Showing papers by "Sreenivas Jayanti published in 2015"

Syngas-fueled, chemical-looping combustion-based power plant lay-out for clean energy generation

Abstract: Of the various clean combustion technologies with carbon capture and sequestration (CCS) possibilities, chemical-looping combustion (CLC) promises to be an efficient and attractive method for oxidizing fuels without the energy penalty required for oxygen separation from air. The present work reports on a detailed thermodynamic analysis of 1,500 MWth, syngas-fueled, CLC-based power generation system which includes a provision for CCS. Taking account of the exothermic nature of the reaction of syngas with the selected oxygen carrier, NiO, in the fuel reactor, operating temperatures of air and fuel reactors are fixed at 900 and 908 °C, respectively. The CLC reactor system operates at atmospheric pressure on fuel/air side, and generates supercritical steam. An overall plant lay-out has been prepared such that the steam side, which is rated at 240 bar/538/552/566 °C, is very similar to that of a conventional thermal power plant making retrofitting a distinct possibility. A detailed analysis of the ideal cycle shows that a highly promising gross cycle efficiency of 41.22 % and net cycle efficiency of 36.77 % can be achieved after accounting for the energy cost of CO2 compression to 110 bar to facilitate CCS.

Comparative analysis of four gas-fired, carbon capture-enabled power plant layouts

Abstract: Emission of carbon dioxide from fossil fuel-fired thermal power plants is a major concern for energy providers all around the world. In this context, carbon capture from thermal power plants and the energy penalty incurred in the process are important issues. The present work reports on a detailed analysis of gas-fired power plant layouts with in-built carbon capture, i.e. the flue gas from these power plants contains mainly carbon dioxide and water vapour. Four layouts, two of which are based on pressurized oxyfuel combustion and two on chemical looping combustion (CLC), have been considered. Based on detailed mass balance, energy and thermodynamic analyses of the power plant layouts, the net efficiencies for each plant have been computed. After accounting for thermodynamic irreversibilities and CO2 compression to 110 bar, these have been found to vary between 31 and 52 % for the four plants. Despite the technological maturity of oxyfuel combustion, it is concluded that CLC-based plants would be future-ready in the sense that they can readily accommodate CCS with only 2 % loss in overall thermal efficiency for CO2 capture.

Shape Optimisation of Curved Interconnecting Ducts

Abstract: Practical ducting layout in process plants needs to satisfy a number of on-site constraints. The search for an optimal flow path around the obstructions is a multi-parameter problem and is computationally prohibitively expensive. In this study, authors proposed a rapid and efficient methodology for the optimal linkage of arbitrarily oriented fluid flow ducts using a single-parameter quadratic/cubic Bezier curves in two/three dimensions to describe the centreline of the curved duct. A smooth interconnecting duct can then be generated by extruding the duct face along the curve. By varying the parameter either along the angular bisector or along the axes of the ducts, a family of Bezier curves is generated. Computational fluid dynamics simulations show that the relationship between pressure drop and the adjustable parameter is a unimodal curve and the optimal connecting duct is the one which has the least pressure drop while satisfying on-site constraints can be used for linking the ducts. The efficacy of the method is demonstrated by applying it to some cases of practical interest. Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 300-306, DOI: http://dx.doi.org/10.14429/dsj.65.8353

Effect of impeller type and density difference on the draw down of low density microspheres

Abstract: Experiments on dispersion of floating solids into continuous liquid medium were carried out with low density microspheres with particle density of 680 kg/m 3 and size 100, 230 and 325 μm in different liquids having density varying from 778 to 1830 kg/m 3 and kinematic viscosity varying from 0.3 to 19 cP. A four-bladed radial impeller and axial paddle impellers with upward and downward flow directions were employed. The critical impeller speed ( N crit ) required for uniform dispersion of particles throughout the continuous medium was experimentally determined for various conditions. Experimental results indicate that the radial impeller with impeller location near the surface required minimum impeller speed for uniform dispersion. Strong effect of the density difference between the particles and the liquid and submergence of the impeller was noted. Based on the experimental results, a correlation in terms of relevant dimensionless groups was proposed for calculating N crit for the three impellers. The overall correlation indicates that the critical impeller speed is not significantly affected by liquid viscosity and particle diameter but that it is strongly influenced by the impeller diameter and the density difference. These results are in agreement with trends reported in the literature.