|Fuel Oil News is pleased to run this two-part White Paper from John E. Batey, PE, president of Energy Research Center, Inc. Emissions of key air pollutants from oil heating equipment have been substantially reduced over the past three decades to levels that are comparable, and in some cases lower than, natural gas equipment. Notwithstanding that fact however, many misperceptions about air emissions from oil equipment remain. This report summarizes the results of extensive research related to air emissions from numerous, highly credible sources, all of which clearly show that heating oil is one of the cleanest fuels in both residential and commercial applications. In fact, as the use of lower sulfur fuel oil and biodiesel/heating oil blends expands, residential and commercial oil heating equipment could readily become the best option for lowering annual air emissions...including greenhouse gases.
Part One left off during a discussion of specific emissions, and this resumes with sulfur oxides.
The sulfur oxides emitted by a fuel are directly related to the sulfur content of the fuel. In recent years, the average sulfur content of home heating oil has been steadily decreasing. Twenty to 30 years ago, average sulfur content was approximately 0.5 percent and even higher in some areas. In recent years, the average sulfur content of home heating oil has been near 0.225 percent (3).
Figure 9 shows recent changes in fuel sulfur content for distillate oil. A low sulfur product with only 0.05 percent (500 ppm) of sulfur has been required for on-highway use for some time and is also being used by some fuel oil dealers for their residential customers. The oil heat industry is moving to make this the standard fuel for all homes, given that it results in an almost 80 percent reduction in sulfur oxide emissions. A new ultra-low sulfur diesel fuel is now required for on-highway use with only 0.0015 percent (15 ppm) sulfur. [Figure 9] Shown on the far right hand side of the chart, this fuel is approaching zero sulfur content and zero emissions, inasmuch as it represents a 99 percent reduction in both. As the use of this product expands over time to residential heating, overall sulfur oxide emissions will decrease towards virtually non-existent.
This dramatic reduction in sulfur oxide emissions is similar to the particulate matter reductions, which occurred from the 1960s to the 1990s. In this case, however, the improvement is not attributable to burner design advances, but rather is the result of using improved fuels with a lower sulfur content. No changes to the heating equipment are needed in order to use the cleaner-burning, lower sulfur fuel, although service intervals can be extended, thus lowering maintenance costs.
Figure 10 presents sulfur oxide emissions in lbs/MMBtu of fuel burned for a range of combustion sources evaluated. It shows that oil and gas emissions are both very low and approach the limit of zero emissions when compared to other common combustion sources.
While No. 2 oil is visible on the chart, it is a miniscule fraction of both coal and residual oil emissions; low and ultra-low sulfur oil products, with or without blended bio-fuels, represent trivial emission levels, as does natural gas and 100 percent biodiesel, which are the lowest. When compared to home oil burner SO2 emission rates, No. 6 residual oil is 10 times higher, and coal with 3 percent sulfur content is more than 17-1/2 times higher. If all of the combustion sources in the U.S. emitted the same low sulfur oxide levels as residential oil and gas heating equipment, acid rain and its related problems would be virtually eliminated.
Residential oil burners produce very low carbon monoxide emissions. Figure 11 shows that No. 6 fuel oil, No. 2 fuel oil, low sulfur No. 2 oil, ultra-low sulfur No. 2 oil, biodiesel blends, and natural gas all emit carbon monoxide at very low rates. Residential oil burners emit only 0.026 lbs/MMBtu, which is lower than natural gas burners at 0.039 lbs/MMBtu. Oil and gas emissions are all much lower than either coal or diesel engines.
It is important to note that the carbon monoxide emission rates shown here are for properly adjusted residential burners. Carbon monoxide emissions from heating equipment, however, can increase by several orders of magnitude if the burner is not properly adjusted or is not supplied with adequate air for complete combustion of the fuel; too much combustion air can also increase CO levels. In extreme cases, high concentrations of carbon monoxide released into the home can produce hazardous and life-threatening conditions that present an immediate health and safety danger to occupants. Residential fuel oil burners typically produce smoke before carbon monoxide levels increase; this serves as a rudimentary, but nonetheless reliable “warning signal” that the system is not running properly. In contrast, gas burners can produce very high CO levels before any smoke is observed. The emission values reported in Figure 11 are for properly adjusted burners that have adequate combustion air supply and are properly vented.
Figure 12 presents carbon monoxide emissions in lbs/MMBtu of fuel burned for the range of combustion sources that were evaluated. When wood burning fireplaces and gas engines are added, the CO emissions from residential oil and gas burners are so small they are no longer visible on the chart.
Other common combustion sources emit significantly greater levels of carbon monoxide: Coal burning emits 7 times more; diesel engines emit 28 times more; wood fireplaces emit 580 times more; and industrial gasoline engines emit 2400 times more CO than home oil or gas heating systems.
Given that modern oil burners produce very low levels of carbon monoxide compared to many other combustion sources, it is certainly safe to say that if all combustion equipment produced the same low levels, carbon monoxide would not be a serious problem in the U.S.
Figure 13 shows that coal, No. 2 fuel oil, low sulfur No. 2 oil, ultra-low sulfur No. 2 oil, and biodiesel blends all emit very low rates of unburned hydrocarbons. Residential oil burners emit only 0.0017 lbs/MMBtu based on BNL tests, which is considerably less than natural gas burners at 0.011 lbs/MMBtu. No. 2 oil emissions are lower than both No. 6 residual oil and natural gas.
Hydrocarbon emissions are generally considered to be as undesirable because some components can directly cause adverse health effects, depending on their chemical composition. Hydrocarbon emissions also contribute to the formation of secondary pollutants in the atmosphere. Furthermore, they interact with nitrogen oxides in the presence of sunlight to form ozone and other oxidants in a series of very complex chemical reactions. These secondary pollutants have been shown to produce various health impacts and can even damage vegetation.
Figure 14 presents hydrocarbon (HC) emissions in lbs/MMBtu of fuel burned for a range of combustion sources evaluated. When diesel engines, gas engines and wood stoves are added, the HC emissions from residential oil and gas burners are so small they are no longer visible on the chart.
Other common combustion sources emit much higher levels of unburned hydrocarbons: No. 6 oil emits 4 times more; natural gas emits 6.5 times more; diesel engines emit 200 times more; gasoline engines emit 1200 times more; and finally, wood fireplaces emit 7,800 times more HC than home oil burners.
Compared to most other combustion sources, modern oil burners release very low levels of hydrocarbons and, thus, are an insignificant source of HC in the U.S.
Greenhouse Gas Emissions: Carbon Dioxide and Methane
Carbon dioxide (CO2) and methane are two of the gases that are emitted by fuel transport and combustion and are suspected of contributing to global warming by absorbing solar radiation in the atmosphere. Carbon dioxide is a non-toxic gas that is a primary exhaust constituent whenever hydrocarbon fuels are burned. Methane is the main component of natural gas, some of which is inadvertently released during natural gas production, transmission, storage and distribution by pipeline to end users. Methane is an extremely powerful greenhouse gas – in fact it is between 30 and 70 times more powerful than CO2 in producing global warming (8,9). Both carbon monoxide and methane emissions must be considered in order to fully evaluate the total cumulative impact of air emissions from various combustion sources.
The rate of carbon dioxide emissions from various combustion sources are shown in Table 1. Heating oil used in homes has a USEPA emission rate for CO2 of 159 lbs/MMBtu. This is higher than natural gas, but lower than residual oil, coal and wood stoves. Figure 15 summarizes the results for CO2 emissions. Biodiesel is much lower because it is a renewable fuel, which re-absorbs carbon during the re-growing process. It is projected that in the very near future, the use of heating oil with biodiesel blends will actually reduce heating oil carbon dioxide emission rates far below even the level emitted by natural gas combustion.
Carbon dioxide is, however, only one part of total greenhouse gas emissions; the impact of methane releases must also be taken into account to fully evaluate the impact of a fuel’s greenhouse contributions. A new term, global warming potential (GWP), calculates the global warming impact of methane released, in terms of its equivalent pounds of carbon dioxide. The combined effect of carbon monoxide and methane emissions can then be evaluated to determine their net impact on the environment.
Natural gas (primarily methane) release rates during storage and transport are difficult to measure and estimates of total emissions vary. The World Resource Institute estimated that methane emissions from natural gas pipelines in 1987 totaled 53 million metric tons. A study by the United Kingdom House of Commons Energy Committee calculated average gas leakage rates worldwide of 4.7 percent of throughput, with 3 percent in North America. Greenpeace reviewed independent studies and found that a 3.5 percent methane release rate from natural gas systems worldwide may, in fact, be a conservative estimate.
Publications by the Gas Research Institute (GRI), (based on joint USEPA and GRI studies), identify some 800,000 gas leaks annually in the U.S. Annual methane emissions in the U.S. from natural gas leakage were calculated to be 314 billion cubic feet, or approximately 1.4 percent of gross gas production (10). The U.S. DOE publication “Natural Gas Annual” shows that from 1994 through 1998, the average “lost and unaccounted-for natural gas” figure represents approximately 2.6 percent of total gas consumption (11). While the concept of “unaccounted-for natural gas” is not directly equivalent to a leakage rate, the figure calculated by U.S. DOE is of the same magnitude as previously-cited estimates of natural gas system leakage rates. This research conservatively indicates that a leakage rate of between 1.4 and 3.5 percent annually is expected in the U.S., which is, therefore, used in this analysis.
Figure 16 presents the impact of these various methane release rates on the GWP of natural gas use. At zero percent leakage, the GWP is equal to the carbon dioxide emissions shown in Table 1. However, as the methane release rate increases, so does the GWP. At a 1.4 percent leakage rate (NG 1.4percent) the global warming potential of natural gas use increases by 14 percent. At a 2.6 percent methane release rate, the GWP increases by 26 percent. At this leakage rate, the GWP of natural gas is rapidly approaching that of home heating oil; if the actual methane release rate rises to 3.5 percent, the GWP of natural gas is higher than home heating oil.
This was noted in a report by Dr. Dean Abrahamson entitled “Relative Greenhouse Effect of Fossil Fuels and The Critical Contribution of Methane” (8), which concludes that heating oil produces less global warming than natural gas if more than 1 or 2 percent of the natural gas leaks to the atmosphere during transmission, storage and distribution.
When biodiesel, a renewable fuel increasingly available to home owners, is blended with heating oil, its GWP can be much lower than natural gas. (See Figure 17).
Figure 17 compares the emissions of greenhouse gases from common energy sources, increasing from the lowest to the highest global warming potential; as detailed below:
• “Biod 100percent” is heating oil consisting of 100 percent biodiesel fuel. Its GWP is only 32, which is the lowest value evaluated. Figure 17 reveals that the lowest global warming potentials for all fuels considered are produced by the biodiesel-heating oil blends. Total global warming emissions for natural gas with a 2.6 percent gas leakage rate are very close to emissions for standard No. 2 fuel oil. If actual gas leakage rates are higher than 2.6 percent, standard heating oil may produce less global warming than natural gas. Given the range and uncertainty in possible leakage rates and emission factors for natural gas, it can be safely concluded that natural gas and No. 2 home heating oil have comparable global warming impacts.
• The next two lowest are home heating oil blends with 35 percent and 20 percent biodiesel, respectively.
• “NG 1.4percent Leak” is natural gas with a leakage rate of 1.4 percent of throughput, using an average methane-to-CO2 global warming ratio of 30 and a methane percentage in natural gas of 90percent.
• The next lowest GWP is “Biod 10percent,” which is heating oil consisting of 10 percent biodiesel fuel.
• “NG 2.6percent Leak” is for natural gas including a gas leakage rate of 2.6 percent of throughput.
• “No. 2 oil”, represents standard petroleum-based distillate heating oil currently used in most homes.
• “NG 3.5percent” is natural gas with a 3.5 percent release rate which has a higher GWP than No. 2 home heating oil.
• “Coal” emissions are elevated because of the higher carbon-to-hydrogen ratio, which produces higher levels of carbon dioxide, as shown in Table 1.
• “Electric” energy has the highest greenhouse gas emissions based on US Department of Energy Publications showing total carbon dioxide emissions and total energy generated (8).
One final factor that has not been included in the present analysis is the emission of greenhouse gases by the energy used to pump natural gas through thousands of miles of interstate and distribution pipelines. This energy requirement is substantially higher than that for heating oil. These added greenhouse gas emissions further diminish the differential between oil and natural gas carbon dioxide emission rates. The Europe-based Fichtner report, “Comprehensive Energy and Emissions Assessment for Heating Systems”, (13) indicates that when these energy pumping and movement factors are included, the greenhouse gas emissions for heating oil and natural gas are essentially equivalent. In some cases, oil may in fact have lower global warming potentials. More quantitative data on the amount of energy used in the U.S. to move natural gas through the interstate pipeline system is required so that this factor can be properly included in future analyses.
In light of the fact that lower CO2 emissions from natural gas are counteracted by the higher methane emissions from gas leakage and other factors, one may reasonably conclude that converting an oil-fired home heating system to natural gas powered equipment will not lower greenhouse gas emissions. By the same token, one may conclude that the increased use of home heating oil containing varying biodiesel blends will substantially lower greenhouse gas emissions. Even at blend levels as low as 10 percent biodiesel in heating oil, the total global warming potential is lower than natural gas, particularly so within the range of expected gas leakage rates.
References cited earlier indicate an average natural gas leakage rate of between 1.4 and 3.5 percent. Therefore, when the full scope of the global warming impact of natural gas methane releases are included, (and temporarily ignoring the energy use for pumping natural gas through pipelines), the net global warming impacts of home heating oil and natural gas are quite similar. Based on these data and analyses, and contrary to the assertions of some local gas distribution companies, we are quite confident in asserting that there would be no meaningful net global warming benefit produced by replacing home oil burners with natural gas burners.
In fact, it can be shown that using home heating oil that contains even a small percentage of biodiesel fuel can reduce greenhouse gas emissions below that of natural gas powered equipment. Future activities to convert homes and businesses that now use natural gas to oil heat, may be recommended to lower greenhouse gas emissions.
Annual Air Emissions
In summary, the total quantity of air pollutant emissions produced by residential oil heating systems each year is extremely low, particularly when compared to total U.S. emissions. Past evaluations completed by Brookhaven National Laboratory and the Oilheat Manufacturers Association have repeatedly demonstrated oil heat’s low annual emissions (14).
Table 2 is a recent update which shows that oil burners account for only 0.005 percent to 0.71 percent of each of the air emissions shown. This is based on U.S. Department of Energy fuel use data for 2004 and U.S. Environmental Protection Agency annual air emissions data for 2005.
When the lower sulfur oxide emissions from ultra-low sulfur fuel oil are included, the emission value for home oil burners falls to 0.005 percent. This is only 5/100,000th of the total, which is a negligible fraction of annual sulfur oxide emissions. Biodiesel fuel blends in home heating oil will further substantially reduce the annual emissions totals shown in Table 1 for particulate matter, nitrogen oxides and sulfur oxides, in addition to lowering greenhouse gas emissions.
It is clear from these emissions data that residential oil burners are not a significant source of air pollution in the U.S., given that the total annual air emissions generated are only a small fraction of one percent of the total annual emissions for all other pollutants.
A comprehensive report on oil burner air emission conducted by Brookhaven National Laboratory concluded: “Residential oil burners generally, and modern equipment specifically, are not significant national emission sources.” (14) The increased availability of low and ultra-low sulfur oil and biofuels further substantiates this conclusion.
Expected Future Air Emissions from Oil Heating Equipment
Air emissions from residential oil heating were significantly higher in the past due to older, less sophisticated equipment design and fuels with a far higher sulfur content. Currently, both the rate and total mass of air emissions from homes heated with oil are very low. In some cases, oil heat systems produce fewer emissions than natural gas and both are very clean burning.
The short and long-term future holds even greater promise for residential oil emissions to decrease below their current low levels to a point where they may, in fact, become the lowest emission source in homes, once the release of greenhouse gases is included. Three important factors will contribute to lower emissions in the future. These are: the continued technological advancement and increased sophistication of oil burner designs; improved fuel quality and the increased use of lower sulfur fuel oil; and the greatly expanded use of biodiesel blends.
Oil burner and heating system component design is continually improving, this results in increased system efficiency, lower fuel use and consumer costs and lower air emissions. The initial development of the flame retention burner more than 30 years ago laid the technical ground work for further innovation, research and development, which continue to this moment. Recent advances include increased burner air supply pressure for better fuel/air mixing, clean-cut fuel pumps and solenoid valves for cleaner burner start-up and shut-down, low-mass boilers and water temperature modulation. These and other advances will continue to improve overall system efficiency and lower air emissions in the future well below their present levels.
The increased availability and expanded use of lower sulfur fuel oil in the future will also substantially reduce sulfur oxide and PM emissions. The expanded use of these fuels is expected to continue as they are now required for both on-highway, off-highway and stationary engine use. A recently concluded, comprehensive field study conducted by the New York State Energy Research and Development Authority (NYSERDA) of the benefits of low sulfur heating oil clearly demonstrated the additional economic advantages of this product (3). Because the heating system ran so cleanly, the necessary maintenance intervals were greatly extended; the lower operations costs more than offset the added cost of the lower sulfur product. Finally, both the National Oil Heat Research Alliance (NORA) and the Oilheat Manufacturers Association (OMA) have fully and enthusiastically endorsed the use of lower sulfur heating oil. Therefore, wide-spread use of low and ultra-low sulfur heating oil is expected in the near future. This will help to further reduce the PM, NOX and SOX emissions from residential oil heating equipment below their already low levels.
The rapidly increasing use of biofuel blends in home heating oil holds the most promise for substantial reduction of key air pollutants from oil burners in the near future. Soy-based biodiesel is now blended by some fuel suppliers into heating oil at 5 percent, 10 percent and 20 percent ratios. The positive emissions benefits are quite meaningful (4). Smoke and PM emissions are lowered with the biodiesel blends and PM emissions may be lower even than natural gas burners when a high percentage blend of biofuels and ULS fuels are used in oil burners. Tests show that conventional oil burners can operate with blue (reduced carbon) flames when higher percentages of biofuels are used. Biodiesel does not contain sulfur, thus sulfur oxide emissions are lowered; nitrogen oxide emissions are also lowered by 20 percent of more when biofuel blends are used.
As discussed in detail earlier, another important benefit of biodiesel blends in home heating oil is the reduction in greenhouse gas emissions. Biofuels, including soy and canola are renewable fuel sources that are subsequently re-grown. During the re-growing process, some of the carbon dioxide emitted when the fuel is burned is recaptured by the new crop, which substantially lowers the net amount of CO2 released. No other common residential energy source can lower carbon dioxide emissions as much as biodiesel blends in home oil burners. In fact, as biodiesel supply and use increases, home heating oil/bio blends may well become the preferred fuel for lowering greenhouse gas emissions in the U.S.
In conclusion, it is clear that oil heat now produces very low emissions of all the key regulated air pollutants of concern in the U.S. As technological developments continue and as the use of low sulfur and biodiesel fuel blends increases in the future, residential oil burners can readily become the preferred environmental choice over all other home energy sources.
1. Emissions Characteristics of Modern Oil Heating Equipment, R. Krajewski, Y Celebi, R Coughlan, T Butcher, and RJ McDonald, BNL Report 52249, July 1990.
2. Compilation of Air Pollutant Emission Factors, Volume I: Stationary Point and Area Sources, Publication AP-42, US Environmental Protection Agency.
3. Low Sulfur Home Heating Oil Demonstration Project Summary Report, John E. Batey and Roger McDonald, BNL-74956-2005-IR, project funded by the New York State Energy Research and Development Authority, Contract No. 4204-IABR-BR-00, June 2005.
4. Combustion Testing of a Biodiesel Fuel Oil Blend in Residential Oil Burning Equipment, John E. Batey, prepared for the Massachusetts Oilheat Council and the National Oilheat Research Alliance, July 2003
5. “Air Emissions Summary Through 2005”, US Environmental Protection Agency, Air Trends, Air and Radiation, updated June 12, 2007.
6. “Table S4, Residential Sector Energy Consumption Estimates, 2004”, US Department of Energy, Energy Information Administration
7. Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus, US Department of Agriculture and US Department of Energy, NREL/SR-580-24089 UC Category 1503, Final Report, May 1998.
8. Dr. Dean Abrahamson, “Relative Greenhouse Effect of Fossil Fuels and the Critical Contribution of Methane”, 1990.
9. Carol Alexander, Greenpeace Energy Campaign, Natural Gas: Bridging Fuel or Road Block to Clean Energy, DRAFT, April 1992.
10. Gas Research Institute Digest, pages 24-26, Fall 1996.
11. Natural Gas Annual, US Department of Energy/Energy Information Administration, 1998.
12. Electric Power Annual, US Department of Energy, DOE/EIA-0348, March 2003.
13. Comprehensive Energy and Emissions Assessment of Heating Systems, Fichter Report.
14. Prospects for Residential Oil Burners with Reduced Emissions, Thomas A. Butcher, Richard F. Krajewski, Yusef Celebi, Roger J. McDonald, and John E. Batey, presented at the Air and Waste Management Association Meeting, 1992.
15. Radian Corporation, Evaluation of the Acceptability of Natural Gas as a Mitigating Fuel for Utility Combustion Sources, US Environmental Protection Agency, Research Triangle Park, NC, PB-91-226449, June 1991.
16. Institute for Gas Technology, Medium and High Pressure Sonic Leak Pinpointing, Gas Research Institute, PB83-228361, May 1983.
17. D. A. Lashof and D. R. Ahuja, Relative Contributions of Greenhouse Gas Emissions to Global Warming, Nature, 15, 1989.
18. US Environmental Protection Agency, National Air Quality and Emissions Trends Report, 1999, Office of Air Quality Planning and Standards, EPA 454/R-96-005, March 2001.
19. Oilheat Advantages Project - Engineering Analysis and Documentation - Efficiency, Clean
Burning, Low Air Emissions, Economics, Safety, and Energy Conservation and New Technologies, Energy Research Center, Inc., for the Oilheat Manufacturers’ Association, July to November 1994.
John Batey has extensive experience in evaluating gas and oil combustion equipment and HVAC systems, and efficiency improvement and air emissions regulations in residential, commercial, and institutional buildings as a research and applications engineer. He served as the principal engineer and laboratory manager at Brookhaven National Laboratory for five years, where he developed and operated a test facility for evaluating oil-fired space heating equipment for the U.S. Department of Energy. Along with numerous articles, he has authored two training books: Advanced Oil Heat - A Guide to Improved Efficiency completed in 1994 for Brookhaven National Laboratory, and A Guide for Efficient Oil Heating in Homes in 1981, co-sponsored by the U.S. Department of Energy and the oil industry as part of a national energy conservation program. And, he continues to work with Brookhaven National Laboratory on their in-house combustion space-heating research projects as well as advising industry trade organizations such as PMAA.