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Papers by Ashish Bhattarai

ACS Publication, 2023

Feedstocks such as coal, biomass, plastics, and their blends have the potential to serve as fuels... more Feedstocks such as coal, biomass, plastics, and their blends have the potential to serve as fuels for the thermochemical conversion process owing to their relatively high calorific values. Nevertheless, the relative proportion of these feedstock blends has a pivotal influence over the overall energy conversion efficiency. Consequently, conducting a comprehensive study to optimize the blend proportion becomes crucial in order to obtain an optimal fuel. The study aims to investigate the thermochemical characterization and kinetics of blends composed of lignite coal, southern pine biomass, and municipal waste plastic blend to optimize the blend proportion. This optimization has been achieved through an analysis of 12 distinct blends, considering factors such as combustion reaction kinetics, combustion stability, and comprehensive combustion indices. The reaction kinetics, including activation energy, pre-exponential factor, and reaction order, were estimated using various methods, including Vyazovkin, Kissinger−Akahira−Sunose, Flynn−Wall−Ozawa, Master-plot, and multidistributed activation energy methods. The investigation revealed that increasing the biomass content within the blends enhances both the combustion stability and combustion performance. The multidistributed activation energy model exhibited a good fit with both the experimental thermogravimetric and the derivative thermogravimetric curves, achieving linear regression fitness values of 0.99 and 0.95, respectively. To showcase the viability of these blends as energy generation feedstock, the optimal blend comprised of 60% biomass, 10% coal, and 30% municipal waste plastic blend, possessing the lowest activation energy (110 kJ/mol), was employed as the feedstock for the fluidized bed oxy-steam gasification process. The gasification process resulted in a synthetic gas consisting of 47.79 mol % H 2 , 27.96 mol % CO, 5.85 mol % CH 4 , and 18.38 mol % CO 2 (nitrogen-free basis) with a cold gas efficiency of 72.88%. The findings of this study can offer valuable insights into global industries engaged in the thermochemical conversion of solid waste materials.

Linköping Electronic Conference Proceedings, 2021

The paper considers a model for floor heating in buildings, with an electrically heated, stratifi... more The paper considers a model for floor heating in buildings, with an electrically heated, stratified water tank, a circulation loop, a detailed description of heat transport through the floor, and a simplistic room model. The model structure is suitable for control of room temperature, and the paper discusses the use of modern simulation tools for control-relevant analysis of such models. The stratification description contains a non-differentiable buoyancy term, and two approximations are studied which circumvent this problem. The results indicate that a boundary layer approach is superior to a log-sum-exp approximation. Important basic control-relevant analysis ideas include step response (time constants), sensitivity analysis (parameter identifiability), the system zeros location (attainable performance), and Bode plots (control synthesis). The paper illustrates how such an analysis can be carried out using tools such as OpenModelica in combination with scripting language Julia.

Linköping Electronic Conference Proceedings

Operator training simulators (OTS) are a valuable tool for improving the competence of both proce... more Operator training simulators (OTS) are a valuable tool for improving the competence of both process operators and engineers. As pumps, compressors and turbines are vital parts of any process plant, accurate modeling of these machines is crucial for a dynamic process simulator. The behavior of the machines is usually described by operating curves provided by the manufacturer. However, these curves are strictly valid only for the specific process conditions they were created for. Accurate prediction of the operation outside of these specific conditions may present a formidable challenge. To further improve the accuracy the NAPCON Simulator, a new dynamic modeling method was developed for the centrifugal compressors. The stability of the developed model was verified by dynamic ramp tests of the operating conditions. Furthermore, the accuracy of the developed model was determined by performing process data tests. The results were promising and, in most cases, an improvement from the performance of the currently implemented model.

IOE Graduate Conference-2019, 2019

This article presents the preliminary design of Archimedean spiral-type wind turbine, one of the ... more This article presents the preliminary design of Archimedean spiral-type wind turbine, one of the emerging horizontal axis wind turbine (HAWT), with the aid of calculations and observations of various geometric parameters by computational fluid dynamics (CFD) analysis. Through simulations conducted by varying the pitch and opening angle at wind velocity of 3.5 m/s, for a turbine of 150 mm diameter, the geometry of final model was selected to obtain maximum power coefficient. Pitch and opening angle selected for final model was 112.5 mm (1.5 times radius) and 60 degrees respectively. Selected model was scrutinized through CFD analysis in range of wind velocity varying from 3.5 m/s to 12 m/s to estimate the power output. At wind velocity of 8 m/s, 10 m/s and 12 m/s, maximum power output was 1.38 W, 2.72 W and 4.74 W respectively, all obtained at the tip speed ratio of 1.5. Maximum power coefficient of 0.25 was attained at this tip-speed ratio, irrespective of wind velocity. Keywords Archimedean spiral-type wind turbine, computational fluid dynamics (CFD), tip speed ratio, power coefficient

ACS Publication, 2023

Feedstocks such as coal, biomass, plastics, and their blends have the potential to serve as fuels... more Feedstocks such as coal, biomass, plastics, and their blends have the potential to serve as fuels for the thermochemical conversion process owing to their relatively high calorific values. Nevertheless, the relative proportion of these feedstock blends has a pivotal influence over the overall energy conversion efficiency. Consequently, conducting a comprehensive study to optimize the blend proportion becomes crucial in order to obtain an optimal fuel. The study aims to investigate the thermochemical characterization and kinetics of blends composed of lignite coal, southern pine biomass, and municipal waste plastic blend to optimize the blend proportion. This optimization has been achieved through an analysis of 12 distinct blends, considering factors such as combustion reaction kinetics, combustion stability, and comprehensive combustion indices. The reaction kinetics, including activation energy, pre-exponential factor, and reaction order, were estimated using various methods, including Vyazovkin, Kissinger−Akahira−Sunose, Flynn−Wall−Ozawa, Master-plot, and multidistributed activation energy methods. The investigation revealed that increasing the biomass content within the blends enhances both the combustion stability and combustion performance. The multidistributed activation energy model exhibited a good fit with both the experimental thermogravimetric and the derivative thermogravimetric curves, achieving linear regression fitness values of 0.99 and 0.95, respectively. To showcase the viability of these blends as energy generation feedstock, the optimal blend comprised of 60% biomass, 10% coal, and 30% municipal waste plastic blend, possessing the lowest activation energy (110 kJ/mol), was employed as the feedstock for the fluidized bed oxy-steam gasification process. The gasification process resulted in a synthetic gas consisting of 47.79 mol % H 2 , 27.96 mol % CO, 5.85 mol % CH 4 , and 18.38 mol % CO 2 (nitrogen-free basis) with a cold gas efficiency of 72.88%. The findings of this study can offer valuable insights into global industries engaged in the thermochemical conversion of solid waste materials.

Linköping Electronic Conference Proceedings, 2021

The paper considers a model for floor heating in buildings, with an electrically heated, stratifi... more The paper considers a model for floor heating in buildings, with an electrically heated, stratified water tank, a circulation loop, a detailed description of heat transport through the floor, and a simplistic room model. The model structure is suitable for control of room temperature, and the paper discusses the use of modern simulation tools for control-relevant analysis of such models. The stratification description contains a non-differentiable buoyancy term, and two approximations are studied which circumvent this problem. The results indicate that a boundary layer approach is superior to a log-sum-exp approximation. Important basic control-relevant analysis ideas include step response (time constants), sensitivity analysis (parameter identifiability), the system zeros location (attainable performance), and Bode plots (control synthesis). The paper illustrates how such an analysis can be carried out using tools such as OpenModelica in combination with scripting language Julia.

Linköping Electronic Conference Proceedings

Operator training simulators (OTS) are a valuable tool for improving the competence of both proce... more Operator training simulators (OTS) are a valuable tool for improving the competence of both process operators and engineers. As pumps, compressors and turbines are vital parts of any process plant, accurate modeling of these machines is crucial for a dynamic process simulator. The behavior of the machines is usually described by operating curves provided by the manufacturer. However, these curves are strictly valid only for the specific process conditions they were created for. Accurate prediction of the operation outside of these specific conditions may present a formidable challenge. To further improve the accuracy the NAPCON Simulator, a new dynamic modeling method was developed for the centrifugal compressors. The stability of the developed model was verified by dynamic ramp tests of the operating conditions. Furthermore, the accuracy of the developed model was determined by performing process data tests. The results were promising and, in most cases, an improvement from the performance of the currently implemented model.

IOE Graduate Conference-2019, 2019

This article presents the preliminary design of Archimedean spiral-type wind turbine, one of the ... more This article presents the preliminary design of Archimedean spiral-type wind turbine, one of the emerging horizontal axis wind turbine (HAWT), with the aid of calculations and observations of various geometric parameters by computational fluid dynamics (CFD) analysis. Through simulations conducted by varying the pitch and opening angle at wind velocity of 3.5 m/s, for a turbine of 150 mm diameter, the geometry of final model was selected to obtain maximum power coefficient. Pitch and opening angle selected for final model was 112.5 mm (1.5 times radius) and 60 degrees respectively. Selected model was scrutinized through CFD analysis in range of wind velocity varying from 3.5 m/s to 12 m/s to estimate the power output. At wind velocity of 8 m/s, 10 m/s and 12 m/s, maximum power output was 1.38 W, 2.72 W and 4.74 W respectively, all obtained at the tip speed ratio of 1.5. Maximum power coefficient of 0.25 was attained at this tip-speed ratio, irrespective of wind velocity. Keywords Archimedean spiral-type wind turbine, computational fluid dynamics (CFD), tip speed ratio, power coefficient