BIOMASS CONVERSION TECHNOLOGY FOR RENEWABLE
ENERGY GENERATION: ANALYSIS, SELECTION
AND TESTING
AUTHORS
SILVINA M. MANRIQUE JUDITH FRANCO
AUTHORS
SILVINA M. MANRIQUE JUDITH FRANCO
AUTHORS
SILVINA M. MANRIQUE JUDITH FRANCO
AUTHORS
SILVINA M. MANRIQUE JUDITH FRANCO
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BIOMASS CONVERSION TECHNOLOGY FOR RENEWABLE
ENERGY GENERATION: ANALYSIS, SELECTION
AND TESTING
BIOMASS CONVERSION TECHNOLOGY FOR RENEWABLE
ENERGY GENERATION: ANALYSIS, SELECTION
AND TESTING
BIOMASS CONVERSION TECHNOLOGY FOR RENEWABLE
ENERGY GENERATION: ANALYSIS, SELECTION
AND TESTING
Biomass Conversion Technology for Renewable Energy Generation: Analysis, Selection and Testing
Authors
Silvina M. Manrique Judith Franco
Non Conventional Energy Resources Investigation Institute (INENCO) of the National Council of Scientific and Technical Research (CONICET) – National University
of Salta, Av. Bolivia 5150, A4408FVY, Salta, Argentina
Research Signpost, T.C. 37/661 (2), Fort P.O., Trivandrum-695 023
Kerala, India
Published by Research Signpost
2013; Rights Reserved Research Signpost T.C. 37/661(2), Fort P.O., Trivandrum-695 023, Kerala, India E-mail IDs: [email protected] [email protected]; [email protected] Websites: http://www.ressign.com http://www.trnres.com http://www. signpostejournals.com http://www.signpostebooks.com Authors Silvina M. Manrique Judith Franco Managing Editor S.G. Pandalai Publication Manager A. Gayathri Research Signpost assumes no responsibility for the opinions and statements advanced by the Authors ISBN: 978-81-308-0527-6
Preface This book summarizes some of the main results obtained in one of the
areas addressed by a doctoral thesis, carried out in the career of Doctorate in
Sciences of the School of Exact Sciences of the National University of Salta,
Argentina. This work was also done in the framework of a project of
experimentation and application funded appropriately for the Energy Program
and Transport Commission, of the Subsecretary of Studies and Prospective of
the Secretariat of Planning and Policies in Science of the Department of
Science, Technology and Productive Innovation.
The interdisciplinary and multidimensional work, they were aspects
necessary for the boarding of the complex systems linked to the utilization
and transformation of resources of biomass, in this case, existing in the Lerma
Valley, province of Salta, Argentina.
This book is written in a simple language - though well it relieves some
technical fundamental aspects - principally orientated to stimulating in
developing countries and Latin Americans, similar experiences of research
and construction of simple technologies that might affect the local
communities, not only with concrete solutions to problematic energetic, but
also with the development and enrichment of the local know-how,
diminishing costs and creating local opportunities.
The authors hope that it fulfills this intention.
The authors
Contents
Biomass conversion technology for renewable energy
generation: analysis, selection and testing 1
1.Clean and appropriate technologies 1
2.Current state of technologies and trends in the field of biomass 3
2.1. Outlook worldwide 3
2.2. National and provincial outlook 5
3. Biomass and technologies in Lerma Valley (Salta, Argentina) 7
3.1. The site of study 7
3.2. The different technological options 8
3.3. Selection criteria 8
3.4. Decision matrix and technological choice 9
4. The Stirling engine: A promissory technology 13
4.1. Path, experiences and applications 13
4.2.The technology: Functioning principle. Strengths and weaknesses 15
4.3. Technology testing: Developing the local know-how 18
5. Conclusion 24
Acknowledgements 25
References 25
Research Signpost
37/661 (2), Fort P.O.
Trivandrum-695 023
Kerala, India
Biomass Conversion Technology for Renewable Energy Generation: Analysis, Selection and Testing,
2013: 1-31 ISBN: 978-81-308-0527-6 Authors: Silvina M. Manrique and Judith Franco
Biomass conversion technology for
renewable energy generation: analysis,
selection and testing
Silvina M. Manrique and Judith Franco
Non Conventional Energy Resources Investigation Institute (INENCO) of the National
Council of Scientific and Technical Research (CONICET) – National University of
Salta, Av. Bolivia 5150, A4408FVY, Salta, Argentina
Abstract. Lerma Valley (Salta, Argentina) has a biomass supply that might be used for bioenergy generation (thermal and electrical applications). Nevertheless, there are no guidelines for the selection of feasible technological devices for the area. The aims of this study were: to identify and to evaluate technologies of bioenergy conversion, and to design, to measure and to build a useful device for electricity generation. The methodology applied was performed through surveys to international experts and local participation. Five technologies were compared by means of six criteria defined in a decision matrix. The Stirling engine was selected for local tests, building it with available pieces on the local market. The prototype, though of low power (30W) and efficiency,
works correctly and it allowed surveying key design and operation parameters. Improvement guidelines are offered and the need for further investigation and experimentation is stated.
1. Clean and appropriate technologies
Thermodynamics have established that the total energy of the universe always remains constant, though, after many conversion processes, the Correspondence/Reprint request: Silvina Manrique, PhD., Non Conventional Energy Resources Investigation
Institute (INENCO), National University of Salta, A4408FVY, Salta, Argentina. E-mail: [email protected]
Silvina M. Manrique & Judith Franco 2
remaining quantity of usable energy diminishes [1]. The processes through which energy turns into useful forms have thermodynamics limited efficiencies, typically only from 10 to 40%. This means that between 60 and 90% of the initial energy turns into energy loss (usually in the form of sound and heat) [2]. Often, these processes produce waste materials (radioactive, greenhouse gases - GHG-, mineral ashes, etc.). The use of clean energy technologies, that includes renewable energy technologies (RET) and energy efficiency (EE) technologies, has grown greatly since past decades. Both technologies reduce the use of energy from conventional sources (as the fossil fuels) but they are different in other aspects [3,4]. EE measures are means and methods to reduce the energy consumed in the provision of a certain good or service, especially compared to conventional energy or standard approximations [4-5]. Dincer and Rosen [6] argue that there is a limit to the improvements towards a greater EE established by thermodynamics laws. They further state that, generally, the aim is to achieve an optimum balance between efficiency and factors such as economic, environmental impacts, security, and political and social acceptability factors. Considering these factors leads us to practical restrictions about the increase in energy efficiency. Hammond [7] observes that though the potential thermodynamics improvements (exergetic) are of around 80%, only 50% of the energy currently used might be saved by technical means, and when the economic barriers are taken into account, this diminishes up to 30%, approximately. EE measures allow energy saving in the most economical way, but do not have great acceptance by the users, and, in many cases, there is not enough official state policy regarding the promotion of these measures [8]. In Argentina, until recently, there were no promotion regulations or policies with regards to EE. In 2007, the National Program of Rational and Efficient Use of Energy-PRONUREE (Decree 140/2007) was launched, which includes a series of steps to follow in the short, medium and long term in order to achieve a greater EE [9]. In the country, the potential of energy saving is associated with all the consumption sectors, and might continually improve with low or no capital investment (for example heat losses or combustion improvement) [10]. The main existing difficulties stem from the fact of considering the energetic consumption as a fixed cost of the productive system, the lack of energy efficiency norms, as well as reliable technical data. RETs are those that transform a renewable energy resource into useful
caloric, electrical or mechanical energy. A renewable energy resource is that
which use does not affect its future availability1 [11-12]. Often, the distinction
or limits between technologies of EE and RET are blurry [4] though it is not
important: the aim of any clean energy resource is to reduce the conventional
energy consumption. Some characteristics shared by the clean energy technologies
___________________________________ 1Except when the resource is overexploited, as it can happen in the case of biomass.
Biomass energy conversion technology 3
can be detected when they are compared with the conventional energy
technologies, as for: i) they produce minor environmental impacts, though they
still must be analyzed in each specific application, since all heating systems,
energy generators, and by extension, energy consumers, have some
environmental impact; ii) they have higher initial costs (costs incurred at the
beginning of the project) that compete with conventional technologies. This has
led to the conclusion that RETs are too expensive, and iii) despite its high
initial costs, they are often cost competitive compared with the conventional
technologies on costs of life cycle basis, especially for certain applications,
since they tend to have lower operation and maintenance costs than
conventional technologies [13-17]. Nevertheless, it is not only important that it
be a clean or slightly pollutant technology, though it is a basic aspect, it must be
evaluated together with other characteristics that will contribute to making a
technology really ―appropriate‖. Appropriate technologies start from the
recognition that technology is not neutral, but cause and consequence of a
certain culture and, therefore, there must be as many ways of finding solutions
to a problem, as there are cultures. These technologies must be, therefore,
appropriate to the environment, appropriate for the task and appropriated by the
people (or appropriating). To be appropriate to the environment they have to
generate the least possible impacts, with the local resources, and without
exceeding the load capacity of the ecosystems in which they are inserted. To be
appropriate for the task they must address the problem - productive or domestic
– of treating it in an effective and efficient way and creating wealth. Finally, to
be appropriated by the people, they must be low-cost, of easy managing and
maintenance, easy to understand, and easy to repeat in a local scale [18-19].
UNDP [18] summarizes these principles in a certain way. Therefore, beyond
the specific technical aspects of the technologies, it is necessary to consider the
cultural and environmental context [20-22] in order to anticipate if a certain
technology will be able to be appropriate for the particular situation and
appropriated by the people of the place.
2. Current state of technologies and trends in the field of
biomass
2.1. Outlook worldwide
Future projections show a strong growth in the role of electricity as a
favorite energy carrier and with a global demand of electricity that increases
rapidly; clean technologies have a critical role to play for the satisfaction of
these needs [23]. Many countries recognize biomass as the major potential
contributor to reach the electricity objectives from renewable sources, though
Silvina M. Manrique & Judith Franco 4
still few countries have specific aims of electricity production from biomass.
The installed capacity of bioenergy increased from 66 GW in 2010 to almost
72 GW at the end of 2011. The United States lead the world in biomass-based
electricity generation, with other significant producers in the European
Union, Brazil, China, India, and Japan. Many sugar-producing countries in
Africa generate heat and electricity from bagasse, in plants of combined cycle
(combined heat and power, CHP).
Biomass includes a wide variety of resources; therefore, different
technologies of electric power generation can be used. The most developed
and extended technology for electricity production is the steam turbine that
operates in a Rankine cycle (traditionally used with fossil fuels). If we
compare the power stations that operate with biomass (like wood, which
implies 80% of electricity from biomass) with those that work on a coal
basis, the former are smaller than the latter (about 30 MW). Nevertheless,
improvements in collection logistics, transportation and storage in the past
decade, and the growth of international trade of pellets, particularly, have
helped to remove constraints of size of facilities, which have increased in the
last years [17]. Nowadays, Tilbury power station in the United Kingdom, that
begun operating in 2012, is the biggest biomass-based power station of the
world, with a capacity of 750 MWe. This coal power station restructured to
biomass begun working partially because a fire caused a failure in the
production; although, it is expected that it will become completely operative
during 2013 [24]. Its annual biomass demand is estimated in 2.3 million tons
of wood pellets per year and it works with CHP cycles. The CHP systems,
whose electricity generation costs are often higher than the standard
generation, are being subsidized by the governments to favor the growth in
the capacity of these cogeneration systems. The technology for medium scale
of commercial available CHP ranges between 400 kW to 4 MW [25].
Throughout the world, besides Tilbury's station, CHP systems with an
electrical capacity of 240 GW are in operation (Alholmens Station, in
Finland, working on the basis of coal, peat and solid biomass) and have an
enormous growth potential, not only in big industrial systems, but also in
small projects in decentralized systems. On the other hand, biomass
gasification reduces the costs bioelectricity generation investment, by means
of the employment of gas turbines [26]. The future of electricity generation
from biomass depends on the technology of Integrated Gasification of
Biomass into Combined Cycle (IGBCC), which offers the highest conversion
efficiencies, of almost 40-45 % [27]. Puertollano's station (Ciudad Real) is
the biggest IGBCC plant in the world. It produces 335 MW and its
gasification technology is named Krupp-Uhde, which now is unified with
Shell technology. There is a wide range of alternatives with IGBCC
Biomass energy conversion technology 5
technology, offering the possibility of using an efficient process according to
the available feedstocks, costs, policies and environmental aspects of every
project. Nevertheless, Ahrenfeldt et al [28] mention that this technology turns
out to be highly promising in power stations of up to 10 MW, as an
alternative to biomass combustion, to achieve CHP decentralized systems in a
scale that had not been sufficiently efficient before.
In line with the improved use of woody biomass, LFG use (sanitary
landfill gas) for electricity production has increased in the last years (which
also reduces GHG emissions into the atmosphere). The total biogas
consumption in Europe was 63 PJ in 2010. In the USA, in 2011, there were
576 projects methane capture from sanitary landfills to generate useful heat
(and electricity) satisfying the heat demand of almost 750,000 households,
for a total of 62 PJ [29]. By the beginning of 2012, near 186 biogas stations
were operating in farms of the United States. Biomethane (purified biogas) is
produced in 11 European countries, and in 9 of them it is injected into the
natural gas networks [17]. With regards to small electricity generation
systems, the thermal gasification is a growing commercial technology in
some developing countries [15]. In China, small domestic biogas reactors
have been applied for rural lighting and cooking. Biogas digesters can be
supplied by small local companies or built by the same rural producers [30].
In a few Chinese provinces, the biogas of the thermal gasifiers also provides
fuel to cook through distribution pipelines. China and India have the greatest
number of domestic installed digesters of the world (near 43 million and 4.4
million of bio-digesters, respectively) in 2011. At the end of 2010, the total of
installed capacity in biogas electrical generation plants was 800 MW in
China, and 91 MW in India.
For combustion processes on a small scale, the stirling engine (SE) are
being revalued, even in isolated facilities of the network, both in farms in
industrialized countries and in small developing countries. Further research is
still necessary, that studies the employment of electricity from biomass, on
small and big scale, to avoid environmental unwanted consequences [31].
These engines are in stages of demonstration and commercialization [32],
with capacities of up to 75 kW [33].
2.2. National and provincial outlook
In Argentina, biomass, considering fuelwood (0.8 %), bagasse2 (1.2%) and
an uncertain participation of "other primaries" (which include agricultural ____________________________________________________________________________
2 Bagasse is ―the dry pulpy residue left after the extraction of juice from sugarcane, used as fuel for electricity generators, etc.‖ (Oxford English Dictionary).
Silvina M. Manrique & Judith Franco 6
wastes, quebracho tree sawdust, black liqueur, and not discriminated solar and wind power) reaches 3.5 % of participation in the national power grip (of a total of more than 76,000 ktep in 2010 [34]), though these values leave out traditional uses of biomass, without record in the provinces [35-36]. Bioenergy could cover 10% of the internal supply of primary energy until 2015 [37] as it is the ambition of the national project Pro-biomass (Project to Promote the use of Biomass for Bioenergy) which seeks to incorporate the generation of 200 electrical MW and 200 thermal MW. This project will add efforts to the national objectives for the generation of 8% of electricity from RES for 2016 (Law 26190). Its first step was executed by means of the GENREN program (Generation of Renewables) which invited tenders for 1000 MW of electric generation of RES in 2009, a 12% corresponding to thermal generation with biofuels (three power stations of 34 MW and one of 8.4 MW, that in the year 2012 had not yet been built for lack of financing). They did not tender in this program other resources of biomass to energy [38-40]. Leaving aside energy crops for biofuels (biodiesel and bioethanol) boosted by the national government and by international markets, which have created great controversies mainly for the changes involved in soil use and associated impacts [41-51], in the country there are more than 80 bioenergy projects in operation, in construction, and portfolio (in thermal and electrical generation), which amounts to 286 MW of installed operative capacity, near 219 MW in construction and 86 MW in portfolio [36]. The province of Salta, in the north of Argentina (that represents 6% of
the national territory) has been identified as one of the provinces with great
potential for biomass exploitation [52]. Its main advantages can be found in
its great surface covered by native forests (23 % of the national total) and the
great diversity of natural ecosystems (originated by changes in altitude,
latitude, exposition, and microclimate) that allow for different productive
activities. Nevertheless, at the moment, there is only one operating biomass
project 40 MW in a Sugar refinery (San Martin de Tabacal, which relies on
bagasse of sugarcane) and of all the projects tendered by GENREN, none of
them have been awarded to the province [40].
According to previous studies, there are biomass resources whose energy
potential might be exploited, especially in Lerma Valley, center of the
province and where the capital city of Salta is located. These studies indicate
a supply of about 260,000 t/year (dry weight), with an energy potential of
almost 3.4 million GJ/year [53], from agricultural wastes (tobacco and
pepper), municipal solid waste (MSW), and fuelwood generated from three
main ecosystems of the region: Chaco, Yungas, and Shrublands [54]. The
agricultural wastes bioenergy and of woody biomass (generated from natural
ecosystems of the area) might be exploited through combustion processes, in
Biomass energy conversion technology 7
heat generation for housings or productive processes. In local applications of
small dimensions, electricity could also be generated. On the other hand, the
bioenergy that could be obtained through processes of anaerobic digestion
from the MSW arranged in a regional sanitary landfill might be used for
electrical purposes. Nevertheless, since there is a great diversity of feasible
devices of being used for these applications, there are neither guidelines nor
experiences that guide in the taking of decisions in the Valley. Therefore,
objectives of this work were: to evaluate energy conversion technologies
feasible of being implemented in the area of study; to design, to measure and
to build an energy conversion device useful for some of the mentioned local
applications, and, finally, to experiment with the constructed technology,
offering guidelines and recommendations for its improvement.
3. Biomass and technologies in Lerma Valley (Salta, Argentina)
3.1. The site of study
This study is concentrated in Lerma Valley, province of Salta, Argentina.
It is a tectonic intermountain depression that is located from the last spurs of
the Eastern Mountain chain to the West, and the Sub Andean Saws to the
East. The average altitude is of around 1,100 to 1,200 m.a.s.l. The total area
is of approximately 5,000 km2 [55], with a maximum length of 144.3 km and
a maximum width of 52.3 km. It is located between the coordinates 24º22.0 '
to 25º43.0 ' South latitude and 65º15 ' to 65 º 48 ' West longitude. The climate
is subtropical with dry season, with precipitations from November to March,
which decrease towards the South, in general terms, related to the effect of
altitude and exposure [56]. The annual medium precipitations fluctuate
between 600 to 800 mm and the annual medium temperature is of
approximately 16ºC [56]. Lerma Valley is divided into 7 departments and 13
municipalities, including the Capital department. Two regions can be
distinguished: i) the plain area, which belongs to an extended plain within the
Valley with a medium gradient of 1%, which is suitable for agriculture and
where urban and service centers are concentrated up to 1,600 m.a.s.l. and ii)
the mountain area that goes along the Valley (> 1,600 m.a.s.l), with
maximum altitudes of 5,000 m.a.s.l. to the West and of 2,000 m.a.s.l. to the
East where a dispersed population predominates. This population is devoted
to self-consumption and extensive farming practices. 70% of the population
of the Valley is located in the plain (urban) area, while the remaining 30%
can be found in the mountain area (rural).
Silvina M. Manrique & Judith Franco 8
3.2. The different technological options
Two techniques were developed for the identification of possible
technologies to implement in the area: a) surveying international expert‘s opinions, in direct consultation with the case of study; b) surveying of updated secondary data sources, and c) local participation. In the case of the latter, the report was performed through workshops (5 in total), interviews to key actors (40 interviews), local surveys (100 surveys), and laboratory work. It was sought to know and to identify the local perception on the possible
technologies to be used for energy conversion of the local available biomass resources. In the case experts consulting, it was performed through an electronic survey prepared on an Excel® spreadsheet format and distributed by e-mail. 21 international experts participated (though we consulted more experts, up to the closing of this work only 21 had responded to the survey). Experts were identified from scientific publications, online search of
researchers in specialized centers, and lists of participants in international events. With a brief initial introduction and details of the project, institution, participants and aims, the surveys were sent in Spanish and English. The surveys were anonymous, since that is what the informants were informed, though it was surveyed data about: genre (M/F), profession, profession segment (government, industry, university, consultancy, non-governmental
organizations, others), primary area of work (production, evaluation, biomass trade, liquid fuels, biomass technologies, etc.), primary scale of operation (local, national, global, supranational), country or region where they work. The obtained information was systematized and processed as the responded surveys were received. Likewise, comments and suggestions were organized in order to be included as facts in the work development. In the cases in
which the suggested application was heat generation, the mentioned technologies were simply: boiler, oven, or "efficient" stove, indicating the impact that the traditional technologies used in remote or rural places have on health and the environment. The offer was more diverse when the considered application was electricity generation (associated in most of the cases to the MSW). Therefore, subsequent analyses were centered in this application, to
define a taking of decisions process for the selection of a particular technology. The main technologies distinguished by the experts were: steam turbines (ST), gas turbines (GT), internal combustion engines (ICE), engines of external combustion (as Stirling or SE) and fuel cells (FC).
3.3. Selection criteria
The consulted participants, at the same time that they pointed out the
technologies of interest, they also mentioned the main criteria for the
Biomass energy conversion technology 9
selection of one or other technology, rating every criterion on an importance
scale from 1 to 100. Finally, the criteria were defined considered as most
significant in selecting a technology, obtaining for each one a score of
relative importance. Some of the consulted literature was [57-64]. On the
other hand, according to the established criteria, the different technologies
under analysis were qualitatively evaluated through a decision matrix. The
decision or prioritization matrix is a tool that helps to rationally compare and
choose among several options or alternatives of problems or solutions on the
basis of a few criteria to set priorities or to take a decision.
Firstly, relative assessments of each option (selected technologies) were
assigned in relation to each factor (comparison criteria). The score
assignment scale varied from 0 to 3, considering which was the performance
that the option or technology had regarding each criterion. Finally, the
assessments were multiplied by the weights and an adjusted sum of every
option was made, placing every technology in a relative order of importance
with regards to the analyzed criteria. Once the most advantageous
technologies were identified, the proposals were ready to be subjected to
further analysis. The main criteria and the indicators defined for each one of
them are shown in Table 1.
3.4. Decision matrix and technological choice
According to the literature, it is possible to observe, in a comparative
way, the technologies behavior - in some aspects - of the technologies
mentioned by the experts, like: ICE3, GT
4, ST, SE
5, CFFA (cell of fuel of
phosphoric acid)6 and CFMC (cell of fuel of molten carbonate), as regard to
the costs of installation and of operation and maintenance (O and M), show in
the Fig.1. It is considered that the technologies would be exploited from LFG
generated by decomposition of the MSW in a sanitary landfill. Regarding
installation costs, for example, within minimal and maximum values of the
different technologies, fuel cells (CFFA and CFMC) are the ones that show
the highest values. If these values are taken as reference for comparative ends
-considering them 100 %- the installation costs of the ST mean 30 % of the
______________________________________________
3The efficiency, consumption, and emissions data reported, belongs to a Caterpillar 3516 SITA
of cycle Otto, operating in a sanitary landfill. 4The information reported belongs to a gas turbine manufactured by Lot Turbines, named Centaur, which is the most common in operation from sanitary landfills. 5The considered characteristics belong to a Stirling engine MOD the IIIrd developed by
Mechanical Technology Incorporated (MTI), working from LFG. 6Cells information used belongs to the CFAF produced by International Fuel Cell, and the CFMC
produced by Energy Research Corporation.
Silvina M. Manrique & Judith Franco 10
Table 1. Main criteria for the evaluation of technologies.
Criteria Indicators Criteria explanation
Installation
Costs (IC)
€ per MW
The high installation costs are generally
associated with the low power range, since
there are a series of fixed costs that in the case of small installation have more repercussion
for installed kW. However, in certain cases,
small installations can do without some control or efficiency improvement systems,
leading to a lower cost for installed kW. In
such cases, the O and M cost can also decrease. Therefore, when using an
installation or O and M cost, it is necessary to observe similar experiences.
Operation
and Maintenance
Costs (CO&M)
€ per MWh
Technologies that require greater maintenance
periods cause a greater extreme suppliers
dependency of these kind of services or internal personnel for the maintenance. The
simpler the design, construction, and lower
number of mobile parts, the lower the O and M costs. However, the auxiliary systems that
can be necessary, such as bombs and funs can
be expensive to support.
Efficiency % of conversion
For each of the technological options, major efficiency in conversion means also lower
emissions, mainly of carbon compounds. It is
expressed in percentages.
Fuel consumption
(Heat rate)
kcal to produce a
kWh
It is another way of expressing the electrical efficiency. The heat rate is a measure used in
the energy industry to calculate how
efficiently a generator uses thermal energy.
Emissions % CO & % NOx,
among others.
Catalyst use to reach acceptable emission levels is frequently too expensive. This causes
an increased installed kW cost. Therefore, not
only from an environmental point of view, but also from an economical point of view,
technologies that generate fewer emissions
are more convenient.
Technology
development level
Necessary investments
to reach commercial
stage. €
Technologies can be at different development levels or states, from the idea phase, followed
by demonstration phase, pilot phase, and
commercial phase. If the investments and support for the development of a technology
is withdrawn, the technology can ―disappear‖
and not reach market stage.
Biomass energy conversion technology 11
Figure 1. Installation costs (€/MW) and operation and maintenance cost (€/MWh) of
thermoelectric technologies.
(highest) minimal value and 34 % of the (highest) maximum value; the ES
represents 28 % of the minimal value and 40 % of the maximum value; the
ICE imply 17 % and 24 % of the values minimally and maximum taken as
reference; and finally, the GT, show the lowest costs between 10 and 18 % of
the reference minimum and maximum values.
Technologies were identically analyzed for each of the selected criteria
(results not shown). As a summary of scores assignment of performance of
the considered criteria for the selected technologies, Table 2 is shown. The
values 0 represent the worst situation, whereas 3 represents the best situation
(fewer costs, major efficiency, minor pollution, major technological
development, etc.), independently of the variable, with the values 1 and 2 in
intermediate order (bad and average situation, respectively).
Table 2. Performance of every option in relation with every criterion. Where:
0 = worst situation; 3 = best situation. Letter ―T‖ denotes ―technology‖.
T
Criteria
CI (€/MW) CO&M (€/MWh) Ef%. CO% NOx% Development
ICE 2 2 2 1 1 3
GT 2 2 2 2 2 2
ST 2 1 1 2 2 2 ES 2 2 3 3 3 2
CF 1 1 3 3 3 0
Silvina M. Manrique & Judith Franco 12
In a second step, the weight of every considered criterion was assigned
(taking an average of the valuations made by the experts) and the weighted
final sum was obtained (Table 3). The technological options were organized
according to their higher or lower rating. In accordance with the comparative
scores achieved, it is possible to observe that one of the most promissory
technologies that might be used in a nearby future in the area is SE (with the
highest score). Though their experimental development is still scarce, their
qualities as pollutant emissions (practically void) and efficiency (discharge in
relation with other technologies), together with technological progresses that
might turn them into a technology that is competitive to the ICE, place SE
among the strategic future options. Not only for its application from LFG, but
also from woody biomass (only available fuel for the high area population of
the Valley).
In an intermediate position, the ICE and the GT, two of the most
employed technologies in electricity generation from LFG, might become
viable options, though the high pollutant emissions levels must be considered
– mainly in the case of the ICE-. If these were to be the selected options,
there are sufficiently proven and spread devices on the market so as to have
access to some of them, without too many complications, mainly when it is
about ICE. Micro turbines, once the costs are reduced, are one of the
technologies that show great versatility for its application on a small scale in
decentralized systems. ST, though it is a widely known and proven
technology, for the scale in which it should be implemented, its low
performance and high emissions, it is not considered to be a sufficiently
adapted technology for its exploitation from LFG of the MSW. Finally, the
FC (fuel cells), in which there is big future expectation, is currently out of
reach for their expensive cost. Further experimental research and
development is still necessary.
Table 3. Decision Matrix with weighted and total valuations.
T
CI (€/MW) CO&M
(€/MWh) Ef%. CO% NOx% Development Total
Weight assigned to the criterion
92 86 66 70 73 82
ICE 2 2 2 1 1 3 877 GT 2 2 2 2 2 2 938
ST 2 1 1 2 2 2 786
SE 2 2 3 3 3 1 1,065 CF 1 1 3 3 3 0 805
Biomass energy conversion technology 13
The SE, with high application qualities and possibilities, results in one of
the most advantageous options to the area, being the lack of demonstration
projects the main constraint. Zmudzki and Lipa [65] state that the amount of
available knowledge with regards to design and construction methods is still
scanty and, by far, insufficiently. The following objective of this chapter was
to contribute in this respect, developing a simple methodological scheme that
allows the visualization of the fundamental aspects of design and sizing, on
the one hand, and locally building and experimenting a biomass-based ES
prototype (that is constituted in one of the pioneering experiences in the
area), on the other hand. It is thus shown, the first results of this building and
experiment.
4. The Stirling engine: A promissory technology
4.1. Path, experiences and applications
The SE has gained popularity in the last decades due to the non-explosive energy conversion to mechanical forms and therefore, its low pollution level compared with ICE [66] and potential to exploit a variety of available energy sources, such as solar power or biomass. The SE, patented in 1816 by Robert Stirling, became popular in the last half of the nineteenth century especially for small domestic-use machines, such as kerosene funs and water pumps [67]. At the beginnings of the 20th century, refined and low-price fossil fuels and the ICE increasingly improved on the basis of these fuels exceeded by far the weight-power relation achieved with the Stirling engines [61, 68]. Only a couple of decades later, the Dutch Philips began to be interested in the modern Stirling. The increase in fossil fuel price together with the increasing environmental damage caused by the ICE led many other researchers to follow his example. On the other hand, the development of new theories and methods of analysis, materials and processes unknown before, stimulated the manufacture of different types of devices with varied applications [69]. In principle, SE is simple in design and construction, and can be operated easily [70]. Heating, cooling and electric power generation from renewable sources, are new fields where the Stirling can be competitive compared to other systems [71]. Many companies (STM Corporation, SOLO Kleinmotoren GMBH, Stirling Energy Systems Inc., Kockums Sweden, etc.), individuals and scientific departments (Department of Mechanical Engineering and of Materials of Kebangsaan Malaysia's University; department of Mechanical Engineering of the Technical University of Denmark; EAFIT's University, Colombia; Institute FEMTO-ST of the Department of Technology of Belfort's University, France, among others) are developing SE design programs and experimentation.
Silvina M. Manrique & Judith Franco 14
Works have been undertaken in aspects of functioning simulation and
design of these engines, in different configurations, mainly from solar power.
Among others, Abdullah et al [72] and Tlili et al [73] present design
considerations for engine type alpha, with base in Schmidt Theory and the
Third Order Analysis and across the use of dynamic models with energy
losses and pressure falls in heat exchangers. Functioning optimization aspects
have been studied by Timoumi et al [74] and Saravia et al [75] from
numerical and computational simulations. Also Parlak et al [68] and Obara
et al [76] perform thermodynamic and exergetic analyses for engines
functioning optimization. Moreover, these engines have been studied in
cogeneration and trigeneration systems, in the search for achieving maximum
energy efficiency [77-81]. Likewise, some functional prototypes in
experimental level have been built from different design methods.
Tavakolpour et al [82], in Iran, use principles of thermodynamics and
Schmidt Theory, adapting it for the modeling of the gamma-type engine from
solar power, and making functioning simulations to optimize the engine
design parameters. Scollo et al [83], in Argentina, built a functional prototype
designed on the basis of energy and scaling similarity principles.
There are few examples of functional prototypes from biomass. Probably
Podesser´s experience [84] is most mentioned, who developed a type alpha
SE, in Austria, heated by the combustion gases of a biomass oven. With a
working gas pressure of 33 bar to 600 rpm, a power of out of 3.2 kW, and
efficiency of 25%, it was tested for rural applications. The real SE
performance, well designed and adjusted, working with a maximum
temperature (Tmax) of 600 ºC (normal metallurgic limit) and a minimum
temperature (Tmin) of 20 ºC (running water temperature), reaches to 33%. In
any case, the first prototypes of any model still not optimized, tend to reach
half this value or less [85]. Podesser [84] makes an evaluation of basic
considerations and technical processes of different technologies and finds out
that the SE working from biomass burning should be the best technical and
economic solution for energy production independent from the network, in
the range of approximately 5 to 100 kWe. Corria et al [86] assume that SE
employment from biomass as source of energy in isolated regions, provide a
steady service, it does not need from other sources of auxiliary generation
and eliminates the high costs associated with the consumption and
transportation of fossil fuels. On the other hand, there are few construction
and essays experiences with engines in beta configuration – creator‘s original
design-and with biomass as a source of heat. Beta engines have been built by
Lira Cacho and Zamora [87] and Karabulut et al [88] of low power and from
low to moderate temperature differential. In both cases, though they mention
the possibility of their employment from biomass, there are no results of
Biomass energy conversion technology 15
those essays, since they were tested from LPG (liquefied petroleum gas).
Therefore, like in many other fields of technology, it is of fundamental
importance the construction and experimentation of this type of engines in
local level. The patents and rights of intellectual property of commercially
built prototypes belong to foreign companies that make it impossible to buy
this device for its employment in rural communities, not only for the high
costs, but also for the technical difficulties that an imported technology can
involve [75]. Therefore, it is important to achieve local knowledge generation
which makes it possible to repeat the experiences with this technology.
4.2. The technology: Functioning principle. Strengths and weaknesses
Described in a simple way, an SE is a device that converts caloric energy
into mechanical energy for alternative compression and expansion of a given
volume of working fluid (air, helium, hydrogen, or even a liquid) at different
temperatures. The change of volumes activates a piston connected to a
crankshaft, which exercises the work of the engine [89].
Similarly to an ICE, SE is based on the cycle of a fluid, which is
expanded and compressed for warming and cooling in order to increase the
pressure. The ideal Stirling cycle (Fig.2b) includes four thermodynamic
processes that act on the working gas [90]: 1-2: isothermal expansion. The
expansion space and the exchanger of associated heat are kept to high
constant temperature, and the gas suffers isothermal expansion absorbing the
heat from the heat source; 2-3: heat removal isochoric (constant volume). The
gas goes across the regenerator that absorbs a part of the heat that will be later
transferred in the next cycle; 3-4: isothermal compression. The compression
(a) (b)
Figure 2. Basic processes of a Stirling engine [90] (a) and graph of the ideal cycle
(pressure - volume) (b).
Silvina M. Manrique & Judith Franco 16
space and the exchanger of associated heat are kept at a low constant
temperature, for which the gas suffers isothermal compression transferring
the heat to the cold source; and 4-1: heat absorption to constant volume
(isochoric). The gas goes past the return regenerator and recovers part of the
heat transferred in 2-3, and then it will warm up more in the expansion space.
A Stirling engine efficiency can be improved by the regenerator - porous
material and with a thermal inconsiderable conductivity - since it can recycle
some of the heat that is removed from the gas during the transference towards
the cold cylinder, and warm up the gas when it is transferred towards the
warm cylinder [91].
The main basic engine elements are: cylinder, displacer, power piston,
the connecting-rod and the crankshaft, cooling sleeve [92,86]. The SE has
primarily three heat exchanges: i) the heater, which must accept heat from a
high temperature burner and deliver heat to the engine working fluid with a
relatively small decrease in temperature; ii) the regenerator, which "supports"
the working fluids thermal energy between the expansion and compression
phases of the engine and then releases the heat energy in the way back. In the
case of the beta configuration, likewise, the displacer fulfills the function of
regenerator, which in other models, are found separately, and iii) the cooler,
which removes two heat sources, one generated from the working fluid
compression, and the heat excess that the regenerator could not eliminate of
the working fluid [67]. According to the positions of the cylinders, pistons
and displacers, the SE presents different configurations. Among the main
configurations, it can be mentioned [93, 85]: i) alpha. Of two cylinders, with
two pistons: a piston and a piston/displacer, which move in two different
cylinders [94]; ii) beta. Of only one cylinder, with two pistons: piston and
displacer. The fluid pressure is supported only by a piston that works at low
temperature. It is the classic SE configuration and most used in engines of
low power - though it has also been used higher powers [85,88]; iii) gamma,
with two cylinders. The engines beta and gamma are called "of
displacement", since the working fluid is moved between the high and low
temperature spaces by the displacer. The compression and expansion is
executed by the power piston. In the gamma configuration, the double
cylinder arrangement offers greater freedom in the transmission design
towards a swivel axis and facilitates construction and assembly. Although,
due to the dead space and the lower specific power reached, they are used
when the advantages of having separated cylinders are bigger that the
disadvantages of specific power [65, 68]. Other configurations can be
observed in [30, 92, 95-96], among others.
Among the possible working fluids there are different gases, liquids or
condensing fluids. It has been experienced with some fluids, whereas others
Biomass energy conversion technology 17
are only theoretical. The use of liquid fluids imposes restrictions on SE (high
pressures, density and inertia of the liquids that do not allow working at high
speeds, etc.)[90]. Therefore, gases are the most used working fluids [94], and
the most important properties that must be taken into consideration when the
engine is being designed are: [93]: molecular weight, or molecules mass
(g for mol gram); viscosity, or resistance to the internal flow (g/cm/sec)
(to 800°K and 1 Mpa, it is a function of the temperature and the pressure);
thermal conductivity (W/cm²/°K/cm) or gas quantity that the heat drives; heat
capacity (J/g°K). It can be to constant (CP) pressure or constant volume
(CV). Comparing air (Nitrogen) with other gases as Hydrogen (H2) and
Helium (He), regarding these properties, a certain air volume will have a
greater gas density, greater mass and weight than the same H2 volume or He
[97]. Viscosity will affect the flow characteristics and flow resistance,
depending on the temperature, being He and air two times more viscous than
H2. H2 and He have conductivity 6 times bigger than air, which implies that a
tube heater designed for air must have an internal diameter much smaller so
that the air can drive heat to all the molecules. Air can only maintain a quarter
of the heat quantity that He can or a twelfth of H2 quantity. Due to on these
characteristics, H2 and He have been consolidated as the most used working
fluids [74,79]. Air, argon and other fluids, are only, nowadays, in small
demonstrative or experimental engines [72,97].
Cooling systems can basically be of three types: i) water cooled: if there
is an inexhaustible water source at room temperature (river, lake, public
network, etc.), it is only necessary to pump it inside the cooling [67]; ii) air
cooling: in this case it is necessary to transmit the heat to the air, and it can be
done by direct convection with air through metallic blades (it is a slightly
efficient transmission and only is in use in small demonstrative engines or in
slow and not pressurized engines that have to work with no assistance during
long periods of time); or water circuit with radiator cooling: it is the most used
system due to its transmission efficiency and free mobility that gives to the
engine. Nevertheless, energy must be consumed to pump water and stimulate
air; iii) cooling by through a cryogenic fluid (nitrogen or liquid helium) or
frozen water. In this case, energy investment and costs increase, so, these
factors must be considered as factors in the decisions taking. The flexibility of
possible heat sources to be used is currently one of the aspects that place this
engine on the spotlight. To the extent of external combustion, this engine can
work with fuels that might damage other engines (internal combustion)
as biogas or siloxanos7, though their main interest lies in renewable energy
_______________________________________________
7Chemical compounds constituted by units of R2SiO, where R is atom of Hydrogen or groups of
carbohydrates.
Silvina M. Manrique & Judith Franco 18
sources such as solar, geothermal, biomass, etc. In the case that the heat source
is some renewable resource, a preliminary diagnosis study must be carried out
that allows to characterize this resource and to estimate its availability and
energy in a certain area and for a certain period of time.
The review of literature on this type of engines shows greater emphasis
on its application strengths rather than weaknesses. Among the former,
environmental, technological, social, and economic aspects are included;
whereas among the disadvantages we can find, above all, matters of financial
order and of information shortage. Although there are, likewise,
technological aspects that still have to be improved [76], it is only a matter of
time for these improvements to be visible. Nevertheless, these advantages
appear especially for applications such as cooling [30], heating, and energy
generation [98], fields where it does not compete mainly with the
predominant ICE. Among the main strengths we can mention: a) achieved
global efficiency. There are prototypes with electrical efficiencies from
22-30%, which makes them competitive with other technologies of small
generation capacity; b) low noise and operation vibration. They can be built
for a silent functioning and without air consumption for propulsion of
submarines propulsion, or at space; c) high reliability and operation security
[90]; d) low maintenance cost; e) relatively few mobile parts; f) mechanically
simple, they start easily (slow and after the initial warming); g) versatility of
heat sources: multiple fuels capacity , including alternative energy; h) long
life [92,95]; i) lower need of lubrication than other alternative machines
(mechanisms and joints in the cold source) [89]; j) applications flexibility:
pumping of water, cogeneration, refrigeration, among others [93]; k) low
NOx emissions and CO [69,89]; possibility of use for cogeneration. The main
weaknesses currently recognized are: a) high cost of capital investment
mainly because they are manufactured in small quantities, and b) the shortage
of information about optimization, viability, costs of construction, together
with the fact that few fuels have been tested [86].
4.3. Technology testing: Developing the local know-how
The point of departure for the SE design and sizing is the aim definition
that is sought or desired application type and the power that is tried to be
achieved: electric power generation, automotion, water pumping cooling, etc.
From that point onwards, it is possible to determine which is the most
appropriate spatial configuration, and choose for the working fluid class that
will be used, type and quality of heat source, available cooling methods. In
later analyses, the revolutions per minute (rpm) will have to be known, the
size and minimal and maximum weight – if there is some constriction - and
Biomass energy conversion technology 19
work pressure. Once each of the previous aspects is defined, it is possible to
apply some well-known equations that are relatively simple [90] to obtain an
approximate estimation of the main parameters of the engine. Among these
formulations, we can find, for instance, West or of Beale equations [95], from
which basic aspects can be estimated, such as engine volume and physical
size, or even rpm and pressure, if they were not defined [83]. The logical
sequence of possible next steps to follow for the design of a Stirling cycle
engine is not considered to be exclusive or lineal, to the extent in which any
change in the considered aspects, can lead to a review of all of them.
Nevertheless, the organization and clarification of central questions will
allow advancing in the sizing of the engine in a sketching stage.
The usefulness of a thermal engine is to turn caloric energy into
mechanical work. For this end, it is necessary to know the mechanical power
(W) and the performance (η), which depend on work conditions or
functioning variables [71]: i) speed (v): understood as the repetition rate of
the cycle [72,89]; ii) average pressure (Pme): The effect of the working fluid
pressure on W and η is almost the same as that of the speed; iii) Temperature
of the heater (maximum temperature, Tmax): the higher the temperature is
the more thermal exchange there will be and, therefore, more W will be
generated and the engine real η will grow [70]; iv) Cooling temperature
(minimal temperature, Tmin): an increase in the cooling temperature, causes,
therefore, a decrease in W and η [83]. P and η are also according the
parameters that define the engine configuration, or design variables [71]: i)
Cylinder capacity (m): is the difference between the maximum and minimum
volumes to which the whole working fluid is subjected in every cycle. The
relation of cylinder capacity with the developed power is linear (but not
proportional). Performance, on the other hand, should not have to be affected
by this parameter, but experience shows that small demonstrative engines do
not have such good results as its bigger equivalent; ii) Relation sweep
volumes (V1/V2): it is the relation between the volume swept by the
compression piston and the one swept by expansion piston; iii) Race-
diameter (r/D) relation: is about 0.5 so much for the expansion camera as for
the compression camera. This relation favors thermal exchange although it
makes the design difficult; iv) Dead volume relation (x): relation between
dead volume (not swept) and the expansion camera volume. The increase in
the interior space of the regenerator and the auxiliary interchangers (increase
of x) affects power in a negative way. The engine must be designed with an x
as low as possible [72]; v) Time lag angle (a): the movement of both Stirling
engine pistons tends to be senoidal8, with the same frequency but with a
_______________
8Graph of the sine function.
Silvina M. Manrique & Judith Franco 20
certain time lag α. Power presents a maximum for values from between
60º and 120º, according to the engine. A first approximation of the power
value that a SE can develop is determined by the Beale's formula, where
W = power of the engine (W); B = Beale's number; Pm = cycle average
pressure (BAR); F = functioning frequency (Hz); V = volume swept by the
power piston (cm3):
W = B.Pm.F.V
The Beale (B) number is a parameter that characterizes the functioning of SE
and can be defined for the engine operation parameters. For engines that
work with a high temperature difference, the typical values for the Beale
number are in the range from 0.11 to 0.15; where a bigger number indicates a
better functioning [95]. It is possible to have an elementary thermodynamic
approximation of the engine functioning, through the employment of the
Ideal Gases General Equation. Though the real values will be much lower
than what is estimated, these values can be used as design reference. The
basic hypotheses for the engine thermodynamic calculation are: i) the fluid of
work is an ideal gas; ii) the total mass of air in the engine is constant; iii) the
dead volumes are zero; iv) if there is a regenerator, it is considered to be
perfect [99]. The steps sequence considered estimating the following
variables: fluid mass; maximum and minimal pressure without volume
variation; average volume; maximum and minimal volume; fluid mass for an
average volume; maximum and minimal pressure with volume variation;
forces waiting in the power piston; power for a given speed. This power
might be increased if the temperature gradient, and medium pressure or rpm
increases. It is worth considering that there is a thermal resistance to exceed
both in the fluid heating and cooling, with which it is heated and cooled less
than it should.
The internal sizing of the engine was performed through two procedures:
i) by means of software simulations and ii) by means of theoretical
approximations. In the first case, SNAPpro software Stirling Numerical
Analysis Program Pro Version 2.0 © by Alan Altman (which belongs to the
INENCO) was used to make of output power simulations modifying any of
the design parameters. In the second case, Schmidt Theory was applied. This
theory is an isothermal calculation method based on the expansion and
isothermal compression of an ideal gas. Though this analysis has limitations,
it can offer an estimation of fundamental parameters of the engine, such as
the cylinder diameter, rotation power and frequency in a preliminary design.
The sequence of steps taken for the prototype building, once the design
and sizing stages were performed, can be summarized as follows: cylinder
Biomass energy conversion technology 21
selection and acquisition with cooling fins for a type beta SE; piston and
cylinder burner selection and acquisition; sheets cut and adjustment of
dimensions; cylinder assembly in fixed base with burner; welding and
bolting; cylinder welding; crankshaft, connecting-rods and cranks
acquisition; crankshaft assembly and test; steering wheel acquisition and
rotary mechanism with crankshaft assembly; control of stroke and
displacement; crankshaft adjustment; adequacy of the working piston; pieces
assembly, engine assembly and putting in functioning from blowpipe.
The engine (Fig.3) consists of: i) a cylinder with cooling fins of a Deutz
of four hoops diesel 913 engine. The cooling fins size 103 mm of length; ii)
cylinder burner (warm area) made in common steel of 1.330 cm3; iii) a piston
corresponding to the cylinder Deutz, of cast iron. Piston and displacing move
in the same cylinder; iv) a displacing placed in an angle of 60 º with regards
to the piston made in sheet of bronze of 1mm; v) connecting-rods, cranks,
crankshaft and steering wheel; vi) external structure with 4 spikes and bolts,
that allows to assure the firmness of assembly of the different parts. There is
a space of 0.02 mm of work between the piston and the cylinder. The piston
was connected to the crankshaft by two bars of duraluminium. Between the
displacing and the cylinder there was a space of 0.5 mm left for the flow of the
Figure 3. Prototype Stirling in full functioning.
Silvina M. Manrique & Judith Franco 22
working fluid. The cylinder interior was done with a rectifying quality finish
and polished. The caloric energy obtained from biomass will be turned into
electric power by means of the engine and an alternator that will be annexed
for the subsequent batteries load in future projects. The main technical
specifications of the prototype built are summarized in Table 4.
Once the engine functioning testing was performed, some building basic
aspects had to be considered: to prevent the displacer from touching the
engine top or low face; to reduce dead volumes as much as possible; to keep
rubbing to a minimum and to balance mobile components, since the gravity
force on the displacer is more or less similar to the force that originates the
piston, and until a good balance is achieved, it is hard to start the engine. The
option at the moment of testing the newly built engine was to work under
atmospheric pressure, to the extent that it did not imply much complexity on
the preliminary prototype. Thermally, for the first tests, the necessary heat for
the engine functioning was obtained through a blowpipe available at the
mechanical workshop. The maximum temperature that was achieved was of
180 ºC in an end of the cylinder burner, for which temperature was being lost
rapidly and the engine stopped.
Some adjustments were made in the connecting-rods and the crankshaft,
as well as in the unions with the piston. The piston stroke was adjusted
depending on what was being observed. The tests used air as working fluid
for temperatures of about between 170 and 200 ºC. It was achieved that even
with low initial temperature- about 250ºC-, the engine kept working. As the
Table 4. Stirling prototype data.
Prototype characteristics
Configuration Beta
Piston stroke 5 cm
Diameter of the piston 10 cm
Space between displacing and cylinder 0.02 mm
Displacement volume 678 cm3
Angle Phase 60º
Relation of compression 1.65
Working Fluid Air
Cooling System Air
Pressure average of work Atmospheric
Nominal speed 200 rpm
Maximum power of the axis 33 W
Biomass energy conversion technology 23
temperature increases speed and engine power also increase. A combustion
boiler was attached to the engine (planning to use solid biomass for its start in
the future). The cylinder burner, across a receptacle of ceramic detachable
fiber, remained perfectly assembled inside the output pipe of combustion
gases (of the boiler). Though boiler and engine work correctly separately,
when they are fitted together, it can be observed that there is as gap between
them causing heat loss and not allowing the engine to start. It was decided to
work on the improvement and testing of the engine when it was checked that
the boiler worked. The leaks were inspected. The rod or backbone of the
linear movement was replaced by one of stainless steel and it was molded to
achieve an acceptable lace for the piston orifice. A new arm was made to 90º
since the previous one showed a hammering with the cylinder sleeve, besides
of a slight twist, which was generating a horizontal displacement in the rod of
the cylinder displacer, causing a possible braking. After the tests and
observing the slow functioning of the engine, it was checked the top and
bottom rings (of retention and carbon, respectively) of the piston (minor
opening to 1 mm), making a new lubrication of the mechanism and rings. The
lubrication of the engine mobile elements is the condition for it to have a long
useful life. Only free piston engines can work without lubrication, since they
take advantage of the same wording gas as lubricating. In this prototype, the
lubrication is done manually, although it is thought in a simple drip
lubrication system by gravity for the top mechanism. For the piston, a dry
system by Teflon rings or using oil-impregnated shutters are possible
solutions. New evidence showed the engine flywheel inertia generated was
not sufficient for operation. We chose to replace the wheel. Finally, two
different wheels were secured and shaped in cast iron, achieving an
approximate weight of 12 kg. Joining bushings were adjusted and the wheel
was assembled. With all the settings, we observed an improvement in engine
speed from 100 to 200 rpm approximately. The different possibilities of
compressing the air within the cylinder to increase the pressure (the projected
pressure is of about 1 Mpa) began to be evaluated. This stage is still in
evaluation.
Unlike the ICE, the SE needs a warming period, and only when this
period is over can the engine start. After the warming, and with a small
manual impulse, the engine works correctly. It is observed that it is really
silent and there are no leaks of smokes. On the other hand, when the heat
source stops, the engine continues working until the temperature diminishes
even up to 90ºC approximately. It can be observed that the maximum power
that can be achieved by the engine is still low, showing the need to check two
central aspects: to increase the cylinder capacity or to diminish the piston
stroke, in order to increase the number of rpm, speed and power. Aspects of
Silvina M. Manrique & Judith Franco 24
driving and heat transfer must be improved in the assembling of the boiler
and the engine. The cold source could possibly be isolated in greater
measure, incorporating, perhaps, a water sleeve. The obtained power values
will be quickly improved when the assembly of the air pump, currently in
design process, is achieved. Some authors have mentioned that in order to
achieve speeds rotations to 3,000 rpm it is necessary to supply heat to
temperatures close to 720ºC. The steering wheel of inertia might be improved
with a system of counterweights and/or to replace it for one that is bigger in
weight and size. In the case of the piston rings, though they retain the oil
since they are not in direct contact with the flame, they should be checked
from time to time and lubricated or be replaced definitively by Teflon rings.
It is being evaluated to work with a dynamo that is not so demanding in
power, for battery load since it can work even if the its load absolutely zero.
Further studies will have to evaluate the following aspects: power, work
pressure, speed, temperature differences, lubrication.
5. Conclusion
The engine built can, in principle, work with any type of available fuel,
which will allow for the future possibility of providing electricity to small
rural communities based on biomass resources. From the technical point of
view, although it has been achieved low output power and efficiency in the
Stirling engine prototype type beta, it is perfectly functional and it has
allowed to survey key parameters of its design and operation. On the other
hand, it has been possible to design and build locally, and with a work
methodology of our own. Future aspects of performance, operation
improvements and working guidelines have been mentioned.
As preliminary conclusions we mention that the SE works, it is of simple
operation, the mechanisms can be composed by commercial available pieces;
it is silent and presents scanty vibrations. It is possible to adapt it to the
employment from residual available biomass. The costs of operation are
relatively low, the toxic emissions are practically void and they only come
from the heat source. On the other hand, the engine assembly to a boiler is
simple. In addition, different devices might be used as heat sources (gasifiers,
boilers of major size, etc.). The materials used in all the cases are those
available at the lowest price and at local reach. A cost analysis will be able to
be performed in future experiences, offering the possibility of estimating its
profitability. It must be considered that the manufacture of a prototype raises
the costs, because it utilizes pieces that are not made of series, and therefore
the components must be made according to the measure of the selected
design. In spite of that, the engine power and the efficiency are still limited,
Biomass energy conversion technology 25
the successful results and the acquired experience will be the basis for its
optimization and later development of a final viable product. The application
of this project to a major scale might involve benefits in the environment as
in the life quality of rural communities, particularly of Lerma Valley, which
has available biomass supply.
Acknowledgements
The authors are grateful to Ricardo Echazú, José Alcorta, Vicente
Morillo, Aldo Nioi, Gerardo Figueroa, and Francisco Borrazás for their
valuable collaboration and technical contributions in the different stages of
the experimental developed project. This work was supported by the Project
INNOVA-T N º E655/07/BIS 2 PET 30, of the Energy Program and
Transport Commission, of the Subsecretary of Studies and Prospective of the
Secretariat of Planning and Policies in Science of the Department of Science,
Technology and Productive Innovation. The counterparts were INENCO
(Non Conventional Energy Resources Investigation Institute), IRNED
(Natural Resources and Ecodevelopment Institute), INTA (National Institute
in Agricultural Technology) and the Municipality of Coronel Moldes.
Likewise, CONICET (National Council of Scientific and Technical
Researches) offered the economic support by means of a Doctoral
scholarship. The students of Engineering in Natural Resources and
Environment of UNSa are greatly acknowledged for their collaboration.
Thanks are also due to the professionals, experts and each one of the people
consulted and linked with this work, for their valuable contribution and
participation.
References
1. Young, H.D. and Freedman, R.A. 2009. Física Universitaria. Volumen 1.
Editorial Addison-Wesley 12va Edición. ISBN: 9786074422887.
2. Resnick, R., Halliday, D., Krane, K. 2008. Física Volumen 2. 5ta. Edición. Grupo
Editorial Patria. México.
3. González Longatt, F. 2004. Tecnologías de generación distribuida: costos y
eficiencia. Unexpo, Puerto Ordaz. www.fglongatt.org/Articulos/A2004-07.pdf.
4. MNRC (Minister of Natural Resources Canada).2009. Clean Energy Project
Analysis: Retscreen® Engineering and Cases Textbook. ISBN: 0-662-39191-8.
M39-112/2005E-PDF.
5. Dewulf, J., Bosch, M.E., Meester, B.D., Vorst, G.V.d., et al. 2007. Cumulative
Exergy Extraction from the Natural Environment (CEENE): a comprehensive
Life Cycle Impact Assessment method for resource accounting. Environ Sci
Technol 41, 8477.
Silvina M. Manrique & Judith Franco 26
6. Dincer, I. and Rosen, M.A. 1998. A worldwide perspective on energy,
environment and sustainable development. Int J Energy Research 22, 1305-1321.
7. Hammond, G.P. 2004. Towards sustainability: energy efficiency, thermodynamic
analysis, and the ‗two cultures‘. Energy Policy 32, 1789-1798.
8. Hanley, N., McGregor, P.G., Swales, J.K., Turner, K. 2009. Do increases in
energy efficiency improve environmental quality and sustainability? Ecol Econ
68: 692.
9. SAyDS (Secretaría de Ambiente y Desarrollo Sustentable). 2009.
www.ambiente.gov.ar. Accesed 20 February 2013.
10. SAyDS (de Ambiente y Desarrollo Sustentable). 2012. Estudio de Mitigación de
emisiones mediante medidas de Eficiencia Energética. Fundación Bariloche E
Instituto De Estudios Del Hábitat (UN La Plata). www.ambiente.gov.ar/
cambio_climatico.
11. Bassam, N. 2001. Renewable energy for rural communities. Renewable Energy
24, 401.
12. Evans, A., Strezov, V., Evans, T. 2009. Assessment of sustainability indicators
for renewable energy technologies. Renew Sust Energy Rev 13, 1082.
13. Wohlgemuth, N. and Missfeldt, F. 2000. The Kyoto Mechanisms and the
prospects for renewable energy technologies. Solar Energy 69 (4), 305.
14. Kishore, V.V.N., Bhandari, M., Gupta, P. 2004. Biomass energy technologies for
rural infrastructure and village power—opportunities and challenges in the
context of global climate change concerns. Energy Policy 32, 801.
15. Singal, S.K., Varun, R., Singh, P. 2007. Rural electrification of a remote island
by renewable energy sources. Renewable Energy 32, 2491.
16. Varun, I., Bhat, K., Prakash, R. 2009. LCA of renewable energy for electricity
generation systems—A review. Renew Sust Energy Rev 13, 1067.
17. REN21 (Renewable Energy Network for the 21st Century). 2008. Renewables
2007 Global Status Report. Paris: REN21. Washington, DC. GTZ.
18. UNDP (Nations United Program Development). 2009. Handbook for Conducting
Technology Needs Assessment for Climate Change. New York, USA.
19. Chandrasekaran, K. and Simon, S.P. 2013. Development of sustainable energy on
generation system leads to eco-friendly society. Sustain Cities Society 8: 1.
20. Tsoutsos, T.D. and Stamboulis, Y.A. 2005. The sustainable diffusion of
renewable energy technologies as an example of an innovation-focused policy.
Technovation 25:753.
21. Pehnt, M. 2006. Dynamic life cycle assessment (LCA) of renewable energy
technologies. Renewable Energy 31: 55-71.
22. Lay, C.H., Sena, W., Huang, S.C., Chend, C.C., Lina, C.Y. 2013. Sustainable
bioenergy production from tofu-processing wastewater by anaerobic hydrogen
fermentation for onsite energy recovery. Renewable Energy 58: 60.
23. Khatib, H. 2004. Energy Permanent Monitoring Panel of the world Federation of
Sciences. Energy Considerations. Global Warming Perspectives. Erice. Sicily.
24. EUROBSERV‘ER. 2012. Solid biomass barometer. Le journal des énergies
renouvelables N° 212.
Biomass energy conversion technology 27
25. Zhang, F. y Cooke, P. (2009), Global and regional development of renewable
energy, Working paper for research project ―Green innovation and
entrepreneurship in Europe‖ http://www.dimeeu.org/working-papers/sal3-green.
26. Demirbas, A. 2006. Biomass gasification for power generation in Turkey. Energy
Sources 28,433.
27. IEA (International Energy Agency). 2007. Biomass for power generation and
CHP. IEA energy technology essentials. Paris: OECD/IEA.
28. Ahrenfeldt, J., Thomsen, T.P., Henriksen, U., Clausen, L.R. 2012. Biomass
gasification cogeneration: A review of state of the art technology and near future
perspectives. Applied Thermal Engineering 50, 1407.
29. EPA (US Environmental Protection Agency). 2011. Landfill Methane Outreach
Program. http://www.epa.gov/lmop, viewed 25 April 2013.
30. Chen, X., Wu, Y.N., Zhang, H., Chen, N. 2009. Study on the phase shift
characteristic of the pneumatic Stirling cryocooler. Cryogenics 49, 120.
31. Larsen, H., Kossmann, J., Petersen, L.S.2003. New and emerging bioenergy
Technologies. Risø Energy Report 2. Risø National Laboratory. 48 p.
32. RFP. 2011. Palo Alto Issues Renewable Power RFP. http://www.
electricenergyonline.com/?page=show_ news&rss=1&id=160960.
33. NYC Global Partners. 2011. Best Practice: Promoting Solar Energy. http://www.
nyc.gov/html/unccp/ gprb/downloads/pdf/Barcelona_SolarEnergy.pdf.
34. Secretaría de Energía de la Nación. Balance Energético Nacional 2010.
www.energia3.mecon.gov.ar/.
35. FAO (Food and Agricultural Organization) (2009). Análisis del Balance de
Energía derivada de Biomasa en Argentina - WISDOM Argentina-Informe Final.
Departamento Forestal Dendroenergía. TCP/ARG/3103. 118 p.
36. Grassi, L. 2012. Relevamiento de proyectos bioenergéticos en Argentina.
Financiado por: PROBIOMASA – UTF/ARG/020/ARG. energia3.mecon.gov.ar/
contenidos/verpagina.php?idpagina=3682.
37. Probiomasa. 2012. Programa de promoción de bioenergía derivada de biomasa.
Secretaría de Energía de la Nación. energia3.mecon.gov.ar/contenidos/
verpagina.php?idpagina=3682. Accesed 17 march 2013.
38. Bondolich, C.V. 2012. Un marco regulatorio integral como el principal desafío
para el fomento y desarrollo de la industria de las energías renovables. INTA. Bs
As.
39. Fuchs, S.H. 2012. El sector de generación de energía solar en Argentina.
Oportunidades y amenaza para las inversiones extranjeras. Graduación del
MBA. Universidad de San Andrés. Buenos Aires.
40. James, C. 2012. The Clean Energy Report: Estado de la industria argentina de
energías renovables. Santiago y Sinclair, Buenos Aires. Argentina.
41. Sarandón, S.J and Iermanó, M.J. 2005a. Sustainability of the Production of
Biodiesel as an alternative fuel In Argentine Republic. III Congreso Brasileiro de
Agroecología, Florianópolis, SC, Brasil. 25, 4pp.
42. Sarandón, S.J. and Iermanó, M.J. 2005b. Energetyc Efficiency of Biodiesel
Production from different oil crops: An Agroecological Analysis. III Congreso
Brasileiro de Agroecología, Florianópolis, SC, Brasil. 601, 4pp.
Silvina M. Manrique & Judith Franco 28
43. Salomon, O.D., Orellano, P.W., Quintana, M.G., Perez, S., Sosa, E.S., Acardi, S.
y Lamfri, M. (2006). Transmisión de la Leishmaniasis Tegumentaria en la
Argentina. Medicina 66, 211-219. Buenos Aires.
44. Seijo, A. 2008. Boletín de temas de salud de la Asociación de Médicos
Municipales de la Ciudad de Buenos Aires. Suplemento del Diario del Mundo
Hospitalario, Año 15 (138). http://www.medicos-municipales.org.ar/bts0708. htm.
45. Van Dam, J., Faaij, A.P.C., Hilbert, J., Petruzzi, H., et al. 2009. Large-scale
bioenergy production from soybeans and switchgrass in Argentina.
Environmental and socio-economic impacts on a regional level. Renew Sust
Energy Rev 13, 1679.
46. Panichelli, L., Dauriat, A. y Gnansounou, E. 2009. Life cycle assessment of
soybean- based biodiesel in Argentina for export. Int J Life Cycle Assess 14,144.
47. Rodriguez, A.M. and Jacobo, E.J. 2010. Glyphosate effects on floristic
composition and species diversity in the Flooding Pampa grassland (Argentina).
Agriculture, Ecosystems and Environment 138 (3): 222.
48. Semino, S. (2008). Can certification stop high soy pesticide use? Pesticide News
82, 9-11.
49. Tomei, J. and Upham, P. 2009. Argentinean soy-based biodiesel: an introduction
to production and impacts. Tyndall Working Paper no.133. /http://tyndall.ac.uk/
publications/working_papers/twp133.pdfS.
50. Gnansounou, E. 2011. Assessing the sustainability of biofuels: A logic-based
model. Energy 36: 2089-2096.
51. Duarte, C.G., Gaudreau, K., Gibson, R.B., Malheirosa,T.F. 2013. Sustainability
assessment of sugarcane-ethanol production in Brazil: A case study of a
sugarcane mill in São Paulo state. Ecol Indicat 30:119-129.
52. GENREN (Programa de Generación de energía eléctrica a partir de fuentes
renovables). 2007. Argentina. http://energia3.mecon.gov.ar/contenidos/
verpagina.php?idpagina=3065.
53. Manrique, S.M., Franco, J., Seghezzo, L., Núñez, V. 2013. Biomass feedstock
availability for the supply of bioenergy in Lerma Valley (Salta, Argentina):
potential, limitations, perspectives. In press.
54. Cabrera, A. 1994. Enciclopedia Argentina de Agricultura y Jardinería. Primera
Reimpresión. Editorial Acme S.A.C.I. Tomo II (1). Buenos Aires.
55. Núñez V, Moreno R, Menéndez M, et al. 2007. Ordenación territorial del Valle
de Lerma. Parte II: Pautas para la planificación, Proyecto 1345. Argentina:
Consejo de Investigación de la Universidad Nacional de Salta.
56. Bianchi, A.R. and Yáñez, C.E. 1992. Las precipitaciones en el noroeste
argentino. INTA. Salta. Argentina.
57. SCS Engineers. 1997. Comparative analysis of landfill gas utilization
technologies. Northeast Regional Biomass Program. Coneg Policy Research
Center, Inc. Washington, D.C. File No. 0293066.
58. Daskalopoulos, E., Badr, O., Probert, S.D. 1998. An integrated approach to
municipal solid waste management. Res, Conservation and Recycling 24, 33.
Biomass energy conversion technology 29
59. Quaak, P., Knoef, H., Stassen, H. 1999. Energy from biomass: a review of
combustion and gasification technologies. World Bank technical paper 422.
Energy series.
60. Sondreal, E.A., Benson, S.A., Hurley, J.P., Mann, M.D., et al. 2001. Review of
advances in combustion technology and biomass cofiring. Fuel Processing
Technology 71, 17.
61. Bove, R. and Lunghi, P. 2006. Electric power generation from landfill gas using
traditional and innovative Technologies. Energy Conv and Manag 47, 1391.
62. Khoo, H.H. 2009. Life cycle impact assessment of various waste conversion
technologies. Waste Management 29, 1892.
63. Huang, K. and Singhal, S.C. 2013. Cathode-supported tubular solid oxide fuel
cell technology: A critical review. J Power Sources 237, 84.
64. Yanovskiy, L.S. and Baykov, A.V. 2013. New prospects for ecologically clean
power and pure water generation units with SOFC. Renewable Energy 56: 72.
65. Zmudzki, S. and Lipa, K. 2000. Design and preliminary results of investigations
of the experimental Stirling Engine SEPS-1. Journal of Kones. Internal
Combustion Engines 7 (1-2), 547.
66. SOLO Stirling Engine. 2002. Technical Documentacion. CD.Best.No:990416102.
Sindelfingen, Germany.
67. Karabulut, H., Aksoy, F., Ozturk, E. 2009a. Thermodynamic analysis of a b type
Stirling engine with a displacer driving mechanism by means of a lever.
Renewable Energy 34, 202.
68. Parlak, N., Wagner, A., Elsner, M., Soyhan, H.S. 2009. Thermodynamic analysis
of a gamma type Stirling engine in non-ideal adiabatic conditions. Renewable
Energy 34, 266.
69. Kongtragool, B. and Wongwises, S. 2007. Performance of low-temperature
differential Stirling engines. Renewable Energy 32, 547.
70. Cinar, C., Yucesu, S., Topgul, T., Okur, M. 2005. Beta-type Stirling engine
operating at atmospheric pressure. Applied Energy 81, 351.
71. Flórez, J.A. and Agramunt, I.C. Ed. 2002. Máquinas térmicas motoras 1.
Ediciones UPC. Barcelona. 260 p.
72. Abdullah, S., Yousif, B.F., Sopian, K. 2005. Design consideration of low
temperature differential double-acting Stirling engine for solar application.
Technical Note. Renewable Energy 30, 1923.
73. Tlili, I., Timoumi, Y., Nasrallah, S.B. 2008. Analysis and design consideration of
mean temperature differential Stirling engine for solar application. Renewable
Energy 33, 1911.
74. Timoumi, Y., Tlili, I., Nasrallah, S.B. 2008. Design and performance
optimization of GPU-3 Stirling engines. Rev Energy 33, 1100.
75. Saravia, L., De Saravia, D.A., Echazú, R., Alcorta, G. 2007. La simulación de
sistemas termomecánicos solares con el programa SIMUSOL, el motor Stirling:
simulación y construcción. AVERMA 11. Argentina. ISSN 0329-5184.
76. Obara, S.; Tanno, I.; Kito, S.; Hoshi, A., S. Sasaki. 2008. Exergy analysis of the
woody biomass Stirling engine and PEM-FC combined system with exhaust heat
reforming. Int J Hydrogen Energy 33: 2289.
Silvina M. Manrique & Judith Franco 30
77. Palsson, M. and Carlsen, H. 2003. Development of de wood powder fuelled 35
kW Striling CHP unit. In: Proceedings of the 11th International Stirling Engine
Conference, pages: 7pp. University of Rome. http://www.vok.lth.se/~ce/
Research/stirling/papers/ST_TA2_5.pdf.
78. Onovwiona, H.I.; Ugursal, V.I., A.S.Fung. 2007. Modeling of internal
combustion engine based cogeneration systems for residential applications.
Applied Thermal Engineering 27, 848.
79. Nishiyama, A., Shimojima, H., Ishikawa, A., Itaya, Y., et al. 2007. Fuel and
emissions properties of Stirling engine operated with wood powder. Fuel 86, 2333.
80. Wang, J.J., Jing, Y.Y., Zhang, C.F., Shi, G.H., et al. 2008. A fuzzy multi-criteria
decision-making model for trigeneration system. Energy Policy 36, 3823.
81. Conroy, G., Duffy, A., Ayompe, L.M. 2013. Validated dynamic energy model for
a Stirling engine -CHP unit using field trial data from a domestic dwelling.
Energy and Buildings 62, 18.
82. Tavakolpour, A.R., Zomorodiana, A., Golneshan, A.A. 2008. Simulation,
construction and testing of a two-cylinder solar Stirling engine powered by a flat-
plate solar collector without regenerator. Renewable Energy 33, 77.
83. Scollo, L., Valdez, P., Baron, J. 2008. Design and construction of a Stirling
engine prototype. Int J Hydrogen Energy 33, 3506.
84. Podesser, E. 1999. Electricity Production in Rural Villages with a Biomass
Stirling Engine. Renewable Energy 16, 1049.
85. Barros, R.W., Aradas, M.E.C., Cobas, V.R.M., Silva Lora, E.E. 2004. Uso de
biomassa como combustível para acionamento de motores Stirling. In: Agrener,
Campinas.
http://www.feagri.unicamp.br/energia/agre2004/Fscommand/PDF/Agrener/Traba
lho%2032.pdf.
86. Corria, M.E., Cobas, V.M., Silva Lora, E. 2006. Perspectives of Stirling engines
use for distributed generation in Brazil. Energy Policy 34, 3402.
87. Lira Cacho, J.G. and Aguero Zamora, V.R. 2007. Generación de energía eléctrica
con un motor Stirling empleando un combustible gaseoso. 8º Congresso
Iberoamericano de Engenharia Mecanica. Cusco.
88. Karabulut, H., Yücesu, H.S., Çınar, C., Aksoy, F. 2009b. An experimental study
on the development of a b-type Stirling engine for low and moderate temperature
heat sources. Applied Energy 86, 68.
89. Boucher, J., Lanzetta, F., Nika, P. 2007. Optimization of a dual free piston
Stirling engine. Applied Thermal Engineering 27, 802.
90. Kyei-Manu, F. and Obodoako, A. 2006. Design and Development of a Liquid
Piston Stirling Engine . Senior Design Project .http://www.engin.swarthmore.
edu/academics/courses/e90/2005_6/E90Reports/FK_AO_Final.pdf
91. Andersen, S.K., Carlsen, H., Thomsen, P.G. 2006. Numerical study on optimal
Stirling engine regenerator matrix designs taking into account the effects of
matrix temperature oscillations. Energy Conv Manag 47, 894.
92. Dhar, M. 1999. Stirling Space Engine Program. NASA / CR--1999-
209164/VOL1. Mechanical Technology Inc., Latham, New York. National
Aeronautics and Space Administration. Glenn Research Center.
Biomass energy conversion technology 31
93. Clucas, D.M. and Raine, J.K. 1994. Development of a hermetically sealed
Stirling Enghien battery charger. J Mech Engineering Science 208, 357.
94. Kuosa, M., Kaikko, J., Koskelainen, L. 2007. The impact of heat exchanger
fouling on the optimum operation and maintenance of the Stirling engine.
Applied Thermal Engineering 27, 1671.
95. Dyson, R.W., Wilson, S.D., Tew, R.C., Demko, R. 2005. Fast Whole-Engine
Stirling Analysis. AIAA–2005–5558. NASA/TM—2005-213960.
96. Rogdakis, E.D., Bormpilas, N.A., Koniakos, I.K. 2004. A thermodynamic study
for the optimization of stable operation of free piston Stirling engines. Energy
Conv Manag 45, 575.
97. Altman, A. 2000. Programa SNAP pro. Guide for the utilization of the software.
98. Hsieh, Y.C., Hsu, T.C., Chiou, J.S. 2008. Integration of a free-piston Stirling
engine and a moving grate incinerator. Renewable Energy 33, 48.
99. Roman, R. 2007. Conceptos Básicos para Diseño de motor Stirling con baja
diferencia de temperatura. Departamento de Ingeniería Mecánica. Universidad de
Chile La cita 100 se agrega a continuación.
100. Cervantes, J. 2007. Metodología para el rediseño de motores de ciclo Stirling.
Tesis de Maestría. Instituto Politécnico Nacional. Escuela Superior de Ingeniería
Mecánica y Eléctrica. México, D.F.
BIOMASS CONVERSION TECHNOLOGY FOR RENEWABLE
ENERGY GENERATION: ANALYSIS, SELECTION
AND TESTING
AUTHORS
SILVINA M. MANRIQUE JUDITH FRANCO
AUTHORS
SILVINA M. MANRIQUE JUDITH FRANCO
AUTHORS
SILVINA M. MANRIQUE JUDITH FRANCO
AUTHORS
SILVINA M. MANRIQUE JUDITH FRANCO
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BIOMASS CONVERSION TECHNOLOGY FOR RENEWABLE
ENERGY GENERATION: ANALYSIS, SELECTION
AND TESTING
BIOMASS CONVERSION TECHNOLOGY FOR RENEWABLE
ENERGY GENERATION: ANALYSIS, SELECTION
AND TESTING
BIOMASS CONVERSION TECHNOLOGY FOR RENEWABLE
ENERGY GENERATION: ANALYSIS, SELECTION
AND TESTING