Project Description

Sludge is a by-product of processes in industry and agriculture. It is very wet, so disposing of it is difficult. A pilot project at Stora Enso’s Heinola Mill in Finland addresses this challenge in the spirit of the bio-based circular economy. The mill used to burn biosludge at its power station for thermal power, but because it is so wet, a fossilbased fuel was needed to support the burning process – an obstacle to the mill’s long-term goal of achieving carbon neutrality.

In 2019, an industrial-scale pilot plant was built at the mill, using a technology developed and patented by the Swedish company C-Green Technology AB. For the first time, bio-sludge is dried in an energy-efficient way with pressure and heat, making it a clean and odourless biofuel. It can then be burned without additional fossilbased fuel. Alternatively, there is a possibility to use it as a growth medium.

Project Purpose

With the pilot plant, Stora Enso is investigating how much CO2 emissions can be reduced with the treatment of bio sludge. Stora Enso’s goal is to reduce the use of fossil fuels and get as close to zero levels of CO2 emissions as is commercially feasible. A high proportion of biomass is already used in internal energy production at most of our mills.

Project Evaluation

The dried biosludge offers many possibilities. For instance, it promotes the circular economy by providing an opportunity to reuse the nutrients it contains. For example, this can be realized by using the final product as a growth medium. The HTC plant can also accept other sludges from outside the Heinola mill, contributing on a larger scale.