optimization
The detailed engineering design of a plant generally follows well-known procedures that need not be detailed in this book. Most engineering depart- ments and companies are well staffed and knowledgeable in that area; how- ever, not all of them are experienced in, or even aware of, some of the specific issues involved in “first implementation of a new process.”
This chapter emphasizes only the additional features that derive from the fact that the plant being designed is the first implementation of a novel process.
10.1 “First implementation” policy
10.1.1 Expected start-up problems
Any new chemical plant, even when it is based on a well-established industrial technology, involves a certain degree of uncertainty and may result in some start-up troubles. These problems may be due to failures in equipment or workmanship, dirt inside equipment or pipes, error of an inexperienced team operating under pressure, etc. Such start-up problems are expected, and they are normally corrected during the first weeks of operation of a new plant.
The first implementation of a novel process can obviously also present these difficulties but, in addition, one should generally expect more serious problems that may require physical changes. The greater degree of uncer- tainty can be attributed to the following:
• It may have been impractical to test everything in advance, for a sufficient period of time.
• High expectations influenced the decision making on the project. • A few years may have passed between the final process package
decisions and the plant start-up, and certain quantitative aspects may
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have changed (i.e., in the raw materials, or in the services supplied); somewhat different factors may have been introduced, either by the team doing the detailed design or by the equipment suppliers.
10.1.2 Design policy
Thus, in the first implementation of a novel process, it would be reasonable to specify, from the beginning of the detailed engineering design of the plant, a design policy that should allow, in general, for:
• An over-designed capacity of most of the individual functions. For example, the electrical motors’ drive power, or the diameter of the smaller pipes, or the capacity of solid feeders could be increased at very little cost.
• A greater degree of flexibility in operation, exceeding what is generally accepted in conventional design. For example, the following typical decisions should not affect the budget much but could be appreciated in the process tune-up: installation of variable-speed drives in some of the agitators and positive-displacement pumps, larger buffer tanks between sections, and manually set variable-level overflows. • Built-in preparations for possible changes and additions of hardware. For
example, more “blind flanges” installed in the piping at the correct places (avoiding dead-end traps) could allow for easier future additions. • Additional engineering effort with very careful attention to any possible cause of problems, according to a detailed list prepared and agreed in advance (see below). This is important in particular whenever well- known, conventional tools (“old horses”) are used in new applications. For example, in the early days of industrial solvent extraction, a new plant could not be operated due to a severe emulsification, which had not been seen in the previous pilot development work. A detailed inspection showed that the impellers installed in the liquid–liquid mixers had very rough edges, which mashed the liquids at high ve- locity. These impellers were returned to the workshop, their edges were ground and polished and this problem disappeared in the plant. The supplier of the impellers had extensive experience with mineral plants, mixing solid–liquid slurries, and had used the same fabrication tech- nique for this new application. After this experience it became standard procedure to include in the specifications for liquid–liquid mixers, this finishing procedure, with reminders on the drawings and in the in- spector’s checklist. But this lesson should also be applied systemati- cally to every specification for adaptation of conventional equipment to “first-time” applications.
Management should accept that the implementation of such design pol- icy may increase the final investment in the plant by about 10 to 20% (rela- tive) over standard practice. This extra margin should be accounted for in
the investment budget, but of course this reserve may be an easy target for budget cuts during construction, unless its importance is clearly understood and agreed to, as a matter of management policy.
10.1.3 Identifying probable causes of problems
The project managers have been expected to display a large degree of self- confidence when appearing before the “higher authorities” to obtain their approval of the investment (“nothing can go wrong, everything is under control”). Then, a few weeks later, they are expected to sit with their engi- neering staff, make a list of every possible cause of problems (the worst case) and define in detail the features that would be needed to prevent or minimize any resulting damage. This situation is very difficult and the review is often “delayed.” This psychological pitfall has been seen over and over again in many projects in different countries and it could be very detrimental.
This problematic situation can be by-passed if the role of the pessimistic “devil’s advocate” in this review is delegated in advance to an experienced external consultant, who has no psychological commitment to any previous claims and no concern that this role may damage his or her career.
Identifying potential problems and ways to prevent them should have contributions from the entire team. Specific professionals will be assigned to be responsible to follow up on these the detailed design process and the purchasing specifications, and to report on any deviation.