[Stoves] TLUD-Oven!

Sun Jul 27 01:48:08 CDT 2014

Dear Crispin, thanks for you comments!

You are very right, I have to minimize heat loss through the top hole of the oven. It sure would maximize efficiency.

I'll try to study your numbers and make some calculations. I am using pellets, which have more or less standard energy density. As I have found, pellets are about 5,23 KWh/Kg. So, if we need 9 KWh, we should need only 1,7 Kg of pellets to get it done. If I reach this, as you say, I'd be at the same efficiency of a gas oven. (I suppose you mean butane or propane gas ovens?) If the other variables where constants, my oven would had half the efficency of a gas oven (like 1/6 efficiency of an electrical one), BUT this is difficult to say, as my oven reached more than 180ºC on the test.

I've been looking at prices of CO2 and CO measurement devices, they are out of my possibilities for now! But I'll look carefully at Siegert Formula, as it is very interesting for understanding primary and secondary air rols.

Keep stoving
Marc
Date: Sat, 26 Jul 2014 05:15:26 -0400
From: crispinpigott at outlook.com
To: stoves at lists.bioenergylists.org
Subject: Re: [Stoves] TLUD-Oven!

Dear Marc

Thanks for sharing the comprehensive report and providing many relevant numbers. The duration of the burn certainly seems adequate for most baking. 

Your comment on heat loss is very relevant. I caution that you cannot tell how much heat is being lost without gas measurements. You might do something that results in a lower exit temperature but an increase in CO (chemical loss) or higher dilution by excess
 air (mechanical loss). You have reached the point where further development needs a combustion analyser. 

If you research the Siegert Formula you will find the appropriate tool for the next stage of development of the burner and oven structure. You need three fuel-specific constants, the temperature, the CO and either the O2 or CO2 concentrations in the exit gases
 to make the calculation (which gives the total heat loss). 

Controlling the primary air flow will control the oven temperature. Adjusting the secondary air flow will optimise the combustion and simultaneously limit heat losses by minimising excess air. 

Bread baking is slightly endothermic. You must also heat the mass of wheat to 94 degrees minimum (in the centre) and evaporate some of the moisture. It takes about 3 kw for 1 hour to bake 16 loaves of 800 g each. That is the performance of a well insulated
 electric oven. That provides a comparison of what energy is need for the actual baking. 

There is a rule-of-thumb for gas ovens (which you have) which is something like 1/3 the electrical efficiency. Maybe Andrew Heggie remembers it. It means it is possible to bake 16 x 800 g loaves with 9 kWh of heat. ‎12.8/9= 1.5 kg of product per kilowatt-hour. 

If the fuel was 15 MJ/kg it would take 2.5 kg to bake the 16 loaves (including preheating) at 180 C.

As you limit the losses, the smaller reactor might turn out to be adequate for your needs.

The above baking information and numbers are based in a real 220 v, 3 kW electric oven and a modelling spreadsheet predicting the time needed to bring the dough above 93 degrees at which point it becomes bread. 

The model predicted 53 minutes and the oven took 55 so the process are reasonably well understood. Bakeries normally test the centre of the loaf ensuring it is 94 C or a little higher. 

Regards 

Crispin 

From: Marquitusus
Sent: Saturday, July 26, 2014 02:46
To: stoves at lists.bioenergylists.org
Reply To: Discussion of biomass cooking stoves
Subject: [Stoves] TLUD-Oven!

Hi,

I'm very glad to send to inform about my last work, the TLUD-OVEN. I wanted to put together the wonderful light thermal mass ovens from
Recho Rocket with the very clean
TLUD technology, and that's it!

The results are very promising: no smoke at all, no soot, very fast heating and very comfortable cooking, as you can leave the fire unattended for about 2h30min, and concentrate on cooking!

I think it can be a really interesting device that can allow very clean and efficient baking.

I send the link to the stoves bioenergylists where I posted the file with the details:

http://stoves.bioenergylists.org/content/tlud-bread-oven

I also attach the temperature profile graph and the full pdf paper with all the details.

Just comment what you think!

Marc

www.cuinessolars.jimdo.com

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