Page 75 - Design of Simple and Robust Process Plants

3.3 Design Philosophies 59

Sprinkler
Inert Vent recovery
Vapor return
H HH
P P
A L A LL
O2
HC HH
L
LL
H HH
H
Loading F T L T T LL L H
L L A L
H2O L H H H
P T
L L
Heating system
Maximum Feed to plant
flow valve H H
P T
L L
Fig. 3.6. Safety provisions of a storage tank for product X.

Some basic questions for storage tank designs from an inherently safer design
perspective based on the four guiding words are:

Minimize
. Do we really need the tank? Could product X be supplied by pipeline?
. Can we avoid storage and handling by direct feeding from process to pro-
cess?
. Did we consider feeding to the process in the gas phase (less inventory of
toxic material)?
. Did we consider a smaller tank?
. Did we consider buying in containers to avoid handling and feed on pressure
into the process?

Substitute
. Do we really need this chemical?
. Could we replace it with a less harmful product?
Consider the effects of vapor pressure, toxicity, flammability, reactivity, inter-reactiv-
ity with other plant components, solidification point, product degradation. All these
properties add to the safety provisions.

Moderate
. Do we really need the chemical in the form as it is?
. Can it be handled in a less harmful form? For example in dilute solution,
another phase, mixing with another inert material. You might consider low-