Method and apparatus for gasifying waste automotive tires to produce high quality solid carbon and non-condensable synthesis gas

Abstract

A method for selectively producing condensable hydrocarbon gases and non-condensable synthesis gases from waste tire chips in a single rotating reactor having a drying and volatizing hearth reaction area contiguous with a reformation hearth reaction area, including the steps of feeding waste tire chips into the drying and volatizing area, heating the tire chips in the drying and volatizing area to a temperature of about 500 C to about 600 C, drying and volatizing the tire chips to form a hot process gas and hot residual solid carbonaceous matter; raising the temperature of the hot process gas and the hot residual solid carbonaceous matter to a temperature in the range of from about 600 C to about 1000 C; and thermally reforming the hot process gas to form a synthesis gas composition; and hot residual solid carbonaceous matter. The apparatus for producing high quality carbon and synthesis gas from waste automotive tires is also disclosed.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/464,896, filed Apr. 23, 2003.

FIELD OF THE INVENTION

The present invention is a method and apparatus for processing waste automotive tires in a gasification reactor for the primary purpose of producing high quality carbon (residual solid) products, and secondary purpose of producing a non-condensable high quality synthesis gas.

BACKGROUND OF THE INVENTION

In 2002, world DRI production set a new world record of 45 million tons.

• • 90.2% was processed by natural gas.
  • 9.8% was coal-based.

Direct Reduced Iron (DRI) is a high-quality metallic product produced from iron that is used for feed stock in electric arc furnaces, blast furnaces and other iron and steel making applications. DRI is produced as lumps, pellets and briquettes.

The following processes use coal as a reductant:

• • SL/RN
  • JINDAL
  • DRC
  • GHAEM
  • CODIR
  • Rotary Hearth Furnace
  • SIIL
  • OSIL
  • TISCO
  • KINGLOR-METOR
  • DEEPAK
  • SCAN
  • SURYAA

Organic matter, including tires, solid waste, or biomass, can be thermally processed according to this invention to provide solid carbon for iron ore reduction in the above processes.

Existing industrial processes that utilize the potential energy contained in waste automotive tires do so primarily by methods of incineration or pyrolysis. For example, aside from environmental considerations, the volatile metal and sulfur content in automotive tires is a limiting factor in the amount of waste tires that can be used as combustion (incineration) energy in cement kilns and steam boilers. Due to the inherent nature of indirectly heated pyrolysis processes and the limiting degree of internal heating and oxidizing agents provided, only about 10% to 15% of the weight is converted into synthesis gas, while 40% to 50% of the weight is converted into a viscous petroleum-like distillate and 40% to 50% of the weight remains as carbon char. Syncrude contamination of the carbon char product decreases its potential commercial applications and value. Further, the inherent nature of indirectly heated retorts (pyrolysis processes) greatly limits the ability to scale-up such processes to achieve acceptable economy-of-scale production levels.

In view of the above limitations of both incineration and pyrolysis processes for recycling waste automotive tires in an environmentally safe and efficient way, the present invention offers advantages of economy-of-scale, high quality synthesis gas and clean carbon char without producing the troublesome viscous petroleum-like distillate by-products. The process of this invention is able to thermally crack and dissociate the complex hydrocarbon vapor/gas (evolved from tire chips during the heating phase) to such a degree than no more than about one-half of one percent (by volume) of gases with a molecular structure having more than two carbon atoms remain in the product synthesis gas stream.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for processing waste automotive tires in a gasification reactor for the primary purpose of producing high quality carbon (residual solid) products, and secondary purpose of producing a non-condensable high quality synthesis gas. The solid carbon is of sufficient quality to replace carbon from natural coal in carbon based metal reduction processes including the production of directly reduced iron in processes such as rotary hearth and rotary kiln reactors. The solid carbon is recovered in a broad range of particle sizes and in addition to uses for direct reduction of metals also has uses in higher value applications including filtering, and as carbon black. The non-condensable synthesis gas produces is of sufficient quality to be piped to associated industrial users. The synthesis gas has a broad range of industrial uses including: fuel gas, being sieved for recovery of higher value hydrogen, carbon monoxide or carbon dioxide, and as a raw material source in production of chemicals. No distillate oil is produced.

This invention is an improvement of the inventions disclosed in U.S. Pat. No. 6,005,149 issued on Dec. 21, 1999, and U.S. Pat. No. 5,425,792 issued on Jun. 20, 1995, both of which are incorporated herein by reference.

OBJECTS OF THE INVENTION

The principal object of the present invention is to provide a method of producing high quality carbon from waste automotive tires.

A further object of this invention is to provide a method of producing high quality synthesis gas from waste automotive tires.

Another object of the invention is to provide apparatus for producing high quality carbon and synthesis gas from waste automotive tires.

DETAILED DESCRIPTION

This invention is a method and apparatus for thermally processing waste automotive tires and to efficiently extract non-condensable synthesis gases rich in hydrogen and carbon monoxide for uses such as; a feedstock for primary chemical processes, a clean fuel gas or (via sieving), a source of higher value hydrogen, carbon monoxide or carbon dioxide gases. The process can be controlled to achieve higher or lower production rates of either synthesis gas or carbon char. Higher char production rates come at the expense of lower synthesis gas production rates and vice-versa.

In particular, the apparatus of this invention is a single rotating reactor that has two contiguous hearth reaction areas, i.e., a drying and volatizing area and a synthesis gas reformation area. The two areas are separated only by the induced and opposing atmospheres generated by the process burners that fire from each end of the disclosed reactor. Gases and fumes formed in the drying and volatizing area flow co-currently with the direction of the burner products induced by the feed-end process burner. Cracking, dissociation, and/or reformation of vaporous hydrocarbon gases issuing from the feed-end of the reactor begins when these evolved gases enter the influence of the counter-current high temperature atmosphere induced by the discharge-end process burner. High turbulence results in the contact zone in which gases from the feed-end collide with the counter-current products-of-combustion from the discharge-end process burner. The high turbulence, induced by the process burner gases, greatly enhances cracking, dissociation and/or reforming of the complex hydrocarbon gases and reduces such gases to more simple molecular forms. The reformed gases move toward the discharge-end of the reactor in a counter-current and chaotic high temperature atmosphere induced by the discharge-end process burner.

Operational objectives and parameters established for process control determines the intensity of input energy from the feed-end and discharge-end burners. Both the feed-end and discharge-end burners are designed to operate specifically with a fuel gas, oil, carbon fines or syngas as the combustion energy source, and near-pure oxygen is provided as the oxidizing agent. Air is not used in either burner; thus, the level of nitrogen in the product synthesis gas is exceptionally low.

A feature of this invention is that it will provide high quality solid carbon and syngas exclusively from automotive tires.

The use of DRI (direct reduced iron) produced in a RHF (rotary hearth furnace) from greenball pellets of pulverized iron ore or iron bearing wastes, and carbon produced from the Thermal/Reduction Gasification (TRG) Process, or other carbon sources, including coal, is an integral part of certain steelmaking processes. Using a portion of the waste gases from the RHF/TRG, the pellets are partially dried and preheated prior to being charged into the RHF. In the RHF, the greenball pellets are raised to a temperature and held long enough to accomplish reduction of the iron oxide to metallic iron.

After discharge from the RHF, the hot DRI is taken directly to the melting operation in insulated canisters to conserve as much latent heat as possible. The overall concept is to reduce thermal energy input to the lowest possible level. Additionally, as the pellets are held during the transfer, the reduction reaction will continue to equilibrium and the final metallization is expected to be well above 90%.

Carbon based DRI has several advantages. It can be discharged hot from the RHF and still contain a high and controllable percentage of carbon. Also, carbon based DRI is advantageous in steelmaking in that it is possible to control the amount of carbon remaining in the DRI pellet after reduction has occurred.

The DRI process is a solid carbon based system. According to the present invention, almost any reasonable source of carbon can be used, such as carbon from shredded automobile tires, municipal and industrial solid waste, or other biomass. Other suitable sources are coal, petroleum coke, coke breeze, lignite or charcoal fines. Each potential source must be evaluated for its overall contribution to the cost per iron unit of the finished DRI product.

When iron bearing metallurgical wastes are proposed as the source of iron units, the average analysis of these wastes is a known quantity in contrast to a questionable positive analysis of steel scrap. This known analysis enables steel mills using such materials to produce consistently cleaner steel, from a contaminant standpoint, than a conventional scrap-based mill. After beginning operation in a facility using iron ore and carbon as the primary raw materials, then operators may substitute the locally available wastes to the fullest extent possible.

The produced carbon char, derived from the thermal processing of organic matter, are utilized as a reductant in reducing iron oxides into metallic metal.

This invention excludes the injection of pulverized coal in blast furnaces, or melting vessels that require fixed carbon injection as a reductant, or a substitute for coal or coke for direct reduced iron processes that require coal to be blended in a pellet.

Also, the carbon char produced from tire chips by this invention can be substituted for the coal utilized in coal based sponge iron processes and the synthesis gas can be substituted for natural gas that is used for direct reduction.

The char product can also be used as fuel to attain the temperatures required in steam boilers that power steam-driven turbines for the generation of electricity. Also, the organic carbon can produce syngas to replace coal as a fuel.

The present invention produces high quality (secondary) carbon char product from gasification of tire chips, such secondary carbon being of sufficient quality to substitute for carbon derived from primary coal, and such secondary carbon being used in the formation “greenball” pellets composed of predetermined mixtures of fixed carbon associated with iron-oxide ore, or other metal oxides, for the purpose of providing the necessary reducing agent needed to produce high quality metallic pellets via solid-carbon-based direct reduction processes including any of the following:

• • Rotary Hearth Furnaces, or
  • Rotary Kiln Furnaces, or
  • Electric Smelting Furnaces, or
  • Other thermal processes, including all such processes that presently use pulverized natural coal or processed coke breeze as fuel for process burners or tuyeres, or other types of process that require additions of solid carbon either for purposes of direct reduction or to provide process energy.

The invented process produces high quality synthesis gas from waste automotive tires, *such synthesis gas being essentially free of condensable hydrocarbons, acids, alkalis, halogens, heavy metals, or particulate matter, and such synthesis gas having a normal heating value between 350 and 425 Btu/scf.

SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION

From the foregoing, it is readily apparent that we have invented an improved method and apparatus for producing high quality carbon and synthesis gas from waste automotive tires.

It is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof, and that various modifications and additions may be made to the apparatus by those skilled in the art, without departing from the spirit and scope of this invention, which is therefore understood to be limited only by the scope of the appended claims.

Claims

1. A method for selectively producing condensable hydrocarbon gases and non-condensable synthesis gases from tire chips in a single reactor, comprising the steps of:

providing a single rotating reactor having a drying and volatizing hearth reaction area contiguous with a reformation hearth reaction area;

feeding waste tire chips into the drying and volatizing area;

heating the tire chips in the drying and volatizing area to a temperature of about 500 C to about 600 C;

retaining the tire chip material on a rotating bed in the drying and volatizing area until the material is substantially completely dried and volatized to form a hot process gas and a hot residual solid carbonaceous matter;

moving the hot process gas into the reformation area;

forming a bed of residual solid carbonaceous matter in the reformation area;

raising the temperature of the hot process gas and the hot residual solid carbonaceous matter in the reformation area sufficiently high to reform the hot process gas;

thermally reforming the hot process gas to form a synthesis gas composition; and

discharging the hot gases and the hot residual solid carbonaceous matter from the reactor.

2. A method according to claim 1 wherein the temperature in the reformation area is in the range of from about 600 C to about 1000° C.

3. Apparatus for thermally processing organic materials to selectively produce condensable hydrocarbon gases and non-condensable synthesis gases, comprising:

a rotary reactor having a longitudinal axis, a feed end and a discharge end, a drying and volatizing hearth reaction area adjacent to the feed end of the rotary reactor for heating, drying and volatizing organic materials to form a hot process gas and a hot residual solid matter;

a reformation hearth reaction area adjacent to the discharge end of the reactor, the reformation reaction area being contiguous with the drying and volatizing reaction area;

means for separating the two contiguous hearth reaction areas;

a feed end process burner;

means for causing gases formed in the drying and volatizing hearth reaction area to flow cocurrently with the products of combustion of the feed end process burner; and

means for removing produced condensable hydrocarbon gases, non-condensable synthesis gases, and hot residual solid carbonaceous matter from the reactor.