Hydrocarbon Processing - October 2021 - GP-26

GREEN TECHNOLOGIES
while the other will be in the process of being heated or cooled
to regenerate the desiccant online mode. Initially, wet product
passes through the operating dehydrator, then is dried and
pumped to the refrigeration, storage and/or export areas of the
plant, as shown in FIG. 4.
The bed is switched to the regeneration cycle after being
saturated with water. In this mode, a slipstream of dried product
liquid is recycled to regenerate the molecular-sieve beds.
The recycled liquid is vaporized with low-pressure stream,
superheated to temperatures of 460°F with a high-pressure
steam, and then routed to the wet tower to remove the previously
adsorbed water.
Moisture detector
Dry product
As the temperature within the tower increases, the water
captured within the pores of the desiccant turns to steam and is
absorbed by the regenerated gas. This gas leaves the bottom of
the tower and is cooled by an air-cooled condenser. When the
gas is cooled, the saturation level of the water vapor is lowered
significantly and water is condensed. The condensed liquid is
recycled to the appropriate upstream reflux drum.
The heating cycle last approximately 11 hr. When the heating
cycle is completed and the bed has been dried, a cold recycle
liquid is passed in an up-flow arrangement through the tower
to return it to normal operating temperatures (about 100°F-
120°F) before placing it back into service to dehydrate the wet
feed stream. The cooling cycle takes approximately 4 hr.
Breakthrough test results for Modules 1 and 2 showed that
600# steam
Product dehydrator
Product dehydrator
Vaporizer
60#
the fixed duration of the heating cycle is much higher than required.
It was noticed that the required regeneration cycle duration
is much less than the existing fixed time where the molecular
sieves are exposed to overheating and energy is wasted.
The average additional heating time was calculated to be 4 hr.
Therefore, it was decided that the regeneration heating cyWet
product
Reflux drum
FIG. 4. LPG molecular sieve process.
cle duration for all fractionation modules should be connected
to the bed top and bottom temperature difference to optimize
the regeneration cycle. As part of this initiative, the regeneration
cycle logic was modified and linked with the bed top and
bottoms temperature difference. Once the temperature difference
reaches 30°F, the heating cycle should be stopped after
45 min. This logic modification was carried out in one of the
module's C3
dehydration systems; after closely monitoring all
and C4
operating parameters for 6 mos, the same logic modification
was implemented in all of the module's C3
dehydration
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cycles. During the testing period, the bed temperature profile
and time interval between consequent absorption cycles were
closely monitored to ensure no adverse impact on bed performance
due to subject modifications.
Implementing the aforementioned recommendation led
to a savings of 9,500 lb/hr of steam, or 9 MMBtu/hr of energy,
and enhanced the molecular sieves life by approximately
15%-20% by avoiding unnecessary overheating.
Takeaway. The successful implementation of several in-house
energy optimization initiatives resulted in 296 MMBtu/hr of
energy savings, reduced plant operating cost, improved EII,
and lowered nitrogen oxide (NOx
) and sulfide oxide (SOx
)
emissions. These results could not have been achieved without
collaborative efforts by operations, engineering and maintenance
teams. GP
PUKHRAJ GARG has worked as Lead Process Engineer with
Saudi Aramco`s Ju'aymah NGL fractionation plant since 2012.
He is a certified PE Engineer with more than 17 yr of experience
in the oil and gas industry. He previously worked with Reliance
Industries, UOP and Dupont as a process engineer. Mr. Pukhraj
holds BS and MS degrees in chemical engineering from Indian
Institute of Technology (IIT) Bombay, Mumbai, India and an
Executive Post Graduate Diploma in capital and finance from Indian Institute of
Foreign Trade (IIFT), New Delhi, India.
NAWAF M. MENAIKHRR has worked as Inspection Unit
Supervisor with Saudi Aramco's Ju'aymah NGL fractionation
plant since 2015. He has also worked as a process engineer in
several NGL plants. Mr. Nawaf holds a BS degree in mechanical
engineering from King Saud University, Riyadh, Saudi Arabia.
26 SEPTEMBER/OCTOBER 2021 | GasProcessingNews.com
http://www.GasProcessingNews.com
Hydrocarbon Processing - October 2021

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