Nowadays, biomass has a well-known potential for producing energy calTiers, such as electricity, heat (steam) and transport biofuels. However, biomass availability is rather limited and stochastically distributed. This could be a major problem in demographically dense regions where land is scarce and biomass may compete with other applications, notably agriculture for food production. In fact, this is the case for the first-generation biofuels (e.g. bioethanol and biodiesel) that are mainly produced from biochemical conversion of food crops such as sugar cane, com or wheat, and vegetable oils from feedstock like rapeseed or palm oil. Moreover, when taking into account emissions from transport and conversion treatments, life-cycle analyses reveal that first-generation biofuels frequently exceed the emission thresholds of fossil fuels .
Second generation biofuels are now being developed as a possible better alternative to the first generation, as they can use non-food crops (e.g. switch grass) or biowastes from different origins (e.g., forest, agriculture, industry, municipalities). Second generation biofuels can also be produced via either biochemical or thennochemical conversion. Among all the existing thermochemical conversion technologies, gasification is gaining interest due to its higher efficiency, larger scales, and reliable operation.
However, biowastes-to-biofuels conversion involves several challenges. Firstly, the existing technology must be fe-designed and optimized to become cost and efficiency competitive with fossil fuels. Moreover, due to the wide diversity of biowastes and biofuels that can be obtained, the most sustainable conversion routes must be properly selected. Hence, an inherent challenge is to develop a reliable model to evaluate the sustainabililY of any process.
In this chapter we present the evaluation of second generation biofuels (SNG, methanol, Fischer-lropsch fuels, hydrogen) as well as heat and electricity, from different biowastes via gasification with subsequent catalytic conversion of syngas. Pre-treatment steps are also considered in order to enhance the low energy density of biomass prior to gasification. However, since pre-treatment is directly affected by local conditions, the Dutch province of Friesland is taken as a case study. The biowaste-to-biofuels routes are modeled in Aspen Plus, and mass and energy balances obtained from simulations are later used for efficiency evaluation. Results are presented in terms of mass conversion yield, energy and exergetic efficiency. The last part of the paper is devoted to explain how those results will be integrated for combined economic and environmental impact analysis.
|Title of host publication||Biomass gasification : chemistry, processes, and applications|
|Editors||J.P. Badeau, A. Levi|
|Place of Publication||New York|
|Publication status||Published - 2009|
|Name||Renewable Energy: Research, Development and Policies|