• Energy Research

Abstract Biogas digestate is a byproduct in biogas plants. Using the dried digestate as solid fuel seems to be a promising alternative. Objectives were to verify whether digestate from biogas plants is suitable as a solid biomass fuel and to classify the digestate according to current regulations for biofuels. Combustion experiments in a biomass combustion facility were carried out to ascertain both, emissions and combustion behavior. Two different digestates were used as test fuel and pressed into pellets. Net calorific value of digestate pellets were between 15.8 MJ/kg and 15.0 MJ/kg with water content of 9.2% and 9.9%. Ash content was between 14.6% and 18.3%, with softening temperature between 1090 °C and 1110 °C. Major compounds of ash were calcium 13.6–17.0%, phosphorous 20.4–26.7%, silicon 18.0–30.4% and potassium with 8.5–15.5%. The average concentration of carbon monoxide was between 104 mg/m 3 and 275 mg/m 3 and 334–398 mg/m 3 of nitrogen oxides. Average dust concentration of 100–106 mg/m 3 has been detected, which was reduced to 40–43 mg/m 3 by using an electric filter. Chemical composition and physical properties of digestate fuel pellets depend on the blend of substrates used as feedstock for biogas production. The digestates investigated in this study can be recommended as a fuel for combustion. The calorific value, the ash properties and the emissions allow their use in the investigated solid biomass combustion unit. Further investigations are required to cover a broader range of digestates and combustion techniques.

Abstract Biogas digestate is a byproduct in biogas plants. Using the dried digestate as solid fuel seems to be a promising alternative. Objectives were to verify whether digestate from biogas plants is suitable as a solid biomass fuel and to classify the digestate according to current regulations for biofuels. Combustion experiments in a biomass combustion facility were carried out to ascertain both, emissions and combustion behavior. Two different digestates were used as test fuel and pressed into pellets. Net calorific value of digestate pellets were between 15.8 MJ/kg and 15.0 MJ/kg with water content of 9.2% and 9.9%. Ash content was between 14.6% and 18.3%, with softening temperature between 1090 °C and 1110 °C. Major compounds of ash were calcium 13.6–17.0%, phosphorous 20.4–26.7%, silicon 18.0–30.4% and potassium with 8.5–15.5%. The average concentration of carbon monoxide was between 104 mg/m 3 and 275 mg/m 3 and 334–398 mg/m 3 of nitrogen oxides. Average dust concentration of 100–106 mg/m 3 has been detected, which was reduced to 40–43 mg/m 3 by using an electric filter. Chemical composition and physical properties of digestate fuel pellets depend on the blend of substrates used as feedstock for biogas production. The digestates investigated in this study can be recommended as a fuel for combustion. The calorific value, the ash properties and the emissions allow their use in the investigated solid biomass combustion unit. Further investigations are required to cover a broader range of digestates and combustion techniques.

Abstract Plant oil as household energy could be a sustainable and locally available alternative for fossil fuel. However, the use of pure plant oil in pressure stoves leads to deposit in the vaporizer. Therefore, objective of this study was to investigate the effect of the degree of unsaturation of plant oils on performance and deposit formation. Soybean oil with an iodine value of 128 g I 2 /100 g was used as well as partly hydrogenated soybean oil with an iodine value of 62 g I 2 /100 g, hydrogenated soybean oil with an iodine value of 1 g I 2 /100 g, and a blend of 50% refined soybean oil and 50% partly hydrogenated soybean oil was confected to obtain an iodine value of 95 g I 2 /100 g. In burning trials, the specific fuel consumption, the required frequency of nozzle cleaning and the amount of deposit in the vaporizer were measured. Results showed an exponential increase of deposits in the vaporizer when iodine value of soybean oil was increased: deposits amounted to 0.26 g/kg of consumed fuel for hydrogenated soybean oil and 0.70 g/kg for the original (untreated) soybean oil. However, an increase in the soybean oil iodine value did not affect fuel consumption, which was 0.296 kg/h for hydrogenated soybean oil compared to 0.286 kg/h for original (untreated) soybean oil. Further research is necessary to investigate the chemical reactions in the vaporizer to identify key precursors (factors) and reactions mechanisms that could influence the formation of deposits in plant oil pressure stoves.

Abstract Plant oil as household energy could be a sustainable and locally available alternative for fossil fuel. However, the use of pure plant oil in pressure stoves leads to deposit in the vaporizer. Therefore, objective of this study was to investigate the effect of the degree of unsaturation of plant oils on performance and deposit formation. Soybean oil with an iodine value of 128 g I 2 /100 g was used as well as partly hydrogenated soybean oil with an iodine value of 62 g I 2 /100 g, hydrogenated soybean oil with an iodine value of 1 g I 2 /100 g, and a blend of 50% refined soybean oil and 50% partly hydrogenated soybean oil was confected to obtain an iodine value of 95 g I 2 /100 g. In burning trials, the specific fuel consumption, the required frequency of nozzle cleaning and the amount of deposit in the vaporizer were measured. Results showed an exponential increase of deposits in the vaporizer when iodine value of soybean oil was increased: deposits amounted to 0.26 g/kg of consumed fuel for hydrogenated soybean oil and 0.70 g/kg for the original (untreated) soybean oil. However, an increase in the soybean oil iodine value did not affect fuel consumption, which was 0.296 kg/h for hydrogenated soybean oil compared to 0.286 kg/h for original (untreated) soybean oil. Further research is necessary to investigate the chemical reactions in the vaporizer to identify key precursors (factors) and reactions mechanisms that could influence the formation of deposits in plant oil pressure stoves.

Hydrothermal treatment (HTT) offers the potential to upgrade low-value biomass such as digestate (DG) or forest residue (FR) by producing solids and liquids for material use or energetic utilization. In this study, microwave-assisted HTT experiments with DG and FR as feedstocks were executed at different temperatures (130, 150, 170 °C) and with different holding times (30, 60, 90 min) to determine the influences on product properties (ash and elemental concentrations, calorific values and chemical compounds). In general, DG and FR reacted differently to HTT. For the DG solids, for instance, the ash concentration was reduced to 8.68%DM at 130 °C (initially 27.67%DM), and the higher heating value increased from 16.55 MJ/kgDM to 20.82 MJ/kgDM at 170 °C, while the FR solids were affected only marginally. Elements with importance for emissions in combustion were leached out in both HTT solids. The DG and FR liquids contained different chemical compounds, and the temperature or holding time affected their formation. Depending on the designated application of HTT, less severe conditions can deliver better results. It was demonstrated that different low-temperature HTT conditions already induce strong changes in the product qualities of DG and FR. Optimized interactions between process parameters (temperature, holding time and feedstock) might lead to better cost–benefit effects in HTT.

Hydrothermal treatment (HTT) offers the potential to upgrade low-value biomass such as digestate (DG) or forest residue (FR) by producing solids and liquids for material use or energetic utilization. In this study, microwave-assisted HTT experiments with DG and FR as feedstocks were executed at different temperatures (130, 150, 170 °C) and with different holding times (30, 60, 90 min) to determine the influences on product properties (ash and elemental concentrations, calorific values and chemical compounds). In general, DG and FR reacted differently to HTT. For the DG solids, for instance, the ash concentration was reduced to 8.68%DM at 130 °C (initially 27.67%DM), and the higher heating value increased from 16.55 MJ/kgDM to 20.82 MJ/kgDM at 170 °C, while the FR solids were affected only marginally. Elements with importance for emissions in combustion were leached out in both HTT solids. The DG and FR liquids contained different chemical compounds, and the temperature or holding time affected their formation. Depending on the designated application of HTT, less severe conditions can deliver better results. It was demonstrated that different low-temperature HTT conditions already induce strong changes in the product qualities of DG and FR. Optimized interactions between process parameters (temperature, holding time and feedstock) might lead to better cost–benefit effects in HTT.

Abstract Plant production in greenhouses in hot and dry climates needs sufficient cooling for optimal production. Conventional pad and fan cooling systems require desalinated water which limits their application. Furthermore, the horizontal ventilation causes undesirable temperature and humidity gradients in the cropped area. To overcome these disadvantages a new air-conditioning system was developed and tested in Greece and Kuwait. This system consists of an air washer, an air distribution unit, a movable thermal screen and an electronic controller. The air washer can be operated with low quality water. Effective cooling, cleaning of the inlet air and uniform temperature and humidity distribution are also points in its favour.

Abstract Plant production in greenhouses in hot and dry climates needs sufficient cooling for optimal production. Conventional pad and fan cooling systems require desalinated water which limits their application. Furthermore, the horizontal ventilation causes undesirable temperature and humidity gradients in the cropped area. To overcome these disadvantages a new air-conditioning system was developed and tested in Greece and Kuwait. This system consists of an air washer, an air distribution unit, a movable thermal screen and an electronic controller. The air washer can be operated with low quality water. Effective cooling, cleaning of the inlet air and uniform temperature and humidity distribution are also points in its favour.

Als Beitrag zur Sicherung der Welternährung fördert das Bundesministerium für Bildung und Forschung (BMBF) unter Beteiligung des Bundesministeriums für wirtschaftliche Zusammenarbeit und Entwicklung (BMZ) seit 2013 mehrere Verbundprojekte, an welchen das Fachgebiet für Agrartechnik der Universität Kassel und das Fachgebiet Agrartechnik in den Tropen und Subtropen der Universität Hohenheim mit Forschungsarbeiten zur Verbesserung der Nutzung von Grundnahrungsmitteln in Afrika beteiligt sind. Ein Schwerpunkt liegt dabei auf der Verbesserung der Nacherntetechnologie zur Vermeidung von Verlusten sowie zur Wertsteigerung durch Weiterverarbeitung. Since 2013, the Federal Ministry of Education and Research (BMBF) and the Federal Ministry of Economic Cooperation and Development (BMZ) is funding several joint research projects to contribute to food security. Agricultural and Biosystems Engineering Group of the University of Kassel and Agricultural Engineering Tropics and Subtropics Group of the University of Hohenheim are contributing to those projects to improve the utilization of staple crops in Africa. Focus is on improvement of postharvest technology to reduce food losses and to add value by processing. Jahrbuch Agrartechnik, vol. 29Jahrbuch Agrartechnik 2017, vol. 29, 2017