SIEMENS

When it comes to scrubbing carbon dioxide (CO₂) from power plant flue gas emissions, amino acid salt is the powder of choice. Its use enables the capture of more than 90 percent of CO₂ . As a result, the scrubbing agent is currently being tested at a pilot facility near Hanau, Germany. The tests are being conducted by Siemens in cooperation with the E.ON power company as one of several cooperative projects involving carbon capture and storage (CCS).

Experts predict that without CCS it will be almost impossible to achieve the 20 percent CO₂ reduction target set by the European Union for 2020 (relative to the base year 1990). This goal poses a dilemma in a situation where demand for energy is rising, thus putting pressure on utilities to respond quickly by burning more coal.

Power plant operators will therefore need to build facilities that emit low levels of CO₂. Indeed, the EU has stipulated that CCS systems must be ready to enter service by 2020. With this in mid, three avenues offer hope for a solution: coal gasification, oxygen combustion (oxyfuel technique), and the separation of CO₂ from flue gas after combustion (see article “Coal’s Cleaner Outlook”, Pictures of the Future 1/2008).

Siemens’ CCS development activities are focusing on coal gasification and CO₂ separation. The latter is particularly advantageous because it requires only the retrofitting of existing power plants, and is thus an attractive option for plant operators. Because Siemens already has a laboratory facility and extensive experience in flue gas scrubbing operations, the company is a soughtafter partner when it comes to cooperation projects for optimizing CO₂ capture systems.

E.ON and Siemens: A Perfect Match. A CCS pilot facility has been operating in Block 5 of the Staudinger hard-coal power plant near Hanau just west of Frankfurt, Germany since September 2009. E.ON will be testing a new CO₂ scrubbing technology there in cooperation with Siemens until the end of 2010.

“Siemens’ experience in this area is twofold,” says E.ON’s Head of Research, Bernhard Fischer. “It’s got the required engineering and power plant construction expertise as well as valuable knowledge in the field of process development for the chemical industry.” As an energy supply company, E.ON is a specialist in the planning and operation of fossil fuel-fired power plants. “Our work with Siemens is perfect for successfully refining CCS techniques and integrating them into the power plant process,” says Fischer. Siemens initially developed its new CO₂ scrubbing technique in a laboratory facility at the Höchst Industrial Park near Frankfurt am Main. In principle, the method - a common one for treating gas in the chemical industry - involves exposing CO₂ to an aqueous scrubbing agent that binds to the gas. To this end, Siemens equipped the Staudinger power plant with a 35- meter-high absorber tower through which a portion of the flue gas is passed.

The tower is packed with structured metal that is exposed to the detergent solution and the gas in a process that captures more than 90 percent of the CO₂ present in the flue gas. The CO₂-saturated solution is then steam-heated in a 20 meter- tall desorber tower until the CO₂ once again emerges as a gas. Two things are essential here: a scrubbing agent that is as environmentally friendly as possible and a cleaning process that uses as little energy as possible. Conventional chemical absorption methods utilize monoethanolamine (MEA). Siemens’ technique, on the other hand, employs environmentally friendly amino acid salts in an aqueous solution. In addition to being easily biodegradable, they are not flammable or toxic. What’s more, the salts do not require high temperatures for CO₂ capture, and once the desorption process is completed, nearly all of the dissolved salt can be reintroduced into the cycle.

“Amino acid salts are ideal CO₂ capture agents,” says Dr. Tobias Jockenhövel, who is responsible for the project at Siemens in Erlangen. CO₂ scrubbing with amino acid salts consumes less energy than other CCS techniques. “We were able to lower our energy requirement from four gigajoules to 2.7 gigajoules per ton of CO₂, which led to a significant cost reduction,” Jockenhövel reports.

With prices ranging from €10 to €20 per ton of CO₂, pollution rights are still relatively inexpensive; but with costs expected to rise above €40, it will pay off for power plant operators to separate, transport, and store CO₂. Conventional monoethanolamine-based CCS techniques lead to an efficiency loss of 11 percent at an 800- megawatt hard-coal plant; the comparative figure with the Siemens method is only nine percent.

Ideal for Finland. State-of-the-art power plants burn coal at an efficiency of 47 percent. “It is therefore already possible to use our technology to operate power plants with low CO₂ emissions at an efficiency of 38 percent,” says Fischer. That figure corresponds to the average efficiency of existing coal-fired plants in Europe.

The current goal, however, is to further improve the chemical properties of the scrubbing agent and the efficiency of the scrubbing process. At present, the test facility near Hanau can process one ton of carbon dioxide per day, which is one ten-thousandth the volume of flue gas produced in Block 5. Plans call for the technique to advance by 2011 to a point where Siemens will be able to build a large demonstration facility that will begin operating in 2015 and be able to separate the CO₂ produced by an entire power plant block.

Power plant operators in Finland are also impressed by Siemens’ CCS technology, which will be used at the Meri Pori power station in the western part of the country. In October 2009 the plant’s operators - Fortum and Teollisuuden Voima (TVO) - selected Siemens Energy from among ten companies to build a CCS demonstration facility by 2015. “Siemens’ technology seemed particularly promising to us,” says project manager Mikko Iso-Tryykäri, “especially because it’s environmentally friendly and has already been tested at a power plant.” The project offers Siemens the opportunity to operate its scrubbing system on a commercial scale at the 565 MW plant, initially by treating about half of the flue gas produced there. The partnership with Siemens will also enable Fortum and TVO to implement one of Europe’s biggest CCS projects. Specifically, the two plant operators plan to retrofit their facility and test the transport and storage of CO₂ in the North Sea together with other companies (see box).

Separating CO₂ from Gas Plant Emissions. Natural gas is a much more climate-friendly fuel than coal, which is why combined-cycle power plants enjoy great popularity. Nevertheless, these plants also produce CO₂, albeit to a lesser degree. Siemens is therefore studying ways to adapt its scrubbing technique to combined- cycle facilities on behalf of Norway’s Statkraft power company.

But there’s a catch: Combined-cycle power plants produce oxygen-rich flue gas, which attacks every kind of detergent. “In view of this, we have modified our technology and now know that it we can also achieve good efficiencies at combined- cycle facilities,” says Jockenhövel. “Efficiency losses in our lab tests are well below eight percent.” The process for CO₂ separation with amino acid salts is fairly advanced, but both the scrubbing substance and the process as a whole need to be further refined if they are to be employed on a commercial scale. Such a large-scale application is the goal of a partnership launched by Siemens with the TNO research institute in the Netherlands in the summer of 2009.

By studying scrubbing techniques that use diverse chemical substances, TNO has discovered that amino acid salts offer a particularly promising option. TNO’s contribution to the partnership is its knowledge of amino acid salts other than those tested by Siemens. Since 2008 TNO has been operating a pilot facility at a coal-fired power plant in Rotterdam, the Netherlands. The plant is similar in size to the one in Hanau.

“Siemens is an ideal partner, and our cooperation has been very successful,” says René Peters, who manages CCS projects at TNO. “TNO provides its expertise in chemicals technology, while Siemens is contributing the knowledge it has gained from its development and implementation of power plant processes,” Jockenhövel adds. Siemens now plans to improve the processes in cooperation with its Dutch partner. The next step will involve testing the refined processes at the Staudinger plant. In the mid term, Siemens plans to build a demo facility for a power plant block by 2014. This could provide conclusive evidence that some powders can scrub flue gas clean.