Tackling industrial waste Cement kilns versus Incinerators - An environmental comparison

2. What types of industrial wastes are considered?

2.1 Which five waste streams are the focus of this study?

The Life Cycle Assessment by TNO states:

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

The used wastes mainly come from Belgium (all directions) and the North of France, the west of Germany (close to Belgium) and the South of the Netherlands.

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
3. Model description, 3.2 Pretreatment and transport, p. 15-16

 See also Annex 1 Waste streams and representativeness

 

2.2 How much waste and fuel is used in cement kilns?

The Life Cycle Assessment by TNO states:

For the environmental assessment five waste streams have been selected (see Table 1 ). These five waste streams cover 91% of the mass input of energy carriers, excluding animal meal and fossil fuel as these last two fuels are no subject of the taxation on secondary fuels.

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
1. Introduction, paragraph 2, p. 7

 

2.3 How well does waste burn?

The Life Cycle Assessment by TNO states:

3.1 Waste characteristics

As stated in the project description and changed during the discussions with the expert panel, the study focuses on five waste streams. The main characteristics of these streams are listed in Table 5. The data for the waste streams are received from the Belgian cement industry and represent the average 2006 values. If possible, minimum and maximum values are given. For the substitution scenarios, Petcokes and Coal are defined. In Annex 1 additional properties of the different waste streams and fuels are given, including the amount of CO2 produced per ton of waste or fuel. Filter cakes are big lumps of fine solids that are filtered under pressure to remove the moisture. Filter cakes still contain about 50% of moisture, but are solid-like materials. Sludges differ from filter cakes. They mostly are less de-watered, and still contain around 70% of water. It are pasty materials, that most often can still flow. The 31,9% that is mentioned in Table 5, is the average moisture content in the sludges after pre-treatment (drying).

The definition of Coal is based on the average composition of coal used in Belgium over the year 2006. The composition of Petcokes is based on actual numbers, as provided by the Belgian cement industry.

Table 5. Summary of main characteristics of waste streams and fuels 

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
3. Model description, 3.1 Waste characteristics, p. 13

 See also Annex 1 Waste streams and representativeness

 

2.4 How and why is waste pretreated in some cases?

The Life Cycle Assessment by TNO states:

3.2 Pretreatment and transport

The pre-treatment of waste and transport to clinker kilns and waste incinerators is included in this study. Table 6 gives an overview of the pre-treatment scenarios as used in this study.

Table 6. Summary of pre-treatment of waste when used in clinker kilns or in waste incinerators 

Both solvents / waste oils and paint / ink residue are pre-treated at a dedicated facility. In this study we have collected data for the transport of waste to the pre-treatment location, input of energy, auxiliary materials and wood residue and emissions of VOC at the Geocycle facility.

Figure 2  shows an overview of the Geocycle activities. In fact the impregnated saw dust silo is not completely closed. VOC-emissions from this silo are taken into account based on the following assumptions:

  • The VOC content on the paint/ink is 10% (mixture of liquid and solid residues and mixture of water based and solvent based paint/inks).
  • 10% of the VOC in paint/ink residues is emitted to air, after impregnation when stored in the open silo. This assumption is based on the expertise of Jurg Liechti of Neosys.

The input of wood residue is entirely allocated to the treatment of paint/ink residues. This also holds for the VOC emission from the impregnated saw dust silo. The other inputs and emissions are allocated based on the mass of treated solvents/waste oils and of paint/ink, and the total amount of waste handled at Geocycle in 2006. Not all wastes that are used in the Belgian cement industry are pre-treated at the Geocycle plant. However, the majority is. Furthermore the different pre-treatment processes are to a large extent alike. Therefore the pre-treatment process at the Geocycle plant is taken as representative.

Sludge is dried before it is used in clinker kilns. The moisture content of the sludge, as it arrives at the pre-treatment site, is around 70%. After drying the sludge contains still around 30% moisture. For the production of 1 ton dry sludge out of wet sludge, 50 Nm3 natural gas is used and 45 kWh electricity. In the case of incineration the sludge is not dried beforehand, but directly fed into the FBC.

The pre-treatment of petcoke, coal and raw meal is included when the input is avoided. Electricity is used for the handling and milling of petcoke and coal. As a result of the milling carbon components are emitted to the air. For these emissions we have used data from a Belgian clinker producer involved in this study.

The pre-treatment of raw meal (in the substitution scenario) consists of mining, transport, crushing and milling. Because limestone is the main ingredient of the raw meal, for the calculation of the impact of pre-treatment and transport, the data of this material are taken as representative for all ingredients. These data are taken from the Eco-invent database, including particulate emissions to air as a result of crushing and milling. The electricity consumption data for milling, crushing and other raw meal handling comes from one of the Belgian clinker producers.

Travelling distances for the thermal treatment of the wastes in cement kilns were determined, based on the real sources, specified by the cement producers. The used wastes mainly come from Belgium (all directions) and the North of France, the west of Germany (close to Belgium) and the South of the Netherlands. The transport distance from France to Indaver is slightly longer, from the Netherlands slightly shorter compared to the distance to the cement kilns. The difference for transports from Germany depends on the location of the cement kiln. The average net result is more or less the same for waste treatment at Indaver and for waste treatment in the cement kilns. For transparency reasons we have taken the same distance and transport means. Travel distances cannot be left out, however, because of the fact that the transport distances for the substituted fuels are not the same. For paint/ink and solvents/waste oils, the transport from the pre-treatment site to the clinker kilns is not accounted for in the transport scenario to waste incinerators, as this waste is not pre-treated before waste incineration. The transport models used are directly derived from Ecoinvent. For transport by road we have used a 32t lorry.

Source & ©: TNO  LCA of thermal treatment of waste streams in cement clinker kilns (2007),
3. Model description, 3.2 Pretreatment and transport, p. 13-16


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