<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
Hi List,<br>
<br>
This is the second in a series covering RPS experience with our
linear hearth.<br>
<br>
We often hear reference to "inappropriate fuels" for gasification
and fuel problems are often cited as the reason for project
failures. <br>
<br>
The RPS hearth was originally designed with wood chips in mind, but
has proven far more flexible. Over time quite a few "problematic"
fuels have been presented to us, often by companies where there is a
significant disposal cost on the business and no other solution.
What one of our colleagues described as the "thorn covered and snare
protected low hanging fruit of the market"<br>
<br>
As we gained experience with our new system we found much of our
knowledge of what works in gasification needed revising as we were
getting results that differed markedly from the literature. <br>
<br>
<b>PLEASE NOTE:</b> These results ONLY apply to the RPS Gasifiers
tested, not other linear hearths or different gasification systems
and results should not be extrapolated. The RPS development units
are the result of a long period of interest and study in
gasification, we are not new comers in the field, it took us 30
years to get it this "simple" whilst working this well.<br>
<br>
<b>SPECIAL WARNING NOTE:</b> Some of these materials shown below
are not suited to ordinary gasifiers. If system temperatures are not
high enough then tyre rubber and some other fossil derived fuels and
man made materials can produce condensates which are potentially
harmful to human health if mishandled. Sewerage sludge and other
organic materials have their own safe handling requirements. We had
suitably qualified and experienced persons present during this
testing and have a formal Health & Safety strategy in place.
Some materials were only tested after it was proven that the system
operated at temperatures and under conditions that were suitable for
their safe thermal destruction.<br>
<br>
Now read on...<br>
<br>
There is a great story from American comedian Bill Cosby who relates
that whilst in Italy he demonstrated his knowledge of Italian by
ordering direct from the restaurant menu…only to discover on being
served that he had ordered whole sparrow complete except for
feathers…he solved his potential embarrassment by ordering bread,
“because an American can eat anything between two slices of bread”!<br>
<br>
The RPS Gasifier is a little like Cosby in his story, it seems to be
able to digest most things organic fed to it so long as it is
sandwiched between two wood chips…<br>
<br>
Quite a few types of biomass can be gasified directly in the RPS
units, everything else tried so far works well if mixed with wood
chips/chunks. On homogenised mixed feed stocks the system comes up
to stable, consistent operation quite quickly, usually within 30
minutes from a cold start. General feed stock parameters identified
so far:<br>
<br>
• Moisture content <25%<br>
• Particle size – 10mm to 75mm (measured on any given side)<br>
• Fines - <33%<br>
• Very flat thin materials can affect system performance as these
can<br>
layer restricting optimal gas flow/heat transfer between pieces.<br>
• Organic liquids such as waste vegetable or mineral oils can be
added<br>
by pre-mixing with wood chip or sprayed evenly onto the top of the<br>
fuel column in the upper hopper.<br>
<br>
<br>
List of materials run so far by type:<br>
<br>
• Hardwood & softwood chips & chunks. <i>Comment: Bread and
butter fuels</i>, keep t<i>he moisture content below 25% and
particle size within recommended range and you won't be
disappointed.</i><br>
<br>
• Green wood chips at 50% mc. (Positive energy balance achieved with
gas quality sufficient for self sustaining flare). <i>Comment:
Really, gas was very poor quality and pre drying is the more
sensible approach, but it did demonstrate that inadvertent clumps
of high moisture content fuel finding its way in doesn't result in
thermal shock and complete system shut down.</i><br>
<br>
• Fine ground mixed species garden mulch chips from street scape
management. <i>Comment:</i> <i>Gas is lower quality with higher
condensate production than for optimum sized wood chips at the
same fan pressure.</i> <i>Char yields tend to be higher but lower
fixed carbon and higher mineral ash content.<br>
<br>
</i>• Macadamia shell. <i>Comment: Stand well back!</i> <i>The
rocket fuel for our gasifier. Multiple outputs including high
quality gas and </i><i>dense </i><i>high grade char</i><br>
<br>
• Shredded woody residues from composting operations including mixed
plastics. <i>Comment: Similar results to ordinary wood chips except
not suited to fixed grate models as material generally comes from
composting operations and can contain ground glass and soil
residues, forming soft clinkers on shut down as temperatures in
the hearth drop, making the following days start up problematic
without a full system clean out. Much more prone to bridging due
to material shapes. On the Mark 3. model with active grate this
was much less of a problem.</i> <br>
<br>
• Sawdust. <i>Comment: Similar results to fine ground garden mulch
only more severe. Mixed blend with wood chips presented no
problems.</i><br>
<br>
• Cotton gin trash <i>Comment: Excellent fuel once it is in the
hearth zone, getting it there past the normal gravity feed upper
hopper fitted to development units has presented problems.
Currently trialling some different (including novel!) approaches
to ensure the in feed works reliably. Alternatively pelleting or
briquette also solves the material handling issue...for additional
plant cost.</i> <br>
<br>
• Sugar cane trash. <i>Comment: Similar handling problems to cotton
trash in that getting it past the upper hopper is a bigger problem
than gasifying it when it reaches the hearth. Lower gas quality
and lower gas volume than wood chips at equivalent fan pressures.
High ash. Not suited to fixed grate models.</i><br>
<br>
• Rice straw. <i>Comment: As for Sugar Cane Trash.</i><br>
<br>
• Oil Mallee residues (leaf and stem). <i>Comment: As for fine
ground garden mulch.</i><br>
<br>
• Sawdust briquettes. <i>Comment: Good fuel similar to quality wood
chips.</i> <i>Higher ash and lower quality char though.</i><br>
<br>
• Pyrethrum briquettes (horticultural residues). <i>Comment: Good
fuel similar to wood briquettes only higher ash and a low quality
char co product, not ideally suited to fixed grate systems as fine
ash builds very quickly, then requiring very high fan pressures to
maintain flow. Works well in active grate model.</i><br>
<br>
• Cattle manure briquettes (40% ash) <i>Comment: Poor fuel due to
40% ash content (due to collection on clay pans with a skid steer
loader!), think pyre thrum briquettes with ground glass added.</i><br>
<br>
• Glycerine/acid oil waste from Bio-diesel production (in a blend
with wood chips). <i>Comment: Awesome wood chip additive </i><i>increases
gas energy content.</i><br>
<br>
• Paulownia chunks. <i>Comment: Think grass in wood chunk form.
Worked well but lower quality gas and char compared to wood chips.</i><br>
<br>
• Grape Marc (in a blend with wood chips). <i>Comment: Mixed in
blend with wood chips worked fine. Subsequent tests with 100%
grape marc pellets gave equivalent result to standard wood chips
but with higher char yield, although with lower fixed Carbon and
higher ash.</i><br>
<br>
• Chipped Industrial Hemp plants (the fibre variety!) <i>Comment:
May well be a law enforcement must have, worked similar to fine
ground woody garden mulch, good flare but higher ash, lower
quality char.</i><br>
<br>
• Sewerage sludge (composted & fresh out of centrifuge) in blend
with wood chips. <i>Comment: Worked well in blend with dry wood
chips.</i><br>
<br>
Non renewable:<b></b><br>
<br>
• Anthracite briquettes <i>Comment: Worked well despite quite high
ash contents, best suited to active grate models. Had a similar
condensate analysis to the wood sample in the previous post, only
with the pyridine replaced by benzene.</i><br>
<br>
• Lignite briquettes <i>Comment: As above only better as they were
much lower ash.</i><br>
<br>
• Low quality high ash black coal straight from the mine (Run Of
Mine). <i>Comment: Not every black looking piece is actually made
of coal, the high ash content seemed concentrated in large rocks,
nonetheless where piece sizes do not exceed 30 mm and the active
grate model is used it looks like a good fuel. Just add water
for really good gas as the mc was below 2%!.</i><br>
<br>
• Mixed electrical transformer waste including compressed cardboard,
Bakelite insulators, lump tar, oil soaked timber, aluminium coated
paper rolls, polyethylene cable sheathing. <i>Comment: As additives
to a standard wood chip feed in low volumes these went through
with no problem.</i><br>
<br>
• Car tyre rubber chips.<i> Comment: Mixed in a blend with wood
chips makes an awesome fuel, when used alone fan pressure has to
be substantially increased or you get a bright orange flame and
copious quantities of condensate the equivalent to crude oil. If
running only on rubber chips then the system has to have wood
chips through it immediately before shut down to replace the
rubber otherwise the cooling fuel pile bonds into a solid
vulcanised mess that takes a lot of breaking up the next day (Ahh
the voice of experience...) </i>
<blockquote
cite="mid:mailman.1.1328205604.30228.gasification_lists.bioenergylists.org@lists.bioenergylists.org"
type="cite"> </blockquote>
Now, some of these were preliminary tests with only 100-200kgs of
material so cannot be called definitive. Testing was done under our
"Suck it and see!" approach, developed after it became apparent that
we could not rely on the experience of others or published
literature to determine how our system would actually respond to
different fuels.<br>
<br>
Much more work remains to be done before commercial models of the
system can be finalised and certified for particular fuels,
nonetheless we are quietly excited. <br>
<br>
2012 looks like developing as the year of validation for RPS, with
much more formal, larger scale and in some cases independently
over-sighted trials in the works. Where confidentially agreements
allow we will report on these projects as results become available.<br>
<br>
<br>
Roll on Year of the Dragon!<br>
<br>
Cheers,<br>
Peter & Kerry Davies<br>
<br>
</body>
</html>