated to remove and convert/crack selected asphaltenes, which are then sufficiently separated in a more efficient solvent extraction process, reducing production of coke and isolating undesirable contaminants (like metals, MCR, and remaining asphaltenes).
Considering the relative complexity and high degree of side chains on the Canadian bitumen asphaltenes, under the operating conditions of the invention disclosed here, the side chains are preferentially cleaved from the core asphaltene molecule to make desired vacuum gas oil to light hydrocarbon range components. The remaining polyaromatic asphaltene cores remain solid at elevated temperatures and pressures above operating conditions and thus separate more readily than non-thermally affected asphaltenes resulting in improved separation processes, such as solvent deasphalting (50) and vapour-solid separation like inertial separation (110).
Further, the heavier hydrocarbons in the bitumen are also mildly cracked to vacuum gas oil, gasoline and distillate boiling range components, all desirable for separation and conversion in refineries. Any major deviations in temperature and heat flux within the bitumen pool in the reactor will lead to coking and increased gas yield and a reduction in the overall crude yield of the original bitumen, and reduced reliability of the operation, increasing the operating cost of the facility.
The invention provides improved apparatus and method for producing a pipeline-ready and refinery-ready feedstock from heavy, high asphaltene crudes (for example, Canadian bitumen), and feedstocks, with utility for any virgin or previously processed hydrocarbon stream, the process and apparatus comprising a pre-heater for pre-heating a process fluid to a design temperature at or near the desirable operating temperature of a reactor; moving the process fluid into a reactor for conversion of the process fluid by controlled application of heat to the process fluid in the reactor so that the process fluid maintains a substantially homogenous temperature throughout the reactor to produce a stream of thermally affected asphaltene-rich fractions, and a stream of liquid hydrocarbon vapour with minimal non-condensable vapour. The stream of vapour is separated into two further streams: of non-condensable vapour, and of light liquid hydrocarbons. The thermally affected asphaltene-rich fraction is deasphalted, using a solvent extraction process, into streams of deasphalted oil liquid, and concentrated asphaltene, respectively. The deasphalted oil liquid and the light liquid hydrocarbons produced in the processes are blended to form a pipeline and refinery-ready feedstock. The concentrated asphaltene is processed in a vapour-solid separation unit (e.g. inertial) to create a dry solid asphaltene by-product.
A sweep gas can be deployed in the reactor, and can be preheated to provide a heat flux source other than the reactor's heaters; similarly, the sweep gas assists in the removal of reactor vapour products.
Deasphalting can be achieved using an open-art solvent extraction process; since the initial process fluid has been separated so that only the heavy asphaltene-rich fractions require deasphalting, extraction processes using high solvent-to-oil ratios are feasible and economical. Improved solvent-extraction performance, using lower solvent to oil ratios and improved DAO yield can be achieved by further concentrating the asphaltene rich fraction before a final extraction step. The process improves on open-art solvent deasphalting utilizing an additional solvent extraction column (rinse column) operating on the asphaltene-rich stream from the primary solvent extraction column to increase pipeline crude recovery and quality.
The SDA process may allow for some portion of the heavy asphaltene-rich hydrocarbon stream to be recycled and blended with the fresh feed to the reactor.
The resulting concentrated thermally-affected asphaltenes can be successfully processed in a vapour-solid separator such as a centrifugal collector, settling chamber or inertial separator to generate a dry, solid asphaltene by-product.
In one embodiment this invention provides an improved process for producing enhanced refinery feedstock and dry thermally-affected asphaltene solids from heavy hydrocarbon, said process comprising:
(a) Pre-heating the heavy hydrocarbon as a process fluid in a heater to a designed temperature;
(b) Moving the pre-heated process fluid to a reactor, and optimally converting asphaltenes in the process fluid within the reactor to produce a stream of thermally affected asphaltene-rich fraction(s), and a stream of non-condensable vapour and lighter liquid hydrocarbon(s);
(c) Deasphalting the thermally affected asphaltene-rich stream with a solvent extraction process into a stream of heavy deasphalted oil (DAO) and a second stream containing concentrated asphaltene;
(d) Separating dry thermally-affected asphaltene solids from the second stream in a separation unit, recovering the process solvent;
(e) the refinery feedstock comprising of at least one of the produced streams.
In another embodiment the invention provides a continuous process where the reactor is a single thermal conversion reactor with an overhead partial condenser operating within the following parameters:
(a) A uniform heat flux of between 7000-12000 BTU/hr sqft introduced to the process fluid within the reactor;
(b) A sweep gas of between 20-80 scf/bbl (gas/process fluid) is introduced within the reactor;
(c) Residence time of the process fluid within the reactor of between 40-180 minutes;
(d) A substantially uniform operating temperature of between 675-775° F. in the reactor;
(e) A near atmospheric operating pressure of <50 psig in the reactor.
In a further embodiment, the refinery feedstock comprises a blend of at least two of the produced streams to be pipeline ready, having an API of greater than 19 degrees gravity, and a viscosity less than 350 Cst at 8° C.; one or more of the produced streams is treated to remove olefins.
In yet another embodiment, the refinery feedstock comprises one or more of the produced streams, suitable for diverse refinery types by virtue of its proportion of vacuum residue.
The invention further provides a process where the integrated process is applied to an existing coker-based bitumen upgrader or refinery by accepting as feedstock the upgrader's or refinery's virgin or processed heavy hydrocarbon streams and providing light liquid hydrocarbon, and heavy deasphalted hydrocarbon process streams to the upgrader or refinery.
In a further embodiment, the integrated process is applied to an existing residue hydrocracking upgrader or refinery by accepting as feedstock the upgrader's or refinery's virgin or processed heavy hydrocarbon streams and providing light liquid hydrocarbon, and heavy deasphalted hydrocarbon process stream to the upgrader or refinery.
In yet a further embodiment, the integrated process is applied to a new bitumen Upgrader, new “sweet crude” refinery or an existing “sweet crude” refinery in lieu of a coking process by accepting as feedstock the upgrader's or refinery's virgin or processed heavy hydrocarbon streams and providing light liquid hydrocarbon, and heavy deasphalted hydrocarbon process streams to the upgrader or refinery.
Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:
The lists of Units, Process Streams and Equipment elements provided below are indexed to numbered components in the Figures, and are provided for the readers' reference.
The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
The feedstock 12 can be a heavy hydrocarbon (virgin or a previously processed stream), such as the heavy hydrocarbon obtained from a SAGD (steam assisted gravity drainage) process, for example Canadian Oil sands bitumen, or from any other suitable source of heavy hydrocarbon. In one aspect, the feedstock 12 can have an API gravity in, the range of 0 to 14.
In one aspect, a recycled portion 70 of the resin stream 54 output from the high performance solvent extraction process 50 can be blended with the incoming feedstock 12 to form the process fluid 14 that passes through process 10. The resin stream may be added to the process fluid in instances in which further crude yield, and/or lighter crude, and/or asphaltene suppression is desired in order to meet treated product characteristic targets. The resin recycle provides the operator with flexibility, through an adjustable flow parameter, to meet production specifications, and allows the plant to handle feedstock variations robustly.
The resin product 54 from the solvent extraction process 50 will typically have a relatively low API gravity. In one aspect, the API gravity of the resin product 54 can have an API gravity between 0 and 10. Depending on the characteristics of the feedstock 12 and the amount of resin product 54 blended with the feedstock 12, the resulting process fluid 14 can have a range of characteristics and particularly a range of API gravities.
The process fluid 14 (obtained entirely from the feedstock 12 or formed as a blend of feedstock 12 and resin product 54 from the solvent extraction process 50) can be routed to the heater 20 where the process fluid 14 can be heated to a desired temperature as it passes through the heater 20 before being routed to the reactor 30 to undergo mild thermal cracking. Reactor 30 maintains a consistent fluid temperature through a uniform application of heat through-out the reactor to allow for mild thermal cracking to occur without coking being a concern or detrimental to the operation and/or performance of the reactor.
In one aspect, the heater 20 will heat the process fluid 14 to a temperature between 675-775° F. before the process fluid 14 is introduced into the reactor 30.
In the reactor 30, the process fluid 14 (heated to between 675-775° F. by the heater 20) undergoes a mild controlled cracking process. Appropriately located heaters are provided in this reactor 30 to maintain the desired constant temperature generated in heater 20 and to apply uniform heat flux for the fluid 14. The heaters provide indirect heat through any source readily available (electric, heat transfer fluid, radiant etc.). To ensure a uniform heat flux, mixing can be applied to the process fluid on a continuous or intermittent basis.
The reactor 30 can be operated in a manner, through optimizing primarily five inter-related process variables (Temperature, Pressure, Residence Time, Sweep Gas and Heat Flux), so as to reduce or even prevent coke from forming during the reaction, and minimizing gas production, while also providing optimal conversion of the asphaltene portion of the heavy hydrocarbon to refinery-ready feedstock components.
The first and second variables involve applying a uniform heat flux between 7000-12000 BTU/hr sq.ft to the entire pool of process fluid in the reactor and maintaining a single operating temperature in the reactor between 675-775° F. This may be achieved by the presence of appropriately sized and located heating devices in the reactor. The number of heaters will be set by calculating the optimal dispersion of heat between any two heaters so as to have a uniform temperature throughout the pool and to avoid peak or spot temperatures significantly higher than the target temperature in the reactor.
The third reactor variable, residence time, can be between 40-180 minutes in the reactor.
The fourth reactor variable, operating pressure, can be maintained at near atmospheric pressure, in any case, to be less than 50 psig, with standard pressure control principles used for consistent performance. The pressure range is controlled on the low end to prevent excessive, premature flashing of hydrocarbon, essentially bypassing the reactor, and limited on the high end to reduce secondary cracking and consequent increased gas yields.
The fifth reactor variable, hot sweep gas 36, in the same temperature range as the process fluid (675-775° F.) 21, is added to the process fluid 14 in the reactor 30 in the range of 20-80 scf/bbl.
The sweep gas 36 can be natural gas, hydrogen, produced/fuel gas from the process, steam, nitrogen or any other non-reactive, non-condensable gas that will not condense to a liquid.
Sweep gas in the dosage of 20-80 scf/bbl of feed is provided to remove the “lighter” hydrocarbon products (i.e. methane to <750° F. boiling point hydrocarbons) as soon as they are formed in the reactor 30 so that there is a minimum of secondary cracking which could increase gas make and potentially increase olefinic naphtha/distillate production.
The sweep gas may also allow the reactor to operate closer to the desired operating pressure (<50 psig) and temperature. The sweep gas 36 can also be used to provide additional heat and/or mixing to the process fluid 14 in the reactor 30.
As discussed with respect to
Each variable may be changed independently, within the ranges suggested, based on the quality of feedstock provided or based on the quality of output desired. Since the 5 noted process variables are inter-related, a multi-variable process control scheme with a prescribed objective function (maximum yield to meet minimum product specifications) will be beneficial to ensure the process operates at an optimal point when any one of the variables is changed or the feed/product situation is altered.
Once the process fluid 14 has remained in the reactor 30 for a sufficient amount of time so that the characteristics of the outputs of the reactor 30 reach desired qualities, a light overhead fraction 32 and a heavy bottoms fraction 34 can be removed from the reactor 30.
The light overhead fraction 32 of the output from the reactor 30 can contain non-condensable vapor products, light liquid hydrocarbon and heavier liquid hydrocarbon. The vapor products can be vapors released from the process fluid 14, such as sour gas, while undergoing thermal cracking, as well as introduced and unconverted or unused sweep gas 36 that has passed through the reactor 30.
The overhead liquid fraction 32 will have a much higher API gravity than the bottom fraction 34. For example, the overhead liquid fraction 32 could typically have an API gravity of 26 or greater. The overhead fraction 32 can be directed to a gas liquid separation unit 40, which can comprise a cooler 41 and separation drum 42, as an example, in which a portion of the overhead fraction 32 that is a condensable liquid product containing naphtha and heavier hydrocarbons can be separated from the gaseous components of the overhead fraction 32. An off-gas line 43 containing undesirable gases such as sour gas, can be provided at the separation drum 42 for those gases to be disposed of, recycled, or subjected to further treatment.
One or more liquid hydrocarbon streams can be produced from separation drum 42. Stream 44, a heavier hydrocarbon than stream 46, can be sent to product blending, while stream 46 can be considered for further bulk hydro-treating prior to product blending.
The bottom fraction 34 can contain hydrocarbons, and modified asphaltenes. Although the characteristics of the bottom fraction 34 taken from the reactor 30 will vary depending on the process fluid 14 input into the reactor 30 and the reactor's operating parameters, in one aspect the bottom fraction 34 can have an API gravity ranging between −5 and 5.
Controllable process variables allow an operator to vary the performance of the reactor 30 to meet the needs of the final product based on changing characteristics of the incoming process fluid 14.
The controllability of the five inter-related variables, residence time, sweep gas, heat flux, temperature and pressure in the reactor 30 allow an operator to vary the performance of the reactor 30.
In this manner, when the characteristics of the feedstock 12 are changed either as different fresh feed or more or less resin recycle 70, the five inter-related process variables can be optimized to avoid the production of coke and minimize the production of non-condensable vapors are produced in the reactor 30. For example, the operator can vary the residence time of the process fluid 14 in the reactor 30 based on the characteristics of the process fluid 14 to obtain the desired yields and/or quality of the outputs 32, 34. Alternatively, the operator can vary the sweep gas, temperature or pressure to achieve similar outcomes. The process variables are inter-related and the minimization of coke and avoidance of excess gas make is challenging and is best determined by pilot operations.
The bottom fraction 34 from the reactor 30 can be fed to a high performance solvent extraction process 50 that can produce a thermally affected asphaltene stream 58, an extracted oil stream 52 and a resin stream 54. The reactor 30 is operated in a manner that significantly limits and even prevents the formation of coke and reduces gas production while converting asphaltenes into more suitable components for downstream processing. Consequently, modified asphaltenes and other undesirable elements remain in the bottom fraction 34 that is removed from the reactor 30.
To maximize the recovery of the desirable refinery feedstock crude the undesirable elements that remain in the bottom fraction 34, the bottom fraction 34 from the reactor 30 must be further treated using, for example, a high performance solvent extraction process 50. The treatment of the bottom fraction 34 by solvent extraction process 50 allows the reactor 30 and the solvent extraction process 50 to be used in conjunction, to produce a suitable full range refinery feedstock crude.
The solvent extraction process 50 can comprise any suitable solvent extraction process. In one aspect, it can be a three stage super-critical solvent process that separates the asphaltenes from the resins in the bottom fraction 34. The output of the solvent extraction process 50 can be an asphaltene stream 58, an extracted oil stream 52 and a resin stream 54. The asphaltene stream 58 is typically undesirable and is removed from the process 10. The extracted oil stream 52 can be of a relatively high quality, with an API gravity range of 9 to 15. The resin stream 54 is typically of a lower quality than the extracted oil stream 52, with an API gravity lower than the extracted oil stream 52. In one aspect, the resin stream 54 can have an API gravity in the range of 0 to 10 API gravity.
The extracted oil stream 52 and the resin stream 54 from the solvent extraction process 50 can be blended along with the liquid product stream 44 obtained from the liquid gas separator 40 to form a final hydrocarbon product 60 meeting the specifications of the pipeline and/or the refinery. In one aspect, this final hydrocarbon product 60 would have an API gravity greater than 19. Typically, the final hydrocarbon product 60 would have a viscosity of 350 CentiStokes (“cSt”) or less. Hydrotreating may be applied to the blended stream 60 in the event olefins need to be reduced to meet a specific pipeline and/or refinery specification.
The resin stream 54 is typically of a lesser quality than the extracted oil stream 52. The recycle portion 70 of the resin stream 54 can be blended with the feedstock 12 to be reprocessed in order to form the final hydrocarbon product 60. As a result, this recycling portion of the resin stream will improve the quality of the final hydrocarbon product 60.
In another aspect, to increase overall recovery of product hydrocarbon from reactor 30 and reduce solvent circulation rates, a high-performance solvent extraction process 50 may include a supplemental extraction process step, rinse column 50e, upstream of the asphaltene stream 58. Instead of sending stream 61, the bottoms of the primary extractor 50c, to an asphaltene stripper or spray dryer as is the case in conventional SDA units known in the art, stream 61 can be sent to a secondary solvent extraction column. Conventionally, additional solvent extraction is performed on the primary deasphalted oil, in the form of a resin extractor 50f, to provide a separate deasphalted heavy oil stream 66. The additional solvent extraction step on the asphaltene-rich stream by rinse column 50e as shown in
Overall solvent use to achieve high hydrocarbon recovery in stream 60 can be 25% less than using comparable open art processes. To obtain desired yields of 99+% DAO (deasphalted oil) recovery in stream 60 while still meeting pipeline and refinery specifications, typical 3-stage extraction processes require solvent to oil ratios in the 8-9:1 range for Canadian Oil Sands bitumen (www.uop.com). As an example, for a 60,000 BPD bitumen flow, the minimum solvent needed is 480,000-540,000 BPD. Using the rinse column 50e arrangement helps to reduce the total solvent circulated since the process step specifically targets the molecules (asphaltenes) that need to be separated from the desired crude (heavy oil). A solvent-to-oil ratio of 3-4:1 in the main extractor 50 a.b.c is only needed (240,000 BPD) to precipitate all of the thermally affected asphaltenes with minimum DAO entrainment. The rinse column, 50e, will have a feed of approximately 6,000 BPD of asphaltene-based components and 750-1000 BPD of crude. A solvent to oil ratio of 15-20:1 in the rinse column 50e would extract the remaining crude requiring up to 140,000 BPD of additional solvent. The total solvent circulated is 380,000 BPD with the rinse column configuration shown as 50e, resulting in a 25% reduction in the amount of solvent circulated. The result is a significant reduction in energy consumption compared to a state of the art 3-stage extraction process. This high performance solvent extraction scheme, including column 50e, can be applied to an existing open-art solvent extraction scheme in operation to further increase crude yield and/or reduce operating costs by reducing total solvent circulation. In another aspect, the new scheme can be used as an improvement to designs in heavy oil recovery that would normally use state-of-the-art solvent deasphalting.
The resulting asphaltene stream 58 can be processed in a 20% smaller asphaltene separation unit, 110. The core portion of the remaining concentrated thermally-affected asphaltenes are solid even at elevated temperatures (above 700° F.) with the side hydrocarbon chains removed, resulting in less volume for the asphaltene separation unit to handle. In addition, the modified nature of the asphaltenes provides for the opportunity for more effective metals reclamation and better feedstock for a clean energy conversion technology (e.g. gasification, catalytic gasification, oxy-combustion for enhanced SAGD production).
The vapour-solid (e.g. inertial) separation unit, 110, separates the asphaltene solids from the solvent vapour and gas remaining in stream 58 using one or more forces, such as centrifugal, gravitational, and inertial. These forces move the asphaltene solid to an area where the forces exerted by the gas stream are minimal. The separated solid asphaltene is moved by gravity into a hopper, where it is temporarily stored. Unit 110 can be either a settling chamber, baffle chamber or centrifugal collector; a device that provides separation of solid and gas. Centrifugal collectors can either be single or multi-staged cyclones. In the event the SDA unit, 50, is overly effective in separating the asphaltenes from the resin, DAO and solvent, stream 58 can be injected with suitable low molecular weight gas (ex. Natural gas, or nitrogen) to provide pneumatic conveyance to the asphaltene solids, that otherwise would be provided by flashing solvent in the line. A pneumatic conveying system may transport solids up to approximately 50 mm size. The solid must be dry, with no more than 20% moisture and not sticky. The thermally-affected asphaltene solids meet the above criteria and thus the process benefits from the ability to use an inertial separation unit, 110.
In a pneumatic conveying system, most of the energy is used for the transport of the gas itself. The energy efficiency of a pneumatic conveying plant is therefore relatively low, but this is often outweighed by easy handling and, in well designed systems, dust free solutions. In general the length of a pneumatic system should not extend 300 m for each pneumatic unit. The products can be conveyed over long distances by connecting the systems in series. There are three basic designs of pneumatic transport systems that can be considered for transporting stream 58 to unit 110:
Process 10 provides a crude feedstock that is pipeline compliant and is optimal for high conversion refiners. Stream 60 has low metals (<20 wppm Ni+V), low asphaltenes (<0.3 wt %), a very low TAN number (<0.3 mg KOH/mg), no diluent, and is high in VGO range material (30-50% of crude). For high conversion refiners (>1.4:1 conversion to coking), the distillation quality of the crude produced in stream 60 will improve utilization of the highest profit-generating units while filling out the remaining units. Table 5 shows the distillation curve of a representative feedstock (dilbit) and the produced refinery-ready feedstock which is a well-balanced crude when compared to other heavy refinery feedstock crudes such as WCS (Western Canada Select). WCS has more heavy residue (950+° F. material) requiring intense conversion and more light material than refiners can profitably refine to transportation fuels.
The combination of reactor 30, high performance solvent extraction process unit 50, and vapour-solid (e.g. inertial) separation unit, 110, exhibits a reduced process complexity. This may be expressed as a Nelson complexity index value of 4.0-4.5, significantly less than 9.0-10.0 for a coking and/or hydroprocessing scheme. Another illustration of improved performance is the reduced energy requirement of 3.93 GJ/tonne feed when compared to a delayed coking process that requires an energy input of 4.70 GJ/tonne feed to operate. This is a 16.4% reduction in energy intensity compared to a delayed coking process. This corresponds to a specific greenhouse gas (GHG) output of 0.253 tonne CO2/tonne feed for the Delayed Coking process and 0.213 tonne CO2/tonne feed for the proposed process. On a product comparison basis, the energy reduction is approximately 25-27% versus a coking process.
When compared to a coking upgrading process and standard reactor and solvent extraction process, process 10 provides a significant improvement in yield by minimizing by-products (Coke and non-condensable hydrocarbons) as noted in Table 6.
As well as being suitable for new grassroots facilities,
Stream 5 can be the bottoms streams from an atmospheric column, vacuum column, or a catalytic cracking unit, noted as unit 200 in
As an example,
As in
1. Maximum yield of incoming crude to plant.
2. Debottlenecking, if existing, or reduction of coking unit size
3. Debottlenecking, if existing, or reduction of residue hydrocracking size
4. Debottlenecking, if existing, or reduction of gasification unit size
5. Overall carbon footprint reduced for complex.
The integrated process in
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.
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