Method and installation for low-temperature pyrolysis of rubber products, steel/rubber composites, and use of the pyrolysis products

Description

The invention relates to an industrial low-temperature pyrolysis method for separating steel/rubber or similar composite products for recovering carbon granulate, pyrolysis oil, residual gas and metallic components, and to the use of the pyrolysis products.

The method is used for the industrial salvaging, especially of discarded rubber products or rubber-like composite products. In connection therewith, a carbon granulate is produced by low-temperature pyrolysis from, for instance, tires, rubber-coated tread links, steel cable reinforced rubber belts and the like. In addition, pyrolysis oil and residual gas are accumulated as well. The metallic components are recovered.

Pyrolytic methods for treating organic materials and material mixtures are commonly known.

For instance, German patent DE 695 11 626 T2 describes the pyrolysis of waste in an internally heated rotary tube furnace.

DE 199 30 071 C2 discloses a method and an apparatus for pyrolysis and vaporization of organic materials and material mixtures. Here, the organic material is brought into contact with the fluidized bed material of the combustion fluidized bed. Pyrolysis products such as gases with condensable substances and carbon-containing residues are produced.

Patent DE 44 41 423 A1 describes a pyrolysis method and an apparatus for the recovery of useable gas from waste. In connection therewith use is made of a pyrolysis drum.

German laid-open patent specification DE 41 26 319 A1 discloses a method of pyrolysis of vulcanized silicone rubber in which the vulcanized material are heated to 350° C. to 700° C. and the resultant volatile siloxanes are condensed. The products obtained are, in particular, siloxanes and fillers.

German patent DE 40 11 945 C1 describes a low-temperature pyrolysis for degassing organic materials in a heated pyrolysis chamber in which the pyrolysis material is compressed and is fed through chamber in this state. Gaseous products of the pyrolysis are removed.

German patent DE 39 32 803 discloses a pyrolytic method by which organic materials are reacted to coal and graphite in a non-oxidizing atmosphere by addition of boric acid/boric oxide and organic nitrogen compounds.

German patent 28 34 475 C2 sets forth a method of treatment of a pyrolysis heating oil. By application of a promoter liquid, the result of this method is a special carbon (acicular coke).

The hitherto known methods operate with rotary tube furnaces, pyrolysis drums, fluidized bed, under pressure, by compressing the material or in an inert atmosphere. This entails increased expenditures for apparatus, material, energy and logistics.

The use of protective gases (non-oxidizing atmosphere) leads to a reduced throughput capacity relative to comparable units. The generation of a fluidized bed requires more energy since, on the one hand, the fluidized bed has to be maintained and, on the other hand, the materials to be pyrolyzed must be mechanically prepared such that they can effectively contact the fluidized bed. Compressing the raw materials in preparation for, and during, the pyrolytic operation also requires more energy.

It is an object of the invention to develop a novel technology particularly advantageous in terms of energy and economy, for the treatment of different rubbers or rubber-like composite materials with the goal of separating rubber/steel or other composites and recovering essential organic components, such as carbon granulate (soot), organic oils and, where applicable, metallic components.

For effectively practicing the novel method new reaction containers and other novel method modules relating thereto are to be developed and applied at the same time.

By developing modules the throughput is to be incrementally increased to correspond to any given market situation. The solution is to be in conformity with the desire for continuity.

In accordance with the invention, the object is accomplished by the elements of claims 1 and 8. The subclaims set forth further advantageous embodiments of the invention.

As conceived, the sequence of the method in accordance with the invention includes the following operational steps and related components:

• • Washing and cutting up of the input materials, such as rubber products, composite products and the like;
  • The rubber products (e.g. discarded tires) are presorted and transported to a washing facility. The washed rubber products are thereafter cut up. The tires may be cut into four pieces, eight pieces or, for operational reasons, they are to be coarsely shredded.
  • Drying of the input materials;
  • Charging the reaction container with input material;
  • The dried rubber products are fed by belt conveyors into a (high) storage container of, for instance, 12 m³ capacity. The reaction containers are filled from the storage container. The filled reaction containers are transported, for instance by a forklift, to a preheater of a pyrolysis furnace.
  • For charging the reaction containers with composite materials, such as rubber-coated tread links, conveyer belts, steel cables various technologies associated with detailed time and temperature windows for the pyrolytic process are available which have been determined through extensive trials. Depending on the goal set, it is also possible to charge the reaction container with a mixture of materials.
  • Execution of the pyrolysis process;
  • After preheating to a predetermined temperature has been completed, the reaction container is placed into a furnace.
  • The furnace chamber is heated in about 30 min by an appropriate process technique. As established by tests which have been conducted, the reaction time in the container is about 2.5 h.
  • The heating phase may take place in two to three stages with a variable dwell time. For a specific cooling phase, two selectively variable dwell times, each at a predetermined constant temperature, are reasonable. These data were derived from specifically developed technological processes. Depending upon input and product to be produced, the reaction temperature is between 350° C. and 500° C. The temperature difference to the desired reaction temperature may, at a maximum, be 15 K to 30 K.
  • The input material is heated in the container by indirect heat transfer. In a low-temperature pyrolysis process, with air oxygen excluded, rubber is broken down to its components. The process takes place under normal pressure. The installed temperature measuring system indicates the actual temperature of the air in the furnace chamber and the actual temperature in the reaction container. The display is a digital one.
  • The gas developed in the pyrolytic process is removed by an waste gas conduit and is cooled by an appropriate technical process. Pyrolysis oil is produced which in its consistency and composition resembles light crude oil or the intermediate products of crude oil processing. To render the process self-sufficient, the proportion of the pyrolysis gas which cannot be condensed, as well as proportions of the oil, may be used for generating the heat required for the process. The heating may selectively be carried out with commercial gas, electrically, with pyrolysis gas or pyrolysis oil. The heating course of the input material follows preset special control curves which by continuously comparing the actual temperature with the required one provide for a computer-assisted control the supply of energy.
  • The dependency of the process control from temperature and time must be presentable histographically. All relevant data as well as the malfunction reports are being documented. Upon termination of the pyrolysis process, termination of the operation is indicated by an optical signal at the furnace.
  • Emptying of the pyrolysis container (reaction container)
  • Cooling of the pyrolysis container to the temperature defined by the prescriptions as a function of product use is always indicated by an optical signal (lamp). Only then will the still closed pyrolysis container be released for further processing. Transportation takes place, for instance, with a forklift.
  • A carbon-iron mixture is present in the pyrolysis container. After opening the container in special rooms and with special work protection, the lid is removed. The opened reaction container is lifted with a lift or forklift and is emptied into a funnel in a low pressure zone without dust by a tilting device. Thereafter, the container is returned to the process and filled again.
  • From the funnel, the mixture of carbon granulate and iron is fed through a conical opening into a grinding mill. The residual carbon granulate still attached to the metal is removed and cut to a diameter of about 50 mm. The iron is removed by electromagnet in a special process. The iron (e.g. spring steel) drops into corresponding containers and is transported away. The carbon granulate is encapsulated and placed into an intermediate container from which it is conveyed to a silo in a dust-free manner. From the silo it can be automatically packaged dust-free into plastic bags and sealed.
    • The plastic bags may be stacked and belted on EURO-pallets for shipment. The silo offers the possibility of loading tank vehicles as well as of conveying the carbon granulate into an outer container (optional). Health, occupation and fire, including explosion, protection are satisfied by specific systems technology which complies with the state of the art.

The operational control of the system is carried out by a central DDC conveyor system or SPS control. It monitors and controls the operation by way of interfaces. The operations and the decisive parameters are schematically presented on a video monitor. Malfunction signals occur automatically error signals are recorded, printed out in clear text, evaluated and automatically forwarded to operational control.

The pyrolysis furnace used is a car tunnel kiln. For this purpose, converted standard hearth ovens from other fields of application are being used.

The loading with the reaction containers takes place in steps. Initially, it is placed by a forklift onto the furnace carriage of the pyrolysis oven. Upon actuation of a push button or the like the furnace carriage is moved into the furnace. The gate is then closed.

Alternatively, a shaft furnace may be used as a pyrolysis oven for receiving a reaction container.

The shaft furnaces used may be standard equipment converted from other fields of application.

The furnace may be positioned above ground or subterraneously. In that case, the reaction container is inserted by an appropriate lifting apparatus, for instance, by traveling winches or hoists. The reaction container may be constructed such that a special seal at the head of the container positions the container within the shaft and also hermetically seals the furnace.

It is within the scope of the present invention to provide for other solution for the structural exterior shape of the reaction container. The container, for reasons of process technology, has to be structured so as to ensure good heat transfer in its interior so that all pieces of input material are heated equally.

In a car tunnel kiln the closed pyrolysis container is moved on the furnace carriage, unloaded by a forklift and placed on the ground for cooling. The operation with a shaft furnace is similar.

By using reaction containers made of high temperature resistant steel which operate without pressure and without inert media it is possible to operate with discontinuous charges. The process thus offers the possibility of appropriately reacting to the kind of material (e.g. automobile summer tires, automobile winter tires, truck tires, special vehicle tires, rubberized thread links, steel cable reinforced rubber belts). The charging technology is constructed on a modular principle. The newly developed process operation eliminates the use of protective gases or liquids.

Another advantage is the avoidance of complex mechanical pre-treatment processes for the input materials. For instance, the tires are only washed and coarsely cut or shredded.

After the start-up, the conduct of the process is substantially self-sufficient in terms of energy.

Another important advantage is that steel-rubber-composites which heretofore could only be separated by a high application of energy, can now be separated without using much extraneous energy or possible wear, and that the output products may be efficiently recycled in high-quality applications so that resources are spared. This opens up some completely new fields of application of the materials recovered by the method.

The method in accordance with the invention and the apparatus may be advantageously used in the processing of used tires, complete used vehicles, electronic scrap, steel-cable reinforced rubber belts, rummer/nonferrous metal composites, plastic-coated chains, rubberized tread links and various technical rubbers.

Further details, characteristics and advantages will be apparent from the ensuing description of an embodiment with reference to the appended drawings, in which:

FIG. 1 is a flow diagram demonstrating the essential process sequence and appurtenant system components;

FIG. 2 is a schematic frontal view, partially in section, showing an embodiment of a car tunnel kiln; and

FIG. 4 Is a schematic frontal view, partially in section, showing an embodiment of a shaft furnace.

The flow diagram of FIG. 1 depicts the sequence of the method in accordance with the invention with appurtenant system components for the treatment of rubber products such as used tires. The used tires 1 are presorted and transported to a washing plant 2 by means of a conveyor belt. The washing operation takes place automatically in a closed cabin. The washing facility is provided with a built-in water recycling unit. Used water is regenerated in a continuous loop in order to prevent an unnecessary burden on the environment and sewage system. For feeding and replenishing the washing plant may use rain water as the processing water.

The washed tires 1 are cut up in a shredder unit 3. Thereafter, the tire parts are dried. The heating register of the drying facility is operated by a heat exchanger which is fed by the pyrolysis process (heat from heat recycling 17).

The temperature control of the drying air is continuous and is carried out by computer-assisted controls which are monitored by a central process control and the target data of which can be changed.

The further process operation includes the following process steps and appurtenant system components:

• • transportation of the dried used tire parts 1 by conveyor belt 5 to the storage container 6;
  • charging the reaction container 7 from the storage container 6;
  • preheating the reaction container 7 in a preheating facility 8;
  • placing the reaction container 7 into the pyrolysis furnace 9 and executing the pyrolysis process. The result of the pyrolysis are reaction products like coal 30, pyrolysis oil 33 and waste gases 34;
  • cooling of the reaction container 7 taken out of the pyrolysis furnace 9 in a cooling facility 10;
  • dust-free emptying of the reaction container in an appropriate facility 12 and return 15 of the emptied reaction container 7 for renewed filling;
  • separating the iron/carbon components 31, 30 in a separation facility 13 with the use of electromagnets;
  • the iron components are stored as metal scrap in container 18;
  • shredding or granulating the carbon 30 in an appropriate facility 14;
  • the carbon granulate 30 is encapsulated and fed to the silo 16 where it packaged 19 in portions and/or stored.

The further processing of the pyrolysis gas 32 by water cooling 21 leads to the formation of condensed pyrolysis oil 33. From this pyrolysis oil 33, products/aromatics P1 to P3 and residual tank oil P4 will be produced by refining/separating/processing 35. The residual oil P4 may be used for the thermal supply and energy production for one's own and others' purposes. The non-condensable pyrolysis gas is temporarily stored as waste gas 34 in a bell-shaped container and is burnt off in a further process at temperatures above 1,200° C. The dwell time is equal to or longer than 0.3 sec. Downstream from where the burning off of the waste gas 34 is taking place, heat conductors are installed into the waste gas oven which by way of the heat recovery 17 feed any excess heat back to the production process.

The heat from the heat recovery 12 may either be fed to the production process, i.e. the preheater 8 for the reaction container 7 and to the pyrolysis furnace 9 for preheating the combustion air 17.1, or heat 17.2. which has not been used can be used for other purposes, e.g. the heating of buildings.

FIGS. 2a and 2b are front and lateral views of a car tunnel kiln 9.1 fi=or the reaction container 7. A given reaction container 7 is placed on a power driven furnace carriage 22. The diameter and height of the reaction container 7 here in use are 1.8 m and 2 m, respectively. The other technical specification of a car tunnel kiln for a reaction container are:

Heating:	e.g. natural gas Hu 8,000 kcal/Nm3;
Contact value:	295 kW per furnace;
max. possible furnace temperature:	600° C.;
Application temperature:	350° C. to 500° C.;
Network voltage:	230/240 V, 50 Hz;
Control voltage:	230 V, 50 Hz.

The pyrolysis furnace 9.1 is completely lined and insulated; it is provided with a lifting gate 23 or the like for closing and opening of the furnace 91. The burner facility 24 consists of two special burners with 2 appropriate conduits and devices for natural gas or process gas or process oil, combustion air or electric heating.

Furthermore, there are present:

• • a combustion air fan as well as gages and control devices for natural gas or process gas or process oil and for combustion air;
  • a gas input conduit with a shut-down valve, pressure regulator, filter, pressure gage and pressure monitor;
  • a heat insulating furnace carriage 22 for receiving the pyrolysis reaction container 7, including drive and a set of wheels below (carrying capacity max. 6,000 kg);
  • a pyrolysis reaction container 7, welded with two tilting rings, curved lid with transport ring and connecting pipe (d=100 mm);
  • the pyrolysis reaction container and lid is made of heat-resistant steel, including rapid closures for the lid, heat resistant seal, cut-off valve;
  • an automatic temperature measuring and control device, mounted in a control cabinet with appurtenant control and regulating devices, with thermal elements 25 in the oven chamber as well as thermal elements 26 in the reaction container;
  • an waste gas pipe 11 for transporting the gas from the pyrolysis reaction container 7 with cut-off valve and rapid connection; the pipe conduit extends through the rear wall of the furnace 9.1;
  • an analogous waste gas conduit 27 for the furnace chamber.

An waste gas conduit 11 enters into the lid of the reaction container. Above the lid, a cut-off valve mechanically connected to the lid and made of high-temperature resistant and vacuum-proof materials is integrated into the conduit. The connection with the continuing waste gas conduit is established by a rapid connection; thereafter the cut-off valve is opened.

When removing the container the sequence is reversed. The container has to be handled such that good heat transfer is ensured in its interior and that all input pieces are heated equally.

FIG. 3 depicts a cross-section of a shaft furnace 9.2 with a reaction container 7.

The technical specifications of a shaft furnace for reaction containers are:

Heating:	E.g. natural gas Hu 8,000 kcal/Nm3;
Contact value:	295 kW per furnace;
Max. Furnace temperature:	600° C.;
Application temperature:	350° C. to 500° C.;
Network voltage:	230/240 V, 50 Hz;
Control voltage:	230 V, 50 Hz.

The pyrolysis furnace 9.2 is completely lined and insulated. The burner facility consists of two special burners with appropriate pipe conduits for natural gas and process gas or process oil and combustion air. Furthermore, there are present:

• • a fan for combustion air with an electrometer and gages and control devices for natural gas and combustion air;
  • a gas input conduit with a cut-off valve, pressure regulator, filter, pressure gage and pressure monitor or facilities for other media;
  • a pyrolysis reaction container 7, sealingly welded with lid, seal, cut-off valve; dimensions: Diameter about 1,500 mm and height about 3,000 mm;
  • The pyrolysis reaction container and lid are made of heat resistant steel, including rapid closures 28 for the lid, two tilting rings and three feet, the lid is curved, it is provided with transport rings and connecting pipes as well as water cooling for the seal; the lid is structured such that it closes the shaft oven at the same time;
  • an automatic temperature measuring and regulating facility built into a switching cabinet with appurtenant control and regulating apparatus;
  • two temperature regulators;
  • two sets of thermal elements (measuring sensors) with compensation lines;
  • a pipe conduit with rapid connection 29 to the cut-off valve at the reaction container for feeding the gas out of the pyrolysis reaction container 7.

Optionally, the lid of the reaction container may be provided with a vacuum-tight recirculation motor. Recirculation leads to particularly uniform drying of the pyrolysis material. Inserts are placed into the pyrolysis container 7 for storing the materials to be pyrolyzed. Spacers and conducting sheets ensure a particularly precise conductance of the pyrolysis gas stream. This ensures a complete and efficient pyrolysis.

The conductance of the waste gas is analogous to that of the car tunnel kiln. Connecting pipes for safety valves and a waste gas conduit of about 80 mm diameter and a vacuum-tight high temperature resistant cut-off valve are provided at the lid. The connection of the feed and disposal conduits is preferably established by rapid connections.

Depending upon the density, up to 4.5 tons of input material can be placed into the container 7. The quantity of filled material consisting of rubber tires is about 0.5 tons. At mixed charge (e.g. rubber strips, rubberized treads) the charge will be about 3.5 tons to 4.5 tons. Container modules of different dimensions are also possible.

The thickness of the container wall corresponds to the static requirements.

The pyrolysis oil produced in accordance with the invention is used as an energy source. With electricity and heat, the pyrolysis oil is advantageously used as a heating oil for the self-sufficient supply for the pyrolysis system.

On the other hand, the pyrolysis oil consists of a number of components which are used as synthesis building blocks for the production of chemicals, polymers and other intermediate products.

The pyrolysis oil contains about 0.4 to 0.16% sulphur and is a black, turbid and easily combustible liquid. It characteristically smells of aromatics and contains cyclopentadiene as well as further bicyclenes and aromatics as synthesis building blocks. More particular, aromatic components such as dipentene, toluene, and xylene were detected. The pyrolysis oil is preferably refined into the dipentene, toluene and xylene components.

Dipentene is particular importance. This chemical compound may be grouped with terpenes and has an agreeable lemon-like odor. This component of the pyrolysis oil is used by the chemical industry in large quantities for the production of solvents, resins and perfumes. Furthermore, dipentene may be used as a surrogate for the fluorinated and chlorinated hydrocarbons (FCHC).

Toluene and xylene are also important starter materials for chemical substances of plant protection agents, dye syntheses, solvents, plastic materials and pigments.

The carbon granulate obtained in accordance with the invention is an inactive filler and is especially suitable as a filler for crude rubber in the production of rubber and tires.

As determined by the BET method, the inner surface of the soot produced from carbon granulate is, depending upon process conditions, between about 77 m²/g and 42 m²/g.

The carbon content of the carbon granulate is about 97.8%, the remainder is ash. Furthermore, the carbon granulate is insoluble in cold acids, such a sulphuric acid, nitric acid, hydrochloric acid or in caustic solutions. Solubility in polar or non-polar solvents has also not been detected. Nitric acid spontaneously decomposes into water and nitrous gases which may be traced to catalytic action of the large internal surface.

The carbon granulate is also used as the starter material for the production of dye pigments for printing dyes. The carbon granulate is an ultra-fine powder which satisfies the high requirements placed on dyes.

Another preferred field of application of the carbon granulate is the production of active coal by a method downstream from the pyrolysis method for enlarging the surface of the carbon granulate to up to 1,000 m²/g.

The active coal thus obtained may be used in filters for purifying water or of gas in exhaust systems. Other fields of application reside in the food stuffs industry and in medicine.

Because of its properties, the carbon granulate swims on the surface of water and absorbs oils present on the water. Also, it is oleophilic and may thus advantageously used on the surface of water as an oil binder or agglutinant. It may also be used on mineral oil contaminated soil or cases of damage caused by oil.

The carbon granulate can also be advantageously used where oil is burning. The carbon granulate may be generally used as a fire extinguisher. Oxygen will be removed from a fire covered and thus extinguished by a sufficient quantity of carbon granulate. Coating glass with carbon granulate results in increased fire resistance coupled with a thermal insulation effect.

A further advantageous field of application of the carbon granulate in accordance with the invention is its use in water retention layers. By using the carbon granulate in layer thicknesses less then sand layers water and plant nutrients can be stored and poor soil of low value may be used as planting locations for vegetables and agricultural products. In accordance with a preferred embodiment of the invention, layer thicknesses of 50 to 100 are used to yield a remarkable success.

In this connection, mention is to be made of the property of the carbon granulate that is releases no substances into the water phase and that, therefore, neither soil nor ground water are contaminated by leaching out of contaminants.

A particularly preferred field of use of the carbon granulate obtained by the invention is its use for producing light-weight building elements which display a special thermal insulation effect. Advantageously, a mixture of a ratio of carbon granulate and cement of 2:1 to 5:1 is used. The preferred ratio is 3:1.

A plate of 10 mm thickness of the mentioned material of the preferred ratio resists an illuminated propane gas flame without any measurable increase in temperature at the opposite surface.

List of Reference Characters

• 1 Input material, used tires
• 2 Washing facility/washing
• 3 Shredder unit/shredding
• 4 Drying facility/drying
• 5 Conveyor facility
• 6 Storage container/silo for charging with reaction containers
• 7 Reaction container
• 8 Preheater/preheating of the reaction container
• 9 pyrolysis furnace
  • 9.1 car tunnel kiln
  • 9.2 shaft furnace
• 10 Cooling facility/cooling of the reaction container
• 11 Waste gas conduit at the reaction container
• 12 Facility for the dust-free emptying of the reaction containers
• 13 Facility for separating iron and carbon
• 14 Facility for cutting-up or granulating carbon
• 15 Returning the emptied reaction container for renewed charging
• 16 Silo for carbon
• 17 Heat from heat recovery
  • 17.1 Preheating of combustion air
  • 17.2 unused heat
• 18 Container for metal scrap
• 19 Packaging of granulate
• 20 Storing of granulate
• 21 Water cooling for pyrolysis gas
• 22 Furnace carriage with drive
• 23 Lifting door
• 24 Burner facility
• 25 Thermal elements furnace chamber
• 26 Thermal elements reaction container
• 27 Waste gas pipe conduit furnace chamber
• 28 Rapid closures
• 29 Pipe conduit with rapid connection
• 30 Carbon
• 31 Iron
• 32 Pyrolysis gas
• 33 Pyrolysis oil
• 34 Waste gases
• 35 Refining, separating, processing