ENVIRONMENTAL IMPACTS OF COMBUSTION

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The negative effects of combustion on the environment – particularly greenhouse gas (GHG) emissions released to the atmosphere that contribute to global warming – have received much attention in recent years. This issue is addressed in the Kyoto Protocol (1997). Canada, which signed the Protocol, aims to reduce emissions between 2008 and 2012 by six percent of 1990 levels. Climate change resulting from global warming is one of the greatest challenges facing not only Canada but also the world. Managing combustion processes better and improving the efficiency of energy generation and use are two of the key strategies for reducing atmospheric emissions.

Therefore, this guidebook is being published in concert with Canadas policy on climate change as one of the tools for implementing it. Canadas goal of reducing GHG and acid-rain emissions can be met only with the co-operation of the owners and operators of combustion equipment. It is beyond the scope of this guidebook to describe the emissions in detail. Instead, a brief ove rv i ew is presented (see Table 2 for a list of some emissions from combustion systems and their effects). More complete information can be obtained from An Energy Efficiency and Environment Primer for Boilers and Heaters.

Table 2. Emissions from Combustion Systems and Their Effects

EMISSION	SOURCE	EFFECT	GHG POTENTIAL RELATIVE TO CO2
CO2 (carbon dioxide)	Complete combustion of carbon in fuel	Global warming	1
CO (carbon monoxide)	Incomplete combustion of carbon in fuel	Smog
SO2 (sulphur dioxide)	Combustion of sulphur in fuel	Smog, acid rain
NOx (nitrogen oxides)	By-product of most combustion processes	Acid rain
N2O (nitrous oxide)	By-product of some combustion processes	Global warming	310
VOCs (volatile organic compounds)	Leakage and evaporation of liquid fuels (from, e.g., vehicles, fuel tanks, fuel pumps, refineries, solvents from paints)	Smog
CH4 (methane)	Principal component of natural gas; leakage from gas wells, pipelines and distribution systems	Global warming	21
H2O (water vapour)	Combustion of hydrogen in fuel	Localized fog
Particulates (dust, soot, fumes)	Unburned or partially burned carbon and hydrocarbons; also ash and dirt in fuel	Smog
Trace elements	Impurities in fuel	Potential carcinogens
Halogenated compounds	Compounds in fuel or combustion air containing halogens (chlorine, fluorine, bromine and iodine)	Potential carcinogens, global warming	Up to 24 000

 

Table 3. CCME* NO_x Emission Guidelines for New Boilers and Heaters

INPUT CAPACITY	NOX EMISSION LIMIT, g/GJ** AND PPM (AT 3% O2)***
	10.5 TO 105 GJ/h (10 TO 100 MILLION Btu/h)	GREATER THAN 105 GJ/h (>100 MILLION Btu/h)
Natural gas	26 (49.6)	40 (76.3)
Distillate oil	40 (72.3)	50 (90.4)
Residual oil with less than 0.35% nitrogen	90 (162.7)	90 (162.7)
Residual oil with 0.35% or more nitrogen	110 (198.9)	125 (226.0)
*      Canadian Council of Ministers of the Environment **    g/GJ = grams of NOx emitted per gigajoule of fuel input ***  ppm = parts per million by volume, corrected to 3% O2 in the flue gas (10 000 ppm = 1%)

To correct ppm NO_x to 3% O₂: NO_x at 3% O₂ = [NO_x measured x 17.9] / [20.9 - O₂], where O₂ is oxygen measured in flue gas, dry basis

To convert ppm NO_x at 3% O₂ to g/GJ: for natural gas, g/GJ = ppm / 1.907 for fuel oil, g/GJ = ppm / 1.808

Table 4. Typical NO_x Emissions Without NO_xControl Equipment in Place

FUEL AND BOILER TYPE		TYPICAL NOX EMISSIONS (PPM AT 3% O2)
Natural gas	Firetube	75-115
	Package watertube	40-90
	Field-erected watertube	45-105
No. 2 oil	Firetube	70-140
	Package watertube	90-150
	Field-erected watertube	40-115
No. 4 oil	Package watertube	160-310
	Field-erected watertube	140-190
No. 6 oil	Package watertube	200-360
	Field-erected watertube	190-330

Although the other GHGs, unit for unit, are much more potent than CO₂ in their effects, the latter is the most important GHG because of its volume. In 1997 it represented three-quarters of Canada's total emissions. Most of the CO₂ is generated by the combustion of fuels, whether for residential, industrial, transportation or electric power generation purposes. So, applying energy efficiency measures that reduce fuel consumption is crucial to reducing CO₂ emissions.

Fuel consumers face a double challenge. One is economic – to get the best value for their fuel budget. The other is environmental – to keep emissions low, at least within legislated limits. Fortunately, what benefits the first objective also benefits the second.

Higher limits are allowed for equipment with a proven higher efficiency than normal and which, therefore, burns less fuel. Provinces and territories are responsible for enforcement and may enact stricter limits. They also have responsibility for determining to what extent the guideline applies to boilers and heaters that are being modified or overhauled.

Emissions of sulphur dioxide (SO₂) and nitrogen oxides (NO_x) contribute to acid rain and, therefore, are also of concern. SO₂ emissions are controlled by limiting the allowable sulphur content of the fuel, but NO_x emissions can be reduced by manipulating the combustion process. Guidelines for new boilers and heaters are presented in Table 3, and An Energy Efficiency and Environmental Primer for Boilers and Heaters describes the strategies for complying with NO_x regulations.

 

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