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.
M.J. Malekzadeh; M. Kiani Dehkiani; M. Sajadiyeh
Abstract
Introduction The limitation of fossil fuels and environmental pollution by using them have encouraged researchers toward renewable fuels. The most important renewable fuels are bioethanol, biodiesel and biogas. Biogas is a gas that is produced from biodegradable fermentation, agricultural products ...
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Introduction The limitation of fossil fuels and environmental pollution by using them have encouraged researchers toward renewable fuels. The most important renewable fuels are bioethanol, biodiesel and biogas. Biogas is a gas that is produced from biodegradable fermentation, agricultural products and wastes, animal waste and urban waste by anaerobic digestion. One of the products that has a significant amount of waste is sugar cane. This plant is widely cultivated in Khuzestan Province and annually produces a lot of waste which is currently not useful. One of the most important wastes is bagasse. Bagasse is the solid residues after crushing sugar cane and extracting it. Bagasse is composed of cellulose (45%), humiculus (27%), lignin (21%), extract (5%) and a small amount of inorganic salts (2%). A lot of bagasse is produced in sugar cane production process (about 240 kg with a moisture content of 50% per ton of sugar cane). Every year, a lot of bagasse is wasted. One of the most useful ways is to convert it into biogas and provide the percentage of the required thermal and electrical energy of the plant. Therefore, in this study, the effect of temperature and percentage of cow manure as an additive on biogas production from bagasse sugar cane was investigated. Materials and Methods The used bagasse in this research was provided from Farabi industry and Cultivation, located 48 km from Ahwaz, and a cow manure was provided from a livestock farm in Hamidieh, Ahwaz. In order to increasing the production efficiency of biogas, sugar cane bagasse was milled. Batch reactors of 4 liters was used to produce biogas from sugar cane bagasse. To control and maintain the working temperature, the reactors were placed in a water bath and the temperature of the bath was kept constant by using the thermal element and the thermostat. Cow manure was used to provide source of microorganisms. Cow manure with 5, 10, 15 and 20% weight percentages (B5, B10, B15 and B20) was blended with bagasse (numeric index of B indicates the percentage of cow manure in the blends). Sodium bicarbonate was used to control the pH of the reactors. Stirring was carried out manually in order to homogenize the materials and prevent the formation of hard layer at the top of the reactors. The amount of produced biogas was daily measured by water displacement method. Another measured parameter was the total Solid Index (TS), which represents the percentage of organic and inorganic matter for materials of the reactors. The experiments were carried out by using eight reactors for 30 days and the results were analyzed by completely randomized factorial design. Results and Discussion The results of variance analysis of biogas production in terms of bagasse to cow manure ratio and temperature changes showed that they had a significant effect at 1% level on biogas production. Considering the interaction effects of temperature and bagasse to cow manure ratios have a significant effect on the produced biogas at a 1% level. The results showed that with increasing in the percentage of cow manure in the materials, the amount of biogas production increased at both temperatures, so that by increasing the ratio of cow manure in the blends from 5 to 20% at 35 and 45 ° C, the produced biogas increased by 27.78% and 81.83%, respectively. By increasing the percentage of cow manure in the blends, the number of microorganisms in the digestion increased, and as a result of their activity, the amount of produced biogas increased. It was also observed that with increasing the temperature of digestion from 35 ° C to 45 ° C, the biogas production for B5, B10, B15 and B20 blends increased by 19.82%, 22.5%, 15.85% and 80.8%, respectively. The highest amount of cumulative production of biogas was obtained 0.3 m3.kg.VS-1 for 45 ° C and 20% cow manure to bagasse ratio. Conclusion In this research, the effect of cow manure in blend of sugar cane bagasse and temperature on produced biogas was investigated. The experiments were carried out at two temperatures of 35 and 45 ° C, and four blends with different weight percentages from cow manure to bagasse (5, 10, 15 and 20 percent). The results showed that with increasing the percentage of cow manure in blends, the amount of biogas production increased. Also, with increasing temperatures from 35 ° C to 45 ° C, the production of biogas in all blends increased.
Biofuels
Mostafa Parsaee; Mostafa Kiani Deh Kiani; Zabiollah Mahdavifar
Abstract
Introduction Anaerobic digestion has progressed rapidly since the late 1960s. With the progress of the anaerobic fermentation process in the world, anaerobic reactors have been developed to digest different types of organic wastes in each country. So various types of reactors have been built, and that ...
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Introduction Anaerobic digestion has progressed rapidly since the late 1960s. With the progress of the anaerobic fermentation process in the world, anaerobic reactors have been developed to digest different types of organic wastes in each country. So various types of reactors have been built, and that they have been in different shapes, dimensions, and operating conditions. One of these reactors is the static granular bed reactor (SGBR). SGBR with its granular bed digests a substrate in less hydraulic retention time (HRT). SGBR is a downstream reactor that consists of active anaerobic granules. The biomass contacts the granular surfaces and does not require the use of mixers, gas, solid, and a separator. The reactor startup is very short since there is no need for some operations, such as extra time to grow microorganisms in the granule. One of the most important residues in the alcohol production plant from molasses is vinesse which has become a major problem in this industry. The conversion of vinasse to biogas and using it to supply the energy of the industry is one of the basic ways to solve this problem. Several studies have been conducted in this field by using various reactors, but there is no research about SGBR. In this study, an SGBR producing biogas from vinasse has been designed and constructed. Also, the performance of the reactor was investigated at three HRTs (2, 3, and 4 days) and the thermophile temperature of 55 °C. Materials and Methods The best diameter to height ratio (reactor volume) in the SGBR is 1:7. Accordingly, the shape of the reactor is a pipe. Based on the volume of the reactor and the maximum pressure inside it, a 4-inch polyethylene tube with a height of 1 meter was selected to carry out the testes. According to the thermophile temperature (55 °C) and the accuracy of the element (0.9 °C), the maximum temperature of the reactor is 329 K. Therefore, the minimum power for obtaining this temperature is 405.316 watts. The water displacement method was used to measure the amount of biogas. An iron sponge was used for removing hydrogen sulfide gas from biogas. Sodium hydroxide solution was used to remove carbon dioxide from biogas. Results and Discussion The reactors were loaded daily with organic matter (86002, 28667, and 21500 mgCOD/L.d) for different HRTs (2, 3, and 4 days). For three HRTs, the amount of methane production was high during the first day which is due to the thermal shock caused by the microorganisms in the granule. Methane production in HRT of 2 days had fewer variations than HRT of 3 and 4 days, and after 13 days, it reached a nearly constant value of 4600 ml/day. For HRT of 3 days, the daily rate of methane production reached a constant value of 4800 ml/day after 12 days and for HRT of 4 days, it reached 4,900 ml/day after 10 days. For HRTs of 2 and 3 days, the rate of methane production per unit of volatile solids had less variation and remained constant approximately after 7 days. The average methane production per unit of volatile solids at HRT of 4 is days higher than the other HRTs. The average methane production for HRTs of 2, 3, and 4 was 379, 380, and 433 CH4 (L)/VS (kg), respectively. The maximum value of methane production was 582 m3/kgCOD, which was obtained at HRT of 2 days. In this study, 31 liters of methane were produced per one liter of vinasse at HRT of 4 days, which was more than other studies. Conclusion In this study, the required heat power and pressure inside the SGBR laboratory have been calculated. The minimum required heat is 261 watts. Also, this reactor should be able to bear at least 4.34 bar for biogas production. The average amount of methane production per unit of volatile solids was 379, 380, and 433 CH4 (L)/VS (kg) at HRTs of 2, 3, and 4 days, respectively. The maximum amount of produced methane was 582 m3/kgCOD, which was achieved at HRT of 2 days, and the maximum percentage of COD reduction was 39%, which was achieved at HRT of 4 days. In general, the results indicated that SGBR produced higher biogas from vinasse than other reactors, but it is not suitable for reducing pollutions.
S Rostami; M Eslami; M. Kiani Deh Kiani
