The simplicity of compressing and storing natural gas is well understood. The idea of CNG marine transport dates back to the 1960s, but early attempts at commercialization were unsuccessful, due to the expense of early pressure vessels and the need for effective safety standards. Today, new technologies, growing market demand, and new guidelines for CNG ships have made their use more viable.

The initial CNG ship designs used cylindrical pressure vessels or bottles joined together with a complex manifold. Hundreds or even thousands of these bottles are required to store significant volumes of natural gas. As a result, these bottle-ship designs were complex and expensive.

Modern CNG ship containment design has taken two directions: improved bottle designs, and a large pressure vessel in the form of a coiled pipeline. This latter, the patented Coselle system, was developed by Sea NG, and requires relatively few pressure vessels and uses a simple, efficient manifold and control system. The system has passed all tests and so far is the only CNG ship to be approved by the American Bureau of Shipping.

While developing the Coselle system in the mid 1990s, Dave Stenning, James Cran, and John Fitzpatrick considered numerous alternatives for storing CNG. Their work resulted in patents for both Coselle and bottle-ship containment vessels. After considerable review the Coselle system was deemed superior in terms of safety, reliability, and economics.

The Coselle system has been referred to as “the floating pipeline” – it is, after all, simply a series of coiled pipelines. It includes a unique CNG containment system – the Coselle – that monitors and controls the gas under all circumstances, as well as customized ships and loading and unloading facilities. While the ships are standard, the loading and unloading facilities are customized to suit each customer’s CNG shipping requirements and circumstances.

The technology is tried and tested. The natural gas industry has been coiling pipeline for years in sub-marine pipe laying. The Coselle is a new application of this proven technology. The coiled pipe becomes the high-pressure container that holds a large quantity of CNG, and can be easily transported by ship.

The Coselle technology sets Sea NG apart from other marine CNG technologies, all of which are bottle-ships of one form or another. One of its biggest advantages is simplicity. Each Coselle consists of several kilometers of small diameter, industry-standard, high strength steel pipe coiled onto a reel. The reel is enclosed and then filled with inert gas. The Coselles are subsequently contained in an inert-gas-filled cargo house. Since the Coselles are so large, only a relatively simple manifold with few valves and controlling systems is required, resulting in a system that is more reliable and less expensive to construct and operate.

In all CNG ship designs, the ongoing and periodic inspection of the pressure vessels is a very important consideration. As Coselles are coiled pipelines, decades of experience in pipeline inspection can be directly applied to them.

The right market conditions for marine CNG exist now; demand for natural gas is increasing every year. Recently, liquid hydrocarbon fuel prices have skyrocketed and the forecast long-term oil price remains high. In addition to these cost pressures, there are growing environmental concerns, making gas, the cleanest fossil fuel, more attractive.

Sea NG provides a reliable means to supply gas to power plants and industries that are not connected to a pipeline grid, as well as markets that are not suited for LNG. Although the range depends on each situation, Sea NG’s Coselle system can serve customers requiring between 20 million and 500 million cubic feet per day, where the sea route to the gas supply is within 2,500 kilometers.

New regulations began developing for CNG ships in the mid 1990s. In determining the rules and guidelines for approving CNG ships, the classification societies looked at the International Gas Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk, the benchmark in any new gas ship design. Then they reviewed their own rules for classing steel vessels, and carried out formal safety assessments, hazard identification studies, and hazard and operability analyses. In addition, the CNG containment system must undergo an extensive testing program. On the basis of this work, standards were developed to ensure that a CNG ship is at least as safe as any other gas ship. With these standards in place, the focus advanced from regulation to commercialization.

The majority of the investment in a marine CNG project is in the ships – about 80 percent. Unlike a subsea pipeline, which cannot be redirected or moved without great expense, the transport capacity of CNG ships can be easily shifted in case demand or supply situations change. In many parts of the world, there are financial and/or political uncertainties that often prevent large-scale energy infrastructure investment. Thus, the mobility of marine CNG significantly reduces the investment risk.

A common misconception is that insurance has been an obstacle to the start-up of the marine CNG industry. Sea NG, with its partners Marubeni and Teekay, have approached the insurance industry and explained the safety of the Coselle system. As a result of that safety and the track record of existing marine-based energy transportation services, it appears that insurance will not impede project implementation. CNG transportation meets or exceeds the safety requirements for other gas carriers.

There is strong interest in marine CNG. For instance, the Caribbean, the Mediterranean, North Africa, and Canada’s east coast are all investigating CNG projects. Until the first projects are finalized, the possible target market remains wide open.

“The industry’s biggest challenge is pioneering the first project,” says Sea NG’s president and CEO, David Stenning. “Understandably, it is difficult for a customer to adopt a new form of natural gas transportation. With the support of Marubeni and Teekay, Sea NG is dedicated to providing a guaranteed solution.” Sea NG is in the latter stages of negotiations on several projects, and is confident it will be first to market.

Lyndon Ward is the director of marketing at Calgary-based Sea NG.