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Rethinking industrial combustion: part 1

Hydrocarbon Engineering,

Fossil fuels play a critical role in today’s economy and are critical in future global economic development and prosperity. The rise of unconventional resources in recent years has contributed to the growth of petroleum and natural gas production (Figure 1), but at the same time it has also increased their energy intensity. From extraction to refining, the oil and gas industry requires significant energy expenses (approximately a quarter of the energy contained in a barrel of oil is used to produce, refine and transport it). Adding to the mix high price volatility and a constant increase of environmental regulations, demand for technologies that can improve economic performance while reducing emissions is at an all time high. The oil and gas industry is now facing significant pressure to increase energy security by implementing energy efficiency and conservation measures, while reducing their overall environmental impact.

Figure 1. Primary energy use by fuel 1980 - 2040 (quadrillion Btu). Source: EIA Energy Outlook 2014.

The combustion of natural gas and other fossil fuels in oil and gas applications results in the emission of smog producing chemical compounds including nitrogen oxides (NOX), one of the criteria pollutants designated by the US Environmental Protection Agency (EPA). In recent years, several highly populated and industrial regions and countries with severe air pollution issues have begun to introduce strict emissions regulations. For example, California’s South Coast Air Quality Management District (SCAQMD) and the San Joaquin Valley Air Pollution Control District (SJVAPCD) have introduced some of the most stringent NOX emissions limits, mandating reductions to below 9 ppm in 2015 and plans for further reductions in the coming years.

Both upstream and downstream, the oil and gas industry deploys a range of boilers and furnaces, which in the US are primarily fuelled with gaseous fuels such as refinery or natural gas. Typically, natural gas is used to produce steam, which is in turn widely used in a range of applications. For example, operators worldwide deploy enhanced oil recovery (EOR) techniques to aid the extraction of heavy oil. The most common, thermal EOR, requires the burning of large amounts of natural gas to generate steam, which is then injected into the reservoir to reduce the viscosity of crude and facilitate its extraction. Furthermore, oil refineries are highly energy intensive and require significant amounts process heat for the production of gasoline, diesel fuel and other chemicals, mostly supplied by burning refinery gas and natural gas.

Traditionally, operators have been able to meet environmental regulations with the use of ultra low NOX burners. However, as regulations become stricter, two kinds of technologies to curb NOX emissions beyond the capabilities of burners that treat post combustion gases have been deployed: selective catalytic reduction and flue gas recirculation systems. The differences and similarities between these options are outlined below:

  • Selective catalytic reduction: SCR systems act on the exhaust gases produced during the combustion process to reduce the amount of NOX released into the environment. Flue gases pass through a catalyst bed, where a liquid reactant (generally ammonia or urea) is injected. SCR systems set off chemical reactions that convert the NOX contained in the flue gases back into molecular N2 and molecular O2.
  • Flue gas recirculation: FGR is another commonly used NOX emissions reduction technology, particularly for industrial boilers and refinery applications. FGR captures part of the flue gases produced during the combustion process, and reinjects them in the burner with the addition of fresh air. The cooled flue gases are able to absorb heat from the flame, thereby lowering peak flame temperatures and inhibiting the formation of thermal NOX. Written by Roberto Ruiz, ClearSign, Combustion Corporation, USA.

Written by Roberto Ruiz, ClearSign, Combustion Corporation, USA.

Edited by Claira Lloyd

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