Pioneering
ethane
technology
Christopher Campos, Ebara International Corp.,
USA, discusses the development of ethane
technology, providing a logistical view of natural
gas liquid products.
M
ichael Faraday is considered by the electrical
engineering community to be one of the
forefathers of induction. Faraday performed
years of distinguished research in electrical
systems, magnetism, material properties and equations. He is
most famous for his theory of induction, which has become
part of the now famous Maxwell Equations. Faraday stated:
“The induced electromotive force in any closed circuit is equal
to the negative of the time rate of change of the magnetic flux
enclosed by the circuit.” This one statement, and associated
equation, resulted in multiple research opportunities and
spawned a new segment for what would become the field of
electo motive force or EMF:
O
ІB =
∫ ∫ B(r, t ) . dA
Σ (t)
It is not apparent how much of an impact
Michael Faraday had on the world of electromagnetism until
one begins to research transformers, reactors, motors,
generators, and even hydrocarbons such as ethane. Faraday
experimented with his theory of induction to the greatest
extent possible in 1831. The general concept of his theory can
be simply represented in Figure 1.
Since alternating current (AC) was not discovered yet,
Faraday had to use the only captured source of electricity at
the time, the direct current (DC) battery (or voltaic cell). The
DC battery supplies a constant stream of current if
connected by a closed conductor loop. Inherently,
magnetism is not associated with it, only an electrical force
from the battery (potential energy). Faraday found that if he
used a common iron object and wrapped the conduit around
half of it and then wrapped a separate closed conduit
around the other half, current would flow through the
second closed loop. Of course, this would appear as magic
back in the 1830s, but Faraday (with independent credit to
Joseph Henry as well) discovered that there was a second
force taking place and that this second force could induce
the electrons in the second closed circuit to move. This
force would be known as induction (Figure 2).
James Clerk Maxwell would take the work of
Michael Faraday, Joseph Henry, Carl Friedrich Gauss,
André-Marie Ampère, and other well noted scientists to
complete the set of famous Maxwell Equations, which
provide the fundamental understandings of the
electromagnetic force (Figure 3).
So how does Michael Faraday relate to ethane? In 1834,
Faraday was applying his electrolysis process (method of
using electrical current through a beaker solution to
determine the resulting outcome) on a potassium acetate
solution. A current applies an electrical force to the solution,
Figure 1. Faraday experiment.
Figure 2. Induction diagram.
Figure 3. Maxwell Equations.
which essentially tears apart the molecules. This resulted in a
hydrocarbon that he initially took for methane.
Independently, research in organic chemistry was testing
ethane by reductions with ethyl cyanide, ethyl iodide with
potassium metal creating aqueous acetates. It was 30 years
later that Carl Schorlemmer correctly concluded that
Michael Faraday’s byproduct was actually ethane, or C2H6.
Ethane via ship
Today, ethane is commonly produced both naturally and as a
byproduct of natural gas liquids (NGLs) from the liquefaction
process of natural gas. Although ethane is abundant at any
natural gas deposit, few LNG processes actually harvest it for
sale. Most ethane is often flared off as a byproduct. However,
the US shale gas boom has led to the separation and
production of large quantities of ethane during the low
temperature liquefaction process from the NGLs.
Reprinted from August 2015
HYDROCARBON
ENGINEERING
Ebara International Corporation, Cryodynamics Division
(EIC Cryo) is no stranger to supplying submerged motor pumps
for liquid ethane and other hydrocarbon liquids. EIC Cryo has
a 40 year history of propane, butane, ethane, ethylene, and
propylene pumps. Most of these applications have been for
land based petrochemical plants. Recently, EIC Cryo has seen
an interest for these hydrocarbon applications for marine
applications. LPG has commonly been traded via LPG marine
carriers around the world, similar to LNG carrier trading.
However, the market for international ethane trading has been
relatively small. Typically, gas carriers have tank volumes
under 30 000 m3.
Recent investment in larger gas carriers was spurred on by
the low cost of US shale gas, with petrochemical plants in
Europe and Asia hedging their future feedstocks on this
supply. This is the case of Reliance Industries, which invested
in the world’s largest gas carrier being constructed by Samsung
Heavy Industries (SHI) in Goeje, Korea. This very large gas
carrier (VLGC) will have a capacity of 87 000 m3 and will haul
mostly liquid ethane feedstock from the US to the Jamnagar
Refining and Petrochemical Complex in Gujarat, India. EIC Cryo
has been awarded the contract to design and manufacture a
submerged motor cargo pump for offloading the liquefied
ethane. Ethane feedstock is somewhat unique in that it is very
inconsistent. Unlike typical methane LNG carriers, the
temperature and density of the ethane feedstock can vary
widely based on the refinery process. EIC Cryo had to develop
a pump that could handle ethane’s coldest range (-100˚C) to a
potential butane laden range of (+0˚C). Additionally, densities
of the product could range from 550 kg/m3 to 610 kg/m3.
In 2008, EIC Cryo performed a technical evaluation that
resulted in installing test fluid transfer pumps in Ebara’s test
facility to transfer LNG or LPG from the test system to the
storage system. This meant that the transfer pumps would
have to be designed for two different hydrocarbons.
Operating temperature range was -168°C to -34°C.
As part of the independent evaluation, EIC Cryo chose the
reliable 2EC-092 pump model that is installed on hundreds of
LNG carriers and LPG carriers. These pumps have proven
reliable and efficient and have generally run for more than
16 000 hours between overhauls. As EIC Cryo performs tests
every day, the pumps would be subjected to multiple starting
and stopping sequences, a long maintenance interval and a
high reliability requirement.
The submerged motor cargo pump, relatively speaking, is a
very simple design (Figure 4). It consists of a motor designed
to be submersed in the pumping fluid, a single piece
construction shaft/rotor assembly, impeller, diffuser and
inducer for low NPSHR. The pump is held together by the
pump and motor housings. The final piece is an end bell
housing, which accommodates the electrical power cables for
the motor, upper motor bearing and discharge nozzle.
As these pumps are designed for low temperature service,
all of the components have to be rated for low temperature
service as well. Additionally, fluid density will affect the
pump’s performance and fluid velocities, requiring more
power for denser fluids. The bearings were specifically
designed by EIC Cryo for low temperature and low viscosity
service. The bearing designs are proprietary of EIC Cryo and
designed to work specifically with submerged motor pumps.
As with the rest of the pump components, the bearing races
and liners have to be sized for the specific fluid temperature
and density it is being designed for (Figure 5).
Ethane applications
Over the years, EIC Cryo has developed a reputation for
innovative and ground breaking technology. EIC Cryo truly is
an engineer to order based company; however,
manufacturing costs for this type of business model can be
expensive and sometimes price is the driving factor for
turnkey projects. This leaves advancements in technology to
corporations who are willing to invest in the next generation
of gas products.
This is the case for Wärtsilä, which has recently developed
and completed testing on its ethane rated 50DF duel fuel
engine. The idea of using ethane as a reliable fuel source is a
novel concept, which could allow the use of boil off gas
(BOG) from the ethane tanks to power a ship’s engine. This is
similar to conventional LNG carrier designs. EIC Cryo has
already invested in this concept with adaptions of current
stripping/spray pumps and dedicated fuel gas pumps to pump
liquid ethane.
Other recent areas of development include high pressure
ethane pumps for regasification to a vapouriser, which are
already in operation. EIC Cryo has received interest from
several parties about taking this process to a marine
application and designing an ethane FSRU.
EIC Cryo is also exploring the development of an ethane
expander to help increase the production efficiency of
liquefying the ethane product. LNG liquefaction
plants have utilised cryogenic expanders for
years to improve their overall efficiencies. By
reducing a portion of the pressure of the LNG
and mixed refrigerant streams across an expander
instead of using a Joule-Thomson valve, the
enthalpy of the stream is reduced, resulting in
lower boil off losses and cooler outlet
temperatures.
Figure 4. 3D cargo pump rendering.
Submerged motors
Submerged motor pumps incorporate detailed
design and physical understanding of hazardous
gas areas. Without the understanding of
hazardous area zones, the concept of the
submerged motor pump could not operate.
Inside a sealed tank environment would be
classified as a Zone 0 (using typical IEC
nomenclature) or non-hazardous, as there is no
Figure 5. Differential pressure from the pump based on different
presence of oxygen. Within a few metres outside
liquid densities.
of the sealed flanged, due to the presence of
oxygen, a hazardous area exists. Should any
Additionally, submerged motor pumps do not require a
leakage occur, then any spark, fire or flame must be contained
mechanical seal or any other sealing device that could be a
per the requirements of the project (NEC, IEC, IECEx, etc.).
source for gas leakage.
Beyond this hazardous zone, the likelihood of explosion or fire
The major component of the submerged motor pump is
is reduced, but electrical equipment must still meet
the motor itself (Figure 6). The motors are of 3 phase, squirrel
requirements of the project (NEC, IEC, IECEx, etc.).
cage, induction design. The stator is fabricated from silicon
Since submerged motor pumps are completely installed
iron laminations and form or random wound copper windings.
inside of the sealed tank environment and the motors are
The windings are protected with an epoxy insulation applied
rated for low temperature service, the pumps can operate
via a vacuum impregnation process to remove air pockets
without the potential for creating a spark, fire or explosion.
HYDROCARBON
ENGINEERING
Reprinted from August 2015
using his theory on an induction motor application (this would
come from another forefather of electricity, Nikola Tesla 1887),
the evolution of this induction technology continues to
advance. In 1929, Pleuger Pumps developed submersible turbine
pumps used in the oil industry. The 1960s saw the first deep
well submersible water pumps. In 1958, the first submerged
motor LNG pump was used on the Methane Pioneer.
Bibliography
Figure 6. Form wound motors being prepared for
epoxy insulation.
during the curing process. The rotor is also made from silicon
iron laminations and then completed with aluminum bars
between the two aluminum end caps. The end caps can be
cast in place or prefabricated. The major consideration is the
tensile stress induced in the bars as the rotor is cooled to
cryogenic temperatures. The differential thermal contraction
properties of the aluminum bars and the silicon iron
laminations must be carefully considered by the motor
designer.
Finally, the submerged motor owes its birth right to
Michael Faraday and his theory of induction leading to the
concept of electrically induced magnetism. Although one
could not know if Faraday had the forethought to think about
Reprinted from August 2015
HYDROCARBON
ENGINEERING
1. 'Frequently Asked Questions About Ethane Crackers', http://www.
alleghenyfront.org/story/frequently-asked-questions-about-ethanecrackers.
2. 'Michael Faraday’s Law of Induction', http://en.wikipedia.org/wiki/
Faraday%27s_law_of_induction.
3. 'Ethane', http://en.wikipedia.org/wiki/Ethane.
4. 'The History of Submerged Motor Pumps in the LNG Industry',
Michael Cords, 24 February 2011, http://www.ebaraintl.com/
technical-papers/the-history-of-submerged-motor-pumps-in-thelng-industry.com.
5. 'Expansive Thinking', Christopher Finley, Hydrocarbon Engineering,
May 2013, http://www.ebaraintl.com/news/expansive-thinkingtwo-phase-liquified-gas-expanders-for-improving-lng-liquefactionplant-efficiency.com.
6. 'South Korea Samsung Heavy Industries to build world’s first
very large ethane carriers for Reliance', Platts, Ramthan Hussain,
Pardeep Rajan, Philip Vahn, E. Shailaja Nair, http://www.platts.
com/latest-news/petrochemicals/singapore/south-korean-samsungheavy-to-build-worlds-first-27535836, 15 August 2014.
7. 'Samsung secures $720 VLEC contract from Reliance', TradeWinds,
Iren Ang Singapore, http://www.tradewindsnews.com/
weekly/341643/Samsung-secures-720m-VLEC-contract-fromReliance, 25 July 2014.
8. 'Wärtsilä 50DF engine successfully demonstrates its capability
to operate on ethane gas', Wärtsilä Corporation Press Release,
4 May 2015, http://www.wartsila.com/media/news/04-05-2015wartsila-50df-engine-successfully-demonstrates-its-capability-tooperate-on-ethane-gas.