Electrically heated steam reforming reactor

Abstract

A method and design of providing high temperature heat for an endothermic gasifier without combustion includes flowing a stream of a first hydrocarbon gas sequentially through an annular plenum and a cylindrical plenum while heating the gas using electrical resistance immersion heating elements. These heating elements may be heated by three phase electrical power, minimizing the number of electrical leads emerging from the top of the heating elements. This method and design reduces the risk of extremely hot syngas exiting the gasifier damaging downstream fittings.

Claims

1. A method for high temperature gasification, comprising: flowing a stream of a first hydrocarbon gas from an entrance of a bottom annular plenum region over one or more heat transfer fins located within the bottom annular plenum region and towards a bottom inlet at a bottom of an annular plenum; flowing the stream of the first hydrocarbon gas from the bottom inlet toward a top outlet of the annular plenum; heating the flowing first gas along the axial length of the annular plenum; flowing the heated gas from the top outlet to a top inlet of a cylindrical plenum and toward a bottom outlet of the cylindrical plenum; heating the flowing gas along the axial length of the cylindrical plenum; converting the first hydrocarbon gas to a syngas by said heating in at least one of the annular or cylindrical plenums; removing the syngas from the bottom outlet; and flowing the removed syngas from the bottom outlet over a heat sink located in a bottom cylindrical can, wherein the heat sink and heat transfer fins are in thermal communication, wherein the bottom annular plenum region is located below the annular plenum region and the cylindrical plenum.

2. The method of claim 1, further comprising transferring heat from the removed syngas to the hydrocarbon gas in the bottom annular plenum region via the thermal communication between the heat sink and the heat transfer fins.

3. The method of claim 1, wherein the annular plenum surrounds the cylindrical plenum.

4. The method of claim 3, wherein the bottom annular plenum region is discrete from the annular plenum.

5. The method of claim 1, wherein said heating in the annular plenum is by a plurality of resistive heating elements each extending along substantially the entire axial length of the annular plenum.

6. The method of claim 1, wherein a wall of the annular plenum includes a plurality of aerodynamic strakes protruding into the flowpath.

7. The method of claim 1, further comprising thermally insulating an outer diameter of the annular plenum.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Some of the figures shown herein may include dimensions. Further, some of the figures shown herein may have been created from scaled drawings or from photographs that are scalable. It is understood that such dimensions, or the relative scaling within a figure, are by way of example, and not to be construed as limiting.

(2) FIG. 1A is a cross sectional representation of an insulated reactor with heating elements inserted downward from the top lid into two flow zones, one with upward flow in the outer annulus and then a flow reversal to downflow in the center of the annulus with flow leaving at the bottom as the reactor exit. Then in both annular flow regions, the flow is enhanced by turbulence-creating features.

(3) FIG. 1B is an enlargement of the top portion of the apparatus of FIG. 1A.

(4) FIG. 1C is an enlargement of a portion of the bottom of the apparatus of FIG. 1A.

(5) FIG. 1D is an external view of the apparatus of FIG. 1A.

(6) FIG. 1E is a cross sectional view of the apparatus of FIG. 1A as looking down along section A-A of FIG. 1A.

(7) FIG. 2 is a cross sectional representation perpendicular to the centerline of the reactor of FIG. 1A which shows how these heating elements are arranged in the two annular regions.

(8) FIG. 3A shows another embodiment in which a high temperature radiation object is used to radiate exit heat on to a fin cylindrical heat exchanger around the outside.

(9) FIG. 3B is an enlargement of the bottom portion of the apparatus of FIG. 3A.

(10) FIG. 4A shows a manifold arrangement according to another embodiment of the present invention where the feed gases are provided into the outer annulus and the hot exit gas leaving the bottom of the reactor in the center. This manifold design preferably provides a counterflow cylindrical tube heat exchanger as a recuperator.

(11) FIG. 4B is an enlargement of a portion of the bottom of the apparatus of FIG. 4A.

(12) FIG. 5A shows top plan views and side cross sectional elevational views according to another embodiment of a reactor with a coil heat.

(13) FIG. 5B shows a cross section of the apparatus of FIG. 5A looking down at line B-B, showing a coil and a thermal radiating block centrally located in this coil.

ELEMENT NUMBERING

(14) The following is a list of element numbers and at least one noun used to describe that element. It is understood that none of the embodiments disclosed herein are limited to these nouns, and these element numbers can further include other words that would be understood by a person of ordinary skill reading and reviewing this disclosure in its entirety.

(15) TABLE-US-00001 1 reformer 2 wires 4 screw 6 busbar 8 thermocouple 10 vertical immersion element 12 sanitary union 14 busbar 15 reactor 16 top flange 19 top 18 gaskets 20 ceramic 22 flow annulus 24 tension wrap 26 wire surface 28 turbulence trips 30 screen 32 fiberglass insulation 34 reactor metal 36 bottom mounting plate 38 insulation 40 mounting screws 42 mounting holes 50 concentric tubes 60 heating elements; annulus 64 heating elements 66 busbar 300 baffle 301 diverted flow 302 exit 306 pipe 308 flange 309 feed flow; flow input streams 310 elbow 311 flow outlet streams 312 flange 314 insulation plates 316 feed ports 318 inlet flows; flow input streams 320 flange pairs 322 port 324 flow outlet streams 326 exit gas 330 plenum box 399 reactor reformer 400 annular tube 401 heat exchanger 402 gas 404 square wrap 406 square wrap 408 plate mixer 410 exterior ceramic blanket 412 reactor ball 414 flow 416 pipe 418 can 420 solid body; heat sink 422 fasteners 423 fins 424 ceramic 426 ceramic insulation 428 base 430 base plate 432 gas flow 434 pipe 436 tangential entrance 438 bottom annular plenum region 440 spiral gaskets 442 O-ring 444 flow 446 annular space 500 thermocouples 504 heating elements 510 annular flow region 514 entrance tube 518 transition points; radius elbow; reactor vessel 520 body 522 heat exchanger 523 exchange plenum 524 bulkhead fitting 526 piping 530 port 532 annular tube 534 heat blanket 536 shape 538 reactor 542 bolting 544 rim clamps 546 lid 548 thermocouples 550 reactor top

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(16) For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. At least one embodiment of the present invention will be described and shown, and this application may show and/or describe other embodiments of the present invention.

(17) It is understood that any reference to “the invention” is a reference to an embodiment of a family of inventions, with no single embodiment including an apparatus, process, or composition that should be included in all embodiments, unless otherwise explicitly stated. Further, although there may be discussion with regards to “advantages” provided by some embodiments of the present invention, it is understood that yet other embodiments may not include those same advantages, or may include yet different advantages. Any advantages described herein are not to be construed as limiting to any of the claims. The usage of words indicating preference, such as “preferably,” refers to features and aspects that are present in at least one embodiment, but which are optional for some embodiments.

(18) Although various specific quantities (spatial dimensions, temperatures, pressures, times, force, resistance, current, voltage, concentrations, wavelengths, frequencies, heat transfer coefficients, dimensionless parameters, etc.) may be stated herein, such specific quantities are presented as examples only, and further, unless otherwise explicitly noted, are approximate values, and should be considered as if the word “about” prefaced each quantity. Further, with discussion pertaining to a specific composition of matter, that description is by example only, and does not limit the applicability of other species of that composition, nor does it limit the applicability of other compositions unrelated to the cited composition.

(19) What will be shown and described herein, along with various embodiments of the present invention, is discussion of one or more tests or analyses that were performed. It is understood that such examples are by way of example only, and are not to be construed as being limitations on any embodiment of the present invention. Further, it is understood that embodiments of the present invention are not necessarily limited to or described by the mathematical analysis presented herein.

(20) Various references may be made to one or more processes, algorithms, operational methods, or logic, accompanied by a diagram showing such organized in a particular sequence. It is understood that the order of such a sequence is by example only, and is not intended to be limiting on any embodiment of the invention.

(21) Various references may be made to one or more methods of manufacturing. It is understood that these are by way of example only, and various embodiments of the invention can be fabricated in a wide variety of ways, such as by casting, centering, welding, electrodischarge machining, milling, as examples. Further, various other embodiment may be fabricated by any of the various additive manufacturing methods, some of which are referred to 3-D printing.

(22) What will be shown and described herein are one or more functional relationships among variables. Specific nomenclature for the variables may be provided, although some relationships may include variables that will be recognized by persons of ordinary skill in the art for their meaning. For example, “t” could be representative of temperature or time, as would be readily apparent by their usage. However, it is further recognized that such functional relationships can be expressed in a variety of equivalents using standard techniques of mathematical analysis (for instance, the relationship F=ma is equivalent to the relationship F/a=m). Further, in those embodiments in which functional relationships are implemented in an algorithm or computer software, it is understood that an algorithm-implemented variable can correspond to a variable shown herein, with this correspondence including a scaling factor, control system gain, noise filter, or the like.

(23) In FIG. 1 are shown various views of a preferred embodiment that is a 7 ton per day electrically heated steam reformer 1 that has a number of vertical immersion elements 10 and a flow annulus 22 in the center to reverse the flow direction from in to out that achieves mixing and generates turbulence to enhance the heat transfer, so that the reactor vessel preferably remains under 12 ft in height, although other embodiments of the present invention contemplate reactor vessels of any height. At the bottom of the reactor is a plurality of concentric tubes 50 that feed the reactor and remove the hot syngas while the exchanging between the two so that the exit syngas is not too hot for downstream piping.

(24) The heating elements (such as those sold by Chromalox and Watlow, as examples) are mounted in the top flange 16 by means of a sanitary union 12 so they can be easily removed and pulled out even if they have blisters and misshapen diameter after service hours. Around the circumference is a triple stack of busbars 6 into which the wires 2 from the elements can be placed, captured by locking screw 4 and be powered electrically. Down the center is inserted a thermocouple 8 for measuring the temperature of the elements in the center of the reactor.

(25) The reactor is lined on the inside with a foam ceramic 20. The insulation also contains a square wire surface 26 to trip the boundary layer and increase the heat transfer from the heating element. There are also square wire turbulence trips 28 located on both sides of the annulus 22. Note that boundary layer tripping devices 26 and 28 are spaced apart along the direction of flow, which provides turbulent mixing with minimal obstruction to the overall flowpath. Further, it is understood that the boundary layer tripping features can be of any shape and orientation, with square cross sectional wires being just one example. The elements could also use a “tension wrap” 24 to further extend the heat transfer surface for more heat transfer.

(26) As the gases enter into the annulus there is placed a screen 30 that generates turbulence to enhance the heat transfer. Because the reactor is insulated by foam and ceramic 20 on the inside, the reactor metal 34 does not have to involve an exotic alloy. On the outside of the reactor vessel is fiberglass or other suitable insulation 32 to prevent a burning hazard.

(27) The flange lid on the top of the reactor 15 is sealed by means of gaskets 18 (such as gaskets provided under the name Spirotallic). At the bottom of the reactor is the plate 36 on which the annulus 22 in the reactor vessel is mounted and welded. The bottom plate 36 has insulation foam 38 to keep the temperatures at a reasonable level, and is attached by means of mounting screws 40. This plate also has mounting holes 42 for mounting the reactor to the frame.

(28) The gas fed to the reactor enters by the concentric tubes 50 (see section B-B) which feeds the gas up the outside of the annulus 22, around the top 19, down to the center and exiting it at the center of the concentric tube 50.

(29) The arrangement of the heating elements at the top of the reactor serves both the outer annular flow region 22 and the inner annular flow region 9 as is shown in a view from the top in FIG. 2. There is a power busbar 66 just above the reactor top 16 where the power is fed to 12 heating elements 60. Here the inner ring 4 of elements 12 draws 24 Amps and the outer ring of eight elements 12 draws 48 Amps. At the outside ring there is a pair of busbars 14 and 66 for distributing the power to the 16 heating elements 64, with each of the busbars handling 48 amps each. The element power is about 5 kW 480 vac WYE with a magnesium oxide internal ceramic. The common mode voltage to ground is 277 vac in this arrangement and the heat flux is 18 W per square inch for a heated length of 88 inches. The total power for all 28 elements is 140 kW. Throughout the cross-section there are seven thermocouples 8 placed down near the heating elements to get a view of the temperature distribution. Their placement is shown as the black dots in FIG. 2.

(30) FIG. 3 show a reactor reformer 399 according to yet another embodiment of the present invention. Device 399 includes a heat exchanger 401 at the bottom of the reactor using a reradiating solid body 420. The gas flow 432 enters the bottom of this reactor through pipe 434 that includes a tangential entry 436 which creates the swirl flow in the plenum region 438 improving the heat transfer on the fins 423. This inlet flow is preheated by the heat transfer from the fins 423 that warms the flow entering the annular space 446 of the reactor 412. Electrical heating elements 402 further heat the gas as enhanced by perforated plate mixer 408 as well as the turbulence created by the turbulence-generating features and boundary layer tripping devices 406 on both sides of the annular tube 400. Gas turbulence is created by square wraps 404 and 406.

(31) The flow in the annulus on the outside of the annular tube 400 flows over the top of this annular tube and down the center as flow 444 flowing over the reradiating body 420 and its base 428. Heated body 420 at operating conditions is a glowing yellow-orange hot surface radiating outward onto the surface of the fins 423. This radiating body 420 sits in the reactor exit flow entering the cylindrical can 418. Heat from flowpath 444 is conducted and convected into radiating body 420, which radiates and conducts heat onto fins 423. Thus, these reactor exit gases, having been cooled by the reradiating body and the fins 423, leaves this bottom can through pipe 416 as a cooled flow 414. This plenum chamber 438 is bolted to the reactor 412 that has internal foam ceramic insulation 426 as well as exterior ceramic blanket 410 on top of the reactor wall 412 to avoid skin burning and is sealed with the spiral gaskets for 440 and a small Indium O-ring 442. This bottom plenum is insulated by ceramic 424 on the sides and the bottom which is held on by screws 422 into this plate 428 which is welded to the bottom base-plate 430. The reradiating body 420 is preferably composed of four sections that can be individually removed through the port above so they can be cleaned and replaced.

(32) FIG. 4 describes a more detailed reactor bottom design for feeding gas to the reactor and extracting the syngas product. In FIG. 4 the reactant gases 309 flow in through flange 308. The flow from the inlet pipe exit 302 impacts baffle 300 where the diverted flow 301 is a mixed into small vortices so that the flow distribution in the bottom plenum box 330 more equally feeds the four annular feed ports 316 producing inlet flows 318. The product syngas leaves the reactor at flow 324 in the single larger port 322 and leaves from the bottom plenum in pipe 306 with the smaller pipe inside. This concentric arrangement serves as a countercurrent heat exchanger to recover the exit heat and use it to preheat the feed flow 309. The flange arrangement 308 permits the gases in this larger pipe to travel around elbow 310 as flow 311 to exit through flange 312.

(33) There are insulation plates 314 inserted in the bottom plenum 330 next to the reactor bottom and plates 312 at the exit pipes above the plenum 330. There are four flange pairs 320 serving flow entering at 318 and the single flange for the exit gas 326 that are accessible with clamps for their seal so that the bottom section can be easily removed for cleaning and installation.

(34) Yet another embodiment of the present invention is shown in FIGS. 5A and 5B, which show a cross section of a 1/10 scale reactor used in a pilot plant to test the concept of an entrance tube 514 with coiled tube heat exchanger 522 with a ceramic reradiating body 520 located at the tube coil center. The very hot syngas enters the coil heat exchanger through port 530 located in this heat exchanger bottom plenum 523. Long radius elbows are used at the two transition points 518 entering and leaving the coiled heat exchanger. The feed gases preheated by the coiled heat exchanger 522 (also detailed in FIG. 5B) enter the annular flow region 510 through a welded long radius elbow 518. A high alloy annular tube 532 is welded to the base of the reactor that is the top of the heat exchanger plenum 523. The exit gases leave the bottom plenum 523 through bulkhead fitting 524 and exit piping 526.

(35) The reactor vessel 518 is insulated from the inside with a foam alumina insert 536 cast into the final shape and preferably surrounded by heat blanket 534 (such as a blanket comprises Kaowool) and a cast foam insulating lid 538 to the reactor. The reactor top 550 has a clamp on stainless lid 546 using steel rim clamps 544 and bolting 542. Through the top of this reactor lid are thermocouples 548 going down into the annular flow region as well as thermocouples 500 going down into the center portion of the reactor. The lid is shown with four immersion heating elements 504 attached to the top of the lid by a sanitary clamp-on fitting.

(36) One embodiment of the present invention is presented in an example that involves validating the electrical heating elements performance using a computational heat transfer model that includes the turbulence promoters shown in FIG. 1 in the two flow passages of the outer annulus and in the center annular core as well as the flow paths shown in the bottom heat recuperator shown in FIG. 3.

(37) The Table 1 below shows the computational heat transfer model results in consideration of the apparatus of FIG. 4 for each of the flow input streams 309 and 318, together with the flow outlet streams 324 and 311. The electrical heating elements 60 and 64 shown placed downward through the lid shown in FIG. 2 are in two groups: first group 64 placed in the outer annular flow region 8 and totaling 16 elements drawing a current of 96 amps, and the second group 60 of 12 elements drawing 72 amps placed in the central region of the annulus 9. The total heating capacity of these groups of elements is 144 kWe. The fixed constants for the calculations are given in the top portion of this table involving 14 rows.

(38) For comparison the heat transfer model predicts that the heat transfer of 504.11 kWe is possible given the gas mass flow of 3500 lbs/hr shown in the row labeled “Gas Flow In”. In the rows below are shown each of the steps of the calculations down to the the 2.sup.nd row from the bottom showing the maximum heat transfer possible of 504.11.

(39) If all the turbulence generator strakes were removed, the total maximum heat transfer achieved is predicted to be 279.75 kWe—nearly double the electrical capacity of the elements of 144 kWe.

(40) Various aspects of different embodiments of the present invention are expressed in paragraph X1 as follows:

(41) One aspect of the present invention pertains to a method for gasification. The method preferably includes flowing a stream of a first hydrocarbon gas from an inlet at the bottom of a first plenum toward a top outlet. The method preferably includes electrically heating the flowing first gas along the axial length of the first plenum. The method preferably includes flowing the heated gas from the top outlet to a top inlet of a second plenum and toward a bottom outlet. The method preferably includes heating the flowing gas along the axial length of the second plenum.

(42) Yet other embodiments pertain to the previous statement X1, which is combined with one or more of the following other aspects.

(43) The method preferably includes converting the first hydrocarbon gas to a syngas by said heating in at least one of the plenums and removing the syngas from the bottom outlet.

(44) Wherein the first plenum is of any shape, and the second plenum is of any shape.

(45) Where in the second plenum is located within the first plenum.

(46) Which further comprises first flowing the stream of the first hydrocarbon gas from an entrance of a first plenum toward the bottom inlet.

(47) Which further comprises transferring heat from the syngas proximate the bottom outlet to the first gas in the first plenum.

(48) Wherein the first plenum includes a plurality of heat transfer fins.

(49) Which further comprises flowing the removed syngas from the bottom outlet over a heat sink.

(50) Wherein the heat sink is a radiative heat sink.

(51) Wherein the heat sink is aerodynamically shaped to minimize resistance to the flow of the syngas.

(52) Which further comprises transferring heat from the heat sink to the first hydrocarbon gas; wherein said transferring heat is by radiation and convection; wherein said transferring heat is substantially by radiation.

(53) Wherein said electrically heating in the first plenum is by a plurality of resistive heating elements each extending along substantially the entire axial length of the first plenum.

(54) Wherein each of the resistive heating elements is substantially linear.

(55) Wherein each of the resistive heating elements has two ends and which further comprises supporting each element at only one end.

(56) Wherein the first hydrocarbon gas includes steam.

(57) Wherein the syngas includes substantial hydrogen.

(58) Wherein the first plenum surrounds the second plenum.

(59) Which further comprises thermally insulating the outer diameter of the first plenum.

(60) Wherein the outer wall of said first plenum includes a ceramic insulator.

(61) Wherein at least one of the inner or outer cylindrical walls of said first plenum includes a plurality of aerodynamic strakes protruding into the annular flowpath.

(62) Which further comprises generating turbulence by the strakes.

(63) Which further comprises generating vortices by the strakes during said flowing the heated gas toward the top outlet.

(64) Wherein a wall of the second plenum includes a plurality of aerodynamic strakes protruding into the flowpath.

(65) Which further comprises generating vortices by the strakes during said flowing the heated gas toward the bottom outlet.

(66) Which further comprises repeatedly tripping the boundary layer during said flowing a stream.

(67) Which further comprises repeatedly tripping the boundary layer during said flowing the heated gas.

(68) TABLE-US-00002 TABLE 1 STEAM REFORMER REACTOR ZONE HEAT TRANSFER ANALYSIS Wellhead Gas Nom = 25 wet tpd Fee Temperature in = 300 ° F. Wellhead Gas Feedrate = 5724 lbs/hr Feedrate in tone = 68.688 Total Process Heat Need = 2.388 mm BTU/hr Total Process Heat Need = 699.7 kW Total Process Heat Need Outside = 2.388 mm BTU/hr 50% Process Heat Need = 699.68 kW Number of 7 tpd size reactors = 9.81 5.14 kW/element Number of elements = 28 144.05 kW total element surface area = 8996.16 in2 Tot. Element No-Fin Area 5.80 m2 Total Element with Fin Area = 16.34 m2 Syngas Temperature out = 900 ° F. Tube Thickness = 0.625 in Tube Thickness = 0.0159 m Recycle Gas Composition, CO.sub.2= 50% Recycle Gas Comp., H.sub.2O = 50% Annulus Flow Gap = 6.000 in Reactor Inner Diameter = 30 in Annulus Diameter = 18.000 in HX tube diameter 4.000 in Hx Tube Length = 80 in Thermal Cond of Inconel tube wall 18.0 W/m-K Feed Water Evap + Superht 117.2 kW Gas in to HX to Annulus Center out Hx out Strm 309 Strm 318 Center in Strm 324 Strm 311 Total units Gas Flow in = 3500 3500 3500 3500 lbs./hr Gas Temp in = 722 1350 1600 1850 1332 ° F. Gas Temp out = 722 1350 1275 1850 1332 ° F. Surface Temp in = 100 400 700 ° F. Surface Temp out = 400 700 900 ° F. Gas Temp in = 657 732 871 1010 722 ° C. Gas Temp out = 383 732 691 1010 722 ° C. Surface Temp in = 38 204 371 ° C. Surface Temp out = 204 371 482 ° C. Gas Ave Temp 793 1005 1054 1283 995 °K Gas Sensible Heat 437 0 289 727 kW Gas Density = 0.152 0.118 0.104 0.082 0.110 kg/m3 Kinematic Viscosity = 0.000400 0.000576 0.000675 0.000886 0.000576 m2/sec Thermal Conduct = 0.2690 0.3100 0.3280 0.363 0.3100 W/m-k Flow Cross Section Area = 0.0730 0.2842 0.1584 0.2842 0.2919 m2 Gas Velocity = 39.8467 13.1791 26.8259 18.9651 39.8467 m/s Reynolds No. = 75,908 17,435 30,283 16,311 52,714 Sq Root Reynolds No. = 276 132 174 128 230 Prandtl No. = 0.717 0.736 0.750 0.775 0.736 Cube Root Prandt No = 0.895 0.903 0.909 0.919 0.903 Strake Fract Turbulence 0.000 0.130 0.130 0.130 0.000 FrOssling No. = 0.800 1.500 1.500 1.500 0.800 Nusselt No. = 197.3 178.8 237.2 176.0 165.9 No Fin heat transfer Area = 0.649 3.317 2.487 3.317 0.649 m2 No Fin Heat Trans Coef = 69.650 72.757 102.096 83.834 67.473 W/m2-K No Fin Heat Flux = 27.02 120.80 119.59 267.41 30.70 504.11 kW

(69) While the inventions have been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.