Natural gas is usually stored and transported in compressed form, that is, compressed natural gas (CNG). Examples of CNG include high pressure transmission pipelines, medium and low pressure distribution and utility pipelines, underground and above ground storage facilities and small volume, high pressure fuel tanks.

Designs and procedures for handling natural gas in compressed form have existed for over 100 years, and with the expanded use of natural gas in everyday life: industry, communities and transportation, these well-proven technologies and designs continue to be expanded and improved upon.

This progress is illustrated by the rapid growth in natural gas vehicles around the world, which is based on the use of small volume CNG storage containers in cars, buses and trucks. This application of CNG has proven to be safe and reliable and accepted by communities and regulators. The International Association for Natural Gas Vehicles (IANGV) is projecting that 50 million CNG vehicles will be on the roads by 2020.

CNG Marine Transport Proven Technology

Marine Transport of CNG – Proven Technology

Given this background, it was logical that technology would be advanced for transporting large volumes of natural gas as CNG on the seas, just as liquid petroleum and petrochemicals have been shipped for decades in large volume tankers. In the late 1960s, Columbia Gas Company developed a CNG containment system aboard a converted ship. This prototype vessel was awarded class certification by the American Bureau of Shipping and received approval from the U.S. Coast Guard for operations in U.S. waters. After about a dozen successful voyages, which proved the CNG marine transport concept, operations ceased due to the low value of natural gas at that time.

In addition to these previous CNG ship operations, natural gas components, such as propane, butane and various LPG mixes, are commonly shipped today in pressurized and chilled storage systems aboard barges and tanker ships.

Developing CNG Marine Transport (VOTRANS™)

EnerSea Marine CNG

EnerSea began its quest to develop a modern CNG marine transport system in 2001 with the development of its VOTRANS (Volume Optimized Transport and Storage system) technology and designs. The VOTRANS system introduced a major breakthrough in the ability to store and deliver compressed natural gas on marine vessels cost effectively. Much more gas can be stored in and delivered from VOTRANS containment systems, and at a correspondingly lower cost, than with previous CNG design approaches.

EnerSea has undertaken an intensive development program to commercialize this technology through engineering, validation, certification and application efforts. The results of these labors are EnerSea ship and barge-based CNG systems for which ABS has declared “…are ready to move directly into project construction” and that “ABS will approve EnerSea ships and barges built with VOTRANS CNG systems.”

CNG Marine Transport Solutions & Applications

Application of EnerSea CNG Marine Transport Systems

CNG marine transport can provide ideal solutions for a wide variety of regional applications, including:

Comparing CNG with LNG Supply Chain

Comparison of CNG with LNG Supply Chain

CNG is often compared with LNG, as both are large volume, marine-based gas transport solutions. However, these two technologies typically target different sectors of both supply sources and energy markets. In summary, the major differences include:

  • Capital Investment: CNG projects do not require massively expensive liquefaction and regasification plants. Thus, the overall supply chain project is typically an order of magnitude less expensive.
  • Footprint and environmental impact is much less for CNG terminals than for LNG terminals.
  • LNG often requires expensive pre-processing of the supply gas to a much higher degree than required for CNG to remove components such as mercury and CO2.
  • CNG does not experience “boil off” gas emissions from ships and storage facilities.
  • CNG is typically more energy efficient than LNG.
  • In summary, CNG targets small-to-medium sized regional gas delivery projects, while LNG must be geared toward large scale, long haul projects.
Project Management Tool & Risk Management

Marine CNG – A Unique Project Management Tool

In addition to providing a cost-effective regional gas development solution in itself, CNG marine transport projects also offer several unique and valuable features for flexibility and risk management:

  • Easy Supply and Market Access: The terminals needed for loading and offloading vessels are simple in design, highly cost- effective (especially compared with LNG liquefaction and regasification facilities), and friendly in their physical footprint and environment benefits. Therefore, CNG may access supply sites and sensitive markets more easily than other marine-based solutions, such as LNG.
  • Redeployability: Unlike pipelines and LNG projects, the great majority of CNG project capital is redeployable to other applications if needed. This provides a unique risk management solution in case unexpected events occur in the supply chain, including reservoir, market, commercial and political risks.
  • Scalability: CNG project capacity is easily scalable by adding vessels to, or redeploying vessels from, the fleet. Therefore, unlike pipelines, upfront investment in capital for speculative capacity is not required, but instead can be employed at the time when such additional capacity may be required. With the above risk management and flexibility features, CNG projects may be able to secure more attractive financing and yield higher “risk-weighted” value to project stakeholders.
Safety & Environmental Benefits

Safety and Environmental Benefits

  • Air quality: CNG delivered to markets to replace fuels such as coal, fuel oil and diesel will significantly reduce CO2 and other emissions; potentially valuable emissions credits may be available in such projects.
  • Project emissions:  CNG has no “boil-off” losses; the use of cargo gas for marine fuel also mitigates bunker use and storage in the shipping operation.
  • CNG terminals have a modest physical footprint and environmental impact to the terminal area.
  • Cargo transfer buoy terminals can be located 5-20 kms from the coast for offshore loading and offloading of CNG vessels in highly sensitive areas.