Preface

Gasification is the thermochemical process of converting carbonaceous material in the presence of an oxidant less than stoichiometric to form a gaseous product at a high temperature. This gas is known as synthesis gas or syngas. Depending on quality, the gas produced can have different uses, including driving internal combustion engines and gas turbines, direct burning, and synthesis of chemical components.

Gasification transforms a solid material into a gas that can be used as fuel or raw material (methane, ammonia, methanol, gasoline). Different from pyrolysis, which mainly aims to obtain solids and sometimes to obtain liquids, gasification seeks a high production of gases, fundamentally containing CO (10%–20%), H2 (4%–17 %), CH4 (2%–5%), and N2 (40%–60%). This difference in objectives characterizes the operating conditions since gasification operates at temperatures higher than those used in pyrolysis and in the presence of gasifying agents such as water vapor to force the production of H2 and CO.

The main objective of gasification is the conversion of biomass into fuel gas, through its partial oxidation at elevated temperatures. Syngas is an intermediate energy source and can be used later in another conversion process to generate heat or mechanical or electrical power, adapting to systems in which solid biomass cannot be used. This fuel gas has a relatively low calorific value, around 4 to 6 MJ/Nm3 (using air as a gasifying agent).

When the biomass enters a gasifier, it first heats up, causing it to dry. Once the temperature is above 400°C, pyrolysis starts, giving rise to a carbon residue (char) formed mainly by carbon and condensable gases (light and heavy hydrocarbons) and non-condensable gases (CH4, water vapor, CO, H2, CO2). When the temperature of the "char" exceeds 700°C, gasification reactions take place, which are divided into heterogeneous (gas-solid) and homogeneous (gas-gas) reactions. This "char" reacts with O2, water vapor, CO2, and H2, and the gases react with each other to produce the final gas mixture.

The result of the process is a gas, whose main constituents are CO, H2, N2, CO2, water vapor, and hydrocarbons or tar (tar). The composition of this gas varies with the characteristics of the biomass, the gasifying agent, and the process conditions. As the C, H, and O reactions for different types of biomass are very similar, the main biomass parameter that influences the gas composition is its moisture content. Thus, with higher moisture content in the biomass, more gasifying agent is needed because the water has to be heated and evaporated. A gas that comes from wet biomass contains relatively large amounts of steam, H2, and N2, compared to dry biomass. For gasification with air, the mixture obtained is a lean gas or gas with a low calorific value (4000 to 6000 kJ/Nm3) since it contains 40 %to 60% N2. The addition of water in the gasifying agent is necessary when one intends to enrich the gas with H2, producing a gaseous mixture of average calorific value.

Overall, thermochemical gasification takes place inside a reactor, which is classified according to the way in which the reactions are carried out: concurrent or countercurrent fixed bed, bubbling or circulating fluidized bed. They are also classified according to working pressure: atmospheric or pressurized (such as entrained flow gasifiers), and according to the gasifying agent, either air, oxygen, steam, hydrogen, or mixtures of these gases.

This book provides a comprehensive overview of the various gasification techniques and applications developed so far to contribute to a better understanding of this important process of obtaining a renewable fuel, essential for the development of a sustainable economy. It presents a collection of works carried out by several researchers addressing a wide range of gasification features, including operating conditions, gasifying agents, coupling with pyrolysis, syngas generation, geographical evolvement in Europe and South America, and many other topics of interest.

 The authors would like to thank the Coordination for the Improvement of Higher Education Personnel (CAPES) and the Portuguese Foundation for Science and Technology (FCT) for the funding provided through project number 88881.156267/2017-01 and DMAIC-AGROGAS: 02/SAICT/2018. This book is also a result of the project "Apoio à Contratação de Recursos Humanos Altamente Qualificados" (Norte-06-3559-FSE-000045), supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement.

> **Valter Silva**  Polytechnic Institute of Portalegre, Portalegre, Portugal

Forestwise, Portuguese Collaborative Laboratory for Integrated Forest and Fire Management, Portugal

## **Celso Eduardo Tuna**

Section 1

Pyrolysis

UNESP-Sao Paulo State University (IPBEN - Bioenergy Research Institute), Guaratinguetá, Brazil

Section 1 Pyrolysis

**Chapter 1**

**Abstract**

**1. Introduction**

**3**

Review Chapter: Waste to Energy

through Pyrolysis and Gasification

Millions of tons of forest residues, agricultural residues, and municipal solid waste are generated in Latin America (LATAM) each year. Regularly, municipal solid waste is diverted to landfills or dumpsites. Meanwhile, forest and agricultural residues end up decomposing in the open air or burnt, releasing greenhouse gases. Those residues can be transformed into a set of energy vectors and organic/chemical products through thermochemical conversion processes, such as pyrolysis and gasification. This book chapter provides information on current examples of gasification on large scale in the world, which typically operate at 700°C, atmospheric pressure, and in a fluidized bed reactor. The produced gas is used for heat and energy generation. Whereas pyrolysis at a large scale operates around 500°C, atmospheric pressure, and in an inert atmosphere, using a fluidized bed reactor. The produced combustible liquid is used for heat and energy generation. The decision of using any of these technologies will depend on the nature and availability of residues, energy carries, techno-socio-economic aspects, and the local interest. In this regard, the particular situation of Brazil and Mexico is analyzed to implement these technologies. Its implementation could reduce the utilization of fossil fuels, generate extra income for small farmers or regions, and reduce the problem derived from the accumulation of residues. However, it is concluded that it is more convenient to use decentralized gasification and pyrolysis stations than full-scale processes, which could be an intermediate step to a large-scale process. The capabilities of numerical models to describe these processes are also provided to assess the potential composition of a gas produced from some biomass species available in these countries.

LATAM has a rising renewable energy market, where more than a quarter of its primary energy is generated from renewable sources, twice the world average [1]. Across the continent, hydropower plays a pivotal role in the energy sector. However, LATAM has also access to biomass resources, which may enable the production of bioenergy, providing the opportunity to exploit a domestic, low carbon, and

in Brazil and Mexico

*José Antonio Mayoral Chavando, Valter Silva,*

*João Sousa Cardoso and Luís A.C. Tarelho*

**Keywords:** Gasification, Pyrolysis, biomass, MSW, RDF

*Danielle Regina Da Silva Guerra, Daniela Eusébio,*

## **Chapter 1**
