Ambient air vaporizer
Green FSRU for the future
Presentation at GREEN4SEA
Athens April 6th 2016
Dr. John Kokarakis
Vice President Technology & Business Development,
Africa, S. Europe Hellenic, Black Sea & Middle East Zone
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FSRU Systems (FSRU=FSU+FRU)
► LNG transfer
system
(offloading
system),
► Storage
tanks, (in
ship)
► Boil-off gas
(BOG)
handling
system,
► LNG
pumping
system,
► Vaporization
equipment,
.
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LNG to FSRU
► Add vaporizers, loading arms and extra pumps to the LNG carrier, upgrade its
power, electrical and control systems and you have an FSRU !
► The self supporting Moss type tanks have strong structural integrity and do not
have operational cargo filling restrictions.
► Membrane tank FSRU has a more efficient propulsion system and may be more
attractive if the intention is to continue using the vessel to trade LNG.
► FSRU storage capacity is dictated by the port and supply logistics.
► Large FSRU operating at send out rate 5 to 6 MMTPA requires feeding of about
145,000 m3 LNG every 5th day.
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Regasification module
• LNG is sent from the tanks to the regasification
skid. Which generally comprises of booster
pumps and vaporizers.
• The booster pumps will increase the pressure to
about 85 to 90 bars.
• LNG is vaporized under supercritical pressure to
enhance heat transfer
• Regasification can be both in open or closed loop
mode.
• FSRU involves sound aggregation of shipping
and energy technology, commercial skills and
marine operating experience.
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Vaporizer types and their selection
• Selection should be based on an economic analysis while meeting the
local emissions and effluent requirements.
• In equatorial regions, where ambient temperatures stay above 18°C, use
of ambient air for heating is the optimum choice. In subequatorial regions,
fuel gas firing is required during winter.
• Integration with waste heat recovery from power plants can be
an
attractive option to consider.
• Types of vaporizers:
–
Open Rack Vaporizer (ORV)
(70%)
–
Submerged Combustion Vaporizer (SCV) (25%)
–
Intermediate Fluid vaporizer (IFV)
–
Ambient Air Vaporizers (AAV)
( 5%)
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Open rack vaporizer
► Low operating cost:
water pumping
energy
► Higher investment
costs
► Need of sea water
intake
► Min. temperature
for seawater
required
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Submerged combustion vaporizer
► Lower investment costs
► Need of dedicated fuel gas installation
► High operating cost by gas consumption - 1.5% of gas send-out
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Ambient air vaporizer
• Moderate investment costs
• Need large installation areas
• Dry ambient air preferred
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SUPERORV Tube Construction – Super performance
► Inside each tube, there are turbulence enhancers for better heat transfer
and preventing LNG mist from spilling to the outlet.
► Vapor phase acts as an insulator. It retards ice formation due to
temperature decrease on the outer tube surface.
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SUPERORV tube for Green FSRU
► A new heat-transfer tube (SUPERORV) suppresses icing on the
outer surface of the heat-transfer tube.
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Intermediate fluid vaporizers (IFV)
► They
use an intermediate heat
transfer fluid in a closed loop to
transfer heat from a heat source to
the LNG vaporizers.
► Intermediate fluid can be ethylene
glycol or propylene glycol or other
low-freezing heat transfer fluids
(propane), suitable for the operating
temperatures.
► Heat transfer for LNG vaporization
occurs in a shell and tube exchanger.
► Source of heat for the fluid can be
waste heat, fired heater, seawater, air
heater or cooling tower.
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Closed vs. Open Loop Vaporizer
• Closed loop systems have minimal effects upon the environment (true
for IVF vaporizers as well)
• Recirculating water must be chemically treated with biocides and
corrosion inhibitors, and a percentage of the recirculating water must be
purged periodically from the system which must be treated prior to
discharge.
• Open loop air systems use a tower to heat LNG directly without the use
of a recirculating water stream. However, they require the use of
massive fans being energy guzzlers. Their use is out of question in cold
climates.
• Submerged combustion vaporizers create significant quantities of fresh
water and carbon dioxide. They also cause emissions of various air
pollutants ( nitrogen oxides, greenhouse gases). They consume
significant quantities of fuel (LNG).
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Environmental Impact
• Does the seawater contain significant amounts of heavy metal ions? (they
attack the zinc aluminum alloy coating and will shorten its life)
•
Does the seawater contain significant amount of sand and suspended
solids? (risk of jamming) Need proper intake filtration system to prevent
solids from reaching the seawater pumps and exchangers.
• Intake and outfall must be designed to avoid cold water recirculation.
• Supplementary heating might be needed using boil-off for the heaters.
• Back-up vaporization must be provided.
• Chlorination of the seawater is necessary to slow down marine growth.
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Seawater treatment issues
► Sodium hypochlorite NaClO is injected to maintain a concentration of 0.2
ppm. Elevated concentrations (“shock chlorination”) of 2.0 ppm would be
injected for 20 minutes every 8 hours, during ORV operation.
► De-chlorination of the effluent may be required to meet environmental
standards.
► Environmental studies are required for the gas pipeline routing options. A
geotechnical exploration program with geophysical seismic profiles is
required to determine the feasibility of the gas pipeline routing and burial
requirements (time and money)
► Large self-cleaning seawater intake screen is provided at the pump inlets.
The screens must block small sea life and other biological materials from
entering. Velocity through the screens is limited to 15 cm/sec.
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Sea water discharge
► Warm seawater is supplied by the pumps to the ORV units at a pressure of 3.5 bars.
Cool seawater exits from the bottom collection basin at about 18oC (typically 9°C
cooler than the seawater temperature at the intake) and flows by gravity to the sea.
► The outflow pipe must be designed to discharge the cool seawater at a location
where the ambient seawater temperature is approximately equal to the effluent
temperature.
► In order to minimize thermal effects upon biota it is required to maintain the decrease
in temperature to less that 3oC at the outer boundary of a 100 meter diameter mixing
zone about the discharge point.
.
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Energy recovery
► Regasification of LNG is an energy guzzler. 220 MW are needed for 1.4E+6 m3/h of
8.25 MPa to heat from -160 0C to 20 0C.
► At least part of the energy used in the liquefaction and regasification processes
should be retrieved.
► Cold energy can be recuperated and they depend on the type of regasification used.
The efficiency of the thermal cycle is proportionate to the difference of heat source
and cold source temperatures (Carnot engine).
► LNG can be the cold source in the direct production of electric energy.
► Waste heat from associated gas-operated power plants can be used in LNG
vaporization.
► Source of heat in the Rankine cycle is condensation enthalpy from a steam turbine
and heat of waste gases in the waste boiler.
► The compression takes place in the liquid phase so the required LNG pumping
power is not high.
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Subcritical & Supercritical Rankine cycle in the p–v system
Need working fluids with low
temperature of condensation
Propane better than butane
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Rankine cycle the PTPXG
► The Rankine Cycle is a thermodynamic cycle which converts heat
into work. The heat is supplied externally to a closed loop with a
particular working fluid, and also requires a heat sink. This cycle
generates about 80% of all global electric power.
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Hydrocarbons exploration in Greece
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