Process Upsets Research Articles

Estimation of Uranium(VI) Concentrations by Temperature Profile in Solvent Extraction Processes Using 30% Tri-n-Butyl Phosphate Diluted with n-Dodecane.

In the counter-current solvent extraction process where 30% tri-n-butyl phosphate (TBP) diluted with n-dodecane is used to extract U(VI), the reaction heat that primarily results from complex formation of TBP with U(VI) causes a heat release near the extraction band where U(VI) is transferred from aqueous to organic phase. This study has shown that the U(VI) concentration profile can be estimated based on a temperature profile by taking account of mass and heat balances in the counter-current solvent extraction process. A computer program UCE has been developed to estimate U(VI) concentrations in mixersettler type extractors by giving a temperature profile and process data of the feed streams as input data. This computer program numerically solves the equations derived from material and heat balances in the solvent extraction process without using distribution ratios. Feasibility of UCE as a tool to detect U(VI) concentration change is discussed by the comparison with the calculation results which are given by the computer program SOLE-91 that calculates profiles of U(VI) concentration and temperature. Since the U(VI) concentration profiles estimated by UCE for hypothetical process upsets agree with the profiles given by SOLE-91, it is concluded that the detection of the position of the U(VI) extraction band is feasible.

The role of instrumentation and process controls in minimizing accidental releases

AbstractMost accidental releases are the result of either mechanical failures or measures taken to prevent such failures, such as, venting through emergency vents, relief valves, or rupture discs. Where the mechanical failure is the result of defective materials, inadequate design, or external factors, little can be done by means of instrumentation to prevent the release. It may be possible, however, to reduce the flow. Many failures are due to process upsets such as overpressure, internal explosions, and runaway reactions. The probability of these failures occurring can be substantially reduced by proper instrumentation.

Detection of process upsets—sample autocorrelation control chart and group autocorrelation control chart applications

This paper presents an application of the sample autocorrelation function to statistical process control where the process data are serially correlated. Two innovative control charts are illustrated: the sample autocorrelation control chart and the group autocorrelation control chart. The important feature is that these control charts will detect shifts in the autocorrelative structure as well as shifts in the mean of the process. The sample autocorrelation function is typically used to identify an appropriate ARIMA model for a time series. The sample autocorrelation function may also be used as the basis of control charts to detect process upsets. Two unique features distingush this application of the sample autocorrelation function to statistical process control. First, the sample autocorrelations are exponentially smoothed estimates. This allows the user to control the sensitivity of the sample autocorrelation control chart. Secondly, the sample autocorrelation control chart is applied to a continuous stream of data—rather than to a static set of data that has been used to fit an ARIMA model.

The process safety impact of distributed control systems

Experience has shown that a Distributed Control System (DCS) can provide enhanced process monitoring and control capabilities, as well as system self-diagnostics, that permit increased safety of process operations. However, this enhanced safety does not come about automatically with the installation of a DCS. The complexity and versatility of the DCS can introduce new failure scenarios leading to process upset and potential relization of process hazards. This paper reviews some novel considerations that should be taken into account when conducting process hazards reviews on facilities controlled by a DCS.

Fault-dynamic modelling of a phthalic anhydride reactor

Abstract A new methodology, fault-dynamic modelling, has been developed for analysis of potentially hazardous situations in the process industries. Traditional fault-tree analysis is used to determine the combinations of component failure that can lead to a particular process upset condition. Realistic dynamic modelling is then used to calculate the time available for corrective action once the upset has started. The method is applied to a phthalic anhydride reactor. The results of the analysis identify three process upsets that can lead to catastrophic failure in 2–5 min if left uncorrected. Other process upsets lead to safe conditions.

USE OF METAL ADSORBING COMPOUNDS (MAC) TO MITIGATE ADVERSE EFFECTS OF HEAVY METALS IN BIOLOGICAL UNIT PROCESSES

Abstract The presence of heavy metals on an intermittent basis in the influent of biological unit processes can lead to process upset and poor removal of organics. Heavy metal breakthrough from a pretreatment process may be caused by a number of reasons. In this study, the feasibility of adding metal adsorbing compounds (MACs) into a sequencing batch reactor (SBR) to mitigate the adverse effects of heavy metals breakthrough was investigated. A powdered activated carbon was found to be an effective MAC for heavy metals concentrations varying from 2 to 20mg/L. Organic removal efficiencies in a SBR using MACs were similar to those of a control SBR with no metals in the influent.

Oil Removal From Oilfield-Produced Water By Cross Flow Ultrafiltration

Abstract The technical and economic viability has been determined for crass flow ultrafiltration of oilfield-produced water with the goal of producing oil-free water for steam generation. Experiments with produced water supplied from various oil producing sites of western Canada have been performed with successful permeation rates and permeate quality. The resistance to membrane fouling and other factors that decrease permeation rate have been determined in long-term experiments. These results have been used to prepare a cost survey of the cross flow ultrafiltration process, and this has been compared to conventional treatment. The results indicate the level of performance that must be maintained in the ultrafiltration process to be economically advantageous. Introduction Enhanced oil recovery (EOR) operations in western Canada often employ stearn to stimulate reservoirs. These steam stimulation operations require large volumes of water for steam generation and injection into the oil-bearing reservoirs. They generate large volumes of produced water which is contaminated with oil, dissolved organic compounds, and inorganic material(1). Because many recovery operations in western Canada are located in water deficient or environmentally sensitive areas, several EOR recovery operations are recycling a portion of their produced water. Oilfield steam boilers that generate 80% quality steam (80% Vapour, 20% liquid) can tolerate minor amounts of total dissolved solids (TDS), hardness, and silica, but require total removal of the oil(2). Conventional treatment for the removal of the oil is limited by the presence of very stable oil-in-water (o/w) emulsions, stabilized by the presence of natural or added surfactants(3, 4). As well, subsequent operations of silica removal and softening perform best when the oil has been removed. Some EOR operations use large amounts of water, sometimes as much as 2 m3 to 10 m3 for every cubic metre of recovered oil. Some of this water may be present in the recovered oil as a water-in- oil emulsion while the balance may be present as a distinct water phase with an o/w emulsion. The produced fluid is generally treated in a free water knock out (FWKO) tank and a high-temperature separator (HTS) to separate as much of the oil and water as possible. Water from the FWKO and HTS is usually combined and sent to a skim tank where some residual oil is removed and recycled to the oil recovery part of the process. The remaining water, with some oil, is often disposed of by deep well injection (below the oil bearing formation) or it is sent to further treatment to prepare it for steam generation. Further treatment may consist of final oil removal by induced gas flotation (IGF) and filtration followed by softening operations such as hot lime softening and ion exchange. All of the oil removal operations with the exception of FWKO require large amounts of demulsifying chemicals to destabilize the emulsions. Occasional process upsets and changes in the nature of the emulsions can cause the failure of these units to remove oil from the produced water, and results in the passage of slugs of oil with catastrophic effects on the subsequent de-oiling and water softening operations.

Recent Advances in Centrifugal Contactor Design

Abstract Advances are being made in the design of the Argonne centrifugal contactor for solvent extraction. These contactors are being built, tested, and used to implement the TRUEX process for the cleanup of nuclear waste liquids. These advances include 1) using off-the-shelf, face-mounted motors; 2) modifying the contactor so that relatively volatile solvents can be used; 3) adding a high-level liquid detector that can be used to alert the plant operator of process upsets; 4) providing secondary feed ports; 5) optimizing support frame design; 6) devising a linear design with external interstage lines so that stages can be allocated as needed for extraction, scrub, strip, and solvent cleanup operations; and 7) developing features that facilitate contactor operation in remote facilities.

The Incorporation of Knowledge-Based Aids Within the Control and Operation of a Powerplant

This paper describes a strategy for the incorporation of knowledge-based aids within the operation and the control of a power-and steam-generating plant. The primary aim of this project is to enhance, not replace, the existing control system(s) with the characteristic qualities of knowledge-based systems or expert systems.In real time, expert systems can improve the efficiency of an operator by acting as an intelligent monitor, reducing the amount of data that he has to cope with. They can point at the likely causes of disturbances and offer advise as to their possible consequences and as to what actions may be taken in order to return to normal operation. Process upsets and disturbances can be simulated and the expert system can use its knowledge about the behaviour and the limitations of the system in order to arrive at a predictive alarming capability. In the long term, this may then lead to a form of predictive control of a plant.An architecture that deals with these topics is proposed and a possible implementation is discussed in detail. Finally, attention is given to the problems of knowledge elicitation, building up the knowledge base, and integrating the system into the existing control software of a plant.

Process Control Instruction at Miami University Linking Classroom, Computers and Laboratories

The problems of teaching introductory modern-day process control at the undergraduate level are discussed. The need for understanding the student's perspective and learning modes is explored. A method for actively involving the student's senses by incorporating theory, computer simulation and laboratory experiences is proposed. An example of how a typical simple system chosen for analysis can be related to real-world performance by including the effects of non-ideal components and process upsets is outlined. An illustration of the use of a microcomputer simulator for such a system is presented.

The effects of organic toxicants on methane production and hydrogen gas levels during the anaerobic digestion of waste activated sludge

Batch serum bottle assays were conducted to examine the response of the anaerobic digestion process to inhibition induced by the pulse addition of four organic toxicants [chloroform, bromoethanesulfonic acid (BES), trichloroacetic acid (TCAA) and formaldehyde]. The impact that increasing levels of inhibition of methane production had on hydrogen response and volatile fatty acid (VFA) accumulation were examined. All of the toxicants, with the exception of formaldehyde, appeared to elicit similar hydrogen response patterns and VFA accumulations for similar levels of inhibition. Results indicate that both the hydrogen and acetate catabolizing methanogenic populations were inhibited to approximately the same extent by chloroform, BES, and TCAA. Severe inhibition of methane production (>70% reduction of methane produced compared to controls) resulted in a rapid accumulation of hydrogen in the gaseous headspace. When inhibition was less severe, hydrogen accumulated to levels only slightly above controls. Based on these preliminary results, there appears to be some limits on the potential of using hydrogen as an early warning indicator of process upset. Results do indicate, however, that monitoring hydrogen in consert with conventional process indicators should improve digester monitoring and may provide more rapid indication of process upsets due to toxic shocks.

Autotuning of Fixed Regulators Using Adaptive Control Techniques

A method for autotuning fixed regulators of arbitrary structure has been developed. A process model is identified under closed loop conditions with a minimum of process upset. The identification is completely automatic with the magnitude of the process perturbation and final shutdown determined internally based upon the continuous estimate of the signal to noise ratio. Controller tuning parameters are established from a closed loop simulation using the identified process model. The tuning parameter calculation includes a weighting factor on the manipulated variable designed to produce varying degrees of damping in the closed loop response. Plant applications in a pulp and paper plant are described.

A rule‐based approach to fault diagnosis using the signed directed graph

AbstractFault diagnosis is the problem of determining the root causes of process upsets. This paper presents a very efficient method of identifying the possible causes of process disturbances using the signed directed graph (digraph) representation of process interactions. The analysis is based on forming logical statements (rules) derived from the process digraph; these are evaluated using on‐line data to yield the diagnosis. Evaluation of rule antecedents is more efficient than the previous algorithmic approach of Shiozaki et al. In the rule‐based approach, the diagnostic criteria are represented explicitly, not hidden by a complex algorithmic procedure. This allows the diagnostic rules to be tailored to reflect the best available knowledge of plant behavior. The rules generated by this technique can be integrated with other rules on plant operations using an expert systems framework.

Fault-Tolerant Microcomputer Control of a Heat Exchanger Network

As the use of digital computers in controlling chemical plants increases, loss of control due to computer failure becomes a major concern. A computer control system which is tolerant to faults of various degrees of severity was developed and experimentally tested using a heat exchanger network. Redundancy and diversity are created both in hardware and software.The computer in the control loop generates new alternatives in handling failures of other devices in the control loop by creating functional redundancy. Consequently, tolerance to sensor failure is achieved by control law reconfiguration. The reassignment of control duties due to hardware, software, or sensor failure creates process upsets similar to temporary process disturbances.

Human factors aspects of advanced process control

Energy conservation practices, such as heat recovery and integration, require that many chemical and related processes use advanced control systems. Many of the more advanced process control strategies and algorithms can cause operator confusion, leading to incorrect operator actions and negating the advantages of the advanced control. If the operator makes a mistake and upsets the process, or fails to respond correctly to a process upset, the loss can exceed the possible savings of the advanced control. Further, the experience can result in the operator not using the control capability in the future. Display and man/machine interface techniques, based on an understanding of human factors and of an operator1s typical analysis of a process, can be used to present information to the o~era tor in a manner which will prevent confusion. This paper discusses techniques for selecting and displaying process and control information to the operator.

A Safety Analysis for the Nuclear Fuel Recovery and Recycling Center

As part of the preliminary design for a proposed nuclear fuel reprocessing plant to be located near Oak Ridge, Tennessee, Exxon Nuclear Company, Inc. has made an extensive analysis of the environmental effects to the public from accidents occurring within the reprocessing complex. Each plant system was reviewed for its response to a spectrum of abnormal events, including natural phenomena, utility failures, equipment failures, operating errors, and process upsets. The analysis has shown that the plant is designed with sufficient confinement barriers and redundancy that in-plant accidents would not result in excessive radiation doses to the public. 2 figures, 1 table.

CRT Man-Machine Communication System in Nuclear Power Stations

Considerable engineering effort has been expended to design an easy-to-use man-machine communication system for the CANDU nuclear power station to provide the operator with relevant, uncluttered, process information immediately, on request, or in response to certain process upsets. This paper will discuss the considerations that influenced the design of the computer-driven coloured CRT display system and its applications in the control room of the CANDU type nuclear power stations.

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Authors

Emissions, Effluents and the Engineer

Abstract The growing concern over pollution control in the U. S. increasingly has placed the engineer in the role of problem solver. It is no longer feasible for the engineer to view problems of disposal of salt water, hydrogen sulfide, well-testing fluids and excess products in a process system as purely technological and economical matters. The active role of engineers in pollution control is discussed. Introduction There was a time when a blossoming black cloud from a gas plant products flare brought only a feeling of sympathy at the loss in revenue the operator was sustaining. Also there was perhaps a friendly hope that the operator could soon cure his process upset. Today the same black cloud brings to many a variety of feelings. First, there is a sharp regret that, along with the suffering of a monetary loss by the operator, our industry image also is suffering a loss. Second comes a frustration that the operator either does not know about the availability of smokeless flare tips or is unwilling to contribute to an improved industry image to the extent of the appreciable installation cost. Third comes a sense of regret that the operator is apparently unaware of what the public is being told by newspapers, radio and television that the nation should support strict laws and regulations to prevent such occurrences. The resulting rules probably will require not only smokeless flares but other costly and constrictive restraints aimed in good faith, but probably with questionable reality at assuring that no act affecting the real or imagined public welfare can be committed with impunity. This is a small example, of possibly doubtful worth, of the way things are changing. I have not used this hypothetical case to promote smokeless flares as a solution to gas plant operating problems. This might be like treating athlete's foot by amputating at the ankle! Location of plant, frequency of upsets, process modifications and a host of alternate solutions are involved. This illustration is intended to bring into focus society's heightened demand for a greater sense of responsibility in matters of conservation. It points out the importance of our accountability to our neighbor, and the public in general, as well as to company stockholders. And it promotes the theme that it is good business to respond to these seemingly conflicting demands. It is old-fashioned to underrate proper disposal of wastes, whether they were intended to be wastes or not. No longer can we simply spread them around and hope that no one notices them. We produced them; society is now saying we must dispose of them without causing inconvenience, or loss or offense to our neighbors. Today conservation is taking on a new meaning, reaching out to encompass quality of total environment. It considers the rivers that once graced and now too often disgrace our land. It ponders how to stretch adequately our natural resources to cover the demands of a mushrooming population while still preserving the quality of living. It pits a critical eye and a creative mind against the mounting tide of wastes-liquid, solid and airborne. Many are seeking solutions. Unless they get the benefit of engineering leadership and guidance, the effort is certain to fall. Origins of Pollution Some say pollution began when ancient man discovered fire; others, when he moved it into his cave. Deeper thinkers point to the ancient Greeks as the first to recognize the salient features of the problem. About 500 B.C., pedocles said, "Know that effluences flow from all things that have come into being." Pollution was put to poetry in the early 1800's by Samuel Taylor Coleridge as he wrote in uncomplimentary words of the city of Cologne: In Cologne, a town of monks and bones, And pavements fang'd with murderous stonesAnd rags and hags and hideous wenches;I counted two and seventy stenches, All well defined, and several stinks!Ye Nymphs that reign o'er sewers and sinks, The river Rhine, it is well known, Doth wash your city of Cologne;But tell me, Nymphs, what power divineShall henceforth wash the river Rhine? Coleridge was not far off in timing the beginnings of today's problems. We have the physical problem of pollution because of a trend originating in the late 1700's, and because of society's choice to enjoy the advantages of this trend without facing up to its ultimate pitfalls. JPT P. 673ˆ

Diagnostic and therapeutic nerve block; general considerations.

The anesthesiologist of today performs a great variety of functions in addition to clinical anesthesia. Among these, perhaps his most important single function and the one that is most gratifying, is the relief of pain. Pain, in its severer forms, as for example trigeminal neuralgia, migraine, or the various colics, is one of the heaviest crosses the human race has to bear. Usually pain is a danger signal or warning of some beginning disease process, trauma, or physiological upset. It also may be the hang-over effect of past disease processes. It can arise from purely psychic origin, which is perhaps the most difficult to alleviate. Transient painful processes usually are no problem, but persistent pain, whether mild or severe, over weeks, months, or years can produce serious and far-reaching sequelae, which affect the patients' work, play, and sleep, alter their personalities, and produce changes in every phase of their daily