Pyrolysis, gasification, and liquefaction (PGL) represent a viable alternative for the
disposal of scrap tires (also referred to as “waste tires” in this report). These technologies
are currently used for the conversion of carbonaceous materials more extensively in
Europe and Japan than in California, but may become more important as the supplies of
natural fuels become depleted. The objective of this report was to assess the
technological, environmental, and economic features of the application of PGL to process
scrap tires.

The disposition of waste tires remains an important issue in California as the population
and corresponding number of waste tires continues to rise. Stockpiling or landfilling of
scrap tires has negative environmental impacts and may not be the most efficient disposal
solution. The State has initiated policies to encourage diversion of waste tires to other
applications such as crumb rubber products, civil engineering projects, and tire-derived
fuel (TDF).

This policy has resulted in a significant waste tire diversion rate increase from 1990 to
2002. In 1990, California diverted 34 percent of its 27 million waste tires to these uses. In
2002, the diversion percent increased to 75 percent of 34 million waste tires. The annual
number of tires disposed of decreased by 50 percent between 1990 and 2002; however,
8.4 million tires were still being disposed of as of 2002. Further, during the late 1990’s,
two major stockpile fires resulted in over $25 million in cleanup costs.

Pyrolysis, gasification, and liquefaction are thermochemical processes whereby
carbonaceous feedstocks are transformed at elevated temperatures. Pyrolysis is thermal
degradation or volatilization of the tires without the addition of air or oxygen.
Gasification is a process that utilizes a reactive agent such as air, oxygen, hydrogen, or
steam. Gasification tends to have a slightly higher temperature range than pyrolysis, with
the resulting products being primarily gaseous in nature. Liquefaction operates in a lower
temperature range than either pyrolysis or gasification and produces a predominantly
liquid product.

This report presents the results of a survey of PGL facilities worldwide. It was found that
PGL technologies have expanded considerably in the areas of coal, petroleum coke,
natural gas, and mixed waste. Only one, commercial facility in Kaohsiumg, Taiwan,
which processes approximately 27,000 tons per year (TPY), was identified that uses PGL
for the processing of a primarily scrap tire feedstock.

In California, the Chateau Energy Group is currently refitting a power plant in Imperial
County with a plasma arc system for gasification of tire-derived fuel, to be used in
conjunction with natural gas to generate up to 45 megawatts of electricity (MWe).
International Environmental Solutions (pyrolysis), Plastic Energy LLC (catalytic
cracking/melting), and Pyromex (pyrolysis), through their representative Innovative
Logistics Solutions, also have facilities in various stages of permitting, construction, or
planning in California that could potentially process tires but are currently targeted for
other feedstocks.

Although the application of PGL to tire feedstocks is limited worldwide, no significant
technical barriers to the use of these technologies in processing tires seem to exist. This is
particularly evident in the significant expansion of PGL use since 2000, including
feedstocks that are more heterogeneous than tires, such as mixed waste. The viability of
any individual facility appears to depend on a number of other factors, including
economic considerations, facility capital costs, feedstock requirements and availability,
and the permitting process.

Empirical data on the environmental impacts of PGL facilities using scrap tires are
limited and depend on the local air permits and exhaust after-treatment systems utilized at
each facility. PGL processes have some emissions advantages compared to conventional
combustion processes, since the former are performed in environments with limited or no
oxygen and have an output volume that is considerably less than that of standard
combustion. Gasification and pyrolysis produce intermediate gases such as natural gas
that are cleaner to combust than other organic waste.

Further, data from other practices, such as PGL of feedstocks other than tires, or the use
of TDF in cogeneration facilities or cement kilns, can provide an indication of the level of
performance that would be obtained for PGL tire facilities. PGL facilities worldwide are
currently operating under stringent regulations with other feedstocks, and it is expected
that facilities equipped with the most advanced air pollution control systems will be able
to meet or exceed the regulatory requirements in California and the rest of the U.S..
Additionally, tests of emissions from facilities using TDF have indicated there are no
significant disadvantages to the use of tires as a fuel or fuel supplement. In a number of
cases, the use of TDF can provide emissions benefits, with the possible exception of the
effects of zinc, which is used in the production of tires.

The ability to produce a range of products can add to the marketability of a PGL system.
Products resulting from PGL processes include electricity, chemicals, and diesel fuel, as
well as residual carbon black. The products can be used to expand the current uses of
scrap tires that include retreading, civil engineering applications, and TDF. Estimates
were made of the potential value of scrap tires transformed by PGL in terms of
electricity, fuels, and other products. It was found that a hypothetical tire PGL facility
with a capacity of 5 million tires per year can produce a gross revenue of over $13.2
million per year, from the combined sales of $9.4 million from synthetic diesel fuel,
$1.25 million from the sale of process heat at natural gas equivalent prices, $1.7 million
from the sale of off-peak electricity, and $0.8 million from the sale of the recovered steel.
On a per-tire basis, the product costs ranged from $2.63 for gasification to $1.29 for
liquefaction. Capital costs for PGL facilities were found to range from $621 to $828 per
metric ton per year.

In addition, the authors performed an evaluation of the economic life of this hypothetical
PGL facility. This included an analysis of operating costs, financing, and revenue
streams. At the present energy prices, it was found that the plant would make an
estimated $1.37 million in profit by the third year of operation. This plant would recover
capital costs in its eighth year, and have a projected annual net profit (discounted cash
flow) of $6.96 million, two years after paying off its loan. A cost sensitivity study
conducted by the authors indicates that these profit margins and the corresponding
economic viability would be enhanced by continuing increases in the costs of electricity
and diesel fuel.

Download the full California Integrated Waste Management Board (CIWMB) report on tire pyrolysis - Technology Evaluation and Economic Analysis of Waste Tire Pyrolysis Gasification, and Liquefaction.