New power stations require assessment for integrating suitable CCS technology. Photo © Istockphoto.com/pixelprof

Even today, owners/operators of fossil-fuel power stations must already ensure that the design of their plants permits the fitting of suitable carbon capture and storage (CCS) technology. The backdrop to this regulation is that the European Union has set itself a reduction target for EU-wide greenhouse gas emissions of at least 20% by 2020 and even up to 80% by 2050, compared to the baseline year of 1990. CCS technology, on the one hand, offers the potential of a clear-cut in direct greenhouse gases. On the other hand, however, it presents plant owners/operators and political bodies with special challenges in ensuring its technologically safe, cost-effective, and legally compliant implementation. TÜV SÜD experts provide impartial support for CCS projects and assistance in the form of integrated system analysis.
 

Technological Approaches
At present, there are three preferred approaches to CCS under development. These three techniques capture carbon dioxide immediately before, during, or after combustion.
 

Pre-Combustion Method
In pre-combustion CCS, the removal of CO₂ from the fuel, e.g. coal, is before the fuel goes into the furnace. At high temperatures, coal converts into a synthesis gas (syngas) that primarily consists of carbon monoxide (CO) and hydrogen (H₂). Capturing of CO₂ from this syngas is by means of physical scrubbing and compressing into a liquid – a state in which it is particularly easy to transport. Regarding the integrated gasification combined cycle (IGCC), the basis for the pre-combustion CCS systems, the focus is currently on improving the highly efficient hydrogen turbines. The feasibility of this CCS technology on a large scale goes for testing as early as 2014 in a commercial-scale demonstration CCS project with a gross output of 450MW. The advantage of the IGCC technology lies in its very small loss of plant efficiency compared to the two other CCS techniques. However, a disadvantage is the complexity of its technology and operation management.

When planning a retrofit or new installation of CCS systems, operating costs are a critical criterion for deciding whether to use a particular technology.

Carbon Capture During
The oxyfuel method aims at affecting fuel combustion in an atmosphere of almost pure oxygen, which, in contrast to conventional combustion in air, produces a flue gas that contains almost zero nitrogen and sulphur compounds. This flue gas primarily consists of CO₂ and water vapor. To reduce the elevated temperature caused by combustion with pure oxygen, the flue gas first passes through a tightly woven fabric to remove the particulate matter, and then moves on for recirculation. When the flue gas cools, the water vapour condenses into water, leaving almost pure CO₂ gas, which easily transports to a storage site. While glass furnaces and melting furnaces already utilize this type of CCS, i.e. oxyfuel firing, the technology is still at the trial stage in electricity generation. A pilot plant in the Lausitz region, with a thermal output of 30MW is one example. The advantages of oxyfuel carbon capture include significant cuts in total emissions and a highly concentrated stream of CO₂ emission. Disadvantage: the production of pure oxygen is relatively energy and cost-intensive.

Carbon Capture After
Post-combustion capture's basis is on chemical scrubbing of the flue gases produced during combustion. In a first stage is the nitrogen removal from the flue gas, which is then passed through a liquid sorbent (amine or lime) that binds the CO₂. By heating the sorbent, the CO₂ separates from the amine or lime molecules and compresses into a liquid state for transport to its storage site. Post-combustion capture has the particular advantage of being the only one of the three techniques usable for retrofitting existing industrial plants and power stations. In addition, chemical flue-gas scrubbing is a fully mature technology and is already in operation in many of today's power stations. CO₂ scrubbing has tested well in a coal-fired power station at Esbjerg, Denmark, since 2006. Another pilot plant, erected at the site of a conventional power station in Niederaußem, Germany, went into service in the summer of 2009.

A disadvantage of the post-combustion method is the fact that CO₂ scrubbing systems require a large amount of space, up to the size of one football field. Moreover, additional operating costs for the chemical processes may add up to EUR 3,000 per hour for a flue gas volume of three million cubic meters per hour. Replacing the CO₂ sorbent in the scrubbing system at regular intervals incurs these costs.

In addition to the three CCS techniques mentioned, other alternatives are in research phases. However, pre-combustion, oxyfuel, and post-combustion CCS are the techniques of choice at present, expected to be readily available on the market in the next few years.
 

Efforts Needed
The chances of using CCS to keep the greenhouse gas CO₂ out of the atmosphere depend first on the maturity and feasibility of the required technologies, and second on the available storage capacities. According to initial, relatively rough estimates by experts, the global storage capacities currently amount to between 100,000 and 200,000 billion tonnes of CO₂. If we want a reliable forecast of the potential for mitigating climate change, accurate calculations of storage capacities is required.

The potential CO₂ storage sites in Germany (including depleted natural gas reservoirs) have the capacity to store the CO₂ emissions produced by German power stations in roughly 40 to 130 years of operation. Competition over land use may pose a problem, as the geological formations, which are eligible as storage sites for captured carbon dioxide are also of interest for other applications, such as compressed air reservoirs, seasonal reservoirs for natural gas or, in the case of saline aquifers, hydrothermal geothermal projects. This aspect also determines the extent to which theoretically existing storage capacities are actually usable for storing captured CO₂.

The potential risks of integrating CCS technology into power station processes do not differ fundamentally from those in other industrial-scale plants. Within the scope of CCS, the transport and storage of CO₂ and the safety of the geological reservoirs are the focus of interest. One of the major risks in CCS, and one not to exclude, is the risk of leakage, i.e. the risk of CO₂ escaping from the storage sites with adverse effects on the direct environment (personal injuries, damage to property) and the climate. Another conceivable risk involves geochemical processes, e.g. the dissolution of carbonate overburden by the carbon dioxide-water mixture, which forms carbonic acid. These geochemical processes involve the risk of leakage and present a risk for the stability of the storage site. Decisions on whether a specific site is suitable for CO₂ storage should depend on the type of storage and on case-by-case risk assessment.
 

CO₂ Logistics
Carbon dioxide capture and long-term storage is only worthwhile when a suitable transport system is available, since it rarely occurs that the storage reservoirs are located near the power generation site. In principle, tankers and pipelines are suitable. For the transportation, the CO₂ liquifies under high pressure. As a result, no existing pipelines are eligible for this purpose. The pressure of up to 200 bar in contrast to gas network (60 bar to 80 bar) requires other pipe sizes and greater wall thicknesses. In addition, several entry points need to be connected. The construction of a new infrastructure has to fall in line with a variety of legal approval and planning processes, which frameworks federal law fully regulates. In addition, a contribution from the public authorities as operators of such a CO₂ pipeline is possible – in light of public acceptance.
 

Integration
CCS installations have major impacts on the operating strategy, and the costs of power generation. Therefore, to ensure the cost-effective generation of electricity, CCS technologies must integrate seamlessly into the processes of a power station and the potential for optimizing operating processes fully exploited. Depending on the type of technology used, CCS may cause loss in efficiency and higher investment costs – disadvantages that require compensation as efficiently as possible. The new generation of coal-fired power stations represents one possibility. By increasing operating pressures and temperatures, and applying new material concepts, the efficiency of a power plant can improve to offset, roughly, the loss in efficiency caused by the use of CCS.

The costs of retrofitting an existing 800MW power station with post-combustion CCS add up to between EUR 300 and EUR 400 million, i.e. almost half of the investment costs spent on the power station itself. These costs include:

• Flue gas desulphurisation
• Flue gas cooling
• Absorber (CO₂ scrubbing)
• Heat exchanger
• Desorber (CO₂ scrubbing)
• CO₂ compressor (for transport)

For efficient energy generation, process, and operations, engineering requires tailoring to the specific technical processes and the subsequent operation of the respective plant. An integrated approach also embraces maintenance and inspection programmes. These programs require examination for their informative value, and for insurance that they satisfy the integrated requirements of the complex system of a power station. Subsequently, plausibility and stresses occurring during operations require assessment. This customized approach ensures both safe and cost-effective operation.

The limitations of CCS – apart from the capital costs of CCS technology – include the increased energy requirements and additional operating costs generated by the CCS system. Estimates assume that, at an early commercial stage, the costs of post-combustion CCS will amount to roughly EUR 30 per ton of CO₂. By 2030, these costs may reduce to roughly EUR 20 per ton of CO₂. As a comparison: the price at the European Climate Exchange (ECX) in Amsterdam for one European Union allowance (EUA) – the right to emit one tonne of carbon dioxide – has ranged from a few cents to more than EUR 30 since the emissions trading scheme (ETS) was launched in 2005. As demand has dwindled in the wake of the recession, EUAs currently sell at a price of just under EUR 13. Among other factors, the cost-effectiveness of CCS will also depend critically on price trends for the EUAs saved by CCS. The key to success, however, lies in balancing the technical and economic challenges of CCS technology for the processes at each individual power station.

Cost Perspective
When planning a retrofit or new installation of CCS systems, operating costs are a critical criterion for deciding whether to use a particular technology. Operating costs include all future expenses for operation, servicing, and maintenance, and the degree of plant availability. They also include costs for the CO₂ transport system and storage site. Maintaining financial reserves for unexpected events during CO₂ transport or storage is sensible in this context.

An integrated, cost-effectiveness analysis, which considers the technological and geological parameters, the legal and corporate framework conditions, and the total cost of ownership (TCO), is crucial for ensuring a cost-effective integration of CCS in the long term. Examples include warranty costs and the subsequent costing of service contracts. Reliable determination of these costs and their optimization is crucial for successful financial planning – from plant design, construction, installation, and commissioning to actual operation.

Practical experience proves that the numerous interfaces between complex system and component solutions frequently cause problems that may affect significantly on later operating philosophy, and even the quality of the systems. To ensure the best possible operating philosophy and plant quality, support by an experienced partner from design and construction to final approval before the system is taken into operation is the best choice. Third-party organizations, such as TÜV SÜD, assist in the systematic prevention of interface problems. Economic, technical, geological, and legal risks must be assessed and controlled from the outset, and problems solved in a way that leads to the desired results.

TÜV SÜD experts provide integrated system analysis and support plant owners/operators in CCS implementation. These services come from teams that have been individually set up, combine technical, business, geological, and legal knowledge, and have long-standing experience in power station and plant engineering.
 

CCS Certification
New power stations require assessment for the possibility of integrating suitable CCS technology, and for their fitness for use of CSS. In this light, the key challenge is balancing the technical and economic needs of CCS technology for each individual power station process. As no generally valid definitions and criteria exist so far, TÜV SÜD developed its own standard. This standard forms the basis of the Fit for Carbon Capture certificate awarded by TÜV SÜD's power station specialists. The certification procedure builds on the documentation of technical facts and measures, and offers improved planning certainty, higher investment security, and wider public acceptance of plant-construction projects.

Outlook
Concrete projects must begin as soon as possible if the climate change objectives will be met 2050. The discussion of CCS cannot be limited to the expected additional costs alone. A fundamentally new way of thinking is necessary in order for the holistic assessment of potential new technologies. In addition, launching open-minded dialog with the affected people and a legal framework created is important. Only then can the existing climate protection technologies, based on the given international climate objectives, be implemented as quickly as possible.

TÜV SÜD Industrie Service GmbH
Power Station and Energy Services
Mannheim, Germany
tuev-sued.de/is