NunnaUuni Oy won the Snow White, Clean Air campaign’s innovation competition for reducing soot pollution. Their success can be attributed to the implementation of the Golden Fire combustion method and the Mammutt soapstone combination, which enables NunnaUuni’s heating stoves to generate less than half the amount of soot pollution compared to conventional accumulative heating stoves commonly used in Finland.
NunnaUuni Oy emerged as the winners of the innovation competition organized by the Climate Leadership Coalition (CLC), Bioenergia ry, Sitra, Finnish Environmental Center, and Nuohousalan Keskusliitto ry in the category of “Manufacturing of heating stoves and small burning.” The competition aimed to find solutions for reducing soot pollution. The winners were announced during the meeting of ministers of the Arctic Council in Rovaniemi on May 6, 2019.
The Arctic region is experiencing more than twice the rate of warming compared to the global climate average. Soot, or black carbon, which consists of fine-grained soot dust, accounts for approximately 20-25 percent of global warming. Fine soot particles warm the atmosphere and, when deposited on snow and ice, absorb sunlight, accelerating the melting process.
Soot pollution is generated by various sources such as the burning of wood, biomass, coal in residential buildings, road traffic, agricultural and construction machinery, industrial activities, energy companies, and the burning of oil and gas residues from oil fields. The impact of soot is particularly significant in the Arctic region as it accumulates on the surface of snow and ice. The damage caused by soot is particularly pronounced during spring and summer when there is more sunlight in the northern regions. Soot is transported to the Arctic region through air masses from the south, but pollution generated within the region also plays a significant role. Member states of the Arctic Council contribute to approximately one-third of the soot-induced warming in the Arctic region.
The majority of Finland’s 2.2 million heating stoves are traditional stoves. In a typical hearth grate, all the combustion air is directed directly beneath the firewood as primary airflow. Consequently, the gases emitted from the burning wood combust between the logs. The heat from the flames accelerates the gasification of the wood, depleting the available oxygen for complete combustion. This leads to the formation of harmful smoke pollution and a loss in heat value. An attempt has been made to address this issue by recommending lighting the firewood from the top. This approach reduces the gasification of the wood only during the initial loading process, resulting in cleaner flue gases. However, when adding wood to an already burning fire, the new wood still ignites from below, quickly leading to an overgassed state.
The most commonly used material for constructing fireplaces, such as bricks, is classified as insulation material due to its low thermal conductivity, similar to other cast products. When combustion accelerates on a typical hearth grate, the heat output increases. However, insulating materials used in the firebox cannot handle such a high heat load, causing a significant portion of thermal energy to escape through the chimney along with hot flue gases. As a result, the energy efficiency derived from firewood is further diminished, necessitating the burning of more wood and contributing to increased pollution.
NunnaUuni initiated extensive research on the thermal properties of different types of soapstone in the early 1990s. By the end of the decade, they discovered that fine-textured magnesite soapstone with a directed structure exhibited excellent heat tolerance and efficient thermal energy accumulation. Consequently, this type of soapstone proved ideal for constructing heat-accumulating fireplaces. The studies conducted confirmed the value of the soapstone used by NunnaUuni, which came to be known as Mammutt soapstone.
The knowledge and certainty surrounding this particular refractory soapstone type allowed for the development of improved combustion technology. At the turn of the millennium, the clean gas combustion method, known as Golden Fire, was developed. This method achieves clean combustion by precisely controlling the airflow, enabling the use of the exact amount of air required during different phases of combustion. A small portion of the combustion air is directed through the holes in the Golden Fire grate beneath the burning wood as primary air to maintain an even burn. Most of the preheated combustion air is directed from the edges of the Golden Fire grate, surrounding and engulfing the burning wood as secondary air, facilitating the high-temperature combustion of gases released from the wood at temperatures ranging from 800 to 1200 °C.
Thanks to the highly heat-tolerant and conductive Mammutt soapstone, NunnaUuni fire chambers efficiently accumulate heat. The thermal conductivity of Mammutt soapstone is over five times higher than that of chamotte stone, allowing the hearth to rapidly absorb the heat generated during efficient combustion.
The soot pollution from the pure gas combustion method of Golden Fire is approximately 40% less than that of stoves with a common hearth grate. Mammutt soapstone’s efficient heat storage capability allows the NunnaUuni stove to store up to 40% more heat from the energy contained in the firewood compared to a similar large accumulative heating hearth made of conventional bricks. Due to the prevention of unnecessary heat and unburned fuel from entering the chimney along with the flue gases, the NunnaUuni fireplace achieves the same level of heat with less than half the amount of soot pollution.