GUIDA ALLA PROGETTAZIONE E ALLA CONDUZIONE DEGLI IMPIANTI DI INCENERIMENTO DEI FANGHI

The goal of this book i sto describe synthetically but rigorously sewage sludge incineration technologies and the code of good practice for the operation which allow to meet the standards of the European Directive 2000/76/CE, guaranteeing that both capital and operating costs are kept reasonably low. Peculiar sludge characteristics needed to define the material and enthalpic balances and for dimensioning the treatment plant units are presented. Specific pollutants monitoring could be needed in particular cases for the environmental possible consequences but it must be pointed out that generally the presence of organic and inorganic micropollutants in sewage sludge are not of concern regarding the gaseous emissions. Lead and cadmium generally enrich in fly ashes while the volatility of zinc and copper is kept quite low for the presence in sewage sludge of calcium and aluminium binding these metals in the solid residue. Therefore, no significant enrichment in fly ashes of these two metals is generally observed. Fundamentals of combustion are outlined and the principle of the "three T" (temperature, time and turbulence) is presented. Equipment characteristics of the three types of furnaces (multiple hearth, fluidised bed and rotary kiln furnaces) generally used for sludge incineration are discussed, as well as those of auxiliary equipment included in an incineration plant (sections of thermal recovery, flue gas treatment, sludge pre-treatment, solid residues management and wastewater treatment. Great attention is paid to sludge drying, which is strategic option in an incineration process to minimize fuel consumption and flue gas production and therefore capital and operating costs. The optimal mode of operation of incineration plants is presented with particular emphasis to the multiple hearth, fluidised bed and rotary kiln furnaces.