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    A Critical Overview of the State-of-the-Art Methods for Biogas Purification and Utilization Processes
    (Mdpi, 2021) Atelge, Muhamed Rasit; Senol, Halil; Djaafri, Mohammed; Hansu, Tulin Avci; Krisa, David; Atabani, Abdulaziz; Eskicioglu, Cigdem
    Biogas is one of the most attractive renewable resources due to its ability to convert waste into energy. Biogas is produced during an anaerobic digestion process from different organic waste resources with a combination of mainly CH4 (similar to 50 mol/mol), CO2 (similar to 15 mol/mol), and some trace gasses. The percentage of these trace gases is related to operating conditions and feedstocks. Due to the impurities of the trace gases, raw biogas has to be cleaned before use for many applications. Therefore, the cleaning, upgrading, and utilization of biogas has become an important topic that has been widely studied in recent years. In this review, raw biogas components are investigated in relation to feedstock resources. Then, using recent developments, it describes the cleaning methods that have been used to eliminate unwanted components in biogas. Additionally, the upgrading processes are systematically reviewed according to their technology, recovery range, and state of the art methods in this area, regarding obtaining biomethane from biogas. Furthermore, these upgrading methods have been comprehensively reviewed and compared with each other in terms of electricity consumption and methane losses. This comparison revealed that amine scrubbing is one the most promising methods in terms of methane losses and the energy demand of the system. In the section on biogas utilization, raw biogas and biomethane have been assessed with recently available data from the literature according to their usage areas and methods. It seems that biogas can be used as a biofuel to produce energy via CHP and fuel cells with high efficiency. Moreover, it is able to be utilized in an internal combustion engine which reduces exhaust emissions by using biofuels. Lastly, chemical production such as biomethanol, bioethanol, and higher alcohols are in the development stage for utilization of biogas and are discussed in depth. This review reveals that most biogas utilization approaches are in their early stages. The gaps that require further investigations in the field have been identified and highlighted for future research.
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    A critical review of pretreatment technologies to enhance anaerobic digestion and energy recovery
    (Elsevier Sci Ltd, 2020) Atelge, M. R.; Atabani, A. E.; Banu, J. Rajesh; Krisa, David; Kaya, M.; Eskicioglu, Cigdem; Kumar, Gopalakrishnan
    Biogas production from different waste resources still has limitations due to its complex structure and slowly biodegradable nature. To improve methane yield and anaerobic digestion performance, various substrate pretreatment methods have been suggested. This paper reviews the latest trends, progress, and research achievements about pretreatment technologies to improve anaerobic digestion efficiency. The pretreatment techniques are divided into four main groups which are physical, chemical, biological, and combined. The effect of inhibitor formation during the pretreatment process is discussed. The energy performance, economics, and environmental impact of these pretreatment technologies are revealed. This study concludes with future trends and emphasizes the necessity of pretreatment methods.
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    Öğe
    Comparative investigation of multi-walled carbon nanotube modified diesel fuel and biogas in dual fuel mode on combustion, performance, and emission characteristics
    (Elsevier Sci Ltd, 2022) Atelge, M. R.; Arslan, Esenay; Krisa, David; Al-Samaraae, R. R.; Abut, Serdar; unalan, Sebahattin; Atabani, A. E.
    Biogas has been investigated as an alternative biofuel in dual fuel operating mode in a direct injection diesel engine. However, there is not sufficient information about using modified fuels with biogas. This study aimed to investigate the effects of modified diesel fuel and biogas on combustion behavior, performance, and emissions characteristics at 1500 rpm constant speed with 5 different load conditions at an interval of 25%. Diesel was modified with multi-walled carbon nanotubes with 30, 60, and 90 ppm. Diesel fuel and three modified fuels were used as pilot fuel and biogas was introduced through the intake manifold with the flow rate of 500 g/h as the primary fuel. Diesel mode fuels were denominated F1 while dual fuel mode fuels were labeled as F2, and the concentration levels were given subscript such as F2 (@60ppm). The experimental study revealed that modified fuel showed better combustion behaviors, performance, and emissions in comparison to diesel fuel. Further, the same trend was observed in the dual fuel mode. The maximum pressure of F2(@60 ppm) was 1% higher than F2 under dual fuel mode at the full load. Moreover, the coefficient of variation of the indicated mean effective pressure for dual fuel mode was found approximately 9.2, 6.9, 6.2, and 7.2% for F2, F2(@30 ppm), F2(@60 ppm), and F2(@90 ppm), respectively at full load. In addition, the energy share of biogas increased by 7.9, 8.7, and 7.1% for F2(@30 ppm), F2(@60 ppm), and F2(@90 ppm), respectively in comparison with F2 at full load. The highest decrease of brake specific energy consumption under the dual mode was obtained to be an 8% drop from F2(@60 ppm) compared to F2 at full load. At the same load, the brake thermal efficiency of F2(@30 ppm), F2(@60 ppm), and F2(@90 ppm) were noted to be 30.2, 30.4, and 30.0%, respectively which are higher than F2 (27.9%). The value of replaced diesel with biogas was noted 0.09, 0.23, 0.24, and 0.22 kg/h for F2, F2(@30 ppm), F2(@60 ppm), and F2(@90 ppm), respectively under the full load condition. Lastly, CO and HC emissions were almost the same value with and without modified fuel for dual fuel mode at the full load. Nevertheless, NO emission was slightly increased with modified fuel compared to F2. From these findings, it can be suggested that 60 ppm multi-walled carbon nanotubes additive can be an optimum level for combustion, performance, and emissions under the dual fuel mode.