IGU DETAILS ENVIRONMENTAL QUALITIES OF GAS

The International Gas Union (IGU) has attempted to measure some of the ways natural gas is a clean burning fuel. An IGU task force headed by F.E. Shephard of British Gas plc issued a report on the environmental qualities of gas consumption, production, and transportation at the World Gas Conference in Berlin. The report, based largely on data from previous studies, examined emissions of nitrogen oxides (NOx) and the gas role in the greenhouse and acid rain. it focused on NOx emissions because

July 22, 1991

3 min read

The International Gas Union (IGU) has attempted to measure some of the ways natural gas is a clean burning fuel.

An IGU task force headed by F.E. Shephard of British Gas plc issued a report on the environmental qualities of gas consumption, production, and transportation at the World Gas Conference in Berlin.

The report, based largely on data from previous studies, examined emissions of nitrogen oxides (NOx) and the gas role in the greenhouse and acid rain.

it focused on NOx emissions because direct emissions of other key pollutants such as particulates and sulfur dioxide are negligible.

IGU FINDINGS

Although gas combustion does produce NOx, emissions per unit of energy produced generally are lower than those for other key fuels (see tables).

Despite the gas advantage in NOx emissions, efforts have been under way for a number of years to improve the fuel's performance in this area, the report points out.

NOx concentrations in flue gas from some new residential space heating and water heating appliances are currently about 30% lower than they were in 1985, it notes.

And new techniques can slash NOx emissions from fan-assisted industrial boilers. Examples and their potential NOx emission reductions are combustion air staging 90%, fuel staging 70%, flue gas recirculation 85%, water injection 50%, and swirling 60%.

TRANSPORTATION FUELS

In transportation uses, gas as compressed natural gas or liquefied petroleum gas doesn't significantly cut NOx emissions in comparison with gasoline.

"It appears unlikely that CNG and LPG can lower these emissions relative to rates for advanced technology gasoline powered vehicles, but they can significantly reduce NOx emissions in comparison with diesel fuel and heavy duty vehicles," the report says.

However, vehicles burning CNG only can reduce evaporative emissions that lead to formation of ozone. And CNG probably cuts carbon monoxide emissions from all types of vehicles. CO emissions from vehicles burning LPG are higher than from those burning CNG but lower than from those burning gasoline.

CNG vehicles also reduce emissions of greenhouse effect gases. The report estimates that on a per kilometer basis, state of the art CNG vehicles produce 80-90% less greenhouse gases than gasoline vehicles.

CNG-only vehicles emit some methane but 30% less carbon dioxide than gasoline vehicles.

ALL USES

In all applications, natural gas can reduce CO2 emissions when substituted for other fuels because of its low ratio of carbon to hydrogen.

Gas combustion releases about 45% less CO2 than coal combustion and about 30% less than gas oil combustion.

The gas contribution to emissions of methane, another important greenhouse gas, is smaller than is generally assumed, the report says.

It estimates the energy sector accounts for about 12% of all methane releases worldwide.

In 1987 hard coal accounted for 31 million metric tons of methane releases, natural gas 12 million tons, oil 11 million tons, and lignite 2 million tons. All the natural gas contribution came from production, transportation, and distribution. The other fuels' contributions included those activities as well as combustion.

The worldwide average gas leakage rate is about 1% of total consumption, the report says. The rate varies widely according to region due to variations in infrastructure and technology. And it decreases as improvements are made in those areas.

Methane's concentration in the atmosphere is increasing about twice as rapidly as that of CO2, and its power to absorb infrared radiation is 20-30 times greater.

But methane's life in the atmosphere is shorter, which reduces the effect.