[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: GSBN:France is Looking for alternatives for burning rice straw
- To: "'GSBN'" GSBN@...
- Subject: RE: GSBN:France is Looking for alternatives for burning rice straw
- From: "Paul Olivier" paul.olivier@...
- Date: Wed, 16 May 2007 07:44:50 +0700
- Reply-to: "GSBN" GSBN@...
- Sender: "GSBN" GSBN@...
I suggest that you consider the rice hull which is far more tough and
resilient than rice straw straw. The hulls could be bagged, and these bags
or sacks could stack in a manner similar to bales. Rice hulls are available
throughout the year at a low moisture content (<12%), and they sell for
virtually nothing. Let me share with you a few reflections that I have put
together on the advantages of rice hulls.
When nature decided how to package a grain of rice, she wrapped this tiny
bundle of nutrients with what is often referred to as a Òbiogenic opal.Ó The
chemical structure of the rice hull, containing amorphous silica bound to
water, closely resembles that of the opal, and this gives the rice hull some
fairly amazing properties. Nowhere could we ever find a cereal by-product so
low in protein and available carbohydrates, and yet, at the same time, so
high in crude fiber, crude ash and silica. Of all cereal by-products, the
rice hull has the lowest percentage of total digestible nutrients (less
The rice hull contains approximately 20% opaline silica in combination with
a large amount of the phenyl propanoid structural polymer called lignin.
Such a high percentage of silica is very unusual within nature, and this
intimate blend of silica and lignin makes the rice hull not only resistant
to water penetration and fungal decomposition, but also resistant to the
best efforts of man to dispose of it. Since rice is grown on every continent
except Antarctica, since it ranks second only to wheat in terms of worldwide
area and production, and since the hull represents on average about 20% of
the rough harvested weight of rice, our planet ends up with an abundance of
this scaly residue.
The hull is a very tough and abrasive packaging material, consisting of two
interlocking halves. It encapsulates the tiny space vacated by the milled
grain, and in proximity to a myriad of other hulls, it forms a thermal
barrier that compares well with that of excellent insulating materials.
Thermal resistance tests on whole rice hulls indicate R-values as high as
3.0 per inch.
Do rice hulls burn? Yes they do, but with difficulty, as Eldon Beagle once
so elegantly explained:
The peculiar silica-cellulose Ôdrinking-straw bundleÕ
structural arrangement of the husks results in an object that does not burn
or even liberate heat in a manner resembling that of any organic substance.
These minute silica-crested tubular structures offer an inherent resistance
to burning. Often they seal off and prevent the thorough, uniform burning
essential to obtaining a desired end-product.Ó
Anyone who has tried to set a match to loose rice hulls understands how
difficult they are to burn. Since air cannot flow freely through a pile of
rice hulls to provide the oxygen needed to sustain rapid combustion, they do
not easily and cleanly combust. The bulk density of loose rice hulls is
similar to that of baled straw, and anyone who has tried to burn a bale of
straw understands the problem associated with the availability of oxygen.
But the simple availability of oxygen does not explain everything.
As we have noted above, the high percentage of opaline silica within rice
hulls is most unusual in comparison to other plant materials, and some
scientists say that during the combustion of rice hulls, the silica ash may
form a ÒcocoonÓ that prevents oxygen from reaching the carbon inside. Other
scientists speculate that, since silica and carbon may be partially bonded
at the molecular level, silicon carbide is formed during high-temperature
combustion, and that the presence of this heat-resisting ceramic impedes the
easy combustion of the rice hull. Still other scientists say that at certain
temperatures, the molecular bond between the silica and carbon in the hull
is actually strengthened, thereby preventing the thorough and uniform
burning of the hull. In any case, even if we do manage to ignite a pile a
rice hull, we find that it tends to smolder rather than flame.
Rice husks are flame retarding and, at ordinary
temperatures, self-extinguishing. A lighted match, tossed onto a pile of
rice husks will generally burn out without producing a self-sustaining flame
in the husks.
Conventional cellulose insulation necessitates the addition of large
quantities of flame and smolder retardants. The concentration of flame and
smolder retardant chemicals (such as boric acid, sodium borate, ammonium
sulfate, aluminum sulfate, aluminum trihydrate, mono- or di-ammonium
phosphate) in conventional cellulose insulation may reach as high as 40% by
weight. These chemicals are expensive to purchase and prepare, and the
cellulosic fiber must undergo extensive preparation to receive them.
Surprisingly, rice hulls require no flame or smolder retardants. Nature has
freely given to this agricultural waste product all of the combustion
properties needed to pass the Critical Radiant Flux Test (ASTM
C739/E970-89), the Smoldering Combustion Test (ASTM C739, Section 14), and
the Surface Burning Characteristics Test (ASTM E84). Recent testing done by
R&D Services indicates an average Critical Radiant Flux (CRF) of 0.29 W/cm2,
a smoldering combustion weight loss between 0.03% and 0.07%, a Flame Spread
Index (FSI) of 10 and a Smoke Development Index (SDI) of 50. Since US
building codes require an FSI of 25 or less, and an SDI of 450 or less, we
see that the rice hull easily passed these tests. In its raw and unprocessed
state, the rice hull constitutes a Class A or Class I insulation material.
All organic materials will absorb or release moisture until they come into
equilibrium with the relative humidity of the surrounding air. The high
concentration of opaline silica on the outer surface of the rice hull
impedes the atmospheric transfer of moisture into the hull. Also, 2.1% to
6.0% of the rice hull consists of a biopolyester called cutin, which, in
combination with a wax produced by the rice plant, forms a highly
impermeable barrier. Nature employs several very effective strategies to
protect the kernel of rice from the water and high humidity generally
associated with the cultivation and growth of this plant.
Consequently, studies done on rice hulls at 25*C indicate that the
equilibrium moisture content of rice hulls at 50% relative humidity is at or
below 10%, while at 90% relative humidity, the equilibrium moisture content
of rice hulls remains at or below 15%.A Moisture Vapor Sorption Test (ASTM
C739, Section 12) conducted by R&D Services indicates a gain in weight of
only 3.23%. This is well below the moisture content needed to sustain the
growth of fungi and mold.
The ASTM Standard Specification for cellulose insulation requires a 28-day
test for resistance to fungal growth (see section 10 of ASTM C1497, ASTM
C1338, Section 6.6 of ASTM C1149 or Section 11 of ASTM C739). Following
these standards, R&D Services inoculated rice hulls with five different
fungal species, and the rice hulls passed these tests without the addition
of fungicides or any other chemicals.
The high concentration of opaline silica on the outer surface of the rice
hull also establishes the effective hardness of the rice hull at roughly the
same values as reported for opal (6 on the Mohs scale). However, due to the
presence of lignin within the rice hull, this hardness is tempered with
flexibility and elasticity. Since the rice hull is hard and yet elastic, it
resists settling and compression far better than shredded newspapers. The
settling of cellulose insulation in a wall cavity can reduce its installed
height by as much as 25%. For this reason it is often necessary to stabilize
cellulose insulation by means of polyvinyl acetate or an acrylic adhesive.
None of these stabilizing compounds are needed with rice hulls, if firmly
vibrated or packed into a wall cavity.
Ordinarily loose rice hulls have an angle of repose of about 35 degrees. But
once firmly packed into a wall cavity, their tiny tips, edges and hairs
interlock to achieve a negative angle of repose. Due to this peculiar
bonding of rice hulls under mild pressure, they stabilize in a very uniform
manner, and no further settling is possible. Also, since it is not necessary
to add fire-retardants, fungicides or any other chemicals to the rice hull,
R&D Services has determined that this benign and stable biomass does not
emit offensive odors (ASTM C739). Likewise, R&D Services determined that
rice hulls do not corrode aluminum, copper or steel (ASTM C739, Section 9).
With rice hulls, we need not engage in a mining or manufacturing process
that generates air pollution, water pollution or erosion. With rice hulls,
we need not engage in a manufacturing process that depletes our reserves of
fossil fuels (as with polystyrene, polyisocyanurate and polyurethane
insulation). With rice hulls, we do not use chlorine-based chemicals such as
phosgene, propylene chlorohydrin or any ozone-depleting chlorofluorocarbons.
With rice hulls, we do not use urea formaldehyde, and surely none of the
phenol formaldehyde used in most fiberglass insulation. With rice hulls, we
do not have to worry about the irritability or cacinogenicity of dust and
fibers. Moreover, those with acute chemical sensitivity should not have to
worry about the off gassing associated with binders in batt insulation, with
ink in recycled newspaper or with VOCs released from foam insulation. Since
rice hulls require no shredding, hammer-milling, fluffing, fiberizing,
binding or stabilizing, they possess, surely in those states where hulls are
available, far less embodied energy than even cellulose insulation. Since
rice hulls do not burn very easily, they require no flame or smolder
retardants, and since they are so tough and durable, nothing prevents them
from being used and recycled over and over again.
Paul A. Olivier
ESR International LLC
27c Pham Hong Thai, Ward 10
Lam Dong Province
Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Texas telephone: 1-214-306-8746 (rings Vietnam)
Mobile: 090-6458735 (in Vietnam)
Mobile: 84-90-6458735 (outside Vietnam)
New website: <a target="_blank" href="http://esrint.com/">http://esrint.com/</a>
Old Website: <a target="_blank" href="http://www.esrla.com/">http://www.esrla.com/</a>
Skype address: Xpolivier
From: GSBN [<a target="_blank" href="mailto:GSBN@...">mailto:GSBN@...] On Behalf Of André de Bouter
Sent: Wednesday, May 16, 2007 4:54 AM
Subject: GSBN:France is Looking for alternatives for burning rice straw
Hello California (and other rice straw users/researchers),
In the south of France rice is grown and I have been contacted recently
by Christelle MONIER an agriculture engineer specialized in durable
vegetable production (Ing?nieur Agronome sp?cialis? en Production
V?g?tale Durable) working for INRA (a well respected agriculture science
She is trying to find alternatives to the burning of the 50 000t of rice
straw per year and is interested in SB as one of the alternatives to
research. Some of the challenges are: the rice is harvested while the
leaves are still green. The straw is taken out of the fields in autumn
while the fields are very wet.
She will buy Bruce King's new bible and is interested in communicating
with some of you who can help her sharing your (rice straw) experience.
Also, don't hesitate to share any other uses of rice straw (to me or via
the list). I'll gladly forward them to Christelle.
La Maison en Paille
--- StripMime Report -- processed MIME parts ---
text/plain (text body -- kept)