Charcoal quality

[Woodworks]

9 hours ago, openspaceman said:

Hotter drives off more volatiles and increases the fixed carbon content. So hotter means less yield but higher carbon content. Carbon has a higher calorific content per kg than wood.

 

 

OK so the fact I will let my retort get up to 700C towards the end of the burn could be why this chap found our charcoal so good. We simply make a more energy dense charcoal than most.

 

"Retorts tend to self limit their temperature because the process goes back to endothermic above about 440C as the structure of the char matrix begins to change and  most of the evolution of the hydrogen and oxygen containing species has finished so the exothermic reactions of the initial pyrolysis products splitting and cracking has finished." 

 

Any chance you could break this bit down for numpty's to understand?  You say it will tend to self limit but it wants to sit up around 600C-650C for much of the burn without careful air control. The temps are taken in the firebox mid hight of the charge chamber.

Edited May 10, 2018 by Woodworks

[openspaceman]

2 hours ago, Woodworks said:

OK so the fact I will let my retort get up to 700C towards the end of the burn could be why this chap found our charcoal so good. We simply make a more energy dense charcoal than most.

700C is very hot for a steel walled retort because at that temperature the steel will oxidise on the outside at least.

2 hours ago, Woodworks said:

 

"Retorts tend to self limit their temperature because the process goes back to endothermic above about 440C as the structure of the char matrix begins to change and  most of the evolution of the hydrogen and oxygen containing species has finished so the exothermic reactions of the initial pyrolysis products splitting and cracking has finished." 

 

Any chance you could break this bit down for numpty's to understand?  You say it will tend to self limit but it wants to sit up around 600C-650C for much of the burn without careful air control. The temps are taken in the firebox mid hight of the charge chamber.

Most of the mass loss is in the temperature range 330C to <500C above 800C the char is almost pure carbon and only 15% of the dry weight of wood used, depending on species. Batch retorts (i.e. those that you initially heat with other means and then they burn their own offgas to sustain the temperature) have given off most of the gaseous pyrolysis products by ~450 C so there is no more fuel to sustain the pyrolysls, as above about 460C the char undergoes a change which requires energy input  it tends to not exceed this temperature in the absence of other heat input. This lower temperature char thus still contains some tars which need to be burnt in a flame else they smoke which makes it poor for indoor cooking (indoor use of charcoal is unwise because of the risk of CO but it happens in many less developed urban areas where a wood fire and associated smoke en mass is unacceptable) . From the little I have seen of imported hardwood charcoal  it typically is much denser than ours and made at higher temperature, so it is harder to light, burns more slowly and gives off little or no smoke.

 

Incidentally it is the fat dripping onto the hot coals, being partially burnt and then condensing on the food that makes flame grilled meat a source of VOCs and free radicals which are best not eaten regularly.