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Revista ingeniería de construcción

versión On-line ISSN 0718-5073

Rev. ing. constr. vol.26 no.2 Santiago ago. 2011

http://dx.doi.org/10.4067/S0718-50732011000200005 

Revista Ingeniería de Construcción Vol. 26 N°2, Agosto de 2011 www.ing.puc.cl/ric PAG. 208 - 223

 

lmproving energy efficiency on production of clay ceramic bricks using lignocellulosic-densified-material based biofuel

Mejora de la eficiencia energética de la producción de ladrillos de cerámica roja a partir del empleo como biocombustible de material lignocelulósico densificado

 

Iván Machado L.*1, José F. Martirena H.*, Idalberto Herrera M.*, Sergio Quiroz**, Maria Jesus Lamela R.**, Raúl Gonzalez L.*

* Universidad Central "Marta Abreu" de las Villas. CUBA.
** Escuela Politécnica Superior de Ingeniería de Gijón (EPSIG) Gijón. ESPAÑA.

Dirección para Correspondencia


ABSTRACT

This work presents some experiences in producing building materials, such as clay bricks, from an alternative energy source that replaces wood or firewood by waste lignocellulosic material submited to the process of densification under low pressure. The densification process at low pressure involves the use of a binder; this paper proposes the use of clay material as binder. The main objective of this study was to evaluate the effect in the consumption of biofuel during the production of handmade bricks, partially replacing wood by densified biomass. Some properties of the biofuel are identified to increase the bricks-to-fuel consumption ratio from 1.1 to 1.4. This improves the efficiency of the production process, reduces specific consumption regarding the use of traditional fuels with its consequent environmental improvement of the process.

Keywords: Eco-materials, bricks, biomass, densification.


 

1. Introduction

The use of agro-industrial process waste currently constitutes a significant source of energy for many Third World countries, however it has not yet reached a proper and consistent use of them as a source of alternative energy for the production of various building materials.

Densification of waste from various sources of biomass is an attractive option for enhancing and improving the properties of such wastes, as may be their lower costs for handling, transportation, storage, etc.. and it increases its calorific volume. (Jamradloedluk, 2005).

The Center for Research and Development of Structures and Construction Materials (CIDEM in Spanish), in collaboration with two other certified research centers, deals for the last five years with the recycling process and densification of wood residues. This is done by using low compaction pressures (up to 5 mega Pascals, MPa) and the use of particular clay material as binder, obtaining a solid agglomerated hereinafter called solid fuel block (BSC in Spanish) or more commonly briquettes, of obvious interest for their application in small industry of building materials (Martirena 2003, Gonzalez 2003).

The clay material is a viable and cheap binder in local ceramics environment, however it is necessary to clarify the effects generated in the physical-mechanical properties and physical-chemical ones of solid biofuel and its impact on the obtantion of fired red brick.

The paper presents the results of research and evaluation of the production of bricks in a typical kiln located in Manicaragua, province of Villa Clara, Cuba and the application of a methodology to implement partial replacement of logs of wood for clay conglomerate material - biomass reducing overall fuel consumption significantly without affecting the physical and mechanical parameters of the bricks.

Manicaragua municipality annual production of bricks reaches 280 000 units / year. Increasingly activity of individual producers of bricks in the zone involves a serious deforestation process, which could cause annually the destruction of about 11.5 ha of forest.

According to Curbelo, 2002, the annual volume of waste lumber in Cuba reaches 70,000 cubic meters. These wastes are used by poultry and swine industries, but sometimes do not have a specific occupation and cause unnecessary pollution in productive areas which are often burned without giving to the generated heat a rational use.

Previous studies were done to determine the availability of residues from wood treatment in Villa Clara. They identify as largest source the sawmills that produce over 75% of the sawdust produced in the region, providing it to local carpentry workshops and the rest as shown in Figure 1. (Gonzalez, 2004).

The sawmills annually evaluated generate about 280 m3 of waste in the form of sawdust, with an energy value of 378 GJ / year, which could be a significant energy potential for production of red ceramic or other applications in industries of local building materials.

A very important stage in bricks production occurs during the burning process in the oven. Almost all the energy is used there, existing a direct relationship between the thermal regime used and the desired properties of clay brick. Thermal regime depends on the level of operation of the oven and the characteristics of the fuel used, ensuring the required temperature profile in the furnace to achieve proper transformation of the clay material and a final product that meets quality specifications.

Increased current demand for wood used in the production of red ceramics in several developing countries has led to a gradual increase in deforestation (Betancourt, 2007), that is why to densify waste biomass could be an attractive option in order to facilitate the use of it as biofuel, in the manufacture of bricks and other ceramic products.

Figure 1. Clay and sawdust sources in Villa Clara, Cuba. Source: Machado 2002; Maps in micro mining

In general, primary and secondary waste processing wood, bagasse, cane straw, wheat, corn, rice and other wastes straw, are characterized by their low density and low calorific value per unit volume so they are inadecuated for direct combustion. (Bhattacharya, 2002).

An important feature of the solid fuel is its density. Different reports evaluate relaxed density of briquettes made with a low compaction pressure of 200 kg / m3 -700 kg / m3 (Jamradloedluk, 2005; Faxälv, 2007). Given the extent of limits adopted by density in front of several factors, it is accepted as part of this work, 450 kg/m3 as densified briquettes minimum value for the technological proposed process.

2. Materials and methods

Waste generated at the mills of this research have a similar particle size distribution, where the sawdust collected randomly shows that the largest fraction of particles is below 2.5 mm in 85% of the analyzed material, however during the management of loose material for the preparation of samples, the screening of material is performed excluding only particles larger than 5 mm. In order to facilitate a greater use of available waste retained material, it is crushed in a hammer mill and sieved through the opening set for that purpose.

Chemical analysis of raw materials for agglomerate obtaintion shows the absence of heavy metals traces or other elements which may be environmental harmful during biomass combustion process.

Clay material is obtained from different sources to ensure diversity of properties, allowing to assess its effect on the stability of the mixture obtained when biomass is added and subjected to low pressure.

Clay material is diluted in water and mixed with biomass in different proportions (10-90, 20-80, 30-70). Then using a universal mechanical testing press ZD-40 with capacity of 500 KN it is compacted in a cylindrical metal mold of length and diameter of 150 mm, also achieving a longitudinal opening in the center block 25 mm in diameter.

Density of briquettes is calculated from average measurements of their size and weight, using caliper and precision digital balance 0.001grs. In the density analysis of briquettes or solid blocks are used the recommendations of the ASAE S269.4. Standard.

Density ratio (DR) has an inverse relationship with respect to density and can assess the stability of the compression process - relaxation of the agglomerated material is obtained from measurements of the variation in the dimensions of briquette and its weight as a result of moisture loss.

Is established through methods of analysis of association among functional variables of some parameters involved in the densification process, while calculating the specific combustion heat (CEC in Spanish) was done according to the percent constituent of chemical elements obtained by elemental and immediate analysis, characterizing samples in terms of moisture, volatiles, fixed carbon and ash, applying Dulong - Berthelot equation (Cukierman 1996).

For the analysis of the burning time or burning ratio (BR) of briquettes made of sawdust at low pressure and clay as aglomerate, a fractional experimental design is produced (DFF in Spanish) where moisture has a significant influence on the specific heat combustion. Also assesses the binder content since, according to Chin (2000), this factor can be modified with high incidence on fuel properties.

To determine the burning time it is implemented a low-temperature combustor (efficient kitchen) with a flue gas analyzer RBR type - ECOM - SG PLUS. The briquettes are entered and the time of ignition of volatile compounds checked, which emit a bright blue flame around the briquette and from the center hole. The evolution of the process is confirmed through the gas analyzer once firing is considered completed and when the remaining solid combustion does not emit the characteristic red glow of burning material and temperature of gas flow invariably begins to sharply decrease.

On the other hand are taken at random three briquettes according to designed treatment. They are placed in a muffle type LH 30/14, Nabertherm, to 500 C for 2 minutes in order to achieve oxidation of solid biofuel, and after assessing the weights difference, combustion efficiency is determine.

Biofuel energy efficiency is related to the complete oxidation and use of heat, so the increase is associated with a decrease in losses, thereby restricting the rate of specific consumption and enabling a consistent environmental improvement process. As a method for efficiency estimation of production of red ceramic bricks, different successive fires are made, which partially replace the wood by the BSC, verifying the specific consumption of densified biofuels, variations in temperature and, as a result, physical mechanical properties of ceramic brick.

3. Development

Relaxed density (RD) and density ratio (DR)

Final density of briquettes depends on several factors including the relationship between the magnitude of compression pressure and stretching or relaxation of material, the initial physical properties of the lignocellulosic material and characteristics of the agglomeration process (pressure, time, nature and percentage of binder content, etc.).

Upon estimating the functional model parameters that relate the relaxed density with the following factors: pressure (1-5 MPa), moisture (water quantity 1-2.5 L / biomass kg), pressing time (15 - 60 seconds) contained binder (10 - 30 percent) and activity of the clay binder, the latter defined by the relationship between plasticity and clay content, assesses the significance level and simplification of model taking from the analysis the less explanatory factors.

The split design of experiments (DFF= 2(5-1)), carried out taking into account the binder content (CA) from the high-activity clay material from Manicaragua municipality determines an average of 596 kg / m3 relaxed density for sample treatments defined by the relationship between factors and levels involved.

Density ratio is defined by Chin, 2000 as ((DH-DR) / DH), where DH is the initial density or the wet one and DR is the final density or the relaxed one.

Figure 2 plots the curve of percentage value of the density ratio versus pressure applied upon varying the activity of the clay material, assuming the same binder content (20%) and humidity (H = 1.7 water liters / sawdust kg) by mixing biomass with different clay materials with structural and physical properties that determine their activity values (high, medium and low).

This confirms the decrease of relaxation with increasing compaction pressure and the tendency to decrease the RD according to the increased activity of the binder.

The values found for the relationship of density go from 17 to 45%, the results correspond to a multiple linear regression model that describes the relationship between RD and 3 independent variables with an inverse relation with the controlled factors. The equation of the model takes the following form:

(1)

Since the p-value in the ANOVA table is less than 0.01, statistically significant relationship exists between the variables for a confidence level of a 99%. R-square statistic indicates that the model explains 87% of the variability in RD, where RD is the density ratio in percentage, P the applied pressure in MPa, while CA is the content of clay binder and AA the degree or activity level of the binder.

Specific Heat of combustion (CEC in Spanish)

In order to determine the influence of manufacturing parameters of densified solid on the value of CEC multiple regression analysis is used, considering factors or variables involved in the process.

Figure 2. RD percentage value as a function of applied pressure and binding agent activity

Low-density briquettes show dependency between CEC of the material and manufacturing process technology. Faxalv (2007) has confirm how sawdust and paper briquettes reach a CEC between 16.2 - 18.1 MJ / kg depending on the binder content and the technological process. According to González (2003) sugarcane straw briquettes achieve a caloric power of 17.87 MJ / kg. However, Martirena (1999), reported 15 MJ / kg. by thermal analysis, which apparently takes into account the level of impact caused by the addition of inorganic binder.

Since the average result of calculations of the specific heat of combustion, it is possible to determine the relationship of the same factors involved. The analysis of adjusting to a multiple linear regression model is given by the experiment design considering the following factors: humidity, pressure, compression time (dwell time) of biomass and binder content (CA) in high and low levels.

The results of the model describes the relationship between CEC and 2 independent variables in the conditions of application of low pressure and the addition of clay binder. The equation of the fitted model takes the following form:

(2)

Since the p-value in the ANOVA table is less than 0.01, statistically significant relationship exists between the variables for a confidence level of 99%. R-square statistic indicates that the model explains 91% of the variability in [2] where CEC is the specific heat of combustion, expressed in MJ / Kg., H is moisture in liters of water L / sawdust kg. and CA is the binder content.

An inverse relationship is manifested between the specific heat of combustion, moisture and binder content. The ratio of the calorific value of densified biomass and moisture has been sufficiently addressed by the scientific community to confirm these results, as presented by Bhattacharya (2002) and others, apparently increasing the binder content produces in this case an effect equivalent to moisture.

Statistical analysis reveals that the pressure is not a statistically significant factor for a confidence level of 90% or more. Despite its low level of significance could be seen as increasing pressure is directly related to the CEC, which can be associated with increased density and probably the percentage of fixed carbon content in the block volume, which in its turn produces an increase in caloric volume, taking the average value of density and CEC may represent 10 590 MJ / m3

Combustion ratio (BR)

The burning ratio (burning rates), characterizes the rate at which the different phenomena occurr related to the oxidation process of lignocellulosic material. Chin (2000) and Cristofer (2006), discuss the importance of its determination since it is related to the necessary considerations for the design of combustion systems.

Figure 3 shows the test result, where it can be seen the value of the ratio of combustion in g / min. In front of density of each treatment arranged according to the experimental design matrix.

The results show the tendency of the rate of combustion taking values from 95 to 128 g / cm., in an inverse proportion to the density of briquette, showing how the binder content may slow down the oxidation process of lignocellulosic material by decreasing its interaction with oxygen.

Figure 3. Combustion ratio as a function of density and activity

These results are consistent with the theory, according Christofer, (2006), the variable of density can influence the burning rate by limiting the diffusion processes and interaction of the oxidizing material. Chin, 2002, states that briquettes burn time increases in proportion to the binder content and to pressing time. In the opinion of the author it may be associated with increased density and possible reduced interaction with oxygen, confirming the results presented.

Performance of biofuel

Fuel efficiency expresses the quality of energy carrier and the process of combustion, which can be defined as the ratio of total weight of sample and the weight of potentially combustible material, expressed in percent. (Assureira, 2002).

This parameter compares relative advantage of occurrence of combustion of briquettes produced under specific conditions, determining which conditions of manufacture and obtention facilitate combustion with respect to each other. From adaptation of several literature expressions, the following calculation can be proposed:

(3)

where:

η = performance;
PTot = Total briquette weight;
PRes = Weight residue;
PCb = Potentially combustible material weight;

PCb= ( PBiomasa - (1- % Shes)) + (Paglom * PPI/100)

Using multiple linear regression method assesses the level of significance of the factors involved, the time factor is not significant for a significance level of 95%. The results adjusted to a multiple linear regression model reveals the average combustion efficiency of sawdust agglomerated material + clay from the description of the relationship between performance and 3 independent variables, the equation of the fitted model is:

(4)

Since the p-value in the ANOVA Table is less than 0.01, statistically significant relationship exists between the variables for a confidence level of 99%. R-square statistic indicates that the model explains about 96% of the variability in performance.

The value of binder is introduced into several percentage and P in MPa.

The functional relationship explains the process where the binder content increases may limit product performance of the fireproofing material that binds clay biomass, which may contribute to the occurrence of unburned material, which shows a complete correspondence of the results of this work with theory.

However efficiency combustion values obtained are relatively high in the range of 92% - 98%. According

Assureira 2002, the combustion efficiency of briquettes made of rice straw obtained by applying low compaction energy can reach values at around 98%, which is comparable to the result obtained in briquettes of the present research.

According to the literature (Ortiz, 2005), the denser a solid biofuel longer it takes to burn and therefore the densified material shows a relative decrease in combustion.

This may correspond to a limited presence of oxygen inside the interconnected pores of densified biomass, which can enhance combustion and therefore the whole process is more difficult, this situation could be favorable for the productors of red ceramics, as in repeatedly traditional fuel (wood) is consumed rapidly or volatilized without allowing furnaces to heated sufficiently, declining in productivity and quality of the ceramic product.

Energy efficiency of biofuel

Energy efficiency of biofuels is related to various factors impacting on a better use of the generated heat, therefore its increase is associated with reduced losses to restrict specific consumption rates and the resulting environmental improvement (Rodríguez, 2000).

In Manicaragua municipality, province of Villa Clara, Cuba, Ramon Bernal Production Cooperative is an important center of production of red bricks.The center has a rustic oven capable of burning 3500-4000 bricks, the same is implemented with the computer analyzer flue gas (RBR-ECOM-SG PLUS), and check temperature variation in timing and content of the gaseous emissions through a pilot program where temperature variables are controlled as well as fire time and fuel load.

Substitution of wood by biofuel is produced in order to obtain temperature versus time curves and versus load for different processes or burning, first with 100% of fuelwood. It is obtained as a comparative approach of theoretical calculation of 100% replacement of wood by BSC maintaining maximum power consumption and the maximum decrease of fuel to achieve 50% energy efficiency. In second place it is produced the replacement of wood in around 30 -50% of the initial amount but remains energy consumption at the same level and eventually performs the reduction of gross energy consumption from the decrease in total fuel.

The decrease of total energy consumption is expected, ensuring temperature levels in a manner that enables transformation of clay (800-900 °C) from a fuel loading system at a rate of 300 kg / h.

Table 1 shows the characteristics of different woods that have been used for charging furnace in the comparative experiments conducted by this study.

Table 1. Immediate analysis results by wood type and BSC

Figure 4 shows experimental oven, which clearly identifies BSC and the flame from the combustion of the solid biofuel and volatile elements.

Figure 5 shows graphically the relationship of fuel versus temperature for different experimental burns and measurements taken during the burning process using the solid block. It is estimated as temperature curves versus load of solid block which reach values of steeper slopes in the case of the use of wood and also it can be seen an important difference in the combustion to achieve reduction of total fuel consumption in burning when used combustible solid block.

Figure 4. Furnace combustion detail, wood substitution by biofuel BSC

Figure 5. Temperature variation with cumulative load

In previous studies of the wood traditionally used and the BSC it is inferred that the contours can be influenced by higher moisture content of green wood which implies a higher initial consumption of heat in the oven, so that additional energy required to remove the moisture of wood causing a concomitant decrease in the temperature of gases.

Additionally this may also be related to the increased volume of gases to be used by the BSC as probably the products of the reactions of the components of the clay material and a higher coefficient of excess air, which improves the heat exchange between fire and the green bricks as well as the retarding effect on the combustion reactions that produces the density of BSC in connection with the content of clay material.

It is shown by the results of experimental burns as possible to reduce the total consumption of traditional fuel to a 15 -20% by weight of the current average value with the consequent improvement of up to 40% in the energy efficiency of the furnace to maintain the value proper temperature for the process to develop successfully without major modifications to existing technology.

Replacement of wood by densified biofuel superior than 50% of the total weight of the fuel may not be practical in terms of traditional kilns, where periodic accumulation of ashes and its subsequent evacuation is becoming a problem for the operational process.

According to Mason (2002,) the best value in energy efficiency reported for these red brick ceramic technology reach 50% but it is possible to analyze different ways to reduce losses caused by chemical lack of combustion, mechanics and other. Improving thermal insulation of walls, re-inject hot gases and improve air-fuel ratio can increase the efficiency of the process.

With the use of proposal alternative energy may increase the ratio on average bricks / kg of fuel from 1.1 to 1.4, this is because the heat needed to dry the fuel is lower than when using only wood, increasing accordingly the relative amount of energy used directly in the process of transforming bricks, also related to the retarding effect produced by the clay material during combustion by lowering the reaction rate of fuel.

Instead the greater speed with which releases heat energy the wood, makes it not fully exploited in the oven, since the coefficient of heat absorption of the brick sets limits on dissemination through its density, just as the greater volume of gases generated during combustion of the BSC can produce a better exchange of heat throughout the column of the oven, which can reduce the lack of isothermal characteristic of this type of installation.

At burnings physical-mechanical field tests are done to the bricks produced (resistance and sound) and visual inspection of 100% for each burning of bricks, with no burnt bricks, the bricks have a red brown colour which indicates proper burning without cracking or deformation. Similarly concluded laboratory tests show there are no effects on the quality of the brick by changing the energy source.

When generating the new heat source a higher level of ashes produced by the traditional fuel requires to remove debris more frequently inside the combustion chamber, so it is recommended to adapt the design of the oven racks to improve their ability to escape from the ashes of the solid block, this principle together with the initial heating of the oven are needed in daily practice for the use of an intensive and relatively higher amount of BSC.

Increasing energy efficiency in production of clay bricks and other ceramic products, can help reduce logging and increase the recycling of waste timber with relevant advantages from the ecological point of view that these actions for obtaining building materials can represent.

4. Conclusions

The proposed technological process confirms obtention of a composite biofuel material, based on a mixture of clay soil densified cellulosic waste timber which facilitates an appropriate management. Density of the solid block tends to increase with activity and content of binder, which in turn influences combustion rate of the slow reaction of biofuel, cooperating in improving the efficiency of the cooking process brick mud to reduce specific fuel consumption compared to wood or wood as traditional energy source.

5. Acknowledgements

Authors greatly acknowledge the following institutions for their support to this study: CITMA, ministry of science, technology and environment of Cuba, UNIOVI Universidad de Oviedo.

6. References

Assureira E. (2002), Combustible alternativo la cascarilla de arroz Palestra Portal de asuntos públicos de PUCP http://palestra.pucp.edu.pe

Betancourt D. Martirena, F. Day R. Díaz Y. (2007), "Influencia de la adición de carbonato de calcio en la eficiencia energética de la producción de ladrillos de cerámica roja Revista Ingenieria de Construcciones Vol. 22, No 3 Diciembre.

Bhattacharya S.C. (2002), Biomass Energy Use and Densification in Developing Countries. Abstract of the first world conference on pellets, Stockholm, 2-4 September 2002.

Chin O. C. y Siddiqui K. M. (2000), Characteristics of some biomass briquettes prepared under modest die pressure. Bimass and Bioenergy, (2000). 18. 223-228.

Christofer R., Marcus O., Rolf Grez and et all (2007), Effect of raw material composition in woody biomass pellets on combustion characteristics Biomass and Bioenergy 31 (2007) 66-72

Curbelo A. García B. (2006), Contribución de la biomasa no cañera a la generación de electricidad en Cuba. / División de Industria y Energía, Agencia de Ciencia y Tecnología, Cuba. (http://www.fao.org/docrep/T2363s0h.htm#TopOfPage) (última visita: Septiembre).

Cukierman A. L., Della Rocca P. A., Bonelli P. R. y Cassanello M. C. (1996), On the Study of Thermo chemical Biomass Conversion. Trends in Chemical Engineering, 3, 129-144.

Dopico Montes de Oca, J.J. Martirena, F. Day R.L. (2008), Desarrollo de hormigones con aglomerante Cal - puzolana fina como material cementicio suplementario. Revista Ingenieria de Construcciones Vol 23 Diciembre. www.ing.puc.cl/ric

González M. L. (2004), "Estudio comparativo de BSC y Maderas en la obtención de eco-materiales" Universidad Central "Marta Abreu" de Las Villas Facultad de Ingeniería Mecánica Departamento: Energía; TD.Tutor: Machado I. Moya, H.I.

Gonzáles R. (2003), Densificación de Biomasa para la obtención de Energía y Materiales de Construcción TGC.. Santa Clara Departamento de Ingeniería Civil T: Martirena F.

Guerra Caridad W. Menéndez E. A y colab. "Estadística" (2006), Editorial Félix Varela, La Habana.

Faxälv O. y Nystrom O. (2007), Biomass Briquettes in Malawi Degree Project Department of Management and Engineering ISSN 1400-3562.

Jamradloedluk J., Panomai C. and et all (2005), Physical properties and combustion performance of briquettes produced from two pairs of biomass species Faculty of Engineering, Thailand.

Machado I, Martirena, F. y col. Obtención de biomasa densificada con baja energía de compactación (2002), CD Memorias 5 TO Simposio Internacional de Estructuras y Materiales de Construcción. Santa Clara

Martirena F. , Machado I. y Seijo P. (2003), Waste to energy technologies targeting the poor. The Cuba case study. Full Proceedings World Renewable Energy Congress Published by Pergamon Press, Elsevier Ltd.

Mason K. (2002), "Ten rules for energy efficient, cost effective brick firing." BASIN, Building Advisory, United Kingdom.

Ortíz L., Tejada A. y Vazquez A. (2005), Aprovechamiento de la Biomasa Forestal producida por la Cadena Monte-Industria. Parte III: Producción de elementos densificados, Revista CIS-Madera.

Pulido A. (2005), Modelos Econométricos. Editorial Félix Varela La Habana.


E-mail: ivanm@uclv.edu.cu

Fecha de recepción: 27/ 04/ 2011, Fecha de aceptación: 27/ 06/ 2011.

Assureira E. (2002), Combustible alternativo la cascarilla de arroz Palestra Portal de asuntos públicos de PUCP http://palestra.pucp.edu.pe         [ Links ]

Betancourt D. Martirena, F. Day R. Díaz Y. (2007), "Influencia de la adición de carbonato de calcio en la eficiencia energética de la producción de ladrillos de cerámica roja Revista Ingenieria de Construcciones Vol. 22, No 3 Diciembre.         [ Links ]

Bhattacharya S.C. (2002), Biomass Energy Use and Densification in Developing Countries. Abstract of the first world conference on pellets, Stockholm, 2-4 September 2002.         [ Links ]

Chin O. C. y Siddiqui K. M. (2000), Characteristics of some biomass briquettes prepared under modest die pressure. Bimass and Bioenergy, (2000). 18. 223-228.        [ Links ]

Christofer R., Marcus O., Rolf Grez and et all (2007), Effect of raw material composition in woody biomass pellets on combustion characteristics Biomass and Bioenergy 31 (2007) 66-72         [ Links ]

Curbelo A. García B. (2006), Contribución de la biomasa no cañera a la generación de electricidad en Cuba. / División de Industria y Energía, Agencia de Ciencia y Tecnología, Cuba. (http://www.fao.org/docrep/T2363s0h.htm#TopOfPage) (última visita: Septiembre).         [ Links ]

Cukierman A. L., Della Rocca P. A., Bonelli P. R. y Cassanello M. C. (1996), On the Study of Thermo chemical Biomass Conversion. Trends in Chemical Engineering, 3, 129-144.         [ Links ]

Dopico Montes de Oca, J.J. Martirena, F. Day R.L. (2008), Desarrollo de hormigones con aglomerante Cal - puzolana fina como material cementicio suplementario. Revista Ingenieria de Construcciones Vol 23 Diciembre. www.ing.puc.cl/ric         [ Links ]

González M. L. (2004), "Estudio comparativo de BSC y Maderas en la obtención de eco-materiales" Universidad Central "Marta Abreu" de Las Villas Facultad de Ingeniería Mecánica Departamento: Energía; TD.Tutor: Machado I. Moya, H.I.         [ Links ]

Gonzáles R. (2003), Densificación de Biomasa para la obtención de Energía y Materiales de Construcción TGC.. Santa Clara Departamento de Ingeniería Civil T: Martirena F.         [ Links ]

Guerra Caridad W. Menéndez E. A y colab. "Estadística" (2006), Editorial Félix Varela, La Habana.        [ Links ]

Faxälv O. y Nystrom O. (2007), Biomass Briquettes in Malawi Degree Project Department of Management and Engineering ISSN 1400-3562.        [ Links ]

Jamradloedluk J., Panomai C. and et all (2005), Physical properties and combustion performance of briquettes produced from two pairs of biomass species Faculty of Engineering, Thailand.         [ Links ]

Machado I, Martirena, F. y col. Obtención de biomasa densificada con baja energía de compactación (2002), CD Memorias 5 TO Simposio Internacional de Estructuras y Materiales de Construcción. Santa Clara         [ Links ]

Martirena F. , Machado I. y Seijo P. (2003), Waste to energy technologies targeting the poor. The Cuba case study. Full Proceedings World Renewable Energy Congress Published by Pergamon Press, Elsevier Ltd.         [ Links ]

Mason K. (2002), "Ten rules for energy efficient, cost effective brick firing." BASIN, Building Advisory, United Kingdom.         [ Links ]

Ortíz L., Tejada A. y Vazquez A. (2005), Aprovechamiento de la Biomasa Forestal producida por la Cadena Monte-Industria. Parte III: Producción de elementos densificados, Revista CIS-Madera.         [ Links ]

Pulido A. (2005), Modelos Econométricos. Editorial Félix Varela La Habana.        [ Links ]

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