Law of Mass ActionRe: Burning ethics

["Kevin Chisholm" <kchishol@fox.nstn.ca>]

Dera Andrew

In response to your query about the "Law of Mass Action", my understanding
is that it goes something like this......

"Reactions tend to move toward an equilibrium condition. To encourage a
reaction to go in a desired direction, one can "tip the scales" by providing
the condition that will encourage the reaction to go in the desired
direction.

Consider a gas reaction

C + 1/2O2  = CO        -4000 BTU/Lb        (1)

in comparison to a reaction

C + O2 = CO2            -14,000 BTU/Lb        (2)

If both were occurring in the same vessel, then high temperatures would tend
to favor the first reaction, which is less exothermiic; it would tend to
move "to the right." At the same temperature, higher pressures would tend to
work against  Reaction 1, in that for it to proceed "to the right", there
would be an increase in gas volume, tending to cause a rise in pressure.
Both reactions would go faster at higher pressure, simply by virtue of the
"reagents being forced into more intimate contact."

Note that Carbon is a small consideration in this case, because as a solid
species, its influence on the volume of reactants is small. If Carbon is
present as a gaseous species, thats another matter....

Consider the following hypothetical reaction,

C3H4O4  = C +2CO + 2H2O        -Z Btu/Lb        (3)

where the hypothetical compound C2H4O4 is some hypothetical solid compound
in the wood.... a sugar, carbohydrate, etc.

Consider another way this hypothetical reaction could go...

C3H4O4  = 2C + CO2 + 2H2O         -ZZ Btu/Lb    4    (4)

Elevated pressure would have a strong tendancy to driving Reaction 3 "to the
left", ie, it would tend to prevent it from occuring, in that when going "to
the right" there is a very large increase in the volume of the products of
combustion.

Reaction #3 is an interesting one in concept. It may be generally
representative of occur in atmospheric pressure charcoal processes, in that
1/3 of the "starting carbon" remains behind as solid carbon (charcoal), and
the other 2/3 goes off as a gas

Because carbon is lost so easily from wood being carbonized at atmospheric
pressures, we know that the solid carbon species in the starting wood must
participate in a reaction where it comes off as a gaseous species, leading
to a lessening of the weight of carbon that stays behind as a solid.

Reaction#3 and #4, if kept under high pressure, would tend to leave the
original "sugar product" (or whatever) behind in the wood. probably somewhat
charred, but with a significant amount of volatiles.... they would thus tend
to give a "smokey charcoal."

Now consider hypothetical  reaction #4 as proceeding in a "two step manner:

C3H4O4  = C +2CO + 2H2O        -Z Btu/Lb        (3:1)

C + 2CO + 2 H2O = 2C + CO2+ 2H20    -Z BTU/Lb    (3:2)

Net Effect:
C3H4O4  = 2C + CO2 + 2H2O         -ZZ Btu/Lb    4    (4)

What is neat here is high pressure will tend to drive Reaction 3:2, which
involves the products from 3:1,  "to the left", and carbon will be recovered
as a solid, to stay behind as charcoal. This is because 4 volumes of
"reactant gas" (on the left) yield 3 volumes of "ptoduct gas" (on the
right.)  The net effect of the "two step reaction" is that we "have our cake
and eat it:"

1: The "sugar species" (or whatever) is reduced to carbon, to yield a
smokeless charcoal (Reaction 3:1)
2: The solid charcoal yield is increased.(Reaction 3:2)

Since all this stuff can be derived from "First Principles", it should
qualify as "being obvious to someone skilled in the trade" and shold thus
void the use of pressure as the basis for a Patent.

I think I am basically right on the principles here.... if not, there are
lots of more highly skilled people on the List to correct me.. :-)

Hope that helps.

Kevin Chisholm

----- Original Message -----
From: "AJH" <andrew.heggie@dtn.ntl.com>
To: <stoves@crest.org>
Sent: Saturday, January 19, 2002 5:38 PM
Subject: Re: Burning ethics


On Fri, 18 Jan 2002 20:45:54 -0400, "Kevin Chisholm"
<kchishol@fox.nstn.ca> wrote:

...del...

I know that you used this as an illustration and have become used to
responses on "stoves" to be muted, whether because of the high lurker
to poster ratio or lack of useful input, but I am unfamiliar with the
Law of Mass Action.
...del...

Mike Antal has announced a process that, by dint of application of the
techniques favouring conditions predicted by the law of mass action,
mentioned ny Kevin, maximises the retention of C to approach its
theoretical maximum (normally taken to be ~52% depending on biomass).
I pointed out that if *all* carbon remained as char then *no* carbon
would feature in the effluent which would be water.

....del....


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