Control of a solar dryer through using a fuzzy logic and low-cost model-based sensor

Solar drying is one of the important processes used for extending the shelf life of agricultural products. Regarding consumer requirements, solar drying should be more suitable in terms of curtailing total drying time and preserving product quality. Therefore, the objective of this study was to develop a fuzzy logic-based control system, which performs a ?human-operator-like? control approach through using the previously developed low-cost model-based sensors. Fuzzy logic toolbox of MatLab and Borland C++ Builder tool were utilized to develop a required control system. An experimental solar dryer, constructed by CONA SOLAR (Austria) was used during the development of the control system. Sensirion sensors were used to characterize the drying air at different positions in the dryer, and also the smart sensor SMART-1 was applied to be able to include the rate of wood water extraction into the control system (the difference of absolute humidity of the air between the outlet and the inlet of solar dryer is considered by SMART-1 to be the extracted water). A comprehensive test over a 3 week period for different fuzzy control models has been performed, and data, obtained from these experiments, were analyzed. Findings from this study would suggest that the developed fuzzy logic-based control system is able to tackle difficulties, related to the control of solar dryer process.

Determinación del riesgo de incendio en una instalación de secado de alperujo = Determination of the risk of fire in an olive-oil mill waste dryer

For the energy valorization of alperujo, residue of the olive oil two phases extraction process, it is necessary to perform a drying process to reduce moisture content from over 60% to less than 10%. In order to reduce primary energy consumption and get an economic return, usually in this kind of drying facilities Gas Turbine CHP is used as a heat source. There have been recently in Spain some fires in this kind of GT-CHP facilities, which have caused high material losses. In some of these fires it has been suggested that the fire was caused by the output of incandescent alperujo in the flue gasesof the drying system. Therefore, the aim of this study is to determine experimentally and analytically under which operational conditions a process of alperujo self-ignition in the drying process can begin, and determine the actual fire hazard in this type of TG-CHP system. For analytical study, the temperature and initial composition of the combustion gases of the Gas Turbine at the entrance of the drying process was calculated and the gas equilibrium conditions reached in contact with the biomass were calculated and, therefore, the temperature of the biomass during the drying process. Moreover, the layer and dust ignition temperature of alperujo has been experimentally determined, according to EN 50281-2-1: 2000. With these results, the operating conditions of the drying process, in which there are real risk of auto-ignition of alperujo have been established.Para la valorización energética del alperujo, residuo del proceso de extracción en dos fases del aceite de oliva, es necesario realizar un proceso de secado para reducir su contenido de humedad de más del 60% al 10% m/m en b.h. Con el fin de reducir el consumo de energía primaria y obtener una rentabilidad económica, normalmente en este tipo de instalaciones de secado se usa la cogeneración con turbina de gas (TG) como fuente de calor. En España en los últimos años han ocurrido algunos casos de incendio en este tipo de instalaciones de cogeneración, que han supuesto pérdidas materiales muy elevadas. Por esta razón, el objetivo de este trabajo es determinar analítica y experimentalmente las condiciones operativas del secadero bajo las cuales podría comenzar un proceso de autoinflamación del alperujo y determinar el riesgo real de incendio en este tipo de instalaciones. Para el estudio analítico, se ha planteado y validado el modelo matemático que permite calcular la temperatura y la composición de los gases de combustión a la entrada y a la salida del secadero, en función de las curvas características de la TG, de las condiciones atmosféricas, del caudal y del grado de humedad de la biomasa tratada. El modelo permite además calcular la temperatura de bulbo húmedo, que es la máxima temperatura que podría alcanzar la biomasa durante el proceso de secado y determinar la cantidad de biomasa que se puede secar completamente en función del caudal y de las condiciones de entrada de los gases de combustión. Con estos resultados y la temperatura mínima de autoinflamación del alperujo determinada experimentalmente siguiendo la norma EN 50281- 2-1:2000, se demuestra que en un proceso de secado de alperujo en condiciones normales de operación no existe riesgo de autoencendido que pueda dar origen a un incendio.

Intra-annual patterns of tracheid size in the Mediterranean tree Juniperus thurifera as an indicator of seasonal water stress

Because climate can affect xylem cell anatomy, series of intra-annual cell anatomical features have the potential to retrospectively supply seasonal climatic information. In this study, we explored the ability to extract information about water stress conditions from tracheid features of the Mediterranean conifer Juniperus thurifera L. Tracheidograms of four climatic years from two drought-sensitive sites in Spain were compared to evaluate whether it is possible to link intra-annual cell size patterns to seasonal climatic conditions. Results indicated site-specific anatomical adjustment such as smaller and thicker tracheids at the dryer site but also showed a strong climatic imprint on the intra-annual pattern of tracheid size. Site differences in cell size reflected expected structural adjustments against cavitation failures. Differences between intra-annual patterns, however, indicated a response to seasonal changes in water availability whereby cells formed under drought conditions were smaller and thicker, and vice versa. This relationship was more manifest and stable at the dryer site

Water harvesting for young trees using Peltier plates powered by photovoltaic solar energy

Young trees transplanted from nursery into open field require a minimum amount of soil moisture to successfully root in their new location, especially in dry-climate areas. One possibility is to obtain the required water from air moisture. This can be achieved by reducing the temperature of a surface below the air dew point temperature, inducing water vapor condensation on the surface. The temperature of a surface can be reduced by applying the thermoelectric effect, with Peltier modules powered by electricity. Here, we present a system that generates electricity with a solar photovoltaic module, stores it in a battery, and finally, it uses the electricity at the moment in which air humidity and temperature are optima to maximize water condensation while minimizing energy consumption. Also, a method to reduce the evaporation of the condensed water is proposed. The objective of the system, rather than irrigating young plants in such a degree as to boost their growth, is to maintain them alive in the dryer periods.

Estudio de la geoquímica orgánica de la Turbera de Las Conchas (Asturias) aplicado a la reconstrucción paleoambiental

ELos biomarcadores (n-alcanos y ácidos n-alcanoicos) presentes en el registro sedimentario de la turbera de Las Conchas (Llanes, Asturias) han permitido identificar períodos de condiciones ambientales húmedas y secas a lo largo de 8.000 años cal BP que pueden ser extrapolados al resto de Europa. Para ello, se analizaron 78 muestras a lo largo de un sondeo de 3,20 m, empleando un cromatógrafo de gases con detector selectivo de masas. Las variaciones en el contenido de biomarcadores se relacionaron con la predominancia de especies de Sphagnum (típicas de condiciones de mayor humedad) o con especies propias de condiciones más secas, como especies de Ericacea (brezos). Se sugiere que los cambios en la distribución de la vegetación están relacionados con las condiciones paleohidrológicas y paleoambientales y, de esta manera, se distinguen cinco períodos secos alternados con cinco períodos húmedos que no están necesariamente unidos a cambios en la temperatura. ABSTRACT Biomarkers (n-alkanes and n-alkanoic acids) present in the sedimentary record of Las Conchas peat bog (Llanes, Asturias) allowed the identification of 5 dry and humid periods in the last 8,000 years cal BP which can be extrapolated to the rest of Europe. For this purpose, 78 samples were analyzed along a core of 3.2 m deep using a gas chromatograph equipped with a selective mass detector. Variations in the biomarker content are related to the predominance of Sphagnum species (typical of humid conditions) or other species typical of dryer conditions, such as Ericacea (heather). This suggests that changes in the distribution of the vegetation were related to palaeohydrological and palaeoenvironmental conditions and, thus, we may distinguish five dry periods alternating with five humid periods which are not necessarily linked to variations in temperature.

Use of thermographic imaging to screen for drought-tolerant genotypes in Brachypodium distachyon

Thermal imaging has been used to evaluate the response to drought and warm temperatures in a collection of Brachypodium distachyon lines adapted to varied environmental conditions. Thermographic records were able to separate lines from contrasting rainfall regimes. Genotypes from dryer environments showed warmer leaves under water deficit, which suggested that decreased evapotranspiration was related to a more intense stomatal closure. When irrigated and under high temperature conditions, drought-adapted lines showed cooler leaves than lines from wetter zones. The consistent, inverse thermographic response of lines to water stress and heat validates the reliability of this method to assess drought tolerance in this model cereal. It additionally supports the hypothesis that stomatal-based mechanisms are involved in natural variation for drought tolerance in Brachypodium. The study further suggests that these mechanisms are not constitutive but likely related to a more efficient closing response to avoid dehydration in adapted genotypes. Higher leaf temperature under water deficit seems a dependable criterion of drought tolerance, not only in B. distachyon but also in the main cereal crops and related grasses where thermography can facilitate high-throughput preliminary screening of tolerant materials.