Patent Application
20120055850
The present disclosure relates generally to the recovery of liquid products from coal feedstocks, and more particularly to a coal liquefaction system and process which utilizes mechanical activation of coal in a solvent medium to extract asphaltenes, followed by cracking of the asphaltenes in a nozzle reactor.
Various processes have been developed in the art for the recovery of hydrocarbons and related products from coal feedstocks. Most of these processes may be classified as direct or indirect coal liquefaction processes.
As seen therein, direct processes 101 typically feature the treatment of a coal feedstock 103 with hydrogen gas to achieve hydrogenation 107 of the feedstock material. Such processes yield liquid fuels 109, such as diesel or gasoline, directly as a result of the hydrogenation 107. Frequently, it is necessary to subject the resulting liquid fuels 109 to further processing to achieve higher end materials such as motor fuels.
Indirect processes 102, by contrast, produce liquid fuels 109 from coal feedstocks 103 through one or more intermediate products. For example, in some indirect processes, the coal feedstock 103 may be processed in a gasifier 111 in the presence of steam 113 and oxygen 115 to produce syngas, which is a mixture of CO and H2. The syngas may then be further processed into liquid fuels 109 through further processes such as the Fischer-Tropsch process 117.
In the Fischer-Tropsch process 117, a set of chemical reactions is utilized to convert syngas 111 into liquid hydrocarbons. Typically, transition metals, such as cobalt, iron, or ruthenium, are used as catalysts in this process. The central reaction in the Fischer-Tropsch process yields alkanes of various chain lengths as the principle reaction products:
(2n+1)H2+nCO→CnH(2n+2)+nH2O (REACTION 1)
where n is a positive integer.
A given implementation of the Fischer-Tropsch process may utilize other reactions and materials to adjust the incoming H2/CO ratio. For example, water shift reactions may be utilized to provide a source of hydrogen:
H2O+CO→H2+CO2 (REACTION 2)
Implementations of the Fischer-Tropsch process are also possible which utilize methane as a feedstock. In such cases, steam reforming may be utilized to convert the methane into CO and H2:
H2O+CH4→CO+3H2 (REACTION 3)
Indirect liquefaction processes are also possible which utilize syngas to generate various intermediate products, some of which, in turn, may be converted into liquid fuels 109. For example, methanol 121 may be synthesized from syngas through the use of copper catalysts. The methanol 121 thus formed may be converted into liquid fuels 109 by the so called Mobil process 123. In this process, methanol undergoes an intermolecular dehydration reaction to yield dimethyl ether:
2 CH3OH→CH3OCH3+H2O (REACTION 4)
The dimethyl ether may then be further dehydrated over a zeolite catalyst (ZSM-5) to yield a gasoline with 80% (by weight based on the organics in the product stream) of C5+ hydrocarbon products. The Mobil process is described in greater detail in U.S. Pat. No. 4,831,195 (Harandi et al.).
Since coal, in its natural state, is relatively chemically inert, various methods have been explored in the art for preparing coal feedstocks for use in liquefaction processes such as those noted above. By way of example, the effect of mechanical activation in a hydrogen-donor solvent (tetralin) on coal liquefaction processes has been investigated. See, e.g., Yu. F. Patrakov, N. I. Fedorova and O. N. Fedyaeva, “Intensification of Coal Liquefaction Process with the Help of Mechanical Activation,” Chemistry for Sustainable Development 13, 295-299 (2005).
Similarly, the effect of mechanochemical treatment on the supramolecular structure of brown coal has been investigated. In some cases, this work involved treating the coal in an activator mill of the centrifugal planetary type with steel balls, and using petroleum fraction with a boiling point above 300° C. as a solvent. See Peter N. Kuznetsov, Lyudmila I. Kuznetsova, Alexander N. Borisevich and Nina I. Pavlenko, “Effect of Mechanochemical Treatment on Supramolecular Structure of Brown Coal,” Chemistry for Sustainable Development 11, 715-721 (2003). Examples of planetary mills may be found, for example, in U.S. Pat. No. 5,513,806 (Falcon-Steward).
Various solvent extraction processes have also been explored in the art for the extraction of liquids from coal feedstocks. Solvent refining or solvent extraction of coal typically involves treating pulverized coal with a suitable solvent, with or without the addition of hydrogen, at elevated temperatures and pressures. Such a process promotes dissolution of the coal by hydrogen-donor activity, and provides a coal extract—which is liquid under the conditions of extraction—and an undissolved coal residue. Most of the ash and sulfur in the coal feedstock is recovered with the undissolved coal residue. The hydrogen-enriched coal extract may then be used directly as a boiler fuel, or it may be used as a precursor to distillate fuels. Solvent extraction may also be combined with a hydrogenation process to produce syncrude.
One example of the foregoing process is described in U.S. Pat. No. 4,298,450 (Ross et al.), which discloses a method for the hydroconversion of coal by solvent treatment at elevated temperatures and pressures. The method utilizes an alcohol having an α-hydrogen atom, such as isopropanol, as a hydrogen donor solvent. In some embodiments, a base capable of providing a catalytically effective amount of the corresponding alcoholate anion under the solvent treatment conditions is added to catalyze the alcohol-coal reaction.
Other methods are also known in the art which utilize alcohols in the extraction of coal liquids. One example of such a process is disclosed in U.S. Pat. No. 4,425,219 (Kroó) et al.). In the process disclosed therein, coal is oxidized at 80° C. to 300° C. in the presence of the vapors of a C1-5 aliphatic alcohol, optionally under the introduction of steam, and the liquid carbon compounds are separated from the resulting product mixture. A further example of this type of process is described in S. Sato et al., “Methanol-Mediated Extraction of Coal Liquid (5). Conceptual Design and Mass Balance of a Continuous Methanol-Mediated Extraction Process”, Energy & Fuels 2002, 16, 1337-1342. There, a process for methanol-mediated extraction of coal liquids is described which consists of (1) methanol-mediated extraction, (2) neutral oil removal, (3) methanol recovery, (4) water treatment, and (5) washing.
In one aspect, a method for producing hydrocarbons is provided. The method comprises (a) subjecting a coal feedstock to mechanical activation in a liquid medium, thereby obtaining a mixture of solubilized asphaltenes; and (b) at least partial cracking the resulting mixture in a supersonic nozzle reactor, thereby obtaining hydrocarbon products derived from the asphaltenes.
In another aspect, a method for cracking coal asphaltenes is provided. The method comprises mechanically activating a coal feedstock in a liquid medium comprising a material which generates hydrogen in situ under a set of cracking conditions; and cracking the mechanically activated coal feedstock under said cracking conditions.
In a further aspect, a method is provided for cracking coal asphaltenes in a nozzle reactor under a set of reactor conditions. The method comprises (a) providing a nozzle reactor having first and second reactant inlets; (b) injecting an activated coal feedstock into the first inlet; and (c) injecting a material into the second inlet which generates hydrogen in situ under said reactor conditions.
In yet another aspect, a system is provided for obtaining hydrocarbon liquids from a coal feedstock. The system comprises a grinding mill which mechanically activates the coal feedstock by grinding it in a liquid medium; and a supersonic nozzle reactor which cracks the activated coal feedstock to generate hydrocarbon liquids.
Despite the aforementioned efforts and advances in the art, coal liquefaction remains hindered as a commercially viable technology for the production of hydrocarbon liquids by the inherent expense of the methods developed to date, and by the notorious instability of the products obtained. Moreover, many coal liquefaction processes developed to date are environmentally unfriendly. For example, many such processes generate significant amounts of carbon dioxide or other greenhouse gasses. There is thus a need in the art for systems and methodologies which overcome these infirmities. In particular, there is a need in the art for coal liquefaction systems and processes which use inexpensive materials and processing conditions, which yield stable products, and which are more environmentally friendly than existing coal liquefaction processes commonly used in the art.
It has now been found that some or all of the foregoing needs may be met by a system and method for coal liquefaction which utilizes mechanical activation of coal feedstocks in a liquid medium, followed by at least partial cracking of the activated coal, preferably in a supersonic nozzle reactor. The liquid medium used in mechanical activation of the coal feedstock preferably comprises a material, such as methanol, which contains covalently bound oxygen. Without wishing to be bound by theory, the use of such a liquid medium during mechanical activation is believed to result in absorption of a significant quantity of the liquid medium by the coal feedstock, and may possibly even include incorporation of molecules of the liquid medium into the lattice structure of the coal.
During subsequent cracking of the mechanically activated coal feedstock in a supersonic reactor, this residual liquid medium is believed to undergo reformation or other chemical reactions to generate hydrogen radicals in situ. The resulting hydrogen radicals quench the hydrocarbon radicals which are generated by the cracking process before they can undergo polymerization and other such undesirable side reactions. This quenching reaction may be enhanced by the intimate mixing of the source of hydrogen radicals and the source of hydrocarbon radicals, and their subsequent close proximity to each other during the cracking reactions. Consequently, the cracking process yields stable hydrocarbon liquid products which can be used in a variety of fuels. Surprisingly, the cracking process is found to yield relatively small amounts of C1-C4 products, the generation of which is typically undesirable in a cracking process aimed at producing liquid hydrocarbons for the production of motor fuels such as gasoline and diesel fuel.
In some embodiments, the liquid medium used during mechanical activation may be partially or wholly taken or derived from the product liquor obtained in a previous iteration of the process. The liquid medium may also comprise materials, such as alcohols (such as methanol), ethers (such as dimethyl ether) or the like, which are common, and hence inexpensive, intermediate products of indirect coal liquefaction.
Certain oxygenated compounds, such as methanol, are known to interact in some fashion with the asphalt content present in petroleum hydrocarbons. This asphalt content is a mixture of asphaltene and maltenes, and is often modeled as a colloid, with maltenes present as the continuous phase and asphaltenes present as the discontinuous phase. By way of example, U.S. Pat. No. 4,324,651 (Rollmann et al.) describes a process in which the asphalt content of a mineral oil is removed by the addition of methanol at temperatures above about 80° C. The process produces an asphalt-rich liquid phase and a methanol-rich liquid phase. When the methanol-rich liquid phase is cooled to a temperature below 80° C., two additional liquid phases are produced, an oil-rich phase and a methanol-rich phase. Hence, in addition to allowing removal of the asphalt content from the petroleum hydrocarbons, this process allows for isolation of the desired hydrocarbon liquids and recovery of the methanol for recycling.
The use of alcohols to solubilized asphaltenes is also known to the art, as indicated in some of the references cited above. However, despite these discoveries, the advantages of oxygenated compounds such as methanol in the recovery of hydrocarbon liquids from coal feedstocks and in the cracking of these liquids have not been fully appreciated. The systems and methodologies disclosed herein capitalize on these advantages.
As seen in
Prior to mechanical activation, the coal feedstock may be subjected to grinding, and more preferably to fine grinding. For example, such grinding may produce coal particles with an average size of about 0.1 mm to about 100 mm, more preferably about 0.5 mm to about 50 mm, and most preferably about 1 mm to about 10 mm.
Solubilization of the coal is preferably achieved through mechanical activation, and more preferably by grinding the coal feedstock in a suitable liquid medium such that at least a portion of the asphaltene content of the coal is solubilized in the liquid medium. Preferably, the liquid medium is an oxygen-containing solvent, more preferably, a solvent in which oxygen is covalently bound. Examples of such solvents may include alcohols (preferably primary alcohols, such as methanol), ethers (preferably dimethyl ether), and alkyl carbonates (preferably dimethyl carbonate). As noted above, a portion of the liquid products derived from a previous iteration of the process may also be used as the solvent, which products will typically contain a significant amount of covalently bounded oxygen.
In some embodiments, the liquid medium may contain other solvents or cosolvents. These include, without limitation, aromatic hydrocarbons and polycyclic aromatic hydrocarbons, saturated naphthenic hydrocarbons, tetrahydronaphthalene, decalin, biphenyl, methylnaphthalene, dimethylnaphthalene, and phenolic compounds such as phenol, cresol and xylenol.
In some embodiments of the systems and methodologies described herein, the liquid medium may include a base which is capable of generating a catalytically effective amount of alkoxide anions under the conditions present during mechanical activation to catalyze the solubilization of asphaltene in the liquid medium. Solubilization under these conditions may involve the net addition of hydrogen to the asphaltene (A) in accordance with the following set of reactions, wherein R and R′ are preferably hydrogen but, more generally, may represent hydrogen or an organic radical, such as an alkyl radical:
—OCHRR′+A→O═CRR′+AH− (REACTION 5)
AH−+HOCHRR′→AH2+—OCHRR′ (REACTION 6)
It will thus be appreciated that, in such a system, the alkoxide ion is regenerated with each cycle, H2 is transferred to the asphaltene, and an aldehyde or ketone is formed as a byproduct.
The above reaction is catalyzed by the addition of the alkoxide anion to the system, or by the addition of another suitable catalyst, such as an alkali metal hydroxide, which forms significant amounts of the alcoholate anion under the conditions used in mechanical activation of the coal feedstock. Hence, the equilibrium
OH−+HOCHRR′H2O+—OCHRR′ (REACTION 7)
lies significantly to the right under coal conversion conditions.
In operation, about 70% to 80% of the volume of the grinding mill 301 is filled with an abrasive slurry (not shown) consisting of a liquid phase and grinding media such as small zirconia, tungsten carbide, etc balls. The grinding discs 323 rotate, thereby agitating the abrasive slurry and grinding the feedstock which, in the context of the present disclosure, is an asphaltene-bearing coal. As indicated in
At the discharge end of the grinding milt (in the vicinity of outlet 319), feedstock and abrasive slurry reach the separator 325, where the abrasive slurry is centrifuged out to the surface of the liner and is pumped back to the feed end of the mill (that is, the end of the grinding mill 301 in the vicinity of the inlet 317), thus retaining the abrasive slurry in the grinding mill 301. The ground feedstock passes through the center of the separator 325 and exits the grinding chamber 305 by way of outlet 319.
It will be appreciated that the foregoing method and apparatus for mechanical activation achieves solubility of asphaltene from coal feedstocks at ambient pressures and temperatures, does not require the use of elemental hydrogen, and is capable of yielding stable products. By contrast, many of the methods developed in the art for asphaltene solubilization are focused on hydrogen uptake, and rely on the use of hydrogen donor solvents in autoclaves under high temperatures and pressures. In addition to being comparatively expensive, such methods often yield unstable products.
While the use of the grinding mill depicted in
In the systems and methodologies described herein, the coal feedstock may be subjected to one or more separation procedures designed to reduce the content of ash or other inorganic materials in the feedstock. Such separation procedures may be implemented after fine grinding (if utilized) but before mechanical activation and/or after mechanical activation. Various separation procedures may be used for this purpose including, but not limited to, mineral or froth flotation, sedimentation, centrifugation, selective agglomeration, or combinations of the foregoing.
Various hybrid separation procedures may also be utilized for this purpose. For example, hybrid processes, such as micro-agglomerate flotation, may be utilized. Micro-agglomerate flotation is a combination of oil-agglomeration and froth flotation. In such a process, small quantities of oil are utilized to promote the formation of dense micro-agglomerates with minimal entrapment of water and mineral particles, after which froth flotation is utilized to extract these micro-agglomerates from the water/dispersed mineral phase. In some implementations, such a hybrid process may alleviate froth overload, water/mineral carryover, and other issues which may be encountered in the ash removal process.
As noted above, solubilization of asphaltenes is preferably achieved in the methodologies described herein through mechanical activation of coal. In some embodiments, however, solubilization may be achieved by other methods or by combinations of methods. For example, solubilization may also be achieved in some embodiments through dry chemical activation, followed by extraction of the asphaltene with a solvent. Solubilization may also be achieved by treatment with solvents (such as, for example, tetralin (1,2,3,4-tetrahydronaphthalene), decalin (bicyclo[4.4.0]decane), tetrahydrofuran (THF), or toluene, pyridine, ethyl acetate, or chemical reagents (for example, through treatment with HCl), through treatment with physical ionizing radiation (for example, UV radiation or prolonged exposure to sunlight), through ion exchange (for example, with Fe2+, Ni2+ or Co2+), or through various combinations of the foregoing.
Referring again to
Compared to petroleum asphaltenes, coal asphaltenes are found to exhibit a much narrower distribution of molecular weights. Thus, coal asphaltenes have a relatively narrow molecular weight distribution, with a full width of about 150 amu and an average molecular weight of about 340 amu. Petroleum asphaltenes, by contrast, display a broader molecular weight distribution, with a full width of about 300 amu, and are heavier on average, exhibiting an average molecular weight of about 680 amu. Coal asphaltenes also have smaller polycyclic aromatic hydrocarbons on average than petroleum asphaltenes. Notably, however, the carbon/hydrogen ratios of the two classes of asphaltenes are similar. Studies suggest that asphaltenes possess large polycyclic aromatic hydrocarbon moieties, and that a preponderance of asphaltene molecules contain only a single fused ring system. See, e.g., Ana R, Paola Hurtado, Bruno Martínez-Haya and Oliver C. Mullins. “Molecular-Weight Distributions of Coal and Petroleum Asphaltenes from Laser Desorption/Ionization Experiments,” Energy Fuels, 21 (5), pp 2863-2868 (2007). Aromatic nitrogen exists in both coal and petroleum asphaltenes. In particular, both types of asphaltenes show substantial quantities of pyrrole and pyridine fractions, and the pyrrole content is found to be greater than or equal to the pyridine content in all cases.
After at least partial solubilization of the asphaltene content of the coal feedstock, it is desirable to crack the asphaltene content to produce liquid products. Cracking essentially fragments the asphaltene molecules into smaller products (for example, from a C60 hydrocarbon to a C15 hydrocarbon) by rupturing one or more covalent bonds in the molecular structure. Such cracking is preferably implemented in a nozzle reactor such as those described in U.S. Pat. No. 6,989,091 (Jorgensen) or U.S. Pat. No. 7,618,597 (Duyvesteyn), the disclosures of which are incorporated herein by reference in their entirety.
The cracking process is explained by Jorgensen in terms of the storage of heat as mechanical vibrations in the molecules being cracked. When the molecules are exposed to moderate temperatures during the cracking process, these vibrations are moderate, and they generate mechanical constraints which, due to the inertia related to the mass of the molecule, are the highest in the middle of the molecule. Consequently, bond cleavage tends to occur in the middle of the molecule under these conditions. However, the more the molecule is heated (or more generally, the more energy it must store), the more it will vibrate. Such vibrations occur according to harmonic modes having several vibration antinodes and troughs, much like the vibrations observed on a piano chord.
Since the troughs of the vibration constitute the seat of the maximum constraints, the molecule will break at these points. Due to harmonic considerations, such troughs tend to occur at integer fractions of molecular length (e.g., at one-third or one-fourth of the molecular length). Consequently, if a molecule is heated excessively so that too much energy is transmitted to it, the molecule will break into very small fragments, stopping at CH4 and even carbon C. It is assumed that mechanical vibrations exerted on coal asphaltene molecules will respond in a similar fashion as with petroleum asphaltenes, even though the molecules are not identical.
The injection passage 515 has a circular diametric cross-section and, as shown in the axially-extending cross-sectional view of
A material feed passage or channel 518 extends from the exterior of the junction of the injection end 512 and the tubular reactor body 514 toward the reaction chamber 516 transversely to the axis B of the interior reactor chamber 516. The material feed passage 518 penetrates an annular material feed port 520 adjacent the interior reactor chamber wall 522 at the end 524 of the interior reactor chamber 516 abutting the injection end 512. The material feed port 520 includes an annular, radially extending chamber feed slot 526 in material-injecting communication with the interior reactor chamber 516. The material feed port 520 is thus configured to inject feed material: (i) at about a 90° angle to the axis of travel of cracking gas injected from the injection nozzle passage 515; (ii) around the entire circumference of a cracking gas injected through the injection passage 515; and (iii) to impact the entire circumference of the free cracking gas stream virtually immediately upon its emission from the injection passage 515 into the reactor chamber 516.
In the particular nozzle reactor depicted in
As indicated by the gaps 538, 540 in the embodiment of
With reference now to
The tubular body 551 of the insert end 550 is secured within and adjacent the interior periphery 564 of the reactor body 544. The mechanism for securing the insert end 550 in this position may consist of an axially-extending nut-and-bolt arrangement (not shown) penetrating co-linearly mating passages (not shown) in: (i) an upper radially extending lip 566 on the reactor body 544; (ii) an abutting, radially outwardly extending thickened neck section 568 on the insert end 550; and (iii) in turn, the abutting injector nozzle 552. Other mechanisms for securing the insert end 550 within the reactor body 544 may include a press fit (not shown) or mating threads (not shown) on the outer periphery 562 of the tubular body 551 and on the inner periphery 564 of the reactor body 544. Seals, e.g., 570, may be mounted as desired between, for example, the radially extending lip 566 and the abutting the neck section 568 and the neck section 568 and the abutting injector nozzle 552.
The non-linear injection passage 560 has, from an axially-extending cross-sectional perspective, mating, radially inwardly curved opposing side wall sections 572, 574 extending along the axial length of the non-linear injection passage 560. The entry end 576 of injection passage 560 provides a rounded circumferential face abutting an injection feed tube 578, which can be bolted (not shown) to the mating planar, radially outwardly extending distal face 580 on the injection nozzle 552.
In the embodiment of
The injection passage 560 is formed in a replaceable injection nozzle insert 590 press-fit or threaded into a mating injection nozzle mounting passage 292 extending axially through an injection nozzle body 594 of the injection nozzle 552. The injection nozzle insert 590 is preferably made of hardened steel alloy, and the balance of the nozzle reactor 600 components other than seals, if any, are preferably made of steel or stainless steel.
The interior peripheries 589, 591 of the insert end 550 and the tubular central section 546, respectively, cooperatively provide a stepped or telescoped structure expanding radially outwardly from the injection end 588 of the injection or injector passage 560 toward the frustoconical end 548 of the reactor body 544. The particular dimensions of the various components, however, will vary based on the particular application for the nozzle reactor, generally 600. Factors taken into account in determining the particular dimensions include the physical properties of the cracking gas (density, enthalpy, entropy, heat capacity, etc.) and the pressure ratio from the entry end 576 to the injection end 588 of the injector passage 560.
The embodiment of the nozzle reactor depicted in
In some embodiments of the nozzle reactor 510 which have one or more non-linear cracking gas injection passages, e.g., 560, such as the convergent/divergent configuration of
In some methods of use of the nozzle reactor embodiment illustrated in
The injection passage 616 can be configured to eject a free stream of cracking gas, such as super-heated steam (not shown) for example, generally conically with an included angle of about 18°. The conical interior section 613 may be configured to surround or interfere with such a free stream of cracking gas ejection stream. In certain such embodiments, after engaging the injected material feed stock adjacent the ejection end 614, the resulting jet mixture—a mixture of cracking gas and material feed stock—preferably makes at least intermittent interrupting contact with the tubular interior section 613 and, if desired, the downstream tubular interior section 615. This intermittent, interrupting contact increases turbulence and concentrates shear stresses into an axially shortened reaction zone within the reactor body 628. Preferably, however, the jet mixture travels through the interior 626 of the reactor body 628 with minimal backflow of any components of the jet mixture, resulting in more rapid plug flow of all jet mixture components through the reactor body 628.
Once the asphaltene feed stock is cracked by the cracking gas ejection stream adjacent the injection end 614, the configuration of the reactor body facilitates substantially immediate cooling of the jet mixture. This cooling of the jet mixture acts to arrest the chemical reaction between the feed stock and the cracking gas ejection stream.
In some embodiments, a catalyst may be introduced into the nozzle reactor to enhance cracking of the asphaltene feed stock by the cracking gas ejection stream. This may be accomplished by disposing the catalyst on a surface which comes into contact with the feedstock, or by mixing the catalyst with the feedstock or cracking gas.
One skilled in the art will appreciate that a nozzle reactor may be utilized in the practice of some of the methodologies disclosed herein to provide enhanced transfer of kinetic energy to the asphaltene feed stock through various means. These include, for example, by providing a supersonic cracking gas jet, improved orientation of the direction of flow of a cracking gas (or cracking gas mixture) with respect to that of the feed stock, and/or more complete cracking gas stream impact with the material feed stock as a result of, for example, an annular material feed port and the telescoped reactor body interior. In some cases, the design of the nozzle reactor may result in reduced retention of by-products, such as coking, on the side walls of the reactor chamber. Embodiments of the nozzle reactor may also be relatively rapid in operation, efficient, reliable, easy to maintain and repair, and relatively economical to make and use.
In some embodiments of the systems and methodologies disclosed herein, a nozzle reactor of the present application may include an injection nozzle that has a flow directing insert around which a first material can flow to increase the velocity of the first material in preparation for an interaction with a second material to alter the mechanical or chemical composition of the first and/or second materials. For example, as shown in
The supporting insert 656 can include one or more support rods 668 connected to a cylindrical portion 665 of the flow directing insert 666. The cylindrical portion 665 includes outer peripheral surfaces that run parallel to the axis of the insert 656. The supporting insert 656 comprises a generally annular shaped fluid flow passage 672 corresponding to the injection passage 654 of the injection nozzle body 652 such that when inserted in the recess 670, the interior periphery of the passage 672 is generally flush with the interior periphery of passage 654. Cross-sectional areas of the fluid flow passage 672 on planes perpendicular to the axis of the fluid flow passage 672 remain substantially the same extending the axial length of the passage 672. In other words, an outer diameter and inner diameter of the fluid flow passage 672 remain generally unchanged throughout the passage.
Fluid, such as cracking gas, is allowed to flow through the nozzle 650 by first passing through a flow inlet opening 674 in the supporting insert 656, the fluid flow passage 672 and a flow outlet opening 676 in the supporting insert. As shown in
When the flow directing insert is positioned within the injection passage 654, a generally annular fluid flow passage 680, defined between the surface of the injection passage and the exterior surface of the flow directing insert 658, is formed.
The flow directing insert 658 comprises a diverging, or expanding, portion 664, a converging, or contracting, portion 666 and a transitioning portion 667 coupling the diverging and converging portions. In the illustrated embodiments, the diverging and converging portions 664, 666 are generally frustoconically shaped and conically shaped, respectively, with abutting base surfaces proximate the transitioning portion 667. The diameter of the diverging portion increases and the diameter of the converging portion decreases along the axial length of the flow directing insert 658 in the fluid flow direction as indicated in
Fluid flowing through the fluid flow passage 672 in the supporting insert 656 exits through the outlet opening 676 of the passage 672 and into the annular fluid flow passage 680. The nozzle can be configured such that fluid flowing through the fluid flow passage 672 and into the annular fluid flow passage 680 flows at a velocity less than the speed of sound, i.e., subsonic flow. As the fluid flows through the fluid flow passage 680, the narrowing of the converging region and the widening of the diverging region help to induce a back pressure, i.e., pressure is higher at the entry of the passage 680 than at the exit of the passage, which increases the velocity of the fluid. The fluid velocity can be increased such that as the fluid exits the transition region its velocity is at or above the speed of sound, i.e., supersonic flow. The fluid remains at supersonic flow through the diverging region and as it exits the nozzle 650 at the end of the diverging region.
Like the nozzle end 512 of
A second particular, non-limiting example of a nozzle reactor which is suitable for use in some of the systems and methodologies disclosed herein is depicted in
In operation, superheated steam is injected through the two laterally opposed first 703 and second 705 steam injectors into the interior of the reactor tube 709 in order to impact a pre-heated, centrally-located asphaltene feed stream simultaneously injected through the feed stock injector 707 into the interior of the reactor tube 709. The nozzle reactor operates to crack the feed stream into lighter hydrocarbons through the impact of the steam feeds with the heavy hydrocarbon feed within the reactor tube. A central asphaltene feed stock jet intersects the steam jets at some distance from the ejection of these jets from their respective injectors.
The chemistry involved in cracking asphaltenes in a nozzle reactor is likely to be complex. However, the following theories and observations provide some insight into why the methodologies described herein are particularly effective in the production of hydrocarbon liquids from coal feedstocks. This is especially true of those embodiments which involve the combined use of mechanical activation in a liquid medium (especially methanol) to extract asphaltene content from coal feedstock, with the use of a nozzle reactor to crack the extracted asphaltene content.
Without wishing to be bound by theory, it is believed that, in the nozzle reactor under supersonic conditions (e.g., Mach 5), gaseous water molecules are converted into hydrogen and hydroxyl radicals according to the following sequence of reactions:
H2O→H.+OH. (REACTION 8)
2*OH.→H2O2 (REACTION 9)
H2O2→H2O+O2 (REACTION 10)
The hydrogen radical is absorbed by the cracked hydrocarbon in a charge neutralization reaction, and the oxygen exits the reactor in the off gas. The foregoing sequence of reactions is consistent with the observation of CO2 and O2 in the off gas. Reactions of radicals of this type may be charge controlled and may be dominated by solvation effects. Moreover, it is known that neutral radicals may be produced in polar environments.
The following reactions are also believed to be important to the cracking of asphaltenes in the nozzle reactor:
In particular, it has been found that, if sufficient counter radical ions are not provided to quench the benzene rings, the cracked material repolymerizes back into heavy materials. By contrast, if sufficient radicals are present, some polymerization still takes place, but such polymerization produces lighter materials instead of gaseous compounds. Surprisingly, the nozzle reactor system is found to produce very little hydrocarbon gas (C1 through C4).
It has also been found that, when methanol is added to the steam in the reactor feed, the methanol undergoes steam reformation to produce hydrogen and CO2. Surprisingly, this reaction occurs without the need for any catalyst.
It has further been found that the fine grinding of coal in a methanol environment results in a certain amount of swelling of the coal feedstock. This is found to result in the incorporation of methanol into the lattice structure of the coal. Consequently, a substantial amount of methanol is transferred with the coal into the nozzle reactor. Since, as noted above, methanol undergoes steam reformation in the nozzle reactor to generate hydrogen, this captive methanol serves as an in situ source of hydrogen.
The overall chemistry of a preferred embodiment of the systems described herein involves, in essence, the conversion of coal (and more particularly, the asphaltene content thereof), methane and steam into gasoline-type products:
C200H180+90CH4+20″HxOy″→36C8H18+10CO2 (REACTION 13)
The term “gasoline-type” product is used here in acknowledgement of the fact that the resulting liquid products of the reaction will typically require further refinement. The presence of methane in the overall reaction reflects the fact that the methanol solvent preferably used in the mechanical activation process may be synthesized from syngas through the use of copper catalysts, and the syngas, in turn, may be synthesized from methane (see REACTION 3).
By contrast, in an overall sense, the Fischer-Tropsch process essentially involves burning the coal to produce carbon monoxide, and then converting the carbon monoxide to gasoline-type products. The overall chemistry for that process is as follows:
C200H180+10CO2→12C8H18+100CO2 (REACTION 14)
It will be appreciated from the foregoing that hydrocarbons can be produced from coal through the methodologies described herein in a much more economically friendly manner than is possible through the Fischer-Tropsch process. In particular, the Fischer-Tropsch process generates significantly more carbon dioxide per unit of gasoline-type product than the process summarized by REACTION 13. More specifically, the Fischer-Tropsch process generates ten times as much carbon dioxide, while only producing one third of the gasoline-type products. When the product stream is directed to higher aromatic products in the diesel-kerosene range (about C15), the differences are even greater, since the amount of natural gas required in the process summarized in REACTION 13 diminishes. In general, the higher the aromaticity of the desired product stream, the lower the C:H ratio required.
Various modifications may be made to the systems and methodologies described herein. For example, while some embodiments of the systems and methodologies described herein may utilize a single solvent for the mechanical activation process, in other embodiments, solvent systems containing multiple components may be utilized. For example, in some embodiments, a (preferably binary) solvent system may be utilized which has a polar component and an aromatic component. The polar component may be, for example, an alcohol or ether. The aromatic component may be, for example, toluene, xylene or the like, or a recycled product from the cracking operation.
In some embodiments of the systems and methodologies described herein, the solvent media used to solubilized the asphaltene content of the coal feedstock may be partially or wholly removed from the extracted asphaltene (although, as noted above, in some cases residual solvent is retained within the asphaltene lattice). In other embodiments, however, the solubilized asphaltene content may be injected with the solvent media into the nozzle reactor. In still other embodiments, a first solvent media may be utilized in the initial solubilization of the asphaltene content, after which the first solvent medium may be partially or wholly removed; then, the asphaltene content may be resolubilized in a second solvent medium, and the resulting mixture may be injected into the nozzle reactor.
Moreover, while a single passage through the cracker is contemplated for some product streams in such systems and methodologies, as indicated in
It will also be appreciated that various additives and processes may be added or incorporated into the process stream, either before, during or after cracking, to change the product profile. These include, for example, the use of water shift reactions and steam reforming. In some embodiments, the C/H ratio during cracking may be manipulated to achieve a desired product mix. For example, the C/H ratio may be adjusted by cracking a mixture comprising some product liquor and the residual methanol in the mechanically activated coal feedstock.
In some embodiments of the systems and methodologies described herein, the coal feedstock may also comprise mixtures or blends of coal with other hydrocarbon materials including, but not limited to, petroleum asphaltenes (including those obtained from the waste streams of other processes), refinery residues, heavy oils, tars, nonvolatile hydrocarbons, and the like. Such blends or mixtures preferably comprise between about 10% to about 99% coal, and about 1 to about 90% other hydrocarbon materials, by weight, more preferably comprise between about 20% to about 90% coal, and about 10% to about 80% other hydrocarbon materials, by weight, even more preferably comprise between about 30% to about 70% coal, and about 30 to about 70% other hydrocarbon materials, by weight, and most preferably comprise between about 40% to about 60% coal, and about 40% to about 60% other hydrocarbon materials, by weight.
Such mixtures often exhibit synergistic effects in some of the processes disclosed herein. For example, when coal is pyrolyzed by itself, a significant portion of the coal is converted into gas, and the production of liquids is typically limited to about 20-25%. Similarly, when heavy oil residues are pyrolyzed by themselves, the production of liquids is typically limited to about 50%. However, when coal and oil residues are combined in the feedstock at a ratio of about 1:1, the production of liquids is found to be about 55%, well above the yield of liquids of about 35-38% that one might expect if the components acted independently of each other. Similar synergistic effects are observed in combustion (when, for example, coal and heavy oil are combined) with regard to oxygen use efficiency and kinetics.
Such mixtures may also be advantageous during fine grinding or mechanical activation. For example, fine grinding or mechanical activation of a mixture consisting of a solid material such as a coal feedstock with a petroleum liquid (such as, for example, a heavy oil) and an oxygenated compound (such as, for example, methanol) may provide some petroleum asphaltene precipitation and hence a more intense contact for methanol uptake by the partially cracked coal phase. In a nozzle reactor of the type described herein, this may provide improved reaction kinetics, since the nozzle reactions are enhanced to some extent by the presence of hydrocarbon vapors that are capable of reacting much faster in the vapor phase with the gaseous radicals derived from steam or other motive fluids.
The above description of the present invention is illustrative, and is not intended to be limiting. It will thus be appreciated that various additions, substitutions and modifications may be made to the above described embodiments without departing from the scope of the present invention. Accordingly, the scope of the present invention should be construed in reference to the appended claims.
