sludge characterisation on the energy level

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The energy utilisation potential is defined by the raw sludge’s net calorific value (NCV). This potential is calculated from the NCV of the organic matter (between 20,900 and 23,000 kJ · kg–1 of organic matter) and this NCV is used to deduce the condensation heat of water contained in the sludge concerned.

Compared with other waste, sludge has a low NCV. For guidance, untreated household waste has an NCV of approximately 8,500 to 9,000 kJ · kg–1 of household waste whereas mechanically dewatered sludge has a NCV of between 1,200 and 1,500 kJ · kg–1 of dewatered sludge (25 % dry matters).

All heat applications are also heavily affected by the specific pollutants covered by atmospheric emissions regulations. In this context, it is essential for the following to be quantified :

  • halogen pollutants (Cℓ, F);
  • sulphur pollutants (S, mercaptans, H2S…);
  • volatile heavy metal pollutants (Hg, Cd, Tℓ);
  • heavy metal pollutants regarded as slightly, if at all, volatile (Sb, As, Pb, Cr, Cu, Co, Mn, Ni, V);
  • dioxin and furan type pollutants.
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