2.1 INTRODUCTION

The characteristics of biomass greatly influence the performance of a biomass gasifier. A proper understanding of the physical and the chemical properties of biomass feedstock is essential for the design of a biomass gasifier to be reliable. This chapter discusses some important properties of biomass that are relevant to gasification and related processes.

2.2 WHAT IS BIOMASS?

Biomass refers to any organic materials that are derived from plants or animals (Loppinet-Serani et al., 2008). A generally accepted definition is difficult to find. However, the one used by the United Nations Framework Convention on Climate Change (UNFCCC, 2005) is relevant here:

[A] non-fossilized and biodegradable organic material originating from plants, animals and micro-organisms. This shall also include products, by-products, residues and waste from agriculture, forestry and related industries as well as the non-fossilized and bio­degradable organic fractions of industrial and municipal wastes.

Biomass also includes gases and liquids recovered from the decomposition of nonfossilized and biodegradable organic materials. In the United States, there has been much debate on a legal definition. Appendix A gives a recent legal interpretation of renewable biomass.

As a sustainable and renewable energy resource, biomass is constantly being formed by the interaction of CO2, air, water, soil, and sunlight with plants and animals. After an organism dies, microorganisms break down biomass into elementary constituent parts like H2O, CO2, and its potential energy. Because the carbon dioxide, a biomass releases through the action of microorganisms or combustion was absorbed by it in the recent past, biomass combustion does not increase the total CO2 inventory of the Earth. It is thus called greenhouse gas neutral or GHG neutral.

Biomass Gasification and Pyrolysis. DOI: 10.1016/B978-0-12-374988-8.00002-7

Copyright © 2010 Prabir Basu. Published by Elsevier Inc. All rights reserved.

Biomass includes only living and recently dead biological species that can be used as fuel or in chemical production. It does not include organic materials that over many millions of years have been transformed by geological processes into substances such as coal or petroleum. Biomass comes from botanical (plant species) or biological (animal waste or carcass) sources, or from a combination of these. Common sources of biomass are:

• Agricultural: food grain, bagasse (crushed sugarcane), corn stalks, straw, seed hulls, nutshells, and manure from cattle, poultry, and hogs

• Forest: trees, wood waste, wood or bark, sawdust, timber slash, and mill scrap

• Municipal: sewage sludge, refuse-derived fuel (RDF), food waste, waste paper, and yard clippings

• Energy: poplars, willows, switchgrass, alfalfa, prairie bluestem, corn, and soybean, canola, and other plant oils

• Biological: animal waste, aquatic species, biological waste