Update on …

                               Update on
                               Pyrolysis
                               ­ a non-traditional
                               thermal treatment
                               technology


HCWH prepared this update to correct the impression that HCWH supports or
promotes pyrolysis, gasification, and plasma arc technologies and to provide
additional information on these controversial technologies. Inclusion of medium and
high-heat thermal technologies into HCWH's "Non-incineration medical waste
treatment technologies" does not mean support for these technologies as alternatives
to incineration. This update provides more information and reinforces HCWH's
concern about the release of pollutants, including dioxins and furans, from these
technologies, as well as the potential for toxic liquid and solid residues. In some
places, including the European Union and in U.S. hazardous waste laws, pyrolysis
and gasification are legally classified as incineration

Thermal treatment of wastes has a long and controversial history. The simplest and
most polluting approach is to burn wastes in an open pit or barrel. Such uncontrolled
combustion provides no containment or treatment of the gases, ashes and other
residues of combustion and associated pollutant releases.

Medical waste incinerators are designed to provide greater control of the combustion
process. However, since chlorine-containing materials are typically included in
medical waste, toxic products of incomplete combustion (PICs), such as dioxins and
furans, are inevitably formed and released in the stack gases and other residues.
The fact that oxygen is integral to the molecular structure of dioxins and furans
suggests that the formation of these particular PICs may be reduced or avoided by
minimizing or completely excluding oxygen from thermal waste treatment.

Thermal waste treatment technologies fall into two broad categories: 1) those in
which wastes are combusted ­ burned in the presence of oxygen, i.e., incineration
technologies; and 2) those in which wastes are heated in the presence of little or no
oxygen so that there is no direct combustion , i.e., pyrolysis (sometimes referred to
as thermolysis) and gasification.

When oxygen levels in an incinerator are reduced to levels below the optimum for
combustion, the incinerator is said to operate in a "starved air", or "pyrolytic" mode.
Pyrolysis, also sometimes referred to as thermolysis, is defined as the thermal
degradation of a substance in the absence or with a limited supply of oxygen.
However, with medical wastes and similar materials a complete absence of oxygen is
unachievable. As a result, some oxidation will occur during pyrolysis so that dioxins
and related products of incomplete combustion are formed.




  Health Care Without Harm, 1755 "S" Street, Northwest, Unit 6B,                     1
Washington, DC 20010 USA. Phone: 202-234-0091. Fax: 202-234-9121
Pyrolysis is typically carried out in a temperature range of 400-800 °C. At these
temperatures, waste materials are transformed into gases, liquids and a solid residue
called `char'. The relative proportions of gases, liquids and char depend on the
composition of the wastes, temperature and the time that the temperature is applied.
Short exposure to high temperatures is termed "flash" pyrolysis, which maximises
the amount of liquids generated. If lower temperatures are applied for longer periods
of time, chars predominate.

While many proponents of modern waste treatment systems refer to pyrolysis as
being a new technology, UNDP (1999), this is not the case. For centuries pyrolysis
has been used in the manufacture of charcoal, FAO (1994), and it is also used
extensively in the petroleum and chemical industries. Of particular interest, many
current medical waste incinerator designs operate via a two-stage process: a
pyrolysis chamber followed by an afterburner, or combustion chamber (e.g., Compact
Power (2002) and Statewide Medical Services (2002)).

Another not-so-modern pyrolytic treatment technology is "gasification", which is
defined as the conversion of a solid or liquid substance into a gaseous mixture by
partial oxidation with the application of heat. Partial oxidation is usually achieved by
restricting the level of oxygen (or air) in the combustion chamber (pyrolysis). The
process is optimized to generate the maximum amount of gaseous breakdown
products, typically carbon monoxide, carbon dioxide, hydrogen, methane, water,
nitrogen and small amounts of higher hydrocarbons.

If the oxidant used is air, the gas produced is called "producer gas" and usually has a
calorific value that is no more than 25 percent that of natural gas. If the oxidant used
in the system is oxygen or oxygen-enriched air, the resultant "synthesis gas" has a
higher calorific value due to the absence of nitrogen, typically 25-40 percent that of
natural gas.

While gasification is a pyrolytic process that is optimized for the maximum yield of
gases, it still generates solid and liquid by-products, which may contain high levels of
toxic contaminants. The degree of contamination will depend on the waste being
treated, the type of technology used and how it is operated.

The heat required for pyrolysis is generated by the combustion of traditional fuels
(natural gas, oil, etc), or by the use of electricity to create high temperature plasmas.
In plasma-based systems the primary source of heat is a plasma torch or arc that
may achieve temperatures ranging from 3000 to 20 000 degrees. Plasmas are
normally generated in a high-energy electrical discharge or arc, and as such require
considerable amounts of electrical energy to operate.

While pyrolysis systems differ in some respects from conventional incineration, they
are sufficiently similar to incinerators to be legally classified as such by the European
Union. Also, the US federal government defines systems which use plasma
consisting of a high intensity electrical discharge or arc followed by an afterburner as
incineration (40 CFR 260.10).

Many proponents of pyrolytic systems maintain that they are not incinerators and do
not generate hazardous by-products, such as dioxins. However, they have not
provided detailed information demonstrating this in full-scale systems treating
medical or other wastes. In fact, limited data from full-scale systems have shown that


  Health Care Without Harm, 1755 "S" Street, Northwest, Unit 6B,                       2
Washington, DC 20010 USA. Phone: 202-234-0091. Fax: 202-234-9121
dioxins, furans and other products of incomplete combustion are formed in these
systems.

A recent review of pyrolysis systems by the UK research group, CADDET(1998),
raises concerns about residues from these processes;

   "The various gasification and pyrolysis technologies have the potential for solid
   and liquid residues from several process stages. Many developers claim these
   materials are not residues requiring disposal but are products which can be used.
   However in many cases such claims remain to be substantiated and any
   comparison of various waste treatment options should consider releases to air,
   water and land."

CADDET (1998) also paid particular attention to liquid residues:

   "The sources of liquid residues from [mass burn combustion] plant are boiler blow-
   down and wet scrubbing systems, when used for flue gas cleaning. Whilst these
   sources remain for gasification and pyrolysis systems using steam cycles or wet
   scrubbers, these technologies can also produce liquid residues as a result of the
   reduction of organic matter. Such residues have the potential to be highly toxic
   and so require treatment. Any releases of liquid residues into the environment
   should therefore be carefully considered."

In their examination of a commercial scale German municipal waste gasification
system operating under pyrolysis conditions, Mohr et al. (1997) found that dioxins
and furans were formed in the process with particularly high levels in liquid residues
from the process. Weber and Sakurai (2001) recently examined the formation of
dioxins and furans under pyrolysis conditions and concluded that they were definitely
formed from wastes containing chlorine and copper. Several other researchers have
found similar results for a range of common wastes, clearly demonstrating that
dioxins, furans and potentially other persistent organic pollutants may be formed in
pyrolysis/gasification systems.

It therefore appears that pyrolysis and gasification systems, while being promoted as
clean non-incineration alternatives, are still capable of generating dioxins, furans and
other pollutants of concern, despite marketing and promotional claims to the contrary.


References:

Advanced Thermal Conversion Technologies for Energy from Solid Waste, IEA
CADDET Centre for Renewable Energy, Oxfordshire, United Kingdom. August 1998.
A joint report of the IEA Bioenergy Programme and the IEA CADDET Renewable
Energy Technologies Programme. http://www.caddet-re.org

FAO, 1994. Integrated energy systems in China - The cold Northeastern region
experience. Food And Agriculture Organization Of The United Nations, Rome, 1994.
http://www.fao.org/docrep/T4470E/t4470e00.htm

Mohr, K., Nonn Ch. And Jager J., 1997. Behaviour of PCDD/F under pyrolysis
conditions. Chemosphere 34: 1053-1064




  Health Care Without Harm, 1755 "S" Street, Northwest, Unit 6B,                      3
Washington, DC 20010 USA. Phone: 202-234-0091. Fax: 202-234-9121
Weber, R., Sakurai, T., 2001. Formation characteristics of PCDD and PCDF during
pyrolysis processes. Chemosphere 45: 1111-1117

Statewide Medical Services, Indianapolis, Indiana, USA.
http://www.med-dispose.com/pyrolysis.html, accessed on Jan 14 2002.

Compact Power, Avonmouth, Bristol, UK. http://www.compactpower.co.uk, accessed
on Jan 14 2002.

Eco Waste Solutions Inc., Burlington, Ontario, Canada.
www.banian.net/pyrolysis.htm

UNDP 1999. A Revolutionary Pyrolysis Process for turning Waste-to-Energy, BIO
ENERGY NEWS, Vol.3, No. 4 September.
www.undp.org.in/programme/GEF/september/page10-15.htm




  Health Care Without Harm, 1755 "S" Street, Northwest, Unit 6B,                  4
Washington, DC 20010 USA. Phone: 202-234-0091. Fax: 202-234-9121