Oxygen-Enriched Combustion Can Reduce Emissions and Fuel Use in Energy-Intensive Industries

Advances in Industrial Energy-Efficiency Technologies

Prepared for:
U.S. Department of Energy
Office of Industrial Technologies
Washington, DC 20585

Produced by:
National Renewable Energy Laboratory
Golden, Colorado 80401-3393

In conjunction with:
Energetics, Inc.
Columbia, Maryland 21046

DOE/CH10093-198
DE93000063
September 1993

Energy is wasted when ambient air is used in the combustion of fossil fuels

When a fossil fuel such as oil or natural gas is burned, oxygen in the combustion air chemically combines with hydrogen and carbon in the fuel to form water and carbon dioxide, releasing heat in the process. Air is composed of approximately 21% oxygen, 78% nitrogen, and 1% various other gases. During air-fuel combustion, the chemically inert nitrogen dilutes the reactive oxygen and carries away some of the energy in the hot combustion exhaust gas. Compared to combustion using pure oxygen or air from which some of the nitrogen has been removed, combustion using ambient air lowers fuel efficiency.

The use of oxygen-enriched combustion air in a number of energy-intensive industrial applications has the potential to reduce the amount of heat lost to the atmosphere by two-thirds. In an effort to promote oxygen-enriched combustion, Praxair, Inc. (formerly Union Carbide Industrial Gases), in cooperation with the U.S. Department of Energy's (DOEžs) Office of Industrial Technologies, is researching and evaluating potential industrial applications for oxygen-enriched combustion systems that are technically, environmentally, and economically feasible.

Photo: Praxair, Inc. has developed the OxyGENTM vacuum pressure swing adsorption system for producing oxygen used in glass melting furnaces. (Photo courtesy of Praxair, Inc.) [provided in source document]

Oxygen-enriched combustion has been tested at two on-line glass melters

The DOE/Praxair project is focused on the glass industry, where low-level oxygen enrichment and auxiliary oxygen-fuel burners have been used in glass melting furnaces since the 1940s. Scientists at Praxair have investigated the energy savings and evaluated the performance of full-scale, 90-100% oxygen-enriched combustion systems at two on-line glass melters.

The first melter at Carr-Lowrey Glass Company in Baltimore, Maryland, is a 75 ton/day (68 metric ton/day) melter that produces flint glass for cosmetic bottle manufacturing. Tests of 100% oxygen-enriched combustion were performed for three weeks in July and two weeks of October 1990. Auxiliary oxygen-fuel burners were then operated for an additional six months to collect information on burner maintenance and durability.

The second melter involved in the project is at a Gallo Glass Company facility that produces flint and green glass for wine bottle manufacturing. The primary objective of converting this melter to 100% oxygen-enriched combustion was to reduce nitrogen oxides (NOx) emissions. An oxygen-fuel combustion system was permanently installed during a 1991 melter rebuild, and testing was initiated in late July 1991.

Photo: The Praxair OxyGENTM vacuum pressure swing adsorption system features a two-bed adsorption cycle that uses a vacuum pressure process and synthetic zeolite to separate oxygen from ambient air. [provided in source document]

In mid-1192, the primary supply of oxygen was changed from liquid oxygen to an advanced oxygen supply system known as vacuum pressure swing adsorption (VPSA). VPSA is an air separation system that uses zeolite adsorbents to separate oxygen from nitrogen and the other components of air. The system consists of two adsorbent beds. As the air passes into the first, nitrogen is adsorbed and oxygen passes through. While the first bed produces oxygen, the second regenerates by purging the adsorbed nitrogen. After a specified period, the pressure swings and the beds reverse functions.

Emission reductions and energy savings were achieved at both test sites

Both of the test sites achieved energy savings as well as emission reductions. Natural gas savings at the Cart-Lowrey facility averaged approximately 15%; Galložs fuel savings were approximately 25%. These fuel savings were attributed to two factors:

  1. First, there was almost no nitrogen carrying heat out of the furnace.
  2. Second, radiation losses through input ports (openings where the fuel, air, or oxygen enter and exhaust gases leave the furnace) were greatly reduced because the ports for oxygen-fuel are much smaller than those for fuel-air.

Reductions in emissions associated with the new technology were observed in both facilities. Following conversion to 100% oxygen, Carr-Lowreyžs NOx emissions were reduced from 21.6 lbs/ton (10.8 kg/metric ton). Part of the NOx emissions was attributed to nitrates in the raw materials. NOx emissions from the Gallo glass furnace, which used no nitrogen-containing raw materials, were reduced from 5.0 lbs/ton (2.5 kg/metric ton) of glass to 0.8 lbs/ton (0.4 kg/metric ton). The particulate emissions at the Gallo melter were reduced by about 25%; particulate emissions from the Carr-Lowrey facility were difficult to quantify because of the changing amount of glass being processed from day to day. Emissions of carbon monoxide and hydrocarbons were also lower at both test sites using oxygen-enriched combustion.

In addition to saving fuel (typically natural gas) and reducing emissions of harmful pollutants, the use of oxygen-enriched combustion eliminates the need for a heat recovery system because of the large reduction in exhaust gas volume. It also reduces defects in the glass because of improved melter control. These benefits make oxygen-enriched combustion a very attractive option for glass producers.

Gallo Glass Company is so pleased with the benefits realized from oxygen-enriched combustion that it has decided to convert all remaining melters at its bottle manufacturing plant-the largest plant of its kind in the nation-to oxygen-fuel firing. This is just part of a trend taking hold in the glass industry. At the beginning of 1993, oxygen-enriched combustion was being used in glass furnaces with a total capacity of 800 tons/day (725 metric tons/day) of glass. This figure is expected to increase fourfold within 2 years.

For More Information:

Industrial Combustion Equipment Program
EE-221
Office of Industrial Technologies
U.S. Department of Energy
1000 Independence Ave., SW
Washington, DC 20585
(202) 586-2098


Return to top of document.

Last Updated: February 13, 1996