MKOPSC Theses and Dissertations

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Active and Knowledge-based Process Safety Incident Retrieval System
(2011-10-21) Khan, Sara Shammni; Mannan, M. Sam; Tretter, Marietta J.; Caverlee, James
The sustainability and continued development of the chemical industry is to a large extent dependent on learning from past incidents. The failure to learn from past mistakes is rather not deliberate but due to unawareness of the situation. Incident databases are excellent resources to learn from past mistakes; however, in order to be effective, incident databases need to be functional in disseminating the lessons learned to users. Therefore, this research is dedicated to improving user accessibility of incident databases. The objective of this research is twofold. The first objective is improving accessibility of the database system by allowing the option of word search as well as folder search for the users. This will satisfy research needs of users who are aware of the hazards at hand and need to access the relevant information. The second objective is to activate the database via integration of the database with an operational software. This will benefit research needs of users who are unaware of the existing hazards. Literature review and text mining of Major Accident Reporting System (MARS) database short reports are employed to develop an initial taxonomy, which is then refined and modified by expert review. The incident reports in MARS database is classified to the right folders in the taxonomy and implemented in a database system based on Microsoft Excel, where the users can retrieve information using folder search as well as word search option via a user friendly interface. A program coded in JAVA is prepared for integrating the incident database with a Management of Change (MOC) software prototype. A collection of keywords on hazardous substances and equipment is prepared. If the keywords exist in the MOC interface, they will be highlighted, and with the click of a button, will return up to ten relevant incident reports. Using an active and knowledge-based system, people can learn from incidents and near-misses and will be more active to reduce the frequency of recurring incidents.
Analysis of the HSEES Chemical Incident Database Using Data and Text Mining Methodologies
(2012-07-16) Mahdiyati, -; Mannan, M. Sam; Tretter, Marietta; El-Halwagi, Mahmoud
Chemical incidents can be prevented or mitigated by improving safety performance and implementing the lessons learned from past incidents. Despite some limitations in the range of information they provide, chemical incident databases can be utilized as sources of lessons learned from incidents by evaluating patterns and relationships that exist between the data variables. Much of the previous research focused on studying the causal factors of incidents; hence, this research analyzes the chemical incidents from both the causal and consequence elements of the incidents. A subset of incidents data reported to the Hazardous Substance Emergency Events Surveillance (HSEES) chemical incident database from 2002-2006 was analyzed using data mining and text mining methodologies. Both methodologies were performed with the aid of STATISTICA software. The analysis studied 12,737 chemical process related incidents and extracted descriptions of incidents in free-text data format from 3,316 incident reports. The structured data was analyzed using data mining tools such as classification and regression trees, association rules, and cluster analysis. The unstructured data (textual data) was transformed into structured data using text mining, and subsequently analyzed further using data mining tools such as, feature selections and cluster analysis. The data mining analysis demonstrated that this technique can be used in estimating the incident severity based on input variables of release quantity and distance between victims and source of release. Using the subset data of ammonia release, the classification and regression tree produced 23 final nodes. Each of the final nodes corresponded to a range of release quantity and, of distance between victims and source of release. For each node, the severity of injury was estimated from the observed severity scores' average. The association rule identified the conditional probability for incidents involving piping, chlorine, ammonia, and benzene in the value of 0.19, 0.04, 0.12, and 0.04 respectively. The text mining was utilized successfully to generate elements of incidents that can be used in developing incident scenarios. Also, the research has identified information gaps in the HSEES database that can be improved to enhance future data analysis. The findings from data mining and text mining should then be used to modify or revise design, operation, emergency response planning or other management strategies.
Analysis of the Thermal Decomposition of Untempered Peroxide Systems
(2016-04-08) Reyes Valdes, Olga Juliana; Mannan, Sam; Vechot, Luc; Moreno, Valeria Casson; Balbuena, Perla; Cagin, Tahir; Mashuga, Chad
Several of the most catastrophic process safety incidents, such as Bhopal and most recently Texas West Fertilizer explosion, were initiated by runaway reactions. Consequences of such incidents include, fatalities, environmental damage, and in some instances corporate bankruptcy. To prevent conditions leading to a runaway, it is necessary to understand the kinetics, and physical and thermodynamic properties of the chemical system. In the present research, calorimetric experiments were coupled with computational chemistry calculations to characterize the runaway behavior of two organic peroxides: Dicumyl Peroxide (DCP) and Cumene Hydroperoxide (CHP). These two reactive systems are particularly challenging due to their untempered behavior and complex kinetics. To characterize the physical behavior of DCP and CHP runaways, adiabatic testing was performed in two equipment. Experimental results suggest that: Scaling up methods used to estimate temperature and self-heating rate profiles on a large-scale, from laboratory data, are inconsistent for fast self-heating rate systems under runaway conditions. Moreover, the use of low thermal inertia or phi factor equipment (more costly and difficult to operate), do not always provide better large-scale estimations. This is due to potential higher heat losses. Pressure discrepancies of up to 27 times were encountered when the phi factor was increased from 1.1 to 1.8. This finding elucidates the necessity of more efforts to scale up pressure behavior. Estimation of gas generation rate from different configuration (closed vs open cell) diverges by up to 2.3 times. Principal sources of discrepancies are: open cell gas temperature assumption, pressure influence on vaporization, and gas dissolution. Due to the complexity of the decomposition reaction of systems under study, grasping knowledge of their thermo-kinetics characteristics by experimental techniques is expensive, time consuming, and probably not possible. In this work, computational quantum chemistry, transitional state theory, and thermodynamic principles are used to achieve a deeper understanding of DCP and CHP decomposition thermos-kinetics. Networks of 12 and 18 reactions for DCP and CHP decomposition, respectively, are proposed. Products of the proposed networks match those reported by analytical techniques. Using this method provides a safe alternative while dealing with complex, highly reactive and unknown systems.
Application of Computational Fluid Dynamics (CFD) to Study Liquefied Natural Gas (LNG) Pool Fires
(2016-12-07) Chaudhari, Dushyant Madhav; Mannan, M. Sam; Glover, Charles; Hasan, Rashid
Liquefied Natural Gas (LNG) pool fires pose a major risk to LNG facilities. The radiant energy from a LNG pool fire can be sufficiently high to threaten the structural integrity of the facility, plant personnel, fire fighters and potentially people beyond the boundaries of the facility. Safety analysis for LNG consequence modeling requires protection of the public against hazards caused by LNG pool fires. Current safety analysis involves the use of empirical models to assess the effects of a pool fire. Application of these models to pool fires of different size pose significant uncertainty in terms of underestimation of key parameters. In this study, a CFD (Computational Fluid Dynamic) software is used to advance the knowledge of LNG pool fire modeling. The Fire Dynamic Simulator (FDS) code is used to simulate pool fire of a small scale experiment to study the sensitivity of different pool fire characteristics on turbulence models. Comparative study of Deardorff turbulence model and constant coefficient Smagorinsky turbulence model was done to see its dependence on combustion model which eventually affects the radiation. Numerical approach used for determining flame geometry was validated by comparing the results with the experiment. Transient fluctuations of the fire were studied to understand the accuracy of fire dynamics captured by FDS. A visual estimation of extents of a three zone representation of pool fire structure was done by observing temperature and vertical velocity profile. This work provides information on sensitivity of pool fire on turbulence model and showed that the use of Deardorff turbulence model gave predictions of radiation, flame length and height closer to experimental values than the constant coefficient Smagorinsky turbulence model. Iso-surface of 450 ⁰C was found to describe the flame geometry of the experiment considered. Pulsation frequency obtained from FDS was compared with experimental data and thus shows the accuracy of FDS in capturing transient fluctuations of fire.
Application of Computational Fluid Dynamics for Liquefied Natural Gas Pool Spreading and Vaporization on Water
(2016-04-22) Gopalaswami, Nirupama; Mannan, Sam; Anand, N.K; Holste, James; El-Halwagi, Mahmoud
Liquefied Natural Gas (LNG) is a cryogenic liquid consisting predominantly of methane compressed to 1/600th of its gaseous volume for transportation. A release of LNG on water during marine operations can occur due to several factors. Upon release, a spreading liquid can form a pool with rapid vaporization, leading to the formation of a flammable vapor cloud. Safety analyses for the protection of the public and property involve the determination of consequences of such releases. The evaluation of consequences resulting from a spill of LNG on water involves the determination of the rate (vaporization rate/source-term) at which flammable hydrocarbon vapor is produced and the dynamics of the spreading pool. Two key parameters which affect pool spreading and vaporization, namely the heat flux to the LNG pool and the turbulence present within the cryogenic pool, are quantified separately through experiments. The heat flux from two different substrates comprised of water and ice is studied. The vaporization mass flux is directly influenced by the water temperature and the release rate. Similarly, the vaporization mass flux is directly influenced by the ice temperature when cryogenic liquid is released on ice. The experiment for quantification of turbulence present in cryogenic pool was performed using a high-speed camera. Flow visualization for turbulence quantification revealed the presence of wavy-structures called ‘thermals’ which catalyzed the vaporization process of cryogenic liquid released on water. The results of key parameters study are implemented in CFD methodology to study the pool spreading and vaporization behavior. The CFD model is validated with an LNG experiment which simulates the LNG spill in space enclosed by two LNG ships during loading operations. The results of the research can be used for decision making in facility siting studies and emergency response planning for near shore/waterfront LNG facilities.
Application of Computational Fluid Dynamics in the Forced Dispersion Modeling of LNG Vapor Clouds
(2013-05-31) Kim, Byung-Kyu; Mannan, M. Sam; Glover, Charles; El-Halwagi, Mahmoud; Duggleby, Andrew
The safety and security of liquefied natural gas (LNG) facilities has prompted the need for continued study of LNG mitigation systems. Water spray systems are widely recognized as an effective measure for dispersing LNG vapor clouds. Currently, there are no engineering guidelines available for water curtain applications in the LNG industry due to a lack of understanding of the complex interactions between the LNG vapor cloud and water droplets. This research applies computational fluid dynamics (CFD) modeling to investigate the forced dispersion of LNG vapor using upward-oriented full-cone spray nozzles. A Eulerian-Lagrangian approach was applied to simulate the energy and momentum exchange between the continuous (gas flow) and discrete (droplets) phases. Discussed are the physical parameters that are essential inputs to the CFD simulation of the water spray-LNG system. The experimental data collected from the Mary Kay O’Connor Process Safety Center’s outdoor LNG spill work in March 2009 at the Brayton Fire Training Field were used to calibrate the physical parameters. The physical mechanisms of the water spray application were investigated using LNG forced dispersion modeling. The effects of momentum imparting from the droplets to the air- vapor mixture, thermal transfer between the two phases (droplet/vapor) and effects of various levels of air entrainment rates on the behavior of the LNG vapors are evaluated. Lastly, the key parametric dependences of the design elements for an effective water curtain system are investigated. The effects of different droplet sizes, droplet temperatures, nozzle cone angles, and installation configurations of water spray applications on LNG vapor behavior are analyzed. This work aims to investigate the complex interaction of the water droplet-LNG vapor system, which will serve in developing guidelines and establishing engineering criteria for a site-specific LNG mitigation system. Finally, the potentials of applying CFD modeling in providing guidance for setting up the design criteria for an effective forced mitigation system as an integrated safety element for LNG facilities are discussed.
The application of expansion foam on liquefied natural gas (LNG) to suppress LNG vapor and LNG pool fire thermal radiation
(2009-05-15) Suardin, Jaffee Arizon; MANNAN, M. SAM; ANAND, N.K.; EL-HALWAGI, M.; HALL, KENNETH R.
Liquefied Natural Gas (LNG) hazards include LNG flammable vapor dispersion and LNG pool fire thermal radiation. A large LNG pool fire emits high thermal radiation thus preventing fire fighters from approaching and extinguishing the fire. One of the strategies used in the LNG industry and recommended by federal regulation National Fire Protection Association (NFPA) 59A is to use expansion foam to suppress LNG vapors and to control LNG fire by reducing the fire size. In its application, expansion foam effectiveness heavily depends on application rate, generator location, and LNG containment pit design. Complicated phenomena involved and previous studies have not completely filled the gaps increases the needs for LNG field experiments involving expansion foam. In addition, alternative LNG vapor dispersion and pool fire suppression methodology, Foamglas® pool fire suppression (PFS), is investigated as well. This dissertation details the research and experiment development. Results regarding important phenomena are presented and discussed. Foamglas® PFS effectiveness is described. Recommendations for advancing current guidelines in LNG vapor dispersion and pool fire suppression methods are developed. The gaps are presented as the future work and recommendation on how to do the experiment better in the future. This will benefit LNG industries to enhance its safety system and to make LNG facilities safer.
Application of Fuzzy Logic to Quantify the Uncertainty in Layer of Protection Analysis
(2017-01-23) Hong, Yizhi; Mannan, Sam; Holste, James; El-Halwagi, Mahmoud; Langari, Reza
Layer of Protection Analysis (LOPA) is a widely used semi-quantitative risk assessment method. LOPA includes both frequency and consequence expressed in an order of magnitude approximation. Compared with Quantitative Risk Analysis (QRA), LOPA provides a simplified but less precise method to assess the effectiveness of protection layers and the risk reduction of an incident scenario. The outcome frequency and consequence of LOPA are intended to be conservative, which makes the risk overestimated. A high risk indicates the requirement of additional Independent Protection Layers (IPLs), which calls for higher installation and maintenance costs. There are different sources and types of uncertainty in LOPA model that need to be identified and quantified. Fuzzy logic is a method to deal with systems that are too complex or not clearly defined. Using fuzzy arithmetic, imperfect data are analyzed in a natural and flexible way. Through the application of fuzzy logic, uncertainty from data and experience from experts can be quantified, and a more accurate and precise risk value can be obtained. Various types of fuzzy logic systems, including type-1 fuzzy logic and type-2 fuzzy logic are studied in this work. The goal of this work is to increase the accuracy and precision of LOPA model while retaining its simplicity. A probabilistic and fuzzy logic hybrid approach is developed to deal with the uncertainty in failure rate data. This method facilitates a more accurate and precise failure rate database considering generic database, plant-specific data and expert experience. It has been applied to a distillation system, with a capacity to distill 40 tons of flammable n-hexane, and the results show that a more accurate failure rate can be achieved with the available data and expert judgment. Furthermore, a type-2 fuzzy logic risk matrix is developed to increase the precision of a risk matrix. This new method also provides an efficient way to aggregate several risk matrices into one universal risk matrix. Its application to aggregate three standard risk matrices has been shown through a case study. This work demonstrates the effectiveness of applying fuzzy logic in quantifying uncertainty in layer failure data to be used in LOPA. Fuzzy logic can also be helpful in other types of risk assessment.
Auditing the Quality of Process Hazard Analysis (PHA) Studies
(2017-07-20) Alshethry, Faisal Abdulrahman M; Mannan, M. Sam; Holste, James C; El-Halwagi, Mahmoud
The petrochemical industry is subject to various federal and local regulations and requirements that are challenging to meet and resource-intensive. Time and human factors often lead to a “check box” mentality where requirements are fully complied with “on paper” with little or no emphasis on quality of compliance. Occupational Safety and Health Administration’s (OSHA) Process Safety Management (PSM) requirements are often exposed to this “check box” mentality, especially the Process Hazard Analysis (PHA) element, which is the engine that drives and affects the whole PSM program. Poor implementation of PHA affects mechanical integrity, operating procedures, training, and emergency response, and is considered a root cause of most major incidents. Unfortunately, poor quality PHAs are widespread, hard to identify and can be more dangerous than conducting no PHA at all since it may provide a false sense of safety. Unfortunately, existing literature as well as recognized and generally accepted good engineering practices (RAGAGEP) do not provide sufficient guidelines for assessing PHA quality. The guidelines proposed in this thesis help in properly auditing PHA studies by identifying traps and bad practices that most companies fall into when performing PHAs. The resulting guidelines are developed based on detailed incident investigation reports where root causes included inadequate PHA performance. In addition, expert opinion expressed in published papers highlighting specific gaps in PHA performance, and best practices of PHA implementation are utilized to identify common gaps and means for auditors to acquire evidence of reduced quality. The biggest contributors to the reduction of PHA quality include failing to consider lessons learned previous incidents, reduced quality of PHA inputs such as process safety information, competence of the PHA team members in their respective fields and time allocated for them to complete the PHA, accounting for human factors when relying on operator action to return the process to its safe state, as well as failing to perform PHAs for non-routine mode of operations. These contributors and others are discussed thoroughly on how they affect quality of PHAs and how auditors would obtain evidence that supports lack of quality. The proposed guidelines compiled in Appendix A should be used as part of an overall PSM audit. Using these guidelines by themselves would result in an incomplete assessment of the PHA. This is due to the fact that effective PHA element implementation depends on several other PSM elements that are considered foundational to PHA implementation quality. Spending the time and money to perform an audit utilizing these guidelines should be seen as a positive investment by facility’s executives as it will unquestionably assist in saving a lot of money and ensure business continuity by closing the gaps in PHA performance and reducing the chance for the “check box” mentality, thus making their facilities, employees, community and assets safer.
Bayesian-lopa methodology for risk assessment of an LNG importation terminal
(2009-05-15) Yun, Geun-Woong; Mannan, M. Sam; Hall, Kenneth R.; Malav?C?r O.
LNG (Liquefied Natural Gas) is one of the fastest growing energy sources in the U.S. to fulfill the increasing energy demands. In order to meet the LNG demand, many LNG facilities including LNG importation terminals are operating currently. Therefore, it is important to estimate the potential risks in LNG terminals to ensure their safety. One of the best ways to estimate the risk is LOPA (Layer of Protection Analysis) because it can provide quantified risk results with less time and efforts than other methods. For LOPA application, failure data are essential to compute risk frequencies. However, the failure data from the LNG industry are very sparse. Bayesian estimation is identified as one method to compensate for its weaknesses. It can update the generic data with plant specific data. Based on Bayesian estimation, the frequencies of initiating events were obtained using a conjugate gamma prior distribution such as OREDA (Offshore Reliability Data) database and Poisson likelihood distribution. If there is no prior information, Jeffreys noninformative prior may be used. The LNG plant failure database was used as plant specific likelihood information. The PFDs (Probability of Failure on Demand) of IPLs (Independent Protection Layers) were estimated with the conjugate beta prior such as EIReDA (European Industry Reliability Data Bank) database and binomial likelihood distribution. In some cases EIReDA did not provide failure data, so the newly developed Frequency-PFD conversion method was used instead. By the combination of Bayesian estimation and LOPA procedures, the Bayesian-LOPA methodology was developed and was applied to an LNG importation terminal. The found risk values were compared to the tolerable risk criteria to make risk decisions. Finally, the risk values of seven incident scenarios were compared to each other to make a risk ranking. In conclusion, the newly developed Bayesian-LOPA methodology really does work well in an LNG importation terminal and it can be applied in other industries including refineries and petrochemicals. Moreover, it can be used with other frequency analysis methods such as Fault Tree Analysis (FTA).
Binary mixture flammability characteristics for hazard assessment
(Texas A&M University, 2005-11-01) Vidal Vazquez, Migvia del C.; Mannan, M. Sam; Caton, Jerald; Hall, Kenneth R.; Holste, James C.
Flammability is an important factor of safe practices for handling and storage of liquid mixtures and for the evaluation of the precise level of risk. Flash point is a major property used to determine the fire and explosion hazards of a liquid, and it is defined as the minimum temperature at which the vapor present over the liquid at equilibrium forms a flammable mixture when mixed with air. Experimental tests for the complete composition range of a mixture are time consuming, whereas a mixture flash point can be estimated using a computational method and available information. The information needed for mixture flash point predictions are flashpoints, vapor pressures, and activity coefficients as functions of temperature for each mixture component. Generally, sufficient experimental data are unavailable and other ways of determining the basic information are needed. A procedure to evaluate the flash point of binary mixtures is proposed, which provides techniques that can be used to estimate a parameter that is needed for binary mixture flash point evaluations. Minimum flash point behavior (MFPB) is exhibited when the flash point of the mixture is below the flash points of the individual components of the mixture. The identification of this behavior is critical, because a hazardous situation results from taking the lowest component flash point value as the mixture flash point. Flash point predictions were performed for 14 binary mixtures using various Gex models for the activity coefficients. Quantum chemical calculations and UNIFAC, a theoretical model that does not require experimental binary interaction parameters, are employed in the mixture flash point predictions, which are validated with experimental data. MFPB is successfully predicted using the UNIFAC model when there are insufficient vapor liquid data. The identification of inherent safety principles that can be applied to the flammability of binary liquid mixtures is also studied. The effect on the flash point values of three binary mixtures in which octane is the solute is investigated to apply the inherent safety concept.
Chemical accident databases: what they tell us and how they can be improved to establish national safety goals
(Texas A&M University, 2000) McCray, Eboni Trevette
The objectives of this research are to examine and critique eight chemical accident databases, document any trends in accident occurrences, develop a strategy for improving current databases, and to establish national safety goals on the basis of those improvements. This synopsis found that it is impossible to draw any conclusions about the state of chemical safety, past or present, based on the information in the various databases. The databases are deficient in many ways. First, they have been developed using inconsistent and faulty data-collecting methods, and the terms used to describe accidents are often ambiguous. Secondly, the ever-changing reporting requirements prevent comparisons to be made from year to year, making trends impossible to identify. Lastly, the databases provide little to no information about the specifics of accidents, and many accidents are incorrectly lumped under the heading of chemical accidents. All these factors compromise the overall quality of the data. Thus, it is very difficult, if not impossible, to make definitive conclusions. In addition, it is impossible to determine the effectiveness of governmental regulations or industry standards and practices, when there is no reliable data available for comparison. Finally, this study makes recommendations for database improvement by addressing each of the deficiencies, developing a structure for a new database, and establishing a foundation for the development of national safety goals.
Chemical Kinetics of Organophosphorus Fire Suppressants
(2018-06-18) Sikes III, Travis Glenn; Petersen, Eric L; Mannan, M. Sam; Jacobs, Timothy; Kulatilaka, Waruna
Organophosphorus compounds (OPCs) have significant fire suppression capabilities but are not well understood. Chemical kinetics mechanisms can provide invaluable information about how OPCs suppress flames; however, the currently available OPC mechanisms are deficient and could use further refinement. In this dissertation, two types of experimental data were taken which can be used as benchmarks to improve mechanisms: laminar flame speeds and ignition delay times. In the laminar flame speed experiments, dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP) diisopropyl methylphosphonate (DIMP), and trimethyl phosphate (TEP) were added to hydrogen/air and methane/air mixtures to assess their suppression capabilities at 0.1% and 0.3% (DMMP only) of the total mixture volume. The experiments were performed in an optically tracked, spherically expanding flame setup at 1 atm and 120 °C. Results show a 30% decrease in laminar flame speed for all OPCs at 0.1% on the methane/air parent mixture. For the hydrogen/air mixtures, the OPCs differentiate themselves by having an increasing suppression effect corresponding with higher carbon moiety, i.e., DIMP (20% overall reduction), > TEP (15%) > DEMP (13%) > DMMP (9%). The OPCs also have an increasing effect with increasing equivalence ratio on hydrogen/air. Ignition delay time experiments were performed in a glass shock tube at ICARE – CNRS. The simple OPCs studied were dimethyl phosphite (DMP), trimethyl phosphate (TMP), and diethyl phosphite (DEP). The OPCs were added as 10% of the fuel in hydrogen/ethylene mixtures diluted with 98% argon. The results show that the three OPCs behave similarly in both hydrogen and ethylene mixtures by decreasing the ignition delay time ~30% at high temperatures and then decreasing in effect until the neat and OPC data are indistinguishable. Additionally, quantum chemistry calculations were performed to improve an existing OPC submechanism using ROCBS-QB3 level of theory for thermochemistry and G3X-K for the transition state calculations. The thermochemistry data are an improvement on previous OPC mechanisms, but overall the model does not predict the ignition delay times. Further OPC submechanism improvement is needed to resolve simple OPC reactions so that larger OPC submechanisms will be able to properly predict OPC behavior in applications such as fire suppression.
Combustion and Explosion of Carbon Nanofibers
(2016-04-13) Zhang, Jiaqi; Mannan, Sam; Mashuga, Chad; Akbulut, Mustafa; Holste, James; Strzelec, Andrea
Although there is a fast growth in the production and application of nanomaterials, very little research about the fire and explosion hazards associated with nanomaterials has been done. Dust explosion studies on micro-size materials show that combustible engineered nanomaterials may possess high risk for explosion because increased specific surface area of nanomaterials may improve the ignition sensitivity and explosion severity. This study focuses on combustion and explosion of carbon nanofibers (CNFs), considering its large-scale production, wide application, and various handling processes. This study characterizes the morphology of CNFs with scanning electron microscope, the particle size distributions with Spraytec and Beckman Coulter, and the thermal stability with thermogravimetric analysis. Explosibility tests are performed in a customized 36-L dust explosion vessel and a minimum ignition energy apparatus (MIKE 3). Combining the characterization tests, explosibility tests, and theoretical analysis, this study provides a good understanding about combustion and explosion risk of CNFs after different processes – milling duration, and annealing at 1500 °C or 3000 °C. In general, this study concludes that the minimum ignition energy of CNFs is higher than 1 J, which indicates a low ignition sensitivity. Minimum explosible concentration of CNFs varies from 105 g·m^-3 to larger than 300 g·m^-3. The maximum overpressure is about 8 bar. CNF is classified as St-1 combustible dust with a deflagration index around 100 bar·m·s^ -1 . It is also found that the smaller agglomerates caused by milling process not only reduces the minimum explosible concentration (MEC), but also increases the maximum pressure increase rate [dP/dt]max. Besides, the annealing process, either 1500 °C or 3000 °C, improves the graphite degree of CNFs and hence decreases the explosion severity with a lower [dP/dt]max. Additionally, the 3000 °C annealing process reduces the iron content within CNFs and hence increased MEC. It is because the pyrophoric Fe-NPs could be ignited remotely with a favorable penetration topology of CNF agglomerates and therefore promotes the heating of unburnt CNFs and facilitates the overall combustion and explosion process. This study also modifies an estimation method for maximum overpressure and proposes a heterogeneous model explaining the influential factors.
Comparative Analysis Between LNG Import and Export Terminals
(2016-05-09) Lamus Gualdron, Guido Alexander; Mannan, Sam; El-Halwagu, Mahmoud; Damjanovic, Ivan
According to the US Energy Information Administration (EIA), the natural gas consumption in the US was 1,726 billion cubic feet in January 2013, and the demand has been increasing rapidly around the world as natural gas becomes the fuel of choice for electric power providers. In order to supply this demand, the US economic interest was focused on the Liquefied Natural Gas (LNG) import terminals installation. However, since 2009, due to dramatic changes in gas production and economy the US has become a net exporter of natural gas. The interest for minimizing the negative consequences associated with LNG terminals has emerged by focusing on the potential damages that may be generated by the flammable and cryogenic characteristics of LNG such as vapor cloud, flash fires, and pool fires. LNG research and regulation have been successfully applied for providing safer conditions at the LNG import terminals. However, the integration of export terminals into the existing LNG network requires a thorough revision of the new challenges imposed by the specific conditions related to the liquefaction facilities. It is intended to determine the exclusion zones for these two particular scenarios through the utilization of PHAST in order to estimate the areas where people, property, or the environment would be more severely affected. A revision about the parameters proposed by the normativity for the estimation of the exclusion zones, in contrast to the particular conditions that might affect the plants located on coastal areas is performed. Additionally, this project seeks to integrate the predicted consequences into real world scenarios by including the implementation of a Geographic Information System (GIS). The georeferenced data will to identify the potential vulnerable areas located near to the LNG facilities. The main goal intended in this project by the combination of these two computational tools (PHAST model and GIS) is to reduce the gap between the consequence estimation of LNG catastrophic events and the incorporation of these results in a real world environment.
Comparison of Batch versus Continuous Process in Pharmaceutical Industry Based on Safety Consideration
(2017-05-03) Chen, Shiqi; Mannan, Sam M; El-Halwagi, Mahmoud M; Morrison, Gerald L
As opposed to the petro-chemical and bulk chemical industry, where continuous processes are widely applied, the pharmaceutical industry still primarily relies on traditional batch process due to the complexity of product, multi-step operation and low-volume production. Considering these conditions, the versatile batch process is more appropriate. Nowadays, driven by the contradiction between increasing demand for drugs and inefficient batch production mode, there is a trend in pharmaceutical industry, that is the transformation from traditional batch process to novel continuous process. Related projects and research that is aimed at analyzing this transition are conducted in worldwide, and the scale of these studies ranges from lab-scale reactions to overall arrangement of the factories. Although continuous pharmaceutical process is thriving, the safety issue in this field is not promoted at the same time. Since the continuous pharmaceutical process is a novel technology, little information can be provided to evaluate its safety level. Moreover, process conditions are usually intensified for continuous process comparing to batch process. It also may bring potential risks and make continuous manufacturing inappropriate for some of pharmaceutical productions. This research provides a comprehensive comparison for batch versus continuous pharmaceutical process by application of Dow’s Fire and Explosion Index. In addition to this conventional safety evaluation, influences from production efficiency and specialties in pharmaceutical production are integrated into the comparison. Production of 2-methyl benzimidazole and peracetic acid via batch and continuous processes are conducted in this research. In these integrative and systematic studies, F&EI values for both cases are higher for continuous processes than batch processes, hence the higher safety level of the continuous process is demonstrated. The ways in which process conditions, production efficiency, and other requirements influence safety level for different production modes are illustrated.
A Computational Fluid Dynamic Evaluation of Unconfined Hydrogen Explosions in High Pressure Applications
(2017-12-06) Edelia, Erfika Maria; El-Halwagi, Mahmoud; Mannan, M. S; Barrufet, Maria A
Over the last few decades, the demand for hydrogen has significantly grown. Its high energy content and relatively small environmental effect make it an ideal energy source and chemical feedstock. However, the perceived high risk of hydrogen in the eyes of society is a key challenge that has to be addressed before any future widespread utilization of hydrogen can be achieved. Hydrogen is highly flammable and combustible when mixed with air. It is also very light and buoyant, resulting in a false assumption that hydrogen will not explode in unconfined space. However, there have been at least fourteen industrial incidents involving an unconfined hydrogen vapor cloud explosion (VCE), which show the knowledge gap in hydrogen safety that requires further research. In this study, the consequences of unconfined hydrogen releases were evaluated using computational fluid dynamic simulation software, FLACS, to determine its potential to explode and to analyze the parameters that can promote hydrogen VCE: initial pressure, time to ignition, and leak height position. This study concluded that high-pressure hydrogen has the potential to build up a large vapor cloud and explode even without confinement. The highest overpressure produced in the simulation was 0.71 barg, which resulted from igniting a hydrogen gas cloud from a 207 bar hydrogen source leaking at 1 m height. This study also gave the recommended distance from a high-pressure hydrogen processing unit to nearby occupied buildings to use in conjunction with industrial spacing tables for fire hazards.
Computational fluid dynamics for LNG vapor dispersion modeling: a key parameters study
(2009-05-15) Cormier, Benjamin Rodolphe; El-Halwagi, Mahmoud; Mannan, Sam; Banerjee, Debjyoti; Glover, Charles
The increased demand for liquefied natural gas (LNG) has led to the construction of several new LNG terminals in the United States (US) and around the world. To ensure the safety of the public, consequence modeling is used to estimate the exclusion distances. The purpose of having these exclusion distances is to protect the public from being reached by flammable vapors during a release. For LNG industry, the exclusion zones are determined by the half lower flammability limits (half LFL, 2.5% V/V). Since LNG vapors are heavier‐than‐air when released into atmosphere, it goes through stages, negative, neutral and positive buoyant effect. In this process, it may reach the half LFL. The primary objective of this dissertation is to advance the status of LNG vapor dispersion modeling, especially for complex scenarios (i.e. including obstacle effects). The most used software, box models, cannot assess these complex scenarios. Box models simulate the vapor in a free‐obstacle environment. Due to the advancement in computing, this conservative approach has become questionable. New codes as computational fluid dynamics (CFD) have been proven viable and more efficient than box models. The use of such advance tool in consequence modeling requires the refinement of some of the parameters. In these dissertation, these parameters were identified and refine through a series of field tests at the Brayton Firefighter Training Field (BFTF) as part of the Texas A&M University System (TAMUS). A total of five tests contributed to this dissertation, which three of them were designed and executed by the LNG team of the Mary Kay O'Connor Process Safety Center (MKOPSC) and the financial support from BP Global SPU Gas (BP). The data collected were used as calibration for a commercial CFD code called CFX from ANSYS. Once the CFD code was tuned, it was used in a sensitivity analysis to assess the effects of parameters in the LFL distance and the concentration levels. The dissertation discusses also the validity range for the key parameters.
Consequence analysis of aqueous ammonia spills using an improved liquid pool evaporation model
(Texas A&M University, 2005-02-17) Raghunathan, Vijay; Mannan, M. Sam; El-Halwagi, Mahmoud; Lindell, Michael K.
Source term modeling is the key feature in predicting the consequences of releases from hazardous fluids. Aqueous ammonia serves the purpose of a reducing medium and is replacing anhydrous ammonia in most of the Selective catalytic reduction (SCR) units. This newly developed model can estimate the vaporization rate and net mass evaporating into the air from a multicomponent non- ideal chemical spill. The work has been divided into two parts. In the first step a generic, dynamic source term model was developed that can handle multicomponent non-ideal mixtures. The applicability of this improved pool model for aqueous ammonia spills was then checked to aid in the offsite consequence analysis of aqueous ammonia spills. The behavior of the chemical released depends on its various inherent properties, ambient conditions and the spill scenario. The different heat transfer mechanisms associated with the pool will strongly depend on the temperature of the liquid pool system at different times. The model accounts for all the temperature gradients within the contained pool and hence helps us establish better estimation techniques for source terms of chemical mixtures. This research work will help obtain more accurate and reliable liquid evaporation rates that become the critical input for dispersion modeling studies.
Consideration of Solar Radiation in Flare Design
(2018-05-01) Taneja, Ankita; Mannan, M. Sam; Girimaji, Sharath; El-Halwagi, Mahmoud
At oil refineries and other chemical processing plants, a flare stack is used to get rid of unwanted or excessive gases and relieve the system of excess pressure. These gases can be generated during different stages of operation like startup or shutdown, maintenance and process upsets. Since flares handle large amounts of toxic and flammable materials, it makes the flaring operation hazardous. Combustion of huge amount of gases releases heat which is radiated to the atmosphere. Heat radiated from the flare makes it important for siting the flare at a proper location. The heat radiation should not exceed recommended threshold levels so that people on-site and the equipment are not affected. Thus, to have a well-designed flare, knowledge of total radiation emitted from a flare is essential. It will aid in accurately estimating the flare height and the area near the flare, which would sustain high levels of thermal radiation. A common point of contention while calculating radiation level emitted from flare is the decision of including solar radiation (SR) in the calculations. API 521 relegates this decision to the flare design company’s practices. Based on expert judgement, some literature states that for all practical purposes, solar radiation contribution can be discounted. The work performed aims at presenting a framework which quantitatively addresses aforementioned obscurity. The analysis helps flare designers to more objectively decide whether to include SR in their analyses or treat it insignificant contribution. The work studies the various factors that cause variation in SR value: location, time, and orientation of the surface. Considering all these parameters, an appropriate value of SR is chosen as the solar contribution to the thermal radiation from the flare. The effect of SR to the design of the flare is quantified by studying the change in effect distance near the flare and the height of the flare. Consequence analysis software PHAST is used to obtain these calculations. In addition, the outcome that SR inclusion will have on the risk posed by the flare due to thermal radiation on personnel is also examined. This is studied by measuring the change in lethality and heat stress caused by radiation exposure.

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