Carbon footprint of wood firers part 2.

I recently wrote a blog post on the carbon footprint of wood, see here for part 1. Through a comment my attention was drawn to a presentation and a pdf file of the presentation on the carbon output of wood entitled “A Change in the Air” accessible by clicking the link. The presentation was given by Nancy Utterback at NCECA in April 2010.

I would like to respond to the assertions in the presentation. Before I do I would like to state I am a wood firer and don’t have any plans to change the fuel I use. I do believe it is better to call a spade a spade though. It was a very interesting presentation to read. I am impressed at how much work the person did to prepare it.

The main thrust of the presentation is that wood is a carbon neutral fuel since when a tree dies it decays and returns the carbon back to the earth. Note 1, see bottom of post for relevant cut and pastes from the presentation pdf.

If this is true then everything the paper rests on is correct. The problem is there isn’t any allowance given for time. Trees don’t decay in the time frame we are talking about. Kilns burn a very large quantity in a very short period, releasing all the carbon into the air in a heated jet of air. Decaying wood is broken down by microbes, weather, etc. The carbon that is digested by living creatures isn’t returned to the air, period. Please see this and this cut and paste from that link.


When trees die and fall to the ground, they usually decay within a few years to decades, releasing CO2 slowly back into the atmosphere. By contrast, when a forest fire occurs, or when forested land is cleared and burned for agriculture, huge quantities of CO2 are released into the atmosphere very quickly. Removing a single tree and turning it into firewood will have a similar rapid conversion, although on a much smaller scale. Under the right conditions, trees in a forest or jungle may become buried or submerged and eventually converted into crude oil and/or coal. That process takes millions of years, but that is where the carbon in our fossil fuels came from.

Trees are one of the best carbon sequestration vehicles, since they are large, long-lived, and decay slowly when they die. My emphasis.

End quote.

Another problem is the carbon released during decay doesn’t all go into the air. I am very unsure about the process of release. There are  small animals, bacteria, microbes and other living organisms that rely on downed trees as part of their life cycle. The soil is enriched by carbon rich byproducts  when a tree decays, the tree supplies nutrients to the next generation of trees, etc. The net effect is not  carbon neutral but as a carbon sink.

The presentation goes into some detail on the steps taken to measure particulates. Particulates aren’t the problem for the most part, carbon is. Note 2

There isn’t any data given for the actual CO2 readings. I find that odd as detailed data is given on particulates.

The fact that kilns meet EPA guidelines is pointed out. I only have to say look at the problem of CO2 in the air to assess the EPA guidelines. Note 3

The page numbers are from the presentation pages. The pdf has several presentation pages on each page.

Note 1.

From pg. 9 of the presentation

We all know that carbon has an impact on the environment. What I hadn’t understood was that
although firing with wood gives off carbon, it is carbon that would be released into the atmosphere
anyway. A tree absorbs carbon and gives off oxygen during its life; this is a good thing.When the tree
dies and rots, or if it is burned, it releases the exact amount of carbon it absorbed. This balance has
been going on since the beginning of time. But when we bring up fossil fuels from deep in the earth,
we release carbon that has been sequestered for millions of years. In a sense, it has been forgotten and
is no longer part of the natural exchange. So when using wood, you fire carbon neutral, but when you
use fossil fuels you are adding unbalanced carbon to the air and contributing to greenhouse gasses.

Note 2

From pg. 9 of the presentation.

We felt confident
that we could reduce or eliminate the
visible emissions, and decided to adopt the new
stoking pattern for future firings.


We were getting more complete combustion when we
changed our stoking pattern, but how much CO was still coming off the stack? The research team
decided to take some samples from the stack to quantify our CO and CO2 emissions and get an idea
of the number of particulates leaving the kiln.


With John’s measuring device we were able to determine that the average particulate matter was
10 micrometers in diameter, with a density of 1 g/cm^3 (one gram per hour). While the density did
vary and the particulates were reduced as the temperature increased, the number of particulates never
exceeded air quality standards. Keep in mind, however, that the EPA is regulating industry. Small
potters’ kilns do not give off enough emissions to be of concern or be measured; the air quality or
regulatory agencies are concerned with tons per year, not grams per firing. No studio potter will ever
reach that quantity of pollutants.This doesn’t mean we shouldn’t do our best; it simply means we are
very, very small in the scheme of things.
In Colorado it rarely rains, but we had one firing we called “the underwater firing” because it poured
for the entire 100 hours, resulting in a “backwash” situation. (“Whale Spirit” was accurately named.)
During this firing, the water concentration made the CO accumulate around the kiln instead of
dispersing and dissipating. Our readings revealed that the moisture in the air had given us unsafe CO
levels in the atmosphere. During the next couple of firings we monitored the air, but never experienced
the high levels of CO around the kiln area again.This confirmed that weather conditions could
affect our kiln site and stokers. Being aware of how far the CO, CO2, and all the particulates were
traveling led us to the next test.

Note 3

By the time the kiln (dubbed “Whale Spirit”) was built, my graduate students had good news.There
are no EPA regulations for the size and kinds of kilns that potters fire, so technically we were already
compliant.We thought about taking the information over to the planning department and being done
with the research, but I still wanted to answer some questions.

The rest of the cut and pastes are somewhat random, from the pdf.

From pg. 7of the presentation

Visible emissions were a
nuisance, but it was far more likely that the unseen
gasses might be more problematic.
Reducing the visible particulates was relatively easy.
An old device called a cyclone can be installed on the
top of a chimney; the velocity of the flame swirls
the particulates, burning more of them, collecting
unburned particulates, and reducing what is released
into the air. There are also catalytic converters that
filter out particulates. Either of these options would
reduce the visible smoke, but they are expensive to
build or buy and would have to be retrofitted to
work on a kiln. Having been a potter for thirty years,
it has been my experience that potters often live on
the edge. Getting potters to keep a special device in
working order seemed an unrealistic goal. I wanted to
find other ways to address the issue, knowing we
could always come back to a catalytic converter or a
cyclone if we had to.


Pg. 8 of the presentation

During the first year, we fired five times, experimenting with several ways to reduce the smoke.
First we changed our stoking pattern, putting
in less wood more often. This turned the
black smoke to gray, and if we paid close
attention we could eliminate the plume completely.
With this new pattern we were still
able to adjust the temperature as before and
used the same amount of wood in the same
100 hours.


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One Response to “Carbon footprint of wood firers part 2.”

  1. How did my carbon credit end up in your kiln? « Togeii's Weblog Says:

    […] blog post of about a week ago has provoked a lot of discussion on a couple of ceramics lists in the U.S. and […]

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