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The science of storage

Logan West

Readinch

Putting greenhouses gases underground is the riskiest part of carbon capture and storage, yet it is often overlooked. Logan West sets out the facts.

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Until recently,
carbon capture and storage (CCS) was a phrase largely reserved for detailed discussions in university laboratories or the research divisions of energy giants. That is not the case today. The technology, which captures carbon dioxide produced by fossil-fuel combustion and stores it in deep geological formations, such as oil fields, now occupies a prominent position in climate-change policymaking and the public debate around cutting carbon.

Held up by its
advocates as a way of reducing carbon emissions while maintaining a secure energy supply, CCS has gained significant traction with the world’s governments. The United States, United Kingdom, Canada and Australia are among the countries to have pledged large sums of public money to high-profile demonstration projects in the last two years. CCS is considered to be particularly important development for China, where around 70% of energy needs are still met by coal. A commercial-scale "clean coal" project is already under way in the city of Tianjin, in north China, but researchers, such as Stanford University’s He Gang, argue more is needed to promote widespread adoption.

The technology’s enormous expense – the cost of one CCS plant is currently estimated at around US$1.5 billion (10.7 billion yuan) – still stands in the way of rapid deployment. And it has been
criticised by some for being a “plaster” for global ills rather than an attempt to deal with the root cause. But more and more policymakers, non-governmental organisations and academics are backing it as one of the many solutions required to cut carbon dioxide output, saying it is an advanced technology with a ready skills base – injecting carbon dioxide underground is an established practice in the oil and gas industry.

CCS is attracting huge global attention. And this week,
chinadialogue will look at some of the key issues surrounding its development. Logan West kicks off the series with an explanation of the process’s storage aspects, while Li Jia and Liang Xi analyse the financial stumbling blocks and possible solutions. Later in the week, the Natural Resources Defense Council presents a detailed account of CCS development in China and the global cooperation needed to promote it. As always, we are keen to hear your views, so do please leave a comment – and get involved in the conversation.



Carbon capture and storage (CCS) is a classic relocation-style response, like landfill or water diversion, that is steadily picking up steam. In fact, the International Energy Agency forecasts that CCS will contribute over 10 gigatonnes of carbon-dioxide emissions reductions in 2050, compared to 11 gigatonnes for renewables.

Why the optimism? The concept is simple, the technology exists, industry is proven to have the capacity and CCS is an adaptation, rather than overthrow, of the existing system. That said, CCS lacks neither flaws – energy inefficiency, high costs – nor detractors. While the topic heats up, details of the process itself often get lost in the debate. But an understanding of carbon-dioxide storage is essential to continuing the discussion.

For the non-geologist majority, storage can be difficult to conceptualise. Where does the carbon dioxide actually go? How does it stay there? What happens if it escapes? The storage process presents the riskiest and most uncertain part of any CCS project. Not only can carbon-dioxide release be hazardous, but its escape also undermines the whole process and wastes a lot of time and money doing so.

So how does storage work? It is important to understand that the carbon dioxide being stored is not like the carbon dioxide people exhale every day. The hot, high-pressure conditions of the kilometre-deep storage zones force carbon dioxide into a supercritical state with a liquid-like density, leading it to “flow”, which restricts its buoyancy.

This carbon dioxide is pumped into what geologists call a reservoir. Beneath our feet are layers of rocks, typically stacked one on top of the other. Reservoirs are layers in which fluids like water – called aquifers – and oil or gases accumulate. The key characteristic of reservoirs is that the rocks contain a lot of interconnected, open pore space, which fluids can move through and fill. The injected carbon dioxide “plume” does exactly this.

There are four main mechanisms for keeping the carbon dioxide plume where it is. The single most important factor is the cap-rock, an impermeable layer above the reservoir that holds in the plume the same way that a bottle cap shuts in the carbonation in a bottle of soda. It is essential that cap-rocks, among other traits, are spread over the whole area of the plume – up to 100 square kilometres – and are free of escape pathways such as leaky faults. The cap-rock and other unique geological structures are the frontline for containing carbon dioxide.

As the plume permeates through the pore spaces, the carbon dioxide becomes trapped as some channels are too tight for it to squeeze through. Then, as the gas interacts with the water in the reservoir, some of it dissolves. Once dissolved, the carbon dioxide loses all buoyancy and cannot move on its own. Eventually, a share of the dissolved substance reacts with the rocks to form minerals, solidifying the carbon dioxide in the subsurface, where it will stay for millions of years.

There is plenty of evidence indicating that these trapping mechanisms have been, are and ought to be successful. Naturally occurring carbon dioxide accumulations have been trapped in the subsurface worldwide for millions of years. Meanwhile, ongoing international demonstration projects are successfully conducting CCS. This has led the Intergovernmental Panel on Climate Change (IPCC) to state that, when done right, 99% of the carbon dioxide stored is likely to be retained 1,000 years after injection – time enough to find emission-free energy.

Still, there are a great number of unknowns. In geology, no two locations will ever be exactly the same. Thus, unlike capture technology, there is no “one size fits all” blueprint for carbon dioxide storage. And, while tools help us image the subsurface, they can only provide a sketch of the reality. Regardless of how thoroughly a site is examined, predicting the movement and reaction of carbon dioxide in the subsurface still involves a lot of guesswork. Experience and data do, however, lower the uncertainty and that is why oil fields make likely first-generation storage targets. Their geology is well understood and the carbon dioxide can sometimes be used to push out previously unrecoverable reserves.

The uncertainty can be managed if regulators and project operators work together to ensure that storage is carried out with the highest precautions and attention to efficacy. The key to successful storage is picking the safest site, analysing potential locations to identify one that will not only trap the carbon dioxide but also has the space to hold it all and allows the gas to be pumped in as fast as it arrives from the source.

To back up such research, collected data should be used to develop models of the reservoir that can simulate what the carbon dioxide is likely to do. Monitoring tools should then be put in place to track what it actually does and to test for leakage. Models and monitoring will function in tandem, with an ongoing assessment of the possible risks and plans for fixing leakage should it occur. Regulators should carefully review all preparation work and data before awarding permits for storage sites. They should also consult with local communities. This makes data transparency essential.

Even with all the precautions, carbon dioxide can still leak and the side effects can be serious. While normally non-toxic, heavy concentrations of carbon dioxide in the air can be deadly to humans and plant life. Such serious side effects are only caused by the rapid release of large volumes of carbon dioxide, which is unlikely to happen. However, more plausible, slow seepage of the gas from storage reservoirs can still be hazardous. Carbon dioxide that escapes into shallow aquifers nearer to the surface will react with the water to form a weak acid that can render groundwater non-potable or unusable for agriculture and industry. This acid could even leach toxic metals from the rocks or soils, which would worsen the health and environmental effects. Even carbon dioxide escaping harmlessly back into the atmosphere still contributes to greenhouse-gas emissions.

This raises the following question: is storage feasible? Technically, yes. Economically, yes; storage costs vary depending on the site but typically account for only 5% of the total project. But what about those estimates suggesting China can hold as much as 2,300 gigatonnes of carbon dioxide – or 100 years’ worth of emissions at the country’s current rate? Don’t let these estimates instill false optimism. They are theoretical figures. So much is still unknown that the true capacity is hard to predict. Geological data in China is still limited and little is actually known about the saline aquifers that show the greatest potential.

Where there is data, it is proprietary knowledge of oil companies, which are reluctant to share it freely. Similarly, some spots good for carbon dioxide storage may lead to conflicts of interest if they possess other important resources. Furthermore, China’s reservoirs tend to be very complex, with abundant faulting that potentially compromises safe containment. Even at top-priority oil reservoirs, issues exist due to the number of old exploration wells that need to be located and plugged to prevent carbon dioxide from escaping.

Finally, just because a site makes geological sense, does not necessarily mean it is practically viable. It does not make economic sense to pump carbon dioxide from Shanghai in the east of China to Xinjiang province in the west, just because there is a good reservoir there. Nor does it yet make sense to pump carbon dioxide directly under Beijing or other heavily populated regions. The uncertainties are still too high to justify taking the risk that the gas might leak and, at the very least, damage water resources.

Still, China may well possess many gigatonnes of realistic storage space – enough to play a significant role – and this is where discussion can move back to the big picture of costs, policy and beyond.


Logan West is a researcher at the Tsinghua-BP Clean Energy Research and Education Centre in Beijing.

Homepage image by Øyvind Hagen for Norway's Statoil shows the Sleipner CCS facility in the North Sea.
 

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WB 奇泽姆

这篇文章提出了许多好观点,然而由于商业机密、信息无法共享的关系,碳封存技术的快速发展受到了阻碍。另外,我们需要更多的研究和补贴,并要求各方拒绝接受碳抵消的额外测试,这些环节的缺失也是阻碍碳封存技术发展的原因。非政府组织和特殊利益方的恐慌同样延缓了该技术的大规模应用。因此,碳捕获与封存将成为缔约国会议的核心问题。双方都必须作出让步。

在石油和天然气领域上的碳捕获与封存已经被证实是可行的。但是能源公司务必要在透明化及公开技术做好万全准备,而也必然会在油气消耗殆尽的前提下才考虑实施。只有在这样,碳抵消才可能脱离补贴。

运用CCS的电力公司必须承担煤炭行业的碳捕获与封存的运输费。只有采纳“谁污染谁受罚”的原则,碳捕获与封存方能在这个行业进步。

同样地在石油与天然气行业,公开基准排放量的报告是非常必要的。而目前没有几个国家要求公开石油和天然气运作中的详细而准确的数据。

WB Chisholm

Many good points made in this article, however the refusal of corporate interests to share the information has hindered the rapid deployment. The drive for more studies, subsidies, and the refusal of parties to accept the addtionality tests for generating offsets has hurt the progress. The scare mongering of the NGO's and special interests has also impeded wide scale usage therefore CCS and sequestration in general will continue to be a major issue at the COP. Concessions must be made by both sides.

CCS in oil and gas fields is well proven however energy companies must be prepared to be transparent and open with the technologies they use and must consider accreditation only after the last oil and gas has been recovered, it is at this stage carbon offsets may be generated without subsidy.

The power companies who use CCS must carry the costs of transportation for CCS in the coal sector and this sector could be driven forward to use CCS if the polluter must pay principal is utilised.

Likewise in the oil and gas sector open transparent reporting on baseline emissions is required, as currently few nations are requiring oil and gas operations to report accurately all leakage.


碳捕获与封存(CCS)是否实用有待观望

谁能担保二氧化碳会保持安全地储存?保险公司不会,不断更朝换代的国家政府也不会。
考虑到一些国家是如此的腐败, 如此的缺乏透明度,谁又能担保当碳捕获与封存系统安装之后会一定被启用?
如果不是绝对安全的话,封存二氧化碳及放射性物质就好像放置一个定时炸弹。但是, 考虑到他们的军事重要性,放射性物质的安全性有可能被优先考虑, 而二氧化碳则不然。
这篇文章强调能源耗损是CCS技术存在的一个缺陷,相信很多人会对此表示讶异。确实,文章作者戳穿了那些CCS宣扬者的谎言,提到说把二氧化碳从上海排送到新疆的费用将非常高昂。 换言之,CCS非解决中国问题之良策。
电用户应该以通过关税的方式负担这些系统的费用,而政府则不能资助这种消费。
目前CCS只是被推荐给发电站, 因为他们是主要人为温室气体排放的来源。谈到导致气候辩护的其他主要因素,比如禁止伐林造地等相关措施也非常必要 。

Practicalities make CCS a non-starter

Who would guarantee that the CO2 would remain stored until safe - insurance companies wouldn't and governments come and go.

Who would guarantee that the CCS system would be used even when installed given the level of corruption and lack of transparency in some countries?

The storage of CO2 and radioactive materials are like a time bomb unless absolutley safe. However, given their military significance, security concerning radioactive materials is likely to be given much greater priority than CO2.

The article asserts that energy inefficiency is not a flaw of CCS - this will surprise many. Indeed, the authors expose the mischief of those promoting CCS by saying that the cost of pumping the CO2 from Shanghai to Xinjiang would be too high. In other words, CCS is not a solution for China.

Electricity users should pay the financial cost of such systems through increased tariffs - government must not subsidise consumption.

CCS is only being proposed for power stations - which are a major cause of anthropogenic greenhouse gas emissions. Other measures, notably a prohibition on forest conversion are essential if other major causes of climate change are to be addressed.


这篇文章跟科学有差距(1)

这篇文章的题目有误导性,因为它与科学基本无关,只是作者自己未被证实的观点而已。虽然作者指出一些有争议的研究议题需要对CCS开展进一步的研究,但是他并没有对这个概念进行完整描述。我会建议作者对CCS做更深入的研究,特别是在批判之前查阅一些科学文献。碳捕获与封存的争议远比在这篇文章所描述的要复杂。以下都是比较好的文献,例如:
-政府间气候变化委员会关于CCS的特别报告:
http://www1.ipcc.ch/ipccreports/special-reports.htm
-2009年9月25日《科学》杂志第325期,R.Stuart Haszeldine发表了一篇很好的评论论文。

The article is not related to SCIENCE (1)

The title is misleading since it is little about “SCIENCE” but only author's own un-approved opinions. Although author pointed out some issues and research topics that require further R&D of CCS, he did not give the whole picture of CCS. I would suggest author to study more on CCS especially from the scientific publications before criticizing. The issues are much complicated than what are presented in the article. Following literature shall be good, for example,
- IPCC CCS Special Report:
http://www1.ipcc.ch/ipccreports/special-reports.htm
- A good review paper published in SCIENCE VOL 325 25 SEPTEMBER 2009 by R. Stuart Haszeldine


在文章的错误(1)

我想指出在文章和编者按的一些错误:
(1)”由于中国大约有70%能源需求依赖于燃煤。因此对于中国而言,CCS技术的发展则尤为重要。一项该技术的商业化推广项目就已经在中国北部城市天津得到开展。然而,一些研究人员,如斯坦福大学的何钢认为,这项技术的全面推广还需要做大量的工作。“
评论:
我相信你指的是在天津的华能煤气化联合循环发电项目。请注意这个是煤气化联合循环发电项目,并不是碳捕获与封存计划。目前中国并没有商业化推广碳捕获封存项目,只有一些由亚洲发展银行支持的可行性研究。请查阅:
http://www.ccchina.gov.cn/cn/NewsInfo.asp?NewsId=20612
还有,天津离北京只有大约只有100公里,并不是在中国的东北部。

Mistakes in the article (1)

I would like to point out some errors in the article (and editorial):
1) “CCS is considered to be particularly important development for China, where around 70% of energy needs are still met by coal. A commercial-scale project is already under way in the city of Tianjin, in north-east China, but researchers, such as Stanford University’s He Gang, argue more is needed to promote widespread adoption.”
Comments:
I believe you mean the Huaneng IGCC project in Tianjin. Please note this is an IGCC project not a CCS project. There is no commercial scale CCS project in China at the moment. Only feasibility study is on-going include the ADB supported project, see
http://www.ccchina.gov.cn/cn/NewsInfo.asp?NewsId=20612
Besides, Tianjin is only ca 100 km away from Beijing. It is not in north-east China.


文章的错误(2)

(2)”地下数千米深的存储区域的高温高压环境使二氧化碳处于高密度的超临界状态,成为“流体”,从而限制了其上升。“
评论:是高压没错,但并不一定非要”高温“。
(3)”尽管如此,这一技术还存在许多未知因素。从地质层面看,没有两处地点的地质条件是完全相同的。因此,与碳捕获技术不同的是,二氧化碳储存技术不存在“放之四海而皆准”的规划方案。“
评论:这个声明完全是不科学的。我不认为二氧化碳储存技术要寻找一个“放之四海而皆准”的规划方案。事实上,就像其他技术一样,二氧化碳的处理也需要“因地制宜”。运用“没有两处地点的地质条件是完全相同”的逻辑来分析,太阳辐射和风速也时刻变化,因此就不可能找到“放之四海而皆准”的方案,那么我们是否就应该停止太阳能和风能的开发呢?
我喜欢中外对话,但是我确实觉得只有高质量的文章才能提高网站的可信性和声誉。

Mistakes in the article (2)

2) “The hot, high-pressure conditions of the kilometre-deep storage zones force carbon dioxide into a supercritical state with a liquid-like density, leading it to “flow”, which restricts its buoyancy.”

Comments:
It is in high-pressure condition but not necessary to be “hot”.

3) “Still, there are a great number of unknowns. In geology, no two locations will ever be exactly the same. Thus, unlike capture technology, there is no “one size fits all” blueprint for carbon dioxide storage.”

Comments: The statement is really non-scientifically based! I wonder if the CO2 storage is trying to find such “one size fits all” solution. Indeed, they have to be solved by case by case which are similar to the implementation of other technologies. There is no such solution even for others. Using the same logic, for example, “there are no two locations will ever be exactly the same” such as solar radiation, wind speed, thus we are not possible to find “one size fits all” … If we shall stop the development of solar and wind energy…?
I like Chinadialog but I do feel high-quality articles will improve the creditability and reputation of the site.


煤气化联合循环发电等同于碳捕获与封存吗?

我同意以上的评论。 煤气化联合循环发电并不等同于碳捕获与封存。 绿色煤电项目采用的是二次燃烧技术来实现捕获的。

IGCC = CCS ?

I agree the comments above. IGCC is not equal to CCS. GreenGen project uses post-combustion technology to demonstrate capture.


数据来源对CCS实施的限制

我同意文章的观点。石油公司掌握着矿石数据。在中国,矿石的形成很复杂。地理勘探者在中国也握有矿石数据。总的来说,外国公司在中国很难实施CCS。

Data source

I agree with you oil companies hold the data. The formation is quite complex in China in general. Geological survey in China also has data. Anyway, it will be difficult for foreign companies to operate CO2 storage in China.


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