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Could pyrolysis save the planet?

There is only one technology that we know of that can reliably suck carbon dioxide out of the atmosphere and sequester it. Photosynthesis. It is what every plant on the planet does every day.

By Mike Ritchie, MRA Consulting Group

Humans have been great at releasing CO2 to the atmosphere and singularly useless at capturing it again.

But could we harness the power of plants at a big enough scale to offset our growing emissions profile?

The answer is yes and the technology could be pyrolysis combined with plant photosynthesis.

To recap, we have been very efficient at finding and burning “old” carbon (coal, oil and gas) in the form of fossil fuels that was created by plants eons past and laid down in sedimentary layers. We have dug up and burned that carbon and by doing so added it to the “new” carbon cycle or the biosphere where we and all other life live.

All of the plants and animals, soil carbon and atmospheric carbon we know can be thought of as “new” carbon. The “old” carbon is the stuff we dig up.

So we have overloaded the new carbon biosphere with old carbon by the burning of coal, oil and gas. That old carbon creates additional carbon dioxide which adds to the normal warming effect of atmospheric CO2, causing global average temperatures to rise.

So we are having an active debate about how we wean ourselves off “old” carbon sources and move to renewables. Good.

But we should also be discussing our capacity to convert new carbon into old carbon by use of new technology.

In particular, can we engineer fast growing plants to suck carbon out of the atmosphere and somehow sequester it in soil so that it becomes “old” again and no longer contributes to the active biosphere.

The answer is yes.

forest with tall trees illuminated by sunlight
Photo by Harry Cooke on

We could grow plants, sequester atmospheric CO2 in lignocellulosic biomass (leaves, branches and woody material of plants) and then using pyrolysis convert this lignocellulosic biomass into biochar (which is a highly stable form of carbon, similar to coal).

That biochar can be crushed to powder, mixed with nutrients and used as a fertiliser on farms to improve plant growth. The carbon in biochar is so stable that it will not decompose. It will remain locked in the soil indefinitely. Its ability to cause climate change is zero.

This system is very different to “clean coal”. Clean coal proponents suggest that they can capture atmospheric CO2 and pump it underground under pressure and store it permanently in rock fissures. The technology has been riven with technical failures, massive cost overruns and is now pretty much discredited by experts.

Biochar on the other hand is known, low risk and has the incredible benefit of enriching soils with carbon and additional nutrients. The capacity of our soils to soak up carbon in the form of biochar is also almost unlimited.

Wow. OK how do we make that happen? Could we do it at enough scale to make a difference?

That is the million dollar question. There has been very little serious research into scaling up biochar processing.

Most pyrolysis facilities around the world are small scale and designed to produce high quality biochar.

MRA recently completed an analysis of the cost of biochar and pyrolysis to replace “clean coal” as a mechanism to offset coal fired power station emissions (or any other emission generator). The findings of that study were:

Using very conservative assumptions, MRA found that the cost of sequestering one tonne of CO2-e through pyrolysis, including obtaining and pyrolyzing wood and spreading the biochar to fields could range from less than a dollar (where the waste producer pays to dispose of the wood) to a maximum of about $95. Conversely, the cost of carbon capture and storage was calculated at $115/t of captured CO2-e. Other studies put the cost even higher, from $130 to $300 and even $750. The price difference is significant.

Not only is biochar cheaper but it also provides a host of other benefits and puts Australia firmly into the path of a more circular economy.

Clearly the idea of growing plants and pyrolyzing them to create biochar requires further investigation. It should be a priority of the coal and gas industry as well as of governments.

We would all benefit if we could create a scale mechanism to convert “new” carbon into “old” carbon and sequester it. That would seriously reduce the threat of climate change and sea level rise.

Why it has not featured in policy discussions is a mystery to me.

But I suggest the time is right to bring pyrolysis in from the dark. And of course, as Scott K. Johnson put it, not spilling a drink is still cheaper than buying a towel to clean it up.

As always, we welcome your feedback on this, or any other topic on ‘The Tipping Point’.

This article has been published by the following media outlets:

Waste Management Review, 29 January 2021


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