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Sewage sludge from wastewater treatment facilities needs to be treated before it can be disposed of. While it is typically processed through an anaerobic digestion process, sludge can also be a good feedstock for alternative fuel production. High-temperature steam gasification is a process that decomposes organic materials into synthesis gas (syngas) with a high hydrogen concentration. In this study, a lab-scale steam gasification system which converts sewage sludge into valuable syngas was developed and experimentally evaluated. This study specifically focuses on investigating the chemical kinetics of syngas generation and feedstock decomposition in a batch process. The syngas generation rates and concentrations of syngas constituents were measured, and changes in carbon balance during gasification were tracked with respect to time, which shows how reaction rates vary over time. It was found that variations in steam flow rates modified the gasification reactions both thermodynamically and hydrodynamically. The gasification processes were fitted into logistics curves to understand the effects of different steam flow rates. The results indicate that the chemical reaction velocity can be controlled to achieve optimum operating conditions, which potentially can reduce both processing time and steam consumption while maximizing the syngas yield. This study would contribute more to the complete understanding of the sewage sludge gasification processes and the kinetics of the gasification chemical reactions. [ABSTRACT FROM AUTHOR]

A mathematical model that describes a trailer scale biomass steam gasification system coupled with a solar collector heat source and a micro gas turbine is reported in this paper. This combined heat and power system is set to a prescribed output of 20 kW e and several system conditions have been optimized in a parametric study to minimize resource consumption rates. Biomass feeding rates under optimal conditions were found to range between 23 and 63 kg/h depending on the types of feedstock and other parameters. Water consumption is reduced through a condensation and recirculation process that is part of a heat recovery unit. Also, solar energy requirements have been reduced by means of a recuperator that extracts heat out of the combustion products. The overall system performance has been evaluated by a utilization factor which was found to range between 30% and 43%. The system has been compared to a baseline case of an air breathing gasification system of a similar scale. It was found that steam gasification produces the syngas with heating values over twice as high as those obtained by air gasification. Steam gasification also led to a 25% and 50% reduction in emission rates of contaminants like CO 2 and nitrogen oxides respectively relative to the baseline case. [ABSTRACT FROM AUTHOR]