[Stoves] Trials on TLUD Gas Burners - Burner Diameter

[Paul Anderson]

Crispin, Julien, Joe,

A few weeks ago a message (below) from Crispin contained this message:
>
> @Paul S Anderson, what do you think of us putting together a chart 
> with a diameter/flow plot for different levels of draft?
>
Although such a chart might be interesting, it is a bit beyond my 
comfort level, and the work would fall to people with such abilities, 
such as Crispin, Julien, and Joe.    I am not able to "appreciate" it 
enough, and I am not sure how it would be used in improving 
cookstoves.   But I and many others are all open to further discussion.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com

On 7/23/2014 6:07 PM, Crispin Pemberton-Pigott wrote:
>
> Dear Julien
>
> This is a good and helpful report with a lot of practical experience 
> built in.
>
> On slide 7 it says "However, heating air decreases its density, so air 
> velocity must increase to maintain the quantity of oxygen mixing with 
> pyrogas."
>
> It is probably worth mentioning, because it is against common sense, 
> that increasing the temperature reduces the density but increases the 
> viscosity. Getting the right size hole is not quite as simple as a 
> pro-rata change in area. That plus of course the shape of the entry 
> hole changes the flow (a lot).
>
> @Paul S Anderson, what do you think of us putting together a chart 
> with a diameter/flow plot for different levels of draft?
>
> Question: In slide 18, it gives the burn rate per unit time per unit 
> volume. I can't grasp that easily. Is the density somehow detectable 
> in there? What is the mass loss rate in g/minute? While I realise that 
> meaningful interpretation requires knowing the volume of fuel 
> involved, I was trying to calculate the water mass out of the burn 
> rate to see what the 'real burn rate' was. It is difficult to do that 
> as the mass per unit time is not the metric.
>
> Is there some other way you can report the burn rate for different 
> fuel moisture levels?
>
> It would be helpful, if you stick to the mg/minute/cm^2 and first 
> factor the mass loss raw data for the moisture content so it is mg_DRY 
> . In that way we can calculate the fuel burn rate and then, using the 
> moisture level, calculate the true realisable energy (potential) value.
>
> Performing this calculation sometimes gives surprises. From the look 
> of the curves, the energy available drops as well as the burn rate. 
> This is intuitive but not always the case. One thing to take a lesson 
> from is the investigation which shows that 15% moisture fuel usually 
> has lower PM emissions in most devices than 10% or 5%, but increasing 
> it above 15% more sees the level rise.  For each stove type there is 
> an optimum.
>
> For the TLUD's with a different burner design, there is probably a 
> different optimal moisture level.
>
> Thanks for sharing the presentation.
>
> Regards
>
> Crispin
>
> Hi Stoves;
>
> In May, I reported to this listserv on some tests I had done with a 
> menagerie of gas burners.
>
> http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/2014-May/008665.html
>
> My tinkering has continued, and some results are attached as a pdf 
> that show some interesting features of ND-TLUDs.  For example, the 
> best I could do for a turndown was about 2x, and turndown is very 
> sensitive to primary air supply.
>
> These tests follow from the earlier work were is was shown that 
> placing a concentrator disk below the secondary air inlets did not 
> result in a flame concentrated above the aperture in the disk.  
> Instead, pyrogas moved radially outward to the underside of the 
> secondary air holes, and became entrained in the jets of secondary air.
>
> In addition, I was using gas burners that were 1.2 x larger than the 
> diameter of the TLUD combustion chamber so as to get more space to 
> manipulate secondary air, and more space for the gas flame to 
> develop.  This work suggested that is was possible to increase the 
> diameter of the gas burner even further.  The current trials put this 
> to the test.  Here is an abstract of the study:
>
> ABASTACT
>
> Gas burners for a natural draft, top-lit updraft gasifier (ND-TLUD) 
> were assessed for visible flame characteristics and their effect on 
> gasification rate.  Two main design options were tested: diameter of 
> the burner and preheating secondary air. Burners were tested on wood 
> chip fuel that varied in moisture content, and primary air was 
> adjusted to get very low to maximal rates of gasification.  Preheating 
> secondary air had no visible effect on the gas flame nor did it alter 
> gasification rate.  Increasing the size of the gas burner from 1x to 
> 1.2x the diameter of the TLUD significantly improved gasification 
> rate, reduced flame height, and reduced visible smoke production.  
> Further increasing burner diameter to 1.5x TLUD diameter didn't cause 
> a further increase gasification rate, and made the reaction unstable 
> at low rates of primary air and high fuel moisture contents.  
> Increasing the diameter of burners to at least 1.2x looked very 
> promising for improving TLUD operation.  Burners of 1.5x may be 
> suitable for TLUDs that only run at high gasification rates. Larger 
> diameter burners will likely cause less air pollution, and should be 
> tested for CO and particulate emissions.
>
> Increasing the size of gas burners could be tested with some of Jock 
> Gill's ideas for increasing flame temperature in the burner.
>
> http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/2014-May/008843.html 
>
>
> All the best,
>
> Julien.
>
>
>
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