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2. Emissions

1. 2.1 OVERVIEW
2. 2.2 EMISSIONS PROJECTIONS
3. 2.3 SULPHUR DIOXIDE (SO₂) EMISSION SOURCES
4. 2.4 TOTAL PARTICULATE MATTER (PM_T) EMISSION SOURCES
5. 2.5 MERCURY EMISSION SOURCES
6. 2.6 MEASURING, MONITORING AND UNCERTAINTY IN EMISSION ESTIMATES
7. 2.7 EMISSION REDUCTIONS REQUIRED TO MEET GAZETTE I TARGETS

2.1 Overview

Emissions of sulphur dioxide (SO₂), total particulate matter (PM_T) and mercury from the 6 base metal smelters have substantially declined over the last two decades. Between 1988 and 2004, SO₂ and PM_T emissions dropped by approximately 60%. Mercury emissions declined by approximately 90% in the same period, with most of the reductions achieved at the Hudson Bay Mining and Smelting (HBMS) facility in Flin Flon, Manitoba. However, HBMS continues to account for approximately 80-85% of total mercury emissions reported by the 6 smelters. Approximately 78% of the reported dioxins and furans emissions are from the Falconbridge, Sudbury, ON operations.

Source: Sums from base metals industry sources. Draft numbers were prepared from Environment Canada's Strategic Options Report for the Management of Toxic Substances from the Base Metals Smelting Sector, 1997 (for 1988 data) and National Pollutant Release Inventory (for 1993-2003) data. Base metal companies reviewed and replaced some of these estimates with their own updated numbers.

A variety of technologies and operating practices have been implemented to reduce emissions at the 6 base metal smelters. Some of the major reductions in SO₂ emissions have come about as a result of installation of sulphuric acid plants. Sulphuric acid plants are operating at 4 of the 6 smelter sites. Gas streams with relatively high SO₂ concentration are captured and directed to these acid plants where the SO₂ is converted into sulphuric acid for sale in North American markets. Smelters with sulphuric acid plants also tend to have lower emissions of mercury, other metals, and PM_T. The principal reason is that gases routed though the acid production process need to be cleaned from these pollutants so that the acid plants operate efficiently and the acid meets market quality specifications. Mercury and other metal emissions may also be low due to the content of ores, and the concentrates processed.

In addition to the installation and operation of acid plants, there are other technologies and operating practices that have contributed to lowering potential emissions over time. Examples of these are listed below. However, not all of technologies listed have been adopted by all facilities, nor to the maximum degree possible. These and additional technical feasible options can be employed to further reduce emissions from the base metal facilities for them to achieve the Gazette I targets.

The sulphur fixation rate is the ratio of sulphur being emitted to air (as SO₂) to the total amount of sulphur (expressed as SO₂) entering the smelter.⁴ The six base metal smelting facilities analyzed in this report differ with respect to their sulphur fixation rate. Facilities that capture the potential SO₂ emissions and make sulphuric acid or liquid sulphur dioxide have achieved higher fixation rates. The two facilities in Manitoba do not operate sulphuric acid plants or other systems to control potential SO₂ emissions. Therefore, fixation rates for these facilities are low, with only some sulphur being captured in the slag, residue, and final products. In 2004, the average fixation rate for the 6 smelters was 67%, ranging from 16% to 91%. The average fixation rate implied by the Gazette I targets for the 6 smelters is close to 95%, based the amount of sulphur entering the smelters, estimated on assumed sulphur to product ratio.

* SO₂e means sulphur expressed as sulphur dioxide equivalent.
# Cheminfo Services estimate for 2004 based on 2003 data.
** Source: Environment Canada, Email correspondence to Cheminfo Services, February 28, 2006

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2.2 Emissions Projections

It is useful for the purpose of estimating costs to achieve the emission targets contained in Gazette I, to develop a projection of emissions to the year 2015. One such scenario, of many possible, is provided in Table 4. It shows that further SO₂, PM_T and mercury emission reductions are being planned by industry as part of the "business-as-usual" scenario. These future estimates take into account emission reduction technologies and practices currently underway. However, these reductions will not be sufficient to achieve the emissions targets contained in Gazette I.

Notes: Excludes major reductions for achieving Ontario MOE Reg. 194/05 emission trading cap in the case of Inco's Sudbury smelter. Includes reductions for which capital costs are already being incurred to achieve some reductions.

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2.3 Sulphur Dioxide (SO₂) Emission Sources

Smelting facilities are designed to remove sulphur, iron, and other metal impurities from concentrates to produce a form of metal that is suitable for markets or for further refining to achieve purity levels acceptable to customers. In examining the sources of SO₂ emissions from base metal smelters it is useful, for the purpose of this analysis, to distinguish between the initial and later stages of the smelting processes. Generally, the initial smelting stages involve partial oxidation of the metal sulphides in the concentrate, while silica fluxing agents are often added for iron removal. Initial stages can involve use of roasters, flash furnaces, electric furnaces, unique reactor designs, as well as other equipment. These account for the majority of the SO₂ generated at smelters (much of it controlled at most smelters), since the sulphur concentration in the material being processed through these stages is high. Stages later in the smelting process can also involve converters and finishing vessels. The amount of SO₂ generated from these sources is typically lower. However, at smelters where SO₂ emissions are already being controlled from the initial smelting process equipment sources, the smelting equipment involved with the latter stages of the process can represent the majority of the SO₂ emissions.

It is often economically more attractive to capture and treat SO₂ (e.g., in a sulphuric acid plant) from the initial smelting stages versus more dilute sources from later stages of the process. Several of the smelters⁵ use conventional technologies of roasters followed by furnaces. The process off-gases from these sources are generally more continuous (or semi-continuous) and higher in SO₂ concentration versus batch converters and other sources found later in the smelting process. Inco Sudbury uses direct flash smelting furnaces and Falconbridge Horne uses its proprietary Noranda Reactor and Noranda Continuous Converter. At Falconbridge's Brunswick lead smelter, the majority of the SO₂ is generated from the sinter machine in the smelting process.

Converting is usually a finishing step at most smelters where it is used to remove residual levels of sulphur, iron and other metal impurities from the furnace mattes in order to meet product specifications. Oxidation "converts" the remaining sulphur to SO₂ and the iron to iron oxide slag. Converting is usually a batch process. However, Falconbridge employs continuous converting at the Horne smelter to achieve a high level of sulphur oxidation in their process. Horne then relies on a series of finishing vessels (operated in batch mode) to further reduce sulphur and iron content, in order to achieve the necessary final product quality specifications. The SO₂ generated from batch converting processes is usually less concentrated than the SO₂ from initial smelting stages (e.g., roasting and furnaces) because the furnace matte contains relatively low residual sulphur levels. In batch converters, the SO₂ concentration declines over time. It is highest when the oxygen is first blown into the matte, and decreases over the blowing period. In some cases, smelters find batch converter off-gases too dilute to be treated in an acid plant. For facilities that operate acid plants, the majority of the remaining SO₂ emissions usually comes from multiple converters or finishing vessels operated in batch mode.

Improved capture systems can enhance the containment of batch converter gases, reducing air infiltration, minimizing dilution of these weak SO₂ streams, and lowering their flow rate. This makes these streams more suitable as feeds for acid plants or other treatment systems (i.e., alkali scrubbing, liquid SO₂ plants). Water-cooled hoods capture the process off-gases coming from the openings of the converters. The percentage of SO₂ captured depends on the tightness of hoods that can be placed over the openings (mouths) of the converters. Secondary capture hoods can achieve higher capture rates. A technical issue is the variability of the gas flow rate and concentration over the blowing cycle.

In addition to other uncaptured sources, fugitive emissions⁶ from converters can often lead to high ground-level concentration (GLC) around the facility. The reason is that the converters have openings, which are required to handle charging (or pouring) of molten matte from large ladles. These openings also present sources of emissions. Fugitive sources of SO₂ are usually a minor portion of total facility emissions.

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2.4 Total Particulate Matter (PM_T) Emission Sources

Particulate matter emission sources can be grouped into two types, namely: process and area sources. The major process sources include roasters, flash furnaces, sintering units, electric furnaces, and converters. Emissions from these sources can be from stacks or fugitive. Fugitive emissions are usually leaks from a variety of equipment, and are not routed through existing stacks. They may exit the buildings that house the processing equipment through roof vents, wall vents, doors, windows, loading bays, and other openings. PM_T area sources include, but are not limited to: dust from unpaved roads; outdoor raw material piles; tailings erosion; material handling operations; mobile equipment and vehicles; and construction activities. There are many pieces of equipment or small areas from which PM emissions can result at each smelter.

Some of the 6 facilities analyzed in this study have yet to develop estimates of PM area sources. They have only estimated and reported process sources from stacks. Therefore, the current and historical emission data reported to Environment Canada's National Pollutant Release Inventory (NPRI) are not on a consistent basis for all facilities. Furthermore, there has been inconsistent reporting of PM_T emissions to NPRI over time.

All of the 6 base metal facilities analyzed in this study operate electrostatic precipitators (ESPs) to address process emissions. Some facilities also operate fabric filters (baghouses) to address PM_T emissions from selected sources. The degree of PM emissions control may be high (i.e., over 90%), but cannot easily be precisely determined since potential PM_T emission quantities (before passing through controls) are not readily available for all sources.

The table below provides an example of the contribution of PM_T emissions from major sources or source groups for one facility, where the process and area sources have both been estimated. The PM_T emissions profile for other facilities will likely be different. In general, area sources can contribute as much as controlled process PM_T sources. For facilities that have yet to estimate area sources, the majority of the PM_T emissions from ESPs and/or baghouses are routed to the main stacks, which represent the major source of reported PM_T emissions.

Base smelter facilities are undertaking operating practices and applying control technologies to address area sources. Even companies that have yet to estimate area source emissions are undertaking measures to minimize emissions. Some of the options that have been being implemented include:

• vegetation (grasses) planting on barren surfaces;
• paving of roads;
• the use of water cannons and sprays to reduce dust;
• covering exposed tailings using dust control agents;
• flooding exposed tailings where possible; and
• creation of barrier zones to minimize dust travel.

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2.5 Mercury Emission Sources

Mercury (and its compounds) as well as other metals may be contained in the ores and subsequently the concentrates fed to smelters. The 6 smelters vary substantially with respect to their mercury emissions due to the amount of mercury in concentrates received and the controls used that reduce emissions.

Mercury contained in the concentrate feed may be volatilized in the high temperature roasters, flash furnaces, electric furnaces, and converters, and carried in the off-gases. It may be combined with particulate matter (PM), which is collected by PM control devices or is emitted. A portion of the potential mercury emissions is controlled through the use of ESPs and baghouses that address PM emissions. However, at high temperatures some metals like mercury may be gaseous and pass through ESPs and other PM control systems. For facilities that have sulphuric acid plants, off-gases are passed through dedicated treatment towers. This removes a high percentage of the mercury, so that only a minor amount is emitted to air. A small portion is contained in the acid product.

Controlling the amount of mercury that enters the smelter is one method of minimizing emissions. HBMS accounts for approximately 80-85% of the total mercury emissions reported to Environment Canada's NPRI by the 6 smelters. At HBMS efforts continue to reduce mercury content in the materials entering the Flin Flon smelter. For example, purchased concentrates processed in 2004 had an average mercury concentration of less than 3.78 ppm. This is considerably lower than some concentrates previously processed, which contained up to 40 ppm mercury. The focus of emission reductions at HBMS is now the reverberatory furnaces, which are believed to account for nearly 80% of the origin of the emissions (routed with other sources through the main stack).

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2.6 Measuring, Monitoring and Uncertainty in Emission Estimates

Emissions are estimated by base metal facilities using different methods for each pollutant. Sulphur dioxide emissions are typically calculated using mass balance approaches. In this case, total sulphur entering the smelter is measured (through sulphur content of concentrates). Total sulphur contained in products (e.g., metals, mattes) and by-products (e.g., sulphuric acid) or waste leaving the plant is also measured. The calculated difference is SO₂ emitted. Periodically, process stacks are measured for pollutant concentration and flow rate, which are then used to calculate SO₂ emission rates. Continuous emission monitors (CEMs) are on some stacks. Particulate matter, mercury, other metals, and dioxins and furans emissions are usually estimated using periodic (e.g., annual, quarterly or more frequent) testing of concentrations in specific stacks. In some cases, emission factors obtained from literature sources (e.g., US EPA AP-42) are applied.

Not all facilities estimate annual fugitive and area sources of PM emissions. These sources can include, but are not limited to: emissions from processes directly to air - not through a stack; road dust from heavy mobile equipment and vehicle traffic; dust from raw material piles; dust from tailings; and loading and unloading activities (e.g., conveyors, transferring operations). All facilities include emission estimates from dedicated process stacks. This presents inconsistencies between facilities with respect to total PM emissions reported.

Source: Ranges based on industry input.

In general, the uncertainty in estimated SO₂ emissions is relatively low in comparison to lower-volume pollutants, such as PM_T, mercury, and dioxins and furans. In some cases, high levels of uncertainty may present challenges in demonstrating compliance with specified emission target limit levels.

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2.7 Emission Reductions Required to Meet Gazette I Targets

The 6 base metal facilities analyzed in this study, their 2004 SO₂ and PM_T emission levels, and the related Canada Gazette I Proposed Notice targets are contained in the table that follows. The overall reduction by 2015 implied by the Gazette I target for SO₂ and PM is approximately 85% versus 2004 emission levels. All facilities would need to achieve some reductions in SO₂ to achieve their targets. The mercury emission target contained in Gazette I for all facilities is 2.0 grams-Hg per tonne of metals produced, as per the requirement of the Canada-wide Standards for Mercury Emissions. The Gazette I Notice contains a specific mercury emission target for Hudson Bay Mining and Smelting, which is 373 kg-Hg/year for 2008. Falconbridge's Sudbury smelter had a specific 2008 dioxins and furans target of 0.5 grams/year grams (I-TEQ).⁷

Table 8: Summary of SO₂ and PM_T Emissions and Gazette I Targets, by Facility

Click to view Table 8

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⁴ Operating practices (e.g., feed selection) and technologies (e.g., pyrrhotite rejection) that reduce the amount of sulphur coming into the smelter are not accounted for in the fixation rate calculations.

⁵ This sequence is used at Hudson Bay Mining & Smelting, Inco Thompson, and Falconbridge Sudbury.

⁶ Fugitive emissions are released through windows, doors, roof vents, wall vents, etc. (not from stacks).

⁷ International Toxicity Quotient.

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