Ideas

(Carbon Sequestration)

Carbon Sequestration Source: Wikimedia Commons

This illustration shows the two principal categories of Carbon Capture and Storage (Carbon Sequestration) - methods of disposing of carbon dioxide (CO₂₎ so that it doesn't enter the atmosphere.  Sequestering it underground is known as Geosequestration while artificially accelerating natural biological absorption is Biosequestration.

There is a third alternative of deep ocean sequestration but this is highly problematic as one of the adverse impacts of rising CO₂ is ocean acidification - already impacting fisheries. 

This paper examines both Geosequestration and Biosequestration and concludes that while Biosequestration has longer term potential Geosequestration on sufficient scale to make a difference is impractical.

The Climate Impact of Carbon Dioxide

Carbon dioxide (CO₂₎ is a trace gas that has a strong greenhouse impact on the Earth’s atmosphere, reducing the re-radiation of the Sun’s heat into space.

The Earth is presently in a warming phase in its long term cycle between ice ages.  The sun is also getting hotter in its cyclical temperature variation. During the past two centuries human population has exploded and mankind has become increasingly dependent on fossil fuels that release CO₂. Warming in turn releases more CO₂ into the atmosphere from natural sources, creating a potential feedback multiplier. With close monitoring over the past 50 years (and evidence from ice cores, sediments and so on) it is now clear that anthropogenic (human generated) CO₂ is the greatest component in the observed increase; and thus a contributing factor in (rather than an outcome of) the global warming presently observed.

The total mass of atmospheric CO₂ is approximately 3,000 giga-tonnes or about 0.041% of the total atmosphere.  But this proportion is presently increasing at a rate of around 0.61% pa exponentially, so the annual rate of increase is now double the rate in the 1970's.

In 2017 World fossil sourced CO₂ production is estimated (U.S. Energy Information Administration) to have totalled around 32.5 billion tonnes (from all fossil sources, including petroleum and gas).

Electricity generation, metals smelting and the mining that supports them are amongst civilisation’s largest enterprises. Modern transportation relies heavily on oil and gas. The harnessing of non-human energy has enabled civilisations to grow exponentially since the steam age without resorting to slavery.

In 2017 coal contributed around 42%, predominantly (67.4%) used to generate electricity and for heat co-generation, and for iron production (12.3%), while oil and gas contributed 52%. Cement making contributed another 4.5%.  Lime calcination, the conversion of limestone (CaCO3) to lime (CaO), for cement, releases significant additional quantities of CO₂

These figures relate to fossil fuels only and do not include agriculture; wood and peat burning; or bush/forest fires.

The impetus for Carbon (CO₂) Capture and Storage (CCS) technology is the observed impact of CO₂ on climate change.

Yet implementing CCS represents a significant additional economic and social cost in terms of:

• additional equipment maintenance and other running costs;

• a significant drop in net fuel efficiency and consequent faster resource consumption;

• a significant increase in transportation infrastructure and its environmental impacts; and

• some very real additional dangers and safety issues. 

The climate gains made need to more than offset these costs.

For the past 50 years petroleum and gas have been the biggest fossil fuel sources of anthropogenic CO₂ but historically coal remains the major contributor and may again overtake petroleum, as oil resources are expected to be depleted first. 

The other great, and often overlooked, source of anthropogenic carbon dioxide is direct human impact on the environment’s natural storage and release mechanisms.  The natural carbon cycle produces and absorbs an order of magnitude more CO₂ than is released by fossil fuels annually.  This natural cycle is being heavily disrupted by human population growth.

Over the past 100 years human population has grown by over five billion people: from less than a billion in 1810 to less than two billion in 1910, we are projected to pass eight billion by 2024.

The impact of this vastly increased human population through deforestation, broad acre agriculture, pastoral/grazing activities, excessive consumption of water, rubbish dumping, pollution of streams, rivers and oceans, over fishing and fire lighting is thought to exceed the release of CO₂ for energy production.

In 1997 peat burning, in Indonesia alone, may have contributed as much as 10% of the total CO₂ released that year.  The pressures of overpopulation and land degradation in the third world combine with rapidly growing energy demands in the second; and too many over-consumers in the first; to make the present global warming trend a serious threat to the future of humanity.

Rapid global warming poses serious threats to economic crops and species habitat and is expected to result in increasingly rapid species extinctions. Higher atmospheric and oceanic energy levels will increase extreme weather events and change rainfall patterns.  These outcomes are increasingly evident.  The melting of the remaining land based ice and ocean expansion may inundate some economically important coastal areas and habitats. 

Although sea level rise is presently the least evident outcome of recent warming it is the aspect most focussed on in public debates.  Sea level rise appears to have been relatively continuous for the past 7000 years as land based ice has steadily contracted. 

Since accurate satellite based observations began in 1993 sea level change has been quite linear averaging 3.4 mm per year. Satellite observations accord with older tide gauge data and together these suggest that globally mean sea level has risen by about a foot over the past 100 years, in line with the long term trend. This is difficult to confirm accurately as in many places the changes in land elevation, relative to mean sea level, are greater than sea level rise due to movements in the earth’s crust.  In the Mediterranean/Aegean classical ports like Ephesus in Turkey are now six kilometres inland whereas others are under the sea.

The metre or more changes projected by glaciologists for the next 100 years are predicated on very much faster ice melting rates in Antarctica and Greenland due to accelerating warming; not on widely publicised melting of floating sea ice that has no significant impact on sea level (as pointed out by Archimedes).  While these melting effects are not yet producing unusual sea level increases, all sea level rise, particularly that due to expansion as a result of warming, contributes to greater tidal surge, altered currents and more energetic cyclones.

The recent population explosion and the shortening time frame for significant variations in the coastline, from thousands to hundreds of years, could result in mass displacements and migratory (refugee) pressure, as the 2008 Garnaut Climate Change Review (Report) warns: 

If sea level rises by a metre or more this century and as much again in the first half of the next, and displaces from their homes the people of the low-lying coasts and river banks of the island of New Guinea, it will not be a problem for Papua New Guinea and Indonesia alone.

If sea level rises and displaces from their homes a substantial proportion of the people of Bangladesh and West Bengal, and many in the great cities of Dhaka, Kolkata, Shanghai, Guangzhou, Ningbo, Bangkok, Jakarta, Manila, Ho Chi Minh City, Karachi and Mumbai, it will not be a problem for Bangladesh, India, Pakistan, China, Thailand, Indonesia, the Philippines and Vietnam alone.

If changes in monsoon patterns and the flows of the great rivers from the Tibetan plateau disrupt agriculture among the immense concentrations of people that have grown around the reliability of water flows since the beginning of civilisation, it will not just be a problem for the people of India, Bangladesh, Pakistan, Vietnam, Myanmar and China…

I'm not sure why Garnaut singled out sea level rise. Nobody is going to drown as a result of not noticing.

This is a subject in which I have direct experience spanning 50 years. I first commuted to work by ferry on Sydney Harbour in 1970 and I still use the ferries to travel to and from the city.  In that time I've noticed no less mud at the end of Mosman Bay at very low tide; nor more inundation on the flat across the Bay at high tide, where it has always flooded on a king tide. But considering the sea walls at the Botanic Gardens, I'm persuaded that the sea level has indeed risen, on average, by around a hand span, just as the satellite data suggests. I've not noticed any panic selling around Mosman.

This appears to me to be an appeal to an investor's concern about property values. Yet from an economist's point of view surely demolition and rebuilding is a normal function of economic activity, counted as economic product and therefore contributing wealth? Very few buildings are constructed to last more than 50 years. So those that come under threat can simply be demolished and build further back. Indeed, huge areas of ancient human habitation have already been inundated so we have long experience. But I'm sure one could make a case for the high cost of moving some 'great cities': it could be bad economic news for some long term infrastructure investments like the world's subways/metros and perhaps sewers.

When compared to the much more imminent impact on food crops and climate related disasters, like cyclones, floods and bushfires, that destroy far more property annually than is damaged by the encroaching sea, sea level rise seems to be a trivial concern. By far the greatest worry is the looming disaster when agriculture and fisheries are further disrupted; fresh water is in even greater demand; there is widespread ecological collapse; and the planet is unable to sustain a population of ten billion people.

Geosequestration

Sequestration of CO₂ underground: below the seabed; in depleted oil or gas reservoirs; or in deep saline aquifers is technically possible and already practiced on a small scale.

Yet the scale required, to sequester the just the current annual increase in world CO₂ emissions (around 220 million tonnes) would be an enormous engineering challenge.  It is one thing to land a man on the Moon; it is another to relocate the Great Pyramid (of Cheops) there.

Disposal of liquid or compressed gaseous CO₂: underground; below the seabed; in depleted oil or gas reservoirs; or in deep saline aquifers is technically possible and is already practiced in some oil fields to improve oil extraction.  But the scale required for meaningful sequestration of coal sourced carbon dioxide is an enormous engineering and environmental challenge of quite a different magnitude. 

Most current work is directed to finding appropriate deep leak proof geological strata below land for the purpose. Undersea sequestration would be an engineering challenge on an even greater scale, and potentially very damaging to ocean organisms coral reefs and fisheries.

As a result of simple chemistry the underground volume required to dispose of carbon dioxide, is substantially greater than that of the coal or the oil that produced it.

For example, the CO₂ produced by burning a tonne of coal is well over twice the weight of the coal used to generate it and the volume (even after being compressed to a liquid) is around five times greater (see the box below):

Thus transporting the CO₂ from the furnace is undertaking that is two to five times the scale (by weight and volume) of delivering the coal that generated it.   

Under CCS, getting the CO₂ from a power station to the sequestration site and injecting it is a much bigger job than mining the coal and transporting it to the power station. This means that the existing power stations are the wrong technology in the wrong place for CCS.  They would need to be located on good sequestration sites; as opposed to being close to the source of coal.

But there are additional reasons to doubt that CCS can be generally applied, even if a new generation of plants make capture economically feasible.

As I have official data for New South Wales Australia (NSW) I will use these as a hypothetical CCS project to illustrate the issues.

The annual production of CO₂ from stationary electricity generation in NSW in 2017 was 66.2 Mt CO_2e.

To put this into perspective:

• These coal burning power stations contributed less than 12% of Australia's annual production of CO₂ in 2017.
• In the same period Australia contributed just 1.16% of global world CO₂ production. 
• So if the following CCS example could be fully implemented it would reduce annual, global fossil sourced CO₂ emissions by 0.14%

Let's assume the whole 66 million tonnes of CO₂ is liquefied. We have seen (above) that it would compress to around 56 million cubic metres (56 GL). Pumped underground this would occupy a volume of about five and a half thousand hectares (13,480 acres) in area one meter thick - every year. Of course it would be dispersed through the strata but unless the strata had many voids the surface would rise in a reverse of the subsidence caused by long-wall underground mining.  It would damage property and seriously disrupt any underground aquifers. 

To be more realistic it's unlikely that the entire output of CO₂ could be captured. Yet to have any impact at all on global carbon emissions and thus climate change, hundreds of thousands of tonnes of CO₂ would need to be sequestered over the life of each new fossil fired power station. Apart from the mass and volumes involved there are handling difficulties. 

At less than 5 times atmospheric pressure liquid CO₂ undergoes a phase transition and becomes a solid, dry ice. To keep it liquid it needs to be kept at a pressure well in excess of five atmospheres[6] at -56.4o C. At ambient temperature it needs to be kept at above 60 atmospheres to remain liquid. To be pumped across the countryside in uninsulated pipelines it needs to be above the critical point pressure of 73 atmospheres.  Any loss of pressure, due to a rupture or a loss of power, may well result in its boiling to gas followed by solidification of sections of the pipeline and/or damage the pumps.

Ordinary carbon steel corrodes in the presence of moist CO₂ and the pipelines need to be lined or made of stainless steel. A very significant and entirely novel infrastructure of large diameter high pressure pipelines and pumping stations will be required.  The pumps need to move large tonnages and volumes of liquid, comparable to a good sized city’s water supply, at very high pressures.

This will consume a lot of energy. The initial compression of the gas to liquid needs to overcome the latent heat of liquefaction of CO₂ (approx 160 kWh/tonne). 

Continuing with the NSW example, according to its Wikipedia entry[7]Liddell power station releases an estimated 14.7 million tonnes of CO₂ to generate 17,000 GWh per year. Assuming no inefficiencies, compressing this gas would consume 14.7 x 160 = 2,350 GWh per year or about 14% (and probably a lot more) of its electricity output. 

As it is expected that this liquid would be pumped into porous strata, where it will fill interstitial voids to perhaps 10% of the volume, several thousand square kilometres of strata would be required annually. These volumes would also require hundreds of kilometres of high pressure distribution pipeline and hundreds of injection bore holes the diameter and depth of oil wells. 

Within a few years, the underground sequestration site (or sites) required for CO₂ would underlie hundreds of thousands of hectares of countryside with high pressure liquid/solid phase CO₂ that would pose, probably insurmountable: geological; engineering; environmental; aesthetic; safety; and cost issues.

To this needs to be added the unknown, but substantial, energy required for transportation to the sequestration sites and for underground injection, as well as vast additional infrastructure; capital and running costs.  Existing gas pipelines burn some of the gas to run pressure booster pumps along the string but these would need to be electric for CO₂, involving additional high voltage lines and inevitable grid losses.

Clever integrated design may potentially reduce some of these overheads (for example some of the heat released during compression may be recoverable at the compressing power station) but it is probable that the additional infrastructure and energy overheads required for CCS would make any future coal fired station so inefficient and resource consuming as to be impractical.

Pumping a few thousand litres down a hole at a test site proves little.  Small scale return of to oil wells has been employed for many years.

Safety Issues

There are a number of safety issues relating to an envisioned new generation of coal fired power stations with CCS.  Coal fired power generation is already intrinsically unsafe and adding CCS would substantially increase these risks and probable deaths. 

Mine and coal transport accidents outnumber deaths and injuries in any competing technology, ash releases remain substantial (despite the advent of bag houses and precipitators). Acids, mercury and other compounds released from flue gasses cause substantial environmental and health damage. 

The health burden of fine particle pollution from electricity generation in NSW, by leading epidemiologist, Dr Ben Ewald investigated the serious health damage NSW’s five coal-fired power stations are causing. The study concluded that each year the power station emissions cause: 279 premature deaths; 233 low birth weight babies (less than 2500g); and 361 new cases of type 2 diabetes.

The US National Council on Radiation Protection and Measurements (NCRP) estimates the average radioactivity of coal is 17,100 millicuries/4,000,000 short tons resulting in a radiation dose to the population from a 1000 MW coal fired plant of 490 person-rem/year; a hundred times more than from a comparable nuclear plant.

The use of ammonia or amides to flush CO₂ from flue gasses (if used) poses additional safety and environmental concerns.  Ammonia is a mildly toxic gas (and liquid) and can cause lung damage and death in humans exposed to concentrations above 400 parts per million. It is highly soluble in water and extremely toxic to aquatic animals. Thus ammonia is potentially environmentally damaging if accidentally released; or if traces remain in the CO₂ stream. Ammonia and amide production facilities also consume relatively high levels of electricity. Alternatives such as membrane technology may solve some of these issues in future.

Adding very large volume movements of CO₂ to this list may be the final ‘show stopper’ for environmental scale CCS.  CO₂ is a relatively non-toxic gas, compared to ammonia, but at around 10% by volume in air it is lethal to humans (anything over 4% is considered very dangerous[8], it is normally under 0.04% in air). The last large natural release of CO₂ was at Lake Nyos in Cameroon in1986.  It killed nearly 2,000 people and all the animals, birds and insects too. It is heavier than air and fills depressions. Depending on concentrations, internal combustion engines may stop, compromising any rescue attempts.  Moving large volumes about the countryside poses significant risks to people and animals.

If CCS was fully implemented for the power industry alone, in just 20 years 1.3 billion tonnes of CO₂ would underlie many hundreds of thousands of square kilometres of rural NSW, in an as yet unabsorbed state. 

Theory has it that in about 10,000 years it will have been fully integrated with the rocks into which it is pumped.  It might then be safe, unless there is ever an igneous intrusion or meteor impact in the area.  But if in the meantime just some of the sequestered CO₂ escaped somehow, due to a borehole malfunction, miscalculation of capacity or an earthquake, Chernobyl (57 direct deaths and 4,000 potentially injured by future cancers) could look like a picnic; and a fraction of a square kilometre of nuclear waste storage, a trivial problem for posterity.

Token projects, of the kind already attempted and mostly abandoned, that sequester a fraction of a facility's CO₂ make such a small difference that they are pointless. Indeed, because of the substantial additional energy consumed to extract compress and pump underground, the overall CO₂ released, to deliver the same energy to market, is likely to increase net CO₂ released to the atmosphere. 

Clearly Geosequestration is no panacea.

Biosequestration

As previously mentioned the vast proportion of CO₂ in the atmosphere is naturally released and is in turn naturally absorbed.  Some is dissolved in rain and ultimately acidifies the oceans but a great deal is absorbed by plants in the process of photosynthesis; consuming water and usually releasing oxygen. 

This is a natural solar collector.  Plant absorption is increased if CO₂ levels rise and plants have access to sufficient water and sunlight.  Trials have been undertaken at higher CO₂ levels with a number of existing economic plants to determine such things as the ‘fertiliser effect’ higher water uptake and increased solar absorption. 

Obviously producing biofuel or food does not permanently sequester carbon and any credit should only apply the solar energy collected by the process; as this, in turn, reduces dependence on other energy sources. To get a full credit, similar technology might produce cellulose that could be charred and buried to improve soils or other carbon rich materials that could be safely buried in depleted mines or other suitable sites. Charing and burying of bagasse, straw and wood-waste is already a recognised sequestration technology.

Natural biosequestration is happening already.  Accelerated Biosequestration is more problematic, in part because the CO₂ emitted by industrial processes is dirty and if used directly would kill most plants or algae. So it must first be cleaned and this can be both difficult and expensive.

It is clear that accelerated CO₂ absorption by conventional agriculture and plants, for example by reticulating CO₂ to greenhouses or forests, would be costly and would not fully deal with the vast quantities of CO₂ involved.  But some plants and bacteria evolved when CO₂ levels were very much higher and it appears to be possible to exploit their genome to modify them or other plants and organisms, to produce economically useful materials; at the same time absorbing large volumes of CO₂.

Several projects are already in underway internationally.  The most interesting involve algae that could be used to produce diesel fuel, directly or as chemical feedstock.  Other, possibly complimentary, options include modifying food crops like rice (to a C4 plant) so that additional CO₂ and sunlight are absorbed (and carbohydrate yields improved).

Again the problem is the scale required to make a difference. A very large solar collection area is required together with plentiful water.  Areas comparable to present broad acre agriculture will be required, probably as shallow lakes.  It would be particularly useful if algae that are comfortable in salt water could be adapted.

Again there are safety issues to be considered. These vast lakes or fields will be filled with genetically modified organisms and the regulatory environment relating to GM organisms and foods would need to be changed accordingly. 

Like the introduction of the Cane Toad to Australia, the cure could well turn out to be worse than the disease.

Alternatives to creating emissions

Most Australian proposals to limit carbon dioxide emissions have remained silent on ‘the elephant in the room’: the role of nuclear power in achieving lower carbon emissions in other countries.

No doubt the silence on nuclear power is politically astute and/or avoiding controversy.  For example the 2008 Garnaut Climate Change Review was not concerned with the actual methods employed and assumes that whatever technology becomes profitable will be used.

Almost all power engineers acknowledge that nuclear power is currently the only practical alternative to coal; wind and solar just won't cut it. There are now several hundred new nuclear power plants in planning and under construction worldwide and China alone is projecting 300.

If carbon sequestration is impractical on a scale that would make a difference, and this paper asserts this is so, it is virtually certain that the impact of an effective emissions reduction initiative would be to make nuclear power inevitable in the new energy mix. This mix would no doubt include increased use of other economic alternatives like solar and wind. 

Photovoltaic solar is already cost competitive with nuclear power in some circumstances and may replace part of our electricity needs as technological progress is made but solar panels do not provide this energy continuously without costly batteries.  While their use is widespread domestically 'going off-grid' is difficult without some complementary source of energy - for example gas.

Where wind is plentiful, wind turbines can make a substantial contribution, but again some means of energy storage is needed to fill those times of peak demand when there is insufficient wind.  This is discussed in more detail elsewhere on this website.

Nuclear electricity is the ‘next best’ economic alternative to coal and as outlined above the engineering challenges involved are trivial compared to CCS. 

If this is so, we have a good idea of what the world aught to look like. Why go through the difficulty of implementing economy distorting mechanisms like those proposed by the Garnaut Climate Change Review, with unknown side effects, when we can simply identify the technology changes we want and implement them? 

When changing to a new phone or television standard we do not tax the old technology to make the new attractive; we simply say that from such and such a date we will no longer use the old and everyone needs to make the appropriate transition arrangements.

One gets the impression that if the authors of the Garnaut Climate Change Review had been engaged to design and build the Sydney Harbour Bridge they would have proposed, instead, a tax on ferries.

To achieve the desired outcome of a transition to nuclear electricity without hidden economy distorting market mechanisms, NSW (and other states, perhaps with explicit Loan Council support or Commonwealth transition funding) could simply take action to progressively replace the present coal burning power stations with similar or possibly larger nuclear stations in the same or similar locations. Existing transmission and other generator independent infrastructure could then be used, minimising cost.

Local employment impacts would be minimised, employees and local residents would be healthier and safer. With appropriate advice and information this improved greenhouse, safety and employment environment would minimise any ‘not in my backyard’ objections to the changes.  The new stations would provide carbon free electricity to support existing industrial and residential purposes and provide for future growth, at a price competitive with that under the Garnaut Climate Change Review proposals.

Additional electricity capacity could be provided for electric trains, public road transport and private cars. These will inevitably become more attractive as oil prices rise and government infrastructure catches up with almost every other comparable city and country in the World.

We will know we have caught up when Sydney (and possibly Newcastle) has a proper Metro network of several intersecting lines linking up-market residential, retail and employment nodes across the city; the State has an updated 25KV electrified freight rail network; and there is a separate very fast passenger train service, at least down the east coast.  These will substantially reduce the transport use of fossil fuel and encourage urban consolidation around the new stations.  New industrial lands could be developed around freight hubs. Technological progress and local industry will be encouraged and stimulated by moving the State’s infrastructure into the 21st Century.

The relative cost of energy is, in any case, expected to increase under existing (undistorted) market mechanisms, encouraging increased energy efficiency.  Most experts predict that oil will increase in price relative to coal and together with new battery technology will encourage the development of new electric and hybrid transport. 

As nuclear power would only replace coal for electricity generation and indirectly for transport, coal would continue to be sold overseas (just as we presently sell uranium but do not consume it; conscious that NSW coal will remain a tiny fraction of the coal consumed worldwide) and used (at an undistorted price) in local metals smelting where there is no alternative.

Conclusion

As a substantial solution to carbon dioxide caused climate change, on sufficient scale to make a difference:

• Artificial Biosequestration may have longer term potential; but
• Geosequestration is impractical as a meaningful solution to the continued use of coal.

Footnotes: