Gavin A

I quite agree. The typical commercial forestry cycle is 40 years which is typically a thinning crop of 70 cubic mtrs per hectare every 5 years starting at year 20 and a final crop of 6 times that amount. So basically you can sustainably harvest 14 cubic mtrs per hectare per annum with enough spare crop to sustain an increase of forestry area of 50% every 40 years.

Just looked up some figures for energy density by mass and volume for timber.
The best is torrefied at 600 kg/m^3 with an energy density of 21.5 MJ/kg.
So if you can harvest 14 m^3/ha y of 'torrefied' timber (being nice here as it can't happen) then 1 square meter will produce 0.84 kg/y, this will have an energy content of 18.06 MJ or 5.02 kWh/y. Seems I was over optimistic when I said 28.5 kWh/y.
I am quite happy to be corrected on both my arithmetic and my data source (http://www.woodgas.com/fuel_densities.htm) as I often make errors this late at night, or in the morning, and I get sleepy after lunch too

Posted By: SteamyTea

Posted By: suneWhere would my hedge be getting its carbon from if not the atmosphere?

It is getting the CO2 from the atmosphere, my point it that it is almost certainly not equal to the CO2 produced when you burn your trimmings. You have to do some measurement and sums to show that the CO2 during emissions is equal to the annual stored CO2, no good saying 'I cut my hedge and burn it as that is better than it rotting', even though you know that that some CO2 will be sequestrated in the soil if left alone.

the alternative is burning fossil fuels and adding carbon to the atmosphere that has been locked away in deep geological storage for millions of years (more likely hundreds of millions of years).

You can't deal with biomass in isolation, as the energy that could have been produced from the biomass will instead be produced from something else, and that something else now and for the forseeable future is fossil fuels.

Posted By: SteamyTea

Posted By: renewablejohnMckay propaganda

Nice to be thought of in the same company.
But would love to see a forest that can supply 1.2264x10^14 kWh/y (that is about what the world population currently uses.

not a single sensible person ever has argued that biomass can or should supply all the worlds energy needs*, therefore this argument is void, and you knew that before you made it.

Posted By: SteamyTea

Posted By: Gavin_Athat has been stored deep underground for millions of years

Yes, stored,not taken million of years to produce. Same as cutting and storing timber for 5 years and then burning it all in one year. There is the production time (the growing) and the Storage time and the Burning time (or natural decomposition). They are all cycles (natural or forced does not matter) and can easily be compared to each other. The planet does not know the difference between today's CO2 emissions or 100 years ago CO2 emission that are still floating about in the atmosphere. Plants are the same, they are not fussy 'eaters'.

The problem we face today with anthropogenic climate change is related to the movement of vast quantities of CO2 from being locked away permanently deep below the ground into the active atmosphere / biosphere carbon cycle resulting in a rapid net increase in atmospheric CO2 concentrations.

Burning biomass from sustainably managed sources has no net impact on this process (outside of the energy required to cut, transport and process the wood which as can been seen above, is of the same order as other renewables)

Burning fossil fuels adds carbon to the atmosphere that was last seen in the atmosphere hundreds of millions of years ago.

I'm actually incredibly surprised that you're even attempting to make this argument, it's very basic stuff and I thought you had a reasonable grounding in this stuff.



*I'll qualify ever as being since the industrial revolution for the pedants.

http://www.biocab.org/Geological_Timescale.jpg

look at the atmospheric CO2 concentrations of the atmosphere over the hundreds of millions of years that these fossil fuel stores were being formed compared to now. That extra CO2 is what is now locked away safely underground. The more of it we burn, the further we head towards the atmospheric CO2 concentrations that were around during the times this carbon was being locked away.

Conversely, the more of it we leave in the ground the less of it can enter the active carbon cycle, and the lower the atmospheric (and oceanic) CO2 concentrations will be.

Posted By: Gavin_AI'm actually incredibly surprised that you're even attempting to make this argument, it's very basic stuff and I thought you had a reasonable grounding in this stuff.

This is why I agree with the original paper.
Your argument is that if biomass is burnt any and all CO2 produced is equally matched by absorption of new plant growth.
May argument is that not all CO2 produced from biomass burning is matched 1:1 because if we increase biomass burning we will be depleting the the natural reservoirs, a trend that has been reversed in recent years possibly through better management and understanding of resources but at the cost of higher atmospheric CO2 levels and ocean acidification. What is trying to be achieved are lower atmospheric levels and increased energy production, If timber growth is the answer to this then I argue that you need an increase in forest year on year, I think we can agree on this. What we cannot agree on is the statements about natural decomposition. I say don't burn and let the land have some (not all, some) of the locked up carbon, you say burning it and letting it be reabsorbed as new growth is better.
The burning of anything with carbon in it will produce CO2, you cannot argue against surely?
So as the original aim was to reduce atmospheric CO2 levels (or at best stabilise them) burning timber is not as good as using it as a building material and from an energy production point of view burning natural gas is better than burning timber.
These two points seem at first not to match up very well as you can use timber to manufacture goods but you can't use natural gas (well some plastics can be made from it but not very effectively). May argument here is that we can produce energy from gas and let the lower CO2/kWh emissions be reabsorbed by increasing timber growth, that is then used to manufacture goods (sequestration in other words). You would produce more and sequester more this way, not ideal but better.
I think it is also worth pointing out that land area is approximately 1/3rd of the planets surface of which only some is suitable for timber production, so resources are limited, as all resources are.

<blockquote><cite>Posted By: SteamyTea
What we cannot agree on is the statements about natural decomposition. I say don't burn and let the land have some (not all, some) of the locked up carbon, you say burning it and letting it be reabsorbed as new growth is better.
</blockquote>

SteamyTea

What is it with a forest cycle that you dont get. In rough analysis terms when a tree grows it absorbs CO2 throughout the whole tree. Approx 50% is above ground and can be harvested to release 50% of the CO2 the remaining 50% stays in the ground and the CO2 is sequestrated. Therefore sustainable forestry can have a REAL impact on reducing CO2 levels and I would argue is better than Natural Gas as it reduces overall CO2 levels due to the sequestration effect of forestry.

Posted By: SteamyTea
Your argument is that if biomass is burnt any and all CO2 produced is equally matched by absorption of new plant growth.

actually, you're missing a crucial bit of my arguement from this sentence, which may help explain your difficulties in agreeing with such a basic point. That sentence should read:-

if biomass from sustainably managed sources is burnt any and all CO2 produced is equally matched by absorption of new plant growth.

This is the basic defining factor determining whether a source is sustainably managed or not, so how you can have a difficulty with this premise is beyond me tbh. In a sustainably managed forest, the forest would be managed on some form of rotation basis, so if it were to be cut on say 30 year rotation, then 1/30th of the forest could be cut per year, with the other 29/30ths left to grow each year. In that year those remaining 29/30th's of the forest would absorb as much carbon (on average) in that year as the 1/30th of the forest that was being cut had absorbed in it's lifetime, and could therefore possibly released via burning in that year. In reality, a significant portion of the carbon the cut forest had absorbed in it's lifetime would remain in the soil / biosphere in terms of the root system, leaf litter and uncollected brash / offcuts, so the carbon store in the soil would increase anyway.

Anyway, let's try one more time to explain the difference between biomass & fossil fuel carbon in terms of the impact of that carbon on atmospheric carbon levels.

Carbon that is locked away in fossil stores deep underground is carbon that is inactive in carbon cycle terms, as it almost entirely has no way of being added to the carbon in the atmosphere without human intervention. Once this carbon is removed from it's fossil stores there is currently no way of putting it back* into those fossil stores within a human rather than geological timescale, it will remain within the active carbon cycle for millenia to come until eventually millions of years from now.

Carbon that is in the biosphere is already active within the carbon cycle. It has recently been removed from the atmosphere through photosynthesis, and left to it's own devices much of it would return to the atmosphere anyway via forest fires or decomposition, with some of it eventually adding to the long term carbon sink in the soil. Even carbon in the carbon sink in the soil isn't really safely locked away though, as changes in the local climate and/or land use techniques can easily create situations where the soil rapidly loses much of it's carbon content to the atmosphere.

Burning carbon from any biosphere resources does not directly add a single molecule of carbon to the active carbon cycle. If we were burning biomass without replanting it then this would move carbon from the biosphere to the atmosphere, but if as is being suggested, we use biomass from sustainably managed sources where at least as much new growth is planted as has been harvested then there will be no net change in atmospheric or biospheric carbon levels from this process directly.

There is a relatively minor level of indirect carbon emissions stemming from the harvesting, transportation and processing elements of the process, but as shown in the lifecycle figures I've quoted, this is an order of magnitude lower than for natural gas, and IRRC are actually comparible with the actual production, processing and transport elements of the lifecycle carbon costs of natural gas anyway.

This arguement about letting the land lock up the carbon from biomass is utter tosh because any biomass that is not used to offset fossil fuels for heating / power production effectively leaves those fossil fuels to continue to be burnt adding far more new (ok very old) carbon to the active carbon cycle than can possibly be locked away by biomass in anything other than geological timescale. In any sustainably managed biomass resource sufficient biomass will be returned to the soil anyway via the roots, leaf litter and windfall/ brash to add to the carbon in the soil and maintain the soil's vitality, there's no need at all to simply not use the biomass at all.

Yes we need a balance, and wood that can be used for building etc should be used for that, but there are huge volumes of biomass that aren't suitable for this purpose or anything else, and making use of this biomass to displace fossil fuels as far as can be done sustainably is the only logical position to take on this subject from a carbon / global warming perspective.


*carbon capture and storage even it if worked would only be capable of putting a fraction of the carbon back into a depeted gas field than had been removed from it.

** arguments regarding particulate pollution are a different kettle of fish, and I'd side with anyone arguing for best available technology (not best practicable technology) to be used to reduce these problems, and even to ban biomass boilers / stoves that can't meet stringent standards. These are valid concerns entirely unrelated to the basic point regarding the low carbon / renewable nature of sustainably managed biomass as a fuel stock.

Compelling arguments, Gavin.

Yes or no then:
"Biomass is a totally carbon-neutral fuel."

And, moreover:
"Given the 1/30th, 29/30ths rule, forestation for biomass is a negative-carbon process."

Posted By: DamonHDJ: very close, not completely zero, until the energy for the chainsaws and transport is itself from biofuels or other zero-carbon sources. (And the food for the workers is made with zero-carbon sauces too.)

Rgds

Damon

Damon

Where nearly there. When our MB Trac forwarder with felling head is converted to woodgas later this year we will be a step nearer. We made the decision to convert because of the price hike in white diesel which the DVLA and VOSA insist we use. If we still had the option of using red I think the decision would have been put off.

Posted By: JoinerCompelling arguments, Gavin.

Yes or no then:
"Biomass is a totally carbon-neutral fuel."

And, moreover:
"Given the 1/30th, 29/30ths rule, forestation for biomass is a negative-carbon process."

depends.

If you had a short rotation coppice system going on in your (larger than usual) garden with no chemical, fertiliser or energy inputs used in the growing, cut by hand and dried naturally by wind and sun then transported to the house by hand and and burnt (ideally in a gassifying, smokeless zone approved wood boiler/stove) that would be carbon neutral.

On larger scales it would not be entirely carbon neutral, but would be of the same order of carbon use per kWh as most other renewables on a life cycle basis as is clear from the life cycle carbon comparison I posted earlier.

so really it's a low carbon option, rather than an entirely carbon neutral option (is there actually such a thing?)

I can see that it could be in some situations, but probably not in most given that much of what's left behind will eventually rot down anyway, and the process of planting, caring for, cutting, processing, transporting etc the biomass isn't going to be insignificant in most cases for largescale biomass production.

As I don't have the time to do the primary research myself to confirm this one way or the other, I'm happy to use the figures from the peer reviewed literature, though I must admit that I've not really checked out exactly how these figures were calculated, what assumptions were made etc.

They are not necessarily big anyway, so *if done sensibly and efficiently* then I take biomass burning to be effectively carbon-neutral.

Rgds

Damon

The discussion covers various aspects of biomass theory but sadly fails to embrace UK reality. Current large power plant projects will require some 50 million tonnes of feedstock to be imported each year. It is understood the current thinking is import of woodchip from Brazil. We know woodchip is 19% air plus water content, this means 1 journey in 5 will be wasted with obvious emissions impact from bulk carriers burning high sulphur heavy oil. The woodchip will require energy input for heat treatment prior to journey in order to reduce pest and disease transmission, the storage proposal on arrival in UK is 200,000 tonne per plant open to the elements creating requirement for substantial energy input to drive out water in processing.
The plants are to be generally positioned on coasts with majority of heat produced dissipated into sea, the Gov 09 renewables report details anticipated 27% operational efficiency for biomass plants. The landlocked plants are to utilise massive blast fans to dissipate waste heat into atmosphere. The plant waste heat will add to sea temperature rise and create direct global warming. Fossil fuel input required by biomass plants must also be considered, a small plant producing 2.3 MW of useful output details 2 no. 8MW diesel burners almost equalling biomass input. I note a straw burning plant where fossil fuel use is only capped by ROCs regs. The use of SRC poses problem of substantial irrigation requirement to ensure maximum yield in large areas of UK which again adds to emissions impact. DEFRA detail minimum 600mm summer rainfall requirement. Another consideration is serious health hazard created by spores from chipped SRC in storage. The discussion on forestry procedure and retained CO2 appears to ignore modern trend to grub out stumps in order to maximise return .
The vision of typical domestic biomass use appears to be man wielding chopper felling local timber transporting it to wood burner in wheelbarrow where after minimising water content the feedstock will be combusted under optimal conditions to ensure minimal emissions. The reality we know generally creates far greater impact, just look at research on wood stoves and compare lab. testing with field results and impact in various locations. The commercial users quote ODT for basis of efficiency ,this gives appearance of lower feedstock requirement for given power out but ignores reality of operation and energy required to achieve ODT. We could apply due diligence and apply BAT to minimise impact but the reality is we currently have no incentive to do so.
A biomass plant illustrates a 22-24 hr shutdown procedure and prolonged start-up during which time emissions are far higher , these are all considerations in assessing true impact of UK massive investment in biomass combustion but most important is health impact. The UK renewables report 2009 confirms this investment in biomass power plants will create £billions in additional NHS costs due to air quality degradation.
Biomass is a very valuable resource but any use must surely recognise full impact of actions taken based on current knowledge. A few years ago biomass combustion was “considered to be carbon neutral” with further knowledge it was classified low carbon but now apparently it can be whatever depending on standpoint. DEFRA have produced a report detailing straw combustion can create GHG impact 38% higher than equivalent fossil fuel,
Surely emphasis on CO2 diverts from overall GHG impact of chosen fuel plus ignores crucial area of health impact.

So Brian what you are saying, the bits that are specifically related to the AECB commissioned discussion paper anyway, seems fairly similar in some ways to what I was saying in my response. I highlighted the larger scale chip and powerstations with planning granted as areas of concern as you will have read...

I have 4 questions about the AECB commissioned paper:

1 - With regard to paper do you agree with the concept put forward of ignoring the uptake part of the biomass carbon cycle?
2 - Do you agree or disagree with the statement 'not all wood can/will be built with'?
3 - Do you agree or disagree that the blanket statement in the paper that burning wood results in higher co2 emission than a gas boiler because the co2 could be sequestered short term by using the wood to build something with only applies where the wood could and would be built with otherwise? ie that it is a statement that is only sometimes true as opposed to always true as it is presented in the paper.
4 - I know that you don't really like biomass burning for a variety of reasons but setting that aside for this question as far as possible so that we can focus on the AECB commissioned paper - do you think that the paper was well written (ie would it have got past peer review do you think?), and if not do you think this was deliberately done to foster polarised debate and headlines? ie do you think that the authors are aware of its limitations but wanted to create more impact?

How about your answers to questions 1-4 SteamyTea?