Advances in Renewable Energies and Power Technologies: Volume 2: Biomass, Fuel Cells, Geothermal Energies, and Smart Grids

By Imene Yahyaoui

Advances in Renewable Energies and Power Technologies Volume 2: Biomass, Fuel Cells, Geothermal Energies, and Smart Grids examines both the theoretical and practical elements of renewable energy sources, covering biomass, fuel cells, geothermal energy, RES, distributed energy, smart grids, and converter control. Dr. Yahyaoui and a team of expert contributors present the most up-to-date information and analysis on renewable energy generation technologies in this comprehensive resource. This volume covers the principles and methods of each technology, an analysis of their implementation, management and optimization, and related economic advantages and limitations, in addition to recent case studies and models of each technology.

Advances in Renewable Energies and Power Technologies: Volume 2: Biomass, Fuel Cells, Geothermal Energies, and Smart Grids is a valuable resource for anyone working in renewable energy or wanting to learn more about theoretical and technological aspects of the most recent inventions and research in the field.

• Offers a comprehensive guide to the most advanced contemporary renewable power generation technologies written by a team of top experts
• Discusses power control and limitations of each technology
• Includes global case studies and models to exemplify the technological possibilities and limitations of each power generation method

• Language: English
• Publisher: Elsevier Science
• Release date: Feb 23, 2018
• ISBN: 9780128131862

Book preview

Advances in Renewable Energies and Power Technologies

Volume 2: Biomass, Fuel Cells, Geothermal Energies, and Smart Grids

First Edition

Imene Yahyaoui

University Carlos III of Madrid, Spain

Table of Contents

Cover image

Title page

Copyright

Contributors

Preface

Acknowledgement

1: Biomass: Some Basics and Biogas

Abstract

1.1 Introduction

1.2 Biomass Classification

1.3 Technological Routes for Energy Conversion of Biomass

1.4 Anaerobic Digestion Process

1.5 Biogas Produced by Anaerobic Digestion Based Systems

1.6 Biogas From Digesters

1.7 Landfill Gas Modeling

1.8 Power Generation Based on Biomass

1.9 Final Considerations

2: Simulation Models of Biomass Thermochemical Conversion Processes, Gasification and Pyrolysis, for the Prediction of the Energetic Potential

Abstract

2.1 Gasification Process

2.2 Pyrolysis Process

2.3 Gasification/Pyrolysis Reactors

2.4 Simulation Models

2.5 Results of the Simulation of the Gasification/Pyrolysis

2.6 Conclusions

3: Biomass Gasification for Power Generation Applications: A Modeling, Economic, and Experimental Study

Abstract

3.1 Introduction

3.2 Materials and Methods

3.3 Results and Discussions

3.4 Economic and Feasibility Study

3.5 Conclusions

4: Fuel Cells: History (Short Remind), Principles of Operation, Main Features, and Applications

Abstract

4.1 Introduction

4.2 Alkaline Fuel Cells

4.3 Direct Methanol Fuel Cells

4.4 Microbial Fuel Cells

4.5 Molten Carbonate Fuel Cells

4.6 Phosphoric Acid Fuel Cells

4.7 Proton Exchange Membrane Fuel Cells

4.8 Solid Oxide Fuel Cells

5: On the Modeling and Control of a Photovoltaic-Fuel Cell Hybrid Energy System

Abstract

5.1 Introduction

5.2 System Components Modeling

5.3 Principle of the Control Strategy

5.4 Results and Discussion

5.5 Conclusion

6: Geothermal Power

Abstract

6.1 Introduction

6.2 Geothermal Energy Resources

6.3 Geothermal Power Plants

6.4 Thermodynamic Design: Parametric Study

6.5 Economic Study

7: Deployment of Renewable Energy Systems: Barriers, Challenges, and Opportunities

Abstract

7.1 Renewable Energy Resources: Current Status and Future Prospects

7.2 100% Renewable Energy System in the Year 2050?

7.3 Smart Energy Management for Autonomous Isolated Areas—The Case Study of Greek Islands

8: Optimal Sizing and Designing of Hybrid Renewable Energy Systems in Smart Grid Applications

Abstract

8.1 Introduction

8.2 A Novel Design and Optimization Software for Autonomous PV/Wind/Battery Hybrid Power System

8.3 PSO-Based Smart Grid Applications in Hybrid Renewable Energy Systems

8.4 Conclusions

Appendix

9: Grid-Connected Microgrids: Demand Management via Distributed Control and Human-in-the-Loop Optimization

Abstract

Acknowledgments

Nomenclature

Symbols

9.1 Introduction

9.2 Problem Formulation

9.3 HVAC Modeling and Automation

9.4 Demand Management Strategies

9.5 Results

9.6 Conclusions and Future Work

10: Distributed Generation Energy in Relation to Renewable Energy: Principle, Techniques, and Case Studies

Abstract

10.1 Introduction

10.2 Distributed Generation Technologies

10.3 Optimal Allocation and Impact of Distributed Generation

10.4 Distributed Generation Management

11: Virtual Inertia for Power Converter Control

Abstract

11.1 Introduction

11.2 Instantaneous Constant Power Control—PQ Control

11.3 Inertial Power Control Strategies

11.4 Excitation System Control Loop

11.5 Turbine and Governor Systems

11.6 Case Study—Comparison Between Conventional and Inertial Power Control Strategies

11.7 Governor and Excitation System Tuning

12: Electric and Hybrid Vehicle Drives and Smart Grid Interfacing

Abstract

12.1 Introduction

12.2 State of the Art of Electric Vehicle

12.3 Classifications of Electric Vehicle

12.4 Energy Management System in Electric Vehicle

12.5 Study of Electric Vehicles in the World

12.6 Simulation of Electric Vehicle

13: Machine Learning Techniques for Data Classification

Abstract

13.1 Introduction

13.2 The Support Vector Machines: SVM

13.3 The K Nearest Neighbors Principle

13.4 The Naïve Bayes Principle

13.5 Conclusion

14: Telecommunication Technologies for Smart Grids: Total Cost Optimization

Abstract

14.1 Introduction

14.2 Smart Metering in Smart Grids

14.3 Energy Management System and Local Management Station

14.4 Typical Communications Technologies for Smart Grids

14.5 Optimization Problem for Minimum Total Costs for Smart Metering Systems

14.6 New Challenges and Solutions for Smart Grid Communication Networks

15: Smart Manufacturing in a SoSE Perspective

Abstract

15.1 Introduction

15.2 Background and Challenges

15.3 SoSE Perspective

15.4 Conclusions

Index

Copyright

Elsevier

Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands

The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom

50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States

© 2018 Elsevier Inc. All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.

This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

Library of Congress Cataloging-in-Publication Data

A catalog record for this book is available from the Library of Congress

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library

ISBN: 978-0-12-813185-5

For information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Katie Hammon

Acquisition Editor: Maria Convey

Editorial Project Manager: Jennifer Pierce

Production Project Manager: Sruthi Satheesh

Cover Designer: Mark Rogers

Typeset by SPi Global, India

Contributors

Shady Hossam Eldeen Abdel Aleem     15th of May Higher Institute of Engineering, Cairo, Egypt

Diego Andina     Universidad Politécnica de Madrid, Madrid, Spain

Simone Baldi     Delft University of Technology, Delft, The Netherlands

Marcelo A. Barone     Federal University of Espirito Santo—UFES, Vitória, Brazil

Dayane Corneau Broedel     Federal University of Espirito Santo—UFES, Vitória, Brazil

Maria Bruno     University of Catania, Catania, Italy

Daniel Carletti     Federal University of Espirito Santo—UFES, Vitória, Brazil

Rubén A.M. Carrillo     Federal University of Itajubá, Itabira, Brazil

Monica Carvalho     Federal University of Paraíba, João Pessoa, Brazil

Sabrina de Angeli Souza     Federal University of Espirito Santo—UFES, Vitória, Brazil

Odair de Barros, Jr     Federal University of Espirito Santo—UFES, Vitória, Brazil

Helder Roberto de Oliveira Rocha     Federal University of Espirito Santo—UFES, Vitória, Brazil

Augusto P.F. Dias     Federal University of Espirito Santo—UFES, Vitória, Brazil

Marco António do Rosário Santos Cruz     Federal University of Espirito Santo—UFES, Vitória, Brazil

Clainer Bravin Donadel     Federal University of Espirito Santo—UFES, Vitória, Brazil

Ali M. Eltamaly

King Saud University, Riyadh, Saudi Arabia

Mansoura University, Mansoura, Egypt

Lucas Frizera Encarnação     Federal University of Espirito Santo—UFES, Vitória, Brazil

Jussara F. Fardin     Federal University of Espirito Santo—UFES, Vitória, Brazil

Rodrigo Fiorotti     Federal University of Espirito Santo—UFES, Vitória, Brazil

Antonio Gagliano     University of Catania, Catania, Italy

Foad Heidari Gandoman     Vrije Universiteit Brussel, Brussels, Belgium

Stéfani V.M. Guaitolini     Federal University of Espirito Santo—UFES, Vitória, Brazil

Francisco Jurado     University of Jaén, Linares, Spain

Christos D. Korkas

Democritus University of Thrace, Xanthi, Greece

Center for Research and Technology Hellas (ITI-CERTH), Thessaloniki, Greece

Elias B. Kosmatopoulos

Democritus University of Thrace, Xanthi, Greece

Center for Research and Technology Hellas (ITI-CERTH), Thessaloniki, Greece

Irene Martín Rubio     Universidad Politécnica de Madrid, Madrid, Spain

Mohamed A. Mohamed     Minia University, Minia, Egypt

Evanthia A. Nanaki     University of Western Macedonia, Kozani, Greece

Francesco Nocera     University of Catania, Catania, Italy

Noshin Omar     Vrije Universiteit Brussel, Brussels, Belgium

Manuel Ortega     University of Jaén, Linares, Spain

Marcia Helena Moreira Paiva     Federal University of Espirito Santo—UFES, Vitória, Brazil

Jose C.E. Palacio     Federal University of Itajubá, Itabira, Brazil

Patrick Trivilin Rodrigues     Federal University of Espirito Santo—UFES, Vitória, Brazil

Carlos E.C. Rodríguez     Federal University of Itajubá, Itabira, Brazil

José J.C.S. Santos     Federal University of Espirito Santo—UFES, Vitória, Brazil

Marcelo Eduardo Vieira Segatto     Federal University of Espirito Santo—UFES, Vitória, Brazil

Adel Mahmoud Sharaf     Engineering and Research Company of SHARAF Energy Systems, Fredericton, NB, Canada

Jair Adriano Lima Silva     Federal University of Espirito Santo—UFES, Vitória, Brazil

Juan P. Torreglosa     University of Huelva, Huelva, Spain

David Vera     University of Jaén, Linares, Spain

George A. Xydis     Aarhus University, Herning, Denmark

Imene Yahyaoui     University of Carlos III of Madrid, Madrid, Spain

Amani Yahyaoui     Sakarya University, Sakarya, Turkey

Nejat Yumuşak     Department of Computer Engineering, University of Sakarya, Turkey

Ahmed Faheem Zobaa     Brunel University London, Uxbridge, United Kingdom

Preface

This book provides a study of the advances in renewable energies focusing especially on biomass, fuel cells, and geothermal sources for energy generation. Moreover, the book is concerned with the application of renewable energies in, namely, distributed energies, electric vehicles, and optimal designing. The book presents explanations about the principle of the mentioned energy sources generation and provides ideas for new research applications related to data classification, telecommunication, etc. Special emphasis is on the power control and the optimum sizing.

The text is presented in such a way to be accessible to researchers with basic knowledge in renewable energies. Each chapter of the book is devoted to a particular problem, as follows:

•Power generation based on biomass

•Simulation models of biomass—thermochemical process for the prediction of the potential energetic through gasification

•Biomass gasification for power generation applications—a modeling, economic, and experimental study

•Fuel cells—concepts and operating principles

•On the modeling and control of a photovoltaic-fuel-cell hybrid energy system

•Geothermal power

•Deployment of renewable energy systems—barriers, challenges, and opportunities

•Optimal sizing and designing of hybrid renewable energy systems in smart grid applications

•Grid-connected microgrids—demand management via distributed control and human-in-the-loop optimization

•Distributed generation energy, in relation to renewable energy—principle, techniques, and case studies

•Virtual inertia for power converter control

•Electric and hybrid vehicle drives and smart grid interfacing

•Machine learning techniques for data classification

•Telecommunication technologies for smart grids—total cost optimization

•Smart manufacturing in a SoSE perspective

These points have been studied in depth by the authors and illustrated by examples. The results are compared with the previous results of the literature, whenever possible. The book contains around 224 figures and 669 compiled references.

This book will open up several interesting research lines, as the results provided can be extended to other problems such as the following:

•Climatic data classification and its effects on the optimum power use

•Integration of renewable energies into the grid

•Application of renewable energies in electric vehicles

•Distributed energy

•Telecommunication technologies for smart grids

The editor

Acknowledgement

The editor would like to express her sincere respect and gratitude to the authors of the chapters who gave their valuable cooperation and suggestions from time to time in successfully completing this book. My gratitude and special thanks go for all the people who helped and advised me when preparing the book.

The true sign of intelligence is not knowledge but imagination.

Albert Einstein

1

Biomass: Some Basics and Biogas

Jussara F. Fardin; Odair de Barros, Jr.; Augusto P.F. Dias    Federal University of Espírito Santo—UFES, Vitória, Brazil

Abstract

Biomass is a primary energy source used since the beginning of civilization. Besides the production of electric and thermal energy, biomass processing withdraws potentially contaminating material contributing to the preservation of the environment. This chapter will address some basic concepts to those who want to get to know this energy source and will present some biogas generation processes through anaerobic digestion based on digesters and landfill gas. It will present the current anaerobic digestion technologies based on digesters and the main methodologies used to model the methane emission potential of the landfill. The goal is to make the reader aware of the importance of this energy source, which is intrinsically related to the daily life of society, closing the cycle involving waste generation, waste transformation, energy generation, and return to society.

Keywords

Biomass; Renewable energy; Biomass use; Biogas; Digesters; Landfill gas modeling

1.1 Introduction

All organic matter is classified as biomass, and it can be used through its conversion in order to generate electricity. Concerns for the environment have increasingly imposed the option for renewable energy sources, mitigating the environmental impact associated with emissions caused by the use of fossil fuels or even by the occupation and flood of large areas for the construction of hydroelectric plants.

Besides using biomass to generate electricity, as reminded by EERE [1], the biomass is the only renewable energy source that can offer a viable supplement to petroleum-based liquid transportation fuels, such as gasoline, jet, and diesel fuel, in the near to midterm, and it can also be used to produce valuable chemicals for manufacturing. EERE [2] defines biomass as an energy resource derived from organic matter. These include wood, agricultural waste, and other living cell materials that can be burned to produce heat energy. They also include algae, sewage, and other organic substances that may be used to make energy through chemical processes. According to FAO, in the context of bioenergy, biomass is any material of biological origin excluding material embedded in geologic formations and transformed to fossil. The biomass definition to IPCC [3] is material of biological origin (plants or animal matter), excluding material embedded in geologic formations and transformed to fossil fuels or peat.

Traditional biomass is defined as the biomass consumed in the residential sector in developing countries to cook and heat and that comes from wood, vegetal charcoal, agricultural waste, and animal manure. Modern biomass includes other usages of biomass, and it is divided in two groups: modern bioenergy and industrial bioenergy [3]. Still according to the IPCC [3], modern bioenergy encompasses electricity generation and combined heat and power (CHP) from biomass and municipal solid waste (MSW), biogas, residential space, and hot water in buildings and commercial applications from biomass, MSW, and biogas, and liquid transport fuels. Industrial bioenergy applications include heating through steam generation and self-generation of electricity and CHP in the pulp and paper industry, forest products, food and related industries.

Biomass is considered a carbon-neutral energy source. Decomposition or burning of organic matter to generate energy releases carbon into the atmosphere. The plants absorb the released carbon that will be used in photosynthesis by delivering oxygen into the atmosphere. In this way, the healthy balance of the composition of the atmosphere is maintained for living beings. Fig. 1.1 shows the complete cycle of energy generation through biomass.

Fig. 1.1 Energy generation cycle from biomass.

From the definitions of biomass, it is observed the strong relationship between sustainable growth and biomass processing, either for thermal or electric energy, for the production of biofuels, or for water treatment. The sustainable future shall go through the correct use and transformation of biomass.

1.1.1 World Outlook and Projection

The annual global primary production of biomass is equivalent to 4500 EJ¹ of solar energy captured each year. Since 2000, the biomass supply grew at an average annual growth rate of 2.3%. Biogas and liquid biofuels had the highest increase at 11.2% and 15.6%, respectively [4]. According to recent studies, the range of the global potential of biomass in 2050 is 1135–1300 EJ [5, 6]; see Fig. 1.2 that presents the contribution of each biomass resource category to the global potential of biomass for energy use in 2050.

Fig. 1.2 Biomass potential for energy use in 2015. Modified from M. Hoogwijk, A. Faaij, R. van den Broek, G. Berndes, D. Gielen, W. Turkenburg, Exploration of the ranges of the global potential of biomass for energy, Biomass Bioenergy 25 (2003) 119–133.

The future estimate of biomass potential varies widely, with the upper limit of the potential of global bioenergy production in 2050 being estimated at 1135 EJ, without affecting the supply of food from food crops. On the other hand, the highest estimate value for the global primary energy demand in 2050 is 1041 EJ. Comparing such values, it is clear that the world's bioenergy potential is large enough to meet the global energy demand in 2050 [5]. These data show the important role that energy from biomass can play in the quality and progress of society.

Between 2000 and 2014, the production of biogas was 11.2%, and specifically in 2014, the production was 58.7 Nm³ corresponding to 1.27 EJ, using an average energy density factor of 21.6 MJ/Nm³. Fig. 1.3 shows the biogas production in continents in 2014 [4].

Fig. 1.3 Biogas production in continents in 2014. Modified from World Bioenergy Association, WBA Global Bioenergy Statistics 2017. http://www.worldbioenergy.org/uploads/WBA%20GBS%202017_hq.pdf.

The bioelectricity generation, during the years from 2000 to 2014, increased by an annual growth rate of 8.2%; Table 1.1 shows this evolution. In the year 2014, the bioelectricity generation was 493 TWh, most of it from solid biomass sources that include wood chips, wood pellets, agricultural residues, and forest residues. Municipal and industrial waste generated about 93.5 TWh, about 19% of the total bioelectricity generation. In Fig. 1.4, it showed the electricity generation from biomass in 2014 [4].

Fig. 1.4 Electricity generation from biomass in 2014. Modified from World Bioenergy Association, WBA Global Bioenergy Statistics 2017. http://www.worldbioenergy.org/uploads/WBA%20GBS%202017_hq.pdf.

Table 1.1

Modified from World Bioenergy Association, n.d. WBA Global Bioenergy Statistics 2017. http://www.worldbioenergy.org/uploads/WBA%20GBS%202017_hq.pdf.)

1.2 Biomass Classification

The biomass, after processed, is converted into feedstock with various features and applications, including bioenergy. Considering bioenergy, the feedstock comes basically from three sources: forest, nonforest, and waste.

Forest biomass is basically composed of wood. This wood can be obtained directly from native or planted forests, always in a way not to harm the environment, or through procedures that use wood without the purpose of generating energy such as wood industry, furniture industry, sawmills, or pulp mills. This biomass shows low moisture and, in general, uses a thermochemical route to suit it for its final use.

Nonforest biomass is produced from cultivation of species selected from energy plantations to obtain alcohol, such as sugarcane. It is also produced from agricultural by-products, like straw and leaves, and agro-industrial by-products, like sugarcane bagasse and rice husk. Furthermore, animal by-products including basically poultry, cattle, and swine manure can also compose this kind of biomass.

The biomass from municipal waste is composed of solid and liquid waste generated in cities and various locations. Most of the trash and sewage is composed of biomass. Table 1.2 based in Lora [7] shows the biomass classification as described in the text.

Table 1.2

Modified from E.E.S. Lora, L.A.H. Nogueira, Dendroenergia: Fundamentos e Aplicações, second ed. Editora Interciência, Rio de Janeiro. 2003.

1.3 Technological Routes for Energy Conversion of Biomass

Biomass for energy purposes needs a conversion step to fit into a specific final use in most of the applications. The biomass conversion processes can be divided into four groups: physical processes, thermochemical processes, biochemical processes, and chemical processes. Each one is associated to a kind of biomass and energy product. Physical biomass conversion processes do not change the chemical composition of the biomass. Thermochemical processes involve high temperatures, using predominantly heat to convert the biomass. The biochemical processes generally occur at room temperature and high humidity, using bacteria or other microorganisms to break biomass through processes like anaerobic digestion. The chemical conversion involves the use of chemical agents to convert biomass into liquid fuels.

Conversion technologies in use are direct combustion, cracking, anaerobic digestion, fermentation, gasification, hydrolysis, liquefaction, pyrolysis, transesterification, densification, pressing, and granulometric reduction.

1.3.1 Processes of Biomass Energy Conversion

The basic definitions that characterize various processes of energy conversion of biomass [7–10] will be presented next:

•Direct combustion—it is the transformation of the chemical energy of the fuels into heat, through the reactions of the constituent elements with the oxygen provided. It is the oldest conversion technology, rather practical, but usually very inefficient in the presence of moisture (20% or more in the case of firewood), and, due to low energy density of the fuel (firewood, straw, waste, etc.), frequently demanding some biomass preprocessing.

•Gasification—it is a process of converting solid and liquid fuels into gaseous, in which thermochemical reactions happen between the biomass and hot steam and air, or oxygen, in quantities lower than the stoichiometric (theoretical minimum for combustion). The objective is the production of a combustible gas, called producer gas. Gasification also generates a special gaseous mixture, the synthesis gas or syngas, rich in hydrogen and carbon monoxide, which can be used in the synthesis of any hydrocarbon.

•Pyrolysis—the pyrolysis process is the thermal degradation of the biomass in total or near-total absence of an oxidizing agent, at temperatures of the order of 500–1000°C, until the volatile material is removed. The main final product of this process is coal with energy density twice as high as the one of the original materials and burns at way higher temperatures. Besides combustible gas, pyrolysis produces tar and pyro-linoleic acid. This final product correlates with the temperature, residence time, and operating pressure during the conversion process.

•Fermentation—it is an anaerobic biochemical process in which microorganisms, such as yeasts, convert sugars from vegetables into alcohol. The final energy product is alcohol, composed of ethanol, in greater proportions and methanol, which can be used as fuel for internal combustion engines. Some of the vegetables used in fermentation are potato, corn, beet, and, mainly, sugarcane.

•Anaerobic digestion—the anaerobic digestion occurs in the absence of oxygen and consists in the decomposition of biomass through the action of microorganisms. The final energy product is biogas, composed essentially of methane (50%–75%) and carbon dioxide. The generated effluent in this process can be used as fertilizer.

•Liquefaction—it is the transformation of wood biomass and agricultural waste into liquid fuel, and this process can be direct or indirect. Indirect liquefaction produces syngas, which reacts with a catalyst and is transformed into methanol or hydrocarbon. Direct liquefaction is the conversion process of biomass into a liquid fuel under moderate temperatures, from 300°C to 400°C, and pressures from 10 to 20 MPa, with the addition of a reducing agent, typically hydrogen or carbon monoxide.

•Hydrolysis—it is the break of lignocellulosic biomass composed of polysaccharides in lower sugars for fermentation and ethanol production. Hydrolysis processes can be divided in two categories: acid hydrolysis and enzymatic hydrolysis.

•Transesterification—it is a process between an ester and an alcohol generating a different ester and a different alcohol. A catalyst is usually used, which may be acid or base. This chemical reaction produces glycerin and a mixture of ethyl or methyl esters (biodiesel). Biodiesel has physicochemical characteristics very similar to diesel oil and can replace it in several applications.

•Cracking—it consists in the break of oil and fat molecules, performed at high temperatures, in the presence of catalysts or not, forming a mixture of chemical compounds with properties similar to those of diesel.

From the energy conversion processes of biomass presented, this chapter will deal with the anaerobic digestion process and the biogas generated in this process.

1.4 Anaerobic Digestion Process

The anaerobic digestion process can be divided into four sequential main steps: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. In hydrolysis, first step of the process, polymers like carbohydrates, lipids, nucleic acids, and proteins are converted into glucose, glycerol, purines, and pyridines by hydrolytic microorganisms. During acidogenesis, second step of the process, acidogenic bacteria convert the products of hydrolysis into methanogenic substrates. Simple sugars, amino acids, and fatty acids are degraded into acetate, carbon dioxide, and hydrogen and into volatile fatty acids and alcohols. In the third step, acetogenesis, products from acidogenesis, which cannot be directly converted into methane by methanogenic bacteria, are converted into methanogenic substrates. Acetogenesis and methanogenesis usually run parallel. Methanogenesis is the fourth and the last step of anaerobic digestion process. This step needs attention once it is a critical step in the anaerobic digestion process. It is the slowest biochemical reaction of the process and is severely influenced by operating conditions. Composition of feedstock, feeding rate, temperature, and pH are some factors influencing the methanogenesis step. Digester overloading, temperature changes, or large entry of oxygen can result in termination of methane production [11]. Fig. 1.5 presents the mainly steps of the anaerobic digestion process [12].

Fig. 1.5 Main steps of the anaerobic digestion process.

The anaerobic digestion process is today utilized in four main sectors of manure and organic waste treatment: manure stabilization, sludge volume reduction and stabilization, industrial wastewater treatment, and organic waste treatment. Treatment of source separated organic fraction of solid household waste is one of the areas with a large biomass potential all over the world. The aim of this application is to reduce the flow of organic waste to other treatment systems, for example, landfill or incineration and to recycle the nutrients to the agricultural sector. Anaerobic digestion treatment of household waste is a technology that still needs to be improved and developed [12].

1.4.1 Operational Conditions to Anaerobic Digestion Process

To produce methane, bacteria need a controlled environment, which has to meet the conditions presented next:

•Anaerobic environment, once the bacteria are only active in the absence of oxygen.

•Relative humidity of at least 50% in the substrate.

•The bacterial activity is conditioned to the temperature. Bacteria can be divided in terms of temperature as psychrophilic (< 30°C), mesophilic (30–40°C), and thermophilic (40–55°C).

•The time required for bacteria to act on biomass during the anaerobic process is called hydraulic retention time and depends on the temperature, causing each group of bacteria to have a different retention time. Psychrophilic bacteria need a retention time from 40 to 100 days, mesophilic bacteria demand from 25 to 40 days, and thermophilic ones need 15–25 days.

•The pH value during the anaerobic digestion process shall be around 7.5.

•Bacteria need a minimum organic load, which is the dry organic matter (OM) per cubic meter of the digester per day (OM/m²/day). The organic load shall be between 0.5 and 5 kg of OM/m³/day.

•The presence of auxiliary substances is required for the metabolism of bacteria such as soluble compounds of nitrogen, minerals, and residual elements.

•Avoid high concentrations of some substances, such as disinfectants, antibiotics, and organic acids, because they inhibit the bacterial activity or even eliminate bacteria.

•Particles on the substrate shall be of smaller dimensions to increase the contact surface of the bacteria with the biomass.

•The substrate shall contain < 5% of dry matter so that the biogas up comes naturally to the surface. On the contrary, it will be necessary to mix it to avoid pressure elevation.

•Avoid fast changes in anaerobic digestion process.

•The substrate shall contain nitrogen, essential element to bacterial metabolism, besides helping regulating pH.

1.5 Biogas Produced by Anaerobic Digestion Based Systems

Anaerobic digestion is a natural biological process. Microorganisms convert complex carbohydrates in biogas in the absence of oxygen; therefore, the biogas can be generated through practically all organic matter. The main feedstock sources to produce biogas are agricultural waste, urban waste, and animal manure. The versatility of anaerobic digestion to process different organic wastes and the versatility of biogas to be used in different ways, added to the contribution to the environment quality, make the anaerobic digestion process and its product, biogas, attractive for two great applications: the generation of renewable energy and waste treatment. In these cases, the anaerobic digestion process can occur in a reactor or a tank or in a landfill. The reactor or tank is called a digester, and when the biogas is generated in a landfill, it is called a landfill gas. This chapter will address these two biogas generation technologies.

1.5.1 Biogas: Characteristics

Biogas is an energy gas, product of anaerobic biodegradation of organic matter. This gas is essentially composed of methane gas and carbon dioxide and can be produced from the main following resources: urban, industrial, and agricultural waste; animal manure; domestic and industrial sewage plants; and dedicated energy crops. The energy contained in a normal cubic meter of methane corresponds to about 10 kWh, and the energy content of biogas is directly related to the concentration of methane. Table 1.3 contains mean values, found in most of the literature, related to the composition of biogas [11].

Table 1.3

Modified from T. Al Seadi, D. Rutz, H. Prassl, M. Köttner, T. Finsterwalder, S. Volk, R. Janssen. Biomass Handbook. University of Southern Denmark Esbjerg, Esbjerg, 2008. Available from: http://www.lemvigbiogas.com/BiogasHandbook.pdf.

For a standard methane content of 50%, the heating value of the biogas is 21 MJ/Nm³, its density is 1.22 kg/Nm³, and its mass is similar to the air (1.29 kg/Nm³). The methane yield present in the biogas depends on the amount of fat, carbohydrates, and proteins contained in the biomass feedstock. Table 1.4 shows this dependency [11].

Table 1.4

Modified from T. Al Seadi, D. Rutz, H. Prassl, M. Köttner, T. Finsterwalder, S. Volk, R. Janssen. Biomass Handbook. University of Southern Denmark Esbjerg, Esbjerg, 2008. Available from: http://www.lemvigbiogas.com/BiogasHandbook.pdf.

Biogas has many energy utilizations. Generally, it can be used for heat production by direct combustion, electricity production by fuel cells or microturbines, and combined heat and power generation or as vehicle fuel.

1.6 Biogas From Digesters

Several technologies for anaerobic digestion process based on digesters have been used around the world. A basic classification of these technologies can be made as follows [10, 11, 13]:

1.6.1 Current Anaerobic Digestion Technologies Based on Digesters

•According to the concentration of the total solids (TS), expressed as a fraction of the wet mass of the prepared feedstock,

Wet systems or low-solids systems: When the concentration of the TS is < 10%–15%. A wet digester will typically process a kind of mud that shall be constantly stirred to prevent solids from precipitating. In general, they are continuous-flow digesters. Wet digesters process feedstock like manure and sewage sludge. These systems need stirring or mixing of the anaerobic digestion substrate during digestion.

Dry systems or high-solids systems: When the concentration of the TS is > 15%–20%. The prepared feedstock has a thick porridge consistency and needs to be mechanically stirred in the case of a continuous-flow digester. Dry systems are more adequate to process solid animal manure with high straw content, household waste and solid municipal biowaste, green cuttings, and grass from landscape maintenance or energy crops. These systems need no stirring or mixing of the anaerobic digestion substrate during digestion.

•According with the process steps of anaerobic digestion,

Single-stage digesters: In single-stage digesters, the several steps of the anaerobic digestion process occur inside a single tank and compete among themselves; for example, acidogenic bacteria diminish pH and may inhibit the methanogenic step.

Multiple-stage digesters: Allows the steps of the anaerobic digestion to happen in separate tanks; for example, in a two-stage digester, the first three steps can occur in a tank, and then, the substrate is transferred to a second tank where the methanogenesis occur.

•According with the digester feeding procedures,

Batch digester: In this kind of digester, biomass feedstock supply is made at once, being removed after the digestion process, this is, it is necessary to interrupt biogas production to provide new feedstock and remove the digested one. The digester receives a new batch of feedstock and the process restarts. Batch digesters are the simplest to build and are usually used for dry digestion, presenting low construction and operation costs.

Continuous digester: Feedstock supply in this digester is made at a continuous rate, and biogas production is constant. Biomass feedstock flow inside the digester is made mechanically or by the pressure of the new load coming into the digester. The construction of this digester can be vertical or horizontal, and according to the biomass feedstock stirring system, it can be completely mixed digesters or plug-flow digesters.

•According with the reaction rate of the substrate during the anaerobic digestion process,

Low-rate systems: They are defined as a system where feedstock typically spends more time in the digester to maximize biogas output. They have high hydraulic retention time and the same as the sludge retention time, and they are suited to animal waste at a low scale.

High-rate systems: They are system where liquids stay in the digester for a short period of time, whereas solids are held longer, that is, the hydraulic retention time is much shorter than the sludge retention time. This allows for a smaller reactor size, while maintain high gas production. High-rate system has been developed in economically advanced countries and is suited to applications at a high scale.

A combination of these.

•According with the largest dimension,

Horizontal: Suitable for agricultural and animal residues.

Vertical: Suitable for sewage treatment.

1.6.2 Digesters

The central element of a biogas generator system through the anaerobic digestion process is the digester, which is a reactor or a tank where organic matter decomposition is processed in the absence of oxygen. The basic parts that form a digester are a biomass feedstock supply system, the digester, a biogas storage system, and a digested feedstock storage system. If necessary, in cooler places, for example, the digester shall have a heating system to keep the substrate at a proper temperature for the anaerobic digestion process. Digesters may be built on the surface of a ground or even underground. They can be horizontal or vertical and can be made of several materials such as concrete, steel, bricks, or plastic. Next subsections will present some of the several types of digesters.

1.6.2.1 Completely Mixed Digesters

This is a continuous type digester with a process temperature between 20°C and 37°C and hydraulic retention time of the 20–30 days. Completely mixed digesters are low-rate systems, and they are typically vertical digesters composed of a tank in which the biomass feedstock received is mixed and heated. Dry digestion may occur in this system, and fresh feedstock is usually mixed with partially digested substrates. The substrate can be continuously mixed or intermittently mixed. Mixing can be accomplished by gas recirculation, mechanical propellers, or circulation of liquid. Sometimes, the process takes place in more than one tank. Completely mixed digesters work best when substrate contains 3%–6% total solids. This technology is most widely used around the world.

1.6.2.2 Plug Flow Digesters

This is a continuous type digester with a process temperature between 35°C and 55°C and hydraulic retention time of the 15–20 days. Plug-flow digesters are horizontal, no mixing and are classified as low-rate systems. This digester type cannot be able to perform a dry digestion due to its low fluidity. Total solids (TS) content of substrate should be at least 10%–15%.

1.6.2.3 Covered Lagoon Digesters

It is a digester that works at room temperature and is suitable for hot weather places with the anaerobic process developing inside a lagoon covered by a flexible or floating gas tight cover. This type of digester typically processes flush manure and has a retention time usually between 30 and 45 days or longer depending on lagoon size. The most efficient structure to this kind of digester is composed of two lagoons in series, a covered one (first cell in Fig. 1.6) used for the anaerobic process and collection of the biogas generated and the other one (second cell in Fig. 1.6) uncovered used to store effluents. The primary lagoon operates at a constant volume to maximize biological treatment, methane production, and odor control.

Fig. 1.6 Covered lagoon. Modified from Bioenergy Training Center. University of Wisconsin-Extension, Type of Anaerobic Digesters. http://fyi.uwex.edu/biotrainingcenter/.

1.6.2.4 Chinese Fixed Dome

This digester was created in China and has widespread in the world in regions with small farms. > 10 million of such fixed-dome digesters have been built in China.

The Chinese model has low cost and is made in masonry, and once it does not have a steel sheet gas holder, a long life of the plant can be expected (20 years or more) [14]. The plant is constructed underground, protecting it from physical damage and saving space. A problem of this kind of digester is that biogas leakage is possible in case the structure is not properly sealed and waterproofed. Fig. 1.7 shows a model of this digester.

Fig. 1.7 Chinese fixed dome where, D is the tank diameter, H is the tank height, h2 is the height of the dome, hi is the height of the input box, Di is the diameter of the input box, ho is the height of the output box, and Do is the diameter of the output box.

1.6.2.5 Indian Floating Dome

The tank of this digester is usually made of brick or concrete, constructed underground, and it has a gasholder normally made of metal like floating dome. The dome can be dipped over biomass in fermentation or over an external water seal. A central wall divides the tank in two chambers forcing biomass circulation inside the digester. The biogas produced makes the dome move vertically, increasing the volume occupied by the digester and keeping the pressure inside the gasometer. Fig. 1.8 presents an Indian model of fixed-dome digester [15]:

Fig. 1.8 Indian floating dome where Hb is the height of substrate level, D is the digester internal diameter, Dg is the gasometer diameter, Ds is the internal diameter of the wall surrounding the gasometer, h1 is the height of biogas tank, h2 is the useful height of the gasometer, hi is the input box height, and ho is the height of the entrance of the pipe with effluent.

In order to guarantee a good efficiency, the biomass that feeds this digester must present total solid concentration lower than 8% and continuous feeding.

1.6.3 Calculation of Biogas Power From Anaerobic Digester System

Dimensioning an anaerobic digestion system requires information concerning potential for biogas generation, and this potential, in turn, depends on the biomass used. A methodology to calculate such potential is presented next.

The first step consists of the collection of data that characterize the biomass used, mentioned as follows:

Dry matter (DryMat)—dry matter percentage or total of solids in the substrate.

Organic matter (OrgMat)—volatile solid percentage present in the dry matter.

Dry organic matter (OrgDryMat)—organic part of the substrate, which is equal to

   (1.1)

Specific biogas production (BiogasEspProd)—amount of biogas in m³ per tons of dry organic matter for each kind of biomass.

Biogas production can be calculated from information on biomass as follows:

Quantity of substrate (SQuant)—value in tons of the quantity of biomass from which biogas production is to be calculated (BiogasProd).

The biogas production in cubic meter is calculated as presented in Eq. 1.2:

   (1.2)

1.7 Landfill Gas Modeling

Landfill is one of the simplest solutions for disposal of community's solid waste. The municipal solid waste (MSW) consists mostly of residential and commercial residues. This includes food waste, trash from yards, gardens and parks, aluminum, wood, concrete, and other discarded building materials and paper.

Despite being a simple solution, the population increase of the last century caused a considerable increase of the landfills, generating serious environmental problems. Likewise, increasing the inhabited area makes it increasingly difficult to find solutions to accommodate all the waste generated by the population. In 2014, the United States alone generated 258 million tons of garbage were generated. Even with the search for so many alternatives and solutions to solve the problem of the existence of landfills, considering the huge and growing mass of waste generated, the landfill remains the most economically viable alternative. However, the environmental impacts arising from the existence of landfills are a problem to be solved [16].

The landfill gas (LFG) is the product of several biochemical processes that occur within a landfill and consists of a combination of gases, such as methane (50%–60%) and carbon dioxide (40%–50%). Both are harmful to the environment and contribute to the depletion of the ozone layer, being one of the biggest contributors to the greenhouse effect. The methane emissions have doubled in the last century, and given that methane is 21 times more harmful to climate change than carbon dioxide, predicted damages may be even worse for the next century.

The solution for this problem was found in the search for alternatives to another problem caused by the conflict between the maintenance of the environment and the population increase, which is the search for alternative sources of energy. The energy crisis due to high consumption and the oil crisis make LFG a highly economical and highly efficient alternative to the environment [17].

The application of methane gas for electricity production depends on the gas potential that will be emitted by a given solid waste disposal site (SWDS). Therefore, a primary engineering task is the modeling of the methane emission potential, or gases, of the landfill. Several models have been developed, considering environmental and climatic aspects and with numerous methodological approaches seeking the best balance between modeling complexity and results precision. The main methodologies adopted in the literature will be discussed in this section.

1.7.1 Parameters to Landfill Models

The search for the predictive model of landfill gas potential is the first step in the development of a methane-based generation system. Such choice should consider the degree of precision of the model adopted, the complexity desired, and the observation of the behavior of this model before other landfills under conditions similar to the one that will be applied. It is also necessary to observe the product and the function of the algorithm chosen to carry out the prediction.

One of the major obstacles to the