Abstract:
A method for liquefaction of coal or other solid carbonaceous material includes passing the material through a reformer having a temperature gradient therein, the temperature gradient generally increasing as the material flows down through the reformer. The more valuable volatile components of the material exit the material at their respective vaporization temperatures, and pass out of the reformer for processing in condensers. Some of each fraction of the volatile material flow is re-heated and recycled through the reformer to supply heat to maintain the temperature gradient, the recycling injection occurring at a level below that where the fraction exited the reformer so that the recycled fraction will again pass out of the reformer to be condensed. At the bottom of the reformer, the non-volatile portion of the carbonaceous material is removed from the reformer for further processing or sale.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority based on U.S. Provisional Patent Application Ser. No. 61/324,151 filed Apr. 14, 2010 and titled “Coal Reformation Process,” the disclosure of which is incorporated herein by this reference. 
     
    
     BACKGROUND 
       [0002]    This invention relates to an improved continuous-feed process for the liquefaction of coal (anthracite, bituminous, sub-bituminous), gob, bitumen, lignite, oil and tar sands, oil shale, and any solid carbonaceous material, including waste material and plastic material and for the distillation of the volatile matter within that solid carbonaceous material into high-value products. 
         [0003]    Until recent decades despite voluminous amounts of CO2 emissions and other contaminants, coal providers have experienced very little ecological pressure from governments. While coal is cheap and produces significant quantities of power, it is also an international “necessity” because the world could not immediately replace this energy source. However, as the world has focused on environmental efficacy, better systems and methods of using the energy stored in coal become more important. 
         [0004]    All coal contains varying concentrations of moisture, sulfur, hydrocarbon compounds (referred to as volatile matter), inorganic ash-forming components, and other components. Some of these components have value while other components are considered contaminants. Synthetic production of liquid fuels (i.e., gasoline and oil substitutes) in the United States has a long history. In the 19th century, dozens of facilities produced oil, gas, grease and paraffin from coal, but by 1873, cheap petroleum caused the last coal oil plant to close. In addition, commercial scale shale oil extraction began in 1857 at shale oil retorts retorting the Devonian oil shale along the Ohio River Valley. However, after crude oil discovery in Pennsylvania in 1859, oil shale industries found it difficult to compete and they were shut down by 1861. 
         [0005]    Historically, economics has been a major impediment to coal liquefaction. Until recent years oil has been easy to find and produce. In addition, a powerful liquid oil industry has lobbied and maintained a unique control over domestic oil production. The international landscape is now aware of the imminent danger of deep water drilling for oil as evidenced by the British Petroleum oil spill in the Gulf of Mexico in April of 2010. 
         [0006]    There are several processes used for coal liquefaction. For example, in the Bergius process, developed by Friedrich Bergius in 1913, dry coal is mixed with heavy oil recycled from the process. A catalyst is typically added to the mixture. The reaction occurs at between 400° C. (752° F.) to 5,000° C. (9,030° F.) and 20 to 70 MPa hydrogen pressure. 
         [0007]    Chevron Corporation developed a process that involved close-coupling of the non-catalytic dissolver and the catalytic hydroprocessing unit. The oil produced was lighter and had far fewer heteroatom impurities than other coal oils. Apparently, the process was scaled-up to the 6 ton per day level, but has not been proven commercially. 
         [0008]    The Karrick process is a low-temperature carbonization (LTC) and pyrolysis process of carbonaceous materials. Although primarily meant for coal carbonization, it also could be used for processing of oil shale, lignite or other carbonaceous materials. These are heated at 450° C. (800° F.) to 700° C. (1,300° F.) in the absence of air to distill out synthetic fuels-unconventional oil and syngas. The Karrick process may be used for coal liquefaction and for semi-coke production. 
         [0009]    In the Karrick process, one short ton of coal yields as much as one barrel of oils and coal tars (12% by weight), 3,000 cubic feet (85 cubic meters) of coal gas and 1,500 pounds (680 kg) of solid smokeless char or semi-coke (for one metric ton, the results would be 0.175 m 3  of oils and coal tars, 95 m 3  of gas, and 750 kg of semi-coke). Yields by volume of approximately 25% gasoline, 10% kerosene and 20% fuel oil are obtainable from coal. Gasoline obtained from coal by the Karrick process combined with cracking and refining is equal in quality to tetraethyl lead gasolines. More power is developed in internal combustion engines and an increase in fuel economy of approximately 20% is obtainable under identical operating conditions. The syngas can be converted to oil by the Fischer-Tropsch process. Coal gas from Karrick LTC yields greater energy content than natural gas. 
         [0010]    Compared to the Bergius process, the Karrick process is cheaper, requires less water and destroys less thermal value (one-half that of the Bergius process). The smokeless semi-coke fuel, when burned in an open grate or in boilers, delivers 20% to 25% more heat than raw coal. The coal gas should deliver more heat than natural gas per heat unit contained due to the greater quantity of combined carbon and lower dilution of the combustion gases with water vapor. 
         [0011]    The cheapest liquid fuel from coal will come when processed by LTC for both liquid fuels and electric power. As a tertiary product of the coal distilling process, electrical energy can be generated at a minimum equipment cost. A Karrick LTC plant with one kiloton of daily coal capacity produces sufficient steam to generate 100,000 kilowatt hours of electrical power at no extra cost excepting capital investment for electrical equipment and loss of steam temperature passing through turbines. The process steam cost could be low since this steam could be derived from off-peak boiler capacity or from turbines in central electric stations. Fuel for steam and superheating would subsequently be reduced in cost. 
         [0012]    Although a Karrick pilot plant was successfully operated in 1935, there is some question as to whether a modern commercial Karrick LTC process plant would fail due to mechanical problems, a postulation based on previous failures of other plants using different processes under different conditions. It is indeterminate as to how “scaleable” the technology is for large-scale production. When oil was significantly cheaper markets for the described coal products were limited, which made such a venture economically unsound. 
         [0013]    Other methods of coal liquefaction involve indirect conversion. Perhaps the main indirect process is the Fischer-Tropsch process, in which coal is first gasified to make syngas (a balanced purified mixture of CO and H2 gas). Next, Fischer-Tropsch catalysts are used to convert the syngas into light hydrocarbons (like ethane) that are further processed into gasoline and diesel. This method was used on a large technical scale in Germany between 1934 and 1945 and is currently being used by Sasol in South Africa. In addition to creating gasoline, syngas can be converted into methanol, which can be used as a fuel or a fuel additive. Syngas may be converted to liquids through conversion of the syngas to methanol, which is subsequently polymerized into alkanes over a zeolite catalyst. 
         [0014]    Unfortunately, each of the prior methods of coal liquefaction have disadvantages. The prior processes tend to focus on turning coal to liquid, with little regard for environmental implications. For example, Fischer-Tropsch produces toxic byproducts and consumes expensive catalysts during the process (cobalt, iron, ruthenium). The prior processes have often not been scalable, and thus were of limited viability. Many also had significant capital costs that tended to render the liquefaction economically suspect. 
       SUMMARY 
       [0015]    This invention involves a coal treatment process that permits removal of moisture, sulfur, hydrocarbon compounds (referred to as volatile matter), and other components in a continuous-feed process by applying heat and steam, with hydrogen re-circulation, in an oxygen deficient atmosphere. The result is separation of the volatile matter into valuable gas and liquid fractions for use or further processing in addition to a highly upgraded coal product. 
         [0016]    In the process, bulk coal or other carbonaceous material is fed into a reformer that has been evacuated of oxygen. The reformer is typically a large metal container mounted generally vertically. In some embodiments, a rotatable shaft extends down into the container and holds agitation plates. A motor attached to the shaft turns the plates to assist in moving the coal through the container. 
         [0017]    One or more vapor draws are mounted at various vertical locations on the shell wall of the reformer container. The vapor draws extract fractions (based on the location of the draws, which in turn is based on a temperature gradient formed inside the container) of the volatile constituents from the heated coal, taking some off for sale or further processing and, depending on the design, recycling portions back into the container. The recycling may include steps such as condensing the gases to extract valuable product, and then heating the gases so as to provide heat to the reformer container. Internal housings on the vapor draws assist in reducing the level of particulates removed from the container by the vapor draws. 
         [0018]    One or more injectors are mounted at various vertical elevations on the shell wall of the reformer container for injecting steam or heated re-circulated effluent into the container. The gases are typically injected into the container using the injector at an elevation below the location of the vapor draw from which the gas was removed. As a result, the injected gases provide heating to the container, but generally are removed through the upper vapor draw, so as to keep the factions generally separated. Thus, in more complicated embodiments there are a series of removals of gases, separation, heating of a portion of the removed gases, and recycling the heated portion back into the reformer container to maintain the temperature gradient. 
         [0019]    Injecting the heated gases into the container at the various elevations of the injectors creates a temperature gradient inside the container. In general, the higher temperatures are near the bottom of the container, and the gradient cools moving up the container. Because of the temperature gradient, more volatile constituents of the coal exit the reformer container through the upper vapor draws and progressively less volatile constituents exit at vapor draws located closer to the lower end of the reformer container. 
         [0020]    Heat is applied to the coal to drive off moisture and vaporize the hydrocarbon compounds and harmful contaminants such as sulfur, mercury and arsenic, thereby removing them from the coal. The steam helps to sweep, or strip, the gaseous components away from the coal and into a series of recovery devices, where these compounds can be condensed, separated, treated and stored. Steam will also react with residual carbon monoxide to form hydrogen and carbon dioxide through the water-gas shift reaction. 
         [0021]    The applied heat converts, due to thermal cracking, some of the heavy coal tar components into lighter, more valuable fuel components such as hydrogen, methane, ethane, propane, butane, gasoline boiling range components, and diesel boiling range components. The vaporized heavier hydrocarbon compounds may be condensed and separated into different fuel streams such as gasoline, kerosene, and diesel, or sold without separation as a supplemental crude oil for further processing at a petroleum refinery. Alternatively, the heavy hydrocarbon stream, including the coal tar, may be further processed through a “hydrocracking” process that uses hydrogen and a nickel-molybdenum catalyst to further break down heavy low-value hydrocarbons into lighter high-value hydrocarbons. The hydrocracking process also provides desulphurization of the feed stream, as well as de-nitrogenation through hydrogenation. 
         [0022]    The lighter hydrocarbon components may be captured, compressed and condensed to form light gasoline, butane, and propane. The remaining gases after compression typically contain hydrogen and methane. This gas can be used as a fuel-gas stream for the process or the hydrogen may be separated out to form a hydrogen-rich stream to be used for other hydrogen consuming processes. 
         [0023]    The reformed coal is removed from the container through an exit near the base of the container and cooled to a temperature low enough to permit contact of the reformed coal with the air. The reformed coal is typically moisture-free. The reformed coal has a higher energy value, perhaps as much as 50% more BTUs per pound over the parent coal, due to the removal of moisture. 
         [0024]    Because the reformed coal has a higher BTU content, less reformed coal is required as fuel for the same energy output. This lower fuel requirement may lead to a 30% reduction in CO2 emissions, by mass. The sulfur content of the reformed coal may be less than 1% of that of the parent coal, and thus produces significantly less SOx emissions when burned. The ash produced from burning the reformed coal is largely free of mercury, and has a much lower concentration of other contaminants relative to ash produced from burning the parent coal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Other features and advantages of the present invention will be apparent from reference to the following Detailed Description taken in conjunction with the accompanying Drawings, in which: 
           [0026]      FIG. 1  depicts a schematic diagram of a coal reformer according to one embodiment of the present invention; and 
           [0027]      FIG. 2  depicts a process flow diagram of one embodiment of the process of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    As depicted in  FIG. 1 , according to one embodiment the present method and apparatus involve a solid-vapor reactive fractionator, or coal reformer  10 . The reformer  10  has an outer shell wall  12 , typically made of steel, and may contain an internal erosion-resistant and corrosion-resistant coating as well as external insulation of known types. The reformer is placed in a generally vertical orientation and thus has an upper end  14  and a lower end  15 . A rotatable vertical shaft  18  passes through a seal bearing  20  in the upper end  14  of the reformer. One or more agitation plates  22  are connected to the vertical shaft at various vertical positions. As depicted in  FIG. 1 , typically the agitation plates  22  are connected at an angle from the horizontal and the vertical. A motor  24  attached to the shaft  18  above the reformer rotates the shaft  18  and thus the agitation plates  22 . 
         [0029]    A plurality of vapor draws  28  are mounted to the reformer  10  at various locations along the length of the outer shell wall  12 . The vapor draws  28  remove vapor from the reformer  10 . Each vapor draw has an internal vapor-draw housing  30  designed to try to reduce the amount of coal and other particulates flowing into the vapor draws and potentially plugging up the vapor draw nozzle or other parts of the apparatus. An external coal separation device such as a cyclonic separator or bag filter may also be used to capture and separate fine coal particles from entering other parts of the downstream process equipment (such as the condensers and economizers discussed below). 
         [0030]    Each vapor draw  28  is placed at a location selected so as to extract different fractions of volatile constituents of the coal. That is, as the “stack” inside the reformer heats, a temperature gradient forms within the reformer, and the lower locations will be hotter than the upper locations. Thus, the vapor draws  28  located higher on the outer shell wall  12  will remove lighter weight hydrocarbons, and those at lower locations will remove heavier hydrocarbons. 
         [0031]    A plurality of injectors  32  are placed at various vertical elevations along the length of the outer shell wall  12 . The injectors inject heated fluids into the reformer  10 . Often the heated fluids are recycled from the vapor draws  28 . That is, as discussed in more detail below, a portion of the hot gases removed by the vapor draws  28  are recycled back into the reformer  10  using the injectors  32 . 
         [0032]    Raw coal or other carbonaceous material is conveyed from a feed hopper  34  and introduced into the reformer  10 . A rotary valve  36  controls the feed rate to the reformer  10  and prevents back flow from the reformer  10  to the hopper  34 . Typically, the process starts by filling the reformer  10  with coal, and then purging air from the interior of the reformer using steam. As the coal is processed and the various fractions extracted from the reformer, additional coal passes through the rotary valve  36  and into the reformer  10 . 
         [0033]    As the coal enters the reformer  10 , it starts to heat up and continues heating up as it travels down the reformer  10  to the point (typically fairly high in the reformer) that moisture and some light volatile organic compounds are stripped from the coal. The moisture, light volatile organic compounds, and other gases (from the re-injection streams, as discussed below) exit the reformer  10  through an upper-most vapor draw  28   a . As can be seen by referring to  FIG. 2 , in one embodiment these vapors are routed to an overhead condenser  42  where the vapors are condensed to liquids such as water, butane, pentanes, and light gasoline components. 
         [0034]    The liquid and residual gas exit the overhead condenser  42  and separate in an overhead liquid separator  44 , which is a three-phase separator that separates the gas from the liquid and separates the hydrocarbon liquid from the aqueous solution. The residual gas from the overhead liquid separator  44  is routed to the suction of a fuel gas compressor  46  and cooled in the fuel gas compressor condenser  48  where fractions such as propane and butane will liquefy and drop out into a compressor discharge three-phase separator  50 . The hydrocarbon liquids from the compressor discharge three-phase separator  50  may then be collected for treating, fractionation, storage, or sales. 
         [0035]    The residual gas from the compressor discharge three-phase separator  50  is treated to removed contaminants such as free oxygen and nitrogen (air), carbon dioxide, hydrogen sulfide, and others. After treating, the resulting gas stream (see  FIG. 2 , stream  52 ) may be sent to a hydrogen purification unit (through a stream  53  shown in  FIG. 2 ) to separate hydrogen from the fuel gas, if desired. The purified hydrogen stream or a slip-stream of the hydrogen-rich fuel gas stream (see  FIG. 2 , stream  54 ) may be heated to 200-260° C. (400-500° F.) in a heater  58  and re-injected back into the reformer  10  through an injector  32   b  above the heavy naphtha vapor draw  28   b  as a heating and stripping medium. 
         [0036]    The liquid from the overhead separator  44  is pumped by a pump  60  and split into two streams. One stream (see  FIG. 2 , stream  62 ) combines with a heavy naphtha stream (see  FIG. 2 , stream  64 ) from the reformer  10 . A second stream (see  FIG. 2 , stream  68 ) is used as a quench stream that is re-injected back into the reformer  10  through injector  32   a  to assist in overhead temperature control. 
         [0037]    Water from the overhead separator  44  may contain ammonia, hydrogen sulfide, and other water-soluble components. This water is contaminated, or sour. Thus, the sour water stream (see  FIG. 2 , stream  70   a ) is combined with other sour water streams  70 , such as that shown at  FIG. 2 , streams  70   b ,  70   c ,  70   d  and  70   e , and sent to treatment. 
         [0038]    The coal continues to heat up as it travels down the reformer  10 . The heating is caused by heated re-injection streams being introduced into the reformer by the various injectors  32  located further down the reformer  10 . As the coal heats from 90-205° C. (200-400° F.), any remaining moisture is removed and any hydrocarbon components that boil in the heavy naphtha range also vaporize out of the coal. These components exit the reformer  10  through the heavy naphtha vapor draw  28   b  at about 205° C. (400° F.). 
         [0039]    The heavy naphtha vapor is condensed in a naphtha condenser  72 . The naphtha liquid and residual gas disengage in a naphtha three-phase separator  74 . The gas from the naphtha three-phase separator  74  is combined with other residual gas streams and is routed to a vapor recovery unit. From there, the gas may be recovered for treating, fractionation, storage, consumption as fuel, or sales. 
         [0040]    The naphtha from the naphtha three-phase separator  74  is pumped by a pump  76  and split into two streams. As depicted in  FIG. 2 , one stream  78  may be used as a cooling medium in an economizer  80 , where that stream is pre-heated and then routed to the radiant section coils of a fired heater  58 , heated to 315-370° C. (600-700° F.) and re-injected into the reformer  10  through the injector  32   c  above the distillate vapor draw  28   c . The other stream  82  is sent to storage and can be further treated, upgraded, and blended into finished gasoline. 
         [0041]    As the coal continues down the “stack” in the reformer  10  and heats up from 205° C. (400° F.) to 370° C. (700° F.), hydrocarbon components that boil in this temperature range (distillates) vaporize out of the coal. These distillate vapors exit the reformer  10  through the distillate vapor draw  28   c  at about 340-370° C. (650-700° F.). The distillate vapors are condensed in the economizer  80  and disengage from the residual gas in a distillate three-phase separator  84 . 
         [0042]    The distillate is pumped out of the distillate three-phase separator  84  by a pump  88  and split into two streams. The first stream (see  FIG. 2 , stream  86 ) goes to storage and can be further processed through an ultra-low sulfur diesel hydrotreater or sold as unfinished diesel. The second stream ( FIG. 2 , stream  92 ) is pre-heated in an economizer  94  and heated up to about 480° C. (900° F.) through the radiant coils of a fired heater  96 . This second stream is then re-injected into the reformer  10  by the injector  32   d  above the heavy coal tar vapor draw  28   d.    
         [0043]    The heavy coal tar vapors exit the reformer  10  through a vapor draw  28   d  and are condensed through the economizer  94 . The heavy coal tar disengages from the residual gas in a coal-tar separator  98 . The liquid coal tar  100  is pumped out of the coal-tar separator  98  via a pump  102  and receives an injection of the hot hydrogen-rich fuel gas stream (see  FIG. 2 , stream  54 ), heated up to 425-480° C. (800-900° F.) from the convection coils of a fired heater  58 . 
         [0044]    The hydrogen enriched coal tar stream is heated up to 650-705° C. (1200-1300° F.) by a fired heater  104 . The coal tar will decompose at these temperatures (thermally crack) into smaller molecules, typically diesel and gasoline components as well as butanes, propane, ethane, methane and more hydrogen. Also, the high temperature and presence of hydrogen, and the metals that are present in the coal, induce both hydrocracking and hydrotreating reactions that further break down the large and heavy hydrocarbon molecules into smaller and more valuable hydrocarbon components such as diesel, gasoline, butanes, propane, ethane, and methane by the reaction of the large hydrocarbon molecules with hydrogen (hydrocracking). These same reactions often remove the sulfur, nitrogen, and oxygen components of the coal by the reaction of these components with hydrogen (hydrotreating). 
         [0045]    The output stream  106  of the fired heater  104  is re-injected into the reformer  10  through the injector  32   e  near the bottom  15  of the reformer  10 . This heats the coal to its final temperature of about 1000° F., drives out the remaining volatile matter from the coal, and recovers the cracked stock created from thermal cracking the coal tar in the fired heater  104 . The hydrocracking and hydrotreating reactions that occur in the reformer  10  utilize the coal and its associated metals as catalysts to further break down the large carbon chains of the coal as well as further remove sulfur, nitrogen, and oxygen from the molecules of the coal. The coal tar stream may be recycled to extinction. 
         [0046]    The hot reformed coal product exits the bottom of the reformer  10  through a rotary valve  38 . A section of the transfer pipe  40  containing the hot reformed coal may be jacketed. Boiler feed water (hot water at about 100° C., ready to boil) flowing through the jacketed pipe  108  may be used to cool the reformed coal to about 120-105° C. (250-225° F.). Typically, as depicted in  FIG. 2 , stream  110 , the boiler feed water is heated up to medium pressure steam  110  and combined with other medium pressure steam  112  to use as a stripping steam to the system as well as other uses throughout the process. 
         [0047]    Steam may also be super-heated up to 425-480° C. (800-900° F.) through the convection coils of the fired heater  96 . The warm reformed coal can be further cooled by flowing cooling water or other cooling medium through an additional section of jacketed transfer pipe  114  to cool the reformed coal down to a safe temperature (typically below 50° C. or 120° F.). A series of jacketed auger-type solids pumps may be used in lieu of the rotary valve  38  and jacketed pipes  108  and  114  to transfer and cool the reformed coal product. 
         [0048]    Once the reformed coal is sufficiently cooled, it is safe to contact the reformed coal with dry air. Dry air may be used at this point to convey the reformed coal to the reformed coal storage silos. The reformed coal may then be used as a fuel or other desired uses. 
         [0049]    The coal reformer  10  and the agitation plates  22  may be made of different materials, but typically would be steel or stainless steel with an internal erosion-resistant and corrosion-resistant coating or liner, appropriate insulation, and sized according to the desired continuous throughput, which is also based on the specific material being processed. The other various components of the process equipment are those known in the art. For example, the condensers may be a standard shell-and-tube type heat exchanger and the heaters may be standard fire heaters or furnaces as known in the art. Similarly, standard piping and valves may be used. Again, each of these items is sized to handle the throughput of the reformer  10 . 
         [0050]    Although the embodiments discussed in this disclosure involve the processing and treatment of coal, the method and apparatus described is suitable for the extraction and fractionation of other solid carbonaceous materials, such as coal (anthracite, bituminous, sub-bituminous), gob, bitumen, lignite, oil and tar sands, oil shale, and solid carbonaceous material including waste material and plastic material. Thus, these solid carbonaceous materials may be processed to distill the volatile matter within that solid carbonaceous material into high-value products. Thus, the present invention has several advantages over the prior art. Although embodiments of the present invention have been described, various modifications and changes may be made by those skilled in the art without departing from the spirit and scope of the invention.