FLOATING APPLICATIONS ON THE RISE
Reprinted from the June 2015 LNG Industry
Christopher Campos, Ebara International Corporation, Cryodynamics Division, USA, takes a look at the acceleration of floating applications in the LNG Industry.
Launched from the Wison Shipyard in Shanghai, China, the Exmar Offshore and Pacific Rubiales Energy Caribbean FLNG is making its slow travel across the Pacific Ocean to its new home off the coast of Colombia in the Caribbean Sea. The Caribbean FLNG looks to be the first commissioned FLNG in the modern era of dedicated floating liquefied natural gas (FLNG) production. Scheduled to be commissioned in late 2015, the Floating Liquefaction, Regasification and Storage Unit (FLRSU) will be providing 69.5 MMcf/d of natural gas or 0.5 mtpa. Black and Veatch was contracted for the topside liquefaction process and cooperated on engineering, procurement, construction, installation and commissioning contractor (EPICI) Wison Offshore & Marine Ltd. for the manufacturing.
The FLRSU features the Black & Veatch PRICO® liquefaction system and will supply approximately 140,000 ~ 160,000 m3 of LNG for export on the spot market. What makes this FLRSU different from typical FLNG’s is the regasification capability. This was added to the barge as part of agreement with the owner of the gas field as a way to supply natural gas to onshore Colombia.
Ebara International Corporation, Cryodynamics Division (EIC Cryo) was awarded the contract for the design and manufacturing of high pressure booster pumps to be used in the regasification process. Unlike typical multi-stage, high pressure pumps used on land-based applications, special design had to be utilized for the marine installation and environment. Simple metals such as carbon steel could not be utilized for these applications given the corrosive nature of the marine environment. Additionally, the close proximity of the booster pumps to the hazardous area location required increased safety on enclosures and junction boxes. Finally, there was the simple obstacle of operating a multi-stage high pressure pump on a floating barge. This meant that the submerged motor pump would have to be able to withstand buoyant forces during operation and non-operation. Modeling these forces required Rotor Dynamic Simulations (RDS) to determine the axial and torsional forces bestowed upon the pump from the heave, roll and sway of the barge.
Radial diffusers were selected instead of the classic axial design in order to provide a compact solution to the multi-stage pump. By using a compact radial diffuser (referenced to shaft) to diffuse the LNG from the impeller vane, the impeller can conveniently fit inside of the housing. Compact fluid passages then transfer the LNG from one stage to the next stage via the housings. This results in almost a 20% reduction in pump height and weight. In many cases, hydraulic efficiency can often increase due to the reduced disk friction caused by moving LNG over elongated axial diffusers. The end result to the consumer is a more compact multi-stage high pressure pump with higher hydraulic efficiency.
These evolving technologies are still being explored as the popularity of FSRU’s become more and more popular. The FSRU offers a quick and relatively inexpensive solution to providing natural gas for any number of applications. Additionally, the use of FSRU’s for supplying fuel to power plants is becoming more and more sought after.
MAMMOTH AT SEA
Royal Dutch Shell plc (Shell) started conceptual design of an FLNG back in the mid 1990’s. In July of 2009, Shell awarded the first FLNG contract to French contractor Technip S.A. (Technip) and Korean shipbuilder Samsung Heavy Industries (SHI). The concept was simple – Technip would design the liquefaction process (topside) and SHI would design the hull and storage tanks (hullside). The collaboration of the three super powers was the first of its kind to develop a marine project of this size. Design of the FLNG known as Prelude FLNG and on May 20, 2011, Shell made the final investment decision to construct Prelude.
EIC Cryo has worked with all three corporations in the past; Technip on many land-based receiving and export terminals, SHI on many LNG Carriers and Shell as an overall supporter of submerged motor equipment. EIC has also worked with Shell on many liquefaction projects using the submerged generator expander to increase LNG production and efficiency while reducing boil-off gas. Shell’s understanding of the LNG expander made perfect sense on land-based liquefaction plants, but would it work on a floating vessel?
In 2010 Shell, Technip and EIC entered into FEED on designing an LNG expander for use on the Prelude liquefaction process. The technology for EIC existed, including utilizing a design improvement of an upward flow orientation to improve shaft balancing and reduce vapor bubbles that may cause cavitation. Vapor bubbles naturally rise and will exit out through the discharge nozzle positioned at the top of the expander. Aside from the proven technology, EIC Cryo adapted the electrical components, instrumentation and inlet vessel/headplate for the marine application.
All submerged motor pumps and expanders utilize a dual glass seal conduit connection (feedthru) to provide a barrier between the non-hazardous area and the hazardous area outside of the sealed vessel. This feedthru contains a purge cavity that can be inertly filled and monitored with nitrogen and added purging systems. Two (2) purge nozzles act as an inlet and outlet to this purge space. Knowing that the pressure of the nitrogen contained in the purge space, any increase in the pressure in the purge space could indicate a leakage of vapor from the seal. Additionally, any loss of pressure from the purge space could indicate a leakage outside of the purge space. There are no specific requirements for monitoring this purge space, even under NFPA 59A, Standard for the Production, Storage and Handling of Liquefied Natural Gas (LNG). However, the technology to add purge monitoring devices is available. EIC Cryo has even developed their own standard system which includes the necessary items of tubing, valves, gauges, pressure indicators and transmitters. Remote transmitters are also available for sending updated data to a monitoring device. The purging system is constructed in a mountable rack and contains inlet and outlet nozzles for connections to a constant supply of nitrogen and power supply connection.
Based on lessons learned from the Prelude FLNG project, FEED has already started on future Shell FLNG projects utilizing the same applications and equipment. The goal will be to streamline the complex design and manufacturing process.
If one does not have approximately $13 Billion to invest on an FLNG, then perhaps one of the simpler options is available. At 5.3 mtpa consisting of 3.6 mtpa LNG, 1.3 mtpa of condensate and 0.4 mtpa of LPG, the Prelude FLNG is a multi-train floating LNG plant. However if 1 ~ 2 mtpa is all that is needed, then perhaps a smaller solution will suffice. This was the goal of the PETRONAS FLNG (PFLNG1) project.
The PFLNG1 project signified the second in a consortium of engineering powers to design and manufacture a super floating facility. At approximately one-fifth of the size of Prelude FLNG, PFLNG1 looked to be designed, manufactured and commissioned in half the time of Prelude. Current estimates estimate the commissioning of PFLNG1 by end of 2015.
EIC Cryo supplied LNG cargo pumps that were selected for offloading and transferring LNG. The LNG Cargo Pump has been around for over forty years. Slowly over the years, the capacity and discharge pressure has been steadily increasing. Most of the cargo pumps have been designed to operate at a power supply of 60 Hz. The PFLNG1 and PFLNG2 were designed to operate at 50 Hz (as is common in Malaysia). So why would this make a difference?
Differential pressure produced by the pump’s hydraulics are a function of the commonly known Affinity Laws. At a fixed trim impeller, the differential pressure developed by a 60 Hz pump will be higher than the differential pressure developed by a 50 Hz pump simply due to the pump’s rotational speed. As a result, if the same capacity and differential pressure is to be developed but using a 50 Hz frequency, then the pump’s fixed impeller trim has to become larger. This is what happened the PFLNG1 as EIC Cryo designed and manufactured one of the largest submerged motor cargo pumps to be mounted in a floating vessel.
In 1975, the Gotass-Larsen Shipping Corporation entered the LNG market with their first LNG Carrier named Hilli. In 1997, Osprey Maritime Limited acquired Gotaas-Larsen and then later formed LNG Shipping company in 2001. Golar World Shipping has been expanding their fleet of LNG Carriers and converted as well as new-build FSRU’s since.
Now nearing 40 years old, the original Golar Hilli LNG Carrier was entering into retirement. Designed with six spherical tanks, the 125,000 cubic meter LNG Carrier (built by Moss Rosenburg, Norway) was given a new life by building a liquefaction process on the topside and using the tanks as storage for the newly processed LNG.
Prior to commencing work, Golar LNG studied the market for FLNG’s and determined a number of opportunities that could use the Golar Hilli FLNG and additional converted FLNG’s. Plans for sister ships Gimi and Gandria are also planned for FLNG conversion. The advantage of going with converted FLNG over land-based and even new-build have been identified by Golar. First, Golar estimates that the conversion would only take 31 months (shorter than a new build and significantly shorter than land-based plant). Secondly, the converted FLNG is estimated to be around $588 Million compared to the $13 Billion estimated for the Prelude FLNG.
Golar LNG contracted Black & Veatch Corporation to conduct a study to provide its proprietary PRICO® liquefaction technology for the FLNG. The converted FLNG would produce around 2.8 mtpa of LNG. The PRICO® LNG technology is a proprietary liquefaction process, however EIC Cryo supported the liquefaction process by adding an LNG Expander to improve the liquefaction production efficiency. The Hilli FLNG will be the second FLNG in the world to feature the submerged generator LNG Expander.
Some analysts believe that floating applications simply cannot replace traditional land-based liquefaction plants, receiving terminals and export terminals. Rather, floating applications can provide an alternative solution to the traditional land-based plant. FLNG’s and FSRU’s can also provide a quicker operation time and potentially reduced cost (depending on the scale of the project).
These are the current evaluations taking place with one such project off the coast of Mozambique for ENI S.p.A (Eni). Eni has a partnership with PetroChina, Galp Energia, KOGAS and ENH to develop the Area-4 region of Rovuma Basin. A FLNG is currently in the evaluation stage utilizing a parallel FEED of multiple consortium EPC’s. This consortium includes Samsung Heavy Industries / Technip, DSME / KBR, and Hyundai Heavy Industries / Saipem / Chiyoda. Each consortium will provide their design of the FLNG concept with estimated construction costs and time to delivery. Final evaluation of the designs and final investment decision will be conducted by the partnership of Eni.
As suppliers and cooperative design solution providers to all of these EPC’s, EIC Cryo expects to provide recommendations and support to each of the designs. EIC Cryo hopes to recommend design influences for the LNG Expander in the liquefaction process as well as solutions for the offloading cargo pumps.