TWO PHASE INJECTOR FOR FLUIDIZED BED REACTOR
A fluidized-bed reactor for producing hydrogen from methane by steam reforming includes a flow splitter that splits a dense-phase flow of a gas having entrained calcium oxide particles into a plurality of equal flow streams. The reactor also incorporates an orifice plate having at least one high-velocity, rocket-style impinging injector for injecting reactants into the reactor bed. The injector includes a central orifice extending perpendicularly through the plate, and one or more adjacent peripheral orifices that extend through the plate at such an angle that respective streams of reactants injected into the reactor bed through the peripheral orifices impinge on a stream of reactants injected vertically into the reactor bed through the central orifice. The injector cooperates with adjacent base-bleed orifices in the plate to provide a uniform distribution and rapid mixing of the calcium oxide particles with a steam/methane gas mixture across the entire bottom of the reactor bed.
This application is a continuation of U.S. Ser. No. 10/869,593, filed Jun. 16, 2004, which is related to U.S. Ser. Nos. 10/271,406, filed Oct. 15, 2002; 10/610,469, filed Jun. 30, 2003; 10/609,940, filed Jun. 30, 2003; entitled “DRY, LOW NITROUS OXIDE CALCINER INJECTOR,” “HOT ROTARY SCREW PUMP,” “SOLIDS MULTI-CLONE SEPARATOR,” and “HYDROGEN GENERATION SYSTEM WITH METHANATION UNIT,” the respective disclosures of which are incorporated herein by this reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
This invention relates to the large-scale production of commercially pure hydrogen gas in general, and in particular, to a dense-phase flow splitter and high-velocity, two-phase injector for use in a one-step, two-particle, fluidized-bed, steam-and-methane reactor used for such production.
2. Related Art
Hydrogen is one of the more common elements found in nature, and is present in many fuels, often combined with carbon, and in a large number of other organic and inorganic compounds. Hydrogen is widely used for upgrading petroleum “feed stocks” to more useful products. Hydrogen is also used in many chemical reactions, such as in the reduction or synthesizing of compounds, and as a primary chemical reactant in the production of many useful commercial products, such as cyclohexane, ammonia, and methanol.
In addition to the above uses, hydrogen is also quickly gaining a reputation as an “environmentally friendly” fuel because it reduces so-called “greenhouse emissions.” In particular, hydrogen can drive a fuel cell to produce electricity, or can be used to produce a substantially “clean” source of electricity for powering industrial machines, automobiles, and other internal combustion-driven devices.
Hydrogen production systems include the recovery of hydrogen as a byproduct from various industrial processes, and the electrical decomposition of water. Presently, however, the most economical means is the removal of hydrogen from an existing organic compound. Several methods are known for removing or generating hydrogen from carbonaceous or hydrocarbon materials. And, although many hydrocarbon molecules can be “reformed” to liberate hydrogen atoms therefrom, the most commonly used is methane, or natural gas.
The use of hydrocarbons as hydrogen sources, or “feedstock” materials, has many inherent advantages. Hydrocarbon fuels are relatively common and sufficiently inexpensive to make large-scale hydrogen production from them economically feasible. Also, safe handling methods and transport mechanisms are sufficiently well-developed to enable safe and expeditious transport of the hydrocarbons for use in the different hydrogen reforming and other generation techniques.
Currently, the majority of commercial hydrogen production uses methane as a feedstock. Generally, steam-and-methane reformers, or “reactors,” are used on the methane in large-scale industrial processes to liberate a stream of hydrogen gas. The generation of hydrogen from natural gas via steam reforming is a well-established commercial process. However, these commercial units tend to be extremely large and subject to significant amounts of “methane slip,” i.e., methane feedstock that passes through the reformer unreacted. The presence of such methane (and other reactants or byproducts) serves to pollute the hydrogen, thereby rendering it unsuitable for most uses without further purification.
The disclosures in the above-referenced Related Applications detail the development by the Boeing Company of the “Boeing One Step Hydrogen” (“BOSH2”) process, which uses calcium oxide particles for the economical, large-scale production of hydrogen with yields that are both larger and purer than prior art processes. The BOSH2 process comprises a “two-particle,” fluidized-bed, steam reforming process that uses two types of solid particles: 1) Relatively large, porous particles of alumina (Al2O3) having a nickel (Ni) catalyst deposited on both their interior and exterior surfaces, for converting methane (CH4) to hydrogen (H2) via the reaction:
CH4+H2O→3 H2+CO2,
and (2) relatively small calcium oxide (CaO) particles for converting the gaseous carbon dioxide (CO2) “byproduct” to solid calcium carbonate (CaCO3) via the reaction:
CO2+CaO→CaCO3.
The fluidized bed reactor is operated so that the large alumina/nickel-catalyst particles remain within the fluidized bed at all times, while the smaller calcium oxide/carbonate particles are entrained with the gas and flow continuously through and out of the bed for subsequent separation and re-use of the calcium oxide CO2-adsorbent.
Significant economic advantages have been shown in the size, throughput, and single-pass conversion efficiencies when using the BOSH2 two-particle fluidized bed process in methane/steam reformer reactors described above. However, as this process has matured over time, certain technical issues have arisen that require resolution. One of these relates to the need for obtaining a very uniform distribution and rapid mixing of both the solid calcium oxide particles and the steam/methane gas mixture across the bottom of the fluidized catalyst bed of the reactor. Uniform splitting of entrained calcium-oxide-particle streams into multiple (i.e., on the order of 6 to 36) feed streams is problematic in dilute, two-phase pneumatic gas flows. The subsequent rapid mixing of these streams with the recirculating fluidized bed material is also important to prevent excessive hot spots within the bed, which could cause over-heating issues. This is because the reaction of the CO2 with the calcium oxide is highly exothermic, and can potentially lead to local, destructive “hot zones” if not accurately counterbalanced by the highly endothermic methane/steam reaction. Therefore, good, uniform dispersions of the methane, steam, and calcium oxide reactants with the contents of the bulk fluidized bed at or near the bed's injectors is necessary and important to ensure reliable reactor operation.
BRIEF SUMMARY OF THE INVENTIONIn accordance with the present invention, apparatus is provided for uniformly and reliably splitting a stream of entrained calcium oxide particles into multiple feed streams, and then injecting those streams, together with the steam/methane gas mixture reactants, into the fluidized bed of a steam/methane reactor such that a very uniform distribution and rapid mixing of both the solid calcium oxide particles and the steam/methane gas mixture is achieved across the entire bottom of the fluidized bed of the reactor.
In one aspect of the invention, the apparatus comprises a very accurate, dense-phase (or “slurry”) flow splitter for the entrained calcium oxide particle feed lines, and in another aspect, comprises a high velocity, “rocket-style” impinging injector with adjacent base-bleed nozzles, or orifices, for an effective reactant dispersion into the reactor's bed.
In one exemplary embodiment thereof, the dense-phase flow splitter comprises an elongated inlet tube having opposite inlet and outlet ends, and a plurality of elongated outlet tubes having opposite inlet and outlet ends. The inlet ends of the outlet tubes are coupled to the outlet end of the inlet tube such that a stream of a gas having particles of a solid entrained therein at or just below the static-bed bulk density of the particles and entering through the inlet tube of the splitter is equally divided among the outlet tubes into substantially equal, constituent dense-phase flows. The respective internal cross-sectional areas of the inlet tubes of the splitter are adjusted such that they are equal to each other and their sum is substantially equal to the internal cross-sectional area of the inlet tube. The interior surfaces of the tubes are made very smooth, and the tubes are configured such that any change in the axial direction of the flow of the stream through the splitter does not exceed about 10 degrees. Advantageously, the outlet tubes are round, or annular, and have a nominal diameter of not less than about 0.25 inches.
An exemplary high-velocity, rocket-style impinging injector for injecting reactants into the bed of the reactor comprises an orifice plate disposed horizontally within the reactor below the fluidized bed thereof. The plate includes a “primary,” or central, orifice that extends substantially perpendicularly through the plate, and one or more “secondary,” or peripheral, orifices disposed adjacent to the central orifice, which extend through the plate at such an angle that streams of reactants respectively injected into the reactor bed through the peripheral orifices impinge on a stream of reactants injected vertically into the reactor bed through the central orifice. For embodiments of the injector that comprise a plurality of the peripheral orifices, the latter are preferably arranged in the plate such that the streams of reactants respectively injected therethrough impinge on the stream of reactants injected through the central orifice at a common point, and at a common, acute angle.
An exemplary embodiment of an advantageous one-step, two-particle, fluidized-bed reactor for the production of hydrogen from methane by a steam reforming process comprises an elongated, vertical closed chamber. The chamber is divided into an upper, fluidized-bed chamber for containing a bed of catalyst particles, and a lower, gas-manifold chamber, by an orifice plate disposed horizontally within a lower portion of the chamber. The plate incorporates at least one of the above high-velocity, rocket-style impinging injectors in it for injecting reactants into the bed of the upper chamber, together with a plurality of “base-bleed” orifices disposed around the injector and extending substantially perpendicularly through the plate for injecting respective streams of reactants from the gas-manifold chamber into the fluidized-bed chamber. The outlet end of one of the outlet tubes of one of the above dense-phase flow splitters is coupled to the central orifice of the injector for injecting a gas, e.g., steam, methane, or a mixture thereof, having particles of calcium oxide entrained therein at or just below the static-bed bulk density of the particles, into the bed of the reactor, and the lower, gas-manifold chamber is pressurized with a mixture of steam and methane for injection thereof into the bed through the peripheral and the base-bleed orifices of the plate.
A better understanding of the above and many other features and advantages of the apparatus of the invention may be obtained from a consideration of the detailed description thereof below, particularly if such consideration is made in conjunction with the several views of the appended drawings.
A schematic, cross-sectional elevation view of an exemplary embodiment of a one-step, two-particle, fluidized-bed reactor 10 for the production of hydrogen from methane by a steam reforming process in accordance with the present invention is illustrated in
The reactor 10 is referred to as a “two-particle” reactor because it uses two types of solid particles, viz., relatively large, porous particles 24 of alumina (Al2O3), which are plated with a nickel (Ni) catalyst, for converting a methane (CH4) feedstock with steam (H2O) in the presence of the nickel catalyst to hydrogen (H2) and carbon dioxide (CO2) gases via the endothermic reaction,
CH4+H2O→3 H2+CO2,
and relatively small calcium oxide (CaO) particles 26 for converting (i.e., adsorbing) the gaseous carbon dioxide “byproduct” generated by the first reaction to a calcium carbonate (CaCO3) solid via the exothermic reaction,
CO2+CaO→CaCO3.
As illustrated in
The gaseous reactants employed in the process, viz., methane 32 and steam 34, are supplied to the reactor 10 from respective pressurized sources 36 and 38 thereof, while the calcium oxide particles 26 are supplied from a suitable dispenser/hopper 40 thereof. As illustrated in
The solid and gaseous reactants enter the base of the bed 28 through the orifice plate 14, as above, and react with each other in the presence of the nickel catalyst particles 24 in accordance with the reactions described above to produce a stream of the desired product, hydrogen gas 44, together with entrained particles 30 of the first byproduct, calcium carbonate. This two-phase flow is then processed in an apparatus 46, such as the high speed “calciners” described in the above-referenced Related Applications, entitled “DRY, LOW NITROUS OXIDE CALCINER INJECTOR”, “HOT ROTARY SCREW PUMP”, and “SOLIDS MULTI-CLONE SEPARATOR”, in which the hydrogen is first separated from the calcium carbonate, and the calcium carbonate then processed into a second, carbon dioxide gas 48 byproduct and calcium oxide particles 26, the latter being re-circulated through the reactor for reuse in the process.
While significant economic advantages have been demonstrated in the size, throughput, and single pass conversion efficiencies of the two-particle, fluidized-bed methane/steam reformer reactor 10 and process described above, certain technical problems have emerged that require resolution. One of these relates to the need to achieve a very uniform distribution and a rapid mixing of both the solid calcium oxide particles 26 and the steam/methane gas reactant mixture 35 across the bottom of the fluidized catalyst bed 28 of the reactor.
In prior art reactors, all of the steam and methane reactants are mixed with the calcium oxide prior to their injection into the fluidized bed of the reactor by means of “tuyere”-type of injectors 300, such as the one illustrated in
However, it has been discovered that efficient, highly accurate flow splitting characteristics can be achieved whenever the solids are transported in lines at or near their static-bed bulk densities (sometimes referred to as “dense-phase” or “slurry feeding”-see, e.g., Sprouse and Schuman, AIChE Journal, 29, 1000 [1983]). Such a flow splitting device 200 for achieving uniform flow splits with these kinds of slurries, or dense-phase flows, is illustrated in the perspective view of
The dense-phase flow splitter 200 comprises an elongated inlet tube 202 having an inlet end 204 and an outlet end 206, and a plurality of elongated outlet tubes 208 having respective inlet ends 210 coupled to the outlet end of the inlet tube, e.g., by soldering, welding, brazing, or epoxy encapsulation, such that the flow of a dense-phase stream entering the inlet end of the inlet tube is substantially equally diverted into, or divided among, the outlet tubes. To effect such a flow division without particle bridging and subsequent plugging, it is preferable that the following conditions be met: The internal cross-sectional areas of the respective outlet tubes should be approximately the same, and their total area should be about the same as that of the larger single inlet tube; any change in the axial direction of the flow of the stream through the splitter should be held to 10 degrees or less; there should be no upstanding discontinuities on any of the internal surfaces of the splitter, i.e., all surfaces should be kept as smooth as possible within reasonable manufacturing tolerances; and, of importance for the types of dense-phase flows contemplated by the present invention, the outlet tubes should be round, or annular in shape, and have a nominal diameter of not less than about 0.25 inches.
As illustrated in
While the flow splitter 200 of the invention overcomes some of the problems associated with obtaining accurate, uniform splitting of dense-phase calcium oxide particle streams 42 into the reactor 10, it alone is not capable of overcoming the problem associated with the conventional tuyere injectors 300 described above, viz., an inability to achieve a uniform distribution and a rapid mixing of both the solid calcium oxide particle stream 42 and the steam/methane gas reactant mixture streams 35 across the entire bottom of the reactor bed 28. Subsequent rapid mixing of these streams with the circulating fluidized bed particles 24 is essential to prevent excessive hot spots within the bed, which could cause overheating of the reactor. This can result because the CO2 reaction with calcium oxide is highly exothermic, and can potentially lead to local hot zones if not carefully counterbalanced by the highly endothermic methane/steam reaction. Good mixing and uniform dispersion of the methane, steam, and calcium oxide reactants with the particles of the fluidized bed at or near the bed's injectors is therefore important and necessary to ensure reliable reactor operation.
The present invention overcomes the rapid, uniform, fluidized-bed mixing problem of the prior art injectors 300 by the incorporation of one or more high-velocity, rocket-style, impinging injectors 20, along with adjacent base-bleed orifices 22, which are located in the orifice plate 14 of the reactor 10, as illustrated in
In the particular embodiment of the injector illustrated in
The particular exemplary embodiment of a high-velocity, rocket-style impinging injector 20 illustrated in
In operation, the pentad injector 20 illustrated feeds the entrained calcium oxide particles 26 stream from the outlet end 212 of one of the outlet tubes 208 of the flow splitter 200 through the central orifice 60 of the injector and into the bed 28 of the reactor 10.
The solids bulk density within this stream should be at or just below the calcium oxide's static-bed bulk density of 30 lbmft3. The solids velocity exiting the central pentad passage should be between approximately 10 to 30 ft./sec. to prevent mechanical erosion of the line. Additionally, the minimum calcium oxide solids flow rate through the central orifice should be not less than approximately 0.05 lbm/sec.
To ensure good mixing with the calcium oxide stream 42 through the central orifice 60, momentum and momentum-flux considerations require that the methane/steam-to calcium oxide mass ratio be maintained at approximately 0.1, and that the gaseous methane/steam jet velocity be set at approximately 650 ft./sec through the peripheral orifices 62. For the overall fluidized bed operating conditions graphed in
The general operational parameters for an exemplary BOSH2 fluidized bed reformer 10 in accordance with the present invention have been mathematically modeled and are depicted graphically in
By now, those of skill in the art will appreciate that the apparatus and processes of the present invention are highly “scalable” in terms of throughput and resulting hydrogen yields, and that indeed, many modifications, substitutions and variations can be made in and to their materials, configurations and implementation without departing from its spirit and scope. Accordingly, the scope of the present invention should not be limited to the particular embodiments illustrated and described herein, as they are intended to be merely exemplary in nature, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.
Claims
1-25. (canceled)
26. A dense-phase flow splitter for splitting a flow of a stream of a gas having particles of a solid entrained therein at or near the static-bed bulk density of the particles into equal constituent dense-phase flows, said flow splitter comprising:
- an elongated, annular inlet tube having an inlet end, an outlet end, and an internal cross-sectional area; and,
- a plurality of elongated, annular outlet tubes having: respective internal cross-sectional areas that are substantially equal to each other, and the sum of which is substantially equal to that of the inlet tube; respective diameters of not less than about 0.25 inches; and, respective inlet ends coupled to the outlet end of the inlet tube such that the flow of the stream through the inlet tube is substantially equally divided among the outlet tubes;
- and, wherein:
- any change in the axial direction of the flow of the stream through the flow splitter does not exceed about 10 degrees;
- the gas comprises steam, methane, or a mixture thereof; and, the solid comprises calcium oxide.
27. The flow splitter of claim 26, wherein:
- the stream of gas and entrained particles has an axial velocity of between about 10 to about 30 ft./sec.; and, the calcium oxide particles have a static-bed bulk density of about 30 lb.subm/ft.3.
28. The flow splitter of claim 26, wherein each of the outlet tubes includes a tube outlet end, and each tube outlet end is associated with a different fluidized-bed reactor.
29. The flow splitter of claim 28, wherein each fluidized-bed reactor comprises an injector plate, and each injector plate is connected with a corresponding one of the outlet tubes.
Type: Application
Filed: May 7, 2009
Publication Date: May 13, 2010
Inventors: Kenneth M. Sprouse (Northridge, CA), Albert E. Stewart (Sylmar, CA)
Application Number: 12/436,965
International Classification: B01J 8/24 (20060101);