[Stoves] Question about the turn down ratio

[Richard Stanley]

Stovers, esp. those in/familiar with  the US part of the Americas and  
more specifically  the Oregon part of all that.

We have remained pretty much silent participants as our interest is  
pretty much focused on just "low tech"  biomass briquetting. --until  
now...

Increasingly arising, are requests for the tech and training here in  
the USA  --for application in the USA to the household cooking and  
heating stove.

As cylinders ranging between 8 to 15 cm in diameter by  X 7 to 10 cm  
height, the briquettes we promote  are mot really adaptable to pellet  
stoves. Although they will do nicely in a open hearth or barbecue, we  
are at a bit of a loss to find a really modern affordable wood stove  
that would fit the bill.
We have been fortunate to have worked with Jon Davies, Kobus Venter,  
Paul Anderson, Sanu Kaji, Lanny Hansen  and others on this list on  
briquette  use in stoves, designed for the third world (or the third   
world parts of the first world) but not on a functional and   
affordable stove for our own nation.

HAving heated our house and cooked largely off a small wood stove  
this past 4 months ( we're doing a near total --far more than  
anticipated at least-- house remodel) I can tell you that finding a  
good looking stove oven burner wood and kindling storage which looks  
like something halfway modern, is functional and affordable --- for  
use with biomass briquettes of the above sizes, is almost non existent.

For the functional oven cooker heater stove, I see lots of 20's retro  
and lots of scandanavian designs for 8+ grand USD, but nothing  
simple, well design and practical for wood or biomass.
Heating stoves yes: Stoves which heat and incorporate an oven and  
stovetop cooking and wood kindling and wood or briquette fuel  
storage,  no...

So we designed one... Its really not rocket science (no pun  
intended,  Approvecho). Doors open out like and oven door, for ---the  
oven---, and also for the combustion chamber to keep ashes headed  
inward, (a side tray handles the ashes away from the food and oven),  
and flat top for cooking / grilling surfaces.  Add on a CO meter/ 
alarm, a timer, and temperature gages for the combustion chamber, the  
oven and the cooktop  mounted well above and behind the cooking  
surface, add glass doors for oven and combustion chamber and a  
perforated 12 ga steel  door for the kindling fuel supply at the base  
---with primary and secondary feed and appropriate insulation at  
optimal locations.

Aside from the glass, the instrumentation, this, thus far is all  
within the realm of a local blacksmith shop, frankly.

But then the bureaucracy of  well intended  regulation hit us in the  
face: The figure I have is 84,000 USD for the magic certification by  
the EPA.

Yikes: Why and how could simple testing procedure for safety,  
efficiency , CO /CO2 and particulates emissions cost so much?

As with our long standing mechanisee press development, I am  
perfectly happy to share the design with anyone who wants to develop  
it and share the returns after costs are all in... but first what am  
I missing on this immense stumblng block of EPA testing..?

  Surely for example, the energy and accredited knowledge base  
accumilated here can provide or at the minimum recomend such a  
testing process/ resource which would satisfy the good EPA at a  
reasonable price and time frame...?

thoughts / advise ?

Richard Stanley,
Legacy Foundation
www.legacyfound.org
State of Jefferson



On Feb 18, 2008, at 8:09 PM, Paul S. Anderson wrote:

> Dear Stovers,
>
> Some very illuminating comments have been made.
>
> Dean wrote:  (much snipped)
>> The pot lid helps very, very much when simmering especially if the  
>> cook does
>> reduce power to keep the water just below rapid boiling which  
>> cooks food as
>> quickly (96C-93C).
>
> Yes, and we should be advocating this whenever possible.  And that  
> means using
> lids in the test measurements that are being consulted to judge  
> which stoves
> are best and get the funding.
>
>> So, in the Water Boiling Test we need to use a pot that is as  
>> representative
>> as possible of pots used in the world.
>
> That is good for being able to compare the lab tests, but quite bad
> considering
> that the test results are used to help make decisions as if all the  
> target
> populations use the same size pots.
>
>> Rob Bailis and Aprovecho did a
>> survey, asking NGOs what they recommended. The range is enormous.  
>> In Central
>> America folks use huge pots. In India folks use tiny pots. Etc.
>>
>> A 7 liter straight sided pot holding 5 liters of water was thought  
>> to be a
>> middle ground.
>      (snipped)
>> Now, the Water Boiling Test also used a standard pot holding 2.5  
>> liters of
>> water which is used in the stove cannot bring to boil the larger  
>> amount of
>> water.
>
> But the quantitative test results from 2.5 liter and 5.0 liter  
> tests are not
> comparible, and very limited data or test runs are available for  
> either size.
>
>> The big problem with using a lid on the 7 liter straight sided pot  
>> is that
>> it affects the turn down ratio.
>   (snip)
>> If a lid is used to simmer at just below the rolling boil state  
>> (between
>> 96C-93C) it is probably not possible to keep the fire lit using  
>> normal sized
>> wood.
>
> THAT statement should say something about the stove in use.   
> Instead, the
> ability to keep the fire going has been turned into an issue of  
> fuel size and
> having a lid on the pot.
>
>  From what I have seen in many countries, there is no "normal sized  
> wood" until
> the actual cookstove is also specified.  Lots of twig-sized wood is  
> used in
> many areas of India.
>
>> If I remember correctly, less than 1/6th the energy of high power is
>> required for simmering with a lid even on a 7 liter pot. So for me  
>> to do a
>> Water Boiling Test with a lid, I normally need to split up the  
>> wood into
>> smaller diameters.
>
> That all depends on what size fuel you start with and the
> characteristics of the
> stove.
>>
>> When a lid is not used, then the Turn Down ratio is around 3-4 and  
>> the
>> larger fire used can be kept going without splitting wood.
>
> In my nearly seven years of serious stove work, I had never heard that
> justification before.  Essentially:  The official water boiling test
> has no lid
> on the pot so that the stove in use (Rocket stove) could keep the  
> simmer going
> but not overly boiling too vigorously while maintaining a preferred  
> size of
> stick wood as fuel.
>
>> Again, it is
>> possible to conduct a Water boiling Test either way. The question  
>> was: which
>> is more indicative of normal use? Thinking that people would not  
>> split wood
>> up very fine and faced with a lot of experimenters being bemused  
>> that their
>> simmering fires went out, we went with an uncovered pot for  
>> simmering. It is
>> another judgment call...
>>
> And I think that it was not the correct judgment call.  It was correct
> for users
> of Rocket stoves, and has reinforced their beliefs in the  
> superiority of the
> Rocket stoves.  But in my opinion it was not correct considering  
> the vast
> variety of other stoves then and now available.
>
> Is it realistic to say that in the standard WBT with a lid on the  
> pot, the
> Rocket stoves would have heavy boiling during the 45 minutes of  
> simmering, and
> therefore yielding significantly different results?  Of course the  
> users could
> opt to use smaller diameter stick-wood fuel which may __or may  
> not___ allow
> that stove to still produce the published results on quantity of  
> fuel used and
> the emissions during the simmer stage.   (data related to the bring- 
> to-boil
> stage does not change unless the physical stove is altered to  
> accomodate the
> simmer stage.)
>
> In another recent message, Dean wrote:
>> However, a stove that is fast to boil was the number one concern of
>> cooks in an extensive survey of Indian cooks.
>
> I agree with that statement.  But for the most part, Indians cook in
> small pots
> without much excess water.  In the Hyderabad area where I have worked
> recently,
> a family of 3 or 4 would make rice, dal (lentals) and chapati  
> (tortilla-like)
> for one main meal.  One burner was generally sufficient to use in a  
> succession
> of pots.  2 cups of water with one cup of rice (or 3 cups with 1.5  
> cups of
> rice) was brought to a boil quickly.  How long does it take to boil 2
> or 3 CUPS
> of water with rice in it?  6 to 9 minutes or average of 7 or 8  
> minutes,
> and let
> it boil for another 4 or 5 minutes.  Then the rice (always with the  
> lid
> on) was
> placed to the side to finish cooking with the heat within the small  
> pot (and
> often without even a cloth cover for retained heat cooking).  That  
> is a bit
> different from the WBT with 5 liters.
>
> Then the same high fire is used to boil the pre-soaked lentales, which
> also was
> with only 2 or 3 cups of water.  Disregarding that many families  
> have pressure
> cookers, allow another 10 to 15 minutes with high fire.
>
> Total time so far is 20 to 30 minutes.  But if the cook fires up two
> burners (as
> in LPG or a TLUD gasifier or a two-hole stick-wood stove), the clock
> time is cut
> in half.
>
> The chapatis are cooked one at a time on a tawa', essentially a  
> slighly
> concave
> circular griddle or mini-"plancha".  Mostly at high fire.  Less  
> than a minute
> each, all are finished in another 10 to 15 minutes.
>
> No meaningful simmer where I was working in India. And no cooking  
> without lids
> except to stir in spices and then replace the lid.
>
> So, I am increasingly LESS impressed by the results of the WBT.  It  
> is nice to
> know that the TLUD emmissions are so low.
> (Thank you Dale Andreatta for the one  set of data from under the
> emissions hood
> using the TLUD as it should be used. --- Yes, much better than my  
> own two test
> runs in 2005 when I was still learning how to use the TLUDs, and still
> won by a
> significant margin the Cat Pee Award for cleanest combustion.)
>
> Finally, Martin Boll wrote:
>> Just want to draw your attention to the well known fact, that
>> small fires (I think [of them] as well turned-down-fires) need
>> small-calibrated fuel/wood, to be managed well.
>
> Hail to small wood!!!!   Hail to small fuel!!!!!     And that includes
> the wood
> chips and hammermill wood and broken twigs, etc. that are so good in
> the TLUDs.
> Although the low fire was not used much where I was working in India,
> the TLUDs
> have a very good turn down ratio.
>
> Paul
> -- 
> Paul S. Anderson, Ph.D., Geography professor - Emeritus
> Telephone:  USA-309-452-7072 (residence and office)
> Internet site:  www.ilstu.edu/~psanders
> For my gasifier stoves info, go to:
> http://bioenergylists.org/contributors#Paul_Anderson
>
>
>
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