Steam Generation from Biomass

Construction and Design of Large Boilers

Esa Kari Vakkilainen

• Publisher: Butterworth-Heinemann
• Year: 2016
• Print ISBN: 9780128043899
• eBook ISBN: 9780128044070
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Steam Generation from Biomass: Construction and Design of Large Boilers provides in-depth coverage of steam generator engineering for biomass combustion. It presents the design process and the necessary information needed for an understanding of not only the function of different components of a steam generator, but also what design choices have been made.Professor Vakkilainen explores each particular aspect of steam generator design from the point-of-view of pressure part design, mechanical design, layout design, process design, performance optimization, and cost optimization. Topics such as fuels and their emissions, steam-water circulation, auxiliary equipment, availability and reliability, measurements and control, manufacture, erection, and inspection are covered.Special attention is given to recovery boilers and fluidized bed boilers, and automated design and dimensioning calculation spreadsheets are available for download at the book's companion website. This book is intended for both design engineers and steam boiler operators, as well as those involved in plant management and equipment purchasing.- Provides a complete overview of biomass steam boilers, including processes, phenomena, and nomenclature- Presents a clear view of how biomass boilers differ from fossil fuel boilers- Covers the most used types of large-scale biomass boilers, including recovery boilers, fluidized bed boilers, and auxiliary equipment- Includes a companion website with spreadsheets, calculation examples, and automatic calculation tools for design and dimensioning

1

Principles of Steam Generation

Abstract

Steam power is dominant in electricity-generating thermal power stations. A brief overview is given on the history of steam generation in general and on steam generators using biomass in particular. Special emphasis is placed on the development of manufacturing methods making changes to boiler construction possible. This is followed by an introduction to the most typical types of steam generator. The utilization of steam generation started in England and coincides with the Industrial Revolution. The first biomass-fired boilers were also built at this time. Increasing efficiency has always been the leading technical driver in steam generator design. Modern fluidized bed boilers and recovery boilers are the two most often utilized types for steam generation from biomass.

Keywords

Steam power; biofuel; boiler types; fire tube boiler; water tube boiler

Chapter Outline

1.1 Introduction 1

1.1.1 History of Steam Generation 3

1.1.2 Modern Boiler Types 12

References 16

The development of the industrial age coincided with the development of heat engines (Morris, 2010). It was the steam engine that liberated man from mainly toiling the land and afforded him the means of improving his living conditions. Currently there are four main types of heat engine in use: internal combustion reciprocating engine, gas turbine, steam power, and rocket engine (Ishigai, 1999). Steam power is dominant in electricity-generating thermal power stations. The part of the process that is used to generate vapor is called steam generation.

The first steam generators developed around coal, especially to pump water away from deep coal mines. Biomass utilization for steam generation started at the same time in regions where coal was expensive. Steam generation from sustainably sourced biomass is gaining more interest as restricting global warming is gaining importance. The Intergovernmental Panel on Climate Change (2011) is of the opinion that, compared to the fossil energy baseline, one can achieve 80–90% fossil carbon dioxide (CO₂) emission reductions when using energy generated from biomass. The International Energy Agency (2014) in their world energy outlook expects bioenergy electricity generation in their 450 scenario to increase fivefold from 2012 to 2040.

1.1 Introduction

A steam generator that uses combustion as its main heat source is often called a boiler. Water that is converted to steam is the most common fluid used in heat engines, which convert heat to work. Steam generation was actually first introduced in apparatus designed to convert heat to the work required for pumping water from mines. For process applications, heat from a steam generator can be used directly to serve the required process purposes (e.g., district heating by steam). In steam generation the heat source, combustion, and the working fluid are separated, typically by a wall of heat-resistant material (e.g., steel tubes).

Electricity generation is one of the main uses of steam generators with a turbine. We can compare currently predominant electricity-generating options in Table 1.1. It can easily be seen that none of the currently prevalent processes totally fulfills the most desired features.

Table 1.1

Comparison of electricity Generation Options (Rogan, 1996)

Process	Cost of	Reliability/Availability		Environmental
	Electricity	Technology	Fuel	Emissions	CO2 (t/MWh)
Most desirable	Low	High	High	Zero	Zero
Coal (pulverized fuel combustion)	Low	High	High	Low	1.0
Coal (advanced)	Medium	?	High	Lower	0.8
Natural gas (combined cycle)	Low	High	Varies	Lower	0.6 0.4
Nuclear	Medium	High	High	Zero	Zero
Biomass	Medium	High	Varies	Low	1.5
Solar/Wind	High	?	Varies	Zero	Zero
Fuel cells	High	?	Varies	Lower	0.3
Hydro	Low	High	Varies	Zero	Zero

Of the listed processes the most typical ones for new installations are still coal-fired boilers, natural gas combined cycle and biomass-fired steam generators. It should be pointed out that biomass is a renewable source of electricity and produces no net fossil CO₂ (IPPC, 2011).

Biomass is a primary source of food, fodder and fibre and as a renewable energy (RE) source provided about 10.2% (50.3 EJ) of global total primary energy supply (TPES) in 2008. Traditional use of wood, straws, charcoal, dung and other manures for cooking, space heating and lighting by generally poorer populations in developing countries accounts for about 30.7 EJ, and another 20 to 40% occurs in unaccounted informal sectors including charcoal production and distribution. TPES from biomass for electricity, heat, combined heat and power (CHP), and transport fuels was 11.3 EJ in 2008 compared to 9.6 EJ in 2005 and the share of modern bioenergy was 22% compared to 20.6%. (IPPC, 2011).

All CO₂ produced by biomass combustion is absorbed back into the forests and other natural biomass, assuming sustainable practices are used.

What will the role of steam boilers be in the future? The world energy consumption keeps on increasing. Currently about 70% of world electricity generation is done using thermal processes. Even with a shift to renewable sources, electricity generation based on steam power plants will continue to grow. In spite of progress in renewable energy, world coal consumption is still expected to grow (IEA, 2015). If we can significantly increase steam generation from biomass, we have the possibility to dramatically decrease our carbon footprint.

1.1.1 History of Steam Generation

There is evidence of the use of steam for motive power as far back as the Ancient Greeks (the first mention is by Heron in 200 BC). The Greeks and Romans used water heaters that have many of the features of modern boilers. Their hot water boilers were for domestic use only. The one in Fig. 1.1 (Croft, 1922) was internally fired, made from bronze and had a water tube grate. You placed the fuel on the grate and let it burn using a natural draft to transfer the heat from combustion to the water inside.

Figure 1.1 Pompeian water heater (Croft, 1922).

After 1600 there was renewed interest in steam. The French, English, and Russians used steam to drive water up into water fountains. Some of the people involved with the first applications of steam were Frenchman Denis Papin, Englishman Samuel Morland, and Italians Galileo Galilei and Evangelista Torricelli.

1.1.1.1 Early Boilers

Boilers were first used for industrial application in England in the 1700s, initially for pumping water from mines. These boilers had a very low efficiency, but as fuel supply was plentiful and th...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• About the Author
• Preface
• Poem
• Disclaimer
• Nomenclature
• 1. Principles of Steam Generation
• 2. Solid Biofuels and Combustion
• 3. Boiler Processes
• 4. Steam–Water Circulation Design
• 5. Thermal Design of Boiler Parts
• 6. Auxiliary Equipment
• 7. Boiler Mechanical Design
• 8. Availability and Reliability
• 9. Direct and Grate Firing of Biomass
• 10. Fluidized Bed Boilers for Biomass
• 11. Recovery Boiler
• 12. Measurements and Control
• 13. Boiler Manufacture, Erection, and Maintenance
• Appendix A. Questions
• Appendix B. H-S Diagram
• Appendix C. Steam Tables
• Index