Aanpak van industrieel afval Cementovens vergeleken met verbrandingsovens - Een milieuvergelijking

5. How are environmental impacts compared?

5.1 What steps are considered in this Life Cycle Assessment?

The Life Cycle Assessment by TNO states:

During the study it was not possible for TNO to retrieve all required data regarding the waste incinerators from Indaver. Indaver was not involved in the project as member of the expert panel. Indaver therefore was not prepared to provide company-specific data, but provided public data only (Annual report 2005). For this reason, with regard to the transfer coefficients for waste incineration, it was required to find other sources of data.

An important source of data proved to be an Eco-invent study performed on a Swiss incineration plant. This hazardous waste incinerator plant is very similar to the rotary kiln of Indaver. Based on this analogy, TNO retrieved transfer coefficients, required for calculation of the environmental impact. The transfer coefficients themselves are presented in Annex 3, together with a more extensive description of the incineration process. Because some of the used Eco-invent data were outdated, a sensitivity analysis is made on this subject in paragraph 4.3.7.

The data of Eco-invent and the data of Indaver were checked against data of a third rotary kiln incinerator, that was described as the best available technique for waste incineration in the 2006 document of IPPC. The plant involved is the hazardous waste incinerator in Vienna: Simmeringer Haide. The most important differences in conversion factors between the plants of Simmering Haide and Indaver are caused by the use of brown coal (for the filter) and the use of fuel oil. This gives rise to slight differences in transfer coefficients, related to the emissions.

For the FBC transfer coefficients were deduces from the Eco-invent values, taking into account the differences between a rotary kiln and a FBC. These main differences concern differences in solid waste streams and in the fact that a FBC does not have any waste water stream. Also these differences are presented in Annex 3.

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
3. Model description, 3.4 Alternative thermal treatment scenarios,
Transfer coefficients for waste incineration, p. 20

3.5 The method of marginal changes

In order to compare the different systems for thermal treatment of waste streams, the decision on the mathematical method is trivial. In regular cases, absolute values of the outcomes of the LCA are simply compared. In this study, however, the systems to be compared are intrinsically different in behaviour and output. Cement kilns produce clinker, alternative treatment processes treat waste and produce heat and electricity. The best method to compare the environmental impact of the thermal treatment of waste streams in those two different processes is the method of marginal changes.

The mathematical method of marginal changes defines changes of a system to a predefined baseline, in this case the 2006 situation. Based on this baseline, small changes to desired and predefined inputs are applied, and the effect on the system is determined. In this study the marginal changes were defined as the extra input of one ton of one of the five predefined waste streams. The applied changes are relatively small compared to the absolute response of the system. Due to this, the linearity requirement is fulfilled. Furthermore, by defining changes to a baseline, the intrinsic function of a system is filtered. In this study, the application of this method is therefore justified. This is also the reason that the energy efficiency of the different cement kilns is out of the scope of this study; not the production of one ton of clinker is the functional unit, but the treatment of one ton of waste (or secondary fuel).

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
3. Model description, 3.5 The method of marginal changes, p. 20

 See also Annex 4 Shadow prices


5.2 What environmental impacts categories are we concerned about?

The Life Cycle Assessment by TNO states:

2.3 Impact assessment

The baseline categories of the CML impact assessment method is used to calculate environmental impact results. A sensitivity analysis will be made using the Eco-indicator 99 method. Table 4  gives an overview of the impact assessment categories in these two methods, and the units of the results. CML is a midpoint method: the results within a category are integrated using equivalency factors. Eco-indicator 99 is a damage-oriented method: the results are expressed in damage units for:

  • Human Health (Disability Adjusted Life Years – DALYs),
  • Ecosystem quality (Potentially Disappeared of Affected Fraction – PDF of PAF, on a certain area during a certain time period)
  • Depletion of resources (surplus energy for future extraction)

Table 4. Overview of Impact categories in CML and Eco-indicator 99 impact assessment methods 

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
2. Study approach, 2.3 Impact assessment, p. 11-12

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