Pulp Mill Becomes a Net Energy Exporter
Funded through Round 2: Industrial Energy Efficiency in 2011, this project involved upgrading Weyerhaueser’s Alberta pulp mill by replacing an outdated evaporator plant with a new, more efficient system. This upgrade aimed to reduce greenhouse gas emissions, lower water usage, and increase energy output and pulp production.
In a multiple-effect evaporator, water is boiled in a sequence of vessels, each of which is at a lower pressure than the last. As the boiling point of the water decreases with pressure, the vapor produced in one vessel can be used to heat the next vessel. As a result, only the first vessel requires a source of external heat.
In this project, the additional two effects, or “stages”, improve the system’s efficiency by using steam more effectively to evaporate water from black liquor, a byproduct of the pulping process. The upgraded evaporator plant also enhances the mill’s ability to generate additional green power. Though it has reached around 18 megawatts as of the report’s completion, the system was designed to produce 23 megawatts of additional power for export to the Alberta power grid. Additionally, the improved system has enabled the mill to become a net energy exporter, contributing to the local grid and reducing reliance on external energy sources. The new system reduces water consumption by 8 per cent and allows better segregation and management of hot, warm, and cold water streams within the mill, optimizing energy usage. The technological upgrade plays a significant role in reducing greenhouse gas emissions, with an estimated reduction of 112,160 tonnes of emissions per year through improved efficiency and increased power generation.
Achieving Results Despite Project Delays
In 2013, the mill saw a 10 per cent reduction in water consumption, beating the project target. The mill also exceeded the six per cent pulp production improvement, meeting the project targets and setting numerous production records. While the project was successful overall, it experienced several delays due to late deliveries of critical components from overseas, and the shortage of skilled labour towards the end of the project further delayed the schedule. These issues highlight the importance of securing necessary materials and human resources early in the project. Additionally, the project successfully met many of its goals, such as steam economy and pulp production improvement, but some targets, like the full 23 megawatts of additional power generation, were not achieved.
What’s next?
Since the completion of this project, many pulp and paper mills around the world have adopted multi-effect evaporators to enhance efficiency, reduce water and energy usage, and lower greenhouse gas emissions. The successful implementation at Weyerhaeuser Grande Prairie has served as a benchmark for other mills looking to modernize their operations. Recent advances in technology focus on enhanced heat recovery systems that reclaim even more energy from the evaporator process, further improving the steam economy and reducing fuel consumption. More recently, there has been growing interest and investment in Alberta in increasing bioelectricity from pulp mills to the power grid.