[Terrapreta] Fwd: Cellulosic biomass into Ethanol conversion.

[Larry Williams]

Sean-------Thanks for these comments. You have filled in some blank  
spots in my understanding of pyrolysis-------Larry



Rich--------Sean comes through on this post. I have been waiting for  
an explanation that clarifies what is happening in the retort that I  
have been using. As mentioned earlier, I have been stalled (not being  
a researcher) as to what I have been seeing. Specifically, Sean's  
comments explain or give me a direction to ponder. The quote below  
covers aspects of both the mound burning technique and the retort  
technique.

For example:
"Pyrolysis is called thermo-chemical reaction because is occurs as a  
result of high heat.  Biology is killed at pyrolysis temperatures.   
When biomass is heated (externally at first) the first thing to occur  
is that water is driven out of the biomass.  Essentially it is boiled  
away and escapes as steam.  Then above 150 C or so, the cellulose and  
lignin begin to decompose, breaking apart the long carbohydrate  
strings.  This is all in the endothermic stage of the reaction.  This  
means it requires the input of heat (or oxygen and complete  
combustion (burning) of some of the biomass feedstock) to continue.   
Eventually though, at about 250 C, the reaction becomes exothermic.   
This means that there is then enough heat being released by the  
decomposing molecules that the reaction becomes self-sustaining,  
without the continuance of added external heat.

In the exothermic stage of a pyrolysis reaction, hot incomplete  
combustion gases are being driven out of a charcoal "bed".  The  
combustion is incomplete because the amount of oxygen is limited.   
The heat breaks up the carbohydrate molecules in the charred biomass,  
rendering some fuel gases; Hydrogen gas-H2, Carbon monoxide-CO,  
Methane-CH4, Ethane-C2H6, etc.  The fuel gases are incomplete  
combustion products.  There was not enough oxygen for them to have  
burned (oxidized).  There are also some complete combustion product  
gases exiting from a pyrolysis reactor/gasifier; Carbon Dioxide-CO2  
and Water vapor-H2O.  CO2 is burned CO.  H2O is burned H2.  Complete  
combustion (burning) means combining with oxygen and releasing heat."

I do think that it is important to learn what the smoke can tell us  
in the pyrolysis process which I will continue (for a while) to vent  
the retort (less than 3 cu ft capacity) while capturing as much of  
the wood vinegar as possible. There have been some questions, in my  
mind, about the heat source (propane) being greater than the energy  
value of the wood vinegar and the charcoal. There are many more  
questions to be answered about the products from the condensate------- 
Larry




Begin forwarded message:

> From: "Sean K. Barry" <sean.barry at juno.com>
> Date: November 9, 2007 10:43:50 AM PST
> To: <still.thinking at computare.org>
> Cc: terrapreta <terrapreta at bioenergylists.org>
> Subject: Re: [Terrapreta] Cellulosic biomass into Ethanol conversion.
>
> Hi Duane,
>
> The thermo-chemical conversion of cellulosic biomass (pyrolysis/FT)  
> into Ethanol is quite different than the bio-chemical conversion of  
> cellulosic biomass into (steam explosion/enzymatic fermentation) or  
> the bio-chemical conversion of plant sugars into Ethanol (yeast  
> fermentation).   Only pyrolysis/FT has the potential to produce  
> biochar as a co-product.
>
> Pyrolysis is called thermo-chemical reaction because is occurs as a  
> result of high heat.  Biology is killed at pyrolysis temperatures.   
> When biomass is heated (externally at first) the first thing to  
> occur is that water is driven out of the biomass.  Essentially it  
> is boiled away and escapes as steam.  Then above 150 C or so, the  
> cellulose and lignin begin to decompose, breaking apart the long  
> carbohydrate strings.  This is all in the endothermic stage of the  
> reaction.  This means it requires the input of heat (or oxygen and  
> complete combustion (burning) of some of the biomass feedstock) to  
> continue.  Eventually though, at about 250 C, the reaction becomes  
> exothermic.  This means that there is then enough heat being  
> released by the decomposing molecules that the reaction becomes  
> self-sustaining, without the continuance of added external heat.
>
> In the exothermic stage of a pyrolysis reaction, hot incomplete  
> combustion gases are being driven out of a charcoal "bed".  The  
> combustion is incomplete because the amount of oxygen is limited.   
> The heat breaks up the carbohydrate molecules in the charred  
> biomass, rendering some fuel gases; Hydrogen gas-H2, Carbon  
> monoxide-CO, Methane-CH4, Ethane-C2H6, etc.  The fuel gases are  
> incomplete combustion products.  There was not enough oxygen for  
> them to have burned (oxidized).  There are also some complete  
> combustion product gases exiting from a pyrolysis reactor/gasifier;  
> Carbon Dioxide-CO2 and Water vapor-H2O.  CO2 is burned CO.  H2O is  
> burned H2.  Complete combustion (burning) means combining with  
> oxygen and releasing heat.
>
> If a charcoal "bed" is moving through the reactor, some charcoal  
> being taken out at the back/bottom end, while new un-charred  
> biomass feedstock is entering in at the front/top end, then  
> charcoal is a released co-product along with the gases exiting the  
> reactor.
> There is a term called "superficial velocity" which is a measure of  
> how fast these reactants (biomass and oxygen, or air) and products  
> (producer gas or synthesis gas and charcoal) are moved through the  
> system.  If the charcoal is not moved out and new biomass moved in,  
> then it will all be consumed, producing only gases, and leaving  
> only ash.  If too much oxygen is supplied then all the produced  
> gases will be complete combustion gases (CO2 and H2O).   If no  
> oxygen is supplied, then the biomass will decompose into a black,  
> gooey, liquid, releasing no gases and no char.
>
> The bio-chemical conversion processes do not operate at these kinds  
> of temperatures.  The enzymes in cellulosic fermentation or the  
> yeast in sugar fermentation cannot tolerate the temperatures in a  
> pyrolysis reaction and still do what they need to do to make the  
> chemical conversion.  There never is any biomass charring occurring  
> in this type of bio-chemical conversion reaction.  For TP  
> enthusiasts, then, pyrolysis/FT to make liquid fuels from biomass  
> is a preferred method, because it can at the same time make charcoal.
>
> It is important to keep in mind the thermodynamics and the energy  
> inputs versus usable energy outputs with a pyrolysis reaction,  
> though.  There is only a finite amount of energy in any biomass.   
> It is stored in the biomass in the form of chemical energy, that  
> which binds the atoms of the cellulose, lignin, and other plant  
> molecules together.  When the reaction goes exothermic, much of  
> that energy is released as direct heat.  There is also heat  
> released from the complete combustion which is also occurring in  
> parts of the biomass.  Some of the energy is released in the form  
> of chemical energy left in smaller molecules, in the fuel gases;  
> H2, CO, CH4.  And, if there is any charcoal left, then some of the  
> energy is left in that solid mass of un-pyrolyzed, un-burned Carbon.
>
> So, when proper accounting is made of the BTU content of inputs  
> (including the BTUs needed to preheat the biomass during the  
> endothermic stage) and the BTU content of the output gases and the  
> char, then it may turn out that the thermo-chemical pyrolysis  
> reactor/FT conversion process is much less energetically efficient  
> than a bio-chemical one.  This means much more feedstock is  
> required to produce the same amount of Ethanol.
>
> Heat losses can significantly reduce the energy efficiency of a  
> pyrolysis reaction. The efficiency might even be upside-down,  
> meaning it always takes more externally input energy input to make  
> the conversion than all of the "usable-for-the-process" energy  
> there ever was in the feedstock and than there will ever be in the  
> all of the resulting products.  Making charcoal from biomass will  
> almost assure that the fuels got from that biomass were "upside- 
> down" energy efficient.
>
> Nothing is FREE!  (except American citizens?)
>
> Regards,
>
> SKB
>
>
> ----- Original Message -----
> From: Duane Pendergast
> To: 'Sean K. Barry'
> Sent: Friday, November 09, 2007 11:18 AM
> Subject: RE: [Terrapreta] range fuels
>
> ...
>
> To supplement, I hoped to get across the idea that the two ethanol  
> processes are equivalent to simply burning the organic material to  
> generate energy. No char is made. All of the "waste" organic  
> material is taken from the land and destroyed in the production of  
> ethanol. On second thought maybe that is not quite true. Perhaps  
> there is a useful organic waste left over from producing ethanol.    
> Certainly some of the carbon content of the cellulose goes into the  
> ethanol and back to the atmosphere as CO2 when the ethanol is  
> burned. It seems the processes pay no attention to, and do not  
> contribute to building soils as would char production in concert  
> with leaving some waste organic material on the land to drive the  
> terra preta process.  The two ethanol production methods will  
> generate the same kind of problems related to land use change  
> (conversion of forests to crop land) already associated with  
> conventional ethanol and biodiesel production - including reduction  
> of carbon content stored in the soil.
>
> I hope you can straighten me out in your next posting.
>
>
> Duane
>
>
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