How ‘green’ are industrial CO2 emissions?

There are various kinds of CO2. Emissions of fossil CO2 that result from the burning of fossil fuel affect the environment. Biogenic CO2 resulting from the burning of wood or biofuels, however, is 'climate neutral'. Scientists at the University of Groningen have developed a method of accurately determining the ratio of these two types of CO2 in industrial emissions, using carbon-14 analysis. The method has proven to be so successful that the University will conduct a follow-up project, financed by RWE.

Because of ‘pay for your pollution’ policies, it is becoming increasingly important for industrial companies and power plants, as well as the government, to be able to determine how much fossil CO2 and how much biogenic CO2 is being emitted into the atmosphere. In accordance with European guidelines, CO2 emissions from fossil fuels must be paid for to an increasing extent.  Emissions from biofuels, however, are exempt.

Composition Unknown

The total amount of CO2 that a company emits can be determined and verified relatively easily and reliably on the basis of the amount of fuel used, as well as by data on burning and emissions. It is much more difficult, however, to determine the proportion of the total CO2 emission that results from the burning of biofuels and is thus exempt from extra charges. This is especially so when the composition of the fuel is unknown, such as when burning waste.

In cooperation with the Essent energy company, the University of Groningen’s Centre for Isotope Research (CIO, a division of the Energy and Sustainability Research Institute Groningen – ESRIG) researched how carbon-14 can be used in practice to determine the proportion of biogenic CO2 in emission gases, as well as the reliability of this method. The results of this research were recently published in the journal Bioresource Technology.

New Application

The carbon-14 analysis, well known as a method of determining the age of archaeological discoveries, has been used for over fifty years to distinguish between fossil and biogenic carbon in, for example, the food industry and atmospheric research. Now this method can also be used to reliably determine industrial carbon emissions.

In carbon-14 analysis, the number of carbon-14 atoms (14C) in a sample is determined. Biofuels contain a certain amount of carbon-14, and the same applies to the biogenic CO2 released when burning biofuels. Because the amount of carbon-14 decreases over time (as opposed to the carbon atoms 12C and 13C), substances that are millions of years old, like fossil fuels, no longer contain carbon-14. Because of this, fossil CO2 also does not contain carbon-14.
If fossil fuels are mixed with biofuels, the relative amount of carbon-14 will therefore increase. The ratio is used to determine the relative amount of biogenic CO2 in emissions.

Verified Method

The method for emission gas was tested at Essent’s Amercentrale power plant. At this plant, the exact amount of coal and biofuel (wood chips) being burned was known. Based on this information, the proportion of biogenic CO2 in the samples could be predetermined. The results from the carbon-14 analyses were very consistent with this information.
At waste burning plant AZN Moerdijk, where the carbon ratio in the waste is unknown, the carbon -14 analysis was then successfully able to determine what proportion of the CO2 in emission gases was biogenic.

The samples from the emission gases did have to be taken to the laboratory in order for the amount of carbon-14 to be determined. In cooperation with RWE (who financially support the project), the University of Groningen will begin research into a method of carbon-14 analysis that can be applied directly and continuously in the field. An agreement on this was signed on 5 March 2010 in Groningen.

Note for the press

More information:
- Sanne Palstra, MSc, tel.: 050-363 4123, e-mail: s.w.l.palstra rug.nl
- Prof. Harro Meijer, tel. 050 363 4739, email: h.a.j.meijer rug.nl

Publication:
Palstra, S.W.L. and Meijer, H.A.J. Carbon-14 based determination of the biogenic fraction of industrial CO2-emissions – Application and validation. Bioresour. Technol., 101, (2010), 3702-3710, doi:10.1016/j.biortech.2009.12.004