Pressure-Swing Dividing Wall Column with Multiple Binary Azeotropes: Improving Energy Efficiency and Cost Savings through Vapor Recompression

This work introduces a novel thermal integration scheme for a pressure-swing distillation train used to separate a mixture of methanol/benzene/acetonitrile. This mixture typically forms three azeotropes as shown through developing its residue curve map with two distillation boundaries at atmospheric pressure. This ternary mixture is traditionally separated via a triple column pressure-swing distillation (TCPSD) scheme, in which, all columns operate at different pressures. Here, the first two columns of the TCPSD are proposed to be replaced by a single column having a dividing wall that allows heat transfer through it. Thus, the resulting scheme is called pressure-swing dividing wall column (PSDWC). Aiming to improve its performance, further advancement is subsequently made by developing the heat intensified PSDWC (HiPSDWC) and vapor recompressed PSDWC (VRPSDWC). The performance of these proposed schemes is evaluated in the context of energy saving and total annual cost (TAC). Among these configurations, it is investigated that the VRPSDWC secures the best performance, providing a 75.67% savings in external energy consumption, which is 2.45 times that of the HiPSDWC. The attractiveness of the best performing VRPSDWC is further quantified by a 13.25% TAC savings and a reasonably short payback time of 2.97 years (3.91 years with considering penalty of 10%)

Dynamic Optimization of Multieffect Seawater Distillation to Gain Insights into Various Feeding Patterns: Productivity, Thermodynamic, Economic, and Environmental Perspectives

Seawater desalination is consistently gaining research interest, as water scarcity looms globally. Multieffect distillation with thermal vapor compression (MED-TVC) has emerged as a promising solution to the freshwater scarcity problem. In this contribution, we put forward a way to gain physical insights into various feeding patterns of MED-TVC and identify a suitable pattern to treat saline water effectively. For this, a dynamic model for a MED-TVC with parallel cross feed (PCF) is first formulated and then validated it with data sets of two different plants showing excellent matching. This validated model is further extended for dynamic multiobjective genetic algorithm-based optimization by framing four conflicting objectives in the aspects of performance ratio (PR), second law efficiency (ηII), freshwater production cost (FWPC), and CO2 emission. With this, we formulate the technique for order of preference by similarity to ideal solution (TOPSIS) embedded nondominated sorting genetic algorithm-II (NSGA-II). A systematic comparison is presented between the optimal performance of the three feeding patterns, namely, forward, parallel, and parallel cross feed MED-TVC operating under optimal configurations. The relative merits and demerits of each feeding pattern are discussed, and among them, the PCF comes out as the front-runner with minimum cost (FWPC) and emission level and maximum performance ratio and thermodynamic efficiency. This study provides a clear and optimal picture based on the stated objectives and properly guides to choose a suitable feeding methodology for seawater desalination in MED-TVC

Novel Thermokinetic Model for Gas Hydrates: Experimental Validation at Diverse Geological Conditions

Most of the natural gas hydrates are found in deep marine sediments and permafrost regions, where the presence of salts and porous media are quite evident. With this, we develop a computationally efficient mathematical model that can expound the clathrate hydrate dynamics in a reservoir-mimicking environment. Along with proposing the chemical potential difference as the driving force to take care of the thermodynamic aspect, a nonstoichiometric reaction with nth-order kinetics is for the first time introduced in the line of adsorption kinetics. To make this thermokinetic model more rigorous, the diffusion part is further formulated with the kinetic factor, along with incorporating various practical aspects, including reaction surface renewal and hydrate formation in nanometer-sized pores of irregular and distributed particles. Finally, to examine the validity of this rigorous model, experimental case studies of methane (CH4) and carbon dioxide (CO2) hydrate formation in various porous media with pure and saline water are used. In addition, we compare the developed model with the existing formulations of gas hydrate dynamics, and it is perceived that the proposed model outperforms the existing models with reference to the experimental data of methane and carbon dioxide hydrate formation at diverse geological conditions