Abstract:
A method of producing syn gas from biomass or other carbonaceous material utilizes a controlled devolatilization reaction in which the temperature of the feed material is maintained at less than 450° F. until most available oxygen is consumed. This minimizes pyrolysis of the feed material. The method and apparatus utilizes the formed synthesis gas to provide the energy for the necessary gasification. This provides for a high purity syn gas and avoids production of slag.

Description:
RELATED APPLICATION 
     This application is a continuation application of Provisional Application Ser. No. 60/303,756, filed Jul. 5, 2001, which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Carbonaceous feed material such as coal, wood chips and other biomass, and the like, have been used to produce synthesis gas which is carbon monoxide and hydrogen. The syn gas reaction is a redox reaction in which steam is combined with carbon at elevated temperatures to produce carbon monoxide and hydrogen. The reaction generally occurs at greater than 1000° F. Generally, the carbonaceous starting material includes oxygen which at elevated temperatures, i.e., greater than 450° F., will react with the carbon and pyrolysis will occur. This is an exothermic reaction. Most syn gas production has utilized the heat generated in this portion of the reaction to fuel the subsequent gasification. 
     Unfortunately, the pyrolysis reaction has several undesired results. Primarily it produces carbon dioxide which must be removed. Further, it produces large amounts of ash and further creates slag. Basically, it raises the temperature of the feed material to above the melting point of the ash, forming slag. Slag is unusable and must be disposed. 
     SUMMARY OF THE INVENTION 
     The present invention is premised on the realization that purer syn gas without significant amounts of carbon dioxide can be produced by controlling the oxidation of the feed material. More particularly, the present invention keeps the temperature of the feed material to less than 450° F. (the temperature at which combustion will occur) until a substantial portion of the oxygen has reacted with more reactive material in the feed such as hydrocarbons and the like. Once the available oxygen has been reacted at below combustion temperature, the feed material temperature is raised to a higher temperature, for example 650° F., prior to combination with super heated stream and subsequent rise in temperature to react with the carbonaceous feed material and produce carbon monoxide and hydrogen, i.e., syn gas. 
     The apparatus of the present invention utilizes the formed syn gas to provide the energy necessary to cause the oxygen to react in the feed and to gasify the carbon, thus enabling one to carefully control reaction temperature at all stages. This allows one to prevent formation of slag, control ash formation and improve the purity of the formed gas. The objects and advantages of the present invention will be further appreciated in light of the following detailed descriptions and drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The FIGURE is a diagrammatic depiction of the apparatus and method of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in the drawing, the reactor  11  used in the present invention includes a feed hopper  12  which introduces material into a devolatilization section  14 . The material from the devolatilization section  14  is directed to a cyclone feeder  16 , which adds steam and directs this through coils  18  that are located in a burner section  22  of furnace  20 . The heated coils  18  lead to first and then second cyclone separators  24 , 26  which separate gas from ash. The ash is collected for further use. 
     As shown in the drawings, the devolatilization section  14  is also located in furnace  20  downstream of burner section  22 . A forced draft burner  28  is used to heat the burner section  22 . The exhaust gases are then directed through the furnace  20  and around the devolatilization section  14  and pulled from the unit by an induced draft blower  30 . 
     The feed hopper  12  is sealed and includes an inlet section  32  and a delumper (not shown). Gas is introduced from the furnace section  22  through valve  36  to reduce moisture and promote flow. This gas is then exhausted back into an outlet line  38  directed to the induced draft blower  30  through line  40 . The feed hopper  12  is connected to the devolatilization section  14  which, as shown, is a series of four cylindrical reaction chambers  42 , 44 , 46 , 48 , each of which include internal auger  50 . A sealed valve  52  is positioned between the feed hopper  14  and the first cylindrical section  42  of the devolatilization section  14 . This valve is a one-way sealed valve, basically a rotating cup which directs feed material into the devolatilization section  14 . All the augers  50  and the feed valve  52  are operated by a single motor (not shown) which drives chain  56  in turn rotating sprockets  57 - 61  and causing the valve  52  and augers  50  to rotate. The first section  42  has an inlet  62  on the right side leading to an outlet  63  on the second side. Gravity directs material from one section to the next. This goes back and forth until the fourth and final section  48  is directed to a pneumatic conveyor such as a cyclone feeder  16 . 
     The cyclone feeder  16  can be any typical cyclone feeder. One particular product is described in U.S. Pat. No. 6,155,751 assigned to Ecotech, the disclosure of which is hereby incorporated by reference. The cyclone feeder  16  has three gas inlets, a nitrogen purge inlet  66  simply for safety purposes and shut down purposes, a syn gas inlet  68  and a steam inlet  70 . 
     Steam is created by super-heated steam coils  72  which run inside burner section  22  of furnace  20 . Steam is pumped from pump  73  into these coils  72  where the heat from furnace  20  heats the steam to about 1500° F. where it is directed into the cyclone feeder  16 . The cyclone feeder  16  then combines the product from the devolatilization section  14  with steam and directs this through reaction coils  18 . Syn gas is added as a diluent to maintain gas velocity. 
     The temperature in the reaction coils  18  should be from about 1300°-1800° F. In the reaction coils  18 , the carbonaceous product from the devolatilization section will react with the seam to form carbon monoxide and hydrogen. The reaction coils  18  lead to the first cyclone separator  24 . This is designed to remove larger ash and unreacted particles. The outlet  25  of the first cyclone separator  24  leads to the first ash collector  78  which is a cylinder with an auger  80 . The auger  80  directs ash from the inlet  82  to the outlet  84  as the ash cools. 
     The first cyclone separator  24  also has a first gas outlet  83  which leads to second cyclone separator  26  which removes finer ash and directs this to the second ash collector  86 . This collector  86  also includes an auger  88  which directs ash from inlet  90  to outlet  92 . Both outlets  25  and  76  are one-way feeder valves similar to valve  52  that allow pressure to be maintained in the system. 
     The syn gas outlet  81  from the first cyclone separator  24  tees off through line  94  to an eductor  96  which directs syn gas back into the cyclone feeder  16 . This controls the gas velocities to ensure that the reactants move quickly through the reaction coils  18 , generally at a minimum rate of about 2,000 feet per minute. 
     Water is added through line  98  to reduce the gas temperature to 800° F. at outlet  100  from separator  26 . The syn gas flows from the second cyclone separator  26  through line  192  to cooling section  104  which, as shown, includes first and second quenching coolers  106 , 108 . Gas flow line  192  goes through the first quenching cooler  106  and is cooled to about 350° F. Then the gas passes through the second quenching cooler  108  and is cooled to about 130° F. The cooling water is then directed through line  111  into a drain  112 . 
     The syn gas flows through line  114  to filter section  116 . As shown, this includes first and second filters  117 , 118 . These are basically redundant filters which allow them to be switched back and forth for alternate use. Syn gas flows from the filter section  116  through lines  120  to a coalescing water cyclone  122 . This removes the remaining water which is directed to drain  112 . The de-watered gas moves through a coalescing filter  124  and then via line  125  to a single stage compressor  126  which operates at about 150 psi greater than the cyclone feeder  16 . An output line  128  from the compressor leads to eductor  96 . The compressor provides the energy for the eductor. 
     The outlet line  125  from the coalescing filter also divides at line  130  and leads to a valve  132 . This valve  132  is open during the start of the compressor  126  to reduce back pressure allowing the compressor to start up. Once the start up is initiated, valve  132  is closed. A second line  134  from the water cyclone separator  122  relieves back pressure. Line  134  is also the collection line for the produced syn gas. It includes a flow meter  136  and product sample port  138 . This leads to a collector (not shown). 
     A syn gas fuel line  140  is directed from line  125  up to line  142  which is directed to the forced draft burner providing the fuel for the burner. Upstream is a propane tank  144  which provides start up fuel for the process. Preferably the reactor coils and devolatilization cylinder are refractory alloys such as 800 HT Incalloy with a rated capacity of 450 psi. 
     The operation of this system is carefully controlled to prevent pyrolysis of the feed material providing a higher quality product and a finer ash material. The feed material can be, for example, coal or any biomass, such as animal waste or wood chips. In particular, in the process of the present invention, the feed is introduced into the feed hopper where it is dried. The product will have perhaps 30%-40% moisture by weight when it is introduced into the initial devolatilization section  14 . 
     The forced draft burner  28  is ignited initially using auxiliary gas source  144 . This will heat the burner section  22  and the exhaust gas will then pass through the reactor around the individual devolatilization cylinders  42 - 48 . The temperature in the fourth devolatilization cylinder  48  will be higher than the temperature in the first devolatilization section  42 . Each of these reactors is a separate reaction zone with each subsequent reaction zone heated to a higher temperature than the preceding reaction zone. This allows for controlled reaction of oxygen in the feed material and enables one to prevent pyrolysis by controlling the exhaust gas flow over the devolatilization section. This is controlled primarily by controlling the speed at which the induced draft blower  30  operates. 
     It is preferable to have the first devolatilization section at around 100° F. with the final devolatilization section at 650° F. or higher. Pyrolysis occurs at about 450° F. Therefore, it is desirable to have most of the free oxygen reacted in the devolatilization section prior to reaching 450° F. Obviously, some small percentage of pyrolysis can occur. But one must minimize pyrolysis to prevent the exothermic oxidation from getting out of control. 
     The end product exiting from the devolatilization section is primarily char. This is combined with steam and syn gas basically as a diluent and transport medium in the cyclone feeder  16 . The ratio of steam to char should be about 1 to 1 on a mole basis calculating the char primarily as carbon. Obviously, no oxygen is added. The temperature of the steam when added should be around 1500°-1800° F. 
     To maintain the velocity in the cyclone feeder  16 , the eductor  96  is used to force syn gas through the reactor. This is generally about three-fourths of the total flow volume passing through the reaction coils  18 . Syn gas is added as opposed to additional steam to reduce waste water which must be removed from the system. The char and steam passes through the reaction coils in about 5 seconds and is directed to first cyclone separator  24 . This removes ash through a one-way valve  25  at the bottom of the separator and directs it into the ash collector  78 . This includes an auger  80  which allows the ash to cool prior to being removed from hopper door  84 . A vent  85  is provided back into the furnace  20  to vent off gases when the hopper door is open. Likewise, the second cyclone separator operates in the same manner. Again, its purpose is to remove additional finer ash. 
     In order to prevent formation of soot, it is important to reduce the temperature of the syn gas to about 800° F. as it is removed from the second cyclone separator  26 . Therefore, quench water pump  83  introduces water at the top of the cyclone separator  26  to reduce the gas temperature to less than 800° F. The gas then passes through line  192  which may be provided with a Shift Reactor (not shown). This then passes through to the first cooling chamber  106  which cools the syn gas to 350° F. (utilizing quench water) to a second cooler  108  which reduces the temperature to 130°-150° F. and then through filter section  116 . 
     The produced gas once filtered to remove water will be a relatively high purity syn gas having a hydrogen to carbon monoxide molar ratio of approximately 1:1. 
     The present invention has many different advantages. Basically, any carbonaceous feed material will be suitable for the present invention. If necessary, additional chemicals can be added to the feed material such as catalysts to enhance syn gas production or other materials to remove undesirable matter. For example, either pot ash or dolomite clay can be added to react with the sulphur permitting it to be removed with the ash. 
     As the present invention reduces pyrolysis and keeps the overall temperature of any formed ash at less than the slag forming temperature, a fine particulate ash is formed which in many cases may have commercial value. Particularly, with respect to livestock waste, various nutrients can be recovered from the ash. This is effected by utilizing the syn gas as the heat source for the reaction as opposed to utilizing oxidation of the feed material to form the requisite heat. 
     This has been a description of the present invention along with the preferred method of practicing the present invention. However, the invention itself should only be defined by the appended claims