Simulations of combustion and emissions characteristics of biomass-derived fuels

Suresh K. Aggarwal

2.1 INTRODUCTION

There is worldwide interest in developing renewable energy sources in a sustainable manner. This is motivated by our excessive reliance on finite fossil energy sources, environmental concerns due to greenhouse gas emissions, and ever-growing energy needs especially due to emerging economies and population growth. A sustainable and carbon-neutral energy future will require a significant broadening of our energy portfolio and reducing reliance on non-renewable sources. While multiple renewable energy sources and technologies will be needed to attain this goal, non-food and regional fuel sources, especially biomass, are expected to play a major role in this effort. Biomass represents one of the primary energy resources in the world after coal and oil, particularly in developing countries (Hall et al., 1991). It refers to a broad variety of feedstock ranging from agricultural waste, such as straw, bagasse, rice husks, olive pits, and nuts, to energy crops such as miscanthus and sorghum (Werther et al., 2000). It also includes algae, forestry waste such as wood chips, bark and thinning, and other solid wastes including sewage sludge, as well as municipal waste. The use of biomass would not only reduce our dependence on fossil energy sources, but also provide energy in a sustainable and carbon neutral manner.

Biomass can be converted to more valuable energy forms via a number of processes includ­ing biological, thermal, and mechanical or physical processes. Figure 2.1 from Gill et al.,

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Figure 2.1. A schematic of various conversion methods and major fuels produced from biomass (Gill et al., 2000).

(2000) provides a schematic of the various conversion processes and major products (fuels) from lignocellulosic biomass.

Biological conversion faces many challenges due to high cost and low efficiency, and is currently limited with regards to feedstock and products (Lin et al, 2006). In contrast, thermo­chemical methods have been extensively investigated for the conversion of biomass to a variety of products, such as energy, fuels, and chemicals. This chapter starts with an overview of thermo­chemical conversion processes, namely direct biomass combustion, pyrolysis and gasification. A brief discussion of various processes involved and fuels produced is provided. This is followed by a discussion of research dealing with biomass-derived fuels. The focus is on the combustion and emission characteristics of syngas and biogas. Both the fundamental and applied research is reviewed. Finally, some research needs are outlined.