Stora Enso pilots sludge-to-biofuels process at Heinola mill

By Mary Page Bailey |

Sludge is a byproduct of processes carried out in industry and agriculture. It is very wet, so disposing of it is difficult. A pilot project at Stora Enso Oyj’s (Helsinki, Finland; www.storaenso.com) Heinola Mill in Finland addresses this challenge using novel technology.

At Stora Enso’s Heinola fluting mill, bio-sludge is a byproduct of wastewater treatment. Previously, the mill would burn the bio-sludge at the power station for thermal power, but because it is so wet, it needed fossil-based fuel to support the burning process. This was not in line with the mill’s longterm goal to achieve carbon neutrality in production.

In 2019, an industrial-scale pilot plant was built at the mill area, 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, and it becomes clean and odorless biofuel. It can then be burned without additional fossil-based fuel.

“Our process, OxyPower HTC, uses an innovative application of hydrothermal carbonization, which converts complex organic compounds into sterile odorless biofuel,” says Erik Odén, CEO of C-Green.

The pilot plant processes 16,000 metric tons of biowaste per year. The resulting biofuel is used in the mill’s power boiler and to heat the nearby town of Heinola, with about 20,000 inhabitants. Heinola Mill has been providing district heat to the city and its residents since the 1980s.

“The treatment of bio sludge produced at our mill offers opportunities for a bio-based circular economy, which supports Stora Enso’s environmental goals. With this technology, we can save both the environment and costs”, says Mikael Sillfors, Development Manager at Heinola Mill.

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 as possible to zero levels of CO2 emissions by technically and commercially feasible means. A high proportion of biomass is already used in the internal energy production at most of the company’s mills.

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