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• Master-slave approach for the modelling of joints with dependent degrees of freedom in flexible mechanisms

  J. Muñoz, G. Jelenic, M. Crisfield

  Commun. Numer. Meth. Engng (2003). Vol. 19 (9), pp. 689-702

  
  

  Abstract

  The analysis of multibody systems requires an exact description of the kinematics of the joints involved. In the present work the master–slave approach is employed and endowed with the possibility of including several more complex types of joints. We present the formulation for joints where some relation between the different released degrees of freedom exists such as the screw joint, the rack‐and‐pinion joint or the cam joint. These joints are implemented in conjunction with geometrically exact beams and an energy‐momentum conserving time‐stepping algorithm.

  Abstract
  The analysis of multibody systems requires an exact description of the kinematics of the joints involved. In the present work the master–slave approach is employed and [...]

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• Thermic Model to Predict Biogas Production in Unheated Fixed-Dome Digesters Buried in the Ground

  G. Terradas, C. Pham, J. Triolo, J. Martí-Herrero, S. Sommer

  Environmental science and technology (2014). Vol. 48 (6), pp. 3253-3262

  
  

  Abstract

  In many developing countries simple biogas digesters are used to produce energy for domestic purposes from anaerobic digestion of animal manure. We developed a simple, one-dimensional (1-D), thermal model with easily-available input data for unheated, unstirred, uninsulated, fixed-dome digesters buried in the soil to study heat transfer between biogas digester and its surroundings. The predicted temperatures in the dome, biogas and slurry inside the digester and the resulting biogas production are presented and validated. The model was well able to estimate digester temperature (linear slope nearly 1, R2 0.96). The results show that a suitable soil temperature profile renders the use of a full thermal model superfluous for buried, unheated, unstirred and uninsulated digesters. Model validation for methane production gave root-mean-square (RMSE) and relative-root-mean-square errors (rRMSEP(%)) of 54.4 L CH4 digester-1 day-1 and 35.4%, respectively. The validation result was considerably improved if only using winter data (RMSE = 26.1 L CH4 digester-1 day-1; rRMSEP(%) = 17.7%). The model performed satisfactorily in light of the uncertainties attached to it. Since unheated digesters suffer critically low methane production during the winter, the model could be particularly useful for assessing methane production and for improving the ability of unheated digesters to provide sufficient energy during cold periods.

  Abstract
  In many developing countries simple biogas digesters are used to produce energy for domestic purposes from anaerobic digestion of animal manure. We developed a simple, one-dimensional [...]

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• Low cost tubular digesters as appropriate technology for widespread application: Results and lessons learned from Bolivia

  J. Martí-Herrero, M. Chipana, C. Cuevas, G. Paco, V. Serrano, B. Zymla, K. Heising, J. Sologuren, A. Gamarra

  Renewable Energy (2014). Vol. 71, pp. 156-165

  
  

  Abstract

  This paper presents the results and lessons learned from four and a half years of implementing low cost tubular digesters in Bolivia. The selection of this technology is justified in comparison with other popular technologies such as fixed dome or floating drum digesters. The highlighted weakness of the tubular model (its short life expectancy), is transformed into a strength, making the low cost tubular digester an appropriate technology for widespread application. The experiences in Bolivia show that the success of biogas programs depend more on socio-economic factors than on the validated technology selected, suggesting that local circumstances are a critical, and often underestimated, factor to be taken into consideration in the praxis. Finally, some testimonies of the use of biol (bio-slurry or effluent) are reported, identifying the high potential of this anaerobic digestion product that provides a food sovereignty approach, reduced expansion of the agricultural frontier, increased agricultural productivity and hence family income, that other household energizing systems do not have. A brief report of lessons learned is also included

  Abstract
  This paper presents the results and lessons learned from four and a half years of implementing low cost tubular digesters in Bolivia. The selection of this technology is justified [...]

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• Improvement through low cost biofilm carrier in anaerobic tubular digestion in cold climate regions

  J. Martí-Herrero, R. Alvarez, R. Rojas, L. Aliaga, R. Cespedes, J. Carbonell

  Bioresource Technology (2014). Vol. 167, pp. 87-93

  
  

  Abstract

  The aim of this research is to evaluate the increase of biogas production with low cost tubular digesters in cold climates using PET rings inside the reactor. Two similar digesters have been operated and monitored in cold weather conditions and have been fed with cow manure. Digester 1 was filled with PET – rings as a biofilm carrier, Digester 2 was kept as a reference. Through the PET – rings the functional surface could be increased by a factor 4.2. The results show that 44% more biogas per KgSV has been produced with the biofilm carrier in use (0.33 m3/kgSV) (reference digester −0.23 m3/kgSV), at an organic load rate of 0.26 kgSV/m3/d. The thermal performance shows that with an adaptation of the low cost tubular digester the slurry temperature can be raised up to 16.6 °C (average) by surrounding temperature of 6.1 °C (average) without using any active heating system.

  Abstract
  The aim of this research is to evaluate the increase of biogas production with low cost tubular digesters in cold climates using PET rings inside the reactor. Two similar [...]

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• Cow, sheep and llama manure at psychrophilic anaerobic co-digestion with low cost tubular digesters in cold climate and high altitude

  J. Martí-Herrero, R. Alvarez, R. Cespedes, M. Rojas, V. Conde, L. Aliaga, M. Balboa, S. Danov

  Bioresource Technology (2015). Vol. 181, pp. 238-246

  
  

  Abstract

  The aim of this research is to evaluate the co-digestion of cow and llama manure combined with sheep manure, in psychrophilic conditions and real field low cost tubular digesters adapted to cold climate. Four digesters were monitored in cold climate conditions; one fed with cow manure, a second one with llama manure, the third one with co-digestion of cow–sheep manure and the fourth one was fed with llama–sheep manure. The slurry had a mean temperature of 16.6 °C, the organic load rate was 0.44 kgvs m−3 d−1 and the hydraulic retention time was 80 days. After one hundred days biogas production was stable, as was the methane content and the pH of the effluent. The co-digestion of cow–sheep manure results in a biogas production increase of 100% compared to the mono-digestion of cow manure, while co-digestion of llama–sheep manure results in a decrease of 50% in biogas production with respect to mono-digestion of llama manure

  Abstract
  The aim of this research is to evaluate the co-digestion of cow and llama manure combined with sheep manure, in psychrophilic conditions and real field low cost tubular digesters [...]

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• The influence of users' behavior on biogas production from low cost tubular digesters: A technical and socio-cultural field analysis

  J. Martí-Herrero, M. Ceron, R. García, L. Pracejus, R. Alvarez, X. Cipriano

  Energy for Sustainable Development (2015). Vol. 27, pp. 73-83

  
  

  Abstract

  The aim of this paper is to understand the influence of the user behavior on tubular digesters performance, through a technical and a social approach in the Bolivian context. Fifteen domestic digesters were evaluated, from which 6 were installed in the Altiplano and other 6 in the Andean Valleys. Data about slurry temperature, feedstock and biogas quality were collected from these 12 digesters, while daily biogas production and feeding pattern were also monitored from further three digesters in the valleys. Because of changes in user behavior along the monitoring period and particular characteristics of the digesters monitored, 5 complete patterns of biogas production and digester management were established. Furthermore, the results of a socio-cultural study with Andean families about the perception of poverty, their needs and the role played by digesters in their expectations in improving life quality, are correlated to the obtained technical data. The technical evaluation shows how the digester management seems to have a seasonal performance throughout the year according to the agricultural calendar. This means that families are more interested in using bioslurry in crops and agricultural improvements than in the use of biogas. The Bolivian government subsidy on liquefied gas seems to be one of the key issues to understand these results. Finally, data also reveals how the thermal behavior of tubular digesters adapted to cold climate that use a passive solar design, is similar to the thermal behavior of valley digesters, and therefore intends to add the same passive heating techniques for warm and tropical climates, to increase slurry temperatures and achieve a higher biogas production.

  Abstract
  The aim of this paper is to understand the influence of the user behavior on tubular digesters performance, through a technical and a social approach in the Bolivian context. [...]

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• How to report biogas production when monitoring small-scale digesters in field

  J. Martí-Herrero, T. Flores, R. Alvarez, D. Pérez

  Biomass and Bioenergy (2016). Vol. 84, pp. 31-36

  
  

  Abstract

  The aim of this research was to evaluate the error originated when biogas production from field monitoring digesters, influenced by the diurnal temperature cycle, was normalized to standard conditions for pressure and temperature (273.15 K and 100 kPa) from local conditions. The biogas production data is often reported without indicating if done under local conditions, whether these conditions have been standardized and, if they have actually been standardized, the standard temperature and pressure is not indicated. In this research ambient and biogas temperature, as well as biogas production were monitored with a 30 min frequency during three consecutive days, in three different tubular digesters. Normalization was realized using the high frequency data collected as reference values, and also using daily biogas production with mean daily biogas, ambient and nearby meteorological station temperatures. The outcome of this research shows that normalization of biogas production can be obtained using daily biogas production and the daily mean ambient temperature with an overestimation by no more than 1.5%, in comparison to the normalization achieved by using high frequency data from biogas temperature and production. Using mean daily ambient temperature or mean daily biogas temperature results in the same overestimation, while using mean daily ambient temperature from a nearby airport weather station pushes the overestimation up to 2.7%. So, if ambient temperature and altitude is identified, biogas production reported in local conditions can be normalized.

  Abstract
  The aim of this research was to evaluate the error originated when biogas production from field monitoring digesters, influenced by the diurnal temperature [...]

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• Household anaerobic digesters for biogas production in Latin America: A review

  M. Garfí, J. Martí-Herrero, A. Garwood, I. Ferrer

  Renewable and Sustainable Energy Reviews (2016). Vol. 60, pp. 599-614

  
  

  Abstract

  This review aims to provide an overview of household biogas digester implementation in rural areas of Latin America. It considers the history of household digesters in Latin America, including technical, environmental, social and economic aspects. Several successful experiences have been promoted during the last decade, including the creation of the Network for Biodigesters in Latin America and the Caribbean (RedBioLAC) that provides a forum to coordinate implementation and research programmes throughout the continent. Although the potential of this technology is well demonstrated, some barriers are identified, such as the need for technical improvements, lack of social acceptance and high investment costs. Thus, further efforts should be undertaken to overcome these barriers and improve the technical performance, social acceptance, economic benefits and environmental impact in order to enhance its wide-spread dissemination in energy poor communities.

  Abstract
  This review aims to provide an overview of household biogas digester implementation in rural areas of Latin America. It considers the history of household digesters in Latin [...]

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• Analysis of energy, CO2 emissions and economy of the technological migration for clean cooking in Ecuador

  J. Martínez, J. Martí-Herrero, S. Villacís, D. Vaca, A. Riofrio

  Energy Policy (2017). Vol. 107, pp. 182-187

  
  

  Abstract

  The objective of this study is to analyze the CO2 emissions and economic impacts of the implementation of the National Efficient Cooking Program (NECP) in Ecuador, which aims to migrate the population from Liquefied Petroleum Gas (LPG)-based stoves to electric induction stoves. This program is rooted in the current effort to change Ecuador's energy balance, with hydroelectric power expected to generate 83.61% of national electricity by 2022, ending the need for subsidized LPG. For this analysis, the 2014 baseline situation has been compared with two future scenarios for 2022: a business-as-usual scenario and an NECP-success scenario. This study demonstrates the viability of migration from imported fossil fuels to locally-produced renewable energy as the basis for an efficient cooking facility. The new policies scenario would save US$ 1.162 billion in annual government expenditure on cooking subsidies, and reducing CO2 emissions associated to energy for cooking in 1.8 tCO2/y.

  Abstract
  The objective of this study is to analyze the CO2 emissions and economic impacts of the implementation of the National Efficient Cooking Program (NECP) in Ecuador, which [...]

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• Monitoreo a escala de real de un digestor anaeróbico de bajo costo instalado en una planta de sacrificio animal

  L. Castro, H. Escalante, M. Carballo, J. Martí-Herrero

  Red de Biodigestores para Latina América y el Caribe (2017). Vol. 1, pp. 37-44

  
  

  Abstract

  Slaughterhouses generate an average 6.5 kg of manure/animal. Day. The animals has a weight between 350 and 400 kg. Manure causes economic, environmental and legal problems for the slaughter companies. The aim of this work, was to stabilize the 5,5 % of cattle manure of FOGASA Slaughterhouse by means of low cost digester. The results show organic matter reduce of 60% volatile solid and an average biogas production of 0,9 Nm/d. During anaerobic digestion process efficiencies were reach in terms of biogas production rate, specific biogas production and reduction of the pathogen content of 0,21 m3biogás/m3digestor d y 0,20 m3biogás/KgSV y 90% respectively. The digestate contained nitrogen, phosphorous and potassium, which is an important feature of fertilizers

  Abstract
  Slaughterhouses generate an average 6.5 kg of manure/animal. Day. The animals has a weight between 350 and 400 kg. Manure causes economic, environmental and legal problems [...]

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