Reactive distillation is a novel technology that has been successfully used in the production of ether fuel additives. This process integrates reaction and separation in a single unit-operation. The interaction of reaction and separation makes the process exhibit complex behavior such as process gain nonlinearity, significant interactions, process gain bidirectionality (i.e., process gain sign change), and steady-state multiplicity. These complex dynamics make process control of the reactive distillation column very difficult. In this work, the nonlinearity of an ETBE reactive distillation column was investigated, and a 2 × 2 unconstrained model predictive control scheme was developed for the product purity and reactant conversion control. The process dynamics were approximated by a first-order plus dead time model to estimate the process model for the model predictive controller. The model predictive controller was able to handle the process interactions well and was found to be very efficient for disturbance rejection and set-point tracking. This controller was stable and performed robustly in the presence of process measurement noise.
Solvent Assisted-Steam Assisted Gravity Drainage (SA-SAGD) process is an enhancement to SAGD recovery technology. In this process a hydrocarbon solvent is injected simultaneously with steam to accelerate the oil production rate and reduce steam-to-oil ratio (SOR) compared to classical SAGD. SA-SAGD is a complex process; its physics and mechanisms are not fully understood. ExxonMobil and its affiliate Imperial Oil have been investigating SA-SAGD through an integrated research program that includes fundamental laboratory work, advanced numerical simulation studies, laboratory scaled physical modeling, and field piloting. This research program aims at in-depth understanding of process physics and mechanisms, evaluating process performance and behavior, and improving SA-SAGD recovery technology.
This paper focuses on SA-SAGD optimization and assessing the effects of operating conditions and solvent choice on the process performance. The complex solvent-steam phase behavior and their interaction under reservoir operating conditions are investigated in the current work. Phase behavior analysis shows that the solvent boiling range affects solvent-steam condensation temperature at the condensation and mixing front and consequently it affects the solvent effectiveness in terms of performance enhancement. The effect of phase behavior on SA-SAGD performance has been evaluated by analyzing experimental and simulation performance data. It is shown that the composition of injected fluid significantly affects the process performance. It is also shown that the solvent composition can be customized to improve SA-SAGD process performance under different operating conditions.
An algorithm for the steady-state simulation of two- and three-phase multistage reactive distillation processes
with equilibrium chemical reactions is developed. In the developed algorithm, the phase stability, phase
equilibrium, and chemical reaction equilibrium calculations are preformed simultaneously. The algorithm
was used to simulate a variety of two- and three-phase reactive distillation processes. The simulation results
were compared against the available experimental data in the literature. Good agreement was observed between
the simulation results and experimental data. A multistage reactive distillation process for the production of
cyclohexanol from the hydration of cyclohexene with two liquid phases present on multiple stages was
simulated. A high-purity cyclohexanol product with a high cyclohexene conversion was obtained for this
process.
The development of a new algorithm for steady-state modeling of multistage three-phase separation columns is presented. In the developed algorithm, prior knowledge of phase pattern in the column is not required. The phase pattern determination and equilibrium calculations are carried out simultaneously. The stability of a phase is determined by coupling a stability equation with the model equations of the column. The resulting nonlinear model equations of the system are solved using an "inside-out" method. The ability and flexibility of the algorithm for the simulation of three-phase separation columns are shown by solving a variety of threephase distillation column examples. The algorithm is also applicable to two-phase separation columns.
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