POST 00668E : WASTE MANAGEMENT
Follow-up on Post 00657E and 00664E
29 April 2004
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In this posting Ville Lehto (mailto:[email protected]) from
Finland discusses the issue of toxic emissions during incineration,
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Thank you for these important documents! I already posted my comments to
Yves too.
As stated, the main problem with incineration has been the formation of
dioxins and furans. The issue of proper operation is related to the same
problem. Bad operation results in incomplete burning and toxic emissions.
It was also written that "Even in high temperature incinerators (>800 °C),
temperatures are not uniform and dioxins and furans can form in cooler
pockets or during start up or shut down periods. Optimization of the
incineration process can reduce the formation of these substances
by, e.g., ensuring that incineration takes place only at temperatures above
800°C, and that flue gas temperatures in the range of 250 to 450°C are
avoided."
We are afraid that the temperature of 800°C might not be enough, and
minimum of 850°C should be preferred. When it comes to cooler pockets it is
better to take a look how these emissions are created. There are three
mechanisms that result in PCDD/PCDF emissions:
1. The fuel/burned material contains PCDD/PCDF, and it doesn't decompose
during the burning process
2. In temperatures 300-800°C organic compounds that contain chlorine form
PCDD and PCDF
3. In temperatures 250-400°C inorganic chlorine and organic compounds form
PCDD and PCDF (De-Novo-synthesis).
Burning at temperatures over 850°C prevents the formation of dioxins and
furans, and the residence time min. 2 seconds make the existing ones
decompose. By ensuring sufficient preheating and burning time, also the
problems with start up and shut down periods can be avoided.
It was also said that "WHO has not established an acceptable limit for
dioxins and furans emissions since:
• most incinerators are unlikely to meet existing standards;
• most incinerators cannot easily be equipped with emission reduction and
control devices;"
My comments are:
- The existing standards are for 50MW plants. For example, the power of our
gas burner is 72 kW. -- There are no standards for small scale incinerators.
- However, there are incinerators that meet existing (50MW) standards for
PCDD and PCDF, and as the technology takes steps forward we believe that
there will be more and more of them.
- Emission reduction devices are not a solution to the problem. The toxic
emissions could be collected e.g. in some filter, but then the problem
would be: What to do with the filters? Instead we should aim at a clean
process.
Some best practices were also listed. I would like to comment the operation
part. The key is that the products must be user friendly. It is
inappropriate to expect that every operator in the field is an expert of
burning theories. With automation it is possible to reduce the demands for
the operator to the level that can be achieved with very little training.
Another point of the user friendliness is that the products should be so
safe to use that the protective equipment is not needed.
I would like to hear everyone's opinions and comments. The issue is
important. Let's keep the discussion alive!
Best regards,
Ville Lehto
Marketing Manager
Mediburner Ltd.
Oulu, FINLAND
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