Browsing by Author "Hanna, Berhanu"

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    Characterization, Valorization and Optimization of Enset /Ensete Ventricosum/ Fibers for Paper Pulp Production
    (Addis Ababa University, 2018-12) Hanna, Berhanu; Zebene, Kiflie (PhD)
    Enset /Ensete ventricosum [Welw.] Cheesman/ is exploited as a food crop in Ethiopia where it represents an important staple food. The plant is harvested and large amounts of biomass residues are originated, mainly from the pseudo stem (i.e., fiber bundles obtained from the leaf sheaths after being scrapped to produce starchy food) and the inflorescence stalk. These materials were studied in relation to their summative chemical composition, composition of lignin, lipophilic and polar extracts. Moreover, their structural characteristics, in view of their valorization, were scrutinized. The analytical studies were performed with the aid of FTIR, GC/MS and Py-GC/MS. The fiber bundles are aggregates of mainly long and slender fibers with low ash, extractives and lignin contents (3.8%. 4.4% and 10.5% o.d. based respectively) and high holocellulose and α-cellulose contents (87.5% and 59.6% o.d. based respectively). The hemicelluloses in the fibers are mostly highly acetylated xylans and the lignin is of the H-type (H:G:S, 1:0.7:0.8). This lignin composition is in line with the FTIR peaks at 1670 cm-1 and 1250 cm-1. The inflorescence stalk has high ash content (12.3% in the main stalk and 24.6% in fines) with a major proportion of potassium, and high extractives, low lignin and α-cellulose contents (25.9%, 5.8% and 17.9% respectively). The stalk includes numerous starch granules in the cellular structure with the predominant presence of parenchyma. The potential valorization routes for these materials are clearly different. The fiber bundles could be used as a fiber source for paper pulp production with the possibility of a prior hemicelluloses removal while the inflorescence stalk has nutritional value for food and fodder. Based on the above result, the Enset fiber was further delignified by sulfur-free ethanol-alkali pulping. Response surface methodology with central composite experimental design was used to evaluate the effects of four independent process variables (pulping temperature, time, ethanol concentration and alkali concentration) on pulp yield, kappa number and color of the resulting pulp. The major parameters influencing pulp yield and kappa number were found to be the alkali concentration followed by temperature. For the predicted optimal pulping conditions, the pulp yield was 69.9% with 4.9 kappa number and 64.5% brightness. The ethanol-alkali pulp obtained at center conditions was characterized by viscosity and strength properties and compared with Kraft pulp, showing comparable burst, tensile strength and tear strength. Results suggest that the valorization of the Enset fibers for production of well delignified, high yield and resistant pulp is a promising approach. The effects of un-catalyzed and alkali-catalyzed (0.1% NaOH) hydrothermal pre-treatment on the fractionation of the Enset fiber bundle material were made to recover hemicellulose sugars prior to ethanol alkali pulping. The treatments were analyzed at 130ºC, 150ºC, 180ºC, and 200ºC and the composition of the solids regarding lignin and monomeric sugar and of the liquid phase were evaluated. Temperature-dependent mass loss was observed in both catalyzed and un-catalyzed treatment. The liquor was rich in oligosaccharides with a maximum recovery achieved with the alkali-catalyzed hydrothermal treatment at 130ºC for GOS (12.4 g/100 g of original dry sample) and at 180ºC for XOS (3.4 g/100 g of original dry sample). The fibrous nature of the material was preserved after the treatment. Hence, the solid residue was further delignified by using ethanol reinforced alkali pulping at near optimum point (40% ethanol conc., 15% alkali conc., 140oC, 60 min). At the optimum point, the maximum pulp yield of treated Enset fiber was found to be 61.0% per original sample (69.6% per treated sample) which is comparable to pulping of original sample 69.1%. Therefore, the hydrothermal treatments can be applied as a first fractionation step in the valorization of Enset fibers, allowing the subsequent use of the solid as a fiber source for pulping.
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    Cost Effective Frequency control of Micro Hydro Power Plant
    (AAU, 2018-03) Hanna, Berhanu; Mengesha, Mamo (PhD)
    Micro Hydro-Power Plants (MHPPs) are a reliable solution for supplying small power consumers in areas located far from the distribution grid. However controlling frequency of the generated power is one of the main problems in micro hydro power plants. This thesis presents a control structure that ensures the frequency regulation of an induction generator (IG). Induction generator is chosen over synchronous generator because it has an advantage with price, robustness, simpler starting and controlling mechanism. The main work of this thesis is to design a cost effective frequency controller for MHPP. For the control of the frequency, a fuzzy logic controller is used. The controller is modeled, designed and simulated to be simple, fast response fuzzy logic based frequency control system and lower cost. For lower cost, the fuzzy logic controller is realized using Field Programmable gate array rather than microcontrollers. The frequency controller controls frequency of the micro hydro-power plant nearly constant. When the flow of water is minimum, the controller is designed to prevent component from damage by initiating a shutdown. It is observed from the simulation results that the overshoot of the fuzzy controller for 75% load change and 0.2 m 3 /s flow rate is 2.74%, 3.04% and 3.46% and the settling times are 20.87, 27.65 and 39.82 seconds. Moreover, the comparison of fuzzy logic controller and PI controller is observed. The fuzzy logic controller has been coded, compiled and simulated in VHDL using ModelSimAltera. From simulation result, the system inferred maximum operating frequency is 5 MHz with a critical path of 199.3 ns.