Measurements Show Less Global Warming from Waste Incineration than Previously Believed

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1 Measurements Show Less Global Warming from Waste Incineration than Previously Believed Lia Detterfelt, Renova AB Contact Lia Detterfelt, Renova AB Box 156, SE Göteborg Phone Executive summary Measurements of the content of fossil carbon in waste incinerated at the Renova plant in Sweden. The measurements were done using C-analysis in six waste samples taken out in a standardized manner and representing a large amount of waste incinerated in about 6 months in The measurements indicate that the contribution to the global warming from waste incineration in Sweden may be highly overrated. Introduction Global warming is the most important environmental challenge of the world today. Taxes and support systems have are used to help fulfill the targets of lowering fossil CO 2 -emissions set by governments. These taxes highly affect the waste incineration industry. There is also an on-going debate whether to consider waste incineration as a green source of electricity and district heating, or not. Waste consists both of biogenic carbon from e.g. paper, food and textiles as well as fossil carbon from e.g. plastics. The carbon in waste is transformed into CO 2 in the incineration process and that originating from fossil carbon is contributing to the global warming. A common way to describe the global warming from incineration is by using emission factors. The emission factors for fossil CO 2 from waste incineration used when reporting the countries contribution to global warming vary much between countries and are often based on general assumptions. For example, the emission factors used when reporting within Europe may vary from kg CO 2 /GJ, depending on country and type of waste incinerated. The emission factor used by Swedish authorities is 25kg CO 2 /GJ and is based on assumptions of the presence of fossil carbon in various materials and the amount of the specific material in the general waste mixture determined in so called pickanalyses.

2 Renova study To get a better knowledge of the contribution from waste incineration to the global warming the waste management company Renova, situated in Göteborg on the West Coast of Sweden, analyzed the fossil content in the incoming waste to the plant using carbon--analysis. Samples were taken from the waste bunker in a standardized manner to represent the entire volume coming in to the plant during approximately one week s time. The method is described by Johansson et al. About 5 tonnes of waste was taken out of the bunker and crushed. After crushing it was spread and divided in two parts, using a wheel loader. One part was removed, the remaining part was spread and divided again. The procedure was continued until only a small amount remained. About 40 kg of waste then taken out and sent to a chemical laboratory, which milled the sample and analyzed it for e.g. chemical composition and heating value. A part of the sample, now in the form of a powder, was sent for C-analysis. Waste sampling was done at four different occasions in a time period of about six months in At two of the occasions a double-sample was sent for C-analysis. Fig. 1 Waste crushing and partitioning at one of the sampling dates at Renova, and the resulting powder of the waste to be analyzed with C The C analysis was done at the Lund University Radiocarbon Dating Laboratory using Acceleration Mass Spectroscopy (AMS) on the gases formed during combustion. The pretreatment of samples by dissolution in an inorganic acid which is normally done before analyzing archeological samples, was excluded to avoid the possibility of bringing carbonates into solution. Since Swedish legislation differ in responsibilities between hushållsavfall ( Municipal Solid Waste, MSW) and verksamhetsavfall ( Industrial Waste) the amount of incoming waste of the two types was noted from the Renova registration system of incoming waste trucks. Results and conclusion

3 % fossil of total carbon Content of fossil carbon out of total carbon in waste at Renova incineration plant in Approx. MSW content out of total waste (%-wt) Fig. 2 Content of fossil carbon in waste at the Renova incineration plant in Göteborg, Sweden in During the incineration process almost all carbon in the waste is turned into CO 2. The fossil part of the carbon in waste is therefore equal to the fossil part of CO 2 of the total amount of CO 2 in flue gas to the atmosphere 1. Since fossil CO 2 -emissions are often described in emission factors, this was also determined by using the analyzed heat values in the samples. effective heating value in wet waste (kg/gj) Emission factors Approx. part of industrial waste in waste (%-wt) Fig. 3 Emission factors for various waste mixtures at the Renova plant in The emission factor used by Swedish authorities is 25 kg/gj. The result implies that the effect on global warming from waste incineration may be highly overrated in Sweden and possibly also in other countries. The fossil carbon content in the six samples varied between 1-12% of the total carbon with a mean value of 7 %. The amount of fossil carbon increased with increasing amounts of industrial waste in the waste mixtures. The mean value corresponds to a fossil CO 2 1 The remaining carbon content in fly ash is less than 3% and the amount of CO and other not completely oxidized C is less than 1%. The fossil part in ash and non-oxidized gaseous C is assumed to be equal to that in the waste.

4 release of 6 kg/gj (LHV, wet samples) which is significantly lower than that used by Swedish authorities and the waste industry which is 25 kg/gj 2. (Naturvårdsverket) Assumptions on the atmospheric concentration One factor that has been proven to be important when determining the fossil carbon content in a sample is the atmospheric concentration of C used in the calculations. Because of nuclear bomb testing, the concentration of C in the atmosphere drastically increased in the 1960s and thereafter decline to a concentration of less than 106% today. In the Renova study the concentration of C in the atmosphere in the year the analysis was performed, was used. This is the standard procedure when dating archeological objects. However, it can be argued that a mean value of the atmospheric content during a number of years when the plant or animal were still alive to absorb carbon should be used. Concentrations between % have been mentioned by laboratories and other studies. When assuming the highest of these values the result is as follows: % fossil of total carbon Content of fossil carbon out of total carbon in waste at Renova incineration plant in Approx. MSW content out of total waste (%-wt) Fossil content of total carbon (%) fossil CO2 (atmospheric concentration of 113%) Fig. 4 Content of fossil carbon out of the total carbon in waste at the Renova plant Göteborg, Sweden. Calculated from the atmospheric concentration of C the year the analysis was performed and as an assumed mean value of 113% The graph shows that also when using a much higher assumed concentration of in the atmosphere (113% ) than in the Renova study, the fossil content in waste is still much lower than previously thought. How to use the results C 2 The total emission factor from waste incineration should also include all greenhouse gases released to the atmosphere. The most important at the Renova plant is N2O (Miljörapport 2009). The contribution of N2O, when using the equivalence factor of 310, shows that the contribution is in the range of 1 mg/gj, which means it is negligible.

5 The results suggest that waste incineration should be considered to be a more biogenic energy source than it is today and that the contribution to the global warming may be much lower than earlier estimated. However, the study only covers one plant in a limited range of time and from a limited set of samples. The study may therefore be seen as a first attempt of measuring the fossil release of CO 2 into the atmosphere during waste incineration and for creating a model for how to measure. To get a better understanding, there is a need to perform a larger study with a deeper discussion on for example sampling techniques in flue gas, what atmospheric concentration is the appropriate to assume and so forth. A study like this was started in September 2010 in Sweden. References Johansson, Ingvar et al, Karaktärisering av fasta inhomogena avfallsbränslen - inverkan av metoder för provtagning och provberedning, Avfall Sverige Rapport F2008:05, ISSN Miljörapport 2008 för avfallskraftvärmeverket och sorteringsanläggningen, inklusive återvinningscentralen vid Sävenäs, Renova 2009 Naturvårdsverket, Beräkna utsläpp av växthusgaser, Appendix Table 1. Description of samples and result of calculations in the Renova study Date sampling Approximate MSW content of total waste volume (%-wt) C activity (pmc) Atmospheric content in the year of analysis (%) Fossil content of total carbon (%) ± (2008) 11 ± (A) ± (2009) 97 ± (B) ± ± (A) ± ± (B) ± ± ± ± 1 3 Crushed industrial waste sampled before delivery to waste bunker

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