Why do some woods produce more ash than others?

[Woodworks]

I have been burning some smallish beech lately 4-6" all nice and dry. It burns great with lots of heat but it creates far more ash than when I burn sycamore and ash with the same moisture content. Does anybody know why this is.

[face cord]

More bark on smaller sized logs, & bark contains soil, sand etc, which is left as more ash volume.

[nepia]

But (sweet) chestnut as a species has a reputation for leaving very little ash so there has to be more to it than that.

I don't know either Woodworks but I'm happy to learn.

[Woodworks]

Thanks face cord

I did not know that

 

This may well be part of it but I don't think it completely explains why this present lot of beech is producing so much as I do sometimes burn small stuff (down to 2") of other species.

[Dave Martin]

I have been burning alot of small round logs this week ( ones that I considered to small to sell ) and have also noticed that they leave alot more ash

[Big J]

I too would be intrigued to learn why this is. Biggest difference I've noticed is between European larch and just about any hardwood species. Larch leaves no ash, whereas most hardwoods do. However, it is notable that due to the lack of ash, it's harder to keep a larch fire in for a longer period of time.

[Stereo]

Most softwoods leave little ash I find and as you say, the ember bed seems to disappear quickly. If you burn some ash or syc etc. you can go back 10 hours later and rake up some hot coals and get it going again with kindling just by opening up the vents. With most softwood I find that the fire is cold and dead half an hour after its burned down.

[face cord]

Science paper on reducing bark impurities in beech trees.

 

Wood energy fuel cycle optimization in

beech and spruce forests

 

http://iopscience.iop.org/1748-9326/7/1/014001/pdf/1748-9326_7_1_014001.pdf

 

Abstract

A novel synergistic approach to reducing emissions from residential wood combustion (RWC)

is presented. Wood energy fuel cycle optimization (FCO) aims to provide cleaner burning

fuels through optimization of forestry and renewable energy management practices. In this

work, beech and spruce forests of average and high quality were modelled and analysed to

determine the volume of fuel wood and its associated bark fraction produced during typical

forestry cycles. Two separate fuel wood bark production regimes were observed for beech

trees, while only one production regime was observed for spruce. The single tree and stand

models were combined with existing thinning parameters to replicate existing management

practices. Utilizing estimates of initial seedling numbers and existing thinning patterns a

dynamic model was formed that responded to changes in thinning practices. By varying the

thinning parameters, this model enabled optimization of the forestry practices for the

reduction of bark impurities in the fuel wood supply chain. Beech forestry cycles responded

well to fuel cycle optimization with volume reductions of bark from fuel wood of between

10% and 20% for average and high quality forest stands. Spruce, on the other hand, was

fairly insensitive to FCO with bark reductions of 0–5%. The responsiveness of beech to FCO

further supports its status as the preferred RWC fuel in Switzerland. FCO could easily be

extended beyond Switzerland and applied across continental Europe and North America.

Edited November 23, 2012 by face cord

[HCR]

Ash (as opposed to unburnt chars) is the mineral content that doesn't burn. Think calcium carbonate, potash (i.e. poassium salts) and various phosphates in diminishing order. As the chemical composition of wood varies from species to species, so does the relative content of these compounds.

 

And then you get impurities that don't actually form part of the chemical structure of the wood as well, sometimes known as adjuncts.

[teepeeat]

Apart from moisture content, does it also not depend a bit on the particular stove setup with regard to efficiency, fire box temperature (in relation to wood type)etc?? These factors seem to be focused on by manufacturers when it comes to emissions and also effect what is deposited in the flue.