[Stoves] FW: REQUEST for complete sets of raw data of cookstove tests.

Fri Apr 26 19:02:51 CDT 2013

Crispin,

Let me revise slightly my last email.

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.

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.

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.

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.

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.

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.

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.

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.

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.

So how does one measure the efficiency of a stove?

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.

Thanks.
Paul Olivier

On Fri, Apr 26, 2013 at 1:43 PM, Paul Olivier <paul.olivier at esrla.com>wrote:

> Crispin,
>
> 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.
>
> 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.
>
> 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.
>
> 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.
>
> 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.
>
> So how does one measure the efficiency of a stove? This is not an easy
> question to answer.
>
> Paul Olivier
>
>
> On Thu, Apr 25, 2013 at 10:06 PM, Crispin Pemberton-Pigott <
> crispinpigott at gmail.com> wrote:
>
>> Dear Paul****
>>
>> ** **
>>
>> Here is the problem restated slightly better without prejudice re other
>> biomass:****
>>
>> ** **
>>
>> 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. ****
>>
>> ** **
>>
>> 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.****
>>
>> ** **
>>
>> 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.****
>>
>> ** **
>>
>> Regards****
>>
>> Crispin****
>>
>> ** **
>>
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>>
>>
>
>
> --
> Paul A. Olivier PhD
> 26/5 Phu Dong Thien Vuong
> Dalat
> Vietnam
>
> Louisiana telephone: 1-337-447-4124 (rings Vietnam)
> Mobile: 090-694-1573 (in Vietnam)
> Skype address: Xpolivier
> http://www.esrla.com/
>

-- 
Paul A. Olivier PhD
26/5 Phu Dong Thien Vuong
Dalat
Vietnam

Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/
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