Mobile Retorts

[openspaceman]

Excellent! A bit of cold hard chemistry. It's taken two years of asking the question to finally have an intelligable scientifically sound answer to the stainless steel retort conundrum.

Thank you openspaceman!

 

 

A lady I know virtually, Priya Karve, was making char from sugar cane leaves in India, using the design of another virtual acquaintance, Yury Yudkevitch, and opted for a number of stainless retorts and they lasted no better than mild steel. The trouble with most retorts is getting a decent heat transfer and to do this the firebox temperature is raised to get a high delta T across the wall, which limits its life. The aim should be to get better heat transfer into the retort and keeping temperature less than 700C.

[the village idiot]

I aim to keep the temperature between 470 and 520 degrees C, certainly keep below 600. I think if I went to 700 degrees my kiln look soon look rather Dali-esque.

Could you elaborate on the Delta T reference, I'm afraid you lost me there.

 

My charge chamber is heated directly from underneath. The temperature is taken from the flue gas emitted from the charge. Presumably I would need to take the temperature of the firebox itself to see what heat strain the base of the inner chamber was coming under?

[difflock]

Delta "T" is simply the difference in temperature.

Say in respect of domestic radiators, rad water temp is 75 deg, air in room is 20 deg.

delta "T" = 55 deg.

This will determine how much heat is transferred from the radiator to the room.

[openspaceman]

I aim to keep the temperature between 470 and 520 degrees C, certainly keep below 600. I think if I went to 700 degrees my kiln look soon look rather Dali-esque.

 

I imagine this is the temperature you measure inside the charge chamber rather than the combustion space? It's the temperature that you need to heat the wood to for it to self sustain pyrolysis, between 330 and 440 C pyrolysis is reckoned to be mildly exothermic, above 440 and you have to supply energy as a proportion of the tars form tiny pieces of graphene like ring structures. The temperature in the firebox will be anywhere between 800C-1600C in places and the steel shell will have a temperature bof an average between the two temperatures on either side. The difference between these two temperatures is what I referred to as the delta T.

 

Could you elaborate on the Delta T reference, I'm afraid you lost me there.

 

 

Heat flows from hot to cold temperature reservoirs. The amount of heat flux from hotter reservoir to the cooler one is a direct ratio to the difference in temperatures between the two reservoirs (the delta T), so to make more heat transfer into the load of wood you want to pyrolyse you either have to take longer, increase heat exchange rate or increase delta T.

 

The reason you need to put heat into the raw material is:

 

1 To raise its temperature to 100C

2 too boil of water and then other volatile organic compounds

3 to raise it to around 330C

 

Of these 2 requires the most heat, so it pays to use dry wood.

 

 

My charge chamber is heated directly from underneath. The temperature is taken from the flue gas emitted from the charge. Presumably I would need to take the temperature of the firebox itself to see what heat strain the base of the inner chamber was coming under?

 

I think you mean the charge chamber is initially heated from a fire underneath, once pyrolysis is initiated offgas from the charge also contributes to the heating.

 

Yes as I said above the average temperature the charge chamber suffers is the average of the firebox and the charge chamber temperatures.

 

The big limitation of this sort of retort is the small heat exchange surface the walls of the retort provides plus the reliance on natural convection and conduction to move heat around inside the charge chamber.

[the village idiot]

This is all great stuff, thanks guys. I'm learning more in one evening than I have got out of the manufacturers of these things in two years!

[felixthelogchopper]

This is all great stuff, thanks guys. I'm learning more in one evening than I have got out of the manufacturers of these things in two years!

 

I know nothing about making charcoal but this thread is very interesting.

[the village idiot]

The big limitation of this sort of retort is the small heat exchange surface the walls of the retort provides plus the reliance on natural convection and conduction to move heat around inside the charge chamber.

 

The Exeter retort seems to manage OK in this department. I always get full conversion of the charge material and as long as I use relatively well seasoned charge wood and very well seasoned fuel wood the 'heating up' stage only takes a couple of hours and uses the amount of wood it takes to make 4 or 5 standard pallets. Once retorting no further fuel is added.

If I could find an affordable way to prevent the warping over time it would be the perfect machine.

[the village idiot]

I know nothing about making charcoal but this thread is very interesting.

 

 

Pop up to Hadleigh Mr. Logchopper and you can have your own personal viewing in the wood.

 

... I do have a beard, but I don't play the banjo!

[felixthelogchopper]

Pop up to Hadleigh Mr. Logchopper and you can have your own personal viewing in the wood.

 

... I do have a beard, but I don't play the banjo!

 

You don't scare me, I live near the Dengie Peninsula. Thanks for the kind offer, I may well take you up on it in the near future.

[the village idiot]

You don't scare me, I live near the Dengie Peninsula. Thanks for the kind offer, I may well take you up on it in the near future.

 

No worries. Is that near the Dengie Marshes? Had a cousin from those parts- webbed feet but a real heart of gold.

 

 

 

He's now my wife:thumbup: