Abstract:
This invention is a heater used to heat the feed process gas from 450° C. to greater than about 600° C. for the fluidized bed reactor (FBR) used for conversion of silicon tetrachloride (STC) to trichlorosilane (TCS). The invention involves stacked heater element carbon plates. The design of the plates allow the plates to act as baffles which improve heat transfer to the feed gas. Also, the heat gradients across each plate is calculated to be approximately 100° C. which is much lower than the gradient seen by conventional vertical heater elements. The design of the present invention prevents electrical grounding. In the design, the elements are surrounded by graphite wrapped in carbon felt to prevent heat loss by radiation and conduction.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an apparatus and method for producing trichlorosilane in which metallurgical grade silicon powder is reacted with hydrogen gas and silicon tetrachloride gas (STC) while being fluidized by the hydrogen gas and STC, thereby producing trichlorosilane. 
         [0003]    2. Description of Related Art 
         [0004]    Trichlorosilane (SiHCl 3 ) used as a raw material for producing high purity silicon may be produced by reacting metallurgical grade silicon powder (Si) of about 98% purity with STC and hydrogen gas. 
         [0005]    The apparatus for producing trichlorosilane includes a reactor, a raw material supply device for supplying metallurgical grade silicon powder to the reactor, and a gas introduction device for introducing hydrogen gas and STC with which metallurgical grade silicon powder is reacted. In the apparatus, the metallurgical grade silicon powder inside the reactor is reacted with hydrogen gas and STC while being fluidized with the hydrogen gas and STC, and the generated gas containing trichlorosilane is discharged from the upper part of the reactor. Conventionally, a heat transfer tube extending vertically in the reactor through which a process gas is heated in a tortuous path is provided inside the reactor. Such heat transfer tube is heated externally by vertical carbon heating elements. The heat transferred to the process gas travels though the vertical tube and is therefore indirectly heated. The heat transfer tube is difficult to scale as increases in size place greater stress on the carbon parts of the tortuous path. 
         [0006]    However the typical vertical tube heater design has a limited contact surface for heat transfer and as a result must have a different heating profile in order to achieve desired reaction temperature inside the reactor. Heat loss due to indirect heating and a limited contact surface for heat transfer can be inefficient depending on the scale of the reactor. 
         [0007]    In order for the conversion reaction to take place, the feed gas must be heated from about 450° C. to greater than about 600° C. At these temperatures carbon heaters suffer from radiant and convective heat loss. Carbon heaters can also be prone to mechanical failure by cracking. 
         [0008]    The desire for improving the heat transfer coefficient in a well-insulated reactor lead to the invention herein. 
       SUMMARY OF THE INVENTION 
       [0009]    Incidentally, according to the study of the present inventor, metallurgical grade silicon powder is fluidized at the lower part of the reactor by ascending hydrogen gas and STC which is introduced from there below, and the metallurgical grade silicon powder is contacted with the hydrogen gas and STC to cause a reaction during fluidization. 
         [0010]    The invention involves stacked carbon elements. The design of the elements allow them to act as baffles which improve heat transfer to the feed gas. Also, the heat gradients across each baffle was estimated to be in the range of about 100° C. which is much lower than the gradient seen by conventional vertical heater elements. The design of the present invention prevents electrical grounding between the heating element, insulation and the reactor. In the design, the elements are surrounded by graphite wrapped in carbon felt to prevent heat loss by radiation and conduction. 
         [0011]    This invention is used to heat the feed process gas for the FBR reactor used for conversion of silicon tetrachloride (STC) to trichlorosilane (TCS). The electrodes in the reactor are powered by a power supply. Power required depends on the throughput of the reactor. The electrodes are surrounded by quartz to prevent grounding with the surrounding insulation. The electrode passes current to the bottom most plate through contact with a carbon nut. Every subsequent plate transfers current to the next plate by a carbon spacer. The potential difference across each plate is low resulting in a low probability for arching. Ceramic sleeves are used to prevent grounding with the carbon rods. When the current has reached the top most plate, the electricity is passed to the return electrode through a carbon rod. One carbon rod does not pass electrical current but acts as a support. Both carbon rods are threaded at both ends so that a nut may be used to compress the entire stack and ensure good electrical conductance. 
         [0012]    The element stack is surrounded by graphite. The graphite provides a concrete medium on which to wrap carbon felt. Even though the graphite is thermally conductive, the carbon felt has superior insulating properties and heating loss to conduction and radiation is minimized. The floating design of the graphite wrapped in felt will help prevent carbon cracking. 
         [0013]    The carbon elements are chamfered reducing stress at natural corners. Heat transfer effect was estimated by considering the element as a cylinder submerged in a fluid. The carbon elements are arranged to provide a good baffle design. The two carbon elements are arranged in first orientation designated as A to B orientation, meaning a carbon element B with a pattern B is stacked on top of a carbon element A with a pattern A which is designated as A to B. A and B patterns are different from each other. The next carbon element to be placed on the carbon element with pattern B is the carbon element A with pattern A which is placed upside down, so that upside down pattern A is the reverse of right side up pattern A. This ensures a good baffling effect for the rising gas to be heated. Next the carbon element B with pattern B is placed upside down on top of upside down carbon element A with pattern A. This orientation is designated as upside down A to upside down B. The pattern of A to B to upside down A to upside down B is continuously repeated among the carbon elements on the heater element stack. In this fashion of carbon element stacking, heat transfer is improved by the good baffle action of the carbon elements. 
         [0014]    The STC feed gas to the conversion rector is heated from about 450° C. to greater than about 600° C. by a novel heater assembly. The gas, once heated, is able to react in the conversion reactor to form TCS. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross-sectional view of a heater element stack; 
           [0016]      FIG. 2A  is a plan view of a first heater element carbon plate A and  FIG. 2B  is a cross-sectional view of the first heater element carbon plate A taken along line  2 B- 2 B; 
           [0017]      FIG. 3A  is a plan view of a second heater element carbon plate B and  FIG. 3B  is a cross-sectional view of the second heater element carbon plate B taken along line  3 B- 3 B; 
           [0018]      FIG. 4A  is a plan view of a heater element ceramic short sleeve and  FIG. 4B  is a cross-sectional view of the heater element ceramic short sleeve taken along line  4 B- 4 B; 
           [0019]      FIG. 5A  is a plan view of a heater element ceramic sleeve and  FIG. 5B  is a cross-sectional view of the heater element ceramic sleeve taken along line  5 B- 5 B; 
           [0020]      FIG. 6A  is a plan view of a heater element carbon space (type #1) and  FIG. 6B  is a cross-sectional view of the heater element carbon space (type #1) taken along line  6 B- 6 B; 
           [0021]      FIG. 7A  is a plan top view of a heater element carbon cap (type #1),  FIG. 7B  is a plan bottom view of the heater element carbon cap (type #1), and  FIG. 7C  is a plan view of the heater element carbon cap (type #1); 
           [0022]      FIG. 8A  is a plan view of a heater element carbon cap (type #2),  FIG. 8B  is a plan bottom view of the heater element carbon cap (type #2), and  FIG. 8C  is a plan view of the heater element carbon cap (type #2); 
           [0023]      FIG. 9  is a plan view of a heater element carbon rod; 
           [0024]      FIG. 10  is a plan view of a heater element carbon nut; 
           [0025]      FIG. 11A  is a plan view of an outlet plenum center spacer ring and  FIG. 11B  is a cross-sectional view of the outer plenum center spacer ring taken along line  11 B- 11 B; 
           [0026]      FIG. 12A  is a plan view of an inlet plenum center spacer ring and  FIG. 12B  is a cross-sectional view of the inlet plenum center spacer ring taken along line  12 B- 12 B; 
           [0027]      FIG. 13A  is a plan top view of an inlet plenum insulation;  FIG. 13B  is a cross-sectional view of the inlet plenum insulation taken along line  13 B- 13 B; 
           [0028]      FIG. 14A  is a plan top view of a heater element insulation;  FIG. 14B  is a cross-sectional view of the heater element insulation taken along line  14 B- 14 B; 
           [0029]      FIG. 15A  is a plan view of an upper carbon insulation perforated plate A and  FIG. 15B  is a cross-sectional view of the upper carbon insulation perforated plate A taken along line  15 B- 15 B; and 
           [0030]      FIG. 16A  is a plan view of an upper carbon insulation perforated plate B and  FIG. 16B  is a cross-sectional view of the upper carbon insulation perforated plate B taken along line  16 B- 16 B. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    Hereinafter, an explanation will be made of an embodiment of the present invention with reference to the drawings. 
         [0032]    An apparatus for producing trichlorosilane is provided with a reactor, raw material supply device for supplying metallurgical grade silicon powder (Me-Si) as a raw material to the reactor, a feed gas introduction device for introducing hydrogen gas and STC which reacts with the metallurgical grade silicon powder, and a gas discharge device for discharging the generated gas containing trichlorosilane. 
         [0033]    The reactor is provided with a body formed substantially in a straight cylindrical shape along the vertical direction, a bottom connected to the lower end of the body, and a large diameter portion connected coaxially to the upper end of the body. In this embodiment, the body is formed with a substantially similar diameter to the bottom and the space therebetween is partitioned by a horizontal distributor plate. On the other hand, a tapered portion is formed at the upper part of the body, and the large diameter portion is integrally connected to the upper end of the tapered portion. The diameter of the tapered portion gradually increases in the upper direction thereof. Thus, the internal space of the body is communicatively connected to that of the large diameter portion. 
         [0034]    The raw material supply device supplies metallurgical grade silicon powder (Me-Si) (for example, the size is 1 μm or more and 1000 μm or less) from a raw material feed hopper via a raw material supply tube connected to the lower part of the body of the reactor. In this configuration, the metallurgical grade silicon powder is supplied by gas transportation using hydrogen as a carrier gas. 
         [0035]    On the other hand, the feed gas introduction device introduces hydrogen gas and STC into the bottom of the reactor via a gas supply tube. 
         [0036]    A plurality of nozzles are fixed along the vertical direction so as to penetrate the distributor plate which partitions the bottom of the reactor from the body. The upper end openings of the nozzles are arranged inside the body and the lower end opening is arranged inside the bottom. Then, hydrogen gas and STC are introduced by the feed gas introduction device into the bottom of the reactor is ejected dispersively into the body by each of the nozzles. 
         [0037]    Further, dispersing materials formed in spheres of various sizes, plate-shaped pieces of various sizes and dimensions with holes or the like are laid densely on the distributor plate. 
         [0038]    The gas discharge device sends the reacted fluid including trichlorosilane discharged from the reactor to a gas purifying system via dust/gas separation devices, and collects the metallurgical grade silicon fine powder (for example, the diameter is 1 μm or more and 200 μm or less) discharged along with the reacted fluid in the dust/gas separation devices to be returned to the raw material feed hopper via a recovery tube or for disposal. 
         [0039]    The feed gas introduction device introduces hydrogen gas and STC into the bottom of the reactor via the gas supply tube. The feed gas must be heated from about 450° C. to greater than about 600° C. Target reaction temperature of greater than 550° C. must be achieved as bulk reaction temperature. Gas temperature out of the heater must be hotter to account for: achieving target temperature; endothermic reaction; thermal loss in reactor bed; and additional thermal loss in heater section. The size of the heater is determined by the desired throughput. 
         [0040]    To heat the feed gas, a heater having a good heat transfer coefficient, good insulation, good mechanical durability with minimal contamination to the feed gas is desired. A heater having a combination heater element and baffle stacked in series and being well grounded and well insulated, as described herein, achieves the desired heating and mechanical requirements. 
         [0041]      FIG. 1  is a cross-sectional view of a heater element stack  1  of the present invention. The heater element stack  1  has the following components: 
         [0042]    a heater element carbon plate A  2  wherein the heater element follows a serpentine path between two alignment holes  17 ; 
         [0043]    a heater element carbon plate B  3  wherein the heater element follows a serpentine path between two alignment holes  17 , a different path design from the serpentine path of the heater element of heater element carbon plate A 2 , and wherein the heater element carbon plate A  2  and the heater element carbon plate B  3  are alternately stacked upon each other arranged as A to B to upside-down A to upside-down B to A to B, etc.; 
         [0044]    a heater element ceramic short sleeve  4  located at one end of each of the stacks of the heater element carbon plates A  2  and B  3  at the alignment hole  17 ; 
         [0045]    a heater element ceramic sleeve  5  extending though each alignment hole  17  of one heater element carbon plate A  2  and one heater element carbon plate B  3  and the heater element ceramic sleeve  5  having a stepped end  18  which serves as a spacer between two heater element carbon plates A  2  and B  3 ; 
         [0046]    a heater element carbon space (type #1)  6  which surrounds the heater element ceramic sleeve  5  and serves as a spacer between two heater element carbon plates A  2  and B  3  such that each heater element carbon plate A  2  and B  3  is spaced from the next heater element carbon plate A  2  and B  3 , at each alignment hole  17 , by the stepped end  18  of the ceramic sleeve  5  on one side and the carbon space (type #1)  6  on the other side; 
         [0047]    a heater element carbon cap (type #1)  7  located between and directly contacting a first electrode and the first heater element carbon plate A  2 ; a heater element carbon cap (type #2)  8  located between and directly contacting a second electrode and the heater element ceramic short sleeve  4  located at one end of each of the stacks of the heater element carbon plates; 
         [0048]    a heater element carbon rod  9  which passes though all heater element ceramic sleeves to prevent contact and subsequent grounding, and is connected at a bottom end to the heater element carbon cap  7  on one side and the heater element carbon cap  8  on the opposite side; 
         [0049]    a heater element carbon nut  10  located at the top of each of the heater element carbon rods  9  opposite the heater element carbon caps  7  and  8  to screw down and hold together the entire stack of heater element carbon plates A  2  and B  3 ; 
         [0050]    an outlet plenum center spacer ring  11  located at the outlet plenum  19 ; 
         [0051]    an inlet plenum center spacing ring  12  located at the inlet plenum  20 ; 
         [0052]    an inlet plenum insulation  13  located at the top and bottom of the inlet plenum  20 ; 
         [0053]    a heater element insulation  14  surrounding the heater element carbon plates A  2  and B  3 ; 
         [0054]    an upper carbon insulation perforated plate A  15  located at the outlet plenum  19  above the heater element insulation  14 ; and 
         [0055]    an upper carbon insulation perforated plate B  16  located at the outlet plenum  19  above the outlet plenum center spacer ring  11  which is on top of the upper carbon insulation perforated plate A  15 . 
         [0056]    The entire heater element stack  1  is surrounded by a water jacket  21 . The heater element stack  1  has a plurality of carbon plates. The embodiment shown in  FIG. 1  has 25 carbon plates, however this number can vary and can include any number of carbon plates depending on the dimensions and desired output temperatures. The number of upper carbon insulation perforated plates can also be varied depending on the heater design. 
         [0057]    The heater element stack  1  operates as follows: The heater element stack  1  is heated by passing electric current from a power supply (not shown) to the first electrode (not shown) to the heater element carbon cap (type #1)  7  located between and directly contacting the first electrode and the first heater element carbon plate A  2 . The electrodes are surrounded by quartz to prevent grounding with the surrounding insulation. The first electrode passes current to the bottom most heater element carbon plate A  2  through contact with the heater element carbon cap (type #1)  7 . Every subsequent plate A  2  and B  3  transfers current to the next plate by the heater element carbon space (type #1)  6 . The potential difference across each plate is low, so the probability for arching is small. The heater element ceramic sleeves  5  are used to prevent grounding with the heater element carbon rods  9 . When the current has reached the top most heater element carbon plate A  2 , the electricity is passed to the return electrode (not shown) through the heater element carbon rod  9 . One heater element carbon rod  9  (the left carbon rod  9  in  FIG. 1 ) does not pass electrical current. Both heater element carbon rods  9  are threaded at both ends so that the heater element carbon nut  10  may be used to compress the entire stack and ensure good electrical conductance. 
         [0058]    The heater element stack  1  is surrounded by graphite. The graphite provides a concrete medium on which to wrap carbon felt. Even though the graphite is thermally conductive, the carbon felt has superior insulating properties and heating loss to conduction and radiation is minimized. The floating design of the felt wrapped in graphite helps to prevent carbon cracking. 
         [0059]    The greatest temperature predicted is approximately 700° C. to 900° C. for heater element carbon plate A  2  number  22  from the bottom of the heater element stack  1 . This is well within carbon&#39;s mechanical abilities and lower than the temperature at which contamination from the carbon is a concern. The temperature gradient predicted across heater element carbon plate A  2  number  11 , from the bottom of the stack for example, is approximately 100° C. This is a smaller gradient then present long vertical heater elements. The top two baffles, the upper carbon insulation perforated plate A  15  and upper carbon insulation  40  plate B  16 , above the heater element stack, ensure complete mixing of the process gas before it passes into the distributor section. The top two baffles, the upper carbon insulation perforated plate A  15  and upper carbon insulation perforated plate B  16  also protect the distributor plate in the distributor section from overheating while minimizing heat loss. 
         [0060]    The feed gas enters into the heater element stack  1  through conduit  22 . The feed gas passes through two inlet plenum insulation  13  members separated by the inlet plenum center spacer ring  12 . The feed gas then contacts the first heater element carbon plate A  2  which acts as a baffle to the feed gas so that the feed gas cannot rise in a straight path from the inlet plenum  20  to the outlet plenum  19 . The feed gas then contacts heater element carbon plate B  3  which also acts as a baffle to the feed gas. 
         [0061]    Thereafter the feed gas rises in the heater element stack  1  contacting the next heater element carbon plate A  2  and the next heater element carbon plate B  3  which are alternately stacked upon each other arranged as A to B to upside-down A to upside-down B to A to B etc. 
         [0062]    After contacting the upper most heater element carbon plate A  2 , the feed gas passes through the upper carbon insulation perforated plate A  15  located at the outlet plenum  19  above the heater element insulation  14  and the upper carbon insulation perforated plate B  16  located at the outlet plenum  19  above the outlet plenum center spacer ring  11  which is on top of the upper carbon insulation perforated plate A  15 . 
         [0063]    The feed gas is adequately heated and passes through the upper plenum  19  and into the distributer (not shown) of the FBR. 
         [0064]    The heater element stack is insulated. At the bottom of the heater element stack  1 , there are two inlet plenum insulation  13  members located at the top and bottom of the inlet plenum  20  separated by the inlet plenum center spacing ring  12 . At the top of the heater element stack  1 , there is the upper carbon insulation perforated plate A  15  located at the outlet plenum  19  above the heater element insulation  14  and the upper carbon insulation perforated plate B  16  located at the outlet plenum  19  above the outlet plenum center spacer ring  11  which is on top of the upper carbon insulation perforated plate A  15 . Between the upper carbon insulation perforated plate A  15  and the upper most inlet plenum insulation  13  member is the heater element insulation member  14 . The entire heater element stack  1  is surrounded by the water jacket  21  to cool the reactor walls to within acceptable tolerances. 
         [0065]      FIG. 2A  is a plan view of the first heater element carbon plate A  2  and  FIG. 2B  is a cross-sectional view of the first heater element carbon plate A  2  taken along line  2 - 2 . The entire first heater element carbon plate A  2  is a heater element. The first heater element  23  follows a serpentine path between two alignment holes  17  on opposite sides of the first heater element carbon plate A  2 . The embodiment shown in  FIG. 2  shows a particular serpentine path, however other serpentine path designs are possible between the alignment holes  17 . The portion of the heater element  23  surrounding the alignment holes  17  is wider than the heater element  23  which winds in serpentine, zigzag pattern between the alignment holes  17 . Heater element  23  of carbon plate A  2  is heavily chamfered. 
         [0066]      FIG. 3A  is a plan view of the second heater element carbon plate B  3  and  FIG. 3B  is a cross-sectional view of the second heater element carbon plate B  3  taken along line  3 B- 3 B. The entire second heater element carbon plate B  3  is a heater element  24 . The second heater element  24  follows a serpentine path between two alignment holes  17  on opposite sides of the first heater element carbon plate B  3 . The embodiment shown in  FIG. 3  shows a particular serpentine path, however other serpentine path designs are possible between the alignment holes  17 . The portion of the heater element  24  surrounding the alignment holes  17  is wider than the heater element  24  which winds in serpentine, zigzag pattern between the alignment holes  17 . Heater element  24  of carbon plate B  3  is heavily chamfered. 
         [0067]      FIG. 4A  is a plan view of the heater element ceramic short sleeve  4  and  FIG. 4B  is a cross-sectional view of the heater element ceramic short sleeve  4  taken along line  4 B- 4 B. The short sleeve  4  is either located between the upper most heater element carbon plate A  2  and the carbon nut  10  or between the lower most heater element carbon plate A  2  and the carbon cap (type #1)  8 . The short sleeve is designed to complete the stack of ceramic sleeves  5  either at the top or bottom of the stack of ceramic sleeves  5 . The short sleeve  4  has a notched design  25  so that it can sit securely in the corresponding indentation in the heater element carbon plate A  2  (or B  3  depending on the heater element stack  1  configuration). While the ceramic sleeve  5  is long enough to be inserted through the alignment holes  17  of two heater element carbon plates A  2  and B  3 , the short sleeve  4  is only long enough to be partially inserted in the alignment hole  17  of one heater element carbon plate A  2  (or B  3  depending on the heater element stack  1  configuration). Short sleeve  4  has a hole  26  for accepting the carbon rod  9 . 
         [0068]      FIG. 5A  is a plan view of the heater element ceramic sleeve  5  and  FIG. 5B  is a cross-sectional view of the heater element ceramic sleeve  5  taken along line  5 B- 5 B. The ceramic sleeve  5  is long enough to be inserted through the alignment holes  17  of two heater element carbon plates A  2  and B  3 . Ceramic sleeve  5  has hole  27  for accepting the carbon rod  9 . Ceramic sleeve also has a stepped portion  18  which create a step of ceramic material which serves as a spacing element between two heater element carbon plates A  2  and B  3 . 
         [0069]      FIG. 6A  is a plan view of the heater element carbon space (type #1)  6  and  FIG. 6B  is a cross-sectional view of the heater element carbon space (type #1)  6  taken along line  6 B- 6 B. Carbon space  6  is in a ring shape with a hole  28  designed to accept carbon sleeve  5 . The carbon space  6  serves as a spacing element between two heater element carbon plates A  2  and B  3 . 
         [0070]      FIG. 7A  is a plan top view of the heater element carbon cap (type #1)  7 ,  FIG. 7B  is a plan bottom view of the heater element carbon cap (type #1)  7 , and  FIG. 7C  is a plan view of the heater element carbon cap (type #1)  7 . The cylindrical carbon cap  7  is a carbon part designed to accept an electrode in a lower hole  30  and the carbon rod  9  in an upper hole  29 . The upper hole  29  and the lower hole  30  do not join, rather they are separated by the carbon cap  7  in between the two holes. 
         [0071]      FIG. 8A  is a plan view of the heater element carbon cap (type #2)  8 ,  FIG. 8B  is a plan bottom view of the heater element carbon cap (type #2)  8 , and  FIG. 8C  is a plan view of the heater element carbon cap (type #2)  8 . The cylindrical carbon cap  8  is a carbon part designed to accept an electrode in a lower hole  32  and the carbon rod  9  in an upper hole  31 . The upper hole  31  and the lower hole  321  do not join, rather they are separated by the carbon cap  8  in between the two holes. 
         [0072]      FIG. 9  is a plan view of the heater element carbon rod  9 . The heater element stack  1  has two carbon rods  9 . The carbon rod  9  is threaded at either end so as to be connected or fitted into either carbon cap  7  or carbon cap  8  at the bottom and threaded with a carbon nut  10  at the top. In the heater element stack  1  in  FIG. 1  the left carbon rod  9  does not pass electric current, rather electric current is passed between the heater element carbon plate A  2  and B  3  by carbon spacer  6 . Electric current is passed down the right carbon rod  9  into the electrode attached to the carbon cap  8 . 
         [0073]      FIG. 10  is a cross-sectional view of the heater element carbon nut  10 . The carbon nut  10  is threaded to screw onto the carbon rod  9 . The carbon nut  10  is screwed onto the carbon rod  9  to compress the stack of alternating heater element carbon plates A  2  and B  3 . Carbon nut has hole  33  to accept carbon rod  9 . 
         [0074]      FIG. 11A  is a plan view of the outlet plenum center spacer ring  11  and  FIG. 11B  is a cross-sectional view of the outer plenum center spacer ring  11  taken along line  11 B- 11 B. The outer plenum center spacer ring  11  is located between the upper carbon insulation perforated plate B  16  located at the outlet plenum  19  above the outlet plenum center spacer ring  11  and the upper carbon insulation perforated plate A  15 . The upper plenum center spacer ring  11  has hole  34  which surrounds the upper plenum  19 . 
         [0075]      FIG. 12A  is a plan view of the inlet plenum center spacer ring  12  and  FIG. 12B  is a cross-sectional view of the inlet plenum center spacer ring  12  taken along line  12 B- 12 B. The two inlet plenum insulation  13  members located at the top and bottom of the inlet plenum  20  are separated by the inlet plenum center spacing ring  12 . The inlet plenum center spacing ring  12  has hole  35  which surrounds the inlet plenum. 
         [0076]      FIG. 13A  is a plan top view of the inlet plenum insulation  13 ;  FIG. 13B  is a cross-sectional view of the inlet plenum insulation  13  taken along line  13 B- 13 B. Inlet plenum insulation has two holes  36  and  38  for accepting carbon rod  9  and a hole  37  for feed gas flow. The heater element stack  1  can have one or more inlet plenum insulation  13  members. In  FIG. 1  there are two inlet plenum insulation  13  members separated by inlet plenum center spacing ring  12 . 
         [0077]      FIG. 14A  is a plan top view of the heater element insulation  14 ,  FIG. 14B  is a cross-sectional view of the heater element insulation taken along line  14 B- 14 B. The heater element insulation  14  has hole  39  which surrounds heater element stack  1 . 
         [0078]      FIG. 15A  is a plan view of the upper carbon insulation perforated plate A  15  and  FIG. 15B  is a cross-sectional view of the upper carbon insulation perforated plate A  15  taken along line  15 B- 15 B. Upper carbon insulation perforated plate A  15  has perforated holes  40 . Additional holes are possible depending on the desired design. At the top of the heater element stack  1 , there is the upper carbon insulation perforated plate A  15  located at the outlet plenum  19  above the heater element insulation  14  and the upper carbon insulation perforated plate B  16  located at the outlet plenum  19  above the outlet plenum center spacer ring  11  which is on top of the upper carbon insulation perforated plate A  15 . Between the upper carbon insulation perforated plate A  15  and the upper most inlet plenum insulation  13  member is the heater element insulation member  14 . 
         [0079]      FIG. 16A  is a plan view of an upper carbon insulation perforated plate B  16  and  FIG. 16B  is a cross-sectional view of the upper carbon insulation perforated plate B  16  taken along line  16 B- 16 B. Upper carbon insulation perforated plate A  15  has a perforated hole  41  and different hole pattern than the upper carbon insulation perforated plate A  15 . Additional holes are possible depending on the desired design. 
         [0080]    The entire heater element stack  1  is surrounded by the water jacket  21  to cool the reactor walls. 
         [0081]    The present invention promotes efficient heating of gas with a longer heater element length (i.e.) the total element length in one example is over 93 feet (28.5 m)), good insulation (i.e.) the total heat loss in the heater section is approximately 6%) and the heater stack  1  design promotes turbulent gas flow (but with heavily chamfered parts the rounded corners of the parts are able to hold the gas flow, promote gas to gas contact and gas to heater element contact and avoid gas delamination). Thus the overall design results in a good heat transfer coefficient. 
         [0082]    The overall design is a floating design where the heater element carbon plate A  2  or B 3 , the ceramic sleeve  5  the carbon space  6  can be removed and replaced without removing all of the heater element carbon plates A  2  or B 3  above or below the part to be replaced. 
         [0083]    Furthermore with the invention design the number and types of parts used is minimized with minimized cost. 
         [0084]    The invention and embodiment are described for illustrative, but not limitative purposes. It is to be understood that changes and/or modifications can be made by those skilled in the art without for this departing from the related scope of protection, as defined by the enclosed claims.