Abstract:
A system and method for collecting hot coal tar gases emanating from a coal containing pyrolytic kiln are described. The hot coal tar gases, comprising a variety of different hydrocarbons as well as inorganic gases arising from the kiln thermal processing are transferred by diffusion and forced convection to a thermal duct in which the temperature is controlled to be maintained at a temperature below that of the kiln. The gaseous hydrocarbon with the highest condensation temperature is the first to liquefy. Additional useful hydrocarbons liquefy as the temperature of the gas continues to cool from the kiln temperature of ˜5000 C to one approaching the minimum duct temperature, ˜175° C. After a number of desirable hydrocarbons present in the coal tar gas have liquefied, the liquid contents are collected, either separately or as a combination of liquid hydrocarbons. The several remaining inorganic and some hydrocarbons gases with condensation temperatures below the minimum duct temperature are separately collected in gaseous form for further processing and/or safe disposal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX 
       [0003]    Not Applicable 
       FIELD OF INVENTION 
       [0004]    Recently, there has been an increasing effort to obtain ‘clean’ coal by processing the coal, as mined, at moderate temperatures in a pyrolytic kiln to drive off harmful, polluting gases. The need for clean coal has been mandated and incorporated in numerous National and International pollution standards in order to prevent health hazards as well as crop hazards such as acid rain. The present invention describes methods for pyrolyzing coal both to drive off harmful gases that can be sequestered, and also to recapture condensed gases that can be further used for clean oxidation, providing useful non-polluting or minimally polluting thermal energy. These gases are recovered in liquid form in a special temperature controlled duct. 
       BACKGROUND 
       [0005]    Coal pyrolysis, in which a portion of coal is converted into a series of gases, was first developed as early as the eighteenth century. However, commercial pyrolysis became more widespread in the early 1900&#39;s. Intense renewed interest in pyrolysis of a variety of raw coals was spurred by the tensions between the West and the oil rich nations of the Middle Eastern countries in the 1970&#39;s. In general, depending on the nature of the raw coal and the exact nature of the pyrolysis process, the gas from coal pyrolysis may contain water vapor, compounds of chlorine, mercury, other heavy metals, hydrogen sulfide, and a range of hydrocarbon volatiles. The solid, non-volatized coal char will contain carbon, a range of hydrocarbon compounds, and traces of other minerals and elemental compounds. The volatized gases can be separated and the individual gaseous products can be further processed for useful chemical applications. At the same time, burning coals that have been properly pyrolyzed reduce air pollutions and hence human health hazards such as emphysema, asthma, and lung cancer. The large number of issued patents involving pyrolysis gives a broad picture of the utility and profitability of gasification of coal by pyrolysis to achieve a cleaner coal. 
         [0006]    The history and detailed time-line of coal 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 Subbituminous 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. 
       SUMMARY OF THE INVENTION 
       [0007]    A system and method for collecting hot coal tar gases emanating from a coal containing pyrolytic kiln are described. First, water vapor and small quantities of oxygen are removed while operating the kiln at moderate temperatures in the range of ˜275 to 500° C. At the upper end of this range, hot coal tar gases are driven from the coal consisting of a variety of useful hydrocarbons as well as inorganic gases. The hot gases are then transferred by way of diffusion and forced convection to a thermal duct in which the temperature is computer controlled to remain at a temperature below that of the kiln, causing certain hydrocarbons to liquefy. The gaseous hydrocarbon with the highest condensation temperature is the first to liquefy as it enters the proximal end of the duct which is kept at the lowest temperature of the duct. Additional useful hydrocarbons liquefy as the temperature of the gas continues to cool from the moderate kiln temperature of ˜5000 C to one approaching the duct temperature, in the range ˜175 C-350 C at the proximal end of the duct. The hydrocarbons with a lower condensation temperature liquefy further down the duct from their original entry point from the kiln. Cooling of the gases occur as the gases flow from the kiln distal end (temperature of ˜500 C) towards the distal end of the duct. After a number of desirable hydrocarbons present in the coal tar gas have liquefied, the liquid contents are collected while several remaining inorganic gases and almost all the water vapor and some gaseous hydrocarbons with lower condensation temperatures remain as gases and are separately sequestered in gaseous form for further processing and/or safe disposal. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0008]      FIG. 1   a  shows a pyrolytic kiln with coal, operated to create coal tar gases, the gases then entering a temperature controlled duct in which certain of the gases become liquefied. The liquefied gases are then transferred to a single collection chamber for use as a fuel, or other useful purposes. 
           [0009]      FIG. 1   b  shows the rotation gear and its connection to the kiln core to provide core rotation. 
           [0010]      FIG. 1   c  depicts the duct in which the hot gases from the kiln are cooled, liquefied and collected. 
           [0011]      FIG. 2  is an alternate duct embodiment with a feature that permits collection of a number of different condensable gases in separate chambers determined by the temperature of the duct. 
           [0012]      FIG. 3  is the master control unit that controls the angular rotation of the core, the speed of the vapor/gas extractor and reacts to the thermal sensing units of the kiln core and the duct to regulate the temperature of the respective temperature control elements surrounding the core and the duct thereby regulating the temperature of the core and the duct by passive convection, conduction and radiation. Additional cooling, if desirable can be supplied by passing water or other coolants through the heater elements of the kiln and the duct. 
           [0013]      FIG. 4 . is a sketch showing the interconnections of both the kiln core and kiln shell to the duct as well as the connection of the control unit to kiln core, kiln shell and duct. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The present invention describes a system and a process for obtaining reusable hydrocarbons from coal that undergo a pyrolysis process. The process is particularly advantageous since it requires no wasteful oxidation of the coal but rather utilizes heat in a near oxygen free atmosphere to drive off gases from the coal, especially numerous hydrocarbon gases, many of which can be oxidized at a later time to obtain useful thermal energy. The present invention describes an alternative to conventional methods for eliminating pollutants from coal by using a unique pyrolysis system and process for driving off and capturing many of the gases which are considered to be pollutants, i.e. mercury, sulfur, hydrogen sulfide and the like. At the same time, the invention provides means for capturing and retaining the valuable hydrocarbons that are desired for future use as fuel. 
         [0015]    The invention uses a pyrolysis process whereby the coal is not burned, but heated to a moderate temperature in a near oxygen free atmosphere in a pyrolytic kiln. The gases driven off in this manner can be separated from the coal and drawn off for future combustible use, safe disposal or re-processing for future use. Certain other gases that are driven off in the pyrolysis kiln are non-condensable in the present invention such as H2, CO, CO2, C2H6, C3H8 and C2H4 (J. H. Campbell, Fuel, 57, 217 (1978). Even though not condensable in the present invention, this invention collects these gases for re-processing by other means since many such gases continue to have other intrinsic value. 
         [0016]    The uniqueness of the present invention lies in part to a method for liquefying the useful hydrocarbons emanating from a hot pyrolysis kiln for pyrolyzing coal without a coal combustion process, then mixing the useful liquefied coal tars (that is, those that can be oxidized at a future time) to the remaining char in the kiln so that both the char and the recovered hydrocarbons can be used for useful clean energy upon oxidation (burning). 
         [0017]    The system of the present invention is designed for reclaiming and collecting/capturing hot coal tar gases and coal gas components in a condensed state from a vapor state by utilizing a near oxygen free pyrolytic kiln to heat the coal causing gaseous volatiles to be driven off from the coal and or coal/biomass. 
         [0018]    A computerized temperature control unit receives controlling signals from at least one thermal sensor mounted within the duct, the thermal sensor also connected to the computer control unit for regulating the duct temperature. The condensed products are released from the duct by way of at least one drain spout coupled or attached to the duct with the duct draining the condensate into a collection chamber through the drain spout. The condensate, in liquid form, is drained from the duct when a slidable shutter, mounted on the drain spout or over the openings on the undersides of the duct, is in the open position. At other times, the slidable spout shutter is in a closed position. The gases cool in the duct and condense along different portions of the duct as they traverse the length of the duct from the kiln. The position along the duct at which they condense will depend on their individual thermodynamic property, that is, the gas with the highest condensation temperature will cool closest to the flange, the one with the lowest, further from the flange as determined by the thermodynamic property of the individual gas. 
         [0019]    Depending on the duct configuration, more than one drain spout can be attached to the duct and for each drain spout and its corresponding slidable shutter; there is a collection chamber in close proximity to the sprout. A fan for the vapor/gas extractor is mounted within the duct at the far or distal end of the duct, opposite to the proximal end connected to the kiln by way the flange. The fan drives uncondensed coal gases from the duct into a collection drum which serves as the vapor/gas extractor which also has a slidable shutter. The contents of the drum can be further processed at a different processing station. 
         [0020]    The duct has a near end, a far end, a top side and an underside, a length in the range from of 1-500 feet. Since the duct need not be linear in length and can be made from sections so that the effective length is non-linear in shape/contour, the total length is measured along the perimeter of the underside of the duct. For a non-linear shaped duct, there is one region of the duct that is lower with respect to ground level than any other portion of the duct to allow for efficient drainage. The drain spouts are rigidly attached and mounted on the underside of the duct. Typical cross-sections of the duct are of arbitrary geometry but have an area in the range 1-100 square feet. The temperature of the duct is maintained at a temperature in the range 175-350 C but can also be set to a uniform temperature, desirable under certain conditions. A uniform temperature along the duct length is useful when condensates are being separately collected in separate or individual collection chambers. 
         [0021]    There are numerous components of coal gas, many of which are useable hydrocarbons when condensed and re-captured in liquid form. The most useful ones include the carbon-hydrogen chemical form CxHy where x is greater than 9 and y greater than 10. The hydrocarbons that condense and are recoverable will have condensation temperatures in the range from approximately ˜175 to 500 C, more specifically, between the minimum temperature set for the condensation duct, and the exit temperature of the gases set at the distal end of the kiln. 
         [0022]    Generally, in the pyrolysis of coal and/or biomass, it is useful to eliminate as much water as possible during the pyrolytic process.  FIG. 1   a  is a drawing depicting a near oxygen free pyrolysis kiln and char outlet for obtaining combustible fuels free of a variety of contaminants. The process separates gases from solids in the kiln and then condenses valuable fuels without pollutants in the condensation duct  102  shown as part of unit  1001 , in  FIG. 1   c . The duct unit  102  is attached to the proximal end of kiln in  FIG. 1   a  where the duct reverts/condenses the useful biofuel gases into liquids. Continuing with  FIG. 1   a , where the pyrolysis process starts at the proximal end of kiln  1000 , the kiln consisting of pyrolytic kiln outer shell  10  and pyrolytic kiln core  11 . Both shell  10  and core  11  have an inner surface, an outer surface a proximal and a distal end as well as a diameter that can be in the range of from 1 to 18 feet. Core  11  receives coal and/or biomass loaded through input airlock  12  mounted to core  11  by a flexible rotary seal. Core  11  also has a helical steel rail  15   a  rigidly affixed within the length of the inner surface of core  11 . In addition, core  11  is mounted concentrically within shell  10  and rotates within shell  10  by way of gear  11   a  as shown in  FIG. 1   b  with  11   a  rigidly attached to the surrounding circumference of the outer surface of core  11  at its proximal end. For rotation of core  11  to occur, gear  11   a  is engaged with gear  170 ,  FIG. 1   b . Upon rotation of core  11 , heated coal/biomass  15  in  FIG. 1   a  is moved from the proximal to the distal end of core  11  by way of the rotating action of ribbed steel rail  11   b . As shown in  FIG. 1   a , core  11  is heated by heater elements straps  13  affixed to the interior surface of kiln shell  10  with heat transferred to the interior of core  11  by thermal conduction, thermal convection and radiation. Coal  15  in core  11  has an initial temperature at or near room or outdoor ambient temperature at the proximal end of core  11 . As coal  15  progresses toward the distal end of core  11 , core  11  and coal  15  approach a temperature up to approximately 500 C. The increasingly higher temperatures in kiln core  11  causes coal gases  100   d  to evolve from heated coal  15  within core  11  in  FIG. 1   a  which enter duct  102  at a temperature up to ˜500 C. Gases  100   2   d  pass from core  11  to duct  102 ,  FIG. 1   c , wherein duct  102  is attached to kiln core  10  and shell  11  by way of flange  101  with a flexible rotating seal to allow for rotation of core and shell  10  and  11  respectively. Flange  101  is rigidly attached to the distal end of core  11  and to the proximal end of duct  102 . The portion of heated coal/biomass that is not gasified by the heat within core  11  remains as solid char  15   b  and is discharged through a second airlock  14  which is rigidly attached to core  11  by means of a flexible rotating seal. The char at the distal end of core  11  is emptied into container  15   c  for subsequent use as fuel. 
         [0023]    Thermal sensors  16  in  FIG. 1   a  are spaced between the inner surface of shell  10  and the outer surface of core  11  along the length of outer kiln shell  10  and core  11  to relay temperatures within the kiln shell  10  to master control unit  3000  shown in  FIG. 3 . Master control  3000  in turn adjusts current to heat straps  13  to provide a predetermined desired temperature in kiln core  10 . Typically desired kiln temperatures are in the range 275 C to 500 C. 
         [0024]    In duct  102 , duct temperature control elements  120  are rigidly affixed to the exterior surface of duct  102  and are also set to any desired temperature via the same master control unit  3000  of  FIG. 3  by way of temperatures relayed to unit  3000  by way of the temperature or duct heat sensor  104   a  in duct  102 . Gases  102   d  that volatilize in core  11  are drawn into duct  102  by thermal diffusion and by fan  109  mounted near the distal end of duct  102 . Coal and/or biomass  15  are transported from the proximal end to the distal end of core  11  by rotation of kiln  11  with the help of the helical strap  15   a  mounted on the inner surface of core  11 . The remaining coal/biomass that has not volatilized in core  11  empties into vessel  15   c  through a second airlock  14  mounted on a rotary seal at the distal end of core  11 . 
         [0025]    During the heating process of coal/biomass  15 , kiln core  11  is rotated by details shown in  FIG. 1   b . Motor  17  is attached to a rotating gear  170 . Rotation of core  11  occurs when gear  170  is engaged with gear  11   a  and gear  170  is made to rotate by way of motor  17 .  FIG. 3  illustrates the kiln and duct master control unit  3000  which receives signals from thermal sensor  16  to regulate the temperature of kiln heater straps  13 , duct heat sensor  104   a  to regulate heater coils  103  positioned around outer surface of duct  102 . In addition unit  3000 , shown in  FIG. 3  is programmed to regulate the speed of duct fan  109  and the speed of gear motor  17 . 
         [0026]      FIG. 1   c  further describes the details of duct  102 . Duct  102  is maintained in a range of temperatures between 175-350 C by way of heater coils  103  wrapped around duct  102 . Heater coils  103  control the temperature of duct  102  by way of thermal conduction to a desired temperature or temperature gradient in conjunction with master control unit  3000  shown in  FIG. 3 . Unit  3000  provides temperature regulation and maintains the temperature of duct  102  at a uniform temperature or temperature gradient along the length of duct  102  and can also be is made to vary as a function of time. Preferably, duct  102  will cycle from its highest temperature to condense and retrieve the highest condensation temperature volatiles and where the temperature of duct  102  is lower, lower condensation temperature volatiles will condense. Duct  102  may be of arbitrary cross sectional geometry with a cross sectional area in the range 1-100 square feet. The length of the duct  102 , which may be linear or non-linear in length from end to end, when measured along its outer perimeter along the underside of the duct, is in the range 1-500 feet. The gases  100   d  having passed from kiln core  11 , maintained at a higher temperature than duct  102 , causes gases  100   d  consisting of various hydrocarbons to condense into a liquid form in duct  102 . Components of gas  100   d  will condense along the length of duct  102  as the temperature of duct  102  is maintained in the range 175-350 C by way of master control unit  3000 ,  FIG. 3  with input to unit  3000  provided by thermal sensor  104   a  that senses the temperature in duct  102 . As the components of gas  100   d  condense in duct  102 , each gaseous component liquefies at a unique temperature controlled by the thermodynamic properties of the each individual gas component. Cooling of gas  102   d  within duct  102  occurs as gas  100   d  passes along the length of duct  102  from proximal to distal end of duct  102  whereby different gas components  102   d  cool and become liquefied  102   a , at different positions along duct  102  as the gas flows from flange  101  towards the distal end of duct  102  with fan  109  mounted internally near the distal end of duct  102 . Fan  109  forces the non-liquefied component gases that have traversed the length of duct  102  to be sequestered in drum  111 . A shutter  110  at the end of the duct is mounted on drum  111 . Shutter  110  is in an open position until drum  110  is to be removed just before which shutter  110  closes. 
         [0027]    In one preferred embodiment, duct  102  is shaped so that one portion of duct  102  is lower in height than any other portion of duct  102 . At this lower position along duct  102  is spout shutter  1005 , rigidly attached to the top of drain spout  105 . In the open position of spout shutter  1005 , gravity causes the liquefied gas components  102   a  in duct  102  to flow into spout  105  into collection chamber  106  where drain spout  105  empties into collection chamber  106 , positioned with drain spout  105  placed in the interior of collection chamber  106 . After the desired components of gas mixture  100   d  have condensed, slidable shutter  1005 , having been in a closed position, opens to cause liquified gases  102   a  to flow into spout  105  and become collected as liquefied gas  107  in collection chamber  106 . 
         [0028]    A second duct configuration is shown in  FIG. 2 . The difference of this embodiment compared to that of  FIG. 1   a  is principally in the shape of the duct and the means for collecting individual condensates in separate collection chambers compared to the single chamber  106  of  FIG. 1   a . Duct  202  is linear in length without the curvature of duct  102  shown in  FIG. 1   a . Duct  202  has a cross-sectional area in the range of 1 to 100 square feet. An array of spouts  205   a ,  205   b , and  205   c  are connected to duct  202 , with spouts  205   a ,  205   b  and  205   c  with a slideable spout shutter  2005   a ,  2005   b  and  2005   c  mounted on the top of corresponding spout  205   a ,  205   b  and  205   c  with each shutter having a closed position and an open position, the latter position when collecting condensate  202   a ,  202   b , and  202   c  into a corresponding array of collection chambers  206   a ,  206   b  and  206   c . This array of spouts with shutters and collection chambers makes it possible to collect separate liquefied hydrocarbon components  102   a  of gas  100   d , each component collected in a separate collection chamber  206   a, b, c  positioned under a drain spout  205   a,b,c . The components of gas  102  have different and distinct condensation temperatures so that a component of gas  100   d  with the highest condensation temperature will be collected first, in collection chamber  206   a , located closest to flange  101 , the component with second highest condensation temperature will be collected further from flange  101 ,  101  than the condensate collected at  206   b , the third highest in  206   c , the furthest from flange  101  compared to the location of  206   a  and  206   b.    
         [0029]    While the embodiment shown in  FIG. 2  has an array of three shutters, spouts and collection chambers, it should be clear to those skilled in the art, that the number in the array can be can be extended to more than three or any number consistent with the dimensions of the duct and the number of hydrocarbons to be separately collected. An array of thermal sensors  2004   a ,  2004   b  and  2004   c  communicate with the master control  3000 , of  FIG. 3 . 
         [0030]    The control unit  3000   FIG. 3  is also used to control the temperature of duct  202 . Unit  3000  also controls and coordinates the open and shut positions of spout shutters  2005   a ,  2005   b  and  2005   c . As stated, the component of gas with the highest condensation temperature of coal/biomass gas  100   d  will liquefy at a position nearest to flange  101 . Each gas with a lower condensation temperature will be collected at a position at a distance further away from flange  101 . 
         [0031]    Fan  109  mounted within close proximity of the far/distal end of duct  202  drives the remaining uncondensed components of gas  100   d  into collection drum  111  when slideable shutter  110  is in an open position. The shutter  110  closes when the drum  111  is to be removed for the re-processing of the uncondensed gases captured within drum  111 . 
         [0032]      FIG. 4  is a schematic diagram showing how kiln shell  10  and kiln core  11  of  FIG. 1   a  are connected via flange  101  to duct  102 ,  FIG. 1   b . In addition, unit  3000 , the control unit, is connected to  10 ,  11  shown in  1000  ( FIG. 1   a ) and  102  shown in  1001 , ( FIG. 1   b ). 
         [0033]    Having described our invention,