Energy and Renewable Energies
Abolfazl Hedayatipour; Mohsen Soleymani; Mostafa Kiani Deh Kiani
Abstract
Introduction In recent years, due to its availability and low environmental pollution, the use of Earth-Air Heat Exchanger (EAHE) has been developed as an efficient energy system in heating and cooling residential buildings and agricultural greenhouses. In this system, air is circulated by a fan through ...
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Introduction In recent years, due to its availability and low environmental pollution, the use of Earth-Air Heat Exchanger (EAHE) has been developed as an efficient energy system in heating and cooling residential buildings and agricultural greenhouses. In this system, air is circulated by a fan through a pipe buried deep in the ground. Depending on the geographical location and soil type, the soil temperature at a depth of 2-3 meters remains unchanged throughout the season. Of course, this depth varies throughout the year and according to climatic changes. The heat exchange between the soil and the air inside the pipe depends on the type of soil and its moisture content, the length and diameter of the air transmission pipe, the depth of burial and the velocity of the air flow (air velocity). Air circulation can be done in an open-loop or closed-loop circuit.Materials and Methods: A factorial experiment was conducted in the form of a completely randomized block design with two factors (pipe length at three levels (34, 17 and 52 meters) and air velocity at two levels (5 and 10 m/s)) in three replications, to investigate the effect of these factors on the coefficient of performance (COP), system efficiency and outlet air temperature. The experiment was conducted in a greenhouse in Arak city, Iran, in Joune 2022. This 150 square meter greenhouse was equipped with geothermal equipment. Air was circulated through a 200 mm diameter PVC pipe buried three meters deep in the ground. Air was circulating through an open loop circuit. Dependent variables were measured during the hot hours of the day (from 12:00 to 18:00) for one week at the end of July. The air temperature at the fan inlet and at 17, 34 and 52 meters along the pipe was measured by a single-channel data logger. Hourly changes in outlet air temperature, COP and efficiency were measured in a 24-hour period and plotted using Excel software.Results and DiscussionThe outlet air temperature for the pipe length of 34 and 52 m did not change when the air velocity decreased from 10 m/s to 5 m/s. But for the pipe length of 17 m, the maximum temperature, COP and efficiency were observed at an air velocity of 5 m/s. Regardless the air velocity, the average temperature of the outlet air for the three levels of the pipe length was 28.5, 25.5 and 25.3°C, respectively. The outlet air temperature was almost the same for the 34 and 52 m pipe lengths. In other words, the optimal length of the pipe is about 34 meters. The mean efficiencies for these two pipe length levels were 0.69 and 0.66, but the COP depended on the air velocity. The average COP for air velocity of 5 and 10 m/s was obtained 1.4 and 2.5, respectively. Based on these results, the best performance of the system in terms of output temperature reduction, cooling efficiency and COP is obtained in situation that the length of the pipe is 34 m and the air velocity is 10 m/s. when the length of the pipe is 17 meters, the temperature of the air outlet at two velocities of 10 and 5 m/s was 29.9 and 27 °C, respectively. The cooling efficiency and COP at two velocity of 10 and 5 m/s, were 0.34, 0.54; and 2.1, 1.7 respectively. If the desired temperature is 28-30 °C, pipe length of 17 m and the air velocity of 5 m/s is recommended. The results of hourly performance analysis showed that the highest difference between inlet and outlet air temperatures, is obtained at middle hours of the day. The higher the ambient temperature, the higher the efficiency of the EAHE system. ConclusionThis system successfully met the cooling needs of a model greenhouse in the weather conditions of Markazi Province in June. Based on the results, the optimal pipe length and air velocity were obtained as 34 m and 10 m/s, respectively. The average air outlet temperature and cooling efficiency were 25.5, 0.66 and 2.5 respectively. The higher the ambient temperature, the higher the EAHE efficiency. This is mainly due to the higher temperature difference between the outgoing and incoming air during the hottest hours of the day. As a result, system efficiency and COP increase at the hottest hours of the day.
Mohsen Soleymani; Vahid Jahangiri Boltaghi; Mohammad Javad Sheikhdavoodi; Zabihollah Mahdavifar
Abstract
Introduction: Biogas, a product of anaerobic digestion of biomass resources, is one of the major renewable energies with the potential to replace fossil fuels. Anaerobic digestion is performed under specific conditions and according to a specific chemical process. Sugar cane is one of the most common ...
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Introduction: Biogas, a product of anaerobic digestion of biomass resources, is one of the major renewable energies with the potential to replace fossil fuels. Anaerobic digestion is performed under specific conditions and according to a specific chemical process. Sugar cane is one of the most common sources of sugar and bioethanol production in the world. In the ethanol distillation process, large quantities of vinasse are produced. The direct consumption of vinasse as fertilizer has many environmental problems. Anaerobic digestion of vinasse is a potential solution to such environmental problems. Factors affecting the performance of an anaerobic digester can be classified into three main categories: (1) raw material characteristics, (2) reactor design, and (3) operating conditions. Among the operating conditions, temperature and pH are the most important parameters, so in this study, these two parameters were investigated.Materials and Methods:The main raw material was vinasse. Some other additives were used to alter its chemical properties. To have a proper substrate composition, the ingredients before loading into the digesters were evaluated for their chemical and physical properties, including pH, concentration and C/N ratio. The bovine rumen contents of 10% of the final volume of input material were added to supply methanogenesis bacteria as well as to modulate the (C/N) ratio.The Total Solid Content (TS), Volatile Solid (VS) and Chemical Oxygen Demand (COD), were evaluated before and after digestion.A series of batch reactor were used to perform the experiment. The experiment was carried out in a split plot design in a completely randomized design. The main and sub-factor was respectively temperature (at four levels of 30, 35, 40 and 45 ° C) and pH (at four levels of 6.8, 7, 7.2 and 7.4), and the experiment was performed in three replication.To measure the volume of gas produced, a 50 ml water tank connected to the digester outlet as a U-tube was used. The amount of water movement in the U-shaped tube is an indicator of the volume of biogas produced. For better detection of water displacement, some color was dissolved in water. Passing the gas produced from the three-molar NaOH solution, its impurities (mainly carbon dioxide) were absorbed, and the resulting pure gas was re-measured using a U-shaped tube. Using the law of complete gases, the biogas volumetric index was converted to the standard gas volume and finally converted to values based on (ml/gVS) and the new values were analyzed by analysis of variance and mean comparison.Results and Discussion:Almost all main and interaction effects on all the factors studied were significant at the 1% probability level. The amount of gas produced increased with increasing temperature but with increasing pH, it first increased and then decreased. The amount of gas produced at 35, 40 and 45 °C was not significantly different. So because of economic and energy constraints, an operating temperature of 35 °C is recommended for anaerobic digestion of vinasse. The graph of the interaction of temperature and pH shows that at higher temperatures the rate of gas production increases with increasing pH. Although the highest gas volume was obtained at pH of 6.8 and 7.4, but the gas produced in the pH range of 7–7.2 was more pure. Therefore, the best combination of pH and temperature to produce the highest and purest gas is 7 and 35 °C, respectively. But since the vinasse produced in the alcohol factories has high temperature and therefore higher temperatures are possible, so 40 °C is also recommended.It was also clearly observed that the smaller the volume of gas produced, the greater its purity.The VS-R factor is also more sensitive to temperature changes than to pH changes. Thus, in anaerobic digestion of vinasse, pH control is more important than temperature control. VS-R performs best at pH 7. This factor was not significantly different at 35, 40 and 45 °C. Therefore, considering the cost of providing more heat at temperatures of 40 and 45 °C compared to 35 °C, 35 °C is the best temperature for manure production with the highest volatile organic matter removal.The COD-R process was similar at all pHs. COD-R at pH 7 was higher at all temperatures than at other pHs. It was also significantly higher at 40 and 45 °C, compared to other temperatures. So like other factors, the best pH and temperature based on this factor are 7 and 40 °C, respectively.Conclusion According to all factors studied, the best pH and operating temperature of anaerobic digestion of sugar cane vinasse is 7 and 35 ° C, respectively. Another important conclusion to be drawn from this study is that changes in all parameters studied are affected by pH changes rather than temperature changes. Therefore, sufficient care must be taken to ensure that pH variations in the anaerobic digestion medium be very low and around the range proposed (about 7).
Energy and Renewable Energies
M. Soleymani; Alireza Keyhani; Mahmood Omid
Abstract
Introduction Replacing fossil fuels with renewable and environmentally friendly fuels is so essential, due to issues such as climate change, increasing fossil fuels prices, energy security and limitations of fossil fuels resources. Alternatives are wind energy, solar energy, geothermal energy, hydropower, ...
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Introduction Replacing fossil fuels with renewable and environmentally friendly fuels is so essential, due to issues such as climate change, increasing fossil fuels prices, energy security and limitations of fossil fuels resources. Alternatives are wind energy, solar energy, geothermal energy, hydropower, biomass and biofuel. Currently, ethanol produced from sugarcane in Brazil or from corn in USA is the most dominant bioufuel in the world. However there is no comprehensive agreement on the environmental benefits of alternative fuels including ethanol. The aim of this study was to conduct a LCA (Life Cycle Assessment) on ethanol produced from sugarcane molasses in Iran and also to compare its environmental impacts with a conventional fossil fuel. Materials and Methods All required data was obtained from Sugarcane Agro-industry and ancillary Industry Development, Karoon Agro-Industry and also from recorded databases. Economic allocation was chosen to allocate emissions between the main product and the byproducts. Also, Simapro software was applied to model and evaluate the life cycle environmental effects in the life cycle of sugarcane molasses based ethanol (from cultivating sugarcane to burn ethanol into the engine). Two different scenarios of ethanol production (existing system and modified system) were considered and the environmental impacts of these two systems were compared with each other. Finally the environmental impacts of whole life cycle of molasses based ethanol were compared to that’s of diesel as a conventional fossil fuel. Results and Discussion Life cycle inventory results showed that electricity, P2O5 and urea respectively had the most negative environmental impacts through the life cycle of molasses based ethanol. Replacing the fossil fuel originated electricity with electricity from renewable resources can have a significant effect on reducing the amount of these negative impacts. Also, producing electricity in the nearest location to the consumption sites will reduce the power transmission losses and consequently reduce these impacts. Since the major share of electricity is used for pumping water to the field, better management of water consumption is so essential. According to the results, in case of emissions, there was significant difference between diesel fuel and sugarcane molasses ethanol in the base scenario. But by modifying the production system and using bagass to produce biogas or electricity (scenario 2), the environmental impacts of life cycle of sugarcane molasses based ethanol would reduce by 10%. Even now, the amount of greenhouse gas (GHG) emission of ethanol is 60% lower than these emissions of diesel fuel. This reduction will reach 70% if wasted bagass in ordinary production system is used to produce biogas and electricity. Comparing with diesel fuel, Molasses based ethanol had less negative impacts on impact categories such as Respiration Inorganics, Climate Change, Acidification/Eutrofication, and fossil fuels and more negative impacts on categories such as Land Use and Carcinogens, only because of using land and also using herbicides and pesticides to cultivate sugarcane. Greenhouse gas emission in the life cycle of one mega joule molasses based ethanol, estimated by Biograce model, is respectively 69, 70 and 60 percent lower than that of gasoline, diesel and natural gas. Due to undeveloped industries to process sugarcane and its byproducts in Iran, studies on the production of ethanol from molasses or electricity from bagass are in the area of waste management. Therefore, in these cases, even if it there was suitable energy or environmental indicato, continuing the production of these products is justified according to other side issues including environmental benefits and employment. Conclusion In terms of environmental aspects, in the current situation there are no significant differences between ethanol and diesel. But if bagass is used to generate electricity, the environmental impact of ethanol production will reach reduced by 10%. Greenhouse gas emissions of ethanol is 60% lower than that of from diesel and this amount will be 70%, if wasted bagass is used to produce biogas or electricity. It is possible to obtain more environmental benefits by applying appropriate management strategies in ethanol production system (such as producing value added products from bagass or other waste materials). Since sugar is the main product in sugarcane industry in Iran and approximately all other byproducts are wasted, to prevent the loss of this valuable byproduct, producing ethanol from molasses, even if in current situation and with current production system is acceptable.
