Carbon capture experiment begins in Germany

Testing officially began in Jaenschwalde in eastern Germany of a system to capture carbon dioxide at power stations, with the Swedish owner, Vattenfall Europe, saying it expects the technology to be practical by 2015. Carbon capture and storage (CCS) is seen as a way to reduce greenhouse gas emissions of large power stations that use fossil fuels like coal and natural gas. Vattenfall's experiment is the first attempt in the world to generate power from lignite, or brown coal, with no carbon dioxide (CO2) emissions. The carbon separation technology used by Vattenfal is based on oxyfuel combustion. Other companies are working on similar technologies for use with hard coal. The result of applying CCS to fossil fuels is an almost carbon-neutral energy system.

Different aspects of CCS need further study though. Scientists have warned against risks like CO2 leakage from the geological formations in which the carbon is supposed to be stored for decades and centuries. However, there is a safer way forward: utilising biofuels with CCS.

Biofuels are already carbon-neutral from the start. By capturing and storing their carbon, the energy system becomes radically carbon-negative. According to some researchers, such systems - called 'Bio-Energy with Carbon Storage' (BECS) - can take us back to pre-industrial CO2 levels by mid-century. BECS effectively takes CO2 out of the carbon cycle; it cleans up our emissions from the past. BECS is a concept that can mitigate climate change radically. Based on the use of competitive biofuels - biomass or biogas - it relies on fuels that can be physically traded on a global market.

We think policy makers should look at and promote BECS today in order to make CCS safer. The reason is obvious: in a worst-case scenario – the failure of storage and CO2 leakage – the carbon dioxide that would be released would not result in a net increase in emissions (since the CO2 was part of the carbon-neutral biomass in the first place). If leakage were to occur with carbon dioxide originating from fossil fuels, the contrary would be the case. In short, starting CCS trials with biomass is the safest way forward.

Oxyfuel combustion
The largest cost hurdle for CCS to become commercially viable is the phase of capturing the carbon from the fuel. Three basic techniques exist: capturing the carbon before the fuel is burned (pre-combustion capture), after it is combusted (post-combustion capture) or during its power generation (oxyfuel combustion). Vattenfall's pilot system uses the latter technique. In oxyfuel combustion the lignite is burned in oxygen instead of air. This produces a flue gas consisting only carbon dioxide and water vapour, which is cooled and condensed. The result is an almost pure carbon dioxide stream that can be transported to the sequestration site and stored. The technique is promising, but the initial air separation step demands a lot of energy:
bioenergy :: biofuels :: energy :: sustainability :: climate change :: fossil fuels :: carbon dioxide :: CCS :: carbon capture and storage ::

Carbon capture energy costs and technology costs are much lower with biogas in a BECS sytem. The carbon fraction present in anaerobically fermented biogas is high, making pre-combustion separation easier (earlier post).

Vattenfall's Chief executive Klaus Rauscher said the oxyfuel technology would next be used at a pilot plant, a bigger, €60 million (US$80 million) system to be commissioned in May next year at Schwarze Pumpe, near the Polish border. He said the Swedish-owned company would ultimately convert all its power stations to oxyfuel technology. "We aim to turn lignite into power in a climate-friendly way," he said in Jaenschwalde.

Scientists from the German University of Cottbus are jointly working on the tests with Vattenfall engineers. After the test and the pilot systems, Vattenfall would commission a 300 megawatt demonstration system between 2012 and 2015 (image, click to enlarge), Rauscher said, with the first economic CO2-free lignite plant likely to go into operation by 2020.