Cesare Saccani

Sewage sludge drying process integration with a waste-to-energy power plant

Dewatered sewage sludge from Waste Water Treatment Plants (WWTPs) is encountering increasing problems associated with its disposal. Several solutions have been proposed in the last years regarding energy and materials recovery from sewage sludge. Current technological solutions have relevant limits as dewatered sewage sludge is characterized by a high water content (70-75% by weight), even if mechanically treated. A Refuse Derived Fuel (RDF) with good thermal characteristics in terms of Lower Heating Value (LHV) can be obtained if dewatered sludge is further processed, for example by a thermal drying stage. Sewage sludge thermal drying is not sustainable if the power is fed by primary energy sources, but can be appealing if waste heat, recovered from other processes, is used. A suitable integration can be realized between a WWTP and a waste-to-energy (WTE) power plant through the recovery of WTE waste heat as energy source for sewage sludge drying. In this paper, the properties of sewage sludge from three different WWTPs are studied. On the basis of the results obtained, a facility for the integration of sewage sludge drying within a WTE power plant is developed. Furthermore, energy and mass balances are set up in order to evaluate the benefits brought by the described integration.

Material and energy recovery in integrated waste management system – An Italian case study on the quality of MSW data

This paper analyses the way numerical data on Municipal Solid Waste (MSW) quantities are recorded, processed and then reported for six of the most meaningful Italian Districts and shows the difficulties found during the comparison of these Districts, starting from the lack of homogeneity and the fragmentation of the data indispensable to make this critical analysis. These aspects are often ignored, but data certainty are the basis for serious MSW planning. In particular, the paper focuses on overall Source Separation Level (SSL) definition and on the influence that Special Waste (SW) assimilated to MSW has on it. An investigation was then necessary to identify new parameters in place of overall SSL. Moreover, these parameters are not only important for a waste management system performance measure, but are fundamental in order to design and check management plan and to identify possible actions to improve it.

Hot waste-to-energy flue gas treatment using an integrated fluidised bed reactor

This paper describes an innovative process to increase superheated steam temperatures in waste-to-energy (WTE) plants. This solution is mainly characterised by a fluidised bed reactor in which hot flue gas is treated both chemically and mechanically. This approach, together with gas recirculation, increases the energy conversion efficiency, and raises the superheated steam temperature without decreasing the useful life of the superheater. This paper presents new experimental data obtained from the test facility installed at the Hera S.p.A. WTE plant in Forlì, Italy; discusses changes that can be implemented to increase the duration of experimental testing; offers suggestions for the design of an industrial solution.