Hydrocarbon Processing - December 2021 - 35

Process
Optimization
J. P. WALTER, TLV Corp., Charlotte, North Carolina
Impact plant performance by improving
the steam system
Petrochemical plants and refineries face production and
profitability challenges on multiple fronts. Some of the typical
difficulties encountered include:
* An unnecessarily poor energy intensity index
or a low-energy efficiency index
* Unplanned maintenance expenditures to fix damaged
and unreliable steam-using equipment (e.g., turbines,
flares, reboilers and ejectors)
* Wasted operating expenditures and experiencing product
loss on avoidable items (e.g., turbine trips, product lines
freezing, reboiler control issues or equipment failures)
* Hassles working around process problems, such as
production bottlenecks, low cutpoints and degrading
vacuum levels
* Concerns on safety and environmental pollution
* Lack of sufficient steam specialist knowledge to address
problems and opportunities
* Trouble applying limited resources to make
improvements when the priority is to keep the plant
running within budget
* Difficulties accurately predicting and demonstrating
the true savings of improvements.
Plant operations are commonly focused on production, and
so they tend to accept energy losses and poor reliability as accepted
practices. As a result, substantial economic opportunities
become invisible. Plants may not know where to start to improve
in areas such as safety, environmental impact, production
rates, product quality, equipment reliability and/or energy efficiency.
One way of impacting all these areas is to treat the plant's
steam system as a crucial heat asset, recognize the importance
of the steam trap population to its health, and to implement a
simple four-step program to protect and improve it.
Four effective steps that impact plant performance.
The following steps are important for improving a plant's
steam heat asset:1
1. Select the right steam trap for the application
2. Install the steam trap correctly
3. Implement a sustainable steam trap management program
4. Optimize the performance of steam-using equipment.
Select the right steam trap for the application. To properly
select a steam trap, it is important to understand:
* The purpose of a steam trap
* How normal operation and failure may affect the
purpose of a trap
* How generic steam trap types operate
* How steam traps can fail (common failure modes)
* Special requirements for specific steam trap applications
that should be considered when selecting steam traps
* A site's experience and bias regarding steam
trap performance
* Factors affecting lifecycle costs (for reliability and
total cost of ownership)
* Specific performance criteria for individual steam
trap models
* How to accurately model steam trap lifecycle costs.
Application-specific guidance. One of the most critical areas
for steam trap selection is considering the application to account
for specific challenges. The most common steam applications
in hydrocarbon processing facilities that require careful trap
selection include steam distribution lines, steam turbines, process
heaters, flares, sulfur pit coils and steam tracing lines (particularly
in the transport of high-viscosity products like sulfur or resid).2
Steam distribution. Steam is generated-as either superheated
or wet quality-and then distributed throughout the
facility to provide process heat to equipment.3
It is essential
that condensate forming in the steam distribution system is
drained immediately and not allowed to back up, as this could
result in water hammer damage and the reduction of process
equipment reliability.4
In general, for these applications, steam
traps with near-instantaneous discharge provide the best performance.
There is commonly the need for these traps to vent
air, so the selection process should consider all requirements.
Subsequently, float and thermostatic traps, as well as thermodynamic
traps containing thermostatic air vents, and thermostatic
balanced-pressure capsules, are recommended.5
Bimetal
traps should never be used for draining steam mains due to their
operating principle requiring deep levels of subcooling, which
can lead to condensate backup. There may also be some special
requirements for steam main drainage (e.g., to drain the boiler
header piping, which follows immediately after steam boilers/
steam generators, for high-temperature super-heated steam lines
or where traps are widely spaced).
Steam tracing. Steam tracing typically accounts for most
steam trap installations in a hydrocarbon processing facility.
Hydrocarbon Processing | DECEMBER 2021 35
Hydrocarbon Processing - December 2021

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