Gas Hydrate Dynamics with Parameter-Free Clathrate Phase Description: Validation for Hydrate Formation and Dissociation.

One of the major challenges involved in clathrate hydrate science that has remained for more than six decades lies in highly parametric clathrate phase estimation. In this contribution, a recently developed parameter-free hydrate phase statistical equilibrium model is employed for the first time to formulate the formation and dissociation dynamics of clathrates and predict their experimental observation at diverse geological conditions. This rigorous thermokinetic model takes into account various practical issues, notably hydrate formation in nanometer-sized pores (confirmed through seismic survey studies), irregularity in porous particle shape and pore size, renewal of the particle surface over which hydrate majorly forms and decays, and th-order phase transformation.

A thermodynamic framework to identify apposite refrigerant former for hydrate-based applications.

High latent heat storage capacity with naturally assisted salt rejection makes the clathrate compounds appropriate for applications towards load management and desalination processes. Adding to these energy savings are the ease of operations provided by water and the mild conditions at which the refrigerant hydrates are occurred. A direct comparison between these hydrates becomes unfeasible due to the scattered experimental data.

Microsecond molecular dynamics of methane-carbon dioxide swapping in pure and saline water environment.

This work aims at proposing the nondestructive methane-carbon dioxide (CH-CO) replacement mechanism as an ecofriendly energy production technique from the natural gas hydrate reserves in seafloor and permanently frozen grounds. Although the experimental data is widely available in literature, this replacement mechanism has not been elucidated at molecular level. In this contribution, we perform the microsecond level molecular dynamic simulations to evaluate two different CH-CO replacement mechanisms: (i) direct CH displacement from hydrate structure, and (ii) dissociation of existing methane hydrate followed by a reformation of mixed CH-CO hydrates.

A Lattice Distortion Theory for Promotor Containing Clathrate Hydrates.

A lattice distortion theory for promotor containing clathrate hydrates is formulated using the statistical thermodynamics based model of van der Waals and Platteeuw in association with the ab initio quantum mechanics to compute the cavity potentials. Despite of high degree of lattice distortion anticipated for large and polar molecules of liquid promotors, their variable lattice energy concept is unreported. With this intention, we estimate the lattice stabilization energy from spin-component scaled second order Møller-Plesset (SCS-MP2) perturbation theory applied with the augmented correlation-consistent polarized double zeta valence (aug-cc-pVDZ) basis set.

Microscopic Molecular Insights into Hydrate Formation and Growth in Pure and Saline Water Environments.

The growth dynamics of natural gas hydrates in saline water has been studied using copious experiments and spectroscopic observations; however, the microscopic evidences to the structural and molecular transformations that they have provided are poorly understood. In this view, we perform extensive molecular dynamics simulations to gain physical insights into the formation and growth mechanism of naturally occurring gas hydrates with a wide variation in the amount of methane (1:5 to 1:18 methane/water ratio) in pure and salt (0-5 wt %) water environments at 50 MPa and 260 K. A couple of new findings analyzed from the number of cages and order parameter are as follows: (a) 1:6 (methane/water ratio) is an optimum ratio for the rapid growth of a properly ordered hydrate in pure water at which the hydrate growth retards with increasing salt concentration, (b) there is an inconsequential difference between methane hydrate dynamics in pure water and 0.

Insights into the competitive adsorption of pollutants on a mesoporous alumina-silica nano-sorbent synthesized from coal fly ash and a waste aluminium foil.

A highly efficient and low-cost alumina-silica nano-sorbent was fabricated and characterized to understand the key factors responsible for its superiority over the existing adsorbents in treating the industry-discharged wastewater for the removal of dyes and heavy metals. As compared to the properties of raw fly ash, the following fundamental improvements were observed for the alumina-silica nano-sorbent: (a) transformation of throttled mesopores into slit-type pores, (b) increment in the surface area by 65-fold, (c) change in the morphology from spherical particles to a flake-type structure with sharp edges, (d) reduction in the average crystal size from 61.143 to 27.

Nonmonotonous Lattice Distortion Model for Gas Hydrates.

A gas hydrate forms when the hydrogen-bonded crystal structure of water entraps the small-sized gas molecules at a relatively low temperature and high pressure. Experimental and spectroscopic studies prove that the inclusion of a guest into an empty cavity leads to the distortion of the hydrate lattice via either the contraction or expansion of the cavity, which depends on the size and functional group of the guest. However, the existing lattice distortion theories represent only the expansion phenomena, and consequently, the degree of distortion is reported as a monotonous function of the size of the guest.

Modeling recovery of natural gas from hydrate reservoirs with carbon dioxide sequestration: Validation with Iġnik Sikumi field data.

Fundamental understanding of guest gas replacement in hydrate reservoirs is crucial for the enhanced recovery of natural gas and carbon dioxide (CO) sequestration. To gain physical insight into this exchange process, this work aims at developing and validating a clathrate hydrate model for gas replacement. Most of the practical concerns associated with naturally occurring gas hydrates, including hydrate formation and dissociation in interstitial pore space between distributed sand particles in the presence of salt ions and in irregular nanometer-sized pores of those particles, irregularity in size of particles and shape of their pores, interphase dynamics during hydrate formation and decay, and effect of surface tension, are addressed.

Computing Anisotropic Cavity Potential for Clathrate Hydrates.

Either concerning to the energy production from natural gas hydrates or employing the hydrate technology to gas handling and seawater desalination purposes, various pure and mixture clathrate hydrates need to be understood in terms of their phase behavior and stability. The ab initio methods have compelling implications in quantifying the anisotropic guest-water interactions that are responsible for the guest-specific nature of the hydrates. Howbeit, the accurate cavity interactions for large guests are obscure due to computational infeasibility.

Fundamental of swapping phenomena in naturally occurring gas hydrates.

Amount of natural gas contained in the gas hydrate accumulations is twice that of all fossil fuel reserves currently available worldwide. The conventional oil and gas recovery technologies are not really suitable to gas hydrates because of their serious repercussions on geo-mechanical stability and seabed ecosystem. To address this challenge, the concept of methane-carbon dioxide (CH-CO) swapping has appeared.

Formulating formation mechanism of natural gas hydrates.

A large amount of energy, perhaps twice the total amount of all other hydrocarbon reserves combined, is trapped within gas hydrate deposits. Despite emerging as a potential energy source for the world over the next several hundred years and one of the key factors in causing future climate change, gas hydrate is poorly known in terms of its formation mechanism. To address this issue, a mathematical formulation is proposed in the form of a model to represent the physical insight into the process of hydrate growth that occurs on the surface and in the irregular nanometer-sized pores of the distributed porous particles.

Neuro-estimator based GMC control of a batch reactive distillation.

In this paper, an artificial neural network (ANN)-based nonlinear control algorithm is proposed for a simulated batch reactive distillation (RD) column. In the homogeneously catalyzed reactive process, an esterification reaction takes place for the production of ethyl acetate. The fundamental model has been derived incorporating the reaction term in the model structure of the nonreactive distillation process.

Dynamic simulation and nonlinear control of a rigorous batch reactive distillation.

This work deals with the dynamics and control of a high-purity batch distillation column with chemical reaction. A heterogeneous esterification reaction between the acetic acid and butanol takes place to produce butyl acetate. The process model is formulated considering variable liquid holdup, UNIQUAC model for thermodynamic property predictions, nonlinear Francis weir formula for tray hydraulics, pseudohomogeneous model to represent the reaction kinetics and rigorous energy balance.

Synthesis of nonlinear adaptive controller for a batch distillation.

A nonlinear adaptive control strategy is proposed for a binary batch distillation column. The hybrid control algorithm comprises a generic model controller (GMC) and a nonlinear adaptive state estimator (ASE). The adaptive observation scheme mainly estimates the imprecisely known parameters based on the available tray temperature measurements.

Nonlinear control of a multicomponent distillation process coupled with a binary distillation model as an EKF predictor.

The work is devoted to design the globally linearizing control (GLC) strategy for a multicomponent distillation process. The control system is comprised with a nonlinear transformer, a nonlinear closed-loop state estimator [extended Kalman filter (EKF)], and a linear external controller [conventional proportional integral (PI) controller]. The model of a binary distillation column has been used as a state predictor to avoid huge design complexity of the EKF estimator.

A hybrid feedback linearizing-Kalman filtering control algorithm for a distillation column.

This paper studies the design of a discrete-time multivariable feedback linearizing control (FLC) structure. The control scheme included (i) a transformer [also called the input/output (I/O) linearizing state feedback law] that transformed the nonlinear u-y to a linearized v-y system, (ii) a closed-loop observer [extended Kalman filter (EKF)], which estimated the unmeasured states, and (iii) a conventional proportional integral (PI) controller that was employed around the v-y system as an external controller. To avoid the estimator design complexity, the design of EKF for a binary distillation column has been performed based on a reduced-order compartmental distillation model.

Globally linearized control on diabatic continuous stirred tank reactor: a case study.

This paper focuses on the promise of globally linearized control (GLC) structure in the realm of strongly nonlinear reactor system control. The proposed nonlinear control strategy is comprised of: (i) an input-output linearizing state feedback law (transformer), (ii) a state observer, and (iii) an external linear controller. The synthesis of discrete-time GLC controller for single-input single-output diabatic continuous stirred tank reactor (DCSTR) has been studied first, followed by the synthesis of feedforward/feedback controller for the same reactor having dead time in process as well as in disturbance.

Nonlinear model-based control algorithm for a distillation column using software sensor.

This paper presents the design of model-based globally linearizing control (GLC) structure for a distillation process within the differential geometric framework. The model of a nonideal binary distillation column, whose characteristics were highly nonlinear and strongly interactive, is used as a real process. The classical GLC law is comprised of a transformer (input-output linearizing state feedback), a nonlinear state observer, and an external PI controller.