Optimization of sub- and supercritical water gasification of rice husk enhanced with iron-doped alkaline-earth catalysts

A Thesis Submitted in Fulfilment of the Requirements for the Degree of Doctor of Philosophy in Sustainable Energy Science and Engineering of the Nelson Mandela African Institution of Science and TechnologyBiomass is a promising renewable energy source widely available worldwide, particularly in developing countries where clean and affordable energy is a major problem. Biomass gasification is an attractive technology that can transform biomasses into a more versatile fuel known as syngas, tar (bio-oil) and biochar. Syngas is a hydrogen-rich gas that could promote a clean and green energy and promote the agriculture sector. The utilisation of syngas would reduce dependence on fossil-based fuels and eventually reduce the carbon footprints. The gasification technology faces operational challenges; one of the problems is tar formation, slow char gasification reaction, and poor performance of catalysts. These challenges are influenced by inappropriate operating conditions and the precursors employed in catalyst synthesis. In this study, the optimisation of noncatalytic and catalytic gasification of rice husk is reported. The rice husk biomass was gasified under subcritical and supercritical water conditions in a batch autoclave reactor. The effect of temperature (350-500°C), residence time (30-120 minutes), and feed concentration (3-10 wt%) is optimised. Moreover, the effect of the addition of natural, calcined and Fe doped limestone and dolomite catalysts on the gasification yield is studied using a response surface methodology. The catalyst was prepared by a facile incipient wetness process using chlorine- and sulphur-free iron (III) ammonium citrate precursor. Optimisation of operating conditions suggests a quadratic model for gasification efficiency, gas volume, char yield, and gravimetric tar. The findings revealed that higher temperatures, longer residence times and lower feed concentrations favoured high gas yields. The lowest tar yield obtained was 2.98 wt%, while the highest gasification efficiency and gas volume attained was 64.27% and 423 mL/g, respectively. The findings of the catalyst characterisation revealed that the predominant reactive site of Fe/limestone catalyst is iron oxide, calcium ferrite, and calcium oxide. Under all conditions tested, the manufactured catalyst was highly active in promoting char gasification, gas volume and gasification efficiency. Tar yield was substantially promoted at low temperatures and high feed concentrations, but at high temperatures and low feed concentrations (500oC, 3 wt%), tar formation was suppressed by 22%, while char gasification was enormously enhanced by 65%. The maximum gas yield of 560 mL/g biomass was obtained under the catalytic conditions of 5%Fe/limestone, 15% catalyst loading, 500oC, 120 minutes, and 3 wt% feed concentrations. Therefore, these findings revealed that the rice husk's energy content could be harnessed using supercritical water gasification to obtain substantial fuel products

Catalytic supercritical water gasification of biomass waste using iron-doped alkaline earth catalysts

This research article was published by Springer Nature Switzerland AG., 2022The objective of this study is to optimise the process of supercritical water gasification of rice husk biomass utilising a low-cost catalyst made from alkaline-earth materials. The interactions between catalyst loading and Fe content on gasification yield were investigated using response surface methodology. The catalyst characterisation findings revealed that the catalysts’ predominant reactive site is on iron oxide, calcium ferrite, and calcium oxide. Under all the conditions tested, the manufactured catalyst was highly active in promoting char gasification, gas volume, and gasification efficiency whilst the tar yield was substantially elevated. The maximum gasification efficiency of 69.57%, gas yield of 402.8 mL/g biomass, char yield 24.68 wt%, and gravimetric tar yield of 57.5 mg/g were obtained under the catalytic conditions of 15% catalyst loading with 5%Fe/limestone, 492 °C, 120-min residence time, and 9.5 wt% feed concentrations. Thus, the manufactured catalyst showed a potential for optimising gasification outputs

Sub- and Supercritical Water Gasification of Rice Husk: Parametric Optimization Using the I-Optimality Criterion.

This research article published by ACS Publications, 2021In this study, rice husk biomass was gasified under sub- and supercritical water conditions in an autoclave reactor. The effect of temperature (350-500 °C), residence time (30-120 min), and feed concentration (3-10 wt %) was experimentally studied using the response surface methodology in relation to the yield of gasification products. The quadratic models have been suggested for both responses. Based on the models, the quantitative relationship between various operational conditions and the responses will reliably forecast the experimental outcomes. The findings revealed that higher temperatures, longer residence times, and lower feed concentrations favored high gas yields. The lowest tar yield obtained was 2.98 wt %, while the highest gasification efficiency and gas volume attained were 64.27% and 423 mL/g, respectively. The ANOVA test showed that the order of the effects of the factors on all responses except gravimetric tar yield follows temperature > feed concentration > residence time. The gravimetric tar yield followed a different trend: temperature > residence time > feed concentration. The results revealed that SCW gasification could provide an effective mechanism for transforming the energy content of RH into a substantial fuel product

Simulation and optimisation of the pyrolysis of rice husk: Preliminary assessment for gasification applications

This research article published by Elsevier B.V, 2020Thermochemical conversion of biomass into useful products is a promising route to harness biofuels. This process is clean, renewable and can reduce the use of fossil fuel. In this study, SuperPro Designer (SPD) software and response surface methodology (RSM) is used to simulate and optimize rice husk pyrolysis process. The SPD simulator was built to handle kinetics and stoichiometric reaction of lignocellulosic composition of rice husk into final products. The SPD simulation and RSM optimization were performed at a temperature ranging from 350 to 800 °C and residence time of 0.25−60 s. The simulated results were in agreement with product yield published in the literature at an average relative error of 6.8 %. The combined effect of temperature and residence time were analysed by using RSM and analysis of variance (ANOVA). A cubic model for bio-oil and quartic model for char and gas yield were proposed. The desirability function in Design-Expert showed that the optimum bio-oil yield (36.72 %) could be attained at a temperature 588 °C and a residence time 0.25 s while the optimum gas yield (73.25 %) could be achieved at a temperature 798.8 °C and a residence time 15.47 s. These findings therefore revealed that the energy content of the rice husk could be harnessed by pyrolysis/gasification to obtain substantial fuel products

Catalytic tar conversion and the prospective use of iron-based catalyst in the future development of biomass gasification: a review

This research article published by Springer Nature Switzerland AG., 2020Biomass is a promising renewable energy source which is available globally, mostly in developing countries where access to clean and affordable energy is a critical problem. Biomass gasification is an interesting technology that can convert biomasses to a more versatile fuel known as syngas, the energy which can substitute conventional fossil fuels in the future. Syngas can amenably be combusted to produce power and heat as well as a feedstock for synthesis of chemicals and other fuels. The biomass gasification is facing severe operational challenges, one of the problems being tar formation and its removal techniques. Tar condenses at reduced temperature, thus causing blockage in the downstream equipment such as compressors and engines. Many studies have considered syngas cleaning by physical removal and thermal cracking unsuitable as they need downstream processing of scrub liquor and utilizes a part of the produced gas in maintaining the thermal cracking temperature, respectively. The utilization of catalysts has been an interesting focus; however, it has not yet been fruitful as many of the developed catalysts deactivate rapidly, and they are expensive or toxic. The motives of the current study are to review tar formation characteristics and trends on catalytic conversion. In addition, the study elucidates the fascinating behaviour of metallic and oxides of the iron-based catalyst under different syngas composition (oxidizing and reducing environments). The behaviours of the iron-based catalyst indicate its fundamental role in developing a catalyst for tar cracking with respect to less toxic, inexpensive, abundant, and regenerable alternatives

Data from the batch adsorption of ciprofloxacin and lamivudine from synthetic solution using jamun seed (Syzygium cumini) biochar: Response surface methodology (RSM) optimization

This research article was published by Elsevier, 2023This dataset expresses the experimental data on the batch adsorption of ciprofloxacin and lamivudine from synthetic solution using jamun seed (JS) (Syzygium cumini) biochar. Independent variables including concentration of pollutants (10-500 ppm), contact time (30–300 min), adsorbent dosage (1-1000 mg), pH (1-14) and adsorbent calcination temperature (250,300, 600 and 750 °C) were studied and optimized using Response Surface Methodology (RSM). Empirical models were developed to predict the maximum removal efficiency of ciprofloxacin and lamivudine, and the results were compared with the experimental data. The removal of polutants was more influenced by concentration, followed by adsorbent dosagage, pH, and contact time and the maximum removal reached 90%

Ecological consequences of microplastic pollution in sub-Saharan Africa aquatic ecosystems: An implication to environmental health

this article is published on December 1, 2023 at HydroResearch volume 7 page 39-54Microplastic pollution (MPs) emerged as a significant environmental concern due to its persistent nature. These MPs particles endure in waters, soils, and even the atmosphere, posing potential threats to the entire ecosystem. Aquatic organisms are at risk of ingesting MPs, leading to accumulation in tissues, ultimately affecting entire food chain. This study aims to provide an overview of sources of MPs, distribution, and potential environmental impacts. MPs have been documented in various substances such as bottled water, salts, seafood, and even the air. However, the full extent of the health consequences on human exposure remains uncertain. Therefore, it is imperative that we draw public attention to the presence of these pollutants in the environment. To mitigate adverse effects of MPs, reducing plastic consumption, implementing improved waste management practices, and advocating sustainable behaviors are essential for well-being of natural ecosystems and the health human populations

Risk Factors for Small-for-Gestational-age and Preterm Births among 19,269 Tanzanian Newborns.

Few studies have differentiated risk factors for term-small for gestational age (SGA), preterm-appropriate for gestational age (AGA), and preterm-SGA, despite evidence of varying risk of child mortality and poor developmental outcomes. We analyzed birth outcome data from singleton infants, who were enrolled in a large randomized, double-blind, placebo-controlled trial of neonatal vitamin A supplementation conducted in Tanzania. SGA was defined as birth weight <10th percentile for gestation age and sex using INTERGROWTH standards and preterm birth as delivery at <37 complete weeks of gestation. Risk factors for term-SGA, preterm-AGA, and preterm-SGA were examined independently using log-binomial regression. Among 19,269 singleton Tanzanian newborns included in this analysis, 68.3 % were term-AGA, 15.8 % term-SGA, 15.5 % preterm-AGA, and 0.3 % preterm-SGA. In multivariate analyses, significant risk factors for term-SGA included maternal age <20 years, starting antenatal care (ANC) in the 3(rd) trimester, short maternal stature, being firstborn, and male sex (all p < 0.05). Independent risk factors for preterm-AGA were maternal age <25 years, short maternal stature, firstborns, and decreased wealth (all p < 0.05). In addition, receiving ANC services in the 1(st) trimester significantly reduced the risk of preterm-AGA (p = 0.01). Significant risk factors for preterm-SGA included maternal age >30 years, being firstborn, and short maternal stature which appeared to carry a particularly strong risk (all p < 0.05). Over 30 % of newborns in this large urban and rural cohort of Tanzanian newborns were born preterm and/or SGA. Interventions to promote early attendance to ANC services, reduce unintended young pregnancies, increased maternal height, and reduce poverty may significantly decrease the burden of SGA and preterm birth in sub-Saharan Africa

Factors influencing ownership of modern houses among households in Iringa district, Tanzania

MSc. ThesisPoor construction with temporary material exposes families to all kinds of health and safety risks, especially from ticks and insects concealed in unfinished mud walls and earthen floors, vermin and snakes in thatch, parasite seeking human host and malarial mosquitoes entering through unscreened windows and doorway. This study was conducted to identify factors influencing the ownership of modern houses among households in Iringa District. Specifically, the study examined the major factors and materials used in constructing modern houses, identified the time in which the households used to accomplish the construction of modern houses. The study involved 70 respondents and 10 key informants from government institutions in Iringa District. Purposeful sampling was used to identify households owning modern houses. Data were collected using a structured questionnaire, interview schedules and personal observations. In addition, secondary data from several sources were collected. Descriptive statistics such as frequencies, percentage and mean were determined. Qualitative data from personal observations and key informant interviews were summarized and reported. Also linear simple regression model was used to analyse data, particularly in determining major factors influencing rural household’s ownership of a modern house. Findings from the study show that majority of modern houses were constructed using burnt bricks (68.5 %) and un-burnt brick (21.4 %). It was noted that factors like income, education, types of occupation, family size, cultural believes, land ownership, and prices of materials had a significant influence on the ownership of modern houses. It was also found that materials used in the construction of houses were locally available in the study area. On the basis of the study findings, it is recommended that the task of constructing modern houses in rural and urban areas should be carried in such a way government provides loan with low interest and trains more masons by using VETA in order to smoothen the construction of modern house