Browsing by Author "Amini, Shahriar"

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    Carbon Capture Utilization and Storage in Methanol Production Using a Dry Reforming-Based Chemical Looping Technology
    (American Chemical Society, 2022) Ugwu, Ambrose; Osman, Mogahid; Zaabout, Abdelghafour; Amini, Shahriar; Norwegian University of Science & Technology (NTNU); SINTEF; University of Alabama Tuscaloosa
    This further investigates the concept of gas switching dry reforming (GSDR) that efficiently converts the two major greenhouse gases (CO2 and CH4) into a valuable product (syngas) for gas-to-liquid (GTL) syntheses. The proposed GSDR is based on chemical looping technology but avoids external circulation of solids (metal oxides) by alternating the supply of reducing and oxidizing gas into a single fluidized bed reactor to achieve redox cycles. Each cycle consists of three steps where a metal oxide/catalyst is first reduced using GTL offgases to produce CO2 (and steam) that is supplied to the next reforming step to produce syngas for GTL processes. The metal oxide is then reoxidized in the third step associated with heat generation (through the exothermic oxidation reaction of the metal oxide and air) to provide the heat needed for the endothermic dry methane reforming step. Experimental demonstrations have shown that a syngas H-2/CO molar ratio between 1 and 2 suitable for methanol production could be achieved. A further demonstration shows that pressure has negative effects on gas conversion. Following the successful experimental campaign, process simulations were completed using ASPEN to show how the GSDR process can be integrated into a methanol (MeOH) production plant.
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    Combined Syngas and Hydrogen Production using Gas Switching Technology
    (American Chemical Society, 2021) Ugwu, Ambrose; Zaabout, Abdelghafour; Donat, Felix; van Diest, Geert; Albertsen, Knuth; Muller, Christoph; Amini, Shahriar; SINTEF; Swiss Federal Institutes of Technology Domain; ETH Zurich; University of Alabama Tuscaloosa; Norwegian University of Science & Technology (NTNU)
    This paper focuses on the experimental demonstration of a threestage GST (gas switching technology) process (fuel, steam/CO2, and air stages) for syngas production from methane in the fuel stage and H-2/CO production in the steam/ CO2 stage using a lanthanum- based oxygen carrier (La0.85Sr0.15Fe0.95Al0.05O3). Experiments were performed at temperatures between 750-950 degrees C and pressures up to 5 bar. The results show that the oxygen carrier exhibits high selectivity to oxidizing methane to syngas at the fuel stage with improved process performance with increasing temperature although carbon deposition could not be avoided. Co-feeding CO2 with CH4 at the fuel stage reduced carbon deposition significantly, thus reducing the syngas H-2/CO molar ratio from 3.75 to 1 (at CO2/CH4 ratio of 1 at 950 degrees C and 1 bar). The reduced carbon deposition has maximized the purity of the H-2 produced in the consecutive steam stage thus increasing the process attractiveness for the combined production of syngas and pure hydrogen. Interestingly, the cofeeding of CO2 with CH4 at the fuel stage showed a stable syngas production over 12 hours continuously and maintained the H-2/CO ratio at almost unity, suggesting that the oxygen carrier was exposed to simultaneous partial oxidation of CH4 with the lattice oxygen which was restored instantly by the incoming CO2. Furthermore, the addition of steam to the fuel stage could tune up the H-2/CO ratio beyond 3 without carbon deposition at H2O/ CH4 ratio of 1 at 950 degrees C and 1 bar; making the syngas from gas switching partial oxidation suitable for different downstream processes, for example, gas-to-liquid processes. The process was also demonstrated at higher pressures with over 70% fuel conversion achieved at 5 bar and 950 degrees C.
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    Development and Modelling of Self-Sufficient Wastewater Treatment with Near Zero Emissions
    (University of Alabama Libraries, 2022) Erguvan, Mustafa; Amini, Shahriar; University of Alabama Tuscaloosa
    A report published by the United Nations Water states that access to clean water will be a significant problem for more than 6 billion people by 2050 with population and water demand increasing. So as to mitigate water shortages, wastewater recovery with proper treatment can have an important contribution. Apart from water shortage, the water-energy-nexus (WEN) has been a key consideration owing to close connection and dependency of water and energy to each other. WEN also plays a key role in wastewater treatment plants (WWTPs), especially in developed countries, due to the fact that treatment of wastewater requires a significant amount of electricity usage. In this dissertation, two different models are developed to investigate the self-sufficiency of WWTPs in terms of energy with near-zero emissions. Chapter 1 discusses current and past studies involving the water energy nexus, wastewater treatment methods, activated sludge process, biomass conversion methods, anaerobic digestion, biogas utilization, self-sufficient WWTPs, CO2 capture techniques as well as oxy – fuel combustion processes. In the second chapter, a numerical model has been created to investigate the energetical self-sufficiency of a novel integrated energy system in a WWTP. The proposed system consists of an activated sludge process, an anaerobic digester, a Brayton cycle, and a Rankine cycle. In order to investigate energy and exergy efficiencies along with self-sufficiency ratio, several parametric studies have been conducted by varying some decision variables. While biological oxygen demand and dissolved oxygen level have been varied in the WWTP part, turbine inlet temperature, compression ratio, and preheater temperature have been used as decision variables in the power cycle. This work presented here suggests that up to 109% of the energy needed to treat wastewater can be provided using the proposed system. The optimum values and dominant parameters to achieve the highest self-sufficiency ratio have been determined as well. The highest exergy efficiencies for the WWTP, cogeneration system and overall system were found to be 58.36%, 44.59%, 36.6%, respectively. A subsequent study investigates the integration of activated sludge process, anaerobic digestion, and an oxyfuel combustion process in a WWTP in order to provide a plant which is not only energetically self-sufficient but also emission free. Several parametric studies have been conducted to investigate their effects on the thermodynamic efficiencies as well as self-sufficiency ratio. The most dominant factors were found to be wastewater strength and compression ratio. While the overall exergy efficiencies varied from 19.38 to 32.59%, self-sufficiency ratio changed from 82.29 to 132.4%. In addition, more than 95% of the CO2 has been captured and recycled in the combustion chamber. This study proves that an energetically self-sufficient WWTP with near zero emission is plausible.