Regasification modules for onboard applications offer multiple benefits master

Regasification modules for onboard applications offer multiple benefits

Wärtsilä Oil & Gas Systems (formerly Hamworthy Oil & Gas Systems AS)regasification modules are designed for use on Floating Storage and Regasification Units (FSRUs) and Shuttle and Regasification Vessels (SRVs).

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Demand for new LNG (liquid natural gas) importation projects is firm, particularly in developing economies. Historically, LNG has been transferred to shore-based terminals for storage in tanks, and then regasification and pressurizing with vaporizing equipment before being delivered to the distribution networks . Rapidly growing needs for LNG have, however, resulted in the development of solutions during the last ten years that are faster and that reduce time, and therefore costs. Placing regasification (regas) equipment onboard allows high-pressure gas to be delivered to land-based networks, either via a floating buoy and submerged pipeline system from an offshore location, or via loading arms on a jetty. Compared to onshore regas facilities, both SRVs and FSRUs offer flexible solutions with a short time from investment decision to start-up. As such, they represent a fast-track way of opening energy markets to natural gas, thereby increasing supply diversity, reducing costs and offering environmental benefits.

Five years of progress

The history of regasification technology within Wärtsilä Oil & Gas Systems is relatively short. A test facility was developed as a joint investment project with Norwegian ship owner Leif Høegh & Co in 2006-2007. Located at Kollsnes in Norway, it was a smaller scale version (approximately 1:1000) than the commercial plants subsequently delivered. Both propane-based and steam-based regas solutions, which are described later in this article, were successfully proven and demonstrated to potential customers from all over the world.

Regas equipment was delivered in 2008-2009 for the Neptune and Cape Anne, the two SRVs being used in the GDF SUEZ Neptune project in the USA. This steam-based solution began operating in 2010. 
Located 10 miles off the coast of Massachusetts, the Neptune deepwater port project was designed to meet New England’s growing demand for natural gas.

Golar LNG’s Golar Winter, part of the Petrobras VT1 project in Guanabara Bay, Rio de Janeiro, was started up in 2009 and has now operated successfully for almost three years. Employing a propane-based regas system, the Golar Winter is capable of supplying gas in quantities sufficient to  generate a major proportion of the electrical energy required by Rio de Janeiro.

Golar LNG’s Golar Freeze is part of the Shell/DUSUP project in Dubai. A propane-based system with one suction drum and three regas process trains, it began operating in 2010 and is designed to supply gas for generating the electrical power required by air-conditioning systems during the summer months.

Common to all of these projects – Neptune, the Golar Winter and Golar Freeze - were complications resulting from the regas system components being delivered on separate skids and the interconnection work being carried out by shipyards.

Developments in 2009-2010 included an improved and patented propane-based regas solution. This incorporates all seawater heating via semi-welded plate heat-exchangers that are easy to clean, and 
a patented recondenser system for recovering boil-off gas. To avoid the interconnection problems, it was decided that equipment should be delivered as complete modules, thereby eliminating the requirement for interconnection work by shipyards and reducing the time required for hook-up to vessel or jetty. Two systems have been recently delivered with these improvements: Golar Khannur for West Java, and Petronas JRU for Melaka.

In addition to the six systems already delivered, Wärtsilä Oil & Gas Systems is currently executing orders for three more. The company has supplied about half of the floating regas units now in operation around the world (see Figure 1).

Regasification modules for onboard applications offer multiple benefits 4
Fig. 1 – Wärtsilä Oil & Gas Systems - projects delivered and under construction.
Regasification modules for onboard applications offer multiple benefits 5
Table 1 – Comparison of propane-seawater and steam-water-glycol systems.

Expanding LNG carrier functionality

Adding regas systems to LNG carriers - SRVS or FSRUs - presents a new set of challenges in terms of both equipment size and integration into the vessel’s existing systems. Also, equipment that was previously located on land must be redesigned to accommodate the unpredictable motion of a seagoing vessel.

Typical deliveries consist of systems that use either steam or seawater for heating and regasifying the LNG. These systems are described in detail on page 32. The choice of heating media usually depends on local regulations and the prevailing climate in the vessel’s operational location. Systems that use seawater as a source of heat to vaporise LNG are more economical than systems which use steam. This is because a steam system requires the burning of fuel at a rate equivalent to some 2.5% of the amount of LNG produced. The energy requirement in a seawater based system is far less as energy is needed only for the pumps.

Heating with an intermediate fluid is utilised in both steam-based and seawater-based systems. A typical system, such as that shown in Figure 2 installed on a conventional LNG carrier, will have a total  export capacity in the range 170-840 tons/h (200-1,000 MMscf/d). Each train typically has an output of 40-210 tons/h, and complete systems comprise several trains with one or more providing redundant capacity. Delivery pressures are in the range of 30-130 bar and depend on the pressure in the receiving grid.

Dedicated pumps in the cargo tank supply LNG to the suction drum, usually at a pressure of approximately 5 bar, i.e. at a temperature below its boiling point at the current pressure. The suction drum acts as a buffer tank, and also as a gas separator to handle gas and liquid returned from the regas trains during certain modes of operation. The pressure of 5 bar means that LNG fed to the trains from the suction drum is a subcooled liquid. In the regas trains, the LNG is pressurised in multi-stage centrifugal pumps and then regasified in the vaporisers. The output of each train is high-pressure (35 - 120 bar) natural gas.

regasification
Fig. 3 – Propane system using direct seawater shell-and-tube heaters .
Regasification modules for onboard applications offer multiple benefits 6
Fig. 4 – New and improved two-stage propane loop (patented).

Steam-based systems

The steam-heated regas system delivered to the Neptune project by Wärtsilä Oil & Gas Systems uses a water-glycol mixture as the intermediate medium. US Coastguard policy for the area meant that it required a solution where seawater could not be used as a source of heat. Neptune consists of two membrane-tank-type SRVs, an offshore terminal with two buoys, and pipelines to shore.

Both vessels are equipped with three regas trains located in front of the trunk behind a large wavebreaker. The suction drum is located on the trunk deck close to the regas trains. Each regas train has a capacity of 210 tons LNG/h and a target send-out pressure of 46-120 bar. All three trains can be operated simultaneously if required.

The main benefit offered by steam-based systems is the fact that the equipment is relatively small. As the heating medium is at a high temperature, the heat exchangers are compact and the regas trains have a small footprint and low weight, making locating them easier.

The drawbacks with steam-based systems are both economical and environmental. From an economic perspective, if LNG is used to produce power for the trains and steam for the vaporisers, approximately 2.5 tons of each 100 tons of LNG processed will be used for these purposes. From an environmental perspective, even though LNG is a relatively-clean power source, the CO2 emissions that result from onboard power and steam production are significant (see Table 1 for a system comparison).

Seawater heating using propane as the intermediate medium

Seawater-heated regas systems that use propane as the intermediate medium have been supplied by Wärtsilä Oil & Gas Systems for two Golar LNG vessels: the Golar Winter and Golar Freeze. On charter to Petrobras, the Golar Winter is a membrane-tank-type FSRU whose initial location was Guanabara Bay. It will eventually be moved to the PECEM terminal close to Fortaleza in northern Brazil. The Golar Freeze is a spherical-tank-type FSRU on charter to Shell/DUSUP and located in Dubai.

Both the Golar Winter and Golar Freeze are equipped with three regas trains, each with a processing capacity of approximately 230 tons/h. Two of the three trains can be operated simultaneously giving a total capacity of some 460 tons/h.

The Golar Winter system can deliver gas at pressures of up to 105 bar. Because the Dubai grid has a low maximum pressure and lower pump pressures save energy, the LNG pumps in the Golar Freeze were delivered de-staged with a delivery pressure of approximately 70 bar. As the remainder of the Golar Freeze regas system is designed to operate at up to 105 bar, the de-staged pumps can be replaced with full-pressure pumps if the vessel is relocated at a future date. 

Regasification modules for onboard applications offer multiple benefits 8
Fig. 5 – Conventional method of recovering (recondensing) boil-off gas.
Regasification modules for onboard applications offer multiple benefits 7
Fig. 6 – Wärtsilä Oil & Gas Systems’ improved and patented boil-off gas recondenser system.

Current projects

Two of the new and improved systems have recently been delivered to Indonesia and Malaysia, and three new regas projects using equipment delivered by Wärtsilä Oil & Gas Systems are currently ongoing. In Indonesia, the seawater-propane regas unit on Golar LNG’s Golar Khannur FSRU, part of the PT Nusantara Regas project in Jakarta, was successfully started up this summer.

Each of the Golar Khannur’s three process trains can process 200 tons/h, and the whole system has a send-out capacity of 500 MMscf/d. It is a “3 x 50%” system, which means that each train can supply 50% of the system’s maximum capacity, and it was delivered as a single 22*20*12-metre module with a dry weight of 25*18*12-metre weight 720 tonnes. The patented boil-off gas recondenser on each train has a capacity of 6 tons/h.

In Malaysia, the Jetty Regasification Unit (JRU) for the Petronas Gas Berhad project at Melaka Jetty was delivered in January 2012, with start-up scheduled for September 2012. Also using seawater-propane technology, the three trains on the JRU each have a processing capacity of 221 tons/h (3 x 50%) and the system has a maximum export capacity of 500 MMscf/d at 70 bar. Delivered as a single-lift, 32x20x13-metre module with a dry weight of 945 tonnes, the patented boil-off gas recondenser on each train has a capacity of 24 tons/h. The reason for the size being larger than that of the Khannur is the large recondensing capacity on JRU.

Wärtsilä Oil & Gas Systems is also supplying Høegh LNG with regas modules for three FSRU newbuildings. All three will be equipped with seawater-propane systems. The PGN Lampang project has three 112 tons/h trains (3 x 33%) and a maximum send-out capacity of 380 MMscf/d. It will be delivered as a single-lift, 20x18x13-metre module with a dry weight of 535 tonnes.

The KlaipedosNafta project in Lithuania, comprising four 115 tons/h trains (4 x 33%) with a maximum send-out capacity of 390 MMscf/d, will be delivered as a single-lift,  25x18x13-metre module with a dry weight of 700 tonnes. The third delivery for Høegh LNG will go to a FSRU sponsored by Colbún S.A. and AES Gener S.A. in Chile. Start-up of this project is scheduled for late 2014.

All Wärtsilä Oil & Gas Systems’ current projects feature the company’s improved and patented seawater-propane solution and patented boil-off gas recondenser solution.
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Fig. 7 – A log PH diagram for Wärtsilä Oil & Gas Systems’ improved and patented boil-off gas recondenser system.
Regasification modules for onboard applications offer multiple benefits 10
Regasification modules for onboard applications offer multiple benefits 11
Fig. 8 – The regas modules supplied by Wärtsilä Oil & Gas Systems feature an uncomplicated vessel interface and rapid hook-up.

Customers benefit in many ways

The modular regas units offered by Wärtsilä Oil & Gas Systems offer a simple and uncomplicated vessel interface, a small number of connections for rapid hook-up (see Figure 8), a choice of heating sources: steam/seawater/combined, easy operation, and quick ramp-up/ramp-down.

Typical delivery times are 12-16 months. The compact equipment design has a small footprint and the use of  propane as the intermediate medium eliminates the possibility that the seawater employed will freeze during operation.

Future synergies

While the regas units supplied by Wärtsilä Oil & Gas Systems offer significant benefits as stand-alone systems, combining them with equipment supplied by Wärtsilä Power Plants allows ‘total scope’ technical and commercial solutions to be offered for both onshore projects and offshore applications such as power barges.

Wärtsilä already supplies EPC power systems (EPC=total Engineering, Procurement and Commissioning contract for the whole terminal), and contracts of this type can also involve supplying gas for a pipeline system. In such cases, the regas equipment can be a part of the total EPC contract. Also, as exhaust gases from the engines in a Wärtsilä power plant contain a lot of heat energy, this can be used in the regasification process.

In cases where all the heat required for regasification can be supplied from exhaust gas, a simple direct ethylene glycol-based regas system using elements of the existing steam-based system is probably the best choice. In cases where the amount of heat that can be obtained from exhaust gases is insufficient, a propane-based solution which uses heat from other sources can be employed.

An EPC solution of this type could in fact constitute a complete combined gas importation terminal and power generation facility, comprising LNG storage tanks, an import jetty, boil-off gas compressors, regasification system, pipework, a 400 MW (or higher output) Wärtsilä power plant and all the required automation and control facilities. Waste energy from the power plant would be used in the regasification system. The ability to deliver a total scope facility of this type and scale represents a significant competitive edge.

Wärtsilä Oil & Gas Systems – LNG regasification solutions

Wärtsilä Oil & Gas Systems is a leading supplier of technology and topsides for floating LNG regasification (regas) facilities. The company’s scope of supply includes the delivery and commissioning of floating LNG regas plants based on either closed-loop technology using steam with water-glycol as the intermediate heating medium, or open-loop technology using seawater with propane as the intermediate heating medium. Similar modular regas plants are available for jetty installation, and compared to traditional shore-based LNG regas terminal projects, solutions of this type allow much shorter  construction schedules. 
 The Wärtsilä Oil & Gas Systems portfolio of LNG regas technologies represents a mature industry benchmark in terms of energy efficiency, robustness and operational flexibility. Solutions are available either as multi-skid deliveries, or as complete turnkey and single-lift topside modules. In addition to pre-contract studies, engineering, construction, installation and start-up, a complete spectrum of services for maintenance, training and operational support is available.

Steam-heated regasification systems

Systems of this type can be used in areas where regulations prevent the use of heat from seawater to vaporise the LNG. Each unit has one or more booster pumps installed in canisters and is designed for send-out pressures of up to 130 bar. The LNG is vaporised by pumping it through a shell-and-tube heat exchanger with the heat being supplied from a water-glycol mixture heated by steam from an onboard system. The natural gas is then sent to the export manifold.

Cascade propane-seawater regasification systems

In cascade regasification systems, LNG is heated using propane in a closed-loop system with the heat being provided by seawater. In situations where the seawater is too cold to supply the required amounts of heat, its temperature can be raised using any available source of heat.

The cascade concept is preferable to arrangements that directly exchange heat with seawater as the latter can increase the risk of the seawater freezing in the heat exchanger. Propane is a satisfactory intermediate fluid because of its thermodynamic properties (it has a lower freezing point than LNG). A HAZID analysis carried out in cooperation with DNV concluded that cascade systems are safer than purely seawater-based systems.

Main advantages of the Wärtsiläs systems

  • Reliable methods of regasifying LNG with low risks of freezing in the system
  • Proven equipment with extensive references.
  • Operational flexibility with regards to send-out pressure and capacity
  • Compact units
  • Short project implementation schedule
  • Environmentally sound, cost-efficient, safe solution

Wärtsilä Oil & Gas Systems AS (formerly Hamworthy Oil & Gas Systems AS) has 50 years of experience in supplying recondensing and cargo-handling systems to the LPG and marine sectors. More recently, Hamworthy used its experience in cryogenic and marine installations to enter the LNG sector. A total of 35 LNG reliquefaction systems for LNG carriers and four shore-based LNG liquefaction plants have now been supplied.

 

Abbreviations  

LNG
Liquefied natural gas, i.e. natural gas in its liquid state. Cooling natural gas to approximately -160°C at atmospheric pressure turns it into LNG and also reduces its volume by some 600 times, making the long-distance transportation of large quantities an economic proposition.

FSRU 
Floating Storage and Regasification Unit: 
a stationary vessel fitted with regas equipment capable of storing large quantities of LNG (often a former LNG carrier). LNG is transferred to the FSRU from LNG carriers, vaporised, then sent to a land-based network from an offshore mooring point or via jetty-based loading arms. 

SRV 
Shuttle Regasification Vessel: a ship which transports LNG in large quantities and also uses its onboard regas equipment to vaporise the LNG before sending it to a land-based network. SRVs work in pairs using separate mooring buoys - the brief overlap between one shuttle arriving and the other departing allows a continuous flow of high-pressure natural gas to be sent out. 

JRU
Jetty Regasification Unit: a shore-based 
regas unit located on a jetty. 

FRU 
Floating Regasification Unit: - usually 
a barge equipped with a regas module. 

FRPU 
Floating Regasification and Power Unit: vessel or barge equipped with both a regas module and power-generation equipment. 

PCHE 
Printed Circuit Heat Exchanger: diffusion-bonded heat exchangers that are 4-6 times smaller than conventional shell-and-tube heat exchangers of equivalent duty. With pressure capabilities exceeding 600 bar, they can cope with temperatures ranging from cryogenic to 900°C. Single units can achieve thermal efficiencies of more than 98%. PCHEs can handle several process streams and their design can incorporate additional functions such as chemical reactions, mass transfer and mixing. 

Regasification modules for onboard applications offer multiple benefits 2
Regasification modules for onboard applications offer multiple benefits 3
Fig. 9 – Regasification module for Golar LNG’s Golar Khannur FSRU, part of the PT Nusantara Regas project in Jakarta

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