Browsing by Subject "process safety"
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Item Data driven process monitoring based on neural networks and classification trees(Texas A&M University, 2005-11-01) Zhou, YifengProcess monitoring in the chemical and other process industries has been of great practical importance. Early detection of faults is critical in avoiding product quality deterioration, equipment damage, and personal injury. The goal of this dissertation is to develop process monitoring schemes that can be applied to complex process systems. Neural networks have been a popular tool for modeling and pattern classification for monitoring of process systems. However, due to the prohibitive computational cost caused by high dimensionality and frequently changing operating conditions in batch processes, their applications have been difficult. The first part of this work tackles this problem by employing a polynomial-based data preprocessing step that greatly reduces the dimensionality of the neural network process model. The process measurements and manipulated variables go through a polynomial regression step and the polynomial coefficients, which are usually of far lower dimensionality than the original data, are used to build a neural network model to produce residuals for fault classification. Case studies show a significant reduction in neural model construction time and sometimes better classification results as well. The second part of this research investigates classification trees as a promising approach to fault detection and classification. It is found that the underlying principles of classification trees often result in complicated trees even for rather simple problems, and construction time can excessive for high dimensional problems. Fisher Discriminant Analysis (FDA), which features an optimal linear discrimination between different faults and projects original data on to perpendicular scores, is used as a dimensionality reduction tool. Classification trees use the scores to separate observations into different fault classes. A procedure identifies the order of FDA scores that results in a minimum tree cost as the optimal order. Comparisons to other popular multivariate statistical analysis based methods indicate that the new scheme exhibits better performance on a benchmarking problem.Item Determining Bounds for a Pressure Hazard Rating to Augment the NFPA 704 Standard(2012-02-14) Hodge, PhillipHazard communication is an essential part of a comprehensive safety plan, especially for those facilities that contain reactive chemicals. There are a variety of means of communicating a chemical hazard, but one of the most prevalent in the United States is the Instability Rating found in the NFPA 704 standard. While the NFPA 704 identifies hazards associated with exothermically decomposing compounds, it neglects compounds that decompose endothermicly to form large quantities of gas. Such compounds have been known to cause accidents due to pressure buildup, such as in the BP Amoco Polymers explosion in 2001. In this work, twenty-five compounds were examined via an APTAC to determine their pressure and temperature profiles. These profiles were then used to determine the amount of gas generated, the gas generation rate, the gas generation product, the onset temperature, and the instantaneous power density. These properties were analyzed to determine those that best represented the instability hazard of the chemical. Ultimately, the molar gas generation rate and onset temperature were chosen to rate the selected chemicals, and new cut-offs were established to divide the chemicals into revised instability groupings. Compounds that did not decompose in the temperature range examined were given the rating of zero. Compounds with low onset temperatures and high gas generation rates were assigned the rating of 4, while chemicals with high T_onset and low dn/dt_maxn were assigned a value of 1. Chemicals with high onset temperatures and high gas generation rates were grouped into rating 3. Group 2 included low onset temperature compounds with low gas generation rates. The cut-offs used to define these regions were 130 degrees C for the onset temperature and 0.01 (1/min) for the gas generation rate. The ratings were found to be comparable to the current NFPA system, but improved upon it by providing a valid rating (group 1) for the chemicals that endothermically generated gas. Detailed plots of the data are provided as well as suggestions for future work.Item Measurement and prediction of aerosol formation for thesafe utilization of industrial fuids(Texas A&M University, 2004-09-30) Krishna, KiranMist or aerosol explosions present a serious hazard to process industries. Heat transfer fluids are widely used in the chemical process industry, are flammable above their flash points, and can cause aerosol explosions. Though the possibility of aerosol explosions has been widely documented, knowledge about their explosive potential is limited. Studying the formation of such aerosols by emulating leaks in process equipment will help define a source term for aerosol dispersions and aid in characterizing their explosion hazards. Analysis of the problem of aerosol explosions reveals three major steps: source term calculations, dispersion modeling, and explosion analysis. The explosion analysis, consisting of ignition and combustion, is largely affected by the droplet size distribution of the dispersed aerosol. The droplet size distribution of the dispersed aerosol is a function of the droplet size distribution of the aerosol formed from the leak. Existing methods of dealing with the problem of aerosol explosions are limited to enhancing the dispersion to prevent flammable concentrations and use of explosion suppression mechanisms. Insufficient data and theory on the flammability limits of aerosols renders such method speculative at best. Preventing the formation of aerosol upon leaking will provide an inherently safer solution to the problem. The research involves the non-intrusive measurement of heat transfer fluid aerosol sprays using a Malvern Diffraction Particle Analyzer. The aerosol is generated by plain orifice atomization to simulate the formation and dispersion of heat transfer fluid aerosols through leaks in process equipment. Predictive correlations relating aerosol droplet sizes to bulk liquid pressures, temperatures, thermal and fluid properties, leak sizes, and ambient conditions are presented. These correlations will be used to predict the conditions under which leaks will result in the formation of aerosols and will ultimately help in estimating the explosion hazards of heat transfer fluid aerosols. Heat transfer fluid selection can be based on liquids that are less likely to form aerosols. Design criteria also can incorporate the data to arrive at operating conditions that are less likely to produce aerosols. The goal is to provide information that will reduce the hazards of aerosol explosions thereby improving safety in process industries.Item Resilient engineered systems: the development of an inherent system property(Texas A&M University, 2007-09-17) Mitchell, Susan McAlpinProtecting modern engineered systems has become increasingly difficult due to their complexity and the difficulty of predicting potential failures. With the added threat of terrorism, the desire to design systems resilient to potential faults has increased. The concept of a resilient system ?????? one that can withstand unanticipated failures without disastrous consequences ?????? provides promise for designing safer systems. Resilience has been recognized in research settings as a desired end product of specific systems, but resilience as a general, inherent, measurable property of systems had yet to be established. To achieve this goal, system resilience was related to an established concept, the resiliency of a material. System resilience was defined as the amount of energy a system can store before reaching a point of instability. The energy input into each system as well as the system??????s exergy were used to develop system stress and system strain variables. Process variable changes to four test systems ?????? a steam pipe, a water pipe, a water pump, and a heat exchanger ?????? were applied to obtain series of system stress and system strain data that were then graphed to form characteristic system response curves. Resilience was quantified by performing power-law regression on each curve to determine the variable ranges where the regression line accurately described the data and where the data began to deviate from that power-law trend. Finally, the four test systems were analyzed in depth by combining them into an overall system using the process simulator ASPEN. The ranges predicted by the overall system data were compared to the ranges predicted for the individual equipment. Finally, future work opportunities were outlined to show potential areas for expansion of the methodology.Item The integration of Dow's Fire and Explosion Index into process design and optimization to achieve an inherently safer design(Texas A&M University, 2006-10-30) Suardin, Jaffee ArizonThe integration of the safety parameter into process design and optimization is essential. However, there is no previous work in integrating the fire and explosion index (F&EI) into design and optimization. This research proposed a procedure for integrating safety into the design and optimization framework by using the safety parameter as optimization constraint. The method used in this research is Dow??????s Fire and Explosion Index which is usually calculated manually. This research automates the calculation of F&EI. The ability to calculate the F&EI, to determine loss control credit factors and business interruption, and to perform process unit risk analysis are unique features of this F&EI program. In addition to F&EI calculation, the F&EI program provides descriptions of each item of the penalties, chemicals/materials databases, the flexibility to submit known chemical/material data to databases, and material factor calculations. Moreover, the sensitivity analyses are automated by generating charts and expressions of F&EI as a function of material inventory and pressure. The expression will be the focal point in the process of integrating F&EI into process design and optimization framework. The proposed procedure of integrating F&EI into process design and optimization framework is verified by applying it into reactor-distillation column system. The final result is the optimum economic and inherently safer design for the reactor and distillation column system.