Patent Publication Number: US-2011076116-A1

Title: Solid fuel conveyance and injection system for a gasifier

Description:
BACKGROUND 
     The invention relates generally to solid fuel (coal, biomass, pet coke and waste, etc) gasification systems, more particularly, to a system for conveying and injecting solid particulate fuel to a gasifier, especially a high-pressure gasifier. 
     Currently, both slurry feeding and dry feeding technologies are commercially utilized in coal gasification systems. Some gasifiers use coal-water slurry for fuel feed, but for the high-moisture content low-rank coal, the slurry feed may not work or the efficiency is too low due to too much water introduced into the gasifier. In this case, a dry feed system is employed. In some dry feed systems, low rank coals may be dried to remove two-thirds, or more, of the inherent moisture present in the coal. This improves the flow characteristics of the solids in the dry feed system equipment and the overall efficiency of the gasifier. However, the overall power production of the plant maybe reduced since the drying process consumes a large amount of energy. In addition, the dry feed system equipment, which may include a compressor, lock hoppers, lock hopper valves, drying equipment and additional storage capacity, results in a relatively expensive system when compared with slurry-based systems. 
     Other fuel feed systems (such as the systems described in U.S. Patent Application No. US20090107046) pressurize and convey high moisture content solid fuel such as coal to the gasifier using solid pumps and moisture removal systems. Solid fuel (e.g. coal) is grinded to a predetermined size and the moisture content within the particulate fuel is adjusted. The fuel is conveyed through a buffer vessel or directly to an injector of gasifier. The solid pumps on upstream of the gasifier facilitate pressurizing the coal from atmospheric pressure at the pump inlet to a pressure above the gasifier operating pressure in order to facilitate pneumatic conveyance of the coal into the gasifier. 
     However, due to the long distance pipeline conveyance, the stability of the solid flow injected into a gasifier is questionable. Also, the solid pump cannot be used as a metering instrument for solid injected into the gasifier in this configuration due to the large buffer tank. Furthermore, solid fuel is injected into a gasifier along with slag additives and recycled fines, which may lead to decreased mixing and carbon conversion. It would therefore be desirable to provide stable transportation of solid fuel to a gasifier and enhance carbon conversion. 
     BRIEF DESCRIPTION 
     In accordance with one embodiment disclosed herein, a system for use in a gasification system, comprises a solid pump that delivers a pressurized fuel and a high-pressure transition vessel. The transition vessel comprises a first inlet connected to an outlet of the solid pump so that all of the fuel from the solid pump passes through the transition vessel, a second inlet for connection to a conveyance gas line, and an outlet through which the fuel is transported to a gasifier. The transition vessel is elongated in the direction of a flow so that a conveyance gas introduced through said conveyance gas line carries the fuel to the gasifier. 
     In accordance with another embodiment disclosed herein, a system for use in a gasification system, comprises a plurality of solid pumps that deliver a pressurized solid particulate fuel and a high-pressure transition vessel. The transition vessel comprises a plurality of first inlets, a second inlet for connection to a conveyance gas line, and an outlet through which the fuel is transported to an injection system of a gasifier. Each of the first inlets is connected to an outlet of the solid pump so that all of the solid particulate fuel from the solid pumps passes through the transition vessel. The transition vessel is elongated in the direction of a flow so that a conveyance gas introduced through said conveyance gas line carries the fuel to the injection system. 
     In accordance with another embodiment disclosed herein, a system for use in a gasification system, comprises an injection system for a gasifier, a plurality of solid pumps that deliver a pressurized solid particulate fuel, and a high-pressure transition vessel. The injection system comprises a slurry injector and a plurality of feed injectors. The transition vessel comprises a plurality of first inlets, a second inlet for direct connection to a conveyance gas line, and an outlet through which the fuel is transported to the feed injectors. Each of the first inlets is connected directly to an outlet of the solid pump so that all of the solid particulate fuel from the solid pumps passes through the transition vessel. The transition vessel is elongated in the direction of a flow so that a conveyance gas introduced through said conveyance gas line carries the fuel to the feed injectors. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  illustrates an embodiment of a system for transporting and injecting fuel in accordance with aspects disclosed herein. 
         FIG. 2  illustrates a cross-sectional view of a gasifier with the injection system in accordance with aspects disclosed herein. 
         FIG. 3  illustrates a partial view of  FIG. 2  showing a feed injector in accordance with aspects disclosed herein. 
         FIG. 4  illustrates another embodiment of a system for transporting and injecting fuel with an auxiliary transition vessel in accordance with aspects disclosed herein. 
         FIG. 5  illustrates another embodiment of a system for transporting and injecting fuel where the transition unit is directly connected to the injector in accordance with aspects disclosed herein. 
         FIG. 6  illustrates another embodiment of a system for transporting and injecting fuel where the transition unit is connected to a feeder in accordance with aspects disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments disclosed herein include a system for transporting and injecting fuel from a solid pump to a gasifier. The system mainly includes a high-pressure transition vessel and an injection system. The transition vessel includes inlets for connection to a solid pump and a conveyance gas line and an outlet through which fuel is transported to the injection system. The injection system includes a slurry injector and a plurality of feed injectors that are connected to the outlet of the transition vessel. As used herein, singular forms such as “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. 
       FIG. 1  illustrates an embodiment of the system  10  for transporting and injecting fuel to a gasifier  12 . The system  10  includes solid pumps  14 , a high-pressure transition vessel  16 , and an injection system  18 . The system  10  is used in a gasification system using solid particulate fuel. In one embodiment, solids pumps  14  are rotary, converging space Solids Transport and Metering pump utilizing Stamet™ Posimetric® feed technology, otherwise known as a Stamet™ solids pump commercially available from GE Energy, Atlanta, Ga. This pump is capable of transporting solids from atmospheric pressure to pressures well over 1000 psig with a strongly linear relationship between pump rotational speed and solids mass flow. 
     The transition vessel  16  includes first inlets  20 , a second inlet  22 , and an outlet  24 . The first inlets  20  are located on the sidewall of the transition vessel  16 . The outlets  26  of solid pumps  14  are directly connected to the first inlets  20  using declining pipelines  28  so that all of the solid particulate fuel  30  delivered by the solid pumps  14  pass through the transition vessel  16 . In one embodiment, the first inlets  20  are at different levels of the transition vessel  16  to enable connection of multiple solid pumps  14 . The second inlet  22  is at the bottom  32  of the transition vessel  16  and is connected to a conveyance gas line  34 . The outlet  24  is at the top portion  36  of the transition vessel  16 . An outlet pipeline  38  connects the outlet  24  to the injection system  18 . 
     The transition vessel  16  is a high-pressure vessel, having an operating range of about 500 psi to about 1000 psi. Solid particulate fuels including, but not limited to, coal, biomass, pet coke, and mixtures thereof, are pressurized by the solid pump  14  and fed into the transition vessel  16  through the pipeline  28 . The conveyance gas  40  enters the transition vessel  16  from the second inlet  22  and carries the solid particulate fuel  30  to the injection system  18  through the outlet pipeline  38 . In one embodiment, the system  10  further includes a distributor  42  or nozzles (not shown) in the transition vessel  16  to distribute the conveyance gas  40  for carrying the solid particulate fuel  30  to the outlet pipeline  38 . 
     The transition vessel  16  is slim and elongated in configuration in the direction of the flow  44  of the conveyance gas  40  through the transition vessel  16  so that the superficial velocity of the conveyance gas  40  is high enough to carry all solid fuel particles  30  to the outlet pipeline  38  immediately after the fuel  30  enters the transition vessel  16 . The transition vessel  16  provides “transition” in that all the solid particulate fuel  30  has to transition or pass through the transition vessel  16  before entering the gasifier  12 . Transition through the vessel  16  alters or adjusts pressure conditions of the solid particulate fuel  30  to enable smooth delivery to the injection system  18 . The solid fuel particles  30  from the solid pump  14  are transported stably and smoothly to the injection system  18  compared to traditional feeder vessel (not shown), eliminating negative effects such as block, plug-in, and rat holing. The transition vessel  16  can be installed on the ground or at the top of the gasifier  12  according to the field conditions. 
     The solid flow in the transition unit and the conveyance line is operated under transport flow regime. Therefore, the residence time of the solid particles in the transition unit can be minimized to several minutes. The volume of the transition unit is thus significantly smaller than the buffer tank used in current gasification systems, normally in the range of about 30 minutes to about two hours of residence time. 
     The system  10  further comprises a purge gas line  46  and a discharge hopper  48 . The purge gas line  46  is in flow communication with the distributor  42  and the discharge hopper  48 . Solid particulate fuel that is not delivered by the conveyance gas  40  will settle in the distributor  42 . A purge gas is introduced in the transition vessel through the purge gas line  46  to clear the distributor  42 . The purge gas transfers undelivered fuel from the distributor  42  to the discharge hopper  48 . The fuel collected in the discharge hopper  48  can be cleared periodically. 
     In one embodiment, the injection system  18  includes a slurry injector  60  and a plurality of feed injectors  62 . Recycled fines and slag additives  68  are made into slurry and injected into the gasifier  12  via the slurry injector  60 . The outlet pipeline  38  from the transition vessel  16  is connected to the feed injectors  62 . The solid particulate fuel  30  is delivered to the gasifier through the feed injectors  62 . The slurry injector  60  is installed on top of the gasifier  12  and the feed injectors  62  are installed on the sidewall  64  of the gasifier  12 . The feed injectors  62  are installed symmetrically around the gasifier  12 , i.e. the feed injectors are installed symmetrically with respect to a central axis  66  of the gasifier  12 . Injectors  62  can be installed horizontally or with some angles for different feedstock with different reactivity. 
     Referring to  FIGS. 2 and 3 , the solid feed injectors  62  are installed at an oblique angle with respect to the sidewall  64  of the gasifier  12 . In one embodiment, the oblique angle is less than 30 degrees with respect to a tangential direction  68  of the sidewall  64 . In another embodiment (not shown), the feed injectors are perpendicular to the sidewall of the gasifier. The feed injector  62  includes a central channel  70  for conveying the solid particulate fuel  30  and a swirl channel  72  concentric with the central channel  70 . The swirl channel  72  includes swirlers  74  to generate swirl gas. Solid particulate fuel  30  is injected through the central channel  70  along with a conveyance gas  40 , such as, for example, Nitrogen or Carbon dioxide, that carries the solid particulate fuel  30 . Gasification agents  76  such as Oxygen or steam are injected through the swirl channel  72  to generate a swirl gas  78 . The symmetrical arrangement of the feed injectors  62  around the gasifier  12  generates a uniform flow field in the gasifier  12 . 
     Due to the effect of the swirl gas  78  from the feed injector  62 , fuel particles with different hydrodynamics characteristics will be separated in the spray. Smaller fuel particles  80  or particles with lower density will be sprayed into the bulk gas phase of the gasifier  12  due to the effect of the swirl gas  78 . But the direction of larger fuel particles  82  or particles with higher density will not be impacted. Larger fuel particles  82  will follow original streamline and attach onto slag on the inner surface  84  of the gasifier  12 . Smaller fuel particles  80  that need short residence time in the gasifier  12  will be gasified in the bulk gas phase. Larger fuel particles  82  that need longer residence time for higher carbon conversion will flow down with slag and react for a longer time. 
     The injection system  18  therefore takes advantage of the hydrodynamics difference between larger  82  and smaller  80  particles to achieve different residence time for different particles. The carbon conversion will be increased and the amount of recycled fines can be significantly reduced. 
       FIG. 4  illustrates another embodiment of the feed transporting and injection system  100  in which the transition vessel is installed near the top of the gasifier  102 . This embodiment is useful where the solid fuel particles are transported to the injector  104  through a short pipeline to minimized instability or blockage during conveyance. The system  100  includes an auxiliary transition vessel  106  in addition to the transition vessel  108 , purge gas line  110 , discharge hopper  112 , distributor  114 , and outlet pipeline  116 , solid pumps  118  that have same configuration as the embodiment described previously with respect to  FIG. 1 . The auxiliary transition vessel  106  can be directly connected to a gasifier injector  104 . The auxiliary transition vessel  106  is scaled-down version of the transition vessel  108  and includes an inlet  120  connected to the outlet pipeline  116  and an outlet  122  connected to the injector. The system  100  further includes a supplemental gas line  124  connected to the outlet pipeline  116  between the transition vessel  108  and the auxiliary transition vessel  106 . A supplemental gas  126  is delivered through the supplemental gas line  124  to stabilize the flow of feed to the gasifier  102 . Supplemental gas line  124  can be connected to the pipeline  116  with certain angles or by using some special design (not shown) such as a gas distributor, porous media or a Venturi. The volume of the auxiliary transition vessel is 5˜20 times smaller than that of the transition vessel  16 , i.e., the solid particle residence time in the auxiliary transition vessel is in the range of 0.5˜10 seconds. 
       FIG. 5  illustrates another embodiment of the system  200  for transporting and injecting fuel to a gasifier  202 . The system  200  includes a plurality of solid pumps  204  and a high-pressure transition vessel  206  that is connected to an injector  208  of the gasifier. The transition vessel  206  includes first inlets  210 , a second inlet  212 , and an outlet  214 . The first inlets  210  are located on the sidewall of the transition vessel  206  and are between the top portion  216  and the bottom portion  218  of the transition vessel  206 . The outlets  220  of solid pumps  204  are directly connected to the first inlets  210  using declining pipelines  222  so that all of the fuel  224  delivered by the solid pumps  204  pass through the transition vessel  206 . In one embodiment, the first inlets  210  are at different levels of the transition vessel  206  to enable connection of multiple solid pumps  204 . 
     In this embodiment, the second inlet  212  is at a top portion  216  of the transition vessel  206  and is connected to a conveyance gas line  226 . The outlet  214  is at a bottom portion  218  of the transition vessel  206 . The outlet  214  of the transition vessel is connected directly to the injector  208 . The system  200  further comprises supplemental gas lines  228  connected to the transition vessel  206 . The supplemental gas lines  228  are downstream of the first inlets  210 . 
     The conveyance gas  230  from the conveyance gas line  226  enters the transition vessel  206  through the second inlet  212  and carries the solid particulate fuel  224  to the injector  208  through the outlet  214 . For some high moisture fuel particles, the outlet  214  may be blocked. The supplemental gas  232  delivered through the supplemental gas line  228  can be utilized to facilitate smooth discharge of solid fuel particles through the outlet  214 . Supplemental gas line  228  can be connected to the transition unit  206  with different angles through different designs (not shown) including gas distributor, porous plate or Venturi. 
       FIG. 6  illustrates another embodiment of the system  300  for transporting and injecting fuel to a gasifier  302 . The system  300  includes a plurality of solid pumps  304 , a high-pressure transition vessel  306 , and a feeder  308 . The transition vessel  306  includes first inlets  310  on its sidewall, a second inlet  312 , and an outlet  314 . The outlets  316  of solid pumps are directly connected to the first inlets  308  using declining pipelines  318 . The second inlet  312  is at a top portion  320  of the transition vessel  306  and is connected to a conveyance gas line  322 . The outlet  314  is at a bottom portion  324  of the transition vessel  306 . The feeder  308  is connected to the outlet  314  of the transition vessel  306 . An outlet pipeline  326  connects the feeder  308  to an injection system  328  of the gasifier  302 . The system  300  further comprises supplemental gas lines  330  connected to the transition vessel  306 , downstream of the first inlets  310  and before the feeder  308  to deliver supplemental gas  332 . 
     The conveyance gas  334  from the conveyance gas line  322  enters the transition vessel  306  through the second inlet  312  and carries the solid particulate fuel  336  to the feeder  308  through the outlet  314 . The fuel  336  is then transported to the injector  328  through the outlet pipeline  326 . Conveyance gas  338  is also provided to the feeder  308  to transport the fuel  336  to the injector  328 . To ensure the smooth solid flow in the feeder  308 , conveyance gas  338  can be introduced into the feeder with different designs (not shown) such as a gas distributor, or a porous plate. Furthermore, a fluidizing gas (not shown) can also be introduced to horizontal feeder  308 . 
     The systems for transporting and injecting fuel to a gasifier described above thus provide a way to smoothly and stably transport solid fuel particles with high moisture content to a gasifier from solid pumps and enhance carbon conversion. The flow pattern is converted from the loose drop flow to the entrained flow and fed into the gasifier with high concentration. Employing the transition vessel can eliminate negative effects such as block, plug-in, and rat holing. Since the transition unit has a small volume, the solid flow in the system is in the transport flow regime, solid pumps can easily control the solid flow rate, especially for turn-up and turndown operations. Also, solid particulate fuel, i.e. dry feedstock, and slurry are injected into the gasifier through different injectors, leading to a better mixing in the gasifier. Different residence times are achieved for smaller and larger particles to enhance carbon conversion. 
     It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.