Showing papers on "Inherent safety published in 2022"

Methodology for Selection of Inherently Safer Process Design Alternatives Based on Safety Indices

Abstract: Safety is a key part of any modern production process and as such is reflected in legislation and work regulations. Decision-making concept based on inherently safer design principles is introduced in this paper. Two case studies representing typical modern chemical processes are studied with the emphasis on their inherent safety level. First case study is a novel process to convert refinery waste into valuable products – production of ammonium thiosulphate. As a second case study, production of ethyl acetate by esterification was selected due to its potential for process intensification through reactive distillation. For each case study, two design alternatives are proposed. Utilising process data, the design alternatives are evaluated using five safety indices and compared to each other to identify the inherently safer one considering fire and explosion hazards as well as toxicity level. Results show that different sensitivity of index methods can lead to different outcomes of hazard potential identification. For the second case study, results of each method were in agreement. However, reverse order of design alternatives was obtained in the analysis of the first case study. As a part of this article, novel processing technique employing geometry of polygons to assess hazard distribution and inherent safety level of different process routes has been introduced and employed. Obtained results suggest possible implementation of the proposed approach to robust multi-criteria decision analysis as a safety assessment criterion.

An Inherently Safer Development Approach for Thermally Coupled Distillation Sequences: Application in Hazardous Chemical Separation

Abstract: Process safety is always a core issue in chemical industry, which is conventionally not taken into consideration during the conceptual design stage of a process flowsheet. Distillation handles more than ninety percent of the separation and purification tasks of hazardous chemicals and accounts for no less than forty percent of the total energy consumption. Therefore, this work presents an inherently safer synthesis framework for thermally coupled distillation sequences with structure constraints, which can efficiently quantify and optimize the inherent safety index of each column configuration in the sequence, based on State-Task Network and Dow’s F&EI. To efficiently quantify the inherent safety index of each column configuration, a series of structure constraints are proposed. Within the superstructure, Hengstebeck-Underwood-Gilliland shortcut method is employed for distillation column design. Finally, two hazardous zeotropic mixture separation examples are performed to demonstrate the feasibility and validity of the proposed synthesis methodology.

Analysis of pressure behavior during runaway reaction with case studies of various depressurization designs

Abstract: In chemical plants, safety valves are installed on process equipment where pressure rise would occur to prevent their rupture. However, it is difficult to estimate accurate vent size for two-phase flow, and the analysis of pressure rise behavior during a runaway reaction is important. However, ISO method sometimes gives unpractical vent size, therefore, a detailed process dynamic simulation model was constructed in this study. A detailed model was constructed with Aspen and Advanced Reactive System Screening Tool (ARSST) experimental data. The model for depressurization from reactor was the refined omega-method of ISO, which was programmed with Aspen Custom Modeler. The case studies of dynamic simulation are carried out and the result of vent size estimated from ISO method were compared. In addition, some case studies on various process conditions and safety valves such as diameters and set pressures of safety valve, the presence of exhaust gas lines and different solvents were carried out. Different combinations of these conditions produced significantly different behavior in the runaway reaction. Therefore, these results lead to the understanding of runaway reaction and may expect to provide some options for constructing safer processes practicably and economically.

Development of a general inherent safety assessment tool at early design stage of chemical process

Abstract: The purpose of process safety is the prevention and mitigation of incidents arising from process-related hazards while inherent safety design is one of the most effective ways to prevent accidents in the process safety management. Inherent safety assessment tools (ISATs) play an important role in the application of inherent safety design. However, many ISATs suffer from various limitations. Hence, we propose a general inherent safety assessment tool to evaluate inherent safety level at the early design stage of chemical process. First, we define two criteria of good inherent safety assessment tools from their purpose, namely reliability and usability. We link the inherent consequence to process parameter and chemical property, subsequently propose a general inherent safety assessment tool for different hazardous sources (e.g., and fire/ explosion, health, environment). The proposed tool can eliminate the uncertainties in the risk-based inherent safety assessment tools and address the problem that the amount of material handled is not considered in the continuous numerical assessment tools. Finally, we use two cases to illustrate the proposed inherent safety assessment tool and compare with the commonly used ISATs. This work can accelerate the inherent safety design at the early design stage to prevent incidents in the chemical process.

A Process Modularity Approach for Chemical Process Intensification and Inherently Safer Design

Abstract: Process intensification through hybrid equipment combining unit operations has the potential for reducing energy demand and improving the safety of a chemical process. Selecting which unit operations to combine into an intensified unit is necessary in developing an intensified process that offers an inherently safer design with reduced energy demand. This paper presents a novel methodology to intensify a chemical process guided by modularity. A process network is decomposed into modules by applying a community detection algorithm to find the process units to be integrated into an intensified "module" to improve the Fire and Explosion Damage Index (FEDI). A case study for the separation of an ethanol-butanol-water mixture illustrates this approach. The results show that the safest design (lowest FEDI) is Alternative 1 which was developed using the approach and correlates with high modularity of 0.607. Energy use is reduced by 25.8% thus also leading to a more energy efficient process compared to the non-intensified design with a lower modularity (0.385). A rather empirically guided design was proposed as Alternative 2 which led to modularity of 0.533, but only 10% energy saving and no improvement in the FEDI. This demonstrates that intensification guided by modularity strengthens integration between the process units while improving both safety and energy efficiency. As such, the approach has a wide potential application to guide the intensification of chemical processes.

Inherently safer process route ranking index (ISPRRI) for sustainable process design

Abstract: The growth of process industries has escalated the probability of loss containment scenarios of hazardous materials that can be tackled via process safety schemes. For preliminary design stage, the inherent scheme is more promising to generate sustainable process designs. For this purpose, various process routes are typically compared to recognize the safer one via numerous indexing methods to eliminate routes with hazardous materials. However, these indices lack in accommodating the equipment characteristics and the underutilization of process and chemical characteristics. Specifically for chemical characteristics, the toxicity aspect has not been engaged for process route selection in conjuction with other aspects. Consequently, an advanced indexing method is consolidated in the present work for the mentioned gaps named as inherently safer process route ranking index (ISPRRI). This method utilizes the equipment, chemical, and process aspects for ranking purposes. MMA process routes have been studied with the proposed method, and the obtained results validate the applicability to identify the less hazardous route and are in agreement with previous indices. The technique would facilitate the design engineers to rigorously compare the process routes to highlight the inherently safer route with less hazardous materials for the desired chemical product.

Towards Environmental Protection and Process Safety in Leather processing – A Comprehensive Analysis and Review

Abstract: Leather process industry requires in-plant process interventions with inherent safety; wherein, enhancement in process efficiency, rather than end-of-pipe treatment are gaining importance. Switching over to alternate processes with statutory requisite such as material safety and toxicological information of chemicals employed, eco-label, Registration, Evaluation, Authorization and Restriction of Chemicals ( REACH) and UN’s Sustainable Development Goals (SDGs) for Leather sector (SDGs) are essential. Herein, these aspects have been linked with safer and eco-benign process development. The present review analyze the environmental, occupational safety concerns and difficulty in overcoming the conventional non eco-benign chemicals, in order to develop alternative cleaner processes through scientific basis with fundamental theory and practice of leather manufacture. Aspects such as mass balance, diffusion phenomena, E-Factor metrics for assessing the clean technology and pollution reduction have been explained. Focus given towards improving exhaustion levels in various stages, eco-benign processes, non-toxic products, use of natural materials, bio-process, novel processes/products, new process systems, 3 R approach, process intensification tools such as ultrasound are analyzed with environmental and cost aspect. In addition, concepts of process safety, modernization of tannery and process engineering of leather making to identify the need for benign methods in processing have been incorporated. Analysis of life cycle assessment and carbon footprint relevant to leather sector are also provided. This unique and novel review includes 257 references with recent information, leading to environmental protection and process safety. The distinctive approach and analysis presented here provides methodology and novel approach for development of eco-benign alternatives, chemicals and systems for Leather and other generic processing industries for green & sustainable development and also form a typical model for preparedness towards future challenges for sustainable development. This comprehensive analysis and review would pave way for switch over from conventional leather process, which has environmental and safety concerns to alternate eco-benign products, processes and systems. Schematic representation of sequence of steps in Leather making on Necessity for switching over to Eco-benign alternatives in processing, pollution reduction at source with SDG; Highlighting hazards of unspent chemicals & worn out materials with Life cycle assessment starting from raw material to final end products and solid waste management.

A review of existing SuperCritical Water reactor concepts, safety analysis codes and safety characteristics

Abstract: SuperCritical Water Reactor(SCWR) applies water beyond the thermodynamic critical point as the coolant, which aims to achieve high efficiency around 45% compared to 33% for existing commercial light water reactors. In order to raise the reactor operating temperature and reactor criticality, the existing SCWR core designs are quite different from those of boiling water reactors or pressurized water reactors, which further effect their safety performance and safety system design. A comprehensive review on existing developed SCWR reactor concepts of different countries, including pressure-vessel type and pressure-tube type SCWRs, as well as thermal, fast and mixed spectrum SCWRs, is carried out to deeply explain the core design features of SCWR. The development methods of safety analysis tool for SCWR are also summarized to shed a light on the key scientific difficulties and how these problems are solved up to now. All the special techniques applied to enable trans-critical simulations are still unphysical and lack of validation. Moreover, the safety characteristics of existing SCWR concepts are discussed. Based on these review work and discussions, the research status of SCWR concepts, safety analysis tool development and safety characteristics are clearly presented. Safety analysis tool validations and more comprehensive accident evaluations should be further carried out to better illustrate the safety performance of these SCWR concepts.

Design and optimization of an inherently safe and sustainable process for the separation of anisole

Abstract: Sustainable process design problems are multi-faceted approaches that pose challenges in terms of the evaluation of indicators to optimize inherent safety, economics, and control. In recent years, chemical engineering has taken advantage of recent advances in process systems engineering more notably considering intensification to generate green and more sustainable processes. This work presents the design and optimization of the anisole separation process under three intensified and one conventional schemes using a systematized methodology to find optimal designs of purification processes where the interactions between the different sustainability indicators are balanced to obtain optimal configurations. The indeces chosen in the course of process optimization (inherent safety, economic, and control) aim at generating green and more sustainable process alternatives. The results indicate that the most intensified processes, as is the case of the Dividing Wall Column (DWC), is the one with the best sustainability indicators, with better inherent safety and better operability despite it being an intensified process with fewer operational degrees of freedom. In addition, the environmental impact after the optimization of each of the processes were evaluated. Separation through DWC resulted in 2.43% savings in economic terms, 0.31% in inherent safety, improved controllability performance, and a 3.35% reduction in environmental impact, in comparison with the conventional sequence used as baseline. This indicates that in the case of anisole separation, process intensification can yield a more sustainable process design.

Dynamic Inherent Safety Analysis of a Distillation Column under Simultaneous Design and Control

Abstract: Inherently safer design (ISD), which focuses on reducing the inherent hazards of a design before applying any safety controls, is one of the most effective and reliable tools for improving the safety of a process. However, while an intensified process may be inherently less hazardous, if the design restricts the controllability of the process, then the design may have a higher risk and be less safe overall. Therefore, considering both the inherent hazard contained within the process and the ease by which these hazards can be controlled is necessary for a more complete evaluation of the inherent safety of a system. The objective of this research is to implement a strategy to simultaneously design and control an inherently safer distillation column. The PARametric Optimization and Control (PAROC) framework is used as a basis for the simultaneous design and control of a distillation column. The Safety WEighted Hazard Index (SWEHI) is incorporated into the PAROC framework, and the distillation column is optimised for cost, while receding control horizon policies are implemented to ensure that the column is capable of controlling disturbances. The dynamic effects of different operating variables on safety are analysed and discussed. The integration of ISD with simultaneous design and control allows for a greater understanding of inherent safety during process design and substantially reduces operability issues that result from an uncontrollable process design and allow for greater tolerance and ease of control.

Inherent safety analysis

Abstract: In this chapter, we discuss inherent safety analysis at the conceptual design stage. The following methods will be introduced: (i) Dow Fire and Explosion Index, (ii) Dow Chemical Exposure Index, (iii) Safety Weighted Hazard Index, and (iv) Quantitative Risk Assessment. The key factors considered in each method to evaluate the inherent safety performance of a process will be highlighted (e.g., operating temperature, mass inventory). The required input information from process design and the resulting evaluation outputs (such as ranking or damage radius) will be detailed. These analysis approaches can be further integrated with process synthesis and design approaches to systematically generate inherently safer process systems as will be showcased in the following chapters.

One of the preferred concepts of new generation power nuclear reactor

Abstract: With an increase in the power of a fast reactor, safety problems appear. The solution of optimization problems of two types showed how these problems can be eliminated. The results of solving two optimization problems of a reactor with mixed mononitride fuel (MN) and lead cooling are presented. The first task is to optimize the layout with restrictions for a number of functionalities. Fulfillment of restrictions for some functionalities will make the reactor self- protected from emergency conditions. First of all, ATWS (Anticipated Transient Without Scram) modes and their combinations are considered. The second task involves optimizing the properties of core materials with the subsequent search for the necessary materials. In the optimization problems, the main requirements for the energy sources of the future (economy, safety, fuel supply) were considered. These requirements are formalized as optimality criteria and restrictions. As a result, it becomes possible to ensure safety at the initial stage of reactor design. Field simulation of ATWS failures is not possible. As a result of solving the first problem, the optimal layout of the reactor was obtained. The solution to the second problem made it possible to choose fuel, based on a mixture of MN micrograins and an uranium metal nanopowder, as the coolant, lead extracted from thorium ores was selected, and nickel-free steel with the addition of nanopowder Y2O3 or TiO2 and tungsten deposition.

Development of small-scale experimental method for vent sizing and observation of runaway reaction

Abstract: Safety valves for reaction runaway are important to install in order to prevent ruptures of equipment. However, safety valves are not easy to accurately design for a pressure increase due to a runaway reaction. A vent-sizing method for two-phase flow was developed by the Design Institute for Emergency Relief Systems (DIERS) under the auspices of AIChE in 1987, and the API standard 520 and ISO 4126–10 was published in 2010s’. These standards defined conservative assumptions. Therefore, sometimes non-realistic results, such as bigger safety valves than the reactor diameter, are obtained. For the investigation of a more accurate design, detailed analysis of safety valves with Aspen were studied in my previous study. Simulation technology gives a great deal of useful knowledge. However, it is necessary to verify the simulation results. Therefore, a 40 mL-scale small test instrument with a safety valve was developed, and runaway experiments were carried out in this study. The results of case studies of simulation corresponded to experimental results. Furthermore, this experimental method can estimate the vent size directly without complicated analysis, such as the ISO method or a detailed simulation. In addition, the combination of case studies of the experiment and simulation provides various additional knowledge, such as moderating measure for runway reaction and preventing measure for occurrence of two-phase flow in the reactor. This study contributes to the design of resilient processes for process upsets and will lead to sustainable and economical design.