Abstracts:Scheduling of production and maintenance plays a fundamental role in the effective operation of process plants. Frequently the two decision processes are independently addressed, overlooking the tight relation existing between the way the plant is operated to produce the required goods and the appearance of maintenance requirements. The presence of degradation phenomena affecting the performance of plant units and limiting the operational choices makes the integration of the two decision processes even more important. In this paper an industrial framework for the integration of maintenance and production scheduling of process plants is presented as well as some considerations on how the presence of plant unit degradation impacts on the scheduling problem. The proposed approach ties industrial key-components such as asset management and production scheduling closer together and represents therefore a contribution to the smart manufacturing revolution. The integrated maintenance and production scheduling problem is formulated as a mixed integer linear program (MILP) and tested on a generic process plant described as a State Task Network (STN).

Abstracts:The ethylene cracking furnace system is central to an olefin plant. Multiple cracking furnaces are employed for processing different hydrocarbon feeds to produce various smaller hydrocarbon molecules, such as ethylene, propylene, and butadiene. We develop a new cyclic scheduling model for a cracking furnace system, with consideration of different feeds, multiple cracking furnaces, differing product prices, decoking costs, and other more practical constraints. To obtain an efficient scheduling strategy and the optimal operational conditions for the best economic performance of the cracking furnace system, a diversity learning teaching-learning-based optimization (DLTLBO) algorithm is used to simultaneously determine the optimal assignment of multiple feeds to different furnaces, the batch processing time and sequence, and the optimal operational conditions for each batch. The performance of the proposed scheduling model and the DLTLBO algorithm is illustrated through a case study from a real-world ethylene plant: experiments show that the new algorithm out-performs both previous studies of this set-up, and the basic TLBO algorithm.

Abstracts:This work describes a simplified dynamic model for control and real time applications in offshore deepwater and ultra-deepwater petroleum production systems. Literature about simplified dynamical models, capable of cover the global architecture of an offshore multiphase production system, is scarce. Hence, the proposed model integrates and adapts partial models available in the literature in order to generate a single model of the whole system. The model, designed to represent slugs generated by the casing heading and terrain/riser concomitantly, was evaluated by comparison with a traditional commercial simulator and was also implemented in two actual production systems. As a result, the model showed the capability of capturing complex dynamical behaviors, such as limit cycles, demonstrated to be numerically more stable than similar models in literature, fast enough to be used in real time applications and proved to be adherent to the commercial simulator and actual operating data from Petrobras production systems.

Abstracts:Supersaturation is a factor of great industrial importance to the crystal growth by affecting the final aspect ratio and morphology of organic compounds. In this work, the qualitative relationship between aspect ratio and supersaturation of benzoic acid (BA) was elucidated for the first time by experimental and simulative study. Experimentally, it was found that the crystal shape of BA changes from needle-like crystal to rectangular sheet and then to hexagonal particles with the increasing supersaturation ranging from 1.029 to 2.941. The increment of supersaturation decreases the average aspect ratio of crystallized particles from ∼20.5 to ∼1.3. Furthermore, a higher supersaturation (σ=1.618) leads to more isotropic hexagonal crystals due to less face discrimination at high crystallization rates. Additionally, we predicted the supersaturation-dependent crystal habit by the modified attachment energy (MAE) model, which yield good agreement with the experimental observed crystals at medium and high supersaturations.

Abstracts:In this paper, we present a control relevant rigorous dynamic model for an ultrafiltration membrane unit in a whey separation process. The model consists of a set of differential algebraic equations and is developed for online model based applications such as model based control and process monitoring. In this model, membrane resistance concept is adjusted to describe the membrane fouling. Based on the observations regarding the permeate flux, we propose a membrane resistance expression consisting of static and dynamic resistances. The empirical expressions for the membrane resistances are identified by solving a parameter estimation problem. The dynamic model is investigated for its predictive capabilities and is further utilised for the study of optimal operation strategies.

Abstracts:In this contribution different objective functions based on the moments of the product crystal size distribution are compared using optimal control theory to solve for the optimal batch trajectory for each objective. For a simple crystallization process model with only nucleation and ordinary crystal growth, and neglecting the contribution of the nucleated mass to the nucleation rate and material balance, mostly analytic expressions are obtained for the optimal control vector. Different objective functions lead to different final values for the costates, which lead to different sets of coupled differential and algebraic equations which must be solved to determine the values of constants numerically. The results of nine different objective functions for three crystal systems are presented. The objective functions based on the lower moment of the nucleated crystals lead to late-growth trajectories while the objective functions based on the higher moment of the nucleated crystals lead to early-growth trajectories, consistent with previous findings. The effect of seed loading is also investigated.

Abstracts:A two-dimensional transient numerical study of the adsorption of CO2/N2 and CO2/H2 mixtures on activated carbon and MOF-177 in a fixed bed is presented. Because most of the commercial CFD codes are not capable of simulating adsorption processes in a straightforward fashion, we developed an additional code to solve for the different species transport including adsorption and diffusion and used Fluent to simulate the adsorption process, fluid flow, heat and, mass transfer.

Abstracts:In this work, we propose a new arrangement for integrating an Autothermal Reforming of Ethanol process with oxygen production with the technology of ITM membranes. In the conventional configuration O2 is first separated from the air and then injected in the reforming process, while in the new configuration O2 is depleted from the air in a counter-current arrangement with a reforming process stream, used as sweep gas. We took from the literature a process for Autothermal Reforming of Ethanol in its optimal operating condition, and scaled it up to pilot size. We assessed the performance of both configurations with Aspen Plus V8.7 and found that the configuration in counter-current arrangement with a process sweep stream has a reduction of the total annualized cost of 27.3% with respect to the conventional separation configuration. Furthermore, we optimize the operating conditions and ancillary structure of the counter-current integrated process, achieving a total annualized cost reduction of 72.2% with respect to the conventional design.

Abstracts:The modelling and design of Simulated moving bed (SMB) processes is normally done using the True moving bed (TMB) approximation. Several studies show that average values obtained at cyclic steady state for SMB units approach the TMB unit at steady state and that this approach is better as the number of columns in the SMB increases. However, studies that evaluate this equivalence under dynamic conditions are scarce. The objective of this work is to perform an analysis of the transient behaviour of two SMB units, with four and eight columns, and compare the results with the ones obtained for a TMB unit. An analysis of the impact of operating variables on the processes performance parameters is performed. The results show that TMB/SMB equivalence is valid only for conditions that do not violate the regeneration/separation regions and that the transient behaviour of the four columns SMB can resemble more the TMB.

Abstracts:A hydrogen production plant with integrated catalytic membrane reactor modules (HP-CMR) represents a new technology option with potentially enhanced environmental performance characteristics. Therefore, HP-CMR techno-economic performance in the presence of irreducible sources of uncertainty (market, regulatory) ought to be comprehensively evaluated in order to accelerate the realization of future demonstration plants. The present study introduces a systematic methodological framework allowing the economic value assessment of various flexibility options in the design and operation of an HP-CMR plant under the above uncertainty sources. The primary objective is to demonstrate the potentially value-enhancing prospects of design flexibility options that capture the inherent optionality element in managerial decision-making to actively respond to uncertainties as they are progressively resolved. A detailed Net Present Value (NPV)-based assessment framework is first developed within which the above sources of uncertainty are integrated through Monte Carlo techniques. Various constructional and operational flexibility options are introduced pertaining to the installation decision and operating mode choice of the carbon capture and sequestration (CCS) unit, and HP-CMR economic performance is comparatively assessed. Finally, under certain scenarios of regulatory action on CO2 emissions, it is demonstrated that quite appealing economic performance outcomes could emerge for HP-CMR plants once design flexibility is introduced.