[Gasification] Why would you want to make heating grade woodgas?

[Kevin]

Dear David

You bring out lots of good points...

----- Original Message ----- 
From: "David Coote" <dccoote at mira.net>
To: <gasification at lists.bioenergylists.org>
Sent: Thursday, April 12, 2012 9:39 PM
Subject: [Gasification] Why would you want to make heating grade woodgas?


> There's a heap of efficient wood burners (fuelwood, chip or pellet) on the 
> market that can convert wood to thermal energy at over 90% thermal 
> efficiency LHV. Some of the new condensing systems are even claiming over 
> 100% on LHV.

# There are several concepts  here...  it is important to distinguish 
between "Combustion Completeness", "Combustion Efficiency", and "Heating 
System Efficiency."

# It is relatively easy to get very high, or complete "Combustion 
Completeness" with wood gas... this is "completeness of burning of the fuel 
gas."

# "Combustion Efficiency", in addition to "Completeness of Combustion", also 
implies a minimum of excess air. Thus one could have 100% "Completeness of 
Combustion,", but a low "Combustion Efficiency" if there was a large amount 
of excess air.

# "Heating System Efficiency" is very dependant on the amount of "heat 
recovery surface available" in teh stove or furnace system. For example, one 
could have 100% Completeness of Combustion, 90% Combustion Efficiency, with 
limited excess air, but only say 40% 40% "Furnace Efficiency", because there 
was insufficient heat transfer area to recover the heat for space or process 
heating.

# So... a separate gasification system can give much better control over the 
fuel burning rate, and the completeness of combustion, but the products of 
combustion must be sent to a "heat recovery system" of some sort, in order 
to get a good "overall system efficiency.
>
> So why would you want to go through a distinct gasification process to 
> produce gas for subsequent combustion in a burner?

# For one thing, a gasifier system for "Heating Grade Gas", can handle a 
wide range of fuel sizes and shapes, with relatively simple feeding systems. 
A Pellet Stove, for example, requires uniform, factory made, expensive wood 
pellets, while a gasifier system can handle coarsely chunked wood or free 
wood chips.

If you're methanating
> the gas like the system developed at Gussing to bring the wood gas up to 
> the standard suitable for addition to the natural gas grid that makes 
> sense from a technical perspective.

# I don't know the Gussing Process, but producing a wood gas with a heating 
value in teh same range as natural gas is well beyond what is considered to 
be "Gasification" on this list.

But if you were just wanting to turn
> the woodgas into space heat?

# The simplest way, of course, is to burn the wood directly, if that is 
practical. Gasification could be advantageous in the following 
circumstances:
1: Where the fuel size and quality is very variable.
2: Where it is desired to keep teh fuel mess and dirt in one location, with 
teh wood gas being piped to a stove/boiler/furnace system in another 
location.
3: Where it is desirable to have several burner systems in different 
locations, supplied from a single gasification unit.
4: A Gasifier system can allow greater control over heat release into the 
furnace/stove/boiler.
5: A gasifier could offer fuel handling and feeding advantages.
6: Ash can be basically confined to the gasifier, with little or no ash 
passing through the burners to the stove/furnace/boiler system.

# So... there may be "Site Specific Advantages" that justify using a 
gasifier, rather than burning the wood fuel directly.

Best wishes,

Kevin

>
> Cheers
>
> David
>
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