Effects of layer inhomogeneities on the process of sewage sludge convective drying

Novak, Lovrenc (author), Širok, Brane (author), Zupanc, Mojca (author), Hočevar, Marko (author)

Convective sewage sludge drying is often carried out in belt dryers, where the air flow is directed through the layer. In such a configuration, drying air properties, as well as the structure of the layer and its homogeneity are key factors affecting the drying process. In the present work, these factors were investigated using laboratory experiments on relatively large sludge samples with a mass of several kilograms. Drying was performed at relatively low drying air parameters (time-averaged temperatures of 65 to 80 °C and velocities of 0.44 to 0.78 m/s). The inhomogeneity of the sludge layer drying was observed by measuring the layer surface temperature with an IR camera. The reduction in layer thickness during drying was measured using an optical laser-based method. Analysis of the data included regression and fitting of the data to parametric drying curves, with the modified Nadhari drying law providing the best fit. The standard deviation of the layer surface thermograms (S) was used as a parameter that accounted for the layer homogeneity and consequently drying evenness. Higher values of S corresponded to lower drying rates and consequently longer drying times, highlighting the importance of producing layers with a homogenous structure. The measured layer thickness reduction rate indicated the overall drying intensity almost from the beginning of drying. Both the surface temperature unevenness and the layer height reduction measurement methods were demonstrated as viable approaches for real-time monitoring of the drying process with potential for application in real-scale dryers.

• Language: English
• Keywords: wastewater sludge, porous layer, drying kinetics, shrinkage, thermography
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2024
• Number of pages: Str. 34-47
• Numbering: Vol. 42, no. 1
• PID: 20.500.12556/RUL-153474
• UDC: 628.336.4:66.047
• ISSN on article: 0737-3937
• DOI: 10.1080/07373937.2023.2259974
• COBISS.SI-ID: 166496771
• Publication date in RUL: 09.01.2024

Record is a part of a journal

• Title: Drying technology
• Shortened title: Dry. technol.
• Publisher: Taylor & Francis
• ISSN: 0737-3937
• COBISS.SI-ID: 5922823

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: blato čistilnih naprav, porozna plast, kinetika sušenja, krčenje, termografija

Projects

• Funder: ARRS - Slovenian Research Agency
• Project number: P2-0401
• Name: Energetsko strojništvo