SUMMARYIn the present work, exergy analysis of a coal-based thermal power plant is done using the design data from a 210 MW thermal power plant under operation in India. The entire plant cycle is split up into three zones for the analysis: (1) only the turbo-generator with its inlets and outlets, (2) turbo-generator, condenser, feed pumps and the regenerative heaters, (3) the entire cycle with boiler, turbo-generator, condenser, feed pumps, regenerative heaters and the plant auxiliaries. It helps to find out the contributions of different parts of the plant towards exergy destruction. The exergy efficiency is calculated using the operating data from the plant at different conditions, viz. at different loads, different condenser pressures, with and without regenerative heaters and with different settings of the turbine governing. The load variation is studied with the data at 100, 75, 60 and 40% of full load. Effects of two different condenser pressures, i.e. 76 and 89 mmHg (abs.), are studied. Effect of regeneration on exergy efficiency is studied by successively removing the high pressure regenerative heaters out of operation. The turbine governing system has been kept at constant pressure and sliding pressure modes to study their effects.It is observed that the major source of irreversibility in the power cycle is the boiler, which contributes to an exergy destruction of the order of 60%. Part load operation increases the irreversibilities in the cycle and the effect is more pronounced with the reduction of the load. Increase in the condenser back pressure decreases the exergy efficiency. Successive withdrawal of the high pressure heaters show a gradual increment in the exergy efficiency for the control volume excluding the boiler, while a decrease in exergy efficiency when the whole plant including the boiler is considered. Keeping the main steam pressure before the turbine control valves in sliding mode improves the exergy efficiencies in case of part load operation.

The emergence of carbon quantum dots (CQDs) opens up new opportunities in different branches of science and technology primarily because of their conducive biocompatibility, tunable bandgaps, and unique optoelectronic properties, namely, photoluminescence (PL) and fluorescence. Although CQDs are given precedence in the literature, the large-scale sustainable synthesis and the purification of CQDs as well as the study of their effects on health and environment remain a challenge. Hence, more sustainable approaches are being developed to make this category of materials widely applicable, specifically in the context of replacing toxic metal-based QDs. Among the reported synthetic protocols employed to prepare CQDs while controlling their properties, the incorporation of various dopants, surface functionalities, and defects into CQDs offers great promises. Amongst the possibilities, nitrogen dopants contribute significantly due to their broader precursor scope, natural abundance in sustainable bioderived resources, and relatively straightforward and inexpensive synthetic protocols, leading to assorted combinations of nitrogen (N)-doped carbon quantum dots (NCQDs). Here, a brief survey is presented on the recent developments of strategies deployed for the preparation of bioderived NCQDs, emphasizing the uniqueness of the synthetic methodology, choice of precursors, and purification strategies. In addition, characterization, properties, and applications of the selected NCQDs are highlighted. The present status and challenges are also discussed along with the future directions.

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Composites were developed from two industrial wastes: recycled polypropylene (R) and fly ash (FA). Surface coating of fly ash (FA) particles with palmitic acid (PA) in different wt % of 1, 2, 3, and 5 were done, and they were incorporated as filler in the R matrix by melt mixing. X-ray diffraction analysis (XRD), mechanical characterization, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and fracture surface analysis were carried out with a scanning electron microscope (SEM) to establish structure–property correlation. Crystallinity changed significantly, resulting in improved properties in 1 wt % PA-coated FA/R (RFAPA1) and 2 wt % PA-coated FA/R (RFAPA2) composites. Impact strength increased by 132% in RFAPA1, and an increase in glass transition temperature was observed in RFAPA1 and RFAPA2. RFAPA1 and RFAPA2 exhibited enhanced thermal stability, and SEM revealed improved interfacial compatibility. These results showed the possibility of using a renewable green chemical like PA as a coupling agent in place of conventional expensive silane coupling agents to develop sustainable value-added polymer composites from environmentally hazardous waste materials.

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