Chemical Engineering December 2014 - 46

annual energy bills in the hundreds
of millions or even billions of dollars,
and energy used in the process
is a major component of variable
cost. In contrast, labor and safety
and human-comfort systems, such
as lighting and space heating, tend
to be more dominant in many of the
smaller, more specialized facilities
that spend much less on energy.
Energy management is also very
different for batch processes than
for continuous ones. In particular,
where many batch operators can
apply " downtime shutdown strategies "
to eliminate unneeded energy
use for much of the time and thus
gain " free " energy savings, this approach
is not generally applicable
in continuous processing.
The process sector does share
some key systems and equipment.
Steam systems are virtually ubiquitous,
as are electric motors, heat exchangers,
pumps and compressors.
However, beyond these common
elements there is great diversity,
from distillation columns, catalytic
reactors and centrifuges to kilns,
crystallizers and belt dryers. Each
system and each type of equipment
has its own issues that must be
considered within a comprehensive
energy-management program.
Energy efficiency opportunities
Opportunities to improve plant performance,
and thus enhance energy
efficiency across the CPI, fall into
four main categories: operational
improvements, effective maintenance,
engineered improvements,
and new technologies. In each area,
robust energy-management programs
can support the behavioral
and process changes needed to capture
and maintain savings and efficiency
improvements.
Operational improvements.
Many operational improvements
can be captured at low or no cost.
Before committing to projects that
require capital expenditure, it is
prudent to ensure that existing
equipment is being used to its full
advantage - to pick up the " lowhanging
fruit. " This idea is illustrated
in the following example:
A project was planned to expand
Courtesy of NLB
FIGURE 1. Heat-exchanger cleaning programs have become an important part of
energy-management systems. Shown here is hydroblasting equipment for cleaning
shell-and-tube heat exchangers
a process unit in a chemical plant.
The expansion required a significant
increase in cooling-water flow,
and as the existing cooling-water
pumps were already fully loaded,
a new pump was included in the
project scope. However, during a
project review, the need for the
new cooling-water pump was challenged,
so the cooling-water system
was surveyed.
Over the years, the cooling-water
system had been expanded and
modified several times to accommodate
changes that had taken place
at the site. The changes included
two additional pumps and several
branches in the piping, so the cooling-water
system had become quite
complex over time.
During the survey, it was found
that cooling water was still flowing
through a section of the plant that
had been abandoned several years
before. When the isolation valves for
this section of piping were closed,
the cooling-water circulation rate
dropped significantly. This freed up
sufficient capacity to eliminate the
need for the new pump in the expansion
project, which reduced the
project cost by $500,000 and saved
$200,000/yr in electricity costs to
run the additional pump.
Operating practices tend to become
ingrained over time. In the
example above, no one questioned
the position of the isolation valves
in the unneeded cooling water circuit.
More generally, operators may
religiously follow procedures that
were developed when the plant
first started up, even though the
requirements of the plant have
changed over time. For example,
these changes could be due to new
feedstocks, different product slates,
changes in throughput or a host of
other factors.
Another way that operating practices
can become skewed is by extending
short-term responses to
specific problems. For example,
a cooler may be bypassed in cold
weather, or a preheat exchanger
may be taken out of service during
a plant upset. These modified configurations
can remain in place and
become the new normal, and they
can remain that way for years.
The immediate response when we
become aware that operating conditions
are suboptimal is to adjust
the process (for instance, shutting
the isolation valves in the coolingwater
example). However, this is
only a short-term fix. The next operating
shift will very likely reverse
the change and restore the status
quo. Furthermore, plant conditions
are constantly changing - the
right solution today may not be the
right one tomorrow or next month.
We need more than just a one-time
change to ensure that we get the
most from our existing facilities.
Additional energy-management
steps might include the following:
* Modify operating-procedure
documentation
* Carry out additional operator
training
* Add control valves
* Implement realtime optimization
systems
* Implement performance monitoring
systems and key performance
indicators (KPIs)
One area that often yields significant
opportunities for operational
improvements is the steam
system - especially more complex
steam systems that include steam
turbines. These systems are subChemiCal
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