<div dir="ltr"><div><div><div>Crispin,<br><br></div><div>Let me revise slightly my last email.<br></div><div><br>If a stove is designed only to produce heat, then it makes sense to
measure efficiency in terms of the production of heat. But if a stove
is designed to produce syngas and biochar, we cannot measure efficiency
only in terms of the production of heat. <br>
<br>In my TLUD stove, both syngas and biochar are produced. The quantity
of each in a given batch cycle depends in part on the speed of the fan.
If the fan speed is high, resulting in a relatively high temperature of
gasification, more syngas and less biochar is produced. If the fan
speed is low, resulting in a relatively low temperature of gasification,
less syngas and more biochar is produced. This ratio of syngas to
biochar is constantly changing throughout the entire batch cycle. Of course, the
operator, trying to cook a meal, is not concerned about the ratio of
syngas to biochar, but only about the right temperature required for cooking.<br>
<br></div><div>In a stove that produces syngas and biochar, we should examine the efficiency at which CO and H2 are produced. In the first minute of a burn, I can look through the burner holes and see open flames within the reactor. When open flames within the reactor are present, CO2 is being produced, and consequently, there are burner holes that do not support a flame. Also if channeling occurs during the process, CO2 is being produced, and again, there are burner holes that do not support a flame. If I try to gasify biomass that is not uniform in grain size, some sections of the gasification front get too much oxygen and other sections do not get enough. Too much oxygen leads to total combustion and the formation of CO2 in the syngas. Once again, there are burner holes that do not support a flame. <br>
<br>This leads me to conclude that the presence of CO2 in the syngas is a strong indicator of an inefficiency in the production of CO and H2.<br><br>In a stove that produces syngas and biochar, only syngas
gets combusted. So if we want to measure efficiency, we might look at
how efficiently air is applied to the syngas in cleanly combusting this syngas. A premix burner should be more efficient than a diffusion burner in combusting syngas.<br><br>With regard to my 150 gasifier, I chose not to go in the direction of a premix burner, because this entails putting syngas under pressure. If syngas is under pressure, gaskets are needed to prevent leakage. If gaskets should fail, then the safety of the stove is compromised. So I had to make a choice between safety and efficiency. So my burner is not a premix burner. Yet the burner housing supplies secondary air at the base of the burner holes in such a manner that the burner does not resemble a typical diffusion burner.<br>
<br></div><div>In the larger gasifiers (diameters 250 mm and 500 mm), we are in a commercial setting, and here I believe that the burner has to be a premix burner. But instead of putting gas under pressure, I have opted to inject secondary air into the burner. A small pipe diverts a portion of primary air into the burner, and the flow of this air is controlled by mean of a valve.<br>
</div><div><br>When syngas exits my TLUD, it contains a lot of heat
(>500 C). To cool down the syngas prior to combusting it would
involve a huge loss of heat. One might argue that syngas burns more
cleanly and more efficiently at higher temperatures. That is why I am
in favor of putting the burner right on the top of the reactor. If more
burners are needed in a kitchen setting, more reactors, each with its
own burner, are put in operation.<br>
<br></div><div>Here in Vietnam it is quite common the see pyrolyzers
with one or more remote burners. The syngas from these units is cooled
down and routed through PVC pipes to remote burners. Most of the heat
contained in the gas is lost, and the process temperature is so low that
a lot of oils are formed and condense out in this cooling process.
Generally these oils are wasted. Both the cooling down of the gas and the
production of oils represent a considerable inefficiency.<br>
</div><div><br></div>So how does one measure the efficiency of a stove? <br><br>If the stove is designed only to produce heat, then we have the look at the efficiency at which heat gets applied to the pot or pan above. But if a stove is designed to produce syngas and biochar, we have to look at the efficiency at which syngas and biochar are produced as well as the efficiency at which syngas is combusted and directed to the pot or pan above. A high efficiency in the production of syngas is generally accompanied by the production of a biochar that is uniform. A uniform biochar does not contain biomass that has been reduced to ash or biomass that has merely been torrefied. A uniform biochar sells at a relatively high price and is generally worth more than the biomass from which it was derived. Here we have a stove that efficiently makes money each time it is used. <br>
<br></div>Thanks.<br></div>Paul Olivier<br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Apr 26, 2013 at 1:43 PM, Paul Olivier <span dir="ltr"><<a href="mailto:paul.olivier@esrla.com" target="_blank">paul.olivier@esrla.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Crispin,<br><br></div><div>If a stove is designed only to produce heat, then it makes sense to measure efficiency in terms of the production of heat. But if a stove is designed to produce syngas and biochar, we cannot measure efficiency only in terms of the production of heat. <br>
<br>In my TLUD stove, both syngas and biochar are produced. The quantity of each in a given batch cycle depends in part on the speed of the fan. If the fan speed is high, resulting in a relatively high temperature of gasification, more syngas and less biochar is produced. If the fan speed is low, resulting in a relatively low temperature of gasification, less syngas and more biochar is produced. This ratio of syngas to biochar is constantly changing throughout the entire batch cycle. The operator trying to cook a meal is not concerned about the ratio of syngas to biochar, but only about the right temperature required to cook a particular dish.<br>
<br></div><div>In a stove that produces syngas and biochar, only syngas gets combusted. So if we want to measure efficiency, we might look at how efficiently air is applied to the syngas in achieving total combustion. What does not get combusted (biochar) should be left out of the equation.<br>
<br></div><div>When syngas exits my TLUD, it contains a lot of heat (>500 C). To cool down the syngas prior to combusting it would involve a huge loss of heat. One might also argue that syngas burns more cleanly and more efficiently at higher temperatures. That is why I am in favor of putting the burner right on the top of the reactor. If more burners are needed in a kitchen setting, more reactors, each with its own burner, are put in operation.<br>
<br></div><div>Here in Vietnam it is quite common the see pyrolyzers with one or more remote burners. The syngas from these units is cooled down and routed through PVC pipes to remote burners. Most of the heat contained in the gas is lost, and the process temperature is so low that a lot of oils are formed and condense out in this cooling process. Generally these oils are used for nothing and have none of the value of either syngas or biochar. Both the cooling down of the gas and the production of oils represent a considerable inefficiency.<br>
</div><div><br></div><div>So how does one measure the efficiency of a stove? This is not an easy question to answer.<br><br></div><div>Paul Olivier<br>
</div></div><div class="gmail_extra"><br><br><div class="gmail_quote"><div><div class="h5">On Thu, Apr 25, 2013 at 10:06 PM, Crispin Pemberton-Pigott <span dir="ltr"><<a href="mailto:crispinpigott@gmail.com" target="_blank">crispinpigott@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5"><div bgcolor="white" link="#0563C1" vlink="#954F72" lang="EN-CA"><div><p class="MsoNormal">
<span style="color:#1f497d">Dear Paul<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="color:#1f497d">Here is the problem restated slightly better without prejudice re other biomass:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="color:#1f497d">If someone is interested in the char, it can be reported – it is in the raw data set. What Ron is proposing, to reduce the energy in the fuel consumed by the heat energy available in the remaining char, is akin to considering the fuel efficiency to be the energy efficiency which is precisely what created for us a problem in the first place. </span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="color:#1f497d">The energy value of the char came from somewhere. Consider a stove that needs 2 tons of biomass per year to operate. If it produces ¼ of a ton of biomass energy equivalent in the form of char, fine. Say so. But saying so does not reduce the two tons of biomass it takes to feed the system. If you have (as you pointed out) a second stove that can utilise the charcoal, then that can be viewed as a ‘system’ by all and sundry, but is still does not change the fact that Stove 1 takes two tons of biomass each year which is what the reported fuel consumption should be. The impact of a system is not the same as the impact of a component of that system. The only debate left is how to report the fuel consumption and by-products.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="color:#1f497d">What has been happening that is wrong, in my view, is that stoves that actually take off 3 tons of biomass per year have been getting credit for taking only one ton and proclaimed to be ‘better’ and ‘more fuel efficient’ than a two-ton stove. Plainly this is not the case and the test method has to report the fuel consumption correctly. It is a problem that the UNFCCC methodology (which measures energy efficiency) does not handle this well and it is being used for CDM trades. People are being cheated.</span><u></u><u></u></p>
<p class="MsoNormal"><span style="color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="color:#1f497d">Regards</span><span><font color="#888888"><u></u><u></u></font></span></p><span><font color="#888888"><p class="MsoNormal">
<span style="color:#1f497d">Crispin</span><u></u><u></u></p><p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif""><u></u> <u></u></span></p></font></span></div></div>
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<br></div></blockquote></div><span class="HOEnZb"><font color="#888888"><br><br clear="all"><br>-- <br>Paul A. Olivier PhD<br>26/5 Phu Dong Thien Vuong<br>Dalat<br>Vietnam<br>
<br>Louisiana telephone: 1-337-447-4124 (rings Vietnam)<br>Mobile: 090-694-1573 (in Vietnam)<br>Skype address: Xpolivier<br><a href="http://www.esrla.com/" target="_blank">http://www.esrla.com/</a>
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</blockquote></div><br><br clear="all"><br>-- <br>Paul A. Olivier PhD<br>26/5 Phu Dong Thien Vuong<br>Dalat<br>Vietnam<br>
<br>Louisiana telephone: 1-337-447-4124 (rings Vietnam)<br>Mobile: 090-694-1573 (in Vietnam)<br>Skype address: Xpolivier<br><a href="http://www.esrla.com/" target="_blank">http://www.esrla.com/</a>
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