Sreenivas Jayanti

Bio: Sreenivas Jayanti is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Pressure drop & Combustion. The author has an hindex of 37, co-authored 142 publications receiving 3884 citations. Previous affiliations of Sreenivas Jayanti include Ohio State University & Imperial College London.

Turbulent flow in a pipe with intermittent rough patches: an analogue of annular two-phase flow

Abstract: The response of turbulent pipe flow to sudden changes in wall roughness and flow cross-sectional area has been studied experimentally and numerically. Changes typical of those encountered by the gas phase in annular gas-liquid flow have been considered. The results show that the flow field and the pressure field can be significantly distorted at these transitions. Good agreement has been obtained between the measured results and those calculated using the Harwell-FLOW3D computational fluid dynamics (CFD) code.

Improving efficiency of CCS-enabled IGCC power plant through the use of recycle flue gas for coal gasification

Abstract: CO2 capture from coal-fired power plants is necessary for continued use of coal as a fuel. Proven CO2 capture techniques such as amine absorption and oxyfuel combustion entail significant energy penalty leading to considerable decrease in the net thermal efficiency of the power plant. Recent studies of high-ash Indian coals show that CO2 has sufficient reactivity for coal gasification in temperature ranges of interest to IGCC. Against this background, we analyse in the present study, a new power plant layout which uses part of the sequestered flue gas stream for high-pressure gasification of the coal within the framework of an IGCC power plant with CO2 capture. Detailed thermodynamic calculations of the new plant layout, referred to here as Oxy-RFG-IGCC-CC, using commercial power plant simulation software show that the optimized Oxy-RFG-IGCC-CC plant with CO2 capture produces power at an overall thermal efficiency of 34.2%, which is nearly the same as that of current generation of pulverized coal boiler-based power plants without CO2 capture or that of a conventional IGCC with post-combustion capture. The proposed simpler layout is also 1.9% more efficient than a comparable CO2-capture-enabled IGCC plant that uses steam for coal gasification.

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.

A New Stable Operating Regime for Oxyfuel Combustion

Abstract: In the present paper, the stability of the new oxyfuel combustion regime titled as Intermediate temperature Diluted Oxygen Combustion (INDOCS) has been demonstrated theoretically. The operating conditions for the INDOCS are different from those of conventional oxyfuel combustion: the concentration by mass of oxygen in the oxidant stream is between 16 to 20% by mass (as opposed to 24% by mass in conventional oxyfuel combustion) and the temperature of the oxidant at entry to the furnace is in the range of 600 to 850 K (as opposed to an ambient temperature of about 300 K in conventional oxyfuel combustion). The method relies on the well-established fact that the stability of the flame increases with preheating of the oxidant (as demonstrated in High Temperature Air Combustion (HITAC) and FLAMELESS combustion regimes). The attendant high peak temperature of the flame can be reduced, to minimize NOx formation, by diluting the oxygen concentration. The overall benefits of this method are stable combustion at diluted oxygen concentrations, lower NOx (if N2 is present due to incomplete separation of oxygen from air), higher concentration of carbondioxide in the flue gases for a more efficient carbon sequestration. Flame structure calculations using the flamelet model of combustion with 35-step methane-air simplified reaction mechanism are used to demonstrate the stability of the flame. Simulations have also been carried out for the geometry of the 300 kW IFRF burner test facility; these show that the decreasing concentration of H and OH radicals in the quarl zone with increasing dilution by CO2 is counteracted by increasing the temperature of the oxidant. One of the principal advantages of this method is that, unlike in the case of HiTAC, the preheat requirements are mild which can be achieved by mixing part of the flue gas with the oxygen separated from air. It can be therefore readily implemented as a retrofitting measure in existing coal-fired plants.Copyright © 2008 by ASME

Numerical Simulation of Coal Combustion in a Tangential Pulverized Boiler: Effect of Burner Vertical Tilt Angle

Abstract: Understanding of the flow field and heat transfer in a boiler is important to meet with the often-conflicting objectives of efficient steam generation, safe operation and minimization of pollutant emissions. Steam generation requires high gas temperatures, which often lead to high NOx emissions. High gas temperatures inside the boiler may also lead to slagging and fouling problems, which adversely affect the heat transfer to the steam side. One of the principal ways of finding a compromise in tangentially fired pulverized coal (PC) boilers, which constitute the majority of the utility boilers, is through tilting the burners. The current work seeks to obtain a detailed understanding of the effect of burner tilt on the flow and heat transfer inside the boiler by utilizing numerical simulations. Computational fluid dynamics (CFD) simulations were performed on a 210 MWe tangentially fired pulverized coal boiler to understand the impact of two vertical burner tilt angles, − 15° and + 15°. The effect of burner tilt was investigated by analyzing the effect on gas flow, temperature distribution, coal particle trajectories and NOx emissions. The results suggest that a downward tilt of the burner (− 15°) has a significant effect on the particle trajectories and the residence time of the particle in the high temperature burner zone. The temperature of the exit gas was reduced by 33 K due to the downward tilt. NOx emissions were reduced by about 5.5% when the burners were tilted downward by 15° which be attributed to two factors, namely the relatively insignificant contribution of thermal NOx mechanism in utility boilers and the role of NOx reburning in reducing conditions.

Ammonia as a possible element in an energy infrastructure: catalysts for ammonia decomposition

Abstract: The possible role of ammonia in a future energy infrastructure is discussed. The review is focused on the catalytic decomposition of ammonia as a key step. Other aspects, such as the catalytic removal of ammonia from gasification product gas or direct ammonia fuel cells, are highlighted as well. The more general question of the integration of ammonia in an infrastructure is also covered.

A review of flow and heat transfer characteristics in curved tubes

Abstract: The performance of heat exchangers can be improved to perform a certain heat-transfer duty by heat transfer enhancement techniques. In general, these techniques can be divided into two groups: active and passive techniques. The active techniques require external forces, e.g. electric field, acoustic or surface vibration, etc. The passive techniques require fluid additives or special surface geometries. Curved tubes have been used as one of the passive heat transfer enhancement techniques and are the most widely used tubes in several heat transfer applications. This article provides a literature review on heat transfer and flow characteristics of single-phase and two-phase flow in curved tubes. Three main categories of curved tubes; helically coiled tubes, spirally coiled tubes, and other coiled tubes, are described. A review of published relevant correlations of single-phase heat transfer coefficients and single-phase, two-phase friction factors are presented.