Method for decreasing an amount of a harmful substance of an off-gas stream formed or used in a thermal treatment of a material

1. A method for decreasing an amount of a harmful substance of a chlorine-containing off-gas stream formed or used in a thermal treatment of a material, the method comprising:

dividing the chlorine-containing off-gas stream into a main stream and a substream;

afterwards, separating at least some chlorine from the main stream;

afterwards, lowering an amount of the harmful substance in the main stream, wherein a chlorine-containing additive is introduced into the main stream to enhance separation of the harmful substance; and

filtering the substream such that a filter cake is separated from the substream, wherein at least part of said filter cake is used as said chlorine-containing additive.

2. The method of claim 1 for decreasing an amount of sulphur content in the off-gas stream, the method further comprising:

introducing a calcium-containing additive into the off-gas stream; and

filtering off at least one of calcium sulphite or calcium sulphate from the off-gas stream,

wherein a reaction of at least one of sulphur dioxide or sulphur trioxide in the off-gas stream forms at least one of calcium sulphite or calcium sulphate.

3. The method of claim 1 wherein the separation of the at least some chlorine from the main stream is caused by cooling the main stream during the thermal treatment of the material.

4. The method of claim 3 for decreasing an amount of sulphur content in the off-gas stream, the method further comprising:

introducing a calcium-containing additive into the off-gas stream; and

filtering off at least one of calcium sulphite or calcium sulphate from the off-gas stream,

wherein a reaction of at least one of sulphur dioxide or sulphur trioxide in the off-gas stream forms at least one of calcium sulphite or calcium sulphate.

5. The method of claim 1 for decreasing an amount of mercury content in the off-gas stream, wherein a reaction involving mercury that forms mercury chloride is caused by:

introducing the chlorine-containing additive; and

filtering off the mercury chloride from the off-gas stream.

6. The method of claim 1 further comprising:

separating the filter cake into a fine fraction and a coarse fraction; and

feeding the fine fraction at least in part back to the main stream of the off-gas stream.

7. The method of claim 1 further comprising treating the filter cake at least in part with water.

8. The method of claim 7 further comprising:

dewatering the filter cake to obtain a dewatered constituent and chlorine-containing process water; and

feeding the chlorine-containing process water used as all or part of the chlorine-containing additive to the main stream of the off-gas stream.

9. The method of claim 8 further comprising mixing the dewatered constituent with the material.

10. The method of claim 8 further comprising adding a calcium-containing additive to the chlorine-containing process water that is fed to the main stream of the off-gas stream.

11. The method of claim 10 further comprising mixing the dewatered constituent with the material.

12. The method of claim 8 further comprising treating at least one of the dewatered constituent or the chlorine-containing process water to decrease, separate, and/or concentrate one or more constituents.

13. The method of claim 1 further comprising:

introducing the chlorine-containing additive into the main stream of the off-gas stream at a point upstream of an off-gas filter; and

discharging at least a portion of a filter cake produced in the off-gas filter.

14. The method of claim 1 further comprising:

firing kiln meal to form cement clinker; and

using the off-gas to be decreased with respect to the amount of the harmful substance to preheat the kiln meal, wherein the off-gas is formed during the firing of the cement clinker.

15. The method of claim 1 further comprising processing one or more raw materials to form kiln meal, wherein the off-gas to be decreased with respect to the amount of the harmful substance is used for drying the one or more raw materials.