Chemistry of hydrocarbon compounds – Production of hydrocarbon mixture from refuse or vegetation – From synthetic resin or rubber
Reexamination Certificate
1998-02-23
2002-04-16
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Production of hydrocarbon mixture from refuse or vegetation
From synthetic resin or rubber
C201S002500, C201S025000
Reexamination Certificate
active
06372948
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved process and apparatus for the destructive distillation or pyrolysis of rubber, such as used rubber tires, to produce liquid and gaseous hydrocarbons and a solid carbonaceous char. More particularly, the invention is directed to an improved process and apparatus for preheating a rubber charge introduced into a distillation oven, cooling the char produced therein, determining the distillation end point and providing a substantially gas-tight distillation oven door seal.
Disposal of discarded rubber tires poses a significant environmental problem. Burning of used tires is undesirable, if not prohibited, due to the attendant air pollution, while landfilling essentially nonbiodegradable rubber rapidly depletes available landfill space.
In devising ways to more effectively dispose of used tires, particular attention has been paid to methods for recovering the raw materials present in scrap rubber. Generally, it is known that scrap rubber may be heated in a sealed distillation oven substantially free of oxygen under conditions of pressure and temperature such that the rubber disassociates into a vapor phase comprising the volatilized hydrocarbon components of the rubber and a solid carbonaceous char. At least some of the vapor phase withdrawn from the oven is, condensed to form various liquid hydrocarbon fractions which are separated from the remaining gaseous hydrocarbons. Both the liquid and gaseous hydrocarbons may be used as fuel sources and may even be recycled to the destructive distillation process to provide some or all of the fuel burned to heat the rubber. After the destructive distillation is complete, the oven and its contents are cooled and the solid carbonaceous char is removed from the oven. After processing to remove any steel scrap, the solid material that remains may be used as carbon black in the production of new tires or as a component in roadway asphalt.
Jarrell, U.S. Pat. No. 5,230,777, discloses a vacuum destructive distillation process and apparatus for recovering hydrocarbon fuel and carbon black from rubber tires. Jarrell describes the operation of two rubber distillation ovens in off-set, batchwise distillation cycles and the conservation of energy by using waste heat removed from one of the ovens during cooling to preheat the rubber charge in the other oven. To achieve this, the two ovens are connected by a valved pressure equalization line. At the end of the distillation cycle in one of the ovens, the pressure in the other oven, which contains a fresh charge of rubber feed, is reduced to provide a pressure differential between the two ovens. The pressure equalization line is then opened to produce a one-way flow of gas between the two ovens until the pressure is equalized. As a result of the gas flow, the oven in which the distillation cycle has just been completed and the rubber char contained therein is cooled and a small amount of the waste heat transferred to the other oven. The transferred waste heat preheats the rubber feed in the other oven, thereby conserving energy by reducing the amount of heat necessary for the distillation.
Although Jarrell achieves a certain degree of energy recovery, gas flow and heat transfer essentially stops as soon as the pressure in the two ovens has equalized. As a result, the waste heat in the cooling oven is not fully utilized in preheating the rubber charge in the other oven, nor does the waste heat from the cooling oven dissipate at an effective rate. Since considerable time must pass to allow the oven and its contents to cool before it can be opened and reloaded with a rubber charge, the processing capacity of the system is limited. Another difficulty encountered in Jarrell and other prior art rubber distillation systems is the inability to accurately determine the end point of rubber pyrolysis so as to consistently obtain a char of desired composition. Furthermore, the door seals on ovens of destructive distillation apparatus often leak during operation due to thermal warping of the door and housing. Leaks in an oven door seal decrease the quality of the hydrocarbon vapor produced and compromise the safety of the apparatus.
SUMMARY OF THE INVENTION
Among the objects of the present invention, therefore, may be noted the provision of an apparatus and process for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char in which energy conservation is improved; the provision of such an apparatus and process in which the cooling time between distillation cycles is effectively reduced to increase the system's processing capacity; the provision of such an apparatus and process in which the end point of rubber distillation can be easily and consistently determined; and the provision of an improved door seal for a destructive distillation oven which substantially inhibits the flow of air into the oven despite thermal warping of the door and housing.
Briefly, therefore, the present invention is directed to a process for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The process comprises heating rubber in the substantial absence of oxygen to a temperature sufficient to pyrolyze the rubber, distill a vapor comprising hydrocarbon from the rubber, and produce a solid carbonaceous char. The vapor produced is partially condensed to produce a liquid fraction comprising hydrocarbon and a remaining gaseous fraction. The carbonaceous char is contacted with a heat transfer gas to transfer heat from the char to the gas and thereby cool the char. The heat transfer gas circulates in a circulation loop which comprises means for removing the heat transferred to the gas from the char.
The invention is further directed to a process for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The process comprises loading a charge of rubber into a first distillation chamber and heating the rubber charge in the substantial absence of oxygen to a temperature sufficient to pyrolyze the rubber, distill a vapor comprising hydrocarbon from the rubber, and produce a solid carbonaceous char. The hydrocarbon containing vapor produced is partially condensed to produce a liquid fraction comprising hydrocarbon and a remaining gaseous fraction. A second charge of rubber is loaded into a second distillation chamber and a heat transfer gas is circulated between the first distillation chamber and the second distillation chamber so that the gas contacts carbonaceous char in the first chamber and contacts the second rubber charge in the second chamber. Circulation of the heat transfer gas results in heat being transferred from the carbonaceous char to the gas in the first chamber and heat being transferred from the gas to the second rubber charge in the second chamber, thereby cooling the char in the first chamber and preheating the second charge in the second chamber.
The invention is further directed to a process for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The process comprises heating a rubber charge in a distillation chamber in the substantial absence of oxygen to a temperature sufficient to pyrolyze the rubber, distill a vapor comprising hydrocarbon from the rubber charge and produce a solid carbonaceous char. The vapor produced is partially condensed to produce a liquid fraction comprising hydrocarbon and a remaining gaseous fraction. The weight loss of the rubber charge in the chamber as a result of pyrolysis is monitored and the heating of the rubber charge is discontinued in response to the weight loss of the rubber charge or a function of the weight loss of the rubber charge.
The invention is further directed to an apparatus for the destructive distillation of rubber to produce hydrocarbon and a solid carbonaceous char. The apparatus comprises a distillation chamber for holding the rubber. The chamber is sealable for the substantial exclusion of oxygen from the chamber. A heating means is associated wit
Gentech, Inc.
Griffin Walter D.
Senniger Powers Leavitt & Roedel
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