Chemical Engineering March 2017 - 49

Process safety in control
Another area of process control deals
with safety instrumented systems (SIS).
Up to this point, the discussion has
centered on control
requirements to
keep the process running in the face of
variability. Safety systems have a single
function, which is to safely shut down
a process if a catastrophe is imminent.
Process engineers may be better prepared
to consider process safety than
most disciplines, at least with regard to
the CPI. The general concept is to evaluate
the risks, in terms of probability, and
the magnitude of the consequences.
Layers of protection are defined and
deployed to reduce the risk of a serious
safety or environmental exposure. Highrisk
possibilities need to employ engineering
solutions to reduce the risk. Some
solutions will include process design,
such as dikes around tanks and pressurerelief
equipment. Controls will also be employed
to reduce the risk, including safety
interlocks. The requirement for high ondemand
availability of the safety-protection
systems leads to specialized safety
systems with redundancy (including triple
redundancy) and pro-active diagnostics
to monitor the health of the safety systems.
One of the first layers of protection
is alarm management, although it is
limited by the presence of the human element
to respond to an alarm (for more
on alarm management, see Chem. Eng.
March 2016, pp. 50-60). Designing
safety-instrumented control systems is a
specialized area that is critical in managing
the risk of hazards in the process. There is
a growing trend to design safety systems
to be integrated into - but still separate
from - the basic control systems. Care
is taken during design to ensure the integration
does not create a vulnerability or
common point of failure of the safety system
function and reliability.
Along with this trend is the increasing
use of diagnostics and capabilities of
" smart " instruments and field devices to
reduce the probability of failure on demand.
This is a critical consideration for
safety systems, because they may not
be employed for long periods of time,
if ever, but then must work when called
upon to shut a process down safely.
Process data
A final area of process control where process
engineers can have a significant impact
is data management and analysis.
Control systems have access to a great
deal of data other than control data. Historization
and archiving of process data
enables process engineers to identify
and prioritize continuous improvement
opportunities and allows management
to make more effective decisions regarding
operation and future investment.
Business systems that manage maintenance
processes, quality processes,
planning processes and other work processes
can be integrated with process
control. This has been enabled by modern
technology for networking, databases,
operator interfaces and enterprise-management
software all working together.
While the nature of integration of these
various systems requires more knowledge
in computer programming, database administration
and networking than chemical
engineers might learn in their academic
programs, the process management requirements
require an understanding of
the process plant and its economic sensitivities.
Chemical engineers are likely to
have a better understanding than most
of the information required by company
managers at both the local and corporate
level in order to make best use of the
data and systems in place. The increasing
wealth and richness of data makes analysis
of that data with evolving " big data "
tools a real opportunity. Networking, data
sharing, and collaboration between the
plant and specialized resources located
far away is the promise of the Industrial
Internet of Things (IIOT).
Concluding remarks
Often the greatest knowledge gap for
a chemical engineer who wants to become
a process automation engineer
is deep knowledge of instrument and
control hardware. This is not an insurmountable
problem, however, because
vendors are happy to share the information
you need. A good salesperson,
perhaps contrary to popular opinion,
can be a valuable and trusted advisor.
The best salespeople know that exaggerating
the benefits of one offering for
immediate sale may win the order, but
will lose the confidence and trust of the
customer for future opportunities.
In most cases, vendors truly do want
to recommend the most economical solution.
To do that, they need to understand
the process and control requireCHEMICAL
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Chemical Engineering March 2017

Table of Contents for the Digital Edition of Chemical Engineering March 2017
