Natural gas came into use in the British cement industry when North Sea gas became available. Although always in general more expensive than coal, it could be made economic by purchasing on an "interruptible" basis. Because it was supplied, like electricity, from a national grid system, it was possible for large users to obtain favourable rates by undertaking to cease usage (i.e. shut down kilns) at the request of the gas supplier on a limited number of occasions every year when the supplier was having difficulty in meeting demand. However, the cost of gas energy relative to that of coal energy soon rose, and gas usage in the industry ceased. Five plants used natural gas: Aberthaw 1972-1980; Pitstone 1971-1981; Rhoose 1972-1979; Tunstead 1974-1986 and West Thurrock 1971-1976.
Natural gas consists mainly of methane, and its properties approximate to those of methane, but its calorific value is somewhat lower, because other alkanes with a lower hydrogen content are present, as are some inert diluents. Like other fuels, although natural gases vary quite widely in composition, their stoichiometric air requirement and CO2 production per unit of heat generation vary little. The following data are based on a large number of British natural gas analyses.
The "typical" value is the average value for those gases having Nett CV values between the 10-percentile and the 90-percentile. The range is the 10-percentile and 90-percentile value for each parameter. The molecular compositions are %v/v at 0°C. The elemental analyses are % by mass. The combustion air used has 50% humidity at 20°C (see composition). "Gross" calorific value is otherwise known as Upper Heating Value. "Nett" calorific value is otherwise known as Lower Heating Value.