Slave Lake Pulp, a subsidiary of West Fraser Mills Ltd., is a 240,000-tonne-per-year Bleached-Chemi-Thermo-Mechanical Pulp (BCTMP) mill located in northern Alberta, Canada. The mill primarily processes aspen to produce market pulp for the global market.
The Customer’s Needs:
Slave Lake Pulp was treating its high-strength wastewater in a conventional activated sludge (CAS) system. The mill knew that the high heating value of methane allows for biogas produced from anaerobic digestion to be recovered and offset fossil fuel consumption. They decided to explore biomethane for power generation—both for its environmental and its cost-saving benefits.
With assistance from the Climate Change and Emissions Management Corporation (CCEMC) and the Government of Alberta, Slave Lake Pulp embarked on a Biomethanation and Power Generation Project that would anaerobically digest pulp mill effluent to generate biogas to be used as green energy. A durable, gastight cover was required as part of the project.
Geomembrane Technologies Inc. (GTI) was contracted to design and install the liner, piping, and cover for Slave Lake Pulp’s new 120,000 m3 (4.2 million ft3) anaerobic reactor. The reactor was constructed in an earthen basin with a concrete perimeter wall lined with a geotextile underlay and geomembrane liner and gas collection cover.
GTI installed the piping to evenly distribute incoming wastewater throughout the front-end of the reactor, where the majority of the biologically degradable organics are digested. The geomembrane cover is insulated to reduce heat loss, and sampling ports on the cover allow easy access to reactor contents.
Biogas generated in the system migrates to the reactor cover perimeter, where blowers pull gas through the biogas scrubbing system, boost the gas pressure, and transmit the scrubbed biogas to a set of three 3 MW gensets designed for biogas applications.
The gas collection cover that GTI designed and installed for Slave Lake Pulp has helped the mill harness the power of biogas from its new anaerobic digestion system. 10.4 GJ of biogas energy is generated per tonne of chemical oxygen demand (COD) anaerobically removed, which corresponds to 4.2 MW on design average and 6.0 MW on peak organic loading days of electrical power. Any biogas not utilized is combusted in a waste gas incinerator.
GTI is proud that its gas collection cover has helped Slave Lake Pulp reduce electrical costs by 43 percent and improve its environmental footprint by limiting the amount of greenhouse gases entering the earth’s atmosphere.