4. Emissions Resulting from the Combustion of Fuel Oils

• 4.1 Inventory of SO_x , PM_2.5 and PM₁₀ Emissions (1995)
  • 4.1.1 Background and Methodology
  • 4.1.2 Overview of Sulphur Oxide Emissions from the Combustion of Fuel Oils
  • 4.1.3 SO_x Emissions from HFO
  • 4.1.4 SO_x Emissions from LFO
• 4.2 Effects of Fuel Oil Sulphur Levels on Emissions
  • 4.2.1 Literature Review
  • 4.2.2 CANMET's test results

In the "Action on Future Standards for Fuel Oils" as described in the Federal Agenda on Cleaner Vehicles, Engines and Fuels¹⁵, Environment Canada indicated its intention to study the benefits and costs of reducing sulphur in fuel oils. To provide background information on this issue, an analysis of the existing emissions of sulphur oxides (SO_x) and particulate matter (PM₁₀ and PM_2.5) from the use of fuel oils in Canada was performed.

Environment Canada's Residual Discharge Information System (RDIS) database is used to compile and store emissions inventory information consisting primarily of Criteria Air Contaminants (CAC)¹⁶ originated from a number of sources at various regions and provinces in Canada. The most recent inventory available is for the year 1995¹⁷.

Estimates of the mass of contaminants (SO_x, PM₁₀ and PM_2.5) released over a one year period were obtained from the RDIS database according to source, location, industrial sector (grouped according to Standard Industrial Classification code), fuel type and industrial process. These emissions estimates were compiled and analyzed at the national and provincial levels according to categories used by Environment Canada for reporting purposes. Further detail regarding the inventories of emissions from HFO and LFO use can be found in the technical paper listed in Appendix 1, titled Canadian Inventory of SO_x, PM₁₀ and PM_2.5 Emissions Resulting from the Combustion of Fuel Oils (October 2002).

The majority of SO_x, PM₁₀ and PM_2.5 emissions from the combustion of fuel oils occur in the eastern provinces.

Total annual emissions of sulphur oxides from the use of HFO are estimated to be 206.1 kilotonnes (kt) nationwide, for 1995 (This represents 5% of CAC). Excluding transportation, open and miscellaneous sources, the combustion of fuel oils accounts for 16% of all SO_x emissions in the eastern provinces. Figures Figure4.1 and Figure4.2 present the regional contributions to the HFO and LFO inventories of SO_x emissions, from which it can be seen that sulphur in fuel oils is clearly an eastern Canada issue.

Figure 4.1: 1995 Canadian Estimated Annual SO_x Emissions from HFO Use by Province

Figure 4.2: 1995 Canadian Estimated Annual SO_x Emissions from LFO Use by Province

In 1995, 97% national emissions of SO_x from the combustion of HFO emissions is concentrated in the eastern provinces of Ontario, Quebec, New Brunswick, Nova Scotia and Newfoundland. Three industrial sectors account for 73% of the eastern SO_x inventory from HFO use: electric power generation, petroleum refining and pulp and paper¹⁸ sectors. Those sectors are also the largest emitters of PM₁₀ and PM_2.5 attributed to the combustion of HFO in eastern Canada¹⁹. The contributions of the various eastern sectors to the eastern SO_x inventory from HFO use are presented in Figure 4.3.

Figure 4.3: Sectoral Contributions to Eastern SO_x Inventory from HFO Use (1995)

The combustion of LFO results in an estimated at 21 kt/y of SO_x emissions, with 94% of these emissions in the eastern provinces of Ontario, Quebec, New Brunswick, Nova Scotia and Newfoundland. Most of the SO_x, PM₁₀ and PM_2.5 emissions from the combustion of LFO in the eastern provinces is from residential and commercial use. Residential and commercial use is responsible for a combined 80% of the SO_x inventory in the east from LFO use. The contributors to the eastern Canada SO_x inventory from LFO use are presented in Figure 4.4.

Figure 4.4: Sectoral Contributions to Eastern SO_x Inventory from LFO Use

Natural Resources Canada's CANMET Energy Technology Center has carried out a literature review of public information on research strategies to examine the impact of sulphur content in fuel oil, fuel oil combustion in stationary combustion equipment and associated gaseous and particulate emissions. (The report listed in Appendix 1 is available on request).

The review indicated that the combustion of fuel oils results in numerous emissions: for example, "Burning heavy fuel oils releases to the environment of a range of gaseous oxides of sulphur, nitrogen and some of the metals present in the fuel. Carbon particulate matters from incomplete combustion or particulates containing a range of sulphate compounds are also released. Depending on the firing conditions they could be supplemented by other pollutants such as Volatile Organic Compounds (VOC), Poly[cyclic] aromatic Hydrocarbons (PAH) and occasionally chlorine, such as HCl. Lowering sulphur content in the heavy fuel oils will lead directly to overall reduction in stack gas emissions of sulphur dioxide."

The review indicated that in oil-fired systems, most of the sulphur in the fuel can be expected to appear in the stack gas as SO₂ with some fuel sulphur that may be oxidized to SO₃ depending on the firing conditions. Typical SO₂ emissions from various grades of fuel oil are provided in Table 4.1. In all cases, SO₂ emissions increased with higher levels of sulphur in the fuel.

The review indicated that a significant fraction (30-50%) of the particulate emissions from the burning of HFO would be less than 2.5 µm in diameter and would contain most of the chemically-bound sulphur with the heavy metals present in the fuel ash.

The U.S. Environmental Protection Agency (EPA) undertook a number of studies conducted on emissions of particulates and hazardous air pollutants from the combustion of a range of fuel oils with different sulphur content. This work indicates, that lowering the sulphur content in the heavy (No. 6) fuel oil from 1.66% wt. to 0.49% wt. (70% sulphur content reduction) reduces total particulate emissions by 86%. It also indicates that total metal emissions are reduced by 87%, mostly due to reduced emissions of vanadium, nickel and lead. Those three metals accounted for most of the metal emissions, but also present were magnesium, chromium, antimony, cadmium, arsenic, selenium, beryllium and mercury, along with ash and chlorine. When sulphur in HFO is reduced, its ash content and chlorine level are also reduced.

Extensive measurements by the EPA of 195 organic compounds during combustion of low sulphur No. 6 oil and high sulphur No. 6 oil, indicate an decrease of total PAH emissions with the lower sulphur No. 6 oil. Lowering the sulphur content in No. 6 fuel oil from 1.66% wt. to 0.49% wt. (70% sulphur content reduction) reduces total PAH emissions by 77%. The PAHs emitted from the combustion of HFO include primarily naphthalene, but also include phenanthrene, fluorene, benzo(g,h,i)perylene, and acenaphthylene, with lesser amounts of acenaphthene, anthracene, benzo(a)anthracene, chrysene, dibenz(a,h)anthracene, fluoranthene, indemo(1,2,3-c,d)pyrene and pyrene. PAHs emitted from the combustion of LFO include all those above, except anthracene and chrysene, plus they included benzo(a)pyrene, benzo(b)fluoranthene, and benzo(k)fluoranthene.

In addition to the extensive literature review, CANMET Energy Technology Center investigated the impact of fuel sulphur on emissions for oil-fired combustion systems, first for LFO and then for HFO.

The test program for LFO examined emissions from five distillate fuels containing sulphur levels from 0.05 to 0.6% wt. Test fuels were prepared by spiking different quantities of sulphur doping agent to the low sulphur (0.05% wt. sulphur) diesel fuel. A residential scale hot water boiler was used as combustion equipment. Emission performance of the fuels, in terms of their particulate matter and gaseous emissions of O₂, CO₂, CO, SO₂ and NO_x was determined and compared. The key emission analysis tool used was CANMET's fine PM sampling system, which is capable of providing source PM concentrations that approximate ambient PM found in the atmospheric plume immediately downwind of the source.

The study indicated that over the range of sulphur concentration studied under selected experimental conditions, flue gas SO₂ emissions increased linearly with the increase of sulphur in LFO (sulphur-spiked diesel fuel), while other emissions remained relatively unchanged. Similar elevation of filterable PM mass concentrations was also observed as the fuel sulphur increased. The results also suggest that a majority of particulate emissions from diesel fuel combustion is in the 2.5 µm size range, and that the sulphate content of particulates would decrease when LFO sulphur is reduced.

Similar investigation using HFO was conducted and results will be communicated as they become available.

¹⁵ Minister of Environment. A Federal Agenda for Cleaner Vehicles, Engines and Fuels. Canada Gazette, Part I, February 17, 2001, pp. 452-457.
¹⁶ Criteria air contaminants are: Total Particulate Matter (TPM), Particulate Matter less than or equal to 10 Microns (PM₁₀), Particulate Matter less than or equal to 2.5 Microns (PM_2.5) Sulphur Oxides (SO_x), Nitrogen Oxides (NO_x), Volatile Organic Compounds (VOC), and Carbon Monoxide (CO).
¹⁷ Since 1995, two oil-fired plants (approx. 2500 MW or 50% of the total oil-fired capacity) have had the boilers converted to dual-fuel capability. These two plants can burn either natural gas or heavy fuel oil. A third unit (100 MW) has been re-powered to a gas turbine operation fuelled with natural gas. Sulphur dioxide emissions from these plants are nearly zero when the plants are fired on natural gas. A fourth oil-fired plant (1050 MW) is in the planning stages of being modified to fire on Orimulsion. The plans are to have this plant equipped with stack gas scrubber for the removal of sulphur dioxide from the flue gas. In total, about 3700 MW (or 75%) of the total oil-fired capacity have, or are about to have, means reduce sulphur emissions.
¹⁸ Since 1995, HFO consumption in the pulp and paper industry has declined approximately 7-9%. This decline in consumption is most likely attributed to fuel switching to natural gas due to new availability, reduction in the energy intensity of production and varying economic conditions. This decrease is not interpreted as a downward trend, but as a specific response to annual economic conditions.
¹⁹ The large percentage of PM emissions reported from the combustion of HFO in the pulp and paper sector can be attributed to the inclusion of other process variables in the facility data reported to provincial/territorial authorities. These emissions are considered to be caused by either the primary fuel source, such as the combustion of wood waste in power boilers, or process losses in lime kilns from the calcination process.
²⁰ Note SO₂ ppmv @ 3% O₂ is not the same as mg SO₂/Nm³, which is the European units.
²¹ W. Lee. "The Performance of Oil-fired Boilers: The Influence of Fuel Sulphur on Emissions and Appliance Integrity." ASHRAE Transactions, vol. 103, part 1, 1997.
²² C. A. Miller, J. V. Ryan and T. Lombardo. "Characterization of Air Toxics from an Oil-fired Firetube Boiler." JA&WMA, vol. 46, pp. 742 - 748, August 1996.
²³ V. V. Razbin, F. D. Friedrich and S. W. Lee. "Heating Plant Performance and Emissions, Nova Scotia Hospital, Dartmouth, N. S." Energy Research Laboratories Division Report ERL-91-86. CANMET, Energy, Mines and Resources Canada, 1991.
²⁴ F. D. Friedrich, V. V. Razbin and F. L. Wigglesworth. NO_x and SO₂ Emissions with No. 6 and No. 4 Fuel Oils at Canadian Forces Base Halifax." Energy Research Laboratories Division Report ERL-92-27, CANMET, Energy, Mines and Resources Canada, March 1992.
²⁵ I. Gulyurtly, H. Lopes and I. Carbita. "The Determination of Emissions of Pollutants from Burning Waste Oils" Fuel, Vol. 75, No. 8, pp. 940-944.
²⁶ H. Whaley, J. Wong, G. Banks and W. Lee. "The Composition and Handling Properties of Several Heavy Bitumen Emulsions." ASME International Joint Power Conference, Minneapolis MN, 1995.