Upgrading Technically Challenging Grass Clippings for Power Generation through Additives Addition

Approximately one third of the world`s population still lacks access to electricity due to the unavailability of fossil fuels locally, the rise in their costs on the international market and the lack of a suitable infrastructure. The utilisation of small-scale biomass downdraft gasification CHP units which are relatively cheap and portable seems a viable option for addressing this need. However, such systems generally require high quality or specialised grade biomass feedstocks for uninterrupted and trouble free operation, the costs of which are often prohibitive even when available locally. More commonly, locally available biomass feedstocks are of insufficiently high quality resulting in problems such as ash melting and the development of corrosive deposits in gasifiers. Upgrading of these low quality biomass feedstock through the use of locally sourced affordable additives could increase the reliability and availability of these systems stability and also create considerable business opportunities for system manufacturers in the global marketplace. In this work, municipal and domestic grass clippings (GGC) was considered as a widely available low cost potential biomass feedstock, and its ash characteristics in the presence of various additives was examined at laboratory scale using a small furnace operated at a temperature typical of the oxidation zone of a downdraft gasifier. The ash of raw grass clippings was severely melted indicating it is not suitable to be used in gasifier units. However, the ash characteristics were remarkably improved on addition of calcium- and phosphorous-based additives, some of which are readily available natural waste materials. Various analytical techniques including SEM-EDS and XRD were employed to understand how the different classes of additive affect the ash transformation chemistry taking place.