The issue of how to effectively and efficiently treat and dispose of the diverse types of wastes generated through living and industrial activities without generating environmental pollution is a major issue confronting Japan and other countries worldwide. The establishment of technologies for recovering useful resources from these general and industrial wastes for reutilization, the so-called recycling technologies, is the most desirable solution.
For the treating of waste tires, which comprise a large proportion of waste, a new pyrolysis technology has been developed recently. This technology allows the pyrolysis residue carbon to be used for manufacturing activated carbon with a quality equivalent to that of coconut shell activated carbon. This March 1994 issue describes the pyrolysis technology and the pilot plant which has been completed in Chikugo-city, Kyushu.

■Waste Tire and Treatment/Disposal Processes

Today in Japan, about 1,500 million tires of various types are manufactured annually, and the number of waste tires generated monthly is an average of 8 million, so the volume of waste tires generated annually is as many as 90-100 million. Naturally, various methods have been developed for treating and disposing of these waste tires. Waste tire treatment and disposal on an industrial scale using tires as a fuel resource was introduced, primarily by the cement industry, by burning waste tires whole or in fragmented chips for kiln firing. Various enterprises are adopting their own means for producing chips, such as fragmenting waste tires mechanically with crushers or freezing with liquefied nitrogen for easier crushing.

However, 3.2% of zinc is added in the process of manufacturing tires, so when using waste tires as a fuel resource, there is the possibility of some zinc being discharged into the atmosphere in vapor form. A cement plant involves high-temperature combustion, so a larger portion of zinc is discharged, but low-temperature combustion will not cause zinc vaporization. For example, a waste tire pyrolysis technique has already been developed for commercialization at the Sumitomo Cement Co. Ltd. Akaho Plant, but no notable progressis is being achieved due to the difficulty of zinc removal.

■Development of New Process

The All Japan Environmental Preservation Association jointly with the Osaka Municipal Industrial Experiment Station has developed a waste tire pyrolysis and activated carbon manufacturing technology that removes zinc efficiently.Ordinarily, zinc is recoverable only at a high temperature of over 1.700℃, but the new patented technology enables zinc removal at low temperature of 800℃.

To commercialize the technology, the association established JCA, Ltd. in Kyushu which, in turn, constructed a new plant equipped with three pyrolysis systems and one activated carbon manufacturing system. The plant was put into operation in November 1993 and is presently shipping out deodorants for household use.

■Plant Site

This plant is situated in Chikushino City, about 40 min. by train from Hakata Station, Fukuoka Prefecture, on a site of about 8.000�u and floor area of 2.000�u.

■Facilities

The plant consists of four sections: for waste tire acceptance, waste tire pyrolysis, activated carbon manufacture, and product packaging.

The waste tire pyrolysis section consists of a 10-t press for bundling several tires together, cartridges for inserting these compressed tires, a system for cartridge feeding and pyrolysis, a system for cooling the pyrolysis gas and conversion into heavy oil, and a space for temporarily storing and sorting residual iron wire and carbon black subsequent to pyrolysis. The main facilities are the SY-M-1000 pyrolysis systems,each capable of treating about 1t of tires in a batch in a cycle of 2-3 operations daily.

At present,three pyrolysis systems are in operation, so a maximum of 9t of waste tires can be treated. A ton of waste tires consists of about 180 tires, so the maximum capacity is 1.620 tires/day.

The activated carbon manufacturing section presently has an activated carbon manufacturing facility with a capacity of 3t/day. A facility with a treatment capacity of 10t is presently under fabrication for installation in the near future, when the treatment capacity will be increased to 13t/day. Facilities have also been installed for storing and conveying the activated carbon product to the packaging section.

The product packaging section has a system for packaging powdered activated carbon automatically, and a newly developed system will be installed for processing activated carbon into sheet from for easier packaging.

■Process Flow

The plant process flow from waste tire acceptance to packaging is described here.

1.Waste Tire Acceptance
Waste tires are delivered to the plant by specialized collectors, and the acceptance volume is adjusted by the plant management in conformance with the plant operation schedule.

2.Waste Tire Compression and Insertion into Cartridges
Stored waste tires are compressed with a 10-t press into bundles of several tires, then inserted into cartridges.

3.Pyrolysis
The waste tires inserted into cartridges are fed into the pyrolysis furnace from the upper part with a hoist crane. Heating uses a burner system, by which heavy oil is combusted first.Within 60 min of commencement of combustion, the furnace temperature rises to 160℃ and a vaporized gas is generated that is used partly as a fuel, and combustion is continued. The waste tires are completely decomposed in about 3 hrs and various substances are recovered such as carbon black, the raw material for activated carbon, iron scraps, and the vaporized heavy oil is recovered in the cooling column. 1t of waste tires provides 350-450kg(about 400 l)of heavy oil with a calorific value of 10.450kcal, 340kg of carbon black and 150kg of iron scrap. About 90kg of the generated oil is used as fuel. Therefore, the total substances recovered by operating the plant fully for one day will be 3.150-4.050kg(about 3.600 l)of heavy oil, 3.060kg of carbon black,1.350kg of iron scrap, and 810kg of gas.

The pyrolysis furnaces presently in use circulate the generated vapor naturally and are characterized by a simple construction. Zinc is contained in the activated carbon and not dispersed outside, so the furnace prevents secondary environmental pollution.

4.Manufacture of Activated Carbon
The carbon black produced by the pyrolysis furnace is conveyed to the activated carbon manufacturing section and charged into a hopper. Carbon black is activated at a low temperature of about 800℃, and since technology for completely recovering zinc is introduced in this stage of activation, quality high-performance activated carbon comparable to that produced from natural material is manufactured. At present, the larger portion of the product consists of powdered activated carbon, but the carbon black will soon be produced in pellet from, then activated and the zinc removed to produce activated carbon in pellet form.

Previously, the activation of carbon black produced from waste tires had been regarded as much more difficult than manufacturing activated carbon from natural material. However, with the new process, roughly 70% of the carbon black generated with the pyrolysis fumace is converted into activated carbon at a high yield of about 70%, so it will be possible to manufacture 3.060kg/day of carbon black, and the production volume of the ultimate activated carbon product will be 2.142kg.

The production capacity of the present activated carbon manufacturing system is 3t/day, and the activation process uses direct combustion with a rotary kiln.

The activated carbon produced by this process is temporarily stored in a hopper, then piped to the packaging section.

5.Packaging
The activated carbon powder is first filled in a special type of paper, next placed in a vinyl package with an automatic machine, and is marketed as a deodorant for home use.

6.Utilization of Waste Tire Activated Carbon
The activated carbon manufactured with this process is shipped out at a domestic price of about \250.000/t. The company is presently studying a plan to produce activated carbon in sheet form for use in the manufacture and sale of furniture and flooring materials for homes, pelletized activated carbon for the manufacture of soil improvement agents, and an agent for purifying industrial waste water and household waste water. The marketability appears promising since the products can be produced at lower cost than those made of natural activated carbon.

Since many inquiries are being received about the waste tire pyrolysis system and activated carbon manufacturing system, the company is presently studying the feasibility of exporting the plant and related technologies. It is also studying methods and conditions of technical licensing at present.
The pyrolysis system is marketed domestically at price of \40million/unit, but since the minimum economic scale will be three units, a pyrolysis plant including ancillary civid engineering and construction costs will be \150-16-million. Naturally, the cost of the activated carbon manufacturing system will differ according to the system scale.

*JCA,Ltd.
Hisadomi1387-3,
Tikugo city.Fukuoka Pref.
Phone:0942-53-1832

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