Physical Insights

An independent scientist’s observations on society, technology, energy, science and the environment. “Modern science has been a voyage into the unknown, with a lesson in humility waiting at every stop. Many passengers would rather have stayed home.” – Carl Sagan

Posts Tagged ‘carbon dioxide

The fallacy of currently operating “clean coal”: Part 2

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Next up we might look at what the coal industry calls “a world-leading low-emissions coal power plant for Queensland” – the ZeroGen project.

Through a staged deployment program, the project will first develop a demonstration-scale 120 IGCC power plant with CCS, with a gross electrical power output of 120 MW. Again – only a gross electrical output of 120 MW, and a net electricity output to the grid which will be significantly less than that – it’s a tiny demonstration-scale plant, which is feebly small by the standards of most coal-fired power stations.

“The facility is due to begin operations in late 2012 and will capture up to 75% of its carbon dioxide emissions. Some of the CO2 will be transported by road tankers for partial geosequestration in deep underground reservoirs in the Northern Denison Trough, approximately 220 km west of the plant.”

(Quoted straight from the NewGenCoal website.)

Again, only some of the CO2 is captured, and only some of that CO2 which is captured is transported, for partial geosequestration.

To facilitate more rapid uptake of the technology at commercial scale, ZeroGen will concurrently develop a “large-scale” 400 megawatt IGCC power plant with CCS. Due for deployment in 2017, the facility will be “one of the first of its kind in the world” and will capture up to 90% of its CO2 emissions. It will be located at a site in Queensland as yet to be determined by a feasibility study. Of course, capturing 90% of CO2 emissions does not mean geosequestration of 90% of CO2 emissions, and in any case, 400 MW of electrical power output is not really a “large-scale” power station at all.

There’s an interesting paper here which provides a realistic analysis of the implementation of retrofitted CO2 capture for an existing pulverised coal power station. Of course, this is a pulverised-coal system under consideration, and not IGCC as the ZeroGen plant(s) are proposed to use, but it is very interesting material nonetheless.

This paper examines the retrofit of a 400 MWe pulverized-coal fired plant, emitting 368 t/h of CO2, to enable CO2 capture while maintaining 400 MWe output, where 90% of the CO2 emitted from the coal plant is captured and sequestered. To do so, the extra energy input required for capturing CO2 was supplied by natural gas-fired gas turbines.

I’ve quoted the key points from the paper below. I’ve applied some minor editing and collation, but most of the material is straight from the paper cited.

Even when CO2 emitted from the gas turbines is not captured, the overall process still have some impact in reducing CO2 emissions, corresponding to an overall reduction in carbon dioxide output to the atmosphere of between 60-70%, with atmospheric CO2 emissions of between 110 and 138 t/h, compared to 368 t/h for the original coal combustion plant, at the cost of a natural gas requirement of about 1350 GJ/h.

When CO2 from the gas turbines is captured, the reduction in CO2 emission is between 68 and 77%, or CO2 emission to the atmosphere of 86-113 t/h. However, a considerably large amount of natural gas is required (around 3140 GJ/h), which is certainly not reasonable.

The total amount of natural gas required is between 3100 and 3300 GJ/h. To put this number into perspective, this amount of natural gas would generate about 460 MWe when used in a combined-cycle gas turbine plant without CO2 capture. The relative emissions are between 23% and 32% of the original coal power plant, which has a significant impact on the reduction of CO2 emissions.

The current industrial price for natural gas, as of August 2008, is USD $9.95 per thousand cubic feet, according to the EIA’s natural gas market page. One thousand cubic feet of natural gas corresponds to a heating value of about 1.09 GJ.

If a plant consumes 1350 GJ/h of natural gas at full output, then that is a fuel cost of 108 million dollars per year – leading to a significant increase in the operational cost of the plant.

For a nameplate capacity of 400 MW, and a capacity factor which we may assume to be, say, 85%, carbon dioxide emissions of between 86 and 138 t/h correspond to CO2 emissions to the atmosphere of between 253 to 406 gCO2/kWhe generated.

The results from this study certainly paint a less optimistic assessment of the carbon dioxide emissions intensity of “clean coal” than the 80-90% reductions estimated by the IPCC. It is not at all “clean coal”.

Indeed, such levels of carbon dioxide emissions intensity are not much better than existing high efficiency combined-cycle natural gas fired gas turbine power plants. Given that the carbon dioxide emissions aren’t grossly worse, and given that gas turbine plants are already established, mature technology which is likely to remain far more economically competitive with this expensive, immature, unproven future technology, it is easy to envision that natural gas will be the main focus of the fossil fuel combustion energy industry over coming years, as opposed to the development of CCS technology, even where emissions trading is introduced.

The exception to this, of course, is where there is a vested interest in keeping the existing coal-fired power plants, and enormous coal-mining infrastructure, even if it is a less than sensible choice on many different levels. Natural gas turbines are of course, along with nuclear power, by far one of the biggest “threats” to the coal mining and coal-combustion electricity generation industry.

Additionally, that’s only considering greenhouse gas emissions from combustion at the power plant – without any consideration of whole-of-life-cycle analysis of coal mining and natural gas production – the enormous scale on which coal is mined, along with the fugitive emissions of methane associated with the production and handling of coal and natural gas, and so forth.

At the Munmorah Power Station in New South Wales, a research-scale pilot plant will capture up to 3000 tonnes of CO2.

“It is hoped the Munmorah project will provide the foundation for a $150 million post-combustion capture and storage demonstration project in NSW, planned for operation by 2013, capturing up to 100,000 tonnes of CO2 each year.

The CO2CRC (the Cooperative Research Centre for Greenhouse Gas Technologies) Otway Project is Australia’s most advanced carbon dioxide storage project. Launched in April 2008, the project involves the extraction, compression and transport and storage of 100,000 tonnes of naturally occurring CO2. The CO2 is being stored in a depleted natural gas reservoir two kilometres below the earth’s surface.

3000 tonnes of CO2? 100,000 tonnes of CO2? That’s nothing. It is just not enough to make any difference to anything. The Munmorah power station emitted 2.1 million tonnes of CO2 to the atmosphere in 2007. Even if 100,000 tonnes of CO2 was captured and sent to geological sequestration, the remaining 95.24% of the CO2 is still going into the atmosphere as usual. Capture and geological sequestration of this 4.76% of CO2 is probably indistinguishable from normal variance in the plant’s total energy output and total CO2 emissions from year to year. You wouldn’t even notice any quantitative difference in the emissions.

In 2007, Eraring power station in New South Wales emitted 13.8 million tonnes of carbon dioxide, and in 2006, Loy Yang Power in Victoria emitted 19.3 million tonnes of carbon dioxide. For there to be any chance of “clean coal” to become a reality in any honest, meaningful way, these are the kinds of quantities of carbon dioxide which must be practically, safely and economically sent to geological sequestration, in their entirety.

There are at least two Cooperative Research Centers in Australia dealing with coal-based energy technology – the CRC for Coal in Sustainable Development, and the CRC for Greenhouse Gas Technologies (The “CO2CRC”.)

As far as I’m aware, there is not one CRC dealing with solar energy, wind energy, nuclear energy, or geothermal energy. There is not one, dealing with any such technologies. We do have industries who want to invest in these technologies as commercial enterprises in Australia, and we do have plenty of good scientists and academics who believe in all these different technologies, and yet, astonishingly, surprisingly, it is only the coal industry which has a showing in the CRC program.

The large energy requirements of capturing and compressing CO2 significantly raise the fuel costs and operating costs of CCS-equipped fossil fuel power plants, with the fuel requirement of a plant with CCS being increased by about 25% for a coal-fired plant, and about 15% for a gas-fired plant.

Additionally, increasing the overall greenhouse gas emissions intensity is increased well above what it’s claimed to be, since the gas is not captured with 100% efficiency. In addition, there are significant increases in capital costs for the plant.

The IPCC Special Report on Carbon Capture and Storage reports that:

“Available technology captures about 85–95% of the CO2 processed in a capture plant. A power plant equipped with a CCS system (with access to geological or ocean storage) would need roughly 10–40% more energy than a plant of equivalent output without CCS, of which most is for capture and compression. For secure storage, the net result is that a power plant with CCS could reduce CO2 emissions to the atmosphere by approximately 80–90% compared to a plant without CCS.”

Since 1996, the Sleipner gas field in the North Sea, the industry’s poster child for large-scale, established, operational geosequestration, has stored about one million tonnes of CO2 per year. A second project in the Snøhvit gas field in the Barents Sea stores about 700,000 tonnes per year.

The Weyburn project is currently the world’s largest carbon capture and storage project.
Started in 2000, Weyburn is located on an oil reservoir discovered in 1954 in Weyburn, southeastern Saskatchewan, Canada. The CO2 injected at Weyburn is mainly used for enhanced oil recovery with an injection rate of about 1.5 million tonnes per year.

These projects are by far the largest operational CO2 geological injection/geological sequestration projects in the world – and there are only a few such facilities in the world. Each such facility does not have nearly enough capacity for carbon dioxide geosequestration to handle the output from even just one large coal-fired power station.

Australia’s coal industry takes public relations up a notch.

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Did anybody else see the full page ad in The Age yesterday (Thursday 13th, I think it was page 7 or page 5) courtesy of the Australian Coal Association, telling us how wonderful CCS “clean coal” technology (i.e. carbon dioxide capture and geosequestration) is, and how it’s proven technology which is already in use, and how it’s going to solve all our problems with regards to anthropogenic CO2 emissions, and maintain active business as usual for the coal industry?

I don’t think so, personally.

You don’t see the ITER consortium taking out full-page page 5 ads in the major papers to promote their technology, do you? That option is about equally as mature and developed, and has just as much potential, if not more, for energy generation, and it’s far more environmentally sound.

I realise that, of course, those full-page newspaper spots must cost a pretty penny, so I did a little bit more investigation in the press.

Coal industry reaches out for love

THE coal industry feels unloved. Its polling tells it Australians have no idea what, if anything, it is doing to reduce its greenhouse gas emissions — and most say they’ve never heard of carbon capture and storage.

So the coalminers want to convert us. Today the Australian Coal Association launches a $1.5 million ad campaign — and a $1 million website — to tell us what it’s doing to develop what it calls “NewGenCoal”.

Association executive director Ralph Hillman predicted that carbon capture and storage would be commercially viable by 2017, and said the industry was investing $1 billion to ensure coal a future as a low-emission technology.

“CCS will work, and we’re investing in demonstrating these technologies,” Mr Hillman told journalists yesterday. “We’re working to implement them on a commercial scale by 2017.”

Back in Hugh Morgan’s day, the coal industry’s global warming strategy was to fund denialist groups. Not now: Mr Hillman said the industry saw climate change as real, and the association’s main goal was to drive the adoption of CCS to tackle it.

Coalminers now pay a voluntary levy of 20¢ for every tonne they mine into the Coal 21 Fund, raising $100 million to help finance CCS pilot plants and, in future, demonstration projects. These include:

* $68 million towards the $205 million trial of an oxyfuel post-combustion CCS system at the Callide power station in central Queensland, to be opened by Resources Minister Martin Ferguson tomorrow.

* $26 million towards a feasibility study to revive the collapsed ZeroGen project near Rockhampton.

* A proposed demonstration scale plant at Munmorah in NSW.

The Federal Government’s climate change adviser, Ross Garnaut, has criticised the industry’s effort as inadequate. In his final report last month, Professor Garnaut contrasted its research and development spending with the amounts paid by farmers out of a much lower revenue base. He said coalminers should beef up their R&D levies to $250 million a year to accelerate the adoption of CCS.

The International Energy Agency warned last month that CCS now costs between $US60 ($A90) and $US75 per tonne of emissions saved, way above the price of wind power or nuclear — and unless R&D efforts were radically stepped up, it might not be commercially viable until 2030.

There is no commercial coal-fired power station anywhere in the world at present which captures even 10% of its CO2 emissions.

The coal industry is quick to hold up their current, active CCS and “clean coal” enterprises as examples – but perhaps it’s worth looking at them a little more closely.

Firstly, we have the coal industry’s “clean coal” technology fund putting $68 million towards the $205 million trial of an oxyfuel post-combustion CCS system at the Callide power station in central Queensland. Where does the rest of the money come from? From state and federal governments, mostly, who are handing these projects lots of money in an effort to appear “clean and green”, and serious about mitigation of CO2 emissions, of course.

Oxyfuel combustion-and-CO2-capture involves the combustion of coal with virtually pure oxygen, rather than air, to fuel a power plant’s boiler. When the coal is burned in pure oxygen, the resulting exhaust gas is mostly CO2 (with a little bit of SO2 as usual, depending on sulfur content in the coal) instead of being mostly atmospheric nitrogen, with a smaller portion of CO2 as well as some SO2 and NO2 as is present when the coal is burned in air. A portion of the exhaust gas is recycled back into the boiler to regulate combustion and keep the oxy-fuel furnace from destroying itself.

Since the product of oxy-fuel combustion of coal is essentially pure CO2, (SO2 can be removed as usual via standard flue gas desulfurisation), the exhaust gas CO2 can be liquefied and sent straight to geosequestration, without the need to distil the CO2 from a mixture of other gases such as N2, hence making CO2 geosequestration easier to do.

Of course, the plant to produce pure oxygen, by compression and liquefaction of air followed by cryogenic distillation of pure O2, is required as part of the oxy-fuel combustion plant, and this is a non-trivial capital expense – and it also requires a reasonably significant energy input during operation.

However, the liquid oxygen produced (boiling at 90 K) can easily be used to liquefy the carbon dioxide output stream (boiling at 195 K), meaning that additional plant, and additional energy input, for the compression and liquefaction of the CO2 output is probably not required. It is claimed by the industry that oxyfuel combustion can be retrofitted to conventional coal power plants with relatively little modification.

There’s some more useful technical detail on the Callide oxyfuel project here. [PDF file, but it is not especially large.]

The graph on slide #4 is interesting, isn’t it – perhaps I’m misinterpreting it, but are Australia’s National Generators Forum really themselves predicting that nuclear energy will make up about 40% of Australia’s electricity supply by 2050, under a scenario achieving a 50% reduction in anthropogenic CO2 emission rates, over 2005 levels, by 2050? I’m surprised that they recognise, and indeed operate with the assumption, that nuclear energy will be the largest single technology on the electricity grid by 2050. Let’s hope that it actually plays out that way.

Then again, perhaps I’m not all that surprised – is there really any way that a 50% reduction in anthropogenic CO2 emission rates over 2005 levels by 2050 could actually be done, in the absence of a significant contribution from nuclear energy?

Back to the oxyfuel-CCS plant, anyway.

According to the table of data given in the above document, a typical 500 MW air-firing plant may have a gross electrical power output of 524 MW, a net electrical power output of 500 MW, and a net thermodynamic efficiency of 41%. Hence, the thermal power is 1278 MW. For the oxygen-firing plant, gross electrical power output is 633 MW, with a net thermodynamic efficiency of 34%, for the same net electrical power output of 500 MW. Hence, the thermal power is 1862 MW – an increase of 46% in the thermal power required from the boiler, and hence an increase of 46% in the amount of coal that needs to be mined, a 46% increase in mountaintop removal, and so forth.

At a net gas flow rate of 180 kg/s, which I assume is the exhaust gas output, from the oxyfuel plant, the 67% concentration of CO2 corresponds to a CO2 output of 868 g CO2 per kWh, or 10,420 tonnes per day (that is, ignoring any < 100% capacity factor, since a coal-fired plant should be operating with a high capacity factor, and I really have no idea what kind of capacity factor to expect from such a plant.)

The Australian coal industry’s efforts to develop and implement oxyfuel combustion with CO2 storage are currently at the demonstration phase. The Callide Oxyfuel Project team is assessing potential sites to the west of Biloela for carbon dioxide geosequestration and plans to select the final location in 2009.

The carbon dioxide will supposedly be transported in road tankers.

Road tankers? Seriously? Obviously that can not and does not work, for carbon dioxide geosequestration on any meaningful scale.

Let’s assume that the trucks leave the station, and travel, say, 50 km to the geoseqestration site. Assuming that the trucks travel at 100 km/h, and ignoring the time taken to load and unload the tankers, (obviously these assumptions are conservatively high to the point of being completely unrealistic) and assuming that one tanker holds 20 tonnes of liquid CO2, then you can move 20 tonnes per truck per hour. If you have, say, 22 tanker trucks, then you can transport the required 10,420 tonnes per day, if those 22 trucks are running non stop for 24 hours per day.

(Keep in mind that those trucks will almost certainly be running on fossil-fuelled, CO2 (and SO2) emitting engines…)

As the CSEnergy presentation notes, oxyfuel combustion, CO2 capture and geosequestration can reasonably be expected to increase the wholesale cost of electricity by between 50% and 75%.

The Callide oxyfuel project is not some important milestone in reducing Australia’s anthropogenic CO2 emissions. It is only a pilot-scale experiment designed to establish the design and operating costs for oxyfuel CCS plants, and to establish the capital and operating costs for these plants.

The project involves the refurbishment and retrofit of only one of the four 30 MW boilers are the currently-mothballed Callide A station, with the compression and purification of 100 tonnes of CO2 per day from a 20% side stream. That’s it – it’s only 30 MW of “clean coal” capacity.

How much CO2 is actually produced, and how much is actually being sent to geosequestration?

Assuming that the retrofitted 30 MW unit continues to operate with a capacity of 30 MW then, extrapolating the above numbers for the 500 MWe case, then the plant will be expected to produce about 625 tonnes of CO2 per day. If 20% of that CO2 is compressed and purified, then that’s 125 tonnes per day. OK, their quoted figures seem reasonable, so let’s work with that – 100 tonnes of CO2 compressed and purified per day. But only 50-75 tonnes per day of CO2 is transported and geosequestered.

To recapitulate: The plant will emit about 625 tonnes of CO2 per day, of which only 50-75 tonnes, 12 percent at the most, is geosequestered.

The atmospheric CO2 emissions intensity, then, is at best 764 gCO2/kWhe.

The Portland Wind Project under construction in Victoria has a nameplate capacity of 195 MW – which is over twice the energy output of the 30 MW Callide A unit, even when the lesser capacity factor of wind, at about 30% or so, is taken into account. At a cost of about 270 million dollars to construct the wind farm, which has zero carbon dioxide emissions, it is clear that even something as simple as wind energy, let alone nuclear, geothermal, solar thermal or anything else, is a far more economically attractive, and a far more environmentally attractive choice than the coal plant – and even typical wind farms generate far more energy than this pilot plant!

I really view “clean coal” in the same skeptical fashion that I treat anything else – such as solar photovoltaics or wind turbines – they can come back and sell their solutions, once they have a solution that realises actual generating capacity by the gigawatt, which can replace or retrofit existing coal-fired generators, with negligible, or essentially negligible greenhouse gas emissions. When the coal industry can capture and sequester all the carbon dioxide emissions from a conventionally sized coal-fired generator, economically, then I’m happy to reconsider the technology.

This plant is more expensive than nuclear, it’s more expensive than wind, and it’s probably more expensive than just about every low-emissions technology, with the possible exception of photovoltaics, it’s getting taxpayer money thrown at it, and it emits at least 764 gCO2/kWhe to the atmosphere.

That’s not “clean coal”; that’s… well, I won’t say what I think in polite company. I’ll leave it for you to think about.

Oxygen geosequestration – perhaps not such a good idea?

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I was listening to The Atomic Show * a couple of weeks ago, and Rod’s guest – John Wheeler, if I remember correctly – raised an interesting point.

Most of the mass of a carbon dioxide molecule is oxygen – so if we talk about sequestration of carbon dioxide underground, aren’t we removing huge amounts of oxygen from the biosphere?

That might present a bit of a problem. That oxygen is kinda important for a few things which I, for one, really care about.

Let’s see about quantifying it. [In case you had never noticed until now, I like quantifying things. I think it’s pretty important.]

The Earth’s atmosphere has a mass of about 5 * 10^18 kilograms, and is comprised of 21% oxygen.

That’s a total of 1.05 * 10^18 kilograms of oxygen.

Total world emissions of carbon dioxide due to anthropogenic technological activity are about 2.7 * 10^13 kg per year, globally. Of course, that will probably increase in future – how fast it will increase, and how we might slow that down – is a problem that many people throughout the world are busy thinking about and working on at present. But let’s just assume, for my purposes, that it doesn’t increase.

Let’s say, just making up some very rough hypothetical numbers here for arguments sake, that we can capture and store 70% of total anthropogenic technological carbon dioxide emissions worldwide, and that we do that for 80 years.

That’s a total of 1.5 * 10^15 kg of carbon dioxide, which corresponds to [ 32 * (1.5 * 10^15 kg / 44) ] 1.1 * 10^15 kilograms of oxygen.

That’s 0.1% of all the oxygen in Earth’s atmosphere – gone – in just 80 years. That’s probably going to be a problem.

Just another reason why, personally, CCS/geosequestration is a bad idea, and isn’t really a worthwhile solution to anything.

[* Shameless promotion – but hey, I personally think it’s a really good podcast and I recommend listening to it.]

Written by Luke Weston

April 16, 2008 at 9:43 am