6.4. Hydrates

Huge quantities of natural gas (primarily methane) exist in the form of hydrates under sediment on offshore continental shelves and on land in arctic regions that experience permafrost such as those in Siberia (hydrates require a combination of high pressure and low temperature to form). However, as of 2010 no technology has been developed to produce natural gas economically from hydrates.

All these natural gas resources can open up avenues for augmentation of natural gas/LNG production over the world.

Therefore, it may be concluded that the existing non-exhaustive natural gas resources and the worldwide LNG technology (as well as forthcoming) can meet the future energy demands. Further, the worldwide shale gas developments, especially in US and Canada, are adding to the energy security.

7. Lifecycle greenhouse gas emissions of lng vs. Oil & coal

Production, transport and exploitation of the energy, all have a great impact on the environment and ecosystems [60]. The majority of the world’s energy is still gained from ecologically unacceptable energy sources, especially fossil fuels which are still dominant energy sources [61]. Since fossil fuels have coal as their base, normal combustion of these fuels results in carbon dioxide (CO₂) emission which is a greenhouse gas [62]. This carbon dioxide mostly ends up in the atmosphere, and with its greenhouse effect, causes global warming. Carbon monoxide (CO) which is produced during incomplete combustion of fuel (combustion without the needed amount of oxygen) is more dangerous as compared to CO₂. CO is an extremely poisonous gas without color, taste or scent, and its concentration of just 0.6% can cause death after only 15 min of the inhalation [63] and [64].

Apart from CO₂ and CO the combusted coal and oil releases NO_x and SO_x particles while combustion of LNG provides an excellent means to reduce particle emissions (PM) to near 99%, sulfur oxides (SO_x) emissions to near 100%, nitrogen oxides (NO_x) to 80%, and 70% fewer GHG emissions [64] and [65] as reported inTable 4. Due to the clean-burning nature of natural gas, LNG powered heavy-duty vehicles can achieve low emission rates without excessive and expensive emission control equipment as is required for diesel engines.

Table 4.

Comparison of fossil fuel emissions (in PPB Btu of Energy Input).

Pollutant	LNG	Oil	Coal
Carbon dioxide	117,000	164,000	208,000
Carbon monoxide	40	33	208
Nitrogen oxides	92	448	457
Sulfur dioxide	1	1112	2591
Particulate	7	84	2774
Mercury	0.000	0.007	0.016

Table options

When burned for power generation, the results are even more dramatic [65], SO₂emissions are virtually eliminated and CO₂ emissions are reduced significantly. Therefore, the increased use of LNG in place of other fossil fuels, like coal and oil, can significantly reduce the emission of greenhouse gases in the atmosphere [66]. Moreover, LNG vessel operations are generally more environmentally friendly than other ships because they use natural gas rather than oil as their primary fuel source for propulsion. LNG is currently being used to fuel public transit vehicles in clean air programs and is accounted for 7% of the world natural gas demand [67].

The role of LNG in GHG reduction in comparison to coal and oil has been reported by many investigators[26], [27], [28], [68], [69] and [70]. Arteconi et al. have studied the comparison of diesel and LNG fuel for use in heavy-duty vehicles in term of GHG emissions throughout their life-cycle, in the setting of the European market and they found that LNG afforded a 10% reduction in GHG emission in comparison to diesel fuel [71]. Further, on the basis of life cycle analysis of GHG emission from different fuels Stefano et al. [72] have reported LNG as a green energy for future.

Graham et al. [73] have compared the GHG emissions from a variety of heavy-duty vehicles and engines operating on a range of different fuels including diesel, biodiesel, compressed natural gas (CNG), hythane (20% hydrogen, 80% CNG), and liquefied natural gas (LNG), and with different advanced after treatment technologies were studied by chassis dynamometer testing, engine dynamometer testing or on-road testing. The results of this study represent that different choices in fuels may have different effects on GHG emissions. The use of natural gas (either as compressed, liquefied, or blended with hydrogen) can reduce GHG emissions at the tailpipe by 10–20% on a CO₂-equivalent basis compared to diesel fuel.

A study on life cycle assessment of GHG emissions from LNG and coal fired generation was conducted by CLNG (Center for Liquefied Natural Gas) [74]. According to this study coal produces 161% grater emissions on a life cycle basis than that of LNG. Moreover, this analysis indicates that the cleanest coal scenario releases 73% more emissions from a life cycle perspective than LNG.

According to Andress et al. [75] CNG and LNG provide modest benefits in reducing GHG emissions when used directly as a motor vehicle fuel. GHG reductions benefits are much greater when natural gas is used to produce hydrogen. Nitrogen oxide (NO_x) emissions reduction of over 75% compared to diesel fuel vehicle has been reported by Frailey [76].

Chen et al. [77] have studied the comparison of two types of air fuelled engines for zero emission road transportation. Their investigation represents that the shaft work output and the coolth of both the fuels increase with increasing working pressure or temperature. Given the working pressure and temperature, liquid air powered engines have a slightly lower specific work outputs than compressed air powered engines. The volumetric energy density of liquid air, however, is much higher than that of compressed air, and liquid air has much higher coolth than compressed air.

The available evidences show that LNG produces the lower GHG emissions as compared to traditional fossil fuels hence; it is an eco-friendly fuel.