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Planning Layout Activities # 1
Though there is no universally followed process plant design methodology, in professional practice, design is always staged. These stages each run from an instruction for the designers to proceed, to the start of the sponsor’s next decision-making process. At each of these stages, many projects fail to proceed, such that only a small percentage of stage one design projects proceed all the way through to plant construction. Since design activity itself costs money, each stage involves only just enough design effort to provide the sponsor with sufficient information to make an informed decision about whether to proceed to the next stage.
Projects must incorporate safety and environmental evaluation from the earliest stages of the project, to enable them both to demonstrate that they have taken the optimal safety option at each step, and to perform all the assessments required for regulatory consents.
The optimal safety option is not the “no risk” or even the “minimal risk” option. The designer balances the cost, safety, and robustness of options at each stage. The only “no risk” option is to do nothing although as this will result in the company making no money, it is not really a “no risk” option at all.
The layout designer, along with the rest of the design team, balances risks to people, the environment, and the company at all stages of design. There is no “right” weighting to these factors. The designer’s job is to provide the information to allow decision makers to apply their own weighting, and make the decision as to whether to commit resources to proceed to the next stage of design and construction accordingly.
Even the preliminary stages of design must consider how the plant layout may be constrained by environmental or health and safety considerations such as:
- The requirement to protect surface waters from contaminated run-off. This will affect drain arrangements and the provision of space for tertiary containment.
- The presence of other development around the site, which may influence the location of the major hazard materials storage. Developments that would have a major influence include schools, hospitals, and other facilities where large numbers of people (especially vulnerable people) may be present.
- Increases in separation between plant items, which may be required to allow for phased construction, or access for maintenance and repair of one process train whilst other process trains continue to operate.
Plant layout may affect environmental impact via aesthetic appearance and the effects of road transport, but most notably by its emissions to environment. The location of emission sources, vents and flares may influence environmental impacts, particularly where there are localized sensitive receptors. Layout may also have an impact on drainage layouts both for surface water run-off, contaminated and hazardous drainage networks.
It is sometimes necessary to apply for permits and legal consents at this stage so that the owner only sanctions the build after these consents are granted. This normally requires an environmental and safety assessment, to a degree of rigor commensurate with the type of plant being proposed. For plants with a potential for major accident hazards, this might entail a full environmental impact assessment in support of the environmental statement, together with a quantitative risk assessment in support of a pre-construction design safety case report.
Environmental and safety risks may be sensitive to layout and need to be addressed in design reviews to proceed to construction and make applications to the regulators.
In addition, it is often a client requirement to build resilience or survivability into the design in order that a minor incident does not escalate or impede the escape of personnel. This may be analysed in terms of frequency criteria on damage to equipment with major inventories of hazardous material, damage to safety related equipment or impairment of escape routes. Alternatively, the client may specify design accident loads which should not be exceeded.
Health and safety analyses consider the protection of health and safety of the surrounding population as well as that of the construction and operational workforce. The layout must therefore provide for adequate protection of the public (at home, recreation, education, health care or at work) from plant hazards under all foreseeable conditions. This degree of protection is usually provided by keeping the risk of major accidents as low as reasonably practicable (ALARP) and the achievement of zero harm to health by control of emissions below “no observable effects” levels.
The preliminary stage of design should also consider how the plant layout may be constrained by environmental or external constraints; for example, protection of surface waters from contaminated run-off will affect drain arrangements and provision of tertiary containment, for which space must be available.
About the book
The second edition of Process Plant Layout explains the methodologies used by professional designers to layout process equipment and pipework, plots, plants, sites, and their corresponding environmental features in a safe, economical way. It is supported with tables of separation distances, rules of thumb, and codes of practice and standards. The book includes more than seventy-five case studies on what can go wrong when layout is not properly considered. Sean Moran has thoroughly rewritten and re-illustrated this book to reflect advances in technology and best practices, for example, changes in how designers balance layout density with cost, operability, and safety considerations
If you found this article interesting, access the entire book, Process Plant Layout, on ScienceDirect. We are pleased to offer you a free chapter from the book called “Planning of Layout Activities”, below:
About the author
Professor Sean Moran is a Chartered Chemical Engineer with over twenty years’ experience in process design, commissioning and troubleshooting and is regarded as the ‘voice of chemical engineering’. He started his career with international process engineering contractors and worked worldwide on water treatment projects before setting up his own consultancy in 1996, specializing in process and hydraulic design, commissioning and troubleshooting of industrial effluent and water treatment plants.
Whilst Associate Professor at the University of Nottingham, he coordinated the design teaching program for chemical engineering students. Professor Moran’s university work focused on increasing industrial relevance in teaching, with a particular emphasis on process design, safety and employability.
Sean’s latest books are also available to order on the Elsevier Store. Use discount code STC317 at checkout and save up to 30% on your very own copy!
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