Greenhouse Gas – Bury it into Oblivion
Options and Risks of CO₂ Capture and Storage

Berlin: Büro für Technikfolgen-Abschätzung beim Deutschen Bundestag (TAB), 2009
Series: Technology Assessment Studies Series, No 2, 142 pages
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Summary

Carbon dioxide (CO2) is inevitably produced when fossil fuels are used and is usually released into the atmosphere, where it affects the climate. One option for climate protection is to capture the CO2 and isolate it permanently from the atmosphere. This is the principle of CO2 capture and storage (CCS), a procedure that is primarily suitable for large, stationary CO2 sources, e.g. electricitygenerating power plants or certain industrial processes (e.g. manufacture of ammonia or cement). CCS is being discussed particularly in the context of coalfired power plants, as these emit the highest amount of CO2 in relation to electricity production. But CCS could in principle be an option for other fossil fuels, too. With the use of biomass, it is even conceivable that the CO2 content in the atmosphere might even be actively reduced. Experts reckon that it takes about 15 to 20 years for CCS technology to reach large-scale maturity.

For an overall evaluation of whether CCS technology is compatible with the principle of a sustainable energy supply, the question of reducing greenhouse gases (GHGs) is not the only central topic. On the contrary, other criteria must be considered, in particular the conservation of exhaustible resources, economic efficiency and social factors, e.g. management of long-term risks in terms of intergenerational fairness and social acceptance.

State of the Art: The Need for Research

The CCS technology chain consists of three elements: separation of CO2 in as concentrated a form as possible at the power plant, transport to a suitable storage site and actual deposition below the earth’s surface.

CO₂ Seperation

There are three options for separating CO2: (1) It can be filtered out of the flue gases after combustion; (2) the carbon can be removed from the fuel before the actual combustion process; or (3) combustion can be conducted in an oxygen atmosphere so that (practically) the only flue gas produced is CO2. These three options are termed (1) post-combustion, (2) pre-combustion, and (3) oxyfuel. The feature common to all the above-mentioned processes for separating CO2 is that they require a considerable expenditure of energy, which reduces the powerplant efficiency by up to 15 percentage points and results in an additional requirement of fuel that can reach 40 %. Each of these methods has specific advantages and disadvantages. Thus, it is still an open question which of them offers the best prospects for the future.

• The post-combustion process as a typical »end-of-pipe« procedure has the advantage of being potentially integrable into existing industrial processes and power plants. However, this advantage of possible retrofitting is offset by relatively high costs and energy losses. CO2 separation using chemical absorption is currently the only commercially available procedure and is used, for instance, for natural gas processing. To be amenable for use in (large) power plants, it would have to be scaled up by a factor of 20 to 50. Further research and development efforts aim at increasing efficiency, particularly by further developing the solvents used, but also at improving process integration and optimizing its deployment in power plants. One interesting perspective could lie in innovative processes (e.g. membrane processes), since these promise greater efficiency and reduced costs. These are currently still at an early stage of research.
• The pre-combustion process in comparison has a lower energy requirement and offers the perspective of producing hydrogen or synthetic fuels from fossil fuels with relatively low CO2 intensity. The disadvantage here, however, is the great complexity of the plants and their operation. Key components for the pre-combustion process are highly efficient hydrogen turbines. These are currently still at the pilot stage and must be significantly further developed before they can be put into commercial use. Progress in membrane technology could contribute to increasing the efficiency and economy of this process. Beyond the development of individual components, further significant challenges are the control of the process chain in its entire complexity on a real power-plant scale and the guarantee of a high level of availability for the whole plant.
• The oxyfuel process has the advantage that a relatively high concentration of CO2 is present here, and the flue-gas stream to be processed is much smaller than for the other processes. The disadvantage of this process is that the production of pure oxygen is bound up with a high use of energy and with considerable expense. Air separation plants for producing oxygen have been in industrial use for some time now. The high energy consumption required for liquefying air, however, makes it seem necessary to significantly further develop this process or alternative methods for oxygen production (e.g. membrane technology). As with the other processes for CO2 separation, integrating the individual steps of the process into an efficiently working overall system is a major task.

Post-combustion, pre-combustion and oxyfuel are processes that can be deployed in the short or medium term for CO2 separation in power plants. In addition, research is being pursued into other alternative separation procedures, which in the long term promise considerable progress, especially with regard to energy requirements and costs. The feature common to these innovative processes is that they are all currently at the stage of conceptual studies and laboratory tests, and their use is only to be expected in 20 to 30 years at the earliest. Promising candidates here include the use of fuel cells, the so-called ZECA process and »chemical-looping combustion«.

CO₂ Transport

For transport, the CO2 must be compressed after separation. The energy consumption required for this corresponds to a loss in power-plant efficiency of about 2-4 percentage points. For the large amounts produced in power plants (in a coal-fired power plant with electrical power of 1,000 MW about 5 MtCO2/yr are produced), the most eligible means of transport are ships and pipelines. Transporting CO2 in pipelines is in principle no different from transporting oil, gas and liquid hazardous substances, which is being done extensively worldwide. The biggest difference in CO2 pipelines is that the materials used must be highly corrosion-resistant. Transporting CO2 by ship is currently only used to a very limited extent; the technology is not essentially different from the conventional transport of liquid gas (liquefied petroleum gas, LPG). Transport by ship is above all suitable for great distances (more than 1,000 km) and amounts that are not too large.

Despite its important function as a link between capture and storage, CO2 transport has so far been accorded little attention by research and – if at all – is mainly discussed in terms of cost. Important questions that should be addressed would include the temporal and geographic coordination of setting up a transport infrastructure, national or regional preconditions or barriers for this and questions of the acceptance of transport through densely populated areas.

CO₂ Storage

For the long-term geological storage of CO2, depleted oil and gas fields and socalled saline aquifers are particularly worthy of consideration:

• Oil and gas reservoirs have the advantage that they have been shown to be enduringly impermeable over millions of years. Thanks to the exploration and exploitation of the repositories, the composition of the rocks and the structural layout of the storage and sealing formations are known very precisely. The biggest problem for storage safety is posed by old abandoned drill holes, which in some cases may be present in large numbers in oil and gas fields. Locating and, in particular, sealing off old drill holes is time-consuming and costly. The injection of CO2 can if applicable be used for prolonging the extraction of oil or gas from almost depleted fields (so-called enhanced oil/gas recovery, EOR, EGR).
• Saline aquifers are highly porous sedimentary rocks which are saturated with a strong saline solution (brine). The space in their pores can be used for CO2 intake, with some of the brine being displaced. For an aquifer to be suitable as a CO2 storage area, there must be a caprock above the aquifer that must be as CO2-impermeable as possible. It has to be assured as far as possible that no CO2 can escape along crevasses, rift zones or similar and that the brine cannot come into contact with groundwater near the surface.

CO₂ Storage Potential

CO2 capture and storage can only provide an appreciable contribution to climate protection if sufficient storage capacity is available to accommodate the separated CO2. The range of current estimates for worldwide storage potential is enormous (from 100 to 200,000bn t CO2), so that they are far too imprecise to allow any reliable estimate of the possible significance of CCS for global climate protection.

In Germany, several natural-gas fields are reaching the end of their production phase and would thus become available in principle in the next few years for storing CO2. The overall storage capacity in aquifers and depleted natural-gas repositories together amounts to about 40 to 130 times the annual CO2 emissions from German power plants (approximately 350 Mt/yr).

The question of whether this potential can be economically tapped for CO2 storage and indeed be used is dependent on a number of geological details, on economic, legal, and political conditions, and on social acceptance. In addition, geological formations which are suitable for CCS are also interesting for alternative forms of use (e.g. geothermal energy, seasonal natural-gas storage). It is thus to be expected that the usable capacity for CCS in practical terms will be considerably smaller than the theoretical potential.

Risks, environmental Effects

The possibility exists all along the CCS processing chain that CO2 will escape – with adverse effects both for the local environment and for the climate. Generally, the risk of technical plants (e.g. separation equipment, compressors, pipelines) is judged to be low or manageable with the usual technical means and controls. The discussion of risk thus concentrates on the geological reservoirs.

Still a matter of controversy is the minimum time that the CO2 must remain underground for CCS to be able to make a positive contribution toward reducing GHGs in the atmosphere. The times discussed usually range from 1,000 to 10,000 years.

The most important processes which could compromise the safety and permanence of CO2 storage according to the state of knowledge today are:

• geochemical processes, particularly the dissolution of carbonate rocks owing to the acidic CO2-water mixture;
• pressure-induced processes, e.g. the expansion of existing small fissures in the caprock through the overpressure of CO2 injection;
• leakage through existing drill holes, relevant particularly in oil or natural-gas repositories;
• leakage via unidentified migration pathways in the caprock (crevasses etc.);
• lateral expansion of the formation water, which is displaced by the injected CO2.

General statements on the safety of particular storage types are only useful to a limited extent and do not suffice by any means for a decision to be made on a concrete CO2-injection site. For this, each potential reservoir must be examined individually with regard to its specific features. To estimate risk profiles of geological reservoirs, it is urgently necessary for further studies and field experiments to be conducted.

The long-term safety of geological CO2 repositories is not only a question of geological features. It is rather the case that appropriate regulation and continuous monitoring are necessary to guarantee a sufficient degree of knowledge so that storage risks can be minimised.

Costs, Competitiveness

The costs of CO2 separation and storage are made up of the costs for the individual process steps (separation, transport, and storage) together. In addition, the degree of loss in power-plant efficiency and the ensuing higher consumption of primary-energy sources must also be taken into account.

The dominant cost factor lies in the expenditure for CO2 separation. Compared with a power plant of the same type but without CO2 separation, the additional costs are estimated at between Euro 26/t and 37/t (in relation to the amount of CO2 avoided). For coal-fired power plants this means almost doubling the cost of electricity generation, and for natural-gas combined-cycle stations it means an increase of 50 %. On the basis of the cost analyses available so far, no clear preference can be inferred for a particular technique (e.g. oxyfuel v precombustion). The costs of preventing CO2 by means of CCS in coal-fired power plants – assuming introduction onto the market in around 2020 – amount approx. to between Euro 35/t and just under Euro 50/t CO2 , while they are significantly higher for natural-gas power plants.

CCS technology will only be deployed on the electricity market if it is competitive with other production options. The prerequisite for this is that production of climate-friendly electricity is rewarded. In other words, the price for CO2 emissions, such as is determined on the European market for CO2-emission certificates (EU allowances, EUA), must be set at least so high that CCS power stations can compete with fossil-fuel power plants without CO2 separation. In the light of the above-mentioned CO2-separation costs, this would mean a price of about Euro 30 to 40/EUA.

A comparison of electricity-generation costs in CCS power plants with other low-CO2 and especially regenerative production methods shows that, in the year 2020, most of the regenerative technologies that have been examined could have reached a cost level similar to that calculated for CCS power stations (in range of Euro 0.05 to 0.07/kWh). Although the prognostic power of such long-term projections should not be overrated, it seems incontestable that CCS will not have the field to itself, but will have to compete with other technologies for low-CO2 electricity generation.

Integration into the Energy System

In Germany, the age structure of the power plants means that in the next two to three decades there will be considerable need for renewals. The contribution that can be made by CCS technology toward reducing CO2 against this background depends strongly on the answers to the following questions:

• When will CCS really be available?
• Is it feasible to retrofit existing power plants with CCS technology?
• Is it a tenable idea to prepare the new power plants being built now to make them fit for later retrofitting (i.e., to make them »capture-ready«)?

Since effective climate protection can only be addressed globally, CCS should also be evaluated from an international perspective.

Timeframe for Availability

In various papers on research strategy, as well as roadmaps, one topic is the projected time in which CCS technology could be available. A common feature of most of these publications is that 2020 is cited as the target year for commercial availability on a power-plant scale. Among experts, though, this is regarded as very ambitious. One reason for the brief time period could be the recognition that the contribution that CCS can make to CO2 reduction becomes increasingly smaller, the longer it takes to make the technology fully available. A look at the currently initiated projects or planned pilot and demonstration projects reveals that it only seems possible to keep to the stated timeframe if the economic and political conditions are favourable.

Potential Retrofitting / »Capture-Ready«

In principle, existing power plants could be retrofitted with CO2 separation equipment. Post-combustion with subsequent flue-gas scrubbing involves the least technical effort and means the smallest amount of intervention in the power-plant process itself. The question of whether power plants really will be retrofitted depends not only on technological feasibility, but crucially on economic viability. Retrofitting power plants is costly and as a rule more expensive that integrating CO2 separation into a new plant. It is to be assumed that retrofitting would only be conducted on a larger scale if the economic incentives for CO2 separation are high enough or if, for example, an obligation to upgrade were introduced.

At first glance, the idea of preparing new power plants today in such a way that they can be retrofitted later with CO2-separation systems in a technically uncomplicated and cost-effective way, as soon as the technology and corresponding CO2 repositories are available, looks like a plausible and attractive proposition. This »capture-ready« concept is currently the subject of much discussion among experts, especially since the EU Commission floated the suggestion that fossil fuel-fired power-plant approvals be confined in future to those that are capture-ready. However, the options for installing capture-ready components in the power plants to be built today are extremely limited.

From today’s perspective, only those measures would be economically acceptable that involve only little cost, e.g. provision of a site for building the CO2-separation plant and maintaining ready access to components which would probably have to be upgraded or replaced in the course of retrofitting. Another factor worth careful attention is the siting of power plants so that they are found close to a potential repository or to existing infrastructure for CO2 transport.

For a robust estimate of whether the capture-ready concept is acceptable, there is still a considerable need for technical-economic analyses. In addition, criteria must be developed which, for example, permit approval authorities to judge the capture-readiness of power plants.

International / Global Perspectives

CCS technology could be particularly attractive for countries which have so far been sceptical about climate-protection measures (e.g. USA) and/or want to continue to use their domestic primary-energy basis of fossil fuels (especially coal; e.g. China, India).

In China alone, between 1995 and 2002 about 100,000 MW of fossil fuel power-plant capacity (primarily coal-fired power plants) was built. For the period 2002 to 2010, it is forecast that a further 170,000 MW will be added. If this trend were allowed to progress unchecked, the success of international climate-protection efforts would be seriously imperilled.

For the deployment of CCS technology to become an attractive option in these and other emerging nations, it would first have to be successfully further developed and proven. The most suitable candidates for this are industrial countries with their technical know-how and financial resources. In the face of the dynamics of power-plant expansion, however, CCS would have to be introduced as quickly as possible, since otherwise the window of opportunity would close again and might remain closed for many decades.

Public Perception and Acceptance

Public perception can have considerable and unexpected effects on planned technological and infrastructure projects. Other disputes – especially with regard to atomic energy and genetic engineering – are a clear illustration of this. Technologies like CCS whose long-term risks to our safety, health and the environment are hard to assess are particularly prone to triggering public unrest and possibly resistance.

Hence, ensuring a high degree of public acceptance should be a high-priority goal from the very beginning. One important prerequisite for acceptance is the creation of transparency by providing comprehensive information both about the aims of CCS in general and about concrete intentions and projects. As the past has shown, however, measures relying purely on information and advertising are by no means sufficient to create acceptance. To avoid crises of acceptance and trust, an open-ended process of dialogue should be initiated between industry, stakeholders, science and the public at an early stage.

Legal Issues

For the testing, introduction and diffusion of CCS technology, a suitable regulatory framework must be created which should have three simultaneous goals: first, establishing the conditions for the admissibility of the various components of CCS technology (separation, transport, storage); second, providing incentives for investing in CCS technology; and third, guaranteeing that CCS does not fail for lack of public acceptance in general and at the storage sites in particular.

Under current law, no procedure exists either for exploring locations to identify repositories or for the storage of CO2. Creating an adequate regulatory framework means a double challenge. If it is assumed, on the one hand, that the rapid introduction of CCS on an industrial scale is in the public interest for the sake of climate protection, then it will be necessary, on the other, to authorize initial CCS projects at short notice in order to gain experience with the technology.

This experience is necessary both for the further development of the technology and for political and legal guidance. In Germany, several companies already have concrete plans with this aim in mind, and some plans are at an advanced stage. The planned projects will be inadmissible, however, if the law as it stands is not amended in the short term.

All the same, a regulatory concept should preferably take all the relevant factors into account: selective use of the limited number of storage facilities available, consideration of competing claims for use, questions of liability, creating transparency, regional-planning challenges, integration into the climate protection regime, etc. Although a regulatory concept of this kind would greatly contribute to promoting acceptance and avoiding conflict, this would require sufficient time for its elaboration, discussion, decision-making, and realization.

Need for Action

On the basis of the current state of our knowledge and assuming there is public interest in the deployment of CCS technology to promote climate protection, the TAB assesses that the following factors should be given priority.

Broadening the Knowledge Base: Closing critical Gaps in our Knowledge

Current knowledge is too inadequate by far to permit any robust assessment of the technical and economic feasibility of CCS or any evaluation of the contribution that CCS can make toward achieving climate targets. For that, numerous critical gaps in our knowledge must be closed.

With regard to research and development in the field of CO2 separation and the technologies for CO2 conditioning and transport, the onus is on industry as the primary actor (power-plant and equipment construction, utilities, chemical industry). The main task for state actors in this context would be to maintain or create a reliable environment so that companies could fully develop the socially desired research initiatives. The fields of action that offer the most promising candidates for justifying the public funding of research would be highly innovative procedures with great potential for public benefit, whether ecological and economic, and cross-section fields (e.g. materials research).

The greatest deficit in our knowledge and the greatest need for research is currently in the area of geological CO2 storage. In this field, there is also a special need for state action. Questions which would represent particularly good candidates for publicly funded research projects would include the interaction of injected CO2 with rock formations, the determination of storage capacity, and investigations into the suitability of geological traps for the long-term storage of CO2. There is an urgent need for research in the field of possible competition from alternative uses (natural-gas storage, geothermal energy). This also includes the question of how to resolve any usage conflicts (e.g. priority rules).

An urgent recommendation is that accompanying research in the social and environmental sciences be integrated into pilot projects at an early stage in order to ensure that technological development can be geared to the criteria of sustainable development and that knowledge about the economic, ecological and social effects of CCS needed for later decisions will be available. This includes the analysis of potentials, risks, and costs, considerations of lifecycle assessment and questions of integrating CCS into the energy system.

Triggering a public Debate

To prevent a lack of acceptance from becoming an obstacle to further development and to the use of CCS technology, a national strategy of communication, information, and participation should be designed and implemented at an early date. This process should be structured so as to leave the outcome open and should sound out whether and how the broadest social consensus possible can be achieved. This is a demanding task which should be initiated before the first concrete siting decisions are to be made. A first possible step in organising this process of communication, namely the establishment of a national »CCS forum «, is being put forward for discussion, and this could bring together all the relevant stakeholder positions in Germany.

Creation of a regulatory Framework

There are several companies in Germany that are already planning concrete CCS projects, some of which are at an advanced stage. However, without early amendments to the current law, these planned projects will be inadmissible. Thus there is urgent need for action here.

A two-step procedure would be ideal: in the course of an interim solution, which should be realised in the short term, the legal preconditions should be created so that projects mainly concerned with research and the testing of CO2 storage can be promptly initiated. The central element in a short-term regulatory framework would be the creation of an approval fact (Zulassungstatbestand) in mining law.

At the same time, a comprehensive regulatory framework should be developed and if possible coordinated at EU level and internationally which accommodates all aspects of CCS technology. This could supersede the interim regulation as soon as CCS is available for large-scale technical deployment.