small-scale biomass power generation

259 Pages·2010·7.47 MB·English

UNIVERSITY OF BERGAMO
Faculty of Engineering
Department of Industrial Engineering

PhD in Energy and Environmental Technology
XXII cycle – year 2010

SMALL-SCALE BIOMASS
POWER GENERATION

Supervisor: Prof. Antonio Perdichizzi
Co-examiner: Prof. Giuseppe Franchini

Thesis by:
Samuel Carrara

Fatti non foste a viver come bruti,
ma per seguir virtute e canoscenza.
(Ye were not made to live like unto brutes,
But for pursuit of virtue and of knowledge.)

Dante Alighieri, The Divine Comedy,
Inferno, Canto XXVI, lines 119-120

Abstract
In recent years considerable attention has been paid to power generation from biomass,
especially in small scale plants. Several plant configurations have been proposed and
investigated, but so far, definitely preferable technological solutions have not been
found yet. Moreover, a comparison of their performances is often difficult, due to the
fact that working assumptions are not always consistent.
The aim of the present work is to provide a full overview on small scale technologies
regarding biomass exploitation (particularly woody one) for power generation, in order
to define the most interesting solutions from a thermodynamic and economic point of
view. Existing configurations or those which are expected to be potentially available on
the market in the near future have been considered. Three plant sizes have been focused:
100 kW , 1 MW and 5 MW . Internal combustion engines (ICE), (micro) gas turbines
el el el
(mGT/GT), both internally and externally fired, and organic Rankine cycles (ORC)
have been taken into account as power plants, while direct combustion and gasification
have been considered for biomass.
Simulations show that the externally fired gas turbine is the most promising technology
at small scale (100 kW ), if a high temperature heat exchanger is available. A gasifier
el
coupled with an internal combustion engine is instead preferable at larger scales
(1 MW and 5 MW ).
el el
An also proposed sensitivity analysis concerning moisture effects shows that biomass
drying with flue gas is generally disadvantageous, even if sometimes (e.g. in gasifiers)
necessary, because of the dryer cost.

Acknowledgements
After twenty-one years, my career as a student comes to an end with this thesis. In this
moment I am thinking back to the people who accompanied me and to the episodes
which occurred during these years: if I had to list all of them, I should probably write
another book! However, someone once said that one book per time is enough, when it is
not too much, then I will just greet and thank the people who were important during the
PhD period and who helped me reach this further goal, starting from the university
teaching staff who bore me again after my bachelor and master degrees.
My dutiful thanks go to my Supervisor, Prof. Antonio Perdichizzi, for giving me once
more the chance to collaborate with his research group and to develop this thesis under
his guidance.
I am very grateful to my Co-examiner, Prof. Giuseppe Franchini, for having me always
granted a huge support: working with him has always been stimulating and pleasant.
My thanks also go to Prof. Gianpietro Cossali, Prof. Giovanna Barigozzi and all the
other professors who have always proven to be very helpful.
I warmly hug all PhD and post-doc students whom I met in these years and who shared
with me the serenity of the positive moments and discouragement of the difficult ones: I
will miss the PhD office and the lunches at Gattopardo’s or Centrale’s!
Naturally, I cannot but thank my parents, my brother, my grand-mother and all my other
relatives, who helped me be what I am now.
My loving thanks go Laura and her family: the gratitude that I fell towards them cannot
be described in few words; my thanks also to Mrs. Schroeder for the appreciated
support.
Obviously I want to thank all friends of mine and all the other people who have been
close to me and that cannot be cited here.
Finally, my special thanks to the ones who, without being seen, help me every single
day from up above.

Table of contents

Table of contents
Table of contents...................................................................................................I

Nomenclature...................................................................................................VII

List of Figures....................................................................................................XI

List of Tables.................................................................................................XVII

Introduction.........................................................................................................1

Chapter 1
Biomass and technologies for its exploitation...................................................5
1.1 Introduction..........................................................................................................5
1.2 The energy issue and biomass role.......................................................................5
1.2.1 Italian situation and perspectives...............................................................11
1.2.1.1 Primary energy..............................................................................11
1.2.1.2 Electric energy...............................................................................13
1.3 Biomass and its chains........................................................................................14
1.3.1 The resource..............................................................................................14
1.3.2 Photosynthesis...........................................................................................17
1.3.3 Conversion principles and chains..............................................................19
1.3.3.1 Alcoholic fermentation..................................................................21
1.3.3.2 Vegetable oil esterification............................................................22
1.3.3.3 Anaerobic digestion.......................................................................22
1.3.3.4 Aerobic digestion...........................................................................23
I
Table of contents

1.4 Woody biomass properties.................................................................................23
1.4.1 Chemical properties...................................................................................24
1.4.2 Physical properties.....................................................................................26
1.4.3 Energy properties.......................................................................................27
1.5 Woody biomass conversion technologies..........................................................29
1.5.1 Combustion................................................................................................30
1.5.1.1 Combustion devices.......................................................................32
1.5.1.2 Emissions.......................................................................................34
1.5.2 Pyrolysis....................................................................................................36
1.5.3 Gasification................................................................................................36
1.5.3.1 Gasifiers.........................................................................................40
1.5.3.2 Syngas treatment...........................................................................49

Chapter 2
Small-scale power plants...................................................................................55
2.1 Introduction........................................................................................................55
2.2 Small-scale power generation and CHP.............................................................56
2.3 Internal combustion engines...............................................................................59
2.4 Gas turbines........................................................................................................64
2.4.1 Micro gas turbines.....................................................................................68
2.4.2 Comparison among ICE, GT and mGT.....................................................75
2.4.3 Externally fired gas turbines......................................................................76
2.5 Organic Rankine cycles......................................................................................80
2.6 Other technologies..............................................................................................86
2.6.1 Stirling engines..........................................................................................86
2.6.2 Steam engines............................................................................................88
2.6.3 Fuel cells....................................................................................................88

Chapter 3
Working hypotheses and preliminary analysis...............................................93
3.1 Introduction........................................................................................................93
3.2 Thermoflex™.....................................................................................................94
II