<cite>A search on the title gives:<br><br><a href="http://www.inl.gov/technicalpublications/Documents/5094547.pdf">www.inl.gov/technicalpublications/Documents/5094547.pdf</a></cite><br><br><div class="gmail_quote">On Sun, Feb 26, 2012 at 8:09 AM, Tom Miles Easystreet <span dir="ltr"><<a href="mailto:tmiles@trmiles.com">tmiles@trmiles.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF"><div>Source ?<br><br>T R Miles Technical Consultants Inc. 503-780-8185<span></span><div><span><a href="mailto:tmiles@trmiles.com" target="_blank">tmiles@trmiles.com</a></span></div>
<div><span>Sent from mobile. </span></div></div><div><div class="h5"><div><br>On Feb 25, 2012, at 4:19 PM, Paul Olivier <<a href="mailto:paul.olivier@esrla.com" target="_blank">paul.olivier@esrla.com</a>> wrote:<br>
<br></div><div></div><blockquote type="cite"><div>Crispin,<br><br>I think that the following sums things up quite well.<br><br><font size="4"><b>A Review on Biomass Torrefaction Process and Product Properties</b></font><br>
<br><i><b>Grindability</b><br><br>Biomass is highly fibrous and tenacious in nature, because fibers form links between<br>
particles and make the handling of raw ground samples difficult. During the torrefaction<br>process the biomass loses its tenacious nature, which is mainly coupled to the<br>breakdown of the hemicellulose matrix and depolymerization of the cellulose, resulting<br>
in the decrease of fiber length (Bergman et al., 2005; Bergman and Kiel, 2005). The<br>decrease in particle length, but not in diameter per se, results in better grindability,<br>handling characteristics, and flowability through processing and transportation systems.<br>
During the torrefaction process the biomass tends to shrink; become lightweight, flaky,<br>and fragile; and lose its mechanical strength, making it easier to grind and pulverize<br>(Arias et al., 2008). Bergman and Kiel (2005) conducted studies on the energy<br>
requirements for grinding raw and torrefied biomass like willow, woodcuttings,<br>demolition wood, and coal using a heavy duty cutting mill. They concluded that power<br>consumption reduces dramatically, from 70–90%, based on the conditions under which<br>
the material is torrefied. They have also found that the capacity of the mill increases by<br>a factor 7.5–15. The most important phenomenon they observed was that the size<br>reduction characteristics of torrefied biomass resulted in a similar product as coal.<br>
<br><b>Particle size distribution, sphericity, and particle surface area</b><br><br>Particle size distribution curves, sphericity, and surface area are important parameters<br>for understanding flowability and combustion behavior during cofiring. Many researchers<br>
observed that ground, torrefied biomass produced narrower, more uniform particle sizes<br>compared to untreated biomass due to its brittle nature, which is similar to coal.<br>Phanphanich and Mani (2011) study on torrefied pine chips and logging residues found<br>
that smaller particle sizes are produced compared to untreated biomass. They have<br>also observed that the particle distribution curve was skewed towards smaller particle<br>sizes with increased torrefaction temperatures.<br>
Torrefaction also significantly influences the sphericity and particle surface area.<br>Phanphanich and Mani (2011) results also indicated that sphericity and particle surface<br>area increases as the torrefaction temperature was increased to 300°C. For ground,<br>
torrefied chips, they found that the sphericity increased from 0.48–0.62%, concluding<br>that an increase in particle surface area or decrease in particle size of torrefied biomass<br>can be desirable properties for efficient cofiring and combustion applications. Also, the<br>
bulk and particle densities of ground torrefied biomass increases as it reduces the inter<br>and intra particle voids generated after milling (Esteban and Carrasco, 2006). Studies<br>have indicated that ground torrefied material results in a powder with a favorable size<br>
distribution and sphericity, allowing it to meet the smooth fluidization regime required for<br>feeding it to entrained-flow processes (gasifier and pulverized coal).<br><br><b>Pelletability<br><br></b>Torrefying the biomass before pelletization produces uniform feedstock with consistent<br>
quality. Densification following torrefaction is considered by several researchers<br>(Lipinsky et al., 2002; Reed and Bryant, 1978 and Bergman et al., 2005). These studies<br>indicated that the pressure required for densification can be reduced by a factor of two<br>
when material is densified at a temperature of 225°C and the energy consumption<br>during densification is reduced by a factor of two compared to raw biomass pelletization<br>using a pellet mill. Densification experiments were carried out on untreated and torrefied<br>
biomass using a piston press (Pronto-Press), which can be operated at different<br>pressures and temperatures, to understand the densification behavior of different types<br>of torrefied biomass. The pellets produced based on the TOP process had higher bulk<br>
densities, in the range of 750–850 kg/m3, with relatively high-calorific value (LHV basis),<br>generally 19–22 MJ/kg. The energy density of TOP pellets ranged from 15–18.5 GJ/m3<br>and is comparable to subbituminous coal, which typically has a value of 21–22 GJ/m3.<br>
The pellets produced had a higher mechanical strength, typically 1.5–2 times greater,<br>than the conventional pellets. The higher mechanical strength of these pellets is due to<br>densification of the biomass at high temperature, which causes the biomass polymers to<br>
be in a weakened state (less fibrous, more plastic). Higher durable pellets from torrefied<br>biomass can be due to chemical modifications, occurring during torrefaction, that lead to<br>more fatty structures that act as binding agent. In addition, the lignin content increases<br>
by 10–15%, as the devolatilization process predominantly concerns hemicellulose<br>(Bergman, 2005). <br></i><br><i><b>Chemical composition of the torrefied biomass<br><br></b>Besides improving physical attributes, torrefaction also results in significant changes in<br>
proximate and ultimate composition of biomass and makes it more suitable for fuel<br>applications. Sadaka and Negi’s (2009) study on torrefaction of wheat straw, rice straw,<br>and cotton gin waste at 200, 260, and 315°C for 60, 120, and 180 minutes concluded<br>
that moisture content was reduced at the extreme conditions (315°C for 180) for all<br>three feedstock’s by 70.5, 49.4, and 48.6%, and the heating value increased by 15.3,<br>16.9, and 6.3%, respectively. Zanzi et al. (2002), in their study on miscanthus<br>
torrefaction made similar observations, where increasing temperature from 230–280°C<br>and time from 1–3 hours increased the carbon content and decreased the hydrogen,<br>nitrogen, and oxygen content. At 280°C, the carbon content increased to about 52%<br>
from an initial value of 43.5% while hydrogen and nitrogen content decreased from<br>6.49–5.54% and 0.90–0.65% for 2 hours of torrefaction. In general, increased<br>torrefaction temperatures result in increased carbon content and decreased hydrogen<br>
and oxygen content due to the formation of water, CO, and CO2. This process also<br>causes the hydrogen-to-carbon (H/C) and oxygen-to-carbon (O/C) ratios to decrease<br>with increasing torrefaction temperature and time, which results in less smoke and<br>
water-vapor formation and reduced energy loss during combustion and gasification<br>processes. In torrefaction studies of reed canary grass and wheat straw torrefaction at<br>230, 250, 270, and 290°C for 30-minute residence times, Bridgeman et al. (2008) found<br>
that the moisture content decreases from an initial value of 4.7%–0.8%. They found that<br>carbon increased 48.6–54.3%, and hydrogen and nitrogen content decreased from 6.8–<br>6.1% and 0.3–0.1%, respectively. Bridgeman et al. (2010) in their studies on torrefaction<br>
of willow and miscanthus indicated that at higher temperatures and residence times, the<br>atomic O: C and H: C ratios are closer to that of lignite coal. Table 6 shows the effect of<br>different torrefaction temperatures on ultimate compositional changes in woody and<br>
herbaceous biomass. Table 2 and 3 indicates the elemental composition of the torrefied<br>biomass at different temperatures and times.<br><br><b>Off-gassing<br><br></b>Storage issues like off-gassing and self-heating may also be insignificant in torrefied<br>
biomass as most of the solid, liquid, and gaseous products that are chemically and<br>microbiologically active are removed during the torrefaction process. Kuang et al. (2009)<br>and Tumuluru et al (2010) studies on wood pellets concluded that high storage<br>
temperatures of 50°C can result in high CO and CO2 emissions, and the concentrations<br>of these off-gases can reach up to 6% for a 60-day storage period. These emissions<br>were also found to be sensitive to relative humidity and product moisture content. The<br>
same researchers at University of British Columbia conducted studies on off-gassing<br>from torrefied wood chips and indicated that CO and CO2 emissions were very low;<br>nearly one third’s of the emissions from regular wood chips at room temperature (20°C).<br>
The reason could be due to low moisture content and reduced volatile content which<br>could result in less reactivity with the storage environment.<br><br>Biomass is porous, often moist, and prone to off-gassing and self heating due to<br>
chemical oxidation and microbiological activity. In general, the biomass moisture<br>content plays an important role in initiating chemical and microbial reactions. Moisture<br>content coupled with high storage temperatures can cause severe off-gassing and selfheating<br>
from biomass-based fuels. Another important storage issue of ground torrefied<br>biomass is its reactivity in powder form, which can result in fire during storage. It is<br>preferred to store the torrefied biomass in an inert environment to avoid accidents due<br>
spontaneous combustion. Kiel (2007) in his laboratory-scale combustion studies of<br>torrefied wood found that it is highly reactive, similar to coal.<br><br><b>Hydrophobicity<br><br></b>An advantage of torrefied pellets over regular raw pellets is that they are hydrophobic<br>
(moisture uptake is almost negligible) even under severe storage conditions. In general,<br>the uptake of water by raw biomass is due to the presence of OH groups. Torrefaction<br>produces a hydrophobic product by destroying OH groups and causing the biomass to<br>
lose the capacity to form hydrogen bonds (Pastorova et al., 1993). Due to these<br>chemical rearrangement reactions, non-polar unsaturated structures are formed, which<br>preserve the biomass for a long time without biological degradation, similar to coal<br>
(Bergman and Kiel, 2005; Wooten et al., 2000).<br><br>Bergman (2005) determined the hydrophobicity of torrefied pellets by immersing them in<br>water for 15 hours. The hydrophobic nature was evaluated based on the state of the<br>
pellet after this period and by gravimetric measurement to determine the degree of<br>water uptake. Bergman (2005) study indicated that raw pellets swelled rapidly and<br>disintegrated into original particles. Torrefied pellets produced under optimal conditions,<br>
however, did not disintegrate and showed little water uptake (7–20% on mass basis).<br>He also concluded that torrefaction conditions play a vital role in the hydrophobic nature<br>of biomass. Sokhansanj et al. (2010) compared the moisture uptake of the torrefied<br>
biomass to the untreated biomass and found that there is about a 25% decrease in the<br>water uptake when compared to the control (Figure 6).<br><br>It is clear that the product characteristics of torrefied material like handling,<br>
milling, and transport requirements are similar to coal. In cofiring operations torrefied<br>pellets allow for higher co-firing percentages up to 40% due to matching fuel properties<br>with coal, and they can use the existing equipment setup for coal.</i><br>
<br>Crispin, in gasifying rice hulls, we speak of a specific rate of gasification which is measured in terms of kg's/m2/hour.<br>To have high gasifications temperatures (roughly from 800 to 1,000 C), the rate of gasification has to be above 100 kg's.<br>
If the rate is too low, only a small amount of gas is produced, and this gas is of a very poor quality.<br><br>But what would happen if the rate were turned down to only 20 kg/m2/hour?<br>Would this lower the temperature to less than 250 C?<br>
Would the "biochar" from this low-temperature pyrolysis look like torrefied biomass?<br>Of course the gas coming off this process would have to be cooled down and processed.<br><br>I could easily imagine a TLUD reactor of a diameter of 0.5 meters and a height of a meter or two.<br>
This reactor would be stuffed with rice straw and pyrolyzed at a very low specific rate.<br>The gas would be cooled to condense out the water, <br>and it would be further processed to recover acetic acid and other compounds.<br>
Would this not give a torrefied straw that could then be pelleted?<br><br>Thanks.<br>Paul<br><br>Thanks.<br>Paul<br><br><div class="gmail_quote">On Sat, Feb 25, 2012 at 9:04 PM, Crispin Pemberton-Pigott <span dir="ltr"><<a href="mailto:crispinpigott@gmail.com" target="_blank">crispinpigott@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div link="blue" vlink="purple" lang="EN-CA"><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Dear Paul<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Thanks for the concise (distillation?) of facts about torrefaction. Just one question:<u></u><u></u></span></p>
<div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal">Torrefaction greatly reduces the amount of power needed for pelletizing.<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p></div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Can you give us a reference on that, or if not, can you suggest a general rule about the reduction in energy requirement? That would be a valuable number to remember.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">The point about processing of fuels is very reasonable. In the South Africa they make paraffin out of coal. Zero sulphur…<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Regards<span><font color="#888888"><br>
Crispin<u></u><u></u></font></span></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p></div></div><br>_______________________________________________<br>
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