In Part 1 of the current series “Gases in the 21st Century” (see gasworld, June 2008, p.50), compressed hydrogen was described as a potential future source of fuel for automobiles, and transport in general, for a cleaner, ‘greener’ future.
Well Compressed Natural Gas (CNG) has enjoyed that accolade for almost a century, though its momentum in the last couple of decades has been rapidly rising on account of growing worldwide anxiety about the quality of urban life.
CNG is essentially a mixture of the gas methane (CH4), with other hydrocarbons such as ethane, propane and butane in varying amounts. It also contains small quantities of several substances including nitrogen, hydrogen sulphide, carbon dioxide, helium (which is highly sought in the off-shore oil industry), water and even mercury.
The latter element is a major source of problems for equipment used to purify CNG on account of the mercury forming amalgams within the process vessels.
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