Unknown input observer design for fault detection and diagnosis in a continuous stirred-tank reactor

Early and accurate fault detection and diagnosis (FDD) minimises downtime, increases the safety and reliability of plant operation, and reduces manufacturing costs. This paper presents a robust FDD strategy for a nonlinear system using a bank of unknown input observers (UIO). The approach is based on structure residual generation that provides not only decoupling of faults from model uncertainties and unknown input disturbance but also decoupling the effect of a fault from the effects of other faults. The generated residual was evaluated through the statistical threshold to avoid fault missing or false alarm. The performance of the robust FDD scheme was assessed by some sensor fault scenarios created in a continuous stirred-tank reactor (CSTR). The simulation result showed the effectiveness of the proposed approach

Carbon dioxide torrefaction of oil palm empty fruit bunches pellets: Characterisation and optimisation by response surface methodology

The carbon dioxide (CO2) torrefaction of oil palm empty fruit bunch (OPEFB) pellets was investigated at various temperatures from 250 to 300 °C and residence times from 15 to 60 minutes. The objective was to investigate the effects of CO2 torrefaction on the yield and characteristics of the torrefied products. The optimal conditions for maximum mass yield (MY) of CO2 torrefaction were also examined by response surface methodology (RSM) using full factorial design. Results revealed that temperature and time significantly influenced the mass (MY), liquid (LY) and gas (GY) yields. The MY and energy yield (EY) decreased with increasing severity of torrefaction, whereas the LY, GY, energy density (DE) and higher heating value (HHV) increased during the process. Characterisation revealed substantial improvements in the microstructure, pH, hydrophobicity and grindability of the torrefied pellets compared with the raw pellets. The thermal ignition and degradation characteristics of the OPEFB pellets were also significantly transformed after torrefaction. The liquid torrefaction products contained an acidic, turbid and pungent mixture of water and organic compounds. RSM optimisation revealed the optimal conditions: temperature of 275 °C and residence time of 35 minutes with the predicted MY of 50.54%, mass loss of ML = 49.46% and HHV = 24.47 MJ/kg. The findings revealed that CO2 torrefaction is a practical approach to clean energy recovery

Physicochemical, mineralogy, and thermo-kinetic characterisation of newly discovered nigerian coals under pyrolysis and combustion conditions

In this study, the physicochemical, microstructural, mineralogical, thermal, and kinetic properties of three newly discovered coals from Akunza (AKZ), Ome (OME), and Shiga (SHG) in Nigeria were examined for potential energy recovery. Physicochemical analysis revealed high combustible but low levels of polluting elements. The higher heating values ranged from 18.65 MJ/kg (AKZ) to 26.59 MJ/kg (SHG). Microstructure and mineralogical analyses revealed particles with a rough texture, surface, and glassy lustre, which could be ascribed to metals, quartz, and kaolinite minerals. The major elements (C, O, Si, and Al), along with minor elements (Ca, Cu, Fe, K, Mg, S, and Ti) detected are associated with clays, salts, or the porphyrin constituents of coal. Thermal analysis showed mass loss (ML) ranges from 30.51% to 87.57% and residual mass (RM) from 12.44% to 69.49% under combustion (oxidative) and pyrolysis (non-oxidative) TGA conditions due to thermal degradation of organic matter and macerals (vitrinite, inertinite and liptinite). Kinetic analysis revealed the coals are highly reactive under the oxidative and non-oxidative conditions based on the Coats–Redfern Model. The activation energy (Ea) ranged from 23.81 to 89.56 kJ/mol, whereas the pre-exponential factor (ko) was from 6.77 × 10–4/min to 1.72 × 103/min under pyrolysis and combustion conditions. In conclusion, the coals are practical feedstocks for either energy recovery or industrial applications

Catalytic pyrolysis of plastics over maghemite-impregnated mesocellular foam using induction heating

Pyrolysis is a key technology that converts unrecyclable end-of-life plastics into value-added products. Nevertheless, the high energy consumption during plastic pyrolysis limits the economic feasibility of a scaledup process. Development of an energy-efficient plastic pyrolysis process is necessary to realise its full potential in the circular economy. Catalysts derived from mesocellular foam possess high acidity and mesoporosity, and exhibit high catalytic activity in chemical reactions. Application of such catalyst in plastic pyrolysis has never been reported. This work presents the catalytic pyrolysis of low- and high-density polyethylene and polypropylene over maghemite-impregnated mesocellular foam (Fe@AlMCF). Fe@AlMCF has a BET surface area of 629.8 m2/g and a strong Brønsted acidity (677 µmol/gcat). The catalyst contains pentagonal and hexagonal packed mesostructure. Induction heating resulted in a rapid increase in reactor temperature (at 65°C /min) and complete plastics conversion within 10 min. Catalytic pyrolysis produced gas products rich in C3 compounds. The liquid products were rich in alkenes (69.7-71.3 %) and alkanes, followed by aromatics (10.4- 12.8 %). These observations indicate that the highly acidic Fe@AlMCF catalysed hydrocarbon aromatization within a short reaction time. Thermal analysis of the spent catalysts revealed considerably high coke yields (5.78 - 6.03 %), as the higher acidity of the original catalyst promoted coke precursor formation. Based on the research findings, induction heating can rapidly and effectively convert plastics into hydrocarbon feedstocks, and Fe@AlMCF is a valuable catalyst for plastic pyrolysis

Environmental evaluation and nano-mineralogical study of fresh and unsaturated weathered coal fly ashes

Coal combustion and the disposal of combustion wastes emit enormous quantities of nano-sized particles that pose significant health concerns on exposure, particularly in unindustrialized countries. Samples of fresh and weathered class F fly ash were analysed through various techniques including X-ray fluorescence (XRF), X-ray diffraction (XRD), focused ion beam scanning electron microscopy (FIB-SEM), field-emission gun scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM) coupled with energy dispersive x-ray spectroscopy (EDS), and Raman Spectroscopy. The imaging techniques showed that the fresh and weathered coal fly ash nanoparticles (CFA-NPs) are mostly spherical shaped. The crystalline phases detected were quartz, mullite, ettringite, calcite, maghemite, hematite, gypsum, magnetite, clay residues, and sulphides. The most abundant crystalline phases were quartz mixed with Al-Fe-Si-K-Ti-O-amorphous phases whereas mullite was detected in several amorphous phases of Al, Fe, Ca, Si, O, K, Mg, Mn, and P. The analyses revealed that CFANPs are 5–500 nm in diameter and encapsulate several potentially hazardous elements (PHEs). The carbon species were detected as 5–50 nm carbon nanoballs of graphitic layers and massive fullerenes. Lastly, the aspects of health risks related to exposure to some detected ambient nanoparticles are also discussed

Torrefaction of oil palm frond petiole: effect of particle sizes, sections and batches

This study aimed to investigate the effect of batches (1, 2 and 3), particle sizes (<250 µm, range of 300 µm to 500 µm), and sections (bottom, middle and top) on combustion performance of the oil palm frond (OPF) petiole after torrefaction at 275 °C. The higher heating value (HHV), mass yield, energy yield, HHV yield and proximate analyses of the untorrefied and torrefied OPF petiole for all cases were determined. The comparison between the untorrefied and torrefied OPF petiole as well as an international benchmark was also performed. In this study, the highest HHV of the torrefied OPF petiole (22.85±0.07MJ/kg) was obtained at the bottom section with the particle size of < 250 µm. Furthermore, the fixed carbon content of the torrefied OPF petiole increased, whereas the volatile matter, moisture content, mass and energy yields decreased for all cases after torrefaction. HHV yield of OPF petiole was recorded up to 141% after torrefaction. The ash content was sufficiently satisfied the international benchmark for most cases, except for top section (300-500µm). The changes in combustion properties of the torrefied OPF petiole for all cases were found to be insignificant whereas significant improvement could be observed when compared to untorrefied OPF petiole. Overall, the study revealed that the appropriate particle size for torrefaction can promote it to be a vital source for energy production from oil palm biomass

Modelling ultrasound waves bubble formation in ethanol/ethyl acetate azeotrope mixture

The separation of an azeotropic mixture such as ethanol/ethyl acetate in distillation process can be enhanced by ultrasound wave. The application of ultrasound wave creates bubble cavitation in the mixture and shifts the vapour-liquid equilibrium favouring the separation of the azeotropic mixture. This study investigates the formation of bubbles in the mixture through modelling and simulation. The results obtained show that bubble formation at low ultrasound frequency is favoured by the increase in intensity, which has a direct relation to sonic pressure. The optimal sonic pressure for bubble formation at equilibrium is 5 atm and conforms to the model for small bubble formation with radius of 0.14 /<m. Furthermore, the maximum possible number of bubbles at equilibrium in the ethanol/ethyl acetate azeotropic mixture of 1 L is 91 × 1015. The developed model can be used to determine the optimal sonic pressure, sound intensity, size of bubble, and possible number of bubbles formed at equilibrium

Geochemical and Advanced Electron Microscopical Characterisations of Artisanal Gold Mining Rejects in Colombia

Artisanal gold mining causes widespread health problems due to illegal exposure to hazardous inorganic compounds, such as arsenic (As) and mercury (Hg). The sources and prevalence of mining pollution are strongly influenced by topography, stream dynamics, soil type, and land use. In the present study, the potential hazardous elements (PHEs), absorption abilities of nanoparticles (NPs), and ultrafine particles (UFPs) were analysed from clandestine gold mining soils in Colombia. The proportions of PHEs including As, Hg, Cu, Cr, and Pb in carbonates, sulfides, clays, oxides, hydroxides, and sulfates were determined by field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and selected area electron diffraction (SAED)/micro-beam diffraction (MBD)/energy dispersive X-ray spectroscopy (EDS). The results revealed that the concentrations of As, Hg, and Zn were significantly higher in clay particles when compared to the other soil samples. Furthermore, Al and Fe manifested excellent PHEs sorption abilities in the artisanal gold mining soils. The results presented will be useful for future mitigation measures in the gold mining areas

Geochemical and Advanced Electron Microscopical Characterisations of Artisanal Gold Mining Rejects in Colombia

Artisanal gold mining causes widespread health problems due to illegal exposure to hazardous inorganic compounds, such as arsenic (As) and mercury (Hg). The sources and prevalence of mining pollution are strongly influenced by topography, stream dynamics, soil type, and land use. In the present study, the potential hazardous elements (PHEs), absorption abilities of nanoparticles (NPs), and ultrafine particles (UFPs) were analysed from clandestine gold mining soils in Colombia. The proportions of PHEs including As, Hg, Cu, Cr, and Pb in carbonates, sulfides, clays, oxides, hydroxides, and sulfates were determined by field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and selected area electron diffraction (SAED)/micro-beam diffraction (MBD)/energy dispersive X-ray spectroscopy (EDS). The results revealed that the concentrations of As, Hg, and Zn were significantly higher in clay particles when compared to the other soil samples. Furthermore, Al and Fe manifested excellent PHEs sorption abilities in the artisanal gold mining soils. The results presented will be useful for future mitigation measures in the gold mining areas

Environmental Impacts of Coal Nanoparticles from Rehabilitated Mine Areas in Colombia

With the possible increase in mining activities and recently projected population growth in Colombia, large quantities of nanoparticles (NPs) and potentially hazardous elements (PHEs) will be of major concern to mine workers, indigenous residents, and surrounding communities. This study highlights the need to regulate the pollution from Colombian mining activities that comply with regional regulations and global strategies. Colombian coal rejects (CRs) from the Cesar Basin, Colombia, were studied primarily by advanced electron microscopic and analytical procedures. Therefore, the goal of this research is to evaluate the role of NPs in the alteration of CRs’ structure in a renewed zone at Cerrejón coal area (La Guajira, Colombia) through advanced electron microscopic (AEMs) methods. The objective of the analysis is to evaluate the incidence mode of nanoparticles, which contain potentially hazardous elements. The bulk crystallography (X-ray diffraction), chemical structure, and morphologies of NPs were studied by high-resolution transmission electron microscopy (HR-TEM), field emission scanning electron microscopy (FE-SEM), micro-beam diffraction (MBD), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDX) procedures. The AEMs provided comprehensive insights into the geochemical evolution of CRs. Consequently, the AEMs can be used as essential tools for CR management in coal mining areas. The regular dimension of detected NPs was found to be above 2 nm. Ultrafine particles of quartz were identified by the advanced electron microscopy. Furthermore, the findings also revealed aluminium, calcium, potassium, titanium, iron oxides, and PHEs in the CRs. The extensive water practice in the coal extraction process combined with atmospheric oxygen supports oxidations of iron sulphide, thus releasing PHEs to the surrounding environment. Dehydration of sulphate salts fluctuate at consistent humidity in the coal mine environments. The study demonstrates the great influence of coal mining activities on the environment and human health