IOMASS CONVERSION TECHNOLOGY FOR RENEWABLE ENERGY GENERATION B Tm

BIOMASS CONVERSION TECHNOLOGY FOR RENEWABLE

ENERGY GENERATION: ANALYSIS, SELECTION

AND TESTING

AUTHORS

SILVINA M. MANRIQUE JUDITH FRANCO

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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


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


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).


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


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).


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


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.


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.


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


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


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.


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


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).


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


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.


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


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.


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


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.


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


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


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,


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.

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IOMASS CONVERSION TECHNOLOGY FOR RENEWABLE ENERGY GENERATION B Tm

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