Abstract:
A fluid bed reactor is configured to process a reactive material to form one or more products. The reactor includes a reaction vessel defining a compartment configured to receive the reactive material. A first cluster of heating conduits at least partially occupies the compartment and extends over a first vertical extent within the compartment. A second cluster of heating conduits partially occupies the compartment and extends over a second vertical extent within the compartment. The first cluster of heating conduits is vertically below the second cluster of heating conduits and spaced apart therefrom by a first separation distance. Feedstock inlets are configured to introduce the reactive material into a region that is vertically between the first and second clusters of heating conduits. The heating conduits in the first cluster have a first thickness while the heating conduits in the second cluster have a second thickness. The first separation distance is at least as great as the smaller of the first and second thicknesses.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a fluid bed reactor for processing a reactive material, which may include inorganic materials, and also carbonaceous materials, such as black liquor and biomass, to process and/or recycle materials and extract energy. More particularly, the present invention concerns such a reactor having two or more spaced apart clusters of heating conduits configured to indirectly heat the fluid bed and materials therein.  
       BACKGROUND OF THE INVENTION  
       [0002]      FIGS. 1A and 1B  show top and side views, respectively, of a prior art reactor, configured as a cylindrical reformer  100 . The cylindrical reformer  100  includes a cylindrical compartment  101  forming a reaction vessel. The reformer  100  comprises one or more pulse heaters  102 A,  102 B, each of which comprises a pulse combustor  104 A,  104 B connected to a respective resonance tube  106 A,  106 B. As seen in  FIG. 1A , the pulse heaters  102 A,  102 B extend in one direction across the diameter of the cylinder. Air and fuel products enter the pulse combustors  104 A,  104 B and the combustion products or flue gas exit the resonance tubes  106 A,  106 B.  
         [0003]     The pulse heaters  102 A,  102 B are of the sort disclosed in U.S. Pat. No. 5,059,404, whose contents are incorporated by reference to the extent necessary to understand the present invention. Such pulse heaters are configured to indirectly heat fluids and solids introduced into a reformer reaction vessel  101 . The resonance tubes  106 A,  106 B associated with the pulse heaters  102 A,  102 B serve as heating conduits for indirectly heating contents of the compartment  101 .  
         [0004]     As seen in  FIGS. 1A and 1B , a second pair of pulse heaters  108 A,  108 B are directed at right angles to the first pair of pulse heaters  102 A,  102 B across the diameter of the compartment. As seen in  FIG. 1B , this leaves vertically extending quadrants  136  within the compartment  101  in regions defined by the crossing pulse heaters.  
         [0005]     The pulse heaters are immersed in a dense fluid bed  110 , which extends from the compartment bottom  112  to approximately the top bed line  114 . The bottommost pulse heater  102 B is located at a height H 1  meters above the distributor  122  to avoid painting the resonance tubes  104 B with liquor  118 . In some prior art systems, the height H 1  is about 2-3 meters.  
         [0006]     Spent liquor  118  is injected into the side of the compartment  101  near the bottom of the dense fluid bed  110 . Generally speaking, the spent liquor is introduced into the compartment via a plurality of inlets  103  that are circumferentially arranged around the cylindrical compartment  101 . Though in  FIG. 1B , only four such inlets  103  are shown, it is understood that other numbers of circumferentially arranged inlets may be provided. In other prior art embodiments, the spent liquor may be introduced through the bottom of the compartment  101  through a plurality of inlets more or less evenly distributed across the bottom, perhaps arranged in an array or other pattern.  
         [0007]     Superheated steam  120 , or other fluidization medium, enters from the bottom of the compartment  101  and passes through a distributor  122 . The distributor  122  helps uniformly spread the entering steam  120 , which then percolates through the dense fluid bed  110 . Product gas  124  leaves from a freeboard area  126  at the top of the compartment  101  after passing through one or more internal cyclones (not shown) used to help drop out entrained bed solids.  
         [0008]      FIGS. 2A and 2B  show an alternative prior art configuration in the form of a rectangular reformer  200 . The rectangular reformer  200  has a compartment  201  with a rectangular cross-section as seen from above (See  FIG. 2B ). A plurality of pulse heaters  102  arranged in one or more rows pass through this compartment  201 . The rows are staggered relative to each other to enhance heat transfer. Each of these pulse heaters  102  comprises a heating conduit in the form of a resonance tube for indirectly heating the contents of the compartment  201 .  
         [0009]     A distributor  222  is provided at the bottom of the compartment  201 , much like in the cylindrical reformer  100 . The bottommost pulse heaters  202  are located at a height H 2  above the distributor  222 . In some prior art systems, this height H 2  is again about 2-3 meters. Moreover, just as in the case with the cylindrical reformer, spent liquor  218  is introduced into the side of the compartment  201  near its bottom. Generally speaking, the spent liquor is introduced into the compartment via a plurality of inlets  203  that are arranged along the walls around the rectangular compartment  201 . In other prior art embodiments, the spent liquor may be introduced through the bottom of the compartment  201  through a plurality of inlets more or less evenly distributed across the bottom, perhaps arranged in an array or other pattern. Meanwhile, product gas  224  leaves from a freeboard area  226  at the top of the compartment  201 . It is understood that the operation of the rectangular reformer  200  is similar to that of the cylindrical reformer  100  described above, in most material respects.  
         [0010]     Upon injection into the fluid bed  110 , the carbonaceous feedstock undergoes drying, devolatilization, char formation and char conversion. In a steam reforming environment, all of these processes are endothermic i.e. require heat input. An issue in the prior art configuration is that drying, devolatilization, char formation and char conversion processes all compete for heat transfer and mass transfer in the region that is above the distributor but below the bottom pulse heater. All these processes are heat sinks and the entering fluidization medium  120  may be another heat sink if it is steam and is at a temperature below that of the fluid bed. The only heat sources are the pulse heaters and these are significantly removed from the heat sinks by the aforementioned distances H 1  and H 2  in the prior art embodiments described above. The only link is the solids circulation rate and if this is not up to par, the feedstock injection region starves for heat and the reactor performance suffers.  
         [0011]     In addition, both heat transfer and mass transfer are important for satisfactory char conversion. The higher the char temperature and the reactant or steam concentration, the greater the char conversion rate. The region just above the distributor  122 ,  222  is characterized by high steam or reactant concentration, which is favorable for char conversion, provided the char temperature could be maintained at the fluid bed temperature. Due to feedstock injection and reduced solids circulation rate, the heat supply is limited which is likely to depress the char temperature and in turn the char conversion rate. In the region of the pulse heaters, the heat transfer is good but the mass transfer may be unsatisfactory if the reactant (steam) bypasses due to channeling, again impairing char conversion.  
         [0012]     Commercial units generally require deep or tall dense fluidized beds to accommodate the large number of heat transfer tubes. Operating these units in bubbling fluidization regime is rather limiting from heat and mass transfer and gas/solid contact standpoints due to the relatively large bubbles, increased bubble coalescence and the propensity for steam/gas bypassing. Conversely, operation in the turbulent fluidization regime affords good gas/solid contact and excellent heat and mass transfer characteristics. This, however, requires a significantly higher superficial fluidization velocity than that for the bubbling regime. One feasible approach is to select a different heat exchanger configuration and a smaller bed material mean particle size.  
       SUMMARY OF THE INVENTION  
       [0013]     In one aspect, the present invention is directed to a fluid bed reformer for converting a carbonaceous material into a product gas. The fluid bed reformer comprises a reaction vessel defining a compartment suitable for receiving carbonaceous material. A first cluster of heating conduits at least partially occupies the compartment and extends over a first vertical extent within the compartment. Each heating conduit in the first cluster is configured to transfer heat from a heat source to the compartment, the heating conduits in the first cluster having a first thickness. A second cluster of heating conduits at least partially occupies the compartment and extends over a second vertical extent within the compartment. Each heating conduit in the second cluster is configured to transfer heat from a heat source to the compartment, the heating conduits in the second cluster having a second thickness. The second cluster of heating conduits is positioned vertically above the first cluster of heating conduits and spaced apart therefrom by a first separation distance, the first separation distance being at least as large as the smaller of the first and second thicknesses. A plurality of feedstock inlets are configured to introduce carbonaceous material into the reaction vessel in a region that is vertically between the first and second clusters of heating conduits.  
         [0014]     In another aspect, the present invention is directed to a method of converting a carbonaceous material into a product gas. The method begins with providing a reaction vessel having the first and second clusters of heating conduits as described immediately above, introducing a fluidization medium into the compartment, introducing carbonaceous material into the compartment in a region that is vertically between the first and second clusters of heating conduits; and then controlling a reaction in the reaction vessel such that at least a portion of the carbonaceous material is converted into a product gas in a fluidized bed.  
         [0015]     In yet another aspect, the present invention is directed to a fluid bed reactor configured to thermochemically or biochemically process a reactive material. The reactor comprises a reaction vessel defining a compartment suitable for receiving a reactive material. A first cluster of heating conduits at least partially occupies the compartment and extends over a first vertical extent within the compartment. Each heating conduit in the first cluster is configured to transfer heat from a heat source to the compartment, the heating conduits in the first cluster having a first thickness. A second cluster of heating conduits at least partially occupies the compartment and extends over a second vertical extent within the compartment. Each heating conduit in the second cluster is configured to transfer heat from a heat source to the compartment, the heating conduits in the second cluster having a second thickness, the second cluster of heating conduits being positioned vertically above the first cluster of heating conduits and spaced apart therefrom by a first separation distance, the first separation distance being at least as large as the smaller of the first and second thicknesses. A plurality of feedstock inlets are configured to introduce a reactive material into the reaction vessel in a region that is vertically between the first and second clusters of heating conduits.  
         [0016]     In still another aspect, the present invention is directed to a method of thermochemically or biochemically processing a reactive material to form a product. The method begins with providing a fluid bed reactor including a reaction vessel defining a compartment suitable for receiving a reactive material, a first cluster of heating conduits and a second cluster of heating conduits, as described above. The method continues with introducing a fluidization medium into the compartment, introducing reactive material into the compartment in a region that is vertically between the first and second clusters of heating conduits; and then controlling a reaction in the reaction vessel such that at least a portion of the reactive material is converted into one or more products in a fluidized bed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     For a better understanding of the present invention and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings, in which:  
         [0018]      FIGS. 1A and 1B  show side and top views, respectively, of a prior art cylindrical reformer.  
         [0019]      FIGS. 2A and 2B  show side and top views, respectively, of a prior art rectangular reformer.  
         [0020]      FIG. 3A  shows a side view of a reactor in accordance with the present invention.  
         [0021]      FIG. 3B  shows a top cross-sectional view of the reactor of  FIG. 3A  taken along lines  3 B- 3 B. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]     The contents of U.S. Pat. Nos. 5,059,404; 5,306,481; 5,353,721; 5,536,488; 5,637,192 and 6,149,765 are incorporated by reference to the extent necessary to understand the present invention.  
         [0023]      FIGS. 3A and 3B  show views of a fluid bed reformer  600  comprising a compartment  601  serving as a reaction vessel  602 . As best seen in  FIG. 3B , the reaction vessel  602  has a rectangular footprint (i.e., a rectangular shape in a horizontal cross-section) comprising two long sides  604 A,  604 B and two short sides  606 A,  606 B. A plurality of pulse heaters  608 A,  608 B pass through the long sides  604 A,  604 B of the reformer vessel  600 . In one embodiment, the pulse heaters  608 A,  608 B are of a sort well known to those skilled in the art, such as those disclosed in U.S. Pat. No. 5,059,404, mentioned above. The resonance tubes  609  associated with these pulse heaters  608 A,  608 B serve as heating conduits for indirectly heating contents of the compartment  601 .  
         [0024]     The pulse heaters  608 A,  608 B are organized into two vertically spaced-apart clusters, a first, or lower, cluster  610  and a second, or upper, cluster  620 . In the embodiment shown, each cluster  610 ,  620  comprises one or more rows of pulse heaters. It is understood, however, that the pulse heaters within a cluster are not required to be arranged in rows, to be in accordance with the present invention.  
         [0025]     As seen in the embodiment of  FIG. 3A , the pulse heaters  608 A belonging to the lower cluster  610  are arranged in a single, horizontal row  612 . Since it is the only row, row  612  serves as both the uppermost row  612  and as the lowermost row  612  of lower cluster  610 . The vertical extent V 1  of the lower cluster  610  is therefore commensurate with the row height R 1 . In this instance, the row height R 1  corresponds to the thickness T 1  of a pulse heater  608 A belonging to this row  612  (or, more precisely, the thickness T 1  of a heating conduit  609  associated with the pulse heater  608 A). Therefore, in the case of a cylindrical heating conduit that is arranged horizontally, R 1  is simply the heating conduit diameter. While three pulse heaters are shown in this row  612 , it is understood that a row may have a different number of pulse heaters instead.  
         [0026]     The pulse heaters  608 B belonging to the upper cluster  620  are arranged in a pair of horizontal rows  614 A,  614 B. In the embodiment shown, the rows  614 A,  614 B of the upper cluster  620  are staggered relative to one another and are vertically spaced apart from each other by an intra-row spacing of V 4 . The upper cluster  620  has a vertical extent V 2  which is greater than the vertical extent of V 1  of the lower cluster  610 , due to the presence of two rows  614 A,  614 B in upper cluster  620 , rather than the single row  612  in the lower cluster  610 . The lowermost row  614 A of the second cluster  602  has a row height R 2  which, in the embodiment shown, corresponds to the thickness T 2  of the heating conduit associated with the corresponding pulse heaters  608 B. When the same types of heating conduits/pulse heaters are used in both clusters  610 ,  620 , the row height R 2  of lowermost row  614 A of the upper cluster  620  is the same as the row height R 1  of the uppermost row  612  of the lower cluster  610 .  
         [0027]     As seen in  FIG. 3A , the first and second clusters  610 ,  620  are spaced apart by an inter-cluster vertical spacing S 1 .  
         [0028]     In one embodiment, the clusters  610 ,  620  are spaced sufficiently far apart so that the vertical spacing S 1  is at least as large as the smaller of the heating conduit thicknesses T 1  and T 2 . When heating conduits in a given cluster have differing thicknesses, then the average heating conduit thickness for that cluster is used as the ‘heating conduit thickness’ for purpose of determining the minimum vertical spacing S 1 .  
         [0029]     In other embodiments, the vertical spacing S 1  is at least as large as the smaller of the two vertical extents V 1 , V 2  (i.e., S 1 ≧min (V 1 , V 2 )).  
         [0030]     In still other embodiments, the vertical spacing S 1  is at least twice as large as the smaller of the two vertical extents V 1 , V 2  (i.e., S 1 ≧2* min (V 1 , V 2 )).  
         [0031]     In the foregoing description of the clusters  610 ,  620 , the pulse heaters  608 A,  608 B in each cluster were arranged in horizontal rows, and so the row heights R 1 , R 2  were the same as the heating conduit thicknesses T 1 , T 2 . It is understood, however, that in other embodiments, the pulse heaters may not be arranged in horizontal rows, but instead may be tilted, or angled, from one wall  604 A to the opposite wall  604 B. In such case, the row heights would not be the same as the heating conduit thicknesses. It is understood that in still other embodiments, the pulse heaters may not even be arranged in rows at all. In all of these instances, however, the vertical spacing S 1  would still be at least as large as the smaller of the heating conduit thicknesses T 1  and T 2 .  
         [0032]     Also, while the first and second clusters  610 ,  620 , respectively, are shown to have an unequal number of rows, it is understood that in some embodiments the two clusters may have an equal numbers of rows, and that this equal number may be 1, 2, 3, or even more. It is further understood that while in the embodiment of  FIGS. 3A-3C , the rows  614 A,  614 B of the second cluster  620  have unequal numbers of pulse heaters  608 B, adjacent rows within a cluster may instead have equal numbers of pulse heaters  608 B. Thus, for example, rows  614 A,  614 B of second cluster  620  may each have three pulse heaters  608 B, the rows still being staggered relative to one another.  
         [0033]     The total number of rows and the total number of pulse heaters  608 A,  608 B in each row can be modified in any given design to suit the size, feedstock type and feedstock throughput of the steam reformer  600 .  
         [0034]     At the bottom of the reformer vessel  602  is a distributor  622  into which a fluidization medium  635 , such as steam, is introduced. Just above the distributor  622  and below the first cluster  610  is an enhanced char conversion zone  640 . The zone  640  provides for good heat and mass transfer and high reactant (steam) concentration and facilitates enhanced char conversion. The vertical extent of this zone  640  will depend upon the char reactivity and the reformer operating conditions with the slower the reaction(s) the greater the vertical extent.  
         [0035]     Between the first cluster  610  and the second cluster  620  is a drying and devolatilization zone  642  with height S 1 , as previously discussed. This zone is conducive to good solids circulation, heat transport and gas-solid contact and serves to maximize drying and devolatilization and minimize tar and char formation. In one embodiment, feedstock inlets, shown generally as  637 , terminate in a region that is vertically between the two clusters  610 ,  620 . Thus, in this embodiment, feedstock is injected into zone  642 , which is separated from the primary char reaction zone  640 , at a position vertically above the first cluster of pulse heaters and vertically below the second cluster  620  of pulse heaters. It is understood that the feedstock inlets  637  are approximately at the same height and spaced apart along the short sides  606 A,  606 B of the reformer vessel  602 .  
         [0036]     Finally, in the region just above the second cluster  620  is a dense bed region  644 , which extends to the top bed line  646 . A freeboard region  648  occupies the topmost portion of the reformer vessel  602 . Product gas  649  exits from the freeboard region  648  via cyclones and other equipment (not shown) known to those skilled in the art.  
         [0037]     It is understood that the pulse heaters  608 A,  608 B of the fluid reformer  600  are under computer control (not shown) so as to vary the firing rate and heat transfer rate to better match the load in the fluid reformer  600  and also enhance reformer turndown.  
         [0038]     It can be seen from the foregoing that in many respects, the fluid reformer  600  of  FIGS. 3A and 3B  is similar to the prior art fluid reformer  200  seen in  FIG. 2 . One principal difference, however, is that the pulse heaters  608 A,  608 B in fluid reformer  600  are arranged into spaced apart clusters  610 ,  620 , whereas the pulse heaters in the prior art fluid reformer  200  all belong to a single cluster. A second difference is that, in some embodiments, the feedstock is introduced into the compartment  602  in a region that is above the lowest pulse heaters and, in one embodiment, is introduced in a region that is between the two clusters  610 ,  620 .  
         [0039]     Operation of the fluid bed reformer to create a product gas from a carbonaceous material begins with an apparatus of the sort described above. This is followed by introducing a fluidization medium in the compartment, introducing a carbonaceous material into the compartment in a region that is vertically between the first and second clusters, and then controlling a reaction in the reaction vessel such that at least a portion of the carbonaceous material is converted into a product gas in a fluidized bed.  
         [0040]     People of ordinary skill in the art are familiar with various aspects of controlling the reaction, such as reactant flows, temperature and pressure monitoring, and the like. In those situations where pulse heaters are used, such control entails operation of the pulse heaters, including adjusting their firing rate, air-fuel mix, and other parameters. The reformer may be configured to operate in a turbulent fluidization regime, and the fluidization medium may consist of one from the group of steam, air, enriched air, oxygen, nitrogen, carbon dioxide, recycle product gas, and mixtures thereof.  
         [0041]     While the above description contemplates a fluidized bed reformer having a rectangular footprint, it is possible to implement the present invention in reformers having other shapes, as well. Thus, for example, a reformer with a square footprint or a cylindrical footprint may benefit from the present invention, so long as sufficient vertical spacing between the pulse heaters and inlets are provided to introduce the feedstock into this region between clusters of pulse heaters.  
         [0042]     Also, while the description above relates to energy conversion and syngas production, it is understood that the reactor may also be gainfully employed for thermochemical or biochemical processing of any reactive material, carbonaceous or otherwise. Thus, it is contemplated that reactive materials such as inorganics may also be processed in such a fluid bed reactor to form one or more desired products.  
         [0043]     In addition, the description above was couched in terms of using pulse heaters as the source of indirect heat provided by the heating conduits. It is understood, however, that the above-described reactor may employ sources other than pulse heaters to produce the heat that is indirectly supplied via the heating conduits  609 . Examples of such other sources include electric heaters within the heating conduits, fire tubes, and the like.  
         [0044]     The above description of various embodiments of the invention is intended to describe and illustrate various aspects of the invention, and is not intended to limit the invention thereto. Persons of ordinary skill in the art will understand that certain modifications may be made to the described embodiments without departing from the invention. All such modifications are intended to be within the scope of the appended claims.