Last month, we discussed the need for project engineers to
talk to process engineers about the water systems as a capital
project takes shape. This months column discusses
additional ways to bridge the communication gap between these
Assess suitability for service
Some industrial plants, such as refineries, have stringent
engineering guidelines and sourcing for components and
materials of construction. In the absence of
clear guidance from the customer, the engineering design firm
will follow its own internal design guidelines. A major
constraint is a cost-competitive procurement process for
equipment that selects lower cost materials, lower quality
components and, sometimes, violates good design guidelines.
Consider the plant owner who agreed with the engineering
firms recommendation to select a demineralizer system
design sized for 150% of the maximum service flowrate because
it reduced the capital cost in the competitive bid. The
industry standard is 200% of the maximum service flowrate.
After several years of operation, the plant replaced one unit
with a larger-sized unit, resulting in a miss-matched set of
demineralizer trains that have a common regeneration system
programmaking it is impossible to optimize the
Assess operability and maintainability issues
Process engineers are experts on this subject and are
responsible for solving the daily issues of operating and
maintaining plant equipment.
Some design issues involve proper specification of online
monitoring equipment and water storage tanks with sufficiently
large working volumes to accommodate the dynamic treated-water
demand profile. Project engineers should consult
process engineers regarding location of sample points, chemical
feed points and online analyzers. Process engineers know the
application guidelines and the reliability and maintainability of
Other problems are design issues. For example, the absence
of a variable-speed drive on the recirculation pump on a
reverse osmosis (RO) cleaning skid, compromises cleaning
procedure for a multi-stage RO unit.
There is a tension when choosing new technologies. Process
engineers vote no because they are unfamiliar with
the operability and reliability of the new technologies
and the cost is higher than conventional technologies.
Conversely, project engineers will vote
yes because the higher capital cost is amortized over the
service life of the plant. The right way to evaluate new technology is suitability for
service. For example, membrane filtration is a perfect
pretreatment strategy to ensure reliable operation of RO units
and packed-bed demineralizers. However, the capital cost is
several time higher than the conventional multi-media
filtration systems. But this incremental cost for new
technology is a very small percentage of the total capital
cost of the project. Conversely, specifying this technology in retrofit projects to
replace conventional filtration is impossible because the
hurdle for return-on-investment is too high.
Other site-specific limitations
The most common site-specific limitations are environmental and plot-plan issues.
These operating issues may be forgotten or dismissed as
unimportant. For example, a Canadian plant considered replacing
its aging demineralizers with RO units until experiencing a
rare shutdown of the entire plant on a cold winters day.
I asked the question, Are we going to size the RO unit to
operate on a cold start or are we going to install
a supplemental bootstrap boiler to supply steam to heat the
water and resize the RO for 25°C? The simpler,
cheaper and more reliable option is demineralizers that are not
so sensitive to water temperatures.
Identify the negotiable cost components
There is always a risk of cuts in project budgets.
Discussion of the negotiable issues by process engineers during
the project design is an excellent idea. A good example is the
installation of a cleaning skid for RO units that uses flexible
transfer hoses instead of permanently installed connections
and, even worse, lacks quick-disconnect flanges. This
configuration makes the cleaning process an onerous and
time-consuming task. Consequently, the operators are unlikely
to clean the RO at the right frequencynot a good choice
to cut costs.
Project engineers must manage a huge number of technical
issues for capital projects. Process engineers can add
significant value to the design process by providing insights
to operability and maintainability of various process designs
and water treatment technologies. To have a successful plant project, both sets of engineers must
talk to each other.
End of series
Part 1, June 2012. HP
Loraine A. Huchler is president of MarTech Systems,
Inc., a consulting firm that provides technical
advisory services to manage risk and optimize energy-
and water-related systems including steam, cooling and
wastewater in refineries and petrochemical plants. She
holds a BS degree in chemical engineering, along with
professional engineering licenses in New Jersey and
Maryland, and is a certified management consultant.