Plan to use LNG carriers for ethylene
New Jersey-based Agility Gas Technologies has received patents covering its innovative proposal for transporting liquefied high-value gases (HVG) on LNG carriers, writes David Tinsley.
The concept is intended to reduce shipment costs and widen the global market for producers of ethylene and other gases, while also enhancing shipping flexibility and profitability. The patents apply to the US and the Gulf Cooperation Council states.
Fundamental to the initiative is the fact that ethylene and propylene, for instance, are more than four times as valuable as methane in terms of mass, reflecting their value and versatility as the building blocks for the production of basic chemicals.
“In general, the US and GCC patents cover shipment of high volume and value commodity chemicals, including ethane and propylene, but especially ethylene in coordination with LNG, to provide a safer and more economical method to move volume chemicals from lower cost production sites to higher value sales sites,” Charles E. Matar of Agility Gas told The Motorship.
Standard LNG tankers can be adapted (requiring what Agility calls ‘slight modifications’) to allow much of the LNG cargo to be displaced by ethylene or other liquefied gases, thereby significantly increasing the value of the shipment. Agility contends that its technology is much cheaper to implement than investing in purpose-built, ethylene-capable liquefied gas carriers (such as those built in recent years) while affording the requisite high safety level.
HIGHER TRANSPORT CAPACITY
By harnessing the cargo volume embodied by deep-sea LNG carriers, its solution offers higher transport capacities than those of the smaller, specialised vessels equipped to load liquefied ethylene or propylene.
Whereas methane’s density is 55% that of air, and has a strong tendency to rise in the open air away from a release, ethylene as a gas has a density close to that of air. Pure ethylene in liquid form has to be transported at -103°C to avoid cargo boiling. Should the evaporated gas escape confinement and mix with air, there is a risk of conflagration or explosion.
Agility states that its technology employs the lower hazard conditions of LNG to make ethylene transport safer. By blending ethylene with LNG and shipping the blend in standard LNG carriers, the boiling temperature of even a 75% weight blend is -151°C. If boiling of the mixture does occur, the gas will contain just 2% ethylene by weight, not 75%. If released by accident or due to a boil-off, the gas mixture would still have nearly the same inherently safer properties as pure methane.
If the ethylene is stored in separate holds (tanks) within the tanker, the LNG (at -161°C) can be used to cool the ethylene and maintain it as a liquid between -103°C and -161°C. Since ethylene does not freeze until -169°C, the LNG cannot freeze pure liquid ethylene. Heat transfer systems are designed so that they can be either powered or passive and inherently safe.
Plans are underway for a demonstration plant to be built by a cryogenic equipment specialist and operated by a cryogenic gas supplier. The demonstrator, at about 1/10,000 scale, is to be located at a research facility in the USA. The rationale for the plant is to provide a working model for process control and a vehicle for showing the effectiveness and safety principles of the patented technology.
Agility hopes that it will subsequently proceed to a joint venture with an ethylene producer or supplier and begin shipping ethylene.
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