Finned tubes are widely used in the convection sections of industrial furnaces to enhance heat transfer efficiency. However, their service life can be limited by thermal, mechanical, and chemical degradation mechanisms, particularly in high-temperature environments where dissimilar materials are employed. This paper focuses on the investigation of finned tube failures observed in the convection section of the dehydration furnace (Unit 104). The tubes were manufactured from ASTM A106 Grade B carbon steel, and the fins from AISI 304 stainless steel. To identify the root causes of failure, several experimental techniques were employed, including optical microscopy, Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), and corrosion testing in accordance with ASTM A262-15 (2021) Practice A. Visual inspections revealed multiple cracks on both tube and fin surfaces. The analyses indicated that sulfide formation on fin surfaces, welding imperfections at the fin–tube interface, and differences in heat transfer coefficients between the two materials contributed to uneven thermal distribution and crack initiation. Furthermore, microstructural examination revealed chromium carbide precipitation and sensitization along grain boundaries in the fin material. The combined effects of these factors promoted crack propagation from the fins into the tube wall, ultimately leading to leakage and fire hazards.
An end-of-pipe technology for processing oily sludge using a hydrocyclone is modeled in this study and then compared with an end-of-pipe technology using centrifugation with a science filter treatment system. The end-of-pipe technology design is proposed based on the characterization of physical and chemical data of oily sludge obtained from a national refinery in Port Harcourt, Nigeria. The aliphatic and aromatic hydrocarbons in the sludge, its metallic components, and water content were characterized using gas chromatography. The ChemCad software is used for computer model simulation of the end-of-pipe system (hydrocyclone and compartment separator) stream flow. The results show that the solids in the underflow from the cyclone contain about 3.8% by mass of hydrocarbons and 4.06% by mass of water. The hydrocarbon content of the hydrocyclone overhead recovered via the component separator bottoms is 97.9%, 1.5%, and 0.9% by mass of hydrocarbon, water, and solids, respectively. The ChemCAD software is used to process laboratory results and simulate stream flow designs. End-of-pipe (centrifugation) filter technologies for sludge treatment are designed for 75% optimal oil recovery, with zero solids and water content in the recovered oil, making it a high-quality product largely due to the filtration system incorporated. The high oil recovery of 97.9% and the low carbon footprint in our proposed end-of-pipe technology model may be attributed to the use of a natural hydrocarbon solvent (kerosene) to process the sludge in a hydrocyclone and separation compartment, which enhanced oil extraction and recovery.
This study explored the photocatalytic degradation process for treating industrial spent caustic wastewater, focusing on reducing chemical oxygen demand (COD). Cu(BDC)/MgO nanocomposites were synthesized via microwave-assisted synthesis and served as efficient photocatalysts. An artificial neural network (ANN) model was developed to estimate COD concentrations and optimize treatment parameters, aiming to achieve superior COD reduction. The research aimed to minimize the hydrogen peroxide-to-COD ratio and to optimize other factors influencing COD removal. The synthesized nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) elemental mapping. Optimal parameters for achieving a 97.55% COD removal efficiency were identified as a nanocomposite dose of 1.30 g/L, an H2O2/Spent caustic wastewater ratio of 1.50 ml/L, a pH of 3.0, a treatment time of 35 min, and an aeration flow rate of 2.50 L/min. Catalyst recycling studies demonstrated the exceptional recyclability and stability of the Cu(BDC)/MgO nanocomposites, showing they could be reused as catalysts even after five treatment cycles. This highlights the potential for prolonged and sustainable use of these nanocomposites in wastewater treatment processes, effectively reducing COD levels in spent caustic effluents.
Biodiesel is a major renewable energy source derived from vegetable oils. Modern techniques are now required to produce biofuels, particularly biodiesel, to improve the efficiency and sustainability of the process. This study focuses on continuous biodiesel production from waste cooking oil via microwave-assisted transesterification in a flow process. Calcium oxide prepared from willow leaf extract was used as a catalyst at concentrations ranging from 1% to 4%, with a microwave power of 20% of the total 800W and an irradiation time of 0.5-7 min. The oil-to-methanol ratio was 50wt.%- 80wt.%, and the reaction temperature was 45-75 ℃. The results revealed that the waste cooking oil can be converted to biodiesel with a yield of (93.43%) in 5 min. with a 70wt.% oil/methanol molar ratio and 3wt.% catalyst. Also, the results indicated that the production of high-quality biodiesel, in accordance with ASTM standards, was facilitated under all operational conditions. The results suggest that microwave heating is a viable approach for achieving high biodiesel yields with shorter reaction times, even in continuous reactions. This is attributed to reduced energy activation. This method is promising for industrial-scale production of high-quality biodiesel, with methanol as the preferred alcohol.
The method involves a sample preparation technique through microwave digestion to extract eight metals (Si, Al, Mg, Ca, Fe, Na, K, and Ti) in Portland (SRM 1888b) and Blended (SRM 1881a) cement traceable to NIST, followed by spectrometric detection and quantitation via the simultaneous system inductively coupled plasma-optical emission spectroscopy (ICP-OES). A 0.2-gram sample of the materials was prepared for closed-system digestion at 1200W. After digestion, solutions were diluted in 50-mL dedicated polypropylene laboratory ware (volumetric flasks) and analyzed. Accordingly, the dilution and calibration patterns were determined. The analyses were performed in five replicates. The detections of Si, Al, Mg, Ca, Fe, K, and Ti following radial mode and Na via axial torch orientation gave satisfactory results. Reproducibility studies were conducted, and ICP-OES configurations were established for each element. The method was developed based on its figures of merit. The procedure was validated with exceptional performance, except that it was not robust at a higher sample mass. Operational maintenance procedures were established when many samples were run. Measurement uncertainty estimation is recommended to identify the sources and effects of measurement errors.
