Burned Weight?

Conservation of mass.

In a closed system, mass is conserved... so if you have 5-10lbs of ashes the rest is the mass of the gases produced while the log is burned.

fm!

Conservation of mass- I never heard of that one. What about the mass of the oxygen consumed.

Perhaps conservation of energy. The energy in the log is conserved during the process of converting it into gasses, heat and light. Some of these have mass, some of these do not. The process requires oxygen which also has mass. If you do not believe mass is interchangeable with energy see E=mc² Fire may not approach this exchange rate, but it follows the same law.

I feel this topic will be visited by a few others (once they arrive at work) with a much more precise and accurate explanation.

This web page explains it well enough. In the article there is an explanation of a burning coal, I think that is analogous enough to a burning log.

fm!

Thanks for the link- Conservation of matter (as in the link) is common, but I do not aggree with the premise of substituting the word mass for matter. They are 2 different concepts, and there are ways to change the mass of objects- without adding (or subtracting) matter.

"They are 2 different concepts, and there are ways to change the mass of objects- without adding (or subtracting) matter." You are entitled to disagree to your hearts content!

Mass is generally accepted as a property of matter. Wikipedia allows for some dissention on this point however.

It seems to work OK for combustion process where everything is accounted for.

This may help.

Guesstimate yes, accurate no.

A lot of weight will be lost through the emission of gasses (global warming)

The unknown water contents will evaporate.

The percentage water and the composition of the wood may differ for species and growing conditions.

The log will also dry out over time.

The phenomena is called "beating about the Bush".

Well, in simple terms, any water in the log will evaporate and go up the chimney. Any carbon in the log will form carbon dioxide, mostly, and go up the chimney. Any hydrogen in the log will form water vapour, mostly, and go up the chimney. Any nitrogen in the log will form nitrogen oxides various, mostly, and go up the chimney. Any sulphur in the log will form sulphur di- and tri-oxides, mostly, and go up the chimney. Any small non-combustibles will form smoke particles, mostly, and go up the chimney.

Which leaves the large non-combustibles, which remain in the furnace as ashes.

The degree of 'mostly' depends on a number of factors, not least of which is the local temperature at the point in the log where combustion is taking place. The water content of the log is a significant factor, as the heat needed to form water vapour places a 'load' on the system that tends to drive down the local temperatures, which is why dry logs burn better than damp ones. Another significant factor is the amount of air passing through the combustion chamber, and another one is the containment of the process, as logs tend to burn better in enclosed stoves.

In terms of species, Ash, as a timber log, produces surprisingly litte ash. Silver Birch produces a lot of smoke, which is why bee-keepers love it as the smoke tends to make the bees drowsy so they don't sting the keeper. Many pine species are full of sap when newly cut, containing lots of high-energy plant sugars, so these tend to burn fiercely at first.

So in summary, it is possible to predict the amount of ash produced if numbers can be attached to the above and conditions maintained constant, and this sort of thing is best done by experiment. Of course, these sort of things are best done in a romantic, secluded setting with a loving partner and a bottle of something special, without being too preoccupied by the numbers and their meaning...

Is there a 'best' coal for trains , and if so why . We don't need to go into coal rank etc , but can you summary the best and why ? Is it 'volatiles' that make Welsh steam-coal so talked about ? . I worked with SASOL for a while , and never even thought to ask which coal is best for making oil ! I suspect you could probably fill a book on this (many do ) , but what quality in coal is most sought , and which quality is least desired ? I'm aware of the nature of coal being organic and hence infinitely variable , but is ther a simple answer . Maybe you know a good reference link on the topic of coal rank and use.

Thanks , Kris.

It varies with the firebox design and the firing technique. An interesting comparison can be made between two similar-sized engines, one being the sole-surviving ex-GER N7 and the other an ex-GWR 56xx, both 0-6-2Ts. The ex-GER engine, with its shallow-angle grate, ran best on a thin fire, whereas the ex-GWR engine with its steep grate needed to be 'boxed-up' to run on the same coal, according to research carried out during the "Steam on the Met" event many years ago.

Perhaps a 'footplate experience day' at a heritage steam railway would be a good way to research this topic?

Thanks. .

The Romney Hythe and Dymchuch Railway is nearby - I shall engage their fantastic bunch of volunteers in chat next time I pass by. I may have finally (somewhat belatedly) developed an interest in the subject (thanks to your feedback ).Cheers.

Iwas environmental engineer at a coke plant for a multi year sentence...

But it was an upgrade from the slag crusher.

We blended hi and low volatile coals to get a very stable coke with good strength as well as by product recovery and low ash. I'm sure that there are similar criteria for steam coal besides BTU/lb. My books are out of reach for the weekend. we'll see...

milo

Nice GURU class response.

milo

"If I burn a log, lets say a 120 pound log, in an enclosure, after it was burnt to ashes, do we have a formula to predict the weight of the ash?"

No one provided an answer to this one. The answer is NO. The weight of the ash residue will depend on the density of the wood and some other minor factors perhaps. Consider two logs of idential size and two of identical weight. In each case one is balsa and the second a dense hard wood such as oak, hickory, black locust, or wood of life. The balsa will leave the least ash and the hardwoods the most.

Mass balance must take into account the amount of Oxygen consumed in burning. Hence mass prior to burning, plus Oxygen consumed, equals total mass after burning.

I'm not sure, if this is true - but I have observed throughout the years that some materials leave a large quantity of ash and others seem to be consumed more completely. Is this just an illusion on my part.

"...forgot what this phenomena is called..."

Evaporation

he he . Nice one .

Taking things to extreme , it will rain down somewhere else later .Eventually another tree will grow. If pretty , we can dance around it . If not it too can be chopped up with a big axe. We can then sit in a cosy huddle watching it burn in the flames. Anyone like marshmallows ? (I'm a Brit , so I shall just have toast.)