[Gasification] A chemist who needs more education??

[Phil Marsh]

This fellow has a Doctorate Degree, I do not, I'm just a dumb farmer, but
making a statement such as "gasifying coal generates more carbon dioxide
than just burning it", has me very concerned about where he went to school
and what he might be teaching. It is my simplistic understanding that fully
oxidizing x moles of carbon will produce y moles of CO2 and that the terms
burning, combustion, gasification, etc just refer to the oxidation route. 

Comments anyone?

Gasification flawed concept
Prince George Citizen
Monday, April 21, 2008
Page 4
By Todd Whitcombe 
I teach a course at UNBC on Industrial Chemistry. 
In it, we discuss the chemistry of sulfuric acid production and making pulp,
of refineries and brewing beer, and of a number of other important
processes. We discuss the uses for their products and the effluents they
produce. Then I have my students write reports about various industries. 

One of my students wrote her report on coal. In a moment of synchronicity,
she handed it in on the same day that there was an article on wood
gasification in the paper. 

I mention this because as she was handing it in, she said: "I don't know
about wood but the stuff that I've read says that gasifying coal generates
more carbon dioxide than just burning it." 

There it is. Gasification does not save carbon dioxide emissions. 
All it takes is a little bit of reading, and a course in Industrial
Chemistry, to actually find this out. Gasification is not a process that is
going to save on greenhouse gases. 

The reason behind this is that wood, coal, or any other carbon containing
compound can be converted from a "solid" to a "gas" but it takes energy. 

A simple example of this process is a candle. Solid wax is melted to make a
liquid which flows up the wick where heat converts it to a gas. 

It is the gaseous organic compounds that we actually see burn. This is why
the heart of a candle flame is brown. 
Gasification essentially takes wood, heats it to the point where it forms a
gas, and then burns the gas. It takes a lot of energy to heat wood and turn
it into a gas. That is energy that doesn't go into the output from the heat
plant. 

Why do this then? The answer is that gasified wood burns both hotter and
cleaner than just burning the wood but at the expense of increased carbon
dioxide production. As I said last week, it's a trade off. 

The amount of extra energy required, and emissions released, depends on the
water content of the wood. More water means extra energy and emissions. 

So, when people start talking about all of the wood waste we have available
for burning, I have to wonder just what they mean and what it will truly
cost to burn. 

Sawdust and wood chips are not particularly dry. Just ask the guys at
Pacific BioEnergy, where they have two massive kilns to dry the wood out
before making pellets suitable for combustion. 

Their clients need dry wood to make burning feasible. At 50 per cent water,
the net heating value of wood is only half of what one obtains at 10 per
cent. Drying wood takes a lot of energy and generates emissions -- a hidden
cost of combustion. 

On top of this, with recent developments in our local industries, sawdust
and wood chips are no longer waste, but valuable commodities. 

Further, if we are talking about the waste wood that litters our forest,
that isn't really waste. The branches and other detritus help to maintain
the forest ecosystem. They are also very wet. Burning wood doesn't seem, to
me, to make a lot of sense. 

The irony of this discussion is that we are presently wasting methane -- at
the sewage plant and landfills, from the refinery, and from agricultural
waste -- which could be used to generate heat much more easily and with way
less impact. Indeed, since methane is a much more potent greenhouse gas than
carbon dioxide, burning it would actually lighten our carbon footprint. And
it gives twice as much energy per tonne of emissions compared to wood. 

Maybe it is time to rethink the whole idea of a heat plant downtown. Or
maybe it will have to wait until after the municipal elections. 

Dr. Todd Whitcombe is a professor at UNBC and a politically active member of
the community. His column appears Mondays. E-mail: whitcomb at unbc.ca

 

Phil Marsh

Alterna Energy Inc.

#102 3645-18th Ave

Prince George, BC, V2N 1A8, Canada

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