Understandable Earth Science

Posts tagged ‘GHG’

Gas sample collection at PACT – Investigating how the CC influences monitoring of the S!

In January 2016, Stuart Gilfillan and I (Stephanie Flude) made the long drive from Edinburgh to Beighton, Sheffield to collect some gas samples from UKCCSRC’s Pilot-Scale Advanced CO2-Capture Technology (PACT) facility. The PACT facility hosts a state of the art, pilot-scale CO2 amine-capture plant that can capture CO2 in flue gases from either a 250kW air/oxyfuel combustion plant (that can burn coal, biomass or gas) or one of the two 330kW gas turbines also hosted at the facility.

The PACT Core Facility entrance and the amine capture absorber and desorber columns.

As we are Earth Scientists, rather than Engineers, we are researching reliable means to trace the fate of CO2 once it has been injected below ground for geological storage. As part of that research we are investigating how the captured CO2 itself can be used as a geochemical tracer. This means I have spent much of the last couple of years tracking down sources of man-made CO2 to sample, and swapping my usual field gear – walking boots, waterproof coat and rock hammer – for steel toe capped shoes, hi-vis jackets, torque wrenches and high pressure hosing. We wanted to collect as many different types of CO2 as possible – from different capture techniques and from different feedstocks, and so collecting samples from PACT was an obvious option.

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Our typical gas sampling equipment – no rock hammers here!

We had arranged to visit while both biomass and natural gas were being air-combusted in the 250 kW plant, allowing us to collect samples derived from two different fuel stocks. We were also hoping to collect gas samples from different parts of the carbon capture system, so we could better understand, and ultimately predict, what controls the inherent fingerprint of captured CO2. For this, we wanted to collect samples of the fuel, the combustion flue gas, the residual gas from the amine absorber column, and the final captured CO2:

pact-schem

Schematic of our ideal gas sampling strategy.

The staff at PACT were very keen to help us collect this range of samples, but early discussions raised some problems with how to collect the samples. The PACT facility had been designed incredibly efficiently, with multiple gas analysis instruments housed on site that directly tap and analyse the gas of interest. Unfortunately for us, this efficient design meant that very few external sampling ports were installed on the system – why add sample ports when you can simply flow the gas you want straight to your analyser? After discussions with Kris Milkowski and Martin Murphy, we settled on the idea of collecting samples from the exhaust vent of PACT’s FTIR system, with some supplementary samples collected straight from an external tap on a combustion flue gas pipe.

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Stuart collecting a sample of combustion flue gas from the flue pipe

Once on site, we spent a few minutes working out the best way to connect our sampling equipment (copper tubes, clamps, and gas-sample bags) to the available ports and how to ensure a strong enough flow of gas to sample. We collected from the flue pipe first and then moved across to the FTIR hut. Sampling here was a little more hectic as we had a 4 minute window to collect the sample while the FTIR was purging the gas of interest. We need to be very careful to avoid air contamination in our samples, and standard procedure for this is to purge our equipment with the gas we are collecting for at least two minutes, leaving just two minutes to collect the sample and hook up the sampling assembly for the next sample.

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Stuart explaining our sampling procedure to Kris in the FTIR hut.

By the end of the visit, we had managed to collect combustion flue gas, absorber outlet, and captured CO2 from both gas and biomass feedstocks. With the critical sampling tasks out of the way, we were treated to a tour of the combustion rig by János Szuhánszki.

Janos introducing Steph and Stuart to the combustion rig.

So what happens next? We have spent the last year analysing the samples for their inherent geochemical and isotopic fingerprint.  We have measured the carbon and oxygen isotope composition (δ13C and δ18O) of the captured CO2, and concentrations and isotope ratios of trace noble gases (helium, neon, argon, krypton and xenon) that are present in the captured CO2 stream. The results have just been submitted in a manuscript to the International Journal of Greenhouse Gas Control, so keep an eye open for that in the near future.

A version of this article also appears on the UKCCSRC Blog site.

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Why we need to stop emitting CO₂ – A.S.A.P.!

In my first climate-related blog I talked about why I was so angry that the world wasn’t taking action to prevent climate change – 10 years ago the wedges concept, introduced  by Pacala and Socolow [1], gave a clear prediction of how our annual CO₂ emissions were increasing and identified ways to reduce emissions. Back then, the world was still thinking in terms of how CO₂ *emission rates* affect climate change. Since then we have realised that emission rates are relatively unimportant and that global cumulative CO₂ emissions are what we need to keep an eye on.

This is because CO₂ has a long residence time in the atmosphere – if we were to completely stop burning fossil fuels and emitting CO₂ today, it would take up to 35 thousand years for all of the CO₂ we emitted since the industrial revolution to be re-absorbed [2] (if you want to know more about that, there is a nice blog here). This means that our CO₂ emissions over decades, even centuries, are pretty much instantaneous on the carbon-cycle timescale.

CO₂ residence

Figure 1: Carbon is stored as fossil fuels for millions of years. When we take it out of the ground and burn it, we are releasing CO₂ instantaneously on geological timescales. It then takes tens of thousands of years for that CO₂ to be removed from the atmosphere and be stored long-term in the Earth.

The amount of global warming will be controlled by the amount of CO₂ hanging around in the atmosphere, and, because it hangs around in the atmosphere for so long, that is controlled by the total amount of CO₂ we have emitted, rather than how fast we are emitting it. In 2009, Allen et al [3] calculated the Earth will warm by ~2 °C for every 3.67 trillion tonnes of CO2 that we emit [4]. If we want a good chance of avoiding global temperature rise of more than 2 °C, the most CO2 we can emit is 3.67 trillion tonnes – total! period! ever!.

Reducing emission rates just delays the 2 °C temperature rise – it doesn’t prevent it. Stabilising emission rates buys us time but doesn’t solve the problem. The only way to solve the problem is to completely stop emitting CO₂.

This next diagram, simplified  from the IPCC 2014 report (Figure SPM.5, p9 [5]), is a nice illustration of  how much we can expect the global temperature to rise because of the total amount of CO₂ we emit. The x-axis shows cumulative CO₂ emissions since 1870 in gigatonnes of CO₂. (GtCO₂) The y-axis shows the temperature increase compared to pre-industrial temperatures. There are different ways of modelling the climate response to carbon dioxide emissions, and that is why this graph is plotted as a grey band, rather than a single line – the band represents the range of expected global warming according to lots of different models and calculations. Those different models and calculations all agree pretty well.

Expected warming from CO₂ emissions

Figure 2. Global warming due to total CO₂ emissions with observed data and future predictions for different mitigation strategies

According the graph, when we have emitted 3670 Gt CO₂ (3.67 trillion tonnes), we can expect the global temperature to have risen between ~1.4 and ~3.1 °C (black dotted line shows 3.67 trillion tonnes vs 2 ܄C).

The black ellipse labelled “Observed” plots our actual total CO₂ emissions between 1870 and 2005 against the observed warming (as an average of the years 2000 to 2009 compared to an average of the years 1861 to 1880). As you can see, it fits the predicted warming very well.

The red line shows the cumulative total CO₂ emitted as of today [4], December 23rd 2014 (2150 Gt CO₂) and that, no matter what happens, we are already committed to global warming of between 0.8 and 1.8 °C.

The other ellipses are predictions for the amount of CO₂ we will have emitted in the year 2100 for different CO₂ mitigation strategies, and the amount of global warming we would expect. Figure 3, below, is simplified from Figure SPM5 of the IPCC 2014 report and shows the corresponding CO₂ emission scenarios. The blue scenario (blue ellipse in Figure 2, blue band in Figure 3) represents the likely outcome if we use an aggressive strategy to cut CO₂ emissions and are actually able to completely stop emitting CO₂ and start creating negative emissions – actively taking CO₂ out of the atmosphere faster than nature. The yellow scenario represents a CO₂ reduction strategy that sees us managing to stabilise global CO₂ emission rates at their current levels (i.e. the emission rate doesn’t increase) and then decrease emission rates in about 30 years time. In this scenario, we would still be releasing around 50 Gt CO₂ every year, to start with, and that means we would have spent our CO₂ budget within about 30 years; by 2100 we would have emitted 4-5 trillion tonnes of CO₂ and would see global warming of 2.5 to 3 °C. The orange scenario shows what would happen if we slow the increase in emission rate and stabilise CO₂ emissions in about 3 years time – by 2100 we would have emitted ~ 6 trillion tonnes of CO₂ and would see global temperature rises of 3 – 4 °C. The red scenario represents “business as usual” – what we would expect to happen if we didn’t make any special effort to reduce CO₂ emissions. In this scenario, emission rates would continue to increase over time and we are looking at > 6.5 trillion tonnes of CO₂ emitted with temperature rises of > 4 °C by the year 2100.

Predicted CO₂ emissions

Figure 3: Predicted annual CO₂ emissions over time for different mitigation strategies

In summary, if we want a good chance at avoiding a 2 °C global temperature rise, then we can’t emit more than 3.67 trillion tonnes of CO₂. We have already emitted more than half of that in just the last 145 years. Our global CO₂ emission rates are continuing to rise and if we don’t take action quickly, we will have reached that limit within 30 years.

Notes and references:

[1]  Pacala, S. & Socolow, R. Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies. Science 305, 968–972 (2004).

[2]  Archer, D. Fate of fossil fuel CO₂ in geologic time. Journal of Geophysical Research 110, (2005)

[3] Allen, M. R. et al. Warming caused by cumulative carbon emissions towards the trillionth tonne. Nature 458, 1163–1166 (2009).

[4] Reference [3] talks about “the trillionth tonne” – why are you talking about a budget of 3.67 trillion tonnes?

CO₂ emissions can be described in terms of mass of CO₂, or mass of C (i.e. the mass of carbon in carbon dioxide): The element carbon has an atomic mass of 12 and oxygen has an atomic mass of 16. So carbon dioxide has a molecular mass of 44, which is 3.67 times greater than the mass of carbon. Allen’s paper [3] and the website http://trillionthtonne.org/ both discuss CO₂ emissions in terms of mass of carbon – emitting 1 trillion tonnes of carbon (as carbon dioxide) will produce 2 °C warming. To convert this to mass of CO₂ we just multiply by 3.67. The graphs I used in this blog post used emissions and emission rates for CO₂ rather than just C, so I used CO₂ emissions and emission rates to make things simpler. The 2150 Gt CO₂ I quoted as having been released between 1870 and today was calculated by looking up the real-time cumulative total C-emissions from http://trillionthtonne.org/ (586 Gt) and multiplying it by 3.67.

[5] http://ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_LONGERREPORT.pdf

Dear World Leaders – WTF do you think you are doing??!!??

Is it too late for us to maintain our comfortable western lifestyles AND avert catastrophic climate change?

Despite all of the lobbying from climate sceptics, the absolute vast majority of scientists have, for years, agreed that release of CO₂ into the atmosphere by humans (both from burning fossil fuels and from cutting down forests for farmland) is the main cause of global warming, and that YES, planet Earth is warming much faster than it would without all that extra CO₂ in the atmosphere.

For years there has been a general agreement in the scientific community that we need to keep CO₂ concentrations in the atmosphere at less than 500 ppm (parts per million – that is the equivalent of 0.05%) if we want to avoid raising the average surface temperature of the earth by 2 °C, which is the maximum temperature rise the Earth can tolerate without irreversible, catastrophic (for our way of life and economy) climate change[1].

Back in 2004, when atmospheric CO₂ levels were ~375 ppm and global CO₂ emissions were ~ 7 billion tonnes of carbon per year, a paper published in Science by Pacala and Socolow[2] looked at our current global CO₂ emissions, the rate they have been increasing and how this affects the concentration of CO₂ in the atmosphere. They calculated that, if we are going to keep the atmospheric concentration of CO₂ below 500 ppm over the next 50 years, annual carbon emissions cannot increase above 7 billion tons per year – i.e. they had to stay the same as in 2004. They also calculated what our carbon emissions would be in 50 years’ time if the rate of emission increased “business as usual” – i.e. if we continued generating more power and emitting more CO₂ without making any effort to reduce emissions. They calculated that, in 2054, our carbon emissions would double to around 14 billion tons per year. That meant, we needed to find a way to reduce carbon emissions by 7 billion tonnes over the next 5 years, and we needed to start doing it quickly.

Wedges1

This graph (after Pacala and Socolow, 2004) compares the maximum amount of CO₂ we can emit per year whilst avoiding raising the atmospheric CO₂ concentration above 500 ppm (blue line) and an estimate of how much CO₂ we will be emitting if we carry on as normal (red line). In short, CO₂ emissions needed to stay the same as they were in 2004 to avoid major climate change. Unfortunately, as the world population increases, and developing countries gain a better quality of life, more energy is consumed and more CO₂ is produced.

But there was hope! Pacala and Socolow pointed out that, even back in 2004, there were plenty of options for reducing our CO₂ emissions – they just needed scaling up. They identified 15 different ways that we could start to reduce our CO₂ emissions by increasing energy efficiency, decreasing energy use, changing land-use, switching to lower carbon power generation and capturing and storing CO₂ from power plants.

To make the task even less daunting, Pacala and Socolow came up with the concept of “stabilisation wedges” (if you look at the space between the red and blue lines on the above diagram, it is kind of wedge shaped). This means that all we needed to do in the short term was to make small changes to reduce our CO₂ emissions, and gradually scale them up to make bigger changes in the long term. To make things even easier, this wedge was split up into 7 separate wedges that were each the equivalent of saving 1 billion tonnes of carbon per year after 50 years. All we needed to do was pick 7 existing CO₂ reduction methods from the list and scale them up so that in 50 years time, each of them would be reducing our carbon emissions by 1 billion tonnes every year. If we include these 7 wedges on the above diagram, it starts to look something like this:

Wedges2

This was brilliant! Pacala and Socolow identified a very real and dangerous problem, but importantly they gave an achievable solution. We could avert catastrophic climate change, if we just started using and investing, NOW, in low-carbon technology.

So what happened?

Fast forward to 2013 when Davis and others published a paper in Environmental Research Letters[3]. They looked at recent CO₂ emissions and worked out whether the wedge system would still work. They showed that in 2010, just 6 years later, worldwide carbon emissions were already more than 9 billion tonnes – that is much higher than Pacala and Socolow predicted for “business as usual”. Not only had the world failed to stabilise CO₂ emissions, it had increased emissions much faster than predicted. Davis et al worked out what would happen to atmospheric CO₂ concentrations if we started implementing the stabilisation wedge NOW. First of all, they worked out that at least 9 wedges would be needed to just *stabilise* carbon emissions over 50 years (i.e. keep emissions at 9 billion tonnes per year). Then they looked at how this would affect the total amount of CO₂ in the atmosphere and calculated that there would still be more than 500 ppm CO₂ by the year 2049;

If, today, we were able to stabilise CO₂ emissions at the same level as they were in 2010, we would reach that scary threshold of 500 ppm CO₂, or a 2 °C global temperature rise in less than 40 years!

I am scared! I am angry!

10 years ago (I am writing in August 2014), the problem of greenhouse gases and climate change was a big scary problem, but it might have been possible to avoid the worst of the damage by starting to make relatively small changes and investing in the right kind of technology and development.

Today, it is too late for that. To prevent 500 ppm of CO₂ in the atmosphere, we need to not only stabilise CO₂ emissions, we need to drastically reduce them. This is because the concentration of CO₂ in the atmosphere responds to the absolute amount of CO₂ we pump out, rather than just the rate we pump it out at – yes, if we pump it out faster, we increase the concentration faster, but if we keep emission rates the same, we are still increasing the concentration and eventually it will become too high; all of the CO₂ we have pumped out since the Industrial Revolution won’t just magically disappear overnight, especially while we continue to cut down forests to make way for farmland. Pacala and Socolow recognised this in 2004, but hoped that new technology would be developed in the next 50 years to not just stabilise, but reduce and maybe eliminate CO₂ emissions. The wedges concept was supposed to be a kickstarter – a way to start taking action to protect our climate NOW. It wasn’t supposed to be a magic wand that can be waved whenever we feel like it – it was a way of  buying us time (50 years) to develop ways to stop emitting CO₂ completely.

Here is what the CO₂ wedges diagram looks like today, adapted from Davis et al, 2013:

Wedges3

I have left on the 2004 “business as usual” prediction line so you can see just how much extra CO₂ we are emitting, compared to what was expected. The red stars show the annual global emissions from 2006 – 2013[4].

Davis et al worked out that now we might need to use as many as 31 wedges just to delay the 2 °C temperature rise until 2060. They also calculated that 1 wedge is the equivalent of creating ~ 1 TW (terrawatt – 1 TW = 1 billion kW) of carbon-free energy. For comparison, the London Array, which is a wind farm of 175 wind turbines and one of the largest wind farms in the world, has a peak-capacity output of 630 megawatts[5] – that is 0.00063 TW. You would need 1600 London Array windfarms, all operating at maximum capacity all of the time, to create just 1 carbon wedge (also consider that most windfarms operate at ~one third efficiency, so 4800 London Array windfarms per C-wedge is more likely).

10 years ago we had an opportunity to prevent long-term damage to our infrastructure and quality of life by making small, gradual changes and small sacrifices to our quality of life and by investing in and developing low-C technologies.

We may have missed that opportunity. Why? Because we all sat back and ignored the problem. We elected governments who give jobs such as “Secretary of State for Environment, Food and Rural Affairs” to climate sceptics. We are more concerned about paying less money for our energy than investing in renewable and low-C energy. We are more concerned about how a wind-farm will alter the view in the British countryside than sea-level rise swallowing entire island-nations. We allow our governments to give in to lobbying from industry when they should be implementing measures that force us all to adopt low-C technology, not just so we can reduce our own emissions, but so that we can fully develop and share this technology with the developing world who can’t yet afford to develop it themselves.

As you can see from the title, I initially addressed this blog to the World Leaders who have failed to take appropriate action on preventing man-made climate change. However, we are all responsible. Each-and-every-one-of-us! The threat of climate change is real and it is scary! Please remember that when you are voting / switching energy provider / buying stuff.

 Footnotes and references:

[1] This is actually much higher than the “safe” concentration recommended in a 2008 paper by James Hansen and others published in the Open Atmospheric Science Journal (http://benthamopen.com/openaccess.php?toascj/articles/V002/217TOASCJ.htm). They noted that the last time there was more than 450 ppm CO₂ in the atmosphere was around 50 million years ago, back when Antarctica was completely ice free! and they suggested that we need to limit CO₂ concentrations to a maximum of 350 ppm to avoid catastrophic, irreversible climate change over the next few decades.

[2] Pacala, S. and Socolow, R., 2004. Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies. Science 305: 968-972 DOI: 10.1126/science.1100103

[3] Davis, S. J., Cao, L., Caldeira, K., Hoffert, M. I., 2013. Rethinking Wedges. Environmental Research Letters 8: DOI: 10.1088/1748-9326/8/1/011001

[4] http://CO2now.org/ and Carbon dioxide information analysis centre http://cdiac.ornl.gov/GCP/carbonbudget/2013/

[5] http://www.londonarray.com/