Evaluation of a lime-mediated sewage sludge stabilisation process. Product characterisation and technological validation for its use in the cement industry |
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Authors: | Rodríguez N Husillos Granados R J Blanco-Varela M T Cortina J L Martínez-Ramírez S Marsal M Guillem M Puig J Fos C Larrotcha E Flores J |
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Institution: | a Eduardo Torroja Institute for Construction Science (CSIC), Serrano Galvache 4, 28033 Madrid, Spain b Auma Consultores en Medio Ambiente y Energía, Travessera de les Corts 302 Bajos, 08029 Barcelona, Spain c ETSEIB-UPC, Universidad Politécnica de Catalunya, Avda. Diagonal 647, 08028 Barcelona, Spain d Cementos Molins S.A., Crta. N-340, 2 al 38, E-08620 Sant Vicenç dels Horts, Barcelona, Spain e Aguas de Barcelona S.A., Avenida Diagonal 211, 08018 Barcelona, Spain f Instituto de Estructura de la Materia (CSIC), C/Serrano 121, 28006 Madrid, Spain |
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Abstract: | This paper describes an industrial process for stabilising sewage sludge (SS) with lime and evaluates the viability of the stabilised product, denominated Neutral, as a raw material for the cement industry. Lime not only stabilised the sludge, raised the temperature of the mix to 80-100 °C, furthering water evaporation, portlandite formation and the partial oxidation of the organic matter present in the sludge.Process mass and energy balances were determined. Neutral, a white powder consisting of portlandite (49.8%), calcite (16.6%), inorganic oxides (13.4%) and organic matter and moisture (20.2%), proved to be technologically apt for inclusion as a component in cement raw mixes. In this study, it was used instead of limestone in raw mixes clinkerised at 1400, 1450 and 1500 °C. These raw meals exhibited greater reactivity at high temperatures than the limestone product and their calcination at 1500 °C yielded clinker containing over 75% calcium silicates, the key phases in Portland clinker. Finally, the two types of raw meal (Neutral and limestone) were observed to exhibit similar mineralogy and crystal size and distribution. |
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Keywords: | Sewage sludge Lime stabilisation Cement reuse Clinker Neutral Alximix |
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