Hydrocarbon Processing - December 2021 - GP-36

PLANT OPTIMIZATION
requires high pressure drop for cooling
and requires the highest quantity of fuel
gas for sales gas compression.
Mechanical refrigeration technology
requires the lowest pressure drop and
lowest quantity of fuel gas; however, this
saving in energy is partially offset by running
the refrigeration compressor.
Turboexpander technology requires a
higher pressure drop for expansion than
a mechanical refrigeration unit, but the
expander and compressor partially compensate
for this.
Recompression requirements. ReFIG.
5. Process scheme for JT valve technology.
compression is required for JT valve
technology, whereas other technologies
do not require recompression, since their
pressure letdown is low.
Feed gas
requirements. Turboexpander
technology can be used for high
feed gas flowrates; however, other technologies
can be used for a wide range of
feed gas flowrates.
Sales gas specification. Sales gas
specifications can be met through all of
the compared hydrocarbon dewpoint
technologies.
Recovery. Sales gas recovery with JT
FIG. 6. Phase envelope for lean sales gas after processing through a JT valve-based hydrocarbon
dewpoint control unit
Application pros and cons. The application
of the JT valve technology processing
route has a number of benefits
and challenges:
* For small, high-pressure feed gas
streams, JT valve is the technology
of choice to yield on-spec
hydrocarbon dewpoint sales gas
* High turndown ratio can be
achieved with this technology
* It is a self-refrigeration process; no
external cooling medium is required
* It requires high pressure drop, and
pressure that is dropped across
the JT valve cannot be recovered;
energy is required to recompress
the on-spec dewpoint gas as per
sales gas injection pressure
* JT valve technology has the
capability to operate on high
turndown, with ease of operation.
Technical comparison of technologies.
Key technology features are compared
in the following sections.
Operation. In the absence of complex
rotating equipment like a turboexpander
or a refrigeration compressor required
for cooling, JT valve technology
has a simple and flexible operation.
Turndown ratio. JT valve technology
has the highest turndown ration
among the proven technologies.
Turboexpander technology has the
lowest turndown ratio among all the options,
as a centrifugal compressor is an
integral part of the turboexpander.
With the use of a screw compressor
as part of the mechanical refrigeration
unit, turndown almost equal to that of JT
valve technology can be achieved.
Reliability and availability. JT valve
technology has the highest
valve technology and NGL recovery with
mechanical refrigeration technology are
highest; however, simulation operating
parameters used will have
an effect on
these recoveries.
Takeaway. The basis application for
each type of hydrocarbon dewpoint
technology should be considered against
the specific requirement of the gas to be
processed. The capital cost of each technology,
which is not considered in this
article, should also be taken into account
along with the limitations and suitability
of the technologies discussed in this article.
The better the technology selection,
the more optimum will be the results. GP
NOTES
a HYSYS
reliability
among all considered options, whereas
turboexpander technology has the lowest
reliability due to the number of rotating
equipment.
Pressure drop. JT valve technology
36 NOVEMBER/DECEMBER 2021 | GasProcessingNews.com
ASAD ASHFAQ LODHI is a
Process Engineer with Zishan
Engineers Pvt. Ltd in Karachi,
Pakistan. With 10 yr of professional
experience in process engineering,
particularly in the gas processing
and refining sector, Mr. Lodhi has
experience in FEED, detailed engineering and
feasibility studies for various oil and gas processing
plants and refineries. Prior to joining Zishan
Engineers, he worked at Descon Engineering.
He holds a BS degree in chemical engineering
and an MS degree in project management, as well
as a NEBOSH International General Certificate.

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Hydrocarbon Processing - December 2021

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