`
Demonstration of a Small scale Mobile Agricultural
Residue gasification unit for decentralized Combined
Heat and Power production
LIFE08 ENV GR 000576 SMARt-CHP
Results and sustainability analysis /
Best practice guidelines
Part A: Demonstration results
analysis
with the contribution of the LIFE+ financial instrument of the European Union
Z. Samaras
D. Mertzis
S. Tsiakmakis
Contact info:
Prof. Zissis Samaras
Laboratory of Applied Thermodynamics
Mechanical Engineering Department
Aristotle University Thessaloniki
P.O. BOX 458 GR 541 24 Thessaloniki Greece
Tel: +30 2310 99 60 14, Fax: +30 2310 99 60 19
e-mail: zisis@auth.gr
http://smartchp.eng.auth.gr
http://lat.eng.auth.gr
Project Title
Action reference
Demonstration of a Small scale Mobile Agricultural
Residue gasification unit for decentralized Combined
Heat and Power production
A4
Report Title
D4 Results and sustainability analysis / Best practice guidelines – Part A: Demonstration
results analysis
Project Manager
Prof. Zissis Samaras
Author(s)
Z. Samaras1, D. Mertzis1, S. Tsiakmakis1
1
Laboratory of Applied Thermodynamics, Aristotle University Thessaloniki
Summary
A Small Mobile Agricultural Residue gasification unit for decentralised Combined Heat and Power
production was designed and manufactured. This unit has a maximum electrical output of 4.7 kW. It
was demonstrated in four different locations in rural areas of Western Macedonia, two in Ptolemaida
and two in Amyntaion, for two weeks in each location. Peach, olive and grape kernels were utilized
during the demonstrations. Over this period, the unit was steadily improved (overcoming technical
and organization problems) to meet the operation target of 240 hours in each location. The data
derived during the demonstration operation were analysed and presented in depth in this study. The
unit is also evaluated regarding energy efficiency. The aforementioned analysis acts as a reference
point for agro-residue utilization promotion in the rural areas of Greece and the Mediterranean
region. The analysis of the demonstration results is discretized into 3 major axes: biomass type
evaluation, gasification performance and CHP unit performance. The contribution of each axis is
evaluated and conclusions regarding overall system efficiency and margin for optimisation are
produced.
Keywords
Combined heat and power, gasification, biomass, mobile energy production unit, energy balance
No of Pages
55
Internet reference
http://smartchp.eng.auth.gr
Project reference number
LIFE08 ENV GR 000576 SMARt-CHP
D3 Demonstration operation report
Contents
Nomenclature....................................................................................................................2
List of figures ....................................................................................................................3
1
Executive summary ...................................................................................................5
2
Introduction ..............................................................................................................7
2.1
Project objectives ..............................................................................................8
2.2
Definition of technical terms ............................................................................8
2.3
Overview of Action 4 - Demonstration results and sustainability analysis /
Best practice guidelines.............................................................................................. 11
3
4
SMARt-CHP unit ....................................................................................................13
3.1
Unit description and operational procedure ................................................. 13
3.2
Demonstration operation summary ............................................................... 15
Demonstration operation results ............................................................................. 16
4.1
Biomass type evaluation ................................................................................. 16
4.1.1
Biomass species characteristics................................................................ 16
4.1.2
Fuel handling and feeding system reliability .............................................. 19
4.2
Gasification performance ............................................................................... 24
4.3
CHP performance analysis ............................................................................. 29
4.3.1
4.4
Results .................................................................................................. 33
SMARt-CHP system evaluation.....................................................................39
4.4.1
Operation stability .................................................................................. 39
4.4.2
Mass & Energy Balance Efficiency ............................................................ 40
5
Conclusions ............................................................................................................. 47
6
Bibliography ............................................................................................................ 50
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LIFE08 ENV GR 576 SMARt-CHP
2
Nomenclature
SMARt-CHP
Small Mobile Agricultural Residue gasification unit for decentralised
Combined Heat and Power production
CHP:
Combined Heat and Power
AUTh:
Aristotle University of Thessaloniki
LAT:
Laboratory of Applied Thermodynamics
LCPPD:
Laboratory of Chemical Process and Plant Design
DHCP:
District Heating Company of Ptolemaida
UACA:
Union of Agricultural Cooperatives of Amyntaion
ICE
Internal Combustion Engine
SME
Small Medium Enterprise
EU
European Union
HHV
Higher Heating Value
ER
Equivalence Ratio
LCV
Lower Calorific Value
D3 Demonstration operation report
List of figures
Figure 1: SMARt-CHP unit layout: 1) Data acquisition, 2) Secondary biomass silo, 3)
Primary biomass silo, 4) Screw feeder 1, 5) Rotary valve, 6) Screw feeder 2, 7) El.
Oven, 8) Reactor tube, 9) Cyclone filter, 10) Fly ash collector, 11) Gas by-pass to
flaring, 12) Valve, 13) Particle trap, 14) Tar removal vessel 1, 15) Tar removal vessel
2, 16) Tar removal vessel 3, 17) ICE-generator, 18) ICE exhaust .......................... 13
Figure 2: Fuel consumption in kg and % of total consumption during the four
demonstrations ................................................................................................. 19
Figure 3: Fuel consumption per demonstration ........................................................... 19
Figure 4: Visible stone residuals in the treated peach kernels ....................................... 20
Figure 5: Comparison of measured fuel flow before and after the sieving versus screw
feeder motor speed ........................................................................................... 21
Figure 6: Comparison of measured fuel flow before and after the sieving versus screw
feeder motor speed ........................................................................................... 22
Figure 7: Gas composition and higher heating value versus reactor temperature–olive
kernels ............................................................................................................. 25
Figure 8: Gas composition and higher heating value versus stoichiometry–olive kernels . 25
Figure 9: Olive kernel producer gas residence time ..................................................... 25
Figure 10: Gas composition and higher heating value versus reactor temperature–peach
kernels ............................................................................................................. 26
Figure 11: Gas composition and higher heating value versus stoichiometry–peach kernels
....................................................................................................................... 26
Figure 12: Peach kernel producer gas residence time .................................................. 26
Figure 13: Gas composition and higher heating value versus reactor temperature–grape
kernels ............................................................................................................. 27
Figure 14: Gas composition and higher heating value versus stoichiometry–grape kernels
....................................................................................................................... 27
Figure 15: Grape kernel producer gas residence time .................................................. 27
Figure 16: Propane Consumption Reduction – 3000rpm............................................... 30
Figure 17: Gas Energy Input Fraction ......................................................................... 34
Figure 18: Total Efficiency of the Mini CHP Unit .......................................................... 34
Figure 19: Electric Power Produced at 80% w/w producer gas ..................................... 36
Figure 20: Thermal Power Produced at 80% w/w producer gas.................................... 36
Figure 21: Reduction of the Electric Power Produced as compared to the propane, for
80% Gas Mass Fraction and the three biomass feedstock ..................................... 37
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LIFE08 ENV GR 576 SMARt-CHP
Figure 22: : Reduction of the Propane Consumption as compared to sole propane as fuel,
for 80% Gas Mass Fraction and the three biomass feedstock ................................37
Figure 23: Operation map (olive kernels) ....................................................................37
Figure 24: Operation map (peach kernels) ..................................................................37
Figure 25: Operation map (grape kernels) ..................................................................38
Figure 26: Total Operation Duration per Demonstration ...............................................40
Figure 27: Real duration on electricity and gasification mode .......................................40
Figure 28: SMARt-CHP Unit’s Mass and Energy Balance ...............................................42
Figure 29: SMARt-CHP Unit’s Sankey Diagram.............................................................43
D3 Demonstration operation report
1 Executive summary
Scope of the LIFE+ project is the demonstration of an innovative small scale mobile
power production unit, for the energy utilization of agricultural residues generated in rural
areas, where large amounts of biomass wastes are available. A Small Mobile Agricultural
Residue gasification unit for decentralized Combined Heat and Power (CHP) production
was designed and constructed by AUTh. The unit consists of a gasification reactor
combined with an internal combustion engine adjusted to work on producer gas for
electrical power and heat, achieving high energy and environmental performance.
The LIFE+ project concerns, amongst others, the transportation and demonstrative
operation of the developed SMARt-CHP unit at two decentralised locations at Ptolemaida
and two at Amyntaion. The data collected during the four demonstrations were analysed
and evaluated. The unit is also evaluated regarding energy efficiency. The
aforementioned analysis acts as a reference point for agro-residue utilization promotion in
the rural areas of Greece and the Mediterranean region. The analysis of the
demonstration results is discretized into 3 major axes: biomass type evaluation,
gasification performance and CHP unit performance.
Regarding feeding performance, all fuels were easily handled after a set of minimum
pretreatment activities. The results show that the fuel’s water content must be lower than
20%, the ash content should be less than 10% to ensure long operations and finally the
size range of the fuel must be close to that of olive kernels (1-3 mm). The feeding system
can reliably handle all fuels within the aforementioned specifications.
Gasification parameters influence gas composition in the same manner for all fuels. The
choice of a fuel for gasification will in part be decided by its heating value. The heating
value of the gas produced depends at least in part on the moisture content of the
feedstock. Ashes can cause a variety of problems. For these reasons even though the
peach derived gas has a higher measured heating value compared to olive and grape gas
,it is not efficient to gasify due to its high moisture and ash content. If the peach kernels
were treated properly, then the ash content would be minimum but the gas calorific value
would remain the same as solids and moisture are removed from the gas prior sampling.
During the demonstration, the maximum producer gas contribution to the engine’s fuel
mixture that was recorded for all three biomass residues was 80 % mass. The rest 20%
mass consists of propane. The producer gas that derives from grape kernel gasification
yields lower power output compared to the gas that originates on peach and olive kernels.
Among these two, olive kernels produce slightly better gas quality. The net el. efficiency
of the unit is heralded as low (6 %). It is though a good starting point for further
optimisation and scale up.
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LIFE08 ENV GR 576 SMARt-CHP
Στόχος του έργου LIFE+ είναι η επίδειξη μιας καινοτόμου μικρής κλίμακας κινητής
μονάδας παραγωγής ηλεκτρικής ενέργειας, για την αξιοποίηση γεωργικών υπολειμμάτων
που παράγονται σε αγροτικές περιοχές, όπου μεγάλες ποσότητες αποβλήτων βιομάζας
είναι διαθέσιμες. Μια μικρή κινητή μονάδα αεριοποίησης γεωργικών υπολειμμάτων για την
αποκεντρωμένη συμπαραγωγής ηλεκτρισμού και θερμότητας (ΣΗΘ) σχεδιάστηκε και
κατασκευάστηκε από το ΑΠΘ. Αποτελείται από έναν αντιδραστήρα αεριοποίησης σε
συνδυασμό με μία μηχανή εσωτερικής καύσης η οποία έχει προσαρμοστεί σε λειτουργία με
αέριο αεριοποίησης για συμπαραγωγή επιτυγχάνοντας υψηλή απόδοση.
Το έργο αφορά, μεταξύ άλλων, τη λειτουργία, μεταφορά και επίδειξη της μονάδας SMARtCHP σε δύο αποκεντρωμένες θέσεις στην Πτολεμαΐδα και δύο στο Αμύνταιο. Τα δεδομένα
που προέκυψαν κατά τη διάρκεια των τεσσάρων επιδείξεων, αναλύθηκαν και
αξιολογήθηκαν. Η μονάδα επίσης αξιολογείται όσον αφορά την ενεργειακή απόδοση. Η
παραπάνω ανάλυση λειτουργεί ως σημείο αναφοράς για την προώθηση της αξιοποίησης
αγροτικών υπολειμμάτων στις αγροτικές περιοχές της Ελλάδα και της Μεσογείου. Η
ανάλυση των αποτελεσμάτων της επίδειξης διακρίνεται σε 3 βασικούς άξονες: τον τύπο
βιομάζας, την απόδοση αεριοποίησης και την απόδοση της μονάδας συμπαραγωγής.
Όσον αφορά την απόδοση τροφοδοσίας, όλα τα καύσιμα διαχειρίζονται εύκολα μετά από
ένα ελάχιστη προ-επεξεργασίας. Τα αποτελέσματα δείχνουν ότι η περιεκτικότητα σε νερό
του καυσίμου πρέπει να είναι χαμηλότερη από 20%, η περιεκτικότητα σε τέφρα θα πρέπει
να είναι μικρότερη από 10% για την εξασφάλιση μεγάλων λειτουργιών και τέλος η περιοχή
μεγέθους του καυσίμου πρέπει να είναι κοντά σε αυτή του ελαιοπυρήνα (1-3 χιλιοστά). Το
σύστημα τροφοδοσίας μπορεί να χειριστεί αξιόπιστα όλα τα καύσιμα εντός των παραπάνω
προδιαγραφών.
Οι παράμετροι αεριοποίησης επηρεάζουν τη σύσταση αερίου με τον ίδιο τρόπο για όλα τα
καύσιμα. Η επιλογή του καυσίμου για αεριοποίηση εν μέρει θα πρέπει να αποφασίζεται με
βάση τη θερμογόνο δύναμη. Η θερμογόνος δύναμη του παραγόμενου αερίου εξαρτάται
τουλάχιστον εν μέρει από την περιεκτικότητα της πρώτης ύλης σε υγρασία. Η τέφρα
μπορεί να προκαλέσει μια ποικιλία προβλημάτων. Για τους λόγους αυτούς, ακόμη και αν το
ροδάκινο παράγει αέριο με υψηλότερη θερμογόνο σε σύγκριση με την ελιά και το
σταφύλι, δεν είναι αποδοτικό στην αεριοποίηση λόγω υψηλής υγρασίας και
περιεκτικότητας σε τέφρα. Αν οι πυρήνες ροδάκινου είχαν επεξεργαστεί σωστά, τότε η
περιεκτικότητα σε τέφρα θα είναι ελάχιστη, αλλά η θερμιδική αξία του αερίου θα
παραμείνει η ίδια καθώς τα στερεά και η υγρασία αφαιρούνται από το αέριο πριν από τη
αξιοποίηση.
Κατά τη διάρκεια της επίδειξης, η μέγιστη συνεισφορά της παραγωγής αερίου στο μίγμα
καυσίμου του κινητήρα που είχε καταγραφεί για τα τρία είδη βιομάζας ήταν 80% κατά
μάζα. Το υπόλοιπο 20% αποτελείται από προπάνιο. Το αέριο που προέρχεται από
σταφύλια παράγει λιγότερη ισχύ σε σύγκριση με το αέριο που προέρχεται από ροδάκινο
και ελαιοπυρήνα. Μεταξύ αυτών των δύο, ο ελαιοπυρήνας, παράγει ελαφρώς καλύτερη
ποιότητα του αερίου. Η καθαρή ηλ. απόδοση της μονάδας είναι χαμηλή (6%). Είναι όμως
ένα καλό σημείο εκκίνησης για την περαιτέρω βελτιστοποίηση και κλιμάκωση.
D3 Demonstration operation report
2 Introduction
LIFE08 ENV/GR/576
SMARt-CHP
“Demonstration of a Small scale Mobile Agricultural Residue gasification
unit for decentralized Combined Heat and Power production”
Project location
Greece (Thessaloniki - Ptolemaida - Amyntaion)
Project start date:
01/01/2010
Project end date:
31/12/2012
Total Project duration (in months)
36 months
Total budget
919,557 €
EC contribution:
450,143 €
(%) of total costs
48.95
(%) of eligible costs
50
1
2
Participant name
Region
Main responsibility in the project
Laboratory of Applied
Central
Coordinator, Scientific Team
Thermodynamics
Macedonia,
(LAT)
Greece
Laboratory of Chemical
Central
Scientific Team, dissemination campaigns
Process
Macedonia,
responsible
and
Plant
Design (LCPPD)
3
Municipal
Greece
District
Western
Explore the potential of SMARt-CHP, to
Heating Company of
Macedonia,
acquire knowledge and experience in
Ptolemaida (DHCP)
Greece
order to support other similar projects on
bio-energy, in order to promote and
disseminate its usage in the wider context
of renewable energy utilisation.
4
Union of Agricultural
Western
Expand the possibilities of utilization of the
Coop.
Macedonia,
agricultural
Greece
Explore additional possibilities for bio-
(UACA)
of
Amyntaion
business
/
products of its members.
entrepreneurship
at
their
locality.
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LIFE08 ENV GR 576 SMARt-CHP
8
2.1 Project objectives
The SMARt-CHP project concerns the manufacturing, demonstration and dissemination of
an innovative 12 kWthermal and 5 kWelectrical small scale mobile gasification unit coupled with
an ICE for energetic exploitation of agricultural residues in rural areas of Greece, where
large amounts of biomass wastes are available; it aims at offering a practical solution to
the problem of biomass logistics, such as biomass residue transportation over long
distances, protection from weather variations, storage and general handling. The work
was structured along the following six (6) actions.
A1: Regional biomass availability profile
A2: SMARt-CHP unit development
A3: Demonstration operation
A4: Demonstration results and sustainability analysis / best practice guidelines
A5: Dissemination of project results
A6: Management and coordination
2.2 Definition of technical terms
Biogas:
A gas produced by the anaerobic digestion or fermentation of
biodegradable materials such as manure, sewage, municipal waste,
green waste, plant material, and crops. Biogas comprises primarily
methane (CH4) and carbon dioxide (CO2) and may have small
amounts of hydrogen sulphide (H2S), moisture and siloxanes.
Bulk density:
Property of powders. It is defined as the mass of many particles of
the material divided by the total volume they occupy
Char:
The solid material that remains after light gases and tar have been
driven out or released from a carbonaceous material during the
initial stage of combustion
Cyclone:
a filter that applies the method of removing particulates from a gas
stream through vortex separation
Equivalence ratio: The mass ratio of air to biomass present in the reactor (gasifier)
Fly ash:
One of the residues generated in combustion or gasification, and
comprises the fine particles that rise with the flue gases.
D3 Demonstration operation report
Fuel cell:
A device that converts the chemical energy from a fuel into
electricity through a chemical reaction with oxygen or another
oxidizing agent.
Gas flaring:
Gas combusting device that is used for burning flammable gases
released by pressure-relief valves
Gas turbine :
A type of internal combustion engine. It has an upstream rotating
compressor coupled to a downstream turbine, and a combustion
chamber in-between.
Heat exchanger:
Equipment built for efficient heat transfer from one medium to
another
Heating/Calorific value: The amount of heat released during the combustion of a
specified amount of a substance
Inverter:
An electrical power converter that changes direct current (DC) to
alternating current (AC). The converted AC can be at any required
voltage and frequency
Lambda sensor:
An electronic device that measures the proportion of oxygen (O2) in
the exhaust gas
Organic Rankine Cycle: The Rankine cycle is an idealised thermodynamic cycle of a
heat engine that converts heat into mechanical work. The heat is
supplied externally to a closed loop, which usually uses water as
the working fluid. The Organic Rankine Cycle uses an organic, high
molecular mass fluid with a liquid-vapor phase change, or boiling
point, occurring at a lower temperature than the water-steam
phase change as a working fluid.
Producer gas:
The fuel gas that is generated during the gasification of biomass
within the oxygen-limited environment of a reactor. It mainly
consists of H2, CO, CO2, CH4 and N2 (when air is the oxidant)
Proximate analysis:A technique that separates and identifies categories of compounds
in a mixture; reported are moisture, ash, volatiles and carbon
content.
Pyrolysis:
The thermochemical decomposition of organic material at elevated
temperatures without the participation of oxygen.
Rotary valve:
A type of valve in which the rotation of a passage or passages in a
transverse plug regulates the flow of liquid or gas through the
attached pipes.
Screw feeder:
A mechanism that uses a rotating helical screw blade within a tube,
to move granular materials.
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LIFE08 ENV GR 576 SMARt-CHP
Silo:
A structure (vessel) for storing granular materials like biomass
residues
Spark timing:
The process of setting the angle relative to piston position and
velocity that a spark will occur in the combustion chamber of an
engine.
Steam turbine:
A device that extracts thermal energy from pressurized steam and
uses it to do mechanical work on a rotating output shaft.
Stirling engine:
A heat engine operating by cyclic compression and expansion of air
or other gas, the working fluid, at different temperature levels such
that there is a net conversion of heat energy to mechanical work.
Stoichiometric ratio:The optimum ratio where all the oxidant is consumed, there is no
deficiency of the oxidant and there is no excess of the oxidant
Stoichiometry:
A branch of chemistry that deals with the relative quantities of
reactants and products in chemical reactions
Throttle:
The mechanism through which the power or speed of an engine is
regulated
Turbocharger:
A forced induction device used to allow more power to be produced
for an engine of a given size. A turbocharged engine can be more
powerful and efficient than a naturally aspirated engine because the
turbine forces more air, and proportionately more fuel, into the
combustion chamber than atmospheric pressure alone.
Ultimate analysis: The determination of carbon, hydrogen, nitrogen and oxygen (by
difference) in a material
D3 Demonstration operation report
2.3 Overview of Action 4 - Demonstration results
sustainability analysis / Best practice guidelines
and
Action 4 (A4) concerns the detailed analysis of the demonstration operation data taking
into account technical, administrative and sustainability aspects. In addition, operational
guidelines and training material that has also been developed throughout the project is
presented. Action 4 consists of three tasks. Task 4.1 concerns the evaluation of the
system’s performance, highlighting technical and administration obstacles for the
successful implementation of SMARt-CHP units. Moreover, a sustainability analysis has
been conducted in Task 4.2, taking into account environmental and socioeconomic issues.
Finally, Task 4.3 focuses on setting guidelines for training and support of potential users
and interested stakeholders, toward understanding the potential of bioenergy utilization,
impelling them in creating and sustaining similar activities and businesses.
Task 4.1 Demonstration results analysis
Operational performance concerning both energy and environmental measures is the
main objective of Task 4.1. Based on data gathered during the demonstrative operations,
the analysis focuses on biomass handling and feeding system reliability, gasification
process performance, producer gas utilization efficiency, heat & electricity production and
overall system reliability and investment feasibility.
Biomass handling and feeding system reliability is evaluated on the basis of continuous
operation and response in manipulated variations of power output requirements. Special
attention is also placed upon the utilization of different biomass residues.
Gasification performance is also an aspect of great importance. Producer gas composition
was monitored and analyzed so that the impact of process variables on gasification
performance (producer gas heating value) can be evaluated.
The system’s dependency (in terms of efficiency and stability) on biomass feedstock and
process parameters has finally been analysed. The SMARt-CHP system is assessed not
only in terms of efficient production but also in terms of overall system suitability for
standardized production, replication, and eventually certification.
Task 4.2 Sustainability analysis
The sustainability aspects of the SMARt-CHP unit are also addressed involving economic,
environmental and social issues. The sustainability analysis is divided into two sub-tasks.
The first sub-task takes into account environmental and social aspects while the second
sub-task addresses financial issues.
SMARt-CHP as a bioenergy utilization system has the potential to contribute to
greenhouse gas emissions reduction and CO2 mitigation. Total CO2 emissions saving
during the demonstration operation is estimated. In addition, a projection is conducted for
long-term operation of SMARt-CHP units on a commercial scale. The indirect targets of
biomass routes ecological impact reduction, increase of the share of biogenous fuels
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LIFE08 ENV GR 576 SMARt-CHP
12
within the energy market, fossil fuel consumption and greenhouse emission reduction are
also evaluated.
As far as social aspects are concerned, bio-energy also offers significant opportunities to
improve regional development, especially in rural areas. The variability of raw materials
and people responsiveness to the adaptation of various process stages is commented.
Special focus is also placed on analyzing possibilities to support agricultural and forestry
sector by providing solutions for additional income to farmers and forest managers.
The sustainability analysis also assesses the financial capacity, both as infrastructure
investment as well as maintenance costs of the regions concerned. The project envisages
the production of cost-effective renewable energy for rural areas and villages, for regional
or national energy supply and infrastructure, for SMEs and production plants. An
economic analysis is conducted using demonstration results as input. The specific
economic analysis is compared to the preliminary economic analysis which was presented
in the project proposal and the main inconsistencies are commented.
Task 4.3 Best practice guidelines
Task 4.3 results in a best practice, guiding and support outcome. Throughout the
guidelines for training and support, partnerships amongst all relevant stakeholders were
promoted and encouraged. Transfer of know–how was thoroughly conducted between
stakeholders and target groups at local, regional and even at a broader EU level.
Promotion and training activities comprise an essential part of the project. Through these
activities regulatory institutions, industry and service companies, SMEs, and local
representatives are able to actively participate and introduce ideas on the promotion of
energy systems based on indigenous agricultural residues resources, and acquaintance of
local community with novel techniques and sustainability concepts.
The role of the local community education and the development of new employment
opportunities within the sector of environmental technology should be a major target.
Moreover the introduction of the local communities, especially in remote rural areas in the
concept of sustainable development will enable to upgrade the current agricultural, trade
and manufacturing practices, having as an ultimate benefit the sustainable use of raw
materials and the utilization of sound environmental practices.
The operational guidelines have been synthesized into training material and a series of
training missions and workshops aspired to achieve penetration of the concept within the
target groups.
D3 Demonstration operation report
3 SMARt-CHP unit
3.1 Unit description and operational procedure
The SMARt-CHP unit has been extensively described in a previous report (D3: SMARt-CHP
demonstration operation). The layout of the unit is presented in Figure 1.
Figure 1: SMARt-CHP unit layout: 1) Data acquisition, 2) Secondary biomass silo, 3) Primary
biomass silo, 4) Screw feeder 1, 5) Rotary valve, 6) Screw feeder 2, 7) El. Oven, 8) Reactor tube,
9) Cyclone filter, 10) Fly ash collector, 11) Gas by-pass to flaring, 12) Valve, 13) Particle trap, 14)
Tar removal vessel 1, 15) Tar removal vessel 2, 16) Tar removal vessel 3, 17) ICE-generator, 18)
ICE exhaust
Biomass is originally stored in the two silos (2 & 3) above the screw feeder 1 (4) which is
the feeder used to modulate the fuel flow into the reactor. The fuel passes through the
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LIFE08 ENV GR 576 SMARt-CHP
rotary valve (5) and the screw feeder 2 (6) before entering the gasification reactor (8) at
the height of the fluidized bed. Olivine is used as bed material. Compressed air flows
through a perforated plate at the bottom of the reactor to ensure fluidization. An electric
oven (7) assists operation start-up.
The produced gas exits the reactor at the top. It passes through a cyclone filter (9) for
particle removal. This residual is collected (10) in vessels. At this point, the producer gas
contains gas phase tars and fine particles. Depending on operation mode, there are two
available routes for the gas. The first route is called the “by-pass” route (11). It is used
during operation start-up and system maintenance. There is no power generation during
this time period. The gas flows to a flaring apparatus outside of the unit where the gas is
burned in order to minimize environmental pollution.
The second route is the electricity production. The gas flows through a heated ceramic
blockage filter (13). Almost 99% of the gas particle load is removed at this stage. After
the filter, the gas flows through a water scrubbing unit consisting of three condensation
stages where the tar content is minimized. The first stage (14) is a water tank where the
gas comes in direct contact with the water in the vessel. After the gas is “washed”, it exits
the vessel from the top. The second stage (15) is a water scrubbing tower. Gas enters the
tower from the bottom. The tower is packed with metal parts which are sprayed with
water from a nozzle at the top of the tower. The gas follows an upward route and exits
the tower at the top as well. The third stage (16) is a heat exchanger. It consists of
copper tubing that is immersed in a water tank. Gas flows through the tubing. The water
in the tank absorbs the excess heat (above room temperature) from the gas to ensure
low gas temperature before the ICE (17).
After gas cleaning, there are also two different routes for the cleaned gas. The first one
leads to the flaring set-up outside the unit and it is used for the excess gas that is
produced and is not introduced into the ICE. The second gas line drives to the ICE. Two
additional high efficiency filters are used at this point to ensure that clean gas flows into
the engine cylinder.
The engine originally runs on propane but it has been redesigned and converted to run
either on propane or on propane-produced gas mixtures. The gas is introduced to the
engine system at the air intake before the propane-air mixing valve. The new “fuel-air”
mixture contains propane and premixed air-gas. The engine is coupled to a generator.
Part of the produced electricity is consumed for the unit’s needs. The remaining power is
supplied to the consumer’s grid. Apart from electric power, hot water is also a product of
the unit. The consumer receives heat from the unit through a plate heat exchanger. This
heat is transferred from the coolant that flows through the engine jacket, the generator
jacket and an exhaust gas heat exchanger.
D3 Demonstration operation report
3.2 Demonstration operation summary
The unit was demonstrated in four different locations in rural areas of Western
Macedonia, two in Ptolemaida and two in Amyntaion. The unit demonstrative operation
lasted two weeks in each location while peach, olive and grape kernels were the
feedstocks used during the unit operation.
During the demonstrations, the unit was improved to meet the operation target hours.
The achieved improvement was remarkable as the unit operated for 50 h in the first
demonstration, 64 h in the second, 140 h in the third and 207 h in the fourth one. It is
clear that depending on the applied circumstances (personnel availability, fuel quality,
proper location), the goal of 24-h operation on a minimum basis of 10 days is an
achievable target. Although the initial goal was 240 hours unit operation in each location,
this was not achieved due to technical and organization issues.
The demonstrative operations were a favorable opportunity to test the unit in real
conditions for long periods. Most raised issues concerned technical details, mostly repairs
and constructions towards system improvement.
Biomass properties were a critical parameter regarding long term operation. Pretreatment
of the fuel before feeding was necessary in order to achieve long and stable operations.
In addition special attention has to be given to gasification parameters like temperature
and air-to-fuel ratio that significantly affect producer gas quality. Finally, the producer gas
is co-combusted in an ICE with propane. A wide range of mixtures was supplied to the
engine (10 – 90% w/w producer gas) to test its responsiveness and stability under
different fuel mixtures.
In the following pages, the data derived during the demonstration operation is analysed
and presented. The unit is also evaluated regarding energy efficiency, sustainability and
economic feasibility. The aforementioned analysis acts as a reference point for agroresidue utilization promotion in the rural areas of Greece and the Mediterranean region.
A detailed description of the demonstrative operations can be found in deliverable “D3:
Demonstration operation report” available online at the project website.
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LIFE08 ENV GR 576 SMARt-CHP
16
4 Demonstration operation results
4.1 Biomass type evaluation
One of the project’s aims is to test the mobile gasification unit on a variety of biomass
feedstocks in order to determine the unit’s versatility and stability under a range of inputs.
Three different biomass fuels were utilised during the demonstration operation in the rural
areas of W. Macedonia, olive kernels, peach kernels and grape kernels. The selected three
residues have similar characteristics and qualified against other “competitors” due to the
reasons presented in Table 1. The selected residues are also compared with the “ideal”
fuel for similar applications that is most often used due to its properties, pre-treated wood
chips.
Table 1: Comparative analysis of the three biomass fuel compared to wood
Olive
Peach
Grape
Wood
Availability
++
++
+++
-
Accessibility
+
++
+++
-
Pre-treatment
+++
-
+
+++
+++
+++
++
++
Size range
+++
+
+++
+++
Calorific value
+++
+++
++
++
Moisture content
++
++
++
++
Ash content
++
+++
-
+++
Ash composition
++
++
-
+++
requirement
Fluidization
behaviour
4.1.1 Biomass species characteristics
The first five listed characteristics in Table 1 regard practical and rheological issues while
the last four concern the chemical nature of the biomass residues. Grape kernels were the
most abundant and easily accessible of the candidate residues. This feedstock is a direct
D3 Demonstration operation report
by-product of wine production. The third and fourth demonstration operations took place
in Amyntaion with the collaboration of UACA. One of the main activities of UACA is wine
production while the UACA Winery is one of the largest in W. Macedonia. As a result,
grape kernels were an ideal candidate, regarding logistics, for utilization during the third
operation at the UACA Winery and the fourth in UACA headquarters just 1 km away from
the Winery. The olive kernels are a direct by-product of the olive-oil production line. They
are already crushed and washed so no pretreatment is necessary prior to utilisation.
Thirdly, peach kernels present excellent chemical characteristics and are also abundant in
the region of W. Macedonia even though pretreatment is necessary (crushing and sieving)
in order to avoid feeding issues.
More specifically, olive kernels were obtained from olive treatment plants. Its average size
is 2.5 mm while almost 70% of the size ranges between 1 and 3 mm. Its size along with
its bulk density (~600 kg/m3) characterize the fuel suitable for the fluidization conditions
that are present in the reactor during operation. The olive kernels have a comparatively
high heating value mainly due to oil still present in the kernels even after treatment by
the olive-oil production plant. On the other side, these oils increase the tar content of the
producer gas.
The most favorable characteristics of grape kernels are availability and accessibility as
mentioned previously. The kernels are naturally dried for 48 hours and then after a single
sieving step they are ready for feeding in the unit. Its size range after the sieving is quite
limited and the average fuel size is similar to olive kernels (2-3 mm). On the other hand,
grape kernels present high ash content.
Finally, peach kernels possess excellent physical and characteristics (very low ash content,
high heating value and high density). However, 3 stages of pretreatment were necessary
in order to utilize peach kernels. Initially, the peach kernels are obtained from peach
compote factories. They are whole, so a crushing stage is performed. The crushed kernels
are then dried and sieved before they are ready for feeding in the unit.
The proximate and ultimate analysis of the three selected biomass feedstocks, their
heating value as well as their ash analysis are given in Table 2 and Table 3. In these
tables, the peach kernels characteristics concern manually cleaned fuel samples. The bulk
fuel is contaminated with dirt and stone dust due to the fact that the kernels were
crushed in a stone crushing facility outside Ptolemaida. The bulk and manually selected
samples are compared in Table 4. The comparison of the two samples shows that the ash
and moisture content in the bulk fuel is multiple times larger from the ash content in
Table 2. This ash is not possible to remove as it is in the same size range as the fuel
itself. This results in lower heating value in the fuel and unfavorable fluidization
parameters due to the high stone residue content in the fuel.
More information on how the fuel was pretreated is available in the deliverable “D3:
Demonstration operation report” available online at the project website.
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LIFE08 ENV GR 576 SMARt-CHP
18
Table 2: Chemical composition of the three biomass fuels
Olive
Peach
Proximate analysis %wt (dry basis)
Moisture
12.30
8.99
Ash
3.63
0.47
Volatiles
79.90
73.59
Fixed carbon
16.47
25.94
HHV [MJ/kg]
20.46
21.88
Ultimate analysis %wt (dry basis)
C
48.59
51.95
H
5.73
5.76
N
1.57
0.80
S
n.d.
0.01
Cl
n.d.
0.53
O
40.48
40.48
Grape
9.13
10.31
65.67
24.02
21.21
52.88
5.42
4.46
n.d.
0.02
26.93
*n.d. = not detected
Table 3: Ash chemical composition of the three biomass fuels (% ash basis)
SiO2
Al2O3
Fe2O3
CaO
MgO
K2O
Na2O
SO3
P 2 O5
Cl
Olive
6.50
0.85
1.06
11.70
3.50
35.10
2.42
1.15
5.85
n.d.
Peach
6.20
0.83
0.87
12.40
6.50
31.20
1.28
1.31
10.65
1.13
Grape
21.50
2.08
2.07
17.10
7.80
22.10
1.08
1.90
3.38
n.d.
*n.d. = not detected
The measurements mentioned above were conducted with the use of the following
equipment:



Proximate and ultimate analysis (Heraeus Thermo Scientific UT-6 air
circulation drying oven, TGA thermostep-ELTRA Gmbh, CHNS analyzerPerkin Elmer 2400 series)
Heating value (LECO AC-350bomb calorimeter)
Ash analysis (Inductively Coupled Plasma-Optical Emission Spectroscopy
(ICP-OES)-Model: Perkin Elmer Optima 5300DV and Inductively Coupled
Plasma-Mass Spectrometer (ICPMS)-Model: Perkin Elmer ELAN 6100)
D3 Demonstration operation report
Table 4: Proximate analysis and heating value of bulk peach and hand-selected samples
Moisture
Ash
Volatiles
Fixed carbon
HHV
[MJ/kg]*
* dry basis
Peach
Peach bulk
8.99
0.47
73.59
25.94
21.88
18.16
18.31
62.76
18.93
19.76
4.1.2 Fuel handling and feeding system reliability
The following two figures illustrate two significant conclusions. Firstly, the total operation
is almost equally distributed among the three biomass residues and secondly, with the
exception of the first demonstration, two different fuels are used per demonstration i.e. in
identical operation conditions. Therefore, all fuels are tested in the same depth and in
different operation conditions thus offering a reliable basis on which fuel dependency of
the operation can be analyzed.
Figure 2: Fuel consumption in kg and % of total
Figure 3: Fuel consumption per demonstration
consumption during the four demonstrations
Peach kernels
Peach kernel was initially chosen due to its intrinsic properties (high heating value, low
ash content) and its compatibility with the fludized bed. The raw material has an average
size of 30 mm so it has to be crushed into finer particles before utilization. For the first
demonstration, the raw material was transported to a local stone mill where it was
crushed. The crushed kernels’ size range varied between 0-5 mm and stone residuals in
the same size range from the milling process were also present. Even after screening of
the fuel to remove fine particles (<1 mm), stone residuals remained in the bulk fuel.
19
20
LIFE08 ENV GR 576 SMARt-CHP
Leaching of the fuel in order to remove stone residuals was not foreseen or possible
within the demonstration timeframe so the peach kernels were used as they were.
Figure 4: Visible stone residuals in the treated peach kernels
The poor quality of the treated fuel in conjunction with several technical issues of the unit
resulted in frequent clogging of the feeding system. The fuel sieving improved the
situation however clogging at the feeders still occurred. The high fuel moisture content
(~18%) also contributed to this phenomenon. Clogging most frequently occurred near the
bottom screw feeder were reverse gas flow was more intense and temperature was
higher (~80°C).
Figure 5 compares the flow behavior between the treated peach kernels before and after
sieving to remove the finer particles (<1 mm). Removal of fines resulted in higher fuel
bulk density (~ 15% increase) and lower variation between sampling (i.e. more constant
flowrate). It is estimated that if the fuel was not contaminated with crushed stone
residuals, feeder clogging would be avoided or minimized similarly to operation on olive
and grape kernels.
D3 Demonstration operation report
Figure 5: Comparison of measured fuel flow before and after the sieving versus screw feeder
motor speed
Olive kernels
Olive kernel was initially chosen due to its intrinsic properties (high heating value, low ash
content), its compatibility with the fludized bed and the minimum pretreatment
requirement. The raw material is already crushed to an average size of 2.5 mm so no
further milling or sieving is necessary. The olive kernels were transported to the
demonstration site with the unit to minimize transportation costs and emissions. Olive
kernels have been extensively used during preliminary testing of the unit in Thessaloniki.
It has been validated as a fuel that offers the possibility for lengthy operations with
minimum stability issues. As a result, olive kernels were used as a “benchmark” fuel in
order to examine the effect of various technical and operational optimizations that were
applied to the unit during demonstration and also to locate whether stability issues
(feeder clogging, bed agglomerations) originate to the fuel quality or other sources.
Grape kernels
As it was mentioned previously, the grape kernels are a by-product of UACA winery. Large
quantities are available every year which are otherwise not utilized. Some pretreatment is
needed before the grape kernels are fed however. The grapes are naturally dried for 2-3
days. At the end of the drying session, the kernels moisture content is below 10%. During
21
LIFE08 ENV GR 576 SMARt-CHP
22
the drying process, agglomerates of kernels are formed. These agglomerates are fragile
and can be easily crushed, however agglomerate crushing was not applied for the
demonstration operation. A simple screening took place instead. As it is depicted in Figure
6, the screening improves the fuel flow characteristics due to the following reasons: the
bulk density of the fuel increases and the fuel flow is more constant due to the smaller
size range of the fuel.
Figure 6: Comparison of measured fuel flow before and after the sieving versus screw feeder
motor speed
Conclusions
Regarding feeding performance, all fuels were easily handled after a set of minimum
pretreatment activities. The results show that the fuel’s water content must be lower than
20 %, the ash content should be less than 10% to ensure long operations and finally the
D3 Demonstration operation report
size range of the fuel must be close to that of olive kernels (1-3 mm). The feeding system
can reliably handle all fuels within the aforementioned specifications.
As far as pretreatment is concerned the following outcomes are highlighted:




The majority of agricultural residues have relatively low moisture content thus
allowing easy and quick drying without the use of special equipment. Even grape
kernels which are a by-product of wine production can be dried naturally.
It is essential that any milling occurs in dedicated systems or in thoroughly
cleaned equipment in order to avoid contamination of the fuel with inorganic
matter or any other non-combusting materials.
Screw feeders are a reliable means of fuel input especially for fluidized beds. Sand
that escapes to the feeding system is impelled back in the reactor through the
motion of the feeder. Screw feeders are also capable of promoting any type of fuel
that is not extra fine or has the form of straws.
The feeding rate is strongly dependent on the fuel properties even of the same
type. More specifically moisture content, average grain size and size range are
some of the major factors affecting fuel flow. As a result, the feeding system
should be calibrated regularly for non-standardized fuels. The calibration interval
depends on the fuel properties variation and should not exceed 1000 hours of
operation.
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LIFE08 ENV GR 576 SMARt-CHP
24
4.2 Gasification performance
The fuel characteristics can significantly affect the stability of the gasification process and
the overall efficiency. Of the above mentioned features, fuel moisture and ash content as
well as heating value are responsible for the quality of the producer gas. Apart from fuel
quality though, gasification parameters are also main determinants of the producer gas
composition and biomass conversion rate. The parameters with the largest effect are
process temperature, equivalence ratio and time residence – gas velocity.
Gasification can be distinguished into three different processes: drying, pyrolysis and char
gasification. These processes occur in different temperature regions (drying 80 – 120°C,
pyrolysis 150 – 400°C, char gasification 400 – 900°C) however due to the homogeneity of
the reactor technology, they occur almost simultaneously in bubbling fluidized beds.
Drying starts while the fuel is still in the bottom feeder. Once the fuel enters the reactor,
all three processes take place. The remaining water content is evaporated, the volatiles
are released, part of which is oxidized by the fluidizing medium, and the remaining char is
oxidized and gasified until it’s mass is low enough to be entrained from the reactor top.
The most important reactions that take place in the bubbling fluidized bed are the
following:
Drying
Pyrolysis
Volatile reactions
→
()
biomass →
+
+
+
+
2CO +
→ 2
2
→ 2
+
+ 2
→
+
+
+
+
+
→
+
+ ℎ
+ 2
→
tars →
Char reactions
( )
+
+
→
+
+
→2
+ 2
→
The resulting gas composition depends on the rate of the described chemical reactions
which is in turn affected by diffusion mechanisms, temperature and stoichiometry. The
first factor requires advanced laboratory measurements and calculations. Thus it is only
qualitatively described concerning two basic approaches, gas residence time and
fluidization quality. Furthermore, char and tar reduction reactions accelerate at higher
temperatures while the presence of air (which is adjusted by stoichiometry) favours
D3 Demonstration operation report
oxidation reactions. Stoichiometry is described by the term “Equivalence Ratio” or “ER”. It
is defined as the ratio of the air mass flow in the reactor to the air mass flow required for
complete combustion of the fuel.
The producer gas composition was measured online during the demonstration operation.
A portable gas chromatographer was used to complete the measurements. During gas
sampling several parameters were also recorded in order to facilitate the analysis of the
results (temperature, fuel flow, air flow) while the sampling point was located upstream
the ICE and downstream all the cleaning devices. The gas composition results are
analysed per fuel and in comparison. Samples were received at three different reactor
temperatures (700, 750 and 800°C), three different air-fuel ratios (ER 25, 30, 40%) for
each one of the three fuels (olive, peach, grape kernels).
Olive kernels
Figure 7: Gas composition and higher heating
Figure 8: Gas composition and higher heating
value versus reactor temperature–olive kernels
value versus stoichiometry–olive kernels
Figure 7 describes gas composition and HHV at three different temperatures for an
Equivalence Ratio (ER) of 30%. The gas heating value increases along with temperature.
CH4 and CO2 are reduced and CO is increased as expected. H2 is reduced but this trend
can be justified through Figure 9. The gas residence time at 800°C is lower than the
residence time at lower temperatures. Thus the gasification reactions are not completed
to the same extent.
Figure 9: Olive kernel producer gas residence time
When ER increases, the CO2/CO ratio increases as well. This trend fits perfectly with the
results in Figure 8. In addition, when ER is above 30%, the combustible gases in the
25
LIFE08 ENV GR 576 SMARt-CHP
26
producer gas are much lower resulting in a significant decrease in HHV. It should be
noted that, in Figure 8 the reactor temperature is 750°C.
Peach kernels
Figure 10: Gas composition and higher heating
Figure 11: Gas composition and higher heating
value versus reactor temperature–peach kernels
value versus stoichiometry–peach kernels
The experimental CO, CH4 and H2 trends in Figure 10 concur with the corresponding
theoretical. Furthermore, the rapid CH4 reduction at 800°C affects the gas HHV as well
due to its own high calorific value (38.8 MJ/m3 versus 12.77 MJ/m3 of H2 and 12.05 MJ/m3
of CO). Regarding ER evolution, the CO2/CO ratio increases as is the case for olive
kernels. However this ratio is decreased between ER=20 and 30% due to the fact that the
gas residence time in 750°C is higher for ER=30% compared to ER=20%.
Figure 12: Peach kernel producer gas residence time
Grape kernels
The gas composition evolution with increasing reactor temperature in the case of grape
kernels is also in accordance with theoretical expectations (Figure 13). The gas HHV
increases slightly due to H2 and CO increase while the CH4 content is relatively low
(< 2%). H2, CO and CH4 on the other hand decrease when more air is induced in the
system per kg fuel (Figure 14). The CO2/CO ratio increases as was the case for the
previous two biomass residues.
D3 Demonstration operation report
Figure 13: Gas composition and higher heating
Figure 14: Gas composition and higher heating
value versus reactor temperature–grape kernels
value versus stoichiometry–grape kernels
The increase in H2 despite the increase in oxidizing medium can be also justified through
the gas residence time factor. In this case the (grape kernels, 750°C) the gas residence
time trend completely justifies the H2 increase.
Figure 15: Grape kernel producer gas residence time
Comparison
As it is described above, gasification parameters influence gas composition in the same
manner for all fuels. However, each fuel possesses different characteristics which are
listed in Table 5. The best characteristics in comparison are highlighted with a wholeyellow star while the worst are highlighted with an empty-white star.
Table 5: Biomass residue characteristics
LCV [MJ/kg]
Moisture [% w/w]
Volatiles [% w/w]
Ash [% w/w]
Ash components increasing
reactivity[K,Ca,Fe % w/w]
Av. size [mm]
Range [+- mm]
Olive
19.2
12.3
79.9
3.63
Peach
18.06
18.16
51.36
14.98
Grape
19.79
9.13
59.67
9.37
47.7
44.4
41
2.5
1.5
3.5
2.5
2.5
0.5
27
28
LIFE08 ENV GR 576 SMARt-CHP
The choice of a fuel for gasification will in part be decided by its heating value. The
heating value of the gas produced depends at least in part on the moisture content of the
feedstock. The amount of volatiles in the feedstock determines the necessity of special
measures (either in design of the gasifier or in the layout of the gas cleanup train) in
order to remove tars from the product gas in engine applications. Ashes can cause a
variety of problems. Slagging or clinker formation in the reactor can be caused by melting
and agglomeration of ashes. If no special measures are taken, slagging can lead to
excessive tar formation and/or complete blocking of the reactor. The reactivity is an
important factor determining the rate of reduction of carbon dioxide to carbon monoxide
in a gasifier. Another interesting point is the assumed positive effect on the rate of
gasification of a number of elements which act as catalysts. Small quantities of potassium,
sodium and zinc can have a large effect on the reactivity of the fuel. Excessively large
sizes of particles or pieces give rise to reduced reactivity of the fuel, resulting in start-up
problems and poor gas quality, and to transport problems through the equipment. A large
range in size distribution of the feedstock will generally aggravate the above phenomena.
For these reasons even though the peach derived gas has a higher measured heating
value compared to olive and grape gas ,it is not efficient to gasify due to its high moisture
and ash content. If the peach kernels were treated properly, then the ash content would
be minimum but the gas calorific value would remain the same as solids and moisture are
removed from the gas prior sampling.
One final outcome of the analysis in this report is that each fuel is most efficiently utilised
in different gasification parameters. Olive kernels yield best results at medium to high
temperature (750-800°C) and at low to medium ERs (20-30 %). The same conclusion
applies to grape kernels as well. However, peach kernel gasification produces best gas
quality at low-medium temperatures (<750°C) as the methane content dramatically
decreases at high temperature.
D3 Demonstration operation report
4.3 CHP performance analysis
One of the most interesting objectives of the project was the analysis concerning the
effects of gasification gas use as an input to the mini-CHP unit and the deduction of
conclusions concerning the suitability of such systems for small scale decentralized energy
production using agricultural residues. Through analysis of the demonstration results,
concerning the mini-CHP unit’s performance (propane and gas consumption, power
production, stability and efficiency for the three different biomass feedstock) an initial
evaluation of the system is aimed.
The system used on the project is the Ecopower Co-Generation Unit, a kind offer by the
company “Moumtzis & Sons” based in Thessaloniki, Greece. The unit utilizes a propane
based gas-combustion engine that drives the generator used for the generation of
electrical power. Simultaneously, the waste heat produced is used for heating and the
preparation of hot water. In the following tables the main characteristics of the mini-CHP
unit and its parts are presented.
Table 6: Ecopower Co-Generation Unit Specifications
Mini CHP
electrical power, modulating
thermal output, modulating
total input power
propane consumption
overall efficiency
exhaust gas after treatment
1.3 - 4.7 kW
4.0 - 12.5 kW
5.9 - 19.0 kW
3
3
0.59 m - 1.9 m /h
>90%
three-way catalytic converter
Gaseous-Fuel Engine
engine
speed range
coolant temperature
water-cooled single cylinder four stroke piston gas
combustion engine, designed for long running time, cubic
3
capacity 272 cm
1200 - 3400 R/min
operation: 75oC to 80oC
short-term: 90oC
maintenance rate
anticipated life of the engine
every 4000 h. or at least once a year
40,000 hrs. (dependent on operational and maintenance)
engine electronics
control of the desired gas-air ratio (λ = 1 - control) and
monitoring the engine operation, realised by a
microprocessor
Generator and Inverter
generator
inverter
brushless permanent magnet generator directly flanged on
the engine, with water cooling system
three-phase inverter with integrated safety monitoring,
microprocessor control
Electical data
voltage / frequency / power
factor
3 x 400V/230V / 50 Hz / cosφ = 0.98 - 1.00
Gas supply
minimal gas pressure
17 mbar
Heating system
heating return temperature
min 35oC, max 60oC
heating supply temperature max
75 C
o
29
30
LIFE08 ENV GR 576 SMARt-CHP
The unit is controlled by its custom software “Ecoserv”. The software gives access to
several adjustments necessary for the correct operation of the unit, such as the
stoichiometric combustion regulation and operation errors check and reset. In addition,
via this software, the user controls the operation point of the unit, by specifying the
engine’s speed (RPM), and also has visual inspection of the overall operation parameters
and performance (power produced, temperatures, lambda sensor values, propane-air
mixer values, etc.).
For the scopes of the project, the engine should be modified in order to operate on
producer gas. Having no access to the system’s controls, it was not possible to regulate it
in order to manipulate crucial parameters like propane flow and spark timing. Thus,
propane would remain the main fuel of the engine and its consumption had to be
minimized indirectly. The idea on how to manually replace propane with producer gas in
the engine is as follows: The ICE is programmed to operate on a stoichiometric air-fuel
ratio as any Otto engine. By injecting extra fuel (producer gas) to the ICE, the air fuel
ratio changes from stoichiometric to rich. In order to achieve again the stoichiometric
ratio, the engine must reduce the primary fuel intake (propane). Hence the mass flow of
producer gas to the engine is gradually increased, while the propane flow is in parallel
reduced. However, some propane must always flow to the engine cylinder through the
fuel line, since the unit software monitors the pressure at the fuel line constantly. As a
result, a propane tank is connected to the fuel line to secure constant pressure. By
utilizing the engine’s lambda sensor, propane intake is minimized while the pressure at
the fuel line remains high enough not to cause a software warning or error. The bottom
limit of the propane uptake is determined by the calorific value of the producer gas
introduced to the engine. The higher the producer gas calorific value, the lower the
propane consumption.
Figure 16: Propane Consumption Reduction – 3000rpm
D3 Demonstration operation report
In Figure 16, the reduction of propane consumption is presented as the gas flow inside
the engine is increasing. The difference between the three data sets, representing the
gases produced by the three different biomass feedstock, is mainly due to the different
composition of each gas and their calorific values, depending on the composition of the
feedstock and the gasification process parameters. In the results section of this chapter,
those results will be further explained.
Methodology Applied
In each operation, all data concerning the engine’s operation were recorded either
manually (propane and gas consumption), using the protocol presented on Table 7, or
automatically (electrical power produced, thermal power produced, gas mixer and throttle
values, engine temperature, exhaust gas temperature, lambda sensor values, etc.) via a
home-grown software which produces a data table as the one in Table 8. These data
were recorded continuously at regular intervals (10 to 20 minutes), and were organized
depending on the biomass feedstock and gasification parameters (temperature, ER). The
collected data are analysed and presented in the following section.
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LIFE08 ENV GR 576 SMARt-CHP
32
Table 7: Manually Measured Data Protocol
Biomass
Feedstock
Gas Input
(l/min)
Initial
Final
Measurement
Propane
Measurement
Propane
Starting Time Consumption Ending Time Consumption
(hh:mm:ss)
Meter Value
(hh:mm:ss)
Meter Value
(liters)
(liters)
Engine
Speed
(rpm)
Comments
Gas
Temperature
(oC)
Propane
Temperature
(oC)
Environment
Temperature
(oC)
Engine Speed
(rpm)
Exh. Gas
Temperature
(oC)
Throttle (-)
Gas mixer (-)
Lambda
Control (mV)
Lambda Engine
(mV)
Lambda Target
(mV)
Coolant
Temperature
(oC)
Th. Power
(kW)
El. Power (kW)
Measurement
Time (s)
Actual Time
(hh:mm:ss)
Table 8: Automatically Measured Data
D3 Demonstration operation report
4.3.1 Results
During the demonstration operations, gasification parameters were usually constant
regarding ER (30%). Gasification temperatures varied between 700-850°C and three
different fuels were utilized (olive/peach/grape kernels). In addition, the engine operated
in the range from 2,200 rpm to the maximum engine speed of 3,400 rpm, as in lower
speeds the engine’s operation was not stable enough when high flow of producer gas was
introduced.
Efficiency
The co-generation unit is designed to operate on a maximum efficiency, of around 75%
when propane is introduced as a fuel, at all operation points – engine speed and gas
mass fraction. This efficiency is calculated from the following relation:
−
=
+ ℎ
Electrical and thermal energy output are directly calculated by the automatically recorded
data. For the total energy input calculation, when produced gas is introduced to the
engine, along with its consumption that is manually recorded, the calculation of its
calorific value is necessary. This is derived by the gas composition analysis for the three
biomass residues and for the different gasifier operation points – reactor temperature and
air-to-fuel ratio. The total energy input is the sum of the produced gas energy input and
the propane energy input.
In Table 9, the results of the calculations of the air-to-fuel ratios for stoichiometric
combustion and the heating values for each produced gas, based on the gas composition
analysis, are presented. From the differences on those two values between the different
fuels and knowing that the volumetric efficiency of the engine is constant, which is
derived as the ratio of the actual quantity of fuel and air introduced into the engine to the
maximum capacity of the cylinder under static conditions, the differences on Figure 16
can be explained.
Table 9: Air-to-Fuel Mass Based Stoichiometric Ratio & Higher Heating Value
Propane
Olive Kernels
Peach Kernels
Grape Kernels
Air-to-Fuel Stoichiometric Ratio [-]
Higher Heating Value [kJ/kg]
15.58
1.47
1.85
1.21
50,343.32
5,697.47
5,862.89
4,787.05
Furthermore, it has to be noted that because of the greater heating value of propane
compared to producer gas (Table 9), the introduced propane, even if much lower, still
represents the higher fraction of the energy input, as presented in Figure 17.
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LIFE08 ENV GR 576 SMARt-CHP
Figure 17: Gas Energy Input Fraction
Having all data necessary for the calculation of the efficiency, as derived by the previous
definition, the results are presented in Figure 18.
Figure 18: Total Efficiency of the Mini CHP Unit
D3 Demonstration operation report
It should be noted that for each operation point and for each feedstock, more than one
point are presented, referring to different produced gas flows inside the engine.
It can be concluded that the introduction of producer gas slightly affects the efficiency, as
derived from the slight variation and the overall reduction, as compared to propane.
These differences are explained mainly by the experimental errors that occurred during
the measurements and the instable operation of the engine, which is designed to operate
steadily for long duration. It is accepted that the average power produced/energy output
has no major errors since it was recorded automatically by the Mini CHP unit’s software.
Though, as far as it concerns the energy input, both propane and producer gas flows
certainly contain errors since they were manually recorded. Especially the producer gas
flow, since it was not stable due to the pressure changes of the upstream system (gasifier
and treatment), had to be frequently adjusted and thus only higher averages of the flow
were recorded in order to account the worst case scenarios for the efficiency. Finally, the
difference between the measured efficiency of the Mini CHP unit compared to the
manufacturer specifications (>90%), is mainly due to the three following points that
certainly deteriorate its condition:



The “mileage” of the Mini CHP system
The not continuous operation – the system is designed to work continuously for
maximum efficiency, thus, frequent stops and restarts of the engine, and highly
frequent change of operation points, certainly affected its operation, decreasing its
overall efficiency
The modifications made to the engine, before its use, for the reset of its
operation.
Overall, the engine’s operation on producer gas, after visual inspection of the engine’s
parts after the demos, did not seem to affect its condition and its life expectancy. This is
certainly due to the high efficiency of the custom made filters before the engine, but also
due to the propane in the fuel mixture, which certainly ameliorated the combustion
conditions. Furthermore, operating the engine only in propane, in high frequency periods,
might as well positively affected the engine’s condition, facilitating the combustion of any
particles or tars remaining inside the engine.
Heat and Power production
The total electric and thermal power produced, for 80% gas mass fraction in the fuel
inserted, which constitutes the maximum gas flow for a stable operation, and for the
three biomass feedstock, is presented in Figure 19 and Figure 20 accordingly.
It is easily deducted that the power produced by the system for the three different
biomass feedstock does not differ a lot. This is firstly because of the fact that, as
mentioned earlier, even in high gas flows, propane still represents an important fraction
of the introduced energy and thus highly affects the energy output (normalizing the
output and making the visual inspection of any existing differences hardly feasible), and
secondly because the three different biomass feedstock gasses slightly differ on their
heating values and on their air-to-fuel ratios.
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LIFE08 ENV GR 576 SMARt-CHP
As expected, produced gases from olive and peach kernels generally produce higher
energy outputs, compared to the one from grape kernels, because of their higher calorific
value. In addition, as it is justified in Figure 22, their higher air-to-fuel ratios mean that
less propane is introduced to the engine thus highlighting olive and peach kernels as more
“attractive” residues compared to grape kernels.
Figure 19: Electric Power Produced at 80% w/w producer gas
Figure 20: Thermal Power Produced at 80% w/w producer gas
It has to be noted that the two graphs above have exactly the same form. This is due to
the fact that the thermal power produced by the Mini CHP system is not measured by any
means (temperature and flow of hot water), but is reported and recorded by the system
as a stable multiple of the electric power produced, which is set by the manufacturer and
is probably based to statistic quality measurements referring to the Mini CHP operation.
In addition to the above and for the scopes of the project, it is interesting to study the
reduction of the produced power – mainly the reduction of the electric power produced,
D3 Demonstration operation report
due to the introduction of the producer gas. This reduction is presented in Figure 21,
where the reduction of the electric power produced, as compared with the one produced
when only propane is introduced as a fuel, for the different biomass feedstock and RPM of
the engine is presented for the maximum stable introduced gas mass fraction. Figure 22
shows the reduction of propane consumption for the same operation points.
Figure 21: Reduction of the Electric Power
Figure 22: : Reduction of the Propane
Produced as compared to the propane, for 80%
Consumption as compared to sole propane as
Gas Mass Fraction and the three biomass
fuel, for 80% Gas Mass Fraction and the three
feedstock
biomass feedstock
As expected, the power produced by the system is reduced as compared to the propane.
This reduction is around 30%, while the reduction on the consumption of propane, as
presented in Figure 22, is around 45%.
Finally, in Figure 23, Figure 24 and Figure 25 operation maps giving the electric power
produced as a function of engine speed and gas mass fraction are given for the three
biomass feedstock.
Figure 23: Operation map (olive kernels)
Figure 24: Operation map (peach kernels)
Those graphs allow a quick inspection of the power produced for different operational
parameters. As expected, the power goes from lower values, on low speeds and high gas
mass fractions, to higher values, as the engine speed is increased or the gas mass
fraction is decreased.
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LIFE08 ENV GR 576 SMARt-CHP
Figure 25: Operation map (grape kernels)
D3 Demonstration operation report
4.4 SMARt-CHP system evaluation
In the previous sections each component of the SMARt-CHP unit was analysed
individually. Having studied in detail the sequential steps of the whole process and the
different parts, the unit is evaluated as a whole concerning energy and mass balance
efficiency, but also other aspects of its operation, in order to generate an overall
evaluation of the system.
In summary, the overall performance of the SMARt-CHP system is evaluated as
satisfactory and not far from target. Even if several operational and technical problems
did not allow the complete fulfillment of the project’s targets, mainly regarding operation
duration, the improvements made to the unit and the experience developed by the team
led to an impressive progress throughout the demonstrations.
4.4.1 Operation stability
In “D3: Demonstration Operation Report”, the operation of the unit during the
demonstrations is described in detail. In, total, the unit operated for 461 hours, following
a remarkable progress curve in its operation duration during the four demonstration
operations: 50 h in the first demonstration, 64 h in the second, 140 h in the third and 207
h in the last (Figure 26 and Figure 27). This progress is mainly due to both technical and
operational ameliorations, based on the experience developed in each demonstration and
the immediate application of any lesson learned. Even though, non-technical factors, such
as personnel availability, fuel quality and proper location that were difficulty managed “on
the field” led to the non-achievement of the 240 hours continuous operation target.
As shown in Figure 2 and Figure 3, the three biomass residues were tested equally during
the demonstrations, in order to collect the necessary data and evaluate them as fuels in
similar applications. Grape kernels application was increased compared to the other two
fuels because the unit was more stable and operated longer due to the realized technical
improvements.
Table 10: Overview of Operation Duration
Demo
Location
Operation
Duration
[hours]
Gasification
Duration
[hours]
Electricity
Generation Duration
[hours]
1
2
3
4
Ptolemaida
Ptolemaida
Amyntaion
Amyntaion
50
64
140
207
50
64
140
207
20
43
91
113.5
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LIFE08 ENV GR 576 SMARt-CHP
40
Figure 26: Total Operation Duration per
Demonstration
Figure 27: Real duration on electricity and
gasification mode
The demonstration operations proved that the unit has reached a state mature enough to
cope with any future demonstration and operate sufficiently and adequately for scientific
studies and experiments. However, such a unit requires better automation and monitoring
equipment in order to operate continuously in a yearly basis producing energy, as well as
deeper scientific and engineering know-how. In the following section, proposed
ameliorations for each part of the unit will be presented.
Finally, the overall system operation in conjunction with the team experience is assessed
as successful. Changes made during the demonstration operations, such as the rotary
valve withdrawal, the change of the last barrel’s pipes with ones with bigger diameter,
and the replacement of the water trap with the high efficiency filters before the engine,
were all proved effective and had long-term results (fewer feeding problems, lower
pressure drops on the different parts, augmented gas quality concerning remaining tars
and chars, etc.).
4.4.2 Mass & Energy Balance Efficiency
One of the most crucial results and outcomes of the demonstrative operations was the
mass and energy balance efficiency of the unit. Studying the total outcome of the unit in
relation to its total input, from an energetic, economic and environmental aspect, is the
most important input for a further sustainability analysis, which in combination with the
information from the previous chapters will allow the design and planning of the future
steps towards the expansion and spread of the project’s objectives and results.
The mass and energy balance, measured for a specific operation point and utilizing grape
kernels as an input is presented in Figure 28. The main gasifier operational parameters
used are: T=750oC and ER=0.3, which represent the average values of the whole
operation, while the engine operates on 3,200rpm.
For the specific measurements, the whole quantity of the produced gas was introduced
inside the engine. The gas route system is designed in order to offer the ability of
D3 Demonstration operation report
adjusting the produced gas flow that enters the engine, leading the remaining flow via a
secondary route to the by-pass and ultimately to the burner. This offers the ability of
studying the effects of the produced gas on the engine, as its flow is increasing, but in
the same time negatively affects the total system’s efficiency as the by-pass flow
represents unutilized energy losses. Targeting to representing the real operational
efficiency of the unit and the minimization of energy losses, during the energy balance
calculation the valves for the by-pass route were totally closed. That way and comparing
the results with other measurements when the valves are open, the exact output losses
through the by-pass, could be calculated and then applied to the whole pool of
measurements.
In Figure 29, resulting from the chart in Figure 28, a Sankey Diagram for the SMARt-CHP
system is presented, expressing its total and partial efficiencies for the different
processes.
A biomass input of 100 kWth is considered the reference for the calculations. All results,
efficiencies, outputs and additional inputs are scaled to 100 kWth input.
The whole process is divided into two parts. The first part contains the gasification and
treatment of the producer gas, beginning with biomass input and resulting to the output
of ready-to-be-used gas. The second part refers to the mini-CHP unit exclusively and the
utilisation of the producer gas.
During the first part, the energy efficiency ratio achieved is 62%, which express the
percentage of the biomass energy input that converts into usable energy of the producer
gas. The main losses on this part refer to pollutant mass losses (tars, chars,
condensates), and to the energy/enthalpy losses due to the cooling of the producer gas
during its treatment.
After treatment and cooling, the producer gas is guided to the mini-CHP system, where it
combusts as a mixture with propane. During this second part, the total efficiency ratio
achieved, taking into consideration as inputs the useful energy from the producer gas and
the introduced energy via propane, and as outputs both the electrical and the thermal
energy produced, is 72%. The electrical efficiency, taking into consideration the same
input but only the electrical power as output, is 20%. It has to be noted that more than
60% of the electrical output returns to the SMARt-CHP unit for self-consumption purposes
and only the remaining is guided to the electricity grid. Losses in this stage refer to the
heat losses of the mini-CHP system that cannot be avoided and used/added to the
thermal output.
Both the two previous parts combined, lead to a total efficiency of 48% for the SMARtCHP unit, considering both electrical and thermal energy as outputs, and biomass and
propane energy as inputs. With the same input but taking into consideration only the
electrical energy as output, the electrical efficiency of the unit reaches 6%, while if only
thermal energy is considered as output, the thermal efficiency reaches 42%. Table 11
compares the SMARt-CHP unit efficiencies, for the two parts and in total, with a variety of
different technologies.
41
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LIFE08 ENV GR 576 SMARt-CHP
Figure 28: SMARt-CHP Unit’s Mass and Energy Balance
D3 Demonstration operation report
Figure 29: SMARt-CHP Unit’s Sankey Diagram
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LIFE08 ENV GR 576 SMARt-CHP
44
Table 11: Efficiency of various biomass based CHP technologies
Biomass
Technology
CHP technology
Electrical
Efficiency
Thermal
Efficiency
Total
Efficiency
Sources
Stirling Engine
15%-35%
50%
65%-85%
1,2,3
Organic Rankine Cycle
8%-23%
52%
60%-75%
4,2,7
Steam Turbine
10%
55%
65%
6,7
Pyrolysis
Steam Engine
Internal Combustion Engine
10%
19%
76%
66%
86%
85%
Biogas Production
Internal Combustion Engine
33%
50%
83%
Biodiesel Production
Internal Combustion Engine
Fuel-Cells
37%
43%
80%
8,9
1,10,11
1,12,13,14
,15
1
8,16
Gas Turbine
25%
56%
81%
6,17,18,19
Micro Turbine
28%
48%
76%
4,16
28%
6%
65%
42%
93%
48%
1,17,20
Combustion
Gasification
Internal Combustion Engine
SMARt-CHP Unit
On the following paragraphs, present losses and suggested ameliorations are presented
and explained. Those losses describe the reasons of the present differences between the
actual efficiencies and the nominal efficiencies of such systems. Suggested ameliorations
aim at decreasing those differences.
Mass and energy loss
A big fraction of the losses on the first part, mainly in the form of heat loss, occur at the
gasifier. This is mainly due to its design restrictions and the need to keep the unit’s
weight low for portability. The design takes into consideration easy and fast unit
assembling and disassembling losing this way some of its efficiency. In detail, adequate
insulation of the gasifier’s parts was hardly feasible, leading to the increase of the
electrical consumption in order to keep the system at elevated temperatures. In addition,
the insulation material was selected due to its low weight even though better insulation
could be achieved via the use of more efficient but heavier materials. It is estimated that
with a better future design those losses would be reduced leading to both the
improvement of the quality and quantity of the produced gas, and the decrease of the
electrical consumption for self-sustainment purposes.
The cyclone has been oversized in order to be able for use in bigger unit’s capacities
(50 kWth), but this leads to its low efficiency in the current unit. The main effect is the
inadequate retention of the bigger particles, which in turn overload the particle trap. This
results in high pressure drops and leads to unstable conditions in the gasification process
and thus to both practical operation problems and increased energy losses.
D3 Demonstration operation report
The particle removal performance of the particle filter was satisfying, but evaluated as
highly sensitive to other parameters such as high loading due to poor cyclone
performance and filter material failure due to high temperatures gradients. Those failures
led to gas by-pass and loading of the gas cooling system downstream the filter, leading to
higher pressure drops and thus higher energy losses.
As presented in the chapter 3.3.1, the demonstration results proved that even if
gasification gas input on the mini-CHP unit does not affect the efficiency of the engine, it
has led to the decrease in the produced power, electrical and thermal, due to the
significantly lower heating value of the gas, compared to propane.
Ameliorations
Concerning the biomass feeding system, the demonstrative operations have shown that a
better dimensioning of the feeders, more suitable for the different biomass feedstock is
essential. This would lead both to the minimization of the necessary pretreatment
concerning the biomass and to an operation optimization with less clogging at the feeding
feeders. Better biomass drying is also essential for the minimization of the feeding
system’s presented problems, but as well to the optimization of the overall performance
of the gasifier and the quality and quantity of the output gas.
As mentioned earlier a better insulation of the gasifier is essential for the minimization of
the heat losses. A new design of the gasifier and its heating system should also regard a
more efficient insulation, easily removable and replaceable during the unit installation,
and at minimum losses. In addition, the addition of a second parallel gas circuit might as
well minimize maintenance duration and as a result increase total electricity production
time.
Downstream the gasifier, a new high efficiency cyclone should be designed and used, as
stand-alone or in conjunction with the existing one, for the efficient retention of large
particles. This is of high importance because, as it is described earlier, this affects both
the particle trap and the whole gas treatment system (high loads, high pressure drops,
higher consumptions, instability), but also the overall efficiency (high pressure drops,
higher consumptions, instability, higher losses).
Similar to the gasifier, a better design of the trap holding construction should aim to a
more effective insulation, easily removable and replaceable, minimizing energy losses.
Furthermore, a second parallel gas route, with a second filter, would allow the continuous
operation of the whole process and the production of energy during the particle filter
cleaning. The char mass losses during the particle trap cleaning, which represent a
considerable fraction of the introduced biomass energy content, could be significantly
reduced by the design of a char collection and re-introduction in the gasifier system,
which is going to allow the char’s further reaction and the complete utilization of the
biomass energy content.
As far as the tar removal system is concerned, the conception, design and construction of
its heating losses exploitation via heat exchangers would augment the overall production
of heat and the total efficiency of the SMARt-CHP unit. In addition, a recycling system for
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LIFE08 ENV GR 576 SMARt-CHP
the barrel’s water should be designed for environmental purposes containing technologies
for the cleaning of the water and the caption of tar.
In the previous chapter, the mini-CHP unit’s efficiency was analysed and it was deduced
that no major ameliorations could be applied, since no access to the system’s electronics
software is granted. However, ideas as the one of turbocharger application, could be
applicable and could augment the efficiency, mainly on higher gas consumptions.
In general, further ameliorations on the unit comprising of automations, redesign of the
unit for scale ups and the installation of auxiliary equipment, such as gas analyzers, are
essential for the completion and the advancement towards a more sustainable product.
Byproducts
The main byproducts of the unit’s operation are: the ash that is collected by the cyclone
and the particle filter, the tars that are collected by the tar removal system and the waste
heat from the tar removal system.
The process’ fly ash contains approximately 50% carbon. Thus it can be reintroduced
inside the reactor, as mentioned earlier, for complete decomposition. In addition, the ash,
after being collected, can be used for: application to forest ecosystems, as fertilizer
(fertilizer or supplement) in agricultural ecosystems, implementation in geotechnical
construction and industrial processes e.g. construction of roads, parking areas, use as a
surface layer in landfills and use as an additive for the production of building materials
(concrete, bricks or cement..), or as fuel in case of having high carbon content. As far as
it concerns the tars, the aim is to increase the rate of their reactions inside the gasifier
and be minimized and converted to syngas in order to utilize their energy content. The
heat in the form of hot water inside the barrels, in temperatures in the range of 60 to
90oC, which now constitutes a byproduct, can be used via heat exchangers and either be
used for biomass drying or increase the total useful heat output in form of warm water. A
further analysis concerning the produced byproducts is presented in Part B of the
Deliverable 4.
D3 Demonstration operation report
5 Conclusions
The data derived during the demonstration operation were analysed and presented in
depth in this study. The unit is also evaluated regarding energy efficiency. The
aforementioned analysis acts as a reference point for agro-residue utilization promotion in
the rural areas of Greece and the Mediterranean region. The analysis of the
demonstration results is discretized into 3 major axes: biomass type evaluation,
gasification performance and CHP unit performance.
One of the project’s aims is to test the mobile gasification unit on a variety of biomass
fuels in order to determine the unit’s versatility and stability under a range of inputs.
Three different biomass fuels were utilised during the demonstration operation in the rural
areas of W. Macedonia, olive, peach and grape kernels.
Regarding feeding performance, all fuels were easily handled after a set of minimum
pretreatment activities. The results show that the fuel’s water content must be lower than
20%, the ash content should be less than 10% to ensure long operations and finally the
size range of the fuel must be close to that of olive kernels (1-3 mm). The feeding system
can reliably handle all fuels within the aforementioned specifications. As far as
pretreatment is concerned the following outcomes are highlighted:




The majority of agricultural residues have relatively low moisture content thus
allowing easy and quick drying without the use of special equipment. Even grape
kernels which are a by-product of wine production can be sun-dried.
It is essential that any milling occurs in dedicated systems or in thoroughly
cleaned equipment in order to avoid contamination of the fuel with inorganic
matter or any other non-combusting materials.
Screw feeders are a reliable means of fuel input especially for fluidized beds. Sand
that escapes to the feeding system is impelled back in the reactor through the
motion of the feeder. Screw feeders are also capable of promoting any type of fuel
that is not extra fine or has the form of straws.
The feeding rate is strongly dependent on the fuel properties even of the same
type. More specifically moisture content, average grain size and size range are
some of the major factors affecting fuel flow. As a result, the feeding system
should be calibrated regularly for non-standardized fuels.
The fuel characteristics can significantly affect the stability of the gasification process and
the overall efficiency. Of the above mentioned features, fuel moisture and ash content as
well as heating value are responsible for the quality of the producer gas. Apart from fuel
quality though, gasification parameters are also main determinants of the producer gas
composition and biomass conversion rate. The parameters with the largest effect are
process temperature, equivalence ratio and residence time – gas velocity.
Gasification parameters influence gas composition in the same manner for all fuels. The
choice of a fuel for gasification will in part be decided by its heating value. The heating
value of the gas produced depends at least in part on the moisture content of the
feedstock. The amount of volatiles in the feedstock determines the necessity of special
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LIFE08 ENV GR 576 SMARt-CHP
measures (either in design of the gasifier or in the layout of the gas cleanup train) in
order to remove tars from the product gas in engine applications. Ashes can cause a
variety of problems. Slagging or clinker formation in the reactor can be caused by melting
and agglomeration of ashes. If no special measures are taken, slagging can lead to
excessive tar formation and/or complete blocking of the reactor. Excessively large sizes of
particles or pieces give rise to reduced reactivity of the fuel, resulting in start-up problems
and poor gas quality, and to transport problems through the equipment. A large range in
size distribution of the feedstock will generally aggravate the above phenomena.
For these reasons even though the peach derived gas has a higher measured heating
value compared to olive and grape gas ,it is not efficient to gasify due to its high moisture
and ash content. If the peach kernels were treated properly, then the ash content would
be minimum but the gas calorific value would remain the same as solids and moisture are
removed from the gas prior sampling.
One final outcome of the analysis is that each fuel is most efficiently utilised in different
gasification parameters. Olive kernels yield best results at medium to high temperature
(750-800°C) and at low to medium ERs (20-30 %). The same conclusion applies to grape
kernels as well. However, peach kernel gasification produces best gas quality at lowmedium temperatures (<750°C) as the methane content (which possesses high heating
value) dramatically decreases at high temperature.
Different fuel type and a range of gasification parameters can affect the performance of
energy production. The main effect is based on the produced gas heating value and mass
flow. As it has been described in detail, the CHP unit produces heat and electricity utilizing
a gas mixture of producer gas and propane. The composition of the mixture depends on
the heating value of the produced gas. Higher gas heating value leads to less propane in
the mixture for identical power output.
In each operation, all data concerning the engine’s operation were recorded either
manually or automatically via a home-grown software. These data were recorded
continuously at regular intervals and were organized depending on the biomass feedstock
and gasification parameters.
During the demonstration, the maximum producer gas contribution to the engine’s fuel
mixture that was recorded for all three biomass residues was 80 % mass. The rest 20%
mass consists of propane. The producer gas that derives from grape kernel gasification
yields lower power output compared to the gas that originates on peach and olive kernels.
Among these two, olive kernels produce slightly better gas quality.
In summary, the overall performance of the SMARt-CHP system is evaluated as
satisfactory and not far from target. Even if several operational and technical problems
did not allow the complete fulfillment of the project’s targets, mainly regarding operation
duration, the improvements made to the unit and the experience developed by the team
led to an impressive progress throughout the demonstrations.
D3 Demonstration operation report
As far as operation stability is concerned, the unit operated in total 461 hours, following a
remarkable progress curve in its operation duration during the four demonstration
operations: 50 h in the first demonstration, 64 h in the second, 140 h in the third and 207
h in the last. Both technical and operational ameliorations based on the experience
developed in each demonstration, contributed to the above-mentioned progress. The
demonstration operations proved that the unit has reached a state mature enough to
cope with any future demonstration and operate sufficiently and adequately for scientific
studies and experiments. However, such a unit requires better automation and monitoring
equipment in order to operate continuously in a yearly basis producing energy, as well as
deeper scientific and engineering know-how.
The net efficiency of the unit is heralded as low (6 %). It is though a good starting point
for further optimisation and scale up. The major reasons for the low efficiency are the
following:





The gasifier insulation material was not the most effective regarding efficiency but
it was chosen mainly due to its low weight.
A second parallel gas route, with a second filter, would allow the continuous
operation of the whole process and the production of energy during the particle
filter cleaning.
No exploitation of the heat losses at the gas cleaning devices.
The use of propane, even in low quantities
The internal electricity consumption is high due to the low overall output of the
unit. The electricity consumption would be lower at higher outputs since it does
not increase linearly with the energy output.
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LIFE08 ENV GR 576 SMARt-CHP
50
6 Bibliography
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of biomass. 100 44 Stockholm, Sweden : KTH – Royal Institute of Technology,
School of Chemical Science and Engineering, Chemical Engineering and
Technology, Division of Energy Processes, 4 February 2013.
2. Daniel Maraver, Ana Sin, Javier Royo, Fernando Sebastián. Assessment of
CCHP systems based on biomass combustion for small-scale applications through a
review of the technology and analysis of energy efficiency parameters. Spain :
CIRCE – Research Centre for Energy Resources and Consumption,Department of
Mechanical Engineering, University of Zaragoza,, 4 August 2012.
3. H.I. Onovwiona, V.I. Ugursal. Residential cogeneration systems: review of the
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