Extending the gas network to all of Qu√©bec‚Äôs spheres of economic activity is no mean feat, particularly when it comes to industries and mines in remote areas. Nevertheless, those enterprises can benefit from the many advantages of natural gas thanks to liquefied natural gas (LNG), as Stornoway has done for its diamond mine.
Energy security for an extremely valuable mine
Containing 22.3¬†million carats of mineral reserves, the Renard Mine is located in northern Qu√©bec. To generate electricity and cover the mine‚Äôs largest energy-consuming thermal needs, Stornoway has opted for liquefied natural gas (LNG), given that:
- the technology is standardized;
- long-term supply is secured;
- the environmental footprint is small compared to that of diesel;
- operating costs are reduced (low natural gas prices).
Flexible supply solutions
For over 45¬†years, √Čnergir has been operating a liquefaction, storage and regasification plant in Montr√©al East. Connected to √Čnergir‚Äôs network, two liquefaction trains are capable of producing 10¬†million¬†GJ of LNG per year, with two tanks able to store 2¬†million¬†GJ of LNG. Loading docks with an integrated scale can fill close to 50¬†tank trucks a day.
When cooled to -160¬įC, natural gas transforms from a gaseous state into a liquid, known as LNG, taking up to 600¬†times less space than in its gaseous state, thus making it easier and safer to store and transport. In its liquid form, LNG is clear, colourless, odourless, non-corrosive and non-toxic, and does not dilute in water or ignite. In the event of a spill, LNG does not contaminate the soil or water.¬†LNG must go through a regasification process before use.
When starting operations (cold start-up), atmospheric vaporizers warm up the LNG to the required temperature.¬†
Numerous LNG deliveries a day to the mine
To power the mine using LNG, the project needed:
- to use a certified LNG carrier, with a permit issued by Transport Canada;
- a fleet of nine cryogenic tankers to keep the LNG in its liquid state during travel (six for transporting and loading, and three in maintenance or held in reserve).
¬†All LNG facilities in the mine meet the requirements of the CAN/CSA-Z276 national standard, which sets out minimum standards for the design, installation and safe operation of LNG facilities.
For the design of tank trucks, Transport¬†Canada requires compliance with specific technical specifications, such as TC338,1 set out under the CAN/CSA-B620¬†standard.2
Six storage tanks at the mine
LNG is transferred from tank trucks to six cryogenic tanks, totalling 1,800¬†m3 of storage,3 by means of discharge pumps and an inventory management system to deliver the LNG to the appropriate tank.
Before being used, the LNG is warmed up by two boilers of 2.5¬†MMBH each and heat exchangers fed by a propylene glycol closed loop system.
LNG for electricity and certain thermal needs
Eight LNG-powered Caterpillar generators4 of 2,050¬†kW each produce the mine‚Äôs electricity. Since they are stationary internal combustion engines, emission rates must satisfy the requirements of the Regulation respecting the quality of the atmosphere (Q-2, r.38). Five generators are required on a permanent basis, producing between 7¬†and¬†9¬†MW to 4,160¬†volts, as needed.
During the mining process, crushers are used to break the rock where diamonds are embedded. These machines require significant electrical power. For smaller loads, transformers lower the tension, first to 600¬†volts, then to 120/240¬†volts. A closed-loop ethylene glycol system is used to cool down the engines and recover energy from the generators‚Äô combustion products. Ethylene glycol circulates in the exchangers and heats a secondary propylene glycol system. This system, with a temperature of 90¬įC, feeds an exchanger installed inside a ventilation duct to heat supply air in the underground mine. Typically, a flow of 100,000¬†cfm¬†of fresh air is required. The temperature is adjusted based on the needs at the bottom of the mine. In the event of a break in the recovery system or during the winter peak, a burner operating directly on natural gas can cover the mine‚Äôs thermal needs.
LNG is also used by unit heaters and ventilation units to cover the thermal needs of the garage where the maintenance and repairs of the mine‚Äôs rolling stock is carried out, as well as the needs of workers‚Äô showering, changing and laundry facilities.
LNG: An economical solution that reduces GHG emissions
Given the high cost of constructing a power line, any thought of connecting the Renard Mine to the electricity grid was discounted. The cost comparisons of generating electricity using different sources of energy revealed that natural gas was economically advantageous. At the time the decision was made, savings amounted to $8¬†million/year compared to oil and diesel, even though the natural gas generators cost more than diesel generators. The return on investment period was a mere four months.
Moreover, energy recovery in combustion products is easy with natural gas engines. This results in a 43% reduction in GHG emissions, as well as a significant reduction in nitrogen oxide and sulfur dioxide emissions.
Simply put, LNG‚Äôs economic attractiveness and the reduction in negative environmental impacts have overwhelmingly convinced Stornoway management.
Guy Desrosiers, Eng., CEM, CMVP
Advisor, Major Industries & Energy Efficiency,¬†DATECH, at √Čnergir
1 Insulated highway tank for gases as refrigerated liquids.
2 Requirements for design, construction, certification, assembly, modification, repair, testing, inspection, periodic re-testing, maintenance, and marking of highway tanks (tank trucks).
3 I.e., 1,080,000¬†m¬≥ of natural gas in its gaseous state, or 41,000¬†GJ.
4 G3520C model.