One of UPM’s 2030 responsibility targets is to recycle or reuse all its process waste. Last year, 89% of all UPM’s total process waste was recovered or recycled. To reach the ambitious goal, innovative methods to utilise every possible side stream are required. One of the trickiest side streams to recycle is moist green liquor dregs, for which UPM has tried to find resource efficient solutions for a long time.
UPM Pulp, along with the UPM Sustainability R&D team has launched a project with Tapojärvi Oy, a Finnish specialist in mining and mill services. The aim of the project is to refine green liquor dregs into products with a lower carbon footprint than corresponding construction materials.
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“This is a world first for utilising green liquor dregs commercially on this scale. We compete with products manufactured from virgin materials, but our assets include cost efficiency and a lower carbon footprint,” says Juha Koskinen, R&D Manager at Tapojärvi Oy.
“Due to its composition green liquor dregs is very difficult to handle. Annually, UPM’s three pulp mills in Finland generate approximately 60,000 tonnes of waste dregs that end up in landfill. It’s our most recent high-volume waste fraction for which we have been developing reuse with established business operations,” says Katja Viitikko, Sustainability R&D Team Lead.
For years UPM Pulp has tried to find a solution for the utilisation and commercialisation of green liquor dregs and, based on that research, the company has created patents for several potential innovations. From 2016 to 2019, UPM implemented a Zero Solid Waste project that studied and tested green liquor dregs’ ability to be processed for the earth construction market. The results of the product development project were promising and confirmed that dregs could be utilised. Since the commercialisation and refinement of side streams is not part of UPM Pulp’s core business, it was decided that the project should be carried out with a partner. Tapojärvi Oy was identified as a company with the suitable product development and marketing skills to complement UPM Pulp’s expertise in developing side streams.
The disused lime kiln at UPM Tervasaari mill was repurposed for processing green liquor dregs. Photo: Katja Viitikko
New life for an old lime kiln
The treatment of green liquor dregs requires the proper machinery and that was found at the UPM Tervasaari mill in Valkeakoski. Testing of the residue began in 2017 with a disused lime kiln at UPM’s closed pulp mill, and a solution was found. The trials proved the kiln’s technical applicability for this new type of production.
“Reusing the old lime kiln turned out to be vital to the project’s success,” says Miikka Saarinen, Energy Manager at the UPM Tervasaari paper mill, who thought of the idea. “However, a touch of creative madness was required to turn the idea into reality.”
Giving the lime kiln a new life is an example of circular-economy thinking, in which all resources are utilised cost-efficiently without additional investments. The Tervasaari lime kiln is heated with natural gas, but the option of using biogas is possible. Moreover, limestone is not required for the treatment of green liquor dregs – contrary to the production of cement – thereby reducing the product’s environmental load.
“The emissions of the end product will be considerably lower than those of cement,” Saarinen explains.
Boosting the forest industry’s competitiveness
The knowhow and results from the Zero Solid Waste project were transferred to Tapojärvi according to the collaborative agreement between the two parties. Tapojärvi has also invested in its own research and development, with the goal of utilising side streams so that the company can introduce low-carbon products into the market. The next step in the collaboration is to implement industrial-scale trials using the Tervasaari lime kiln. The idea is to utilise both green liquor dregs and ash. The intention is to verify the positive research results from UPM Pulp’s previous trials and based on these, develop operations further.
“If all goes as planned and the product recipes are confirmed around the turn of the year, we can initiate trials at the mill in spring 2022,” says Koskinen. “The trials will give us more experience with the products and their manufacturing. After testing, we will select the products with the potential to be placed on the market.”
Productising UPM Pulp’s side streams and those of UPM in general is beneficial to both business and the environment. It also contributes to the long-term competitiveness of the pulp business and increases the market value of the circular economy.
“In this project, the stars have truly aligned. Green liquor dregs will soon no longer be dumped into landfills, but they will be used as raw material for products with the potential to decrease emissions in the construction industry,” Koskinen says with hope.