by Reidar Strande | Wärtsilä Oil & Gas Systems
Tord Johnsson | Wärtsilä Power Plants




Most experts predict that natural gas demand will see strong growth in the future, growing at a compound annual growth rate (CAGR) somewhere in the region of 7-8 per cent. According to the International Energy Agency, we could be entering “a golden age for gas”. In its World Energy Outlook 2012, the agency projected gas demand to rise from 3.3 trillion cubic metres (tcm) in 2010 to 5.0 tcm in 2035. Its share of the global energy mix rises from 22 in 2010 to 24 per cent in 2035, all but catching up with coal. Meanwhile, ExxonMobil’s Energy Outlook 2040 published in January 2013, forecasts that natural gas will emerge as the number one fuel for power generation within the next 30 years, accounting for 30 per cent of global electricity generation.
With global LNG (liquefied natural gas) demand expected to show strong growth, LNG production is forecasted to jump from 270 million t/year in 2011 to 350 million t/ year in 2016, according to the International Gas Union’s (IGU) World LNG Report 2011. This growth in production will have to be accompanied by a similar expansion in LNG receiving terminal capacity, since gas production is often not in the same location as consumption.
Recently Wärtsilä took a significant step towards taking full advantage of this booming LNG business. In January 2012, the company gained expertise in small-scale LNG liquefaction, regasification, and LNG fuel systems through its acquisition of Hamworthy plc. These new capabilities go hand-in-hand with the company’s existing expertise in ship propulsion and power plant/land-based design and construction.

LNG production
Wärtsilä Oil & Gas has developed innovative LNG production plant solutions based on well-proven equipment and process control principles, which are suitable for small to medium size liquefaction capacities. The LNG production facility in Snurrevarden, Norway was the first freestanding small scale LNG plant in Northern Europe.
Since then Wärtsilä Oil & Gas has delivered a number of complete onshore LNG production facilities, including the introduction of an improved liquefaction system with double expanders based on the reverse Brayton cycle. The LNG production plant for Gasum in Finland, delivered in 2010, uses surplus liquid nitrogen (LIN) for the LNG generation and incorporates new technology that reduces LIN consumption by 50 per cent.


Wärtsilä Oil & Gas has also developed the energy efficient NewMR liquefaction technology for even lower capacities than its usual small and mid-scale LNG plants (below 50 tonnes per day). In the growing liquid biogas fuel market, this technology adds to the value chain. Wärtsilä Oil & Gas will deliver a biogas liquefaction plant to the Municipality of Oslo during spring 2013.



LNG transport
Most of the growth in the global LNG market is expected to occur in large production plants - exceeding roughly 1 million t/year - in Australia, Asia, the US and parts of Africa, mainly Mozambique. There are also a number of smaller scale plants that will make the LNG business more local. Typically, large LNG carriers transport LNG from the points of production to consumption locations.
Since their introduction in 2006, 65 per cent of all new LNG carriers have been fitted with Wärtsilä dual-fuel (DF) engines. Wärtsilä recently achieved the milestone of supplying DF propulsion engines to 100 LNG carriers, and has sold altogether some 720 DF engines to both marine and land-based applications, accumulating six million running hours of experience with the technology.



Floating storage regasification units
In recent years there has been a growing interest in ship and jetty-based LNG regasification systems. In a jetty regasification unit (JRU), the regas unit is mounted on a dedicated jetty while a floating storage unit (FSU) is moored alongside to hold the LNG buffer stock. Shuttles then bring the LNG to and from the FSU before being fed to the JRU in preparation for feeding to the gas grid or power plant. This was a solution that Wärtsilä Oil & Gas provided for Malacca in Malaysia.
The ship-based option, more commonly known as a floating storage and regasification unit (FSRU), is essentially a LNG carrier converted by the addition of on-board storage and regas facilities. FSRUs present a strong economic case when compared with onshore import terminals. With no need to go through onshore planning procedures, they can typically be built in half the time - around two years - and at half the cost in some instances. FSRUs can also be built in remote areas with an associated subsea pipeline.


An increasing number of LNG importers want to take advantage of the cost and timing benefits offered by the jetty/ regas vessels option, but they also want to be able to keep the ships on station in uninterrupted service for several years. They also want to be able to process larger quantities of LNG than converted FSRUs are capable of. This joint requirement has led to a number of orders for FSRU new builds.
New builds typically consist of a pair of vessels that together fulfill the same role as a FSRU. This configuration makes use of a barge-mounted regasification plant combined with an LNG carrier used as a floating storage unit. This approach obviates the need for a propulsion system on the barge floating regas unit. At the same time, a conventional LNG carrier can be easily prepared for its floating storage role. So far, Wärtsilä has delivered 10 floating LNG terminals, representing a market share of about 40 per cent. Reconverting the LNG at import terminals requires a very large amount of energy in the form of heat for LNG vaporisation. Some FSRUs can actually provide the same amount of heat that could be supplied by a 1,000 MW nuclear power plant. To vaporise 14 million cubic meters per day would require in the region of 100 MW of heat.


Many companies use seawater only to provide the heat for vaporisation but this can have drawbacks. Over the last several years, Wärtsilä has been developing its FSRU technology to increase the process efficiency, reliability and economics. A key Wärtsilä LNG regasification technology utilises propane and seawater in cascade loops to warm the LNG. Wärtsilä built its first pilot to demonstrate propane loop technology in 2005. Propane is used in the first stage to heat the LNG from -160˚C to -10˚C in a heat exchanger. In the second stage, the LNG can be heated further using seawater as a heating medium. Propane is a suitable heating medium as it does not freeze at the -160˚C temperature of the LNG. Its use in the first stage reduces the risk of freezing the seawater in the heat exchanger. Also, the latent heat from the propane is used for the vaporisation, which is more efficient and reduces the volume of the heating medium compared to competing technologies.


In the cascade system’s first stage heat exchanger, heat is exchanged against the propane circulating in a closed loop. The propane enters the heat exchanger at approximately 0˚C and 4.7 bar as gas. In the heat exchanging process, the propane is condensed and leaves the exchanger in a liquid state at about -5˚C. The propane is then pumped by the circulating pump and heated against seawater in titanium, semi-welded-plate heat exchangers. Here the propane is evaporated and heated to 0˚C before returning as gas to the printed circuit heat exchanger. Wärtsilä regas units use a type of printed circuit heat exchanger that allows for a compact unit capable of withstanding high pressures. The simplicity of control of the regas units using this technology has been proven at a demonstration plant. The robustness in terms of turndown capability, ramping up and ramping down, has also been demonstrated. Unlike other heat exchangers, the units are not susceptible to the fatigue caused by large changes in temperature. Wärtsilä is also able to provide FSRUs for situations where seawater cannot be used.


Here, steam from the ship’s boiler system and cooling water from Wärtsilä’s engines can be used for vaporisation. The shipboard LNG regasification systems have capacities in the 50-1,100 tonnes per hour (tph) range, and sendout pressures ranging from 46 to 130 bar. As an example, a system based on the use of 630 tonnes/hour trains can provide a regasification capacity of 720 million standard cubic feet of gas per day, and discharge a 145,000 cubic meters LNG carrier in approximately four days.


Integrated receiving terminal and power plant
Wärtsilä has a long history in building power plants in the 1-500 MW range based on modular 1-20 MW engine units capable of running on fuel oil or gas, or on dual-fuel engines that can use both without modification. These power plants can be used to generate electricity only, or combined heat and power if there is also a requirement for heat as such in industrial applications. There are a number of synergies between the power station and the regasification plant. Obviously the power plant can utilise the natural gas produced for power generation, but there are other opportunities for integration of the two systems.
When the LNG arrives at the country of destination, it is received at a terminal where it is stored and regasified before being fed into the gas grid or piped to a power plant for electricity generation.