CARBON BLACK PRODUCTION FROM WASTE TYRES

 

Development Program

- Concentrate on production of carbon black as the economical driver; maximize carbon black production

- Solve solid material and gas handling problems to make the process reliable as a continuous commercial process

- Process oil, gas and steel should be a recovered products with value

- Major equipment in the plant should be proven design; no mechanical design stretches.

- Jan 1997 laboratory work commenced

- Batch kiln tests were conducted to study time-temperature versus product quality

- Experience showed material handling into and out of the kiln was  a major challenge; as well as gas handling and oil collection

- Pilot plant facilities were setup to evaluate the whole system on a continuous basis

 

Pilot plant runs were conducted to evaluate

- Time-temperature relationships

- Carbon char quality and yield

- Oil quality and yield

- Gas quality and yield

- Mass balance

- Design changes

- Develop analytical data for all products

 

Materials processed in pilot plant included:

Passenger tyres with steel

Passenger tyres without steel

Off-road tyres

Manufacturer rejects

Mixture of off-road & passenger tyres

Mixture of passenger & truck tyres

 

Conclusions

- Pyrolysis of scrap tyres can produce economically viable products (carbon black, oil, gas and steel) in an environmentally sound manner using commercially available equipment

- Pyro black has applications in a wide variety of rubber and plastics applications

- Pyro oil can be used for fuel, generation of carbon black, refiner feedstock for chemical recovery

- Pyro gas can be used in numerous applications; process gas, power generation, etc.

- Steel belting can be recycled to electric furnaces

- Tyre pyrolysis offers the opportunity to process millions of tyres each year in an economical and genuine environmentally friendly manner without production of waste materials

 

Metso Minerals Process Research & Test Centre

CARBON BLACK PRODUCTION FROM WASTE TYRES
By Bob P. Faulkner

 

ABSTRACT
Metso started a development program in 1997 to develop a process to convert waste tires into valuable commodities. A review of numerous approaches revealed short-comings in the various approaches either process, mechanical, combination of factors, or trying to emphasis the production of low value products. A market study revealed that a process that could produce a good grade of carbon black would be economically feasible. This paper discusses the laboratory and pilot plant development, commercial plant status and current status.

 

INTRODUCTION
In 1998, in the USA, 270 million scrap tyres were generated; 177.5 million went to a market, 92.5 million accumulated in stockpiles. In 1998 there were estimated to be 500 million tires in stockpiles around the United States. Tire shipments in 1999 were 316 million tyres showing a growth rate of 5.3% and are projected to grow at a yearly of rate 2.2% in the 2000’s. In the last 3 years there have been only 73 million tires remediated and there have been 59 tire fires. The 500 million tyres stockpiled plus the 92.5 million accumulated in 1999 represent approximately 8 million barrels of oil, 1.7 million tons of carbon black, 69.5 trillion Btu’s or 200,000 MW electricity. Approximately one-half of these resources are available on a yearly basis, which in today’s market represents about $640 million dollars of recovered resources. The above numbers indicate a growing problem and hence an opportunity if the tires can be treated in an environmentally sound manner and produce the marketable products indicated above. Recognizing the growing problem not only in the United States but worldwide, Metso initiated a development program in 1997 to apply our process knowledge of reduction systems and controlled thermo-chemical reactions to the problem and determine if marketable products could be produced from scrap tyres. The first step was to perform a market study to assess what products that could be produced from tyres that would make a process economical. The market study indicated that a carbon black of good quality could support the tire treatment process.

The second step was to review prior art and determine why other processes or ventures went astray. The review indicated several problem areas; mechanical problems, feeding and discharging, process control, and process economics focused on low value products.

 

DEVELOPMENT PROGRAM OBJECTIVES

Based upon the, prior art, market review and a review of our in-house concept, we initiated a development program with the following objectives.

 

1. Determine if a good quality carbon black could be produced on a laboratory scale batch test.

2. Develop a reliable tire feeding system.

3. Develop process conditions to produce a product so as to optimize the process economics.

4. Resolve solids discharge problems.

5. Develop a suitable means of recovering oil from a non-condensable gas stream containing particulates.

6. Assess product quality.

7. Develop budget cost for commercial plant and assess economic potential.

 

LABORATORY BATCH TEST
The initial step in the program was to perform several laboratory batch tests to evaluate process conditions and determine carbon char quality. The laboratory test device, used is an indirect fired batch kiln. This device allows us to vary time, temperature while obtaining samples at determined time intervals without disturbing the kiln atmosphere. The samples were then analyzed to develop the kiln profile necessary to achieve the desired product. The results indicated that it should be possible to make a medium grade carbon black and the process economics should be able to support the capital investment, operating cost and return a profit based only on the sale of carbon black. The next step was to demonstrate that it could be done in a pilot plant on a continuous basis.

 

PILOT PLANT OPERATION
The indirect fired batch kiln test data provided a time temperature profile to produce a given quality of product. This kiln profile developed in the batch kiln was the starting point for the indirect fired kiln, continuous pilot plant. The pilot plant was set up using an existing indirect kiln.

 

The first effort was to resolve the feed problem with tire shreds, screw feeders do not work and the tire shreds will not fall freely through a normal feed pipe. The feed system had to be a positive feed mechanism and at the same time there had to be a minimum amount of air leakage into the kiln. Numerous designs were tried over a period of several weeks and finally based upon some similar experience with difficult material handling problems the feed end problems were resolved. The final design (patent pending) is a lock hopper with a modified Archimedes screw configuration. The next step was to test the kiln in a hot mode to evaluate the process conditions and products. The design allows the char and steel to be collected separately. The pilot plant was now operated under varying process conditions on a continuous basis to evaluate these conditions on the resulting char product. The first test condition concentrated on the char production and the off-gas containing the oil mist was merely oxidized, scrubbed and discharged. After several months of operation the optimized process condition for producing the desired char was established. Based upon the pilot plant work a preliminary commercial plant design was developed for a plant processing (100 tons/day of nominal tire shred feed. These plant designs were considered primarily because commercial kilns of this size have been built and are presently operating. This commercial designed was based on recovering the carbon and fully oxidizing the off-gas containing the oil mist.

 

A study of the commercial plant design and mass balance indicated that a significant cost was associated with the air pollution control system when the off-gas containing the oil mist was oxidized. Therefore, a study was initiated to evaluate an oil condensing system that could handle extremely fine oil aerosol in a dirty gas environment. The off-gas system was designed minimize the amount of entrained carbon in the gas stream, but over the long run it was going to be there, thus the design had to accommodate the fine entrained carbon. Commercial systems were all found inadequate, to handle the off-gas stream we were dealing with, based upon our previous experience. Therefore, a condenser system design was developed and installed in the pilot plant. The design incorporated several features, which we considered necessary to both condense the very fine oil mist and handle the particulate in the gas stream. After several weeks of testing and modifications a final design was arrived at, and patents filed. The pilot plant including the oil condensing system was then operated in several campaigns continuously over several days and then several campaigns for a shorter period of time of 8 to 10 hours evaluating various types of tire feed and process conditions. These results indicated the carbon black from the system would function in a variety of rubber compounds, either as a blend or as stand-alone filler. The oil can be upgraded to remove the sulfur, used directly in some applications, as a blend with other heavy oils, or can be used to generate carbon black. The gas can have several applications; generate electricity, waste heat boiler, process gas for other operations or combination of uses.

 

COMMERCIAL PLANT DESIGN
The commercial plant design for PYReco is of 200 tons/day.

 

CONCLUSIONS
The laboratory and pilot plant work have demonstrated that tire shreds can be continuously processed to make a consistent carbon black product that is usable in rubber compounding. Numerous independent laboratories have evaluated the carbon black product and shown that the product can be used in styrene butadiene rubber (SBR), and ethylene propylene rubber (EPDM) rubber compounds. Either as a blend with other commercial carbon blacks or as a total replacement of the commercial black, depending upon the product. Other synthetic rubber (SR) compounds are also being evaluated. PYReco is now planning to build a commercial plant on Teesside, UK.