Prospects of Mixtures as Working Fluids in Real-Gas Brayton Cycles
This paper discusses the thermodynamic characteristics of the closed Brayton cycles in which the compression is placed near the critical point of the working fluid. Under these conditions, the specific volumes of the fluid during the compression are a fraction of the corresponding values under ideal gas conditions, and the cycle performances improve significantly, mainly at moderate top temperatures. As the heat is discharged at about the critical temperature, the choice of the correct working fluid is strictly correlated with the environmental temperature or with the temperature of potential heat users. To resort to mixtures greatly extend the choice of the right working fluid, allowing a continuous variation of the critical temperature. These cycles have a high power density, and the use of ordinary turbomachinery is accompanied by high capacities (tens of megawatts). In the low power range, microturbines or reciprocating engines are required. One important constraint on the choice of the right working fluid is its thermochemical stability that restricts the operative temperatures. Among the organic compounds, the maximum safe temperatures are limited to about 400 °C and, forecasting high temperature applications, it could be interesting to explore the potentiality of the inorganic compounds as secondary fluids in binary mixtures.
The exploitation of the physical exergy of liquid natural gas by closed power thermodynamic cycles. An overview
The world trade in LNG (liquefied natural gas) has tripled in the last 15 years and the forecasts are for its further rapid expansion. Although the cryogenic exergy of the LNG could be used in many industrial processes, it is recognized also as a source for power cycles.
Parboiled rice effluent: A wastewater niche for microalgae and cyanobacteria with growth coupled to comprehensive remediation and phosphorus biofertilization
Abstract The potential of microalgae and cyanobacteria for bioremediation of wastewater by nutrient uptake combined with simultaneous biomass production is a well recognized perception of today's world. The present study illustrates the treatment of a highly polluted wastewater generated during parboiling of paddy in rice mill industries, widely operational in developing countries where rice is the staple food crop, with the help of microalgal and cyanobacterial isolates capable of growing at high rates in parboiled rice mill effluent (RME). This endeavor leads to comprehensive bioremediation of the said effluent and subsequent use of the harvested biomass as slow release phosphorus biofertilizers and the treated effluent for crop irrigation. The RME-acclimatized algal consortium demonstrated highest growth in terms of fresh weight and greatest remediation efficiency at the end of 36 days' treatment of RME, with 93.9% phosphorus and 100% ammonia-nitrogen removal, 98.7%, 91.6% and 93.5% reduction in biological oxygen demand, chemical oxygen demand and total dissolved solid, respectively, and an increment of 186 ± 0.3 mg L − 1 dissolved oxygen, bringing down the pollutants level well below the discharge limits suggested by Central Pollution Control Board, India. Additionally, microalgae in the consortium aggregated in clumps spontaneously in presence of the filaments of Phormidium sp. facilitating easy harvest. The RME-acclimatized algal consortium demonstrated highest accumulation of polyphosphate (poly-P) (0.76 ± 0.01% of dry weight) as well as highest release of phosphorus in non-sterile soil emphasizing the essential role of soil phosphorus solubilizing organisms to leach soluble phosphorus from the insoluble poly-P present in the biomass. The rice seedlings watered with treated RME also showed improved growth effect on shoot height and leaf width. The study results establish the suitability of RME as an excellent growth media for microalgae and cyanobacteria.