Gasification of Sewage Sludge Enriched with Plant Biomass - Modeling and Tests

Abstract

The article presents results from experimental and numerical investigation on gasification of dried sewage sludge enriched with biomass from Virginia Mallow at a mass ratio of 0/100%, 50/50% and 100/0% in tests and in the range from 0 to 100% in theoretical analysis. in order to effective utilization of sewage sludge. The dried sludge can be subjected to thermal processing of gasification at temperature above 850°C. However, there are some difficulties in obtaining this temperature due to high content of mineral substances transforming into large amounts of ash during gasification. Unfavorable feature of sewage sludge being significant impediment to gasification process is its high ash content up to 40% by mass. As observed, one of the main characteristics of lignocellulosic biomass like Virginia Mallow, which makes it appropriate for thermal processing, is the low amount of mineral content below 2%. It contributes to more stable and efficient gasification process (less combustibles found in ash). Furthermore, due to large ballast of ash in sewage sludge, it was not possible to obtain sufficiently high gasification temperature (observed maximum was 800°C). In turn, addition of Virginia Mallow caused that the process temperature possible to achieve, was 950°C. Thus, sewage sludge was mixed with high energy component in order to improve the gasification parameters and obtain better quality syngas. A zero-dimensional, two-zone model was developed with aid of the kinetics mechanism by CREEK Modeling Group to model and predict gasification of low calorific substances enriched with high calorific biomass. Obtained results showed that sewage sludge can be completely gasified at presence of Virginia Mallow leading to production of syngas with its calorific value of approximately 4 MJ/Nm3. Furthermore, calculations performed for the case of gasification of the sewage sludge without biomass enrichment showed much smaller content of hydrogen in syngas.