Tackling industrial waste Cement kilns versus Incinerators - An environmental comparison

4. How is industrial waste incinerated?

Two types of waste incineration are relevant to the present study

Energy recovery is but a side product of waste incineration, the main objective being waste disposal.

The choice of one or the other incinerator for a given waste is made based on its characteristics, such as moisture content, the amount of ash that remains after combustion, etc.

Such incinerators are operated at different sites in Flanders by the waste management company Indaver. Since Indaver was not involved in the project and only wanted to deliver public data, the assessment of the process is mainly based on the annual report 2005 (previously available on www.indaver.be ) as well as on detailed information available for Swiss incineration plants using the same technologies.

Both types of incinerators consist of:

Ashes or other solid residues from any of these steps are generally disposed of in landfills. More...

 

4.1 How are waste incinerated in rotary kiln incinerators?

The largest hazardous waste incinerator in Belgium is a rotary kiln incinerator of Indaver located near Antwerp. The incineration is carried out with energy recovery and intensive flue gas purification. Specific waste in liquid or paste form, such as paint or ink residues can be injected into the incinerator directly without pre-treatment. The system is also suitable for solvents and waste oils and wastewater filter cake.

It is called rotary kiln incineration, because the main combustion chamber is a nearly horizontal cylinder that rotates slowly around its axis. The wastes are fed into the slightly higher end of the cylinder and gradually move down towards the lower end while being mixed and heated at more than 1 000°C.

The use of wet scrubbers in the flue gas cleaning system leads to a wastewater discharge to surface water. More...

Table 3: Recovered energy delivered to external users 

 

4.2 How are wastes incinerated in fluidised bed incinerators?

In a fluidised bed incinerator , such as the Indaver facility located in Doel, wastewater sludge can be incinerated in combination with other wastes that burn well, for instance fluff (high calorific value waste).

It is called fluidised bed incineration, because a hot bed of sand is used to transfer heat directly to the waste. In the furnace sand and waste are circulated by a strong airflow at a temperature of at least 850°C.

Unlike, rotary kilns, fluidised bed incinerators use a semi-dry flue gas cleaning system which avoids any wastewater discharge to surface water. More...

Table 3: Recovered energy delivered to external users 

 

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

The main focus of the comparison is the environmental impact of adding an extra tonne of waste to the incinerator.

Adding one tonne of a specific type of waste to the process produces a certain amount of electricity and steam, though energy recovery is but a side product of waste incineration.

Table 3: Recovered energy delivered to external users 

In a rotary kiln incinerator, 23,1% of the energy content of waste is recovered, mostly as steam (20,9%) but also as electricity (2.2%).

In a fluidised bed incinerator, 35.6% of the energy content of waste is recovered, mostly as steam (25,4%) but also as electricity (10,2%).

To assess how the addition of 1 extra tonne of waste would increase emissions to air, water and soil the different constituents of the waste are considered including content in heavy metals, sulphur, chloride, and carbon. For each substance that goes into the incinerator it is determined how much would be emitted to the atmosphere or to water and soil.

Table 1: Average properties of selected waste streams and fules 

Fine ash and other solid residues that leave the incinerator to be disposed of in a landfill are considered an emission to the environment.

Emissions avoided as a result of avoided steam and electricity production by other power generators are also taken into account. More...


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