Vinu R

This paper reports the critical reviews on the gassing tendency of different insulating fluids along with the precautionary measures to be considered during their fault diagnosis in transformer insulation. The experimental techniques and procedures for identifying the gassing due to electrical and thermal stress along with the stray gassing phenomenon has been elucidated. The different interpretation schemes used for determining the faults in transformers results in unexpected errors when the historical data relating to mineral oil is used for the other alternative fluids. Mineral oil and natural ester show a positive gassing tendency compared to synthetic ester which exhibit a negative gassing tendency. The stray gases are mostly due to breakage of C-C bonds under normal operating temperature of transformer. Among the different hydrocarbons, hydrogen and ethylene are more predominantly formed under lower temperatures. The silicone oil and ester fluids are more stable even under localised hot spots simulated observing a lesser gassing compared to the mineral oil. The impact of additives along with the oxygen and water content in the insulating fluids can lead to the stray gas’s causing confusion towards the identification of actual faults occurring in transformers. Furthermore, the regeneration of insulating fluids using different adsorbents reduces the gassing tendency depending on the number of cycles used for its reclamation.

Thermal aging of natural ester oil shows drastic reduction in partial discharge inception voltage (PDIV) and a significant variation is observed only above a certain aging time, under AC, DC, high frequency AC voltages and with harmonic voltages with different total harmonic distortion. Weibull distribution studies on PDIV measurements indicate a reduction in scale parameter (α) with increase in thermal aging temperature. A characteristic reduction in breakdown voltage was observed with the thermally aged ester oil, under AC, DC and standard lightning impulse voltage. The breakdown voltage variation with aged ester oil follows normal distribution. Ultraviolet (UV) analysis of ester oil thermally aged at 160°C has revealed a regular shift of the derived absorbance parameter to longer wavelengths. The interfacial tension and turbidity exhibits an inverse relationship with the thermally aged ester oil. Gas chromatography/mass spectrometric analysis of the thermally aged ester oil predicted the formation of more carboxylic acids and ketones with aging duration. The steady-state fluorescence on thermally aged ester oil exhibits a shift in its emission profile, which is in tandem with the UV absorption spectroscopic analysis. Fluorescence analysis can be adopted as a real-time monitoring tool in transformers, to understand the condition of liquid insulation. The viscosity dependence on the wavelength of derivative absorption maxima follows a direct relationship with the thermally aged natural ester oil.

Pyrolysis conditions and mechanism greatly influence the quality of tar and char from coal, which eventually determine their further usage. This work investigates the pyrolysis of three coking coals and a non-coking high ash Indian coal via microwave-assisted and conventional heating, and the influence of heating rate, coal type, and heating mechanism on product yields and tar composition. Microwave pyrolysis experiments were conducted in a home-built microwave reactor, and analytical pyrolysis experiments were conducted in a Pyroprobe® interfaced with gas chromatograph-mass spectrometer (Py-GC/MS). The tar yields from microwave pyrolysis of coking coals were similar (∼7 wt.%), while it was slightly high from high ash Indian coal (∼11 wt.%). Char yields from both microwave and analytical pyrolysis were similar (78 ± 1.5 wt.%). Microwave pyrolysis tars were rich in naphthalene derivatives and polyaromatics with more than 45% selectivity, while analytical pyrolysis tar was rich in monoaromatics (>30%). There was no significant variation in the selectivities of other organic fractions. High selectivity of polyaromatics in microwave pyrolysis tar is due to the generation of localized hotspots, which led to excessive cracking of primary pyrolysis vapors. The higher heating value (HHV) of microwave pyrolysis tar was 32–33 MJ kg−1, while that of analytical pyrolysis tar was higher (35–36 MJ kg−1), which is attributed to the presence of more monoaromatics in the latter. Hydrogen and methane were the major components in the gaseous fraction. Coal chars were characterized using different techniques, and they were rich in carbon (≈80 wt.%) with high energy content (29 MJ kg−1).

The demand for higher volumetric calorific value of fuels for modern high performance aircraft has led to development of nanofuels that opens a promising future for enhancing the energy density of liquid fuels. This paper intends to study the effect of addition of boron nano-particles (NPs) on the burning characteristics of JP10 fuel droplets for various particle mass loadings (2%, 5%, 7% and 10%). Stable suspension of the NPs was achieved by adding Span80 and Tween80 as surfactant followed by ultra-sonication of the mixture. The fuel droplet was suspended on a horizontal quartz fiber. All experiments were conducted under atmospheric conditions. The droplet burning process was recorded using a high speed camera. The burning of pure JP10 and JP10 plus surfactant (without NPs) were also studied. In case of burning of pure JP10 fuel, the linear trend in time evolution of normalized droplet surface area suggested that the droplet burning follows the classical d2 − law and formation of bubbles inside the droplet was observed. However, these bubbles did not lead to puffing, which though occurred for JP10 plus surfactant (no NPs). This means that addition of surfactants, which has low burning rate, modifies the droplet burning process. In case of nanofuel droplet, burning

This study is focused on the valorization of heterogeneous municipal solid waste collected from the landfill using hydrothermal liquefaction process using glycerol as a co-solvent. The effects of temperature (300–350 °C) and residence time (15–45 min) on the yields and quality of the product fractions were investigated at 8 wt% solid loading. The yield of bio-crude significantly increased from 15.2 wt% with water as the solvent, to 58 wt% with water-glycerol (1:1 v/v) as the solvent possessing an energy content of 35.6 MJ/kg at 350 °C, 30 min. The quality of the bio-crude obtained using glycerol was comparable to that using tetralin as a hydrogen donor co-solvent. Phenolic compounds and cyclooxygenates were the major compounds in the bio-crude, and aliphatic hydrocarbons increased with residence time. Maximum energy recovery of 95% was achieved in the products with an energy consumption ratio of 0.43 for the bio-crude signifying the energetic feasibility of the process.

While oleaginous yeasts have been extensively investigated for single-cell oil production, less attention has been paid towards valorization of the erstwhile-discarded de-oiled biomass. The current study demonstrates the valorization potential of the de-oiled biomass through production of bio-crude by hydrothermal liquefaction process. The performance of the process was enhanced by using glycerol as co-solvent and also by optimizing the processing conditions. Glycerol addition enhanced the bio-crude yield up to 50 wt% with an improved energy content of 32 MJ/kg. The major organic groups found in the bio-crude are acids, esters and phenolics. Typical energy recovery achieved in bio-crude was in the range of 43–62%. Thus, strategic valorization of yeast into green crude with net energy gain, as evident from the energy balance, implies the process is energetically favourable.

The growing concerns on climate change, energy demand and depleting fossil fuel reserves have diverted the focus of the 21st century toward renewables. A wide range of technologies such as transesterification, gasification, pyrolysis, aqueous phase catalytic reforming and hydrothermal liquefaction (HTL) are used for producing biofuels and chemicals from a wide range of feedstocks. Due to its immense flexibility in handling a wide variety of organic substrates, ranging from dry to wet residual biomass, algae, sewage sludge, plastics and municipal solid wastes, HTL is regarded as a “feedstock agnostic technique.” The bio-crude obtained from HTL is a dark viscous liquid, which is immiscible with water and has a better calorific value with lower oxygen content than the bio-oil obtained from pyrolysis. Various organic compounds such as aromatics, aldehydes, ketones, alcohols, carboxylic acids, esters, and straight and cyclic hydrocarbons make up a major portion of the bio-crude, with its composition strongly dependent on the type of feedstock. The products from HTL can be considered as a renewable source of biofuels, bio-based specialty chemicals, and bio-products in a circular bioeconomy. This critical review will assess the possibilities of deriving chemicals, fuel molecules and bio-products from a range of feedstocks via HTL technology with special emphasis given to (a) characteristics and applications of different products from HTL, (b) possibilities of tailoring the selectivity to specific chemicals by using catalysts, (c) challenges and opportunities in integrating the HTL products in the existing refinery infrastructure and (d) industrial potential and economics of the process.

A fundamental understanding of reaction chemistry and pathways in fast pyrolysis of microalgae is hindered by the complex structure of proteins, lipids and carbohydrates that constitute them and the interactions among the intermediates at short timescales. In this study, bovine serum albumin (BSA), sunflower oil (SO) and potato starch (PS) were chosen as microalgae model compounds representing proteins, lipids, and carbohydrates, respectively. Fast pyrolysis of individual and binary mixtures of the model compounds was investigated at 500 °C using an analytical pyrolysis reactor interfaced with a gas chromatograph/mass spectrometer (GC/MS) and a Fourier transform infrared spectrometer (FTIR) to investigate the composition of pyrolysates and their time evolution. The composition of BSA, SO and PS was chosen to be 1 : 2, 1 : 1 and 2 : 1 (wt. basis) to emulate the microalgae composition. Fast pyrolysis of BSA : SO mixtures promoted esterification of carboxylic acids and alcohols, whereas BSA : PS and SO : PS mixtures promoted the formation of carboxylic acids via syn-elimination of esters, while inhibiting the decarboxylation pathway. The presence of SO and PS altered the pyrolysis mechanism of BSA by inhibiting the formation of aromatic hydrocarbons and nitrogen-containing compounds. The time evolution of C-H (aromatic and aliphatic), N-H, O-H, and CO stretching vibrations was monitored up to 60 s using in situ FTIR. The maximum vapor evolution time for fast pyrolysis of SO (50 s) was higher than that for BSA and PS (both 8-10 s). The addition of BSA and PS to SO increased the rate of evolution of volatiles, with the maximum vapor evolution occurring at shorter time periods. The first order apparent rate constants of fast pyrolysis followed the trend: 0.294 s -1 (PS) > 0.162 s -1 (BSA) > 0.107 s -1 (BSA : PS (2 : 1)) > 0.073 s -1 (BSA : SO (2 : 1)) > 0.048 s -1 (SO : PS (2 : 1)). Fast pyrolysis char was characterized by FTIR and GC/MS, and it contained polycyclic nitrogen compounds. The plausible reactions including the interactions among the various intermediates were unraveled, and a tentative mechanism was proposed.

Coulson and Richardson’s Chemical Engineering: Volume 3A: Chemical and Biochemical Reactors and Reaction Engineering, Fourth Edition, covers reactor design, flow modelling, gas-liquid and gas-solid reactions and reactors.

In this study, mesoporous activated biochar with high surface area and controlled pore size was prepared from char obtained as a by-product of pyrolysis of Prosopis juliflora biomass. The activation was carried out by a simple process that involved H2O2 treatment followed by microwave pyrolysis. H2O2 impregnation time and microwave power were optimized to obtain biochar with high specific surface area and high adsorption capacity for commercial dyes such as Remazol Brilliant Blue and Methylene Blue. Adsorption parameters such as initial pH of the dye solution and adsorbent dosage were also optimized. Pore size distribution, surface morphology and elemental composition of activated biochar were thoroughly characterized. H2O2 impregnation time of 24 h and microwave power of 600 W produced nanostructured biochar with narrow and deep pores of 357 m2 g-1 specific surface area. Langmuir and Langmuir-Freundlich isotherms described the adsorption equilibrium, while pseudo second order model described the kinetics of adsorption.