Abstract:
An apparatus and process for pyrolyzing waste tire chips, the tire chips passed into an inclined rotary kiln having an output end. The tire chips are saturated by oil in the inclined rotary kiln and are pyrolyzed by indirectly heating with a heated gas. The pyrolyzed tire chips and oil produces a vapor product and a solid product that are separated within the kiln by gravitational separation. The vapor product is processed to condense oil and a portion of the condensed oil is recycled to the rotary kiln. The solid product is separated into oil and char, a portion of the oil recycled to the inclined rotary kiln for saturating the tire chips. The vapor product following the oil removal is used to produce the heated gas to heat the rotary kiln.

Description:
This application is a 371 of PCT/US99/07163, filed Mar. 31, 1999, which claims benefit of 60/080,329, filed Apr. 1, 1998 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a continuous temperature variance pyrolysis process and apparatus for recovering valuable oil products, carbon black, steel, and uncondensed vapors from tire chips. 
     BACKGROUND OF THE INVENTION 
     Over the past few decades the growth of illegal tire dumps has become a major environmental and health problem. Waste tires are generated in the United States at an estimated rate of approximately 240 million tires per year. Of the 240 million waste tires, approximately 200 million are estimated to be land filled or stockpiled. However, the very characteristics that ensure durability of the tires also make their disposal difficult whereby discarded tires can last between 500 to 1000 years in the environment. Therefore, these tires pose a unique landfill problem. In addition to becoming breeding grounds for countless varieties of vermin and mosquitoes, discarded tires are known to “float” to the surface, exerting sufficient force to rupture the landfill cap. Moreover, piles of discarded tires, such as those existing at numerous sites around the world, can serve as fuel for sustaining combustion once the piles are somehow set ablaze, such as by lightning or by accidental or purposeful human agency. 
     In order to prevent such major environmental hazards, increasingly the waste tires have been shredded into more manageable tire chips. While some companies continue to burn the whole tire for fuel, many others use the tire chips to fuel other processes. However, with the utilization of these methods, valuable byproducts such as carbon black are needlessly wasted. Moreover, gas emissions from the burning process can prove harmful to the environment. 
     One economically feasible and environmentally effective means for disposing of the tire chips is through the process of pyrolysis. The tire chips can be pyrolized to yield saleable products including gases, useful oil and carbon black. 
     Pyrolysis is the process of utilizing heat to cause a chemical change in a substance. In particular, the actual pyrolysis process is the result of the heat-induced chemical decomposition of organic materials in the absence of oxygen. Saturating the chips with process oil effectively facilitates the pyrolysis to yield pyrolytic gas, oil, and a char-steel mixture. The char is a fine particulate matter composed of carbon black, char and other inorganic materials, such as zinc oxide, carbonates and silicate. 
     Pyrolysis is especially appealing for tire chip disposal because each product and by-product of the pyrolytic process is marketable. The generated gas has a heat value of from about 170 to 2,375 BTU/ft 3 . The produced light oils can be sold for gasoline additives to enhance octane, and the heavy oils can be used as a replacement for number six fuel oil. The solid char can be upgraded and sold as carbon black. 
     Pyrolysis poses little to no harm to the environment because of the absence of harmful emissions. However, upgrading char to carbon black and the pyrolytic process itself can prove expensive. Moreover, tire pyrolysis can prove economically detrimental if an efficient process is not utilized to produce a sufficient amount of product yield. Examples of such systems are disclosed in U.S. Pat. No. 4,983,278 issued Jan. 8, 1991 to Cha et al.; U.S. Pat. No. 5,389,691 issued Feb. 14, 1995 to Cha et al.; and U.S. Pat. No. 4,647,443 issued Mar. 3, 1987 to Apffel. 
     Accordingly, there continues to be a need in the industry for improvements in the effective pyrolytic disposal of tire chips. 
     SUMMARY OF THE INVENTION 
     The present invention discloses an apparatus and process for pyrolyzing waste tire chips to extract carbon black oil, and various gases. The tire chips are fed into an inclined rotary kiln and exposed to heat at continuously varying temperature as the tire chips move through the kiln. Within the kiln, the tire chips are soaked in oil such that a chemical reaction occurs, resulting in a dry solid product and a gaseous, vapor product. The solid product is subsequently fed through a magnetic separator which separates the steel from the remaining char. The char can then be upgraded to yield carbon black. 
     The gaseous product stream passes through multiple condenser/scrubbers to yield a purified form of oil for storage, char for conversion into carbon black, and uncondensed gas used as fuel for the kiln. 
    
    
     These and various other features and advantages, which characterize the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B together depict a flow diagram for a pyrolysis process for extracting products from tire chips in accordance with the present invention, with FIG. 1A depicting a portion of the process for the char and heavy oil recovery, and FIG. 1B depicting a portion of the process for vapor condensation. 
     FIG. 2 provides mass and energy balances for the tire pyrolysis process depicted in FIGS. 1A and 1B. 
     FIG. 3 provides mass and energy balances for the product discharge hood depicted in FIGS. 1A and 1B. 
     FIG. 4 provides mass and energy balances for the Condenser/Scrubber depicted in FIGS. 1A and 1B. 
     FIG. 5 provides mass and energy balances for the Engine depicted in FIGS. 1A and 1B. 
     FIG. 6 provides mass and energy balances for the Plenum depicted in FIGS. 1A and 1B. 
     FIG. 7 provides mass and energy balances for the Stack Gas depicted in FIGS.  1 A and  1 B. 
    
    
     DETAILED DESCRIPTION 
     It will be noted that FIG.  1 A and FIG. 1B depict portions of the same process, and placed together, depict a preferred embodiment of the present invention for extracting products from waste tire chips. For purposes of facilitating discussion, the process has been divided into two figures. Therefore, conduit streams that have been truncated in FIG. 1A have been numbered from 1 to 5 to correspond to identical numbers in FIG. 1B to show the continuation of the conduit streams. 
     Referring now to FIG. 1A, shown therein is a process flow diagram illustrating an apparatus  10  for the pyrolysis of tire chips, constructed in accordance with the present invention. While the present invention is described in detail hereinbelow, it will be noted that details of construction involving the usual piping, valving, electrical systems, and controls associated with the process equipment of the type herein described will be known to people of ordinary skill in this area of technology and need not be included herein. 
     As the production of waste tires increases, there is an ever increasing need to find improvements in methods of disposal. To this end, the present invention provides a pyrolysis process for decomposing tire chips into oil, carbon black and gas. 
     In FIG. 1A, an engine  12  provides a heated gas to a kiln  14  for heating the kiln  14  to the desired temperature to initiate the pyrolysis process. The kiln  14  is a large double drum assembly that tilts slightly upward at its output end with an inner cylinder or drum rotating slowly so that the solid contents of the inner cylinder are augered to the upper end. An outer cylinder forms a shell about the rotating inner drum, and an annular space is formed between the inner drum and outer shell. Such rotating drum kilns are conventionally known and need not be described further herein except to note that the movement of the contents within the rotating inner drum is achieved by auger members disposed along the internal surface of the rotating inner drum. 
     The exhaust gas of the engine  12  is conveyed to pass through the annular space between the outer shell (not shown) and the inner rotating drum (not shown) of the inclined rotary kiln  14  and passed therefrom as exhaust gas, as shown. A plurality of tire chips  16  are fed into the rotating drum of the inclined rotary kiln  14  for pyrolytic heating. As the tire chips  16  travel through the inclined rotary kiln  14 , the tire chips  16  are immersed in a flow of recycled oil  18  while the tire chips  16  begin to break down as the tire chips  16  are exposed to a continuous variance of temperature, increasing from about 237° F. to 1000° F., preferably from 400° F. to 500° F., with a maximum oil yield occurring at 450° F. The coolest temperature is at an input end of the inclined rotary kiln  14  while the hottest temperature is at an output end of the inclined rotary kiln  14 . The low temperatures expended during the pyrolysis expends a lower amount of energy and thereby provides a more efficient process. The high temperatures in the inclined rotary kiln  14  cause volatile hydrocarbons to vaporize and to pass out of a kiln discharge hood  26 . The pressure within the kiln  14  ranges from approximately 3 in. of H 2 O to about 5 in. of H 2 O. 
     At the completion of the pyrolysis process, the tire chips  16  have been effectively decomposed to their solid, elementary components  20 . The solid product,  20 , because of the absence of combustion, comprises mostly char, metal, and fabric material. This solid product  20  passes from the kiln  14  to an ash conveyor  22 . The ash conveyor  22  carries the solid product  20  to a magnetic separator  24 , wherein steel is separated from the char ash. The char is subsequently stored for later conversion to carbon black. 
     Turning now to FIG. 1B, shown therein is a continuation of the tire pyrolysis process wherein the flow diagrams for vapor condensation and oil and solid recoveries are shown. As shown, the incline of the inclined rotary kiln  14  facilitates gravitational separation of the solid product  20  and the vapor product  28  so that the less dense vapor product  28  drifts to the top of the inclined rotary kiln  14  while the more dense solid product stays at the bottom of the inclined rotary kiln  14 . Gravitational separation facilitates efficient separation of the vapor product  28  from the solid product  20  without introducing foreign purging agents. The vapor product  28  is sent to a first condenser/scrubber  30  to extract any remaining oil. The vapor product  28  is subsequently sprayed with cooled, recycled oil  32 , causing the larger molecules (generally eight or more carbon atom&#39;s) to condense. The oil condensate  34  exits from the bottom of the first condenser/scrubber  30 . 
     Returning to FIG. 1A, the oil condensate  34  follows three paths. The first oil stream  18  is recycled back into the kiln  14  to wet the tire chips  16 . A second stream  36  of condensate  34  passes through a first air cooled heat exchanger  38 . A third stream  40  of condensate  34  mixes with the air cooled second stream  36  before flowing into an oil/solids separator  42 . The oil/solids separator  42  precipitates the solid char from the oil. The solid char is collected for later conversion to carbon black. The separated heavy oil from the oil/solids separator  42  follows two distinct streams. A first stream  44  of heavy oil is collected in a storage unit while a second stream  46  is recycled back into various points of the first condenser/scrubber  30  to facilitate condensation. 
     Continuing now with FIG. 1B, uncondensed vapor product  28 A in the first condenser/scrubber  30 , such as the light oils, passes through a mist eliminator  48  and is passed to a second condenser/scrubber  50 . The second condenser/scrubber  50  is contacted with recycled oil  32  from the storage unit, causing the light oils to condense. The oil condensate  52  is separated into two different streams: a first stream  54  of the oil condensate  52  passes through a second air cooled heat exchanger  56 ; and a second stream  58  of oil condensate  52  mixes with an air cooled stream  60  of condensate before entering into an oil/water/solid separator  62 . The oil/water/solid separator  62  separates oil from the solid char, with some oil collected within the storage unit and another portion of the oil introduced back into the second condenser/scrubber  50  to facilitate condensation. The collected char is conveyed to a separate site for such use as the production of carbon black. 
     The gas remaining after the oil recovery, pyro-gas  64 , is fed from the second condenser/scrubber  50  to the engine  12 , which is operated in a useful manner, such as to power a generator for producing electrical power. The exhaust of the engine  12  is directed to the annular space between the outer shell and the inner drum of the inclined rotary kiln  14 . Of course, it will be understood that the object is to use the heating valve (enthalpy) of the pyro-gas  64  to usefully heat the inner drum of the inclined rotary kiln  14 , and it is within the scope of the present invention to use the pyro-gas  64  in any manner to achieve such object. For example, the pyro-gas  64  can be combusted and the products of combustion passed through the annular space between the outer shell and the inner drum of the kiln  14 . 
     A detailed analysis of the mass and energy balances for the apparatus and process of the present invention are presented in FIGS. 2-7. Provided in FIG. 2 is a table of the overall mass and energy balances for the product and process as depicted in FIGS. 1 A- 1 B. It should be noted that for the kiln  14  to effectively tumble and rotate, the kiln  14  should not be filled to more than about twenty percent of its capacity. Therefore, the twenty percent capacity of the kiln  14  along with the  60  foot length of the kiln  14 , as depicted in the table in FIG. 2, determines the design parameters of the process, and allows a total feed rate of 10,000 lbs/hr. Both tire chips-(solids) and the oil are fed into the kiln  14 . 
     Turning to FIG. 3, shown therein is a table containing mass and energy balances for the kiln discharge hood  26 . The kiln discharge hood  26  provides an outlet for the vapor product  28  which enters the first condenser scrubber  30 . Note that the shell heat loss of 7740 BTU/hr indicates the amount of heat given off by the kiln discharge hood  26 . 
     Turning to FIG. 4, shown therein is a table containing mass and energy balances for the condenser scrubber  30  wherein the vapor is separated from the oil to yield a gaseous phase and an oil phase. The inlet flue flow of 7576 lbs/hr equals the amount of gas flow out of 7576 lbs/hr from the kiln discharge hood as depicted in the table in FIG.  3 . 
     Turning now to FIG. 5, shown therein is a table containing mass and energy balances for the engine  12  that drives the process and apparatus as depicted in FIGS. 1A-1B. The total gas flow or electric power of 14,047 lbs/hr is a measurement provided by a manufacturer of the engine  12  as used in driving a process as depicted in the present invention. It should be understood that the details of construction of the engine  12  are not believed to be necessary for the present disclosure and will be readily understood by those skilled in the art. 
     Turning to FIG. 6, shown therein is a table containing mass and energy balances for a plenum (not shown) of the kiln  14 . The plenum is an area around the kiln  14  wherein exhaust from the engine  12  circulates to heat the kiln  14 . The exhaust exit temperature of 1350° F. heats the kiln  14 . Heat is released through flue gas exiting the plenum at a flue gas exit temperature of 690° F., thereby heating the kiln  14  at a lower temperature. 
     Turning now to FIG. 7, shown therein is a table containing mass and energy balances for stack gas used to vent the process and apparatus of the present invention as shown in FIGS. 1A-1B. A stack (not shown) allows excess heat from the process of the present invention to be vented to the atmosphere. The gas to atmosphere of 2,458,330 BTU/hr allows a determination of the 3.14 ft 2  stack area required. It should be understood that the details of construction of the stack are not believed to be necessary for the present disclosure and will be readily understood by those skilled in the art. 
     It is clear from the above description and the example provided that the present invention is well adapted to carry out the objects and to attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments have been described for the purposes of this disclosure, it will be appreciated that numerous changes in the arrangement of steps and apparatus components can be made by those skilled in the art. Such changes are encompassed within the spirit of this invention as defined by the appended claims.