Tackling industrial waste Cement kilns versus Incinerators - An environmental comparison

1. What waste treatment options are compared and why?

The Life Cycle Assessment by TNO states:

1. INTRODUCTION

Febelcem is the association of Belgian cement producers. In the current practice of cement production, and more specifically the clinker3 production, alternative fuels made from specific waste streams are of considerable importance. Febelcem has asked TNO to make an environmental comparison of waste treatment in clinker kilns with treatment in waste incinerators. The environmental assessment is a response on the proposed change in taxation on secondary fuels.

3 Clinker is the output product of the burning process. The main raw material is calcareous rock like limestone. It is the main constituent of cement.

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
1. Introduction, p. 7

The study started in February 2007 and was finalised in June 2007. It is conducted in cooperation with an expert panel, consisting of

  • OVAM4
  • Wallone representatives (chair)
  • VITO4
  • Neosys
  • cement producers: Holcim, CCB and CBR
  • Febelcem

4 The representatives of OVAM and VITO had (and still have) objections to some of the “starting points” of the study, and therefore cannot fully agree with the conclusions of the study. Their comments, and the reactions of the authors, are given in Annex 6.

2. STUDY APPROACH

2.1 Goal and scope

The goal of the study is :

The comparison of the environmental performance of the thermal treatment of a number of specific waste streams in the clinker production process with the thermal treatment of these waste streams in waste incinerators.

The target audience of the report is, besides Febelcem and its members, the Belgian authorities, the Belgian special waste processors and experts in the field of waste incineration. To follow the ISO guidelines for LCA and to improve the quality of the LCA study, an expert panel was consulted four times during the performance of the study. Jürg Liechti of Neosys acted as reviewer. The review statement and the reviewer’s recommendations, as well as the comments made by the expert panel members (and the authors’ reaction on that) are included as Annex 6 to this LCA report.

The following parties were represented in the expert panel:

5 The representatives of OVAM and VITO had (and still have) objections to some of the “starting points” of the study, and therefore cannot fully agree with the conclusions of the study. Their comments, and the reactions of the authors, are given in Annex 6.
VITO5 Katleen Briffaerts
Ministère de la Région Wallonne Philippe Decornet (chairman)
OVAM (representing the Flemish authority)5 Luk Umans and Dries Gommers
Febelcem Benoit Lussis and Michel Calozet
CCB/Italcimenti Eric Derycke (Chef de Département Développement Environnement)
CBR/Heidelberger Cement Fabrice Foucart and Gaetan de Maere (Environmental Affairs Managers)
Geocycle/Holcim Olivier Barbery (Director)
Neosys Jürg Liechti (reviewer)

In the LCA study two systems are being compared with each other:

  1. the use of specific waste streams as alternative fuels in the Belgian clinker production;
  2. the incineration of these specific waste streams in dedicated waste incinerators in Belgium.

The time frame for comparison is the current situation with the focus on the year 2006.

The function that is provided by both product systems and that is the single base for comparison is the functional unit . To this functional unit all input and output flows will be referred. For this comparison the functional unit is defined as follows:

The thermal treatment of 1 ton of a specific waste in Belgium in 2006.

The approach used to compare the two systems with each other is that of comparing the marginal changes . This means that the changes and effects are studied that result from a minor change in a system. In this study the marginal change is the treatment of one (extra) ton of waste in either system.

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
1. Introduction, paragraph 3,
2. Study approach, 2.1 Goal and scope , p. 7-9

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 3 Waste incineration, Annex 4 Shadow prices, Annex 6 Comments of reviewer and panel members

 

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