In this study, we first report the development of a robust and efficient finite volume based adsorption process simulator, essential for rigorous optimization of a transient cyclic operation without resorting to any model reduction. We present a detailed algorithm for the common boundary conditions encountered in nonisothermal and nonisobaric adsorption process simulations. A comprehensive comparison of the high-resolution total variation diminishing (TVD) schemes, namely, van Leer and Superbee, with the weighted essentially nonoscillatory (WENO) finite volume scheme is performed, and trade-off plots are presented to identify the numerical scheme most suitable for attaining speed and accuracy at the same time. The simulator is then used to perform rigorous optimization of a four-step process for postcombustion CO2 capture from dry flue gas on zeolite 13X. The aim is to identify operating conditions at which the purity and recovery demands are met and to calculate corresponding energy consumption and process productivity. The purity–recovery and energy–productivity Paretos are generated using multiobjective optimization. It is shown that, for a strict vacuum swing adsorption (VSA) process, an evacuation pressure of 0.02 bar is required to satisfy regulatory demands of attaining a CO2 purity and recovery of 90%. It is also quantitatively shown that pressurizing the flue gas is detrimental to the energy consumption of process, although offering improvement in productivity.

Water resource management impacts almost all aspects of the economy, in particular health, food production and security, domestic water supply and sanitation, energy, industry and environmental sustainability. For the last several decades, seawater has become an important source of fresh water as it is one of the most abundant resources on earth. Desalination is the process of removal of salts from seawater and is postulated to be a core technology in alleviating this problem. Clathrate hydrate based desalination (HyDesal) is a potential technology for seawater desalination. Salts are excluded from hydrate formation, thereby resulting in solid hydrate and concentrated brine. After separation from brine, the solid hydrate crystals upon dissociation produce pure water. In this work, a detailed review of the literature (both patents and publications) so far on HyDesal is critically evaluated, and prospects and directions to commercialize the HyDesal process are presented. Further, innovation by coupling LNG cold energy with HyDesal can make it economically attractive and can strengthen the energy−water nexus.

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Scheduling of crude oil operations is a complex nonlinear problem, especially when tanks hold crude mixes. We present a new mixed-integer nonlinear programming (MINLP) formulation and a novel, mixed-integer linear programming (MILP)-based solution approach for optimizing crude oil unloading, storage, and processing operations in a multi-CDU (crude distillation unit) refinery receiving crude from multiparcel VLCCs (very large crude carriers) through a high-volume, single-buoy mooring (SBM) pipeline and/or single-parcel tankers through multiple jetties. Mimicking a continuous-time formulation, our primarily discrete-time model allows multiple sequential crude transfers to occur within a time slot. It incorporates several real-life operational features including brine settling and tank-to-tank transfers, and is superior to other reported models. Notably our algorithm avoids concentration discrepancy and MINLP solutions by identifying a part of the horizon, for which its linear relaxation is exact, and then solving this MILP repeatedly with progressively shorter horizons. By using 8 h time slots and a hybrid time representation, an attractive approach to this difficult problem is presented

The capture and concentration of CO 2 from a dry flue gas by vacuum swing adsorption (VSA) has been experimentally demonstrated in a pilot plant. The pilot plant has the provision for using two coupled columns that are each packed with approximately 41 kg of Zeochem zeolite 13X. Breakthrough experiments were first carried out by perturbing a N 2 saturated bed with 15% CO 2 and 85% N 2 feed, which is representative of a dry flue gas from coal-fired power plants. The breakthrough results showed long plateaus in temperature profiles confirming a near adiabatic behavior. In the process study, a basic four-step vacuum swing adsorption (VSA) cycle comprising the following steps: pressurization with feed, adsorption, forward blowdown, and reverse evacuation was investigated first. In the absence of any coupling among the steps, a single bed was used. With this cycle configuration, CO 2 was concentrated to 95.9 6 1% with a recovery of 86.4 6 5.6%. To improve the process performance, a four-step cycle with light product pressurization (LPP) using two beds was investigated. This cycle was able to achieve 94.8 6 1% purity and 89.7 6 5.6% recovery. The Department of Energy requirements are 95% purity and 90% recovery. The proposed underlying physics of performance improvement of the four-step cycle with LPP has also been experimentally validated. The pilot plant results were then used for detailed validation of a one-dimensional, nonisothermal, and nonisobaric model. Both transient profiles of various measured variables and cyclic steady state performance results were compared with the model predictions, and they were in good agreement. The energy consumptions in the pilot plant experiments were 339-583 6 36.7 kWh tonne 21 CO 2 captured and they were significantly different from the theoretical power consumptions obtained from isentropic compression calculations. The productivities were 0.87-1.4 6 0.07 tonne CO 2 m 23 adsorbent day 21. The results from our pilot plant were also compared with available results from other pilot plant studies on CO 2 capture from flue gas.

A systematic analysis of several vacuum swing adsorption (VSA) cycles with Zeochem zeolite 13X as the adsorbent to capture CO2 from dry, flue gas containing 15% CO2 in N2 is reported. Full optimization of the analyzed VSA cycles using genetic algorithm has been performed to obtain purity‐recovery and energy‐productivity Pareto fronts. These cycles are assessed for their ability to produce high‐purity CO2 at high recovery. Configurations satisfying 90% purity‐recovery constraints are ranked according to their energy‐productivity Pareto fronts. It is shown that a 4‐step VSA cycle with light product pressurization gives the minimum energy penalty of 131 kWh/tonne CO2 captured at a productivity of 0.57 mol CO2/m3 adsorbent/s. The minimum energy consumption required to achieve 95 and 97% purities, both at 90% recoveries, are 154 and 186 kWh/tonne CO2 captured, respectively. For the proposed cycle, it is shown that significant increase in productivity can be achieved with a marginal increase in energy consumption. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4735–4748, 2013

in Wiley InterScience (www.interscience.wiley.com).Higher crude prices have made it even more imperative that refiners blend low-quality and high-quality crudes optimally to maximize their margins. Mathematical modeling of crude blending results in bilinear terms, which combined with commonly used feed quality specifications, make crude scheduling a large, nonconvex, mixed-integer nonlinear optimization problem. The existing literature algorithms and software (DICOPT/GAMS and BARON/GAMS; Brooke et al., GAMS: a user's guide, GAMS, 1998) fail to solve practical instances of this difficult and useful problem. In this paper, we first enhance the practical utility of our previous crude scheduling algorithm by adding 15 properties and corresponding linearly additive indices, which are used in the refinery industry to ensure feed quality. Then, we propose some new iterative strategies to improve the robustness and solution quality of this algorithm. We also propose a partial relaxation strategy to increase its solution speed. We prove its enhanced performance using 24 industry-scale examples, and estimate bounds on solution quality. In contrast to existing algorithms or software that fail to solve most of these problems, our revised algorithm solves all problems successfully and gives profits within 6% of our computed upper bounds. 2007 American Institute of Chemical Engineers AIChE J, 53: 2007 Keywords: crude oil, scheduling, refinery, short-term scheduling, blending operations, mixed-integer linear program, crude quality IntroductionCrude oil costs account for nearly 80% of a refinery's turnover.1 Crude oils vary significantly in compositions, product yields, properties, and prices. Premium crudes such as West Texas Intermediate (WTI), Brent blend, etc. sell roughly $15 per barrel higher than the low-quality crudes such as Arabia heavy, Soudieh, etc. Most refineries use varying blends of several crude oils over time to exploit the higher margins of low-cost crude oils. With declining supplies and increasing prices of premium crude oils, the challenge facing the refiner is how to best exploit the greater margins of the low-cost crudes to increase profits. However, the low-cost crudes are almost always high in less-than-desirable components or traits such as sulfur, aromatics, high residue, etc., and cause processing and/or product quality problems in crude distillation units (CDUs) and downstream units. Therefore, a key issue in the refinery business is to identify and process optimal blends of low-cost and premium crudes to minimize the operational problems yet maximize profit margins. As noted by Kelly and Mann, 1,2 scheduling of crude oil operations in a refinery is an critical task that can save millions of dollars per year, if done in an optimal manner. However, that is easier said than done. This paper addresses the crude scheduling problem described by Reddy et al.3 for a typical marine-access refinery. As mentioned by them, the task of crude oil scheduling in today's refinery is becoming increasingly com...

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