Energy and Renewable Energies
Davood Mohammadzamani; Mahdi Jafari; Mohammad Rasooli
Abstract
Introduction The yield of methane production in the anaerobic digestion processes of municipal organic solid waste alone is low. Adding animal waste or other additives to municipal solid waste as feed for anaerobic digestion system not only increases the relative composition of methane, but also increases ...
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Introduction The yield of methane production in the anaerobic digestion processes of municipal organic solid waste alone is low. Adding animal waste or other additives to municipal solid waste as feed for anaerobic digestion system not only increases the relative composition of methane, but also increases the rate of biogas production (Rivas-García, 2020). Carbon and nitrogen are essential elements for the growth and reproduction of aerobic microorganisms. The balanced ratio for C/N in the process is between 20-30. Simultaneous digestion is used to balance the C/N ratio (Yousefi & Bahri. 2021). This process has many advantages, including the synergistic effect of microorganisms, increasing the stability of the process, increasing the efficiency of biogas, increasing the recycling of nutrients and reducing odor.
Materials and Methods This research was carried out with the aim of increasing the rate of biogas production, reducing the feed retention time in the digester and increasing the amount of biogas production, by investigating the effect of co-digestion of urban solid organic waste with cow excrement using anaerobic digestion method. For this purpose, 52 samples of mixed urban waste (during the year 1400, once a week and one sample each time) were prepared from the waste transfer station of Qazvin city, and in order to investigate the effect of animal manure on the studied variables, from a cattle farm located in 50 kg of fresh manure was collected in the region. After preparing the samples, a laboratory bioreactor was used to perform the experiments. The biogas production process was carried out in two stages. In the first stage, urban waste materials were used, and in the second stage, a combination of urban waste materials and animal manure was used.
Results and Discussion The ratio of carbon to nitrogen (C/N) in the primary feed and residual materials was obtained in the first and second stages. In this way, this ratio was estimated as 19.39 and 27.64 for the primary feed and the remaining materials in the first stage and 18.60 and 28.23 respectively for the second stage.
In this study, the amount of ash decreased during the process, which indicated the participation of this substance in improving the activity of microorganisms. In both stages of the experiments, the organic matter of the primary feed decreased during the digestion process, which indicates the decomposition of these materials during the process. Also, the conversion percentage of dry material from primary feed to secondary material in stage 1 and 2 was 8.2% and 10.5%, respectively, which shows that in the second stage, in which the combination of animal manure was used, the percentage of conversion The dry matter is more and the process has progressed towards the production of biogas.
The changes in the pressure of biogas inside the tank in the experiment related to stage 1 reached its maximum value (0.19 bar/kg) within 23 days after the start of the process, and then stabilized at 0.14 bar/kg of solid material in the last seven days. Is. Since the criterion for the completion of the digestion process was pressure stabilization in seven consecutive days, therefore, after 38 days, the first stage process was completed and the biogas and residual (secondary) materials were discharged. The maximum biogas pressure in the second stage test was 0.28 bar/kg of solid material, which was achieved on the 15th day, and finally, after 26 days, the pressure reached 0.16 and stabilized at this pressure for seven days. Therefore, the digestion process in the second stage lasted for 32 days. Therefore, it can be seen that by using animal manure in the primary feed and keeping other variables constant, the retention time has decreased by 6 days compared to the first stage.
The maximum amount of biogas produced in stage 1 was equal to 6.27 liters/kg of solid matter and in stage 2 it was equal to 10.3 liters/kg of solid matter. As can be seen, by using animal manure in combination with urban organic waste, the volume of biogas production has increased under the same conditions. Taking into account the cumulative amount of biogas production, it was found that in stage 1 and 2, 140.89 and 230 liters/kg of solid biogas were produced during the digestion period, respectively. Therefore, the efficiency of biogas production has increased by 38%. Although the total amount of biogas produced in both stages of the experiments compared to the theoretical values obtained in this study (at the rate of 370 liters/kg of solid matter) and also reported by other researchers (Salehoun, et.al, 2020 and Kozminesky , 1995) has been less.
Conclusion According to the results of this study, it was found that in the second stage compared to the first stage, the role of the two elements carbon and nitrogen in the biogas production process became more effective and one should expect more biogas production in the process, because the increase in the conversion of organic matter and nitrogen is The more effective decomposition of these materials by microorganisms has been achieved by adding animal manure to the primary feed.
According to the results obtained from this study, it can be concluded that in the process of biogas production, the combination of animal manure with urban organic waste, in addition to reducing the retention time, can help to increase the efficiency of biogas production, which in this study A 38% increase in biogas production was observed in the case of using a combination of animal manure with urban organic waste compared to using only urban organic waste. Although the role of other variables such as temperature, type and amount of stirring, type of initial preparation of materials in terms of size, humidity, pH, addition of yeast and bacteria, degree of impurity and toxicity of materials, ratio of carbon to nitrogen, type and size of reactor and other examined the variables.
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.
Energy and Renewable Energies
Ahmadreza Abdollahpour; Reza Tabatabaee; Jafar Hashemi
Abstract
Introduction: Agricultural residues and wastes are the main source of biomass for use in bioenergy production and animal and poultry feed production industries. These biomasses in their original form have a large volume and low energy (per unit volume) and require a lot of space and extensive movement. ...
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Introduction: Agricultural residues and wastes are the main source of biomass for use in bioenergy production and animal and poultry feed production industries. These biomasses in their original form have a large volume and low energy (per unit volume) and require a lot of space and extensive movement. Therefore, one of the methods of optimal use of these biomasses is to transform them into pellets, which have more mass and energy per unit volume and enable their easier use and transportation. Currently, biomass has the fourth place in energy supply after oil, natural gas and coal and provides approximately 14% of the world's energy needs. The use of biomass, especially in European Union countries, as an attractive source for replacing fossil fuels is developing and expanding. The use of biomass as fuel has significantly reduced the amount of environmental pollutants, so that the amount of CO2 absorbed from the atmosphere during biomass growth is similar to the amount produced during combustion, followed by a net cycle of production. Materials and Methods: The raw materials for making pellets were prepared from spruce wood sawdust (collected from a sawmill in Sari) as well as corn stalk and soybean residues in the fields of Dasht Naz in Sari. The desired materials were transferred to the laboratory in the necessary amount and kept at ambient temperature until the experiments. The samples were first crushed into 20 mm sizes and then powdered using a grain mill (Mehr Tehiz company, Iran) and passed through 18 mesh sieves in the range of 1 mm to make pellets. A palletization mechanism was used to compress the pellet. This system was designed and built in biosystem mechanics of Sari University of Agricultural Sciences and Natural Resources. The material was placed inside a steel mold with a cylinder inner diameter of 8.05 mm and a height of 150 mm with a blocked end. A piston with a diameter of 8 mm connected to the driving arm of the tension-compression test machine was used to compress the material. Loading by a piston with a quasi-static speed of 5 mm per minute is compressed to a pressure of 1300 N.Results and Discussion: In this research, the mechanical and thermal properties of pellets made from the combination of spruce sawdust and corn and soybean residues were evaluated. In the present study, the effect of four combinations of agricultural and forest materials at two moisture levels (12% and 18% based on fresh weight) on the indices of density, compressibility, Hausner ratio, strength and calorific value of the produced pellets were investigated and evaluated. it placed. The results showed that the pellet density at 18% humidity was lower than the density at 12% humidity. The highest density related to the combination of 60% spruce wood sawdust-40% corn stalks was obtained with a value of about 149 kg/m3 and the lowest value related to 100% soybean stalks was about 110 kg/m3. Also, the ratio of Hanser and CI in the combined pellets that have a higher percentage of sawdust and also in the combination of sawdust with corn stalks are within the permissible range. The highest pellet strength was 23.8 N/cm corresponding to 100% sawdust at 18% humidity and the lowest was 15.4 N/cm corresponding to 100% soybean stalk at 12% humidity. The calorific value of the pellets is in the range of 14.37 to 18.52 MJ/kg, which is the minimum value for the pellet made from 100% soybean stalk at 18% humidity and the maximum value for the pellet made from 100% fir wood sawdust and It was obtained at a humidity of 12%. Therefore, the use of agricultural wastes and their proper combination is a good option for the production of biofuels due to their density and strength.Conclusion: The type of biological waste and moisture percentage affect the physical and mechanical properties of the produced pellets. In general, the combination of spruce wood sawdust with corn stalks and soybean improved the mechanical and thermal properties of the pellet. Hanser's ratio and compressibility in the combined pellets that have a higher percentage of sawdust and also in the combination of sawdust with corn stalks are within the standard range. Also, in the compositions that have a higher proportion of spruce wood sawdust and lower moisture, the density and strength factors of the pellet increase. The highest and lowest calorific values were obtained in a higher ratio of sawdust and a higher ratio of corn, respectively. Therefore, it is possible to make pellets from the waste of garden and agricultural products that have good density and strength and high calorific value.
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.
Energy and Renewable Energies
M Rekabi; M. H Abbaspour Fard; H Mortezapour
Energy and Renewable Energies
M Mozafari; A Ghazanfari Moghadam; H Hashemipour Rafsenjani; A Atae
