Green FSRU for the future - safety4sea.com · Green FSRU for the future Dr. John Kokarakis Vice...

Green FSRU for the future

Dr. John Kokarakis

Vice President Technology & Business Development,

Africa, S. Europe Hellenic, Black Sea & Middle East Zone

Presentation at GREEN4SEA

Athens April 6th 2016

2 GREEN4SEA ATHENS APRIL 6th 2016


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,

.


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.


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.


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) ( 5%)

– Ambient Air Vaporizers (AAV)


Open rack vaporizer ► Low operating cost:

water pumping energy

► Higher investment costs

► Need of sea water intake

► Min. temperature for seawater required


Submerged combustion vaporizer

► Lower investment costs

► Need of dedicated fuel gas installation

► High operating cost by gas consumption - 1.5% of gas send-out


Ambient air vaporizer

• Moderate investment costs

• Need large installation areas

• Dry ambient air preferred


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.


SUPERORV tube for Green FSRU

► A new heat-transfer tube (SUPERORV) suppresses icing on the outer surface of the heat-transfer tube.


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.


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).


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.


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.


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.

.


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.


Subcritical & Supercritical Rankine cycle in the p–v system

Need working fluids with low temperature of condensation

Propane better than butane


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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