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Planning Layout Activities #2
Plant layout is a subset of process plant design, which itself fits into the wider background of an overall project lifecycle. The details of project lifecycles vary between industries, but there is a common core- Conceptual, FEED, Detailed and For Construction Design Stages.
Conceptual design of process plants is sometimes carried out in an ultimate client company, more frequently in a contracting organization, and most commonly of all in an engineering consultancy.
In this first stage of design, it is important to understand operational constraints, identify the sufficiency and quality of design data available, and produce several rough designs based on the most plausibly successful approaches. As the various process options will have different footprints on a site, even the initial selection of technology and rough budget costing will ideally need to consider layout.
At the end of the process, it should be possible to decide rationally which of the candidate design options is the best one to take forward to the next stage.
The key factor in conceptual design studies is usually to gain an understanding of the economic and technical feasibility of several options as quickly and as cheaply as possible. Since 98% of conceptual designs do not get built, it is simply not economic to spend large amounts of money investigating them.
Front End Engineering Design (FEED) provides sufficiently accurate data to inform rational decision making on the economic viability, process safety and robustness, environmental and social impact of the proposed project. FEED layout involves determining the relative positions and separation distances of the principal process units and buildings.
Information for FEED layout usually comes from the consultant’s conceptual design, in the form of PFDs and datasheets giving the approximate sizes of process units. Many site details will be known if an existing site is being developed, but they are usually vague for a ‘greenfield’ project. The layout designer must estimate areas necessary for construction, maintenance, and operation of the plant.
Safety of the design, from an operational and maintenance point of view, is the designer’s highest priority, but cost and process robustness come a close second.
Subsequent design reviews involve close co-operation between the process and layout designers, particularly when carrying out hazard assessment. Operation, maintenance, and construction staff may participate in the review, though this is relatively unusual nowadays since design and operating companies are usually separate entities.
Since differing layouts can vary widely in construction costs, a selection of preliminary layouts should be produced, and the more promising ones refined to identify the best one. In the case of a new but unknown site, site selection is often carried out at the end of FEED design. Reviews will involve reconciling the FEED layout to the candidate sites.
One purpose of detailed design is to provide detailed costs to allow the project sponsor to provide sanction to proceed with the project. A second, equally important purpose is to provide comprehensive hazard, environmental and social assessments to the regulatory authorities, to obtain detailed planning permission.
Agreement with the appropriate authorities is ideally obtained by the end of Detailed Design, to avoid any subsequent waste of time and money to carry out the modifications required to meet legal requirements.
Similarly, there must be agreement on all aspects of the design amongst the various disciplines because it can become very costly to alter layout during design for construction, and such alterations could make it necessary to reapply for planning permission.
A more accurate version of the deliverables from the previous stage is produced, based on the more detailed design. Once this has been completed, a design review or reviews can be carried out, considering layout, value engineering, safety, and robustness issues. Where necessary, modifications to the process design to safely give overall best value should be made.
Design for Construction
After sanction, the various disciplines produce the detailed design for construction, based on the previous work, plus any constraints imposed by sanction, contract, or planning approval. “Design for Construction” is the most time-consuming stage. Any changes to the layout at this or later stages can be very costly in repeating design effort, and in delaying the project.
Although piping and layout design are arguably different activities, many organizations combine them in the same department. In design for construction, this team first produces the final layout model and/or drawings, then piping arrangements are designed, followed by isometrics.
On projects that utilize 3D CAD modelling software, the piping arrangement must be designed in the 3D model prior to 2D drawing generation. On projects utilizing 2D CAD, the drawings are the result of design development as it occurs.
The results of the design for construction stage are the details required for equipment orders and site contracts , plus the detailed drawings and materials listings needed for construction. The kinds of drawings concerned with layout and piping are described in Chapter 7.
Design for construction virtually always takes place in a contracting organization. The detailed design will be sent to the construction team, who may wish to review the design once more with a view to modifying it to reflect their experience in construction and commissioning. There can also be benefits from involving the construction sub-contractors in the detailed design phase, so they can see the full context of what they are supplying.
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
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 co-ordinated 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 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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