Francesco Cherubini, Anders H. Str0mman

Department of Energy and Process Engineering, Norwegian University of Science and Technology

(NTNU), NO-7491 Trondheim, Norway
*Corresponding author: E-mail: francesco. cherubini@ntnu. no

1 INTRODUCTION

1.1 Background

Driven by the increase in industrialization and population, the global demand for energy and material products is steadily growing. Since the world primary sources for energy and chemicals are fossil fuels, this growth raises important issues at environmental, economic, and social levels. Petroleum is exploited at a much faster rate than its natural regeneration through the planet C cycle, and the larger part of petroleum and natural gas reserves is located within a small group of countries. This production and consumption pattern is unsus­tainable because of equity and environmental issues that have far-reaching implications. In addition, there is a common increasing perception that the end of the cheap fossil era is around the corner, and prices for crude oil, transportation fuels, and petroleum-derived chemicals are likely to steadily increase in the years to come (Bentley et al., 2007; Greene,

2004) . Climate experts widely agree that emissions of greenhouse gases (GHG), such as car­bon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), arising from fossil fuel combus­tion and land-use change as a result of human activities, are perturbing the Earth’s climate (Forster et al., 2007). Global warming and other issues can be mitigated by shifting from fossil sources to renewable energy resources, which are more evenly distributed than fossil resources and cause less environmental and social concerns.

Among the other energy sources, biomass resources are extremely promising since they are widespread and cheaply available in most of the countries. Today, biomass constitutes about 10% of the global primary energy demand, and it is mainly used in inefficient and tra­ditional applications in developing countries (GBEP, 2007; IEO, 2009). Modern uses of bio­mass are restricted to developed countries to produce space heating, power, transportation biofuels (mainly bioethanol and biodiesel), and few chemical products. Given the variety of applications for biomass sources, it is extremely important to select the most promising options under environmental, economic and resource perspectives. Electricity and heat can be provided by several renewable alternatives (wind, sun, water, biomass, and so on), while bio­mass is very likely to be the only viable alternative to fossil resources for production of transportation fuels and chemicals. Today, more than 90% of the fossil carbon is used only for its energy content (Marquardt et al., 2010). This pattern is not likely to be followed in the future for biomass because of the lower efficiency in converting biomass into energy and the lower energy density of biomass than fossils. Stemming from these considerations, some authors convincingly argued that electricity should be produced by an increasing share of rene­wable sources, and the use of biomass be restricted to the production of transportation biofuels and carbon-based chemical products (Agrawal and Singh, 2010; Marquardt et al., 2010).