Nishith Vora

Model Reduction of Multiple Time Scale Processes in Non-standard Singularly Perturbed Form

This work considers multiple time scale models in non standard singularly perturbed form. These systems naturally arise as descriptions of detailed rate-based process models of fast-rate chemical processes with several large parameters of different orders of magnitude. We propose a systematic framework to derive representations of the dynamics in individual time scales. A nonlinear coordinate transformation is presented to yield a standard singularly perturbed form of the original system. This approach is applied to a representative multiple time scale chemical process with reactions whose reaction rates span different orders of magnitude.

Predictive Heat Exchanger Efficiency Monitoring

The performance of heat exchangers degrades with time due to fouling or deposition of material on the heat transfer surface. The fouling of critical exchangers in manufacturing plants results in a significant cost impact in terms of production losses, energy efficiency, and maintenance costs. While most plants monitor their exchangers to some degree, the ability to effect real and sustainable improvements requires four components: (1) real time monitoring; (2) an advance warning mechanism; (3) the ability to diagnose the cause of fouling; and (4) the ability to treat the cause in order to slow or reverse the degradation. CHeX is a comprehensive tool which monitors, predicts, and diagnoses heat exchanger performance. The unique features of this advanced technology include: numerous data cleaning steps to improve data quality and isolate a net fouling trend, an adaptive model which learns from the past to predict performance three years in advance, and knowledge-based diagnostics which identify the probable cause(s) of fouling and recommend corrective actions. The final control action is performed by a field engineer in adjusting the fouling treatment. The scope of the current paper includes only the detection and prediction features. To date, CHeX has been validated at three chemical processing plants, for fourteen exchangers. Selected case studies shall be presented to demonstrate the power of its algorithms over traditional calculations.© 2005 ASME

Nonlinear model reduction of reaction systems with multiple time scale dynamics

We consider a broad class of nonisothermal spatially homogeneous reaction systems that exhibit dynamics in multiple distinct time scales, and address the systematic derivation of reduced order nonlinear models in the individual time scales. The proposed model reduction method is applied to a hydrogen oxidation reaction system.

Nonlinear model reduction of chemical reaction systems

We consider a broad class of nonisothermal, spatially homogeneous reaction systems, with fast and slow reactions. The dynamic model of such systems exhibits stiffness (time-scale multiplicity) but is not in a standard singularly perturbed form. For such systems, we address the derivation of reduced order nonlinear models of the slow dynamics, through (i) the identification of algebraic constraints that need to be satisfied in the slow time scale (e.g. reaction equilibrium constraint in the case of fast reversible reactions), and (ii) the derivation of state-space realizations of the resulting differential algebraic system that describes the slow dynamics.

Predictive Performance Assessment of Heat Exchangers for Proactive Remediation

Efficiency of industrial heat exchangers degrades over time as a result of deposition of the extraneous matter present in the heat-exchanging medium. Many times the degradation is rapid enough to take a heavy toll on the overall plant economy. It is therefore important to keep a closer watch on heat exchanger performance so that a suitable corrective action can be initiated the moment any abnormality is detected. While most plants monitor their exchangers to some degree, ability to effect real and sustainable improvements requires four components: (1) near-real time detection capability; (2) an early warning system (3) capability to diagnose the cause of fouling; and (4) right expertise to treat the cause in order to slow or reverse the degradation. CHeX2 is a comprehensive tool that we have developed, which monitors, predicts, and diagnoses heat exchanger performance. This tool has been designed to cover a wide range of heat transfer equipments namely simple heat exchangers, condensers and partial condensers with both the shell and tube-side condensation. The unique features of this advanced tool include: numerous data cleaning steps to enhance data quality and isolate a net fouling trend, an adaptive model which learns from the past to predict performance three years in advance, and knowledge-based diagnostics which identify the probable cause(s) of fouling and recommend corrective actions. A trained field engineer takes the final control action by adjusting the fouling treatment. The scope of the current paper includes only the detection and prediction features. To date, CHeX has been validated at three chemical processing plants, for fourteen exchangers. Selected case studies shall be presented to demonstrate the power of its algorithms over traditional calculations.

Analysis and nonlinear control of an ethyl acetate reactive distillation column

In this work, we study a reactive distillation column for the production of ethyl acetate. Initially we propose a configuration that involves feeding the two reactants in different trays and allows obtaining higher conversion and purity than the conventional configuration that involves feeding in a single tray. A nonlinear controller is then designed to control the product purity in this new configuration with good set-point tracking and disturbance rejection properties, and its performance is compared with that of a linear proportional-integral (PI) controller.

Nonlinear non-stiff models of reactive distillation columns with two-time-scale dynamics

Abstract In this paper, we address the dynamic modeling of reactive distillation processes, where the presence of fast reaction or momentum transport induces two time scale dynamics. We present a systematic modeling framework that allows identifying the source of time Scale multiplicity and deriving nonlinear non-stiff models of the slow dynamics.

Time scale multiplicity and nonlinear control of an ethyl acetate reactive distillation column

In this paper, the dynamics and control of a reactive distillation column for the production of ethyl acetate are studied. Initially, the existence of fast and slow dynamics corresponding to the liquid flow rates, and the liquid compositions and hold-ups, respectively, is documented and analyzed. A description of the slow dynamics of the column is derived using singular perturbation arguments, and is used for the synthesis of a nonlinear feedback controller. The performance and robustness of this controller are evaluated and compared with those of a controller based on the exact two time scale model.