Hydrocarbon Processing - October 2021 - GP-25

GREEN TECHNOLOGIES
ing capacity that avoided any large impact on customer supply.
It is worth mentioning that it takes approximately 8 hr to start
a new boiler should the need arise, while steam production can
be ramped up by 10%/min in an operating boiler.
As an alternate approach, standard deviations in the feed
fluctuation for the last several years were calculated to estimate
steam demand and the steam reserve required to handle feed
fluctuations. Sudden cogeneration unit and boiler trips were
also considered for establishing a new steam reserve strategy.
Analyzing all operating parameters in detail, the plant's team
recommended maintaining a steam reserve between 350,000
lb/hr and 650,000 lb/hr (equivalent to one Cogen capacity)
to reduce fuel gas consumption, increase financial benefits
and improve plant EII KPI.
The recommended steam reserve was sufficient to handle
feed fluctuations and plant processing capacity during one
cogeneration or boiler trip. Lowering the steam reserve from
1.1 MMlb/hr to the recommended level reduced boiler fuel
gas consumption; increased boiler loads close to the MCR
limit and enhanced boiler efficiency; eliminated excessive
steam venting, which saved both energy and water; and reduced
the load on excess steam condensers. The new steam
reserve and boiler operation strategy reduced boiler startup/
shutdown frequency, which reduced boiler maintenance costs
and enhanced boiler life span.
FIGS. 1 and 2 demonstrate the reduction in boiler steam reserve
and improvement in plant fuel gas index, respectively.
The actual steam reserve reduced from 1.1 MMlb/hr from
2015-2016 to an average of 490,000 lb/hr from 2017-2020. It
is worth mentioning that this subject strategy was implemented
during the middle of 2017, so from 2018-2020 the average
steam reserve was maintained at 423,000 lb/hr. Similarly,
due to the reduction in the steam reserve, the fuel gas index
reduced from 36 sft3
/bbl (2015-2016 average) to 27 sft3
/bbl
(2017-2020 average).
Maintaining steam reserve between 350,000 lb/hr and
650,000 lb/hr resulted in a savings of 242 MMBtu/hr of energy
due to the increase in boiler MCR and efficiency. This
lowered fuel gas consumption, eliminated steam venting and
reduced excess steam condenser load.
Adip propane trim heater shutdown. The purpose of the
Adip unit is to remove H2
S and COS contaminants from C3
hydrocarbon streams produced from the depropanizer column
overhead to meet product and environmental performance
specifications. The Adip unit must also be operated in such a
way as to provide efficient operation of downstream treating
units: merox and molecular sieve dryers. The objective of the
Adip propane trim heater is to increase propane temperature
downstream of the extractor and before the mixer settler configuration
in all modules. Using 60-psig steam, the Adip propane
trim heater heats C3
to 135°F to ensure proper ADIP/
propane mixing. Mixing ADIP and propane helps to remove
any remaining COS from the propane product after the extractor
in the mixer settler configuration. An Adip propane process
configuration is shown in FIG. 3.
An assessment was completed to check if Adip propane trim
heaters in all modules can be shut down to save energy without
impacting the product sulfur specifications. A field test was
ADIP propane trim heater
Using 60-psig steam, E-146
heats C3 to 135°F to ensure
proper ADIP/propane mixing.
Mixing ADIP and propane
helps to remove any
remaining COS from the
propane
E-146
FCV
C-141
Settler Pump
From ADIP cooler
G-148 A/B
Liquid propane from depropanizer
reflux pump
FIG. 3. Adip treating overview.
conducted by bypassing the Adip propane trim heater in Module
1 and 3 for almost 1 yr to span an entire winter and summer.
During this shutdown, periodic lab results were analyzed for
H2
S and COS removal impact and to determine any impact on
the net product sulfur specifications. The long period data analysis
revealed no sulfur removal impact due to the subject heater
bypass, and total product sulfur, H2
S and COS from the Adip
unit during both summer and winter periods remained intact.
Based on the test results, it was decided to shut down and
mothball the Adip propane trim heaters in all modules. One
reason the product sulfur specification was not impacted as
a result of the trim heater bypass was that the plant receives
significantly less acid gas (H2
S and COS) along with feed
compared with the design value. This was confirmed by comparing
the design and actual acid gas loading based on feed
composition analysis and the actual acid gas flaring flowrate
vs. its design value. Therefore, bypassing the subject heater
had no impact on meeting the product sulfur specifications.
Shutting down the propane trim headers resulted in a total
steam savings of 50,400 lb/hr of energy, or 45 MMBtu/hr.
Additionally, shutting down the subject heaters resulted in a
~1.5 % reduction in the overall plant EII.
LPG dehydration system regeneration cycle automation.
During a routine LPG dehydration unit breakthrough test, it
was noticed that the fractionation modules dehydrators heating
cycle duration was fixed at 11 hr, while the required duration
varies depending on the molecular sieves' performance
and condition.
As per industry best practices and desiccant supplier/
vendor recommendations, regeneration heating should be
completed once the temperature difference between the vessel
inlet and outlet stabilizes at 27°F-36°F over a period of
45 min-60 min. Therefore, it was recommended to automate
the heating cycle duration to be linked with the inlet and outlet
temperature differences to achieve the optimum heating
cycle duration to avoid overheating the molecular sieves and
conserve energy. This brings an estimated steam savings of
9,500 lb/hr, or 9 MMBtu/hr.
Molecular sieve process description. At any given time,
one of the dehydrators will be adsorbing water from the feed,
Gas Processing & LNG | SEPTEMBER/OCTOBER 2021 25
To ADIP flash
drum D-150
Treated propane
to merox unit
Coalescer
Settler
Mixer
ATM
Settler
G-147 A/B
Condensate
tank
Hydrocarbon Processing - October 2021

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