Faculty Publications

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    Synthesis of renewable carbon biorefinery products from susceptor enhanced microwave-assisted pyrolysis of agro-residual waste: A review
    (Institution of Chemical Engineers, 2022) Rajasekhar Reddy, B.R.; Sridevi, V.; Kumar, T.H.; Sankar Rao, C.S.; Palla, V.C.S.; Suriapparao, D.V.; Undi, G.S.
    Valuable renewable carbon biorefinery products can be obtained by using agro-residual biomass as a feedstock. Bio-oil, gas, and char products can be obtained from Microwave-assisted pyrolysis (MAP) by converting agro-residual waste. In MAP, the process variables like microwave power, temperature, heating rate, raw materials, susceptors, and catalysts play an important role to alter the product spectrum. The temperature, heating rate, and pyrolysis time can be tuned to obtain the desired products during biomass decomposition. The obtained carbonaceous products can be used as intermediated feedstocks to synthesize a variety of end products. Hence, in this review, the application of MAP for the conversion of agro-residual waste is discussed. Special focus is given to the interaction of microwaves with susceptors. This manuscript provides background, current status, progress, and future scope of MAP technology for waste valorization. The objectives of the review are to address (i) The necessity of environmental protection, (ii) The role of biorefinery in the biomass conversion, (iii) The advancements in the MAP for the resource recovery, (iv) The mechanism of heat generation from microwaves, (v) The effects of process parameters, susceptors, and catalysts in MAP, (vi) The interactions of biomass and susceptors during the pyrolysis, (vii) The formation of valuable renewable carbon products and (viii) The future scope and challenges for the integration of MAP in solid waste management. © 2022 The Institution of Chemical Engineers
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    Understanding the role of modeling and simulation in pyrolysis of biomass and waste plastics: A review
    (Elsevier Ltd, 2022) Ramesh, R.; Suriapparao, D.V.; Sankar Rao, C.S.; Kumar, T.H.
    The valorization of resources from biomass and plastic waste using thermochemical platforms is an innovative approach. Pyrolysis is thermochemical technology that is very effective in the production of fuels and chemical intermediates. It's conducted by conventional heating, solar heating, and microwave-controlled heating. Compared to conventional pyrolysis, microwave-assisted pyrolysis is more advantageous. The temperature distribution, mass transfer, and heat transfer rates depend on the operation mode through process parameters. The optimization of the pyrolysis process is crucial for scale-up. Computer-assisted modeling and simulation techniques help to develop suitable configurations and experimental methods for better efficiencies. Modeling allows the identification of optimum operating parameters and understanding of transportation mechanisms involved in pyrolysis. Modeling, simulation, and optimization are ideally suited to understanding and analyzing the complex stages of pyrolysis. This review provides insight into existing heat, mass, and momentum transfer models for pyrolysis. The effects of transport properties on pyrolysis are dealt with. © 2022 Elsevier Ltd
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    Dynamic performance comparison of two configurations of middle vessel batch distillation column for the separation of ethanol/propanol/butanol mixture
    (John Wiley and Sons Ltd cs-journals@wiley.co.uk, 2020) Narayana, M.S.; Arthanareeswaran, G.; Sankar Rao, C.S.
    This paper deals with Aspen Plus and Aspen Dynamics of the middle vessel batch distillation for the separation of mixtures of ethanol/propanol/butanol. Two configurations of middle vessel batch distillation have been considered, namely, the conventional middle vessel batch distillation (Configuration 1) and the modified middle vessel batch distillation column (Configuration 2). Steady-state simulations have been performed in Aspen Plus and exported to Aspen Dynamics for dynamic simulation. Dynamic studies show that Configuration 1 requires less time than Configuration 2 to obtain more than 95% of the compositions of ethanol, propanol, and butanol. The efficacy of the two controllers is assessed by the performance indices of integral of square error, integral of absolute error, and integral of time-weighted absolute error. Configuration 1 is found to have better performance than Configuration 2. © 2020 Curtin University and John Wiley & Sons, Ltd.
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    Novel strategies for glucose production from biomass using heteropoly acid catalyst
    (Elsevier Ltd, 2020) Nayak, A.; Pulidindi, I.N.; Sankar Rao, C.S.
    Bioethanol and direct glucose fuel cells pledged clean energy to the world. Cellulose depolymerization for glucose production has been a successful approach in bioethanol production. Heteropoly acids (HPAs) are strong Brønsted solid acid catalysts for biomass hydrolysis. Keggin type HPAs, namely, Silicotungstic acid (HSiW), Phosphotungstic acid (HPW), and Phosphomolybdic acid (HPMo), were used for the hydrolysis of lignocellulosic biomass to glucose. Five different biomass feedstocks, namely, miscanthus, sugarcane leaves, switchgrass, sunflower seeds, and bamboo leaves, were examined for the feasibility of total reducing sugar (TRS) yield through the composition analysis and catalytic biomass hydrolysis. Sunflower seeds contained the maximum holocellulose with 90.6%, and switchgrass contained the least i.e., 77.63%. Among the five biomass tested, switchgrass resulted in the highest TRS (5.77 wt/dry wt. %) with HPMo catalyst at a catalyst to biomass ratio of 30:100 (wt./wt. %), a reaction temperature of 120 °C for 3 h. The reaction parameters for depolymerization were optimized for all three HPAs, and the optimized conditions were 3 h and 120 °C. HPMo showed maximum TRS yield (5.77 wt/dry wt.%) among the three HPAs at 30:100 catalyst to biomass ratio. However, a catalyst to biomass ratio of 20:100 (wt./wt.%) was economical (5.25 wt/dry wt.%) for commercial application. © 2020 Elsevier Ltd
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    Robust decentralized proportional–integral controller design for an activated sludge process
    (John Wiley and Sons Ltd, 2020) Anchan, S.S.; Sankar Rao, C.S.
    This paper presents the design of a decentralized proportional–integral (PI) controller for a wastewater treatment plant (WWTP). The aeration rate and the return recycle sludge rate are manipulated inputs to the WWTP process, while substrate and biomass concentration are considered as the output variables. The study is divided into two segments: A decentralized controller is designed based on the best pairing in the first segment, and in the second segment, a decoupler is developed to reduce the interactions. Decouplers are generally used to create independent loops in the multivariable control loops. Each decoupled subsystem is converted to first order plus time delay (FOPTD) model using a system identification toolbox to design independent diagonal controllers. The numerical simulations have been performed to evaluate the effectiveness of the presented methods. Furthermore, a robustness study has also been carried out by taking into account multiplicative input and output uncertainties, and it is found that the controller designed based on minimizing the integral of absolute error (IAE) criteria shows more robust. © 2020 Curtin University and John Wiley & Sons, Ltd.
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    Simultaneous separation of ternary mixture using modified dual compression middle vessel batch distillation column: Control and dynamic optimization
    (Taiwan Institute of Chemical Engineers, 2022) Desikan, B.; Krishna, P.; Sankar Rao, C.S.
    Background: Multivessel batch distillation has been found to be an effective method for the separation of multi-component mixtures. In this article, an effort has been made to devise a fast middle vessel batch distillation column (MVBDC) for the ternary separation of an Ethanol/Propanol/Butanol mixture by the means of inducing vapor compression in the system. Methods: ASPEN PLUS V12 has been used to generate the initial steady-state flowsheet of the process for equipment sizing. In contrast, ASPEN Dynamics was used to evaluate the performance of the batch distillation with various control structures and to perform a dynamic optimization on the proposed batch distillation column. MATLAB was used to identify single-input single-output transfer functions for more effective PID controller tuning. Significant Findings: The proposed Middle vessel batch distillation was found to separate each component of the mixture to a purity of 99 mol% in 22 h (for the cascade control structures) and 21.73 h (for the temperature control structure). This was found to be significantly lesser than the batch time of a conventional batch distillation column (28.12 h), while the energy consumed by the proposed column was 3.4 MMkcal lesser than the energy consumed by the conventional column. Dynamic optimization further reduced the batch time by 14.4% while simultaneously reducing the energy consumed by 20.3%. © 2022 Taiwan Institute of Chemical Engineers
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    Centralized Proportional Integral Controller Design for the Activated Sludge Process
    (John Wiley and Sons Inc, 2022) Anchan, S.S.; Sankar Rao, C.S.
    The design of a centralized proportional integral controller for a single-tank activated sludge process is presented. The relative normalized gain array (RNGA) and dynamic relative gain array (dRGA) were adopted for enhancing the closed-loop performance of a multivariable system. The dRGA method gave superior and acceptable responses compared to the RNGA method. The designated error indices decreased significantly for the dRGA method compared with the RNGA method. The dRGA method is simple and effective, since it considers the process dynamics to provide an accurate interaction assessment. The designed centralized controller overcomes the limitations of the decoupler for stability challenges when compared with decentralized controllers. © 2022 Wiley-VCH GmbH.
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    A Simple Method to Design a Decoupler for a Proton Exchange Membrane Fuel Cell
    (John Wiley and Sons Inc, 2022) Goyal, I.; Reddy, S.; Sankar Rao, C.S.
    A decoupling control system is designed by a simple tuning-free method for the multi-input multi-output model of a proton exchange membrane fuel cell. The decoupler minimizes the interactions among the loops and is designed by estimating the relative normalized gain array and dynamic relative gain array for the closed-loop model. The proportional integral controller settings are estimated using the partial model matching method. The performances of the proposed method are studied based on closed-loop performances of control variables and time integral errors that are compared with the synthesis method. The proposed controller performs better in terms of integral of time-weighted absolute error. © 2022 Wiley-VCH GmbH.
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    Multiobjective temperature trajectory optimization for unseeded batch cooling crystallization of aspirin
    (Elsevier Ltd, 2022) Ashraf, A.B.; Sankar Rao, C.S.
    Batch cooling crystallization is a type of crystallization wherein supersaturation is brought about by reducing the temperature of the crystallization system with time. It is commonly used in the chemical and pharmaceutical industries to manufacture a wide variety of crystalline products. This work deals with multiobjective optimization of unseeded batch cooling crystallization of Aspirin. A novel method involving temperature changes rather than temperatures of the crystallization mixture over time has been discussed in this study. Optimization studies were carried out to minimize the coefficient of variation and maximize mean size. Optimization was carried out using the benchmark NSGA-II and NSGA-II hybrid optimizers available in MATLAB. A standard algorithm to select a trade-off point on the Pareto front is also discussed. Rigorous simulation studies were carried out to determine the best temperature trajectory by inspecting the crystal size distributions generated using the method of characteristics. © 2022 Elsevier Ltd
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    Improved PID controller design for an unstable second order plus time delay non-minimum phase systems
    (Elsevier B.V., 2022) Patil, P.; Anchan, S.S.; Sankar Rao, C.S.
    Principally the fundamental limitations for achieving better control performance is caused due to the existence of positive zeros. This study proposes a method to stabilize the unstable non-minimum phase Second Order Plus Time Delay (SOPTD) process. It adopts the Taylor series expansion to produce the equal order of numerator and denominator for the closed loop transfer function. The coefficient of corresponding powers of s, s2 and s3 in numerators are equated to α, β, γ times of the denominator and solved for PID controller setting using multi-objective optimization problems. The stability of the controller is then analysed by minimizing the Integral Time weighted Absolute Error (ITAE) and maximum sensitivity function using MATLAB solvers. The observations from various simulation studies clearly suggests that the proposed method provides significant superior responses when compared with the methods reported. © 2022 The Author(s)