Coal fired power stations - we love you really

[John J]

Drax only burns wood chip now. The coal mills taken out of use.

[Chris Hogg]

Drax burns seven million tonnes of wood pellets per annum*. That's about 13.3 tonnes per minute, or bearing in mind that the pellets are partially dried, about 25 tonnes of green wood equivalent, per minute, or about one fully-grown tree per minute, maybe more. Puts all this tree planting to absorb CO2 into perspective. How many tree whips do you have to plant to get the equivalent new growth of 25 tonnes per minute?

[The Natural Philosopher]

Obviously you have to plant one new tree whip per minute.

[Andrew]

So is Greece, and they also mine and burn lots of open-cast coal.

[Steve Walker]

One per minute or 525,000 per year (assuming no failures). OK that won't absorb it straight away, but once what is planted now is mature, the mature trees that you were cutting down would be balanced by the ones reaching maturity each year.

Of course it will be more to allow for failures and for losses in cutting, drying and shipping the wood.

A proportion of the wood chippings will be from waste wood from trees grown for timber though.

[Chris Hogg]

One per minute, obviously and as you say, but those trees would have to be mature when they were felled. You'd have to be planting them at that rate for many years before they reached maturity, probably for about fifty years or so. So you'd have had to plant something over 26 billion trees before you could reach an equilibrium (50x525,000). 26 billion trees is some eight times the number we already have, and that would be just to feed Drax 'carbon-neutrally', let alone all the other sources of CO2 that trees are supposed to be going to compensate for.

There was a discussion about it here a few years ago, giving a much more detailed calculation than I've done here, but I can't find it now.

[Chris Hogg]

See my reply to TNP.

[The Natural Philosopher]

Planting trees for firewood you wouldn't let them grow that long. About

20 years probably. But agreed, biomass is as shit way to do renewable energy except that it does give you a stored energy product.

Your maths is totally out. 20x365x24x3600 = 10,512,000 - a shade over ten million trees, to feed Drax.

David Mackay reckoned that biomass was about 0.1W/sq m IIRC. Or it might have been 1W

so for Drax, we have 4GW. at .1W/sq m, 10^5W /sq km. = 100kW/sq km. so

10 sq km per MW or 40,000 sq km to generate 4GW.

An area the size of most of Scotland.

HOWEVER there are places on this earth where nothing BUT scrubby trees grow - Think Canada.

Try doing it again.

[critcher]

well it didnt do any good did it, they a still gone.

[Chris Hogg]

But would a 20-year-old tree weigh 25 tons? I was speculating and I really don't know, and my suggestion was primarily based on weight of green wood consumed (before converting to partially as dried pellets) of 25 tons/minute, rather than tree age. I volunteer with a woodland conservation group, and the trees planted 20 years ago are nowhere near 25 tons, more like 5 at a guess, if that. But different trees grow at different rates, depending on species and local environment.

+1

<chuckle>

My maths is not as bad as yours! :-) 20x365x24x3600 = 630,720,000. You've got an extra 60 in there (it's one per minute, not on per second), and if you use 50 years rather than 20, you get my figure.

He settles on a figure of about 0.5W/sq.m (p.48)

Using Mackay's value of 0.5W/sq.m gives 8,000 sq.km

Not quite Scotland, but still pretty big! And that's just for Drax. By the time they've converted all the vehicles to electric, and domestic heating, and industry, there'll be no room for solar panels, wind generators, growing food, or anything, really!

Or...er...Siberia, where all the Russian oil and gas comes from. In view of recent events, perhaps not!

[Andy Burns]

Sounds like the opposite of Easter Island

[Tim Streater]

That should be 20 x 365 x 24 x 60 (one / min) but the 10.5 million is correct.

[Andrew]

Don't be silly. Too cold. Southern US states are warm and humid, where trees grow faster.

[Chris Hogg]

So more of a typo than a miscalculation.

Something similar with my claim that 50x525,000 is about 26 billion. Should have been 'about 26 million' of course.

[ARW]

The drive to Donny has never been the same since they demolished the towers at Thorpe Marsh. You could see the all the way down Marr drag

[John J]

The fly ash from Thorpe Marsh had excellent properties to blend with cement to make a grout mix for tunnel lining. Not any more of course.?

[John J]

Spending some time near Selby yesterday i noticed in the morning two of the cooling towers at Drax were issuing vapour then later on around tea time another two started wishing vapour. Presumably another generating unit was being brought up for the evening/overnight load. Being quite prominent on my horizon I'd be interested if the output of Drax was available as a live feed not just lumped in with biomass. ?

[Andy Burns]

I don't think they show their own output separated from other biomass outputs, but have a poke around Drax Electric Insights

[The Natural Philosopher]

TBH its about all the biomass that shows up there - there is less than

100MW of 'non Drax'

[whisky-dave]

Any idea of the differncies bewteen the 'brown" coal the germans are burning and the standard 'black' stuff we used I've heard it's less energy dense (and they have lots of it) but how does word out pollution and emiisions wise in the modern burners, probably difficult to work out and even then adjusted with some tree planting payback scam.