Wood pellets: Renewable, but not carbon neutral

Wood pellets: Renewable, but not carbon neutral
Turning forests into fuel comes at a cost to the environment. Credit: Antonia Gravante

A return to firewood is bad for forests and the climate. So reports William Schlesinger, President Emeritus of the Cary Institute of Ecosystem Studies, in an Insights article published today in the journal Science.

In the race to meet clean standards, biomass energy is often touted as neutral. To satisfy European Union (EU) demand, forests in the United States are turned into wood pellets and shipped overseas, to the tune of 7 million metric tons annually. When these pellets are burned in the EU, the electricity they generate helps fulfill Paris Agreement commitments.

The stage is also being set for a potential uptick in biomass energy in the US, as Congress may declare biomass carbon neutral in an effort to revive the American forest product industry. A tax on fossil carbon would further incentivize US demand for wood pellets.

But turning forests into fuel has hard limitations. Accounting for often ignores the critical role forests play as a sink for that might otherwise accumulate in the atmosphere. As Schlesinger reports, each year, an estimated 31% of the carbon dioxide emitted from human activities is stored in forests.

Native forests store more carbon dioxide than their plantation counterparts. Harvested pellets require fossil energy during manufacturing and overseas shipping. As Schlesinger explains, "The benefits of wood power must be discounted by the loss of the carbon sequestration that would have occurred in the original forests if they had not been harvested."

Wood pellets: Renewable, but not carbon neutral
The Southern US is more intensively harvested and has far fewer forest reserves than the North and West. At the same time, the region is a hotspot for plant and animal biodiversity. Credit: David Allen

He notes, "It makes no sense to have Europeans embracing wood pellets as carbon neutral, while overlooking the carbon dioxide emitted during shipment and the losses of carbon storage from forests in the United States."

Then there is biodiversity to consider. In the southeastern US, pine plantations are a major source of pellet wood. Yet pines are of limited value in preserving the region's rich biodiversity. As demand for wood pellets rises, old growth forests are also put under pressure of harvest. A myriad of species rely on these globally rare ecosystems.

Schlesinger concludes, "Ultimately, the question is what kinds of forests are most desirable for the future. Recent research indicates that unless forests are guaranteed to regrow to carbon parity, production of wood pellets for fuel is likely to put more carbon dioxide into the atmosphere and preserve fewer species on the landscape during the next several decades."

Biomass shortfalls include:

  • Fossil fuels power wood pellet export. Wood pellets produced in managed forests in the southern hemisphere are shipped to Europe where they are burned. The amount of energy required to power this shipping process can account for 25% of the total carbon emissions associated with biomass-fueled energy generation in Europe.
  • Timber plantations do not store as much carbon as natural forests. It would take 40-100 years for a managed forest to store as much carbon as a natural one. Trees planted to produce wood pellets are often cut within 20 years, which is not enough time for them to take in the carbon released by the harvest and combustion of the previous 'generation' of natural forest.
  • Monoculture degrades biodiversity. Timber plantations, which are typically dominated by a single tree species, cannot support the diversity of life found in natural forests. Also, increasing demand for wood drives up the price of raw , incentivizing the harvest of biologically diverse old-growth forests.
  • Cleared forests are vulnerable to non-forest development. New trees are not always planted where forests have been cut for fuel. In such cases, the potential of the existing is completely eliminated.

Explore further

To curb climate change, we need to protect and expand US forests

More information: "Are wood pellets a green fuel?" Science (2018). science.sciencemag.org/cgi/doi … 1126/science.aat2305
Journal information: Science

Citation: Wood pellets: Renewable, but not carbon neutral (2018, March 22) retrieved 21 September 2019 from https://phys.org/news/2018-03-wood-pellets-renewable-carbon-neutral.html
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Mar 22, 2018
The astonishing stupidity of the AGW Cult knows no bounds.
These are the ignorant A-Holes who preach that they will save us.

Mar 23, 2018
Nothing like walking in a neighbourhood of houses in winter, smelling fireplaces. 20 years from now, if the geenloons have their way, we'll all be in high density Soviet-style apartments with cold water freezing to death.

Mar 23, 2018
I totally agree with

"It makes no sense to have Europeans embracing wood pellets as carbon neutral, while overlooking the carbon dioxide emitted during shipment and the losses of carbon storage from forests ..."

However, ALL that means is that wood pellets, along with hydrogen fuel production which most scientists agree is another flawed strategy doomed to fail, isn't the answer.

Obviously, the unsustainable continuation of burning of fossil fuels for the foreseeable future, just as proposed by many a moron here with all their hateful straw mans against those far smarter than they are, is also not the answer although nobody denies we have to all alow a reasonable intermediate period where we must continue to burn some but decreasing quantities of fossil fuels while we are converting to more sustainable sources of energy.

Renewables and/or nuclear and electric vehicles is the answer.
Some biodiesel or methane from waste organic matter might sometimes also help.


Mar 23, 2018
Renewables and/or nuclear and electric vehicles is the answer.


Synthetic hydrocarbon fuels is the answer.

Renewables and nuclear power don't go together unless there's a massive energy buffer between them, and between renewables and the consumers, which won't come from electric batteries due to the sheer scale and cost of it. Even the largest megabatteries we have, in contrast to the societies' energy use, are like trying to power an house by a single AAA cell.

Synthetic hydrocarbons provide a cheap and scalable means to store energy and fit everything together, and since you'd be having large quantities of chemical fuels around, battery-electric vehicles become pointless as well. Why haul a ton of batteries when a gallon of butanol does the same trick?


Mar 23, 2018
Harvested pellets require fossil energy during manufacturing and overseas shipping.

I wouldn't go that far. Currently they *use* fossil energy for this but they do not *require* fossil energy. the energy for manufacture and shipping can come from renewables, too.

He notes, "It makes no sense to have Europeans embracing wood pellets as carbon neutral, while overlooking the carbon dioxide emitted during shipment and the losses of carbon storage from forests in the United States."

It depends what it makes sense compared to. Does it make sense on an absolute level where carbon neutrality is the only goal? No. Does it make sense on a level where reduction of emissions is the goal by replacing much worse forms of energy generation like coal, oil or gas? Most certainly.

Mar 23, 2018
Even the largest megabatteries we have, in contrast to the societies' energy use, are like trying to power an house by a single AAA cell.

Eikka

Can you handle the concept of 'using more' batteires than some illogical totally arbitrary insufficient numbers of them for the job you personally chosen to consider.
If just one of them isn't enough, have you ever considered the possibility of 'using more' than one?
Why must a house just use just 'one' battery? Why the superfluous constraint?

+ how do you propose we make these "Synthetic hydrocarbons"?

Mar 23, 2018
I think we need a reality check here. Please note the following facts:
1) Forests are not generally cut down to produce bioenergy.
2) Forests are cut down (and replanted) to produce lumber and pulp products (We all live in a house and we all use toilet paper, read books, etc)
3) Bio energy such as pellets is produced in order to more effectively utilize sawmill waste (sawdust, planer shavings, etc) that was once burned simply to get rid of it.
4) Forest companies (which supply products that we all demand to have) have become very innovative in utilizing by-products such as trim blocks, chips, sawdust, shavings, black liquor, hog fuel, etc to produce electricity, heat, trim, pulp and paper, and a score of other products in order to more responsibly make use of our precious forest resource.
5) Public demand for forest products has never been higher...why wouldn't companies utilize their resources in the most efficient manner?

Mar 23, 2018
6) You may very well be using electricity produced by bioenergy to read this post while you sip your tropically sourced Starbucks latte in its paper cup in a building made using timber in a concrete jungle that is destroying the planet. You have an impact...yes YOU.

Mar 23, 2018
The production of synthetic *whatever* just consumes the energy, which is supposed to generate.


So do batteries. The question is, whether the end product is less valuable or more valuable than the input.

If just one of them isn't enough, have you ever considered the possibility of 'using more' than one?
Why must a house just use just 'one' battery? Why the superfluous constraint?


That's a scale comparison, not a constraint. The point is to illustrate what sort of task we're dealing with. Just as it takes a ridiculous number of AAA batteries to be of any meaninful power reserve for a household, even the largest megabatteries we can build are equally tiny for the task of storing energy for the grids.

+ how do you propose we make these "Synthetic hydrocarbons"?

Power-to-gas synthesis, for starters. Push the synthetic gas into the gas grid, and you instantly got a hundred terawatt-hours worth of storage space almost for free.

Mar 23, 2018
This again exposes the absence of any think through by the preponderance of AGW useful idiots. Note not all of the AGW are uneducated and can't reason. Like corn ethanol the collateral and unintended consequences of renewables are not in the global environmental equation.

This is what I have seen, particularly in northern Minnesota. The damage to the forest environment and overall environment as a whole far outweighs the benefits. Most, 99.99%, of the northern forests are early first growth. It is harvested when tree diameters reach 6 inches and less. This is for pulp, wood pellets, and other wood products. When cut the entire tree, leaves, twigs, and trunk are taken. Nothing is left to return to the soil. Further the leafy mulch resulting from about 20 years of accumulation is now severely damaged. The leafy much is like a sponge. Once removed runoff increases substantially with what are now freed debris and the poor soil.

cont

Mar 23, 2018
This goes into the purest lake in the US, Lake Superior. This also denies any chance for any return to an old growth forest, which is an entirely different environment which I believe 99.99% of American's have no concept of.

When the green renewable advocates push this, why should we think that the rest of their arguments stand up to reason?

There is the real potential for clean nuclear energy. Why not put that onto the table??

Mar 23, 2018
Can you handle the concept of 'using more' batteires than some illogical totally arbitrary insufficient numbers of them for the job you personally chosen to consider.


One Elon Musk's megabattery can hold 129 MWh. That's the equivalent of a large dump-truck-load of coal. A small to medium size powerplant gobbles it up in an hour.

A country the size and population of Germany uses about 500,000,000 MWh of electricity a year. That's not including all energy, only electricity. The difference in magnitude between the two is approximately 1 : 4,000,000

This choice of comparison is arbitrary, but not illogical.

It is perfectly obvious that the energy storage must be some significant fraction of the total energy demand, We know that renewabe energy has seasonal variation in the range of 10-50% such that even hydroelectric power can produce 50% less energy year-to-year.

Current strategic energy reserves around the world typically last up to about 3 months

Mar 23, 2018
Similiarily, if you had 4 million AAA batteries, you'd have about 4,000 kWh of energy, which is about 2-3 months of your power demand in the northern hemisphere.

You might not need more than a tenth of that, some week's worth of storage, but that's still a completely ridiculous pile of batteries, even if you did use a more sensible format than AAA, and then you have to keep replacing them every 10 years because they decompose and wear out.


Mar 23, 2018
Whether is practical or not I don't know. The new class of USN super carriers launch planes via Electromagnetic Aircraft Launch System (EMALS). This requires a huge surge of energy, which batteries and capacitors can't provide. The solution is the low tech flywheel. With technology being what is it seems that this could be a load leveler. The only difference is a grid flywheel load leveler would have to hold energy for a longer time period. It might not be a great idea for cars, but a stationary flywheel would seem feasible.

The EMALS flywheel returns to its prior energy level in less than a minute.

Mar 23, 2018
In energy business the energy content is the relevant measure of value.


Yes, and in the general economics, money is the relevant measure of value.

Most of the electricity is going to go into making some sort of product, like producing fertilizers or plastics, or metals etc. and most of those processes are going to involve turning the electricity into chemicals somehow - so you might as well skip the batteries alltogether and just produce the chemicals, or their precursors. For example, case hardening steel gears for windmills require heating the gears in an oven with CO gas, and where do you get CO if not from natural/synthetic gas? These are also very large ovens that are heated by gas anyways because drawing the power from the grid would cause all sorts of transmission issues and very high costs.

Same thing with the wood pellets. They're far more valuable as chemical feedstock in the absence of oil, than being burned for simple heat.

Mar 23, 2018
the energy content is the relevant measure of value


There's also different value associated with different forms of energy, which depends on context.

For example, there might be megawatt-hours of energy in the heat of sewage, but no effective means to make any use of it, therefore it is low value energy. Electricity is high value energy for things like running lights and computers, but very low value energy if you want to produce a ton of cheap steel, but again high value if you want to make a ton of aluminium.

Likewise, in an automobile, electricity can be lower value than gasoline, because you can't carry as much electricity as you can gasoline. You may need three times as much energy in gasoline to have the same effect, but that price is negated by the fact that you need to buy zero batteries, which results in less energy used elsewhere in the economy.

The energy content per se is not -the- relevant metric of value, but -a- relevant metric of value.

Mar 23, 2018
Antialias,

We need to get to zero CO2 emissions. Biofuel doesn't make the grade. It increases global warming and destroy valuable habitat. Stop hemming and hawing.

The whole approach by your side is wrong. We need a CO2 tax, not government and politicians picking technologies. A CO2 tax will favor fossil fuels with CC2, hydro, nuclear, and conservation. Fossil fuels are not away. Their energy density guarantees that they will be used as they are economic. Even so-called Green Germany still gets nearly 90% of primary energy from fossil fuels.

Mar 23, 2018
Another clickbait article. The author of the underlying paper (if he's not being misrepresented in the article, a distinct possibility) assumes that the wood pellets are made from whole trees, when in fact they're made from scraps left over after rendering lumber from the trees. They are, in other words, made from what would otherwise be waste.

Mar 24, 2018
We need a CO2 tax, not government and politicians picking technologies.


And a CO2 tax isn't? The unintended consequence of punishing CO2 emissions is that it doesn't care where the carbon comes from, so carbon-neutral synthetic fuels get thrown out the window even if the carbon was drawn out of thin air. Even making exceptions for it would harm the transition by punishing mixed use.

The author of the underlying paper (if he's not being misrepresented in the article, a distinct possibility) assumes that the wood pellets are made from whole trees, when in fact they're made from scraps


When the demand goes up, pellets get produced out of virgin trees for a lack of scraps.

Unfortunately the chemical processing of wood into plastic and solvent industry requires more chemicals and energy


Less than starting from simpler precursors. For example, lignin in wood is already a thermoplastic. Google for Arboform, it's simply modified wood.

Mar 24, 2018
Whole trees are shipped from the US to Europe and burnt for electric power. Jungles are being cut down to produce biofuels such as biodiesel and ethanol. The renewable movement is just anti-fossil and anti-nuclear and not pro energy. When politics is the main driver of a movement logic and science take a second seat.

Mar 24, 2018
Da Snob,

Another clickbait article. The author of the underlying paper (if he's not being misrepresented in the article, a distinct possibility) assumes that the wood pellets are made from whole trees, when in fact they're made from scraps left over after rendering lumber from the trees. They are, in other words, made from what would otherwise be waste.


You're making that up, There is no waste. If not to pellets, then to fiberboard, chipboard, OSB, other product fillers, etc. Go to an Ikea and check out their furniture or a building materials store. Should twigs be left behind that is sponge and nutrients for the soil top cover.

The bark of hardwood trees creates a profitable product.

I told you that above. You prove my first point.

If it isn't used for pellets, it will be used somewhere else.

cont

Mar 24, 2018
The author:

William H. Schlesinger
Cary Institute of Ecosystem Studies, Post Office Box AB, Millbrook, NY 12545, USA.

Is located in the area where this is self evident. There are no waste piles by small mills. Some of the material is used for local farm purposes.

Don't pull stuff out of your arse. .

Mar 24, 2018
When will the madness end? Soluble nitrates and phosphate laden with uranium onto the ground for subsidized corn or other, then process the hydrocarbon into biogas with the use of energy, to make a hydrocarbons, to produce CO2 as a substitute to less environmentally damaging other fossil fuels. Thus increasing global food prices so more marginal land is put under plow with even more nitrates per acre and deforestation destroying the lungs of the planet.

Which is better for the environment, biogas or fracking oil and gas which takes near no energy to refine and is as clean or cleaner than biogas. Fracked ethane, butane, propane, hexane, etc. are far better feed stocks for plastics, fertilizers, oils, etc. than renewables. While fracked oil/gas is so superior, environments actually require Boston to import oil from Russia.

On spot, without regard for any moral values the Belgian Congo 19th early 20th century = Nazi concentration camps without fences.

Mar 24, 2018
We need to get to zero CO2 emissions. Biofuel doesn't make the grade.

I agree. It is a tideover at best.

The figure of merit is total CO2 emission from now until close to zero (i.e. sustainable) CO2 emission is reached. So we're looking at the integral of CO2 emissions over this time interval.

We need some time to change everything over to full renewables (wind, solar, hydro...possibly fusion). Renewable powerplants have to be built, storage set up, grids adapted, ...
During that time we'll have a mix which includes gas, coal and oil. If wood/biofuel can lower the amount of coal/gas/oil in this timeframe then the overal integral is decreased because while they emit net CO2 they emit far less than fossil fuels do.

So yes: biofuels aren't an ultimate solution, but they can be a benefit during the transition period.

Mar 24, 2018
Also we should not forget that coal, gas and oil are conflict materials. Some countrie have them, others don't. Some countries are dependent on fossil fuel deliveries from countries that are nominally their enemies (e.g. half of Europe gets huge gas deliveries form Russia). Wars are waged over them (Iraq).
Some countries buy up the available stocks on the world market. Other countries (e.g. many in Africa) are left behind because they cannot even now support the industries that would allow them to change over.

Biofuels can reduce this source of conflict by making countries more independent on foreign energy sources for the time being until everyone is able to supply their own needs on renewables.

Mar 24, 2018
As forests mature they soak up less and less carbon per acre.

If your goal is to maximize carbon sequestering then your optimal approach is to cut all the forests down, plant them to pasture and graze sheep, goats, cows, pigs, chickens and other livestock on them. This maximizes the cycle of carbon uptake with the fast growing forages while as a side line producing high quality food - no grain supplement is needed and virtually no petroleum is needed. Another side benefit is the soil quality improves dramatically over time with the forage growth / grazing cycle.

If your goal is to keep fossil fuels in the ground instead of adding them the carbon cycle then burning firewood makes a lot of sense instead of burning petroleum or even natural gas. Firewood also keeps the cycle local and the money in the local economy most of the time.

Either way, I would not suggest cutting all the forests down but pasture based agriculture and firewood are good tools in the arsenal.

Mar 24, 2018
As forests mature they soak up less and less carbon per acre.


How does that work?

Mar 25, 2018
@Eikka, no one is cutting down forests to make wood pellets and the article doesn't say so. No reference in the article says so, and I checked them. (The article is open access.)

You're lying about alternative energy again, @Eikka.

Mar 25, 2018


http://www.audubo...g-europe

Da If you bothered to do an internet search the info is easy to find. This article was from 2013.

Mar 25, 2018
Did you actually read the article?

Here's a quote:
For most trees, the lower 30 feet were sawed off and placed into one pile, earmarked for a lumber mill. Treetops up to 40 feet long were sorted for [a pellet mill].
That's instead of leaving it on the ground or burning it in situ or shipping the whole tree to the lumber mill where that part would be burned.

Oops.

Mar 25, 2018
You'll also find that the pellets are made from a large number of sources other than lumber waste; these include coconut shells, fruit bunch leavings, palm kernel shells, and industrial waste. https://en.wikipe...let_fuel

I did a survey of several pellet companies (high google and bing hits) and found that they claim that their pellets are made from waste of various sorts. Without an audit it's difficult to tell how true this is, but there are numerous references.

This is a controversial subject, not one that is a matter of established fact. Presenting it as fact is a lie, plain and simple. Certainly, laws that affect it need to be carefully considered and audits of the sources need to be instituted to ensure protection from activities like logging entire trees, but lumber is much more valuable as lumber, so there are at least some economic protections from this type of activity.
[contd]

Mar 25, 2018
[contd]
Here in the US West, where I live, most pellet factories use lumber and logging waste. One type of waste is dead trees from pine beetle infestations; another is the removal of stumps and branches left in a clearcut, before replanting. This has the effect of preventing further infestation by pine beetles and other pests, since they have nothing to eat. Another type is underbrush growing beneath the trees, which permits a ground fire, which is relatively slow and easy to put out, to progress to a top or crown fire, the fastest moving and most dangerous kind of forest fire. Numerous sources confirm this and have called for cutting of underbrush to prevent it; several of the largest fires here in recent history have been shown to progress in just this manner and there are calls for this type of forestry to be accelerated, with predictable whining by timber companies about who will bear the cost, and demands for the forest services and fire services to do it all.

[contd]

Mar 25, 2018
[contd]
You can drive from Southern California to Northern Washington and see clearcuts with no replanting all along the way. This is not good, but wood pellets are not to blame. The practice of clearcutting is to blame, along with pine beetle. If pine beetle gets into a stand the only way to stop it is to clearcut, and it works better if you pull the stumps too since it doesn't permit the pine beetle larvae to live beyond one season.

So if you think this is a simple issue and a stick to beat up biomass fuel with because you're a rightwingnutjob, sorry, you got no data to stand on, what you propose (lying about the sources of the pellets) is illegal under consumer protection laws, consumers are informed (to the extent they are interested, caveat emptor), and legislation is ongoing.

So bring your sources. I am open to reliable sources but typical wingnut blathering by known sources will be dismissed where it is opposed by conflicting data. The jury is still out.
[contd]

Mar 25, 2018
[contd]
I am inalterably opposed to clearcutting whole trees with usable lumber to make pellets alone. This is a waste. I am less opposed to it in cultivated lumber than virgin lumber. I do not see good evidence that trees are being cut for pellets alone, but I agree that it is a possibility. I support making laws to institute audits, supported by taxes on exported wood pellets, and laws to require environmental and carbon output statistics to support the practice.

Now let's have some actual data instead of partisan whining on both sides. Above I only mentioned right propaganda, but I have to point out that the very form of the Audubon Society requires them to present what amounts to left propaganda. I refuse to be taken in by either.

Mar 25, 2018
Oh and a new term: "Carbon positive." Perhaps even with a number to indicate the effective carbon change in the atmosphere: C+50 could, for example, designate a source that puts out 50% of the atmospheric carbon it absorbs over, say, 50 years, half an atmospheric lifetime for CO2.

Mar 25, 2018
Actually two of the pellet mills whose sites I canvassed were Canadian.

You might want to read about this a bit more before you try to make up conspiracy theories about it, @macurinetherapy. Nobody's using up good lumber trees to make wood pellets. It's not economical.

Mar 25, 2018
Now you're just making stuff up off the top of your head. This is why I call you @macurinetherapy.

Mar 25, 2018
I wonder if the author realizes that if trees are not harvested and put to some kind of use, including firewood or pellets that are burned, they will eventually die, fall down, and rot in the forest returning all the carbon they sequestered to the atmosphere. So how are wood pellets not carbon neutral!? Does the author even know what he or she is talking about?

Mar 26, 2018
I wonder if the author realizes that if trees are not harvested and put to some kind of use, including firewood or pellets that are burned, they will eventually die, fall down, and rot in the forest returning all the carbon they sequestered to the atmosphere. So how are wood pellets not carbon neutral!? Does the author even know what he or she is talking about?


Consider an old growth forest, it will have the highest amount of carbon contained within the grow-rot-grow cycle. Present forest management practices reduce total sequestration per unit of land. Wood not removed yields a net capture now. How many GtC/y could be removed if harvesting stopped would not be trivial. Here an acre will gain 10s of tons per year and it might take 100 years or more to reach equilibrium..

Mar 26, 2018
The humus (leave mulch) will increase hugely.

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