Executive Summary
Federal, provincial and territorial environment ministers are taking action to better protect human health and the environment by endorsing and implementing the new Air Quality Management System (AQMS). The AQMS includes Canadian Ambient Air Quality Standards for fine particulate matter and ground-level ozone, Base Level Industrial Emissions Requirements (BLIERs) and local Air Zone Management by the provincial/territorial jurisdictions. For the Aluminium Sector, BLIERs were developed for total particulate matter (TPM), polycyclic aromatic hydrocarbons (PAH) and sulphur dioxide (SO2) and it was recommended that a code of practice be developed to help reduce emissions of PM2.5. This Code of Practice (Code) applies to operational activities related to the primary aluminum sector, including:
- alumina reduction (electrolysis) plants with prebaked anode technology;
- prebaked anode plants;
- green coke calcining plants; and
- bauxite refining plants.
There are currently 11 facilities operating in at least one of the primary operational activities. Secondary activities, including port and/or rail services for transporting raw materials, regional hydroelectric plants, electrolytic cell relining centres, and value-added product facilities, are not covered by the Code, nor are activities associated with the alumina reduction process using Söderberg technology.
The Code was developed by Environment Canada in consultation with aluminum industry representatives and other stakeholders. Information on operating procedures and best practices is taken from various sources, including technical and scientific journals, as well as environmental codes of practice published by Environment Canada, the European Commission, the World Bank and the Light Metals Research Centre (LMRC) at the University of Auckland in New Zealand.
The Code outlines concerns associated with PM2.5 emissions for each of the primary operational activities (Section 3) and makes recommendations to control and reduce these emissions (Section 4). These recommended practices can be used by the primary aluminum industry, regulatory agencies and the general public as a source of technical and policy guidance but do not negate any regulatory requirements. Where warranted, the implementation should be supported by a program designed for establishing best practices on PM2.5 emissions (Section 5) in a context of continuous improvement.
Table S-1 lists recommended measures designed to limit PM2.5 emissions for each of the following activities:
- operation of alumina reduction plant;
- operation of prebaked anode plant;
- facility monitoring and maintenance;
- off-gas treatment centres and other scrubbers;
- materials handling and storage; and
- fuels.
Due to inherent technological constraints, the overall objective of the Code is not to eliminate PM2.5 emissions completely, but rather to control them using effective measures and best practices. Moreover, the Code does not take into consideration practices that would require an existing facility to make major technological changes. In designing a new facility, other technologies can be taken into consideration to further minimize emissions. These technologies include high draft ventilation of pots activated when opening the hoods, or a regenerative oxidation system to eliminate pitch emissions.
| Subject | Recommendation |
|---|---|
| Opening of electrolytic cell hoods |
A01
Optimize work methods for opening a minimum of hoods at once, and open them only once work begins. Close hoods as soon as work is complete.
|
| Gas extraction system |
A02
Regularly diagnose the extraction efficiency of ventilators in relation to power supply, flow rate and pressure loss. Make adjustments as needed to maximize extraction rate.
|
| Changing of prebaked anodes |
A03
Optimize work methods to minimize the time required to change anodes and cover them with cover material.
|
| Alumina crust covering cryolite bath |
A04
Put in place a program to monitor cracks in the crust by way of a visual inspection or an automated system. Ensure that the cover material is appropriate and effective as a sealant.
A05
Cover the taphole with cover material once the tapping or sampling work is complete.
|
| Tapping of cryolite bath and molten metal |
A06
During tapping activities, reroute fumes evacuated by the crucible inside the pot using flexible tubing.
|
| Cryolite bath spatter and spills |
A07
Minimize and recover cryolite bath spills and spatter on the floor.
A08
Pour the bath into the cell launder at an optimal speed to reduce pouring time while avoiding spatter. Avoid pouring too slowly.
A09
Clean the cryolite bath residue from the cell launder with a spade (or equivalent) when loading is complete.
|
| Skimming of carbon dust |
A10
Cool the hot carbon dust (dross) inside the pot. Minimize the time spent in the potroom.
|
| Control of operating parameters |
A11
Control and maintain an optimal bath level in the pot to prevent an unintended rise in bath temperature and direct contact with moist air. These two phenomena exacerbate the formation of fluorinated particles.
A12
Prevent, control and minimize the anode effect. After manual or automatic suppression of the anode effect, cover the cracks with cover material.
|
| Casting of molten aluminum |
A13
Maximize casting centre output. Limit discharges.
|
| Subject | Recommendation |
|---|---|
| Baking furnace |
B01
Run an effective baking furnace pit filling system with packing coke to limit coke loss in the building. Train operators to standardize work methods for handling packing coke.
B02
Operate and monitor negative pressure in the baking furnace.
|
| Cleaning of anode butts |
B03
Operate effective dusty air extraction and filtration systems for the anode butt cleaning process.
|
| Crushing of frozen bath |
B04
Treat gases released from the crushing of frozen bath using dust collectors or the GTC of the alumina reduction plant or the FTC of the anode baking furnace.
|
| Subject | Recommendation |
|---|---|
| Maintenance activities | C01
Regularly inspect, according to a set schedule, the alumina reduction plant's facilities, including fume exhaust ducts, the alumina supply system and the pot superstructure. In the event of breakdowns or malfunctions, make repairs or install appropriate replacements as soon as possible.
C02
Regularly inspect, according to a set schedule, the prebaked anode plant facilities, including systems for anode butt cleaning, frozen bath crushing, and calcined coke grinding and sieving as well as the baking furnace. In the event of breakdowns or malfunctions, make repairs or install appropriate replacements as soon as possible.
C03
Regularly inspect, according to a set schedule, the green coke calcining and cooling facilities, including sealing joints and other mechanisms that could potentially lead to a gas leak. In the event of breakdowns or malfunctions, make repairs or install appropriate replacements as soon as possible.
C04
Regularly inspect, according to a set schedule, alumina calcining facilities and boilers at the bauxite refining plant. In the event of breakdowns or malfunctions, make repairs or install appropriate replacements as soon as possible.
C05
Put in place an employee training plan in support of an approach for preventing premature wear and untimely breakdowns due to improper operation of the facilities.
|
| Alumina reduction plant cleaning activities | C06
Use a HEPA vacuum to clean the floor of the potroom.
C07
Regularly clean the ceiling of the pots.
C08
Regularly clear the feeder/breaker of solid residues to reduce the size of the hole in the crust after injection, thus decreasing emissions (corollary to Recommendation A05).
|
| Subject | Recommendation |
|---|---|
| Monitoring of operations (GTC, FTC, PFTC) | D01
Monitor daily gas flow for each compartment of the baghouse in the scrubber (where applicable), ensuring it is uniform. Monitor pressure loss in order to identify anomalies requiring correction.
D02
Adjust the cleaning frequency and duration of scrubber baghouses (where applicable) to balance gas flow for each compartment and maximize collection efficiency.
D03
Wherever possible, limit recycling of enriched alumina in GTC and FTC injection reactors without influencing HF capture. Monitor the daily recycling rate to ensure it is optimal.
D04
For the FTC only, operate the cooling tower so as to capture most of the tar contained in the baking gas. Otherwise, add a prefilter (e.g., ceramic packing) to capture most particulate and condensable matter, including tar.
|
| Monitoring of operations (pyroscrubber) | D05
Optimize the operating parameters of the pyroscrubber to maximize incineration of coke particles in addition to VOCs. As needed, follow up with a system designed to detect particles leaving the pyroscrubber and adjust accordingly.
|
| Monitoring of operations (boiler followed by a baghouse) | D06
Optimize the performance of the cyclones and baghouse based on the total particle load. As needed, replace bags with more efficient ones.
|
| Monitoring of operations (venturi wet scrubber) | D07
Monitor daily gas flow through the scrubber based on the flow of water fed through the venturi, the ratio of which has a direct effect on pressure loss and the effective capture of particulate matter, including PM2.5. Optimize performance based on the system in place.
|
| Maintenance of scrubbers and related systems | D08
Regularly inspect, according to a set schedule, the scrubber, including the superstructure, sealing joints, ventilator (corollary to Recommendation A02), alumina (or calcined coke) supply system and baghouse (if applicable). Repair any breakdowns or malfunctions as soon as they are noted.
D09
For the baghouses, replace the bags at the end of their service life. Do not wait until a breakdown occurs.
D10
For the GTC and FTC only, follow a set schedule to regularly inspect ducts that are prone to accumulation of hard gray scale. Clean if too much has accumulated.
|
| Subject | Recommendation |
|---|---|
| Monitoring of facilities and their outputs | E01
Monitor emissions of particulate matter from dust collectors. Investigate the causes of sudden increases in particulate matter emissions and make necessary adjustments.
E02
Carry out a visual check of pneumatic injection and mechanical handling systems according to a set schedule in order to detect leaks. Make repairs as soon as possible.
|
| Maintenance of dust collectors | E03
Periodically monitor and maintain dust collectors and replace bags when they reach the end of their service life (corollary to Recommendations D08 and D09).
|
| Transportation of anode butts | E04
Use one of the following measures:
|
| Green coke storage | E05
In the coke calcining plant, unload the green coke in a closed building. Move green coke between various transfer points using closed conveyors or similar equipment.
|
| Red mud disposal | E06
Set up physical and/or chemical barriers for red mud dumping in order to limit dusting in warm, dry and windy weather conditions.
|
| Subject | Recommendation |
|---|---|
| Type of fuel |
F01
With regard to particulate matter emissions, use hydro power instead of fossil fuels if the current system allows. Otherwise, use natural gas instead of fuel oil (or another heavy fuel).
|
| Consumption rate |
F02
For boilers and alumina calciners, minimize natural gas or fuel oil consumption per tonne of alumina produced using efficient heat recovery systems.
|