Abstract:
The invention provides an apparatus that thermally processes solid waste such as municipal solid waste to generate heat for production of steam that is employed to generate electrical power. The apparatus provides clean efficient gasification of refuse derived fuel to minimize air pollutants such as nitrogen oxides and uses released thermal energy to produce steam for electricity. Carbon in the solid waste is converted to synthesis gas or syngas that is combusted to generate steam or electricity. The apparatus recovers energy from residual carbon that is normally rejected by air fed gasifiers and partially recycles the flue gas to control combustion temperature and oxygen content in the fuel gas burner. The apparatus extends boiler service life by reducing the temperature of hot gases entering the boiler and produces clean electrical energy from materials that otherwise would be discarded as environmentally damaging waste.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Pat. No. 9,284,219 issued on Mar. 15, 2016, the complete disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to an apparatus that produces thermal or electrical energy from a variety of carbonaceous solid waste materials. The invention relates to the production of supplemental cementitious material (SCM) from high carbon coal fly ash, wherein carbon in the fly ash and coal is thermally processed to produce synthesis or combustion gas. More particularly, the present invention relates to the production of SCM from high carbon coal fly ash, wherein carbon in the fly ash and coal is thermally processed to produce synthesis or combustion gas for generating steam to produce electrical power and wherein oxides are added to the thermal process to form cementitious materials having desired properties. 
       BACKGROUND OF THE INVENTION 
       [0003]    Coal fly ash (CFA) is a solid particulate by-product of coal combustion that can be removed from the flue gas stream by cyclonic separation, electrostatic precipitation and bag house filtration. CFA may contain environmental toxins, such as arsenic, beryllium, boron, cadmium, chromium VI, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, vanadium, among other environmental toxins. In the past, coal fly ash was released into the atmosphere as a result of inadequate particulate removal from coal combustion flue gasses. 
         [0004]    Coal-fired power plants now employ methods for capturing the CFA from the flue gas stream using various techniques, including cyclonic separation, flue gas desulferization units, electrostatic precipitation, and/or bag house filtration, among other techniques. The CFA is generally stored proximate to the coal power plants in wet or dry impoundments. Alternatively, the CFA is disposed in landfills. Under appropriate conditions, it is known to use the CFA as a supplemental cementitious material (SCM) in concrete mixes. The CFA includes pozzolanic materials, such as ceramic spheres (mainly silica and alumina). When used in concrete mixes, the pozzolanic materials can enhance the long term quality, durability, and compressive strength of the resulting concrete. 
         [0005]    In addition to the toxic components of CFA described above, coal-fired power plants generate sulfur and nitrogen oxide (SOx and NOx) emissions. If released into the environment, these oxides form weak acids upon contact with surface waters or precipitation. Power plant operators often use activated carbon to absorb SOx and NOx, as well as other acid gasses and toxic pollutants such as mercury, thus reducing harmful emissions in the flue gas stream. 
         [0006]    The activated carbon used to absorb these pollutants increases the overall carbon content of the solid particulate material, including CFA that is recovered from the flue gas. Federal regulations prohibit using the CFA in cement and/or concrete mixes if the carbon content exceeds approximately 6%, as determined by loss of weight upon ignition (&gt;6% LOI). 
         [0007]    One reason that the high carbon CFA cannot be used in concrete is that the carbon interferes with air entrainment (the intentional creation of tiny air bubbles in concrete), introduced to increase the durability of hardened concrete. Thus, the activated carbon used to clean the flue gas may render the recovered CFA unusable as supplemental cementitious material. This, in turn, can result in more CFA being stored at dry landfills or in wet slurry impoundments. 
         [0008]    Accumulations of coal fly ash and associated bottom ash and boiler slags in landfills and wet impoundments constitute a major environmental hazard. These impoundments can fail, causing billions of dollars of damage in the process. In addition, toxic components of the CFA may leach into ground water when the CFA is stored in unlined impoundments. The ponds and impoundments where much of the CFA is stored by the operators of coal fed power plants are an increasing environmental concern. The Environmental Protection Agency has proposed rules to require that CFA not used in concrete be stored in lined landfills or other approved sites. Enforcement of the rules could greatly increase the cost of CFA disposal, thereby increasing the cost of energy generated from coal. 
         [0009]    Gasification is a process wherein organic carbonaceous (mainly organic) materials are dissociated at high temperatures in an oxygen-starved environment to form a gas known as synthesis gas, or syngas, or producer gas. The syngas includes mainly carbon dioxide, carbon monoxide, hydrogen, methane and water vapor, as well as trace amounts of sulfur and other oxides. 
         [0010]    If the thermal reactor is operated as a gasifier and is air fed (as opposed to oxygen fed only), the syngas stream also contains nitrogen gas. This latter form of syngas, which includes di-molecular nitrogen in relatively large quantities, is more specifically referred to as producer gas. However, according to common usage of terms, the gas phase product from the thermal reactor will be referred to as syngas throughout this application. Gasification is an efficient and relatively clean method of converting organic materials to energy, as compared to combustion or incineration. 
         [0011]    The thermal reactor/gasifier is brought to operating conditions, including operating temperature, by combusting a suitable fuel source, such as natural gas or diesel fuel. The operating temperature is attained before the feed material is introduced into the gasifier. The air inflow rate, fuel moisture content, and fuel feed rates are tightly controlled to maintain the desired temperature and oxygen partial pressure for gasification to proceed efficiently. 
         [0012]    In this regard, additional air may be provided to the thermal reactor, which operates as a gasifier, to increase the amount of oxidation that occurs. Additional air may be used when converting some feedstocks. In some circumstances, it may be preferable to use the injected air to combust most or all of the produced syngas before it leaves the thermal reactor. Alternatively, the syngas may be combusted in a separated oxidation chamber or steam boiler, or in a boiler to which a furnace has been affixed. 
         [0013]    What is needed is an apparatus and method of reprocessing coal fly ash to recycle otherwise unusable high carbon CFA for use as an SCM. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention advantageously provides apparatuses and methods of reprocessing coal fly ash (CFA) to produce cementitious materials having desired properties, such as pozzolanic or hydraulic reactivity, or both. According to one embodiment, the present invention uses thermal treatment to remove carbon from high carbon coal fly ash. The carbon in the fly ash can gasified to form a syngas that may be used to fire a boiler, which generates steam to drive a turbine generator to produce electricity. The high carbon fly ash waste can be gasified or combusted in a fluidized thermal reactor, depending on the characteristics of the feedstock material and the ancillary fuel used. This waste to energy process is referred to as the “ash to energy and cement” (“ATEC”) process. 
         [0015]    The present invention further provides methods and apparatus for making hydraulically active cementitious material that imparts additional compressive strength to the resulting concrete, when used as a partial substitute for portland cement in concrete mixes. 
         [0016]    Excess carbon in the CFA may result from incomplete combustion of coal, use of activated carbon in the flue gas clean-up train, or other factors. CFA composition commonly includes oxides of calcium, silicon, aluminum, iron and magnesium, as found in hydraulic cement. However, these elemental constituents, especially calcium, are generally not found in coal fly ash, or in other coal combustion products, such as bottom ash or slag, in the relative concentrations appropriate for the production of hydraulic cement or hydraulically reactive SCM. 
         [0017]    It will be clear to one skilled in the art that for each different type of CFA to be reprocessed, specific formulation and reprocessing methods are employed based on at least the initial CFA properties, the desired SCM type, the CFA rough classification (C or F), the fixed carbon content, the moisture content, the elemental composition, the calcium oxide content, the silicon oxide content, the alumina content, and the alkali content, among other properties. 
         [0018]    The present invention can be used to re-process both fresh and stored CFA, whether dry or ponded (wet). The present invention provides several economic and environmental advantages for long term storage or disposal of CFA as compared to current practices, as well as to other methods of removing carbon from high carbon fly ash. As described below, the SCM produced from high carbon fly ash according to the present invention can enhance the early compressive strength of concrete and can be used as an additive in high strength concrete. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0019]    A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following description when considered in conjunction with the accompanying drawings wherein: 
           [0020]      FIG. 1  illustrates a system schematic diagram illustrating the overall ash to energy and cement (ATEC) process, according to one embodiment of the present invention; 
           [0021]      FIG. 2  illustrates a system diagram illustrating the overall ash to energy and cement (ATEC) process, according to a second embodiment of the present invention; 
           [0022]      FIG. 3  illustrates a rotating kiln, kiln feed, and SCM nodule quench elements of the present invention. 
           [0023]      FIG. 4  illustrates an electron micrograph image of high carbon fly ash, showing the readily distinguishable carbon particles and ceramic spheres (cenospheres); 
           [0024]      FIG. 5  illustrates an electron micrograph image and elemental composition table for Portland cement and reprocessed high carbon ash according to one embodiment of the present invention; and 
           [0025]      FIG. 6  illustrates a chart of compressive strength for Portland cement and cement formed from reprocessed fly ash mixture, based on a number of cement curing days. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0026]    As an initial matter, while certain embodiments are discussed in the context of well-known cement mixtures, which are hereby incorporated by reference, the invention is not limited in this regard and may be applicable to any cement mixtures. The present invention provides a method and an apparatus for reprocessing CFA, and especially high carbon CFA, using a thermal process that produces hot synthesis gas, combustion gas and flue gas. 
         [0027]    One of ordinary skill in the art will readily appreciate that CFA compositions vary widely. Generally, Class C CFA materials have relatively higher calcium oxide content and are more likely to exhibit cementitious reactivity prior to thermal reprocessing. By contrast, Class F CFAs typically have relatively higher silicon oxide content and are more likely to yield pozzolanic SCM materials. As described below in detail, practice of the invention entails the adjustment of process conditions depending on the CFA type. 
         [0028]    Referring now to the drawing figures,  FIG. 1  illustrates an exemplary coal fly ash re-processing and beneficiation structure  100  provided in accordance with principles of the present invention. When the thermal reactor  104  is operated in a gasification mode, ancillary carbonaceous materials may be added to the thermal reactor  104  during the thermal treatment process in order to increase the quality and quantity of produced syngas  106 . Water may be introduced into the feedstock in the form of moisture or supplemental steam in order to increase the hydrogen content of the syngas  106 . One of ordinary skill will readily appreciate that other forms of water may be used. Increasing the hydrogen content of the syngas  106  increases the calorific value of the syngas  106 . 
         [0029]    Inorganic oxides, such as bed material  103 , may be introduced into the thermal reactor  104  to achieve a desired cementitious material product. Depending on properties of the starting materials and on selected process parameters, the product material may exhibit various characteristics, including pozzolanic characteristics or hydraulic cementitious reactivity. According to one embodiment of the present invention, the resulting synthesis (syngas) gas  106  or combustion gas may be used to generate steam for powering a turbine  123  or for powering another electrical energy source  124 . 
         [0030]    A source of unprocessed or raw CFA  101  may be obtained from dry landfills or wet impoundments, among other sources. The raw CFA  101  may be stored in a silo or hopper prior to being processed. Ancillary fuel  102 , which also may be stored in a silo or hopper prior to introduction into the thermal reactor  104 , may include coal, shredded tires, waste oil, waste coal, or other high BTU materials. 
         [0031]    The bed materials  103  may be used to produce hydraulically active cementitious material from CFA  101 . The bed materials  103  may include limestone or other materials with sufficient calcium oxide content. For example, sand, coal combustion bottom ash and properly sized boiler slag all can be used as bed material  103 , which serves the function of distributing and transferring heat in the thermal reactor  104  when the thermal reactor  104  is operated in fluidized bed mode. Crushed limestone is a preferred component of the bed material  103 . As show more specifically in  FIG. 2 , the CFA  101 , ancillary fuel  102  and bed material  103  may be stored in containers, such as hoppers or silos, in preparation for processing. 
         [0032]    Coal fly ash  101 , ancillary fuel  102 , and bed materials  103  may be introduced into the thermal reactor  104  by suitable mechanical devices, such as an auger or other mechanical device. The materials entering the thermal reactor  104  are selected according to the properties of the CFA  101  and the desired characteristics of the resulting cementitious product  116 . 
         [0033]    The thermal reactor  104  produces a gas stream, including a fuel rich hot syngas or a mostly oxidized syngas  106 , depending on the operating conditions of the thermal reactor  104 . The syngas  106  exiting the thermal reactor  104  may include entrained solid particles that may be removed by the cyclone  107 . Solid particles  108  removed from the overhead syngas  106  stream may be sent to the kiln  109  for further processing. A portion of clean syngas  111  may be routed to the kiln  109  to be used as a kiln fuel. 
         [0034]    In embodiment where the thermal reactor  104  is configured to operate as a gasifier, a portion of the clean syngas  117  may be diverted and mixed with air  130  that is introduced into an oxidizer  118  to produce hot gases  119  for heating a steam boiler  120 . Steam  122  from the boiler  120  is used to drive a gas turbine  123 , which in turn drives an electrical generator  124  to produce electric power  125  for sale to the grid. 
         [0035]    The thermal reactor  104  produces ash  110  having a desired elemental and oxide composition that is conveyed to the rotating kiln  109 . The ash  110  is heated to sufficient temperature to form clinker or nodules  112 . For example, the ash  110  may be heated to a range of between 1300° and 1500° C. The clinker or nodules  112  may be cooled and ground or milled to make hydraulically reactive or pozzolanic cementitious material. The hot clinker or nodules  112  leaving the kiln  109  are cooled in quench chamber  113  by a counter current air stream from an air source  105 , for example. The warm air produced by the quench chamber may be used as feed air the thermal reactor  104 . The feed air may be used to fluidize the bed material  103  within the thermal reactor  104 . The cooled clinker material  112  may be blended in the blender/grinder  114  with additives  115  and may be ground to a desired particle size in the blender/grinder  114  to produce a hydraulically or pozzolanically reactive cementitious material  116 . 
         [0036]    The clean syngas  111  extracted from the cyclone  107  may be used to fire the rotating chamber of kiln  109 . The hot gas from the rotating kiln exhaust  121  is directed to the boiler  120 , where the thermal energy content is used to help generate steam  122 . Flue gas  126  from the boiler  120  is sent through the gas clean up train  127  before being released through a suitable stack as flue gas  128 . 
         [0037]      FIG. 2  illustrates a second exemplary coal fly ash re-processing and beneficiation structure  200  according to principles of the present invention. Ash re-processing and beneficiation structure  200  generates synthesis gas  206  that fires a boiler  220  to produce steam for driving a steam turbine  223  that generates electricity. 
         [0038]    According to one embodiment, coal fly ash  201  is stored in a silo or hopper that provides fresh or stored CFA  201  to an air classifier  229  or other suitable device for separating high carbon fly ash fraction from a low carbon fly ash fraction. One of ordinary skill in the art will readily appreciate that CFA compositions vary widely, and that some CFA materials will be suitable for size separation to generate high carbon content and low carbon content fractions, while other CFA materials will not be suitable for such separation. 
         [0039]    In the case where size separation is possible, fly ash source  201  may be coupled to an air classifier or particle size separation unit  229  that separates CFA particles based on particle size and density criteria, among other criteria. For example, the air classifier  229  separates high carbon fraction coal fly ash (generally smaller particles) from low carbon fraction coal fly ash (generally comprised of larger diameter particles). One of ordinary skill in the art will readily appreciate that various techniques, such as electrostatic separation or other techniques, may be employed to separate the high carbon fraction coal fly ash from the low carbon fraction coal fly ash. 
         [0040]    An ancillary fuel hopper  233  may be provided to store fuel from an ancillary fuel source  202 . The fuel may include pulverized coal, shredded tires, or mixtures of these or other high BTU materials. Alternatively, the ancillary fuel hopper  233  may store other fuel sources. The air classifier  229  and bed material source  203  may deliver the high carbon CFA fraction and ancillary fuel mixture  231  to a mixing hopper  232 . 
         [0041]    A first SCM product  230  may include cementitious materials, such as pozzolanic supplementary cementitious material, removed from the feed CFA material  201 . The air classifier  229  need not be used when the carbon content of the CFA  201  is sufficiently high or the CFA  201  is not amenable to separation of high carbon and low carbon fractions by air classification. If needed, a pelletizer (not shown) may be used to consolidate the CFA  201  and/or ancillary fuel  202  prior to introduction into the thermal reactor  204 . 
         [0042]    The mixing hopper  233  may deliver a mixture of pulverized fuel source to the thermal reactor  204  in a metered manner at a rate so as to maintain the desired temperature in the thermal reactor  204  for allowing gasification and/or full combustion reactions to proceed. In the embodiment depicted in  FIG. 2 , the thermal reactor  204  operates as a gasifier and maintains a temperature in the range of 800 to 1200° C. 
         [0043]    The mixing hopper  232  is provided to mix high carbon CFA fractions  231 , and bed material  203 , including calcium oxides, silicon oxides, iron oxides, and aluminum oxides or other materials. The mixing hopper  232  delivers the mixed materials to the thermal reactor/gasifier  204  using a suitable delivery device, such as an auger screw feed. The mixing hopper  232  may include structures that blend or mix the components therein, including the high carbon fraction CFA  101 , among other components. Ancillary fuel  202  fed from hopper  233  may be pelletized, if needed. As desired, ancillary fuel  202  from the ancillary fuel hopper  233  may be delivered to the thermal reactor  204 . 
         [0044]    In the embodiment illustrated in  FIG. 2 , the thermal reactor  204  may be coupled directly or indirectly to a bed material source  203  that feeds inorganic oxide materials to the thermal reactor  204 . The inorganic oxide materials may include limestone, coal combustor bottom ash, silica sand, silica fume, or other inorganic oxide materials. The bed material  203  helps distribute heat when a bed within the thermal reactor  204  is fluidized. The bed material  203  also may participate in the formation of calcium silicates and other cementitious components in the thermal reactor  204  or kiln  209 . 
         [0045]    The thermal reactor  204 , which operates as a gasifier in this embodiment, may be coupled to an ambient air source  205  that provides pressurized ambient air during the gasification process via an air pump  234 . The pressurized ambient air may be preheated in the kiln quench unit  213  and introduced to the thermal reactor  204  to maintain an oxygen partial pressure and/or to fluidize the bedding material within the thermal reactor  204 . 
         [0046]    The CFA source  201  and the bed material source  203  introduce CFA and calcium rich components, such as crushed limestone, lime, or other materials, into the thermal reactor  204 , along with liquid or solid ancillary fuel materials, such as coal. According to one embodiment, the CFA and calcium rich components are heated in the thermal reactor  204  to temperatures of 1,000 degrees C. or greater, causing the formation of synthesis gas. The synthesis gas includes mainly nitrogen, carbon dioxide, carbon monoxide, hydrogen, and methane, water vapor and other volatile components. During the gasification process, the carbon and hydrogen in the coal and the CFA or other ancillary fuel is converted into synthesis gas  206 . 
         [0047]    Water may be introduced into the thermal reactor  204  in the form of moisture that is included in the ancillary feed or a separate steam injection, among other sources, to enhance the hydrogen content of the syngas  206 . The hydrogen results from the water/gas shift and other known gasification reactions that proceed in a reducing atmosphere at high temperatures and in the presence of known catalysts. 
         [0048]    A conduit is coupled to the thermal reactor  204  to extract the synthesis gas  206 , which may include entrained solid particles. The synthesis gas  206  is directed to a cyclone  207  that removes particulate matter  208  from the synthesis gas  206 . Clean syngas  217  exits the cyclone  207  and enters the oxidizer chamber  218 , where air  238  from pump  239  is injected to promote combustion. The oxidizer chamber  218  increases the temperature of the clean syngas and air mixture before the mixture is delivered to the boiler  220 . The particulate matter  208  may be directed to the kiln  209 . 
         [0049]    Combustion of the clean syngas  217  produces hot gas that enters a final re-oxidation unit or burner  241 , where additional air from pump  240  is used to complete the combustion process. Hot combustion gases  219  exiting the final re-oxidation unit or burner  241  enter the boiler  220 . The boiler  220  produces steam  222  that is directed to a steam turbine  223 , which can be a multi-stage turbine incorporating both back pressure and condensing stages. Other turbine configurations may be used. The steam turbine  223  can drive an electrical generator  224  that produces electrical power  225 , which can be conveyed to a power grid (not shown) for sale and distribution. 
         [0050]    A condenser  243  may be coupled to the steam turbine  223  for condensing to water the low pressure steam  242  exiting the steam turbine  233 . A cooling tower  245  may be provided to dissipate heat from the steam using a heat exchanger and evaporator in which a heat exchange fluid is circulated. The heat exchange fluid is typically water  246 ,  247 . The low pressure steam cooling device  245  is provided when a condensing turbine stage is not used. A water conditioner (not shown) may be provided to condition condensate water  244  before the condensate water  244  is returned to the boiler  220 . Additional feed water  255  and boiler circulating feed water may be provided to a water conditioning unit  254  as needed to maintain boiler water quality. 
         [0051]    Flue gas  226  exiting the boiler  220  may be cleaned before being released. Flue gas clean-up components may include a flue gas desulfurization unit  227 , an electrostatic precipitator  248 , and a bag house  249  with carbon or lime injection, or both. Particulate materials recovered from these flue gas clean-up units  227 ,  248  and  249  can be recycled to the thermal reactor  204 . The clean flue  251  gas is pressurized by a pump  252  and released through a stack  253 . The flue gas clean-up train may include process units as needed. Commonly the flue gas clean up train includes at least a bag house  249  to remove the particulate from the flue gas stream. Bag house particulate matter  250  may be recycled to the thermal reactor or gasifier  204 . 
         [0052]    In the present embodiment, the thermal reactor  204  delivers inorganic solids, such as spent bed material  203 , inorganic ash and bottom ash  210 , among other solids, to the kiln  209 . Alternatively, the inorganic ash and bottom ash  210  may be captured without further processing in the kiln  209 . The kiln  209  is described in more detail in  FIG. 3 . According to one embodiment, the kiln  209  may be a rotating kiln that is fired or heated using clean synthesis gas  217 , coal or other fuel. 
         [0053]    The ash  210 , which includes CFA inorganic components, calcium oxides, and other inorganic and oxide materials, is removed from the thermal reactor  204  after gasification. This heated ash  210  becomes inorganic ash or vitreous frit material depending on the temperature attained in the thermal reactor  204 . The heated bottom ash  210 , together with the ash  208  from the cyclone, is heated and mixed further in the kiln  209  to form partially fused material, such as nodules or clinker  212 . Inorganic ash may also be entrained in the syngas leaving the reactor  104 . This inorganic ash  208  is subsequently separated from the syngas by the cyclone  107 . Clinker  212  is a solid material produced by the thermal reactor  204  and/or kiln  209  that is partially fused (mainly in the kiln  209 ) to from lumps or nodules  212 . These nodules  212  exit the kiln and are cooled in the quench unit  213 . The quench unit  213  produces cooled nodules or clinker particles  235  that are stored in a hopper  236 . 
         [0054]    The rotary kiln  209  may also receive particulate material  208  from the cyclone  207  and hot bottom ash  210  from the thermal reactor  204  as feeds. The clean syngas  217  can be used as fuel for various devices. Coal or other suitable fuel also may be used to fire the rotary kiln  209 . Hot exhaust gas  221  exiting the kiln  209  may be routed to the boiler  220  to produce steam  224 . 
         [0055]    Any inorganic material introduced by the bed material source  203 , or that remains from the gasification of the coal or ancillary fuel, may produce oxides that are removed from the thermal reactor  204  to the kiln  209  through incorporation of the oxides in the nodule or clinker  212  produced in a kiln  209 . The low carbon inorganic bottom ash  210  product resulting from the gasification of the inorganic material includes calcium, silicon, aluminum, and iron oxides, among other products present in approximately the same ratios as in ordinary portland cement (see Table 1 below). After carbon burn-out and partial formation of calcium silicates, the low carbon inorganic bottom ash  210  product may be recovered as a low carbon cementitious material product or processed further in the rotating kiln  209 . 
         [0056]    The nodules or clinker  235  may be processed to yield a reactive SCM with hydraulic or pozzolanic cementitious characteristics. The partially fused material and clinker  237  exiting the hopper  236  can be subsequently ground to a suitable particle size in grinder  214  for use as a cementitious material or hydraulic cement  216 . 
         [0057]    Further processing may include addition and mixing of additive materials  215  such as gypsum, powdered limestone, or other materials. In the present embodiment, the product is hydraulic cement  216 . In this and other embodiments, the reactive cementitious material product may be further ground and mixed with clean pozzolanic materials, such low carbon coal fly ash, to form the final cementitious material  216 . 
         [0058]      FIG. 3  illustrates an exemplary kiln unit structure  300  of a coal fly ash re-processing and beneficiation structure according to principles of the present invention. The kiln unit  300  includes a rotating refractory-lined kiln drum or chamber  312 , a drive mechanism  305  and quench chamber  313 . The kiln rotating chamber  312  receives the hot bottom ash material  301  from the thermal reactor (not shown) using an auger  302  or other suitable device that limits the backflow of hot gas  329  from the kiln unit  300  into the thermal reactor  204 . The kiln refractory lined drum or chamber  312  is heated by a burner  306  that uses syngas, pulverized coal or other fuel  325 . Hot combustion gases  329  exit the rotating kiln  312  through exhaust port  303  and can be directed to a cyclone (not shown) or directly to a boiler (not shown) for generation of steam. 
         [0059]    Ambient air  308  and/or pre-heated air  309  are admitted to the kiln chamber  312  under slight pressure to allow partial combustion of the fuel  235 . The temperature gradient in the refractory  304  lined rotating kiln chamber  312  is such that the bottom ash  301  material entering the kiln  312  is increased to approximately 1450 degrees C. before exiting the rotating portion of the kiln  312  into the receiver portion  317  of the kiln. 
         [0060]    A lock mechanism  310  allows the hot clinker to enter the quench chamber  313  by force of gravity. The quench chamber  313  is isolated from the receiver portion  317  by the lock mechanism  310 . The quench chamber  313  includes a set of baffles  320  that direct a countercurrent of air  308  produced by air pump  311  over the nodules as they descend to the grate hopper  314 . A portion of the pre-heated air  316  may be pumped to the thermal reactor/gasifier (not shown) via air pump  315 . A portion of the pre-heated air  316  may be routed to the kiln  312  via air pump  307 . A grate hopper  314  may be coupled to the kiln quench chamber  313  to receive and further cool the clinker or nodules. The quench chamber  313  may deliver the clinker or nodules to the hopper  314  for further cooling and storage prior to further processing. 
       Formulations and Products of the Present Invention 
       [0061]    It will be clear to one ordinarily skilled in the art that the variety in the types and composition of CFA, and the desire for specific characteristics of SCM and cementitious materials, results in the adjustment of the method and apparatus of the present invention to account for these various conditions, compositions and end product requirements. As an illustration of the variety of CFA and other coal combustion products that can be used as feed stocks and bed materials in the process of the present invention, Table 1 below lists oxide compositions for Portland cement, as well as typical Class C and Class F fly ash materials and bottom ash from the combustion of a bituminous coal. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Typical oxide compositions for bottom ash and Class F and Class C coal fly ash. 
               
             
          
           
               
                   
                 Coal Combustion Products (Typical) 
               
             
          
           
               
                 Portland Cement 
                 Class C 
                 Class F 
                 Bituminous 
                   
               
             
          
           
               
                   
                   
                 Common 
                 Weight 
                 Fly Ash 
                 Fly Ash 
                 Bottom Ash 
                   
               
               
                 Oxide 
                 Shorthand 
                 Name 
                 Percent 
                 Wt % 
                 Wt % 
                 Wt % 
                 Oxide 
               
               
                   
               
               
                 CaO 
                 C 
                 lime 
                 64.7% 
                 22.3%  
                  1.5% 
                  1.2% 
                 CaO 
               
               
                 SiO 2   
                 S 
                 silica 
                  21.% 
                 36.3%  
                 56.8% 
                 51.0% 
                 SiO 2   
               
               
                 Al 2 O 3   
                 A 
                 alumina 
                  6.2% 
                 18.4%  
                   26% 
                 22.2% 
                 Al 2 O 3   
               
               
                 Fe 2 O 3   
                 F 
                 ferric oxide 
                  2.7% 
                 7.7% 
                  8.5% 
                 20.3% 
                 Fe 2 O 3   
               
               
                 MgO 
                 M 
                 magnesia 
                  2.6% 
                 4.6% 
                 0.96% 
                  0.8% 
                 MgO 
               
               
                 K 2 O 
                 K 
                 alkalis 
                 0.61% 
                 0.8% 
                  2.8% 
                 2.26% 
                 K 2 O 
               
               
                 Na 2 O 
                 N 
                 alkalis 
                 0.34% 
                 3.7% 
                 0.28% 
                 0.25% 
                 Na 2 O 
               
               
                 SO 3   
                 S 
                 sulfur dioxide 
                  2.0% 
                 2.7% 
                 0.27% 
                 0.23% 
                 SO 3   
               
               
                 CO 2   
                 C 
                 carbon dioxide 
                 na 
                 1.4% 
                  1.2% 
                  1.0% 
                 TiO 2   
               
               
                 H 2 O 
                 H 
                 water 
                 na 
                 1.2% 
                  0.4% 
                 0.35% 
                 P 2  O 5   
               
               
                   
                   
                   
                   
                  33% 
                   8% 
                 11.5% 
                 Carbon* 
               
               
                   
               
             
          
         
       
     
         [0062]    Each type of fly ash may result in specific formulations and reprocessing methods based on an initial Class C or Class F classification and fly ash content, among other factors. Fly ash characteristics may include fixed carbon content, carbon content, moisture content, elemental composition, calcium oxide content, silicon oxide content, alumina content, and alkali content, among other fly ash characteristics. 
         [0063]    For example, the CFA classification and content are used to select additive materials for both the thermal treatment process and kiln firing and grinding. According to one embodiment, the invention may produce resulting cementitious materials having early stage hydraulic reactivity characteristics or pozzolanic activity characteristics only. The invention may produce other types of resulting cementitious materials having enhanced commercial value as compared to raw, unprocessed material. 
         [0064]    According to one embodiment and referring to  FIG. 2 , the kiln  209  may be programmed to maintain a temperature above approximately 1,450° C. in order to form a phase of the calcium silicates that produces hydraulically reactive product cementitious materials. The reactions that proceed in the rotating kiln can also form oxides with calcium to silicon ratios for both tricalciumsilicate and dicalciumsilicate. 
         [0065]    According to one embodiment, the invention may be used to remediate Class F CFA taken from wet CFA storage impoundments. Prior to remediating the wet Class F coal fly ash by producing reactive SCM, the bulk elemental composition of the dried feed (moisture content less than 30%) may be adjusted to contain approximately 22% SiO 2 , 5% Fe 2 O 3 , 5% Al 2 O 3 , 2% MgO and 66% CaO by weight. For example, the required elemental composition (or oxide composition) ratio may be achieved by adding CaCO 3  and Fe 2 O 3  to the Class F fly ash and mixing the resulting feed mixture in the feedstock blender  232  or in the bed material source  203 . 
         [0066]      FIG. 4  is an electron micrograph of a high carbon Class C fly ash that, in this raw form, is unsuitable for use as an SCM in concrete mixtures. This micrograph is provided as a comparison with micrographs of the re-processed CFA according to the (ATEC) process of the present invention shown in  FIG. 5 . The  FIG. 4  micrograph shows the presence of carbon depicted as a large dark amorphous object in the center of the field. Also visible in the  FIG. 4  micrograph are the fly ash cenospheres depicted as hollow spherical ceramic objects of various sizes. Comparison with the micrographs and elemental composition of the processed material in  FIG. 5  show that the carbon and the cenosphere structure are both absent in the reprocessed material. The re-processed product material of the present invention has an appearance and overall elemental composition that is very close to that of hydraulic (portland) cement illustrated in  FIG. 5 . 
         [0067]      FIG. 5  illustrates an SEM image of Portland cement  501  and a measured average elemental composition  502  of Portland cement.  FIG. 5  further illustrates an SEM image of the ATEC hydraulically active cementitious product  504  and an elemental composition listing  503  of the ATEC hydraulically active cementitious product made from high carbon CFA subjected to ATEC processing. 
         [0068]    The ATEC hydraulically active cementitious product  504  exhibits hydraulic reactivity, as does the Portland cement. Elemental composition  503  of the ATEC hydraulically active cementitious product is similar to the elemental composition  502  of Portland cement. The ATEC cementitious material product may be cast to mortar samples without the addition of Portland cement. Furthermore, comparing the fly ash image shown in  FIG. 4  to that of the ATEC product  504  shown in  FIG. 5 , shows that the structure of the fly ash has been substantially changed by ATEC re-processing according to the present invention. For example, the cenospheres illustrated in  FIG. 4  are broken down and the carbon bodies shown in  FIG. 4  are absent in the SEM image of the ATEC hydraulically active cementitious product  504 . According to one embodiment, the ATEC cementitious product may provide a 50% substitute for Portland cement in a standard ASTM mix that generally includes 2.75 parts sand to 1 part Portland cement, with 0.4 parts of water by weight. This formulation yields highly workable and readily finished cement. 
         [0069]      FIG. 6  is a table that compares the compressive strength data of concrete having a mixture of the reprocessed fly ash compared to a sample of 100% Portland cement at 7 days and at 35 days after casting. The reprocessed fly ash (ATEC cementitious product) sample includes 20% fly ash replacement for the Portland cement that is normally used in an ASTM mixture as described above. The high relative strength of the fly ash mixture after both 7 and 35 days shows the hydraulic activity of the coal fly ash as re-processed by the present invention. The compression testing was performed in accordance with ASTM standard 109C. 
         [0070]    As shown in  FIG. 6 , these tests demonstrated that, rather than reducing the 7 day compressive strength of the concrete as would be expected in the case of fly ash substitution, the samples with the ATEC material have compressive strength of up to 6% greater than that of the 100% Portland cement mix. As can be seen, this increase in compressive strength compared to the 100% Portland cement mix was still observed at 35 days after casting. 
         [0071]    The compressive strengths for the control samples show that the capability to enhance the strength of concrete mix was a result of the ATEC re-processing. Controls include a high carbon Class C CFA as received and a high carbon Class C CFA with the carbon removed by heating at 1000 degrees C. Note that the highest compressive strength of any material tested, including 100% Portland cement was achieved by the ATEC samples at both 7 and 35 days of curing. 
         [0072]    One of ordinary skill in the art will readily appreciate that the early (7 day) compressive strength of the cement with the SCM substituted for 20% of the portland cement is remarkably high, both in relative and absolute terms. At 7,338 psi, the resulting material qualifies as a high strength concrete. Generally, the substitution of 20% of the portland cement in a mixture is expected to result in an approximate 10%-20% deficit in compressive strength at 7 days as compared to concrete made with 100% Portland cement. However, the addition of the ATEC cementitious product of the present invention resulted in a 6% increase in compressive strength. 
       Application Example of the Present Invention 
       [0073]    As an example of a preferred embodiment, the invention may be used to reprocess high carbon Class C coal fly ash having a carbon content in excess of 30%, as determined by loss on ignition (“LOT”) and an average calorific value of approximately 5,000 BTU/lb, to produce a hydraulically reactive cementitious material that imparts high strength characteristics to the concrete from mixes in which it is used.  FIG. 4  is an electron micrograph image of Class C high carbon fly ash as received from a coal fired power plant. 
         [0074]    The Class C high carbon fly ash includes hollow glassy cenospheres of varying sizes was well as carbon particles. A relatively large dark amorphous carbon particle is apparent in the center of the viewing field of in  FIG. 4 . In an unprocessed state, the carbon renders the fly ash unusable as a supplementary cementitious material. 
         [0075]    Referring now to  FIG. 2  and  FIG. 3 , prior to thermal treatment in the thermal reactor  204 , the fresh or dry-stored Class C high carbon fly ash material  201  is mixed in the feed stock blender  232  with desired bed materials  203 . An amount of pulverized coal or ancillary fuel  202  needed to bring the total average calorific value of the feedstock to greater than approximately 9,200 BTU/lb is charged into the thermal reactor/gasifier  204  from ancillary feed sources  202  and storage hopper  233 . A combination of water and pulverized coal or other hydrocarbon oil is used to maintain synthesis gas or syngas quality and adequate fuel calorific value. 
         [0076]    To produce a hydraulically reactive cementitious material, a mixture of the high carbon Class C coal fly ash and crushed limestone and pulverized coal is transferred from the feed stock blender  232  into the thermal reactor  204 , which is operated in the reducing mode as a gasifier in this example. The weight proportion of the Class C coal fly ash to crushed limestone in this example was 2:1. This proportion may vary depending on the amount of calcium oxides needed to reach the desired Ca:Si elemental composition ratio in the overall material. Normally this elemental composition ratio (in terms of Atomic %) will be slightly in excess of 3:1, as shown in the elemental composition table  503  for the ATEC process cementitious material product  504  in  FIG. 5 . 
         [0077]    The residual inorganic oxides left behind after the removal of carbon, water and other volatiles during the gasification process at temperatures of up to approximately 1,000 to 1,300 degrees C. are then introduced into the rotary kiln unit  209 . At sufficiently high temperatures of approximately 1,300 degrees C. or higher, and with proper rotary mixing, the calcium, silicon, iron and aluminum oxides residues from the coal, CFA, limestone and sand begin to form calcium and aluminum silicates and ferrites. 
         [0078]    Within the rotating kiln  209 , the temperature of the residual oxides is increased to approximately 1,450 degrees C. for a period of time needed to complete the formation of hydraulically reactive dicalcium and tricalcium silicates. Adequate mixing of the various components within the rotating kiln  209  is important to the production of suitable reactive cementitious materials. 
         [0079]    The optimal temperature profile to be achieved and maintained in the kiln  209  will vary depending on the state and composition of the inorganic feed  210  entering the kiln  209 . Thus, the temperature values provided herein are only approximate. The proper temperatures to be used are those that result in a partially fused clinker or nodule materials which, when properly quenched and ground, yield a hydraulically active cementitious material. The hot clinker or nodules  212  and associated particles leave the kiln  209  via the locking mechanism  310  and enter the quench chamber  313 , where they are cooled, and thereafter are stored and further cooled in a grated hopper  314 . 
         [0080]    The clinker or nodules  212  and associated particulate matter may be mixed with other active ingredients or chemical admixtures to produce other types of cement, including ground granulated blast furnace slag cement, pozzolana cement, hydraulic cement, among other cement. The grinder  214  includes a grinding mechanism that mixes the clinker, nodules, particulate matter and any desired additives. The resulting ground cementitious mixture may be stored as product  216 . 
         [0081]    One of ordinary skill in the art will readily appreciate that custom additive formulations, custom process conditions, custom equipment and custom gasifier conditions will be determined based on a type of CFA initially provided and the properties and types of cementitious material. 
         [0082]    The hydraulically active ATEC cementitious material produced by the invention, as described in the above example, can be used to impart enhanced compressive strength to concretes and mortars when used to replace between 20% to 50%, or more, of the Portland cement ordinarily used in the mixes for these materials. This characteristic of the present invention is of value in that it allows the production of high strength concretes using material that would otherwise be solid waste. 
         [0083]    The invention offers several advantages over existing systems for the remediation of high carbon coal fly ash. The ATEC system of the present invention performs low-cost or no cost re-processing and recycling of fresh coal fly ash that would otherwise be deposited in landfills. The invention also reduces an amount of limestone and clay needed to make cement, with consequent reductions in energy costs and carbon dioxide emissions. Furthermore, the invention generates synthesis gas that may be used to generate electricity by a steam turbine or other energy-producing device. In other words, the system produces more energy than an amount needed to operate the reprocessing plant, which can be sold at a profit. 
         [0084]    Additionally, the invention can provides carbon credits by the permanent disposal or recycling of high carbon fly ash that may be used in emerging cap and trade markets in the United States and/or elsewhere. These outcomes that result from the development and deployment of the present invention will have substantial positive impact on the economy and the environment. 
         [0085]    The present invention provides a system that uses an ash-producing gasification process to yield both electrical energy and a carbon-free fly ash material that may be formulated into reactive SCM. The carbon-free fly ash material includes fine grained crystalline ash material. By reprocessing the CFA in a reducing atmosphere, the invention forms reactive cementitious materials, such as the various calcium silicates and other reactive species. 
         [0086]    Another advantage of the present invention is that the carbon in the high carbon CFA is converted to synthesis gas, which provides a source of the heat energy needed to drive the cement forming reactions. Otherwise, prior to this invention, the carbon in the high carbon CFA rendered the CFA unusable as an SCM for cement. The invention further provides post consumer additives that may be used in paints, coatings, plastics and other products. As described above, the invention provides a system that performs environmentally friendly conversion of waste to energy for remediating hazardous CFA impoundments. 
         [0087]    The present invention also provides for the permanent and safe sequestration, in concrete, of toxic metals such as mercury, lead, arsenic and others toxic elements found in coal fly ash. Concrete is well recognized as an effective material to sequester and immobilize the metals found in CFA. These elements become chemically bound to the concrete matrix, and for all intents and purposes, do not migrate out of the matrix. 
         [0088]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.