[Stoves] Model R TLUD test #1 results

Crispin Pemberton-Pigott crispinpigott at outlook.com
Tue Sep 12 12:08:35 CDT 2017


Dear Jock

You can make the disk in the centre much larger. Fears about interfering with the draft in the chamber are not to be over-stated. The draft is driven by temperature, and it takes a lot of constriction to overcome the draft.

There is a general rule for velocities in pipes which is that significant flow restrictions do not start to appear at a velocity less than 3 metre per second. This of course applies when there are large chimneys available You have in effect a very short chimney so the force is low.

There is on the Stoves list a Draft Calculator<http://www.newdawnengineering.com/website/library/Stove%20Testing/Draft%20Calculator/Chimney%20Draft%20Calculator.xlsx> that will calculate for you the draft of each section of the stove, if you enter the upper and lower temperatures, and the vertical distances. It works for both up and downdrafting, in case you stove is complex. There are a couple of versions hanging around, one doing 5 sections and the other 8.

If you make measurements with different constructions, you can watch the draft evolve. Constricting the outflow may increase the temperature and not change the draft at all. Hard to say - so calculate.

If you have a series of thermocouples and a logger, say, eight, you can create a chart of the temperature profiles and therefore a draft profile as the fuel burns.

Regards
Crispin



All,

The R in model R stands for retort.

I slightly modified the system I wrote about the other day by adding a 3 inch disk. This hangs down from the center of the top of the stove pipe cap (see photos).  It hangs down just below the bottom of the cap.  This means it is suspended a little into the the reactor can, below the injection point of the secondary air.  This accomplishes a number of things:

1. It divides the system into two distinct parts
               Pyrolysis chamber
               Combustion chamber

2. It forces the pyrolysis gases to the edges where it meets the incoming secondary air.

3. It increases the concentration of the gases - they are less diffused when they mix with the secondary.  Thus it is also a concentration device/technique.

4. it significantly reduces the penetration of the secondary air into the pyrolysis chamber.  This minimizes the cooling of the pyrolysis process by stray secondary air.  Further, this makes the pyrolysis chamber much more retort like. Hence the name Model R.  That is, the pyrolysis chamber is approaching the state of being a fully closed retort.

5. Run time went from 36:30 to 46:30 which smoothed out the rate of gas production.  Made it less wickedly non linear.

6. Made good Biochar with fewer than 30 bits of pellets that were not fully charred.  Best results in this system yet.

7. Tamed the flames.  Long periods with the flame with a great deal of blue in them.  Significant amount of time with the flames totally in the combustion chamber, not emerging through the vent holes.  (Video to follow)

8. Temperatures were in the 700 - 800 F range, a bit lower than the run away burn I had before installing the 3 inch disk.  But cleaner.  Less smoke.  Gases less acrid.

The 3 inch disk covers only 25% of the area of the aperture in the reactor can.  This suggests it would be interesting to try a slightly larger disk.  The question is whether or not this would reduce the draft by too much?  The three inch disk may be a happy medium that creates a well balance system as a whole.

I hope that others will explore the R TLUD concept as it appears to be a fruitful opportunity.

Comments?  Suggestions?

Regards.

Jock

[image1.JPG]


Note:  This washer had been previously used in other experiments.  The tan deposit on the bolt head was from this test run.




[image2.JPG]


Note the total absence of soot on the lower portion of the bolt suspending the washer.  This would be the portion of the bolt lowest in the combustion chamber.


[image3.JPG]


I suspended the washer such that it hung just below the bottom of the stove pipe cap.  This means it was about 2 cm inside the reactor an, BELOW the point of secondary air injection.  This may be the sweet spot that gives the largest combustion chamber and yet forces the gases into the incoming secondary air.  I will have to try a run with the washer a bit higher up.  Note that the nut on top of the washer, i.e. In the combustion chamber is soot free - still nice and shiny.




[image4.JPG]



You can just barely make out the blue flames.  They are very hard to. Photograph in daylight.  The blue sensors on camera chips, only 25% of the total array,  are notorious for being weak in this area.


[image5.JPG]



I used the taller draft can to offset the loss of draft caused by the 3 inch washer.


Jock Gill
P. O. Box 3
Peacham, VT 05862

Cell: (617) 449-8111

Extract CO2 from the atmosphere!

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