[Gasification] Wood heating in the UK - whole log gasification

Tom Miles tmiles at trmiles.com
Sat Dec 28 11:18:02 CST 2013



Our concern with wood smoke in Oregon started in the mid-1970s when a friend
measured the atmospheric concentration of respirable particles (PM <10
micron) in our Portland-Vancouver air shed. He found that more than 60% of
the sub-micron particles came from wood smoke. Our Department of
Environmental Quality began a concerted effort to determine causes and
improve chimney and stove efficiency. Early in the process we relied on
talent from New Zealand (Don Pullen, Department of Health, Christchurch, now
AP Consulting) and elsewhere for assistance. People, like Jay Shelton,
Richard Hill and Larry Dobson, had been working on improving wood
combustion. Our 1979 conference drew scientists from around the world and
resulted in 1300 pages of studies and presentations. (Richard Hill and I
co-chaired a session on new designs at that conference.) Our Oregon standard
for wood heating appliances became the US EPA standard and was modified or
adopted in many parts of the world. Since then the documentation and science
has become well advanced. We have seen many "gasifier" stoves developed.
Wood pellet burners were top performers in the early studies because of the
control of air and fuel. It is no surprise that they continue to be
important residential appliances but in the US there are 10 times as many
stick wood burners as pellet burners. 


There is always room for improvement. Outdoor Wood Boilers (OWB) were
developed with many of the same flaws of cooling the fire as have been
discussed here and caused serious problems in certain air sheds. It has
taken regulation and extensive collaboration between regulators and (in the
US more than 60) suppliers to improve OWB emissions. The emissions and
efficiency standards that were proposed by the collaboration of suppliers
and regulators (ASTM Working Group ~2004 on) were better than the rules
promulgated by the USEPA but the EPA lost its patience with the (ASTM)
standards process and simply imposed its regulations. European wood boilers
are often more advanced but sometimes require highly processed fuels.    


As David and many health researchers have pointed out direct causal
relationships between wood smoke and health are not well documented but
there is abundant evidence that indirect routes do cause health problems.
(In 2010 technical groups advising the Global Alliance for Clean Cookstoves
advocated more health studies but for some reason the money goes to other
activities.) In developing countries where wood is used for cooking trauma
such as skirt fires, and burns are serious health problems. Utilities and
health officials have banned wood or encouraged alternative fuels is some
troublesome air sheds. The state of Massachusetts has set high thresholds
for combustion efficiency and emissions from biomass burning of all kinds,
including heating appliances, due to health concerns. 


Science and regulation is well advanced but that doesn't mean that you can't
attain health and efficiency goals buy the judicious application of
combustion fundamentals. This often includes the careful use of gasification
where it can have the greatest impact. 





From: Gasification [mailto:gasification-bounces at lists.bioenergylists.org] On
Behalf Of David
Sent: Saturday, December 28, 2013 8:29 AM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] Wood heating in the UK - whole log gasification



On 12/28/2013 12:57 AM, Jason wrote:

PS. I have one aquaintance in New Zealand that is challenging the science
around respiratory disease and emissions from wood smoke. He says the link
is tenuous and the early bogus studies keep getting repeated and used as
justification to ban wood stoves. 

Water is necessary for life and too much can drown you. Similarly with some
things, a little can be of benefit. I recall a study of woodcutters that
showed they had increased resistance to colds, and this was attributed to
intermittent exposure to wood smoke. On the other hand, the WHO says that
1.6 million people die every year from exposure to indoor air pollution,
i.e. also (for the most part) wood smoke. (Coal smoke is far more deadly.)
The epidemiology is pretty well established.

The term of art is hormesis, for which wikipedia offers the definition:

Hormesis is the generally favorable biological response to low exposures to
toxins and other stressors. A pollutant or toxin showing hormesis thus has
the opposite effect in small doses as in large doses. ...


As far as the most common contributors to air pollution, it may end up that
airborne particulate matter of a certain size range, particularly where the
makeup of the particles includes irritants leading to inflammation, will be
seen to be most at fault for negative impacts on health. Not wood smoke,
exactly, in other words, but some things found in wood smoke, may well be
identified as the key bad actors. That would be my current best guess, where
I am solidly grounded in nearly perfect ignorance.

It may be hard to get around the better safe than sorry approach that many
might be inclined to take. The future promises to have more regulation, from
almost any point of view.



David William House

"The Complete Biogas Handbook" www.completebiogas.com 
Vahid Biogas , an alternative energy consultancy www.vahidbiogas.com 

"Make no search for water.       But find thirst,
And water from the very ground will burst." 

(Rumi, a Persian mystic poet, quoted in Delight of Hearts , p. 77) 




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