![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
ABSTRACT
A model was developed to simulate the sewage sludge gasification in an atmospheric fluidised bed gasifier using Aspen Plus. The model here presented was based on the Gibbs free energy minimisation and the restricted equilibrium method was used to calibrate it against previously published experimental data obtained in a lab-scale gasification plant. A sensitivity analysis of the model was carried out by modifying parameters such as the temperature, equivalence ratio (ER) and the steam-to-biomass ratio. The modeled results were in good agreement with the experimental data (especially when air was used as gasifying agent) and reproduced satisfactorily the experimental trends found for the gas composition, the carbon conversion (Xc) and the cold gas efficiency (CGE) under different gasification conditions. Operating at higher temperatures increased the production of H2 and CO, as well as the Xc and the CGE. The increase in ER produced higher Xc, yet the CGE experienced slight changes due to a decrease in the lower heating value of the resulting syngas, as well as the oxidation of combustible gases. The use of air+steam as gasifying agent increased the H2 content of the produced gases but decreased the accuracy of the model.
Implications: Gasification is an available alternative to produce energy as well as several raw materials from sewage sludge. The syngas obtained from this technology totally depends on the type of gasifier and the operation conditions, which can be optimized with the help of models. In this work, a relatively simple model was built using ASPEN PLUS. Despite its simplicity, the outputs of the model are in good agreement with experimental results what makes its use interesting for assessing scaling-up possibilities from lab-scale to pilot-scale gasification processes.
Abbreviations and acronyms
| daf | = | dry and ash-free |
| ER | = | equivalence ratio, defined as the ratio between the flow rate of air introduced into the gasifier and the stoichiometric flow rate of air required for complete combustion of the sludge |
| LHVgas | = | lower heating value of the produced gas, MJ/Nm3, dry basis |
| SB | = | steam-to-biomass ratio, defined as the flow rate of steam fed to the reactor divided by the flow rate of sludge (daf) |
| Nm3 | = | cubic meter, normal conditions (0 °C, 101 kPa) |
| Ygas | = | gas yield, Nm3 dry gas/kg sludge, daf |
| XC | = | carbon conversion, weight of carbon in the produced gas divided by weight of carbon in the sludge introduced in the gasifier |
| CGE | = | cold gas efficiency = LHV of gas divided by the LHV of sludge |
Supplemental data
Supplemental data for this paper can be accessed on the publisher’s website.
Additional information
Funding
Notes on contributors
Juan Manuel de Andrés
Juan Manuel de Andrés, Ph.D., is an assistant lecturer at the Universidad Politécnica de Madrid (UPM).
Michel Vedrenne
Michel Vedrenne, Ph.D., is a principal technical consultant at Ricardo Energy & Environment in London.
Matteo Brambilla
Matteo Brambilla is Part-time research fellow at the Universidad Politécnica de Madrid (UPM).
Encarnación Rodríguez
María Encarnación Rodríguez, Ph.D., is a senior scientist and the head of the UPM research group on environmental technologies and industrial resources.
