The processing plant uses conventional gravity separation and flotation methods to produce clean coal from raw feed.
Report context
This NI 43-101 technical report for Greenhills Coal Operations, British Columbia, dated February 2023, describes the recovery methods employed at the process plant. The flowsheet design was based on testwork results, study designs and industry standard practices.
Processing route
Breaker
Coal is fed to the breaker where rock larger than 2 inches is separated from the coal. Coal larger than 2 inches in size is broken and passed through perforated breaker plates. Broken coal is fed to the raw coal silos. Rejects from the breaker are piled and subsequently hauled to the coarse coal reject spoils using loaders and trucks.
Wash plant
GHO has two raw coal silos with a holding capacity of up to 1,800 tonnes each. The silos store raw coal before processing.
Deslime screens are large vibrating screens that split the coal feed into different sizes. Material greater than 1.0 mm reports to the coarse circuit. Material less than 1.0 mm reports to the fines circuit.
Heavy media cyclones separate coarse rock from coarse coal. Coarse coal exits from the top, while coarse rock exits from the underflow. Vibrating screens are used for cleaning and dewatering, and exciters are used to throw the material across the deck.
Magnetite is used to control fluid density. Magnetite has a solid density of 5.1, but the process dilutes it with water to a specific gravity range of 1.40–1.54. The higher density water/magnetite slurry helps more material float, meaning more ash (more rock), but also more coal, is recovered in the product. Magnetite is recovered through washing at the reject and clean coal screens, and then passed over magnetic separators.
Flotation cells are used to separate the fine coal. Fine material from the cyclones is sent to the first stage or rougher flotation cells. Kerosene and methyl isobutyl cabinol (MIBC) are used to form bubbles when agitated, and the coal sticks to the bubbles and floats to the top. The rock sinks and goes out the underflow. The resulting concentrate goes to the clean coal thickener, and underflow goes to the scavenger flotation cells.
The scavenger cells provide a second opportunity to float any coal that may have not floated in the rougher. The resulting concentrate goes to the clean coal thickener, and underflow goes to the refuse thickener. The thickener rakes move thickened material to the disc filters, which use vacuum pressure to extract water from the coal, producing a filter cake.
Dryer
Discharge from disk filters (filter cake), fine coal centrifuges and basket centrifuges are combined to feed the dryer. The dryer is fueled with natural gas, and the heat produced evaporates moisture from the coal. The dryer takes coal from the plant at approximately 16% moisture and dries it to approximately 8% moisture.
Storage and rail loadout
GHO has two clean coal silos with a holding capacity of up to 14,000 tonnes each, used to store clean coal before it is railed. GHO loads unit trains, which carry approximately 16,000 tonnes per train. The trains, operated by CPR, are gravity loaded from chutes at the bottom of the clean coal silos. During loading the cars are sprayed with a flocculent to prevent dusting during transportation.
Key reported parameters
| Parameter | Design value | Actual (GHO feed avg) | Basis |
|---|---|---|---|
| Raw coal silo capacity | 1,800 t each | , | Design |
| Clean coal silo capacity | 14,000 t each | , | Design |
| Unit train capacity | ~16,000 t per train | , | Design |
| Deslime screens capacity | 720 t/h (15 t/h/ft of width) | 750 t/h | Design / actual |
| HMCs capacity (raw) | 828 t/h raw | 530 t/h | Design / actual |
| HMCs capacity (volume) | 2,586 m³/h | 2,586 m³/h | Design / actual |
| Clean coal screens capacity | 480 t/h | 421 t/h | Design / actual |
| Centrifuges capacity | 1,500 t/h | 421 t/h | Design / actual |
| Spirals capacity | 2–3 t/h/start (144–216 t/h) | 188 t/h | Design / actual |
| High frequency screen capacity | 60 tph, min 35% solids | 88 tph | Design / actual |
| Roughers capacity (volume) | 2,304 m³/h | 1,760 m³/h | Design / actual |
| Scavengers capacity (volume) | 1,632 m³/h | 1,200 m³/h | Design / actual |
| Disk filters capacity | 132 t/h dry | 157 t/h feed, 116.5 t/h wet recovered (91 t/h dry) | Design / actual |
| Decanters capacity | 72–91 t/h | 92 t/h | Design / actual |
| Dryer feed moisture | ~16% | , | Actual |
| Dryer product moisture | ~8% | , | Actual |
| Plant power consumption | , | 85,000,000 kWh/year | Actual |
| Average water usage | , | 1.68 Mm³ | Actual |
| Kerosene dosage | 15 L/min | 672 mL/min | Design / actual |
| MIBC dosage | 15 L/min | 107 mL/min | Design / actual |
| Flocculant system dosage | 378 L/min | 63 L/min | Design / actual |
Project website: https://www.glencore.ca/en/evr/operations
Note: Design capacities and actual average feed rates are reported as presented in Table 17-1 of the technical report. Testwork results informed the original flowsheet design but specific testwork data are not provided in the recovery methods section.
Technical qualifications
The flowsheet design was based on testwork results, study designs and industry standard practices. Yield forecasts were included in Section 13.3 of the report, but are not reproduced here. The report does not provide performance data or economic analysis in the recovery methods section. The report basis is February 2023.
Source: Greenhills Coal Operations, British Columbia, NI 43-101 Technical Report, February 2023, Section 17.0 Recovery Methods.
