Page 57 - Handbook of Natural Gas Transmission and Processing Principles and Practices

compliance to strict design and safety standards, design factors to ensure supply security, financial
institution requirements, and site remote locations. Plant costs throughout the value chain have
been declining through design innovations and cost optimization. Further advances in the LNG
technology can be expected in coming years in the areas of liquefaction and shipping, which can
lead to lower overall project costs (Cornot-Gandolphe et al., 2003 and Mokhatab et al., 2014). In the
recent years, a floating LNG (FLNG) design, where processing and storage facilities are based on a
vessel moored offshore in the vicinity of the production fields, has been proven to reduce costs,
making development of small and remote gas reserves, offshore gas viable. The FLNG technology
can reduce costs by minimizing the offshore platforms and pipelines, eliminating the need for port
facilities, minimizing skill labor at the job sites, and reducing the plant delivery date. Vessel
construction can be carried out in a low-cost location. However, there are potentially many
commercial and technical challenges that need to be resolved during the development phase. The
key is to delineate these challenges and provide innovative solutions to solve these problems (Chiu
and Quillen, 2006 and Mokhatab et al., 2014).

1.10.3. Compressed Natural Gas

Gas can be transported in containers at high pressures, typically 1800 psig for a rich gas

(significant amounts of ethane, propane, etc.) to roughly 3600 psig for a lean gas (mainly
methane). Gas at these pressures is termed compressed natural gas (CNG). CNG offers proven
technology that has the potential to provide an early to market, economic solution for remote
offshore gas developments with small to medium reserves or for associated gas reserves in large oil
field developments. It could work where subsea pipelines are not viable because of distance, ocean
topography, limited reserves, modest demand, or environmental factors, but where LNG is also not
economical due to its high cost of liquefaction and regasification facilities, or feasible due to
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community or safety issues. In addition to being a cost-effective solution for regional gas projects,
CNG transport projects also offer several unique and valuable solutions in terms of flexibility and
risk mitigation compared to the LNG projects (i.e., easy supply and market access, redeployability,
and scalability).
The energy consumed in operating a CNG facility is only about 40% of that of an LNG plant of
the same capacity. Thus, the threshold volume of gas reserves needed to support a CNG project is
comparatively small, provided the shipping costs can be kept low. However, the containment for
CNG is heavier than that for LNG, so the payload per unit weight shipped is smaller. Greater than
85% of a CNG project costs are likely to be associated with the ships, which are based upon
conventional bulk carriers with at least four competing certified containment designs (Hatt, 2003):
EnerSea (US) VOTRANS carbon steel pressure cells; Trans Ocean Gas (Canada) fiber reinforced
plastic (FRP) covering high-density polyethylene cells; TransCanada CPV steel liner cell
overwrapped with a glass fiber laminate; and Sea NG (Canada) patented Coselle of coiled X70 high-
strength steel pipe wound into a cylindrical storage container. EnerSea's VOTRANS (Volume
Optimized Transport and Storage) containment systems is the most cost-effective CNG solution in
the marketplace due to greater gas storage/delivery efficiency. With most of the capital costs
invested in the technology in the vessels, it is important to have a large and experienced shipping
company such as Teekay at the helm (Wood and Mokhatab, 2008).

1.10.4. Gas-to-Liquids
In gas-to-liquids (GTL) transport processes, natural gas is converted to a heavier hydrocarbon
liquid and transported to the consumers. The technology of converting natural gas to liquids is not
new. In the first step, methane is mixed with steam and converted to syngas or synthetic gas
(mixtures of carbon monoxide and hydrogen) by one of a number of routes using a suitable catalyst
technology (Keshav and Basu, 2007). The syngas is then converted into a liquid using a Fischer-
Tropsch (FT) process (in the presence of a catalyst) or an oxygenation method (mixing syngas with
oxygen in the presence of a suitable catalyst). The produced liquid can be a liquid fuel, usually a
clean burning motor fuel (syncrude), or lubricant, ammonia, methanol, LPG substitute, or some
precursors for plastics manufacture, e.g., urea, dimethyl ether (DME), or chemical feedstocks
(Knott, 1997; Skrebowski, 1998; and Apanel, 2005). The environmental benefits of clean burning

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