Chemical Engineering January 2022 - 34

Feature Report
Health, Safety and
Environmental Considerations
for Process Synthesis
Following this approach to assessing health, safety and environmental risks can steer engineers
to consider more inherently safe process options earlier in process synthesis
Thane Brown
Proctor & Gamble (ret.)
IN BRIEF
WHAT IS PROCESS
SYNTHESIS?
HOW TO THINK ABOUT
HSE
METHODOLOGY
EXAMPLE
UNADDRESSED RISKS
AND HAZARDS
CONCLUDING REMARKS
D
uring process synthesis in the
chemical process industries (CPI),
engineers make decisions that
determine the inherent health,
safety and environmental (HSE) risk level of
a process. This article proposes a simple
approach for identifying and assessing the
major HSE hazards during synthesis.
Understanding the risk level during synthesis
enables the engineer to consider inherently
safer designs (ISD) while developing the
flow sheet. If risk levels are not considered
during synthesis, higher risk processes will
result, because decisions are hard to change
once the flow sheet has been finalized. Most
of the resistance to process design changes
comes from trying to avoid the need to repeat
expensive research and development
work, as well as avoiding schedule delays.
To understand the value of ISD, consider
the Bhopal, India incident where, in 1984,
an accidental release of the chemical methyl
isocyanate (MIC) occurred at a facility for
manufacturing the insecticide Sevin. MIC, an
intermediate in the production process for
Sevin, is a highly toxic chemical. A National
Research Council (Washington, D.C.; www.
nationalacademies.org) study stated that
more than 40 tons of MIC were released, killing
close to 3,800 people and seriously injuring
between 100,000 and 200,000 [1]. Had
there been an inherently safer process at the
Bhopal plant, the accident might have been
prevented, or its severity greatly reduced.
What is process synthesis?
Process synthesis is the creation of a process
for manufacturing a product that meets
customer-based quality specifications, has
an appropriate level of HSE risk, and meets
business and economic requirements [2].
When complete, process synthesis will have
defined the following:
* A block flow diagram of the process, show34
ing
all major process steps and flow streams
* Process operating conditions
* Material specifications for raw materials,
catalysts, solvents, processing aids, packaging
materials and so on
* Material and energy balances
* Required materials of construction
* Process design data, such as reaction kinetics
and physical properties
* Scale-up criteria
* Major HSE hazards
How to think about HSE
HSE is a broad topic dealing with the safety
of plant employees, of the physical plant, of
the community and of the environment. Each
of these constituencies is affected in its own
way by a production process.
* Plant employees may be affected by
chemical exposure, fire, explosion, noise and
injuries
* The physical plant may be affected by fire,
explosion and overpressure situations
* The community may be affected by accidental
releases of substances, fires, explosions,
noise, pollution, landfills and the disposal
of hazardous chemicals
* The surrounding environment may be
affected by planned emissions and discharges,
toxic wastes, accidental releases
and fugitive emissions
In the previous definition of process synthesis,
the phrase " appropriate level of HSE
risk " requires further explanation. Generally,
risk is thought of as the following:
Risk = (Severity of Incident) × (Likelihood of
Occurrance)
or
Risk = (Human and/or Economic Loss
Potential) × (Probability of an Incident)
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Chemical Engineering January 2022

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