WO2014171960A1

WO2014171960A1 - Apparatus and method employing microwave resonant cavity heating for visbreaking of hydrocarbon fluid

Info

Publication number: WO2014171960A1
Application number: PCT/US2013/058476
Authority: WO
Inventors: David O'brien; Amin SAEEDFAR; Shawn David Taylor; Brian Oliver Clark; Wai-Ming Tam; Merlyn Xavier PULIKKATHARA; Tracy NEITZ; Simon ANDERSEN
Original assignee: Schlumberger Canada Limited; Services Petroliers Schlumberger; Schlumberger Holdings Limited; Schlumberger Technology B.V.; Prad Research And Development Limited; Schlumberger Technology Corporation
Priority date: 2013-04-17
Filing date: 2013-09-06
Publication date: 2014-10-23

Abstract

Apparatus and methods are described for microwave heating of hydrocarbon fluid inside a resonant cavity that supports resonance of microwave radiation at one or more resonant frequencies. The hydrocarbon fluid is loaded into a pipe realized from a material primarily transparent to the microwave radiation. The pipe is configured to extend through the resonant cavity and to enter and exit the resonant cavity. Microwave radiation supplied to the resonant cavity, the resonant cavity itself, and the pipe can be configured to heat hydrocarbon fluid loaded into the pipe to a reaction temperature suitable for visbreaking of the hydrocarbon fluid. The reaction temperature can be in the range of 350°C to 500°C, which is suitable for visbreaking of heavy oil. The pipe can be configured to provide pressurized flow of the hydrocarbon fluid through the pipe during heating such that it remains in a liquid phase.

Description

APPARATUS AND METHOD EMPLOYING MICROWAVE RESONANT CAVITY HEATING FOR VISBREAKING OF HYDROCARBON FLUID

BACKGROUND

Field

[0001] The present application relates generally to thermal processing of materials. More particularly, the present application relates to the use of electromagnetic energy (specifically microwave energy) to promote a chemical process or reaction, such as visbreaking of a hydrocarbon fluid where the molecular bonds in hydrocarbon molecules are broken so that smaller or lighter weight hydrocarbons are created in order to irreversibly reduce the viscosity of the hydrocarbon fluid.

Related Art

[0002] While heavy oil is becoming a regular feedstock to most refineries, its inherent high viscosity presents a significant challenge in transporting the heavy oil from the wellsite to commercial upgrading and refining facilities. A number of options have been or are currently used, including tanker shipments by rail, tanker truck, or barge, diluting of the heavy oil for pipeline transportation, and viscosity reduction by visbreaking for pipeline transportation.

[0003] The most common method of transport is blending heavy oils with diluents to reduce the viscosity to a lower value that makes pipeline transport of the heavy oil technically and economically feasible. The diluents may be solvents, condensate liquids, naphtha, or light conventional oils that are compatible with the heavy oils. Such methods require large and readily available volumes of diluents as well as infrastructure to blend, transport, and recover the diluents at the other end of the pipeline. Since the costs of diluents and pumping additional volumes of liquid are significant, alternative viscosity reduction methods that can be deployed at a wellsite location prior to pipeline transport are attractive.

[0004] Alternative approaches to reduce the viscosity at the wellsite typically involve chemically altering the composition of the heavy oil using a visbreaking process deployed within a surface facility (e.g., gas-fired visbreaker) or by in-situ upgrading techniques (e.g., electromagnetic (EM) heating techniques at radiowave (RF) or microwave (MW) frequencies).

[0005] Heavy oil has a high molecular weight fraction (typically referred to as a residual fraction) that distills at temperatures above 524°C. Visbreaking involves heating the heavy oil to a reaction temperature (typically in the range of 350°C to 500°C) where thermal cracking of the heavy oil will take place with relatively low conversion of the residual fraction. Typically, no more than 30 percent of the residual fraction of the heavy oil is converted, with the result being that just enough material is converted to reduce the viscosity but not significantly alter the quality of the heavy oil. Note that visbreaking is a different process than conventional upgrading (e.g., delayed cokers and fluidized bed cokers) where the composition of the feedstock is significantly altered to produce a higher quality oil for refining. Moreover, the conventional upgrading process typically handles large production volumes in the range of ten thousand to hundreds of thousands of barrels/day and requires expensive infrastructure to be viable and is therefore limited to refinery locations. However, visbreaking techniques at wellsite surface facilities can be more attractive for preparing pipeline-ready heavy oils since the production volumes are lower and such techniques involve reduced and simplified infrastructure. [0006] Visbreaking is typically carried out by a gas-fired heated tubular reactor that provides directional heating from outside to inside (i.e. heat flow from the tube wall to the oil contained inside the tube). While effective and relatively efficient, this mechanism introduces the risk of thermally-driven fouling on the inside of the reactor tube walls. The fouling, or buildup of insoluble coke particles on the tube walls, must be cleaned at regular maintenance intervals leading to scheduled shutdowns to replace and clean the reactor tubes.

SUMMARY

[0007] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0008] In an embodiment of the subject disclosure an apparatus and method is provided to heat hydrocarbon feedstock (such as heavy crude oil) by microwave radiation confined inside a resonant cavity. Microwave radiation is generated by an EM source and delivery system and supplied to the resonant cavity by a power coupler, which may be an iris coupler. The resonant cavity is a sealed vessel that confines microwave radiation supplied thereto and supports resonance of the supplied microwave radiation at one or more resonant frequencies. The coupling strength of the power coupler that operably couples the EM delivery system to the resonant cavity can be tuned such that the effective load impedance matches the output impedance of the EM delivery system in order to maximize power transfer. The hydrocarbon feedstock is loaded into a pipe made of a material primarily transparent to microwave radiation, such as sapphire. The pipe is configured to extend through the resonant cavity and to enter and exit the resonant cavity. In this manner, the hydrocarbon feedstock is contained within the interior space of the resonant cavity and physically isolated from the interior space of the resonant cavity by the pipe wall. The microwave radiation supplied to the resonant cavity, the resonant cavity itself, and the pipe can be configured to heat the hydrocarbon feedstock loaded into the pipe to a reaction temperature suitable for visbreaking of the hydrocarbon feedstock. In one embodiment, the reaction temperature is in the range of 350°C to 500°C, which is suitable for visbreaking of heavy crude oil feedstock (i.e., the thermal cracking of the heavy crude oil feedstock with relatively low conversion of the residual fraction such that the viscosity of the oil is reduced without significantly altering the quality of the oil). Pumps and valves can be fiuidly coupled to the opposed ends of the pipe outside the resonant cavity and configured to provide a pressurized flow of the hydrocarbon feedstock through the pipe during the heating process such that it remains in a liquid phase so as to suppress the gas phase and avoid two-phase flow.

[0009] The resonant frequency(ies) supported by the resonant cavity can lie in a frequency band between 0.1 GHz and 100 GHz.

[0010] The resonant cavity can be configured to focus microwave radiation at the resonant frequency to a localized area within the internal space of the resonant cavity. This localized area can be occupied by the tubular member within the internal space of the resonant cavity for efficient heating. In one embodiment, the resonant cavity can be configured to resonate microwave radiation at a desired transverse magnetic (TM) or transverse electric (TE) mode, such as the TMoio mode. In this case, the tubular member can extend along an axis of the resonant cavity defined by the TMoio mode. [0011] The resonant cavity can be defined by an elongate body having a longitudinal axis, and the tubular member can be configured to extend inside the resonant cavity along the longitudinal axis of the body. A plurality of thin members (e.g., discs) can be disposed along the longitudinal axis of the body. The members can define a series of resonant cavity sections with

corresponding interior spaces. The members can have apertures that are configured to allow for propagation of microwave radiation through the interior spaces of the series of resonant cavity sections. The tubular member can extend through the interior spaces of the series of resonant cavity sections to allow for heating of hydrocarbon fluid within the tubular member by microwave radiation confined within the interior spaces of the series of resonant cavity sections.

[0012] At least one soaker section can be disposed downstream of the resonant cavity. The soaker section is configured to contain hydrocarbon fluid and limit heat loss from the contained hydrocarbon fluid. The soaker section can include a tube or pipe or any pressure-containing vessel that contains the hydrocarbon fluid with thermally-insulative material that surrounds the tube or pipe. The soaker section can also include an active heater element (such as heat tape or a coil) that is disposed between the thermally-insulative material and the tube, pipe, or pressure vessel.

[0013] An inlet port and an outlet port can be sealably coupled to opposed ends of the tubular member outside the resonant cavity.

[0014] A thermally-insulative material that is transparent to microwave radiation can surround the tubular member within the resonant cavity and/or may be placed against the cavity wall.

[0015] The hydrocarbon fluid can flow at a controlled flow rate through the tubular member while being heated by the microwave radiation confined within the interior space of the resonant cavity. Alternatively, the hydrocarbon fluid can remain stationary inside the tubular member while being heated by the microwave radiation confined within the interior space of the resonant cavity.

[0016] The hydrocarbon fluid heated by the apparatus can be crude oil, heavy oil, or bitumen.

[0017] A mathematical model can be used to determine the size of the tubular member, the resonant frequency of the microwave radiation, the geometry of the resonant cavity that supports such resonant frequency, and the required residence time in order to carry out desired visbreaking of a given flow rate of hydrocarbon fluid.

[0018] In another aspect, an apparatus for heating a hydrocarbon fluid with microwave radiation includes a plurality of microwave resonator heater sections, wherein each microwave resonator heater section includes a resonant cavity and a corresponding tubular member. The resonant cavity of a given microwave resonator heater section defines an interior space and is made of material that is primarily reflective to microwave radiation. The resonant cavity is a sealed vessel that confines microwave radiation supplied thereto and supports resonance of supplied microwave radiation at one or more resonant frequencies. The tubular member of the given microwave resonator heater section is configured to extend through the interior space of the resonant cavity and enter and exit the resonant cavity of the given microwave resonator heater section. The tubular member is made of a material that is primarily transparent to microwave radiation. The plurality of microwave resonator heater sections are configured such that the tubular members of the plurality of microwave resonator heater sections contain hydrocarbon fluid that is subject to heating by microwave radiation confined within the interior spaces of the resonant cavities of the plurality of microwave resonator heater sections. [0019] The resonant frequency(ies) supported by the resonant cavities of the plurality of microwave resonator heater sections can lie in a frequency band between 0.1 GHz and 100 GHz.

[0020] Multiple EM source and delivery systems can supply microwave radiation to

corresponding resonant cavity heater sections. An EM source and delivery system can cooperate with a power splitter to split microwave radiation into multiple legs for supply to a number of the resonant cavity heater sections.

[0021] A flow splitter and associated tubing can distribute an inflow of hydrocarbon fluid to the tubular members of the plurality of microwave resonator heater sections.

[0022] At least one soaker section can be disposed downstream of the plurality of microwave resonator heater sections. The soaker section is configured to contain hydrocarbon fluid and limit heat loss from the contained hydrocarbon fluid. The soaker section can include a tube or pipe that contains the hydrocarbon fluid with thermally-insulative material that surrounds the tube or pipe and/or may be placed against the soaker section wall. The soaker section can also include an active heater element (such as heater tape or a coil) that is disposed between the thermally-insulative material and the tube or pipe. A plurality of soaker sections can be disposed downstream of the plurality of microwave resonator heater sections.

[0023] Further features and advantages of the subject application will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present application is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the present application, in which like reference numerals represent similar parts throughout the several views of the drawings.

[0025] FIG. 1 is a schematic cross-sectional view of an exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation confined in a resonant cavity.

[0026] FIG. 2 is a color diagram illustrating the amplitude of the electric field distribution in the resonant cavity of FIG. 1 during an exemplary visbreaking process.

[0027] FIG. 3 is a color diagram illustrating the power loss density distribution in the resonant cavity of FIG. 1 during the exemplary visbreaking process.

[0028] FIG. 4 is a curve that shows the required inner diameter of the resonant cavity body of FIG. 1 operating at 2.45 GHz as a function of inner diameter of the hydrocarbon-containing pipe (with the pipe made of alumina and with a fluid pressure of 1000 psi (70.3 kg/square cm)). Such a curve can be created for any frequency, fluid pressure, and pipe material, which results in dimensional change of the apparatus shown in FIG. 1.

[0029] FIG. 5 is a plot of the reflection coefficient (Sn of the S-parameters) in the resonant cavity of FIG. 1 over a frequency range, which shows the TM₀io mode as well as its neighboring, undesired modes. [0030] FIG. 6 is a schematic cross-sectional view of a second exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation confined in a resonant cavity.

[0031] FIG. 7 is a color diagram illustrating the amplitude of the electric field distribution in the resonant cavity of FIG. 6 during an exemplary visbreaking process.

[0032] FIG. 8 is a color diagram illustrating the power loss density distribution in the resonant cavity of FIG. 6 during the exemplary visbreaking process.

[0033] FIG. 9 is a schematic cross-sectional view of a third exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation confined in a resonant cavity.

[0034] FIG. 10 is a color diagram illustrating the amplitude of the electric field distribution in the resonant cavity of FIG. 9 during an exemplary visbreaking process.

[0035] FIG. 11 is a color diagram illustrating the power loss density distribution in the resonant cavity of FIG. 9 during the exemplary visbreaking process.

[0036] FIG. 12A is a curve that illustrates the required inner diameter of the resonant cavity body of FIG. 9 for a TMoio mode operating at a resonant frequency of 2.45 GHz as a function of the inner diameter of the hydrocarbon-containing pipe.

[0037] FIG. 12B is a curve that illustrates the required inner diameter of the resonant cavity body of FIG. 9 for a TMoio mode operating at a resonant frequency of 0.3 GHz as a function of the inner diameter of the hydrocarbon-containing pipe. [0038] FIG. 13 is a curve that illustrates the reflection coefficient (Sn of the S-parameters) in the resonant cavity of FIG. 9 as a function of frequency, which shows a single TM₀io mode at a frequency at or near 2.45 GHz.

[0039] FIGS. 14A and 14B are top and front views, respectively, of an exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation; the apparatus employs four microwave resonator heater sections and one soaker section similar to the components of the design of FIG. 9.

[0040] FIGS. 15A and 15B are top and front views, respectively, of an exemplary embodiment of an apparatus for heating hydrocarbon fluid employing microwave radiation; the apparatus employs four microwave resonator heater sections and two soaker sections similar to the components of the design of FIG. 9.

DETAILED DESCRIPTION

[0041] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present application only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present application. In this regard, no attempt is made to show structural details in more detail than is necessary for the fundamental understanding of the present application, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present application may be embodied in practice. Furthermore, like reference numbers and designations in the various drawings indicate like elements. [0042] The embodiments of the present application disclose apparatus and methods for microwave heating of a hydrocarbon feedstock (such as heavy crude oil) inside a resonant cavity defined by a body made of an electromagnetic conductive material. Microwave radiation is generated by an EM source and delivery system and supplied to the resonant cavity by a power coupler, which may be an iris coupler. The resonant cavity is a sealed vessel that confines microwave radiation supplied thereto and supports resonance of the supplied microwave radiation at one or more resonant frequencies. The impedance of the power coupler that operably couples the EM delivery system to the resonant cavity can be tuned such that the effective load impedance matches the output impedance of the EM delivery system in order to maximize power transfer. The hydrocarbon feedstock is loaded into a pipe made of a material primarily transparent to the microwave radiation, such as sapphire, quartz, or alumina. The pipe is configured to extend through the resonant cavity and to enter and exit the resonant cavity. In this manner, the hydrocarbon feedstock is contained within the interior space of the resonant cavity and physically isolated from the interior space of the resonant cavity by the pipe wall. The microwave radiation supplied to the resonant cavity, the resonant cavity itself, and the pipe can be configured to heat the hydrocarbon feedstock loaded into the pipe to a reaction temperature suitable for visbreaking of the hydrocarbon feedstock. In one embodiment, the reaction temperature is in the range of 350°C to 500°C, which is suitable for visbreaking of heavy crude oil feedstock (i.e., the thermal cracking of the heavy crude oil feedstock with relatively low conversion of the residual fraction such that the viscosity of the oil is reduced without significantly altering the quality of the oil). Pumps and valves can be fluidly coupled to the opposed ends of the pipe outside the resonant cavity and configured to provide a pressurized flow of the hydrocarbon feedstock through the pipe during the heating process such that it remains in a liquid phase so as to suppress the gas phase and avoid a two-phase flow.

[0043] The resonant cavity supports or facilitates at least one mode of electromagnetic radiation within the radio wave and microwave frequency band - the frequency band between 0.1 GHz and 100 GHz. As used herein, the term "mode" refers to a particular pattern of a standing

electromagnetic wave that satisfies Maxwell's equations and the applicable boundary conditions of the resonant cavity. In the cavity, the mode can be any one of the various possible patterns of standing electromagnetic waves. Each mode is characterized by its frequency and standing wave pattern. The electromagnetic field pattern of a mode depends on the frequency, refractive indices, or dielectric constants of the materials of the cavity, the pipe and the hydrocarbon, and the cavity geometry.

[0044] A transverse electric (TE) mode is one whose electric field vector is normal to a particular plane of reference. Similarly, a transverse magnetic (TM) mode is one whose magnetic field vector is normal to a particular plane of reference.

[0045] The actual field distribution inside the resonant cavity is a superposition of the modes therein. Each of the modes can be identified with one or more subscripts (e.g., TE₀₁₀). Each subscript attributes to the boundary condition in a particular dimension in the three geometric dimensional Maxwell's equations. For a resonant cavity, each of the three geometric dimensions has one boundary condition, resulting in three subscripts. For standing wave, or resonant, modes, the modes are discreet and the subscripts are integers. In general, the larger a particular subscript the more modes are present in the standing wave in that particular geometric dimension. The resonant frequencies of different modes have different sensitivity to the geometric dimensions, so the density and distribution of the mode frequencies in the frequency spectrum of a particular resonant cavity depends on the ratio of its geometric dimensions. It is possible to manipulate the ratio of the geometric dimensions of a resonant cavity to locate the mode of interest, e.g. TM₀io, to a region in the frequency spectrum where the mode density is relatively low, which reinforces single mode resonation. In case the frequency of the mode of interest is near or overlaps with the frequencies of one or more other modes, simultaneous resonation of more than one mode can occur. The resulting electromagnetic field pattern will be the superposition of the fields of individual modes, which in general does not show the same types of strong maxima and minima field values within the cavity.

[0046] FIG. 1 illustrates an embodiment of an apparatus 11 for visbreaking of a hydrocarbon feedstock (such as heavy crude oil) through focused heating by microwave radiation inside a resonant cavity. The resonant cavity is defined by an elongate cylindrical body 13 of circular cross-section and opposed end caps 15. The body 13 and end caps 15 are made of a metallic material (such as aluminum, stainless steel, copper, bronze, or any electrically conductive metal) that is primarily reflective of microwave radiation with minimal absorption. Each end cap 15 includes an outward extending neck 17 that defines a central passageway through the respective end cap 15. In this manner, the end caps 15 are configured to receive and support a pipe 19 that extends through the end caps 15 and through the center of the body 13 along the central longitudinal axis of the elongate body 13. The pipe 19 is made of a nonconductive material (such as sapphire, quartz, ceramic, alumina, or other suitable material) that is primarily transparent to microwave radiation. The opposed ends of the pipe 19 that extend beyond the respective necks 17 of the end caps 15 interface to corresponding ported tube receptacles 21. Each ported tube receptacle 21 is shouldered on a support flange 23 and retained to the support flange 23 by a retainer 25. The support flange 23 is fastened to tie rods 27 that are fastened to the respective end cap 15 as shown. A high pressure seal 29 is provided for each ported tube receptacle 21 adjacent the interface of the ported tube receptacle 21 and the respective support flange 23 in order to prevent fluid leakage at this joint.

[0047] The hydrocarbon feedstock 31 to be treated is loaded inside the pipe 19 and is physically isolated from the body 13 of the resonant cavity. A temperature sensor 33 that is formed of a material that is primarily transparent to microwave radiation, such as a single-crystal sapphire optical fiber temperature sensor, can be inserted inside the pipe 19 and placed in direct contact with the hydrocarbon feedstock 31. The temperature sensor 33 can extend through the pipe 19 outside the resonant cavity through neck 17 and corresponding ported tube receptacle 21 such that it is coupled to associated light processing equipment for deriving temperature of the hydrocarbon feedstock 31 at one more positions inside the pipe 19 during the visbreaking process. Pumps and valves can be fluidly coupled to the opposed ported tube receptacles 21 and configured to supply a pressurized flow of the hydrocarbon feedstock 31 inside the pipe 19 during the visbreaking process such that it remains in a liquid phase so as to suppress the gas phase and avoid two phase flow in the pipe 19. This provides better control by minimizing the variability in the residence time and temperature profiles experienced by the hydrocarbon feedstock during the visbreaking process, which in turn provides improved control of the targeted visbreaking reactions. In one embodiment, the hydrocarbon feedstock flow is pressurized up to 5000 psi (351.5 kg/square cm) inside the pipe 19 during the visbreaking process such that it remains in a liquid phase so as to suppress the gas phase and avoid two phase flow in the pipe 19. [0048] An EM source is configured to generate and supply microwave radiation via a waveguide or coaxial cable to a coupler 35 which interfaces to the body 13. The coupler 35 guides the supplied microwave radiation into the body 13 and can provide for impedance matching of the waveguide transmission system to the impedance of the body 13. There are many designs available for the coupler 35, including but not limited to iris couplers and loop couplers. FIG. 1 shows an iris coupler design which comprises a waveguide 37 and plate 39 with a tuned iris geometry attached to the outside of the body 13. The waveguide 37 and plate 39 are realized from a metallic material (such as aluminum, stainless steel, copper, bronze, or any electrically conductive metal) that is primarily reflective of microwave radiation with minimal absorption. The resonant cavity defined by the body 13 and end caps 15 can be elongate in nature with the coupler 35 disposed nearer one end of the resonant cavity (and thus further away from the other end of the resonant cavity) as evident from FIGS. 2 and 3.

[0049] The microwave energy generated and supplied by the EM source is centered at a predefined frequency, which can range between 0.1 and 10 GHz depending on the specific flow rate requirements of the system as described below in more detail. The geometry of the resonant cavity defined by the body 13 and end caps 15 is configured to resonate at the predefined frequency of the microwave energy generated and supplied by the EM source. Furthermore, the microwave energy and the resonant cavity and the pipe 19 are configured to heat the

hydrocarbon feedstock loaded into the pipe 19 to a reaction temperature suitable for visbreaking of the hydrocarbon feedstock. In one embodiment, the reaction temperature is in the range of 350°C to 500°C, which is suitable for visbreaking of heavy crude oil feedstock (i.e., the thermal cracking of the heavy crude oil feedstock with relatively low conversion of the residual fraction such that the viscosity of the oil is reduced without significantly altering the quality of the oil). In all cases, the geometry of the resonant cavity can be configured to ensure that the vast majority of the microwave energy in the cavity is concentrated along the central axis of the pipe 19. The material of the body 13, the end caps 15, and the coupler 35 is optimized to minimize microwave energy reflection and enable a high-Q resonant cavity, and thereby allow the maximum amount of microwave energy to heat the hydrocarbon feedstock fluid to the desired reaction temperature, while avoiding coke buildup on the inside walls of the pipe 19. If allowed to form on the pipe walls, coke will ultimately lead to the loss of cavity resonance - an undesired outcome. This can be achieved by operating the resonant cavity in an optimal TMoio mode with the option of operating at additional single TM and TE modes. TE modes can also be excited, for example, simply by rotating the coupler 35 and the corresponding iris by 90 degrees.

[0050] The design of the resonant cavity (body 13 and end caps 15) is configured to provide the maximum and most efficient energy transfer into the hydrocarbon fluid flowing in the pipe 19. Through microwave power coupling optimization and impedance matching, the resonant cavity can be tuned in order to minimize the reflected power from, or equivalently, to maximize the transmitted power into, the resonant cavity for the desired transverse magnetic (TM) or transverse electric (TE) mode. The minimized reflected power, or equivalently the maximized transmitted power, results in the maximum energy transfer into the resonant cavity and thus the most efficient operation. In order to deliver the microwave energy to the relatively low loss hydrocarbon feedstock whose dielectric loss tangent is on the order of 10^~3 to 10^~2, the heating process requires the microwave energy to be focused on the center of the resonant cavity along the length of the pipe 19 and hence achieves a desired heating profile in the hydrocarbon feedstock and avoids "hot spots." In order to meet this requirement, the resonant cavity can be designed to operate at a single TMoio mode with the ability to operate at additional single TM and TE modes if desired. Additional undesired modes can be suppressed through mechanical means or electrical means or avoided by a precise frequency tracking technique.

[0051] FIG. 2 shows the amplitude of the electric field distribution in the resonant cavity of FIG. 1 during the visbreaking process. FIG. 3 shows the power loss density distribution in the resonant cavity of FIG. 1 during the visbreaking process. In both FIGS. 2 and 3, the microwave energy has a TMoio mode at a resonant frequency of 2.45 GHz. The results are desirable since the majority of the microwave energy is focused on the hydrocarbon feedstock contained inside the pipe 19 and thus provides efficient and controlled heating of the hydrocarbon feedstock.

[0052] The thermal reactions (i.e. upgrading reactions) of the visbreaking process are controlled by flowing the hydrocarbon feedstock in a liquid phase through the resonant cavity defined by the body 13 and end caps 15. The hydrocarbon feedstock enters the resonant cavity from the end of the pipe 19 closest to the coupler 35. The hydrocarbon feedstock then flows through the pipe 19 past the coupler 35 and exits the pipe 19 at the end furthest from the coupler 35. In the case of FIG. 1, the fluid flow of the hydrocarbon feedstock is from right to left. In the case of FIGS. 2 and 3, the fluid flow of the hydrocarbon feedstock is from left to right. As indicated by FIG. 2, as the hydrocarbon feedstock flows through the pipe 19 and into the resonant cavity, it is exposed to a rapidly increasing power intensity which leads to rapid heating. The peak rate of heating occurs as the hydrocarbon feedstock passes by the coupler 35, after which the rate of heating decreases. At this point, the hydrocarbon feedstock is at or close to the desired

(upgrading) reaction temperature, which can be in the range of 350°C to 500°C. As the hydrocarbon feedstock travels the remaining length of the pipe 19 within the resonant cavity, the rate of heating continues to decrease towards a minimal level. This provides enough heating to ensure the reaction temperature is maintained within the desired operating range of the resonant cavity.

[0053] The amount of conversion (i.e., visbreaking) of the hydrocarbon feedstock is dictated by the amount of time that the hydrocarbon feedstock remains at the desired reaction temperature, also known as the residence time. The desired flow rate, the length of the pipe 19 inside the resonant cavity (i.e., the resonant cavity length), and the inner diameter of the pipe 19 of the apparatus of FIG. 1 can be used to determine the residence time. Therefore, the apparatus of FIG. 1 may accommodate larger flow rates by increasing the diameter of the pipe 19. For the case where a TM₀io mode is desired, the microwave energy is focused on the center of the pipe 19. In this case, in order to accommodate an increase in the pipe diameter, the inside diameter of the resonant cavity body 13 must increase to accommodate a decrease in the operating resonant frequency. FIG. 4 is a curve based on mathematical analysis using a perturbation technique that shows the required inner diameter of the resonant cavity body 13 operating at 2.45 GHz as a function of the inner diameter of the pipe 19 with the pipe 19 made of alumina and with a fluid pressure of 1000 psi (70.3 kg/square cm). Such a curve can be created for any frequency, fluid pressure, and pipe material, which results in dimensional change of the apparatus shown in FIG. 1. The only dimension affecting the cavity design operating at the TMoio mode is the inner diameter of the resonant cavity body 13 and not its length (i.e., the dimension along the length of the pipe 19). This is a particular advantage of the TMoio mode in a cylindrical resonant cavity because the resonant cavity can be of arbitrary length without changing the operating frequency of the TMoio mode. The apparatus of FIG. 1 can also be configured to accommodate larger flow rates by other mechanisms, such as by adding one or more additional resonant cavity heater sections (similar the resonant cavity heater section of FIG. 1) configured in a parallel arrangement (similar to FIGS. 14A/14B and 15A/15B) or in a series arrangement, if desired.

[0054] The apparatus of FIG. 1 can employ well known monitoring and control mechanisms to maintain the desired resonance mode (e.g., TM₀io mode) and the desired heating efficiency, as well as the desired fluid temperature during the visbreaking process. FIG. 5 is a plot of the reflection coefficient (Sn of the S-parameters) over a frequency range showing the TM₀io mode as well as its neighboring, undesired modes. Resonance control may be achieved by i) frequency tracking, where the power source frequency is frequently updated to maintain the desired resonance mode and/or ii) by the use of tuning mechanisms to control the volume of the resonant cavity, including, but not limited to, mechanical and thermal measures. Resonance control can involve monitoring and assurance of the minimization of the reflection coefficient (Sn of the S- parameters) or of the maximization of the transmission coefficient (S₂₁ of the S-parameters) during the visbreaking process. Temperature control can utilize the temperature sensor 33 to detect the temperature of the hydrocarbon feedstock and control the level of microwave power in order to achieve the desired reaction temperature of the visbreaking process.

[0055] The location of the coupler 35 can be dictated by the desired location for rapid heating of the hydrocarbon feedstock. For example, the coupler 35 can be located anywhere along the length of the resonant cavity. In the exemplary design of FIG. 1 , the coupler 35 is located closer to the inlet end of the resonant cavity, where the hydrocarbon feedstock enters into the resonant cavity. This can provide rapid heating of the hydrocarbon feedstock to the desired reaction temperature immediately upon entry to the resonant cavity. The remaining length of the resonant cavity is then left to maintain the reaction temperature of the hydrocarbon fluid to the exit port. [0056] Advantageously, the apparatus of FIG. 1 produces rapid heating of the hydrocarbon feedstock while maintaining relatively cool temperatures on the walls of the resonant cavity body 13 and end caps 15. A thermally-insulative material that is primarily transparent to microwave radiation can be used to cover the pipe 19 containing the hydrocarbon feedstock inside the resonant cavity body 13 of FIG. 1 in order to limit heat loss (and thus reduce the energy input requirements of the EM source) and maintain the desired reaction temperature.

[0057] FIG. 6 illustrates an embodiment of an apparatus 111 for visbreaking of a hydrocarbon feedstock (such as heavy crude oil) through focused heating by microwave radiation inside a resonant cavity. The apparatus 111 of FIG. 6 is fundamentally the same as the apparatus 11 of FIG. 1 except for the addition of metallic thin discs 41 that are disposed inside the elongate body 13 and extend transverse to the longitudinal axis of the elongate body 13 and the pipe 19. The discs 41 are spaced from one another along the length of the elongate body 13 to define a number of shorter-length resonant cavities that are disposed adjacent one another within the body 13. The sequence of shorter-length resonant cavities is disposed adjacent a main resonant cavity (the resonant cavity adjacent the pipe inlet and the coupler 35). In this configuration, the adjacent shorter-length resonant cavities may be coupled to the main resonant cavity and to one another through apertures in the discs 41. The shorter-length resonant cavities behave like single mode cavities by suppressing other modes. Apertures in the discs 41 allow for signal attenuation as microwave energy propagates from the main resonant cavity through the sequence of shorter- length resonant cavities. The metallic surfaces of the discs 41 also function to mirror the microwave signal in each respective cavity, which lessens the attenuation of the signal and increases the overall heating length of the hydrocarbon feedstock inside the pipe 19. In addition, by configuring the number of discs 41 and their locations along the axis of the body 13, the focus of electric field intensity can be changed so that a designated part of the hydrocarbon feedstock receives more microwave energy. Moreover, the number of employed discs 41 , their spacing and the aperture size on each disc 41 can be optimized for performance enhancement. The main resonant cavity and the adjacent sequence of shorter-length resonant cavities mimic the operation of a multi-mode resonator cavity. The main resonant cavity can operate with a TMoio mode, if desired. In this case, a frequency tracking system can be used to ensure the main resonant cavity is operating at the frequency of the desired resonance mode (e.g., TM₀io mode).

[0058] FIG. 7 shows the amplitude of the electric field distribution in the resonant cavity of FIG. 6 during the visbreaking process. FIG. 8 shows the power loss density distribution in the resonant cavity of FIG. 6 during the visbreaking process. In both FIGS. 7 and 8, the microwave energy has a TMoio mode at a resonant frequency of 2.45 GHz. The results are desirable since the majority of the microwave energy is focused on the hydrocarbon feedstock contained inside the pipe 19 and thus provides efficient and controlled heating of the hydrocarbon feedstock.

[0059] The thermal reactions (i.e., upgrading reactions) of the visbreaking process are controlled by flowing the hydrocarbon feedstock in a liquid phase through the main resonant cavity and the shorter- length resonant cavities, where such resonant cavities are defined by the body 13 and end caps 15 and the discs 41. The hydrocarbon feedstock enters into the end of the pipe 19 closest to the coupler 35 and flows through the pipe 19 within the main resonant cavity supplied with microwave radiation via the coupler 35. The hydrocarbon feedstock then flows through the pipe 19 into the shorter-length resonant cavities and exits the body 13 at the end furthest from the coupler 35. In the case of FIG. 6, the fluid flow of the hydrocarbon feedstock is from right to left. In the case of FIGS. 7 and 8, the fluid flow of the hydrocarbon feedstock is from left to right. As indicated by FIG. 7, as the hydrocarbon feedstock flows through the pipe 19 and into the main resonant cavity, it is exposed to a rapidly increasing power intensity which leads to rapid heating. The peak rate of heating occurs as the hydrocarbon feedstock passes by the coupler 35, after which the rate of heating decreases. At this point, the hydrocarbon feedstock is at or close to the desired (upgrading) reaction temperature, which can be in the range of 350°C to 500°C. As the hydrocarbon feedstock travels through the remaining length of the pipe 19 within the shorter-length resonant cavities defined by the discs 41 , the rate of heating continues to decrease towards a minimal level. This provides enough heating to ensure the reaction temperature is maintained within the desired operating range of the apparatus.

[0060] For the apparatus of FIG. 6, the desired flow rate, the length of the pipe 19 extending through the main resonant cavity and the smaller-size resonant cavities (i.e., the total resonant cavity length), and the inner diameter of the pipe 19 can be used to determine the residence time of the hydrocarbon feedstock flowing within the pipe 19. Similar to the apparatus of FIG. 1 , the apparatus of the FIG. 6 may accommodate larger flow rates by increasing the diameter of the pipe 19. For the case where a TM₀io mode is desired, the microwave energy is focused on the center of the pipe 19. In this case, in order to accommodate an increase in the pipe diameter, the inner diameter of the resonant cavity body 13 must increase to accommodate a decrease in the operating resonant frequency. The apparatus of the FIG. 6 can also be configured to

accommodate larger flow rates by other mechanisms, such as by adding one or more additional resonant cavity heater sections (similar to the resonant cavity heater section of FIG. 6) configured in a parallel arrangement (similar to FIGS. 14A/14B and 15A/15B) or in a series arrangement, if desired. A thermally-insulative material that is primarily transparent to microwave radiation can be used to cover the tube 19 containing the hydrocarbon feedstock inside the resonant cavity body 13 of FIG. 6 in order to limit heat loss (and thus reduce the energy input requirements of the EM source) and maintain the desired reaction temperature.

[0061] FIG. 9 illustrates an embodiment of an apparatus 1 1 1 1 for visbreaking of a hydrocarbon feedstock (such as heavy crude oil) through focused heating by microwave radiation inside a resonant cavity. The apparatus 1 1 1 1 of FIG. 9 is fundamentally the same as the apparatus 1 1 of FIG. 1 except for the addition of a soaker section 43 disposed outside the resonant cavity defined by the body 13 and end caps 15. The soaker section 43 covers a length of the pipe 19

downstream of the resonant cavity. The soaker section 43 provides insulation or/and heating to such length of pipe 19 and to the hydrocarbon feedstock disposed therein in order to ensure the desired reaction temperature of the hydrocarbon feedstock is maintained over such length of pipe 19. The soaker section 43 can be realized by one or more layers of thermally-insulative material, such as mineral fiber, glass fiber, silica, aerogel, or other suitable insulating material, that surrounds the length of pipe 19. Such thermally-insulative material insulates the length of pipe to minimize conductive heat loss from the hydrocarbon feedstock disposed in the length of pipe. The soaker section 43 can also include resistive heat tape or heater coil wrapped around the length of pipe under the thermally-insulative material. The resistive heat tape or heater coil can be configured to apply heat to the length of pipe 19 and to the hydrocarbon feedstock disposed therein as desired. The resonant cavity can operate with a TMoio mode, if desired. In this case, a frequency tracking system can be used to ensure the resonant cavity is operating at the optimal frequency of the desired resonant mode (e.g., TM₀io mode).

[0062] FIG. 10 shows the amplitude of the electric field distribution in the resonant cavity of FIG. 9 during the visbreaking process. FIG. 1 1 shows the power loss density distribution in the resonant cavity of FIG. 9 during the visbreaking process. In both FIGS. 10 and 1 1 , the microwave energy has a TMoio mode at a resonant frequency of 2.45 GHz. The results are desirable since the majority of the microwave energy is focused on the hydrocarbon feedstock contained inside the pipe 19 and thus provides efficient and controlled heating of the

hydrocarbon feedstock.

[0063] The thermal reactions (i.e. upgrading reactions) of the visbreaking process are controlled by flowing the hydrocarbon feedstock in a liquid phase through the resonant cavity defined by the body 13 and end caps 15. The hydrocarbon feedstock enters the resonant cavity from the end of the pipe 19 closest to the coupler 35. The hydrocarbon fluid then flows through the pipe 19 past the coupler 35 and into the soaker section 43 and exits the pipe 13 at the end furthest from the coupler 35. In the case of FIGS. 9 to 11, the fluid flow of the hydrocarbon feedstock is from right to left. As indicated by FIG. 9, as the hydrocarbon feedstock flows through the pipe 19 and into the resonant cavity, it is exposed to a rapidly increasing power intensity which leads to rapid heating. The peak rate of heating occurs as the hydrocarbon feedstock passes by the coupler 35, after which the rate of heating decreases. At this point, the hydrocarbon feedstock is at or close to the desired (upgrading) reaction temperature, which can be in the range of 350°C to 500°C. As the hydrocarbon feedstock travels through the length of the pipe 19 in the soaker section 43, the soaker section 43 provides insulation and/or heating to such length of pipe 19 and to the hydrocarbon feedstock disposed therein in order to ensure the reaction temperature of the hydrocarbon feedstock is maintained over such length of pipe 19. This provides enough heating to ensure the reaction temperature is maintained within the desired operating range of the resonant cavity over the length of the soaker section. Advantageously, the soaker section 43 provides a relatively accurate control over the level and the uniformity of the temperature profile of the hydrocarbon feedstock necessary for the visbreaking to occur. [0064] For the apparatus of FIG. 9, the desired flow rate, the length of the pipe 19 extending through the resonant cavity (i.e., the resonant cavity length) together with the length of pipe 19 of the soaker section 43, and the inner diameter of the pipe 19 can be used to determine the residence time of the hydrocarbon feedstock flowing within the pipe 19. The apparatus of FIG. 9 can be configured to accommodate larger flow rates by using any combination of i) increasing the diameter of the pipe 19 and the resonant cavity body 13, ii) adding one or more additional resonant cavity heater sections (similar the resonant cavity heater section of FIGS. 9, 10 and 1 1) configured in a parallel arrangement (FIGS. 14A/14B and 15A/15B) or a serial arrangement, iii) increasing the dimensions (e.g. length and diameter of a cylinder) of the soaker section 43, and iv) adding one or more additional soaker sections (similar the soaker section 43 of FIG. 9) configured in a parallel arrangement (FIGS. 15A/15B). For the case where a TMoio mode is desired, the microwave energy is focused on the center of the pipe 19. In this case, in order to accommodate an increase in the pipe diameter, the inside diameter of the resonant cavity body 13 must increase to accommodate a decrease in the operating frequency. FIG. 12A is a curve that illustrates the required inner diameter of the resonant cavity body 13 as a function of the inner diameter of the pipe 19 for a TMoio mode at a resonant frequency 2.45 GHz. FIG. 12B is a curve that illustrates the required inner diameter of the resonant cavity body 13 as a function of the inner diameter of the pipe 19 for a TMoio mode at a resonant frequency of 0.3 GHz. This shows that a decrease in the resonant frequency from 2.45 GHz to 0.3 GHz will allow for an increase in the maximum diameter of the pipe 19 that can be accommodated in the resonant cavity.

Following this approach, a range of flow rates may be achieved by simply adjusting the resonant frequency and the inner diameter of the resonant cavity body 13 in order to maintain the desired resonance mode; in most cases, the TMoio mode. [0065] Compared to the apparatus of FIGS. 1 and 6, the use of the soaker section 43 outside the resonant cavity decreases the length-to-diameter ratio of the resonant cavity. Among the complete TE and TM mode spectrum, the TM₀io mode has a unique property that its frequency is cavity-length-independent, whereas other modes exhibit an increase in frequency as the cavity's length-to-diameter ratio decreases. FIG. 13 illustrates the reflection coefficient (Sn of the S- parameters in dB) in an exemplary embodiment of the resonant cavity of FIG. 9 as a function of frequency, which shows a single TM₀io mode at a frequency at or near 2.45 GHz. Such single TMoio mode operation significantly simplifies any necessary resonance control mechanism and results in higher energy efficiency and lower design and hardware costs, such as suppression of neighboring modes. Also, the microwave coupler 35 of the apparatus of FIG. 9 is located at the center of the resonant cavity body 13, which enables a longitudinally symmetric EM field pattern, which enhances the stability of the desired longitudinal temperature profile along the length of the pipe 19 inside the resonant cavity. The enhanced stability results in higher energy efficiency and significantly simplifies resonance control, such as field profile monitoring.

[0066] It should be noted that the apparatus of FIG. 9 employs a pipe 19 (of material primarily transparent to microwave radiation) that extends along the entire length of the central axis of the resonant cavity as well as the entire length of the soaker section 43. Note that transparency to microwave radiation is only required in the resonant cavity. Thus, the hydrocarbon fluid that flows through the soaker section 43 can be contained inside a pipe, cylindrical vessel, or vessel of any shape made of a metallic material that is non-transparent to microwave radiation, such as stainless steel, nickel alloy, or other material strong enough for the pressure conditions of the visbreaking process. Thermally-insulative material can surround the pipe or vessel of the soaker section 43 to limit heat loss. An active heater element, such as heat tape or a heater coil, can be used to heat the fluid in the soaker section, if desired. A thermally-insulative material that is primarily transparent to microwave radiation can be used to cover the tube 19 containing the hydrocarbon feedstock inside the resonant cavity body 13 of FIG. 9 in order to limit heat loss (and thus reduce the energy input requirements of the EM source) and maintain the desired reaction temperature.

[0067] As mentioned above, scaling of the apparatus of FIG. 9 to achieve higher flow rates can be performed by using different combinations of the resonant cavity heater sections and soaker sections (vessels). In all cases, the hydrocarbon feedstock flows into the microwave resonant cavity heater sections followed by the soaker section(s). The number of microwave resonant cavity heater sections is dictated by the flow rate of the inflow of hydrocarbon feedstock that is to be processed (upgraded) and the flow rate capacity of each resonant cavity heater section or the given pipe volume and required residence time. The number of soaker sections (or vessels) will depend on the volume requirement, required residence time, and operational restrictions, such as physical space, pressure handling capabilities, and flow restrictions.

[0068] For illustrative purposes, two possible examples of apparatus for larger flow rates are shown in FIGS. 14A/4B and 15A/15B. In the apparatus of FIGS. 14A/14B, the inflow of the hydrocarbon feedstock 10 is divided by a flow splitter and associated tubing to a parallel arrangement of four microwave resonant cavity heaters similar to the design of FIGS. 9, 10, and 11 that bring the hydrocarbon fluid to the desired reaction temperature using microwave energy supplied at 12. The output flow of the four microwave resonant cavity heaters is combined and fed into a single soaker vessel, where the hydrocarbon fluid is allowed to remain for the desired residence time before exiting the apparatus at 14. In the apparatus of FIGS. 15A/15B, the inflow of the hydrocarbon feedstock 10 is divided by a flow splitter and associated tubing to a parallel arrangement of four microwave resonant cavity heaters similar to the apparatus of FIGS. 9, 10, and 1 1 that bring the hydrocarbon fluid to the desired reaction temperature using microwave energy supplied at 12. The output flow of the four microwave resonant cavity heaters is combined and fed into a parallel arrangement of two soaker vessels, where the hydrocarbon fluid is allowed to remain for the desired residence time before exiting the apparatus at 14. In both apparatus, the four microwave resonant cavity heaters and the soaker vessels are similar to the respective parts of FIGS. 9, 10, and 1 1 as described above.

[0069] The apparatus of FIGS. 14A/14B and 15A/15B can employ multiple EM source and delivery systems for supplying the microwave radiation to corresponding resonant cavity heaters of the apparatus. Alternatively, a single EM source and delivery system can employ a power splitter to split the microwave radiation into multiple legs for supply to the resonant cavity heaters of the apparatus. In other configurations, multiple EM source and delivery systems and one or more power splitters can be used to supply the microwave radiation to the resonant cavity heaters of the apparatus.

[0070] The apparatus of FIGS. 14A/14B and 15A/15B can also employ well known monitoring and control mechanisms to maintain the desired resonance mode (e.g., TMoio mode) and heating efficiency, as well as the desired fluid temperature during the visbreaking process. Resonance control may be achieved by i) frequency tracking, where the power source frequency is frequently updated to maintain the desired resonance mode and/or ii) by the use of tuning mechanisms to control the volume of the resonant cavity, including, but not limited to, mechanical and thermal measures. Resonance control can involve monitoring and assurance of the minimization of the reflection coefficient (Sn of the S-parameters) or of the maximization of the transmission coefficient (S₂₁ of the S-parameters) during the visbreaking process. Temperature control can utilize the temperature sensor 33 to detect the temperature of the hydrocarbon feedstock and control the level of microwave power in order to achieve the desired reaction temperature of the visbreaking process.

[0071] Table 1 is a summary of exemplary calculations illustrating how scaling of the resonant cavity of the apparatus of FIG. 9 can be achieved.

Table 1

"Resonant Residence Time" is the total time (in seconds) that the hydrocarbon feedstock is heated inside the microwave resonant cavity to provide the

Temperature Increase to the desired reaction temperature; "Temperature Increase" is the temperature increase (in °C) from the temperature of the hydrocarbon feedstock at the inlet to the desired reaction temperature in the resonant cavity;

"Res. Freq." is the resonant frequency (in GHz) of the microwave resonant cavity;

"Operating ID_pipe" is the inner diameter (in cm) of the pipe 19;

"Flow Rate" is the flow rate (in barrels per day or BPD) of the hydrocarbon feedstock that flows through the pipe 19;

"Cavity Diameter" is the inner diameter (in cm) of the resonant cavity body 13 that contains the pipe 19; it is dictated by Res. Freq.; and

"Cavity Length" is the length (in cm) of the resonant cavity body 13; it is dictated by the Flow Rate and the inner diameter of the pipe 19 to satisfy the desired Resonant Residence Time.

[0072] In the exemplary Table 1, it is assumed that a Resonant Residence Time of 30 seconds is required for the case where the microwave radiation in the resonant cavity heats the hydrocarbon feedstock from an initial temperature below the 350-500°C range of the reaction temperature to a desired reaction temperature within the 350-500°C for the visbreaking process. In this manner, the microwave radiation heats the hydrocarbon feedstock to raise its temperature by 100°C. In order to provide the hydrocarbon feedstock at the initial temperature (100°C less than the desired reaction temperature), the hydrocarbon feedstock can be preheated. Such preheating reduces the amount of microwave energy that is required to heat the hydrocarbon feedstock to the desired reaction temperature for thermal visbreaking. Such preheating can be carried out through conventional means, such as electric, gas fired, coal burning, or other suitable fluid heating schemes. Table 1 can be derived from practical maximum diameters determined from plots like FIGS. 12A and 12B. Then, for each operating resonant frequency, it is possible to determine the dimensions of the resonant cavity and the flow rate that can be achieved.

[0073] For example, referring to the fifth row of Table 1, for a flow of hydrocarbon feedstock (i.e., heavy crude oil) at a rate of 0.26 BPD and a required Resonant Residence Time of 30 seconds to heat the hydrocarbon feedstock from a temperature of 310°C (after preheating) to a reaction temperature of 410°C (a temperature increase of 100°C), the resonant cavity of the apparatus of FIG. 9 can be configured to operate at a resonant frequency of 2.45 GHz with a resonant cavity inner diameter of 7.37 cm and a pipe inner diameter of 1.00 cm. In this case, the length of the resonant cavity is 18.4 cm as dictated by the hydrocarbon feedstock flow rate of 0.26 BPD and the 1.00 cm inner diameter of the pipe 19 to satisfy the desired Resonant

Residence Time of 30 seconds.

[0074] In another example, referring to the last row of Table 1 , for a flow of hydrocarbon feedstock (i.e., heavy crude oil) at a rate of 150.00 BPD and a required Resonant Residence Time of 30 seconds to heat the hydrocarbon feedstock from a temperature of 340°C (after preheating) to a reaction temperature of 440°C (a temperature increase of 100°C), the resonant cavity of the apparatus of FIG. 9 can be configured to operate at a resonant frequency of 0.300 GHz with a resonant cavity inner diameter of 58.32 cm and an inner pipe diameter of 8.50 cm. In this case, the length of the resonant cavity is 146.0 cm as dictated by the hydrocarbon feedstock flow rate of 150.00 BPD and the 8.50 cm inner diameter of the pipe 19 to satisfy the desired Resonant Residence Time of 30 seconds.

[0075] The residence time of the hydrocarbon feedstock flowing through the system necessary for the visbreaking process is a function of the reaction temperature. Higher reaction

temperatures require shorter residence times. Table 2 below illustrates exemplary reaction temperatures and residence times for heavy crude oil.

Table 2

[0076] Referring to the second row of Table 2, a reaction temperature of 410°C requires a residence time of 32 minutes. In this case, the heavy crude oil feedstock is preheated to a temperature of or near 310°C and the resonant cavity operates to heat the heavy crude oil feedstock to or near the reaction temperature of 410°C. The soaker section 43 is configured to maintain the heated hydrocarbon feedstock at the reaction temperature for 31.5 minutes (with the resonant cavity providing the necessary heating for the remaining 0.5 minutes of the requisite 32 minute residence time). The soaker section 43 can be one vessel (similar to the apparatus of FIGS. 14A/14B), a parallel arrangement of vessels (similar to the apparatus of FIGS 15A/15B) or a series arrangement of vessels, if desired.

[0077] Referring to the third row of Table 2, a reaction temperature of 440°C requires a residence time of 8 minutes. In this case, the heavy crude oil feedstock is preheated to a temperature of or near 340°C and the resonant cavity operates to heat the heavy crude oil feedstock to or near the reaction temperature of 440°C. The soaker section 43 is configured to maintain the heated hydrocarbon feedstock at the reaction temperature for 7.5 minutes (with the resonant cavity providing the necessary heating for the remaining 0.5 minutes of the requisite 8 minute residence time). The soaker section 43 can be one vessel (similar to the apparatus of FIGS. 14A/14B), a parallel arrangement of vessels (similar to the apparatus of FIGS 15A/15B) or a series arrangement of vessels, if desired.

[0078] It is also contemplated that multiple microwave resonant cavities can be fluidly coupled to the downstream soaker section or vessel(s). The multiple microwave resonant cavities can be arranged in a parallel arrangement (similar to the apparatus of FIGS. 14A/14B and 15A/15B) or a series arrangement, if desired. In the parallel configuration, the hydrocarbon fluid inflow is distributed over the multiple resonant cavities by a flow splitter and associated tubing, which reduces the necessary resonant cavity length. In the series configuration, the multiple cavity lengths can be added together to realize the necessary cavity length, which allows for a reduction in length of the respective individual resonant cavity. [0079] Other configurations follow from the other reaction temperatures and corresponding residence times listed in Table 2. A similar approach can be used to configure the apparatus of FIGS. 1 and 6 to support a variety of reaction temperatures and corresponding residence times.

[0080] It is contemplated that the hydrocarbon fluid will flow at a controlled flow rate through the apparatus during the visbreaking process as described herein. In other embodiments, the valves and pumps can be configured to control the hydrocarbon fluid flow such that it remains stationary within the apparatus during the visbreaking process.

[0081] Contrary to conventional heating techniques, the visbreaking of the hydrocarbon feedstock by heating through microwave radiation results in localized heating through the oscillating of polar and non-polar molecules in the hydrocarbon feedstock, which results in heating the hydrocarbon feedstock from within. This internal heating prevents thermally driven fouling from occurring on the interior wall of the pipe inside the resonant cavity(ies) of the apparatus. The use of microwave heating also offers the advantage of more rapid heating of a targeted volume of hydrocarbon feedstock and offers the potential for economically visbreaking smaller production volumes. The apparatus and methodology of visbreaking can be used to irreversibly reduce the viscosity of a variety of hydrocarbon fluids, such as heavy crude oil, other viscous crude oil, and bitumen.

[0082] The apparatus as described herein have a small footprint as compared to the traditional systems for upgrading heavy oil. The apparatus may be located at a wellsite or in a production field so that the heavy oil may be upgraded before it is transported from the wellsite or production field. It is contemplated that the apparatus can be mounted on skids or trucks and brought to the wellsite or production field for use. [0083] The resonant cavity of the apparatus as described herein employs a cylindrical cross- sectional shape. Other cross-sectional shapes, such as rectangular cross-sectional shapes, can also be used for the resonant cavity.

[0084] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words 'means for' together with an associated function.

Claims

CLAIMS What is claimed is:

1. An apparatus for heating a hydrocarbon fluid with microwave radiation, comprising:

a resonant cavity defining an interior space, the resonant cavity realized by material that is primarily reflective to microwave radiation, and the resonant cavity configured to confine microwave radiation within its interior space; and

a tubular member that is configured to extend through the interior space of the resonant cavity and enter and exit the resonant cavity, the tubular member realized from material that is primarily transparent to microwave radiation;

wherein the tubular member is further configured to contain hydrocarbon fluid that is subject to heating by microwave radiation confined within the interior space of the resonant cavity.

2. An apparatus according to claim 1, wherein the resonant cavity is configured to resonate microwave radiation at a resonant frequency.

3. An apparatus according to claim 2, wherein the resonant cavity is configured to produce a predetermined standing-wave pattern of the microwave radiation at the resonant frequency.

4. An apparatus according to claim 2, wherein the resonant frequency lies in a frequency band between 0.1 GHz and 100 GHz.

5. An apparatus according to claim 2, wherein the resonant cavity is configured to focus the microwave radiation at the resonant frequency to a localized area within the internal space of the resonant cavity, wherein the localized area is occupied by the tubular member within the internal space of the resonant cavity.

6. An apparatus according to claim 5, wherein the resonant cavity is configured to resonate microwave radiation at a desired TM or TE mode.

7. An apparatus according to claim 5, wherein the resonant cavity is configured to resonate microwave radiation at a desired TMoio mode such that the focused microwave radiation in the localized area within the internal space of the resonant cavity lies along an axis of the resonant cavity defined by the TM₀io mode.

8. An apparatus according to claim 7, wherein the tubular member extends along the axis of the resonant cavity defined by the TM₀io mode.

9. An apparatus according to claim 2, further comprising an EM source that is configured to generate and deliver microwave radiation at the resonant frequency.

10. An apparatus according to claim 9, further comprising a power coupler that is operably coupled between the EM source and the resonant cavity, wherein the power coupler is configured to direct microwave radiation at the resonant frequency supplied by the EM source into the resonant cavity.

11. An apparatus according to claim 10, wherein the power coupler is positioned near where the tubular member enters the resonant cavity.

12. An apparatus according to claim 1, wherein the hydrocarbon fluid is heated by the microwave radiation confined within the interior space of the resonant cavity to a desired temperature for visbreaking of the hydrocarbon fluid in order to irreversibly reduce the viscosity of the hydrocarbon fluid.

13. An apparatus according to claim 12, wherein the desired temperature for visbreaking of the hydrocarbon fluid is in the range between 350°C and 500°C.

14. An apparatus according to claim 12, wherein the pressure of the hydrocarbon fluid inside the tubular member is controlled such that the hydrocarbon fluid remains in a single liquid phase while being heated by the microwave radiation confined within the interior space of the resonant cavity.

15. An apparatus according to claim 14, wherein the pressure of the hydrocarbon fluid inside the tubular member is controlled to a desired pressure between atmospheric pressure and 5000 psi (351.5 kg/square cm).

16. An apparatus according to claim 1, wherein the resonant cavity is defined by an elongate body having a longitudinal axis; and the tubular member extends inside the resonant cavity along the longitudinal axis of the body.

17. An apparatus according to claim 16, further comprising a plurality of thin members disposed along the longitudinal axis of the body, the members defining a series of resonant cavity sections with corresponding interior spaces, wherein the tubular member extends through the interior spaces of the series of resonant cavity sections to allow for heating of hydrocarbon fluid within the tubular member by microwave radiation confined within the interior spaces of the series of resonant cavity sections.

18. An apparatus according to claim 17, wherein the members have apertures that are configured to allow for propagation of microwave radiation through the interior spaces of the series of resonant cavity sections.

19. An apparatus according to claim 1, further comprising at least one soaker section disposed downstream of the resonant cavity, wherein the soaker section is configured to contain hydrocarbon fluid and limit heat loss from the contained hydrocarbon fluid.

20. An apparatus according to claim 19, wherein the soaker section includes a tube or pipe that contains the hydrocarbon fluid with thermally-insulative material that surrounds the tube or pipe.

21. An apparatus according to claim 20, wherein the soaker section includes an active heater element that is disposed between the thermally-insulative material and the tube or pipe.

22. An apparatus according to claim 1, further comprising an inlet port and an outlet port that are sealably coupled to opposed ends of the tubular member outside the resonant cavity.

23. An apparatus according to claim 1, further comprising a thermally-insulative material that surrounds the tubular member within the resonant cavity, wherein the thermally-insulative material is primarily transparent to the microwave radiation.

24. An apparatus according to claim 1, wherein the hydrocarbon fluid flows at a controlled flow rate through the tubular member while being heated by the microwave radiation confined within the interior space of the resonant cavity.

25. An apparatus according to claim 1, wherein the hydrocarbon fluid remains stationary inside the tubular member while being heated by the microwave radiation confined within the interior space of the resonant cavity.

26. An apparatus according to claim 1, wherein the hydrocarbon fluid is selected from the group consisting of crude oil, heavy oil, and bitumen.

27. An apparatus for heating a hydrocarbon fluid with microwave radiation, comprising:

a plurality of microwave resonator heater sections, each microwave resonator heater section including a resonant cavity and a corresponding tubular member;

wherein the resonant cavity of a given microwave resonator heater section defines an interior space and is realized by material that is primarily reflective to microwave radiation, the resonant cavity configured to confine microwave radiation within its interior space;

wherein the tubular member of the given microwave resonator heater section is configured to extend through the interior space of the resonant cavity and enter and exit the resonant cavity of the given microwave resonator heater section, and the tubular member is realized from material that is primarily transparent to microwave radiation; and

wherein the plurality of microwave resonator heater sections are configured such that the tubular members of the plurality of microwave resonator heater sections contain hydrocarbon fluid that is subject to heating by microwave radiation confined within the interior spaces of the resonant cavities of the plurality of microwave resonator heater sections.

28. An apparatus according to claim 27, wherein the resonant cavities of the plurality of microwave resonator heater sections are configured to resonate microwave radiation at a resonant frequency.

29. An apparatus according to claim 28, wherein the resonant cavities of the plurality of microwave resonator heater sections are each configured to produce a predetermined standing- wave pattern of the microwave radiation at the resonant frequency.

30. An apparatus according to claim 28, wherein the resonant frequency lies in a frequency band between 0.1 GHz and 100 GHz.

31. An apparatus according to claim 27, further comprising multiple EM source and delivery systems for supplying the microwave radiation to corresponding resonant cavity heater sections.

32. An apparatus according to claim 27, further comprising an EM source and delivery system that cooperates with a power splitter to split microwave radiation into multiple legs for supply to a number of the resonant cavity heater sections.

33. An apparatus according to claim 27, further comprising a flow splitter and associated tubing that distributes an inflow of hydrocarbon fluid to the tubular members of the plurality of microwave resonator heater sections.

34. An apparatus according to claim 27, further comprising at least one soaker section disposed downstream of the plurality of microwave resonator heater sections, wherein the soaker section is configured to contain hydrocarbon fluid and limit heat loss from the contained hydrocarbon fluid.

35. An apparatus according to claim 34, wherein the soaker section includes a tube or pipe that contains the hydrocarbon fluid with thermally-insulative material that surrounds the tube or pipe.

36. An apparatus according to claim 35, wherein the soaker section includes an active heater element that is disposed between the thermally-insulative material and the tube or pipe.

37. An apparatus according to claim 34, wherein a given soaker section is fluidly coupled to at least two microwave resonator heater sections.

38. An apparatus according to claim 34, wherein the at least one soaker section comprises a plurality of soaker sections disposed downstream of the plurality of microwave resonator heater sections.

39. A method for heating a hydrocarbon fluid with microwave radiation, comprising:

supplying microwave radiation to a resonant cavity defining an interior space, the resonant cavity realized by material that is primarily reflective to microwave radiation, and the resonant cavity configured to confine the microwave radiation within its interior space; and loading hydrocarbon fluid into a tubular member that is configured to extend through the interior space of the resonant cavity and enter and exit the resonant cavity, the tubular member realized from material that is primarily transparent to microwave radiation;

wherein the hydrocarbon fluid loaded into the tubular member is subject to heating by microwave radiation confined within the interior space of the resonant cavity.

40. A method according to claim 39, wherein the resonant cavity is configured to resonate microwave radiation at a resonant frequency.

41. A method according to claim 40, wherein the resonant cavity is configured to produce a predetermined standing-wave pattern of the microwave radiation at the resonant frequency.

42. A method according to claim 40, wherein the resonant frequency lies in a frequency band between 0.1 GHz and 100 GHz.

43. A method according to claim 40, wherein the resonant cavity is configured to focus the microwave radiation at the resonant frequency to a localized area within the internal space of the resonant cavity, wherein the localized area is occupied by the tubular member within the internal space of the resonant cavity.

44. A method according to claim 40, wherein a mathematical model is used to determine the size of the tubular member, the resonant frequency of the microwave radiation, the geometry of the resonant cavity that supports such resonant frequency, and the required residence time in order to carry out desired visbreaking of a given flow rate of hydrocarbon fluid.