Disclosed is a combi stove (1) arranged for combusting both logs and granular material. The combi stove (1) comprises a common combustion chamber (2) arranged so that both the logs and the granular material may be combusted in the common combustion chamber (2). The combi stove (1) further comprises ash collecting means (3) arranged under the combustion chamber (2) and a front aperture (4) through which logs may be placed in the combustion chamber (2). Also the combi stove (1) includes a granular material combustion area (5) arranged in the combustion chamber (2), wherein the granular material combustion area (5) comprises a bottom combustion surface (6) including bottom airflow apertures (7) arranged to enable an airflow to the granular material during a combustion of the granular material in the granular material combustion area (5), wherein the granular material combustion area (5) is at least partly surrounded by a granular material area sidewall (8) comprising sidewall airflow apertures (9) arranged to enable an airflow to flue gasses generated during a combustion of the granular material in the granular material combustion area (5), and wherein at least a part of the granular material area sidewall (8) is releasable from the granular material combustion area (5). Furthermore, a use of a combi stove (1) is disclosed.

A co-firing process is described using cleaned coal and processed biomass to reduce adverse by-products in a coal combusting apparatus. The coal feedstock comprises an aggregate blend of cleaned coal and processed biomass. The biomass feedstock comprises processed biomass pellets. The total energy density is predetermined and can be similar to the coal component or higher than the coal component. The intracellular salt in the processed biomass is at least 60 wt % less for the processed organic-carbon-containing feedstock used to make the processed biomass pellets than that of the starting un-processed processed organic-carbon-containing feedstock. The cleaned coal has a sulfur content that is 50 wt % less than that of un-cleaned coal before it passed through the coal-cleaning sub-system.

A co-firing process is described using cleaned coal and processed biomass to reduce adverse by-products in a coal combusting apparatus. The coal feedstock comprises an aggregate blend of cleaned coal and processed biomass. The biomass feedstock comprises processed biomass pellets. The total energy density is predetermined and can be similar to the coal component or higher than the coal component. The intracellular salt in the processed biomass is at least 60 wt % less for the processed organic-carbon-containing feedstock used to make the processed biomass pellets than that of the starting un-processed processed organic-carbon-containing feedstock. The cleaned coal has a sulfur content that is 50 wt % less than that of un-cleaned coal before it passed through the coal-cleaning sub-system.