DE69706689T2 - Intermittent, continuous process for the extraction of purified activated carbon from used tires and device therefor - Google Patents

Description

Background of the invention

The present invention relates to a novel intermittent continuous process and apparatus for producing purified activated carbon from scrap tires or similar material. It relates in particular to a treatment process for efficiently producing activated carbon with increased added value from waste rubber such as scrap tires by means of an intermittent continuous treatment process without causing secondary environmental pollution; the by-product oil gas is recovered and used as a source of external heating for decomposition by cracking and activation, thereby recovering resources. The invention also relates to an apparatus for use in this process.

Due to the development of public transport network and the popularity of cars and motorcycles, the number of old tires from consumables has increased sharply and has become a problem for an immediate solution in terms of environmental protection.

To solve this problem of used tires, three methods have been used so far, namely burial, incineration and pyrolysis. In burial, the used tires are thrown away and buried as general garbage and therefore not recycled. This is a waste of resources and such a The process will not be discussed here. In incineration, the waste tires are crushed and the weight (volume) is reduced to produce a fuel, particularly for use in special boiler burners for recovering the heat energy from the fuel for heating buildings, etc. However, since this process involves direct combustion, a new problem arises in terms of cost and facilities for treating secondary pollution such as removal of smoke, odors, combustion ash and separation of steel wires. As for fission decomposition (dry distillation), the waste tires are crushed and then placed in a sealable fission furnace in which the crushed waste tires are decomposed at high temperatures by thermal fission and dry distillation, and the gases produced by the decomposition are then cooled, separated and absorbed to produce fuel oils, fuel gases, charred substances and steel wire as residue. The fuel oils and fuel gases are for general use and a part of them can be consumed in the thermal cracking furnace. The ash residues must be buried separately or treated magnetically to separate the steel wire, while the remaining carbonized matter, after pulverization and granulation, is used as low-grade activated carbon for use as a filler in tire manufacturing. Although such a process brings a considerable result in recovering resources for reuse and also reduces the problem of environmental pollution related to smoke removal, the facilities and process systems are far from ideal and the process operates only in batches. The operation may be stopped and is not continuous, and the process steps may be occur multiple times and result in a waste of energy resources. The process requires significant improvements.

Japanese Patent Application No. Showa 58-25348 discloses a method and an apparatus in which old tires are directly introduced into an incinerator and the gases produced are discharged to the outside through a smoke outlet. The charred substances are recovered through a pipe, while on the other hand a liquid melt is drawn from the bottom of the incinerator as fuel. However, this direct and open combustion method is harmful to the environment due to a foul smell and black smoke.

On the other hand, US Patent No. 5,326,791 teaches a process for the cleavage decomposition and oil treatment of thermoplastic high molecular weight compounds and thermal hydraulic separation of non-hydrolyzable waste plastics.

None of the above prior art references refers to a process or plant for the recovery of activated carbon from rubber or waste tires or discloses a precise plant for the possible recovery of activated carbon from waste tires; moreover, no proposals have been made concerning an improved process or device in batch-wise fission decomposition to improve production energy.

Summary of the invention

Accordingly, it is a main object of the present invention to provide a process for the recyclable treatment of waste tires and similar materials, in which waste tires are introduced into a specially designed sealed furnace of the treatment plant for cracking and decomposition and are subjected therein to an intermittent and continuous overall treatment for the purpose of extracting activated carbon and obtaining fuel oil and fuel gas as by-products, the latter being used as a heating source of the plant, thereby considerably increasing the production energy of the process and at the same time reducing the process costs.

Another object of the present invention is to provide an apparatus for the recyclable processing of waste tires and similar materials, with which it is possible to process the waste tires intermittently and continuously without shutting down the furnace or stopping it for cleaning, or without replacing the tank in the furnace for cracking and decomposition, and as a final product activated carbon with a high added value is obtained.

Furthermore, it is an object of the present invention to provide a waste tire recycling plant capable of recovering almost all of the matter from waste tires and converting them into resources, thereby solving the problem of environmental protection.

Short description of the drawing

The foregoing and other objects, features and advantages of the invention will become apparent from the following more particular description of preferred embodiments of the invention, which are illustrated in the accompanying drawings.

Fig. 1 shows a flow diagram of the inventive plant for the recyclable processing of used tires; and

Fig. 2 shows a longitudinal section of the furnace for fission and decomposition according to the invention.

Detailed description of the invention

Reference is made to Fig. 1 and 2, and the inventive plant for the intermittent and continuous processing of waste tires and the like will now be described in detail as follows.

T denotes waste tires, 1 a belt conveyor and 2 a shredding device, and the waste tires T are transported on the belt conveyor 1 to the shredding device where they are shredded into pieces with a size of less than 5 cm (the smaller the better). The shredded waste tires then pass via a belt conveyor 3 into a feed container 4. At the outlet end of this feed container there is a device 5 for automatic, continuous-intermittent metering and introduction of the shredded particles, which introduces a certain amount of shredded particles from time to time into a fission and decomposition reactor 6. This reactor 6 has a double bottom Reaction vessel 61 for splitting dry distillation and a closed furnace body 62 which surrounds the reactor vessel 61 and heats it. The reactor vessel 61 has a stirrer 63 inside which is described further below.

In the reactor vessel 61, the crushed particles are gasified after heating, breaking down and decomposing. The temperature inside the reactor tank 61 is always maintained at 400ºC to 600ºC, preferably between 450 and 550ºC, while the pressure is maintained at a value of 1.0 to 2.5 kg/cm². The oil gas MG produced during gasification is led through an outlet at the top of the reactor vessel 61 via a pipe L1 into the condenser 7, where it is cooled to below 50ºC or room temperature and then passed into a vessel 8 for separating oil and gas. As the combustible liquid, ie the fuel oil F, condenses, it collects at the bottom of the separator 8 and is pumped by a pump 9 through a pipe L2 into an oil storage tank 10 where it is stored. The non-condensable gases, i.e. the fuel gas G, are compressed in the compressor 11, are fed through a pipeline L3 into an absorption tank 12 where impurities and odorous substances are absorbed, and then into a gas storage tank 13. The fuel oil F and the fuel gas G thus obtained pass through the pipelines L4 and L5 to the burners 64 at the bottom of the furnace body 62 of the fission and decomposition reactor 6 for combustion and heating of the reactor tank 61, and unused fuel oil F and fuel gas G can be made available as fuel to other facilities of the factory or their surroundings. In this way, all the thermal energy required to operate the reactor 6 is supplied by the extracted oil and gas, thereby saving energy resources On the other hand, the fuel oil and the fuel gas can serve as reserve fuel if the reactor 6 is heated electrically and a power failure occurs.

Through analysis, it was found that the uncondensable fuel gases consist mainly of methane and ethane, which can be reused or sold after storage in the storage tank 13. On the other hand, the fuel oil can be used as heavy oil for combustion. If further purification is required, the fuel oil can be refined into light oil and heavy oil by sending it separately through a refinery where it is filtered and fractionally distilled (not shown).

On the other hand, the largely solid carbonized substances remaining at the bottom of the reactor tank 61, namely the soot C, after accumulation of a certain amount, are discharged through the upper and lower bottom cones 65 and 66, respectively, to the inlet of a screw conveyor 14 from the bottom of the furnace. This conveys the residue through an outlet pipe 14a into a water tank 15 for cooling the soot. In the middle region of the outlet pipe 14a there is an orifice 14b which is supplied with an inert gas such as nitrogen and, together with a water seal formed by the cooling water tank 15, represents a double seal for shutting off the gas which is generated as a result of the high temperature and low pressure in the reactor tank 61, thereby ensuring a double safeguard against the escape of this gas into the atmosphere.

The cooled carbonized substances C are fed via a belt conveyor 19 to a magnetic separator 16 in which the steel wire S contained in the carbonized substances is held, separated and then transferred to a steel wire container 17. After separating the steel wire S, the carbonized substances are then successively fed by means of acid and alkali resistant belt conveyors or other suitable apparatus 19a, 19b into an alkali bath 18 and an acid bath 20 in which the substances C are purified by alkalis and pickled by acids to remove ashes or impurities containing ZnS, ZnO, FeS, Fe₂O₃ and CaS which are acid soluble and SiO₂ which is alkali soluble. Substances C are then sent to a water bath 21 for washing with water, and a pure and clean soot C is obtained. This soot is transferred by another belt conveyor 19c to a drying oven 22 where it is dried. The dried soot is then collected in a feed tank 23 and then sent to a fine mill 24 where the soot is ground to a fine powdered carbon C1 of 100 to 200 mesh. The powdered carbon then passes into a cyclone 26 where fine carbon powder is separated. The carbon powder is then transferred to the activation oven 25 where activation takes place by means of a steam stream at a temperature maintained at over 700ºC. The product obtained is activated carbon 9 with a very high degree of purity. In detail, the fine carbon powder C1 is introduced into the reaction chamber 252 of the activation furnace 25 via a filling funnel 251, the temperature in the reaction chamber 252 is kept above 700ºC, preferably between 800 and 900ºC, and air and steam are introduced separately, namely through a steam inlet a and a Air inlet b. In the reaction chamber 252, the fine carbon powder C1 is heated and brought into contact with steam, whereby activated carbon is formed by an activation reaction, which is then transported by means of an air stream through a pipe 253 into the activated carbon collection chamber 254 and then into a storage barrel 255. The reference numeral 257 indicates a normally closed opening which is provided for cleaning purposes.

As an example, a construction of the fission-decomposition reactor 6 used according to the invention is shown in detail in Fig. 2, wherein the reactor 6 has a cylindrical reaction tank 61 and a cylindrical furnace body 62 with a large diameter that encloses the reactor on the outside. On the peripheral wall of the furnace body 62, a number of burners 64 are attached for uniformly heating the interior of the furnace body 62 from top to bottom and on all sides.

Inside the reaction tank 61 there is a stirrer 63, the upper end of which is supported in an upper cover 67. This stirrer 63 is provided with large blades 632 and small blades 633, which are mounted one above the other on a shaft 631, and is capable of performing an up-and-down movement. When the cylinder 634 is driven, the stirrer 63 moves up and down and causes the solid materials inside the reaction tank 61 to move vertically, so that these solid materials, which had previously been introduced into the reactor, are exposed to a high-temperature heat environment. While the materials are sufficiently and uniformly heated, a scraping off of the charred substances which are attached to the have settled on the inner walls of the tank so that the substances can be heated and decomposed in a relatively short time and the effectiveness of thermal decomposition is increased.

The outer wall of the reaction tank 61 is preferably provided with a helically arranged heat absorption plate in order to increase the heating surface and to make better use of the energy by extending the duration of the flame exposure. The bottom of the reaction tank 61 has an upper end and lower bottom parts in the form of a double cone 65, 66, and an outlet 651 at the bottom of the upper bottom part 65 is closed by a lower outlet cover 681, whereby the pneumatic cylinder 68, attached externally to the lower bottom part 66, can open and close the outlet cover by its pushing movement.

The bottom of the lower bottom part 66 is shaped to form a material outlet which projects into the inlet of the screw conveyor 14 which is driven by a motor M. When the pneumatic cylinder 68 comes into operation and the lower cover 681 opens by pivoting about one end and due to its own weight, the carbonized substances which have accumulated in the reaction tank 61 fall into the lower bottom part 66 due to their own weight and the vertical movement of the agitator 63, and then through the outlet part 661 into the screw conveyor 14. After the discharge of the carbonized substances has been completed, the pneumatic cylinder 68 starts to operate and pushes the lower cover 681 upwards and tightly closes the outlet 651. In order for the crushed substances to enter the reaction tank 61 in a uniformly distributed manner and to be distributed there accordingly, the supply opening of the tank is preferably provided with a baffle 612 at the lower part.

The hot lust stream exiting the furnace body 62 of the reactor 6 can be fed for reuse through a pipe LO and a distributor 69 to the lower area of the upper floor part, a drying room or any other place where heating is required.

Thanks to the special design of the reactor 6, the materials introduced into it are well distributed and fall down in a scattered manner, and the up-and-down movement of the stirrer 63 in the reaction tank 61 keeps the materials in a fluid and scattered state. While the sinking speed is thus reduced, the contact time with the hot air increases, whereby the surface area of the materials appears to be at a maximum limit of an effective heating surface, and since the tank bottom 65 is provided with many heat transfer plates 621 which absorb waste heat from the air flow of the distributor 69, the materials have a good heat transfer effect when they reach the tank bottom 65. In this way, the entire reaction process can be completed in a short time.

The splitting decomposition reaction is an endothermic process, and in the known batch mode, where large quantities are introduced, a very large amount of heat is required to provide the amount of heat required for the reaction. However, according to the present invention, the materials are introduced into the reaction tank on a small scale, that is, intermittently and yet continuously, and no large amount of heat is required. Furthermore, because the reaction according to the invention in a state of upward and downward movement, it is possible to complete the reaction in a very short time. Depending on the composition of the material and the size of the crushed particles, this time is about 30 to 50 minutes, and this also saves heat energy.

For alkaline cleaning of the charred substances, a 2 to 3% NaOH solution is preferably used, while for acid pickling (treatment) a 7 to 15% HCl solution is generally preferred. After alkali treatment and acid pickling, the ash content of the charred substances can fall below 3%. Since only SiO (SiO2) is dissolved during alkali cleaning and the majority of the ash content dissolves in acids rather than alkali, alkali cleaning can, if necessary, be dispensed with and only acid treatment carried out for economic reasons.

After treating a mixture of used tires of different origins according to the invention, the following contents were determined, namely about 10 to 12% fuel gas, about 25 to 30% fuel oil, about 50 to 55% activated carbon, about 10 to 12% steel wire and 5 to 9% others.

According to the steam activation method of the present invention, the activation process can be carried out and completed in a few minutes, and the purified soot was activated at two temperatures, namely 800ºC and 900ºC, respectively, and activated carbon having the following properties was obtained: Table 1

It should be emphasized that the shredded scrap tire pieces are metered and intermittently introduced into the upper part of the reaction tank 61, and under the influence of external heating with stirring in the reaction tank 6, the shredded particles carry out the intermittent and continuous cracking and decomposition reaction, forming oil, gas and the carbonized substances. After cooling and separation, the oil-gas mixture separates into fuel gas and fuel oil for use in the reactor. In addition, the carbonized substances that have accumulated in the tank are intermittently ejected. After absorption of the steel wire in a magnetic separator and alkali and acid treatments to remove the ash content and purify, the substances are activated by steam to form activated carbon. This process has achieved the effectiveness of completely reducing the amount of waste tires and recovering resources in the most efficient plant.

List of reference symbols:

T old tires

1 belt conveyor

3 Sponsors

4 feed containers

5 automatic dosing

6 reactor

61 Reaction tank

62 Furnace body

63 Stirrers

64 burners

65 upper floor part

66 lower floor part

67 upper cover

7 Capacitor

8 Oil/gas separation tank

9 Pump

10 Oil storage tank

11 Compressor

12 Absorption tank

13 Gas storage tank

14 screw conveyors

15 Cooling water tank

16 magnetic separators

17 steel wire containers

18 Alkaline cleaning

19 Belt conveyors

20 Acid stain

21 Water wash

22 Drying oven

23 Feed tank

24 Mill

25 Activation oven

251 funnel

252 Reaction chamber

254 Activated carbon collection chamber

255 filling barrel

2 shredders

26 cyclone separators

611 Heat absorber plate

612 Deflector

68 pneumatic cylinders

681 lower cover

69 distributors

Claims (6)

A process for the intermittent, continuous production of purified activated carbon from waste tires, according to which waste tires are crushed and fed into a reactor for splitting and decomposition, where the crushed waste is dry distilled and decomposed to obtain a gasified substance and carbonized substances in the form of solid particles, and after which the solid carbonized substances, after being discharged from the bottom of the reactor to the outside, are subjected to a series of treatments: water washing, magnetic separation, alkaline cleaning and acid pickling to separate iron wires and remove metal-containing ash content, after which, after cleaning, the substances are granulated to the desired particle size and introduced into a steam-flow activation furnace, where the particles are activated at the steam inlet and in the high temperature state to form powdered activated carbon, and in which the gasified substance is condensed and oil-gas separated to form combustible oil and gas by-products, a part of which is used as Fuel can be fed to said reactor to heat it from the outside, characterized in that said shredded waste is fed quantitatively, intermittently and continuously into the reactor and finely distributed inside the reactor by means of a distributor plate to be subjected to the heat decomposition reaction by an agitator which moves back and forth moved up and down, whereby the solid carbonized substances produced, when they have reached a predetermined amount, are emptied from the double bottom parts of the reactor onto a screw conveyor and transported back into a cooling water tank with a water seal effect for cooling. 2. A method according to claim 1, wherein the outlet end of a discharge pipe of said screw conveyor is below the water surface of the cooling water bath and halfway along said discharge pipe a closure device with an inert gas passage leading into the interior is arranged to obtain a double closure effect so that no gas can penetrate into the reactor from the outside during the discharge. 3. Apparatus for the intermittent, continuous production of purified activated carbon from scrap tires, comprising a reactor for cracking and decomposing for the thermal decomposition of crushed pieces of scrap tires, a series of units for emptying and transporting solid carbonized substances produced during cracking decomposition and, after alkaline, for magnetic separation, acid pickling and alkaline cleaning to remove iron and ash content, and thereafter for grinding the substances into powder to form purified soot, and an activation furnace for activating the purified soot, characterized in that said reactor for cracking and decomposing consists of: a furnace body for heating from the external environment, and a Reaction bath having an upper cover and a double-conical bottom part, an agitator arranged inside the bath, the upper end of which is supported by a vertical pneumatic cylinder which is attached to said cover and is arranged to carry out up and down agitating movements, a heat-absorbing sheet arranged helically around the outer wall of said bath, a discharge opening arranged in the upper bottom of said conical bottom part with a bottom cover which is arranged to open and close the discharge opening by means of a pneumatic cylinder attached to the outer wall of the lower bottom, and a discharge opening arranged in the lower bottom which is connected to the inlet opening of said screw conveyor mounted underneath. 4. Device according to claim 3, wherein the reaction bath of said reactor for splitting and decomposing is provided in the upper region with an oil-gas outlet and the upper cover is provided at a suitable location with an automatic, intermittently raw material dosing device which has an inclined distributor plate below the outlet. 5. Apparatus according to claim 3, wherein in the double bottom part of said reactor bath the upper bottom and the lower bottom are separated by a heat insulating material and on the upper bottom part an exhaust gas introduction opening is formed which leads from the furnace body via pipe and distributor means into the Burnt high temperature gas leads to heating of the bath floor. 6. Device according to claim 4, wherein the outlet in the lower bottom of said reaction bath for emptying is connected directly to the inlet opening of said screw conveyor and its outlet opening is connected to a discharge pipe with an opening directed downwards to below the water surface of the cooling water bath, while the middle section of said discharge pipe not located in the cooling water bath has a closure part with an inert gas passage, so that a double gas closure effect is created between the screw conveyor and the cooling water bath in order to prevent gas from penetrating into the cooling water bath from the outside.