Tackling industrial waste Cement kilns versus Incinerators - An environmental comparison

4. How is industrial waste incinerated?

The Life Cycle Assessment by TNO states:

3.4 Alternative thermal treatment scenarios

For the LCA study to Febelcem the environmental impact of waste, when treated in the cement industry is compared with the environmental impact when incinerated in a suitable incineration system. The following starting points are used:

  • The five specific waste streams are:

    1. Solvents and waste oils
    2. Filter cake
    3. Industrial sludges
    4. Paint, ink residues
    5. Fluff
  • Based on the Belgian situation, using the processes of Indaver

The most suitable incineration system for the indicated five waste streams is not in all cases the same type of incinerator. In principal, three incinerator types have been taken into account, namely a rotary kiln, a FBC (Fluidised Bed Combustor), and a grate incinerator. Based on specific information of Indaver (Mr.Wauters) it is assumed that the Rotary Kiln is most suitable for the incineration of solvents / waste oils, paint/ink residues and filter cakes, and that the FBC would be used for the incineration of industrial sludges and fluff. The grate incinerator would not be used for the treatment of one of the five waste streams. The selection of the alternative thermal treatment options is made on the basis of the physical properties of the waste streams, such as moisture content, viscosity, ash content, particle size, etc.

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns , (2007),
3. Model description, 3.4 Alternative thermal treatment scenarios, p. 18
 See also Annex 3 Waste incineration

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


4.1 How are waste incinerated in rotary kiln incinerators?

The Life Cycle Assessment by TNO states:

The rotary kiln incinerator plant at Indaver (in Antwerp) consists of a rotary kiln with afterburner, a steam boiler and a flue gas cleaning system. The flue gas treatment is based on a wet system with wet scrubbers, resulting in a waste water stream, causing emissions to surface water. After passing the dustfilters (ESP = Electro Static Precipitator) and wet scrubbers a pilot filter using (activated) coal is operational to clean the flue gasses to such a degree, that they can easily strike all threshold limits for emissions to the air. Residues like slag (after treatment for removal of metals), boiler ash, ESP-ash and filter cake are solid residues that are landfilled. This incineration process is shown in figure 4 .

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
3. Model description, 3.4 Alternative thermal treatment scenarios, p. 18-19

 See also Annex 3 Waste incineration


4.2 How are wastes incinerated in fluidised bed incinerators?

The Life Cycle Assessment by TNO states:

A fluidised bed combustor (FBC) is a quite different incinerator (see figure 5 ). In the case of Indaver, also the flue gas cleaning system differs from the system of the rotary kiln. The most relevant difference is the fact that the FBC is provided with a semi-dry flue gas cleaning system, resulting in a larger amount of solid residues, but without a remaining waste water stream.

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
3. Model description, 3.4 Alternative thermal treatment scenarios, p. 19

 See also Annex 3 Waste incineration


4.3 How much energy is recovered when burning a tonne of waste in an incinerator?

The Life Cycle Assessment by TNO states:

Table 3 shows the substitution scenarios for waste incinerators. They are as far as possible based on the Belgian situation, with the perspective of marginal change. The selected waste streams are regarded as if they were treated by Indaver. At the Antwerp site (rotary kiln) energy is recovered from the incineration of (hazardous) waste. Part of this energy is used within the process as steam and electricity; the remaining is delivered, as steam and electricity, to other processes at the Antwerp site. The same holds for the Fluidised Bed Combustor of Indaver. The system is in both cases balanced by subtracting the avoided energy production from the impact of incineration – to keep the functionality the same between the two systems (cement kiln and incinerators). The substitution for waste incineration is based on the caloric value of the waste, similar to clinker kilns (see Table 2 ).

Table 3. Recovered energy delivered to external users in MJ per MJ caloric content of waste 

For the externally delivered energy the avoided production of steam and electricity is subtracted from the system. To reflect the actual situation the Belgian electricity mix is used as the avoided product. For steam it will be the conventional generation of industrial process steam.

For Solvents/waste oils, an additional substitution scenario is calculated, as in the review panel it was argued that increased input of solvents/waste oils decreases the need for supportive fuel (light oil) for start up of the waste incineration plant. For the other waste streams this is not a realistic scenario, as (solid) wastes cannot directly replace diesel oil. Even for solvents/waste oils this is only a marginal, and not representative scenario, because in practice only 2% (based on caloric value) of fuel oil is being used per ton of waste. Besides, Indaver uses waste oil as a supportive fuel. This could be replaced by the specific waste stream ‘solvents / waste oils’, but in LCA terms this is the same material, not leading to a real substitution

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
2. Study approach, Substitution scenarios, p. 10-11

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