Page 222 - Design of Simple and Robust Process Plants

5.7 Simplification and Ranking per Unit Operation 207
5.7.6
Fluid Transport

Fluid transportation needs differentiation in liquid and gas transport, the main
difference being the type of mechanical device used ± a pump versus a compressor
or blower. The types of sealing and bearing will not be discussed at this point. Ear-
lier, we referred to a saying, ªThere is no component more reliable than no componentº.
This is specifically applicable to fluid transport, and will be reflected on in the
priority ranking. The selection of the different types of machinery is considered a
design issue, and is not discussed in this section. The different types of machinery
mostly have a specific operational area with some overlap, and can be outlined as:

Liquid transport Gas transport

1. Gravity flow 1. Displacement of liquid
2. Flow through pressure difference 2. Pressure difference by vapor pressure
3. Pump, centrifugal 3. Gas/liquid pump as liquid ring pump
4. Positive displacement pump 4. Fan
5. Blower
6. Compressor, centrifugal
7. Compressor, positive displacement

5.7.7
Piping

Piping may appear simple, but can make the overall process system very compli-
cated. In general, piping networks grow during piping development, usually at the
point when the discussion begins regarding ªwhat if ?º situations (scenarios).
This always leads to an inventory of possible things that might occur, and which
require all types of provisions including cross-connection, bypass provisions, back-
up lines, new loading lines, recycle lines ± all with their required instrumentation.
Subsequently, all of these lines and connections need to explored for potential
hazard, through a HAZOP study, which inevitably will add more provisions such as
check valves, instruments, and safety devices. This entire situation requires a revised
approach to be taken.
An engineer once had to automate a storage area for a plastic plant. The storage
contained storage silos in addition to blending hoppers which were provided with
material from four production lines and also from several extruder lines applied for
product up-grading. At the beginning of the project, he tried to find some logic in
the pipe network. The situation was such that nearly all options were available, but
most of them were not utilized, and the operator was not even aware of all the
options. What the engineer did was to start designing a new piping system as if
nothing were available. When he had completed the design, the engineer went into
the plant to search for the availability of these lines. His next step was to eliminate