Thermochemical Processes

**Chapter 28**

**Abstract**

technology are briefly discussed.

steam, carbon dioxide, flue gas

A comparison is presented in **Table 1**.

**547**

**1. Introduction**

Gasification of Biomass

*Thanh Phong Mai and Dinh Quan Nguyen*

Gasification is an indirect combustion of solid and liquid biomass by converting them to combustive syngas. Gasification is an alternative process for the traditional combustion, in which the emission of dust and toxic gases can be minimized. In this chapter, a comparison of these two biomass-to-heat conversion processes applied on biomass is presented in term of environmental impacts and technological benefits with a hope to provide readers a basic view of choices. Gasification is classified as in term of gasification agents, non-catalytic and catalytic process, and plasma assisted process. Popular types of gasification equipment, aka gasifiers, are introduced with working principles, through which the advantages and weakness of

**Keywords:** gasification, gasifier, biomass, indirect combustion, direct combustion, syngas, plasma, updraft, downdraft, cross-draft, bridging, tar, charcoal, hydrogen,

For the last decades, the demand for renewable energy has been increasing intensively due to the crude-oil crisis and the alert of global warming. Among the alternatives for fossil fuels to generate heat, biomass is an abundant neutral carbon source, of which its conversion to heat does not break the balance of the atmosphere's air contents [1]. Combustion of biomass has been the most direct and simple process to produce energy. However, the traditional combustion of biomass, such as wood, charcoal, straw, husks, etc., often leads to the emission of smoke, dust, fumes, volatile compounds and toxic gases due to incomplete reactions and fine particles dragged out

of the system by the flue gas [2]. Although several combustion methods were invented to increase efficiency and reduce emission of pollutants, such as fixed bed rocket type, and fluidized bed technology, the direct combustion of solid fuels is still

In contrast, gasification of biomass can minimize the emission of pollutants. Syngas produced from gasification of biomass can be optionally purified before being combusted. Ultimately, the combustion of gaseous fuels inherently has higher efficiency than that of solid matters. That is because the oxidation of a solid object in oxygen/air is gradually happening from its outer surface into the inner layers, which can be described as a heterogeneous process, while a combustive gas like syngas can be burned at a very high mass transfer rate in a homogeneous process.

The gasification phenomenon of carbonaceous materials was possibly observed in the human history as very early as the invention of fire. Gasification was found as the ignition and combustion of smoke released from smoldering coal, wood, straw,

one of the major causes of the industrial air pollutant in the world [3].
