Abstract:
Solid carboniferous fuels contain varying quantities of moisture, mercury, chlorine, nitrogen, sulfur, heavy metals and other materials that attain vapor pressure at elevated temperatures. The cost effective removal of these degrading and sometimes hazardous materials is important to the further use of the fuel for combustion via chemical looping to prevent contamination of the oxygen carrier medium. The solid fuel is cut, shredded, ground or sieved to appropriate size, and heated in a chamber that can exclude oxygen and air thus preventing ignition. The unwanted materials are driven in the gaseous state and extracted for recycling or safe disposal. The solid fuel cleaned of pollutants exits the chamber and is cooled below ignition temperature prior to contact with oxygen. The solid fuel thus purified is more appropriate for combustion via chemical looping.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Related to Application 12-908061 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX 
     Not Applicable 
     FIELD OF THE INVENTION 
     The present invention relates to the general topic of clean fuels for use in future combustion. The need for clean fuels is urgent to prevent further worldwide air pollution by harmful contaminants inherently present in nearly all carboniferous fuels. These contaminants, if not removed from the fuel feed stock are either released upon combustion, or costly to remove after combustion. Typical fuels are coal and the hydrocarbons that can be released from coal, and numerous calorific biomass species such as grass, wood, algae, farm waste and peat to mention the most common. Since many of the contaminants are harmful to all forms of life, a considerable effort has been undertaken over the last several decades to find ways to release and capture these contaminants prior to combustion. Some of these contaminants can then be re-processed for useful commercial purposes while some must be sequestered or safely disposed of in other ways. The present invention provides novel means for releasing and capturing most of the inherent contaminants prior to utilization in combustion thereby giving rise to a more efficient and less costly way for obtaining a contaminant free fuel. By removing water vapor and other contaminants such as mercury (Hg), chlorine (Cl), sulfur (S), arsenic (As) and the like, a more efficient combustion process can take place to cause the resulting energy production to be cheaper, less polluting and more efficient. 
     BACKGROUND OF THE INVENTION 
     Coal and biomass combustion has occurred for several millennia. However, commercial upgrading of combustion through the addition of combustion catalysts, increased oxygen or chemical oxidation of hydrocarbons became more widespread in the mid to late twentieth century and early twenty-first century. Combustion is the reaction of oxygen combining with carbon and hydrogen in the fuel in an exothermic reaction. Briefly, combustion catalysts are additives to the fuel that seek to generate more complete combustion of the hydrocarbons, or reduce problems with ash or emissions in the flue gas. Increased oxygen, oxygen over firing, or oxy-combustion all seek to increase the proportion of oxygen above the 20% in ambient air in order to improve combustion efficiency and reduce emissions. Chemical looping combustion employs a metal oxide to deliver oxygen for a chambered combustion reaction with hydrocarbons, and then recycles the metal for oxidation prior to looping back to the fuel reaction chamber. In general, depending on the nature of the raw coal and/or biomass in addition to the exact nature of the combustion process, the emissions from coal and biomass combustion generally contain large quantities of carbon dioxide and water vapor, and smaller emissions of acid gases, compounds of chlorine, mercury, additional heavy metals, hydrogen sulfide, and a wide range of inert ash material. 
     The history and detailed time-line of coal clean up through pyrolysis are well documented and found on a variety of websites. Details of a pyrolysis process can be found, for example, in “Kinetic Studies of Gas Evolution During Pyrolysis of Sub-bituminous Coal,” by J. H. Campbell et al., a paper published May 11, 1976 at the Lawrence Livermore Laboratory, Livermore, Calif. Numerous issued U.S. patents describe methods for the reduction of sulfur in coal, for example, U.S. Pat. No. 7,056,359 by Somerville et al. Their process involves grinding coal to a small particle size, then blending the ground coal with hydrated lime and water, followed by drying the blend at 300-400 degrees F. U.S. Pat. No. 5,037,450 by Keener et al. utilizes a unique pyrolysis process for denitrifying and desulfurizing coal. Here the sulfur and nitrogen content of coal is again driven off in gaseous form and sequestered for possible further use. Related art is described in U.S. Pat. No. 4,862,485, which teaches means for forming coal pellets by mixing coal particles with polyvinyl alcohol, calcium oxide and/or magnesium oxide and water. U.S. Pat. No. 4,738,685 teaches how to cold press coal fines with molasses, an inorganic hardening agent such as calcium carbonate, calcium phosphate, iron oxide, aluminum oxide or optionally with an acid. Additional teachings relevant, though differing from the present application can be found in U.S. Pat. Nos. 4,618,347, 4,586,936. 4,169,711 and U.S. Pat. No. 5,916,826. Patent application No. 20100162619 describes a method using a Mallard process at a pressure of 5 bar at an elevated temperature for compacting biofuels together with some limited amount of peat or lignite. 
     A more recent system has been proposed and published as USPTO application 20090020456 (Jan. 22, 2009) by Tsangaris et al, relating to the gasification of fossil fuels, fuels that are then used to process a variety of unconventional sources of oil sources such as tar sands and shale oil. 
     Additionally, in U.S. application Ser. No. 12/631,302, Lawrence F. McHugh et al instruct us in the oxidation of solid fuels via metallic oxide chemical looping, and points out that over time, minerals in the coal ash contaminate the oxygen carrier. 
     Chemical looping combustion (“CLC”) provides for the exothermic oxidation of hydrocarbons without ignition. Most CLC systems provide two chambers and a method of transporting grains of metallic oxide from one chamber to the other and then back to the first chamber, completing the loop. Metallic oxides are chosen for the ease with which they take on or give off an oxygen atom. For example, iron oxide is found in about 12 different forms, of which FeO and Fe 2 O 3  are two common forms. In a CLC unit, one might find iron oxide grains in one chamber and pulverized coal or biomass, ground solid hydrocarbons, in the other chamber. When air is conveyed through the first chamber, FeO is converted into Fe 2 O 3  in an exothermic reaction taking Oxygen atoms from the air. The grains of Fe 2 O 3  are transported into the other chamber with ground solid hydrocarbons. In this second chamber, Fe 2 O 3  is converted to FeO in a second exothermic reaction that combines hydrocarbons with oxygen to make water, H 2 O, and carbon dioxide, CO 2 . The iron oxide is then returned to the first chamber to be re-oxygenated. These paired exothermic chambers give off heat energy that is useful to do work for example, by the making of steam power. A pure CLC system uses pure oxygen from the air and pure hydrocarbons. When the hydrocarbons are not purified before CLC, then minerals in the coal and biomass that result in ash, may contaminate metallic oxide that serves as the oxygen carrier and result in lost efficiency and added processing cost. 
     The present application describes unique and novel systems and methods for obtaining calorically rich, nearly contaminant free combustibles for chemical looping combustion consisting of coal and biomass. The invention involves the preprocessing of the coal and biomass so resulting in major energy saving during the combustion stage, and preservation of the oxygen carrier free of contamination. The biomass can consist of algae, switch grass, wood matter, such as sawdust and/or wood chips, as well as manure to mention a non-exhaustive number of useful caloric components. 
     One of the several ways the present invention is particularly efficient is that it recovers and recycles the water vapor that is released from coal and biomass upon heating in a typical combustor. The fuel to be combusted which has already had the water removed makes the heat transfer of combustion considerably more efficient. At the same time, other contaminants such as S, H 2 S, Cl, Hg, As, Se and other minerals that have also been removed prior to CLC increases the efficiency and quality of the combustion process. Many of these impurities can then be recycled for further useful industrial applications. This form of recycling instead of disposal waste management is becoming recognized world wide as a necessary and achievable goal to reduce pollution and potential climate change. 
     The present invention is a further development of the work in the inventor&#39;s application Ser. No. 12/908,061 and is presented to make any claims different from said earlier application. 
     While some of the waste products from the burning of fossil fuels and biomass can be recovered or recycled, most are disposed of in landfill. This type of disposal is wasteful and in itself potentially polluting, clearly not an environmentally friendly or economical way to proceed. Various government agencies have now put laws into effect that make certain forms of this type of disposal illegal which can result in substantial fines. 
     SUMMARY OF THE INVENTION 
     The present invention describes an apparatus and method for pre-processing coal and biomass that save energy in the chemical looping combustion process. Specifically, the pre-processing kiln is attached to a water cleanup station to capture the water vapor that is released near the proximal end of the kiln. A wet scrubber is attached near the distal end of the kiln to capture pollutants and certain hydrocarbons prior to combustion. The removal of both the water vapor and the pollutants greatly reduces the cost and increases the efficiency of the chemical looping process while preserving the integrity of the oxygen carrier. Means for sizing the coal and biomass also aids in the efficiency of the combustion reaction. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a flow diagram illustrating the successive steps required for pre-processing of biomass and coal to be brought to a clean and near contaminant-free condition for efficient chemical looping combustion. 
         FIG. 2  is a block diagram illustrating the components of the invention and their interconnections to bring the raw coal and or biomass into a state essentially free of water vapor and pollutants for subsequent efficient chemical looping combustion. 
         FIG. 3  illustrates a biomass sizing tool consisting of a biomass cutting/shredding device, designed to bring the biomass into a desired shape or volume for further efficient processing. A side and cross sectional end view are shown. 
         FIG. 4  is a sketch of the coal sizing tool for crushing coal, the device takes feedstock coal and crushes it to the desired shape or volume for subsequent efficient processing prior to gasification. Both a side and cross sectional end view are shown. 
         FIG. 5  a show a side view of the kiln used for pre-processing the coal and bio fuels prior to chemical looping combustion.  FIG. 5   b  shows a part of the kiln in cross section along with a motor drive to provide rotation of the kiln during pre-processing of the coal and biomass. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention describes a system and method for pre-processing coal and biomass prior to further use in combustion by chemical looping of an oxygen carrier. The basic components utilize, a source of coal and biomass that brings the coal to a desired size using a first sizing tool for reducing the coal to maximize efficiency, a second sizing tool to cut or shred the biomass to the optimum size for operation in the a kiln. The main objective is to remove as much water and other contaminants in the kiln prior to the step of conversion of the kiln contents. The kiln is one that has an outer shell and an inner core concentrically positioned within the outer shell, the inner core free to rotate within the outer shell. The kiln temperature is controlled by way of master control module which also controls the speed of rotation of the inner kiln core, receives signals from the thermal sensors within the kiln and regulates the oscillatory motion of the two sizing tools which operate by way of motors that causes and up and down motion of a first piston, with a perforated block to crush the coal, second piston attached to cutting blades to shred the biomass and, each crushed and shredded to their desired respective sizes. The thermal signals also are used to regulate the temperature of the kiln by way of heater coils affixed to the outer surface of the kiln outer shell. 
     The sized coal and biomass are directed to a hopper by way of a chute from each sizing tool, where the hopper is affixed to the proximal end of the kiln and where the proximal end has an airlock attached to the kiln inner shell so that the coal and biomass can enter the kiln without admitting oxygen to the kiln. On heating of the coal and/or biomass, water vapor is emitted and drawn off to a water cleanup station by way of a duct extending from near the kiln&#39;s proximal end. A duct is positioned near the distal end of the kiln, to evacuate gaseous contaminants such as Cl, Hg, S, Se, and As and some hydrocarbons into an activated charcoal filter or a wet scrubber which separates and sequesters the contaminants for future use or safe disposal. Any useful hydrocarbons that evolve can also be sequestered separately for further use. 
     Typically the master control unit controls the kiln temperature in order to maintain the proximal end of the kiln in the range 125-200 C, the distal end in the range 450-500 C. The sized coal and biomass enter the kiln&#39;s proximal end though the airlock; are heated without combusting, and exit the kiln at the distal end at the higher temperature with the help of a screw drive. The solid contents of the kiln are moved from proximal to distal end by way of a helical steel rail firmly affixed to the inner surface of the kiln core upon rotation of the kiln core. 
     The coal-sizing tool comprises a first container with one open end with a chute at the opposite end through which the coal exits after sizing. A centrally located first piston, has one end within the container connected to a perforated block, with the opposite end located exterior to the sizing tool container. The exterior part of the piston is connected to a first motor to cause the piston to undergo vertical oscillatory motion, by crushing the coal within the container to the desired size. The size will be determined by the rate of oscillation and the impact produced by the crusher. The coal moves from the proximal to the distal ends of the sizing tool by way of a first conveyor belt positioned at the bottom of the sizing tool container. The preferred volume of the exiting coal is in the range of 0.25-10 cm 3 . 
     The biomass-sizing tool comprises a second container, open at its front end with a chute attached to the opposite open end through which the biomass exits. The motion from front (proximal) to distal ends makes use of a second conveyor belt located at the bottom of the sizing tool. A second piston extends into the container with a block attached to the piston and a set of blades attached to the block. The opposite end of the piston extends outside of the container and is driven by a second motor to provide vertical oscillatory motion to the piston and thereby to the blades to produce cutting of the biomass to a preferred size, preferably in the range of 0.25-40 cm 3 . 
     The important novelty of the present invention is to provide a system that receives pre-processed coal and or/biomass for further oxidation or gasification where the pre-processing eliminates most water vapor from the coal and biomass as well as the contaminants. This pre-processing results in a more efficient, cost saving way to combust coal and biomass where the coal and biomass exit the kiln as a pre-heated char, substantially free of pollutants that would otherwise be more costly to remove during or after the combustion via chemical looping combustion. 
     The Invention can be further understood by referring by referring to  FIG. 1  where  100  describes the steps of the process invention in conjunction with  FIG. 2  which indicates the block diagram in  200 . The start of the process is described in  FIG. 1  and starts at  1001 . This is followed by the loading  101  of coal, the loading  102  of biomass, each into their respective sizing tools to provide the desired sizes of each. The coal is crushed  103  and the biomass is cut or shredded  104 . Biomass and coal are collected  105  in collection hopper  105  to be heated in heated kiln  106 . Kiln heating of the coal and biomass results in the emanation of vapor and contaminants that are released from the coal and biomass in the kiln. Cleaning of the water vapor  108  from the kiln occurs in a water clean-up station while the other contaminants are introduced to an activated charcoal filter or wet scrubber and separated in step  107 . Steam is generated in step  111  from the hot water vapor and recycled for other utilization. The chemical looping combustion process  112  is thus protected from contamination. Some valuable hydrocarbons initially mixed with the contaminants are released  109  from the wet scrubber and directed to be further combusted via chemical looping combustion at  112 . Kiln heat also results in char formed from the hot coal as well as hot biomass, both of which are released in step  110  from the kiln and then further released to be combusted via chemical looping combustion  112 . 
     The steps indicated in  100  are further clarified the block diagram,  FIGS. 2. 201  and  202  show the initiating steps of available coal and biomass respectively. Coal  201  is fed into sizing tool  204  for obtaining a desired size of coal while biomass  202  is directed into biomass sizing tool  203 . The contents of  203  and  204  are directed into hopper  212  by way of separate conveyor belts within sizing tools  204  and  203  (not shown here). Hopper  212  is fixedly attached to kiln  207  where the water vapor developed in the heated kiln near the kiln&#39;s proximal end is directed to a water clean-up station  205 . Contaminants that are given off in heated kiln  207  are drawn off near the distal end of kiln  207  and directed to a wet scrubber that separates and sequesters contaminants from useful hydrocarbons of the type CxHy and directs them to a tank  208 . Subsequently the contents of  208  are directed into combustor  211 . The fully pre-process heated contents of kiln  207 , consisting of heated biomass and char are emptied into container  210  and then sent by a conveyor belt to a chemical looping combustion chamber  211 . The hydrocarbon contents of  208  are also directed into a chemical looping combustion reactor  211 . 
       FIG. 3  illustrates the biomass sizing tool or sizer  203  shown here in a side view (a). The side view, shows a portion of piston  301  exterior to the sizing tool container  306 , where exterior portion of piston  301  is connected to a motor (not shown) to cause  301  to move in an oscillatory motion with the lower part of piston  301  extending into the interior of container  306  and rigidly attached to block  302 . Block  302  is in turn fixedly attached to cutting blades  303 . A conveyor belt  304  moves the biomass from the proximal to the distal end of sizing tool  203 . The distal end of 203 is attached to chute  305  for emptying the contents of the sized biomass to hopper  212  shown in  FIG. 2 . 
       FIG. 3  shows the cross sectional view (b) of the biomass sizing tool or sizer  203  with piston  301 , block  302 , blade  303  and belt  304 . The double headed arrow indicates the up and down oscillatory motion of piston  301 . 
       FIG. 4  indicated by  400  shows details of coal sizing tool  204 . The side view is shown in a) of  FIG. 4 . A portion of piston  401  is shown outside of coal sizing tool container  406  while a portion of piston  401  extends into the interior of container  406 . The end of piston  401  extending into container  406  is attached to block  402  and block  402  is attached to a crusher  403 . A conveyor belt  404  moves the crushed coal from the proximal to the distal end of container  406 . The distal end of  406  empties the crushed coal by way of a chute  405 . The vertical arrows indicate the oscillatory motion of piston  401 . A cross sectional end view of the coal sizing tool is shown in b) of  FIG. 4  with piston  401 , block  402  and crusher  403  as well as conveyor belt  404 . 
       FIG. 5   a  in  500  shows details in a side view of kiln  207 , water cleanup station  205  and wet scrubber  206 . Kiln  207  consists of an outer shell  501  and has a concentrically mounted, rotatable inner core  502 . Kiln shell  501  has heater coils  506  wrapped around its outer surface. Heat sensors  507  are mounted in the annular space between inner core  502  and outer shell  501 . Kiln rotation mechanism  503  is further described in  FIG. 5   b . In  FIG. 5   a  an airlock  505  mounted at the proximal end of shell  501  admits the contents of coal and biomass in hopper  504 . Airlock  505  and char ejection screw drive  509  prevents air (oxygen) from entering kiln core  502  so that the kiln is anaerobic and can be heated above the temperature of ignition of the resident coal and biomass without combustion. A helical steel rail  508  mounted onto the inner surface of kiln core  502  causes the contents of kiln core  502  to move from proximal to distal ends upon rotation of kiln core  502 . Char ejection screw drive  509  is mounted at the distal end of inner kiln shell  501  serving to discharge the pre-processed coal and biomass from kiln core  502  for delivery to the chemical looping combustor  211 . Open flange  511  at the proximal end of kiln shell  501  connects kiln shell  501  and kiln core  502  to hopper  504  in conjunction with airlock  505 . At the distal end, flange  510  fixedly attached to outer shell  501  and outer shell  501  to eject the solid contents of kiln core  501 . Duct  514  connects the proximal end of the kiln shell  501  for drawing off water vapor to the clean-up water station  205  (shown in  FIG. 2 ), while duct  515  connects the distal end of kiln  501  to the wet scrubber for separation of contaminants from the hydrocarbon output  208  of wet scrubber  206  that goes to chemical looping reactor  211 . 
       FIG. 5   b  shows a cross section of the kiln rotation mechanism  503 . Gear  516  is attached to a motor (not shown) and engages gear  513  that is fixedly attached to the outer circumference of kiln inner core  502 . 
     Given this disclosure it will become apparent to one skilled in the art that alternative equivalent embodiments are possible such as the wet scrubber  206  can be replaced by activated charcoal filters. 
     These equivalent embodiments are also within the contemplation of the inventors.