Ralph W. Pike

Theory and practice of simultaneous data reconciliation and gross error detection for chemical processes

Abstract On-line optimization provides a means for maintaining a process near its optimum operating conditions by providing set points to the process’s distributed control system (DCS). To achieve a plant-model matching for optimization, process measurements are necessary. However, a preprocessing of these measurements is required since they usually contain random and—less frequently—gross errors. These errors should be eliminated and the measurements should satisfy process constraints before any evaluation on the process. In this paper, the importance and effectiveness of simultaneous procedures for data reconciliation and gross error detection is established. These procedures depending on the results from robust statistics reduce the effect of the gross errors. They provide comparable results to those from methods such as modified iterative measurement test method (MIMT) without requiring an iterative procedure. In addition to deriving new robust methods, novel gross error detection criteria are described and their performance is tested. The comparative results of the introduced methods are given for five literature and more importantly, two industrial cases. Methods based on the Cauchy distribution and Hampel’s redescending M-estimator give promising results for data reconciliation and gross error detection with less computation.

Optimal implementation of on-line optimization

Abstract Results from a theoretical and numerical evaluation of on-line optimization algorithms were used to recommend the best way to conduct on-line optimization. This optimal procedure conducts combined gross error detection and data reconciliation to detect and rectify gross errors in plant data sampled from the distributed control system. The Tjoa-Biegler method (the contaminated Gaussian distribution) was used for gross errors in the range of 3σ – 30σ- or the robust method (Lorentzian distribution) for larger gross errors. This step generates a set of measurements containing only random errors which is used for simultaneous data reconciliation and parameter estimation using the least squares method. Updated parameters are used in the plant model for economic optimization that generates optimal set points for the distributed control system. Applying this procedure to a Monsanto sulfuric acid contact plant, a 3% increase in profit and a 10% reduction in SO2 emissions were projected over current operating condition which is consistent with other reported applications.

Solubility and Henry's law constant for alcohols in water

Abstract A new correlation which provides reliable solubility values down to very, very low concentrations is presented for solubility of alcohols in water. The correlation is based on boiling point temperature of the alcohol and can be used for engineering studies involving health, safety and environmental considerations. Results for water solubility and Henrys law constant are provided for a wide variety of alcohols. Representative solubility values (parts per million by weight) are 74,000 for n -butanol (C 4 H 10 O) and 4.0 for 1-dodecanol (C 12 H 26 O).

Ablation and radiation coupled viscous hypersonic shock layers.

Coupled ablator shock layer solutions for the stagnation point are presented for typical hyperbolic entry atmospheric flight conditions. These solutions were obtained by numerically solving the stagnation line shock layer equations and quasi-steady ablator equations. These equations included ablation and radiation coupling within the viscous shock layer, line and continuum radiation for both air and phenolic-nylon ablation species and local thermodynamic equilibrium throughout. The results presented provide a sound basis for understanding many of the processes characteristic of hypersonic shock layer heating.-

CFD analyses of complex flows

Computational fluid dynamics (CFD) of complex processes and complicated geometries embraces the transport of momentum, heat, and mass including the description of reaction kinetics and thermodynamics. The paper outlines the numerical models available for analyzing these processes and presents examples of such methodology. The unprecedented growth in computer capability has resulted in efficient simulations of most transport phenomena. The aerospaces interest in high-pressure turbulent combustion has created efficient computational tools for analyzing run-away-reactions in the process industries. Practical turbulence models, generalized thermodynamic properties, and extensive chemical kinetics data bases are currently used in three-dimensional, steady-state simulations. However, industrial needs have challenged CFD modelers to improve their flow solvers in order to simulate flows with more complicated physics, such as spray combustion, acoustic waves, transient start-up and shut-down, and flow instabilities. In addition, the practicality and efficiency of numerical simulations are highly dependent on the submodels employed, such as reaction mechanisms and turbulence models. There has been some progress in generalizing CFD tools, but more development is needed. Most of all, more high-quality and critical test data are required to validate the CFD simulations of complex processes. The laminar transport equations have been averaged by various means to locally describe both turbulent and multi-phase flows. Spray combustion, stirred-tank reactors, fluidization of catalytic beds, and highly exothermic supercritical reactors are among the several validated examples, which illustrate todays technology. The designers access to public-domain, open-source software offers powerful methodology for his use. Such software and the variety of available modeling techniques will be inventoried to demonstrate the scope of computational transport methodology. The current state of CFD models will be assessed to address the need for future research.

An approach to on-line optimization of chemical plants

Abstract An effective approach to on-line optimization of chemical processes has been demonstrated using flowsheeting (ASPEN PLUS) for process optimization and parameter estimation and the Tjao-Beigler algorithm implemented in a mathematical programming language (GAMS/MINOS) for data reconciliation and gross error detection. Results for a Monsanto sulfuric acid plant with a Bailey distributed control system showed a 17 % improvement in the profit and a 25 % reduction in the stack gas emissions over the current operating conditions. Details of the methods used are described.

Source reduction from chemical plants using on-line optimization

An effective approach for source reduction in chemical plants has been demonstrated using on-line optimization with flowsheeting (ASPEN PLUS) for process optimization and parameter estimation and the Tjao-Biegler algorithm implemented in a mathematical programming language (GAMS/MINOS) for data reconciliation and gross error detection. Results for a Monsanto sulfuric acid plant with a Bailey distributed control system showed a 25% reduction in the sulfur dioxide emissions and a 17% improvement in the profit over the current operating conditions. Details of the methods used are described.

Nonequilibrium Flow and the Kinetics of Chemical Reactions in the Char Zone

Abstract In the temperature range of 500–2500°F, nonequilibrium flow analysis predicted only a small change in pyrolysis gas composition as the gases flow through the char zone. Essentially all of the reactions took place in the temperature range of 2000–2500°F. Comparing nonequilibrium flow with the two limiting cases, the energy absorbed in the char zone for frozen flow was two-thirds that of nonequilibrium flow, and equilibrium flow was about four times that of nonequilibrium flow at the 2500°F level.

Density of liquid—Organic compounds

Publisher Summary This chapter presents the density of liquid for organic compounds in tabular form. For the tabulation, an equation is selected for correlation of liquid density as a function of temperature. The tabulation is arranged by carbon number such as C, C2, and C3 to provide ease of use in quickly locating the data by using the chemical formula. The compound name and chemical abstracts registry number (CAS No) are also provided in columns. Values for regression coefficients are given in the adjacent columns. The temperature range for use is also given in columns (TMIN and TMAX). The equation should not be used for temperatures outside this range. The next column provides the code for the tabulation. The last two columns provide a representative temperature and value for liquid density at the representative temperature. The compilations of CRC, Daubert and Danner, TRC, and Yaws are used extensively for liquid density. Estimates of liquid density are primarily based on Schroeder correlation, Le Bas method, and Tyn-Calus equation. A comparison of calculated and data values is also presented for a representative compound. The graph shows favorable agreement of equation and data.

An Advanced Process Analysis System for Improving Chemical and Refinery Processes

An advanced process analysis system has been developed to perform comprehensive evaluations on chemical plants and refineries for process improvements. The system integrates programs for on-line optimization, chemical reactor analysis, flowsheeting, pinch analysis and pollution indices. These programs are used interactively and share plant data through a database. Results from applying the system to a Monsanto/IMC Agrico contact process for sulfuric acid include an increased profit, reduced emissions and improvements in the chemical reactors and heat exchanger network which demonstrates the applicability of the system for pollution prevention.