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A note to me from Dr. Neil Carman:
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For one thing, most TDF stack tests I have reviewed do not sample and analyze for the
range of air toxics and heavy metals, and these reports should be ignored in comparisons
of toxics/metals if the data is not available.
I have obtained several test reports and the raw data often reveals the process
fluctuations especially in emissions during the stack performance tests.
You will observe NOx, for example, cycling up and down by large ppm shifts, because cement
kilns are very large systems and balancing the kiln's process conditions is like juggling
many parameters at the same time. The NOx fluctuations are not at all reflected in the
final averages for, say, a 2-4 hour stack test burning TDF. That means if you only
evaluate the final average NOx data, you will not be aware of the significant NOx
perturbations taking place according to the test results. Kiln operators may not be aware
for several minutes that the kiln is in upset, and so correcting the kiln's problems takes
time to react after-the-fact of what is happening.
I recommend that you ask Kaiser and another cement kiln to give you a plant tour,
especially the Control Room to see the process controls and monitoring systems as it is
quite complicated. Then it will be all too obvious that these complex processes greatly
fluctuate up and down as they cycle through the conditions, although at times you may
observe some steady-state periods, but I believe these to be more the exception than the
rule (also depending on the type of kiln).
I generally agree that there is a tendency, even here in Texas, to skew the stack test
data in favor of burning TDF as showing no statistical difference-to-showing that it burns
cleaner than coal such as lower NOx.
One example is an EPA dual-chambered incinerator TDF stack test in the early 1990s that is
cited as proving how well TDF burns, but cement kilns/lime kilns/boilers are not
dual-chambered combustion systems--but are only single chambered systems.
All modern incinerators (medical, commercial, municipal, commercial-private hazardous,
industrial and super-fund units) are basically dual-chambered systems to obtain high
combustion efficiencies and using a single combustion chamber for incineration is totally
illegal today for the most part. Single chambered incinerators were built in the
1930s-60s, and then dual-chambered units were built to improve combustion.
Dual-chambered incineration is a standard federal and state requirment throughout the US I
am sure. Single chambered incinerators have almost all been shut down and observing their
stacks will convince anyone why they do not work well enough to protect public health. I
am not an advocate of incineration, however, since even the best state-of-the-art units
today experience problems of one type or another.
My point is that burning TDF in many cement kilns/lime kilns/boilers means that combustion
is occurring only in a single burn chamber. But yet TDF is made of complex materials
requiring different combustion conditions such as oxygen, temperature, turbulence and
residence times. The extender oils are much higher molecular weight chemicals and will
require more oxygen, higher temperatures, longer residence time and more turbulence to
burn as efficiently as the styrene-butadiene polymer in the SBR rubber. TDF contains
roughly 25% extender oils and when they burn in the open air, that's what gives tires the
ugly black smoke plumes and not the 50% SBR or 25% carbon black. -----
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